We present a general 3-D spectral collocation method for the analysis of diffractive optical elements (DOEs). The method computes a direct solution to the Maxwell's equations in the time domain. The computational domain is decomposed into a number of small subdomains in which a high-order Chebyshev spectral collocation scheme is used to approximate the spatial derivates in Maxwell's equations. The local solutions in each subdomain are integrated using a Runge-Kutta scheme, and the global solution is reconstructed by using the characteristic variables of the strongly hyperbolic set of equations. A smooth mapping technique is used to correctly model curvi- linear boundaries thus making the method a strong tool for analyzing, e.g., grating couplers with analog surface reliefs. The accuracy and efficiency of the method is verified using simple test cases and examples of the analysis of analog grating couplers of finite length are given. The examples demonstrate the superior properties of the method such as the low number of points per wavelength needed to accurately resolve wave propagation and the absence of numerical dispersion.

Diffractive optical elements comprising sub-wavelength aperiodic surface reliefs of finite length require the use of rigorous solvers for Maxwell's equations. We present a detailed analysis of Focusing Grating Couplers (FGC's) using a recently introduced 2D spectral collocation method. The method, solving Maxwell's equations in the time domain, is based on a high-order Chebyshev collocation scheme has the advantage over traditionally used Finite Difference methods that much fewer points per wavelength is needed to accurately resolve wave propagation in diffracting structures. At the same time, the new method exhibits no numerical dispersion in contrast to, e.g., the Finite Difference Time-Domain method. In this presentation we analyze a number of sub-wavelength FGC's with lengths of up to 1000 wavelengths. The FGC's use analog surface reliefs due to their superior diffraction properties. For structures yielding a perpendicular out- coupling, we find that typically 10 - 12 collocation points per wavelength is sufficient. We find that the focal length depends strongly upon the depth of the surface relief, e.g. that a significant shift of the focal plane from the value expected from geometrical optics is seen if deep surface reliefs are used.

This paper presents the concept and feasibility demonstration of an improvement of the LCD projector optics. An innovative concept of integration of an holographic filter in the optical head allows for laser pointer tracking. The filter retrieves the positioning information of the pointer on a PSD (Position Sensitive Device). The detector is interfaced with the LCD matrix in order to project a pattern on the screen. Several software options can be implemented for remote control of the slide show. We present the holographic geometry optimization, the experimental recording, and results.

Joint transform correlation systems are proposed for detecting defects in optical fibers. When joint transform spectrum of the reference and the signal fibers is sampled, off focus operation has been adopted. The corresponding influence on detection results is discussed in theoretical analysis, computer simulation and experimental comparison. In addition, a correlation processor is demonstrated, in which after the light from a He-Ne laser being expanded and filtered via a spatial light filter, it passes a Fourier transform lens without being collimated. This processor is actually an equivalent of joint transform correlator with long focal length Fourier transform lens. The experiment results of detecting defects in fibers are also given, which indicate that joint transform correlation systems can be used for automatic fiber defects detection.

The control of optical wavefronts can be accomplished in many ways and a wide array of static optical components have been developed to address this task. However, for many applications, the use of static optics limits the usefulness of the system. With the recent development of advanced micromachining methods, a new degree of flexibility has been introduced. The application of Micro-Electro-Mechanical Systems (MEMS) technologies to the field of optics has opened new doors for reconfigurable surfaces which can control the reflection, transmission or diffraction of light. This paper will present one such class of devices based on the patented MEMS Compound Grating (MCG) in which a mechanical structure is created that can alter the diffractive behavior of the device through the active reconfigurration of the surface. The rulings of the MCG consist of doubly constrained beams with a custom electrode structure for controlled electrostatic adjustment. Using this ability to actively influence the diffraction of incoming light, increased information can be extracted without the addition of extra optical components. For example, this unique feature can resolve the order- wavelength uncertainty in as spectral instrument thus removing the limitation of free spectral range typical of spectrometers based on conventional diffraction gratings. This ability has implications for a wide variety of optically based sensor systems. The current status of the MCG development will be presented including materials and performance issues and initial integration into both commercial and custom, prototype spectrometers.

The principle of optical scanning holography with circular gratings (CG) as the scanning field is presented. The generation and reconstruction processes of the scanning holography are described. These processes are numerical simulated by computer and the results are achieved. It is shown that the resolution power of the reconstructed image of CG scanning hologram is higher than that of FZP scanning hologram.

The concept of irregular virtual phased-array overcomes some fundamental and practical obstacles in developing an optical phased-array with large scanning angle. In the irregular phased-array, array elements assume random positions; thus, an irregular phased-array can always produce only one beam, with no extra grating lobe, regardless the (average) center-to- center spacing between elements. Therefore, large size phase- modulator and large spacing can be used, which enhances the performance and simplify the structure of the phase-array. A virtual array is generated by an array of lenses that is coupled with an array of the phase-modulators such that the virtual array become the effective representation of the phased-array, and the physical size, shape and positions of the phase-modulators and lenses are no longer directly relevant. Thereby, the array of the phase-modulators and the array of the lenses can all be regular array, and only the virtual array needs to be an irregular array, which makes the structure of an irregular phased-array very simple. An irregular sub-array technique is also applied for further simplification. Computer simulation results are reported to illustrate some characteristics of the irregular phased-array.

Lasers are widely used in industrial fabrication for engraving, cutting and many other purposes. However, material processing at very small scales is still a matter of concern. Advances in diffractive optics could provide for laser systems that could be used for engraving or cutting of micro-scale patterns at high speeds. In our paper we focus on the design of diffractive elements which can be used for this special application. It is a common desire in material processing to apply 'discrete' as well as 'continuous' beam patterns. Especially, the latter case is difficult to handle as typical micro-scale patterns are characterized by bad band-limitation properties, and as speckles can easily occur in beam patterns. It is shown in this paper that a standard iterative design method usually fails to obtain diffractive elements that generate diffraction patterns with acceptable quality. Insights gained from an analysis of the design problems are used to optimize the iterative design method. We demonstrate applicability and success of our approach by the design of diffractive phase elements that generate a discrete and a continuous 'Y2K' pattern.

Holographic gunsight was first conceived in the 1970s and prototypes were fabricated using a He-Ne laser as the illuminating source. The laser source was too costly and fragile and these prototype units were too bulky to be viable as a commercial product. With the advent of low cost laser diodes, EOTech introduced into the commercial market a compact holographic gunsight for small arms in 1996 which has since become one of the most popular gunsight in the U.S. and in Europe. In this paper, the design of the second generation holographic gunsight is described. The optical path travels predominantly in the vertical direction which reduces the length and the weight of the sight by a third. The optical design challenges include the generation of a stable holographic image with changes in the laser emission wavelength, circularization of the laser elliptical beam profile, and the production of high quality optics at low cost. The opto-mechanical design challenges include very fine angular adjustments, stability over large temperature range and the ability to withstand the recoil of powerful handguns.

We demonstrate the design and performance of an array-type diffractive element, which is capable of modifying the beam of a matrix-type vertical-cavity-surface-emitting-laser (VCSEL). The diffractive element was designed for line-of-sight or non- line-of-sight multi-beam transmitter with a maximum illuminating angle of 50 degrees. To demonstrate wide-angle illumination, a single element providing the largest 50-degree illumination angle was designed and fabricated. The element was designed in the paraxial domain by the geometrical map- transformation method. Beam deflection to the desired angle was performed by Lohmann's detour-phase principle. The local diffraction efficiency of the binary element was analyzed by rigorous electromagnetic diffraction theory. The element was fabricated as a pixel-array, in which the pixel size was 200 nm X 200 nm and the size of the element was 250 micrometer X 250 micrometer. The performance of the element was characterized by measuring the irradiance at the observation plane by a CCD-camera, and by measuring the diffraction efficiencies of three diffraction orders with a separate detector. The measured diffraction efficiency and the irradiance distribution of the element for the -1st order was 27.5%, which was in fair agreement with the calculated 23.9% efficiency after taking the real properties of the VCSEL beam into consideration.

Previously, we have reported the first demonstration of holographic two-photon induced photopolymerization (H-TPIP) in the construction of transmission holograms. This technique relies on the coupling of a two-photon absorbing chromophore and a photocurable optical resin. Several different systems have been successfully explored; all involving varied reaction pathways. Since the initial report, we have also expanded this technique to reflection holograms and some bulk structures. While the applications for this process are widely ranging, the underlying physical mechanisms still require a great deal of investigation. In this work, we report on some of the photo-physical mechanisms involved in the H-TPIP technique. Specifically, we will report on evidence for mass-transport phenomena, and the role of localized thermal loading. We also discuss a preliminary model, which examines the coupling between the chromophore's excited state population, initiation of the polymerization reaction, and localized thermal deposition.

Planar integration of various optical systems appears for some years as a way to reduce alignment problem and to build small size, robust and monolithic devices. An original planar integrated interferometric sensor is presented in this paper. It is based on the separation and control of polarization states in a substrate mode holographic system in order to obtain the optical path difference between two scanning spots. A unique planar system is used for projection of the spot and for recombination of probe beam reflected on the tested surface. The monolithicity and the differential nature of the element lead to a very good insensitivity to external vibrations. The sensor is a multilayered structure composed of a reflective polarizing holographic element sandwiched between two planar substrates. Probe beams are coupled in and out of the system by diffraction on a reflective Substrate Mode Hologram that constitutes a fourth layer. These two types of holographic elements are recorded in high index modulation photopolymer: Omnidex^TM HFR-600 from DuPont. Design, realization and application are demonstrated and discussed.

We present a modified simulated annealing algorithm for the design of diffractive optical elements whose basic cell is constrained by a symmetry similar to that of the reconstruction field. Compared with the conventional SA algorithm, our approach permits better designs with reduced computational efforts.

Planar optical systems provide an efficient way to integrate multiple optical components into a compact optical substrate. Both lithographically formed surface relief gratings and holographically formed volume gratings have been used to implement diffractive optical elements in planar optic systems. These systems and sub-assemblies are useful for local distribution of optical signals in optical interconnect and other information processing applications. However when signals are propagated over distance greater than 5 - 10 cm alignment, beam diffraction effects, and substrate uniformity become major issues that limit signal fidelity. One approach to solving this problem is to combine free-space planar optic local distribution systems with fiber optic waveguides for long distance signal transfer. This extension provides a framework for integrating data communication and network environments to realize new forms of distributed information processing architectures. Additional signal capacity and effective data transfer rates can be obtained by incorporating wavelength multiplexing and de-multiplexing techniques in the interconnect system. However, diffractive type planar optical elements typically require high spatial frequency gratings that are sensitive to the polarization state of the incident optical beam. This property can have significant impact on the bit error rate of signals transmitted through hybrid fiber/planar optical distribution systems. In this paper we compare the polarization properties of surface relief and volume gratings for planar optic wavelength demultiplexing operations.

A signal analyzer is being developed that is based on a periodically tapped optical fiber. The spatial distribution of taps produces a waveform that is weighted by a spatial light modulator (SLM), optically Fourier transformed, and then detected with a video camera to continually display the power spectrum of the signal propagating in the fiber. The analyzer resolution and bandwidth is dependent on the distribution and number of taps. Taps have been formed in the core of fibers using UV light. Both single step beamsplitter and localized phase grating taps have been generated. Bragg grating taps tilted at 45 degrees with respect to the fiber axis were generated in order to diffract light directly out of the side of the fiber.

In this paper we present a study on the performance of diffractive lenses as a function of their f/#. To this end, we study two- and three-dimensional lenses that consist of binary, four-, eight-, and sixteen-level diffractive profiles over a range of f/#s. Lens performance is characterized in terms of diffraction efficiency for lenses of different number of levels and f/#.

During some last years an interest has grown in usage of membrane elastic primary mirrors in both beam-projecting and imaging telescopes comprising a nonlinear-optical correction system. Theoretical and experimental studies of these mirrors based on a plane membrane uniform in thickness, at pressure applied along the normal to its surface and tension applied at its edges, have shown that aberrations of such a mirror (with aperture approximately 3 m and relative aperture approximately 1:2) are in the visible wavelength range too large to be compensated with the use of the existent correction systems. In this paper it is proposed for improvement of optical quality of the mirror surface to employ either a plane- membrane mirror variable in thickness or a mirror based on an initial-surface-profile membrane. The presented numerical results of calculation of both the mirror shape and the range of aberration parameters for these mirrors show that aberrations available prove to be lower in magnitude than those of the required level.

A compact electrically-addressable spatial light phase modulator module is described. The module consists of an electrically-addressed liquid crystal display (LCD), an optically-addressed phase-only spatial light modulator (SLM), one of which substrates is a fiber optic plate (FOP), a laser diode, and collimating optics for it. The module size is 95 mm long, 55 mm wide, and 90 mm high. The module had a nearly 100% reflectivity and a diffraction efficiency close to the theoretical maximum. Surplus diffraction light caused by the pixelized structure was reduced to approximately 3%, almost 50% of which was in the LCD alone. A reflection type of SLM would cause another power loss of the readout light by a half mirror, which was set up so as to separate the incident and reflected lights. An oblique incidence readout method was evaluated in the module, instead of the half mirror scheme, for the readout. We have found adequate alignments among the polarization and incident directions of the readout light, and the corresponding liquid crystal orientation. Consequently, almost no degradation in diffraction efficiency was observed for the incident angle within 45 degrees.

Optically-addressed liquid crystal spatial light modulator has been investigated, in which a polyimide photosensitive layer has been simultaneously sensitized with dye and fullerenes. Dynamic modulator characteristics have been measured by the second harmonic (532 nm) of a pulsed Nd-laser under the Raman- Nath diffraction conditions. The ways of enhancing sensitivity (from 10^-6 to 2 (DOT) 10^-7 J(DOT)cm^-2) have been found. The fulfillment of the Forster resonant conditions allowed the Forster model to be applied for the results interpretation. The comparative data have been presented for modulators with both impurity free and dye- and fullerene-doped polyimides.

The importance of spatial light modulators (SLMs) in optical systems is increasing. This paper presents our work on an SLM system based on Sony LCD. We show the optimization of the LCD modulation behavior concerning the application as dynamical diffractive element, and the implementation of images and filter functions in optical correlators and pattern projection systems. Measurements of the coupled amplitude and phase modulation and the planarity of the display at different wavelengths lead to correction functions and several optimized operation modes, e.g. gray scale or binary amplitude modulation. The optimization in the amplitude mode leads either to high contrast images of reduced gray levels or to a mostly linearized full gray scale mode. A similar way leads to optimized modes for the phase modulation and to a realization of a total phase shift of 2(pi) . The increase of the processing performance of phase-only filters in optical correlators is presented. Furthermore, diffraction efficiency (DE) measurements of Fourier holograms addressed to the SLM prove the optimization process, compared to the non-optimized and the theoretical DE-values. So, estimations can be made concerning the application of the SLM as dynamical diffractive element.

We have incorporated membrane mirror technology over a discrete array of pixel wells to create both high-efficiency optical shutters and spatial light modulators (SLM). A continuous metalized-membrane mirror with greater than 98% reflectivity minimizes optical insertion loss. This mirror is electrostatically deformed into the wells with either a common electrode (shutter) or pixilated electrodes (SLM). By using a spatial filter, analog intensity optical modulation is realized. Both 1-D (linear) and 2-D grating pixel patterns have been investigated. With the appropriate pixel dimensions, both coherent monochromatic and broadband incoherent light within the 0.25 to 10.6 micron range can be modulated with contrast ratios up to 1000:1. Small well sizes (approximately 10-micron diameter) allow for modulation speeds up to 1 MHz. The theoretical foundations for the well layout, the membrane mirror deformation and its diffraction properties, and the design trade-offs are detailed. We have applied our membrane mirror technology to CMOS VLSI circuits creating a high-speed, high-efficiency spatial light modulator capable of 80 X 64 resolution and scalable to HDTV standards. The membrane mirror SLM provides either amplitude or phase modulation. In the phase modulation mode, at least two waves of stroke per discrete well are possible.

Reflection-mode optical phase modulators based on the structure of thin ferroelectric interferometers (TFIs) have been demonstrated. The tunable TFIs in a Gires-Tournois configuration were fabricated entirely with thin film processing techniques, resulting in solid-state and high-speed phase modulators with low driving voltage. Phase tunable spatial light modulators (SLMs) and laser beam steering devices can be constructed with variations of the basic TFI structure. Recent experimental data on the SLMs and beam steering devices are presented. Design principles, fabrication procedure and the preliminary performance of the devices are described.

We present here results of laboratory and field experiments using two novel active optic elements, a membrane mirror, and a dual frequency nematic liquid crystal. These devices have the advantage of low cost, low power consumption, and compact size. Possible applications of the devices are astronomical adaptive optics, laser beam control, laser cavity mode control, and real time holography.

We proposed a novel method to realize selective erasure of holographic index gratings in the photorefractive crystals. This scheme is based on the self-enhancement of the index gratings in the photorefractive materials. It is a save-erase- restore procedure, namely, save wanted information-erase unwanted information-restore wanted information. Simple experimental results are also presented. The requirement in this scheme is that the material has the effect of self- enhancement, i.e. the index grating is transmission grating, the product of the coupling constant and the thickness is above the threshold of the self-enhancement. But it eliminates the critical requirement of preventing vibration in the previous (pi) -phase-shift scheme.

Photorefractive crystals have many applications in holographic storage, optical communications, and nonlinear optical information processing. One problem is that the photorefractive holographic index gratings can be erased in the readout process. Several non-destructive approaches have been proposed and demonstrated in different photorefractive materials. Based on the initial research of domain fixing on KNSBN crystals, we studied the high order harmonic gratings during electrical domain fixing process in KNSBN crystals. In this paper, we mainly focus on the properties of the first order and second order harmonic index gratings of Mn-doped KNSBN crystal during electrical domain fixing process at room temperature. Domain fixing in Rh:SBN was also investigated, and the results in Mn:KNSBN and Rh:SBN were compared. In Mn:KNSBN crystals, the second order harmonic grating becomes stronger after fixing. This may be the main reason of the high noise in the revealed grating, which affects the image quality and fidelity. In addition, the effect of the accumulated charges in the revealing process was also discussed.

The properties of non-uniform volume hologram grating are analyzed in detail using the coupled Fabry-Perot etalons physical model of volume hologram. The diffraction spectra of non-uniform volume hologram are simulated with computer. A matrix method is introduced, which relies on the calculation of the reflected and the transmitted fields at an interface between two dielectric slabs of dissimilar refractive indexes. A kind of non-uniform refractive index distribution is used in simulation. Simulation results are in accordance with the analyzing results by the method of solving nonlinear differential equations and our previous experimental results.

In this paper, gratings to apply for the optical interconnection are designed using a genetic algorithm (GA) for a robust and efficient schema. The real-time optical interconnection system architecture is composed with LC-SLM, CCD array detector, IBM-PC, He-Ne laser, and Fourier transform lens. A pixelated binary phase grating is displayed on LC-SLM and could interconnect incoming beams to desired output spots freely by real-time. So as to adapt a GA for finding near globally-cost solutions, a chromosome is coded as a binary integer of length 32 X 32, the stochastic tournament method for decreasing the stochastic sampling error is performed, and a single-point crossover having 16 X 16 block size is used. The characteristics on the several parameters are analyzed in the desired grating design. Firstly, as the analysis of the effect on the probability of crossover, a designed grating when the probability of crossover is 0.75 has a 74.7[%] high diffraction efficiency and a 1.73 X 10^-1 uniformity quantitatively, where the probability of mutation is 0.001 and the population size is 300. Secondly, on the probability of mutation, a designed grating when the probability of mutation is 0.001 has a 74.4[%] high efficiency and a 1.61 X 10^-1 uniformity quantitatively, where the probability of crossover is 1.0 and the population size is 300. Thirdly, on the population size, a designed grating when the population size is 300 and the generation is 400 has above 74[%] diffraction efficiency, where the probability of mutation is 0.001 and the probability of crossover is 1.0.

We describe the Fresnel field of pixelated diffractive elements with simple formulas. These formulas are employed to compute the reconstruction field of finite Talbot array illuminators and to analyze the performance of pixelated lenses. A simple relation to analyze the diffraction efficiency of pixelated lenses is presented. We also show that a pixelated lens with the appropriate parameters exhibits an apodized point spread function that is originated in the finite size of the pixel's pupil. This effect, that we call self-apodization, is experimentally verified by encoding a one-dimensional pixelated lens onto a liquid crystal spatial light modulator.

We show that a finite Talbot array illuminator (TAI) with reconstruction field at a fraction of the Talbot distance (z equals MZ_T/N), can be interpreted as an array of M (or 2M) interlaced pixelated lenses sharing a common focal length f equals MZ_T/N. We found also that the transmittance of a finite TAI can be expressed as a single pixelated lens modulated by a phase grating whose basic cell has M (or 2M) pixels. Based on this description of a TAI we propose a method to improve its performance as generator of a finite spot array at the reconstruction plane.

For the miniaturization and the integration of a spectrometer, the imaging system of the spectrometer should be simplified. A hybrid diffractive-refractive element is designed and fabricated, which combines the functions of dispersion and imaging. The element is composed of a lens and a special hologram. The lens is just a normal plano-convex one. And the hologram is used to take the role of grating in conventional spectrometer. It is recorded by two spherical waves, and the positions of the centers of the two waves are optimized to compensate the aberrations of the element. When the element is illuminated by collimated beam, the components of a spectrum range 400 - 800 nm from the light source are dispersed and focused on a plane with good image qualities and linear arrangement of the spectrum points. Experiment results are given. The element could be designed freely in size to be applied in various types of spectroscopic analysis systems.

This paper aims at the request of dividing different waves. The request is often met in the field of color pickup. Dividing different waves is realized by introducing binary optical element. Based on scalar diffraction theory, the distribution of its diffraction field was calculated and the fabrication parameters were also optimized. The element is fabricated with Sol-gel method. We also built the testing system and obtained some results of the experiment.

Novel compact devices for wavelength division multiplexing and demultiplexing are presented. These devices are based on planar optics configurations. A method for designing and recording such planar devices is described. Experimental procedures and results for devices that can handle three closely separated wavelengths in the visible as well as near infrared radiation are presented.