Proceedings Volume 5459

Optical Sensing

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Proceedings Volume 5459

Optical Sensing

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Volume Details

Date Published: 1 September 2004
Contents: 10 Sessions, 50 Papers, 0 Presentations
Conference: Photonics Europe 2004
Volume Number: 5459

Table of Contents

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Table of Contents

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  • Biological Sensing
  • Techniques for the Mid-Infrared
  • Fibre Bragg Gratings
  • Microscopy and Imaging
  • Active and Passive Components
  • Session 9
  • Distributed and Multiplexed Sensing
  • Poster Session
  • Environmental and Chemical Sensing
  • Polarimetric Techniques
  • Session 9
  • Poster Session
  • Biological Sensing
Biological Sensing
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Development of a biosensor based on a prism coupler method
Stephen Couvignou, Luc Trudel, Roger A. Lessard, et al.
Agar is a complex mixture of polysaccharides. It is widely used in microbiology as a jellifying agent to obtain solid culture medium that can then support the growth of bacteria, yeasts and other microorganisms. Although this substrate has a daily use in biology and microbiology, its physico-chemical properties are still not well known. Consequently, a characterisation of a solid bacteriological medium infected or not by Escherichia coli type bacteria can be realized on thin films obtained by spin coating. The present study using a prism coupler method gives a sensitive tool to detect photo-physical change in the medium. This method could allow us to detect the presence of bacteria. Results obtained are reproducible on different samples and might be qualitatively compared with conventional imagery. This method should enable a rapid detection of the growing of bacteria on the studied medium.
Multiparametric fluorescence probing of nanoscale compositions and biological systems
Andrey S. Klymchenko, Guy Duportail, Yves Mely, et al.
We demonstrate a possibility for simultaneous probing of several microscopic physicochemical properties of supramolecular systems using the dye molecules existing in several forms of the ground and/or excited states. This idea is realized on a series of 3-hydroxychromone dyes, which exhibit the Excited-State Intramolecular Proton Transfer reaction resulting in two excited state tautomeric forms. Microenvironment of these dyes can be characterized by a number of characteristic energies of absorption and emission transitions (positions of the corresponding bands) and by redistribution between the forms (relative intensities of the bands). We demonstrate that the positions and relative intensities of fluorescence excitation and emission bands can serve as independent variables with different sensitivity to polarity, electronic polarizability, electric field effects, hydrogen bonding acidity and basicity, thus, allowing multiparametric description of probe environment. The results of numerous applications of this approach in the studies of neat solvents, solvent mixtures, proteins and phospholipid membranes are presented.
Near-infrared oxymeter prototype for noninvasive analysis of rat brain oxygenation
Francesco Crespi, Maurizio Donini, Andrea Bandera, et al.
The feasibility of non-invasive analysis of brain activities was studied in the attempt to overcome the major limitation of actual in vivo methodologies i.e. invasiveness. Optic fibre probes were used as optical head of a novel, highly sensitive near infrared continuous wave spectroscopy (CW-NIR) instrument. This prototype was designed for non-invasive analysis of the two main forms of haemoglobin: oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb), chromophores present in biological tissues. It was tested in peripheral tissue (human gastrocnemius muscle) and then reset to perform measurement on rat brain. In animal studies, the optical head was firmly placed using stereotaxic apparatus upon the sagittal line of anaesthetised adult rat's head, without any surgery. Then pharmacological treatments with saline (300μl s.c.) amphetamine (2mg/kg) or nicotine (0.4mg/kg) were performed. Within 10-20 min amphetamine substantially increased HbO2 and reduced Hb control levels. Nicotine produced a rapid initial increase followed by a decrease of HbO2. In contrast to amphetamine, nicotine treatment also reduced Hb and blood volume. These results support the capacity of our CW-NIR prototype to measure non-invasively HbO2 and Hb levels in the rat brain, markers of the degree of tissue oxygenation, index of blood level then of the state of brain metabolism.
Techniques for the Mid-Infrared
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Mid-infrared light sources at room temperature based on lead chalcogenides
Regine Glatthaar, Joachim Nurnus, Uwe Vetter, et al.
We report on the development of epitaxial thin film materials for optical pumped light emitting devices in the wavelength range of 4-5 μm. The active layers are lead selenide (PbSe) thin films grown by molecular-beam epitaxy (MBE) on single crystalline, infrared transparent BaF2 substrates. The electrical properties of the layers were determined by van der Pauw Hall measurements. A dependency of the PL intensity on the dopant type and carrier concentration was found. To increase the output power, layers with antireflection coatings were grown and characterized by Fourier-transform infrared (FTIR) spectroscopy and photoluminescence (PL) measurements. A further possibility to increase the extraction efficiency is surface texturing. Infrared imaging and PL measurements at samples with different surface structures, prepared by wet chemical etching, are presented. To improve the heat dissipation, which is a problem of optical pumped devices due to the small efficiency and pump densities up to some kW/cm2, the BaF2 substrates were removed and the active layers were transferred to different heat sinks with significantly higher thermal conductivities. Afterwards the PL intensities were compared among each other.
Chalcogenide glass fibers used for in situ infrared spectroscopy in biology and medicine
Julie Keirsse, Bruno Bureau, Catherine Boussard-Pledel, et al.
Chalcogenide glass optical fibers possess very low optical losses in the middle infrared range from 2 to 12 mm. They were used to implement remote infrared spectroscopy, known as Fiber Evanescent Wave Spectroscopy (FEWS). Due to their hydrophobic behavior, such sensor is especially suitable for application in biology and medicine where water is a nuisance to detect relevant information. Moreover, the design of the sensor using tapered fibers enables to improve the signal to noise ratio. Then, once coupled with unsupervised analysis technique such as Principle Component Analysis (PCA), it has been shown that this tool is efficient to differentiate between obese and control mice by recording their serum FEWS spectra. The same method has been carried out to detect in situ the both phenotypes of a bacterial culture.
Imaging of carbon monoxide distributions around igniting n-heptane droplets after excitation with a quantum cascade laser at 4.6 µm
Alfons Burkert, Wolfgang Triebel, Christian Eigenbrod
Carbon monoxide distributions around igniting n-heptane droplets were determined using absorption measurements. The emission of a quantum cascade laser at 4.6 μm was shaped to a parallel laser beam using a lens. For detection, a plane through the droplet, perpendicular to the laser beam was imaged onto the focal plane array of a mid-infrared camera. For background suppression a long-pass filter was mounted in the detection ray path. To estimate the detection sensitivity of the set-up, CO absorption in a reference cell was measured. In addition, CO transmission spectra were calculated for different temperatures based on HITRAN 2000 catalogue.
Performance of a far-IR TES bolometer on monolithic sapphire membrane
The performance of a high Tc (~90 K) transition-edge superconducting (TES) bolometer on a monolithic sapphire membrane is presented and discussed. It is compared to the performance of a previous TES bolometer on non-monolithic sapphire substrate. The development and optimization of monolithic sapphire membranes is critical for the fabrication of 1 and 2-D arrays of TES bolometers. Moderately cooled and optimized TES bolometers are expected to be the replacements of choice for thermopiles and other room temperature thermal sensors on far IR instruments on future planetary missions.
Fibre Bragg Gratings
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Structural health monitoring by embedded fiber Bragg gratings
Thomas Alt, Kathrin Badstuebner, Bernd Michel, et al.
At Fraunhofer Institute for Reliability and Microintegration IZM, Fiber Bragg Gratings (FBG) are used for online measurement of mechanical deformations and temperature changes within electronic packaging and mechatronic systems. Encapsulation processes with rapid prototyping materials like stereolithography resin and vacuum casting polymers are monitored, as well as high volume production processes like Reactive Injection Molding (RIM). This paper discusses the effects that occur when the geometrical and mechanical properties of the measured object are comparable to the sensing system and when the fiber optic sensor is significantly influencing the measurement. Package reliability in electronics is intensively studied at our institute [1] and this paper will evaluate the ability of FBG to detect structural changes like cracks and delaminations within electronics. By embedding the fibers directly into the polymer packaging the sensor can be used for continuous lifetime monitoring of the system, starting with real-time cure monitoring during production processes and ending with structural health monitoring during product lifetime and quality testing.
Characterization of twin Bragg gratings for sensor application
Christophe Caucheteur, Karima Chah, Frederic Lhomme, et al.
Twin gratings are important devices for sensor application. They are formed by two gratings inscribed in cascade in a single fiber. We present here a detailed study of twin Bragg gratings. We first show the evolution of twin Bragg gratings spectra versus the spacing between the gratings and their length. Owing to the coupled mode theory, we explain the particular shape of the various spectra. Then we demonstrate the influence of the reflectivity of each Fiber Bragg Grating on the global spectral response of the two cascaded FBGs. All the gratings we have inscribed are simulated using the Transfer Matrix Method in order to retrieve their parameters (grating length, period, index modulation and distance between gratings)from experimental reflection spectra. Finally we characterize these FBGs for temperature sensing. We discuss the design suitable to sensor applications and describe the interrogation technique used in this case. We use a digital algorithm based on Fast Fourier Transform. It offers precise, fast and absolute measurements.
Interferometric and fibre Bragg grating sensor interrogation using an arrayed waveguide grating
David C. C. Norman, David J. Webb, Ralf D. Pechstedt
We investigate the use of an arrayed waveguide grating (AWG) to interrogate both fibre Bragg grating (FBG) and interferometric sensors. A broadband light source is used to illuminate both the FBG and interferometric sensors. Reflected spectral information is directed to an AWG with integral photodetectors providing 40 electrical outputs. To interrogate interferometric sensors we investigated the dual wavelength technique to measure the distance of a Fabry-Perot cavity, which produced a maximum unambiguous range of 1440μm with an active sensor. Three methods are described to interrogate FBG sensors. The first technique makes use of the reflected light intensity in an AWG channel passband from a narrow bandwidth grating, giving a usable range of 500με and a dynamic strain resolution of 96nε/√Hz at 30Hz. The second approach utilises wide gratings larger than the channel spacing of the AWG; by monitoring the intensity present in corresponding AWG channels an improved range of 1890με was achieved. The third method improves the dynamic range by utilising a heterodyne approach based on interferometric wavelength shift detection providing a dynamic strain resolution of 17nε/√Hz at 30Hz.
Gratings in novel fibre geometry for applications in shape sensing
A long period grating (LPG) fabricated in progressive three-layered (PTL) fibre is described. The grating with a period of 391μm, had dual attenuation bands associated with a particular cladding mode. The dual attenuation bands have been experimentally characterised for their spectral sensitivity to bending, which resulted in the highest sensitivity to bending seen for this particular fibre and temperature. The spectral characteristics of the fibre have been modelled giving good agreement to the experimental data as well as showing that the attenuation bands are both associated with the second order HE/EH2,n cladding mode.
Type 1A fibre Bragg grating photosensitivity and the development of optimum temperature invariant type I-type IA strain sensors
A. George Simpson, Kyriacos Kalli, Lin Zhang, et al.
Type 1A fibre Bragg gratings (FBG) form only after the erasure of a standard grating in hydrogenated germanosilicate fibre, under prolonged UV exposure. They are distinct from other grating types as they exhibit a uniquely large increase in the mean index of the core, readily identifiable by a large red shift in the Bragg wavelength. Type 1A gratings can surpass the conventional mean index change by a factor of six with a typical red shift of up to 20nm, interpreted as a mean index increase of up to 1.9x10-2. Importantly, 1A gratings have been shown to exhibit the lowest temperature coefficient of all FBG, which makes them ideal for use as temperature compensated, dual grating sensors. We report on the formation of Type 1A gratings and the correlation between the mean index change of the grating and the growth of a loss band at close to 1400nm that is associated with the formation of OH centres within the fibre. We present annealing data comparing the decay of Type 1 and Type 1A gratings. Finally, we demonstrate a dual temperature compensated strain sensor system, based on two adjoining Type 1 and Type 1A gratings, which have been formed using a common phase mask, yet with central wavelengths many nm apart.
Interferometric visualization and demodulation method for measuring quasi-static strain in fiber Bragg grating sensors by a simple rotating etalon filter
Optical fiber sensors are the ideal system to monitor "smart structures" and on-site/real time stress measurements: they can be in fact easily embedded or attached to the structures under test and are not affected by electro- magnetic noise. In particular a signal from a Fiber Bragg grating sensor (FBG) may be processed such that its information remains immune to optical power fluctuations. Different interrogation methods can be used for reading out Bragg wavelength shifts. In this paper we propose a very simple interferometric method for interrogating FBG sensors, based on bi-polished silicon sample acting like an etalon tuneable filter (ETF). The Bragg wavelength shift can be evaluated by analyzing the spectral response of signal reflected by the FBG sensor and filtered by the ETF that is continuously and rapidly tuned. Tuning was obtained by rotating the ETF. Variation in the strain at the FBG causes a phase shift in the analyzed signal. The overall spectral signal, collected with time, consists in an interferometric figure which finesse and fringe contrast depending on the geometrical sizes and facets reflectivity of the silicon sample. The fringe pattern, expressed by the Airy's formula, depends on the wavelength l of the incident radiation and on the angle of incidence. The phase of fringe pattern can be retrieved by a standard FFT method giving quantitative measurements of the quasi-static strain variation sensed by the FBG. In this way, the method allows a valuable visualization of the time-evolution of the incremental strain applied to the FBG. Principle of functioning of this method is described and first results obtained employing such configuration, are reported.
High-resolution characterisation methods for narrow line-width fiber Bragg gratings
Gesine Grosche, Michael Eggert
Special, narrow-linewidth fiber Bragg gratings (FBGs) can serve as wavelength references for both sensor applications and optical telecommunications. With line-widths of a few GHz and contrast exceeding 95%, phase-shifted FBGs offer a good alternative to etalons or gas cells as easy-to-use and cost-effective wavelength references. To enable calibration and to assess the wavelength stability of newly developed FBGs down to parts in 107, quantifying drifts caused e.g. by aging, polarisation dependence, residual sensitivity to temperature or strain, we have developed high resolution measuring methods which are linked to a traceable wavelength. We present results from three complementary methods based on Fourier Transform spectroscopy, tunable laser spectroscopy and a new laser stabilisation technique using polarisation modulation. For the central wavelength of phase-shifted FBGs we achieved an accuracy below 10-7.
A high-performance miniaturized time division multiplexed sensor system for remote structural health monitoring
Glynn D. Lloyd, Lorna A. Everall, Kate Sugden, et al.
We report for the first time the design, implementation and commercial application of a hand-held optical time division multiplexed, distributed fibre Bragg grating sensor system. A unique combination of state-of-the art electronic and optical components enables system miniaturization whilst maintaining exceptional performance. Supporting more than 100 low-cost sensors per channel, the battery-powered system operates remotely via a wireless GSM link, making it ideal for real-time structural health monitoring in harsh environments. Driven by highly configurable timing electronics, an off-the-shelf telecommunications semiconductor optical amplifier performs combined amplification and gating. This novel optical configuration boasts a spatial resolution of less than 20cm and an optical signal to noise ratio of better than 30dB, yet utilizes sensors with reflectivity of only a few percent and does not require RF speed signal processing devices. This paper highlights the performance and cost advantages of a system that utilizes TDM-style mass manufactured commodity FBGs. Created in continual lengths, these sensors reduce stock inventory, eradicate application-specific array design and simplify system installation and expansion. System analysis from commercial installations in oil exploration, wind energy and vibration measurement will be presented, with results showing kilohertz interrogation speed and microstrain resolution.
Deformation monitoring of wooden works of art using FBG sensors
Riccardo Falciai, Cosimo Trono, Giancarlo Lanterna, et al.
Wood support is an essential element of the works of art and is highly sensitive to the environmental climate modification. Wood deformations may have irreversible destructive effects on the work of art. The use of fiber Bragg grating (FBG) sensors for the quasi-distributed in-situ measurement and continuous monitoring of the painted wood panel deformations is proposed. FBG sensors have high resolution low invasivity and intrinsic safety. The effects of relative humidity changes were measured on a wood panel, by monitoring the deformations in the wood structure using an array of fiber Bragg gratings glued to different critical points.
Microscopy and Imaging
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Autocorrelator for multiphoton microscopy
Franco Quercioli, Alessandro Ghirelli, Bruno Tiribilli, et al.
Multiphoton microscopy is a relatively new and rapidly growing field of applied optics where Ti:Sapphire ultrafast laser sources and related technology find a wide application. Laser beam diagnostic techniques specially devoted to this kind of application has been widely developed in these last years. Research efforts have been addressed to the evaluation and the eventual correction of the laser pulse duration widening due to group velocity dispersion caused by the microscope optics. Temporal characterization is thus a fundamental task when operating a ultrafast laser system for multiphoton microscopy applications and it is carried out by means of autocorrelators specially designed to perform pulse width measurements at the focus of the microscope objective. In the present communication, an innovative autocorrelator set-up and a simple metrological procedure are reported.
All solid state imaging infrared/imaging LADAR sensor system
Joachim Barenz, Rainer Baumann, Frank Imkenberg, et al.
A compact dual mode sensor is under development at BGT addresssing autonomous guidance, target detection and classification/identification for everal military and civilian applications. The dual mode sensor consists of an imaging infrared sensor and an imagin Ladar sensor both in snapshot mode. This paper presents the concept of the dual mode sensor and shows the current development status. Critical components such as a compact laser source, fiber-array for image plane sampling, wavelength selective infrared beam splitter and micro-lens arrays for Ladar field-of-view steering are presented in detail.
Confocal micro-optical distance sensor for precision metrology
Increasing demands for controlling tolerances of small mechanical and optical components require improved measurement techniques. In particular, components with a complex geometry such as small holes or channels are difficult to access by classical tactile measurement systems. These systems are also limited in their measurement speed. Optical distance sensors do not have many of these disadvantages, but the sensor heads are normally too large to access e.g. small holes. Presented in this paper is a novel microoptical sensor concept using the chromatic confocal principle for distance gauging applications. This is used in high aspect ratio cavities with a diameter of about 2 mm. The distance resolution of the sensor is aimed to be in the sub-micrometer range.
Avalanche photodiode-based optical coherence tomography
Optical Coherence Tomography (OCT) is used to perform in vivo high-resolution imaging of biological tissue microstructures. In the present study, we evaluate the optimum conditions to use Avalanche photodiodes (APDs) in OCT to achieve maximum signal-to-noise (S/N) ratios. The optical sources employed in OCT have a large bandwidth. Due to beating within the source line-width, excess photon noise (EPN) is generated in addition to shot noise (SN). Usually, high speed OCT requires large optical power, which makes the EPN to dominate over the SN. Therefore, balanced detection is used to reduce the EPN. We analyse the optimisation of the OCT configuration with respect to the APD noise performance. When using APDs, another parameter has to be considered in the S/N analysis: that of the voltage across the APDs, which determines, both, the gain and the noise.
A time-of-flight line sensor: development and application
Rolf Kaufmann, Michael Lehmann, Matthias Schweizer, et al.
A new miniaturised 256 pixel silicon line sensor, which allows for the acquisition of depth-resolved images in real-time, is presented. It reliably and simultaneously delivers intensity data as well as distance information on the objects in the scene. The depth measurement is based on the time-of-flight (TOF) principle. The device allows the simultaneous measurement of the phase, offset and amplitude of a radio frequency modulated light field that is emitted by the system and reflected back by the camera surroundings, without requiring any mechanical scanning parts. The 3D line sensor will be used on a mobile robot platform to substitute the laser range scanners traditionally used for navigation in dynamic and/or unknown environments.
Optical simulation for CMOS imager microlens optimization
This paper describes a new methodology we have developed for microlens optimization for CMOS image sensors in order to achieve good optical performances. On one hand, the real pixel is simulated in an optical simulation software and on the other hand simulation results are post-processed with a numerical software. In a first part, we describe our methodology. We start from the pixel layout description from standard micro-electronic CAD software and we generate a three-dimensional model on an optical ray tracing software. This optical model aims to be as realistic as possible taking into account the geometrical shape of all the components of the pixel and the optical properties of the materials. A specific ray source has also been developed to simulate the pixel illumination in real conditions (behind an objective lens). After the optical simulation itself, the results are transferred to another software for more convenient post-processing where we use as photosensitive area a weighted surface determined from the fit of angular response simulation results to the measurements. Using this surface we count the ray density inside the substrate to evaluate the simulated output signal of the sensor. Then we give some results obtained with that simulation process. At first, the optimization of the microlens parameters for different pixel pitches (from 5.6um to 4um). We also have studied the polarization effects inside the pixel. Finally, we compare the measured and the simulated vignetting of the sensor, demonstrating the relevance of our optical simulation process and allowing us to study solutions for a pixel pitch of 3μm and less.
Novel design and prototyping of a micro-optical distance sensor considering a distributed fabrication
A novel design for a compact and robust micro optical distance sensor is presented. It is suitable for mass fabrication by micro molding known form the LIGA technique [1] and automatic assembly. Due to a modular design approach a distributed fabrication of the device modules is currently implemented. This allows a separate fabrication of the modules at several manufacturers each one being an expert for the special technology needed to fabricate the module. During the design phase not only the optical specification of the sensor system but also all requirements given by the manufacturers, such as easy manufacturability with high throughput as well as defined interfaces need to be considered.
Simulations and experimental research of fiber optic contrast-based dislocation sensor
Mieczyslaw Szustakowski, Norbert Palka, Wieslaw M. Ciurapinski
The dislocation sensor based on the contrast phenomenon in an unbalanced fiber optic Michelson interferometer with a 3 x 3 coupler and a semiconductor multimode laser. Periodic contrast oscillations, which depend on a laser spectrum, occur if a measuring arm of the interferometer is elongated. A conception of the elongation sensor that based on linearization of contrast oscillations is shown. A virtual model of the sensor was built for simulations. For real parameters of 1-m long sensor, 5-mm measuring range with 12-mm uncertainty was obtained. Next, a setup of the sensor and signal processing scheme of real sensor is presented. During measurements we obtained 5-mm measuring range with ±28-mm uncertainty. Explanation of these differences and conclusion to further research are formulated.
Active and Passive Components
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Silicon planar technology for single-photon optical detectors
In this paper we report the results relative to the design and fabrication of Single Photon Avalanche Detectors (SPAD) operating at low voltage in planar technology. These silicon sensors consist of pn junctions that are able to remain quiescent above the breakdown voltage until a photon is absorbed in the depletion volume. This event is detected through an avalanche current pulse. Device design and critical issues in the technology are discussed. Experimental test procedures are then described for dark-counting rate, afterpulsing probability, photon timing resolution, quantum detection efficiency. Through these experimental setups we have measured the electrical and optical performances of different SPAD technology generations. The results from these measurements indicate that in order to obtain low-noise detectors it is necessary to introduce a local gettering process and to realize the diode cathode through in situ doped polysilicon deposition. With such technology low noise detectors with dark counting rates at room temperature down to 10c/s for devices with 10mm diameter, down to 1kc/s for 50mm diameter have been obtained. Noticeable results have been obtained also as far as time jitter and quantum detection efficiency are concerned. This technology is suitable for monolithic integration of SPAD detectors and associated circuits. Small arrays have already been designed and fabricated. Preliminary results indicate that good dark count rate uniformity over the different array pixels has already been obtained.
Spectral response of an infrared superconducting quantum detector
We analyze the spectral performance of recently developed single-photon quantum detector that consists of a narrow, nanometer sized meander-line made from ultra-thin superconducting film. The detector exploits a combined detection mechanism, in which avalanche multiplication of quasiparticles after absorption of a single photon and the bias current jointly produce a normal domain that results in a voltage pulse developing between the meander ends. With either the wavelength increase or the bias current decrease, the single-photon detection regime exhibits a cut-off. The wavelength, at which the cut-off occurs, varies from infrared waves to visible light depending on the superconducting material and operation conditions. Structural and geometrical non-uniformities of the meander line smooth out the otherwise expected sharp drop of the detection efficiency beyond the cut-off. We refine the early detector model and propose a tentative explanation of how superconducting fluctuations may additionally extend the detection efficiency beyond the cut-off wavelength.
Speed- and sensitivity-enhanced integrated optical sensor with divided photodiode
Generally, a high-speed optical sensor consists of a photodiode and a transimpedance amplifier. If a large photosensitive area is demanded, the resulting large junction capacitance of the photodiode limits both the bandwidth and the noise behavior of the transimpedance amplifier. Therefore we suggest an innovative approach, which divides the photodiode into four electrically isolated sections. Each of the four-quarter photodiodes is connected to a transimpedance amplifier and their output voltages are combined with a summation amplifier. The capacitance of each of the four-quarter photodiodes is only one fourth of the capacitance of the undivided photodiode, therefore the bandwidth of the innovative optical sensor is 223MHz, which is three times as high as the bandwidth of a transimpedance amplifier with an undivided photodiode. The photo-sensitivity is more than doubled to 75mV/μW.
Session 9
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Sampled chirped fiber gratings as distributed pressure sensors
Swee Chuan Tjin, Lipi Mohanty, Nam Quoc Ngo
Fiber gratings have been studied for their applications in sensing and communications. Many sensing applications of the uniform fiber Bragg grating, chirped fiber grating and long period grating have been studied, proposed and commercialized. Sampled chirped gratings have been studied for multichannel dispersion compensation in DWDM systems. In this paper, we show that the sampled chirped fiber grating can be used as a distributed pressure sensor. The chirp provides ease of manufacture of many gratings. The sampling results in many small, uniform grating-like structures. This fact can be used to simulate a distributed sensor over the length of the sampled chirped grating. When a surface comes into contact with the sensor, the distribution of the pressure determines the shift in central wavelength of the various sub-gratings. The sub-grating that experiences the maximum pressure will show maximum wavelength shift whereas adjacent sub-gratings will show less shift. This can also give the location of the pressure. The sensor design comprises of a sampled chirped grating embedded in unidirectional fiber-reinforced composite prepreg. The prepreg enhances the mechanical strength and the unidirectional embedding reduces birefringence. The number of layers in the prepreg stack varies the sensitivity. Such distributed pressure sensors can be applied in robotics, ergonomics, and in the biomedical field.
Distributed and Multiplexed Sensing
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Miniaturised optical displacement sensor
Frank Gindele, Frank Gaul, Silvio Kraus M.D., et al.
The primary object presented in this contribution is the miniaturization of a displacement sensor system with the potential for high accuracy measurements and for cost-effective production in polymers. The measurement of linear displacements can be performed by different methods e.g. magnetoresistive, potentiometric, electromagnetic or inductive encoder systems. For movements in the millimeter range and above the most precise systems are based on optical methods. The displacement measurement of our sensor system uses the intensity modulation of two amplitude gratings, moving relative to each other and illuminated by a LED. To increase the system resolution and the signal quality the grating/detector combination is divided into four areas which are phase shifted to each other. The grating period is 25 μm with a geometrical accuracy below 1 μm. The amplitude gratings have been processed on a glass substrate lithographically. Applying electro-discharge machining a miniaturised optical bench for the passive alignment of the optical and the opto-electronic components has been realised. The sensor has an overall size of 6x4x3 mm3 and is designed for the future replication in one single polymer part. In combination with an electronic interpolation the sensor will be capable for a sub-micrometer accuracy.
Poster Session
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Detection of condensed vapours and their refractive indices using photorefractive crystals
Vladislav Matusevich, Katsiaryna Pismennaya, Armin Kiessling, et al.
We present an experimental set-up for the optical detection of condensed vapours or liquids and their refractive indices using photorefractive crystals (e. g. Barium-Calcium-Titanate or Barium-Titanate). Hereby we use a self-pumped phase conjugating mirror along with the effect of total reflection. The modulation of the signal beam in order to avoid background illumination is not necessary due to the phase-conjugated reflection. The detection of different condensed vapours or liquids and their refractive indices is possible by the variation of the input angle of the signal beam.
Environmental and Chemical Sensing
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Real-time monitoring of volcanic emissions with a laser-based fiber spectrometer
Alessandra S. Rocco, Gianluca Gagliardi, Livio Gianfrani, et al.
Recent progress in telecom-based optoelectronic devices and low power laser sources has provided new powerful tools for in-situ monitoring of volcanic areas in real-time and for long periods, with unprecedented accuracy and resolution. Such techniques represent a great improvement if compared to the traditionally used "in-situ" sampling techniques such as gas chromatography and mass spectrometry which result often impractical or dangerous, and do not allow temporally continuous monitoring Optical communication diode lasers, which emit visible and IR radiation with mW power, operating on single mode at room temperature, are ideal sources to develop high sensitivity gas analysers based on absorption spectroscopy techniques. Their possible use in conjunction with fiber components is particularly advantageous in the perspective of developing networks for simultaneous monitoring of many geochemical and geophysical parameters. We report on the field tests of a novel Portable Diode Laser Spectrometer (PDLS), operating at a wavelength of 1.99μm and based on direct absorption spectroscopy, for high precision, accurate and real-time, simultaneous measurements of CO2 and H2O concentrations. We used an open-path configuration, positioning the detection bench, equipped with a a Herriott cell especially designed for measurements in hazardous environment, at different sites of the fumarolic areas. With such a configuration we can take advantage of the long optical path-length allowed by the multiple-pass cell (20.3m). The measured CO2 and H2O concentrations vs. time are shown. This work was supported by GNV-INGV, in the framework of the project "Development of spectroscopic integrated system for remote and continuous monitoring of volcanic gases".
Online fully automated measurement of Cr(VI) concentration in water by a fiber optic probe: measurement accuracy improvement and evaluation
Giulio D'Emilia, Emanuela Natale
In this paper a methodology is described to be implemented in a simple and low cost automatic measuring apparatus for on line measurement of Cr(VI) concentration in water, which is able to be controlled by a PC and to be inserted in an integrated environmental control multi-sensor network. Measuring section is a miniaturized fiber optic probe, whose working principle is light absorption of the complex Chromium (VI) - Diphenylcarbazide. Device design and set up guidelines of an automatic measuring device are described in order to get a reliable, effective and user friendly configuration and to reduce measurement uncertainty depending on interfering quantities of different type, fluid dynamic, optical, environmental, taking into account "in situ" measuring conditions.
The fiber optic Sagnac interferometer application for recognition of the rotational seismic events
Leszek R. Jaroszewicz, Zbigniew Krajewski, Lech Solarz
In the paper a new area of the fiber-optic SAgnac interferometer applications are discussed. The presented devices basing on well-known optical gyroscope configuration are optimized for detection of other special physical quantitites. Generally it is a rotational seismometer designed for calibration of the other electromechanical types of such devices, as well as a new sensor for detection of rotational seismic events. The detection of absolute rotation by the system is advantageous in comparison to the other rotational seismometers, which calculate rotational events in indirect ways. The paper desribes comparison of the data obtained from teh fiber-optic rotational seismometer and the electromechanical one. Moreover, on this base the construction of new system with resolution 10 E-8 rad/s is also presented in this paper.
Online water color monitoring by means of fiber optic technology in a water recycling plant
Anna Grazia Mignani, Andrea A. Mencaglia, Leonardo Ciaccheri, et al.
After each step in the recycle process at the CONSER-IDRA water recycling plant (Prato, Italy), the water is stored in reservoirs. Up to now, the quality of the process has been monitored by taking samples from the reservoirs and analyzing them in the laboratory. This work presents a more efficient fiber optic system that provides online monitoring by measuring water color directly in the reservoirs. The system uses a fiber optic probe to perform absorption spectroscopy in the visible spectral range. The feasibility of using fiber optic technology for online monitoring has been confirmed by the positive results of several days of validation testing.
Remote gas analysis using fibre optic links and near infrared absorption
George Stewart, Gillian Whitenett, Joanna P. Marshall, et al.
This paper describes the potential application of optical fibre addressed systems in remote gas spectroscopy. The paper will first describe the basic principles of the spectroscopic measurements and the reasons why such measurements find applications complementing more established mid infrared and electrochemically-based systems. We shall describe some practical field trials and the results obtained there from. Finally we shall discuss the potential offered by new approaches in laser design and system architectures to enhance the range of addressable species and the sensitivity which these remote detection systems may achieve.
Polarimetric Techniques
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Investigations on the stability of polarimetric fiber laser sensors in harsh environments
Andreas Frank, Klaus Bohnert, Karim Haroud, et al.
The stability of a polarimetric Fabry-Perot fiber laser sensor for fluid pressure up to 100 MPa is investigated. The fluid acts on one of two elliptical-core fiber sections in the laser cavity producing a shift in the differential phase of the two orthogonal polarization modes and thus a variation in the beat frequencies of the corresponding longitudinal laser modes. The second fiber section, with a 90-degree offset in the core orientation, compensates for temperature-induced phase shifts. Dispersion in the birefringent fiber Bragg grating reflectors is employed to enhance the resolution of the sensor to a few parts in 106 of the free spectral range. Investigations on sensor stability address the effect of the fluid on the integrity of the fiber, creep caused by various types fiber coatings, as well as the intrinsic stability of erbium-doped and undoped sensing fibers under pressure and temperature changes. It is found that moisture-free silicone oil does not cause any fiber deterioration even in case of a bare fiber. Silicon nitride and gold coatings (1 mm thick) cause significant signal drift, whereas no drift is observed for carbon coatings. Highly doped elliptical-core sensing fiber exhibited drift in the differential optical phase while un-doped fiber did not.
A sensitivity-enhanced optical heterodyne polarimeter for the measurement of optical rotation angle of chiral media
A novel heterodyne polarimeter is designed to measure the concentration of chiral media. Optical common-path for the interference of the TE and TM waves, after a polarizer, is set up in our system to reduce noises from the environment. A phase-variable waveplate is placed behind the sample to enhance the phase signal change of rotation of polarization introduced by the sample itself. This enhancement can be excess two orders in amplitude when the retardation of the phase-variable plate is set close to 180 degree. With this polarimeter, the measurement of optical rotation angle with high sensitivity of 6.5×10-4 degree experimentally can be achieved when phase retardation of the phase-variable waveplate is 178.5 degree. We expect that, by further improvement, it can be applied in noninvasive blood glucose concentration monitoring for diabetics in the future.
Extrinsic fibre Fabry-Perot interferometer for vibration and displacement measurement: the benefit of polarization decomposition
Elisabeth Ouisse, Vincent Metivier, Noel Servagent, et al.
We have successfully developed a new design of an extrinsic fibre Fabry-Perot interferometer (EFPI) sensor dedicated to the characterization of vibration and displacement of a target. This device, based on a low finesse Fabry-Perot cavity formed by the end of a 'sensing' optical fibre and the target, gives information on the direction of the motion without the use of an additional reference arm. The incoming light, emitted by a 1310 nm laser diode, is decomposed according to two orthogonal polarization orientation inside the cavity. The two resulting interference signals are then carried back by the same optical fibre and sent to two photodiodes via a coupler and a polarizing beam splitter. With a relatively simple signal processing, a precision of λ/4 is achieved for the measurement of the displacement, for which the direction is also extracted. In addition, one can determine the velocity of the motion, that have been successfully compared with a reference sensor. The use of a polarization maintaining fibre as sensing arm, not mandatory for monitored laboratory set-up, allows the use of this sensor principle even with external perturbation (temperature changes, mechanical stress...).
Automatic in-line fiber-optic polarization analyzers
In the paper two different configurations of automatic in-line fiber-optic polarization analyzers are presented. The principle of operation is based on birefringence modulation in the standard single-mode fiber and suitable detection of the harmonic amplitudes of the output electric signals. In the first one, called Fiber-Optic Polarization Analyzer, the polarimetric configuration with polarization modulation by squeezing a single-mode fiber is used. In the second, called Fiber-Optic Interferometric Polarization Analyzer, the modified Sagnac interferometer with standard piezoceramic ring modulator is applied. For both configurations briefly theoretical analysis of the polarization phenomenon is presented. As a main part of the paper the experimental results of the state as well as the degree of polarization parameters measurement are shown. In the experimental systems digital oscilloscope, function generator and PC with HPiB card and HP-VEE software for identification polarization parameters are used. In conclusion both systems are compare - especially form measurement time and errors points of view.
Session 9
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Scattering of light by sound on a nanoscale
Adnen Mlayah, Jesse Groenen, Guillaume Bachelier, et al.
We report on light scattering experiments (Raman-Brillouin) in semiconductor quantum wells and quantum dots nanostructures. All measurements were performed under resonant excitation of the optical transitions involving confined electronic states. The scattered light was detected in the very low-frequency range around the Rayleigh line. We observe strong oscillations of the scattered intensity. Their period and relative amplitudes depend on the sample characteristics (size, density and spatial distribution of nano-objects). We show that such signal originates from interference effects due to the interaction between sound waves and the excited electronic density. By comparing simulated and measured spectra, we are able to extract, from the experiments, sample characteristics such as average size and size distribution of quantum dots. This optical sensing technique, namely Raman interferometry, is similar to the well-known X-ray diffraction technique, in the sense that it allows imaging of electronic states in the reciprocal space. Moreover, we show that Raman interferometry is a surface sensitive technique. By using quantum dots and quantum wells as Thz acoustic-detectors we are able to measure the reflection of sound waves at the sample surface. The surface characteristics (nano-scale roughness and oxidation) can be addressed using this method.
Fiber optic dilato-spectroscopic sensor: simultaneous thermal, spectral, and physical analyses of materials
Balkarransingh Degamber, Darren Winter, John Tetlow, et al.
This article describes a novel technique to obtain simultaneous spectral, thermal and dilatometric data on polymers as they are heated through their glass transition temperatures and melting points. The technique links an infrared spectrometer and an optical spectrum analyser, through a combination of fibre optic probes, to a custom-modified differential scanning calorimeter. The latter is used to obtain thermal-based information such as the enthalpy of fusion and the glass transition whilst the infrared spectrometer is used to obtain chemical information of the polymer sample. The optical spectrum analyser was used in tandem with the fibre optic probe to obtain simultaneous dilatometric data off the processed sample using an interferometric technique. This combined and simultaneous analytical technique negates the need for three independent experiments to obtain thermal, spectral and chemical information. Another advantage of this simultaneous technique is that the polymer sample is subject to a single and controlled thermal environment.
Poster Session
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Two-dimensional velocimetry measurements with self-mixing technique in diode pumped Er glass laser
Luc Kervevan, Herve Gilles, Sylvain Girard, et al.
The optical feedback into a class B laser can be used as optical velocimeter. This self-mixing technique is simple, self-aligned and very sensitive on low cooperative target. However, the resulting frequency beating only allows deducing the longitudinal speed component along the laser beam. In some cases, such geometry becomes unpractical compared to classical laser Doppler velocimetry (LDV). By using two beams geometry, we have demonstrated the possibility to simultaneously measure both transverse and longitudinal components of the speed vector. This new self-mixing scheme is demonstrated using a single-frequency diode pumped Yb3+:Er3+ phosphate glass laser selected for its inherent very high sensitivity to optical feedback. The principle is validated on a rotating disc with diffusing surface and the tangential linear speed of the disc is precisely measured from 1m/s up to 10m/s without knowing the exact orientation of the disc. Moreover, the technique is spatially selective thanks to the peculiar dynamical response of the laser showing three characteristic beating frequencies in the power spectra when the target is precisely located at the focus point. The dynamic and resolution of the optical sensor are discussed depending on the characteristics of the laser and the geometry of the optical design.
Advanced Hg1-xCdxTe detectors based on MBE-grown multi-layer structures for IR spectroscopy and synergy with IR-fiber optics
Galina Chekanova, Mikhail S. Nikitin, Viacheslav Artyushenko, et al.
High performance large active area photoconductors based on MBE-grown multi-layer structures consist of homogeneous narrow-gap n-Hg1-xCdxTe absorbing layer (n-absorber) blocked by thin adjacent graded-gap Hg1-xCdxTe layers have been fabricated and examined. Large active area (from 0.25 mm x 0.25 mm to 2.25 mm x 2.25 mm) Hg1-xCdxTe photoconductors with improved responsivity in Mid-Wave 3.0-5.5 μm (MWIR); Long-Wave 8-14 μm (LWIR) and Very Long-Wave 14-20 μm (VLWIR) infrared spectral ranges are very attractive for use in state-of-the art IR imaging, analytical and spectroscopic equipment. Synergy of advanced Hg1-xCdxTe detectors with IR-fiber optics, especially based on polycrystalline infrared (PIR-) fiber (4-18 μm) cables and bundles, provides above mentioned equipment with qualitatively new possibility like as remote probing of the objects which are difficult to access or beyond direct optical access. Availability of innovative Hg1-xCdxTe epitaxial material (half-finished products of photoconductors - three-layer sensitive structures grown by MBE in single run) open perspective to manufacture and offer improved detectors for much number of applications. Low temperature MBE growth technique provides better tuning of detectors' spectral responsivity curves to the ordered spectral ranges. Measurements performed on fabricated photoconductors showed significantly increased value of peak responsivity and high level of detectivity.
Discrimination between normal and cancerous cells by gap-FRAP: feasibility in endoscopy
Several reports show that cancerous cells are linked to early decrease in gap-junction number and functionality diminution. This precancerous phenomenon may be accessed by different fluorescence techniques and particularly by gap-FRAP technique (gap-junction fluorescence recovery after photobleaching). Measurements at cell or tissue scale allowed by this method lead to consider its potential interest in endoscopic technics applied to early cancer detection. Experiments were performed on HT-29 (human colon adenocarcinoma), MCF-7 (human breast cancer cell) and CCD-1137Sk (human Fibroblasts) in the presence of 5.6CFDA. Dye was bleached by laser light (488nm) during few seconds depending on the region of interest (one or fewer cells). Fluorescence recovery kinetic after photobleaching was measured by imaging and spectral analysis with a confocal laser scanning microscope as reference technique. Then, a microspectrofluorimeter was used in order to evaluate the faisability on a fiber optics based system offering measurement condition close to the tissue clinical endoscopy conditions.Preliminary results obtained on the various cells lines show significant differences in kinetics for normal and cancerous cells. We have shown that CCD-1137Sk line cells possess functional communicating junctions, contrary to the carcinogenic HT-29 and MCF-7 cells. Results obtained by microspectrofluorimetry are related to confocal microscopes ones confirming the feasibility in endoscopy.
Angular and spectral selectivity of resonant cavity light emitting diodes used as resonant cavity photodetectors
Mihail M. Dumitrescu, Emil-Mihai Pavelescu, Charis Reith, et al.
We have explored the operation of resonant cavity light-emitting diodes (RC-LEDs) used as resonant cavity photodetectors (RC-PDs). Our experiments were conducted using a variety of components, operating in diverse wavelength ranges and having different structural characteristics (different distributed Bragg reflector mirror reflectivities, different detuning, etc.). The measurements show a clear and systematic angular and spectral dependence of the RC-PD photodetected signal. The angular and spectral photosensitivity is derived not only from the quantum well absorption but largely from the microcavity enhancement factor and from the photodetection efficiency condition, which both are dependent on angle and wavelength. The detuning of the microcavity and the extension of the distributed Bragg reflector (DBR) stopband control the extension of the photosensitivity spectral window and the front/top DBR mirror reflectivity controls the angular wavelength selectivity. The fact that the RC-PDs' angular and spectral selectivity can be controlled by proper microcavity design, together with their high bandwidth, opens the possibility of using the same RC-PD device for detecting different WDM channels.
H-bond sensing with 3-hydroxyflavones: steady-state and time-resolved fluorescence studies
Vasyl V. Shynkar, Andrey S. Klymchenko, Alexander P. Demchenko, et al.
The 4'-dialkylamino derivatives of 3-hydroxyflavone find many applications as molecular probes, since their two-band fluorescence spectra produce a strong response to different intermolecular interactions including H-bonding. The results of our steady-state and time-resolved studies in neat and mixed solvents reveal an important and probably unique property of these dyes: their ground-state equilibrium between H-bonded and non H-bonded forms is not changed significantly on excitation to the normal (N*) excited state. In the excited state, new H-bonds do not form but those already existing in the ground state can disrupt on a slow time scale. This last process is probably coupled with the slow excited-state intramolecular proton transfer (ESIPT) reaction of the H-bonded form of the dye. These dyes do not change significantly the distribution between H-bonded and non H-bonded species in their environment and therefore they can provide a measure of the H-bonding potential of their environment. Due to this feature, they can serve as unique sensors of the H-bonding potential in unknown media. This sensing can be provided by the dramatic change of the relative intensities of their two separated emission bands.
Temperature-referenced high-sensitivity point-probe optical fiber chem-sensors based on cladding etched fiber Bragg gratings
Point-probe optical fiber chem-sensors have been implemented using cladding etched fiber Bragg gratings. The sensors possess refractive index sensing capability that can be utilized to measure chemical concentrations. The Bragg wavelength shift reaches 8 nm when the index of surrounding medium changes from 1.33 to 1.44, giving maximum sensitivity more than 10 times higher than that of previously reported devices. More importantly, the dual-grating configuration of the point-probe sensors offers a temperature reference function, permitting accurate measurement of refractive index encoded chemical concentrations.
Refractive index measurement using multimode fibers with long period grating
In this work, we report the influence of ambient refractive index changes on the output power of a multimode fiber with long period grating (LPG) written on it. It is seen experimentally that the cladding mode profiles of such a LPG sensor is very sensitive to the change in refractive index of the surrounding medium. In order to study the influence of ambient refractive index, we have utilized LPG with different periods (100 micrometer, 250 micrometer and 500 micrometer) and multimode fibers with different core diameter (200 micrometer and 400 micrometer). The variation in the output power as a function of different period and fiber dimensions is also investigated. In addition to the many advantages of optical sensors, the unique features such as low insertion loss, low back reflection and easy fabrication of LPG sensors make the present measurement system simple, reliable and accurate for measuring refractive index of the medium surrounding the cladding.
Fiber optic sensor for use in flat dilatometer for geotechnical investigation
Giulio D'Emilia, Giuseppe De Vecchis, Emanuela Natale
The possibility of using fiber optic sensors in geo-technical measurements is investigated with the aim of improving measurement performances of parameters which are of geo-technical interest and which can be indirectly measured starting from geo-technical probe strain data. This work refers to the use of real geo-technical probes and particular attention has been paid to the flat dilatometer, in order to evaluate the effect on measurement performances (resolution, sensitivity, accuracy) of using fiber optic sensors with respect to traditional ones. Design methodology is described in order to detect solutions able to improve not only measurement accuracy, but also resolution and reliability. In particular the effect of sensor position, size and installation has been studied by means of a theoretical and experimental study. Preliminary tests are discussed, which allowed to experimentally verify the system behaviour and which have been carried out on a test rig specifically designed and set-up.
Biological Sensing
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Optical multichannel sensing of skin blood pulsations
Janis Spigulis, Renars Erts, Indulis Kukulis, et al.
Time resolved detection and analysis of the skin back-scattered optical signals (reflection photoplethysmography or PPG) provide information on skin blood volume pulsations and can serve for cardiovascular assessment. The multi-channel PPG concept has been developed and clinically verified in this study. Portable two- and four-channel PPG monitoring devices have been designed for real-time data acquisition and processing. The multi-channel devices were successfully applied for cardiovascular fitness tests and for early detection of arterial occlusions in extremities. The optically measured heartbeat pulse wave propagation made possible to estimate relative arterial resistances for numerous patients and healthy volunteers.