The iterative direct binary search (DBS) algorithm for the synthesis of binary computer-generated holograms (CGH's) has been shown to yield lower reconstruction error and higher diffraction efficiency than conventional methods; but it is computationally intensive. To ameliorate this disadvantage, an acceleration technique is described which makes feasible the design of CGH's with moderate space-bandwidth product. The ability to control both the magnitude and phase of the reconstructed wavefront is an important advantage of DBS over the use of phase shaping to improve diffraction efficiency with conventional methods for CGH synthesis. To verify this capability, a procedure has been developed for measuring the phase of the reconstructed wavefront.

A fundamentally energy efficient, two element holographic beamformer for converting a Gaussian beam into a rectangular uniform beam in the far-field was designed, fabricated, and tested. The design method is based on a modification of the Gerchberg-Saxton iterative Fourier transform algorithm to include an x-y separability constraint on the phase of one of the holographic elements. This modification gave a design with improved beamforming performance. The two required holographic elements were fabricated using a combination of optical and computer-generation techniques. The experimental results verify the effectiveness of the design approach.

The fabrication of binary optics using high quality lithographic processes requires binary masks with constant phase contours. Parameter driven software for the development of these masks has been developed at Perkin-Elmer. Applications include zone plates, aspheric lenses, and optics described using Zernike polynomials, arbitrary phase functions, and sampled phase arrays.

Two optical designs for infrared imagers, a fast (F/1) staring system and a slower (F/2.4) scanning system, are discussed to demonstrate the advantages and limitations of using hybrid diffractive/refractive elements as replacements for conventional elements. Each case is compared to a conventional design of all spherical elements satisfying a specific set of hypothetical requirements for resolution, field-of-view, and spectral bandwidth (8-12 μm). We find that as much as a 33 percent reduction in the number of elements can be achieved in the slower system using hybrid elements. For the fast system, spherochromatism greatly limits the performance of the hybrid design. A table is presented showing the trades among F-number, field-of-view, bandwidth, and materials needed to maintain constant resolution in the fast system.

Diffractive Optical Elements can be used to manipulate wavefronts in very complex ways. They can be used to manipulate, the amplitude, phase, and polarization of a wavefront. In this presentation we discuss optical components whose feature size is larger than one wavelength, about equal to one wavelength, and smaller than one wavelength. We outline the analytical development which describes these elements.

A zero-based representation of binary-phase gratings developed by Dammann [1,2] has been reported as one means for generating an array of point sources. Dammann gratings have since be used as beam splitters and combiners for coherent communications [3,4] and for designing array generators [5,6] and interconnects [7-9] for optical computing. Dammann's original design assumed a one-dimensional, symmetric array of sources generated by a binary-phase grating. However, designs for producing asymmetric arrays [10], two-dimensional arrays [10,11], and multi-phase gratings [6,10] have recently been proposed. In this work these extensions are used to develop a procedure for designing quarternary, or 4-level, phase gratings capable of realizing an arbitrary array of coherent sources. The distinction between coherent and incoherent array generation is noted and used to show that Dammann's method of binary-phase grating design is less effective than other methods when maximum diffraction efficiency is desired. Although only one-dimensional gratings are discussed, extensions to two-dimensional quarternary-phase gratings are straightforward. The design and construction of two-dimensional gratings is discussed in Refs. 8, 10, and 11.

A general algorithm is presented for the computer intensive task of data fracture for electron beam written holograms. This process can be used for both open and closed fringe holograms, and is particularly well suited to producing holographic optical elements. The software, specifically written for efficient performance on a micro-processor, is compatible with a standard E-beam lithography system. Recent advances in the memory and processing speed of desk top computers allow this package to achieve performance similar to existing encoding methods residing on main-frame computers. Hardware and software requirement shall be discussed, as well as wavefront encoding accuracy and limitations of the lithography system.

The design and fabrication of a holographic beamsplitter that will produce multiple phase and amplitude matched output beams from a collimated laser beam is discussed. Multiple exposures are recorded in a dichromated gelatin (DCG) plate to make the output beams seem to emanate from a single point with high diffraction efficiency and low scattering. During fabrication, a technique was developed to verify that the relative phasefronts of all the output beams are matched. The holograting can be designed such that any relative phase, amplitude and angle between the output beams as well as different recording/readout wavelengths can be specified for a variety of applications. A deterministic method of calculating the optimum Bragg angles for the recording beams has been developed to compensate for the wavelength shift between the recording laser and the readout laser. A special emphasis is given to the application of using a laser diode for readout. Specifically, a double grating method is utilized for making the element less sensitive to wavelength drift common to laser diodes. A single small component has been fabricated with output beams in-line with respect to the input beam axis such that it can be configured into compact and rugged optical systems.

The Computer Imaging Branch of the Corporate Manufacturing Technology Center at Texas Instruments has developed a series of high precision laser writers with effective pixel sizes ranging from 10 microns to 0.5 micron. Although developed for printed circut board and semiconductor photomask applications, the speed and resolution of the systems make them useful for the generation of computer generated holograms, and for applications in binary diffractive optics. These laser writing systems are described, and some applications to computer generated holograpy and binary diffractive optics are presented.

We have developed an opto-mechanical technique for the direct writing of blazed surface relief diffractive elements (kinoforms) in photoresist. An important feature of the technique is that the circular zones or rulings which are written one zone at a time, can be of any width and radius with a profile tuned to give optimum response at any required wavelength in the visible and IR. Standard zone plates, diffractive linear axicons, ring focus elements and compound elements have been made and their performance evaluated. By using the electron beam lithographic facilities at Rutherford Laboratory, binary amplitude zone plates with polygon rather that circular zones have been made in chrome on glass substrates. These have subsequently been copied into photoresist as binary phase zone plates to give a higher diffraction efficiency. Current work is concerned with the production of wavefront aberration compensating diffractive elements and with elements for optical testing.

Binary optics is an emerging technology whereby light is directed, combined or distributed by an optical material having a binary or "stepped" phase structure. By employing multiple mask lithography in the fabrication process, we produce computer-generated diffractive elements having optical efficiencies that were previously beyond reach. In this paper we use binary optics technology to generate a high quality aspheric corrector plate which we employ in a Schmidt telescope.

We present a new approach for fabricating multiple phase level holographic optical elements in fused silica. The approach utilizes electron-beam lithography, and it is particularly applicable for devices with minimum feature sizes below 1 μm. We have succeeded in fabricating arrays of multiple phase level optical elements with minimum features of 0.4 μm. We also report on the diffraction efficiencies of cylindrical f/1 lenses with 3 mm focal lengths. The results agree very well with the theoretical predictions. We also predict that an increase in diffraction efficiency of as much as 10 % can be realized from the outer portions of a holographic lens through better registration of the multiple layers.

A new holographic optical element that combines the beam-multiplexing properties of binary-phase computer-generated holograms with the efficiency of volume holograms formed in dichromated gelatin is described. Experimental results for an element that improves both the efficiency and signal-to-noise ratio of a computer-generated hologram are presented. The possibility of using this element as an optical interconnect is discussed.

A wide variety of wavefront encoding methods are currently used in the generation of holographic filters. To provide a basis for evaluation, different encoding techniques must be tested under similar conditions. A selection of five wavefront encoding methods are used to produce holographic filters. These filters are then contrasted on the basis of their experimental performance. The results of these tests are presented, as well as a general comparison of the five encoding techniques.

Holographic gratings recorded in photopolymer media are formed by mechanisms different from those that form gratings in silver halide media. Unlike the latent images formed in silver halide media (prior to chemical development), phase-only holograms in photopolymer media start to form almost immediately upon exposure. Measurement of the holographic grating growth with time provides information about the underlying photochemical and diffusion processes, and can also be useful in the control of exposure and processing. Experimental techniques for measuring the evolving grating are discussed, and illustrated with measurements made on Polaroid's DMP-128 photopolymer holographic recording material.

We tried to record computer-generated holograms (CGHs) on an optical disk by using an optical disk mastering machine. Phase-only Lohmann type and interfererence type CGHs are recorded. The mastering machine used is described and results on reconstruction of CGHs are presented.

For optical memories holograms with high diffraction efficiency, large signal to noise ratio, and disturbance resistance are required. Computer-generated quantized phase holograms are presented and shown to meet these needs.

Agile steering of a Helium-Neon laser beam (λ = 632.8nm) has been demonstrated using a complementary pair of 5-cm-aperture diffractive microlens arrays in the Galilean telescopic geometry. Having as many as 60,000 F/5 microlenses, each with parabolic phase profile and 200-μm diameter, results in nearly aberration-free beam steering over 11° field of view for ±100 μm lateral displacements of one array relative to the other. Wavefront quality and steering efficiency of the deflected beam has been measured as a function of steering angle and is compared to a simple theoretical model.

A bifocal intraocular lens is described which has been surgically implanted in a number of patients in the United States and Europe with promising results. The posterior surface of this lens includes a blazed phase zone plate which directs most of the light to two diffractive orders. The combination of this diffractive structure and the conventional refractive surfaces of the lens provides simultaneous bifocal vision for the patient.

A new concept optical head, using a holographic optical element has been developed. This holographic element combines three optical functions, beam splitter, focusing error detection and tracking error detection optics functions. A polarizing beam splitter function is also combined for magneto-optical disk head use. These holographic optical elements are computer generated holograms fabricated using electron beam lithography technique. A new optical configuration has been designed for this optical head to remove the influence of wavelength variation in the laser diode used for a light source. The off-set signal in tracking error signal has been reduced by introduction of the holograms which are used only for detecting tacking error. The stable operation and high read out S/N ratio have been obtained by applying this holographic optical element.

We have developed a compact holographic disk for an all holographic line scanner for diode laser printers. The scanner consists of only a holographic disk and a holographic lens for laser scanning and focusing. No other optics are necessary. The holographic disk performs straight line scanning. The optical power is achieved by a holographic disk and lens. To make the disk more compact, while retaining a required scanning width and scanning beam, the increasing of deviation from a straight line and scanning beam aberration need be overcome. In this paper, we investigate the required phase transfer functions of the holograms to realize the compact holographic disk.

Several aspects of computer-generated diffractive optical elements (DOE), including, design, fabrication, and applications in the areas of lens elements, beamsplitters, optical servo systems, and laser diode optics are addressed.

In this paper we discuss two "real-time" (turn around times of a few seconds up to a minute) systems for display of three dimensional computer data using computer generated holograms. In one system the computer generated hologram is written on a high-resolution CRT in contact with a liquid crystal light valve. The liquid crystal light valve modulates a coherent, collimated, polarized readout beam with the data that is displayed on the CRT. The modulated beam is then used to reconstruct the object that had been encoded in the hologram on the CRT. In the second system the computer generated hologram that had been displayed on the CRT is imaged and recorded on a thermoplastic plate. The developed thermoplastic plate can then be used to reconstruct the object with a coherent beam.

We describe an optical head design using two spherical lenses and two HOE's. This study was intended to show the feasibility of using HOE's to improve the performance of optical head for Read/Write optical disc drives. The two HOE's correct the spherical aberrations of the lens, change the elliptical beam to a circular one and compensate for wavelength shift up to +, - 5 nm. Experiments have been performed to confirm these concepts. The HOE's were made optically in the visible wavelength using an intermediate CGH. Ideally the HOE's are to be generated by a computer and preferably written directly by an e-beam machine. Since at that time all the commercially available e-beam shops we contacted lacked the confidence in making such high resolution CGH, we decided to use the Optical-CGH approach. Actually this approach offers several advantages. First we can make large and high resolution ir HOE immediately. Secondly we can even make Bragg (or volume) ir hologram using visible light. Basically we create a pre-distorted CGH from which the final HOE can be made using visible light. The final HOE can then be reconstruct at the ir wavelength without aberrations. The techniques used here can be extended to optical head designs using aspherical lenses. The HOE's function can then be, in addition to beam shaping, to achieve a larger wavelength compensation, to correct the residual chromatic and aspherical aberrations of the aspherical lenses. The astigmatism of the laser diode can also be corrected by the HOE's. The possibility of an optical head using only HOE's (no lenses) will be discussed. Computer simulations and experimental results are shown.

This paper describes the fabrication of computer-generated holographic lenses in fused silica; the lenses are designed to collimate the output beams of diode lasers. The lenses are cylindrical to collimate the beams in one direction at a time and to maximize the fill factor in the laser array. The lens patterns were written into resist on the substrate using an electron beam. The lenses were transferred to the fused silica substrate via reactive ion etching. Two layers of etching were demonstrated.

The use of computer generated holograms (CGHs) in aspheric testing is reviewed in light of current capabilites of electron-beam written CGHs. Merits and limitations of various Twyman-Green and Fizeau interferometer configurations are discussed. Methods and guidlines for designing and specifying a CGH are presented.

Array generators are optical systems which split a single beam from a laser source into a one- or two-dimensional array of beams. We are interested in the generation of spot arrays for illuminating two-dimensional arrays of optical logic devices in an optical digital computer. A variety of solutions to this problem has been offered, among them the use of computer generated diffraction gratings [1,2,3], holographically produced lenslet arrays [4] and phase contrast methods based on spatial filtering [5]. Binary Dammam gratings and arrays of lenslets have also been employed by Veldkamp et al. [6,7] for the inverse task of coherent coupling of the output beams of several laser diodes. In the following, we want to discuss two different techniques for array generation. The first one is an extension of the theory of binary phase gratings to multilevel phase gratings. The use of multiple phase levels helps to increase the efficiency of the array illuminator. The second method employs lenslet arrays. However, as opposed to the method described in reference [4] in which the lenslets simply focus an extended laser beam down to many small spots, we perform an optical Fourier transformation of the lenslet array. This technique offers the possibility to generate very small spots because the full aperture is used. It also helps to reduce the problem with the nonuniformity of the array due to the effect of the spatially nonuniform intensity profile of the illuminating laser beam. Both techniques will be discussed in more detail in sections 3 and 4. First, we start with a short description of the fabrication of multilevel phase structures.

An optical interconnect system employing Computer Generated Holograms (CGH's) for a shared memory computer is described. The CGH's serve three functions: the concentration of light onto the communication modulators, implementation of butterfly connections between processing elements and memory modules, and provision of optical system output signals. Binary phase CGH components have been designed to provide these functions for a prototype shared memory computer. It is shown that system requirements can be met with the use of a lensless double pass holographic system and an iterative CGH encoding method. This encoding method is an extension of the Iterative Discrete On-axis encoding method to the Fresnel diffraction regime. The computer run time of this algorithm can be significantly reduced by setting the initial CGH transmittance equal to an approximation of the final pattern.

Holography and optical processing often require coherent input beams with intensity distributions which are different from the usual Gaussian distribution of a laser. Aspherical lenses are used to perform general beam-shaping in order to obtain the required intensity distributions. Computer generated holograms [CGHs] can also be used for beam-shaping. The calculation of these CGHs consist of two steps. First the required transformation equations, which will transform the available intensity distribution into the required intensity distribution, are derived from the two known intensity distributions with the aid of an integral equation. Then these transformation equations are substituted into differential equations from which phase functions are determined which are then encoded as CGHs. Two CGHs are required to perform the transformation. The first one diffracts the light to form the required intensity distribution a distance away. At that position the second CGH is placed to cancel the diffraction in order to retain the new intensity distribution. The resulting intensity distribution remains stationary from then on. This method has been implemented in terms of software. Various CGHs have been produced with the aid of this software. General intensity distributions are produced with these CGHs and the results are presented in this paper.

An architecture which uses a single modulator in a joint transform correlator is proposed. Normally, the single most expensive component in an optical correlator is the spatial light modulator, thus this implementation would greatly reduce the cost and size of optical pattern recognition systems. The deformable mirror device (DMD) is a potential candidate for implementation of the single modulator correlator because of its ability to operate at KHz processing speeds.

New computer generated hologram (CGH) recording techniques are discussed and initial demonstrations provided. CGHs are advantageous in fabricating lensless optical systems (with the lens elements recorded on the CGH). Applications include the lensless optical Hough transform (HT) and matched spatial filter (MSF) correlators. These new CGHs allow binary recording of complex functions with a reduced space bandwidth product (SBWP) compared to other techniques.