Search

In this paper we describe the propagation of the coherent component of an electromagnetic wave in a colloidal system with large inclusions using an effective-medium approach. We show that the effective medium is nonlocal spatially dispersive and derive expressions for the nonlocal longitudinal and transverse components of the dielectric response, L and T . Numerical calculations of the wave-vector dependence of these response functions are displayed. The dispersion relation for the transverse modes is calculated and compared with the results obtained using well-known approximations for the effective index of refraction. It is also shown that some of these approximations have actually a nonlocal nature, explaining why it is not possible to use them to calculate, for example, the reflection properties of the colloidal system using conventional continuum electrodynamics. We also calculate the effective nonlocal electric permittivity and effective nonlocal magnetic susceptibility and show that this more traditional description is equivalent to the one using L and T .

In this paper, we propose a method to determine refractive index changes and its dispersion of diluted solutions by analyzing the refraction of light by a hollow prism containing the medium to be characterized. The system uses a double prism refractometer to compensate the dispersion of the medium and the output beam is analyzed with a spectrophotometer resulting in a faster measurement with a simple setup. The system was calibrated using solutions of sucrose in water. We present experimental results of the characterization and monitoring of water oxidation as an example of potential applications.

This work shows that in many practical situations it is possible to obtain the dielectric constant of coatings on plain conductive substrates by means of a single electrode-sample capacitance measurement without precise knowledge of its thickness. 3D simulations of spherical electrode-dielectric coating-conductive plain substrate capacitive system are performed in order to determine theoretically the suitable electrode dimension for a coating thickness range of interest.

We calculated the real and imaginary parts of the effective refractive index of blood as functions of wavelength from 400 to 800 nm; we employed van de Hulst's theory, together with the anomalous diffraction approximation, for the calculation. We modelled blood as a mixture of plasma and erythrocytes. Our results indicate that erythrocyte orientation has a strong effect on , making blood an optically anisotropic medium except when the erythrocytes are randomly oriented. In the case in which their symmetry axis is perpendicular to the wave vector, equals the refractive index of plasma at certain wavelengths. Furthermore, the erythrocytes' shape affects their contribution to in an important way, implying that studies on the effective refractive index of blood should avoid approximating them as spheres or spheroids. Finally, the effective refractive index of blood predicted by van de Hulst's theory is different from what would be obtained by averaging the refractive indices of its constituents weighted by volume; such a volume-weighted average is appropriate only for haemolysed blood. We then measured the real part of the refractive index of various blood solutions using two different experimental setups. One of the most important results of our expriment is that is measurable to a good degree of precision even for undiluted blood, although not all measuring apparatuses are appropriate. The experimental data is self-consistent and in reasonable agreement with our theoretical calculations.

We analyze a method recently proposed to retrieve the size, refractive index, and concentration of particles in nonabsorbing nanofluids from measurements of the complex effective refractive index of two dilutions of the nanofluid [Opt. Lett.39, 559 (2014)]. The method uses simple formulas to retrieve the particles' parameters. First, we discuss precautions needed with the new method when inferring the refractive index of the particles from measurements of the imaginary part of the effective refractive index of two dilutions of the original nanofluid. Then we analyze the use of this methodology to obtain some average radius in the size of polydisperse suspensions and in the case of suspensions of weakly absorbing particles. We also perform an error analysis considering fixed errors in measurements and calculating the errors in the retrieved size, refractive index, and concentration of particles. Finally, we characterize experimentally nanofluids of polymeric particles fabricated of poly(methyl-methacrylate) (PMMA) and polystyrene (PS) for which we achieved an uncertainty of 5×10(-3) and 1×10(-2) in the determination of the particle refractive index, respectively, and a precision better than 3% in the determination of their radii.

In photoacoustic imaging, the signal attenuation is a well-known source of artifacts over the image reconstruction. It is recognized that this is caused by optical absorption effects and by the ultrasound broadband scattering. However, the sound dispersion is generally neglected, although it appears notably in thick or heterogeneous tissues. In the present Letter, we give an experimental example in which both attenuation and sound dispersion are dealt with as relevant features to be taken into consideration. An analytic perspective of these perturbations leads us to a waveform transport-model extension that provides a linear description of the induced acoustic effects. We find a near match between the theoretical predictions and the experimental results in the frequency domain. These outcomes approximate projection data that represent forward solutions in photoacoustic image reconstruction.

In this work, we deal only with the case of a uniform dielectric film on top of a flat conductor. Our goal is to demonstrate the possibility to measure the thickness and dielectric constant of the dielectric coating by capacitance measurements in a nondestructive way and to estimate the resolution of this technique.

We propose a simple technique for determining the refractive indices of highly absorbing materials. This method uses two transmittance measurements at oblique incidence. A theoretical analysis of the proposed method is presented. The refractive index of water was experimentally determined with a relative error ranging from 0.12% to 1.3%. We discuss the extension of this method to spectroscopic measurements.

Throughout all this paper we are going to analyze one application of the optical beam deflection method, the procedure for its development, as well as its ideal implementation to reach measurements of displacements that could be the most accurate and of the smaller scale possible, this condition is essential for the magnitude of the results to evaluate. We also give and introduction of the optical beam deflection method, it is characteristics and some of their latest applications as an auxiliary technique on research and commercial fields. This present work will be analyzed the laser beam deflection technique, the procedure to apply, as well as its ideal implementation in order to obtain measures of displacements that can sense to the most exact and of smaller possible scale, obtaining results from microns, micrometers and until nanometers. The importance of this work resides in that the technique although is simple and has easy implementation, the results that can hurtle they are very reliable; thanks to it, the laser beam method of deflection has been not only diffused in many fields of the science and the technology of the optics, but also in those where its application is innovating. This has ended up being a technique of huge utility on interdisciplinary use and has been used to measure physical parameters in a great variety of experiments.

We show the non-local nature (spatial dispersion) of the effective electromagnetic response of a colloidal system. We derive closed expressions and display numerical results for both, the effective non-local electric permittivity and the magnetic susceptibility.

International audience; We present the design of an innovating integrated planar structure adapted for intensity or phase measurements. It is based on the evanescent prism decoupling of the optical signal from a waveguide used as the sensing element. The device is formed by successive thin film sputtering deposition. A TiO2 crystalline layer forms the gas sensing element from which light is coupled out by a planar high refractive index prism. We experimentally validate the structure.

We present a scattering theory model for the coherent reflectance of light from a turbid colloid in an internal reflection configuration. We compare with experimental measurements obtained with turbid suspensions of spherical latex particles and irregularly shaped TiO2 particles. When the colloidal particles are not small compared to the wavelength of radiation, the reflectance curve as a function of the angle of incidence predicted by the scattering theory model, differs appreciably from that predicted by Fresnel’s relations with an effective refractive index. Therefore, when the particles size is comparable or larger than the wavelength, one can not determine the effective refractive index in the usual way using a critical angle refractometer. We provide some insight to why Fresnel’s relations do not work with turbid media.

We carry out a detailed analysis of angle-sensitive devices based on the critical-angle effect. We consider their use in measuring small angular deflections of a laser beam. We establish the diffraction limit to the sensitivity for optical-angle sensors based on reflection and transmission of a laser beam. We find that this limit is identical to that of the triangulation scheme when using a position-sensitive detector or the autocollimation scheme. We analyze the main proposals to date of optical-angle sensors based on the critical-angle effect, focusing on their maximum sensitivity and their polarization dependence in practical conditions. We propose and analyze theoretically a novel and simple angle-sensitive device for sensing optical-beam deflections with very low polarization dependence and a maximum sensitivity close to the diffraction limit when used with typical laser beams. We discuss the basic principles for designing this type of device, provide numerical results, and point out a convenient fabrication procedure.

We present a theoretical study of an erbium-doped optical fiber operating in the superluminescent regime. Experimental results for different pump power levels and fiber length show that the theoretical model could render useful information for predicting parameters such as total output power, spectral bandwidth and optimum fiber length to achieve the superluminescent regime. These types of sources could have direct application in wavelength multiplexed arrangements of fiber sensor, fiber gyroscopes or in general, in any sensors in which a broad wavelength and stable light source is required.

We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the material under study. An optical angle sensor is used to measure the laser deflection providing a simple and compact experimental arrangement. We demonstrate the principle of operation of the sensor and simple procedure that can be used to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reflection and transmission of the light in a random medium are composed by coherent and incoherent waves. The coherent one can be modeled as interacting with a medium with effective optical coefficients. In a random dilute suspension, the coherent wave travels in a medium with an effective index of refraction given by the van de Hulst formula. This effective index is, in general, complex. The imaginary part takes into account the loss of the coherent wave due to scattering. Internal reflection, due to random particles in suspension defines a critical angle determined by the effective index of refraction of the particles in suspension. The curve of reflectivity is smoothed near the critical angle by the imaginary part of the effective index of refraction. One can show that the diffuse component of the reflection tends to zero at the critical angle. In this work, laser reflectometry near the critical angle is used to study particle adsorption on a flat surface. We monitored the adsorption of polystyrene particles with positive and negative charge in suspension. This method allows the direct measuring of reflectivity and its angle derivative on the prism surface where is formed the film.

In this work we present the development of an optical probe which can be used to measure the absolute value of the real and imaginary parts of the refractive index of transparent, opaque or turbid liquids indistinctly. The device can work as a portable, immersion-type, critical-angle refractometer or as a high resolution optical sensor to monitor physical or chemical processes in liquids. The instrument is based on scanning laser reflectometry and measures the reflectance angular-profile around the critical angle. It also measures directly the angle-differential profile of the reflectivity by dynamic reflectometry. For sensing variations of the RI, one can monitor in time either the reflectance or its angular derivative in the vicinity of the critical angle. The uncertainty of the instrument in measuring the real part of the RI can be 10 -6 . The sensing resolution can be 10 -7 when monitoring the differential reflectivity. When the RI is harmonically modulated in time (of RI), it is possible to achieve a resolution as high as 10 -10 . The applicability of the technique to turbid media consisting in suspension of particles is briefly discussed. We also show that the RI of liquid sample can be monitored through a physical or chemical process if the liquid is vigorously stirred. Regarding the instrument design, we use a novel mechanism to control the angle of incidence which allows to keep all components fixed (laser, detector, semi-cylindrical lens, angle modulator, and cables), except for a mirror and a collimating lens. It only requires linear displacements, for which a conventional micrometer is enough. This design is a considerable improvement over the typical laboratory arrangement used by several authors, and permits to have a portable, compact instrument with all the capabilities of the laboratory technique. The design offers a wide measurement range as to cover most water solutions. We believe the device offers an acceptable balance between size and stability. We give results obtained with an experimental prototype of the device. The aim of this work is a general overview of the foundations of the technique, the development of the sensor and some applications.

We study the coherent reflectance of electromagnetic waves from a random system of identical spheres with radius comparable to the wavelength of the incident radiation. An effective-medium theory for this system is developed and it is found that the effective-medium must posses an effective magnetic permeability, even if the spheres are nonmagnetic, in order to be consistent with continuum electrodynamics. The physical origin of this magnetic effect is discussed and we conclude that it is due to the induction of closed currents in the spheres, being then analogous to the mechanism proposed by Ampere when he tried to explain the origin of magnetism. It turns out that the effective magnetic permeability as well as the effective electric permittivity depend on the angle of incidence and the polarization of the incident wave. We derive formulas for the coherent reflectance from a half-space and display numerical results.

We describe a low noise measuring system based on interdigitated electrodes for sensing bioelectrical signals. The system registers differential voltage measurements in order of microvolts. The base noise during measurements was in nanovolts and thus, the sensing signals presented a very good signal to noise ratio. An excitation voltage of 1Vrmswith 10 KHz frequency was applied to an interdigitated capacitive sensor without a material under test and to a mirror device simultaneously. The output signals of both devices was then subtracted in order to obtain an initial reference value near cero volts and reduce parasitic capacitances due to the electronics, wiring and system hardware as well. The response of the measuring system was characterized by monitoring temporal bioelectrical signals in real time of biological materials such as embryo chicken heart cells and bovine suprarenal gland cells.

We investigate experimentally the determination of the effective refractive index (RI) of a turbid particle suspension from the angle dependence of light scattered by the particles and then transmitted into a transparent prism of higher RI. We assembled a versatile experimental device that may be recognized as an Abbe-type refractometer in which the sample is illuminated from the prism side and use it to measure the intensity profile of diffuse light refracted into the prism around the critical angle. By fitting a recently proposed theoretical model we extract the complex RI of turbid suspensions of particles from the measured intensity profiles. We show that the real part of the effective RI is readily obtained with good precision regardless of how the sample is illuminated, whereas obtaining the imaginary part is done with less precision but nevertheless useful measurements can be obtained. The effective RI obtained with this method compares very well with the so-called van de Hulst effective RI and the one derived from Keller's model of the effective propagation constant.

We investigate theoretically and experimentally the performance of low-noise capacitive sensors based on polyvinylidene fluoride (PVDF) piezoelectric films to sense water-borne ultrasound signals for their use in photoacoustic tomography. We derive a mechanical-to-electrical transfer function of a piezoelectric capacitor sensor of infinite lateral dimensions and arbitrary thickness assuming that an ultrasound wave is normally incident. Then, we analyse the response for obliquely incident ultrasound waves on sensors of large but finite area and derive an expression for the angle dependence of the sensor's response. We also present experimental different measurements with home-made sensors and compare with our theoretical model. We present measurements of the sensors' response to harmonic signals of variable frequency in the range from 0.5 to 50 MHz and of the angular-dependence factor at 6 MHz. Additionally, because of the scope of interest in these kinds of sensors, we also tested the sensors' response for photoacoustic perturbations. These are generated by laser pulses from directly impinging on the sensor and from ultrasound perturbations produced on neoprene by the same kind of laser pulses and then travelling through water to the sensor.

We discuss the use of photo-reflectance near the critical angle (PRCA) to monitor small changes of the RI of highly turbid liquids. The theory of the reflectance of a laser beam near the critical angle for an external medium with a complex RI is summarized. The applicability of PRCA to sense highly turbid media is demonstrated experimentally on bovine milk samples. We give experimental results showing the temporal variation of the refractive index (RI) during three different processes in bovine milk: (1) Mechanical stirring, (2) temperature changes, and (3) pH variations around the isoelectric point of the casein micelles (micelle aggregation). RI changes in the order of a few times 1 X 10-3 are observed during the experiments. The experimental results show that the RI of milk can be used to track physico-chemical changes in time allowing one to measure the time constant of the different process. The design of a compact RI probe for in situ applications is discussed. The miniaturization of such a probe will probably limited by factors other than the loss of sensitivity. A novel angle-of-incidence control which requires only linear displacements of some of the optical components (no rotation) is proposed and shown to be feasible. Such an optical probe may be used in the dairy industry and in general in the food industry or food science research laboratories. It could give additional analytical power to the food scientist, engineer, or technician.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Etude de la transition interfaciale liquide-liquide dans le systeme eau-ethanol-benzene-sulfate d'ammonium. Determination de la dimension des gouttelettes et des angles de contact

In this paper we analyze the effect of the laser beam divergence on the sensitivity of optical sensors based on surface plasmon resonance (SPR) using the Kretschmann configuration. The analysis is done by assuming that a Gaussian beam is employed. Numerical results are presented that show quantitatively the influence of the laser beam's waist on the SPR curve main characteristics. An example using the exact Fresnel coefficient, with optimal parameters reported in the literature is fully analyzed. Our results may be important in the design of SPR optical sensors using fiber or integrated optics.

We discuss an optical reflection technique to sense very small variations of the refractive index that can be applied to absorbing and non-homogeneous media. The technique offers the possibility of being integrated, using MOEMS technology into a compact optical probe for a variety of applications, and may be the core for a new class of generic sensors. It consists of AC-modulating the angle of incidence near the critical angle and measuring the reflectivity variations. This technique may be a useful alternative to design a refractive index probe for absorbing and inhomogeneous media were other techniques are strongly limited. The theory necessary to use, develop, and design appropriately these kind of sensors is summarized, and experimental results validating the theory are given. A possible design of a fiber-optic probe based on the modulation of the index of refraction of a micro-prism through the elasto-optic effect is given.

In this work the Guided Beam Deflection Method is introduced as a potential tool to design a variety of low-cost IO sensors. A theoretical analysis of the propagation and deflection of confined Gaussian beams in slab waveguides is given. The proposed method is compared to interferometric techniques in terms of sensitivity. It is found that both techniques have sensitivities of the same order of magnitude, however, IO beam deflection sensors may be less expensive than interferometric ones.

Augusto GarcIa-Valenzuela, J. M. Saniger, and C. GarcIa-SegundoCentro de Instrumentos, UniversidadNacional Autonoma de Mexico, Cd. Universitaria A.P. 70-186,Mexico D.F. 04510, Mexico.ABSTRACTWe investigate theoretically the limit to the resolution imposed by the fundamental optical noises in film-based chemicalsensors interrogated by optical reflectometry. We suggest a dynamic reflectometry approach as a possible technique toachieve the ultimate resolution. We fmd that a theoretical resolution around 1010

We derive an optical model for the light intensity distribution around the critical angle in a standard Abbe refractometer when used on absorbing homogenous fluids. The model is developed using rigorous electromagnetic optics. The obtained formula is very simple and can be used suitably in the analysis and design of optical sensors relying on Abbe type refractometry.

We investigate the spectral response to ultrasound waves in water of low-noise capacitive sensors based on PVDF polymer piezoelectric films. First, we analyze theoretically the mechanical-to-electrical transduction as a function of the frequency of ultrasonic signals and derive an analytic expression of the sensor's transfer function. Then we present experimental results of the frequency response of a home-made PDVF in water to test signals from 1 to 20 MHz induced by a commercial hydrophone powered by a signal generator and compare with our theoretical model.

In this work, the effect of film thickness on the photoluminescence (PL) spectra of Si quantum dots embedded in silicon nitride films is investigated experimentally and theoretically. The films were deposited by remote plasma enhanced chemical vapor deposition using the same SiH2Cl2/H2/Ar/NH3 mixture and deposition conditions, in order to obtain films with similar composition and approximately equal average size (∼3.1 nm) of Si quantum dots. Only the deposition times were varied to prepare five samples with different thicknesses ranging from ∼30 nm to 4500 nm. Chemical characterization by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy were carried out in order to check that the composition in all films was the same. The structure, average size, and size distribution of the Si quantum dots were deduced from High-Resolution Transmission Electron Microscopy. The thickness of the films was determined by ellipsometry and interferometry of UV-Vis transmission spectra. It was found experimentally that the increase of the thickness above a few hundreds of nanometers produces significant distortions of the PL spectra of the films, such as peak shifts and the appearance of shoulders and multiple peaks suggesting interference effects. Comparing the experimental results with theoretical simulations, it is shown that these distortions are mainly due to interference effects and not to intrinsic changes in the films. The approximation used to simulate the PL spectra as a function of film thickness allows improving the fitting between simulated and experimental spectra by changing some optical parameters and can be helpful to further investigate the intrinsic optical properties of the films.

We study theoretically the extinction of collimated light in random systems of highly scattering particles embedded in nonabsorbing media. We aim to provide rough guidelines on the behavior of the extinction coefficient in the so-called dependent-scattering regime. We base our analysis on Keller's second order perturbative approximation to the effective propagation constant. To gain physical insight, we also analyze a simple model based on the physical notion that particles in a dense system scatter light in an effective medium.

We derive a simple model for the angular-intensity profiles of diffuse light transmitted from a turbid colloid into a transparent medium of higher refractive index (RI) near the critical angle. Adjusting this model to experimental profiles obtained with an Abbe-type refractometer offers a sensitive and robust way of measuring the complex effective RI of highly scattering media.

We study the possibility of improving the theoretical limit to the resolution of the optical beam deflection method (OBDM) by reflecting the beam from a curved surface. We suggest a new detection scheme by measuring the average intensity over a cross section of the beam after it is reflected from a cylindrical mirror. We show that there is a possibility of decreasing the theoretical minimum detectable angle (MDA) as compared to the usual OBDM when the beam grazes the cylindrical mirror.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Given a sensing task, in general there are a variety of methods that can be used to accomplish it. These methods may incorporate charge sensing, current/voltage dc/ac measurements, magnetization, or optical measurements to achieve the desired sensing task. In addition to these schemes or sensing means, one should also decide on the structure of the sensor. The structure of the sensor, will clearly depend on the identity of the parameter that one wishes to sense (this is usually called measurand) and also, it will depend on the sensing mean. Thus, we separate the sensing shell, which is the structure of the sensor, from the sensing mean which is the physical scheme that is used to read the sensor shell. Clearly, sensor shell and sensing means are interdependent. Using this division of sensors to different parts, we are able to compare merits of different sensing means and sensor shells to each other.

Using a multiple-scattering formalism, we derive closed-form expressions for the coherent reflection and transmission coefficients of monochromatic electromagnetic plane waves incident upon a two-dimensional array of randomly located spherical particles. The calculation is performed within the quasi-crystalline approximation, and the statistical correlation among the particles is assumed to be given simply by a correlation hole. In the resulting model, the size of the spheres and the angle of incidence are both unrestricted. The final formulas are relatively simple, making the model suitable for a straightforward interpretation of optical-sensing measurements.

Immense computational power of today's processors cannot be fully utilized unless appropriate sensors and actuators are developed to link them with the outside world. A method is presented here to compare different sensors with each other and to evaluate their relative merits. Sensors are decomposed into two essential building blocks: a sensor shell and a sensing mean. Eleven different types of sensors, having the same sensing shells, are analyzed and compared to each other.

We present a comprehensive derivation of the so-called diffuse to near-normal-viewing reflectance factor of an architectural paint coating and its measurement with an integrating sphere. We focus our attention to the surface correction terms and consider the case when the surface is rough. We point out limits of the standard formula with the so-called Saunderson corrections commonly used for paint coatings. We provide and discuss a corrected definition of the roughness-dependent "gloss factor" needed to describe specular-component excluded measurements. We show that as the roughness of the surface increases, the specular-excluded reflectance-factor increases, approaching its value with the specular-component included.

The propagation of diffuse light in turbid media is usually modeled with radiative transfer theory. When diffuse light travelling in a turbid colloid is reflected and transmitted at a flat interface where there is a refractive index mismatch, it is not clear whether one should assume the incident diffuse-light is travelling in a medium with a refractive index equal to that of the background medium (usually referred to as the matrix) or if one should assume it travels in an effective medium. Most authors simply avoid this issue and most often use the refractive index of the matrix. While this might be a good approximation for dilute turbid media one may suspect that for highly scattering materials it may not be the case. In this work we investigate experimentally this issue. Our experimental results provide clear evidence that diffuse light inside the turbid colloid travels in an effective medium and not in the matrix.

In this work we assess experimentally a new methodology for sizing non-absorbing colloidal particles in situ. It requires measuring the real and imaginary part of the effective refractive index per unit volume fraction occupied by the particles. The mean size and refractive e index of the particles are determined from a suitable model for the effective refractive index of dilute colloids. We present results of experiments made with polystyrene and silica nano-particles and compare them with dynamic light scattering and electron microscopy measurements.

We revise basic concepts behind the surface correction terms to the diffuse reflectance of a paint coating and its measurement with an integrating sphere. We question the validity of using the Fresnel relationships to calculate the surface reflectance terms in the case of paint films. Results of measurements on a white paint covered with an index-matched transparent slab are presented. From these results we infer the internal diffuse reflectance of the surface and obtain noticeable discrepancies from the prediction of Fresnel relationships.

Garcia-Valenzuela, and M. Tabib-AzarDepartment of Electrical Engineering and Applied PhysicsCase Western Reserve UniversityCleveland, Ohio, 44106.1. ABSTRACTA multimode symmetric Y-junction waveguide is investigated and the optical power transmission andconversion efficiency between the lower and higher modes was calculated. Overlap integrals of thefields of the incident and transmitted guided-wave modes at the Y-junction were used and it is shownthat there is a possibility of transmitting up to 29 percent of the incident optical power into the outputbranching waveguides at very large branching angles. Results show that an appropriate branchingangle of the Y-junction can be used to selectively transmit the waveguide modes into the outputbranches and this can be used advantageously in integrated optic devices. A very simple model usingray optics is developed to explain the results on physical basis. With this simple model we developeda simple framework to interpret the results of the overlap integrals.

We propose an array of electrostatically driven torsional mirrors for optical signal processing. This 10-element device is 1-dimensional with pixels of 50 micrometers X 250 micrometers . The device is basically a hybrid integrated optical device which is fabricated in silicon and can be integrated with photodetectors and processing electronics to create elements of the so-called 'smart pixel' class of spatial light modulators. This class of devices will find application in many areas of optical processing including optical interconnects, optical switching, optical image analysis and optical neural networks. We discuss the design and fabrication of mirror arrays and electrode strips that are used to actuate them. The resonant frequency and deflection angle v.s. applied voltage of the fabricated devices are measured and compared with theoretical predictions.

This paper describes the usage of neural networks in the application of speckle patterns, as seen at the output of an optical waveguide, for sensing displacement/force. The neural network trained for displacement values within a 1.5 micrometers range is found to generalize with less than +/- 0.02 micrometers error in the input range. It is found that a functional-link net with 11 functional links and 3 neurons can be trained for a convergence criterion of 1e-05 in less than 3000 iterations. The error in the individual targeted output during training was less than +/- 0.01 micrometers . Thus an integrated-optics sensor is now feasible.

The modulation of the deflection of a 2D guided optical beam in a planar waveguide is analyzed for sensing applications. The deflection is caused by a gradual change in the depth of the planar waveguide transversal to the direction of propagation. The beam deflection angle could be used for sensing the refractive index of the external medium among other variables. We present numerical results to evaluate the possibility of developing a glass-integrated structure for refractive index sensing.

We analyze the determination of the dielectric constant of macroscopic solid samples in a nondestructive way from measurements of the capacitance between a pointer electrode and the sample's surface. We assembled an experimental device and found that an accuracy of 1% or better can be attained with common laboratory instrumentation.

The transmission of an optical beam through the compound cell of a differential refractometer with an absorbing sample is analyzed. Formulas for the lateral shift and the deflection angle of the transmitted optical beam for a complex refractive-index difference are obtained.

In this paper we study a passive optical ranging method based on several photometric measurements from the light radiated by an object and derive the range from these measurements. We discuss different techniques to obtain the profile of the interrogated object. The first technique uses two photometric measurements, while the other two use three photometric measurements. We evaluate these techniques in terms of noise and sensitivity. Preliminary experimental results indicating the feasibility of the method using CCD cameras and dual photo-detector set-ups are shown.

We propose a simple technique to determine the distance to an object from two passive photometric measurements. The technique offers the possibility of developing fast and inexpensive passive optical range sensors for different applications.

This article describes a simple and fast angle-scanning reflectometer. Approximate formulas for the design and implementation of this type of reflectometer are provided. An experimental device was assembled and its performance was evaluated. The instrument scans the angle of incidence of a laser beam in a range of 5°–10° in less than 0.2ms. The reflectance equivalent noise of our experimental device was about 0.005. The instrument is suitable to measure the coherent reflectance versus the angle of incidence from light diffusing samples.

We describe a fast and accurate method for the measurement of refractive index spectra of absorbing layers from transmittance spectra at two angles of incidence. The method is less sensitive to surface conditions than other photometric techniques.