Four different thin DOE pattern generation techniques used at National Optics Institute (NOI) are discussed and compared: laser direct writing in photoresist, microlithography with e-beam masks, holographic recording, and laser assisted microfabrication. NOI special equipment used for each technique is described and applications are presented.

Two dimensional arrays of Fresnel zone micro lenses were fabricated and coated with antireflection layers by ion-beam-sputter deposition technique. The thickness of the layers was controlled by a reflection-wideband-monitoring-system with high accuracy. The lenses have a circular aperture of 2 mm and focal lengths of 70 mm and 20 mm for the wavelength of 0.63 micrometers and focal lengths of 29 mm, 8 mm, and 5.6 mm for the wavelength of 1.52 micrometers . The blazed profile in each zone was approximated by an eight level profile. Such stepped profiles were recorded with several masks, written with e-beam and with photolithographic technology. Our measurements reveal that the spot-sizes of the fabricated microlenses are close to the diffraction limited values, and the diffraction efficiency for the eight level structure is 83 percent.

Binary optics can produce microlenses and lens arrays with theoretical diffraction efficiency as high as 95% for eight-phase level devices. Due to shadowing, mask misalignment, and etching errors that accumulate during fabrication, the actual diffraction efficiency can be reduced to less than 70%. Advances in mask design and e-beam writing have reduced mask misalignment errors to less than 0.2 micrometers but the major issue is the accuracy of the RIE process that is used to transfer a lithographic pattern into the substrate. RIE has two limitations for binary optic applications. First, it cannot be readily employed for the wide range of possible optical substrates of interest (Al₂O₃ for example), and second, since the pattern is etched directly into the substrate, there is no simple means to calibrate the etch depth during the process. Thin film deposition of the binary structure addresses both of these limitations. It is applicable to a wide range of materials, and accurate in process monitoring of the deposit permits precise control of the feature height. In this paper, we report on eight-phase level binary optic microlenses processed by deposition of SiO₂ on fused silica and Al₂O₃ on sapphire using a projection lithography system. Photoresist processing was achieved by image reversal and lift-off technique. The microlens arrays (in a square format) were designed for (lambda) equals 0.632 micrometers with two microlens sizes of 120 micrometers X 120 micrometers and 240 micrometers X 240 micrometers having speeds of F/12 and F/6 (at the corners), respectively. Optical characterization has demonstrated that the microlens arrays are near diffraction limited and diffraction efficiency is in excess of 80%.

This paper discusses the formation of GRIN lenses by optical exposure of photopolymer (Du Pont) and the setting up of a simplistic test experiment for evaluation of resulting polymer optical elements. An essential aspect of the work relates to the duration of the exposure. We address the question of differences of performance related to whether the exposure time is greater than or less than the characteristic time scale of monomer diffusion.

An automated visible-infrared optical measurement system has been used to characterize the imaging performance of binary optic microlenses. Measurements of the point spread function (PSF) were made, from which the modulation transfer functions (MTFs) were derived. Diffraction efficiencies may also be measured using the same system. PSF measurements on both infrared and visible microlenses are in close agreement with theoretical predictions. Data on both IR and visible microlens arrays are presented.

This paper describes micro-optics research activities in Japan ... field categorized in two parts: devices and applications. In the... introduce GRIN devices, grating Fresnel lenses and mold press lenses ... applications we talk about parallel optical communications and optical computing.

Holographic optical elements for interconnecting electronic switching stages with light of 1.5 micrometers wavelength are presented. These elements include deflection holograms recorded in dichromated gelatin for deflecting the light and diffractive spherical gratings fabricated by microstructuring for focusing and collimating the light. The diffraction efficiency of these elements can reach 90% and focused spot sizes can be within the diffraction limit.

Microlens arrays play an important role in atmospheric wavefront sensors used by ground based astronomers in order to obtain diffraction limited images of stars in the presence of wavefront disturbances introduced by the earth's atmosphere. One technique for making these arrays is to use a two axes rastering process for engraving in photoresist coatings, producing square lenses with no room left between them. Obviously the efficiency of the arrays depends on the quality of the lenses. The surface shape is normally checked qualitatively with Nomarski and quantitatively using stylus profiling. Phase stepping microscopy has recently been applied to the problem, for measuring the shape of individual lenses and comparing the results with spherical profiles. The initial results have been very successful. Some typical examples are given and the results discussed to show the potential of such work in improving the quality of microlens arrays.

An overview of binary optics fabrication techniques, optimized to obtain high-quality micro- optics in visible and infrared materials, is presented. Maximum optical efficiency has been achieved for diffractive quartz microlenses at (lambda) equals 633 nm by controlling the critical fabrication parameters of alignment and etch depth. The degradation in optical efficiency of four-phase-level fused silica microlenses, resulting from an intentional 0.35 micrometers translational error, has been systematically measured as a function of lens speed (F/3 - F/65). Novel processing techniques that enable the fabrication of IR and visible refractive micro-optic arrays such as multilayer resist techniques, deep anisotropic Si-etching, and the formation of analog polymer lenslet arrays are described. Initial results are presented for both monolithic and hybrid integration of layered refractive micro-optic systems.

Spectacles have been designed for correcting the double vision associated with various forms of strabismus (`squint'). These correctors consist of light-weight, refracting Fresnel wedge prisms that can bend the optic axis by large deviations, while maintaining a relatively thin profile. Using a special mold structure, compatible with cost-effective production, a continuously variable range of prism angles can be pressed in suitable substrates, such as polycarbonate. The flat surface of the prism is embossed with a binary optics diffraction grating for compensating the prism's inherent color dispersion. Over a wide range of deviation angles, the Fresnel prism combined with the right grating achieves uniformly excellent quality of the perceived image, well suited for ophthalmological applications.

Micro-optics can be used to significantly increase the effective fill factor of focal planes. This, in turn, can enhance the overall performance of an imaging system in a number of ways. In this paper, we study the efficiency of different types of micro-concentrators, considering both the imaging and non-imaging varieties. The effective fill factor of a focal plane enhanced by a micro-concentrator is shown to be a function of three parameters: the type of micro- concentrator, the difficulty of the required concentration, and the severity of diffraction effects. For typical focal plane applications, both imaging and non-imaging concentrators are capable of increasing the effective fill factor to almost 100%.

The evolution in design, fabrication, and performance of diffractive optical elements manufactured for use as focusing elements in CO₂ industrial lasers is discussed.

Two classes of DOE in which fabrication is based on the technology used in microelectronics are considered: multiorder binary-phase (Dammann) gratings, and diffractive aberration correctors. Calculating the structure of the element is necessary to take into account the unavoidable technological deviations from the theoretical profile. The current presentation describes the methods and results of computation and fabrication of up to 41 equal orders gratings with optimal combination of diffraction efficiency and technological stability and aberration correctors for the focusing objectives of a laser player. The variants of such objectives permitting reduction of the technological difficulties of corrector fabrication are discussed.

Common-use diffractive lenses have microrelief zones in the form of simple rings that provide only an optical power but do not contain any image information. They have a point-image response under point-source illumination. We must use a more complicated non-point response to focus a light beam into different light marks, letter-type images as well as for optical pattern recognition. The current presentation describes computer generation of diffractive micro- optical elements with complicated curvilinear zones of a regular piecewise-smooth structure and grey-level or staircase phase microrelief. The manufacture of non-point response elements uses the steps of phase-transfer calculation and orthogonal-scan masks generation or lithographic glass etching. Ray-tracing method is shown to be applicable in this task. Several working samples of focusing optical elements generated by computer and photolithography are presented. Using the experimental results we discuss here such applications as laser branding.

For enhancing the light efficiency of lenslet array, the technique of binary optics has been used. Most binary lenslet array are designed of an array of Fresnel zone plate. A zone plate has simultaneously convergent focal points as well as divergent foci, so the intensity on either side is reduced. We have designed a lens array which combines the real focus with virtue focus, thus the intensity obtained is much higher than in a conventional array. In fabrication, four phase levels and eight phase levels have been used, high efficiency is thus obtained. Twelve X twelve, 16 X 16 equal intensity arrays have been produced. Testing of the phase structure and other parameters also are introduced.

It is found that a volume and a refractive index are varied as a result of an ion exchange process on glasses. This effect is used to produce microlenses and relief diffraction gratings. UV exposure and a thermal treatment result in a crystalline phase growth on photoglass- ceramics and polychromatic glasses. This effect leads to volume and refractive index exchange in the exposed zone. The exposure through masks enables the formation of volume phase holograms, gradient elements, and periodic relief structures on the photosensitive glasses surface and volume. The creation of ion-diffusants or microcrystals concentration gradients leads to a sample bending. This effect was used to produce the second order surface.

This paper reports design and fabrication of reflective phase relief kinoform with 16 phase levels. This kinoform converts a single beam to a 5 X 5 beam array. The measured diffraction efficiency is 76.16%, near the designed one of 79.68%. The aperture of the kinoform is 10 mm X 10 mm.

A new family of optical and optoelectronic elements is offered that's operation is based on controlling the current filament in semiconductors having an S-shaped current-voltage characteristic (CVC). The current filament is controlled by the action of fields (optical radiation, magnetic or electric field). The S-shaped CVC is a result of low-temperature avalanche ionization of shallow impurities in semiconductor epitaxial layers induced by an electric field (E approximately equals 1 - 10 V/cm). New elements, we shall call them cryo-elements, possess a low specific dissipated power on the order of 10^-9 W/micrometers ³. The characteristic time of current filament formation is about 10^-9 s. For controlling the current filament an extremely low (several photons per square micrometer in the region of fundamental absorption) light intensity is sufficient. The filament control is possible in a band from UV to IR.

The current presentation describes an interferometer which may be used to improve correction of interferometric measurements. In this device reference wavefront is created in the process of laser beam diffraction when it is focused on 0.5 (lambda) pinhole. The low value of about (lambda) /100 for wavefront errors or (lambda) /200 for the surface errors proves the good quality of the optical systems. A new interferometer has been used for optical shop testing of precision microscope objectives, laser beam researches, etc. Some applications of the new interferometer are presented.

Using technologies originally developed for the electronics industry, like photolithography, e- beam writing, and dry etching, good quality diffractive elements with useful physical properties can be produced directly upon a given surface. Particularly interesting are grating structures in which the macroscopic properties differ from the microscopic properties. An example of this is when the dimensions of the micro-structure of the grating are much less than the incident wavelength. In this case the properties of the material in the microstructure are `averaged over,' in effect producing a new artificial or distributed index material. In this paper we discuss our preliminary results modelling, making, and measuring several such diffractive artificial index elements for use in the far IR.

We have developed a method of producing micro-lenses on soda-lime glass plates by combining the techniques of laser annealing and an ion-exchange method, henceforth referred to as the `laser ion-exchange method.' The use of this technique makes it possible to simultaneously increase the refractive index on both sides of a glass plate at the laser beam irradiation zone. The increase in the refractive index on both sides complement each other to make a high quality micro-lens with a very short focal length. This method can be applied for producing circular, noncircular, linear, and array micro-lenses.

Surface feature optics, including binary optics, sinusoidal gratings, and high-fill factor micro- lens arrays, are being intensively developed for use in beam splitting and optical computing. Most are fabricated in plastics, and are therefore subject to such general disadvantages as limited optical transmission and high CTE. Some can be scribed in silica but dimensions are limited and fabrication costs are extremely high. Using a sol-gel process it is possible to fabricate surface feature optics in pure silica by a room-temperature molding technique. This technique provides the advantage of the highly favorable optical qualities of silica, including broadband transmission, low CTE, and exceptional resistance to laser damage. The sol-gel process is a room temperature casting operation in which the glass replicates the surface of the mold. Molds used in the sol-gel process can be fabricated from plastics and epoxies using common injection molding and press forming operations or via more sophisticated techniques. The manufacture of several prototypes is reported in terms of processing and characterization to determine the fidelity of the replication and their ability to fulfill required optical specifications.

It is shown that waveguide lenses, input/output couplers, and beam-splitters can be achromatized using conventional components in combination with diffractive elements. Experimental results are presented which show that it is possible to obtain achromatic performance over wavelength ranges that are larger than the wavelength range associated with conventional laser diodes.

Refractive microlens arrays with lens speed F/1 to F/5 are fabricated by the PROM (photoresist refractive optics by melting) technique. Optimal PROM fabrication parameters are determined from interferometric measurements of the optical quality. Elements in a hexagonal PROM microlens array, composed of 10,000 200 micrometers diameter F/2 lenses on 205 micrometers centers, exhibit less than one-tenth wave deviation from sphere. Four planes of these F/2 microlens arrays, each containing 10,000 lenslets have been assembled into an afocal imaging system.

The paper describes a new high NA planar microlens witha swelled structure (S- PML) designed for a laser diode (LD) array. The center to center spacing of the S-PML is 250 micrometers which is adjusted to the most ordinary LD array to be used in optical fiber communication system. The diameter of the S-PM is 85 micrometers and the focal length is 110 micrometers . The NA of the S-PML is 0.37. We evaluate the coupling loss between an LD and a single mode fiber using the S- PML. The coupling losses were 6.2 dB for 1.3 micrometers LD and 7.6 dB for 1.55 micrometers LD, respectively.

Surface-normal optical devices are appropriated for highly parallel information processing and high-speed switching. They should be combined, not only with electric circuits, but also with micro-optics which include beam propagating, focusing, splitting, coupling, and deflecting functions. Planar microlenses (PMLs) have flat surfaces and may facilitate their integration with surface-normal optical devices. Diffractive optical elements (DOEs) may have various functions, and they are fabricated on substrate surfaces in surface-normal optical devices. Combination with PMLs and DOEs may bring optical interconnections for parallel processing. We propose various module structures and experimental results using these microlens arrays and vertical to surface transmission electro-photonic devices. (VSTEPs).

Holographic optical elements (HOEs) are compact and flexible in their function: they can integrate focussing deflection and beamsplitting into a single element. Optical systems consisting of several elements can be built by recording planar HOEs side by side onto a common planar substrate -- a light guiding plate. By folding the light path, i.e., using multiple reflections within this plate, the light is guided from one HOE to the other. This concept is investigated for two applications: (1) An optoelectronic board to board interconnection based on holographic coupling elements on a light guiding plate: Diode lasers and pin diodes were used as optoelectronic transmitters at a data rate of 500 MBits/s. The coupling elements were volume gratings, recorded in dichromated gelatine (DCG) and coated onto the surface of the light guiding plate. Inside the plate the light was guided by total internal reflection. An overall loss of this transmission system of -2.6 dB over a distance of 11 cm was observed. (2) A miniaturized sensor head for the optical measurement of velocities of fluids based on laser Doppler velocimetry (LDV): HOEs mounted onto a glass substrate are used for beamsplitting and deflection. Volume holograms in DCG exhibit good optical efficiency (75% transmission of a cascade of two HOEs). In contrast to conventional sensor heads with diffractive devices one can achieve achromatic behavior which makes the sensor insensitive against wavelength drifts or mode hopping of a semiconductor laser.

A novel compact two dimensional optical sensor is proposed. The sensor consists of a piezoelectric actuator driven dual axis miniature optical scanner, a silicon photo diode, and a micro collimated light source with a micro Fresnel lens. By monitoring the beam intensity reflected from the object, the object position and the object size are determined, since the irradiated beam position is precisely identified by monitoring the phase of the applied ac voltage to the actuator. The sensing area as wide as 15 X 15 degrees is achieved with a simple configuration.

The monochromatic diffraction patterns from phase-only spatial light modulators, such as deformable mirror- and liquid crystal-SLMs, are routinely modeled using the fast Fourier transform. Random errors in phase have typically been evaluated by Monte Carlo analysis. This can require the averaging of numerous runs to find the expected value of intensity and its standard deviation. However, the pixel structure of current modulators, which allows each pixel to apply arbitrary piston or tilt modulation, greatly simplifies the form of the expectations. Specifically, we assume that the parameters of piston, and likewise tilt, describing the entire SLM transmittance are Gaussian, independent, and identically distributed random variables. Expressions for the expected value of the Fourier plane intensity spectrum and its standard deviation, and for propagation of the intensity pattern to any arbitrary observation plane using the angular spectrum of waves formulation are presented. Each expression reduces to a small number of Fourier transform operations that may be efficiently calculated by the FFT.

We propose a novel TE/TM mode splitter for an integrated optical detection device for magneto-optical disk pickup. The new mode splitter is monolithically integrated on a Si substrate with pin-photodiodes. This device is composed of optical waveguides A and B with effective indices of refraction N^A and N^B, where N^A > N^B. These two waveguides are connected by a tapered transition region. The light wave guided in waveguide A is incident on the tapered transition region at an angle of incidence greater than the critical angle for the TE₀ mode and smaller than the critical angle for the TM₀ mode. The TE₀ mode is totally reflected and the TM₀ mode is totally transmitted at that region so that this device works as a TE/TM mode splitter. We fabricated the mode splitter's tapered transition region using a novel wet etching process, then examined the TE/TM mode splitting operation using a GaAlAs laser diode ((lambda) equals 0.788 micrometers ). When both TE₀ and TM₀ modes were exited in waveguide A, the extinction ratios of the TE₀ and TM₀ modes were measured with the integrated photodiodes. The extinction ratios were -25.4 dB for the TE₀ mode and -23.3 dB for the TM₀ mode. These values are sufficient for practical application. Furthermore, the polarization detection function was experimentally confirmed using a Faraday rotator.

Birefringence in multiple quantum well (MQW) layers is utilized in a novel way to realize high performance two-dimensional spatial light modulators (SLMs). The polarized light is coupled into MQW layers using a grating. The light is modulated by an externally applied electric field which changes the birefringence in each pixel. The modulated light is recovered using a turning mirror similar to those employed in surface-emitting laser configurations. The usage of birefringence is shown to result in significantly higher contrast ratios than obtained in devices (e.g., SEEDs) using only electroabsorption. Both electrically and optically addressed structures are described.

We report on a novel method for generating sub-micron lithographic patterns in photoresist through the use of a scanned sub-wavelength optical aperture. The aperture consists of the tip of a single-mode optical fiber that is drawn down to a diameter of 80 nm and coated with aluminum. The fiber tip is manipulated with a modified scanning tunneling microscope (STM) that brings the tip into proximity of a photoresist-coated substrate. The resolution is primarily a function of the aperture diameter and tip-to-sample separation. A linewidth of 200 nm has been achieved in preliminary experiments.

This wavelength division multiplexer (WDM) architecture employs a number of dispersion compensated gratings in a guided-wave structure to perform the major functions of wavelength multiplexing or demultiplexing. The characteristic performance analysis, including wavelength dispersion, effect of beam divergence, and power budget are presented.

A method for producing a distributed feedback D fiber dye laser is presented. Existing fiber dye lasers are produced by placing a tapered single mode fiber into a dye solution. The evanescent field of a doubled YAG laser beam traveling in the fiber is used to pump the dye into fluorescence. Optical feedback and lasing action are achieved using external mirrors or a resonant fiber ring. In our scheme a segment of D fiber is etched to within a few microns of the fiber core. The etched fiber is placed in a solution of R6G dye. The etching is controlled using an in situ monitoring technique we have developed. An argon ion laser beam is focused into the fiber. Because of the small core size of the D fiber we use, there is sufficient energy in the evanescent field to cause the dye to be fluorescent. Diffraction gratings are produced generated by a holographic technique. We create diffraction gratings with periods of less than .3 (mu) using this technique. A miniature fiber dye laser could provide a compact source for short laser pulses for use in spectroscopy and communications.

Miniaturized opto-electronic and opto-electro-micromechanic hybrid integrated components are developed utilizing newly developed micro active semiconductor devices (e.g., laser diode, pin-point emission LED), micro optic passive devices (e.g., micro Fresnel lens, grating devices), and micro actuators. As a typical example, high-performance collimated and focused light sources, optical sensing devices, and two dimensional optical scanner are presented in detail.

We report fabrication of refractive microlens arrays in fused silica (SiO₂) with a variety of pitches, diameters, and focal lengths. Typical f-numbers range from f/1.5 to f/5. Melted photoresist lenses are made on a fused silica substrate, and etched into the SiO₂ using reactive ion etching (RIE) by carefully controlling the etch ratio. Techniques for microlens testing and measurement are discussed.

This paper presents a proposed application of the quantized fraction Fresnel zone plate (QF- FZP), a binary optics element, for increasing propagation distance of directed radiation beams. The design procedure and formula of QF-FZPs based on the vibration vector method are presented. If a QF-FZP of four quantized phase levels is used, the propagation distance of directed radiation beams can be prolonged 1.5 times further while the incident radiation beam maintains the same intensity. Finally, Fresnel-Kirchhoff diffraction theory is used for analyzing the axial intensity distribution of directed radiation beams diffracted by QF-FZPs.

Some peculiarities of phase-structure transformations of glass-ceramics materials and ceramics are investigated under laser irradiation. The influence of a CO₂-laser beam with a radiant flux density of about 10⁶ W/m² at a surface of glass-ceramic plate leads to the change of a ratio between amorphous and crystalline phases in the microvolume of a substance. It permits us to control the optical properties of glass-ceramics and to receive an optical transparent channel in the surface layer of an optically opaque specimen. Spherical micro-lenses are formed by an optically opaque specimen. Spherical micro-lenses are formed by an amorphization through the whole of the substance melting and quickly cooling down. The optical image quality is assessed by modulation transfer function measurements for different parameters of micro-lenses. It is stated that the micro-lenses could be useful for optical signal processing of objects with spatial frequencies to 15 mm^-1. It is possible to produce micro-optics arrays with different spatial periods, focal lengths, and sizes of each element. Prospects also are outlined for local modification of optical properties of some ceramics by a scanning device which is capable of forming the desired configuration of temperature field inside the specimen.

A one-dimensional array of surface-emitting microlasers was bonded onto a glass substrate that contains a matching array of microlenses and mirrors. The bonding was achieved by solder bump bonding with indium being used as the solder material. The alignment precision is within +/- 2 micrometers. The optical substrate provides a simple interconnection scheme that routes the light from each laser to a well defined output position. The lenses are implemented as diffractive elements and are fabricated by lithography and dry etching.