Optical Frequency combs can be used as a tool for fully controlling the phase and frequency information of light waves, i.e., “optical synthesizer”. It provides powerful tools not only in frequency metrology as “ultraprecise frequency ruler” but also in broad area since light wave can be used to its full extent with an extremely wide dynamic range. Frequency-traceable length measurement using frequency combs provides direct realization of the definition of meter, remote calibration using a GPS technology, and precise measurements of wide range of lengths by taking advantage of high dynamic range in frequency measurements. In this paper, ultrahigh-precision length metrology using fiber-based optical frequency combs are presented. By precisely controlling the frequency and phase of the combs, self-correction of air refractive index and noise cancellation in fiber path in interferometer are demonstrated. Heterodyne interferometry of 61- m path-length based on two-color optical frequency combs is developed for air-refractive-index correction. Measured two-color optical-path-differences agreed with calculations with 10⁻¹¹ for 10-hour. Corrected distance variation agreed with thermal expansion of base-plate. A fiber-based optical frequency comb interferometer with 168-m-length reference path was stabilized to nm-level with fiber noise cancellation technique using a single frequency CW laser. Extremely wide range interferometric fringe scanning of 3.3-m path length

Deterministic Phase Retrieval techniques (DPRTs) employ a series of paraxial beam intensities in order to recover the phase of a complex field. These paraxial intensities are usually generated in systems that employ plane-wave illumination. This type of illumination allows a direct processing of the captured intensities with DPRTs for recovering the phase. Furthermore, it has been shown that intensities for DPRTs can be acquired from systems that use spherical illumination as well. However, this type of illumination presents a major setback for DPRTs: the captured intensities change their size for each position of the detector on the propagation axis. In order to apply the DPRTs, reescalation of the captured intensities has to be applied. This condition can increase the error sensitivity of the final phase result if it is not carried out properly. In this work, we introduce a novel system based on a Phase Light Modulator (PLM) for capturing the intensities when employing spherical illumination. The proposed optical system enables us to capture the diffraction pattern of under, in, and over-focus intensities. The employment of the PLM allows capturing the corresponding intensities without displacing the detector. Moreover, with the proposed optical system we can control accurately the magnification of the captured intensities. Thus, the stack of captured intensities can be used in DPRTs, overcoming the problems related with the resizing of the images. In order to prove our claims, the corresponding numerical experiments will be carried out. These simulations will show that the retrieved phases with spherical illumination are accurate and can be compared with those that employ plane wave illumination. We demonstrate that with the employment of the PLM, the proposed optical system has several advantages as: the optical system is compact, the beam size on the detector plane is controlled accurately, and the errors coming from mechanical motion can be suppressed easily.

We propose a super-resolution microscopy with a confocal optical setup and an example-based algorithm. The example-based super-resolution algorithm was performed by an example database which is constructed by learning a lot of sets of a high-resolution patch and a low-resolution patch. The high-resolution patch is a part of the high-resolution image of an object model expressed in a computer, and the low-resolution patch is calculated from the high-resolution patch in consideration with a spatial property of an optical microscope. In the reconstruction process, a low-resolution image observed by the confocal optical setup with an image sensor is converted to the super-resolved high-resolution image selected by a pattern matching method from the example database. We demonstrate the adequate selection of the patch size and the weighting superposition method performs the super resolution with a low signal-to noise ratio.

Structured Illumination has gained wide use in 3D optical metrology systems and 3D Super-Resolution Microscopy (SRM). Both applications use a spatial light modulator (SLM) to project a series of complex images onto the surface of a device-under-test [1] and into biological samples, respectively [2, 3]. In 3D optical metrology a camera-based inspection system is used to assess these images and calculate an accurate 3D profile. In 3D-SRM, the fluorescent emission from specific markers is detected to reconstruct biological structures below 250 nm. This paper outlines the features of Forth Dimension Displays’ new 3.1 MPixel SLM and driver solution and describes design aspects for its application in structured illumination.

In this investigation, a simple optical configuration and technique to improve the performance of spectrally-resolved interferometry (SRI) is proposed and experimentally verified. SRI has the fundamental limitation in the measurement range caused by the spectral bandwidth of an optical source and the spectral resolution of a spectrometer to detect the spectral interference density. Especially, the minimum measurable range of SRI is determined by the bandwidth of the source and this minimum measurable range becomes a dead zone in SRI. The proposed method can eliminate the dead zone without the minimum measurable distance and extend the measurable range of spectrally resolved interferometry (SRI) twice based on the bandwidth separation by a dichroic beam splitter (DBS). The benefit of this dichroic SRI is that it can be simply implemented with a DBS and another reference mirror from the typical SRI. Feasibility experiments were performed to verify the principle of the dichroic SRI and the result confirmed the effectiveness of this method as the extended measuring range.

This paper discusses a method to measure the thickness of thin layers deposited on a reflective substrate. A Michelson type interferometer with three wavelengths produces color interferences. A color sensor records the tint that is produced. The color interferences are approximated by a model based on the measurement of the laser intensities obtained with the reference mirror only. An iterative process leads to unambiguous algorithmic convergence and high accuracy thickness measurement. This method is simple, robust, compact, and single shot. The method does not need for angular scanning over the field of measurement (about 75mm²). The measurement on the surface yields a histogram of the thickness distribution and there is no requirement for any reference points (e.g. no need to make a groove or a walk on the layer). A thickness measurement performance of 50nm was demonstrated for homogenous polymer films deposited on silicon wafer. Set-up and digital image processing are discussed.

We demonstrate that the recently proposed master-slave interferometry method is able to provide true dispersion free depth profiles in a spectrometer-based set-up that can be used for accurate displacement measurements in sensing and optical coherence tomography. The proposed technique is based on correlating the channelled spectra produced by the linear camera in the spectrometer with previously recorded masks. As such technique is not based on Fourier transformations (FT), it does not require any resampling of data and is immune to any amounts of dispersion left unbalanced in the system. In order to prove the tolerance of technique to dispersion, different lengths of optical fiber are used in the interferometer to introduce dispersion and it is demonstrated that neither the sensitivity profile versus optical path difference (OPD) nor the depth resolution are affected. In opposition, it is shown that the classical FT based methods using calibrated data provide less accurate optical path length measurements and exhibit a quicker decays of sensitivity with OPD.

To apply phase-shifting interferometry (PSI) to in-situ measurement, we have proposed an algorithm to detect and suppress phase-shifting error and contrast fluctuation. The phase shift and contrast are analyzed in spatial-frequency domain. The strength of baseband and sideband implies the pattern contrast. The position and phase angle of the sideband indicates the tilt gradients and translational value of phase shift. Thus, the phase shift error and contrast fluctuation could be extracted. A contrast-compensated equation is established to calculate the wavefront phase. The proposed algorithm was applied to the interferograms subjecting to vibration and wavefront phase was calculated. The experimental results show that, under vibration of one micron amplitude and 60Hz frequency, the error of wavefront PV value is less than 0.01wave and the 2σ repeatability is less than 0.01wave. For no hardware is required, the proposed algorithm provides a cost-effective method for wavefront in-situ measurement with PSI.

Few-mode fiber (FMF) has become very popular for use in multiplexing telecommunications data over fiber optics. The simplicity of producing FMF and the relative robustness of the optical modes, coupled with the simplicity of reading out the information make this fiber a natural choice for communications. However, little work has been done to take advantage of this type of fiber for sensors. Here, we demonstrate the feasibility of using FMF properties as a mechanism for detecting flexure by exploiting mode coupling between modes when the cylindrical symmetry of the fiber is perturbed. The theoretical calculations shown here are used to understand the coupling between the lowest order linearly polarized mode (LP01) and the next higher mode (LP11x or LP11y) under the action of bending. Twisting is also evaluated as a means to detect flexure and was determined to be the most reliable and effective method when observing the LP21 mode. Experimental results of twisted fiber and observations of the LP21 mode are presented here. These types of fiber flexure sensors are practical in high voltage, high magnetic field, or high temperature medical or industrial environments where typical electronic flexure sensors would normally fail. Other types of flexure measurement systems that utilize fiber, such as Rayleigh back-scattering [1], are complicated and expensive and often provide a higher-than necessary sensitivity for the task at hand.

Based on the attractive elasto-optic properties of single-mode microstructured polymer optical fibres (SM mPOFs) reported elsewhere,10 mode polarisation may be used as sensing probe for several parameters of interest like mechanical pressure. We report on a simplified detection scheme that does not require measuring the actual polarisation state of the light emerging from the mPOF. A polariser and a photodetector in a proper configuration are only required. The detected light intensity shows a high linearity with applied force to the mPOF.

Distributed optic fiber sensor is a new type of system, which could be used in the long-distance and strong-EMI condition for monitoring and inspection. A method of external modulation with a phase modulator is proposed in this paper to improve the positioning accuracy of the disturbance in a distributed optic-fiber sensor. We construct distributed disturbance detecting system based on Michelson interferometer, and a phase modulator has been attached to the fiber sensor in front of the Faraday rotation mirror (FRM), to elevate the signal produced by interfering of the two lights reflected by the Faraday rotation Mirror to a high frequency, while other signals remain in the low frequency. Through a high pass filter and phase retrieve circus, a signal which is proportional to the external disturbance is acquired. The accuracy of disturbance positioning with this signal can be largely improved. The method is quite simple and easy to achieve. Theoretical analysis and experimental results show that, this method can effectively improve the positioning accuracy.

In this paper we show how resolution enhancement in digital holographic microscopy (DHM) and reference-less phase retrieval approach is obtained by using modulated illuminations. The modulated illuminations, including structured illumination and speckle illumination, are generated by a spatial light modulator and used to illuminate the sample. The holograms or diffraction patterns of the object wave under these illuminations are recorded, from which the phase is reconstructed accordingly. The resolution of the reconstructed image has been improved, when the spectrum of object waves along different illuminations are synthesized.

Sparsity properties of digital holograms have been investigated for application in compressive holography, permitting the discovery of the sparsest reconstruction plane in which the recovery of digital holograms is suitable. Recent approaches for denoising and phase retrieval are also proposed exploiting the sparsity properties of digital holograms. Thus it can be shown a strong correlation between holograms sparsity and focal plane detection, making a sparsity measure coefficient as a candidate to be used for focus plane calculation. Here we implement different sparsity metrics, that are able to measure a degree of sparsity of reconstructed digital hologram and we investigate their relation with the automatic focusing criterions, highlighting the possibility to use a sparsity measure as refocusing metric as well as the contrary, i.e. using image contrast coefficients as sparsity measures. Our analysis will be reported for digital holograms recorded in both lensless and microscope configuration and for both amplitude and pure-phase objects.

Twilight-field method for obtaining interference fringes with high contrast in in-line digital holography regulates only an intensity of the reference light to be close to one of the object light that is ultra weak scattering light from a nanoparticle using a low-frequency attenuation filter. Three-dimensional position measurement of a 40 nm gold nanoparticle held in optical tweezers in water was performed with an inline, low-coherence digital holographic microscope with the twilight-field method.

We propose a complete framework for the synthesis of 3D holographic scene, combining multiple color holograms of different objects by applying adaptive transformations. In particular, it has been demonstrated that affine transformation of digital holograms can be employed to defocus and chromatic aberrations. By combining these two features we are able to synthesize a color scene where multiple objects are jointly multiplexed. Since holograms transformation could be introduce artifacts in the holographic reconstructions, principally related to the presence of speckle noise, we also implement a denoising step where the Bi-dimensional Empirical Mode Decomposition (BEMD) algorithm is employed. We test the proposed framework in two different scenario, i.e. by coding color three-dimensional scenes and joining different objects that are (i) experimentally recorded and (ii) obtained as color computer generated holograms (CCGH).

Optical diffraction tomography (ODT) is a non-invasive method for quantitative measurement of micrometre-sized samples. In ODT a series of multiple holograms captured for various illumination directions with respect to a sample is processed using a tomographic reconstruction algorithm. The result of tomographic evaluation is 3D distribution of refractive index. Data acquisition in ODT is commonly realized in two ways, either by rotating a sample under fixed illumination and observation directions (object rotation configuration - ORC), or by scanning the illumination direction of a fixed sample (illumination scanning configuration - ISC). From the purely theoretical standpoint, the ORC configuration is superior to ISC due to larger (in terms of volume) and more isotropic optical transfer function. However, the theoretical maximal resolution achievable with ORC is lower than that provided with ISC. Moreover, the quality of tomographic reconstructions in ORC is significantly degraded due to experimental difficulties, including problematic determination of location of the rotation axis. This applies particularly to displacement of the rotation axis from the infocus plane that is either disregarded or detected with object-dependent autofocusing algorithms, which do not provide sufficient accuracy. In this paper we propose a new ODT approach, which provides solution to the both mentioned problems of ORC – the resolution limit and the rotation axis misalignment problem. The proposed tomographic method, besides rotating a sample in a full angle of 360°, uses simultaneous illumination from two fixed, highly off-axis directions. This modification enables enlarging the ORC optical transfer function up to the ISC limit. Moreover, the system enables implementation of an accurate, efficient and object-independent autofocusing method, which takes advantage of the off-axis illumination. The autofocusing method provides accurate and reliable detection of axial location of the rotation axis, enabling precise alignment of the tomographic data.

We propose a new type of interference objective that makes use of two partially-reflective beamsplitter plates arranged coaxially with the objective lens system, in an assembly that is better suited to large fields of view than the traditional Michelson design. The coaxial plates are slightly tilted to direct unwanted reflections outside of the imaging pupil aperture, providing high fringe contrast with spectrally-broadband, spatially extended white light illumination. Examples include a turret-mountable 1.4× magnification objective parfocal with high-magnification objectives up to 100×, and a dovetail mount 0.5× objective with a 34×34mm field for wide-field measurements of surface form.

Small and precise cones are one of the most important functional surfaces for valve seats of today's modern common rail injection systems for Diesel engines. We have investigated two concepts of interferometric systems for industrial examination of small-size conical geometries: white-light-interferometer with an endoscopic probe and a special formmeasuring- machine with an interferometric stylus. Endoscopic probes are critical for small and deep drillings, and the optical layout becomes very complex and expensive. To increase the universality of small size cone measuring systems, we followed the concept of a special scanning form measuring machine using a single-measuring-point interferometric stylus. We have performed first measurements and repeatability tests on the shop floor. Based on standard capability evaluation (Cgk and Cg) we have achieved the following measuring system capabilities: angle T< 0.07°, roundness T<0.3 μm, Pt Value <0.3 μm.

This work analyses samples of the widely used encapsulant of photovoltaics modules, ethylene vinyl acetate (EVA). The samples were cross-linked using a lamination technique for different curing times (0 - 20 minutes). The cross-linking characterization is done by determinating the material dispersion with the aid of a combined temporal- and spectral domain white-light interferometer. With the proposed technique it was possible to discriminate the differences in crosslinking for the given curing times. One important feature of this approach is the possibility to perform space resolved measurements of the crosslinking state with μm-resolution. Furthermore the paper discusses the mathematical analysis and processing of measurement data and shows a prototype solution for the fast and automated data acquisition for industrial application.

We present a scanning white-light interferometer (SWLI) for close-to-machine applications in the presence of environmental vibrations. It combines an area measuring white-light interferometer and a punctual measuring laser distance interferometer (LDI) in one device. The measurement spot of the LDI is within the field of view of SWLI. The LDI measures any distance change during the white-light measurement with a high temporal resolution. With the knowledge of the real distance changes during the measurement we can compensate for the influence of environmental vibrations on the white-light correlograms. The reconstruction of the white-light interference signals takes place after measurement by reordering the captured images in accordance with their real positions obtained by the LDI. With this system we are able to reconstruct completely distorted and unusable SWLI signals and to determine the 3D topography of the measurement specimen from these reconstructed signals with high accuracy. We demonstrate the feasibility of the method by examples of practical measurements with and without vibrational disturbances.

Vertical scanning interferometry (VSI) techniques are widely used to profile microscopic surface structures of industrial products. This paper introduces a high-precision fast optical measurement system with an optimized small sensor head for the measurement of precision surfaces on a turbine blade or blisks (blade integrated discs). The non-contact measurement system is based on a low coherence interferometer (LCI), which is capable of fast profiling of 3D sample surface with a nanometer resolution and has a larger measurement range compared to conventional microscopes. This results in a large amount of sampled data and a high computational time for the evaluation of the data. For this reason, the used evaluation algorithm in this paper is accelerated by the Compute Unified Device Architecture (CUDA) technology, which allows parallel evaluation of the data stack on independent cores of a General Purpose Graphics Processing Unit (GPGPU). As a result, the GPU-based optimized algorithm is compared with the original CPU-based single-threaded algorithm to show the approximate 60x speedup of computing the Hilbert Transformation, which is used to find the depth position in the correlogram of each pixel of the sampled data. The main advantage of the GPU computing for the evaluation algorithm of the LCI is that it can reduce the time-consuming data evaluation process and further accelerates the whole measurement.

Optical techniques are usually related to laboratory rooms, which are places equipped with temperature, humidity and vibration control. These techniques are very suitable for fast measurements due to their non-contact nature and full-field capability. Among them, optical methods based on the speckle phenomenon have had a great development during the last two decades because of the development of digital image processing, cameras, computers, lasers and optical components. Speckle techniques have the advantages cited for optical methods. Additionally, they are adequate for the evaluation of real components without further preparation of the surface and without high time consuming to be analyzed. This paper supplies tools, tips and reference parameters to develop interferometers based on the speckle phenomenon to be used outside the laboratory room. Finally, applications outside the lab for the measurement of mechanical and residual stresses are presented. These examples show the high potential of speckle metrology as an auxiliary tool for structure integrity assessment.

Speckle interferometry is a well established technique for the optical characterization of rough objects, with the quantification of deformations as one particular application of interest. Owing to its common path property, a speckle-shearing interferometer is often the natural choice as a setup. Like other speckle techniques, however, speckle-shearing interferometry suffers from the existence of phase singularities present in the speckle patterns. Phase singularities introduce ambiguities into the phase unwrapping process and make this evaluation step highly sophisticated. In this work, we attempt to reduce the number of phase singularities by physical means, i. e. by applying an incoherent averaging of multiple, mutually independent speckle intensities. The effect of the incoherent averaging on the number of phase singularities has been investigated theoretically, by computer simulations, and experimentally. To obtain high contrast fringes in connection with a shearing setup, which would not be the case for a simple extended light source, a periodically structured light source with a period matched to the shear distance is applied. It turns out that the number of phase singularities may indeed be reduced, but only to a certain extent.

This paper presents a modular device based on digital speckle pattern interferometry (DSPI) combined with an instrumented indenter. The system is divided in two modules, the interferometric and the indentation module. The former uses a diffractive optical element (DOE) to obtain radial in-plane sensitivity. This module measures the whole shallow displacement field generated by the indentation print on the surface of the material under testing. The latter module is sized suitably with the interferometric module. The indentation module uses a mechanical/hydraulic scheme to provide the system a high loading capability. A piezoelectric loading cell and an inductive transducer are used to simultaneously measure the load applied on the ball indenter and its penetration on the material. For the experimental tests, a bench capable to apply in a specific pipe a very well-known bending moment was used. This bench is mounted with two 12- meters pipes disposed horizontally. A transverse load is applied in the central cross-section of both pipes. The load application is made by a hydraulic actuator and measured with a load cell. Strain-gages are also used in a half-bridge configuration to measure the strain in the 8 cross-sections distributed along the pipe length. Each cross-section was measured by the proposed instrumented indentation system and compared with the strain-gages and load cell measurements. The results obtained show an uncertainty level around 20-30% of the measured bending stress. Good agreement was found between the computed bending stress using the strain-gages, load cell and the proposed method using the instrumented indentation system.

Speckle interferometry is one of important deformation measurement methods for an object with rough surfaces. Some technologies have been proposed in speckle interferometry. Under these technologies, the fringe analysis based on the idea of "difference of phase method" has been proposed by processing the information of speckle patterns on each pixel of camera. However, because there are a lot of speckle noises in the speckle pattern, a high resolution analysis cannot be realized by this method. To solve this problem, the novel fringe analysis method using a new optical system was proposed. The phase map is calculated with "phase of difference method" in this method. The deformation signal is extracted by an enhanced filtering technology for realizing a high resolution fringe analysis. In this new fringe analysis method, it is known that the measuring accuracy depends on some experimental conditions. In this paper, the relationship between the measuring accuracy and the measurement conditions of the method is discussed by using experimental results. It is confirmed that the S/N ratio of the fringe signal in the analyzing process is the important factor concerning the accuracy.

Self-referencing interferometry has been widely used in wavefront sensing. However, currently the results of wavefront measurement include two parts, one is the real phase information of wavefront under test and the other is the system error in self-referencing interferometer. In this paper, a method based on maximum likelihood estimation is presented to calibrate the system error in self-referencing interferometer. Firstly, at least three phase difference distributions are obtained by three position measurements of the tested component: one basic position, one rotation and one lateral translation. Then, combining the three phase difference data and using the maximum likelihood method to create a maximum likelihood function, reconstructing the wavefront under test and the system errors by least square estimation and Zernike polynomials. The simulation results show that the proposed method can deal with the issue of calibration of a self-referencing interferometer. The method can be used to reduce the effect of system errors on extracting and reconstructing the wavefront under test, and improve the measurement accuracy of the self-referencing interferometer.

A technical realization of a multispectral camera is proposed, by multiplexing a light source with six different spectra. A monochrome line scan camera with six pixel rows is used as detector. The special feature of this acquisition approach is its high speed capability. The scan speed is as high as the frame rate of the line scan camera and not affected by the multiplexing. As application a chromatic confocal microscope was build up. From a data acquisition perspective up to 284 million 3D points per second can be measured. A real time signal processing is proposed, too.

In the development of new eco-cements for ecologically friendly construction, the porosity, surface structure and chemical nature of the material can influence the bioreceptivity of the surface and the aptitude or not of environmental micro-organisms to form biofilms. Such films are the source of biocontamination that can lead to a degradation in the structural properties over time. Accurate measurement of surface roughness and topography are important to help in the understanding of this interaction. Optical profilers are well adapted to the quantifying of large surface roughness typical of cementitious materials, being more rapid and better able to cope with high roughness compared with stylus and near field probe techniques. But any given surface profiler typically has specific range limits in terms of axial and lateral resolution and field of view, resulting in different roughness values according to the type of optical profiler used. In the present work, unpolished and polished cement paste samples have been measured with two different systems, one using interference microscopy and the other, chromatic confocal sensing. Comparison of the results from both techniques using the method of window re-sizing, more commonly used in tribology, has been used for calculating the average roughness parameters at different scales. The initial results obtained show a successful overlap of the results for the unpolished samples and a slight separation for the polished samples. The validation of the measurements is demonstrated together with a revealing of differences in the measurements on different types of surfaces due to variations in instrument performance.

The calibration of the height axis of optical topography measurement instruments is essential for reliable topography measurements. A state of the art technology for the calibration of the linearity and amplification of the z-axis is the use of step height artefacts. However, a proper calibration requires numerous step heights at different positions within the measurement range. The procedure is extensive and uses artificial surface structures that are not related to real measurement tasks.

Concerning these limitations, approaches should to be developed that work for arbitrary topography measurement devices and require little effort. Hence, we propose calibration artefacts which are based on the 3D-Abbott-Curve and image desired surface characteristics. Further, real geometric structures are used as an initial point of the calibration artefact.

Based on these considerations, an algorithm is introduced which transforms an arbitrary measured surface into a measurement artefact for the z-axis linearity. The method works both for profiles and topographies. For considering effects of manufacturing, measuring, and evaluation an iterative approach is chosen. The mathematical impact of these processes can be calculated with morphological signal processing.

The artefact is manufactured with 3D laser lithography and characterized with different optical measurement devices. An introduced calibration routine can calibrate the entire z-axis-range within one measurement and minimizes the required effort. With the results it is possible to locate potential linearity deviations and to adjust the z-axis. Results of different optical measurement principles are compared in order to evaluate the capabilities of the new artefact.

Microstructure surface topography is a key aspect of micro-nano measuring research for it has an obvious influence on the performance and quality of micro-nano devices. Scanning white light interferometry is a common method of testing surface profiling. In this paper, a color CCD camera, rather than a black-and-white CCD camera, was utilized to acquire white light interference images, which contain information of RGB channels. Based on acquired color interference images, wavelet transform method was employed to calculate phase value of corresponding channel in each scanning position. Then zero-optical-path-difference positions were accurately determined via a constructed evaluation function and least square method. Surface topography was eventually obtained via linear relationship of relative height and the zero-optical-path-difference position. The proposed method was verified by simulation and experiment of measuring standard step provided by VLSI Standards Incorporated.

High-resolution contactless optical 3D measurements are well suited for determination of state and position of gas turbine vane cooling-holes during maintenance rework. The air flow through the cooling-holes protects the turbine vanes from the high temperatures. However, the coating needs to be renewed during repair of the vanes. The renewal process can lead to partially or completely filled cooling-holes. This paper describes a newly developed procedure to automatically detect and reopen such holes by laser-drilling for an effective new repair process. The turbine vane is scanned by a fringe projection based optical 3D scanner. The resulting 3D pointcloud delivers plenty of detail to automatically detect the cooling-holes. Poorly detected or undetected cooling-holes are interpolated from properly detected neighboring cooling-holes and reference default cooling-holes. For the resulting laser-drilling process the precise orientation in the vane mount must be known. To this end, position and orientation of the scanned vane in relation to the reference vane is determined. To validate the approach, numerous experiments regarding the cooling-hole extraction-performance were satisfactorily conducted. Real drilling experiments confirmed those findings and were used to validate the entire process.

Sheet-bulk metal forming is a new production process capable of performing deep-drawing and massive forming steps in a single operation. However, due to the high forming forces of the forming process, continuous process control is required in order to detect wear on the forming tool before production quality is impacted. To be able to measure the geometry of the forming tool in the limited space of forming presses, a new inspection system is being developed within the SFB/TR 73 collaborative research center. In addition to the limited space, the process restricts the amount of time available for inspection. Existing areal optical measurement systems suffer from shadowing when measuring the tool’s inner elements, as they cannot be placed in the limited space next to the tool, while tactile measurement systems cannot meet the time restrictions for measuring the areal geometries. The new inspection system uses the fringe projection optical measurement principle to capture areal geometry data from relevant parts of the forming tool in short time. Highresolution image fibers are used to connect the system’s compact sensor head to a base unit containing both camera and projector of the fringe projection system, which can be positioned outside of the moving parts of the press. To enable short measurement times, a high intensity laser source is used in the projector in combination with a digital micro-mirror device. Gradient index lenses are featured in the sensor head to allow for a very compact design that can be used in the narrow space above the forming tool inside the press. The sensor head is attached to an extended arm, which also guides the image fibers to the base unit. A rotation stage offers the possibility to capture measurements of different functional elements on the circular forming tool by changing the orientation of the sensor head next to the forming tool. During operation of the press, the arm can be travelled out of the moving parts of the forming press. To further reduce the measurement times of the fringe projection system, the inverse fringe projection principle has been adapted to the system to detect geometry deviations in a single camera image. Challenges arise from vibrations of both the forming machine and the positioning stages, which are transferred via the extended arm to the sensor head. Vibrations interfere with the analysis algorithms of both encoded and inverse fringe projection and thus impair measurement accuracy. To evaluate the impact of vibrations on the endoscopic system, results of measurements of simple geometries under the influence of vibrations are discussed. The effect of vibrations is imitated by displacing the measurement specimen during the measurement with a linear positioning stage. The concept of the new inspection system is presented within the scope of the TR 73 demonstrational sheet-bulk metal forming process. Finally, the capabilities of the endoscopic fringe projection system are shown by measurements of gearing structures on a forming tool compared to a CAD-reference.

In industrial metrology, the system of fringe projection for the fast determination of 3D surface data is established. The combination of areal and structured projection with two-dimensional optical sensors and triangulation measurement principle allows very high measurement point densities with reasonable accuracy. There are great difficulties with high gloss surfaces and with very dark surfaces for state of the art systems. Transparent materials cannot be measured using the visible spectrum of light. We have therefore developed a new structured light projection system that solves these problems. For the first time the physical principle of energy conversion is utilized in areal structured light projection. We are presenting first results to show the advantages and the capability of this new measurement principle.

In many application areas, stereo vision-based active triangulation systems are used to reconstruct the three-dimensional (3-D) surface shape of measurement objects. Typically, in order to solve the correspondence problem and increase the accuracy of the pixel assignment, a sequence of patterns is projected onto the object's surface and simultaneously recorded by two cameras. Most 3-D measurement systems are limited to static objects. In order to enhance their speed, it is necessary to use fast cameras as well as fast projection systems. Although high-speed camera systems are available, pattern projection at high frame rates is a difficult task and only a few techniques exist at the moment. In this contribution, we compare two different projection approaches, a laser-based speckle projection unit and an LED-based multi-aperture projection system, with regard to the achievable point cloud completeness and accuracy.

The paper presents the development of a system for the measurement of the shapes and dimensions of rotationally symmetric forgings under high temperature. These large semi-finished products are measured with demands for accuracy on the order of millimeters. The challenge is to design a measurement system that overcomes the problems caused by high temperature and provides results instantly without interrupting the production process. The proposed approach exploits the fact, that the measured parts have simple rotationally symmetric shape. It is based on the assumption that (in the simplest case) the actual shape can be determined from four boundary curves which lie in two mutually perpendicular planes. These four boundary curves can be obtained by determining the edges of the forging in two images. The proposed approach has been incorporated into a software application created in Matlab programming environment. Hence the system does not use added illumination resolving edge detection and scale calculation is a crucial step. The main parts of the system, such as calibration, edge detection, spatial orientation, and the evaluation of information about the shapes and dimensions of the measured parts, have been designed so that the entire measurement process takes only a few seconds. The article focuses on the individual parts of the software application. It discusses the suitability of using particular mathematical models and the designed multi-step edge detection method, which is based on thresholding, directional median filtering and validation and correction of detected edge points.

Shearography (speckle pattern shearing interferometry) is a non-destructive testing technique that provides full-field surface strain characterization. Although real-life objects especially in aerospace, transport or cultural heritage are not flat (e.g. aircraft leading edges or sculptures), their inspection with shearography is of interest for both hidden defect detection and material characterization. Accurate strain measuring of a highly curved or free form surface needs to be performed by combining inline object shape measuring and processing of shearography data in 3D. Previous research has not provided a general solution. This research is devoted to the practical questions of 3D shape shearography system development for surface strain characterization of curved objects. The complete procedure of calibration and data processing of a 3D shape shearography system with integrated structured light projector is presented. This includes an estimation of the actual shear distance and a sensitivity matrix correction within the system field of view. For the experimental part a 3D shape shearography system prototype was developed. It employs three spatially-distributed shearing cameras, with Michelson interferometers acting as the shearing devices, one illumination laser source and a structured light projector. The developed system performance was evaluated with a previously reported cylinder specimen (length 400 mm, external diameter 190 mmm) loaded by internal pressure. Further steps for the 3D shape shearography prototype and the technique development are also proposed.

We present a fast method for measuring a curved specular surface defect, which is the temporal modulated deflectometry. The system uses correlation image sensor, which is developed by us. The correlation image sensor(CIS) outputs temporal correlation between intensity signal and reference signal. We moves rectangular pattern to generate temporal signal. There is no need to use sinusoidal intensity pattern for phase measuring deflectometry(PMD) because CIS captures only fundamental frequency component of rectangular wave projected on the screen. Hence, the methodology we proposed has a potential for fast inspection system using only single frame.

Optical surfaces feature a wide range of length scales from “figure” down to “finish”, but the mid-spatial frequency structure (MSF) holds growing significance. Cost-effective production of systems demands answers to multiple layers of related questions, such as how best to quantify MSF, assess its optical impact, and employ existing production tools to meet MSF requirements. These answers evolve as new production technologies are introduced. I present general observations about a few of the associated challenges and attempt to clarify some essential aspects related to quantifying MSF as well as estimating its impact.

We review various metrology techniques for the characterization of refractive microlenses and microlens arrays (MLAs). The limitations and strength of each technique are analyzed. The goal is to obtain more stable and repeatable metrology routines for micro-optics manufacturing. This analysis comprises both techniques for the characterization of individual microlenses and the analysis of a very large number of microlenses in array configurations. Metrology of spherical and aspherical lens profiles, surface properties, aberrations, Strehl ratio, and focal properties will be presented.

The concept of traceability is presented for the interferometric form measurement of optical surfaces. The calibration chain for interferometric flatness measurement is evaluated in detail, showing that only a few influence quantities are significant. For spherical surfaces, the complexity increases as the measurement separates into sphericity and radius measurement. Traceability in asphere metrology is much more complex, and some aspects are discussed in terms of the example of the Tilted-Wave Interferometer concept.

Point diffraction interferometer (PDI) has become the high degree of accuracy device. In the optical wavefront testing the measurement accuracy is much higher than 1.0 nm RMS. In the paper there is presented a new version of PDI with two independently controlled beams using a pinhole plate with two pinholes as a beam coupler instead of a single-mode fiber or single-pinhole plate. Theoretical analysis of the pinhole diffraction wavefront and double pinholes diffraction interference is given. The PDI is used to investigate an interferometer reference lens and compare measurement results. The device can test high NA, the interference is obtained in circularly polarized light, and fringe contrast is adjustable to measure surfaces with different reflectance. The measurement repeatability now has been sub-nm RMS (measured NA = 0.33). The experiment result provides guarantee for the measurement in the high degree of accuracy. In the double pinholes PDI, generating two ideal spherical waves through two pinholes, one wave is as the reference wavefront for interference test, another ideal wavefront is reflected to the pinhole plate by the test mirror, and the tested wavefront and reference wavefront bring interference. Advantages of such arrangement of the PDI are: high maximum numerical aperture (NA = 0.55), distinct fringe patterns of high contrast, high accuracy of surface figure testing and wave-front repeatability RMS error 0.3 nm.

Speckle interferometry in the thermal wavelengths range (long-wave infrared, 8-14 μm), combining a CO₂ laser and recording with an uncooled microbolometer camera is presented. In this wavelength range specklegrams are affected by the thermal radiation emitted by objects at room temperature. This allows simultaneously capturing temperature and surface shape information about objects. The FANTOM project is based on this concept and an instrument was developed to take advantage of this natural data fusion. It has been used in a variety of nondestructive testing applications where both information are useful, specifically in aeronautical composite structures.

In the paper we present different problems which may occur during measurements of displacements/strains and shape of engineering objects including the necessity of recalculating of coordinates of measurement results and performing measurements in climate chambers. The first example refers to metal plates segments that are objects of complex geometry and are di cult to be measured with a single 3D DIC setup from only one direction, the second one is a composite cylindrical container with programmed faults, while the third one is a mirror subjected to thermal load in a climate chamber. Presented applications shows a flexibility of the method in different measurements tasks, however in each of these cases, an individual approach to experiment preparation and planning was required.

This paper describes an extended theory of the displacement of the objective speckle pattern resulting from displacement and/or deformation of a coherently illuminated diffuse object where the influence of the surface shape is included via the linear surface gradients. An experimental system capable of measuring the translational scaling factors, the ratios of speckle shift to object translations, to an accuracy of ± 0.02 and a repeatability of approximately ± 0.008 is described which was used to experimentally measure the speckle shift for a range of detector positions and surface gradients. The original expressions developed by Yamaguchi¹ and the new extended expressions² are then compared with experimental results for measurements on zero surface gradients, i.e. the mean surface lying in the x-y plane. The divergence of Yamaguchi’s expressions from experimental results for off-axis detector positions that was first observed by Světlík³ was confirmed, and the new expressions shown to successfully predict translational scaling factors for off-axis positions. The new expressions are then compared to the experimental results for a range of surface gradient magnitudes and directions, as well as detector positions both on and off-axis, and shown to successfully predict the observed speckle shift.

An optical system for the automatic recalibration of large machine tools during the machining process has been developed. The system provides an error signal during operation in order to compensate for structural deformations of axis and sliding parts. Those signals are used to reach a global positioning error below 50 microns on 3-axis translation stages, having range of several meters. One collimated diode laser beam has been mounted to the machining table reference system. Three resistive-type 2D-position-sensing devices are used to locate the beam on each axis. Before the first two sensors in the optical path, the beam is split by a wedge pentaprism in two secondary beams. The first one propagates linearly along the sensor for the displacement measurement. The second one is deflected with a fixed 90° angle and defines the sampling direction of the next axis. By duplicating the system using a second pentaprism on the latter deflected beam, three axis are monitored. In order to avoid any active electronic devises on the milling head, a passive corner cube is placed on the side of the head. Laser beam is then back reflected on a final position-sensitive sensor mounted in proximity of the second pentaprism. Additional channels consisting in laser beams back-reflected by mirrors on similar position sensing devices were used to acquire angular measurements as well. The tests performed on the prototype demonstrate the capability of mapping the actual deviations from the ideal linear translation with an error of 25 um along the full axis travel.

A phase shifting method was developed for Coherent Gradient Sensing (CGS) using a three-step phase shifting method. Three different inteferograms were obtained by changing the distance between two gratings. The phase filed can be calculated accurately from the three inteferograms. The interference fringes (phase field) in reflection mode represent the gradient contours of the out-of-plane displacement of a surface. The curvatures and shape of the surface both can be calculated by numerical methods using the fringe patterns. The measurement principle and experimental setup were introduced in detail. As an application, a standard specimen with a curvature radius of 5 m was measured. From the analysis of the experimental results, we find that the relative error of the curvature using this method was about 0.78%. The method has good potentials for measuring the slopes, curvatures and shapes of thin film/substrate systems.

This paper presents an innovative approach for an automated evaluation of mixture ratios and the detection of impurities in viscous materials. The measurement method is based on fluorescence imaging and works on a non-contact basis. The principle of the measurement setup is that three similar fluorescence images are available in different optical paths. 2D-sensor-arrays having a resolution of 1024 pixel × 1280 pixel are used for the image acquisition. A one-to-one mapping restricts the size of the fluorescence images to 5.3 mm × 6.66 mm. The vertical and horizontal resolution in the images is limited to 5.2 μm; this corresponds to the dimensions of a pixel. Due to the use of an x, y-shifting table in the measurement setup, it is possible to investigate a larger area of the measurement object. To get more information of the measurement object, each image is filtered in a different wavelength range. The center wavelength of the used bandpass filters are 405 nm, 420 nm, and 440 nm. The evaluation of the mixture ratio is realized with an acceptance range in a three-dimensional coordinate system. The determination of the number, positions, areas, and maximum dimensions of contained impurities is implemented by a dedicated threshold algorithm. The minimum detectable impurity size with the used measurement setup is 5.2 μm. Both evaluation approaches work in a real-time and automated process. Advantages of the presented system are the low level of expense for the maintenance and the universality due to the use of optical standard components.

Non-destructive analysing tools are needed at all stages of thin film process-development, especially photovoltaic (PV) development, and on production lines. In the case of thin films, layer thicknesses, micro-structure, composition, layer optical properties, and their uniformity are important parameters. An important focus is to express the dielectric functions of each component material in terms of a handful of wavelength independent parameters whose variation can cover all process variants of that material. With the resulting database, spectroscopic ellipsometry coupled with multilayer analysis can be developed for on-line point-by-point mapping and on-line line-by-line imaging. Off-line point-by-point mapping can be effective for characterization of non-uniformities in full scale PV panels or big area (even 450 mm diameter) Si-wafers in developing labs but it is slow in the on-line mode when only 15 points can be obtained (within 1 min) as a 120 cm long panel moves by the mapping station. Last years [M. Fried et al, Thin Solid Films 519, 2730 (2011)], a new instrumentation was developed that provides a line image of spectroscopic ellipsometry (wl=350- 1000 nm) data. Earlier a single 30 point line image could be collected in 10 s over a 15 cm width of PV material. Recent years we have built a 30, a 45 and a 60 cm width expanded beam ellipsometer which speed is increased by 10x. Now, 1800 points can be mapped in a 1 min traverse of a 60*120 cm PV panel or flexible roll-to-roll substrate.

In general in industrial manufacturing a larger lot size gives the potential to decrease the production costs. There is however also a big demand on individualization in order to cover all customer requirements. These individual requests of a customer lead to a production complexity and cannot always be covered within the current manufacturing processes sufficiently. In metrology we can see an equivalent situation. A metrology tool should be suitable for a large variety of parts. E.g. in shape metrology, the tool should be able to measure any kind of shapes (spheres, tips, steps, etc.). As a standard measurement tool is not adjusted to an individual measurement task, the best performance is not reached equal wise for all shapes.

In this paper we want to present a new approach for shape metrology of parts, fabricated in small lots: the individualized optical metrology based on additive manufacturing. Thereby the main idea is that the sampling signal of an optical metrology tool is individually adapted to the shape of the object to be inspected. This can be reached by an individual design of the optics, leading to a complex shape of the optical components. In order to manufacture these complex shaped optical parts, additive manufacturing (3D printing) is used.

Temperature drifts, tool deterioration, unknown vibrations as well as spindle play are major effects which decrease the achievable precision of computerized numerically controlled (CNC) lathes and lead to shape deviations between the processed work pieces. Since currently no measurement system exist for fast, precise and in-situ 3d shape monitoring with keyhole access, much effort has to be made to simulate and compensate these effects. Therefore we introduce an optical interferometric sensor for absolute 3d shape measurements, which was integrated into a working lathe. According to the spindle rotational speed, a measurement rate of 2,500 Hz was achieved. In-situ absolute shape, surface profile and vibration measurements are presented. While thermal drifts of the sensor led to errors of several mµm for the absolute shape, reference measurements with a coordinate machine show, that the surface profile could be measured with an uncertainty below one micron. Additionally, the spindle play of 0.8 µm was measured with the sensor.

Optical inspection systems require fast image acquisition at significantly enhanced resolution when utilized for advanced machine vision tasks. Examples are quality assurance in print inspection, printed circuit board inspection, wafer inspection, real-time surveillance of railroad tracks, and in-line monitoring in flat panel fabrication lines. Ultra-highspeed is an often demanded feature in modern industrial production facilities, especially, where it comes to high volume production. A novel technology in this context is the new high-speed sensor for line-scan camera applications with unmatched line rates up to 200 kHz (tri-linear RGB) and 600 kHz (b/w), presented in this paper. At this speed, the multiline- scan sensor provides full color images with, e.g., a spatial resolution of 50 μm at a transport speed of 10 m/s. In contrast to conventional Bayer pattern or three-chip approaches, the sensor presented here utilizes the tri-linear principle, where the color filters are organized line-wise on the chip. With almost 100% fill-factor, the tri-linear technology assures high image quality because of its robustness against aliasing and Moiré effects leading to improved inspection quality, less false positives and thus less waste in the production lines.

Nowadays, optical-electronics measuring instruments for control the linear deformations in the monitoring industrial constructions (turbines, dams, booms, bases plates, walls, etc) are used effectively. Autocollimating and auto-reflecting schemes are two main basic of such systems. The autocollimating system has larger sensitive than auto reflecting ones. However, the auto reflecting system is more effective for using IR LED as a source and using CCD matrix as a photo-receiver. In addition, the auto-reflecting system has larger working distance than autocollimating system. The experimental test-bed of auto-reflecting system for alignment control was realized. Parameters of a system are the following: IR LED L2656-03 with power 9 mW as sources of radiation; the focal length of autocollimators objective is 250 mm, the matrix change couple devise as photo-receiver with dimension of pixel 2.2μm. The experimental error of this system is 0,007 mm on a working distance of 0.5 m and 0.06 mm on a distance of 8 m.

Structural vibrations can be measured with optical digital holography. Such a method provides measurements with a very high spatial resolution and is a nonintrusive technique. This method is based on the interference between a reference laser beam and the field diffracted by the studied object. Using a high speed camera, it can also be implemented in the time domain to investigate non-stationary problems.

In this paper, we present a recent investigation which shows that the high-speed digital holography is comparable with classical laser vibrometry. Furthermore, an experimental investigation of the vibratory field inside the Acoustic Black Hole is discussed. The principle of digital holography is explained and it is used here to provide a full field measurement of the velocity field at the extremity of the structure.

The nonlinear dynamics of a semiconductor laser with optical feedback (OF) combined with direct current modulation of the laser is demonstrated to suffice for the measurement of subwavelength changes in the position of a vibrating object. So far, classical Optical Feedback Interferometry (OFI) has been used to measure the vibration of an object given its amplitude is greater than half the wavelength of emission, and the resolution of the measurement limited to some tenths of the wavelength after processing. We present here a methodology which takes advantage of the combination of two different phenomena: continuous wave frequency modulation (CWFM), induced by direct modulation of the laser, and non-linear dynamics inside of the laser cavity subject to optical self-injection (OSI). The methodology we propose shows how to detect vibration amplitudes smaller than half the emission wavelength with resolutions way beyond λ/2, extending the typical performance of OFI setups to very small amplitudes. A detailed mathematical model and simulation results are presented to support the proposed methodology, showing its ability to perform such displacement measurements of frequencies in the MHz range, depending upon the modulation frequency. Such approach makes the technique a suitable candidate, among other applications, to economic laser-based ultrasound measurements, with applications in nondestructive testing of materials (thickness, flaws, density, stresses), among others. The results of simulations of the proposed approach confirm the merit of the figures as detection of amplitudes of vibration below λ/2) with resolutions in the nanometer range.

The results of an experimental investigation on the vibrational behaviour of a rotating disk are reported. This disk is a prototype that simulates a component of an aircraft engine. The air flow through the gap between the edge of the disk and the casing, produced because of the pressure difference between the upstream and downstream parts of the disk, might force the disk to flutter under certain circumstances. This situation is simulated in a wind tunnel. The main goal of the tests is to evaluate the vibrational behaviour of a rotating disk, obtaining the correspondence between the vibration frequencies of the disk and the pressure differences when the disk is rotating at diverse speeds. An innovative noncontact technique is utilised, which employs three optical sensors that are angularly equidistributed on the casing of the wind tunnel. In order to verify the results given by the optical sensors, a strain gauge was mounted on the surface of the rotating disk. The results show a perfect agreement between the vibration frequencies detected by both kinds of sensors, proving that the combination of both allows the calculation of the nodal diameter corresponding to the vibration of the disk.

A novel range-resolved interferometric signal processing technique that uses sinusoidal optical frequency modulation is applied to multi-surface vibrometry, demonstrating simultaneous optical measurements of vibrations on two surfaces using a single, collimated laser beam, with a minimum permissible distance of 3.5 cm between surfaces. The current system, using a cost-effective laser diode and a fibre-coupled, downlead insensitive setup, allows an interferometric fringe rate of up to 180 kHz to be resolved with typical displacement noise levels of 8 pm Hz^-0.5. In this paper, the system is applied to vibrometry measurements of a table-top cryostat, with concurrent measurements of the optical widow and the sample holder inside. This allows the separation of common-mode vibrations of the whole cryostat from differential vibrations between the window and the sample holder.

Laser Doppler vibrometry (LDV) is a well-known interferometric technique to measure the motions, vibrations and mode shapes of machine components and structures. The drawback of commercial LDV is that it can only offer a pointwise measurement. In order to build up a vibrometric image, a scanning device is normally adopted to scan the laser point in two spatial axes. These scanning laser Doppler vibrometers (SLDV) assume that the measurement conditions remain invariant while multiple and identical, sequential measurements are performed. This assumption makes SLDVs impractical to do measurement on transient events. In this paper, we introduce a new multiple-point laser coherent detection system based on spatial-encoding technology and fiber configuration. A simultaneous vibration measurement on multiple points is realized using a single photodetector. A prototype16-point laser coherent detection system is built and it is applied to measure the vibration of various objects, such as body of a car or a motorcycle when engine is on and under shock tests. The results show the prospect of multi-point laser coherent detection system in the area of nondestructive test and precise dynamic measurement.

Industrial automation has developed rapidly in the past decades. Customized fabrications and short production time require flexible and high speed inspection systems. Based on these requirements, optical surface inspection systems (OSIS) as efficient and cheap systems for detecting surface defects and none-defects becomes more and more important. To achieve a high recognition rate, huge amounts of image data of defects need to be stored. We introduce a virtual surface defect rendering method to obtain large amount of defect images. In this paper, the ray tracing methods are applied to realistically simulate camera images in OSIS. We used three different bidirectional reflectance distribution function (BRDF) rendering models to describe the scattering between collimated white light and aluminum materials.

Controlling surface appearance has become essential in the supplier/customer relationship. In this context, many industries have implemented new methods to improve the sensory inspection, particularly in terms of variability. A trend is to develop both hardware and methods for moving towards the automation of appearance inspection and analysis. If devices inspired from dimensional control solutions generally allow to identify defects far apart the expected quality of products, it do not allow to quantify finely appearance anomalies, and decide on their acceptance.

To address this issue, new methods devoted to appearance modelling and rendering have been implemented, such as the Reflectance Transformation Imaging (RTI) technique. By varying the illumination positions, the RTI technique aims at enriching the classical information conveyed by images. Thus each pixel is described by a set of values rather than one value classically; each value corresponding to a specific illumination position. This set of values could be interpolated or approximated by a continuous model (function), associated to the reflectance of the pixel, generally based on a second order polynomial (namely, Polynomial Texture Mapping Technique). This paper presents a new approach to evaluate this information from RTI acquisitions. A modal projection based on dynamics (Discrete Modal Decomposition) is used to estimate surface reflectance on each measurement point. After presenting the acquisition device, an application on an industrial surface is proposed in order to validate the approach, and compare it to the more classical polynomial transformation. Results show that the proposed projection basis not only provides closer assessment of surface reflectance (modelling) but also yields to a more realistic rendering.

The aim of the paper is to show the capabilities of the method of averaging of speckles in time to detect the area of nucleation of fatigue crack, registration since its start and contactless determination of crack velocity without stopping cyclic loading.

In this paper, we describe a simple and cost-effective method and measuring device for automatic detection of welding. The sensor is to be used in automatic darkening filters (ADF) of welding helmets protecting the operator from intensive hazardous UV radiation. For reasons discussed in detail below, conventional sensor principles used in ADF are being out-dated. Here, we critically revise some alternatives and propose an approach comprising an optical distance sensor. Its underlying principle is triangulation with two pin-hole cameras. The absence of optical components such as lenses results in very low cost. At first, feasibility is tested with optical simulations. Additionally, we present measurement results that prove the practicability of our proposal.

We have demonstrated a modified fringe reflection method to compensate the warpage measurement errors caused by the height difference between optical reference mirror and wafer sample surface. We have used a linearity analysis approach to obtain the parabolic height errors for a 4-inch sapphire wafer warpage measurement, which is around 1.48 μm of 100 μm height difference. The experimental results shows the warp discrepancy of 6-inch sapphire wafer is less than 1 μm compared with the reference Tropel instrument.

The basic composition and measuring principle of Laser Doppler Velocimeter (LDV) are discussed, and the superiority of LDV been the external velocity observation system of the strapdown inertial navigation system(SINS) is analyzed. For study of the RLG inertial navigation system and the LDV which is self-developed by our own department, the feasibility of SINS/LDV composite system is proved, and vehicle navigation tests have been conducted. Taking the DGPS as reference, the results show that the maximum positioning error of SINS/LDV composite system is 8 meters in one hour test while the maximum positioning error of pure SINS reaches 1130 meters. Results show that the SINS/LDV composite system can effectively inhibits the time accumulated navigation errors, and the high accuracy self-contained navigation can be realized.

Photonic Crystal Fibers (PCFs) have special structures and offer a number of novel design options, such as very large or very small mode areas, high numerical aperture, guidance of light in air, and novel dispersion properties. PCFs have become an attractive field for the researchers and they are trying to work on these to get their properties applied in dispersion related applications, sensing applications and much more. PCFs sensors are widely used in bio-medical applications. The sensitivity and performance of sensors are enhanced due to novel applications of PCFs. This paper outlines a novel design for a generalized biomedical sensor by collaborating PCF and electro-optic effect of Lithium Niobate (LiNbO₃) based Mach-Zehnder interferometer (MZI) structure.

Plastic injection molded lenses have improved its performance and, nowadays, are as usual as glass lenses in image forming devices. However, the manufacturing process induces the surface generation and the material transformation in the same stage. Moreover, the process also includes an annealing stage to remove the internal stress with temperature cycles but only works up to a certain level and not beyond, leaving relevant traces for high values. During the manufacturing process of a plastic lens, a liquid-solid phase transformation occurs, and in this transition not all the volume of the lens achieves the same density. This change of density is translated into a local change of refractive index that can be expressed as a retardation phase plane using the Jones Matrix notation. The detection and measurement of the value of the retardation of the phase plane is thus the clue to manufacture good and controlled quality plastic lenses.

We have tested an in-line polariscopic arrangement to obtain a 2D map of the tension distribution in the bulk of the lens. This test is performed in the first 30 seconds after the injection molding process for two main reasons: first the stress values are still high because the lenses do not have enough time to relax the internal tensions and obtain the final shape, and second, we can remove the wrong lenses in the first moments and introduce only the good lenses in the annealing stage.

The proposed instrument is based in a transmission polariscopic arrangement. A collimated light beam is used to illuminate the sample, once the light crosses the sample, it is collected with an afocal system and the image is recorded in a CMOS sensor. Selecting an afocal system to capture the image is a useful decision because the lateral magnification can be maintained when small changes in the sample position are introduced. However the produced lenses can vary their focal lengths from on series to another. To avoid problems with the change of the focal length, the lens is introduced in a matching index and the polariscopic measurement is done. The proposed polariscopic arrangement uses two lineal polarizers, one acting as polarizer and the other acting as analyzer. This system instead of using one lineal polarizer and a lineal polarizer with an extra lambda/4 plate provides us an extra degree of freedom, enabling the possibility to put a certain degree of polarization in a well determined position of the lens, in our case the center of this lens.

The aim of this study is to select the minimum number of sets polarizer-analyzer and the right wavelengths to obtain a sure selection of the right lens. The preliminary results show that use two different wavelengths 470 & 627 nm is a good option to obtain a robust image. The second free variables that must be adjusted to obtain good values is the minimum number of set polarizer-analyzer necessary to obtain confident results. In our first tests it seems that recording only at 0, 15, 30 and 45 degrees is enough to get good results.

Mathematica description and first results for a PMMA lens are presented, however the number of measurements must be diminished to obtain an easy in-line implementation

The dimensional field testing activity described in this paper allowed measuring the vertical and transverse dynamic displacement related to the main span (with a dimension equal to 1012 meters) central section of a long-span suspension bridge – the 25^th of April Bridge (P25A), in Lisbon (Portugal) – using an optical system composed by high focal length lens (600 mm), digital image sensor and active infrared LED targets. Maximum values of 0,53 m and 0,29 m were obtained for the vertical and transverse displacements without rail traffic on the P25A. Passenger train circulation on the bridge’s lower rail deck increased the vertical displacement up to 1,69 m. The applied measuring system was subjected to an in situ calibration procedure (SI traceable), showing maximum deviations close to 1,3 mm with an expanded measurement uncertainty (in a 95% confidence interval) around 3,0 mm, in a favorable observation scenario (winter season with low vertical thermal gradient in the atmosphere). Field studies of optical phenomena such as atmospheric refraction and beam wandering effect by turbulence were also performed, aiming the validation of developed refraction correction models and the quantification of targets image coordinates dispersions (0,13 pixel in winter season a 0,56 pixel during summer season).

To handle the issue of the nonlinear carrier phase due to the divergent illumination commonly adopted in the fringe projection measurement, we propose a principal component analysis (PCA) based carrier removal method for Fourier transform profilometry. By PCA, the method can decompose the nonlinear carrier phase map into several principal components, where the phase of the carrier can be extracted from the first dominant component acquired. It is effective and requires less human intervention since no data points need to be collected from the reference plane in advance compared with traditional methods. Further, the influence of the lens distortion is considered thus the carrier can be determined more accurately. Our experiment shows the validity of the proposed approach.

The investigation of transparent optical layers is a growing field of application of white-light interferometry. Robust algorithms exist that extract the signal components from different layers inside a transparent structure. The separated signal contributions are then evaluated individually. Two contradicting situations have to be accounted for when low-coherence interferometry is used to measure layer structures. First, with a low NA system and a short coherence light source, the optical path difference between the layers is measured. Second, if a high NA interferometer and a long coherence light source is used, the limited depth of focus limits the correlogram width. In this case, the layer thickness is underestimated. In this paper a 2.2 μm thick reference layer is studied. This layer was measured with different interferometric systems: Michelson and Mirau interferometers with magnifications from 5x to 100x. Furthermore, light sources with different temporal coherence length were used. If lateral resolution is unimportant, the combination of a low NA measuring system and a low coherence length light source provides a larger distance between the signal contributions from different boundary layers and therefore better separation, bias correction, and higher accuracy, compared to a high NA system. The interferometer system can be calibrated by measuring the layer thickness of a small structure with respect to a substrate. Such a calibration permits performing measurements with a high NA interferometer and a low coherence light source. The main contribution of this paper is to compare and discuss results of these different options of layer thickness measurement with respect to measurement accuracy and uncertainty influences.

Due to the increase in production of the angle transducers characterized by high accuracy and high speed of operation [1], there arises a need for metrological control of their function parameters. This challenge can be successfully met involving the dynamic goniometer systems (DG), which consist of the optical angle encoder (OAE) or the ring laser (RL) [2].

The dynamic laser goniometer systems [2], the scale of which is produced by the ring laser, can be successfully used for calibration of the angle encoders. The ring laser operating in the mode of the angle measurement during its rotation has a number of undeniable advantages, such as high degree of uniformity and potential accuracy. However, alongside with the advantages it has several limitations, such as the measurement error increase at low rotation velocity values and instability of the angular scale factor [2]. Integrating the ring laser and the optical angle sensor, the angular scale of which is characterized by a considerably lower uniformity, but a greater degree of stability, provides for the studying of the metrological characteristics of the dynamic goniometer, expansion of the range or its angular operation velocity and its operation in static mode. The articles covers the issues of constructing the dynamic goniometer for calibration of angle encoders as well as the methods and results of its studies.

This work presents a primary analysis of an adaptive laser scanner based on two-mirror beam-steering device and focustunable components (lenses with tunable focal length). It is proposed an optical scheme of an adaptive laser scanner, which can focus the laser beam in a continuous way to a required spatial position using the lens with tunable focal length. This work focuses on a detailed analysis of the active optical or opto-mechanical components (e.g. focus-tunable lenses) mounted in the optical systems of laser scanners. The algebraic formulas are derived for ray tracing through different configurations of the scanning optical system and one can calculate angles of scanner mirrors and required focal length of the tunable-focus component provided that the position of the focused beam in 3D space is given with a required tolerance. Computer simulations of the proposed system are performed using MATLAB.

The idea of using spatial filtering velocimeter is proposed to provide accurate velocity information for vehicle autonomous navigation system. The presented spatial filtering velocimeter is based on a CMOS linear image sensor. The limited frame rate restricts high speed measurement of the vehicle. To extend measurement range of the velocimeter, a method of frequency shifting is put forward. Theoretical analysis shows that the frequency of output signal can be reduced and the measurement range can be doubled by this method when the shifting direction is set the same with that of image velocity. The approach of fast Fourier transform (FFT) is employed to obtain the power spectra of the spatially filtered signals. Because of limited frequency resolution of FFT, a frequency spectrum correction algorithm, called energy centrobaric correction, is used to improve the frequency resolution. The correction accuracy energy centrobaric correction is analyzed. Experiments are carried out to measure the moving surface of a conveyor belt. The experimental results show that the maximum measurable velocity is about 800deg/s without frequency shifting, 1600deg/s with frequency shifting, when the frame rate of the image is about 8117 Hz. Therefore, the measurement range is doubled by the method of frequency shifting. Furthermore, experiments were carried out to measure the vehicle velocity simultaneously using both the designed SFV and a laser Doppler velocimeter (LDV). The measurement results of the presented SFV are coincident with that of the LDV, but with bigger fluctuation. Therefore, it has the potential of application to vehicular autonomous navigation.

The technique proposed in this paper provides a quality control components surface flatness by non-destructive and contactless way, with high resolution and increased sensitivity. The control is done in real time and instantaneously on all inspected surface. The technique has found various applications in diverse fields, from biomedical to industrial and scientific applications. In many industrial metrology applications, contactless and non-destructive shape measurement is a desirable tool for, quality control and contour mapping. This method of optical scanning presented in this paper is used for precision measurement deformation in shape or absolute forms in comparison with a reference component form, of optical or mechanical components, on surfaces that are of the order of few mm² and more. The principle of the method is to project the image of the source grating to palpate optically surface to be inspected, after reflection; the image of the source grating is printed by the object topography and is then projected onto the plane of reference grating for generate moiré fringe for defects detection. The optical device used allows a significant dimensional surface magnification of the area inspected for micro-surfaces, which allows easy processing and reaches an exceptional nanometric imprecision of measurements. According to the measurement principle, the sensitivity for displacement measurement using moiré technique depends on the frequency grating, for increase the detection resolution

It’s considered the problem of the increase to tens of meters working distance of the optical-electronic autocollimators is studied when determining the angular position of objects. To solve this problem it is proposed to use a quadrangular pyramid-shaped reflector. By means computer models comparative analysis of the effectiveness of the proposed reflector and traditional flat mirror was carried out. Type of algorithm that allows to realize the required accuracy at longer distances was defined. Also radiation properties of systems of mirrors in the form of mirror-symmetric angles are investigated. Comparison of such mirror systems and proposed quadrangular pyramidal reflector was carried out.

Molecular condensation nuclei (MCN) method is used in production engineering and process monitoring and relates to optical metrology methods of measuring the concentrations of various contaminants in the environment. Ultra high sensitivity of MCN method to a class of substances is determined by measuring the optical scattering aerosol particles, at the centers of which are located the detectable impurities molecules. This article investigates the influence of MCN manifestations coefficient (ratio of the concentration of aerosol particles to the concentration of molecules detectable impurities) on the sensitivity of the MCN detector. The MCN method is based on the application of various physicochemical processes to the flow of a gas containing impurities. As a result of these processes aerosol particle that are about 106 times larger than the original molecule of the impurity are produced. The ability of the aerosol particle to scatter incident light also increases ~10¹⁴ ÷10¹⁶ times compared with the original molecule and the aerosol particle with the molecule of the impurity in the center is easily detected by light scattering inside a photometer. By measuring of the light scattering intensity is determined concentration of chemical impurities in the air. An application nephelometric optical metrology scheme of light scattering by aerosol particles ensures stable operation of reliable and flexible measuring systems. Light scattering by aerosol particles is calculated on the basis of the Mie’s theory as aerosol particle sizes comparable to the wavelength of the optical radiation. The experimental results are shown for detectable impurities of metal carbonyls. Gas analyzers based on the MCN method find application in industries with the possibility of highly toxic emissions into the atmosphere (carbonyl technology of metal coatings and products, destruction of chemical weapons, etc.), during storage and transportation of toxic substances, as well as in the inspection of large-scale objects. There are some perspective areas of use MCN detector: prevention of illegal use of dangerous substances, revealing of their origin and leakage paths by means of marking with special non-radioactive chemical compounds; investigation of large-scale atmospheric circulation with the help of marking substances; nondestructive inspection for highly efficient filters with indicating agent concentration and for the inspection of the devices of high level tightness (heat-exchangers of fast nuclear reactors).

All surveying instruments and their measurements suffer from some errors. To refine the measurement results, it is necessary to use procedures restricting influence of the instrument errors on the measured values or to implement numerical corrections. In precise engineering surveying industrial applications the accuracy of the distances usually realized on relatively short distance is a key parameter limiting the resulting accuracy of the determined values (coordinates, etc.).

To determine the size of systematic and random errors of the measured distances were made test with the idea of the suppression of the random error by the averaging of the repeating measurement, and reducing systematic errors influence of by identifying their absolute size on the absolute baseline realized in geodetic laboratory at the Faculty of Civil Engineering CTU in Prague. The 16 concrete pillars with forced centerings were set up and the absolute distances between the points were determined with a standard deviation of 0.02 millimetre using a Leica Absolute Tracker AT401.

For any distance measured by the calibrated instruments (up to the length of the testing baseline, i.e. 38.6 m) can now be determined the size of error correction of the distance meter in two ways: Firstly by the interpolation on the raw data, or secondly using correction function derived by previous FFT transformation usage.

The quality of this calibration and correction procedure was tested on three instruments (Trimble S6 HP, Topcon GPT-7501, Trimble M3) experimentally using Leica Absolute Tracker AT401.

By the correction procedure was the standard deviation of the measured distances reduced significantly to less than 0.6 mm. In case of Topcon GPT-7501 is the nominal standard deviation 2 mm, achieved (without corrections) 2.8 mm and after corrections 0.55 mm; in case of Trimble M3 is nominal standard deviation 3 mm, achieved (without corrections) 1.1 mm and after corrections 0.58 mm; and finally in case of Trimble S6 is nominal standard deviation 1 mm, achieved (without corrections) 1.2 mm and after corrections 0.51 mm.

Proposed procedure of the calibration and correction is in our opinion very suitable for increasing of the accuracy of the electronic distance measurement and allows the use of the common surveying instrument to achieve uncommonly high precision.

High precision optical encoders are used for many high end computerized numerical control machines. Main requirement for such systems are accuracy and time of measurement, therefore image processing are often performed by FPGA or DSP. This article will describe image processing algorithm for detecting and measuring pitch position on invar scale, which can be easily implemented on specified target hardware. The paper proposed to use a one-dimensional approach for pitch recognition and measure its position on the image. This algorithm is well suited for implementation on FPGA and DSP and provide accuracy 0.07 pixel.

Reflection Z-scan technique allows the measurements of optical nonlinearities of highly absorbing media and surface of transparent media, when transmission Z-scan can not be used. However, Reflection Z-scan needs multiple measurements under strong laser pulse excitation in the scanning process. This can induce damage in the sample in some cases. In this paper, a Non-scanning Reflection Technique (NRT) for measurement of optical nonlinearities is presented to overcome this drawback. Both the nonlinear refraction index and nonlinear absorption coefficient can be determined by measuring the reflection in combination of variable attenuator and an aperture. Based on the Fresnel theory, a theoretical analysis of Non-scanning Reflection Technique (NRT) demonstrates the feasibility of this approach is given and a general expression for the normalized reflectance is derived. In order to illustrate our analytical results, we performed a numerical simulation of the normalized reflectance. Besides, retardance and size of the induced phase plate also make contributions to the normalized reflectance. Moreover, this technique shows a higher sensitivity property compared with traditional reflection Z-scan method.

The paper analyzes the construction matters and metrological parameters of the electrooptic converter to control linear displacements of the large structures of the buildings and facilities. The converter includes the base module, the processing module and a set of the reference marks. The base module is the main unit of the system, it includes the receiving optical system and the CMOS photodetector array that realizes the instrument coordinate system that controls the mark coordinates in the space. The methods of the frame-to-frame difference, adaptive threshold filtration, binarization and objects search by the tied areas to detect the marks against accidental contrast background is the basis of the algorithm. The entire algorithm is performed during one image reading stage and is based on the FPGA. The developed and manufactured converter experimental model was tested in laboratory conditions at the metrological bench at the distance between the base module and the mark 50±0.2 m. The static characteristic was read during the experiment of the reference mark displacement at the pitch of 5 mm in the horizontal and vertical directions for the displacement range 400 mm. The converter experimental model error not exceeding ±0.5 mm was obtained in the result of the experiment.

The purpose of this research is the development of a system for fabricating high-speed and long-time measurements of wide-band vibration using fiber Bragg gratings (FBGs) to determine the health of structures. We developed a real-time FBG interrogation system using wavelength swept laser. This system can perform real-time measurement of reflected wavelength from a multiple FBG at a temporal resolution of 0.1 ms. The authors also constructed a database system for managing the data obtained from high-speed and long-time measurement. This database system manages data using a relational database and transfers information on FBG reflected wavelengths obtained from this measurement system via the local network. We have demonstrated that this system is able to measure reflected wavelengths from a multipoint FBG at a temporal resolution of 0.1 ms over 24 hours, it was shown that this system could also monitor instantaneously applied high-speed vibrations.

Nuclear graphite has been widely used as moderating and reflecting materials. However, due to severe neutron irradiation under high temperature, nuclear graphite is prone to deteriorate, resulting in massive microscopic flaws and even cracks under large stress in the later period of its service life. It is indispensable, therefore, to understand the fracture behavior of nuclear graphite to provide reference to structural integrity and safety analysis of nuclear graphite members in reactors. In this paper, we investigated the fracture expansion in nuclear graphite based on PDE image processing methods. We used the second-order oriented partial differential equations filtering model (SOOPDE) to denoise speckle noise, then used the oriented gradient vector fields for to obtain skeletons. The full-field displacement of fractured nuclear graphite and the location of the crack tip were lastly measured under various loading conditions.

The oil-film interferometry skin friction technique is described and applied to subsonic and supersonic flows. The details for applying the technique are discussed. Results are shown for tests that illustrate the oil-film's good ability to measure the skin friction in a large scale. It is anticipated that continued development of this program will be necessary for use of oil-film technique to become widespread.

A design for simultaneously measuring the polarization state of light based on division of wave front is presented. An incident light beam is divided by a composite beam splitter into four branches. The four branches of light are detected by four different independent detecting units respectively. The measured signal values from the four detecting units are used to form a signal vector. The instrument matrix of the system is obtained by calibration experiment. The Stokes vector describing the polarization state of an incident light is obtained by the matrix calculation by using the signal vector and the instrument matrix. The calculated result for an incident light is in good agreement with the measurement one.

Video data require a very large memory capacity. Optimal ratio quality / volume video encoding method is one of the most actual problem due to the urgent need to transfer large amounts of video over various networks. The technology of digital TV signal compression reduces the amount of data used for video stream representation. Video compression allows effective reduce the stream required for transmission and storage. It is important to take into account the uncertainties caused by compression of the video signal in the case of television measuring systems using. There are a lot digital compression methods. The aim of proposed work is research of video compression influence on the measurement error in television systems. Measurement error of the object parameter is the main characteristic of television measuring systems. Accuracy characterizes the difference between the measured value abd the actual parameter value. Errors caused by the optical system can be selected as a source of error in the television systems measurements. Method of the received video signal processing is also a source of error. Presence of error leads to large distortions in case of compression with constant data stream rate. Presence of errors increases the amount of data required to transmit or record an image frame in case of constant quality. The purpose of the intra-coding is reducing of the spatial redundancy within a frame (or field) of television image. This redundancy caused by the strong correlation between the elements of the image. It is possible to convert an array of image samples into a matrix of coefficients that are not correlated with each other, if one can find corresponding orthogonal transformation. It is possible to apply entropy coding to these uncorrelated coefficients and achieve a reduction in the digital stream. One can select such transformation that most of the matrix coefficients will be almost zero for typical images . Excluding these zero coefficients also possible reducing of the digital stream. Discrete cosine transformation is most widely used among possible orthogonal transformation. Errors of television measuring systems and data compression protocols analyzed In this paper. The main characteristics of measuring systems and detected sources of their error detected. The most effective methods of video compression are determined. The influence of video compression error on television measuring systems was researched. Obtained results will increase the accuracy of the measuring systems. In television image quality measuring system reduces distortion identical distortion in analog systems and specific distortions resulting from the process of coding / decoding digital video signal and errors in the transmission channel. By the distortions associated with encoding / decoding signal include quantization noise, reducing resolution, mosaic effect, "mosquito" effect edging on sharp drops brightness, blur colors, false patterns, the effect of "dirty window" and other defects. The size of video compression algorithms used in television measuring systems based on the image encoding with intra- and inter prediction individual fragments. The process of encoding / decoding image is non-linear in space and in time, because the quality of the playback of a movie at the reception depends on the pre- and post-history of a random, from the preceding and succeeding tracks, which can lead to distortion of the inadequacy of the sub-picture and a corresponding measuring signal.

The paper deals with the sequential Monte Carlo method applied to the problem of interferometric signals parameters evaluation. A stochastic model of interferometric signal formation is presented. Detailed description of the algorithm is given. The sequential Monte Carlo method modification based on the assumption of Gaussian posterior probability density function of parameters is proposed. The peculiarities of the algorithm and its modification are considered and discussed. The results of parameters evaluation are presented. Data processing rate of proposed methods is estimated and analyzed.

Laser induced damage for nanosecond pulse duration is attributed to the existence of defects. The growth and polishing, as well as coating deposition, may induce versatile kinds of defects, including dig, scratch and inclusion. It is special important to get the information of the defects, such as size and location, which is the basis to know the origin of the defects and figures out effective techniques to eliminate it. It is quite easy to get the information of the defects with micron-level resolution, but it is time-consuming and is not suitable for fast inspection of the large aperture (hundreds of millimeters). In this work, on-the-fly image capture technique was employed to realize fast inspection of large aperture optics. A continuous green laser was employed as illumination source to enhance and enlarge the image of bulk defects. So it could detect the submicron-scale defects. A transmission microscopy with white light illumination was employed to detect the surface defect. Its field of view was about 2.8mm×1.6mm. The sample was raster scanned driving by a stepper motor through the stationary illumination laser and digital camera, and the speed to scan the sample was about 10mm/s. The results of large aperture optics proved the functions of this fast inspection technique.

The subjects of this paper are optical rotary encoders and methods for a minimizing of measured errors of the controlled process of rotary encoders. In addition, the paper describes measuring methods and equipment for the automated accuracy control of optical rotary encoders and a method for compensation of measured errors. The paper presents a novel special coupling device for control encoders. The design of the novel coupling device provides an unrestrained connection between controlled and reference encoders. The elaborated experimental setup increases the calibration accuracy of rotary encoders considerably.

In this paper, we extended the measurement method of mid-frequency wavefront error to spherical and aspherical components. Some influence factors like the system error of interferometer, environment variation, surface parallelism of optics, polarizations of interferometer illumination, and the wavefront distribution of optics are analyzed in detail. Some optimized measurement strategies for different kinds of optics are suggested. Finally, experimental measurements on flat optics, spherical and aspherical optics are performed to testify the suggested measurement methods, respectively.

When we use laser to measure the focal ratio degradation of astronomical fibers, we have to reduce the speckle contrast to fit the output spot to a 2-D Gaussian-like function. The origin speckle contrast is near to 100%. The simple average method doesn’t work because the speckle patterns are stable. We tried several ways to disturb randomly the transmission phase of the light modes inside the fiber to be tested. Both non-contact fiber-disturb-mode device (NCFDMD) and contact fiber-disturb-mode device (CFDMD) were established and tested. The NCFDMD is to set a vibrating phase plate against the output end of the tested fiber. The CFDMD is to set the vibrating device in the middle of the fiber. Under different vibration frequency we compared the contrast of speckle patterns. We set different exposure time of the CCD camera to check the effects. For NCFDMD, the exposure time should be long enough, for example 30 ms, to guarantee enough different patterns could be collected to suppress the contrast of the speckle and get good Gauss-like pattern. For CFDMD, we compared three kinds of fibers with different core-diameters. We found that 65-70 Hz is the optimized vibration frequency for all fibers and 30 ms is the best exposure time. The introduction of the phase modulation could dramatically suppress the speckle under coherent illumination. The measurement accuracy could be enhanced according to the speckle suppression

Phase-shifting is a well-known technique for phase retrieval that requires a series of intensity measurements with certain phase-steps. Harmonics and linear phase-shift errors are the main source of errors in interferometry. In this work we present a systematic algebraic approach for the generation of phase-shifting algorithms(for interferograms with arbitrarily phase-steps) insensitive to harmonics and linear phase-shift errors.

Systems based on quadrant photodiode can be used for solving different angular position measurement tasks. But such systems have accuracy problems. Solving these accuracy problems makes systems based on quadrant photodiode applicable for different industrial inspection processes such as positioning and pointing systems and interferometer experiments. For example angular drift in a laser beam can be a serious concern in interferometer experiments where anomalous fringe shifts can be caused by such drift.

The packing presswork is an important factor of industrial product, especially for the luxury commodities such as cigarettes. In order to ensure the packing presswork to be qualified, the products should be inspected and unqualified one be picked out piece by piece with the vision-based inspection method, which has such advantages as no-touch inspection, high efficiency and automation. Vision-based inspection of packing presswork mainly consists of steps as image acquisition, image registration and defect inspection. The registration between inspected image and reference image is the foundation and premise of visual inspection. In order to realize rapid, reliable and accurate image registration, a registration method based on virtual orientation points is put forward. The precision of registration between inspected image and reference image can reach to sub pixels. Since defect is without fixed position, shape, size and color, three measures are taken to improve the inspection effect. Firstly, the concept of threshold template image is put forward to resolve the problem of variable threshold of intensity difference. Secondly, the color difference is calculated by comparing each pixel with the adjacent pixels of its correspondence on reference image to avoid false defect resulted from color registration error. Thirdly, the strategy of image pyramid is applied in the inspection algorithm to enhance the inspection efficiency. Experiments show that the related algorithm is effective to defect inspection and it takes 27.4 ms on average to inspect a piece of cigarette packing presswork.

Optical passive methods for temperature measurements such as thermography or optical pyrometry are very interesting because they allow a non-intrusive measurement when the emissivity is known. The knowledge of this coefficient is critical for determining the actual temperature of a surface from the thermal radiation emitted in a wavelength band. The bichromatic pulsed pyrometer allows to overcome the knowledge of this parameter provided that precautions are taken in the choice of the values of wavelengths. When the object to be measured is placed in harsh environments, such passive optical methods are greatly disturbed by the presence of an optically absorbing medium. They are also distorted when the measured objects are located in very hot environments emitting intense disturbing radiation. In this study, we present an active bichromatic radiometric method for measuring the temperature of a surface in harsh environments. The method is based on a localized excitation by a modulated laser source in the infrared range. Detecting the temperature modulation, which is correlated with the excitation, is performed using a lock-in amplifier able to extract the signal embedded in a noise up to a million times superior. Working at short wavelengths (visible range and near infrared range) offers a large dynamic range and minimizes the error due to variations in emissivity with the wavelength. This system collects the radiation emitted by the object at a distance from a few meters up to dozens of meters depending on the configuration of the optical system. Both the principle and the design of the active bichromatic optical surface thermometer are presented and discussed. To demonstrate the method, results obtained on a molten ceramic stream are presented.

The sapphire fiber-optic temperature sensor based on Black-Body radiation law, is a new technique of high-temperature measurement in extreme environment, which combines techniques of radiometric thermometry and optical-based temperature measurement. In this paper, a system is established and tested. Results approved that the sapphire fiber-optic temperature sensor based on Black-Body radiation law has high sensitivity and is suitable for 800-1600° temperature measurement.

Temperature sensing is one of the key requirements for Structure Health Monitoring (SHM) in various applications. The intensity modulated optical fiber sensors are excellent candidate for this area of applications due to their relatively low cost, simple structure and diversity of applications. This work relates mainly to the feasibility evaluation of embedding optical fiber sensor into ceramic coating obtained by thermal spray process and the thermal response of the embedded sensor. The sensor principle and the specimen configuration are firstly presented, a 3D model is then built up in order to evaluate the effects of temperature variation on deformations of the optical fiber sensor which finally lead to the variation of optical intensity. First results of thermal response are discussed.

Measurement of rotation of plane of polarization of linearly polarized light can provide information about the concentration of the optically active system with which it interacts. For substances containing sugar, accurate measurement of rotation of linearly polarized light can provide quantitative information about concentration of sugar in the material. Measurement of sugar concentration is important in areas ranging from blood sugar level measurement in body fluids to measurement of sugar concentrations in juices and other beverages. But in many of these cases, the changes introduced to the state of polarization considering a sample of practical proportion is low and the measurement of low optical rotations becomes necessary. So methods with higher sensitivity, accuracy and resolution need to be developed for the measurement of low optical rotations. Here we describe the development of a compact, low cost, field portable, device for rotation sensing leading to sugar concentration measurements, using speckle de-correlation technique. The developed device measures rotations by determining the changes occurring to a speckle pattern generated by a laser beam passing through the medium under investigation. The device consists of a sample chamber, a diode laser module, a ground glass diffuser and a digital sensor for recording of laser speckle patterns. The device was found to have high resolution and sensitivity.

The purpose of this article is to examine the method of angular position measuring of a point source in a system with a CCD array by means of linear dimension - time slot - code transformation and assessment of the potential accuracy of the method, which is determined by instrumental irremovable random errors of measurement in terms of optimal processing of incoming information with a single reading it with CCD - lines. This work introduces an optoelectronic system circuit with CCD arrays with stretched sensing elements and a point of reference for angular position measuring.

In this case the arrays have images projections of both the reference point source and the target point source, whose angular position is measured with high precision. From the CCD array output the signals arrive at an optimal (or apt) linear filter, and then to the signal peak position detection circuit, which provides the minimum error due to noise impact. Pulse edges, corresponding to the signals maximum, make a time interval filled with high-frequency counting pulses. The number of pulses in this interval will correspond to the measured angular position of the target point source.

In terms of the statistical decision theory this work analyses random errors given the signals spectral function that, in turn, accounts for the transfer function of the optical system and the CCD array as an image analyzer. This article also presents analysis of how measurement accuracy depends on frequency of information readout from the CCD-arrays for different values of signal-to-noise ratio.

Error analysis of the proposed optoelectronic circuits showed that measurements can be made upon a single readout with an accuracy of 0.01 and even 0,001 pixels.

Optical spectroscopy is without doubt one of the most important non-contact measurement principles. It is used in a wide range of applications from bio-medical to industrial fields. One recent trend is to miniaturize spectral sensors to address new areas of application. The most common spectral sensor type is based on diffraction gratings, while other types are based on micro mechanical systems (MEMS) or filter technologies. The authors represent the opinion that there is a potentially wide spread field of applications for spectrometers, but the market limits the range of applications since they cannot keep up with targeted cost requirements for consumer products. The present article explains an alternative approach for miniature multichannel spectrometer to enhance robustness for hand held field applications at a cost efficient price point.

The integration of quality control in manufacturing process contains this paper and discusses the possibilities for integrated quality control in CNC milling machines without clamping off a workpiece.

For these concepts non-contact measurements with image processing sensors have significant benefits for data acquisition in rapidity and a high grade of flexibility. New effective measurement strategies can be developed in effect of the quality controlling in the machining area. These includes classical geometric measurement applications from optical 2D but also options for 3D measurement tasks like determining roughness or other typical image processing applications.

This paper presents the challenges for the implementation of an optical sensor system in the machining area of milling centers. Primarily a suitable location in the machining area must be found and an associated strategy has to be developed. The integrated optical image sensor system should be protect against impurity and does not derogate in his functionality. For the full integration as a quality control loop, the results must feed into the machine control. Thus a further interface between measurement program and a machine control is necessary.

Another major field of research exists in the optical components. Especially the illumination, image sensor and lens are selected and adaptable for the measurement tasks after the considerations of the above-mentioned basic requirements.

The presented research provides a suitable solution to make the CNC manufacture more efficient. Quality controls of the work piece can be executed within the CNC process and potential post processing can be performed simultaneously.

The internal shape and alignment of accelerator discs is crucial for efficient collider operation in the possible future compact linear collider. We applied a custom made and calibrated Fourier domain short coherence interferometer to measure the height of 40 and 60 μm machined steps on a copper disc in our laboratory. The step heights were determined to be: (43.0 ± 3.1) μm and (46.5 ± 3.2) μm for the 40 μm nominal step, and (46.6 ± 3.6) μm for the 60 μm nominal step. The errors represent 95% confidence level uncertainties and include uncertainty contributions from the calibration, refractive index of air, cosine error, and surface roughness. The step heights were validated by a calibrated contact stylus profilometer which resulted into (44.5 ± 0.8) μm and (45.9 ± 1.0) μm for the 40 μm nominal step, and (45.5 ± 1.7) μm for the 60 μm nominal step at 95% confidence level. The results show feasibility for noncontacting absolute shape and step height characterization with micrometer-level accuracy. This instrument is a first step towards a quality assurance tester for the accelerating structures of the compact linear collider.

The research of the nonexcluded air control error componentin optoelectronic systems the spatial position of distant objects control based on dispersion method is provided. It is invited to consider the influence of the air tract on the direction of an optical beam. There is some methods of the nonexcluded air control error component determination in the paper.

Continuous development of high-speed railway traffic in the world toughens requirements, including to the accuracy of installation and control of provision of a railway track. For the current technologies of service of a railway track using its absolute coordinates the perspective decision is creation along railway lines of a special fiducial network. In this case by means of optical-electronic systems, concerning reference points, obtaining the objective information on actual position of a railway track in a longitudinal cross-section and the plan with a margin error which isn't exceeding 1,5 mm in rather severe conditions of continuous operation of traveling machines at speeds up to 10 km/h is possible.

Autocollimator’s principle of operation is regarded from the optical imaging point of view. The aberration influence on measurements is presented through both ray geometry and wave front approaches. The role of measurement setup properties is considered. Simulation and experimental results are presented to bring preliminary estimates.

An optical method for in- plane rotation angle measurement based on hardware sampling moiré is presented. This method is investigated and introduced as a new technique for in- plane rotation angle measurement. Equations are derived and theoretical calculation and experiment are done base on these. Experimental results confirms that measurement accuracy in order of 0.1 degree conform to expectance results. Advantages of this technique are simplicity, high sensitivity and measurement and direction determination of rotation angle in the same time.

This paper presents results of development of a hydroacoustic activity method based on use of vibrosensitive properties of optical fiber with fiber Bragg gratings. Analysis of changes for parameters of radiation in reflected signals, which take place due to microscopic hydroacoustic impacts on the optical fiber, allows to determine position of the source and to identify its class. The practical usage of the suggested approach has demonstrated its essential viability.

High precision optical contactless position measurements are a key technology in modern industrial inspection. The characteristics of the different types of retroreflective materials and devices, require specialized designs of optical systems to precisely measure their properties. Various instruments are available to measure the retroreflective characteristics rather in the laboratory or under real conditions. Main parameters, such as aperture angles and the tolerances on observation angle and entrance pupil must be considered when designing such systems or large inaccuracies will occur. This paper presents results of the theoretical and experimental analysis of the errors of autoreflection schemes for alignment control based on corner-cube retroreflectors, which investigated the influence of the most significant factors.

Holography dates back to the year when Dennis Gabor reported on a method to avoid spherical aberration and to improve image quality in electron microscopy. Gabor’s two-step holographic method was pioneer but suffered from three major drawbacks: the reconstructed image is affected by coherent noise, the twin image problem of holography that also affects the final image quality, and a restricted sample range (weak diffraction assumption) for preserving the holographic behavior of the method. Nowadays, most of those drawbacks have been overcome and new capabilities have been added due to the replacement of the classical recording media (photographic plate) by digital sensors (CCD and CMOS cameras). But in the Gabor’ regime, holography is restricted to weak diffraction assumptions because otherwise, diffraction prevents an accurate recovery of the object's complex wavefront. In this contribution, we present an experimental approach to overcome such limitation and improve final image resolution. We use the phase-shifting Gabor configuration while the CCD camera is shifted to different off-axis positions in order to capture a bigger portion of the diffracted wavefront. Thus, once the whole image set is recorded and digitally processed for each camera's position, we merge the resulting band-pass images into one image by assembling a synthetic aperture. Finally, a superresolved image is recovered by Fourier transformation of the information contained in the generated synthetic aperture. Experimental results are provided using a USAF resolution test target and validating our concepts for a gain in resolution of close to 2.

Modern structural elements are often made of laminated polymer materials or composites on the base of polymer matrices. The proper functioning of these elements may be of vital importance especially in automotive and aerospace industries, in gas and oil transportation. The major problem in their performance is a possibility of a sudden and irreversible delamination caused by various factors. We propose and study a NDT approach aimed to detect delamination areas in adhesively bonded layered structural elements made of different materials. The proposed approach is evaluated by use of holographic detection and monitoring of the evolution of bulk strain solitons generated in such structures.

Imaging and measurement of diffusion process in liquid solutions is a challenging and interesting problem. Especially the mixing of binary liquid solutions in real-time provides an insight into the physics of diffusion as well as leads to measurement of diffusion coefficient, which is the most important parameter of a diffusing liquid solution. Accurate measurement of diffusion coefficient is important in areas ranging from oil extraction to pollution control. Interferometric methods provides very accurate measurement of diffusion coefficients albeit they impose very stringent optical conditions. Here we describe the development of a compact, easy to implement, easy to use and inexpensive device for imaging and quantification of the diffusion process. This technique does not require the stringent optical conditions of interferometric techniques. It computes the diffusivity values by measuring the amount of deflection happening to a line pattern printed on a paper and projected through the sample cell. The measured diffusivity values varied by less than 1%, with the values of diffusivities reported in literature.

Image registration techniques are used among different scientific fields, like medical imaging or optical metrology. The straightest way to calculate shifting between two images is using the cross correlation, taking the highest value of this correlation image. Shifting resolution is given in whole pixels which cannot be enough for certain applications. Better results can be achieved interpolating both images, as much as the desired resolution we want to get, and applying the same technique described before, but the memory needed by the system is significantly higher. To avoid memory consuming we are implementing a subpixel shifting method based on FFT. With the original images, subpixel shifting can be achieved multiplying its discrete Fourier transform by a linear phase with different slopes. This method is high time consuming method because checking a concrete shifting means new calculations. The algorithm, highly parallelizable, is very suitable for high performance computing systems. GPU (Graphics Processing Unit) accelerated computing became very popular more than ten years ago because they have hundreds of computational cores in a reasonable cheap card.

In our case, we are going to register the shifting between two images, doing the first approach by FFT based correlation, and later doing the subpixel approach using the technique described before. We consider it as ‘brute force’ method. So we will present a benchmark of the algorithm consisting on a first approach (pixel resolution) and then do subpixel resolution approaching, decreasing the shifting step in every loop achieving a high resolution in few steps. This program will be executed in three different computers. At the end, we will present the results of the computation, with different kind of CPUs and GPUs, checking the accuracy of the method, and the time consumed in each computer, discussing the advantages, disadvantages of the use of GPUs.

Temperature data play an important role in the combustion chamber since it determines both the efficiency and the rate of pollutants emission of engines. Air pollution problem concerns the emissions of gases such as CO, CO₂, NO, NO₂, SO₂ and also aerosols, soot and volatile organic compounds. Flame combustion occurs in hostile environments where temperature and concentration profiles are often not easy to measure. In this study, a temperature and CO₂ concentration profiles optical measurement method, suitable for combustion analysis, is discussed and presented. The proposed optical metrology method presents numerous advantages when compared to intrusive methods. The experimental setup comprises a passive radiative emission measurement method combined with an active laser-measurement method. The passive method is based on the use of gas emission spectroscopy. The experimental spectrometer device is coupled with an active method. The active method is used to investigate and correct complex flame profiles. This method similar to a LIDAR (Light Detection And Ranging) device is based on the measurement of Rayleigh scattering of a short laser pulse recorded using a high-speed streak camera. The whole experimental system of this new method is presented. Results obtained on a small-scale turbojet are shown and discussed in order to illustrate the potentials deliver by the sophisticated method. Both temperature and concentration profiles of the gas jet are presented and discussed.

Ever higher output power of fiber lasers leads to growing requirements on the fibers used. The increasing intensity of light in the fiber core is compensated by enlargement of the area of the doped core. The guiding properties of the optical fiber are significantly affected and must be very accurately defined. This high intensity leads to significant deviations of the guiding properties of the optical fiber during laser operation due to absorption and thermal effects. In particular, information about the change in group-velocity dispersion(GVD) during operation is important for the development of high power fiber laser systems. In an effort to gather such knowledge, this paper presents the results of dispersion characterization measurements using ytterbium-doped large-mode-area double-clad fibers which are cladding pumped at a wavelength of 975 nm. The direct measurement of the GVD in the emission range of the ytterbium-doped fibers (1000 nm to 1150 nm) is shown.

GVD characteristics of two different large-mode-area double-clad fibers with defined launching pump laser power level were systematically analyzed. The dispersion parameters for different fiber designs and various doping levels are investigated over a broad spectral range in the emission area of Yb-doped fiber samples for controlled sets of operating parameters. The experiment utilizes a supercontinuum source developed within this laboratory as well as a Mach-Zehnder interferometer with a dual-channel spectral-detection system sensitive to wavelengths from 0.95 μm to 1.75 μm. Temporally resolved spectrograms recorded at distinct delay positions enable the detection of interference fringes for the equalization wavelength. By applying a Sellmeier polynomial fit to the wavelength dependent differential group-delay function, the GVD can be derived. The measured Yb-doped large-mode-area fibers show a variation of the doping concentration between 0.7 mass percent to 3 mass percent of ytterbium. The measurement of the Yb-doped large-mode-area fiber with or without optical load on the sample during the measurement was examined.

The improved autocollimation system for measuring three-dimension angular deformations of pipe sections at large constructions as support tube of radio telescope mirror is analyzed. New type of the reflector for autocollimators is researched. The reflector is the trihedral mirror composition of three reflecting sides. It advantage is the measurement pitch, yaw and torsion as three angular rotation of controlled object. The second advantage of reflector is the measurements on the large work distances. Causes are the small value of the conversion coefficient and two orthogonal reference axes of trihedral reflector. The technical characteristics of the experimental setups of new reflector are presented. The features of trihedral reflector as the reflectors for optic-electronic autocollimators are discussed.

During the designing and operation of extensive engineering facilities is particularly important as the task of controlling the spatial position of elements of their design in real time. This task is often complicated by variable external conditions: fluctuations in ambient temperature, humidity, wind speed, level of background light, etc. In this article we discussed some solutions to solve this problem. We proposed an original method for solving the system of differential equations to calculate the coordinates of the objects. It’s verified the possibility of designing the system of measurement of the deformation through the control of individual structural parts. We provide the physical simulation of the system for controlling the position of the roof of large buildings. Much attention was devoted to the experiments to confirm the theoretical results.

Autocollimating systems for roll angle measurement with tetrahedral reflector, which has the small deviation from 90° in two dihedral angles between reflecting sides is considered. Established that autocollimator scheme with symmetrical track of the beam relative to roll axis with addition re-reflection allow implement precision measurement roll angle.

In this work it is shown that the refractive index and temperature distribution of atmospheric Dielectric Barrier Discharge (DBD) plasmas are measured by Moiré deflectometry. Fringe analysis is used to calculate Moiré deflection and to evaluate refractive index in different points of plasma. By Sa-Ha equation and considering the first ionization, the dependence of refractive index and temperature, electrons, ions and molecules number densities of DBD plasma is obtained. By knowing this relation between plasma parameters, the spatial distributions of the plasma refractive index and temperature are evaluated. The advantages of this method are: simplicity, non-contact, non-destructive measurement, low cost, high accuracy and direct measurement of refractive index gradient.

The article is devoted to problems of research and development of hyper - chromatic lenses for optical coherence tomography. The article discusses the possibility of developing hyper - chromatic lenses for a given spectral range made of glasses only. It is proposed to use the kinoform as the main power element of lens. There are shown the results of the analysis of the aberration properties of kinoform, as well as conclusions about the impossibility of its use as a single component of hyper - chromatic lens. There are shown the formulas for calculating the overall characteristics of a kinoform. The study also considered the method of calculation of hybrid lens consisting of a kinoform and lens parts. The article gives examples of hybrid lenses developed with the main characteristics and overall quality characteristics.

Optical methods of three-dimensional profilometry have been of growing interest in both industrial and scientific applications. These techniques provide absolutely non-destructive measurement due to their non-contact nature and maintain their high precision in a large field of view. Most of these techniques however, are based on interferometry which happens to be considerably sensitive to environmental noises such as turbulence and vibration. We have used the phenomena of Fresnel diffraction from phase-steps instead of interferometry to maintain a higher precision and reduce sensitivity to environmental noises. This phenomena has been recently introduced as a method for precise measurement of wavelength, thickness and refractive index. A 2D array of reflective disks are placed above the test surface to provide the required phase-steps. In this paper, theoretical principles of Fresnel diffraction from phase-steps are discussed and the experimental results of testing an optical flat surface are presented. A flat mirror surface has been tested as an optical test surface and is been profiled. The results show that the method is precise and is not sensitive to environmental noises such as vibration and turbulence. Furthermore, the method seems to be a powerful means for testing of curved surfaces, too.

Milk is an emulsion of fat globules and casein micelles dispersed in an aqueous medium with dissolved lactose, whey proteins and minerals. Quantification of constituents in milk is important in various stages of the dairy supply chain for proper process control and quality assurance. In field-level applications, spectrophotometric analysis is an economical option due to the low-cost of silicon photodetectors, sensitive to UV/Vis radiation with wavelengths between 300 - 1100 nm. Both absorption and scattering are witnessed as incident UV/Vis radiation interacts with dissolved and dispersed constituents in milk. These effects can in turn be used to characterize the chemical and physical composition of a milk sample. However, in order to simplify analysis, most existing instrument require dilution of samples to avoid effects of multiple scattering. The sample preparation steps are usually expensive, prone to human errors and unsuitable for field-level and online analysis. This paper introduces a novel digital imaging based method of online spectrophotometric measurements on raw milk without any sample preparation. Multiple LEDs of different emission spectra are used as discrete light sources and a digital CMOS camera is used as an image sensor. The extinction characteristic of samples is derived from captured images. The dependence of multiple scattering on power of incident radiation is exploited to quantify scattering. The method has been validated with experiments for response with varying fat concentrations and fat globule sizes. Despite of the presence of multiple scattering, the method is able to unequivocally quantify extinction of incident radiation and relate it to the fat concentrations and globule sizes of samples.

In this work we are trying to assess the application of array detectors and digital information processing to the system with the optical equisignal zone as a new method of evaluating of optical equisignal zone position. Peculiarities of optical equisignal zone formation are described. The algorithm of evaluation of optical equisignal zone position is applied to processing on the array detector. This algorithm enables to evaluate as lateral displacement as turning angles of the receiver relative to the projector. Interrelation of parameters of the projector and the receiver is considered. According to described principles an experimental set was made and then characterized. The accuracy of position evaluation of the equisignal zone is shown dependent of the size of the equivalent entrance pupil at processing.

In this paper we introduce a system for deflection measurement of floating dry docks. The system contains two measurement channels observing opposite directions of the dock. It also includes set of reference marks, an industrial computer and a display. Each channel contains CMOS camera with long focal-length lens. Reference marks are implemented as IR LED arrays with 940 nm working wavelength for better performance within bad weather conditions (e.g. fog, rain, high humidity etc.). In the paper we demonstrate results of an analysis of different optical schemes for coupling the oppositely directed channels of the measurement unit and show that the scheme with two image sensors with separated lenses is an optimal option, because it allows usage of nonequidistant location of reference marks and demonstrates the least value of parasitic shift caused by rotations of the measuring unit. The developed system was tested both on specially-designed setup and in real infrastructure of a floating dry dock. The conducted tests proved that a measuring error of the system is smaller than ± 1.5 mm within the measurement range of ± 150 mm when deflection of 100 m dock is measured. Obtained results showed that the system demonstrates an ability to work in a harsh environment including poor weather conditions.

Focal length of a lens is measured in a Lau setup with binary gratings. An integer order of Lau fringes appears in some conditions where a proper relation is satisfied between the involved separation distances of the setup elements, gratings periods, wavelength, and focal length of the test lens. Focal length of the lens is given by fitting the relevant theoretical curve with some unknown constants, including the focal length, to the gained experimental data. Precision of this measurement is of order of 1 mm for a lens with focal length of about 30 cm.

We report the use of the Raman spectral information of the chemical compound toluene C₇H₈ as a reference on the analysis of laboratory-prepared and commercially acquired gasoline-ethanol blends. The rate behavior of the characteristic Raman lines of toluene and gasoline has enabled the approximated quantification of this additive in commercial gasoline-ethanol mixtures. This rate behavior has been obtained from the Raman spectra of gasoline-ethanol blends with different proportions of toluene.

All these Raman spectra have been collected by using a self-designed, frequency precise and low-cost Fourier-transform Raman spectrometer (FT-Raman spectrometer) prototype. This FT-Raman prototype has helped to accurately confirm the frequency position of the main characteristic Raman lines of toluene present on the different gasoline-ethanol samples analyzed at smaller proportions than those commonly found in commercial gasoline-ethanol blends. The frequency accuracy validation has been performed by analyzing the same set of toluene samples with two additional state-of-the-art commercial FT-Raman devices. Additionally, the spectral information has been contrasted, with highly-correlated coefficients as a result, with the values of the standard Raman spectrum of toluene.

The paper deals with the creation of integrated monitoring systems. They combine fiber-optic classifiers and local sensor networks. These systems allow for the monitoring of complex industrial objects. Together with adjacent natural objects, they form the so-called geotechnical systems. An integrated monitoring system may include one or more spatially continuous fiber-optic classifiers based on optic fiber and one or more arrays of discrete measurement sensors, which are usually combined in sensor networks. Fiber-optic classifiers are already widely used for the control of hazardous extended objects (oil and gas pipelines, railways, high-rise buildings, etc.). To monitor local objects, discrete measurement sensors are generally used (temperature, pressure, inclinometers, strain gauges, accelerometers, sensors measuring the composition of impurities in the air, and many others). However, monitoring complex geotechnical systems require a simultaneous use of continuous spatially distributed sensors based on fiber-optic cable and connected local discrete sensors networks. In fact, we are talking about integration of the two monitoring methods. This combination provides an additional way to create intelligent monitoring systems. Modes of operation of intelligent systems can automatically adapt to changing environmental conditions. For this purpose, context data received from one sensor (e.g., optical channel) may be used to change modes of work of other sensors within the same monitoring system. This work also presents experimental results of the prototype of the integrated monitoring system.

The development of absolute distance measurement methods have been enabled by new kind of lasers, special digital signal processing electronics, algorithms and new materials for optics. The phenomenon of the mode-lock of the femtosecond pulse laser increased a number of potential applications with distance surveying where that stable generator of very short and periodically repeated coherent pulses can be used. The main aim of the work is a description of precise measuring method with absolute scale which is able to determine the length of unknown distance with direct traceability to a time standard. The principle of the method is based on a passive optical cavity with mirrors keeping measured distance, in our case a piezoelectric actuator. Time spacing of short femtosecond pulses generated by mode-locked laser is optically phase locked to the cavity free spectral range. A value of the repetition frequency of the laser determines the measured distance. The exact value of the frequency/period of the femtosecond pulse train is detected by a frequency counter. The counting gate of the counter is synchronized with a highly stable oscillator disciplined by H-maser or GPS received signal from atomic clocks. The work shows methods how to overcome problems with dispersive optics in the passive cavity and a way of phase lock of the femtosecond laser repetition rate to free spectral range of the cavity. This measuring technique is demonstrated on length characterization of the piezoelectric transducer which belongs to ultra-precise positioning actuators.

This work is oriented towards our research in the field of splicing and ending of optical frequency references based on hollow core photonics crystal fibers (HC-PCF). This type of references is very promising optical element to replacing classic bulky absorption cells for laser frequency stabilization. We prepared and present methods of splicing HC-PCF to standard telecommunication fiber by a fiber splicer. A special care was taken to optimize the splicer setting and to find and obtain a splice with minimal optical losses between HC-PCF and SMF. The manufactured fiber cell was closed at one side by connecting to SMF and second fiber end was prepared for placing into the vacuum chamber with the help of vacuum-tightened connection to be used as a optical frequency reference based on the acetylene gas for frequency stabilization of the laser standards.

We report on the results of the common collaborative project of applied research where the Institute of Scfientific Instruments (ISI) of the Academy of Sciences of the Czech Republic and a company Meopta – optika joined their effort in development of high-precision interferometric systems for dimensional metrology and nanometrology. This research exploits previous results in the field of laser standards of optical frequencies and the methodology of interferometric metrology of length together with detection systems of interference signals and their processing at the ISI and the production technology of precise optical components at Meopta – optika. Within this project we developed a compact, solid-state frequency stabilized laser referenced to iodine transitions and technology of iodine cells for laser frequency stabilization. A fundamental setup of the laser interferometer has been arranged and tested. The company Meopta – optika contributes with development of new technology for processing and polishing of high-precision flat-surface optical components.

Semiconductor lasers found a foothold in many fields of human activities, mainly thanks to its small size, low cost and high energy efficiency. Recent methods for accurate distance measurement in industrial practice use principles of laser interferometry, which are based on lasers operating in the visible spectrum. When the laser beam is visible the alignment of the industrial interferometer makes the measuring process easier. Traditional lasers for these purposes for many decades - HeNe gas laser - have superb coherence properties but small tunable range. On the other hand laser diodes are very useful lasers but only if the active layer of the semiconductor equips with a passive selective element that will increase the quality of their own resonator and also prevents the structure of its higher longitudinal modes. The main aim of the work is a design of the laser source based on a new commercial available laser diode with Distributed Bragg Reflector structure, butterfly package and fibre coupled output. The ultra-low noise injection current source, stable temperature controller and supply electronic equipment were developed with us and experimentally tested with this laser for the best performances required of the industrial interferometry field. The work also performs a setup for frequency noise properties investigation with an unbalanced fibre based Mach-Zehnder interferometer and 10 m long fibre spool inserted in the reference arm. The work presents the way to developing the narrow-linewidth operation the DBR laser with the wide tunable range up to more than 1 nm of the operation wavelength at the same time. Both capabilities predetermine this complex setup for the industrial interferometry application as they are the long distance surveying or absolute scale interferometry.

Multipath interference in bend-insensitive optical fibers is experimentally evaluated in the 1300 nm wavelength range, describing how this phenomenon originates and how it can be measured by a setup based on a tunable laser. The characterization of bend-insensitive fibers from different manufacturers is presented; all the considered fibers exhibit a negligible effect in patchcords longer than 10m, whereas jumpers with length ≤ 2m can produce multipath interference at detrimental levels above -30dB. The phenomenon is even more evident in the cascade of offset-spliced short jumpers made of bend-insensitive fiber; preliminary results showed a large rise of the MPI when two or more jumpers are shortly spaced.