A theoretical approach to the design of high efficiency multilevel thin film phase-only gratings is reported. The discussion shows that a film optimum thickness and refraction index must be set in designing DOE components with maximum diffraction efficiency. Experimental results related to the grating''s chromatic behavior vs. the thin film parameters are also presented. These results show good agreement with the expected values foreseen by theory.

This paper addresses a set of problems accessible via the technology of photopolymers. Though most interest in micro-optic fabrication centers around the older technology of melted photoresist and the much newer area of binary optics, much can be learned from the area of photopolymers of the graded index type. Recent advances in the technology of the DuPont materials for example, make possible the fabrication of novel micro-optic systems. We examine the manufacture of micro-lens arrays using contact and other forms of lithography. The relative merits of simple refractive optics and graded index optics are discussed. This work has been applied to the formation of specialized diffusion screens for image projection and the advantages are pointed out in the discussion.

The microlens array reported in this paper is for enhanced optical coupling of near IR photons into the edges of the Rockwell solid-state photomultiplier (SSPM). Here the edge-illumination is necessary to achieve the required quantum efficiency of near IR photons in the SSPM, a device which is capable of photon counting. SSPM detection requires a method of highly efficient optical coupling to the gain medium to concentrate light with a 100 fill factor where lenslets are centered with a precise 0.2 micrometers accuracy. The microlens array is designed for a center wavelength of 1.3 micrometers , 1975 micrometers pixel dimension and a speed of f/4, which results in the array being nearly diffraction limited. The smallest feature size is 0.9 micrometers for the 8-phase level devices. From this design, we have successfully fabricated an 8-phase- level SSPM microlens array which demonstrates a 0.2 micrometers alignment accuracy among all three mask levels. SEM studies of the microlens show a high-quality surface finish and near vertical sidewalls. Optical characterization demonstrates that the microlens array is diffraction- limited at the design speed and design wavelength, with diffraction efficiency higher than 84.

We report the development of binary optic microlens arrays in GaAs. The application of this microlens array is for (gamma) -hardening of HgCdTe focal plane arrays. We intend to reduce the effective spot size of the picture elements and provide significant nuclear hardening for the focal plane array by considerable volume reduction of the detector elements. The microlens design is an eight-phase level approximation to an ideal kinoform lens. The lenses are designed to focus into the GaAs or air with a focal length of 480 micrometers or 148 micrometers respectively, at (lambda) equals 9 micrometers . Arrays of square lenses and individual circular lenses were fabricated. The square lens dimensions and f-numbers are 120 micrometers X 120 micrometers , f/1.23; 240 micrometers X 240 micrometers , f/0.62; and 480 micrometers X 480 micrometers , f/0.31, respectively. Designs include correction for spherical aberration. A set of four 10X projection masks was designed using graphic language (GPL) interfaced to computer-generated binary optics elements. The binary optic pattern was etched into the 3'' diameter GaAs substrate by reactive ion etching. Highly anisotropic etch profiles were obtained with feature heights in excess of 2 micrometers . Measured microlens efficiency for f/1.23 microlenses was as high as 60. The average measured value for a whole array was 55. Measurement of the point spread function at (lambda) equals 10.6 micrometers demonstrates optical concentration. This demonstration of binary optic microlenses in GaAs is of considerable importance to the future integration of purely optical and optoelectronic functions on a single wafer.

This paper describes the fabrication and testing of 64 X 96 arrays of microlenses used for fill-factor enhancement of uncooled infrared detector arrays. Each lenslet represents a f/0.9 Fresnel phase lens at 10 micrometers wavelength. All arrays were etched into silicon wafers as either 8-level or 16-level staircase kinoforms. When integrated with a detector array having 20 fill factor, these microlens arrays were capable of increasing the magnitude of the measured signal with f/2.2 fore-optics by 2.5-fold.

Teledyne Brown Engineering (TBE) has designed a binary optic microlens array that will increase the efficiency of a spatial light modulator (SLM). This paper discusses the design procedure and predicts the simulated performance. It is demonstrated that conventional ray trace modeling is inadequate for micro-optic design due to diffraction effects. A scalar wave solution correctly simulates this phenomenon under most conditions.

We have used the advantages of the photolithographic process to build a Hartmann-Shack type wavefront sensor using a 65 X 50 element binary optic lens array as the wavefront sampling element. The inherent accuracy and versatility of the lithographic process has reduced sampling and calibration errors associated with classic Hartmann sensing by allowing the lens array geometry to be tailored to CCD detector geometry with extreme precision. Combined with a quad-cell centroiding algorithm and wavefront reconstruction routines based on the successive over relaxation (SOR) algorithm, we present a wavefront sensor with submicron spot position accuracy, uniform response curves for all spots in the array, high dynamic range, and relative insensitivity to laboratory environmental vibrations. Experimental results obtained during a comparison of its performance to established wavefront methods are presented.

A goal of our work with binary optics is to identify the underlying efficiency limits of the technology. To aid in our understanding, we have designed a mask set that incorporates ten different 200-micrometers square lenslet designs with speeds ranging from f/0.8 to f/61 as single elements and as 10 X 10 arrays. The f/6 lenslet of the set is also used in 3.2 cm diameter arrays for an afocal imaging relay application. To measure efficiency reliably, we have developed a dedicated apparatus: the `EtaMeter.'' Based on a dual-beam, single- detector, self-referencing approach, the system offers low-noise performance, long-term stability, and excellent repeatability. EtaMeter measures relative efficiency with 0.001 precision and, when calibrated, gives absolute efficiency measurements accurate to 0.005. We have measured the optical efficiency of several devices and compared the results to benchmark calculations, concentrating on the effects of layer-to-layer alignment accuracy for 8-phase-level devices. For an f/4.5 microlens we find a distortion-induced excess loss of about 1.5/0.1 micrometers misregistration. For an f/4.5 microlens with overlay registration better than 100 nm, we achieve an absolute efficiency of 0.85, corresponding to 96 of the prediction.

A novel laser coupling module composed of a 1.3 micrometers single-mode fiber and a small laser package ((phi) equals 5.6 mm) which builds in a single thin microlens and a 0.78 micrometers emitting laser diode is proposed. A micro Fresnel lens with a high numerical aperture (0.45) and short focal length (0.65 mm) has been utilized for the first time as a laser-to-fiber coupling lens. The proposed laser coupling module measures about 2.8 mm between a laser facet and a fiber edge. The coupling efficiency of 23 in experiment is shown to be adequate for short- haul transmissions and fiber-to-the-home applications. Because all of the elements that compose the present module are able to be obtained at low prices, the design could reduce the cost of laser modules.

A selection of some of the optical data processing applications of computer-generated holograms (CGHs) is presented.

Computer-generated holograms for laser diode (LD) focusing are described. A quantitative description of design tradeoffs is given. The LD parameters (not parallel input light) are included. Multiple CGH lenses, nonequal focal lengths in x and y, positive and negative focal lengths in the same lens, circular focal spots and equal variance focal spots, attention to focusing angles, and 1-D LD array collimation for optical data processing applications are considered.

The Gerchberg-Saxton phase retrieval algorithm results in a phase profile which varies continuously, which is extremely difficult to fabricate. Binary optics technology offers a viable solution to this fabrication problem. We describe a modified Gerchberg-Saxton phase retrieval algorithm which incorporates the binary optics fabrication process into the iterative loop. This algorithm is used to optimize the phase profile of a multilevel phase grating which achieves a 2-D Gaussian fanout. The surface-relief structure which practically implements this optimized phase profile was fabricated. The results of the fabrication process are summarized and the experimental measurements on the fanout element are presented.

On 1 May 1991 a seminar was held at the National Physical Laboratory on the subject of microlens arrays. This would appear to have been the first such meeting to be held in Europe and the purpose of the present paper is to summarize European work that was presented there.

A CO2 laser is used to ablate concave lenslets in fused silica; these lenslets are then used to replicate or mold convex lenslets in plastic. The lenses range in size from 100 micrometers to 500 micrometers in diameter with speeds from f/1 to greater than f/10. The size and speed of the lenses can be controlled by changing the power, size, and exposure time of a focused CO2 laser beam. The ablation process is repeatable and lends itself easily to making large arrays of lenslets, limited in size only by the travel constraints of the mechanical stages that move the fused silica work piece. The entire process has been computerized so that an array of micro- optic lenses can be made accurately to any specification. Lenslets have been made in arrays of 1 X 10 to 60 X 60 with spacings of 300 micrometers to 2 mm between the centers of the lenslets.

We have developed a technique for fabricating fast, well corrected cylindrical microlenses. With this technique we have made a number of different microlenses with dimensions and focal lengths in the range of a few hundred micrometers , and diffraction limited numerical apertures as high as 0.9. The microlenses are specifically designed for applications where they can increase the radiance or otherwise enhance the optical characteristics of laser diode light. The fabrication method we use is very versatile, and the microlenses produced this way would be very inexpensive in production quantities.

The possibility of optic1 components forming by the laser action on the optical glass and gIass-bornin .nateriais attracts atthntion of nny investtgatnrs tcday1° . This action Is based on local het.ing cont.roi.I€xI In area and time. Local heatihg forms In glasses and glass-borniiw nbsriaIs a new macro structure with var ...iable density and .consequently difterent. value of refraction index RI ) n in the laser treatnent one ( LTL ) The density ot these rraterIals is defin€d by local temperature T, and ooolIn rate O1 /t . As a result of the heatIng - coolth cycle we can receive a local zone with a definite di3xcter D and form ( of the optical eiernt s pipi I and also with a certain optical force fl/fø . where f - a focal length of the eleirient. . The results of treatment are ire to be defined by certain physical processes. which accompany heating and fast cciin,g of glass- t:Lke n.ter ials.

Two of the many applications for microlens arrays are fill factor improvement in focal plane arrays and collimation of laser diode arrays. Most lenslet arrays made for fill factor improvement consist of immersion lenses that themselves do not have a 100 fill and the evaluation of such lenses is not representative of their use in an imaging system. Alternative designs are investigated. Anamorphic optics are required to correct for the astigmatism present in laser diode output. An array of micro-optics with toroidal refractive surfaces can be used to collimate or focus the light. We report on the fabrication and evaluation of such anamorphic micro-optics.

Integral imaging is potentially a powerful scientific recording method. Advances in fabricating microlens arrays coupled with new optical arrangements offer systems which accommodate ''near'' and ''far field modes'' have improved image resolution and operate in real time. True optical models can be produced and the image space interrogated.

Microlens arrays in surface relief having a pitch of 125 micrometers have been fabricated. The microlens arrays have excellent uniformity and a range of focal lengths can be fabricated. The microlenses can be directly formed on a chromium pattern or on plane glass by contact printing. The route to replication is via electroforming and subsequent embossing in clear material. By registering two microlens arrays a 3-D image can be formed at a 1:1 conjugate distance.

Refractive microlens arrays with f numbers ranging from f/1 to f/5 have been fabricated using a melted photoresist technique. The photoresist surface profile has been accurately reproduced in the underlying SiO2 substrate using etching techniques. Surface profile and optical performance characteristics of these microlenses are reported. Spherical microlenses are shown to have nearly diffraction-limited performance.

Microlens arrays which image a full size document onto a photoreceptor for copying or transmitting purposes are currently of much interest. In particular those arrays which have total conjugate distances less than 10 mm are important because of the compactness they afford in the contact image sensor (CIS) unit design. In this paper the fabrication of such a one-to-one array utilizing the photosensitive glass-based SMILE tm process is described. The performance of the array in terms of contrast vs. spatial frequency for a facsimile document reader application is tested in a commercial CIS unit. The overall measured performance is examined in terms of the process parameters involved in the lens fabrication. Advantages and disadvantages of the microlens array relative to other methods are considered.

We have developed a video Hartmann wavefront sensor that incorporates a monolithic array of microlenses as the focusing elements. The sensor uses a monolithic array of photofabricated lenslets. Combined with a video processor, this system reveals local gradients of the wavefront at a video frame rate of 30 Hz. Higher bandwidth is easily attainable with a camera and video processor that have faster frame rates. When used with a temporal filter, the reconstructed wavefront error is less than 1/10th wave.

The 2-D integrated planar microlens (PML) is expected to be used in connection with various 2-D devices in parallel optical fiber communication systems. In this paper, we demonstrate recent progress of PML and its light coupling characteristics. The coupling characteristics between (1) LD and single-mode fiber, (2) LED and GI-50 fiber, (3) single-mode fiber and single-mode fiber, and (4) single-mode fiber and detector were evaluated.

The use of microfabrication techniques allows one to build integrated free-space optical systems which can be useful for applications in optical computing and switching. This paper gives an overview of the fabrication of diffractive micro-optical elements, their integration using the concept of planar optics and their hybrid integration with gallium arsenide chips. Finally, optical clock distribution and space-variant interconnects based on the use of lenslet arrays are considered as examples for applications of integrated micro-optics.

Some of the main advantages of optics in processing are due to the 3-D nature of the optical wavefield. Current planar integration only utilizes one- or two-dimensional light propagation in waveguides. Technologies to achieve an integration of classical optical components in three dimensions are available.

A novel super compact dual axis optical scanner composed of a miniature resonator driven by a piezoelectric actuator and a micro-collimated light source using a micro Fresnel lens has been developed. The scanner is able to scan an optical beam in two directions with a scanning angle of more than 20 degrees, and its dimensions are 30 mm X 20 mm X 20 mm.

A Ushaped fiberoptic refractive index sensor and its aI ications are described. For longdistance measurements fabrication method using si I ca glass fibers is investigated. The lowloss silica class fiber sensor is applied to multi point measurements based on optical time domain reflectometry(OTDR). Application of the sensor to humidity measurement and the monitoring of human skin condition are also proposed.

Through advances in semiconductor miniaturization technology microrelief patterns with characteristic dimensions as small as the wavelength of light can now be mass reproduced to form high-quality and low-cost optical components. In a unique example of technology transfer from electronics to optics this capability is allowing optics designers to create innovative optical components that promise to solve key problems in optical sensors optical communication channels and optical processors.

The laser assisted chemical etching technique (LACE) is capable of generating high quality aspheric microlenses, as well as other miniature components such as prisms and waveguides. Using a calculated intensity map it is possible to individually specify the optical properties of each element in the array. To date, arrays of high quality lenslets have been fabricated with specifications ranging from f/0.7 to f/10 with spacing of 50 to 300 (mu) . Microlenses have been generated in glass, silicon, CdTe and sapphire having 95 fill factors with figure quality better than 1/10th wave.