All-optical switching has been achieved in zero-gap directional couplers containing either a single or multiple quantum wells. The mechanism which is due to free carrier induced refractive nonlinearities at near band-gap resonant frequencies has an instantaneous turn-on time and a recovery time that depends on the speed at which the carriers are dissipated. A recovery time as short as 130 ps has been obtained experimentally by the application of an external dc bias which sweeps out the carriers from the quantum wells.

We have measured carrier sweep-out times as a function of electric field applied perpendicular to GaAs/AlGaAs multiple quantum wells at different pump power levels in picosecond pump- probe experiments. Resonant tunneling was observed at 5V at low pump pulse energies. At higher excitation levels, the effects of space charge build-up were found to significantly alter the transient nonlinear optical response due to changes in the time constants associated with vertical carrier transport in the screened field.

Optical switching is often thought of as the Holy Grail of optical signal processing. Techniques used to switch optical fiber paths have become a subject of on-going research and development, and optical switch performance continues to improve. In the past few years, new optomechanical fiber optic switch technologies have been developed by DiCon Fiberoptics which offer readily available fiber optic switches with stable, low losses. These fiber optic switches offer tremendous potential for systems requiring optical signal routing.

We have developed techniques for fabricating extremely low-loss channel waveguide structures on silicon substrates. We have made and evaluated waveguides consisting of combinations of Corning 7059 glass, phosphorus-doped silica glass (PSG), and boron-doped silica glass (BSG). The waveguides were fabricated on the surfaces of oxidized silicon wafers. The 7059 waveguides were patterned in rf-sputter-deposited films, and the PSG waveguides were made using atmospheric-pressure, chemical vapor deposition (APCVD), low-pressure, chemical vapor deposition (LPCVD), and plasma-enhanced, chemical vapor deposition (PECVD). BSG was used strictly as a cladding layer for many of the waveguides. We present a comparison of the waveguides prepared by these methods, and discuss the processing techniques used to make channel waveguides with propagation losses less than 0.01 dB/cm. The processes we used allowed us to make waveguides with cross-sections ranging from rectangular to nearly circular, and to build multiguide structures with the waveguides stacked vertically or arranged side by side. Applications for these waveguides include low-loss splitters and combiners, high-finesse resonators, switches, and wavelength division multiplexers/demultiplexers.

A working model of an optical backplane has been built to demonstrate the feasibility of incorporating free space, multifaceted and angularly-multiplexed, holographic interconnect technology to enhance the electronic processing architecture. This new design will allow special configurations for parallel and distributed processing and can be made compatible with standard electrical bus connections. The current demonstrator unit contains four transceiver boards in a standard 19 in. rack-mount chassis. It can support bidirectional 125 MHz transmission per channel with a loss budget (allowable optical attenuation) of 30 dB for large fan-out (> 20 boards). Interconnection holograms have been designed to compensate for the large wavelength drift of laser diodes expected to be the result of temperature fluctuations in the processor box. The design also allows a large mechanical tolerance for board misalignment and vibration. Multiple interconnection patterns, each set representing a particular architecture, can be recorded on a single substrate to provide reconfiguration. The proposed holo-backplane can interconnect multiple transmitters and/or receivers (each could support different logic and/or signal levels) per board to realize truly flexible processing schemes.

In this paper, we examine board-to-board two-way communications with holographic optical elements. For this application, substrate-mode holograms with a high efficiency (> 90%) and broad angular bandwidth (Full Width at Half Maximum > 8 degree(s)) are fabricated. The experimental results for two-way communications between two circuit boards with these elements are given.

This paper deals with the holographic dispersion effects in a single-mode holographic waveguide interconnect system. The analysis is concentrated on the effect of wavelength shift in laser diodes due to the variation of environmental temperature.

Diffraction-limited beam operation at high output power levels (0.5 W cw and 1.5 W pulsed) has been demonstrated from resonant-optical-waveguide (ROW) array structures. Uniphase mode operation is achieved without the need for active phase control. As a result, a reliable monolithic device capable of watt-range coherent output power is obtained.

This paper presents the results of the design and fabrication of a 1.25 Gb/s wideband light emitting diode-based transmitter which employs a commercial LED as the optical source. The transmitter is capable of launching -13 dBm of optical power into a 100/140 micrometers optical fiber. The wide bandwidth and high optical power are achieved by using an active matching and filtering technique. A prototype MMIC LED transmitter demonstrated a bandwidth of 350 MHz to 1.35 GHz. A design with a predicted 3 dB electrical bandwidth from few hundred megahertz to several gigahertz is given.

Characterization procedures of different types of semiconductor lasers in a typical transmission line are investigated, with particular attention paid to unavoidable low-level optical feedback. The asymmetric response between front and rear facets is compared with the symmetric response of the solitary device.

Liquid Crystal Televisions have received extensive attention in the literature for use as input and Fourier plane devices in joint transform correlators, and for use in other optical processing architectures requiring television rate inputs. The device has also been used in incoherent optical neural network systems at Penn State University. Recent research has also investigated the hybrid phase and amplitude modulating properties of the LCTV in a joint transform correlator. These properties will now be applied to the well known Vander Lugt matched filter correlator. The results of employing the LCTV as a phase-only input device for making and addressing photographic matched filters is presented. Experiments using the LCTV as both the input and filter plane modulator in a mixed phase and amplitude mode also is discussed.

The performance characteristics of three unique optically-addressed spatial light modulator (SLM) structures have been experimentally investigated. The measured parameters include maximum resolution, visibility, imaging response time, and write light sensitivity. The modulators investigated include two relatively new technologies, the ferroelectric liquid crystal (FLC) SLM from the University of Colorado-Boulder and the amorphous silicon photoconductive twisted nematic liquid crystal SLM from GEC-Marconi Research, and a well established industry benchmark, the Hughes Liquid Crystal Light Valve (LCLV). A comparison of these devices in terms of the above performance parameters is discussed in this communication.

A new high-speed driver has been developed for the magneto-optic spatial light modulator (SLM). The driver allows the output of an image sensing device such as a CCD array to drive the SLM. Using digital circuitry, high frame rates are made possible. Furthermore, the digital nature of the interface allows real-time digital image processing to be performed on input imagery; the input image can be processed by a 3 X 3 kernel. For example, functions such as noise filtering, edge detection, or thresholding can be performed in real-time. Adaptive filters or multiple filter operations on the same data are also possible. Processed imagery can be displayed on the SLM at over 400 frames/second. In addition, the interface can be applied to other electrically-addressed SLMs. The potential for higher frame rates is possible with faster electronic components.

High-contrast spatial light modulators (SLM) involving memory on the base of shape memory effect are developed. SLM configurations and control are described. Some characteristics of SLM are investigated.

The exposure of birefringent guided wave devices to ionizing radiation can result in nonequivalent signal attenuations over the eigenmode axes and to highly interactive crosstalk between the coupled waveguides. This paper discusses the response of polarization maintaining (PM) fibers and directional coupler waveguides exposed to accelerated electrons, and reports on advances made in delineating and understanding the response mechanisms involved.

Co⁶⁰ radiation-induced attenuation is measured by optical time domain reflectometry (OTDR) techniques and compared to conventional optical throughput measurements. Relative advantages and disadvantages of the OTDR technique are discussed.

We examine measurement issues which arise in the testing of integrated optical devices subjected to ionizing radiation. Many of these issues are not addressed by measurement procedures developed for optical fibers. We outline the complexities involved in the measurement of integrated optics as they relate to size, function, and materials. Pertinent waveguide parameters include attenuation, changes in refractive index, photorefractive effects, and polarization effects. Optical measurement techniques are reviewed, with particular attention paid to spatial and temporal resolution, dynamic range, and the capacity for remote measurement. Suggestions are made to improve the reliability of testing and allow better comparison between laboratories.

Optical guided wave devices can experience crosstalk and mode-switching in the presence of ionizing radiation. This paper discusses the response of LiTaO₃ and LiNbO₃:Ti directional coupler waveguides to exposures of linearly accelerated electrons. A comparison of the waveguides in terms of sensitivity to the ionizing radiation is made.

When the time it takes to access a tape is too long, and the storage capacity of a magnetic disk is too small, then optical disk technology can be applied to provide the best of both worlds; fast access and high storage capacity. Optical disk provides random access media with larger capacities than magnetic disk. Optical disk jukeboxes and libraries can provide huge storage capacities online. Storage intensive applications such as signal processing, image processing, voice recognition, scientific data collection, CAD/CAM, supercomputers, medical imagery and visualization drive the demand for huge online capacity and fast access.

As an extension of an existing electron beam deflector, an optical analog-to-digital (A/D) conversion scheme is presented. As a fast theta modulator, a wide-band acousto-optic (A-O) deflector that performs a voltage to optical beam deflection angle mapping is used. Using a GaP A-O deflector, a proof-of-principle 6-bit A/D converter is experimentally demonstrated.

An optical computing model used in a number of projects consists of arrays of optical logic gates interconnected in free space. The arrangement of optical logic arrays and optical interconnects is governed by the complexity of the optics rather than by the needs of the digital circuits being implemented. Thus, unlike an electronic technology, the physical layout of a digital optical computer that adheres to this model cannot easily be separated from the functional behavior since they are tightly coupled. In order to manage digital design for this optical computing model there is a need for developing a methodology to the design process. Progress toward such a methodology at Rutgers University is described here.

An optically implementable algorithm, which separates a long data stream into several shorter sequences based on the Chinese Remainder Theorem (CRT), is described in this paper. Using this algorithm, the convolution/correlation of long data streams are performed by small scale vector-matrix multiplications, which can be realized using the state-of-the-art optical algebraic processing technologies. Computer simulation results of this algorithm are presented. A suitable optical processing architecture is also proposed.

This paper documents an investigation on the architectures and algorithms for performing logic (or Boolean equations) using self electro-optic effect devices (SEEDs). Three algorithms and architectures for performing logic are examined -- using lookup tables with series connected SEEDs (or Symmetric-SEEDs), using a preset cycle with series connected SEEDs, and using NMOS and CMOS architectures. Contrasts are examined between the architectures with cascadeability, component, and optical interconnectivity considerations.

We report on the design and simulation of optical switches for use in communication networks. These switches are promising due to their large bandwidth potential and high switching speeds. These advantages are limited however, by high power dissipation, and device and material constraints. Architectural advances in the design of optical switches are expected to lead to improved performance and higher reliability. A 2 X 2 rectangular switch based on directional couplers is designed and simulated using PUFF. Factors employed to optimize this design include the refractive index of the substrate, LiNbO₃, and the dimensions of the titanium waveguide. Simulation of the design prior to construction of the switch permits optimization of the PUFF results. These include the scattering parameters and their frequency response. Architectural considerations for optical switches are then evaluated using the 2 X 2 switch as a building block. Several blocking and nonblocking architectures such as crossbar matrix, double crossbar, and planar switch are designed. The system crosstalk, insertion loss, and signal to noise ratio for the architectures are calculated as a function of switch dimensions.

We demonstrate an InP-based optoelectronic integrated logic circuit for use in optical interconnection networks. The electrical power and control of the circuit are provided by optical sources. The logic circuit can be dynamically tuned to operate as an amplifier, a bistable switch and a latch/reset.

We have fabricated metal-semiconductor-metal photodetectors with sub-100 nm finger spacing and finger width on MBE-grown GaAs, which are, to our knowledge, the smallest ever reported. Dc measurement shows that they have low dark current and high sensitivity. Monte- Carlo simulations demonstrate that the response time of the photodetectors for a 30 nm finger spacing can be as short as 0.4 ps, and the cut-off frequency can be over 1 THz.

This paper describes a coherent detection receiver (CDR) with adaptive image rejection capability which is also compatible with existing monolithic integrated optics and MMIC technology. It details the component selection and circuit layout tradeoffs that were considered for the design and fabrication of the CDR in monolithic IC format. An optical `half receiver' IC with waveguides, phase shifter, 3 dB coupler, and balanced mixer diodes has been constructed and tested. Measurements and results for this chip are given and discussed. An initial design and simulated results for the microwave (intermediate frequency) IC are also given and discussed.

Optical preamplification has been shown to significantly improve the sensitivity of receivers for wideband lightwave systems when compared with conventional electronic postamplification. However, the large size and relatively fragile nature of optical preamplifiers assembled from discrete optoelectronic components (i.e., hybrid assemblies) has discouraged the use of optical preamplifiers for system applications. This paper discusses the technology required for integrating a semiconductor optical amplifier with a high-speed photodetector on the same chip, [1] and the expected performance of such a device. The monolithically Integrated Optical Preamplifier (lOP) is expected to combine the performance of hybrid receivers with the functionality of a single optoelectronic component. In addition, this integrated device can be used as a lossless optical tap for network monitoring and/or system reconfiguration, functions that are highly desirable for advanced network architectures.

We report the performance of an InP-based integrated spectrometer and consider its application in wavelength division multiplexed (WDM) systems. The wavelength multiplexer/demultiplexer operates in the 1.5 micrometers fiber band and disperses 1 nm spaced signals over a spectral range of 75 nm. Crosstalk between the channels is -19 dB and the optical performance of the spectrometer is essentially insensitive to the polarization of the incident light. Use of the device in multiwavelength telecommunication and computer local area networks is discussed.

An interferometric optical-time-domain reflectometer is presented. The system is a low- coherence interferometer using a superluminescent diode and has a spatial resolution of 20 micrometers . A high-sensitivity system is described which performs balanced and narrow band detections and has a detectable limit of -130 dB, which is 10 dB lower than the Rayleigh scattered light power in optical fibers. A polarization-independent system is proposed which adopts polarization-diversity detection to suppress the influence of the polarization fluctuation of the scattered light. A CO₂ laser probing method is applied using the thermo- optic effect to identify scattering centers in optical circuits. Measurement of fault locations, reflectivity, and characterization of optical components with the systems are also described.

A novel technique to determine the coupling length as a function of wavelength in directional couplers, especially in the case of weakly coupled, symmetrical directional couplers, is described. The technique is illustrated by using Ag⁺ - Na⁺ ion-exchanged directional couplers in BK7 glass. Application of this technique to asymmetrical directional couplers is also addressed.

A small simplex hermaphroditic connector has been designed for use in tactical fiber-optic communications systems and robotic vehicle applications. The rugged connector is intended for use wherever bi-directional transmission is required. It was designed to operate while meeting environmental and mechanical conditions typically encountered in tactical applications. This single-fiber connector is available in both multimode and single-mode versions. Measurements of prototype connectors show insertion loss of less than 1 dB when installed on either 50/125 im multimode fiber or singlemode fiber. This connector was designed to include some of the features of the TFOCA connector. In particular, these comprise cable retention hardware which requires neither special tools nor adhesives, waterproofing seals, and ease of cleaning without special kits. However, the simplex unit employs ST® connector technology whereas the TFOCA included biconic components. The connector was designed to accommodate cable diameters ranging from 2 to 4 mm, and is capable of withstanding tensile loads up to 1335 newtons. Operating temperature range is from -46° to +71°C. The new connector is 1.4 cm in diameter and 8.6 cm long, including bend limiter, and weighs less than 30 gm. A complementary bulkhead receptacle shares the same hermaphroditic interface and may be mounted on panels up to 6.4 mm thick. EMI shielding has been incorporated in the unit.

Laser diode waveguides are probed using low coherence optical reflectometry. Reflections from the launch optics, front facet, and rear facet are located with a resolution of approximately 10 micrometers . Diodes mounted in pigtailed packages and on chip carriers have been studied.

A method is proposed for the optical implementation of image algebra (IA) which would map the graph of a transformed IA expression directly to an optical architecture. The IA is a concise, mathematically rigorous notation which unifies linear and nonlinear mathematics in the image domain. Due to its clarity and inherent parallelism, the IA has been successfully employed in the specifications of image- and signal-processing algorithms for parallel computers such as the ERIM Cyto-SS, Honeywell Prep, and Thinking Machines' Connection Machine (CM-1 and CM-2). In this study, we consider the utility of IA as a descriptor of optical processing, as well as the optical implementation of image-algebraic operations over a finite subset of the Euclidean plane. For real-valued imagery, many IA operations can be realized via magnitude-only computation. Thus, incoherent illumination could be employed. Algorithmic examples are derived from the signal- and image-processing literature, as well as from set and graph theory, and include insertion sorting, cellular automata, morphological image operations, and morphological neural nets. Complexity analyses and implementational issues are discussed in terms of functional properties of the IA operator set, subject to optical propagation constraints.