Digital video technology is becoming increasingly important to the networked society. The natural interface to digital video is a digital display, one that accepts electrical bits at its input and converts them into optical bits at the output. The digital-to-analog processing function is performed in the mind of the observer. Texas Instruments has developed such a display with its recent market introduction of the Digital Light Processing^TM (DLP^TM) projection display. DLP technology is based on the Digital Micromirror Device^TM (DMD^TM), a microelectromechanical systems (MEMS) array of semiconductor-based digital light switches. The DMD switching array precisely controls a light source for projection display and digital printing applications. This paper presents an overview of DLP technology along with the architecture, projection operation, manufacture, and reliability of the DMD. Features of DMD technology that distinguish it from conventional MEMS technology are explored. Finally, the paper provides a view of DLP business opportunities.

'Laser chips' are new miniaturized light sources which exhibit a large panel of properties unattainable to laser diodes but in many cases required for optical systems. The batch process fabrication of these devices and their excellent reliability make micro-chip lasers very suitable for industrial production and low cost micro-systems. This paper summarizes some recent advances in this field.

With over 100 million units per year, the optical pick up is probably the most widely produced electro optic assembly on these days. It is also the driving force of semiconductor laser production with development of higher power for high data rate recording and shorter wavelength for high density. The production of CD pick up is of course highly cost driven; over 20 years of optical storage history and ten years of CD, the reduction in size, power consumption and cost can be compared to the evolution of integrated circuit. Diffractive optics plays a significant role in this roadmap, although as will be seen not all functions can be expected to be played by diffractive optics. Refractive lens will remain the leading technology for all functions that involve strong bending of the rays. In the near future the production of CD and CD-ROM player is expected to reach a plateau at twice today's production but MO drives and soon DVD are taking off.

The vast majority of liquid crystal (LC) devices are used today in displays and image projection systems. The goal of this work is to demonstrate that with LC other helpful optical components can also be built. Two classes of devices are presented. The first class represent 1-dimensional spatial light modulators with high resolution electrodes to be used as beam steering devices. These devices are parallel LC cells and represent electrically controllable birefringent phase gratings. The second class involves what we call polarization converter devices and which represent the passive LC devices. These nematic LC devices are fairly easy to fabricate and a new class of light fields can be generated with them, namely linearly polarized light with axial symmetry. These fields are very difficult to generate unless the LC components described here are used.

LETI has developed new reliable and low cost diode pumped solid state microchip lasers using a collective fabrication approach. Very compact microchip lasers consist in small cubes (typically 1 mm³), cut in a wafer of laser crystal with plane parallel polished faces on which dielectric mirrors are deposited. In order to reduce the threshold of plane parallel microchip lasers we have achieved microspherical shapes on laser materials by using a two step micro-optic fabrication technique based on photolithography and melting of photoresist followed by a selectively controlled etching process. These spherical shapes such as microlenses were transferred into the substrate by ion beam milling (IBM), forming microspherical mirrors on the laser cavities. By this way we have also produced large arrays of microlenses of low numerical aperture in silica substrate by using a selectively controlled reactive ion etching (RIE) process. In both etching techniques the selectivity, defined as the ratio between the etching rate of the substrate and the resist, can be adjusted (from 0.1 to 3 in our experiments) by controlling the fraction of oxygen in the gas. Low numerical aperture microlens arrays of 100 to 200 micrometer in diameter and 110 to 250 micrometer in pitch have been made with limits of f/15 in photoresist and f/100 after etching In YAG and f/40 in silica. The laser threshold of stabilized microchip lasers in Nd:YAG with spherical shape of 3 mm in radius of curvature and 150 micrometers in diameter, is then lowered from 40 to 2 mW.

Microtechnology offers the possibility to fabricate photonic devices. Especially the LIGA technique allows the fabrication of micro-optical benches for free-space optical set-ups, with mounts for inserting hybrid components structured to micrometer accuracy well aligned to each other. These optical benches are not only used to build up passive optical devices but also opto-mechanical systems have been realized. Also concepts to integrate active optical components like laser and photo diodes have been tested. In the paper the concept and the technology to fabricate hybrid micro-optical systems is described. Two systems, a bi-directional transceiver module and an opto- mechanical by pass switch have been fabricated and evaluated. Their performance data prove the ability of the concept of micro-optical functioning modules based on free- space micro-optical systems fabricated by LIGA technique and assembly.

Our investigation is focused on microlens arrays for microsystems and sensor applications. Arrays of refractive lenses (2 micrometer to 5 mm lens diameter) have been fabricated by melting resist technology. Microlens arrays have been transferred in fused silica (reactive ion etching) and replicated in polycarbonate and polymer (embossing, casting). Lens arrays have been integrated into lithographic systems, sensors and neural networks.

It has now been widely established that AFM probes (silicon as well as silicon nitride) are relaxant devices for the conversion of near field evanescent waves into far field propagating photons. From several points of view these probes seem to be more convenient than the usual tapered optical fibers which makes the tip a really mesoscopic object. Also simultaneous atomic force microscopy (AFM) or shear force microscopy (SFM) topographic images can be acquired containing meaningful information. In this paper we describe consistent experimental results on the capture of the evanescent wave by such probes which have been equipped with a carbon 'super tip' in order for them to attain higher resolution performances especially on the rugged surfaces of semiconductor processed devices. The experiments are performed on an indium phosphide surface in a PSTM configuration at lambda equals 1.06 micrometer. The intensity versus distance curves obey the classical model of optical conversion in spite of the very sharp aspect of the tip. It is also shown that the guiding properties of the super tips leads to a narrower beam output. The capture mechanism involved is discussed.

We propose a new fabrication method for monomode optical integrated devices. As an example, we show how a deeply buried planar waveguide can be obtained by assembling two half waveguides. These ones are realized by ion exchange and the assembling method is the wafer direct bonding (WDB). The optical properties are studied and compared with theory. The results prove that direct bonding, as in VLSI batch technology, is a low cost and high performance technology for optical devices fabrication.

Silicon micromachining, thin-film-multilayer-technology, integrated optical circuits and micro-optics were combined to realize optoelectronic microsystems. The potential of silica based inorganic waveguide materials and optical polymers were investigated and compared with respect to their process compatibility and their ability for integration with electronic, optoelectronic and micromechanical functions. An integrated optical modulator, an optical 2 by 2-switch and a micro-optical receiver were realized as test devices. The results reveal advantages of polymeric materials with respect to the optical functions of modulating or switching of light on the basis of thermo- optical phase shifting. However, the integration of the various process steps into a complete microsystem could only be accomplished with silica based optical circuits.

During a fiber-to-waveguide connection process, it can be important to determine accurately the absolute distance between the end of the fiber and the edge of the optical waveguide without visual control. We investigate here the use of a low-coherence optical source whose light, transmitted by the fiber, is launched into the waveguide in order to control the alignment. The end faces of the waveguide and of the fiber form a Fabry-Perot cavity for the transmitted light beam. The optical transmission versus the distance exhibits a fringe pattern whose visibility is related to the coherence properties of the broadband source. We deduce the absolute distance from visibility measurements, we assess the accuracy of the method, and the results are compared with the direct distance measurements.

The greatest hindrance to wider applications of micro-optics is the inefficiency of the mounting process. Currently there are attempts to remedy this through transferring the know- how from the manufacture of great repeater lenses etc. into the micro-optical technology. Additionally there are necessary new methods for handling and exact positioning. The discussed mounting equipment consists in a six-axis robot, some special developed grippers, a working station for the adjustment and a dosage device (ink-jet and stamp- transfer technique). In future some ideas for special equipments of precision mounting are to be realized. The range of accuracy contents about 0.5 to 5 micrometer and some arcsec.

The purpose of this paper is to investigate an integrated X/Y motion system, compatible with silicon process that will allow the positioning of micro-optical devices. The basic actuator, used for this system is referred as scratch drive actuator (SDA). SDA is able to produce a 1-D displacement, so, by combining several SDA, multi-degree of freedom motion is obtained. First, the SDA dimension dependent yield was analyzed. From this study, SDA with 50 micrometer long and 70 micrometer wide scratching area are appropriate for the integrated alignment system. According to these dimensions, various X/Y stages configurations are designed and fabricated as well as other actuated components such as long springs, integrated snapping devices and also nonrectangular shaped SDA. Two-dimensional motion of a 150 micrometer by 150 micrometer polysilicon stage have been demonstrated, proving the SDA out force is able to overcome friction effects of this kind of device. Active snapping system have been also successfully implemented. Control schemes for the X/Y motion and for the alignment are now under investigation.

The principles of the acousto-optic and electro-optic deflectors are shortly reviewed. A novel electro-optic prism-array laser beam deflector is proposed and experimentally investigated. Domain inversion in LiNbO₃ has been successfully applied to realize the new deflector. The digital deflector mode has been investigated and characteristics like deflection angle, driving voltage, etc. have been measured.

The Digital Micromirror Device^TM (DMD^TM) represents a breakthrough in large-scale integrated spatial light modulators. At the heart of each DMD display lies an array of five hundred thousand micromirrors fabricated on a single piece of silicon. Successful operation of the DMD array depends on the robustness, similarity, and reliability of each individual pixel and the ability to control all the pixels over time. This paper describes the challenges facing a pixel design and many of the recent improvements found in the current DMD architecture. Finally, we present the concept of a solution space, which is a measure of the architecture's ability to meet the design objectives.

The utilization of micro-optical components in systems for optical beam deflection and modulation offers the possibility for realization of miniaturized switches and scanners. As the required displacement of the micro-optical components for efficient beam manipulation is quite small, high speed actuators with small electrical power consumption can be used. We present a variety of micro-optical configurations and discuss their potential for the creation of different types of miniaturized scanners, switches and modulators. First experimental results and even prototypes of modulators and switches have been achieved, indicating that the combination of micro-optical components already available and semiclassical piezoelectric actuators leads to new types of switching and modulation systems for a very broad spectrum of applications.

A novel coupling structure between two waveguides is proposed. We use electromechanical actuation to change the gap between two superimposed waveguides. This in turn allows for evanescent wave coupling to induce complete energy exchange after typical length of 250 micrometers at a wavelength of 0.6328 micrometer. This device should work as a directional coupler and allow out of the plane interconnection opening the way to 3D coupling matrix. We present here the simulations (optical and mechanical) used to evaluate the device behavior and all its relevant geometrical parameters. Development of oxynitride waveguide using low pressure chemical vapor deposition is reported and also the silicon based process compatible with waveguides used to obtain a bending waveguide supporting structure with through-the-wafer contacted electrodes. Finally actuation of bending waveguide is also described and further developments are discussed.

Our main research topic is the integration of micromechanics and micro electronics to perform new kinds of microwave device functions. We presently focus our work on the realization of microwave antennas, which can be tilted mechanically to perform the spatial scanning of the emitted microwave beam. We present in this paper the mechanical part of the device: the tilting support on which microwave antenna has to be patterned. This mechanical support is a fused quartz plate metallized on both its faces, suspended by two thin torsion hinges and electrostatically driven by two fixed electrodes. Deflexion angles of 10 degrees may be obtained with voltage under 100 V.

The operation of optical position encoders relies on careful mechanical alignment of the detection system relative to a scale. We present a novel optical position encoder based on a glass scale, a dedicated photodetector array and a micro- optical imaging system. The complete detection unit is small enough to fit into the housing of the detector heads of standard Moire based incremental position encoders. Operating with a scale of 20 micrometer period, our working demonstrator achieves a resolution of up to 10 nm while offering a tolerance of plus or minus 80 micrometer in the distance from scale to detection system and a high angular mounting tolerance. The interpolation error was experimentally determined to be below 0.1 micrometer for an angular misalignment of plus or minus 12 mrad. The position encoder system is equally well suited for the setup of high- resolution linear and rotary incremental encoders which are employed in precision machine tools.

A high-resolution interferometric rotation encoder has been developed and characterized. It is based on the principle of a heterodyne interferometer. The frequency shifting was done by modulation of the injection current of a laser diode and a fiber-optical delay line allowing a compact system design. Light wave aberrations produced by the scale (i.e. rotary grating disk) are pre-corrected by using computer-generated holograms (CGH). Combined analogue and digital signal processing allow high resolution as well as high measurement rates. The designed prototype yields a resolution of 0.03 arcsec (i.e. 25 bit) corresponding to 3 nm resolution of displacement of the 38 mm diameter disk-scale. The measuring rate of 1 MHz allows a rotation speed resolution of 0.013 rpm at a maximum speed of 300 rpm.

We present the prototype of a laser feedback interferometer for displacement measurement with micrometric resolution and directional discrimination, which we propose for applications in industrial environment. The instrument incorporates a PC-interfaced electronic unit connected with the optical head, which is very compact thanks to the selected optical configuration and to the use of a semiconductor laser. Infrared as well as red emitting lasers have been used for operation on reflecting and diffusing targets.

In this work we report on a novel angular and positional sensor based on the phenomenon of attenuated total reflection that occurs at a metal-dielectric interface when the conditions for the excitation of a surface plasma wave in Kretschmann configuration are satisfied. The reflectivity of the metallic surface exhibits a very sharp dip at an angle of incidence corresponding to the phase-matching condition for the coupling of energy from the incident beam to the resonant surface mode. The typical width of the resonance is a few mrad, thus making feasible the direct measurement of small angular movements by just detecting the intensity of the reflected light. By means of a simple optical setup this sensitivity can be exploited to build a position-sensitive detector capable of nanometric resolution. Tests have been carried out on several Ag depositions. The angular resolution obtained has been in the 0.2 to 0.4 arcsecs range; the sensitivity to linear displacements has been tested monitoring the motion of piezoelectric actuators and is better than 5 nm over a range of a few microns. We have verified that the proposed method does not require beams of high optical quality and permits in principle a considerable simplification over interferometric systems. Well-established technological processes might be used for its implementation, keeping its cost at a competitive level with respect to other devices of the same potential sensitivity.

To control electro-mechanical engines, high-resolution linear and rotary encoders are needed. Interferometric methods (grating interferometers) promise a resolution of a few nanometers, but have an ambiguity range of some microns. Incremental encoders increase the absolute measurement range by counting the signal periods starting from a defined initial point. In many applications, however, it is not possible to move to this initial point, so that absolute encoders have to be used. Absolute encoders generally have a scale with two or more tracks placed next to each other. Therefore, they use a two-dimensional grating structure to measure a one-dimensional position. We present a new method, which uses a one-dimensional structure to determine the position in one dimension. It is based on a grating with a large grating period up to some millimeters, having the same diffraction efficiency in several predefined diffraction orders (multiple grating). By combining the phase signals of the different diffraction orders, it is possible to establish the position in an absolute range of the grating period with a resolution like incremental grating interferometers. The principal functionality was demonstrated by applying the multiple grating in a heterodyne grating interferometer. The heterodyne frequency was generated by a frequency modulated laser in an unbalanced interferometer. In experimental measurements an absolute range of 8 mm was obtained while achieving a resolution of 10 nm.

Optical microsystems typically include photosensitive devices, analog preprocessing circuitry and digital signal processing electronics. The advances in semiconductor technology have made it possible today to integrate all photosensitive and electronical devices on one 'smart image sensor' or photo-ASIC (application-specific integrated circuits containing photosensitive elements). It is even possible to provide each 'smart pixel' with additional photoelectronic functionality, without compromising the fill factor substantially. This technological capability is the basis for advanced cameras and optical microsystems showing novel on-chip functionality: Single-chip cameras with on- chip analog-to-digital converters for less than $10 are advertised; image sensors have been developed including novel functionality such as real-time selectable pixel size and shape, the capability of performing arbitrary convolutions simultaneously with the exposure, as well as variable, programmable offset and sensitivity of the pixels leading to image sensors with a dynamic range exceeding 150 dB. Smart image sensors have been demonstrated offering synchronous detection and demodulation capabilities in each pixel (lock-in CCD), and conventional image sensors are combined with an on-chip digital processor for complete, single-chip image acquisition and processing systems. Technological problems of the monolithic integration of smart image sensors include offset non-uniformities, temperature variations of electronic properties, imperfect matching of circuit parameters, etc. These problems can often be overcome either by designing additional compensation circuitry or by providing digital correction routines. Where necessary for technological or economic reasons, smart image sensors can also be combined with or realized as hybrids, making use of commercially available electronic components. It is concluded that the possibilities offered by custom smart image sensors will influence the design and the performance of future electronic imaging systems in many disciplines, reaching from optical metrology to machine vision on the factory floor and in robotics applications.

Optical detection techniques are at present mainly based on an array of silicon detectors or charge coupled devices (CCDs). CCDs output a signal proportional to light intensity that is converted into digital numbers and fed into a computer for further processing. While this solution offers the possibility of high precision computation and is thus well suited for signal restitution (compression of images, filtering, etc.) and measurement techniques, it is usually not satisfactory when perceptive tasks are required in real- time and embedded in a microsystem, like for example in the case of optical motion detection of a ball in a pointing device like a trackball. Photonic microsystems based on the assembly of optical elements and an analog VLSI circuit as the optical detector and processing unit, hereafter called 'artificial retina,' provide a new way to develop innovative sensors when real-time processing, low-cost, low-power and portability are required. Combining the processing capabilities of optical components, and not only their imaging properties, with the massively parallel, collective and non-linear processing of a large number of signals on the artificial retina has lead to successful industrial photonic microsystems. The present paper discusses the use of artificial retinas in photonic microsystems. The resulting properties and the constraints on the optical front-end design, as well as on the assembly of the microsystem, are illustrated through some industrial realizations.

The development of integrated optical interferometers for chemical sensing and refractometry is reviewed. The optical configurations are Mach-Zehnder-, polarization-, and Young- interferometer. The problems of signal processing -- ambiguity and signal fading -- are discussed. Applications are gas sensing, immunosensing, and differential refractometry. The chemical and biochemical sensors base on evanescent wave sensing.

By the LIGA technique it is possible to fabricate the optical part of a microspectrometer system for the NIR. It is based on a plate-type waveguide whereas on top of one of these plates a self-focusing reflection grating and structures for coupling in and out of the radiation are microstructured. Two prototypes, one for the wavelength range between 1.6 micrometer and 2.0 micrometer and the second for the range from 2.7 micrometer to 3.3 micrometer, have been fabricated and evaluated. The efficiency of both is in the range of 20%, the resolution is 9.8 nm, res. 34 nm. Both components have been designed in a way that they can be combined with a detector array. Thus it is evident that microspectrometer units without movable parts and sizes in the range of several cubic centimeter can be fabricated using LIGA technique. In the paper the fabrication process as well as the evaluated results are described.

A new conception of adaptive microsensor based on single beam dynamic holographic interferometry SBDHI is presented. A practically unlimited number of read and readout hologram cycles without application of external electric field using supersmall 0.12 micrometer dynamic holographic grating in double-doped titanium sillenite photorefractive crystal created by low power He-Ne or diode laser leads to invention of a portable, high stability, low-cost device for fast optical measurements on-line. A pen-size real-time SBDHI for stress measurements in this films and vibration mode visualization in situ has been constructed.

Fiber evanescent field analysis (FEFA) is a novel promising sensing technique for on-line and in situ analysis of hydrocarbons in water. With a conventional IR light source and FTIR spectroscopy it allows multicomponent analysis, while using MIR-tunable diode lasers results in more sensitive and faster single component analysis. Compared to common attenuated total reflection elements, silver halide (AgCl/Br) fibers offer more convenient application for remote sensing and field measurements because the fibers can be used for both, guidance of MIR radiation to and from the sensing part, and the sensing part itself. At present these fibers are multimode. The sensor response can be expected to depend strongly on the mode distribution in the fiber. We hence performed a model calculation that allows us to compare the FEFA absorption and the intrinsic fiber losses for given mode distributions and dependent on the optical parameters such as the coupling conditions and the fiber design. In order to link theoretical results to experimental data, the theory is based on an internal mode distribution derived from far field fiber emission data. We present far field data and the resulting internal distributions.

This paper describes a novel optical fiber remote strain sensor which is based on the FMCW technique and consists of only one single piece of single-mode birefringent fiber. The lead-in and lead-out fibers which are simply separated from the strain sensing fiber by two short twisted fiber portions are insensitive to environmental changes so that the sensor can remotely detect the strain variation of a distant construction. Other advantages of the sensor, such as no fiber junctions, no feedback light, long sensing fiber, higher resolution (4 microstrain) and large dynamic measurement range (5000 microstrain) are demonstrated in this experiment.

This paper describes a new birefringent fiber strain sensor which is based on the FMCW technique. The sensor comprises a single length of elliptical core birefringent fiber with a mirror attached at the far end and a mode coupler in the middle. The strain variation of the fiber sensing probe can be measured by detecting the phase shift of the beat signal which is produced by two forward-coupled polarization mode beams. The experimental results demonstrated that the sensor has many advantages, such as (1) high resolution (2 microstrain), (2) large dynamic measurement range (5000 microstrain), (3) large signal intensity and good signal contrast, (4) long and length-adjustable sensing probe, (5) long and environment-insensitive lead-in and lead-out fiber, (6) simple signal processing, and (7) low cost.

An angular scan triangulation range sensor using an integrated array of light-emitting diodes (LEDs) and a lateral-effect position-sensing detector is described in the paper. A range map is obtained by means of fast electronic scanning of the LEDs of the array. No moving parts are needed for the scanning. The sensor output is a set of object surface coordinates or other parameters describing the shape, size and position of the object. A compact version of the sensor was manufactured and tested to perform angle measurements and surface profile determination for obstacle detection and collision avoidance in the blasting robot applications. Based on the experimental tests of the sensor within the range 0.2 - 2 m, it is found that the performance of the sensor is sufficient for many applications in profile measurement and obstacle detection in robotics and machine automation.

In this paper we present an integrated optics displacement sensor with an interference head, where one-dimensional fringe pattern is created, allowing multiphase detection. Waveguides placed in the interference pattern are sampling four ideally pi/2 phase shifted signals. The four phase detection allows us to overcome the difficulties of intensity and contrast variation by suitable electronic treatment and offers potentially very high resolution displacement measurements. The interference fringe spacing and therefore equal phase shifts between the signals is controlled by the geometrical parameters of the mask design and therefore insensitive to fabrication tolerances.

Short grating period and high spatial frequency zones in holograms are features which diffractive elements must exhibit to be considered as the core of future optical microsystems. Wavelength scale feature size is the way to system miniaturization, to large aperture and high efficiency as well as to simplicity. The implication is a systematic resort to electron beam lithography (EBL). A tandem of two EBL tools is shown to fit the specific requirements of diffractive optics and to allow the exploitation of the application potential of this technology.

The mass production of micro-optical surface reliefs by replication is a fast developing technology. Surface structures are transferred from a master into polymers with high accuracy. In most cases the master is a nickel-shim fabricated by an electroplating process. This metal master can be utilized for the usual replication technologies like embossing, casting and injection moulding. An alternative method for manufacturing micro-optical surface profiles is embossing without metal master but using resist profiles or etched structures as a master. This replication technology may be advantageous if the fabrication of a metal master is too costly, e.g. if only a few replicated copies are needed. The structures and profiles which are presented in this article are replicated in UV-curable and chemical curable polymers.

This paper reports on a methodology for fabrication of arbitrarily shaped structures using technologies common to standard IC manufacturing processes. Particular emphasis is put on the design and use of halftone transmission masks for the lithography step required in the fabrication process of mechanical, optical or electronics components. The algorithms to transfer an initial height profile into a design representation in the common data format GDSII are discussed. This set of data could be used directly by a commercial mask shop. The great data amount of a reticle layout has been reduced significantly by a first order data compaction. The possibly nonlinear influences of the different process steps on the transfer function have been regarded. The specific parameters for the mask making and the resist process are determined. Several components like shaped gratings or lenses have been realized in resist up to 10 micrometers thick. In the field of transferring the pattern into a substrate material like silicon or glass, a dry etching process was evaluated.