This PDF file contains the editorial “The First Scientific Paper” for OE Vol. 43 Issue 11

A hybrid encryption and decryption technique for optical information security is proposed. In this method, the iterative Fourier transform algorithm is employed to optimize the encrypted hologram and the decryption key as binary phase-only diffractive optical elements, which were fabricated by electron-beam lithography. In a simple optical setup, the optical decryption is implemented by superimposing the encrypted hologram and the decryption key. Numerical simulation and optical experiment confirm the proposed technique as a simple and easy implementation for optical decryption.

A 1x8 multimode interference coupler with a strong confinement structure in the multimode region was proposed and fabricated on silicon-on-insulator material. In the multimode region, the waveguide was etched to the buried silica layer so as to realize the strong confinement and obtain better resolution of the self-imaging effect, while in the input/output ports, the rib waveguides with the large cross-section rib structure were designed to satisfy the single-mode condition, with which the device could be efficiently coupled with single-mode fibers or other waveguide devices. The fabrication process was also specially designed to eliminate the photolithography alignment error.

A thermo-optic variable optical attenuator (VOA) based on a Mach-Zehnder interferometer and multimode-interference coupler is fabricated. Not a single-mode but a multimode waveguide is used as the input and output structures of the optical field, which greatly reduces the coupling loss of the VOA with a normal single-mode fiber. The insertion loss of the fabricated VOA is 2.52 to 2.82 dB at the wavelength of 1520 to 1570 nm. The polarization dependent loss is 0.28 to 0.45 dB at the same wavelength range. Its maximum attenuation range is up to 26.3 dB when its power consumption is 369 mW. The response frequency of the fabricated VOA is about 10 kHz.

A sinusoidal phase-modulating two-grating surface profile measuring instrument is reported. This instrument can precisely measure tiny rises and falls of the surface of an object. The (+1,0)th- and (0,+1)th-order beams diffracted from two identical binary step gratings produce a interference pattern with uniform intensity and phase distribution. When one grating is moved relative to the other, the phase of the interference pattern is changed. A sinusoidal phase-modulating technique is applied to measure this phase change precisely. The phase distribution of the interference pattern is independent of the wavelength and intensity of the light source. No change in the measurement results happens when the wavelength and intensity of the light source fluctuate. The instrument is simple in its optical configuration.

Schlieren photography normally uses a background light source grid or mirror system to send light through a sample area and a second grid or a knife edge at the camera to block nondeflected light. We describe a new technique that uses the inactive areas between CCD or CMOS sensor pixels as the second grid, so only a background grid is needed. This simplifies the setup and lowers the cost of the system.

This PDF file contains the editorial “Diffractive Optics” for OE Vol. 43 Issue 11

A new compact surface plasmon resonance (SPR) sensor is presented. The integrated design employs two surface relief gratings imprinted in an injection-molded polymer chip. These gratings replace the traditional glass components usually found in existing SPR sensor systems and offer a low-cost, compact, and robust SPR system with high performance.

Micro-optics offers the ability to realize massively parallel, surface-normal interconnects at the chip scale. In this context, we investigate the integration of a 10-Gbytes/s, 850-nm vertical-cavity surface-emitting laser (VCSEL) with a 2×2 array of continuous surface profile, diffractive optical elements to demonstrate a prototype system that incorporates 3-D, highly dense, parallel optical interconnects. The integration is achieved using a novel conductive polymer-based flip-chip process, which is implemented using conventional fabrication techniques. We present experimental results from the design, fabrication, integration, and characterization of the prototype system.

For spatiotemporal transformation and processing of ultrashort-pulse laser beams, serious design constraints arise from dispersion and diffraction. At pulse durations in 10-fs range, temporal and spatial parameters of propagating wave packets are coupled and significant inhomogeneities appear. To enable a controlled shaping or encoding and a reliable detection or decoding with 2-D spatial resolution, specific advantages of thin-film micro-optical arrays can be exploited. Transmitting and reflecting components of extremely small conical angles are used to generate multiple nondiffracting beams and self-imaging phase patterns. With novel-type metal-dielectric microaxicons, low-dispersion reflective devices are realized. Beam propagation is simulated numerically with Rayleigh-Sommerfeld diffraction theory. For ultrafast time-space conversion, matrix processors consisting of dielectric thin-film microaxicons are tested. Transversally resolving linear and nonlinear autocorrelation techniques are applied to characterize the space-time structure of localized few-cycle wave packets shaped from Ti:sapphire laser beams at pulse durations down to 8 fs. Bessel-like X waves are generated and their propagation is studied. In combination with autocorrelation, wavefront analysis of ultrashort-pulse lasers with Bessel-Shack-Hartmann sensors operated in reflection setup is demonstrated.

With surface-relief structures, optical functions that are required for radiation power management such as antireflection, light trapping, or light distribution and redirection can be obtained for new applications in solar energy systems and in displays. There, structures with submicrometer features must be distributed over large areas homogeneously. We address the design and the whole experimental process chain from the microstructure origination on large areas to the replication and the system integration in the specific application. Topics are antireflective surfaces for solar systems and displays, light trapping in polymer solar cells, sun protection systems for facades, and diffusers for projection displays and in glazing. For the microstructure origination we investigate the suitability of holographic recording in photoresist using a large-scale interferometer. We use an argon ion laser as a coherent light source at a wavelength of 364 nm. Periodic and stochastic interference patterns are recorded in positive photoresist with the interferometer setup. In the case of periodic structures, grating periods between 200 nm and 20 µm are realized. By carefully modeling the resulting resist profiles it is possible to originate even prismatic surface-relief profiles. Structures with good homogeneity are originated on areas of up to 4800 cm² by optimizing the interferometer setup and the photoresist processing.

Computer-generated holograms (CGH) are on their way to becoming a state-of-the-art component in interferometry. We give an overview on recent developments in calibration and testing of aspheric surfaces with CGH. The starting point is a new absolute calibration method for binary Fresnel zone mirrors (FZM) that allows separation of the errors introduced by the imperfectly written FZM pattern from the errors of the substrate and from the interferometer errors. This leads to a variety of applications for FZM, ranging from absolutely calibrated spherical master surfaces to quality control of CGH fabrication. We then focus on a major application of binary CGH: null tests for testing of aspheric surfaces. Useful test setups are described and an alignment strategy utilizing auxiliary structures in the periphery of the CGH is discussed. The section on binary CGH culminates with the first absolute test method for measuring aspheric surfaces and systems. We close our overview with diffractive transmission spheres. Diffractive transmission spheres offer high accuracy of the generated wavefront, low weight, and new alignment possibilities with the help of flexible auxiliary structures. They are fabricated in a grayscale technique that provides high-efficiency blazed structures. Prototypes are shown and measurement results are given.

Diffractive optical technology is rapidly becoming an indispensable tool for the creation of high-efficiency optical beam-shaping devices within a wide range of industrial and research activities. The high damage thresholds of typical materials used in diffractive optical element fabrication make them highly suited for deployment in high-power laser systems. We present two high-power applications of diffractive optical elements designed using an ultrahigh fidelity, ultrahigh efficiency design technique and demonstrate the advantages, in terms of optical alignment, that can be achieved by combining the diffractive structures with a multilevel diffractive lens.

We present a comparison of some of the most used iterative Fourier transform algorithms (IFTA) for the design of continuous and multilevel diffractive optical elements (DOE). Our aim is to provide optical engineers with advice for choosing the most suited algorithm with respect to the task. We tackle mainly the beam-shaping and the beam-splitting problems, where the desired light distributions are almost binary. We compare four recent algorithms, together with the historical error-reduction and input-output methods. We conclude that three of these algorithms are interesting for continuous-phase kinoforms, and two, namely the three-step method proposed by Wyrowski and the over-compensation of Prongué, still perform well with multilevel- and binary-phase DOE.

The quadratic phase function is fundamental in describing and computing wave-propagation-related phenomena under the Fresnel approximation; it is also frequently used in many signal processing algorithms. This function has interesting properties and Fourier transform relations. For example, the Fourier transform of the sampled chirp is also a sampled chirp for some sampling rates. These properties are essential in interpreting the aliasing and its effects as a consequence of sampling of the quadratic phase function, and lead to interesting and efficient algorithms to simulate Fresnel diffraction. For example, it is possible to construct discrete Fourier transform (DFT)-based algorithms to compute exact continuous Fresnel diffraction patterns of continuous, not necessarily bandlimited, periodic masks at some specific distances.

The Talbot effect is one of the most basic optical phenomena that has received extensive investigations both because its new results provide us more understanding of the fundamental Fresnel diffraction and also because of its wide applications. We summarize our recent results on this subject. Symmetry of the Talbot effect, which was reported in Optics Communications in 1995, is now realized as the key to reveal other rules for explanation of the Talbot effect for array illumination. The regularly rearranged-neighboring-phase-differences (RRNPD) rule, a completely new set of analytic phase equations (Applied Optics, 1999), and the prime-number decomposing rule (Applied Optics, 2001) are the newly obtained results that reflect the symmetry of the Talbot effect in essence. We also reported our results on the applications of the Talbot effect. Talbot phase codes are the orthogonal codes that can be used for phase coding of holographic storage. A new optical scanner based on the phase codes for Talbot array illumination has unique advantages. Furthermore, a novel two-layered multifunctional computer-generated hologram based on the fractional Talbot effect was proposed and implemented (Optics Letters, 2003). We believe that these new results should bring us more new understanding of the Talbot effect and help us to design novel optical devices that should benefit practical applications.

The phase mask is a diffractive optical element that is widely used for fabricating the fiber Bragg gratings (FBGs) for telecom and sensing applications. We analyze the near field diffraction of the phase mask with periodic phase-shift errors, e.g., stitching errors. Our analysis shows that the stitching errors generate sidelobe peaks beside the main diffraction orders of the phase mask. Experiments in the far-field diffraction prove the analysis results, so that we can estimate the e-beam writing field size by the far-field diffraction. We obtain the diffraction near field distribution using the Talbot formula, which explains, for the first time at our best knowledge, how the stitching errors are transferred into the FBG with the same periodicity during the side-writing process. We find out that the noise energy in the near field varies with the phase mask to fiber spacing. An optimal spacing can be found and used in order to reduce the stitching error related sidelobes in the FBG spectrum.

A wafer scale UV replication process is described that is suitable for mass production of micro-optical components. The fabrication process is divided into two phases. In phase 1, the design and mastering is done and a wafer-sized embossing tool is fabricated. In phase 2 of the process chain, the batch fabrication process is performed. From a single embossing tool, several identical wafer-sized replicas are fabricated that are then diced into the final components. Single-sided as well as double-sided replicas can be made. The economical flexibility of the UV replication chain is demonstrated through two application examples: High-quality components that pass strict environmental tests, which compete with etched silica structures, and low-cost micro-optical components, which compete with microinjection molded parts. All UV-replicated components have in common that they exhibit excellent optical quality and pass an IR reflow process.

We report on the design fabrication and characterization a 3-λperiod grating composed of subwavelength ridges of progressively varying widths for operation at 10.6 μm. The grating is blazed into the first transmitted order (an efficiency of 80% is measured) under TM polarization and over a broad range of angles of incidence. The fabrication involves contact photolithography, reactive-ion etching, and an evaporation deposition over the etched structure. The result validates the use of photolithography, a low-cost technology, for the manufacture of efficient blazed binary diffractive elements for thermal imaging (the 8- to 12-μm IR band).

A simple reflow technique and reactive-ion etching are employed to fabricate and integrate a refractive square-apertured arch Si microlens array (MLA) on the back of an IR focal plane array device (IRFPA), resulting in the formation of a monolithic MLA/IRFPA device. The fabricated on-chip Si MLA behaves as optical concentrators and is used to collect most of the incident light from each pixel area on a smaller photosensitive area of the IRFPA, causing the IR response characteristics of the monolithic device to be improved greatly when compared with an ordinary IRFPA device without the MLA. The advantages of employing the reflow technique and the reactive-ion etching lie not only in the excellent surface smoothness and dimensional uniformity of the fabricated MLA, but also as a cost-effective and mass production technology.

A profile formation and control approach has been developed for manufacturing micro-optical elements with continuous profile and deep relief depth. Based on Dill's exposure model, an effective expression for determining the exposure dose function is established by using a supposition of equivalent exposure threshold inside a resist layer. An analytical simplified formula is further deduced by taking absorbance as constant B, and the approximate condition is discussed. For evaluating the simplified formula, the profile error was calculated and analyzed by simulation. With the exposure dose function, the binary mask for manipulating the light distribution by means of a moving-mask lithographic method can be designed. Experimental results are given and show the comparative performance to the required profile and relief depth. A series of refractive microlens arrays with aspherical profiles, a wide range of numerical apertures (0.005 to 0.6), and high fill factors were accomplished in the lab and may be applied to many systems.

Volume phase holographic gratings (VPHGs) possess unique properties that make them attractive for numerous applications. After reviewing major VPHG characteristics through theory, we discuss some aspects of the dichromated gelatin recording material and the holographic recording process. The large-scale VPHG research facility set up at the Center Spatial de Liège enables production of VPHGs up to 380 mm in diameter, with fringe frequencies from 315 to 3300 lp/mm. We describe the work that has been undertaken in our laboratory to remove the last limitations inherent in VPHGs.

An original optical design for two-step recording of holographic diffraction gratings is presented. It combines the merits of the two previously developed methods. On the one hand, due to the two-step recording one can use wide possibilities for the aberrations compensation. On the other hand, one can record both the grating objective and the final grating in spatially incoherent light. This simplifies the technology of the holographic recording. Previously, one must use spatially coherent light for at least one of two recording steps. Our method does not require the use of additional optics. Both surfaces of the grating objective blank have a spherical form. The blank of the final grating can be plane concave, which is usual for diffraction gratings. Since the blaze angle of the grating recorded in the counterpropagating beams is determined by the recording geometry, and the efficiency of the grating depends on the polarization of the incident light, the transmission calculations taking into consideration the polarization are also provided. The transmission of the system is optimal for the s-polarized light, additional increasing of the transmission can be achieved by use of an immersion grating objective.

An attempt is made to use the phenomenon of three-order light diffraction with direct transitions between all the optical modes in uniaxial single crystals for the implementation of all-optical logic-based devices. The exact and closed analytical model for describing this strongly nonlinear phenomenon is exploited to consider the feasibility of applying such an effect to perform all-optical switching. An opportunity for designing two versions of the key components for all-optical J-K flip-flops and the possibility of arranging a 3-bit digital register are revealed and algorithmically estimated.

Simple resonant structures that permit holographic reflection filtering are studied. The filters under study work under a 45-deg incidence for a wavelength of λ=632.8 nm, a condition useful for future inclusion in substrate mode systems. First, the influence of the structural parameters of the grating and the waveguide on the position and the shape of the resonance peaks are studied by numerical computation. The numerical results, obtained within the rigorous coupled wave theory, are compared with the measured response of some filters. These filters contain a grating recorded by holography deposited on the substrate. In the case of the bilayer filter, a waveguide is introduced between the grating and the substrate. Second, the numerical results are used for the conception of an active substrate mode spectral filter built from electro-optic zinc oxide.

The use of diffractive optical elements (DOEs) is increasing for several industrial applications, such as beam shaping and optical filtering. Most elements modulate the phase of the incoming light or its amplitude, but not both. To overcome this limitation, we developed a full complex-amplitude modulation DOE. We employed well-established integrated circuit fabrication steps to fabricate the devices at relatively low cost and with high precision. Using this approach, the new element's optical performances are improved even for near-field operations. With this device it is possible to obtain the total control of the zeroth order transmitted light, resulting in low-noise reconstructed images.

We analyze the behavior of complex information in the Fresnel domain, taking into account the limited capability to display complex values of liquid crystal devices when they are used as holographic displays. To do this analysis we study the reconstruction of Fresnel holograms at several distances using the different parts of the complex distribution. We also use the information adjusted with a method that combines two configurations of the devices in an adding architecture. The results of the error analysis show different behavior for the reconstructions when using the different methods. Simulated and experimental results are presented.

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To fabricate a diffractive optical element (DOE) with optimum surface profile, we characterize the relation between the developed height profile on the photoresist and the optical density (OD) value of a high-energy-beam-sensitive (HEBS) gray-scale photomask with high-resolution gray steps. The lithography characteristics of a gray step less than 10 μm are inspected in detail. The gray patterns with various gray-step widths are fabricated for the investigation of the relation between the OD values and the height profiles on the specific photoresist. We demonstrate the dependence of the photoresist height profiles on the width of the gray step, and this dependence agrees well with the simulation results from our model. We provide a proper method to design the OD value of a gray-scale photomask for the fabrication of DOEs with precise surface profiles.

A new method for calculating the transmittance function of a multilevel diffractive optical element is described. Multiple internal reflections in the diffractive optical element induce phase and amplitude modulation errors that deviate from the conventional transmittance function model. A transmittance function model of a multilevel diffractive optical element is devised, taking these multiple internal reflections into account. The results show that a surface relief profile of a multilevel diffractive optical element without phase modulation errors can be constructed based on the proposed model.

We report the early stage development of an intrinsic fiber optic sensor to detect the presence of nerve agent sarin simulant dimethyl methylphosphonate (DMMP). The sensor design is based on the modified cladding or coating approach. Conducting polymer polypyrrole is the chemo-optic transducer, i.e., is used as a modified cladding material. Sensitivity to approximately 134 ppm of DMMP is demonstrated in the developed sensor, with a sensor response of 20 mV and a response time of 2 sec. Morphology characterization of the polypyrrole is performed by scanning electron microscopy. Selectivity study of the developed sensor is presented by exposing the sensing element to other gases like acetone and ammonia. Influence of temperature and humidity on the developed sensor is investigated, along with ambient aging of polypyrrole films.

Intensity scintillation variances and intensity probability density functions (PDFs) were experimentally measured for broadband (2 nm), 980-nm laser light reflected by two or more corner cube retroreflectors as a function of retroreflector lateral spacing over a short (75 m) atmospheric optical path. The PDFs transitioned from broad double-peaked beta-shaped densities to lognormal as the retroreflector spacing was increased to exceed the optical field's lateral coherence length. Specific spacing for a given average atmospheric structural C_n² eliminated interference between the light beams returned by the retroreflectors.

The visual performance of liquid crystal displays (LCDs) has usually been evaluated by visual inspection during the manufacturing process. One of the visual problems hardest to recognize are regions of low contrast and nonuniform brightness called mura. The accurate and consistent detection of the mura is extremely difficult because there are various shapes and sizes of mura and the inspection results tend to depend on the operators. We conducted a study on the quantitative evaluation of mura based on visual analysis, intending to clarify the detection method and create an automated mura inspection process. We developed an algorithm and a hardware system based on a commercially available charge-coupled-device camera and a personal computer system with an image processor board. This system can successfully identify and evaluate mura. The algorithm was developed from research on visual analysis and human perception. We converted the front-of-screen images from the LCDs into distributions of luminance information, and the mura regions were distinguished from the background area using our novel algorithm. Our identification method can also distinguish between the muras caused by flaws in the LCD cells and the intentionally designed nonuniform luminance distribution of the backlight.

We numerically analyze and compare the mode and dispersion properties of three different microstructured optical fibers with the same square array of different-shaped air holes: rhombic, square, and circular. We use a full vectorial finite-difference method. The analysis shows that the properties of microstructured optical fibers depend on the hole area, hole shape, and wavelength to different extents. The effects of air hole shapes on the properties of microstructured optical fibers can be treated as the perturbations for sufficiently small air filling factors. For larger air filling factors the properties of microstructured optical fibers are clearly affected by the air hole shape. This dependence is useful for understanding the properties of microstructured optical fibers.

We present a new rate-constrained [rate and distortion (R-D)] motion estimation algorithm using Kalman filter to enhance the performance of the conventional R-D motion estimation at a relative low computational cost. We try to amend the incorrect and/or inaccurate estimate of motion with higher precision by using a Kalman filter. We first obtain a measurement of the motion vector of a block by using the existing R-D motion estimation scheme. We then generate the predicted motion vector utilizing the interblock correlation in neighboring blocks. Based on these two motion information, a simple 1-D Kalman filter is applied to obtain the optimal estimate of the motion vector. Simulation results show that the proposed technique can efficiently improve the R-D motion estimation performance.

We demonstrate a simple technique for determining numerical values of carrier lifetimes and linewidth enhancement factors in a semiconductor optical amplifier (SOA) for various SOA input optical powers. For this purpose we use SOA self-gain modulations and the conversion of frequency modulation to intensity modulation.

A hybrid wavelength-division-multiplexing transport system based on 1.3-μm optical transmitters and praseodymium-doped fiber amplifiers is proposed and demonstrated. It uses one wavelength for AM vestigial-sideband CATV, one wavelength for 256-QAM digital passband, and one wavelength for OC-48 digital baseband signals. Good performance with respect to composite second order and composite triple beat has been obtained at an acceptable carrier-to-noise ratio for CATV; and a low bit error rate has been achieved for 256-QAM and OC-48 digital signals over a 70-km single-mode fiber transport.

This article discusses a digital filtering technique to improve the temperature resolution of a Raman fiber optic distributed temperature sensor. A frequency-domain digital filtering algorithm has been used for this typically time-domain task to show that by reducing the effect of noise introduced by analog electronics and the quantization noise of the analog-to-digital converter in the detection and data acquisition stages, superior temperature resolution is achievable. An important feature of the filtering scheme used is that no spatial inaccuracy is introduced into the ranging of hot zones, despite the highly nonlinear phase response of the filter. Digital filtering used for postprocessing of data shows clearly and unambiguously a temperature resolution of 5 K in the present setting of our experiment, with the possibility of much greater improvement. Merely using analog signal conditioning does not provide the same clarity and uniqueness in temperature resolution and spatial location that digital filtering offers. This digital filtering scheme offers greater flexibility and versatility than mere signal-averaging approaches to improve the SNR of such systems. The filter's ability to reject deterministic interfering frequencies of appreciable energy content is also demonstrated by simulating such frequencies of much greater energy than the actual signal.

The space thermal environment is one of the important factors that affect the image quality of a space optical remote sensor (SORS), so discussing the relationship between image quality and the temperature field of a SORS is necessary for thermal control to improve image quality. In this paper, a new thermo-optical analysis method is proposed for the optostructural system of a SORS. Thermal-elastic distortions of all components of an optostructural system, resulting from temperature field changes, cause dimensional instability of the system. This instability is described in terms of changes of position (translations along and rotations around coordinate axes), equation parameters, and roughness of optical surfaces. Then, the theory of homogeneous coordinate transformations and linear fitting of revolving conicoid surfaces are applied to processing of data from finite-element analysis to obtain all the thermally induced dimensional instabilities. Finally, these instabilities were incorporated in optical models (e.g., Zemax) to calculate the thermally induced degradation of image quality (modulation transfer function, wavefront error, etc.). The results of thermo-optical tests suggest that this method is effective.

Measurement of micro structures is a key issue in microtechnology, and it will influence the production efficiency and quality of large-scale integrated circuits. An experimental study on the factors affecting the accuracy of measurement of micro structures has been carried out with a laboratory-built DXY-1 type linewidth measuring system. The experiment results show that the repeatability of the system is better than ±0.005 μm, and the difference between the nominal and measured values is less than ±0.02 μm.

An interferometric range finder that uses both phase-locked and modulation-amplitude-locked techniques in a sinusoidal phase-modulating interference signal is described. It allows us to perform unambiguous and real-time distance measurement. Also, external disturbance superimposed on the interference signal is eliminated by the feedback control. Our preliminary experiments indicate a measurement error of 17.7 μm rms.

The scattering of light from cylindrical surfaces is studied using Kirchhoff's scalar theory. The angular distribution of the mean scattered intensity is obtained as a function of the characteristic statistical parameters of the heights and this expression is used to characterize cylindrical rough surfaces by measuring the quotient T/σ; between the correlation length (T) and the roughness (σ) of the surface. It is shown that the scanning process inherent to usual detection systems can be replaced by single-step detection by using a screen and a CCD camera. This method can be applied to on-line wire surface testing where conventional procedures are inadequate.

Measurement of the roughness of solid surfaces by digital speckle correlation of video signals is reported. Speckle patterns appearing in the diffraction field of a laser-illuminated sample are taken by a CCD before and after the change of the incident angle or the laser wavelength, and their cross-correlation is calculated from which surface roughness can be evaluated. The theoretical cross-correlation function is first derived that describes speckle displacement and decorrelation. Its peak height is then provided as a function of the change of the incident angle or the wavelength. The decorrelation curve against speckle displacement is shown to depend on the surface roughness. The derived analytical relationships were verified by numerical simulations that used two-dimensional arrays of random numbers with various maximum values representing the maximum surface roughness. The relationship between the normal correlation calculated by the theory and the phase-only correlation adopted in the experiment was also evaluated by the simulation. In experiments various roughness standards for metal were measured by using a quick processor employing the phase-only correlation algorithm. The results were compared with those obtained from a mechanical stylus, and good agreement was observed between them for root-mean-square roughnesses between several micrometers and several tens of micrometers.

The intracavity photon density and the initial population-inversion density are assumed to be Gaussian spatial distributions in the rate equations of a laser diode end-pumped passively Q-switched Nd:YVO₄ laser with Cr⁴⁺:YAG saturable absorber. These space-dependent rate equations are solved numerically. In an experiment, such a laser has been realized. The dependences of pulse width, pulse repetition rate, single-pulse energy, and peak power on incident pump power were measured, and the experimental results are consistent with the numerical solutions.

2-D optical phased array antennas formed by a liquid crystal on silicon (LCOS) spatial light modulator are described for free-space laser communication and high-resolution wavefront control. The device consists of an 2-D array of 1024×768 phase modulator elements, each with controlled voltage, and can induce a phase shift from 0 to 2π for wavelengths up to the near IR. When the device is used as a wavefront corrector, 18.7 waves peak-valley (at 632.8 nm) of aberration in the optical system is corrected to a residual of 1/9 wave peak-valley, or 1/30 wave rms. The Strehl ratio improved from 0.006 to 0.83 after correction. An additional linear phase ramp was added to the correction phase ramp to simultaneously correct and steer the laser beam. Continuous steering over ±4 mrad in the X-Y plane with a steering accuracy higher than 10 µrad has been obtained. The 1-D beam-steering efficiency is 80% at the maximum steering angle of 4 mrad. These results suggest that an LCOS device can be used to achieve very high-resolution wavefront control at very high efficiency.

The proposed method uses the environment of a correlator to control the phase and amplitude modulation properties of its filter's spatial light modulator. The filter's operating curve is obtained by means of calculations that use the reconstructed Fourier transform of the correlation plane. This characterization allows one to select a good adjustment for the filter's brightness and contrast values as well as finding appropriate values for a better coding.

When a continuously deforming object is measured by electronic speckle pattern interferometry (ESPI), the speckle pattern recorded on a camera sensor changes constantly. These time-dependent speckle patterns would provide the deformation history of the object. Various objects are applied with both linearly and nonlinearly varying loads and speckle patterns are captured using a high-speed CCD camera. The temporal intensity variation of each pixel on the recorded images is analyzed by a robust mathematical tool—Morlet wavelet transform instead of conventional Fourier transform. The transient velocity and displacement of each point can be retrieved without the necessity of the temporal or spatial phase unwrapping process. The displacements obtained are compared with those from a temporal Fourier transform, and the results show that the wavelet transform minimizes the influence of noise and provides better results for a linearly varying load. System error in the wavelet analysis for nonlinear load is also discussed.

Stereo correspondence can be formulated as an optimization problem. In this formulation, however, most of the existing solutions adopt gradient-based approaches, whose performance is dependent on the initialization. This paper presents a genetic-algorithm-based solution that is not gradient-based and thus should have less sensitivity toward the quality of the initialization. A specific coding design is employed that represents each solution candidate for the three-dimensional description of the imaged scene as an individual that embraces numerous chromosomes. Through a set of specially designed genetic operators, a population of such individuals is allowed to evolve to reach a globally optimal or near-optimal solution. Our solution scheme also includes a coarse-to-fine search strategy to reduce the matching ambiguity and the computations needed. Experimental results on synthetic and real images illustrate the performance of the approach.

Star acquisition is one of the most time-consuming routines in star-tracker operation. In the star image, a star point spread function (PSF) represents a near-Gaussian distribution. The star extraction consists in finding the highest-intensity pixel among the PSFs, collecting the adjacent pixels, and then calculating the star centroids in the star image plane. The candidate highest-intensity pixels are the maximum extremum points of the underlying intensity function of a digital star image. To extract star from the star image, the cubic facet model is applied to fit the underlying intensity surface in star acquisition procedure. A new extraction approach, using surface-fitting methods to approximate locally the image intensity function, and then using the partial derivatives of the fitted surface to make decisions regarding the maximum extremum points, is proposed. A number of experiments are carried out on simulated star images. The experimental results demonstrate that the proposed method is efficient and robust.

The Johnson criteria have been shown to be fundamentally flawed due to their insensitivity to effects below the limiting frequency. This flaw makes predictions for many modern imaging systems inaccurate. A new target acquisition metric, the targeting task performance (TTP) metric, has been developed that provides better accuracy than the Johnson criteria. Further, unlike the Johnson criteria, the TTP metric can be applied directly to sampled imagers and to imagers that exhibit colored (spectrally weighted) noise due to frequency boost. Experimental data using both target recognition and target identification tasks show the problems with the Johnson criteria and illustrate the robust performance of the TTP metric. The simplicity of implementing a range performance model with the Johnson criteria is retained by the TTP metric while extending applicability of the model to sampled imagers and digital image enhancement.