A reflective intensity-modulation-based fiber optic position sensor is studied. The sensor consists of input and output channels attached with graded-index (GRIN) lenses. The input channel launches a collimated probe beam onto a sample, and then the output channel collects the light reflected and scattered from the sample. Light power from the output channel directly depends on the distance between the sensor head and the sample (the proximity), which defines a modulation function to characterize the sensor. For practical purposes, effects of sample reflectivity on sensor response are discussed for the cases of specularly reflective and Lambertian diffusive samples. Effects of sample rotations are also studied.

A method of parallel image transmission through a single optical fiber based on 2-D spectral multiplexing is presented. The method is realized with the multistripe holographic diffraction gratings. Each stripe in the gratings has its own ruling period and height. An experimental setup for the parallel image transmission is described and the transmitted images are represented.

This paper describes a general-purpose photoelastic fiber optic accelerometer having a sensitivity of 2 V/g and a resolution of 2.5 mg over a frequency range extending from 0 to 600 Hz. The unit has a linear amplitude range of 0 to 5g and is sealed in an aluminum case having outside dimensions of 41 mm335 mm320 mm. It relies on a force transducer made from an optically birefringent material and measurements are made based on the principles of photoelasticity. A low-cost LED is employed as an incoherent light source; multimode optical fibers with a hard plastic cladding are used to transmit signals between the transducer and the conditioning electronics.

The response of interferometric fiber optic gyroscope (IFOG) sensing coils to a time-varying, axial thermal gradient (ATG) is investigated. Sensing coils wound with Panda polarization-maintaining fibers in straight and quadrupolar wind configurations developed in our earlier study examining the effect of time-varying, radial thermal gradients (RTG) are used with similar arrangement and experimental setup. Induced gyroscope bias drift, measured as a function of temperature and time, is presented and correlated for both winding configurations using our earlier model. Our results show that the quadrupolar wind is more susceptible to an ATG than a RTG. Moreover, although an ATG is exclusively introduced, a small residual RTG is still present and has a relatively large effect on the straight wind coil.

We investigate the possibility of using a Fourier optic method for on-line determination of the quality of paper. A spatial light modulator is used for the incoherent to coherent image conversion that is necessary since most paper types are opaque. Three different properties are studied, namely crepe frequency, periodicity and amplitude of wire marks and surface structure anisotropy, all of them important factors for controlling the production process. The experiments show that it is indeed possible to achieve good results in measurements down to an exposure time of about 1/1000 s.

Cylindrical holography is being developed in order to capture 180-deg fields of view of ballistic events. The ultimate goal is to capture a three-dimensional reconstruction of the fragments fields, within a computer, that exist behind an armor plate that has been penetrated by a projectile. In this paper, we detail the methodology, design, and experimental results for a cylindrical hologram system used as the first stage of a data capture system. An 18-ns-pulse-width, 3-J ruby laser is used as the illumination source for these 45.7-cm-diam holograms. Descriptions of the optical layouts for recording and reconstructing these holograms are presented. For ballistic applications, the primary challenge has been the mitigation of the large flash caused by the projectile-target interaction. Temporal and spectral data from the flash are presented, followed by several possible flash reduction techniques, including narrowband and neutral-density filtering. Experimental holographic results for this ongoing effort are presented.

The accuracy of 3-D measurement using a single image of a four-point coplanar target of known size is studied. The factors that influence accuracy are analyzed and experimental techniques are used to establish their individual effect on accuracy. Experiments show that the four-point coplanar target has two solutions for real images and that mixing these causes large errors. It is concluded that when the target is approximately parallel to the image plane, the accuracy is significantly better compared to other target orientations, and that image distance is a critical factor affecting accuracy in the depth, while the effect of the other factors on accuracy is relatively insignificant. A new calibration technique is introduced that determines an average image distance over the image plane within the depth of focus and improves accuracy at close range.

Particles leaving spacecraft surfaces will interfere with the remote observation of emissions from objects in space, the earth, and its upper atmosphere. The goal of our analysis is to create a methodology that will permit the particle environment surrounding spacecraft to be quantitatively assessed, the particle composition to be determined from its spectral distribution, and the orbital particle source to be estimated from the particle composition and trajectory analysis. We report on the analytical tools we developed to permit this goal to be achieved: (1) predictions of radiant intensities over the UV-IR as a function of size and composition, (2) predictions of the image produced by near-field out-offocus particles for staring and scanning sensor systems, and (3) automated image processing tools for particle trajectory analyses and image enhancement. We present a review of the sources, sizes, and composition of particles observed in local spacecraft environments. Predictions of the optical radiance signatures generated by likely contaminant species are made for several compositions and sizes as modeled and observed on previous space observations. Predictions of the spectrally structured radiances for silver, aluminum, alumina, carbon, solid carbon dioxide, water ice, silicon dioxide, and titanium dioxide are presented. The predictions were exercised in the analysis of the orbital particle environment surrounding the shuttle using observations from the sensitive CIRRIS1A IR radiometer/interferometer. The range and size of discrete particles were extracted from the temporally varying spectral radiances on detector arrays. The difficulty of locating particle events within large databases motivated the development of automated particle identification algorithms. Previous space missions have observed particles in selected wavelength regions. The Midcourse Space Experiment (MSX) (successfully launched in Spring 1996) will provide simultaneous spectral coverage from 0.1 to 26 ? m that will permit particle composition to be extracted through analysis. We also present illustrations of how the automated extraction and enhancement algorithms will facilitate the analysis of the large MSX optical data bases. Particle detection thresholds and effects on sensitive UV-IR instruments are presented. The goal of this effort is to assess the effectiveness of the practices and procedures instituted by the MSX satellite, to enable contamination source identification and to guide remedies for future space missions. These predicted radiances and effects will enable future system designers to assess the potential impact of particles on their mission’s performance.

The recognition of surface shapes using structured light is an important component of many industrial vision systems. The iterative correction algorithm (ICA) for the recognition of cylindrical objects is based upon a predictor-corrector approach which utilizes an initial estimate for the surface parameters, followed by iterative parameter refinement. A predicted passive image is generated using the current surface parameter estimates and significant features are extracted and compared with those in the true passive image. The estimated surface parameters are corrected based upon feature disparities. In this paper, the ICA is enhanced with a new method for computing passive-image point coordinates and tested. Future research directions are indicated.

Automated visual inspection tasks are frequently concerned with the examination of homogeneously textured surfaces such as fabrics, wallpapers, machined surfaces, and floorcoverings. Often, the images taken from such surfaces are degraded by an intensity inhomogeneity due to the image acquisition process. This inhomogeneity is considered to be an irrelevant and disturbing signal component, which should be suppressed to enhance the desired texture component and to ease a subsequent texture analysis. We show that, especially for textured surfaces, it is not always reasonable to assume a pure multiplicative composition of the texture signal and a disturbing inhomogeneity. We introduce a notion of homogeneity of n’th degree based on first-order statistics and present image processing methods for the homogenization of first, second, and infinite degree. For the homogenization of second degree, we propose a computationally efficient frequency domain signal processing method with high homogenization performance and low nonlinear distortion. Furthermore, we suggest a high-performance homogenization of the infinite-degree technique that equates the local histograms to a global histogram, which is adapted to the given image data. We compare the proposed homogenization methods visually and quantitatively with the well-known homomorphic filtering technique, which assumes a pure multiplicative inhomogeneity. We demonstrate that our methods achieve much better results for synthetic as well as for realistic images of textured surfaces.

Carry-free addition and borrow-free subtraction on the redundant modified signed-digit number are adopted for lensless polarizationencoded optical shadow casting (POSC). First, a new recoding truth table, which has a symmetrical complemented relationship between the input minterms (entries that produce an output of 1 or 21) and their corresponding output bits, is developed for the redundant signed-digit numbers. Then, the carry-free POSC adder/subtracter is designed by determining the encoding of the redundant input bits for generating the sum/difference output bits and the source light-emitting-diode pattern. Two design methods are presented: direct implementation and truthtable partitioning. It is shown that the number of pixel subcells in the input encoding of the POSC system can be significantly reduced using the new symmetrical recoding algorithm for the modified signed-digit number representation.

For small unresolved or partially resolved objects, the prediction of the performance of an infrared (IR) sensor system depends not only on the optics and the atmosphere, but also on the geometry of the sensing elements within the detector. The apparent scintillation caused by subpixel displacements of the detector from the optimum position is investigated. The effect is linked to the system point spread function (PSF) as well as the shape and size of the object. The effect of the shape and size of the sensing element, the optics, and the viewed object are simulated. The simulation also evaluates the effect that vibrations or pointing accuracy have on the performance of the sensor system for different types of targets. Results are presented that show that the variation in contrast of objects due to the shape and size of the active portion of a detector and the position of the target projection on the detector can be significant, and should be taken into account when estimating system performance. Although these effects are most significant in wide field of view surveillance systems, narrow field of view systems are also described and evaluated.

We describe a novel integrated optic comb filter consisting of two single-mode guides placed symmetrically about a central multimode guide. Phase-matched coupling to the various modes of the multimode guide occurs at a series of wavelengths to give both a channel-drop and a channel-pass response. We used and extended coupled-mode theory to analyze and predict the filter performance in terms of its design parameters. The theoretical results presented should prove useful in the practical fabrication of the device and demonstrate the trade-offs required between the filter parameters of linewidth, extinction ratio and sidelobe levels.

Three-section distributed Bragg reflector (DBR) lasers emitting in the 1.5-?m wavelength region are characterized for use as a light source in a spectrometer for gas analysis. The three-section DBR lasers facilitate a wide, continuous tuning range while preserving the output power at a constant level. Typical characteristics for three-section DBR lasers and potentials and limitations of these lasers in gas-monitoring applications are discussed. A fiber optic system for high-sensitivity gas detection using wavelength-tunable DBR lasers is also presented.

We study the effect of the pumping beam focus position on the output of an end-pumping diode laser-pumped solid state laser by calculating the changes in the overlap of the intensity distribution functions of the pump and the oscillating beams. It is shown that the output power is strongly pump position dependent, and the optimized pumping position is a function of the pump beam and the oscillation mode spot sizes. Our experimental results agree well with our theoretical predictions.

A lidar-transmissometer intercomparison was made during an international experiment held in the German Alps to characterize the vertical structure of aerosols and clouds. The transmission path was 2325-m long and inclined at 30 deg along the slope of a steep mountain ridge. The transmissometer consisted of a Nd:YAG and a CO2 laser located in the valley and a large-mirror receiver that captured the full beams on the mountain top. Two lidars, one at 1.06 ?m and one at 1.054 ?m, were operated with their axes approximately parallel to the transmissometer axis but separated by a horizontal distance of the order of 20 to 40 m. The first lidar was operated in retroreflector mode and the relative transmittance was determined from the reflection off the mountain ridge above the cloud layer. The second lidar had a special receiver designed to make simultaneous recordings at four fields of view. The range-resolved scattering coefficient and effective cloud droplet radius are calculated from these four-field-of-view measurements by solving a simplified model (Bissonnette and Hutt, 1995) of the multiply scattered returns. The two simultaneous solutions for the scattering coefficient and effective droplet size make possible extrapolation at wavelengths other than the lidar wavelength of 1.054 ?m. The main measurement event analyzed lasted 1.5 h and produced transmittances ranging from less than 5% to more than 90%. The comparisons show good correlation between the transmissometer data and all lidar solutions including extrapolation at 10.59 ?m. The experiment also indicates the possibility of doing active imaging through optically thick clouds and demonstrates that lidars can measure turbulence structures in the atmosphere.

A high-resolution incoherent-detection Doppler lidar has been constructed at the University of Michigan Space Physics Research Laboratory. The lidar uses multiple Fabry-Pe´ rot interferometers to measure the Doppler shift of aerosol-backscattered light and to attenuate background light. In this way, vertical profiles of the horizontal wind field are obtained with high spatial and temporal resolution. It has been found that if the transmission functions of the etalons are not properly aligned, a systematic error in the Doppler-shift determination can result. This error is dependent on the relative aerosol loading of the atmosphere and can be quite large. For large etalon offsets the wind error can be in excess of 10 m/s. Even for small offsets and high aerosol loadings, the wind determination can be biased by as much as 1 m/s. A previously developed model and inversion process can be modified to allow for an offset between the etalons and recover data without bias.

A Na mesospheric density lidar or ‘‘guide star’’ illuminator can be tuned by visually observing the pattern of laser-induced fluorescence inside a Na illumination lamp soon after it has been turned off. Optimum tuning occurs when the fluorescence is trapped inside the lamp and appears to fill the bulb as a whole.

For some applications, it has been assumed that scattering from an object placed near a highly reflecting substrate such as aluminum can be approximated by the scattering from that object placed near a perfectly conducting substrate. We examine this approximation by comparing the calculated scattering from dielectric spheres resting on plane substrates that are perfectly conducting and composed of aluminum. Examination of the Mueller polarization matrix elements shows appreciable differences between these two scattering systems. The differences, however, become small at scattering angles where the intensities are relatively large.

Advances in optical coating and materials technology have made possible the development of instruments with substantially improved efficiency in the extreme ultraviolet (EUV). For example, the development of chemical vapor deposited (CVD) SiC mirrors provides an opportunity to extend the range of normal-incidence instruments down to 60 nm. CVD SiC is a highly polishable material yielding low-scattering surfaces. High UV reflectivity and desirable mechanical and thermal properties make CVD SiC an attractive mirror and/or coating material for EUV applications. The EUV performance of SiC mirrors, as well as some strengths and problem areas, is discussed.

A new experimental technique is proposed to determine refractive indices of liquids and isotropic solids at different wavelengths. A Pellin-Broca hollow prism filled with a liquid sample produces the spectrum (of the liquid prism) on the photographic plate of the camera. A plane reflector, mounted at a small angle to the normal of the exit face of the prism, also forms a direct image of the collimator slit in the plane of the same photographic plate. All the necessary information for determining the refractive indices (for different wavelengths) is extracted directly from the spectrogram without using any goniometric system. Experiments are conducted with the liquid prisms of isopropyl alcohol, water, and benzene. The results of the experiments are compared with those obtained by a Pulfrich refractometer (critical angle method). The proposed new technique gives the refractive indices for visible and invisible spectral lines to an accuracy of20×10-5.

A guest/host material system in which the guest molecule is a functionalized, optically nonlinear, chromophore is described. A verification of the crosslinking process, an assessment of the nonlinear properties of the chromophore, using Solvatochromic methods, and an investigation of the electric field induced molecular orientation using secondharmonic generation are included.

Free-space optical communication between satellites networked together can make possible high-speed communication between different places on earth. The use of optical radiation as a carrier between the satellites creates very narrow beam divergence angles. Due to the narrow-beam divergence angle and the large distance between the satellites, the pointing from one satellite to another is complicated. The complication is due to vibration of the pointing system caused by two stochastic fundamental mechanisms: (1) tracking noise created by the electro-optic tracker and (2) vibrations created by internal satellite mechanical mechanisms. We derive mathematical models of signal, noise, approximate SNR, and approximate bit error rates of optical communication satellite networks as functions of the system parameters, the number of satellites, and the vibration amplitude. The optical intersatellite network model considered includes transmitter satellite, repeater satellites, and receiver satellite all networked together. These models are the basis for pointing system design of appropriate complexity and performance to make the network as simple and inexpensive as possible. An example of practical communication between Anchorage in Alaska to Johannesburg in South Africa by a free-space optical communication network composed of nine low-earth-orbit satellites is given. From the analysis it is clear that even low vibration amplitude of the satellite pointing systems decreases dramatically the network performance.

The use in mirror system design of double-curvature surfaces such as sections of toroids or ellipsoids is discussed. Four design examples are presented that illustrate how double-curvature surfaces could be used to advantage in mirror system design.

First we show that a binary amplitude grating, altered by a suitable discrete phase modulation is transformed, by Fresnel diffraction, into another binary grating with reduced opening ratio. We employ this process as the basis for discussing segmented versions of Talbot array illuminators that can be displayed with liquid crystal displays.

A simple technique is devised to measure the angles of 90-, 45-, 45-deg and 60-, 30-, 90-deg prisms without using expensive spectrometers, autocollimators, and angle gauges. The method can be extended to unpolished and opaque prisms made of materials other than glass.

A stepped magnification stereo microscope and a stereo zoom microscope are designed and fabricated using a modular concept. A resolution of 4 ?m is achieved with both instruments. The design details are discussed.

The application of analog/digital converters and inverse techniques for optical receiving by photon detectors, when their output single pulses are strongly overlapped, is described. It is shown that the counting of overlapped pulses can be realized by a set of linear transformations—conversion of single pulses into decayed oscillations, digitizing, averaging, Fourier deconvolution, normalizing, and digital filtering. This method does not use discriminators, being insensitive to the pulse shape. The theoretical analysis is supported by computer simulations and experimental data. It is shown that photon statistics can be saved into the retrieved optical profiles at mean counting rates exceeding 1 GHz. The retrieving error is not higher than Poisson fluctuations. This method is effective simultaneously in the both typical regimes of photon detectors—photon counting and overlapping. It can be applied in lidar remote sensing, time-resolved spectroscopy, etc.

The extinction ratio (ER) and the throughput or reflectance for the unextinguished s polarization (Rs ) are calculated for infrared reflection polarizers that consist of a low-index transparent layer embedded in a high-index transparent substrate. The dependence of ER and Rs on the depth and width of the buried layer is illustrated by iso-ER and iso-Rs contours for a specific SiO2-in-Si IR reflection polarizer that operates at 3.5-?m wavelength and 80-deg angle of incidence. The two cases of a uniform layer with sharp boundaries and a diffuse Gaussian layer are considered. The diffuse-layer model employs Bruggeman’s effectivemedium theory and is intended to simulate devices that are fabricated by the oxygen-ion implantation of Si. The effect of an outermost oxide film and the angular and wavelength sensitivities of these polarizers are determined.

We discuss three different optical techniques that can be employed for synthesizing wavefields with a periodic variation of linear polarization states. An experimental support of our proposal is included.

A new optical noncontact sensor is proposed for measuring profiles of an object with 3-D free-form surfaces. The sensor consists of both low-resolution and high-resolution optical systems. Two linearly polarized laser beams from the sensor are focused on the object surface to be measured. Some of the depolarized components of light scattered from the object surface, i.e., the polarized components orthogonal to those of the incident beams, are detected to exclude specularly reflected light. The triangulation method is applied to the low-resolution optical system, which can be used to detect a wide range of height. The astigmatic focus error method is applied to the high-resolution optical system to detect the focused positioning signal of the object surface more precisely than with the low-resolution system. Using a measuring instrument fabricated with the new optical noncontact sensor, 3-D profiles of diffuse reflection surfaces and metal surfaces on which both specular reflection and diffuse reflection occur can be measured. Adverse effects of surface roughness, scratches, and diffraction on measurements can be reduced.

Platinum silicide (PtSi) staring array detectors have recently been developed and applied in a number of applications to perform medium wave infrared (MWIR) observations and radiometry. PtSi detectors have a strongly wavelength dependent response function, which results in a requirement to have much more a priori knowledge of an object to perform radiometric calculations than is required of a flat response detector. The impact of this wavelength dependence is examined and radiometric calibration procedures are developed for both resolved and unresolved targets.

We have investigated the effect of resist thickness, linewidth, and pitch on UV reflectance spectra. This technique exploits the property that conventional novolak resists are very absorptive from 200 to 300 nm, while substrates are significantly more reflective. For line-space developed resist features of constant pitch, we observe that the reflectance in this wavelength range varies periodically with ? and increases linearly with decreasing linesize. The dominant factor in wavelength dependence is the constructive/destructive interference of the measurement light from the air-resist and air-substrate interfaces. The linesize dependence at constant pitch and resist thickness is predominantly controlled (within proper boundary-condition regimes) by the percentage of the substrate exposed. The gross periodicity of the deep UV (DUV) reflection spectra for patterned films is correlated with resist thickness in a manner similar to the resist-thickness dependence of UV reflection spectra for unpatterned films. Simulation of DUV reflectance from patterned films showed semiquantitative agreement with experimental results.

Photothermal techniques are widely used in thin film characterizations and are particularly useful in studying laser-induced damage in optical coatings. The specific applications include measuring weak absorption, characterizing thermal conductivity, detecting local defects, and monitoring laser-interaction dynamics and determining laser damage thresholds as well as thermal impedance at boundaries of multilayers. We take an overview of the principle of photothermal techniques, the various detection methods, and the progress made during the last decade in applying these techniques to optical thin films. The further potential and limitations of the techniques will also be discussed, with emphasis on in situ studies of laser interaction with thin films and local defects.

A surface plasmon resonance based wavelength selector is described. An attenuated total-reflection device can be configured so that the reflected intensity of light is a maximum when the resonance condition is achieved. When the device is illuminated with polychromatic light at a fixed angle, the wavelength at which resonance is achieved shows a transmission maximum. By using an appropriate electro-optic material in the device, the wavelength of maximum transmission can be varied. Numerical results are presented.

A technique employed in the development of antivignetting filters to be incorporated in wide-angle or telephoto-lens optical systems is described. An obvious attraction of this approach is that it requires no knowledge of the optical prescription, only data determined from certain measurements performed on the lens in question. These measurements include such parameters as entrance pupil location, type of vignetting, and intensity distribution across the image plane. To illustrate its effectiveness the technique is applied to an 85-deg-field-of-view camera objective and results are discussed.

The solid angle aperture of highly multimode rectangular step-index waveguides is calculated with mode theory and geometrical optics. There is a difference between the results of the two different approaches, the geometrical optics aperture is larger and includes the aperture obtained from mode theory. A possible cause for this discrepancy is discussed.

We investigate a class of Gabor-type matrices and develop simplified Gabor-type matrix operations. The usual matrix-multiplication in the class is proved to be easily performed with O(ab log b)?O(N log N) complexity. Consequently, we are able to propose fast algorithms for determining the inverse of Gabor frame operators and the square roots of the Gabor frame operators as well as the dual Gabor and tight Gabor wavelets. A necessary and sufficient condition is derived for a Gabor triple (g,a,b) to generate a Gabor frame. It is very easy to predetermine the quality of a given (g,a,b) and the stability of Gabor synthesis.

In this paper, some comments are made about fabrication parameters to reduce undesirable thermal drift in the optical output of z cut Ti:LiNbO3 (LN) modulators. In this regard, covering the LN surface with a semiconducting Si layer was reported to effectively shield the waveguides from pyroelectrically induced charges and to successfully suppress the drift1.