The components in optical projectors are becoming increasingly smaller due to the need for increased output resolution and the desire for small form-factor devices. One such component is Liquid Crystal (LC) panels, that utilize periodic micro-lens arrays which become more sensitive to diffractive effects as the period becomes near/sub wavelength. This paper explores the diffraction effects within these systems through numerical modeling. Traditionally Ray tracing techniques have been used for analyzing projection systems and has led to significant improvements in illumination uniformity and efficiency. However, increasingly complex projector designs that incorporate smaller geometric features like micro/nano lens arrays, including coherent diffraction and interference effects arising from such structures, cannot be handled by ray-tracing approaches alone. Rigorous electromagnetic (EM) wave optics based techniques, such as finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA) which solve Maxwell’s equations must be used. These rigorous EM techniques, however, have difficulty in analyzing the larger projector structures due to computational resource limitations. We use a mixedlevel optical simulation methodology which unifies the use of rigorous EM wave-level and ray-level tools for analyzing projector performance. This approach uses rigorous EM wave based tools to characterize the LC panel through a Bidirectional Scattering Distribution function (BSDF) file. These characteristics are then incorporated into the ray-tracing simulator for the illumination and imaging system design and to obtain the overall performance. Such a mixed-level approach allows for comprehensive modeling of the optical characteristic of projectors, including coherent effects, and can potentially lead to more accurate performance than that from individual modeling tools alone.

Pushbroom hyperspectral imaging systems require relative motion with respect to the target for hyperspectral data acquisition by means of spatial scanning, which increases the equipment cost and limits the application scenarios. We address this by introducing a pushbroom system with an internal line-scanning unit consisting of a slit aperture mounted on a piezoelectric linear motor. Different slit positions have tilted incidence angles at the grating, resulting in shifts of diffraction patterns relative to the imaging sensor. We demonstrate a method to compensate this shift by using a rotating arm controlled by a stepper motor to reposition the camera based on slit position.

There is demand for small-size lens units for endoscope and industrial applications. Polished glass lenses with a diameter of 1 - 2mm exist, however plastic lenses similar in size are not commonplace. For low-cost, light-weight, and mass production, plastic lens fabrication is extremely beneficial. Especially, in the medical field, there is strong demand for disposable lens unit for endoscopes which prevent contamination due to reuse of the lens. Therefore, high mass producible and low cost becomes increasingly important. This paper reports our findings on injection-molded ultra-small size plastic lens units with a diameter of 1.3mm and total thickness of 1.4mm. We performed optical design, injection molding, and lens unit assembly for injection moldable, high imaging performance ultra-small sized lens units. We prioritize a robust product design, considering injection molding properties and lens unit assembly, with feedback from molding simulations reflected into the optical design. A mold capable of high precision lens positioning is used to fabricate the lenses and decrease the variability of the assembly. The geometric dimensions of the resulting lenses, are measured and used in the optical simulation to validate the optical performance, and a high agreement is reported. The injection molding of the lens and the assembly of the lens unit is performed with high precision, and results in high optical performance.

Freeform optical systems are playing an important role in the field of illumination engineering for redistributing the light intensity, because of its capability of achieving accurate and efficient results. The authors have presented the basic idea of the freeform lens design method at the 117th annual meeting of the German Society of Applied Optics (DGAOProceedings). Now, we demonstrate the feasibility of the design method by designing and evaluating a freeform lens. The concepts of luminous intensity mapping, energy conservation and differential equation are combined in designing a lens for non-imaging applications. The required procedures to design a lens including the simulations are explained in detail. The optical performance is investigated by using a numerical simulation of optical ray tracing. For evaluation, the results are compared with another recently published design method, showing the accurate performance of the proposed method using a reduced number of mapping angles. As a part of the tolerance analyses of the fabrication processes, the influence of the light source misalignments (translation and orientation) on the beam-shaping performance is presented. Finally, the importance of considering the extended light source while designing a freeform lens using the proposed method is discussed.

Stent quality control is a critical process. Coronary stents have to be inspected 100% so no defective stent is implanted into a human body. We have developed a high numerical aperture optical stent inspection system able to acquire both 2D and 3D images. Combining a rotational stage, an area camera with line-scan capability and a triple illumination arrangement, unrolled sections of the outer, inner, and sidewalls surfaces are obtained with high resolution. During stent inspection, surface roughness and coating thickness uniformity is of high interest. Due to the non-planar shape of the surface of the stents, the thickness values of the coating need to be corrected with the 3D surface local slopes. A theoretical model and a simulation are proposed, and a measurement with white light interferometry is shown. Confocal and spectroscopic reflectometry showed to be limited in this application due to stent surface roughness. Due to the high numerical aperture of the optical system, only certain parts of the stent are in focus, which is a problem for defect detection, specifically on the sidewalls. In order to obtain fully focused 2D images, an extended depth of field algorithm has been implemented. A comparison between pixel variance and Laplacian filtering is shown. To recover the stack image, two different methods are proposed: maximum projection and weighted intensity. Finally, we also discuss the implementation of the processing algorithms in both the CPU and GPU, targeting real-time 2-Million pixel image acquisition at 50 frames per second.

The paraxial focal length is still the most important parameter in the design of a lens. As presented at the SPIE Optics + Photonics 2016, the measured focal length is a function of the aperture. The paraxial focal length can be found when the aperture approaches zero. In this work, we investigate the dependency of the Zernike polynomials on the aperture size with respect to 3D space. By this, conventional wavefront measurement systems that apply Zernike polynomial fitting (e.g. Shack-Hartmann-Sensor) can be used to determine the paraxial focal length, too. Since the Zernike polynomials are orthogonal over a unit circle, the aperture used in the measurement has to be normalized. By shrinking the aperture and keeping up with the normalization, the Zernike coefficients change. The relation between these changes and the paraxial focal length are investigated. The dependency of the focal length on the aperture size is derived analytically and evaluated by simulation and measurement of a strong focusing lens. The measurements are performed using experimental ray tracing and a Shack-Hartmann-Sensor. Using experimental ray tracing for the measurements, the aperture can be chosen easily. Regarding the measurements with the Shack-Hartmann- Sensor, the aperture size is fixed. Thus, the Zernike polynomials have to be adapted to use different aperture sizes by the proposed method. By doing this, the paraxial focal length can be determined from the measurements in both cases.

Fabrication and characterization of submicron optical waveguides is one of the major challenges in modern photonics, as they find many applications from optical sensors to plasmonic devices. Here we report on a novel technique that allows for a complete and precise characterization of silica optical nanofibers. Our method relies on the Brillouin backscattering spectrum analysis that directly depends on the waveguide geometry. Our method was applied to several fiber tapers with diameter ranging from 500 nm to 3 μm. Results were compared to scanning electron microscopy (SEM) images and numerical simulations with very good agreement and similar sensitivity.

Present alignment methods already have an accuracy of some microns, allowing in general the fairly precise assembly of multi element optical systems. Nevertheless, they suffer decisive drawbacks, such as the necessity of an iterative process, stepping through all optical surfaces of the system when using autocollimation telescopes. In contrast to these limitations, the wavefront based alignment offers an elegant approach to potentially reach sub-µm accuracy in the alignment within a highly efficient process, that simultaneously acquires and evaluates the best optical solution possible. However, the practical use of these capabilities in corresponding alignment devices needs to take real sensor behavior into account. This publication will especially elaborate on the influence of the sensor properties in relation to the alignment process. The first dominant requirement is a highly stable measurement, since tiny perturbations in the optical system will have an also tiny influence on the wavefront. Secondly, the lateral sampling of the measured wavefront is supposed to be as high as possible, in order to be able to extract higher order Zernike coefficients reliable. The resulting necessity of using the largest sensor area possible conflicts with the requirement to allow a certain lateral displacement of the measured spot, indicating a perturbation. A movement of the sensor with suitable stages in turn leads to additional uncertainties connected to the actuators. Further factors include the SNR-ratio of the sensor as well as multiple measurements, in order to improve data repeatability. This publication will present a procedure of dealing with these relevant influence factors. Depending on the optical system and its properties the optimal adjustment of these parameters is derived.

This paper presents system-level analysis of a sensor capable of simultaneously acquiring both standard absorption based RGB color channels (400-700nm, ~75nm FWHM), as well as an additional NIR channel (central wavelength: ~808 nm, FWHM: ~30nm collimated light). Parallel acquisition of RGB and NIR info on the same CMOS image sensor is enabled by monolithic pixel-level integration of both a NIR pass thin film filter and NIR blocking filters for the RGB channels. This overcomes the need for a standard camera-level NIR blocking filter to remove the NIR leakage present in standard RGB absorption filters from ~700-1000nm. Such a camera-level NIR blocking filter would inhibit the acquisition of the NIR channel on the same sensor. Thin film filters do not operate in isolation. Rather, their performance is influenced by the system context in which they operate. The spectral distribution of light arriving at the photo diode is shaped a.o. by the illumination spectral profile, optical component transmission characteristics and sensor quantum efficiency. For example, knowledge of a low quantum efficiency (QE) of the CMOS image sensor above 800nm may reduce the filter’s blocking requirements and simplify the filter structure. Similarly, knowledge of the incoming light angularity as set by the objective lens’ F/# and exit pupil location may be taken into account during the thin film’s optimization. This paper demonstrates how knowledge of the application context can facilitate filter design and relax design trade-offs and presents experimental results.

Nowadays, digital holographic systems are based on two main optical schemes: off-axis (OA) and inline (IL) holographic systems. In OA set-ups, the reference and the object beams present a relative angle at the registration plane. Thus, a real image of the object can be obtained without the influence of conjugated images by performing a spatial filtering at the reconstructed plane. IL configurations are less sensitive to vibrations and air flows than OA configurations, but the undesired influence of conjugated images in the final hologram is not avoided. To overcome this limitation, a number of IL based methods have been proposed. One interesting approach is the phase-shifting technique, which leads to efficient holograms for IL applications. However, due to the time-sequential nature of this technique, it is somewhat inappropriate for dynamic processes. We present a new method, for IL digital holography, based on a doublesideband (DSB) filter. This method not only removes the conjugate images in the reconstruction process but also reduces the distortions that usually appear when using single-sideband filters. Moreover, it is only time-limited by the acquisition time of the CCD camera. The appropriateness of the technique to be applied in dynamic processes was tested for the tracking of micro-particles. To this aim, particle holographic images were obtained by using the DSB method and afterwards processed with digital picture recognition methods, this allowing us to accurately track the spatial position of the particles. By using this approach, the instantaneous trajectory and velocity described by glass microspheres in movement were experimentally determined

Photonic technology has pushed the limits of astronomy ever more in recent years. Especially, integrated optics (IO) has led to new standards in accuracy and stability in the field of astronomical interferometry where several beams need to be coherently and simultaneously combined. We follow and extend the IO concept by writing mid-IR waveguides in gallium lanthanum sulfide (GLS) using Ultrafast Laser Writing (ULI). Here, we report on the monochromatic and broadband interferometric capabilities in the mid-IR of such combiners. Finally, we outline the way to a fiber-fed IO 4-telescope instrument for next-generation astronomical interferometers.

Due to the exotic freeform surface exhibited by Progressive Addition Lenses, a new characterization approach that takes into account the projection of the eye pupil over the lens is required. In this work, a locally resolved description of the performance of the lens has been obtained by calculating the Modulation Transfer Function (MTF) for uniformly spaced subaperture positions. This quality metric is conveniently suitable to characterize imaging systems, because it describes the contrast resolving capabilities of the lens as a function of the spatial frequency. In addition, it is independent of the eye perception of the test engineer. The MTF has been indirectly calculated using Experimental Ray Tracing, by extracting the values of the ray slopes of each subaperture from the complete ray traced data. By following this procedure, two-dimensional maps are generated using two different criteria. The first criterion is based on the determination of the normalized spatial frequency where the MTF has declined by 50 %. The second one uses a simplified Strehl ratio. Also, the results for different subaperture diameters are obtained without the need for changing the setup or repeating the measurements.

Optical coherence tomography (OCT) has great potential for the examination of oil paintings, particularly for celebrated masterpieces by great artists in history. We developed an OCT system for large field of view (FOV), high definition (HD) imaging of oil paintings. To achieve large FOV, we translated the sample using a pair of high-precision linear motors and performed sequential volumetric imaging on adjacent, non-overlapping regions. Through 3D OCT imaging, the surface terrain and subsurface microarchitecture of the paintings have been characterized and visualized.

Advanced Driver Assistance Systems (ADAS) are embedded in cars to increase safety and reduce traffic congestion, and next generation about full autonomous vehicle intends to increase productivity of the driver and whole population of drivers. It is currently one of the most dynamic segments of the car industry, demonstrating an annual growth of around 25%. Photonics in both visible and infrared spectra has a big role to play in this field. This article will present the results of a current study about infrared-enabled ADAS functions. Strong cost’s decrease in infrared technologies, active 3D infrared imaging, night vision as well as computational capacities pave the way for increased use for infrared technologies in the car.

Imec has developed a process for the monolithic integration of optical filters on top of CMOS image sensors, leading to compact, cost-efficient and faster hyperspectral cameras that make the technology attractive for industry. To calibrate the sensor, we introduce a full pixel response model that takes into account the inherent properties of the optical filters. This model is then used to derive a calibration method that enables more accurate and robust measurements of the spectral reflectance of a scene. The calibration method is then extended to take into account the normal manufacturing variations between different sensors to perform an inter-sensor calibration. We experimentally validate this method by scanning reference targets with different types of sensors and demonstrate that accurate and reproducible reflectance measurements are obtained.

Coherent optical frequency-domain reflectometry (C-OFDR) is a distance measurement technique with significant sensitivity and detector bandwidth advantages over normal time-of-flight methods. Although several swept-wavelength laser sources exist, many exhibit short coherence lengths, or require precision mechanical tuning components. Semiconductor distributed feedback lasers (DFBs) are advantageous as a mid-to-long range OFDR source because they exhibit a narrow linewidth and can be rapidly tuned simply via injection current. However, the sweep range of an individual DFB is thermally limited. Here, we present a novel high-resolution OFDR system that uses a compact, monolithic 12-element DFB array to create a continuous, gap-free sweep over a wide wavelength range. Wavelength registration is provided by the incorporation of a HCN gas cell and reference interferometer. The wavelength-swept spectra of the 12 DFBs are combined in post-processing to achieve a continuous total wavelength sweep of more than 40 nm (5.4 THz) in the telecommunications C-Band range.

Automated spectroscopic profiling (mapping) of a 200 mm diameter near infrared high reflector (centered at 1064 nm) are presented. Spatial resolution at 5 mm or less was achieved using a 5 mm × 1.5 mm monochromatic beam. Reflection changes of 1.0% across the wafer diameter were observed under s-polarized and p- polarized conditions. Redundancy was established for each chord by re-measuring the center of the wafer and reproducibility of approximately <0.1% was demonstrated by duplicate measurements. These measurements demonstrate informative spatial spectroscopic information can be obtained on large diameter samples. Multi-angle Photometric Spectroscopy (MPS) was used to measure the reflectance and transmittance of a sample across a range of angles (θ_i) at near normal angles of incidence (AOI). A recent development by Agilent Technologies, the Cary 7000 Universal Measurement Spectrophotometer (UMS) combines both reflection and transmission measurements from the same patch of a sample’s surface in a single automated platform for angles of incidence in the range 5°≤|θ_i|≤85° (i.e. angles on either side of beam normal noted as +/-). We describe the use of MPS on the Cary 7000 UMS with rotational (Φ) and vertical (z) sample positioning control. MPS(θ_i,Φ,z) provides for automated unattended multi-angle R/T analysis of at 200 mm diameter samples with the goal to provide better spectroscopic measurement feedback into large wafer manufacturing to ensure yields are maximized, product quality is better controlled and waste is reduced before further down-stream processing.

Computed radiography (CR), which is one of the most useful methods for dental imaging and nondestructive testing, uses a phosphor imaging plate (IP) because it is flexible, reusable, and inexpensive. Conventional IP scanners utilize a galvanometer or a polygon mirror as a scanning device and a photomultiplier as an optical sensor. Microelectromechanical systems (MEMS) technology currently provides silicon-based devices and has the potential to replace such discrete devices and sensors. Using these devices, we constructed an ultra-compact IP scanner. Our extremely compact plate scanner utilizes a module that is composed of a one-dimensional MEMS mirror and a long multi-pixel photon counter (MPPC) that is combined with a specially designed wavelength filter and a rod lens. The MEMS mirror, which is a non-resonant electromagnetic type, is 2.6 mm in diameter with a recommended optical scanning angle up to ±15°. The CR’s wide dynamic range is maintained using a newly developed MPPC. The MPPC is a sort of silicon photomultiplier and is a high-sensitivity photon-counting device. To achieve such a wide dynamic range, we developed a long MPPC that has over 10,000 pixels. For size reduction and high optical efficiency, we set the MPPC close to an IP across the rod lens. To prevent the MPPC from detecting excitation light, which is much more intense than photo-stimulated light, we produced a sharp-cut wavelength filter that has a wide angle (±60°) of tolerance. We evaluated our constructed scanner module through gray chart and resolution chart images.

Scanning white light interferometry (SWLI) is a label free optical 3D imaging modality with a vertical sensitivity of a few Ångströms (Å). However, this optical far-field system, is laterally diffraction limited and resolves only a few hundred nanometers. We overcome this limit with microspheres that each produces a photonic nanojet. Thus sub- 100 nm features can laterally be resolved. To validate the performance of Photonic nanoJet based Interferometry (PJI) we compared it to techniques that provide sub-100 nm lateral resolution; Super-Resolution SWLI, atomic force microscope, and scanning electron microscope. We used a recordable Blu-ray disc as sample. Such a disc features a grooved surface topology with heights in the range of 20 nm and with distinguishable sub-100 nm lateral features that are unresolved by diffraction limited optics. We achieved agreement between all three measurement devices across lateral and vertical dimensions.

A stair case height Bio-Transfer-Standard (BTS), developed and produced at the University of Helsinki (UH), was measured in two laboratories. The Round Robin test aims to determine whether BTS works with different optical profilers in different laboratories. First the artefact was measured at UH using a custom-built Scanning White Light Interferometer. Then BTS was measured at Sensofar-Tech, S.L. using an S-neox-type interferometer working either in Phase Shifting Interferometry mode or in Imaging Confocal Microscopy mode. To remove the influence of system calibration, a method featuring sample shifting and measurement subtraction was used. The BTS features eight lipid bilayer steps that each are 4.6 ± 0.1 nm tall on average. All 30 measurements done by four different operators at the two laboratories agree to within 0.1 nm which agrees with theoretical estimates and with measurements done using a surface plasmon resonance technique. The Round Robin results show the applicability of the newly developed bio-imaging transfer standard for calibrating 3D optical profilers.

We present two applications of spectroscopy to help in the development and production of fast moving consumer goods. We have developed an instrument which combines time-gated Raman spectroscopy integrated with a fiber optic probe bundle for multi-spectral, multi-point investigation of the distribution of chemicals in complex powder mixtures by separation of their individual Raman spectra. The combined instrumentation design is designed for application in a production environment. This finds particular utility in monitoring the production and potential segregation of washing powders, which require consistency; particularly in the developing world where the efficiency of washing with small amounts of powder is beneficial. However, washing powders, in line with many powder products, have the additional problem of an overwhelming fluorescence signal which is stronger than the Raman signal, arising from the use of artificial whiteners added to such powders. We overcome this through the use of a novel time-gating method separate the “instantaneous Raman signal” from the time delayed fluorescence emission. We will also present a novel use of confocal microscopy in obtaining high resolution images of fluorescently labelled mascara on eyelashes. This is achieved by mixing mascara with a small amount of fluorescein powder. From these images it is possible to see phenomena such as the bridging of mascara between lashes and to accurately determine the thickness of the mascara. This technique has potential in the testing of mascara by cosmetic companies, and also in monitoring other reactions which involve a waxy substrate which adheres to a curved surface. The two methods demonstrate how significant commercial challenges can be solved through the application of methods more associated with academic research.

Rapid identification and the quantitative analysis of crystalline content and the degree of crystallinity is important in pharmaceuticals and polymer manufacturing. Crystallinity affects the bioavailability of pharmaceutical molecules and there is a strong correlation between the performance of polymers and their degree of crystallinity. Low frequency/THz-Raman spectroscopy has enabled determination of crystalline content in materials as a complementary method to X-ray powder diffraction. By incorporating motion stages and microplates, we have extended the applicability of THz-Raman technology to high-throughput screening applications. We describe here a complete THz-Raman microplate reader, with integrated laser, optics, spectrograph and software that are necessary for detecting low-frequency Raman signals.

In powder materials scattering is also affected by particle size and the presence of cavities, which lead to a lack of precision and repeatability in Raman intensity measurements. We address this problem by spatial averaging using specific stage motion patterns. This design facilitates rapid and precise measurement of low-frequency vibrational modes, differentiation of polymorphs and other structural characteristics for applications in pharmaceuticals, nano- and bio-materials and for the characterization of industrial polymers where XRPD is commonly used.

Cost effective multi-wavelength light sources are key enablers for wide-scale penetration of gas sensors at Mid-IR wavelength range. Utilizing novel Mid-IR Si-based photonic integrated circuits (PICs) filter and wide-band Mid-IR Super Luminescent Light Emitting Diodes (SLEDs), we show the concept of a light source that covers 2.5…3.5 μm wavelength range with a resolution of <1nm. The spectral bands are switchable and tunable and they can be modulated. The source allows for the fabrication of an affordable multi-band gas sensor with good selectivity and sensitivity. The unit price can be lowered in high volumes by utilizing tailored molded IR lens technology and automated packaging and assembling technologies. The status of the development of the key components of the light source are reported. The PIC is based on the use of micron-scale SOI technology, SLED is based on AlGaInAsSb materials and the lenses are tailored heavy metal oxide glasses fabricated by the use of hot-embossing. The packaging concept utilizing automated assembly tools is depicted. In safety and security applications, the Mid-IR wavelength range covered by the novel light source allows for detecting several harmful gas components with a single sensor. At the moment, affordable sources are not available. The market impact is expected to be disruptive, since the devices currently in the market are either complicated, expensive and heavy instruments, or the applied measurement principles are inadequate in terms of stability and selectivity.

Using light-beam scanning technology based on a potassium tantalate niobate (KTa_1-xNb_xO₃, KTN) single crystal, we constructed a wavelength-swept light source for industrial applications. The KTN crystal is placed in an external cavity as an electro-optic deflector for wavelength scanning without any mechanical operation. Cavity arrangement and mechanism elements are specially designed for long-term stability and environmental robustness. In addition, we updated the handling of the KTN crystal. We used a pair of thermistors for accurate temperature monitoring, and weakly irradiated the crystal with a 405-nm light during operation to achieve drift suppression. We selected a moderate repetition rate of 20 kHz to suit the practical application. The output of the light source was 6.2 mW in average power, 1314.5 nm in central wavelength, and 83.3 nm in bandwidth. The interference fringes of the light enable us to specify the thickness of a wafer sample by the peak positions of the point spread functions. We measured the thickness of a silicon wafer as 3651 μm in the optical path length using a reference quartz plate. The distribution of the obtained values is about 0.1 μm (standard deviation). We experimentally confirmed that this property persists continuously at least over 153 days. Our light source has a remarkable feature: extremely low timing jitter of the sweep. Thus, we can easily reduce the noise level by averaging several fringes, if necessary.

Standard visualisation systems capture two- dimensional images and need more or less fast image processing systems. Now, the ASP Array (Actives sensor pixel array) opens a new world in imaging. On the ASP array, each pixel is provided with its own lens and with its own signal pre-processing. The OCT technology works in "real time" with highest accuracy. In the ASP array systems functionalities of the data acquisition and signal processing are even integrated onto the "pixel level". For the extraction of interferometric features, the time-of-flight principle (TOF) is used. The ASP architecture offers the demodulation of the optical signal within a pixel with up to 100 kHz and the reconstruction of the amplitude and its phase. The dynamics of image capture with the ASP array is higher by two orders of magnitude in comparison with conventional image sensors!!! The OCT- Technology allows a topographic imaging in real time with an extremely high geometric spatial resolution. The optical path length is generated by an axial movement of the reference mirror. The amplitude-modulated optical signal and the carrier frequency are proportional to the scan rate and contains the depth information. Each maximum of the signal envelope corresponds to a reflection (or scattering) within a sample. The ASP array produces at same time 300 * 300 axial Interferorgrams which touch each other on all sides. The signal demodulation for detecting the envelope is not limited by the frame rate of the ASP array in comparison to standard OCT systems. If an optical signal arrives to a pixel of the ASP Array an electrical signal is generated. The background is faded to saturation of pixels by high light intensity to avoid. The sampled signal is integrated continuously multiplied by a signal of the same frequency and two paths whose phase is shifted by 90 degrees from each other are averaged. The outputs of the two paths are routed to the PC, where the envelope amplitude and the phase calculate a three-dimensional tomographic image. For 3D measuring technique specially designed ASP- arrays with a very high image rate are available. If ASP- Arrays are coupled with the OCT method, layer thicknesses can be determined without contact, sealing seams can be inspected or geometrical shapes can be measured. From a stack of hundreds of single OCT images, interesting images can be selected and fed to the computer to analyse them.

An innovative real-time imaging Stokes spectropolarimeter is presented. The main unit of the polarimeter is an integral polarization-holographic diffraction element, which enables the complete analysis of the polarization state of light to be carried out in real time. An element is recorded by a special holographic schema using circularly and linearly polarized beams. As a result it decomposes an incoming light into orthogonal circular and linear diffraction orders. Upon simultaneous CCD intensity measurements of the corresponding points or areas in the diffraction orders and further data reduction through the calibration parameters we get real-time Stokes images of a light source. The further reduction of Stokes images allows to determine detailed polarization state of a light coming from a point or extended space object in a narrow or a wide spectral range. The operating spectral range of the polarimeter is 500-1600 nm with diffraction efficiency equal to 20% at 532 nm, 16% at 635 nm and 2% at 1550 nm. The laboratory calibration tests were obtained with a quasi-monochromatic point size depolarized light source which further were circularly or linearly polarized with known polarization parameters and a degree of polarization near to 100%. The theoretical model of relations between measured intensities in different diffraction orders and Stokes parameters, earlier developed by the authors (Kilosanidze B., Kakauridze G. SPIE Proceedings, vol. 8082-126, 2011), were used to calibrate the polarimeter. The laboratory tests show that the resulting errors for single measure are near of 10^-2 or less.

Optical sensors based on Fiber Bragg Gratings (FBGs) are used in several applications and industries. In order for fiber optic sensors to compete with electrical sensors, several critical parameters of both the sensors and sensor interrogators need to be in place such as performance, cost, size, reliability relevant to the target application. Here we have developed a tunable laser based optical interrogator which delivers high performance (up to 8kHz sweep-rate and 120dB dynamic range) and precision (<100fm) by optimizing the laser calibration of a telecom tunable laser and incorporating optical periodic wavelength references (e.g. MZI) to correct and compensate for wavelength non-linearity and noise during operation. Scaling up optical sensing systems to deliver high level of performance over a large number of sensors is enabled by synchronizing multiple interrogators. Further improvements can be achieved by using photonic integrated circuit (PIC) technology which reduces the footprint, cost, and improves performance. There exists several PIC technology platforms (e.g. InP, Si, TriPlex) that could be used to develop different optical building blocks used in the interrogator. Such building blocks include the tunable laser, couplers, photodiodes, MZIs, etc. are available on the InP platform. Here we have demonstrated the operation of an interrogator using PIC technology to replace many of the discrete optical components. The design and chip manufacturing was carried out as part of an InP multi-project wafer (MPW) run under the EU PARADIGM project. A custom package supporting fiber arrays was designed and manufactured to demonstrate the PIC functionality in an optical interrogator.

A torsion experimental sensing setup based on a Mach-Zehnder interferometer (MZI) with photonics crystal fiber is presented. The MZI was fabricated by fusion splicing a piece of photonic crystal fiber (PCF) between two segments of a single-mode fiber (SMF). Here, a spectral MZI fringe shifting is induced by applying torsion over the SMF-PCF-SMF. As a result a torsion sensitivity of 35.79 pm/ and a high visibility of 10 dB were achieved. Finally, it is shown that the sensing arrangement is compact and robust.

Incoherent broadband cavity enhanced spectroscopy can significantly increase the effective path length of light-matter interaction to detect weak absorption lines over broad spectral range, for instance to detect gases in confined environments. Broadband cavity enhancement can be based on the decay time or the intensity drop technique. Decay time measurement is based on using tunable laser source that is expensive and suffers from long scan time. Intensity dependent measurement is usually reported based on broadband source using Fabry-Perot cavity, enabling short measurement time but suffers from the alignment tolerance of the cavity and the cavity insertion loss. In this work we overcome these challenges by using an alignment-free ring cavity made of an optical fiber loop and a directional coupler, while having a gain medium pumped below the lasing threshold to improve the finesse and reduce the insertion loss. Acetylene (C₂H₂) gas absorption is measured around 1535 nm wavelength using a semiconductor optical amplifier (SOA) gain medium. The system is analyzed for different ring resonator forward coupling coefficient and loses, including the 3-cm long gas cell insertion loss and fiber connector losses used in the experimental verification. The experimental results are obtained for a coupler ratio of 90/10 and a fiber length of 4 m. The broadband source is the amplified spontaneous emission of another SOA and the output is measured using a 70pm-resolution optical spectrum analyzer. The absorption depth and the effective interaction length are improved about an order of magnitude compared to the direct absorption of the gas cell. The presented technique provides an engineering method to improve the finesse and, consequently the effective length, while relaxing the technological constraints on the high reflectivity mirrors and free-space cavity alignment.

We will review the state of the art for on-chip, Raman-based sensing using waveguides including our recent work with sorbent-coated waveguides for trace gas sensing showing parts-per-billion limits of detection. We will show that signal enhancements due to scattering that takes place in the evanescent field coupled with a thin hypersorbent polymer coating can yield Raman efficiencies which are nine orders of magnitude larger than traditional micro-Raman techniques. We will also discuss challenges with gas component discrimination and in moving toward a fully integrated photonic circuit architecture for handheld Raman-based trace gas sensors.

Dispersion spectroscopic sensing of trace gases, measuring the anomalous dispersion at a molecular resonance rather than absorption, has experienced increased attention in the past view years. Their advantages over absorption based spectroscopic sensing are the independence of signals from laser power and their linearity with concentration, even for optically thick samples. In this contribution, we give a comparative discussion of performance, noise and limitations of dispersion and absorption spectroscopy. We relate dispersion spectroscopy to phase-shift rangefinding, for which figures of merit are available in literature. Based on our analysis we conclude that dispersion spectroscopy cannot outperform absorption spectroscopy in most experimental situations. In some applications, where the optical power reaching the detector is unstable, dispersion spectroscopic techniques can, however, be advantageous.

Improving the sensitivity of silicon-based CMOS and CCD in the deep-UV is an area of ongoing interest. Lumogen has been used for this purpose for many years but has several known issues including limitations to its use in both vacuum and radiation harsh environments. Quantum Dots (QD) offers a more robust alternative to Lumogen. The fluorescence wavelength of QDs is tunable and can be fabricated to match the peak sensor quantum efficiency. Aerosol jet printing (AJP) is being used for the deposition of QDs on a variety of substrates and on commercially available sensor arrays. While the films deposited onto various substrates have a surface morphology characterized by aggregate formations, the insight obtained will lead to much more uniform layers in the near future. Organic residues common to this process, that compromise the UV performance, have been minimized.

We propose two different in-line optical schemes for the implementation of Biaxial Crystal (BC) based polarimeters. Unlike already existing BC polarimeters prototypes, our proposed architectures only require of a single BC and only one CCD camera, this leading to more feasible and cheaper prototypes. The first scheme is restricted to linear metrology and we provide its interest to be applied under low-intensity conditions. The second architecture is suitable for complete polarimetry, this being achieved by including an optical module to properly split and steer the input light. The BC polarimeters were implemented and tested by measuring different known input polarizations and we obtained excellent results in terms of accuracy and repeatability.

Hyperspectral imaging allows the collection of both spectral and spatial information. This modality is naturally fitted for object and material identification or detection processes, and has encountered a large success in the agriculture and food industries to name a few. In snapshot spectral imaging, the 3D cube of images is taken in one shot, with the advantage that dynamic scenes can be analyzed. The simplest way to make a hyperspectral camera is to put an array of wavelength filters on the detector and then integrate this detector with standard camera objectives. The technical challenge is to make arrays of N wavelength filters and repeat this sequence up to 100‘000 times across the detector array, where each individual filter is matched to the pixel size and can be as small as a few microns. In this work, we generate the same effect with just one N wavelength filter array which is then multiplied and imaged optically onto the detector to achieve the same effective filter array. This was first outlined by Levoy and Hoystmeyer using microlens arrays in a light field camera (plenoptics 1.0). Instead of building our own light field camera we used an existing commercial camera, Lytro™ and used it as the engine for our telecentric hyperspectral camera. In addition, the tools to extract and rebuild the raw data from the Lytro™ camera were developed. We demonstrate reconstructed hyperspectral images with 9 spectral channels and show how this can be increased to achieve 81 spectral channels in a single snapshot.

Imec has developed a process for the monolithic integration of optical filters on top of CMOS image sensors, leading to compact, cost-efficient and faster hyperspectral cameras. Linescan cameras are typically used in remote sensing or for conveyor belt applications. Translation of the target is not always possible for large objects or in many medical applications. Therefore, we introduce a novel camera, the Snapscan (patent pending), exploiting internal movement of a linescan sensor enabling fast and convenient acquisition of high-resolution hyperspectral cubes (up to 2048x3652x150 in spectral range 475–925 nm). The Snapscan combines the spectral and spatial resolutions of a linescan system with the convenience of a snapshot camera.

Manufacturing of precise structures in MEMS, semiconductors, optics and other fields requires high standards in manufacturing and quality control. Appropriate surface topography measurement technologies should therefore deliver nm accuracy in the axial dimension under typical industrial conditions. This work shows the characterization of a dispersion-encoded low-coherence interferometer for the purpose of fast and robust surface topography measurements. The key component of the interferometer is an element with known dispersion. This dispersive element delivers a controlled phase variation in relation to the surface height variation which can be detected in the spectral domain. A laboratory setup equipped with a broadband light source (200 - 1100 nm) was established. Experiments have been carried out on a silicon-based standard with height steps of 100 nm under different thermal conditions such as 293.15 K and 303.15 K. Additionally, the stability of the setup was studied over periods of 5 hours (with constant temperature) and 15 hours (with linear increasing temperature). The analyzed data showed that a height measurement of 97:99 +/- 4:9nm for 293.15 K and of 101:43 +/- 3:3nm for 303.15 K was possible. The time-resolved measurements revealed that the developed setup is highly stable against small thermal fluctuations and shows a linear behaviour under increasing thermal load. Calibration data for the mathmatical corrections under different thermal conditions was obtained.

SWIFTS^TM technology has been known for over five years to offer compact and high-resolution laser spectrum analyzers. The increase of wavelength monitoring demand with even better accuracy and resolution has pushed the development of a wavelength meter based on SWIFTS^TM technology, named LW-10.

As a reminder, SWIFTS^TM principle consists in a waveguide in which a stationary wave is created, sampled and read out by a linear image sensor array. Due to its inherent properties (non-uniform subsampling) and aliasing signal (as presented in Shannon-Nyquist criterion), the system offers short spectral window bandwidths thus needs an a priori on the working wavelength and thermal monitoring.

Although SWIFTS^TM-based devices are barely sensitive to atmospheric pressure, temperature control is a key factor to master both high accuracy and wavelength meter resolution. Temperature control went from passive (temperature probing only) to active control (Peltier thermoelectric cooler) with milli-degree accuracy. The software part consists in dropping the Fourier-like transform, for a least-squares method directly on the interference pattern. Moreover, the consideration of the system’s chromatic behavior provides a "signature" for automated wavelength detection and discrimination.

This SWIFTS^TM-based new device - LW-10 - shows outstanding results in terms of absolute accuracy, wavelength meter resolution as well as calibration robustness within a compact device, compared to other existing technologies. On the 630 – 1100 nm range, the final device configuration allows pulsed or CW lasers monitoring with 20 MHz resolution and 200 MHz absolute accuracy. Non-exhaustive applications include tunable laser control and frequency locking experiments

Heterodyne Phase Sensitive Dispersion Spectroscopy (HPSDS) is a new method for molecular dispersion spectroscopy that provides an output linearly dependent on the concentration of gas, inherent baseline and normalization-free operation and an extended dynamic range in comparison with absorption-based spectroscopic methods. Besides this, HPSDS provides capabilities for the implementation and deployment of gas analyzers without any need for calibration and all data processing and concentration retrieval procedures are straight forward. HPSDS is based on the measurement of the change in the refractive index of the gas under study in the vicinity of the molecular resonances of interest, and most of the characteristics of the method come from the fact that this change in the refractive index is directly proportional to the concentration of gas. Experimental demonstrations of HPSDS have already been performed in the 1.5 μm optical range, where it is possible to take advantage of high-speed optical intensity modulators and optoelectronics. Here, we present a HPSDS system operating in the Mid-Infrared based on a directly modulated Quantum Cascade Laser (QCL). This instrument has been experimentally validated through the measurement of the concentration of atmospheric carbon monoxide. Taking also advantage of the study of the performance of the HPSDS system that was preformed, the main capabilities and also current limitations of the method are discussed.

A miniature Raman spectrometer was designed in a rapid development cycle (< 4 months) to investigate the performance capabilities achievable with two dimensional (2D) CMOS detectors found in cell phone camera modules and commercial off the shelf optics (COTS). This paper examines the design considerations and tradeoffs made during the development cycle. The final system developed measures 40 mm in length, 40 mm in width, 15 mm tall and couples directly with the cell phone camera optics. Two variants were made: one with an excitation wavelength of 638 nm and the other with a 785 nm excitation wavelength. Raman spectra of the following samples were gathered at both excitations: Toluene, Cyclohexane, Bis(MSB), Aspirin, Urea, and Ammonium Nitrate. The system obtained a resolution of 40 cm^-1. The spectra produced at 785 nm excitation required integration times of up to 10 times longer than the 1.5 seconds at 638 nm, however, contained reduced stray light and less fluorescence which led to an overall cleaner signal.

In this work, a low cost optical pH sensing system that allows for small volume sample measurements was developed. The system operates without the requirement of laboratory instruments (e.g. laser source, spectrometer and CCD camera), this lowers the cost and enhances the portability. In the system, an optical arrangement employing a dichroic filter was used which allows the excitation and emission light to be transmitted using a single fibre thus improving the collection efficiency of the fluorescence signal and also the ability of inserting measurement. The pH sensor in the system uses bromocresol purple as the indicator which is immobilised by sol-gel technology through a dip-coating process. The sensor material was coated on the tip of a 1 mm diameter optical fibre which makes it possible for inserting into very small volume samples to measure the pH. In the system, a LED with a peak emission wavelength of 465 nm is used as the light source and a silicon photo-detector is used to detect the uorescence signal. Optical filters are applied after the LED and in front of the photo-detector to separate the excitation and emission light. The fluorescence signal collected is transferred to a PC through a DAQ and processed by a Labview-based graphic-user-interface (GUI). Experimental results show that the system is capable of sensing pH values from 5.3 to 8.7 with a linear response of R²=0.969. Results also show that the response times for a pH changes from 5.3 to 8.7 is approximately 150 s and for a 0.5 pH changes is approximately 50 s.

The current paper describes the application of lens-free imaging principles for the detection and classification of wear debris in lubricant oils. The potential benefits brought by the lens-free microscopy techniques in terms of resolution, deep of field and active areas have been tailored to develop a micro sensor for the in-line monitoring of wear debris in oils used in lubricated or hydraulic machines as gearboxes, actuators, engines, etc. The current work presents a laboratory test-bench used for evaluating the optical performance of the lens-free approach applied to the wear particle detection in oil samples. Additionally, the current prototype sensor is presented, which integrates a LED light source, CMOS imager, embedded CPU, the measurement cell and the appropriate optical components for setting up the lens-free system. The imaging performance is quantified using micro structured samples, as well as by imaging real used lubricant oils. Probing a large volume with a decent 2D spatial resolution, this lens-free micro sensor can provide a powerful tool at very low cost for inline wear debris monitoring.

Microscopy imaging with a single technology is usually restricted to a single contrast mechanism. Multimodal imaging is a promising technique to improve the structural information that could be obtained about a device under test (DUT). Due to the different contrast mechanisms of laser scanning microscopy (LSM), confocal laser scanning microscopy (CLSM) and optical beam induced current microscopy (OBICM), a combination could improve the detection of structures in integrated circuits (ICs) and helps to reveal their layout. While OBIC imaging is sensitive to the changes between differently doped areas and to semiconductor-metal transitions, CLSM imaging is mostly sensitive to changes in absorption and reflection. In this work we present the implementation of OBIC imaging into a CLSM. We show first results using industry standard Atmel microcontrollers (MCUs) with a feature size of about 250nm as DUTs. Analyzing these types of microcontrollers helps to improve in the field of side-channel attacks to find hardware Trojans, possible spots for laser fault attacks and for reverse engineering. For the experimental results the DUT is placed on a custom circuit board that allows us to measure the current while imaging it in our in-house built stage scanning microscope using a near infrared (NIR) laser diode as light source. The DUT is thinned and polished, allowing backside imaging through the Si-substrate. We demonstrate the possibilities using this optical setup by evaluating OBIC, LSM and CLSM images above and below the threshold of the laser source.

A fiber based plasmonic sensor design is proposed. In principle, both the top surface insulator/metal interface and bottom surface can support SPP decoupled modes. The combination of sensitive interferometric techniques and the optimization process of the design and the material yields to enhanced sensitivities in range of 11000 nm/RIU.

Femtosecond infrared (fs-IR) written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent to the advanced gas turbine engines under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper discusses fabrication and deployment of several fs-IR written FBG arrays, for monitoring the sidewall and exhaust temperature gradients of a gas turbine combustor simulator. Results include: contour plots of measured temperature gradients contrasted with thermocouple data, discussion of deployment strategies and comments on reliability.

A phase demodulation method for short-cavity extrinsic Fabry-Perot interferometer (EFPI) based on two orthogonal wavelengths via a tunable optical filter is proposed in this paper. A broadband light is launched into the EFPI sensor and two monochromatic beams with 3dB bandwidth of 0.2nm are selected out from the reflected light of the EFPI sensor. A phase bias is induced between the two interferential signals due to the wavelength difference of the two beams. The wavelength difference will have an affect on the sensitivity of demodulated signal, which has been theoretically and experimentally demonstrated. The maximum sensitivity can be obtained when the phase bias is 0.5π corresponding to the wavelength difference of 1/4 FSR of the EFPI spectrum. The acoustic wave induced phase variation can be interrogated through an optimized differential cross multiplication (DCM) method. A normalization process is induced into the traditional DCM method to eliminate the influence of ambient temperature and pressure fluctuation induced spectrum shift on output signal. This means that, once the wavelength difference is fixed, the wavelength variation of each individual beam will have little influence on the amplitude of demodulated signal. The EFPI sensing head is formed by a 3μm-thick aluminum diaphragm, which has a SNR of more than 53dB. Through the proposed demodulation scheme, a large dynamic range and good linearity is acquired and Q-point drift problem of traditional EFPI sensor can be solved. The demodulation scheme can be applied to other kinds of short-cavity EFPI based acoustic sensors.

In this article, we propose a fiber displacement sensor based on a few mode fiber loop sandwiched between two single mode fibers (SMF). The proposed sensor is flexible due to the tunable resolution and dynamic range. The FMF is coiled to a fiber loop by making a knot. The in-line MZI sensing structure is fixed on a two dimensional (2D) translation stages. By moving one stage while another stage is fixed, the displacement is applied on the sensing structure. The resolution of the translation stage is 10μm. The few mode fiber loop acts as the transducer for the displacement sensing. The displacement will change the radius of the few mode fiber loop, which leads to a wavelength shift of the interference pattern. When the fiber loop has different initial radius, the same displacement will cause a different curvature variation. So the sensitivity of the wavelength shift to the displacement is dependent on the initial radius. A smaller initial radius of the loop will lead to a larger sensitivity, higher resolution but smaller dynamic range, so it is proper for micro displacement sensing. On the contrary is the lager initial radius that is proper for sensing in a large dynamic range. By simply adjusting the initial radius of the transducer loop, different sensitivity and resolution can be reached. Experimental results show the sensitivities of 0.267nm/mm, 0.384nm/mm, 0.749nm/mm and 1.06nm/mm for initial loop radius of 1.9cm, 1.5cm, 1cm and 0.75cm, respectively.

Color is an important metric for determining the quality of petroleum products, as it is a characteristic readily observed by operators and end users and can also be indicative of the degree of refinement of a petroleum product. There are two primary color standards covering a wide range of petroleum color in industry; ASTM D 156 (Saybolt Color Scale) and ASTM D 1500 (ASTM Color Scale). For highly refined petroleum products the industry uses the Saybolt color scale, ranging from 30 at the clearest to -16 at the darkest. Fuels that are darker in color than -16 on the Saybolt scale are tested using the ASTM Color scale, which ranges from 0.5 at the clearest to 8 at the darkest. As fuels age (increased time from the point of refinement), their color darkens because of oxidizing olefins, such as ethylene and propylene. Traditionally, this color scale is measured using a series of photodiodes and optical filters with a blackbody light source. The spectroscopic method described in this paper incorporates a white LED designed for maximizing color measurements. The spectra are processed using CIE 1931 color space, which is then converted into CIELab color space. Results using this method are accurate and repeatable.

The market of miniature and micro spectrometers is evolving fast. The technology is getting ever smaller and cheaper while keeping high performances. The market is attracting new players: spin-offs from major research institutes, large companies outside the classic spectroscopy market, software providers with innovative analytical solutions, …

The goal of this involvement is to bring spectroscopy closer to the end-users and provide spectrometers able to operate on-field or in-line. The high potential of compact spectrometers is recognized for a wide variety of applications: chemistry, pharmaceutics, agro-food, agriculture, forensics, healthcare, consumer applications, … But its emergence as a large volume market faces a major bottleneck. Each application implies specific processes and analyses and specific parameters to control, i.e. a specific interpretation of the raw spectra in order to provide information usable by nonphotonic experts.

Who is going to pay for that adaptation effort? Are there ways for reducing the adaptation costs, by means of selflearning algorithms and/or flexible and easily adaptable sensors? In other words, who is going to catch the value?

In this article, we will investigate the potential of each major industrial application market and provide market data. We will also wonder, what are the strengths and weaknesses of the different players - spectrometer manufacturers, algorithms developers, full-systems providers, … - to catch the value of the compact spectrometer market.

An Automatic Optical Inspection (AOI) system for optical inspection of imaging devices used in automotive industry using an inspecting optics of lower spatial resolution than the device under inspection is described. This system is robust and with no moving parts. The cycle time is small. Its main advantage is that it is capable of detecting and quantifying defects in regular patterns, working below the Shannon-Nyquist criterion for optical resolution, using a single low resolution image sensor. It is easily scalable, which is an important advantage in industrial applications, since the same inspecting sensor can be reused for increasingly higher spatial resolutions of the devices to be inspected. The optical inspection is implemented with a notch multi-band Fourier filter, making the procedure especially fitted for regular patterns, like the ones that can be produced in image displays and Head Up Displays (HUDs). The regular patterns are used in production line only, for inspection purposes. For image displays, functional defects are detected at the level of a sub-image display grid element unit. Functional defects are the ones impairing the function of the display, and are preferred in AOI to the direct geometric imaging, since those are the ones directly related with the end-user experience. The shift in emphasis from geometric imaging to functional imaging is critical, since it is this that allows quantitative inspection, below Shannon-Nyquist. For HUDs, the functional detect detection addresses defects resulting from the combined effect of the image display and the image forming optics.

Recently, CMOS image sensors (CISs) have become more and more complex because they require high-performances such as wide dynamic range, low-noise, high-speed operation, high-resolution and so on. First of all, wide dynamic range (WDR) is the first requirement for high-performance CIS. Several techniques have been proposed to improve the dynamic range. Although logarithmic pixel can achieve wide dynamic range, it leads to a poor signal-to-noise ratio due to small output swings. Furthermore, the fixed pattern noise of logarithmic pixel is significantly greater compared with other CISs. In this paper, we propose an optimized linear-logarithmic pixel. Compared to a conventional 3-transistor active pixel sensor structure, the proposed linear-logarithmic pixel is using a photogate and a cascode MOSFET in addition. The photogate which is surrounding a photodiode carries out change of sensitivity in the linear response and thus increases the dynamic range. The logarithmic response is caused by a cascode MOSFET. Although the dynamic range of the pixel has been improved, output curves of each pixel were not uniform. In general, as the number of devices increases in the pixel, pixel response variation is more pronounced. Hence, we optimized the linear-logarithmic pixel structure to minimize the pixel response variation. We applied a hard reset method and an optimized cascode MOSFET to the proposed pixel for reducing pixel response variation. Unlike the conventional reset operation, a hard reset using a p-type MOSFET fixes the voltage of each pixel to the same voltage. This reduces non-uniformity of the response in the linear response. The optimized cascode MOSFET achieves less variation in the logarithmic response. We have verified that the optimized pixel shows more uniform response than the conventional pixel, by both simulation and experiment.

A 3dimensional (3D) imaging is an important area which can be applied to face detection, gesture recognition, and 3D reconstruction. In this paper, extraction of depth information for 3D imaging using pixel aperture technique is presented. An active pixel sensor (APS) with in-pixel aperture has been developed for this purpose. In the conventional camera systems using a complementary metal-oxide-semiconductor (CMOS) image sensor, an aperture is located behind the camera lens. However, in our proposed camera system, the aperture implemented by metal layer of CMOS process is located on the White (W) pixel which means a pixel without any color filter on top of the pixel. 4 types of pixels including Red (R), Green (G), Blue (B), and White (W) pixels were used for pixel aperture technique. The RGB pixels produce a defocused image with blur, while W pixels produce a focused image. The focused image is used as a reference image to extract the depth information for 3D imaging. This image can be compared with the defocused image from RGB pixels. Therefore, depth information can be extracted by comparing defocused image with focused image using the depth from defocus (DFD) method. Size of the pixel for 4-tr APS is 2.8 μm × 2.8 μm and the pixel structure was designed and simulated based on 0.11 μm CMOS image sensor (CIS) process. Optical performances of the pixel aperture technique were evaluated using optical simulation with finite-difference time-domain (FDTD) method and electrical performances were evaluated using TCAD.