A Finite Element Method (FEM) for open region scattering problems with arbitrarily shaped outer boundary is considered to model diffractive objects. In open region problems it is necessary to introduce an artificial boundary to limit the area of computation. Therefore, boundary conditions are implemented to absorb the outgoing waves with as little reflection as possible. It is desirable to use Absorbing Boundary condition (ABC) which can truncate the region conformal to the geometry of the scatterer. Thus, a smaller computational domain and a more efficient numerical solution are achieved. In this talk a local ABC for arbitrarily shaped outer boundaries is used which preserves the sparsity of the resulting matrix after discretization. The second order ABCs are implemented to solve the Helmholtz equation numerically in the frequency domain. Different two-dimensional scatterers are considered. First, a study of Fresnel zone plates is conducted. The intensity and distribution of the focal points for different orders and thicknesses is discussed. Next some reflection gratings are studied and verified by comparing the results to theoretical derivations. Last a two-dimensional hologram is modeled.

For applications in Doppler radar processing, it is necessary to convolve a one-dimensional signal with spatially scaled versions of a single reference. To achieve this one can expand the reference in one dimension, image it though a system that has variable-magnification in this dimension, and perform a one- dimensional convolution with the input signal in the orthogonal direction. To realize the variable magnification imaging system, we consider the construction of a telescope that uses two hybrid diffractive-refractive elements. The refractive component for the elements is a cylindrical lens that provides bias focussing power. The diffractive component for the first element provides the modulation of the optical power necessary to achieve variable- magnification. The second diffractive component is used to correct the phase of the output image and produce a collimated output. Closed form and iterative designs are presented.

The rigorous coupled-wave model is used to determine the polarization of diffracted waves from two superimposed volume gratings with their grating vectors in the same plane. The phase relations used in computing the phase shift of diffracted beams are derived. The relative phase difference between orthogonal components of the + 1 diffracted order is computed for a single grating and two superimposed gratings. The level of induced ellipticity in polarization is greater for light diffracted from a multiplexed grating than from a single grating. Experimental and theoretical results show that the phase shift of a beam diffracted from two superimposed gratings has both positive and negative values.

We discuss the efficiency of diffractive elements in the intermediate region between the paraxial domain and the resonance domain of diffractive optics. In the paraxial domain, the efficiency is bounded from above by an upper limit provided by scalar diffraction theory. In the resonance domain, this limit can be exceeded. The transition that takes place as the element leaves the paraxial domain is illustrated by numerical simulations with exact electromagnetic diffraction theory, and interpreted with physical arguments. Our evidence indicates that the efficiency can rise substantially above the paraxial upper bound only if the signal effectively fills a half-space.

Dispersion and aberration compensation techniques in diffractive optics and holography are reviewed. It is shown that the basic analyses of chromatic dispersion, and both types of Seidel aberrations (wavelength-related and geometric), apply for both holographic optical element (HOEs) and diffractive optical elements (DOEs), based on grating composition.

We have developed a two-dimensional, multibeam, binary optic based scanner for transmission/receiver functions for LADAR and other applications under a Small Business Innovation Research (SBIR) contract from Eglin Air Force Base. Multibeam scan provides many unique advantages including: increased data rate for pulsed lasers; increased scan coverage; and programmable broadcasting for optical interconnect applications.

In recent years design concepts for diffractive elements which can be used in the paraxial domain of diffractive optics has dominated the literature. We present a design concept for periodic and non-periodic structures which is embedded in the design theory of diffractive elements. It is suitable for diffractive elements having continuous or multilevel profiles with optimized diffraction efficiency. This paper is based on reference.

The paper presents an approximate analysis of the conical diffraction by planar volume gratings. Explicit expressions are derived for the coupling constants and the dephasing between different diffraction orders. The results of the approximate coupled-wave theory are compared with the rigorous numerical solution of the three-dimensional boundary value problem for a specific configuration. A two-wave coupled-wave theory is presented and an analytical solution is given.

The design and fabrication of a low cost laser diode to fiber optic coupler is discussed. A single diffractive optical element was used to provide uniform coupling efficiency over a 40 nm bandwidth. The element was optimized to maintain constant coupling efficiency with small tilts and decenters. An iterative method referred to as radially symmetric iterative discrete on-axis (RSIDO) encoding was used to determine optimum fringe placement and profile.

Along with the rapid growth in fixed diffractive and holographic element technology in recent years has come intensive interest in active, dynamic diffractive elements which can be electrically programmed or switched. Two different classes of electrically controllable diffractive structures may be distinguished. The more familiar class are the programmable spatial light modulators, addressed on a pixel-by-pixel basis. Less familiar is the emerging concept of monolithically switched holograms, now an active subject in several laboratories. These have a fixed, prefabricated diffractive structure whose diffraction efficiency can be modulated as a whole. Whereas spatial light modulators typically are restricted to relatively small arrays of pixels on the order of 256X256 and correspondingly low diffraction efficiencies, monolithic holograms can be of extremely high resolution, optical quality, and diffraction efficiency, with the equivalent of one million times higher pixel density. Such elements can yield new devices significantly different from SLMs, particularly if the material is also of sufficiently high optical quality to permit series stacking. Along these lines, Foster-Miller has been developing applications for a promising material, liquid crystal infused Polaroid holographic photopolymer, which appears to be a possible basis for many such devices. The present paper reviews some of our applications trials to date, including lab demonstrations of laser beam diverters, programmable beamlet array generators, dynamic lenses, fiber optic switches, both reconfigurable and continuously tunable wavelength filters, holographic optical memories and memory structures, and thermal applications for switching of white light or sunlight.

Most applications which have considered in diffractive optics in recent years are related to micro-optics and optics in computing. We will briefly describe two examples of the capabilities of diffractive optics in optical material processing.

Clearly, efficient use of space is desirable for optical systems. We suggest that a space filling curve such as the Peano curve offers useful clues to realizing compact modular optics.

Multistage interconnection networks (MINs) are used to create wide diameter networks with a logarithmic number of stages. To further reduce the costs of constructing and operating this type of network, these stages can be stored in a volume hologram and accessed sequentially to achieve the same functionality as a MIN. We discuss the design of such a system and demonstrate a prototype that uses infrared sensitive photorefractive lithium niobate to store a wavelength multiplexed volume holographic lens array. The holograms were recorded at 800 nm and several stages were multiplexed in a single hologram, each separated by as little as 0.6 nm. The optical system performance was analyzed and the results discussed.

Diffractive Optical Interconnect Elements (DOIEs) provide several advantages over conventional bulk elements such as spherical, cylindrical, and other conventional forms. With respect to DOIEs for digital switching networks, the technology offers the ability to form four-dimensional, free space optical interconnects within attractive boundary conditions. 'Smart' pixels detect the incident light from a large fan-in array of optical beams. After detection, the signal reaches threshold between the 0-1 level. It is then inverted, amplified, and re-emitted by an output laser diode. The output beam is redirected to a predetermined number of subsequent 'smart' pixels through the DOIE.

This paper describes optical systems which compensate for the wavelength dispersion and distortion that arise in diffractive fan-out elements. Two approaches are investigated, a space variant and a space invariant. In the space variant approach, microlenses or diffractive optical elements were introduced in the system correcting the wavefronts. In the space invariant approach refractive and diffractive lenses compensates for the chromatic aberrations and shifts in beam direction that are caused by the fan-out element. Several designs for such compensating optical systems are presented, along with simulated results.

The recording characteristics of DuPont's HRF-150 photopolymer film are described. The application of these films for data storage using the 3-D holographic disk architecture is presented. The required system's bandwidth due to the photopolymer's limited thickness is shown to be the limiting factor of the storage capacity of these thin films and not the material's dynamic range. A new multiplexing method (peristrophic multiplexing) that significantly increases the film's capacity and changes the limiting factor from system bandwidth to material dynamic range is presented.

Two types of holographic 3D imaging systems are considered. The first one is based on a so-called selectrogram, i.e., the structure that can be registered by using the light scattered by the object as a reference one. The distance to the object is not limited in this case because it does not effect the capability of the light scattered by the object to interfere with itself. Two methods that permit us to increase the diffraction efficiency of the selectogram are discussed and investigated. The first one involves the focusing of the image of the object in the region located near the surface of the selectogram. Special convenience of this method is that it is also accompanied by the increase of the candlepower of the optical system at the stage of the selectrogram recording. The second method to enhance the diffraction efficiency of the selectrogram involves the increase of the real physical depth of the recording by increasing the inclination of the rays that intersect the holographic layer. The Dupont photopolymer films that were sealed between two glass prisms with the help of immersion were used for the recording in this case. As a result of simultaneous applications of these methods, the brightness of the image reconstructed by the selectrogram became comparable with that of the image reconstructed by the hologram. The second type of a 3D imaging system being considered is designed for the recording of 3D holographic copies of small valuable objects. The parameters of this system are strongly influenced by the phenomenon of the shrinkage of the light-sensitive layer of the photographic plate. This phenomenon was eliminated by using photopolymer light- sensitive layers for the hologram recording.

Diffractive optics can be used for the projection of patterns in, for instance, laser material processing or microlithography. We compare diffractive optics with conventional pattern projection methods with respect to efficiency, resolution and field, influence of coding and illumination. We describe an experiment in diffractive pattern projection with an excimer laser.

We discuss the encoding of new types of binary optical elements onto programmable spatial light modulators (SLMs). After introducing the technique and limitations, some past work will be reviewed and new ideas presented.

The output from a Dammann grating can be modified by forming the Fourier transform lens onto a programmable spatial light modulator. We show how the positions and numbers of the outputs can be varied. In addition, the technique allows analysis of the phase of the diffracted beams.

Design and preliminary results of a prototype laser projection system are presented. This system consists of a HeCd laser, an expansion system, a laser beam profile reshaping system, and a holographic diffraction grating which divides the amplitude of a laser into four coherent beams. These four beams are then recombined together to generate an interferometric pattern on a photosensitive substrate. In this paper, the particular significance of the reshaper with respective enhancement of system performance will be addressed. Since most laser beam irradiance profiles do not have a uniform distribution of light intensity across its diameter, the interference pattern will have the maximum intensity at the center and will trail off at the edges if a Gaussian beam profile is utilized. In order to correct this problem, a two plano- aspherical lens system has been designed and fabricated. This system converts the Gaussian beam into a uniform profile beam without truncating the laser beam. Experimental results will be given and discussed.

Long-focal-length microlens arrays is one of the main components of the Shack- Hartmann type wavefront sensor. For an application in astronomy we have developed a specific microlens manufacturing process based on photolithographic techniques. At first, in this paper, we briefly report on the procedure and we highlight the programmable possibilities according to scientific and technical specifications. Secondly, we describe the different studies we have worked out to improve the technique and determine its limitations. Finally, the results of mechanical and optical tests are compared with computing simulations in order to qualify the microlens arrays manufactured through this technique. In conclusion, the technique we have developed in our laboratory is fast and reliable; the microlenses manufactured with this procedure are diffraction-limited. This photolithographic technique is easy to transfer to an industrial manufacturing environment, each step of the process being programmable.

Based on the theory of computer generated hologram and fabrication of binary optical element, a new micro-optic element for optical disk memory read-write heads is proposed. This element is small in size (5mm in diameter, 1mm in thickness), light in weight (<0.03g), and high in diffraction efficiency (36.64%). It is with three optical functions required for an optical head, splitting beam, producing the focusing error signal and the tracking error signal. When this micro-optic element is used to replace four conventional optical elements (a diffraction grating, a beam splitter prism, a collimating lens and a cylindrical lens) of common optical head, a sophisticated optical head can be produced.

The planar waveguide device transforming the monochromatic light beam to the array of uniform intensity parallel light beams emitted into free space has been demonstrated. This beamsplitter can be used to design three-dimensional integrated optical circuits and also it may be one of the elements of the optical processor with a variable logic structure. A set of these beamsplitters combined with the semiconductor laser array can be used to make the light beam matrix source. In our work the planar optical waveguides fabricated by Ag-ions diffusion into glass substrate were used. The beamsplitter input and output elements formed in As₂S₃ layers on the waveguide surface constitute the thin relief diffraction gratings with the asymmetrical groove profiles. The fabrication of the gratings consists of interference and selective etching techniques. The case of slight interaction of the waveguide mode with the output gratings was realized. The samples providing 16 and more output light beams with good uniform intensity were produced. The measured uniformity error was found to be +/- 5%. The fabrication of the high efficiency beamsplitter is also discussed.

Computer generated holograms (CGHs) and diffractive optical elements (DOEs) have become increasingly important in lens fabrication, artificial intelligence, optical computing research, and in other applications where diffraction based optical manipulation is required. Research in these areas has been hampered by the lack of an affordable and practical system capable of printing large format, high resolution diffractive optical elements. We describe a new design for a DOE printer, based on a modified step-and-repeat printing method, which reduces these problems.

DuPont holographic photopolymers have been used to fabricate high quality holographic optical elements. The wide spectral sensitivity possible in these materials allows imaging near the desired HOE playback conditions. Multicolor imaging with ion and dye lasers using these materials is discussed. Mastering materials and methods are described for reflection and transmission HOE replication. HOE performance is compared to performance predicted by coupled- wave theory and HOE applications using these materials are described.

A low-cost process for replicating diffractive optics has been demonstrated using radiation-curable liquid photopolymers on plastic substrates. Two- and eight-level f/10 quartz master elements were embossed into liquid photopolymers and subsequently cured under pressure using high-intensity ultraviolet (UV) radiation. The quartz master is easily separated from the hardened replica and immediately available for reuse. High-fidelity replicas with the same surface polarity as the original master can be made from nickel electroforms. For obtaining good optical image quality replicas, quartz masters were found to be significantly better than nickel masters. High- fidelity replication of surface relief structures was verified using an optical microscope, a Scanning Electron Microscope (SEM), and a 2-D scanning profilometer. Nearly theoretical diffraction efficiency (39.4% versus 40.5%) was achieved with the two-level f/10 replica. Optical image quality was degraded by substrate warping and submicron surface roughness as evidenced by increasing distortion of the blur spot over larger replica diameters. Less than 10% shrinkage was measured in the vertical dimension with no shrinkage measured in the horizontal plane. Although optical image quality applications are limited, the process is suitable for applications such as polarizers and microlens arrays.

Switchable holographic gratings are desirable for a wide range of applications in diffractive optics. Liquid crystalline materials look attractive for these devices because of their large field- induced birefringence. The combination of electro-optical liquid crystals with photopolymeric holographic materials offers a unique single system approach to the economical fabrication of switchable holograms. We report on the progress in our development of a novel system where holographic gratings are recorded in a single step process and consist of periodic polymer-dispersed liquid crystal planes. Gratings have been recorded with high diffraction efficiency (approaching 100%) and narrow angular selectivity (<1 degree(s) FWHM). The diffraction efficiency can be controlled electrically or thermally

The fabrication process of refractive microlens arrays with a continuous surface relief is described. The elements are fabricated with a laser beam lithographic system and are directly written into photoresist. By this method the manufacturing of lenses with a broad range of numerical apertures N.A. is possible. Lenses with different diameters in the range from 25 to 100micrometers were written in photoresist. Furthermore, a modified technique with two subsequent exposures is applied which simplifies the procedure for generating the data and writing the lens topography. First attempts to transfer the structures into the substrate by ion etching show positive results. A first suggested fabrication method of the spherical microlenses by an exposure technique using a z-stepped probe chuck is also discussed.

Some years ago we had elaborated the new photopolymer composite to record in real time (or quasi real time) the various volume phase transmission-transmission holographical devices: gratings, lenses, beam-multiplicators, narrow-band filters. The nonreversible real-time recording on the photopolymers was based on the chain radical polymerication reaction and resulted in phase transition from liquid monomer/olygomer mixture to a solid with spatially modulated surface and volume. Unfortunately, in most cases the polymerizing recording is followed simultaneously by the shrinkage and the variation of the bulk index reaction. Unlike the transmission holograms the recording of the reflection holograms in real-time mode becomes impossible until these effects can be limited or aborted. The present paper contains the corresponding results of investigation of the photopolymer recording real-time modes of the reflection holographic gratings: (1) photopolymer composites with the smallest variation of the bulk refraction index during the real-time recording, (2) effect of a shrinkage on the diffraction efficiency of gratings, (3) limitations of the post-polymerized amplification of a holographic recording for the reflection gratings, and (4) the capillary-induced filling of the phase plates of the reflective hologram gratings as the tentative explanation of the positive results.

Diffractive optical elements (DOE) are widely used as important parts of various optical and integrated optics devices in variuos applications: spectroscopy, laser beam shaping, waveguides input-output elements, spatial filtering,optical disk systems, etc.16. In recent time vacuum-evaporated inorganic resists on the base of chalcogenide vitreous semiconductors (ChVS) have shown to be good registering media for DOEs fabrication48. Such media are characterized by high9 or even super high'° resolution, good optical uniformity and acceptable sensitivity in wide spectral region. The produced relief can be as positive, as well as the negative one, depending on the nature of selective etchant, the resist utilized and on the scheme of relief formation. For imaging applications among the wide range of photoinduced phenomena exhibited by ChVS most frequently are used the photodoping effect5'6'8 and photoinduced ChVS layers solubility changes4'5'7. Both effects lead to substantial changes in ChVS layers solubility rates and this makes possible the production of various relief images. It is well known that fabrication of DOEs blazed profile significantly improve the DOE's efficiency performance and enable to control the spectral region of maximal light concentration of diffraction gratings. In present work we report on the use of ChVS layers (of As-S-Se composition) for the fabrication of structures with the asymmetrical profiles for integrated and diffractive optics •with the help of direct recording ( using the sawtooth-like exposure ) or additional relief treatment.

Design considerations of a spectrograph, employing volume holographic optical elements (HOEs) as the dispersing element and as a spectral filter for rejection of Rayleigh scatter, are discussed. This spectrograph configuration, referred to as axial transmissive, is compared to the Czerny-Turner, another commonly used configuration. In particular, theoretical and experimental comparisons of throughput and signal-to-noise ratio (S/N) are given. Measurements relating to the point-spread function of both spectrographs are presented.

Multilevel diffractive optical elements for transforming Gaussian beams into rectangular distributions with uniform intensity profile are presented. The effects of different parameters, particularly the phase quantization, on the output field are discussed. It is shown that the interference between the different diffraction orders results in non-uniformity of the output intensity profile. The design is refined to minimize this non-uniformity. The performance of the final design is theoretically analyzed. Actual elements were fabricated and tested and the experimental results are presented. Fabrication considerations are also discussed along with suggestions for improvements.