In this paper we present a hybrid diffraction model that uses a scalar-based approximation over those regions of the boundary that satisfy the scalar criteria and a vector-based solution over those that do not. In analyzing diffractive optical elements (DOEs) it is necessary to use a vector- based model when the feature sizes within the DOE profile approach the scale of the illumination wavelength. However, in many instances only certain regions of a profile contain such small scale features. In these cases it is inefficient to perform a vector-based analysis over the entire profile. Therefore, we have developed a method that allows for the concatenation of scalar- and vector-based solutions. This is achieved by simply assigning the surface field values according to the scalar approximation over those regions of the profile that satisfy the scalar criteria, and using the finite-difference time-domain method (FDTD) to determine the surface fields over those regions that contain small scale features. In combination these methods create a surface profile that can be propagated to any plane, or region, of interest. In the course of our paper we will discuss the formulations of scalar diffraction theory and the FDTD, in addition to the method for propagating the concatenated boundary fields.

An optical disk system has been proposed that stores the bit-formatted data in three dimensions as microscopic reflection holograms in a thin photosensitive layer. Each microhologram represents one bit. High storage densities can be achieved by combining multiplexing methods and multilayer storage. A theoretical model for microholographic gratings generated by two focused counterpropagating Gaussian beams predicts high values of diffraction efficiency, more than 95% for single microhologram. Physical principles of microholographic storage have been experimentally verified. This article reports on recording and characterization of microholograms in DuPont HRF-800 photopolymers.

In this paper a novel analytical approach to evaluate spectral performances of non-ideal rectangular Bragg gratings, integrated in a slab waveguide is proposed. The effect of errors in the photolithographic definition of the grating, in particular in the period width, is investigated. We refer to gratings fabricated by means of standard e-beam photolithography apparatus. As a comparison, a numerical approach based on the Equivalent Multilayer Theory, combined with the Effective Index Method, is also presented. This procedure allow us to verify the theoretical limit of the analytical approach to better understand its range of applicability.

New applications for diffractive optics and increasing demand for volume production of components have been motivating forces behind advances in fabrication technology for diffractive optical elements. The most common fabrication methods include the multiple masking and etching approach developed at MIT's Lincoln Labs in the mid 1980's, laser or electron-beam direct writing, diamond turning, and holographic exposure. Replication of optical components using embossing or injection molding techniques is relatively common. While all these methods are well established and have their own respective advantages and disadvantages, researchers have continued to explore new fabrication methods. Three techniques with a great deal of promise for diffractive optics fabrication include grayscale lithography, near-field holography, and methods of so called `soft lithography'. Each of these techniques offers the potential to reduce fabrication costs, improve performance, or allow new applications of diffractive technology. In this paper, we will present results of research performed on these fabrication methods and discuss advantages and disadvantages of the various techniques.

Technologies generally used for fabrication of kinoform diffractive optics include; direct writing, plastic molding, diamond turning, and photolithography. Photolithographic methods (either contact or projection) are generally suitable for mass production in glass. Two types of masks are used with photolithographic methods; binary chrome masks and gray scale masks. Contact lithography with binary chrome masks generally limits minimum features sizes, and thus minimum zone widths, due to performance degradation from alignment errors between multiple masks. For example, the minimum zone width of a high efficiency eight-level kinoform is eight times the minimum feature size. Alternatively, gray scale mask technology uses a single mask which eliminates the alignment error problems. Smooth profile (not stair- stepped) high efficiency kinoform zones as well as three microns have been fabricated with this technology. In this paper we report on a direct experimental comparison of costs and performance for a blazed grating with 6-micron zones fabricated with multiple binary chrome masks and a single gray scale mask.

For many applications such as lithography and material processing it is important to generate a specific laser irradiance profile. In this paper we discuss design, fabrication, and testing considerations for three beam shapers. These beam shapers transform a 632.8 nm Gaussian intensity profile beam into a square, circle, and ring flat top irradiance profiles. The designs were tailored to minimize the usual sensitivity to fabrication errors. Simulation and empirical results are presented showing very good uniformity in the flat top beams. Other possible beam shapes are presented as well as design performance improvements with analog profile diffractive surface relief structures made with gray scale masks. The issues and difficulties of designing and fabricating UV beam shapers are also discussed.

An advanced holographic anti-counterfeit method and device is proposed to make the labels, which are used to identify the commercial products, being highly difficult to duplicate. This method provides a dot-matrix hologram, which is formed with a synthesized image including a random dispersed background pattern and a creative graphic design as a hidden pattern encoded into the background pattern. The background pattern is visible to the naked eyes of a viewer, but the hidden pattern can be viewed only through a special viewing device, such as a lenticular lens sheet. If the lenticular lens sheet covers the hologram irrelevantly or with an unfitted specification, the hidden pattern can't be decoded, and the moire effect will appear. A logo of U.S. MAIL is demonstrated as the encoded pattern, and the synthesized image is recorded in a 35 mm X 35 nm dot- matrix hologram on the photo-plate.

The optical system for writing down and reconstruction 2D hologram matrix, consisted of Fourier-holograms of data pages is developed. This system may be used in page-based holographic card storage devices, includes two separate parts--data writing and data reading devices. By this concept data writing down may be made by unique stationary device and data reading realized by some quite simple devices of different users. The hologram write down arrangement included laser source beam splitter, object, and reference parts. Object part includes beam telescope expander, 2D spatial light modulator, and Fourier-objective. Spatial light modulator forms input data page. Reference part include cylindrical lens beam expander, and 1D spatial light modulator. Reference beam is directed to the holographic media plane with the perpendicular incidence. The hologram matrix string is written down by simultaneously discrete moving of arrangement object part entries. Herewith the image placement of the input data page does not change. This hologram write down arrangement allows us to make data page reconstruction to the matrix photodetector directly by the light of compact semiconductor laser. Moreover, it is necessary to provide only 1D mechanical moving while data reading out from the hologram matrix.

First order perturbation theory is used to extend Kirchhoff's approximation of thin diffraction screens and to describe surface relief structures with large modulations. The range of validity is investigated for both, the thin element approximation as well as the perturbation approach. The perturbation description is applied to the design of diffractive optical elements. Our results also illustrate the relation between the tolerance of the design against changes in the incident field and the modulation depth of the diffractive surface relief.

An advanced versatile, low-cost polymeric waveguide technology with Bragg gratings has been developed for filter applications in optical communications. Bragg gratings are photochemically formed in single mode polymeric waveguides using holographic techniques. The resulting gratings exhibit excellent filter characteristics; 99.997% reflectivity in a 2 cm grating, which corresponds to refractive index modulation of the order of 10^-3, 0.2 nm width in the reflection peak at the 3 dB point in reflectivity, and no sidelobes in the reflection spectrum. The mechanism of the grating formation is discussed; its understanding enables us to enhance the filter characteristics of the gratings. The impact of temperature and humidity on the filter performance is also presented. The shift of the reflection maximum is 0.23 nm/ degree(s)C. The Bragg shift for a 90% change in relative humidity is 0.2 nm.

A newly developed multi-functional microscope named Morphinscope and which possesses versatile metrology functions such as that of a confocal microscope, a photon tunneling microscope, a laser based phase-shifting interferometry microscope, and an ellipsometer is presented. This microscope can switch between its various measurement functions by simply rotating its turret, which makes it a low-cost choice for surface analysis. This instrument satisfies the design goal of providing the user with a versatile instrument that can undertake various metrology functions with only one instrument. This design point circumvents a major limitation facing today's surface analyses, i.e., once after a defect is identified, the effort in locating the same defect again with a different instrument is a difficult if not impossible task. As a phase shifting interferometer has in inherent drawback in reconstructing the phase map of a non-homogeneous surface, an ellipsometer can come to the rescue by measuring the complex index of refraction of the surface. More specifically, the Fresnel equation can be used to calculate the phase change of inhomogeneous surfaces due to reflection in order to retrieve the measured complex index of refraction. Combining this understanding, this Morphinscope has the possibility of retrieving the surface profile of a non-homogeneous media.

Among liquid crystal spatial light modulators (LC-SLMs), LC- SLM with the photosensitive layer based on polyimide is of the highest resolution and of the highest sensitivity. In the present paper resolution, sensitivity, and speed of LC- SLM with polyimide doped with fullerene (FDPI) have been investigated in comparison with those of LC-SLM with dye doped polyimide (DDPI). For the study the holographic technique has been applied using the second harmonic of a pulsed Nd-laser under condition of Raman-Nath diffraction. LC-SLMs with fullerene-doped polyimide has been found to show the highest sensitivity, which has been 10 times higher than that for other LC-SLMs. The effect has been due to a creation of additional donor-acceptor complexes in polyimide doped with fullerene. Diffraction efficiency of LC-SLM with FDPI is less than the one of LC-SLM with DDPI. This fact is related to faster relaxation of holographic grating in FDPI.

The perspective opportunity to fabricate gray-scale masks was given LDW-glasses (LDW--Laser Direct Writing) from Canyon Materials, Inc. LDW-glass blanks contain a large number density of coloring specks of silver in a surface glass layer. A focused laser beam is used to heat erase these coloring specks. Experiments on the influence of laser radiation on LDW-glasses was carried out using a circular laser writing system. The transmittance value from the blank of 0.1 - 5% up to 70 - 80% depending on laser beam power is obtained with the current write scheme. Results of research of LDW-glasses behavior in a wide range of laser beam scanning speeds are described. Laser pattern generation in LDW-glass including the spatial resolution is discussed. The technology of fabrication of continuous-phase diffractive elements was tested by making exemplary Fresnel lenses. Total 80% efficiency for quartz Fresnel lenses with minimal zone width of 8 micrometers was readily achieved in the preliminary experiments.

Micromirrors supported by S-shape girders were fabricated and their angular deflections were measured using a laser- based system. A micromirror consists of a 50 micrometers X 50 micrometers aluminum plate, posts and an S-shape girder. Two electrodes were deposited on two corners of the substrate beneath the mirror plate. 50 X 50 micromirror array were fabricated using the Al-MEMS process. The electrostatic force caused by the voltage difference between the mirror plate and one of the electrodes causes the plate to tilt under the girder touches substrate. Bias voltage of the mirror plate is between 25 approximately 35 V and signal pulse voltage on the electrodes is 5 V. A laser-based system capable of real-time two-dimensional measurements of the angular deflection of the micromirror was developed. The operation of the system is based on measuring the displacement of a HeNe laser beam reflecting off the micromirror. The resonance frequency of the micromirror is 50 kHz when the girder touches the substrate and it is 25 kHz when the micromirror goes back to flat position, since the moving mass is about twice of the former case. The measurement results also revealed that the micromirror slants to the other direction even after the girder touches the substrate.

Model adaptive liquid crystal lenses are described with the emphasis on their performance. Process of the lens calibration is described and numerical and experimental calibrations are carried out. Imaging by the modal adaptive lens is implemented, as well as the focusing in the feedback system based on the adaptive LC lens.

By use of lens modules and diffractive optical elements, a new design approach is applied to the digital still camera lens system. The optimum initial design satisfying the specific requirements, and the real lens design obtained from the lens modules are presented. An initial design with a focal-length of 3.6931 mm is derived by assigning appropriate first-order quantities and third-order aberrations to each module along with the constraints required for the optimum solutions. In order to have a compact camera system, refractive and diffractive elements are used. This hybrid real lens, which is equivalent to the lens module, can be quickly obtained by matching the first- order quantities and the third-order aberrations of the module at a given conjugate. The constraints are the first- order quantities and third-order aberrations of the module obtained in the initial design. Compared to conventional design, this approach dramatically saves time and effort. The separately designed elements are then combined to establish an actual camera system. Finally, residual aberration balancing results in a lens which has enough performance over an f-number of 4.0 and is expected to fulfill all the requirements of a digital still camera lens.

Diffractive Continuous Phase Relief Elements are very attractive due to the high efficiency reachable and to the good replication capacities. Unfortunately standard optimization techniques usually generate discontinuous phase relief elements. In this paper we propose a new design method based on a multi-dimensional parameters optimization. The algorithm leads to a parametric optimization according to a merit function wholly defined by user. We report on the theory and the development of this method, illustrating the results obtained through the example of a flattop generator.

Photopolymers are studied as holographic recording material for computer-generated phase filters for pattern recognition by optical correlation. The analysis was performed using a copying process with a computer-generated filter, which is produced by means of a high resolution graphic device, as a master. In this work the low spatial frequency response of the photopolymer as holographic material is studied. The copying process used in this work consists of storing the pattern contained in the master in a photopolymer used as a holographic recording material. This photopolymer does not work in real-time, it is possible to store the holographic optical element for a long time because the dye is finished during exposition and the chemical process is not necessary after exposition. We used partially coherent light, from a high pressure mercury lamp. The photopolymer used in these experiments was composed of acrylamide and triethanolamine as the coinitiator, photoinitiated with a dye, yellow eoxine. Components were supported by a film of poly(vinylalcohol). The resulting thickness of the film was approximately 70 micrometers . Diffraction gratings and Fresnel lenses were obtained as phase holograms by index and thickness modulation, monitored with an electron microscope. First order diffraction efficiency achieved was 30%.

A high efficiency, low cost, low voltage operation liquid crystal on silicon beam steering device with multiple angles addressing capability is developed. Currently, seven steering angles with as high as 92.7% efficiency are achieved within 2.85 v. The device's design consideration, fabrication process as well as the characterization results are described.

Spherical-reference volume holograms exhibit spatial selectivity to the location and color of the reconstructing beam. We show that this property enables tomographic operations on extended incoherent polychromatic objects, and derive the shapes and spectral contents of the reconstructed slices for several holographic arrangements.

Previously, a method of incorporating a microlens within a standard fiber optic ferrule was described. In this paper, the micro-rod and wafer fabrication concepts are explained, the wafer mapping/layout processes used to create the microlens substrate are detailed, and packaging in standard ferrules and v-grooves are described along with coupling results.

Compact holographic memory architecture with phase conjugate readout and diffraction suppression by internal reflection is investigated. The pixel size requirement for a competitive system is determined. The bandwidth of the holographic recording in LiNbO₃ is broad enough to support the pixel size requirement by theoretical calculation and experimental measurement. Holograms of 1 micrometers ² pixel size binary data are recorded and reconstructed with this system. The pixel size limit, signal noise ratio and the storage density for holographic recording in photorefractive crystals are discussed.

We discuss a white-light processing system that produces a dynamic, achromatic Fourier transformation over the visible spectrum. The system includes an achromatic Fourier transform lens system and a low-dispersion spatial light modulator. A programmable phase mask can only write patterns with a spatial frequency appropriate for one wavelength. However, this problem is resolved by scaling broadband light from a point source to a common spatial frequency using an achromatic Fourier transformer. Then, the programmable phase mask must produce the same phase profile for all wavelengths. Using a chiral smectic liquid crystal (CSLC) spatial light modulator can minimize the wavelength dependence of the phase shifting elements. Phase modulation is accomplished by re-orientation of the optic axis in a plane transverse to the direction of propagation in a manner similar to mechanical rotation of a waveplate. The position of the optic axis is the same for all wavelengths and ideally so is the induced phase shift. We present experimental far field diffraction patterns due to a CSLC spatial light modulator that produces a binary broadband phase mask and an achromatic Fourier transform lens system. An analog modulator is also introduced. Applications for this technology include optical process, beam steering and adaptive optics.

Standard laser welding practices are limited by the intensity profile of the beam and spot size. The introduction of Diffractive Optical Elements (DOE) to the welding process allows for new beam shapes that are better suited to the welding process. A particular problem in laser welding is the joining of dissimilar materials. Because these materials have different material properties including different melting temperatures, it is difficult to synchronize the welding process using a single spot. Additionally, significant thermal stresses are introduced by the welding process because of the keyhole weld shape formed by a gaussian beam. By using a power splitting DOE, two spots of unequal intensity distributions may be projected onto each side of the weld joint. This paper discusses the use of DOEs in laser welding and joining of dissimilar materials. Results are presented from the testing of several candidate aerospace materials.

Active electro-optic sensors, that is, sensors that transmit as well as receive (typically laser) light are of increasing importance to the military but also can have application in areas such as industrial inspection and machine vision. These systems frequently require some form of agile pointing ability. We describe how potential active electro-optic sensors may be implemented using nonmechanical devices to steer and shape the transmitted and return light. Functions of the nonmechanical devices may include large angle pointing, beam stabilization, and adaptive beam shaping. The requirements on the nonmechanical devices that will allow them to perform these functions are presented.

Holographic polymer-dispersed liquid crystals are switchable holograms exhibiting electrically controllable diffraction efficiency. Such devices form the building blocks for several applications under active consideration including spatial light modulators. Several demanding requirements are placed on switchable holograms for these applications, such as high diffraction efficiency, wide on/off dynamic range, low optical scatter, low switching voltage and power consumption, high speed, uniformity and repeatability, low cost, and manufacturability. We describe the challenges and progress in meeting many of these goals.

In most advanced imaging systems designed for low light level applications, the heart of the detection process is an image intensifier. While such imaging systems are ideal in low light, they are sensitive to sudden increases in brightness levels within the field of view. These sudden bright spots are caused by a variety of sources (both intentional and not) and can result in a loss of contrast, blinding of the imaging system and damage to the components. As a safety measure against this situation, most systems incorporate global methods for automatic protection against bright sources. Unfortunately, this results in loss of gain and image contrast over the entire field of view, even if the bright source occupies only a small portion of the image. Exposure control over individual segments of the image is required. We present initial results from a unique implementation of the Digital Micromirror Device (DMD^TM) technology. Through proper placement of the DMD in the optical path and by providing an automatic feedback control loop from the intensified digital imager, sections of the image plane can be automatically diverted from the optical path by controlling the mirror pixels in those affected areas. An innovative approach, the DMD-based Anti-Blooming System (DABS), has been developed. Using rapid digital processing, this control can be ultimately implemented between frames of the imager to both preserve the hardware and allow for seamless return to a high contrast image. Repeated polling of the image plane through the feedback loop will allow for active control of the intensified image. A system description of the DABS and successful results from initial closed loop operation are presented.

Analogue contact lithography is a suitable technology for the fabrication of continuous surface profiles. In this field HEBS-glass gray scale masks have a great potential, for instance for producing microoptical elements. This paper summarizes detailed investigations on the electron beam exposure of HEBS-glass masks. At first we give an idea of the effects we obtained by exposing HEBS-glass masks with different kinds of e-beam writers (Gaussian beam and variable shape e-beam writer). We found thermal effects and a bottleneck effect which have different consequences for the gray level of the exposed mask. To understand its physical causes the bottleneck effect was investigated in detail. Based on this knowledge we introduce two different strategies to overcome the problems caused by the different concepts of the e-beam writer. Selected examples of fabricated profiles demonstrate the facilities of HEBS-glass using these strategies.

The Digital Light Deflector (DLD) can be used to deflect a laser beam without using moving parts. The DLD consists of cascaded pairs of deflecting and switching elements. In each stage, a birefringent element deflects the incident beam by two possible angles. The accompanying electro-optic switch selects the incident linear polarization state, thus deciding the output deflection for that stage. By cascading together N stages with successively increasing deflection angles, 2-to-the-power-N output angles are possible. Many earlier DLD devices utilized inorganic electro-optic materials and required high power. The only prior low-power DLD, using nematic liquid crystal deflectors, suffered from significant scattering losses and was not optimized for wide-angle steering. We present an improved liquid crystal DLD (LC-DLD). This LC-DLD makes use of smectic A liquid crystalline deflecting prisms, resulting in a substantial reduction of scattering losses. This device can also be designed to reduce steering error at wide angles. Steering error reduction is accomplished by optimizing the geometry and orientation of each deflector. Fabrication methods, guidelines for choice of viable smectic materials, and design optimization techniques are discussed.

Using two micro lens arrays and a MEMS micro shutter array, an intensity modulating Spatial Light Modulator is being developed at MEMS Optical, Inc. (patent pending) for high speed printing applications. The micro lens arrays are used to focus incident light to a point and then expand it back to its original size. At the focus point, a Foucault micro shutter array is used to modulate the amount of light allowed to pass through the aperture. The purpose for this device is for exposure control for high-speed electronic printing applications. The drive mechanism is based on an electrostatic lateral comb interdigitated drive. Design analysis shows a rise time of 1 - 2 microseconds for high voltage systems. This array of shutters is being implemented in a CMOS compatible process, and is capable of being integrated with on chip circuitry for opening and closing the shutters. The apertures are made using deep RIE etching, and the shutters are released using plasma etching. The result is an electronically controlled method of exposing a photosensitive surface at high speeds for the printing industry, with or without lasers.

Controllable surface roughness can be used to program the complex transmittance of individual pixels for the purpose of designing Fourier transform holograms. We are developing a photolithographic process for the fabrication of these custom diffuser pixels. Continuous variation of the recording parameters requires extreme accuracy. Therefore, we initially consider the possibility of designing diffractive optics with a small number of effective complex values: e.g. 0.5 magnitude at -120, 0, and 120 degrees. A recently developed ternary pseudorandom encoding algorithm then can be used to encode any desired fully complex function. Simulated designs of spot array generators are used to show that fidelity improves by increasing the number of roughness cells per pixel. Further improvements result from using more complex values, as is shown for designs with an additional zero-valued transmittance (represented by a completely randomly rough pixel). These results indicate that it is practical to fabricate high-fidelity custom diffractive optic functions with only a few recording states. The major advantage of this technique is that any desired complex-valued modulation pattern can be directly encoded and fabricated on a pixel-by-pixel basis, thereby accelerating the speed of both the design and the fabrication process.

Refractive microoptical elements were originally fabricated by mass-transport smoothing in gallium phosphide. Mass- transport smoothing is based on surface diffusion at elevated temperatures and allows the generation of highly efficient semiconductor microoptics. Starting from a master element, we have developed a replication technique for transferring microoptical surface reliefs into other semiconductor materials, such as gallium arsenide (GaAs). The technique uses a cast and dry etch process. Two different refractive microoptical elements have been replicated into GaAs, a Fresnel biprism and a concave micromirror. The elements have been characterized and show the high fidelity of the replication process.

Circle-to-point conversion has been used for collecting the output of an etalon where a suitable detector of equal area circular zones was not readily available. The output is converted to a line of points so that it may be read with a simple and readily available linear CCD detector. The purpose of this work was to determine the feasibility and practicality of making circle-to-point optical converters with up to 24 equal area annuli in a 24 mm diameter form factor. Each annulus redirects light into a focus and all foci lie in a straight line with equal spacing between them. The principal working wavelengths were 532 and 355 nm. The first approach was a step and repeat fabrication process using high resolution stepping stages to register 24 masks and a master HOE. The second method consisted of writing software that would generate the desired optic in the form of a single binary mark. An 8X photo reducer and a 4f optical processor were also used to improve performance. Both methods worked well and many samples of each were delivered with the goals being met. Work on the UV portion could not be completed on time but a simple RIE machine was configured and exposures into photo-resist were successfully made using a DCG hybrid master. The resist copies were etched with CF4 and O2 to make copies in fused silica. Further work will require an ion source to reduce losses in the UV HOEs by etching at an angle to the surface.