This PDF file contains the editorial “What kind of future are we looking for?” for OE Vol. 39 Issue 10

The performance merits of the phase-shifting joint transform correlator (PSJTC) are evaluated based on the criteria of light efficiency and discrimination capability. The PSJTC is shown to possess much higher light efficiency (three orders of magnitude) and much better discrimination capability (three times with the selected images) than does the conventional joint transform correlator (JTC). The PSJTC is combined with the circular harmonic expansion to achieve a full rotationinvariant correlation with high light efficiency and high discrimination capability. Computer simulation results and 3-D computer plots are presented.

Compensation for spatial light modulator device imperfections can be achieved using digital electronics. Optical computing applications, requiring accurate phase or amplitude modulation, can then make use of low-cost, enhanced devices. Using electronic compensation, corrections can be made for a nonsquare aspect ratio in the aperture window and a nonlinear phase response-which may also be nonuniform over the aperture. The corrections for these imperfections are implemented using low-cost field programmable gate arrays. This technology enables real-time compensation and is easily adapted to suit a wide range of display devices. The performance enhancement is demonstrated using a popular Seiko-Epson liquid crystal television display operating as a phase modulating spatial light modulator. These developments greatly extend the utility of readily available, inexpensive, spatial light modulators.

A contrasted statistical processing approach to obtain improved probabilities of false alarm when performing automatic target detection is presented. The technique is based on analyzing each sector of the image and comparing it with surrounding windows in which the desired statistical property is calculated. The contrast of the statistical property is extracted using the prediction or the prediction-correction equations. The contrast of the statistical property is shown to be a good discriminator of the target from its background allowing the reduction of the detection threshold applied over the stationary region while maintaining a constant false alarm probability.

Most existing intensity-based edge detection techniques are unable to detect edges of objects placed in a background whose intensity is same as that of the object surface, i.e., in a homogeneous background. This is mainly because under such conditions, a clear demarcation in intensity does not exist at the edge pixels. Thus, gradient- and difference-based operators such as the Sobel, Roberts and Prewitt operators are not capable of detecting the edges completely due to the absence of intensity variations at the edges. A technique for detecting the edges of multiple objects placed in a homogeneous background is proposed. In this technique sinusoidally coded stripes (fringes) are projected obliquely onto the object surfaces to form a fringe pattern image. Due to the depth of the object, intensity break points can be observed in the image and the edges can be detected by locating these points. In a simulation study, analysis carried out on the raw fringe pattern images to detect the edges, based on the proposed technique, shows that the detection error increases with the standard deviation of Gaussian noise. Analysis carried out on a phase image, obtained by applying the phaseshift method, however, shows a significant improvement in accuracy. The accuracy is also found to be almost unaffected by background noise. The results of edge detection using the proposed technique on real images are presented.

Highly p-doped silicon/silicon-germanium (Si/SiGe) quantum well (QW) structures are grown by molecular beam epitaxy (MBE) on double-sided polished <100)Si substrates for mid-IR (3 to 5 ?m and 8 to 12 ?m) detection. The samples are characterized by secondary ion mass spectroscopy (SiMS), x-ray diffraction, and absorption measurements. Single mesa detectors are fabricated as well as large-area focal plane arrays (FPAs) with 256x 256 pixels using standard Si integrated processing techniques. The detectors, based on heterointernal photoemission (HIP) of photogenerated holes from a heavily p-doped (p+ + ~5x 1020cm-3) SiGe QW into an undoped silicon layer, operate at 77 K. Various novel designs of the SiGe HIP's such as Ge- and B-grading, double- and multi-wells, are realized; in addition, thin doping setback layers between the highly doped well and the undoped Si layer are introduced. The temperature dependence of dark currents and photocurrents are measured up to 225 K. In general, we observe broad photoresponse curves with peak external quantum efficiencies up to next ~0.5% at 77 K and 4?, detectivities up to 8x 1011 cm?Hz/W are obtained. We demonstrate that by varying the thickness, Ge content, and doping level of the single- and the multi-QWs of SiGe HIP detectors, the photoresponse peak and the cutoff of the spectrum can be tuned over a wide wavelength range. The epitaxial versatility of the Si/SiGe system enables a tailoring of the photoresponse spectrum which demonstrates the advantages of the SiGe system in comparison over commercially used silicide detectors.

Avalanche photodiodes (APD) are solid state quantum detectors suitable for low level light detection in the visible and near infrared regions. These devices are commercially available from many manufacturers and are fabricated using several different solid state structures. In this paper a comparison between the well developed reach through structure (RTS) aPd and the relatively newer super low ionization ratio, k, (SLIK) APD structure will be discussed. The comparison is based on the experimental characterization of two APDs with these structures. The characterization setup and experiments will be described which include the calibration of the APDs, temperature response, bias voltage response, and noise measurements including noise-equivalent-power and detectivity D*. For this comparison the selected RTS APD is the EG&G C30955E, currently used by the lidar atmospheric sensing experiment (LASE) instrument. The selected SLIK ApD is the EG&G C30649E, which is proposed for LASE development. The characterization experiments where done in order to develop an advanced atmospheric water vapor differential absorption lidar detection system.

One of the detector systems used for the Coronal Diagnostic Spectrometer instrument aboard the Solar and Heliospheric Observatory satellite is an intensified CCD camera. The intensifier section consists of a bare microchannel-plate detector proximity focused onto a phosphor, the light from which is then focused by a lens onto the CCD. Since the positions of the spectral lines are fixed on the detector, this leads to decreased efficiency in those areas of the detector where the strongest lines fall. The steps used to track this differential scrubbing of the detector in flight, and to remove these effects from the data, are described. Implications for future space missions are discussed.

Quantum well IR photodetectors (QWIPs) have been proposed for use in space-based sensing applications. These space systems place stringent performance requirements on IR detectors due to low-irradiance environments and the associated requirement for low- temperature operation. We demonstrate that under these conditions, the responsivity of a QWIP detector depends on frequency and that the shape of the frequency response varies with operational conditions. This nonlinear frequency response is empirically similar to dielectric relaxation effects observed in bulk extrinsic silicon and germanium photoconductors under similar operational conditions. Radiometric characterization data demonstrate how the frequency response varies with temperature, photon irradiance, and bias voltage. These data also show that at low irradiances and temperatures, the detector response is extremely slow, with response times on the order of seconds. The performance of the QWIP detector is described using standard figures of merit including responsivity, noise, and specific detectivity (D*). We also describe the performance of an IR focal plane array (IRFPA) made with QWIP detectors, under operational conditions that result in long response times. The dependence of this time constant on photon irradi- ance and operating temperature is also described.

The discrete cosine transform (DCT) has wide applications in speech and image coding. We propose a fast DCT scheme with the property of reduced multiplication stages and fewer additions and multiplications. The proposed algorithm is structured so that most multiplications are performed at the final stage, which reduces the propagation error that could occur in the integer computation.

We present a novel measurement method to measure the echo rating baseband parameter at the subscriber. A relation between the echo rating and the in-channel frequency response is found from both theoretical derivations and experimental results. We use the inchannel frequency response rf parameter to simultaneously indicate the echo rating performance. This proposed novel echo rating measurement method is simpler and more cost-effective than the conventional measurement method.

We present the modeling and the performance of a polarization active imager at ? = 806 nm. The device operates in a monostatic configuration, using a semiconductor laser to illuminate the target and a telescope to create the image on a CCD matrix. Dual images (intensity and polarization degree) of different scenes are obtained by a new method (only two images acquired) and analyzed, showing the experimental validation of this concept. An application of this active imager to the detection of a target buried in the background (same reflectivity but different polarization degree) is proposed. Field experiment results are reported.

In phase shifting in photoelasticity, phase unwrapping is one of the crucial steps in the processing of determining the total fringe orders. This task is tedious, particularly when ambiguity exists in an irregular phase map. Currently the phase-unwrapping process is usually performed line by line with prior knowledge of the total fringe order for at least one point after eliminating the isoclinic ambiguity. In this paper, a novel method is proposed, which can automatically perform the phaseunwrapping process directly based on the result of phase-shifting independent of the status of ambiguity and no prior knowledge is needed of the total fringe order for at least one point. The basic idea of this method is to exploit the relationships between phase retardations caused by three different loads applied on a specimen to find directly the total fringe order at each point. Experiments on a 'C' shape specimen under compression are provided as demonstrations.

A stable interferometer with two zone plates to measure a concave mirror figure is developed. The principle of the measurement is based on the radial shearing interference in which the measuring wavefront from the entire mirror surface under test is referred to that from the central part. On-machine experiments show that the interferometer is stable and compact enough to be applicable to in-process measurement for diamond turning at about 0.06 ?m p-v accuracy.

A diode laser pumped solid state laser design capable of generating several simultaneously emitted spatially separate and wavelength tunable beams is presented. The laser design was demonstrated in a dual-beam configuration using Tm,Ho:YLF as laser material. Laser oscillation in two TEM00, longitudinal multimode cw beams of 80-mW maximum output power was demonstrated. The wavelength difference between the beams was tuned over a 15-nm-wide range using one solid etalon as a tuning element.

We present a long wave IR zoom scene projector, designed and built by Optics 1, Inc. Research on the thermal analysis and compensation is conducted. An effective thermal compensation scheme is proposed to enable the zoom projector to maintain its performance when it is operating between 0 and 40°C. The final testing results prove the design performance.

The spatial resolution and sensitivity of the Fourier transform method for fringe detection is analyzed. The spatial resolution degradation due to Fourier transform is discussed through a signal processing technique. It is found that the upper limit of spatial resolution for displacement measurement is half the carrier fringe pitch, or half the grid pitch for the grid method. The formulation of sensitivity using signal processing and communication theory is also performed and analyzed. Measures to improve the spatial resolution sensitivity are discussed.

This paper presents a self-calibration technique for calibrating a high-resolution scanning white light interference microscope in the Z-direction. The calibration result, which consists of the mean sensitivity and the linearity error, can be obtained from two sets of profile measurement data before and after a small shift ?z of the sample in the Z-direction. To assure the accuracy of the calibration, a method of measuring and controlling ?z, in which a laser interferometer is used as a reference, is proposed. Using the proposed method ?z, as well as the calibration result, can be ensured to an accuracy that is determined by the stability of the interferometer and that of the calibration target. A calibration setup consisting of a PZT for generating ?z and a built-in compact interferometer for monitoring ?z is constructed. In addition, calibration experiments are performed after investigating the basic performance of the built-in interferometer. The effectiveness of the proposed self-calibration method is confirmed from the experimental results.

A new method of fringe analysis by subfringe integration algorithm (SIA) is proposed to analyze moire deflectograms and to map the phase object, in which the fringe phase is retrieved and phase object message is obtained automatically. Optical tomography is applied to the moire deflectometry for the measurement of asymmetric phase object. The convolution backprojection algorithm is used to obtain the 3-D temperature field. Theoretical analysis, experimental result and simulation calculations are presented.

A fast learning method for neural networks learning system using fuzzy controlling is proposed. By the fuzzy controlled theory, the learning rate and the nonlinear gain of the output function in the back- propagation algorithm are adjusted based on training error and training time. The effectiveness of this learning method is demonstrated in optical pattern training.

Advanced optical design methods using the tools of nonimaging optics (instead of conventional imaging tools) produce ultracompact devices that combine high collection efficiency with a concentration (or collimating) capability close to the thermodynamic limit. After a general overview covering the most important design methods and devices in nonimaging optics, two of these designs, the so-called RX and RXI, are presented. Even though it is designed within the nonimaging framework, the RX device nevertheless has imaging properties that complement its valuable performance as a nonimaging device. The RXI is extremely compact: its aspect ratio (thickness/aperture diameter) is less than 1/3. When working as a receiver, that is, by placing a photodiode in the correct position, it attains an increase in irradiance that takes it beyond 95% of the theoretical thermodynamic limit (i.e., a concentration of 1600 times with an acceptance angle of ±2.14 deg). As an emitter, similar intensity gains can be obtained within an angle almost as large as 95% of the thermodynamic limit. The combination of high concentration factors, relatively wide acceptance angles, simplicity, and compactness makes these devices almost unique. The measurements carried out with several RXI prototypes, all of them made by PMMA injection, are also presented.

We report the results of our research and development in techniques for producing elliptical x-ray mirrors by controlled bending of a flat substrate. We review the theory and technique of mirror bending with emphasis on the optical engineering issues and describe our design concepts for both metal and ceramic mirrors. We provide analysis of the various classes of error that must be addressed to obtain a high quality elliptical surface and a correspondingly fine focus of the x-ray beam. We describe particular mirrors that have been built, using these techniques, to meet the requirements of the scientific program at the Advanced Light Source at Lawrence Berkeley National Laboratory. For these examples, we show optical metrology results indicating the achievement of surface accuracy values around and, in some cases, below 1 ?rad as well as x-ray measurements showing submicrometer focal spots.

We present a fast 2-D phase retrieval approach used to perform optical phase modulation of a microelectromechanical-deformable mirror (MEM-DM). Traditional solutions to beamsplitting, beam steering, and beam shaping (BS3) involve multiple and sometimes costly optical components. For example, beamsplitting is normally accomplished with beamsplitters, beam steering is normally achieved with gimbaled mechanical devices, and beam shaping is normally done with addressable, polarized, and potentially absorptive devices such as LCDs. Using the phase retrieval algorithm with a desired far-field amplitude pattern as a constraint, a segmented wavefront control device is shown to simultaneously perform the functions of BS3. The MEM-DM used is a foundry- microfabricated device that is attractive for optical phase modulation applications primarily because of its inherent low cost and low drive voltages. The MEM-DM shapes the beam based on the results of a modified Fienup and Roggemann/Lee phase retrieval algorithm implemented within the system. The optical bench setup and the experimental results for BS3 are presented. Measured experimental data show good agreement with model simulations. A comparison between analog MEM- DMs and a digitally controlled MEM-DM is presented. Overall, experimental results demonstrate the efficacy of the phase retrieval algorithm and a single phase control device in solving optics problems normally solved through traditional techniques and multiple devices.

A modified Monte Carlo algorithm for the calculation of the impulse response on infrared wireless indoor channels is presented. As is well known, the characteristics of the room where the IR diffuse channel is implemented can lead to problems in communication, such as a multipath penalty on the maximum baud rate or hidden-station situations. Classical algorithms require large computational effort to calculate the impulse response in an ordinary-size room. Monte Carlo offers the possibility of validating the assumptions made for these classic algorithms (basically, the Lambertian nature of all reflections) with a computational complexity that is determined by the accuracy desired by the user. We have developed a mixed ray-tracing-deterministic algorithm that assures that each ray contributes to the final channel response function as many times as it rebounds with an obstacle. It increases dramatically the number of contributions and reduces, to the same extent, the time required for an accurate simulation. Extensive simulation results are presented and are compared with those of other simulation methods. We demonstrate that the method presented here is much faster than Monte Carlo classical simulation schemes. It can be used as a method of simulation in itself or as a validation algorithm for other comparative studies of pulse broadening.

This paper describes design and experimental results for the future airborne multispectral sensor with six bands between visible and infrared regions. The multispectral sensor features single optics using off-axis three-mirror reflective optics to provide same field of views for all six bands and dichroic mirrors to separate the spectral range into six bands. The off-axis three-mirror optics provides an obstruction free FOV with a wide spectral range and high spatial resolution over a wide FOV. The six bands consist of three visible bands, a near infrared band, an MWIR band and an LWIR band. The 10,000 element CCD sensors are used for the three visible bands and the near infrared band. The 960 element HgCdTe linear arrays are used for the MWIR and the LWIR bands. The results of experiments reveal that the ground-base multispectral sensor has a wide spectral range from 0.4 ^m to 10 xm, the wide FOV over 5.7° and the high spatial resolutions of less than 10 xrad for visible and near infrared bands and of less than 104 xrad for the MWIR and the LWIR bands. The overall MTF at the center of the FOV is more than 0.3 at Nyquist frequency for all bands.

We describe a model for evaluating the performance of deconvolution from wavefront sensing systems, including a realistic simulation of the wavefront sensor measurements under high and low photon fluxes. This model is applied to analyze the behavior of different deconvolution filters for both pointlike and extended objects, whose images are degraded by Kolmogorov turbulence. In the situations considered, the results show a performance substantially similar to that of the modified Wiener and regression filters, and is superior in both cases to that of the classical Wiener filter.

Conventional stationary reticle seeker uses an analog signal processing technology to extract a target position in the field of view. The analog technology is optimized for only frequency modulation signals, which makes it difficult to use various and adaptive signal processing, and causes the performance limit of the conventional technology. We propose a novel adaptive digital signal processing algorithm to overcome the performance limit. The proposed algorithm classifies the modulation signals into the FM and FM/AM signals and applies a different signal processing algorithm, which is optimized for the modulation characteristics of each signal. The algorithm also employs an adaptive clipping level to minimize the noise effect. Our simulation results show that the proposed algorithm is superior to the conventional one in terms of the linearity of the static gain curve, tracking performance, and robustness against noise.

We report the implementation of a low-loss core-cladding waveguide structure of an a axis Nd:MgO:LiNbO3 single-crystal fiber with a step refractive index profile and the demonstration of a frequency- doubled laser made from such a cladded crystal fiber. The laser-heated pedestal-grown a axis single-crystal fiber, with an elliptical crosssectional area of 200x 150?m, is further shown with a Mg ion indiffusion process. Electron probe microanalysis is used to measure the Mg ion concentration distribution in the Mg-diffused layer. After several trials, diffusion parameters suitable for achieving a core-cladding waveguide structure with a step refractive index profile are obtained. The optical and structural properties of the cladded crystal fibers are also characterized. Room-temperature second-harmonic generation with such a cladded crystal fiber is demonstrated. At room temperature, cw green laser output with a power of 10 ?W at the wavelength of 0.532 ?m is achieved. The origin of the relatively low conversion efficiency is discussed.

A new method for designing two-channel causal stable IIR PR filter banks and wavelet bases is proposed. It is based on the structure previously proposed by Phoong et al. (1995). Such a filter bank is parameterized by two functions ?(z) and ?(z), which can be chosen as an all-pass function to obtain IIR filterbanks with very high stopband attenuation. One of the problems with this choice is that a bump of about 4 dB always exists near the transition band of the analysis and synthesis filters. The stopband attenuation of the high-pass analysis filter is also 10 dB lower than that of the low-pass filter. By choosing ?(z) and ?(z) as an all-pass function and a type-II linear-phase finite impulse response (FIR) function, respectively, the bumping can be significantly suppressed. In addition, the stopband attenuation of the high-pass filter can be controlled easily. The design problem is formulated as a polynomial approximation problem and is solved efficiently by the Remez exchange algorithm. The extension of this method to the design of a class of IIR wavelet bases is also considered.

Holographic interferometry (HI) and electronic speckle pattern interferometry (ESPI) are widely used in nondestructive testing (NDT). In the HI and ESPI measurement techniques, the deformations are made visible as fringe patterns while an inspected sample is loaded. Defects will lead to typical local deformations deviating from the global deformation. To achieve automatic detection of the defect characteristics, the wavelet transform (WT) method is used. Wavelets can be used to generate a multiresolution analysis of a signal and they are very sensitive to the changes in a transient signal or an abrupt signal if suitable wavelets are chosen. These changes correspond to the partial fringe patterns caused by the local defects in HI and ESPI nondestructive testing. We demonstrate how the Morlet wavelet is used to detect the defect-induced partial fringe patterns from the global fringe pattern in HI and the ESPI nondestructive testing.

This PDF contains the communication section including "Experimental realization of sculptured-thin-film polarization-discriminatory light-handedness inverters"

Optical object recognition has been approached mainly from two points of view. The first one is based on the extraction and matching of local features of the object, such as contours or perspectives,1 and the other is based on the correlation of the object in global form2,3.