Polysilicon microbeams in integral vacuum enclosures on silicon substrates have optical and mechanical properties that provide excellent opportunities for fiber-optic sensors. The microbeam, shell, and silicon substrate form a structure with Fabry-Perot-like properties that functions as an optomechanical modulator. When the beam vibrates incident light is modulated and reflected light is used to sense vibration of the beam. Thus, the structure can be used as a mechanical vibration or acoustic emission sensor. Microbeams attached to the substrate at both ends are highly strain sensitive and form the basis of a variety of sensors, including pressure sensors, accelerometers, strain, vibration, and temperature sensors. Excitation at the wafer level by a polymer film piezoelectric transducer provides a simple non-contact optical method for testing the microbeams before the water is cut into sensor die. Modulated light from a laser diode can also be use to excite the microbeams into resonance. The test results suggest that optically resonant microbeams can be used for low-cost precision fiber-optic sensors. Fiber-optic sensors are especially attractive for aerospace applications because optical fibers provide wide-bandwidth communication capability while eliminating electromagnetic interference (EMI), ground loops, and shielding requirements.

LIGA technology has been used to fabricate linear gratings having free-standing nickel walls a few micrometers wide and as much as 50 micrometers high and period on the order of 10 micrometers . With additional MEMS processing steps, such as devices are intended for use in a tunable infrared filter. Prediction of optical performance is a particularly challenging problem for gratings with these parameters and materials and requires a robust Maxwell solver. We have applied our own code, described elsewhere, in the form of a finite element implementation of equivalent variational problem to examine the optical properties of this class of gratings. Here, we describe our predicted results for transmittance as a function of wavelength and polarization for various grating parameters and incident conditions. Measurements of fabricated gratings were also carried out, and the predictions are shown to agree well with the measured data. The filter cutoff is shown to be sensitive to cone angle of the incident radiation, and the implications of this effect on system performance are discussed.

We have explored a new family of 6 mm imaging endoscope designs for laparoscopes. These designs use a `solid' relay lens made up of plastic lens components bonded together in a repetitive fashion to form a long, monolithic relay element without air spaces. The lack of air spaces allows for the elimination of coatings and spacing elements. This simplifies construction and should considerably lessen cost. A four element objective lens is presented for the system which uses a plano-convex sapphire element as a combination window and lens element. The other three lens elements are plastic, and produce an image which is `buried' in the monolithic relay. Two designs are discussed, a relatively inexpensive, `single use' design, which incorporates easy-to-fabricate, low-temperature plastic lens elements, and a more expensive, `autoclavable' design, using high-temperature plastic lens elements. Both designs exhibit good optical resolution, and high optical throughput and contrast.

Cantilever beams of piezoelectric heterogeneous bimorphs (ZnO-on-Si₃N₄ bimorphs) have been designed and fabricated on silicon wafers for applications as micro-mirrors. The bimorph is a composite beam comprised of a bottom layer of Si₃N₄ and a top layer of ZnO which has been metallized with Au/Cr film on both surfaces. A metallized rectangular pad near the tip of the bimorph has been designed to serve as a deflecting micro-mirror. The fabrication procedures of the bimorphs using surface-machining method with ZnO as the sacrificial layers are presented in the paper. Measurement of the deflection of the bimorph as a function of dc voltages showed two different regimes of voltage dependence. For voltage magnitude less than 1 volt, small and linear deflection was obtained which was consistent with the theoretical prediction. At voltage magnitude larger than 1 volt, large deflection was obtained with quadratic dependence on the magnitude of the applied voltage. The large deflection can be attributed to joule heating effect due to current conduction in the semiconducting ZnO. The fundamental resonance frequency of the bimorph has been measured and is in close agreement with the predicted value obtained from the Euler-Bernoulli beam equation. Because of the quadratic dependence on the voltage, resonance can be obtained even though the frequency of the driving signal was only at half of the true resonance frequency. Air damping was observed which led to a reduction of the Q-factor. To test the bimorph for micro-mirror display applications, a HE-Ne laser beam has been directed at a metallized pad at the tip of the bimorph. A sinusoidal signal superimposed with a dc bias has been applied to the bimorph. The scanning range of the reflected laser beam is reported and discussed in the presentation.

Several authors have given overviews of microelectromechanical systems, including microactuators. In our presentation we review some of these results, and provide a brief description of the basic principles of operation, fabrication, and application, of a few selected microactuators (electrostatic and surface tension driven). We present a description of a three- level mechanical polysilicon surface-micromachining technology with a discussion of the advantages of this level of process complexity. This technology is capable of forming complex, batch-fabricated, interconnected, and interactive, microactuated micromechanisms which include optical elements. The inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. Two examples of microactuators fabricated using this process are provided to illustrate the capabilities and usefulness of the technology. The first actuator is an example of a novel actuation mechanism based on the effect of surface tension at these micro-scale dimensions and of a microstructure within a microstructure. The second is a comb-drive-based microengine which has direct application as a drive and power source for micro optical elements, specifically, micro mirrors and micro shutters. This design converts linear oscillatory motion from electrostatic comb drive actuators into rotational motion via a direct linkage connection. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism.

An effective and universally useful means of adjustment in the realm of precision engineering and optics became possible with the realization of a new driving mechanism. In contrast to traditional adjustment methods, the mechanical component is situated in its final position before the start of the adjustment process. Specific mechanical impulses generated to be a striking mechanism are transmitted either directly to the mechanical component or indirectly to its housing (carrier). This results in minute linear motions or fine angular motions caused by the stick-slip-effect. The following paper explains the preliminary results of our theory and our experiments. A prototype of the electro-mechanical striking mechanism has been researched and developed by the Fraunhofer Institution for Applied Optics and Precision Engineering, Jena, Germany. PC-based algorithm software allows fast and exact positioning for precision engineering and micro-optical components. The described arrangement makes possible step-by-step adjusting movements with the minimum resolution of the steps to 0.5 arcsec.

The Texas Instruments flexure beam micromirror represents one of the most promising structures for production because of its reproducibility, which results from its symmetrical supporting structure. Flexure beam micromirrors modulate light in phase with a piston-flap motion that changes the length of the optical path. The device allows us to perform analog phase modulation by balancing spring and electrostatic forces. To fully use the analog phase capability, we need a mixed-signal circuit to drive it, but fortunately, micro-mirror technology is compatible with IC processes. Texas Instruments owns not only this unique micromirror design, but also a world-class mixed-signal production line. The main issue in production is maintaining the hinge strength to overcome stress caused by nonuniformity while staying within the range of analog CMOS driver compliance restrictions.

We are developing integrated micro-opto-mechanical systems (MOMS) based upon wafer integration of optical and micro-electromechanical components. In this paper, we describe our developments in micro-opto-mechanical systems in the area of microscanners and moveable optical elements. The microscanners are based upon the fabrication of micro-optical elements on the rotors of large diameter, i.e. 500 to 2,000 micrometers , polysilicon micromotors and have resulted in two approaches to scanning. In the first approach, nickel plating and high-aspect- ratio photolithography were used to produce 175 micrometers diameter, 20 micrometers tall nickel polygon reflectors on the rotors of polysilicon micromotors. These polygon microscanners are suitable for planar scanning as well and other planar applications such as optical fiber and waveguide switches. In a second approach, 2 - 4 micrometers spatial period diffraction gratings were fabricated on the solid rotors of polysilicon micromotors. Such devices are suitable for applications requiring out-of-plane scanning, e.g., bar code readers, and take advantage of planar processing. Chemical-mechanical polishing was used to reduce the polysilicon rotor's average surface roughness (R_a) from 420 angstrom to below 17 angstrom, improving the optical performance of the diffraction gratings. Diffraction grating microscanners using salient pole micromotors have been operated at voltages as low as 45 V, with maximum operational speeds of 1100 rpm. Although microscanners based upon rotating reflectors and diffraction gratings are significant, future MOMS also require linear motion of optical elements and optical waveguides to carry light between optical elements. To this end, we have produced optical reflectors on linear translational comb actuators.

We have designed and built integrated, movable micromirrors for on-chip alignment in silicon- optical-bench technology. The mirrors are fabricated using surface micromachining with three polysilicon layers. A polysilicon-hinge technology was used to achieve the required vertical dimensions and functionality for alignment in hybrid photonic integrated circuits. The positioning accuracy of the mirrors is measured to be on the order of 0.2 micrometers . This precision is shown theoretically and experimentally to be sufficient for laser-to-fiber coupling. In the experimental verification, we used external actuators to position the micromirror and obtained 45% coupling efficiency from a semiconductor laser (operating at 1.3 micrometers ) to a standard single-mode optical fiber. The stability and robustness of the micromirrors were demonstrated in shock and vibration tests that showed that the micromirrors will withstand normal handling and operation without the need for welding or gluing. This micromirror technology combines the low-cost advantage of passive alignment and the accuracy of active alignment. In addition to optoelectronic packaging, the micromirrors can be expected to find applications in grating-tuned external-cavity lasers, scanning lasers, and interferometers.

Microjet printing methods are being utilized for data-drive fabrication of micro-optical elements such as refractive lenslet arrays, multimode waveguides and microlenses deposited onto the tips of optical fibers. Materials used for microjet printing of micro-optics to date have included optical adhesives and index-tuned thermoplastic formulations dispensed at temperatures up to 200 degree(s)C onto optical substrates and components. By varying such process parameters as numbers and locations of deposited microdroplets, print head temperature and orifice size, and target substrate temperature and surface wetability, arrays of spherical and cylindrical plano-convex microlenses have been fabricated with dimensions ranging from 80 micrometers to 1 mm to precision levels of just a few microns, along with multimode channel waveguides. Optical performance data such as lenslet f/#s and far-field diffraction patterns are presented, along with beam-steering agility data obtained with an optical telescope system assembled from microlens arrays printed by this process.

A highly miniaturized optical scanner integrated with a photo detector has been developed for miniaturization of scanning type of optical sensors. The scanner is fabricated by silicon micromachining technologies and is driven by a piezoelectric actuator. It is capable of two dimensional scanning and photo detection. The scanning angle is over 40 deg X 30 deg and the photo detecting sensitivity is 0.49 A/W for 680 nm wavelength light.

We demonstrate the fabrication of an out-of-the-plane Fabry-Perot interferometer (FPI) `on-a- chip' using the single crystal reactive etching and metallization (SCREAM) process. A modified version of this process is also developed to generate a fully suspended Fabry-Perot interferometer (FPI) `on-a-frame.' The optical device is mounted on a released frame, which includes suspended contact pads and oxide isolating segments. During the process, the total structure (with 8.6 mm² surface area) is fixed to the substrate through serpentine springs. Then, using a pair of fine tweezers, these springs are clipped and the thin membrane- like structure is lifted off the substrate and placed exactly between self-aligned input and output single-mode optical fibers. The suspended FPI `on-a-frame' is made from freely released beams of dimensions comparable to fiber diameter with a vertical depth of 107.5 micrometers . The mirrors of the FPI, which consist of a series of (lambda) /4 SiO₂ and Si film stacks separated by an initial gap distance of 10 micrometers , attract each other when a bias is applied across these capacitor-type plates and tune broad-band IR light into a specific wavelength.

A novel micro focusing optical device controlled by a piezoelectric thin film micro actuator has been presented. This device is provided by bonding two micromachined substrates, which are a glass substrate integrated with a surface emitting light element and a micro Fresnel lens on each surface, and a silicon substrate with a diaphragm type of piezoelectric thin film actuator on it. The surface of the thin film is used as a movable reflection mirror. Focusing is performed by changing position of the mirror surface along the optical axis. In the case of applying the micro lens with 1.3 mm of diameter and 0.33 of N.A. to this focusing device and the thin film actuator capable of several micron displacement, focal point shifting of over 100 mm is obtained. Applying the device to optical senors such as a barcode reader, miniaturization of the light source and high resolution detecting for wide range could be possible.

Single crystalline silicon has very well known and predictable mechanical, optical, and electrical properties and is easily manufactured with consistent results. It is also integrated circuit compatible and leads to incorporation of circuits and high quality piezoresistors which are available to monitor motion for self-testing. We present for the first time a novel surface micro-machining process using merged epitaxial lateral overgrowth (MELO) silicon to demonstrate the fabrication of single crystal silicon, free standing cantilever beams 1 mm long and 5 micrometers X 10 micrometers in cross section. These beams had no evidence of stress related bending and were free from the substrate, returning to its original position after numerous electrostatic deflections. MELO has also shown great potential for advanced BJT and MOSFET device applications, hence active devices can be incorporated into the deflecting beam arrays. Diodes fabricated in the beams show excellent characteristics with average ideality factors of 1.01. Note that the technology permits adding of single crystal silicon to selected areas, hence it is an additive process as compared to traditional subtractive methods that deposit films over the entire wafer.

The development and testing of lens array prototypes for human use is described. The major issues addressed during this effort were the optical gain achievable from individual lenslets, visual acuity of the overall device, overall device weight and cost. We describe the techniques used to develop lens array devices using off-the-shelf glass achromats which provided large optical gain and high visual acuity. We then describe the development of plastic achromats which provide equivalent visual performance at a fraction of the cost and weight of the glass prototypes.

We analyzed the optical and mechanical performance of several designs of agile beam steerers based on refractive microlens arrays for sensing and imaging applications in the visible and infrared wavebands. Ray-trace analyses showed that the best design is capable of steering narrowband illumination +/- 25 degree(s) in two dimensions with nearly diffraction-limited performance. The maximum steering angle depends on the materials. We found that imaging the field of regard takes significantly more time than scanning it unless cameras with very high frame-rates are used. We performed many parametric studies that can be used to optimize the design for any application. We compared optimal designs for microlens-array and conventional galvanometric agile beam steerers. The microlens-array agile beam steerer provides significant improvements in scanning speed, random access pointing, energy consumption, mass reduction, and volume reduction.

Fabrication issues of microlens arrays, made by first forming photoresist microlenses, by patterning and reflowing photoresist islands under temperature, and then transferring this into the substrate by a dry etch process, were studied. Photoresist microlenses were reliably fabricated within a range of aspect ratios. The desired sag of the microlenses in the substrate was controllably achieved by adjusting the etch selectivity. Etching behavior of fused silica in mixtures of fluoroform with oxygen or sulfur hexafluoride was studied in detail. High quality microlens arrays were fabricated in fused silica, silicon and germanium, and selected lenses were characterized.

Optical trapping is a novel technique that utilizes radiation pressure for the non-contact manipulation and control of micron sized particles including living cells and micro-organisms. Typically, optical trapping is performed using a high power microscope and a complicated optical setup to form a single beam optical gradient trap or `optical tweezers.' Recent work has demonstrated three dimensional optical trapping using the counterpropagating beams from two optical fiber cleaves. This results in a simple and low cost implementation of an optical trap. Our paper discuses a refinement of this technique using pigtailed 1.3 micrometers semiconductor lasers and tapered lensed optical fibers with hemispherically machined microlens ends. Our optical trap consists of two tapered fiber lenses separated by distances of between 100 and 400 microns, with optical power ranges between 2 and 40 mW. Adjusting the relative powers of the optical fibers allowed us to trap and position 3, 5 and 10 micron beads over axial distances of several hundred microns. Our refinements improve trap accessibility while simultaneously increasing the trap stability. We have also used a ray optics model to simulate the performance of the optical fiber trap and predict the forces generated throughout the trapping volume. Axial and transverse trapping efficiencies up to 0.1 are predicted. The model can be used to predict trap strength and stability for various combinations of fiber spacings and particle sizes. Experimental observations of trapping and manipulation of 3 micrometers , 5 micrometers , and 10 micrometers beads are also presented and compared to the model.

The effective-index method and Marcatili's technique were utilized independently to calculate the electric field profile of a rib channel waveguide. Using the electric field profile calculated from each method, the theoretical coupling efficiency between a single-mode optical fiber and a rib waveguide was calculated using the overlap integral. Perfect alignment was assumed and the coupling efficiency calculated. The coupling efficiency calculation was then repeated for a range of transverse offsets.

Semiconductor laser diode (LD) coherent light source coupling is critical to integrated optic (IO) performance. Direct external coupling of conventional (CD layer) LDs is often inefficient, introduces noise, and is generally counter to the IO micro-concept. Two options are suggested; fiber optic coupling to the IO chip aperture and integration (hybridization) of micro-LDs within the IO chip itself. Selection of the optimal LD for integration into IOs depends on a variety of parameters specific to the IO application. As an example, laboratory displacement measurements were carried out with a conventional (780 nm) edge emitting LD externally attached to an IO Michelson interferometer (IOMI) chip at the waveguide aperture. Measurement error analysis identifies errors and suggests how digital, thermal, electronic, and optical source errors can be minimized through electronic design and micro-LD components. Characteristics of LDs, VCELS and ring-laser didoes, such as threshold current, operating voltage, thermal effects, mode structure, loss mechanisms, and related coupling characteristics are compared. Recommendations for improving analog/digital conversion and software methods, as well as applications of vertical cavity surface-emitting lasers and semiconductor ring lasers coupled to IO chips are discussed.

The progress of modern optics and laser technologies is substantially influenced by two factors: (1) Development of semiconductor lasers (SL), lines and matrix with power of 1 - 100 W at room temperature and their applications in industry, medicine, ecology, etc. (instead of YAG:Nd, He-Ne, and other types of lasers). (2) Broad development of fiber-optics systems in industry for delivery of laser radiation, in medicine as medical tools and fiber-optics nets for diagnostics in medicine and environmental applications. Also, the following directions are very important now: (1) Microsystem technique, which often includes micro-opto-electro- mechanical components in an integrated unit. (2) Integrated optical systems which consist of a number of special micro-optical components (MOC) like wave-guides, optical interconnections, geodesical lenses, special diffraction elements, etc. (3) Information technique for optical communication, cable television, optical recording, data storage, optical diagnostics in complicated technological processes and constructions, in medicine, biology and ecology, etc., which are now more and more connected with fiber-optical systems. All these new or relatively new fields of laser applications in optics demand a new much more variable component base, which could not be fabricated by traditional means of optical technology (mechanical polishing technique).

This paper reviews applications of diffractive optics to optical resonators using diode laser arrays and wide-stripe diode-laser amplifiers as the gain medium. The mode profile can be tailored to any desirable shape by proper design of the diffractive optics. By optimizing additional cavity parameters, these resonators can be designed to discriminate against higher- order cavity modes, insuring single-spatial-mode operation. As a first example, we show a diffractive laser mirror designed to excite a uniform-intensity supermode of an AlGaAs laser array. The effect of varying the phase of this array on modal discrimination is studied. In the second example, a laser mirror is designed to produce a super-Gaussian beam profile in a wide-stripe semiconductor laser amplifier. Two-and-eight-tenths watts of diffraction-limited optical power is obtained.

Fast cylindrical microlenses are an ideal solution for correcting astigmatism and beam ellipticity in laser diodes. Many laser diode applications require a diffraction limited non- astigmatic circular beam. The traditional way of accomplishing this is by use of an anamorphic prism pair in combination with a cylindrical lens. Through proper design it is possible to encompass the effects of these three elements in one microlens. Such an element is known as a virtual point source (VPS) microlens. The VPS microlens reduces the divergence of the fast- axis of a laser diode to that of the slow axis while at the same time forcing the fast and slow axis to appear to emanate from one point. Since a microlens has dimensions similar to those of multimode fibers it allows a laser diode to maintain its compact size while producing a diffraction limited circular wavefront. The design and implementation of the VPS microlens has been reported. A typical microlens has a working distance of 30 micrometers and requires sub-micron positioning accuracy as well as mounting techniques that can maintain this precision lens alignment over time. We address the issues of microlens characteristics, alignment tolerances, and bonding techniques.

We have investigated the effect on a laser diode's frequency of optical feedback from a short external cavity made from a precision cylindrical microlens collimator. Since the microlens collimates the laser output radiation to a diffraction limited beam, reflected light from the planar surfaces of the microlens is reimaged at the output facet, providing very efficient optical feedback into the laser cavity. Feedback from the external cavity can be used to control the longitudinal mode characteristics and emission frequency of the laser by varying the microlens position. Based on the results of these experiments we are developing a simple, compact, and robust tunable laser diode system that utilizes an orthogonal pair of collimating microlenses to form a short external cavity for longitudinal mode and frequency control. The resulting system will generate a circular, collimated beam of single frequency, tunable laser radiation.

The collection efficiency and collimation ability of high numerical aperture circular and cylindrical GaP lenses were evaluated using single index-guided and gain-guided laser diode emitters. Comparisons were made between 200 micrometers focal length cylindrical lenses (NA equals 0.75) fabricated by an accurate repetitive step-wise etching method and 70 micrometers focal length cylindrical lenses (NA > 1) fabricated by a simple resist reflow technique. Lens arrays (200 - 300 micrometers fl, 0.5 - 0.75 NA) fabricated by the repetitive resist-etch method were used to collimate the output of a diode bar consisting of 100 index-guided elements. Refocusing of the collimated light with a macro-optic (for pumping a Nd:YVO₄ laser) produced a spot that was on average 2 - 3 times larger than the diffraction limit and contained up to 88% of the total bar output. The deviation from the theoretical limit was examined in terms of lens fabrication accuracy and alignment tolerances between the diode and lens arrays, which were shown to be on the order of 1 - 2 micrometers .

The design, fabrication, and testing of a collimating lens array is discussed. The lens array is a hybrid design using a cylinder lens along with a binary optic element array. The binary optics were made on silicon dioxide substrates, patterned with a contact print excimer laser mask aligner and reactive ion etched. The lens array is designed to collimate 100 individual laser sources on a 100-micrometers pitch. The 1-cm lens array collimates lasers array sources laterally (along the axis of the array) using only the binary optic elements. In the other highly divergent axis of the diode laser array, the lens array corrects cylinder lens aberrations with the binary optic elements and does the gross collimation with the cylinder lens. The results were 50 percent transmission and 50 percent Strehl ratio, both very disappointing. Possible causes of the poor performance are in both design and fabrication.

The ability to condition the radiance of laser diodes using shaped-fiber cylindrical-microlens technology has dramatically increased the number of applications that can be practically engaged by diode laser arrays. Lawrence Livermore National Laboratory (LLNL) has actively pursued optical efficiency and engineering improvements in this technology in an effort to supply large radiance-conditioned laser diode array sources for its own internal programs. This effort has centered on the development of a modular integrated laser diode packaging technology with the goal of enabling the simple and flexible construction of high average power, high density, two-dimensional arrays with integrated cylindrical microlenses. Within LLNL, the principal applications of microlens-conditioned laser diode arrays are as high intensity pump sources for diode pumped solid state lasers (DPSSLs). A simple end-pumping architecture has been developed and demonstrated that allows the radiation from microlens- conditioned, two-dimensional diode array apertures to be efficiently delivered to the end of rod lasers. This architecture enables the generation of pump bemas that are scalable in absolute power with intensities approaching 100 kW/cm². To date, pump powers as high as 2.5 kW have been delivered to 3 mm diameter laser rods. Such high power levels are critical for pumping solid state lasers in which the terminal laser level is a Stark level lying in the ground state manifold. Previously, such systems have often required operation of the solid state gain medium at low temperature to freeze out the terminal laser Stark level population, so as to minimize losses resulting from reabsorption of the laser radiation. The necessity of low temperature operation has rendered such systems impractical for many applications. Our recently developed high intensity pump sources overcome this difficulty by effectively pumping to much higher inversion levels, allowing efficient operation at or near room temperature. Because the end-pumping technology is scalable in absolute power, the number of rare-earth ions and transitions that can be effectively accessed for use in practical DPSSL systems has grown tremendously. Unique laser systems for applications in fields such as medicine and remote sensing can now be simply realized. We have also been involved in programs to evaluate the use of direct diodes for material processing applications. Here, diode radiation from an extended two-dimensional microlens-conditioned array is focused and delivered directly onto a work piece. Systems based on this concept can be utilized in the heat treating and hardening of metals. Another application of microlens-conditioned laser diode arrays is in the direct coupling of their radiation to optical fibers. Direct diode-to-fiber coupling has recently been demonstrated for a medical application in which 22 W of cw 690 nm radiation was delivered from a microlens-conditioned stack of AlGaInP laser diode bars through a 1 mm core fused silica fiber. This approach used a simple and inexpensive 1 cm focal length lens to direct the microlens-conditioned radiation from the diode stack into the optical fiber.

The use of scanning probe microscopies -- such as scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM) to study carrier transport through semiconductor heterostructures -- is reviewed. The ability of BEEM to probe buried structures below the surface can be exploited to study heterostructure band-offsets and resonant tunneling through quantum structures. It is shown that BEEM can serve as a powerful probe of the spectroscopy of such structures. The implications of such studies for research on quantum dots and the characterization of new optoelectronic materials are discussed.

A promising approach for efficient microlenses and compact diode laser systems is reviewed. Development of one-step etching of the lens preform and effective wafer protection in mass transport has led to a considerably simplified process and increased reproducibility. Anamorphic microlenses have been fabricated and demonstrate capability for simple compact optics for tapered high-power diode lasers, with coupling of 347 mW into a single-mode fiber. GaAs microlenses have been developed as a first step toward monolithic laser/lens integration. Simple hybrid integration has been demonstrated with a direct mounting of microlenses on packaged lasers.

GaP lens arrays have been routinely produced in large formats (substrate dimensions up to 1.5 by 1.0 cm) with high yield and uniformly good finish. Diffraction-limited performance for collimation of single-mode diode lasers has been demonstrated. Laser-diode bars and coherent 2-D surface-emitting arrays have also been collimated with low transmission losses (98%) for 2.5 micrometers > (lambda) > 0.8 micrometers . Microlenses up to 300 micrometers in diameter with f/#s as low as 0.7 have been enabled by a new mass transport fabrication technique using sealed quarts ampoules rather than a flowing tube furnace. In this modification only small pieces of phosphorus are required (no phosphine or hydrogen); consequently, little safety burden is incurred, and initial expenses are reduced. The mesa-step-spacing was increased from 10 micrometers to 15 micrometers , and, by additional chemistry control, 30 micrometers spacings have been demonstrated. Also, time-at-temperature for mass-transport smoothing has been shortened to as little as 8 h. Mass-transport chemical mechanisms and material incompatibilities are discussed. Smoothing in the fused-quartz ampoules is shown to be self- terminated by wafer oxidation, probably caused by oxygen from thermal equilibrium dissociation of the silicon dioxide ampoule. This mass transport technique lends itself to a wide variety of novel lens fabrication strategies and clearly extends the potential applications.

Refractive and refractive-reflective arrays of circular as well as cylindrical thin-film microlenses in linear, hexagonal and rectangular arrangements on solid glass/quartz plates and flexible polymer foils have been produced with an improved vapor-deposition technique using shading hole masks and a planetary rotation system. Up to 1000 solitary elements with pitches of 170...350 micrometers and diameters of 50...350 micrometers have been deposited on solid quartz plates and flexible polymer substrates. Focal lengths of typically 1.5...20 mm have been realized. Additional global envelope functions of phase and/or reflectance have been realized. Different types of segmented lasers including imaging and self-imaging arrays as coupling, outcoupling and focussing components have been tested. Graded reflectance micro-mirror arrays (GRMMA) have been used as refractive-reflective elements for solid-state lasers with unstable Talbot resonators which deliver arrays of phase-coupled, focused partial beams. Arrays of diode laser beamlets have been generated by optical transformers combining rod lenses (fibers) with microlens arrays. New schemes for side-on and end-on pumped solid-state lasers and fiber array lasers containing microlens arrays have been developed.

The control of optical distortion is useful for the design of a variety of optical systems including those used for laser scanning. A lens used for focusing a scanned laser beam onto a flat image field with constant intensity profile must also satisfy the f-(theta) condition, i.e., the image height is proportional to the input field angle itself, so that the scan velocity across the image plane remains constant. The lens needs to be free from coma, astigmatism, and field curvature and must have a prescribed amount of distortion. We describe the design and development of a diffractive f-(theta) lens and present experimental verification of the theoretical predictions.

Proper exposure of the photoconductor in an electrophotographic printing system is essential for high quality printing. Gas lasers such as helium-neon and helium-cadmium lasers do not lend themselves to easy electronic power control. To set proper exposure in an electrophotographic system, it is necessary to deal with a number of time varying factors including laser intensity, acousto-optic modulator efficiency, photoreceptor sensitivity, and toner developability. A nematic liquid crystal based variable laser attenuator was developed as a means of setting exposure accurately in a closed-loop exposure control system. This paper describes some of the design considerations and performance parameters for the variable attenuator. The system is compact, low cost, has high throughput, provides an exposure range > 100:1, and has sufficient speed to reset exposure between consecutive prints. The liquid crystal variable attenuator is used in a variety of Xerox printing products including the DocuTech Production Publisher and the Xerox 4850 Highlight Color Laser Printer.

A method of understanding the behavior of multiple coaxial Bessel beams is presented. An attempt to develop a way to modify the longitudinal behavior of Bessel beams is discussed by analogy to a multiple plane wave interference pattern. It is shown, both with theory and numerical simulation, that the summation of several coherent Bessel beams of differing convergence will alter the performance of the propagating beam in a predicable manner.

Recently, photonic atoms (dielectric microspheres) have enjoyed the attention of the optical spectroscopy community. A variety of linear and nonlinear optical processes have been observed in liquid microdroplets. But solid state photonic devices using these properties are scarce. A first of these applications is the room temperature microparticle hole-burning memory. New applications can be envisioned if microparticle resonances can be coupled to traveling waves in optical fibers. In this paper we demonstrate the excitation of narrow morphology dependent resonances of microparticles placed on an optical fiber. Furthermore we reveal a model for this process which describes the coupling efficiency in terms of the geometrical and material properties of the microparticle-fiber system.

We present an introduction to some of the critical considerations in designing pickup systems for optical data storage.

In recent years there has been an increasing interest in using diffractive optical components in data storage systems such as CD-ROM drives and compact disc players. This paper reviews a number of different diffractive optical components that have been used in commercial products and how they are used in the optical pickup heads. Considerations for manufacturing these types of diffractive optics are also discussed.

Holographix, Inc. has developed a family of holographic laser scanning systems for printing applications. These systems have been designed to significantly reduce production costs without compromising print quality. Holographix has been awarded several patents on its designs and licenses its technology to OEMs. The optical designs for these systems, developed with Optical Research Associates (ORA^R), range from `low-end' laser scanners for 300 dpi and 600 dpi desktop printers to prepress scanners with 1200 dpi and greater resolution. The designs are well corrected for linearity and line bow. Unique features of these designs are telecentricity at the focal plane and the achromatic correction for both cross-scan and in-scan errors due to wavelength variations. The achromatization capability allows the use of laser diode sources for a major cost savings and telecentricity improves in-use performance. This paper briefly describes the concept of holographic laser scanning and key features of the optical designs.

The need for improved vision in various undersea applications has been recognized for decades. Improvements in underwater cameras and lenses have followed similar improvements in land-based cameras, but limitations associated with the image transfer characteristics of the medium have been primary obstacles in developing high performance systems. The application of lasers to the imaging formation process has provided a means of acquiring long range images and has, at least partially, formed the basis for the development of high power blue- green laser technology. Unlike atmospheric applications, underwater images can be formed only over small distances -- perhaps only tens of meters. Distance is primarily determined by the optical power available, the system geometry, the detection means, and (primarily by) the optical attenuation of the medium. The attenuation is governed by absorption and scattering processes which act to either remove or redirect photons originating from the source of illumination. In spite of the limitations imposed by these effects, considerable progress has been made over the past several years toward increasing the image formation range and image quality. These gains have been made through the use of nonconventional image formation techniques and laser technology. This paper reviews the classically described methodologies for underwater image formation, as well as their limitations, and discusses recent developments that extend imaging capability beyond the construction of 2-dimensional reflectance maps. For example, a system under development produces three-dimensional maps of the image space using a scanning laser configuration. The scene is viewed from a separate location to provide depth information via triangulation. The detector provides an estimate of position of the apparent landing spot of the laser beam for each scan angle from which a depth estimate is calculated. The system is designed to scan a 20 X 20 degree field-of-view at distances from 0.5 to 1.5 meters with a resolution of about 1 millimeter.

Laser scanning method has been applied to an interactive computer screen to provide a large- scale whiteboard interface to computer generated images. Optimizations in pen tracking and ink simulation were found necessary to give a natural pen feel attractive as an alterative to the keyboard and mouse.

Images printed on paper or film can suffer from artifacts caused by the laser scanner used to generate the image. These image artifacts can detract from the information content of the presented image. In order to design a laser raster output scanner (ROS) which faithfully reproduces digital information, knowledge of the types of artifacts and visibility thresholds of these artifacts are needed. This paper attempts to characterize the various imaging artifacts capable of being generated by ROS systems.

There is a problem of creation of the system of the halftone and colored laser-beam recording of high resolution. Obstacles have influence on them more than on binary systems of laser- beam recording. Periodical fluctuations of speed of scanning are particularly dangerous. These fluctuations are connected with the vibration of the mechanism of movement of the light sensitivity material. They create a parasitic effect on the recorded image. The cardinal way of disposing of the problem is recording on an immovable material. These records can be made by the system of the two-coordinate angular scanning of the laser-beam. This system has geometrical distortions. Questions of correction of geometrical distortions are considered in this article. An objective with negative distortions is proposed by us for correction of geometrical distortions of one coordinate. We propose to make a correction of the geometrical distortions for a bi-coordinate scanning system by an electronic method. The essence of the electronic method is a modulation of the timing frequency of recording by a function of the correction of distortions. A module of the two-coordinate scanning was elaborated and investigated. The module contains two deflectors, an interferometric system, a block of the control and a three-lens objective with negative distortions. Resolution of scanning of the module is 10,000 X 10,000. Area of recording is 300 X 300 mm. Horizontal sweep frequency is 150 Hz. Error of the position of a beam is +/- 0.002 mm.

Technical developments in the past few decades have led to scanners with greater accuracy and higher frequencies of operation at larger scan angles with wider apertures. The causes of this evolution of galvanometric and resonant scanners, whose attributes make sophisticated applications possible, are given in order to anticipate future requirements and technologies for the next generation of these scanning devices.

This paper analyzes the sources of error which shape the accuracy of a flat field raster scanning engine. It briefly describes the critical characteristics of the optical elements, scanners, electronics, laser, and structural design selected to build an engine with a system of accuracy of 0.35 micron, a 3.5 micron spot, and a telecentric work area of 25 mm diameter.

As the speed and accuracy requirements increase for Galvanometer based optical scanners so does the need for higher performance test equipment. This paper summarizes the practice and challenge of designing such instruments.

In the article there is an estimation of the maximum speed of electromagnetic and piezoceramic deflectors. The estimation takes into consideration properties of used materials and working conditions. Analytical dependences are received. They connect the maximum speed, an angle of deflection, and an aperture of light beam. It's found out that the maximum speed of electromagnetic deflectors is 5 - 10 MHz and the maximum speed of piezoceramic deflectors is 1 - 3 MHz. A mathematical model of the electromechanical deflector is elaborated. Mathematical simulation of transitional processes is conducted. Influence on the transitional process of the first and the second mechanical resonance was investigated. An experimental research of deflectors with the maximum parameters was made.

The performance of the rotary encoder is crucial to the accuracy of pixel addressing of a laser beam scanning system. In this paper, a theoretical analysis is conducted on a variety of error factors affecting encoder performance. These factors include code disk eccentricity, line-to- line error, shaft repeatable wobble and NRW, speed control and zero-delay jitter. Measurement techniques of these error factors at full operating speeds are discussed. Practical correction methods of these errors are also suggested. It has been demonstrated in a production environment that with the help of proper error measurement and correction techniques, enhanced performance of the rotary encoder with arcseconds of repeatable error and sub-arcsecond of non-repeatable error can be achieved, which exceeds the most stringent specifications so far on encoder performance in the field of laser beam information scanning.