It has now become a pattern, if not yet a tradition, to review the activities of your journal Optical Engineering at the end of each calendar year. Thus in this and the next month’s editorial I will present the data in a format similar

This PDF file contains the editorial “Optical Engineering in Small Companies” for OE Vol. 35 Issue 02

A prototype of a vertical scanning long trace profiler was used to measure the surface of a polished x-ray telescope mandrel in a vertical configuration and provides a 3-D view of the surface figure and slope errors. The design of the prototype system is described and experimental results are presented. Results indicate that the prototype instrument is capable of an absolute height measurement accuracy of about 50 nm with a repeatability of better than 20 nm, and a slope measurement accuracy of about 1 microradian.

Axial intensity scans provide a noninterferometric method for measuring aberration content of a focused beam. Applications of the technique include the determination of the conic constant of aspheric mirrors (without the need for a null lens).

Defects on spherical curved objects cannot be easily identified because of the object image boundary effect. Spherical transform methods are developed to solve the problem and successfully applied in an automated defect sorter. A spherical transform is obtained by compensating the intensity gradience on curved objects. Defects below the background level can be extracted through a preservation transform. The defect extraction is enabled by a uniformly distributed plane image through two-step transformations and the defect position is determined by allocation process. The results show the effectiveness of the processing methods for the high-speed on-line defect identification on fruit packing lines.

The point diffraction interferometer (PDI) is modeled using the GLAD diffraction code. The behavior of the interference fringe pattern is examined as a function of f /#, aberration type, and lateral and axial translation of the PDI.

The photocontrolled millimeter-wave (MMW) antenna is an alternative approach to the phased array. It offers a high potential to decrease fabrication cost. We describe a new MMW scanning antenna controlled by light. The basic antenna element is a semiconductor plate containing a photoinduced plasma grating (PIPG). By changing the grating period and rotating the grating, the device is able to scan a MMW beam in two dimensions. To enhance antenna efficiency, we use an antenna design that takes advantage of the reflectance of the MMW mirror behind the semiconductor plate. We found that the pulse duration of the pumping light can strongly affect the antenna’s output. Our calculations demonstrate that diffusion is responsible for decay of antenna efficiency.

The design of laser radars and the determination of laser radar signatures of various vehicles require accurate data on the reflectivity of the target materials to far-field laser illumination at many different wavelengths. Modeling software is required that will take the monostatic reflectance data as input and combine this data with geometrical models to develop a laser radar signature. Consideration of enhanced backscattering can be critically important in developing laser radar signatures. This is illustrated by the comparison of two signature models of the same airplane—one developed using bidirectional reflectance measurement data at 2 deg from the retrodirection, and the other developed from monostatic measurement data at true retrodirection. When a reflecting metal substrate is coated with a thin layer of weakly rough dielectric, as is often the case with naturally occurring metal oxides on a parent metal surface, a giant enhanced backscattering peak is observed that will further enhance the lidar signature.

The enhanced backscattering of light from a randomly rough surface, which is manifested as a narrow peak in the retroreflection direction in the angular distribution of the intensity of the light that is scattered diffusely, has been extensively studied. Both theoretical and experimental investigations have shown that the height of the peak is never more than twice the height of the background at the position of the peak. We report the observation of a giant enhanced backscattering of light from a randomly weak rough dielectric film on a reflecting metal substrate, in which the ratio of the height of the peak to the height of the background at its position is greater than 10. It is found that this giant enhanced backscattering peak is accompanied by concentric circular interference fringes, whose axis is normal to the mean scattering surface, with both the specular and backscattering peak on the same ring. A possible mechanism for the giant backscattering is suggested.

A novel principle of a high-speed 3-D camera is presented. This 3-D camera system is able to achieve the instantaneous full-frame 3-D imaging capabilities that no other commercially available 3-D image acquisition systems or 3-D rangefinders can currently achieve. There are no mechanical moving parts in this system, therefore the mechanical design can be very simple and reliable, and there is no ‘‘eye-safe’’ problem. The 3-D camera can be integrated using all off-the-shelf products, which leads to a very low production cost and short development period. The 3-D camera is also able to provide normal 2-D intensity image of the scene using a single camera, which will greatly facilitate the object recognition and the sensor fusion tasks in machine vision applications. Simulations and hardware experiments have been performed, and the results are presented.

A six-feature all-sky star field identification algorithm is developed to match approximately detected star fields with reference star fields. It is also integrated with a CCD-based imaging camera. The experimental performance of the star pattern identification algorithm was tested and verified at the Table Mountain Observatory. A set of observatory tests on star fields with this intelligent camera are presented.

A feature-based approach to visual/IR sensor image registration is presented. This new method overcomes the difficulties caused by the discrepancy in data’s gray-scale characteristics and the problem of feature inconsistency. It employs a wavelet-based feature extractor to locate point features from contours based on local statistics of the image intensity. Matching is carried out at multiresolution levels based on point features. A consistency-checking step is involved to eliminate mismatches. The algorithm is accurate, robust, and fast. It is capable of handling images with considerable translation, scaling, and rotation. Details on the registration algorithm including feature extraction, matching, consistency checking, and the image transformation model are discussed. Experimental results using real visual/IR sensor data are presented.

The most current research and development in optical signal processing and its applications at Essex Corporation is summarized. In progress for more than a decade, this work has evolved from the development of highly specialized algorithms for the intelligence community to more general domains embracing such diverse areas as radar signal processing, medical ultrasound and magnetic resonance imaging, acoustic tomography, and cellular and satellite communications. Essex develops algorithms and designs, fabricates, and tests breadboard designs and transforms these into rugged, compact products for use in harsh environments. Descriptions of the most important investigations in these areas are presented. An image synthesizer called ImSyn™ is described that forms images from the measured spatial Fourier components of the object to be imaged. Applications to synthetic aperture radar, acoustic tomography, medical resonance imaging, and synthetic aperture microscopy are shown. An acousto-optic radar signal processor is described that can produce high-resolution, high-dynamic range range- Doppler maps from instantaneously wideband radar returns. A design for a fiber optic true-time delay beamformer is presented. Finally, an optoelectronic telecommunications switch is discussed.

A translation sensitivity adjustable compact optical correlator (TSACOC) utilizing a convergent reference wave has been designed and tested. Its properties and performances, including the location of the correlation peak and the effects of lateral and longitudinal displacements for both filters and input images, are systematically analyzed based on the nonparaxial approximation for the reference beam. The theoretical analyses have been verified in experiments. By discussing the practical problems encountered, we have found that the tolerance of the system to the input lateral displacement can be conveniently increased by changing a geometric factor of the system. This property is very important to a TSACOC with a pinhole aperture attached to an ordinary detector at a fixed place. In addition, the effectiveness of the TSACOC for fingerprint recognition is also presented.

We have experimentally demonstrated the feasibility of a scale, rotation, and translation invariant all-optical processor for automatic target recognition. This simple processor consists of a single Fourier lens and uses a phase-coded input image of the target obtained by the recording of the original image onto a phase-only material through a Ronchi-type grating. A logarithmic distance measure is introduced to separate two classes of targets under the experiment. A real-time implementation of the processor is suggested utilizing a specially designed spatial light modulator.

Design parameters for the miniaturization of optical correlators are presented based on technical specifications of the SLMs used. A system constant of an optical correlator is defined in terms of the pixel spacing of the SLMs. Technical parameters are analyzed to design miniature optical correlators that can be constructed with presently available SLMs.

We describe the effort to design and construct a high-speed low-energy digital optical processor that is currently in progress at Opti- Comp Corporation. The reasons for believing that it is possible to build optical processors that have lower switch energies than are possible with electronic processors are discussed. Two systems, a second-generation digital optical computer (DOC II) and a high-performance optoelectronic computer (HPOC), which are under development at OptiComp, are described. Both systems are based on high optical fan-out emitters and high optical fan-in detectors. Finally, potential practical applications for the high-performance optoelectronic computer are discussed.

Recent progress in sol-gel-processed second-order nonlinear optical and photorefractive materials for photonics applications is described. A number of composites have been prepared in an effort to obtain superior and cost-effective replacements for inorganic crystals. These composites are described followed by a series of measurements indicating the usefulness of these composites in the area of secondorder nonlinear optical applications and photorefractive optical information storage and processing.

A compact, rugged, and low-cost three-dimensional optical storage system based on space and phase-code multiplexed volume holograms is presented in this paper. Holograms are recorded at a 2-D grid of locations in a holographic medium, such as photorefractive crystal or photopolymers. At each location, multiple holograms are stored via phase-code multiplexing. By combining the space and phase-code multiplexing techniques, such a 3-D optical storage system has the potential to achieve very large storage capacity and high data access rate. In this paper, the optical architecture is described and the system integration is discussed. Preliminary proof-of-concept experimental results are provided.

A system to convert an analog optical system to a digital one in an optical environment using basic symmetric self-electro-optic effect devices (S-SEEDs) is detailed. It is shown that quantization and binary encoding can readily be achieved using the logic capabilities of S-SEEDs. A quantizer prototype has been constructed and proper operation observed. The effect of the hysteresis inherent in the S-SEED is discussed and three techniques are proposed to eliminate the problems caused by hysteresis. The logic operations needed for the construction of the binary encoder with the minimum number of S-SEEDs are facilitated using a reference beam. An alternate, efficient design of the binary encoder is also presented. Using a novel time quantization technique, a sampling rate in excess of 1 gigasamples/s is achievable.

The basic elements of Bragg–Fresnel multilayer optics are multilayer gratings. In this paper, the fabrication process for the simplest Bragg–Fresnel multilayer optics is given; the diffraction measurements at 8-keV x rays of multilayer gratings are presented; and the measurement results in the diffraction spectrum are analyzed and discussed in detail.

The shape, depth, and maximum change in refractive index profile are of the most important parameters to be controlled when developing gradient refractive index (GRIN) lens blanks. Generally refractive index profiles are measured by standard interferometers such as Mach–Zhender, Twyman, and Shearing interferometers. These methods generate a large amount of data and need rigorous computation. A new kind of deflectometery is reported that can measure a GRIN profile using the interference pattern generated by a birefringent lens. Results based on this method are presented for radial GRIN glasses developed by Ag+-Na+ and Na+-Li+ ion exchange in alkali aluminosilicate glasses.

The steady-state temperature of uncovered skin depends, besides other factors, on skin blood flow, but the correlation between the two parameters is low. The steady-state temperature of thermally insulated skin is less affected by the environment and the temperature gradients underneath and is therefore expected to better reflect skin blood flow. In the present study, comparative measurements of steady-state temperature were performed on uncovered skin and on partially thermally insulated skin. The device for the thermal insulation was constructed of a Teflon capsule with an infrared fiber, which conveyed a portion of the infrared radiation emitted from the skin into an infrared radiometer. Temperature was recorded on the hand and forearm, at heart level and above it, for uncovered and thermally insulated skin. The measurements showed that the temperature of thermally insulated skin better reflects the temporal and spatial changes of skin blood flow than uncovered skin temperature. The noncontact temperature measurement of partially thermally insulated skin provides, therefore, a method for qualitative assessment of changes in skin blood flow.

We describe a simple method for measuring the long radius of curvature by using a half-aperture bidirectional shearing interferometer. The method is based on the direct comparison of the fringe widths in the two fields. This is very convenient for quantitative interpretation of the fringes. Detailed analyses for optical arrangements and achievable accuracy are presented.

Some applications of optical surfaces require, in addition to measurements of their absolute deviations from flatness, measurements of the spatial frequency spectrum of these errors. A simple method which can be used for this purpose is described.

A touchless interference method that can be used to calibrate gauge blocks or length bars with lengths from 0.01 mm up to 1 m is proposed. The method is based on a comparison of two gauges, with one of them used as a reference. Polychromatic synthesized light from three laser diodes is used to determine end surface positions. Distances referring to these positions are measured by a wavelength-stabilizedlaser interferometer. Error sources are analyzed in this method. The accuracy of the comparison depends on the accuracy of the interferometer used to measure displacement. In the case of long gauge blocks, accuracy is limited mainly by uncertainty in the gauge block temperature.

A new type of two-wavelength interferometer which applies a phase-lock technique is described. The wavelength tunability of a laser diode (LD) is used for phase modulation and phase control in this interferometer. Since the two wavelengths are derived from a single LD in our system, the optical system is simple and there is no need to consider the fluctuation of relative wavelength between the two LD’s in the conventional two-wavelength interferometers. The equivalent wavelength ? is 15 mm and the measurement accuracy reaches ~?/400. The error sources in the system and the error analysis are also described.

The design of a pseudospark chamber, a high-voltage (>100 kV), high-current density, low-emittance and high-brightness electron beam source which can provide high-quality beams for free-electron lasers (FELs), driven by a modified pulse line accelerator, is presented. Based on the hollow cathode (HC) effect and the pseudospark (PS) empirical formula, the HC parameters, the cathode-anode separation, and the working gas pressure region are determined. The general experimental setup of the high-brightness PS-produced electron beam source is shown.

Optical fibers of 50-µm core diameter are investigated for high-quality beam delivery of moderate power (30 W cw) Nd:YAG laser light. The fiber output near-field profile is important for materials processing applications, but is dependent on the modal distribution within the fiber, together with any intermodal interference. Launch optics design, mode-coupling, and modulation techniques are investigated as methods of controlling this beam profile, together with any associated beam quality (M2) changes. As an example application, high-precision, small kerfwidth cutting of stainless steel is demonstrated.

To better understand the passive torsional motion and to quantify the torsional motion of an insect, we developed a new scanning beam method that can measure with high resolution the variation in both the torsion angle and shape of an insect wing during pure flapping motion. This new method is based on the conventional principle used in a laser beam displacement probe with a position detector, but introduces the use of an acousto-optic deflector, which enables us to pass the scanning laser beam over the wing. Therefore, by measuring the relative displacement between the beam spots on the wing, we can determine the passive variation in both the torsion angle and shape of an insect wing with high resolution. According to the waveform supplied to the acousto-optic deflector, we define both a two-point scanning method, which we use to measure the variation in torsion angle, and a multipoint scanning method, which we use to measure the variation in shape. We apply these methods to a dragonfly wing at different flapping frequencies, and compare the results with those determined using a high-speed video camera. The good agreement between the two methods shows that the scanning beam method can be effectively applied in the field of biomechanics to study the torsion angle variation and shape variation of an insect wing.

The determination of the position of an image inside a complex scene by means of correlation is sometimes difficult owing to the appearance of spurious peaks. When the lateral peaks are lower than the central correlation, they can be eliminated simply by binarizing the output plane by a threshold function. However, if this is not the case, we have to use special filter designs, which suffer from such difficulties as a low optical efficiency. In this paper we present a new possibility for eliminating the lateral peaks through the combined action of several filters that can be used to correct the problem in a wide range of situations.

Digital chaotic behavior in an optically processing element is reported. It is obtained as the result of processing two fixed trains of bits. The process is performed with an optically programmable logic gate, previously reported as a possible main block for optical computing. Outputs for some specific conditions of the circuit are given. Digital chaos is obtained using a feedback configuration. Period doublings in a Feigenbaum-like scenario are obtained. A new method to characterize this type of digital chaos is reported.

A modular neural network architecture has been used for the classification of remote sensed data in two experiments carried out to study two different but rather usual situations in real remote sensing applications. Such situations concern the availability of high-dimensional data in the first setting and an imperfect data set with a limited number of features in the second. The learning task of the supervised multilayer perceptron classifier has been made more efficient by preprocessing the input with unsupervised neural modules for feature discovery. The linear propagation network is introduced in the first experiment to evaluate the effectiveness of the neural data compression stage before classification, whereas in the second experiment data clustering before labeling is evaluated by the Kohonen self–organizing feature map network. The results of the two experiments confirm that modular learning performs better than nonmodular learning with respect to both learning quality and speed.

An extensive set of measurements of the scintillation of a laser propagated over long horizontal paths through atmospheric turbulence, at altitudes spanning the tropopause was recently obtained. These measurements were made over sequences of parallel but displaced paths, like the rungs of a ladder. It is shown here that the intensity reductions caused by scintillation of two parallel paths separated by 35.6 m are partially correlated. Further, the correlations between paths with discrete experimental separations are used to construct the correlation functions for arbitrary path displacement. The variance in continuous moving averages of the relative intensity is then found in terms of the correlation functions, parameterized by the distance the propagation path is swept through the turbulence. An empirical formulation is developed for use in assessing the expected distribution of intensity reductions in various laser systems. This analysis recovers the statistics of atmospheric scintillation for the important regime in between the two extremes of a snapshot and a long time average.

We present noise measurements of a phase fluorometric oxygen sensor that sets the limits of accuracy for this instrument. We analyze the phase sensitive detection measurement system with the signal ‘‘shot’’ noise being the only significant contribution to the system noise. Based on the modulated optical power received by the photomultiplier, the analysis predicts a noise spectral power density that was within 3 dB of the measured power spectral noise density. Our results demonstrate that at a received optical power of 20 fW the noise level was low enough to permit the detection of a change oxygen concentration of 1% at the sensor. We also present noise measurements of a new low-cost version of this instrument that uses a photodiode instead of a photomultiplier. These measurements show that the noise for this instrument was limited by noise generated in the preamplifier following the photodiode.

The San Marco 5 carried the airglow-solar spectrometer instrument (ASSI). This 18-channel spectrometer measured the solar and terrestrial radiation in the wavelength region between 20 and 700 nm for 9 months in 1988. The ASSI extreme ultraviolet (EUV) channels showed significant sensitivity changes during the mission. The sensitivity changes of the EUV channels are quantified by comparing ASSI solar EUV irradiance measurements to the solar EUV irradiance derived from a solar proxy model. A sensitivity change model is developed that shows that exponential curves can adequately describe the sensitivity changes of the ASSI optics and detectors. The November 10 calibration parameters and the sensitivity change model can be used to derive the EUV terrestrial airglow brightness for the time period of the ASSI mission. Analysis of the solar Lyman-? irradiance measured by the ASSI, the solar mesospheric explorer (SME), and the upper atmosphere research satellite (UARS) has led to a revised Lyman-a irradiance for the San Marco mission. For example, the ASSI November 10, 1988, Lyman-? measurement is 5.3 X 1011 photons cm-2 S-1 versus the reported SME measurement of 3. X 531011 photons cm-2 S-1.

A method for 3-D image recording and reconstruction when using a so-called reference-free selectogram is suggested. According to this method, the light scattered by the object is filtered by a horizontal slit and then is split into two components with the help of a diffraction grating that is positioned just in front of a thick-layered photographic plate. The interference pattern that originates as a result of the interaction of the components formed by the diffraction grating is recorded in a lightsensitive layer in the form of a deep volume hologram. The reconstruction of the image is performed by using light scattered by a diffusing screen. The theoretical analysis of the recording and reconstruction process of the reference-free selectogram is given. We show that the wave field of the radiation reconstructed by a reference-free selectogram reproduces an object wave field within the accuracy of a random phase shift. We also show that the structure of the 3-D hologram recorded by the axis point of the object does not depend on the wavelength of the recording light. Results are presented on an experiment on the recording and reconstruction of the reference-free selectogram. The selectogram was recorded in a thick-layered light-sensitive material called reoxan. The image reconstructed by the selectogram was located in a plane where the recorded object was placed. This fact has proven the threedimensional character of the image. The advantages of the referencefree selectogram are its low requirements in the coherence of the recording and reconstructing light and also its insensitivity to the vibrations of the setup during recording.

We describe a method for improving the images reconstructed from three-dimensional computer-generated holograms. This method utilizes iterative operations of the Fourier and inverse Fourier transforms, and the holograms are created with equally distributed complex amplitudes of the object consisting of several cross sections. From numerical experiments, we have obtained the improved images in all reconstruction planes with a few iterations. The reconstructed images were enhanced rapidly with an increase in iterative operations, but the image improvement approached a constant value after a certain point and this was also confirmed numerically from the mean-square-error of the images.

Without mechanical scanning in the transverse direction, we selectively extract image slices from an object hidden behind random scattering media with an inexpensive, easy-to-operate, cw superluminescent laser diode, a CCD camera, and broadband electronic holography. System sensitivity is about 10-10 of the incident optical power. An efficient image processing algorithm is developed to eliminate the effect of phase noise in the electronic holography and enhance the recovered image. Submillimeter spatial resolution and 40-mm depth resolution is achieved. The SNR is limited by the dynamic range of the CCD camera.

Particle image velocimetry (PIV) has been used to study the in-cylinder flow within a single-cylinder optical spark ignition engine. The engine had a standard four-valve pentroof cylinder head geometry, a compression ratio of 10.5:1, and was motored at a crank speed of 1000 rpm. Double exposed PIV images were recorded from a range of vertical and horizontal measurement planes within the engine’s glass cylinder. The images were interrogated using digital autocorrelation to give maps of two-dimensional instantaneous velocity. Successful PIV measurements have also been made under firing conditions in the unburned gas ahead of the flame front, with the engine being skip-fired using a propane/air mixture. The use of PIV for the characterization of realistic in-cylinder flow fields under a variety of inhospitable conditions has therefore been demonstrated. Limitations in the current technique are briefly discussed and methods for overcoming these limitations are described.

Several of my colleagues and friends often commented on the lack of a compact, comprehensive, and contemporary reference text in photonics. What they were looking for was Applied Photonics by Chai Yeh. In 14 chapters the author presents the most important aspects of photonics in a truly cogent fashion and sets the record straight for numerous misconceptions.