Miniaturization of mechanical systems promises opportunities for progress of science and technology in new directions. Micromechanical devices and systems are inherently smaller, lighter, faster, and possibly more precise than their macroscopic counterparts. Microfabrication provides a powerful tool for batch processing and miniaturization of mechanical systems into a dimensional domain not accessible by conventional (machining) techniques. Furthermore, microfabrication provides an opportunity for integration of mechanical systems with electronics for closed-loop control to develop high-performance microelectromechanical systems (MEMS). In the most general form, MEMS would consist of mechanical microstructures, microsensors, microactuators, and electronics integrated in the same environment. This paper provides an overview of several MEMS topics including fabrication technology, materials, microsensors, and microactuators.

A micromachined cantilever beam accelerometer is described in which beam deflection is determined optically. A diving board structure is anisotropically etched into a silicon wafer. This diving board structure is patterned from the wafer backside so as to leave a small gap between the tip of the diving board and the opposite fixed edge on the front side of the wafer. In order to sense a realistic range of accelerations, a foot mass incorporated onto the end of the beam is found to provide design flexibility. A silicon nitride optical waveguide is then deposited by low pressure chemical vapor deposition (LPCVD) onto the sample. Beam deflection is measured by the decrease of light coupled across the gap between the waveguide sections. In order to investigate sensor response and simulate deflection of the beam, we utilized a separate beam and waveguide section which could be displaced from one another in a precisely controlled manner. Measurements were performed on samples with gaps of 4.0, 6.0, and 8.0 micron and the variation of the fraction of light coupled across the gap as a function of displacement and gap spacing was found to agree with overlap integral calculations.

We present an integrated Si micromechanical Mach-Zehnder interferometer based on the ARROW structure. The interferometer has its reference arm supported by the Si substrate and the sensing arm is suspended over a cavity realized using Si surface micromachining techniques. An applied pressure causes deflection of the suspended arm resulting in optical path elongation and hence in an optical phase shift with respect to the reference. The design of the interferometer was based on simulations of the photonic transport in the ARROW for the different geometric parameters. Silicon integrated circuit technology was employed for the interferometer fabrication i.e. low temperature CVD oxide for the core and second cladding and LPCVD poly for the first cladding layer. Prior to surface micromachining, the composite waveguide structure was annealed so as to minimize the residual stress and hence the sag in the free standing sensing arm.

Silicon micromechanics technology has formed the basis of a range of compact and reliable sensors, measuring variables such as pressure, force and acceleration. Most micromechanical sensors require some form of electrical read-out. Therefore, these sensors are classified as electrically active. Electrically passive sensors also have many applications, and the best examples of such sensors are those based on fiber optic technology. In this paper, we describe a sensor which combines the advantages of both silicon micromechanics and fiber optics. Specifically, an accelerometer has been fabricated, and initial results on the performance of this device are presented.

We present the design and analysis of a microfabricated silicon pressure transducer. The operating principle for this device is based on the evanescent modulation of power in an integrated optical waveguide. A silicon diaphragm attenuator is initially separated from the waveguide by a precise microfabricated gap spacing. When external pressure is applied to the sensor, the silicon attenuator is moved into closer proximity with the waveguide, and light is coupled out of the waveguide into the attenuator. Thus, by monitoring the light intensity at the output of the waveguide, one can deduce the pressure applied to the silicon diaphragm. Packaging considerations have played an important role in the development of the device and have led to the use of anti-resonant reflecting optical waveguides (ARROWs), which are etched down to form a rib in order to provide confinement in the lateral direction. These waveguides provide good spatial and index matches to single-mode optical fibers. Numerical simulations of device performance have provided information critical to the design of the sensor.

This paper describes the usage of neural networks in the application of speckle patterns, as seen at the output of an optical waveguide, for sensing displacement/force. The neural network trained for displacement values within a 1.5 micrometers range is found to generalize with less than +/- 0.02 micrometers error in the input range. It is found that a functional-link net with 11 functional links and 3 neurons can be trained for a convergence criterion of 1e-05 in less than 3000 iterations. The error in the individual targeted output during training was less than +/- 0.01 micrometers . Thus an integrated-optics sensor is now feasible.

This paper presents a general theoretical investigation of the crossing waveguide structures constructed by large-size single-mode rib semiconductor waveguides. The theoretical model is based on beam propagation method and effective index method. The propagation characteristics of three kinds of structure are analyzed and compared. The numerical result show that these structures exhibit similar characteristics at large crossing angles but divergences exist at small crossing angles. It is found that mode-interference doesn't exist in y-junction.

A multimode symmetric Y-junction waveguide is investigated and the optical power transmission and conversion efficiency between the lower and higher modes was calculated. Overlap integrals of the fields of the incident and transmitted guided-wave modes at the Y- junction were used and it is shown that there is a possibility of transmitting up to 29 percent of the incident optical power into the output branching waveguides at very large branching angles. Results show that an appropriate branching angle of the Y-junction can be used to selectively transmit the waveguide modes into the output branches and this can be used advantageously in integrated optic devices. A very simple model using ray optics is developed to explain the results on physical basis. With this simple model we developed a simple framework to interpret the results of the overlap integrals.

Micromechanical bridges and cantilevers sensitive to external forces have been fabricated upon Si substrates. They are used as optical waveguides and part of sensor circuits. The waveguides consist of sandwiched layers of an SiO₂ buffer, an Al₂O₃ waveguide and an SiO₂ cover. The bridges and cantilevers with very small dimensions such as 100 micrometers in length, 5 micrometers in width and 2.5 micrometers in thickness have been successfully produced. Such bridge- or cantilever-shaped waveguide structures have been applied in acoustic signal detection and noise monitoring. In this paper, the bridge and cantilever structures will be analyzed and experimental results on sound measurement will be presented.

Piezoelectric thin film actuator-based fiber-optic switches are introduced as low loss, high interchannel optical isolation 1 X 2 and 2 X 2 fiber-optic switches. A macroscale PZT actuator is built and tested. Preliminary results from a microscale actuator are given. Optical switch configurations and fabrication procedures are highlighted.

An integrated-optic Mach-Zehnder interferometer is used as a Fourier transform spectrometer to analyze the input and output spectra of a temperature-sensing thin-film etalon. This type of spectrometer has an advantage over conventional grating spectrometers because it is better suited for use with time-division-multiplexed sensor networks. In addition, this spectrometer has the potential for low cost due to its use of a component that could be manufactured in large quantities for the optical communications industry.

A Nd:YAG LASER operating at 1.064 micrometers was used to deposit CdS thin films on glass and GaAs (100) substrates. Depending on the substrate temperature, the as-deposited films were either cubic or hexagonal dominant. At a substrate temperature of approximately 200 degree(s)C, predominantly cubic structured films were grown while at approximately 400 degree(s)C the hexagonal phase was formed. The films were in the stoichiometric ratio of 1:1 for Cd:S. The surface of the films were optically smooth. Optical transmission revealed the room temperature absorption edge for the cubic films was close to 515 nm, and that of the hexagonal films was approximately 500 nm. At a temperature of 10 K, the absorption edge of the cubic film was 502 nm. Raman spectrum studies revealed the locations of the first two longitudinal optical (LO) modes for the cubic films were close to that of the hexagonal films.

The photoconducting static and dynamic properties of the system poly-N- vinylcarbazole/Copper-phthalocyanin are investigated. The organic photoconductors are deposited from solution on planar indium tin oxide electrode patterns. An all-organic photodetector with polyanilin electrodes is realized. The possible integration of the photodetector directly into a passive or active organic waveguide is demonstrated. As an example an integrated organic opto-optical switch detector system is discussed.

The aim of this paper was to investigate the optical and electrooptical properties of Ga₂O₃ - PbO - Bi₂O₃ glasses as a potential material for mid-infrared and nonlinear optics. The light transmittances of the examined glasses were measured, short- and longwave spectra limits, dispersion dependencies, optical energy gaps, reflection and absorption coefficients were determined. The molar refractions were calculated. The refractive index dependence on the optical beam intensity for the 1.06 micrometers wavelength was investigated.

A new design for a miniature Fabry-Perot Interferometer (FPI) mounted on the tip of an optical fiber for sensing applications is presented. The Fabry-Perot Cavity (FPC) is formed by a micromachined corrugated silicon diaphragm anodically bonded to a pyrex substrate. In this way, this devices takes advantage of the sensitivity and selectivity of an optical interferometer combined with the small size, lightweight and EMI immunity properties of optical fibers to create compact, lightweight and almost entirely dielectric sensors for the measurement of pressure, acceleration, sound, electric and magnetic field, etc. in remote, dangerous or inaccessible places. A discussion on the operation and fabrication of the FPC is given, along with experimental results obtained in its application as an electric field sensor.

The integration of micromachined devices into integrated optic systems offers the potential for both miniaturization and improved performance of these systems. In this paper, an electromechanical switch integrated with an optical waveguide is described that is suitable for phase and intensity modulation and thus modulation or switching functions. The electromechanical switch is fabricated using surface micromachining techniques and consists of a multilevel polyimide platform, some regions of which are suspended 2 - 3 micrometers above the waveguide surface and other region 15 micrometers above the waveguide surface. The platform is free to move in the vertical direction. Application of voltage between the platform and substrate brings the platform into intimate contact with the waveguide, thus changing the waveguide transmission characteristics. Extensions of this technique to multiple platforms in series to create multibit digital modulation is easily envisioned.

We propose an array of electrostatically driven torsional mirrors for optical signal processing. This 10-element device is 1-dimensional with pixels of 50 micrometers X 250 micrometers . The device is basically a hybrid integrated optical device which is fabricated in silicon and can be integrated with photodetectors and processing electronics to create elements of the so-called 'smart pixel' class of spatial light modulators. This class of devices will find application in many areas of optical processing including optical interconnects, optical switching, optical image analysis and optical neural networks. We discuss the design and fabrication of mirror arrays and electrode strips that are used to actuate them. The resonant frequency and deflection angle v.s. applied voltage of the fabricated devices are measured and compared with theoretical predictions.

An integrated-optic channel waveguide device is configured as a biosensor. The device measures a refractive index change on the waveguide surface, so it is called a biorefractometer. With an appropriate overlay or selective coating, the device can monitor proteins in blood or pollutants and bio-warfare agents in water. We describe the design, fabrication, and testing of a sensor employing a waveguide Mach-Zehnder interferometer configuration. The device is fabricated in a glass substrate using potassium ion exchange. A patterned glass buffer layer defines the sensing and reference arms of the interferometer. A silicone-rubber macro-flow cell confines the liquid above the integrated-optical waveguide device. Salt solution data show that the biorefractometer has a sensitivity ((Delta) n_eff/(Delta) n_Liquid) of 2 X 10^-3 and can measure refractive index changes of about 0.005. Data obtained for antigen-antibody binding of the protein IgG indicate that a 10 percent signal change occurs in approximately 1 minute for a 10 (mu) g/ml concentration level.

This paper reviews the field of silicon-based integrated microsensors. These devices are implemented using fabrication technologies developed for integrated circuits, and lend themselves easily to low cost and high volume production. They are typically much smaller, more precise and stable, have less drift, and are much more reliable than their discrete counterparts. The addition of on-chip integrated circuits to the silicon sensors enables the processing and amplification of low level signals recorded by the sensors, and allows the device to be more easily interfaced and integrated into an electronic measurement and control system. The fabrication of silicon integrated microsensors is reviewed, and a number of examples are discussed. These examples include a multichannel integrated silicon microprobe for the recording of neural signals form the brain cells, and a multi-element infrared thermal detector based on silicon-gold thermopiles.

A new mode of operation for a high-multimode fiber optical sensor based on the detection of modal interference (speckle sensor) is described. The main mechanism in which the sensor is based is coupling between different modes due to curvature induced upon bending of the fiber. In contrast to previous work, the variation of the length of the fiber under such curvatures may be neglected in this work. A sensor of this kind was implemented and showed a resolution of 10^-11 m in displacement and 10^-10 N in force. The 'spring' constant of the sensor is relatively small (5.6 N/m) compared to similar sensor. A detailed theoretical analysis of the mechanism involved in the transduction process is given. The potential use of this sensor in atomic force microscopy (AFM) is discussed.

Photon scanning tunneling microscopy (PSTM) is used to characterize Si3N4/Si02 optical channel waveguides being used for integrated optical-micromechanical sensors. PSTM utilizes an optical fiber tapered to a fine point which is piezoelectrically positioned to measure the decay of the evanescent field intensity associated with the waveguide propagating mode. Evanescent field decays are recorded for both ridge channel waveguides and planar waveguide regions. Values for the local effective refractive index are calculated from the data for both polarizations and compared to model calculations.

A new family of optical and optoelectronic elements is offered whose 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 external fields (optical radiation, magnetic or electric field). The S-shaped CVC is a result of low- temperature impurity breakdown (LTIB) in semiconductor epitaxial layers induced by an electric field (E 1 - 10 V/cm). New elements, we shall call them LTIB-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.

We demonstrated that active integrated optical (IO) devices based on the IO nanomechanical effect can be actuated by electrostatic forces. In particular, we demonstrated: (1) an intensity modulator, (2) the deflection, and (3) the focusing and defocusing of a guided wave in a planar waveguide.

Deformable Mirror Devices (DMDs) have been under development at Texas Instruments for several years, primarily as spatial light modulators for free-space optical applications such as analog phase modulation and digital projection imaging. A DMD consists of one or more electrostatically deflectable micromechanical aluminum mirror elements, including both micromirrors suspended from thin flexible hinges and membranes. These devices are fabricated using low temperature silicon-compatible semiconductor processing techniques, and thus can be monolithically fabricated over any addressing circuitry. In the last few years DMDs have been integrated into optical fiber switching systems, and efforts are underway to integrate them as routing switches onto optical waveguides. The DMDs used for optical fiber switching are torsion-hinged devices similar to those used for projection imaging. These devices have been integrated with multimode fibers to construct a 4 X 4 multimode optical fiber cross-bar switch with a 19 dB optical (80:1) extinction ratio for all 16 channels. Extinction ratios of 73 dB optical (20 X 10⁶) have been achieved for single point single mode switches. The waveguide switches currently under development are deformable membranes which are monolithically fabricated on silicon wafers with phosphosilicate glass (PSG) waveguide directional couplers to form optical time delay path selection switches. In this paper we describe the fabrication of deformable mirrors, their integration with optical fibers and waveguides, and the resulting system performance.