We describe a compact optoelectronic switching technology for interconnecting multiple computer processors and shared memory modules together through dynamically reconfigurable optical paths to provide simultaneous, high speed communication amongst different nodes. Each switch provides a optical link to other nodes as well as electrical access to an individual processor, and it can perform optical and optoelectronic switching to covert digital data between various electrical and optical input/output formats. This multifunctional switching technology is based on the monolithic integration of arrays of vertical-cavity surface-emitting lasers with photodetectors and heterojunction bipolar transistors. The various digital switching and routing functions, as well as optically cascaded multistage operation, have been experimentally demonstrated.

We have developed a demultiplexer known as a Colliding Pulse Mach- Zehnder (CPMZ) suitable for OTDM systems capable of ultrafast all- optical demultiplexing and address recognition. Recently we have demonstrated a polarization and wavelength independent device, called a Terabit Optical Demultiplexer, which is capable of all-optical demultiplexing of Tbit/s pulse train with 650 fJ of switching energy, and which can be integrated on a chip. This device has achieved a 10 ps switching window. Both devices are wavelength compatible with all of the low loss transmission windows of optical fibers.

Single-mode optical D-fiber is fabricated and coupled to a buried polymer acrylic waveguide by a novel technique with a transcision and alignment ways. The D-fiber is fabricated by lapping the cladding layer of a single-mode fiber to the core. Optical waveguides and alignment ways are made with polymers by photodefinition. This technique combines the optical elements with a transcision placed perpendicular to the optical axis of the waveguide to offer an efficient coupling of single- mode fiber to optical waveguide with an excess coupling loss of 0.25 dB. This coupling loss is found using a cutback experiment and buried polymeracrylic waveguides. Also, this coupling technique has been used to achieve excess passive-coupling losses of 0.9 dB.

Semiconductor diode lasers are playing important roles in high speed information processing, telecommunications, and high speed measurement and diagnostic systems. This paper presents recent developments in the generation, amplification, and utilization of high power modelocked optical pulses from traveling wave semiconductor optical amplifier devices.

As part of the activities of the ARPA-funded, Ultra-Fast Optical Communication Consortium, hardware is being developed which is designed to provide an interface between a parallel array of 1 Gb/s electronic data sources and a 100 Gb/s, single-wavelength fiber optic channel. The input device is an integrated-optic tapped delay line (TDL) whose taps are set by the parallel electrical data streams which are then strobed by a 2 psec pulse to create an n-but optical word with an internal data rate of 100 Gb/s. A prototype device which uses arrays of fixed TIPE gratings for beam splitting and combining and which uses an array of electro-optic gratings as switched is currently being fabricated in a planar LiNbO₃ waveguide. Preliminary results and alternative TDL designs will be discussed. The output device, which employs waveguide second harmonic generation in a specially-designed GaAlAs waveguide, converts the temporal optical word into a spatial array of optical signals which can be detected in parallel. Experimental results will be presented which demonstrate that the serial-to-parallel converter can operate at rates exceeding 100 Gb/s, and can be expected to result in bit error rates of better than 10^-9 in a high-speed data link. The use of the integrated optic devices in CDMA as well as TDMA systems will be discussed.

We describe an integrated structure comprising a fiber bragg grating and a semiconductor-doped fiber for all-optical switching at laser diode poser levels. The operation of the device is based on intensity induced wavelength shift of a probe signal. The doped-fiber section serves as a Kerr medium. Results include switching power as function of device length.

In November 1994, the Optoelectronics Technology Consortium (OETC) demonstrated a working 32-channel bus with data transmission rates of up to 622 Mbps per channel and bit error rates of better than 8 X 10^-15. The optoelectronic data bus provides a parallel, 32- channel, high-density (140 micrometers pitch), point-to-point, connection using existing GaAs IC, silicon optical bench (SiOB), and multichip module (MCM) technologies. In the course of developing the data bus, a number of integration issues arose that required the specialized talents of a team of individuals with diverse expertise. These individuals were located in at least four different geographical areas and were employees of four separate companies that had come together in a precompetitive industrial alliance. Communication between the team members was paramount in preventing design details from becoming serious integration issues. This paper will briefly describe some of the OETC data bus system integration issues encountered and them summarize the technical results.

We report the observation of self-sustained pulsation and transient self-pulsation in laser diodes at 1300 nm and the effect of optoelectronic feedback on the pulsations. Transient self-pulsation has a lifetime of a few minutes with frequencies up to 7 GHz. The linewidth of self-pulsation is on the order of 0.5 GHz. With optoelectronic feedback, the transient self-pulsation can be stabilized and enhanced. The center of frequency of feedback-sustained pulsation is dependent on the passband of the bandpass filter in the feedback loop. The linewidth of feedback-sustained pulsation is significantly reduced to about 20 kHz. The feedback sustained pulsation can be frequency modulated. Applications of the feedback-sustained pulsation subcarrier multiplexed optical networks.

The construction and operating characteristics of a compact self starting mode locked erbium fiber laser are described in this paper. The laser employs a Fabry-Perot cavity with a fiber grating as one reflector and a nonlinear mirror based on a saturable absorber as the other. It operates at a pump power of less than 50 mW and produces mode locked pulses of 16.5 ps duration at a frequency of 3.25 MHz and a peak power of about 20 W.

We report the demonstration of a 4-bit optoelectronic-switched silica- waveguide time-delay network. Targeted for insertion into a 96-element L-band conformal array, the optical time-shifter provides 16 programmable time-delays in steps of 0.248 nsec. By characterizing its RF insertion phaser and synthesized pulse response, we verified that the relative time-delays generated by the waveguides were within 15 psec of their designed value.

We have fabricated a > 10 GHz high speed optoelectronic (OE), selector switch with high isolation (> 57 dB). This switch was used as a receiver for a microwave network demonstration with simulated satellite feeds of FM video and microwave BPSK digital channels.

An electro-optic lithium niobate waveguide switch using a symmetric 1 X 2 directional coupler structure and a two-section, unequal-length, (Delta) (beta) phase-reversal electrode is described. The device exhibits a step-like response to switching voltage. This response eliminates the need for precise voltage control to achieve low crosstalk. Switching characteristics of the device and experimental results are presented.

Several studies have been performed recently that demonstrate the reliability of lithium niobate Annealed Proton Exchanged (APE) Integrated Optical Circuits (IOCs). Studies have been performed on APE IOC die as well as pigtailed and packaged devices. The tests indicate that the reliability of APE IOCs meet or surpass the needs of most military and commercial applications.

We used morphological filters to approximate wavelet scaling functions for multiresolution processing of an image. Because some spatial light modulators (SLMs) can only display binary data, wavelet processing of binary images is inhibited. Therefore, we considered an alternative way - morphological processing - to generate a wavelet representation that consists entirely of binary elements. The effects of these filters are dependent on the input signal and cannot be generalized. Therefore, we used a statistical approach to approximate the scaling functions or various wavelets using morphological filters.

This paper introduces an optical implementation of the classic Rotman lens beamformer for use in ultra-wideband array antenna beamforming applications. The optical version described here features volume holograms as lens ports, arranged on geometric contours which follow modified Rotman's lens design equations. Modification of Rotman's lens equations, modeling of ray propagation in the lens, and the design process for this holographic Rotman lens are described in detail. Currently, a free-space experiment is in process to validate this design at 10 GHz, and to provide insight on the use of diffractive optics technology for millimeter-wave applications. Experimental results will be reported in detail in the near future.

A novel system that is capable of switching/routing 2D images in arbitrary configurations is described. The switching network can be reconfigured in a few microseconds with high light efficiency.

We have designed, built, and tested a sixteen channel fiber optic switching system based on the use of a bulk acousto-optic (AO) Bragg cell. The operational configuration known as a 'barrel shift' was developed specifically for fiber optic data acquisition system upgrades for the Collider Detector at Fermilab (CDF) in Batavia, Illinois. The prototype switch was delivered to CDF and is planned for tests targeting CDF upgrades in the next few years. Its use is intended for switching systems that specifically route time division multiplexed data channels. The acousto-optic barrel shifter (AOBS) simultaneously switches 16 parallel input optical fibers through a sequence of 16 separate states; after a complete cycle, all input channels have been routed to all output fibers for a total of 256 separate connections. The performance of the switch was demonstrated by switching transition times of 1 microsecond(s) ec, bit-error-rates (BERs) less than 10^-12 at 1.2 Gbits/sec, operation over a range of optical wavelengths from 1285 nm to 1320 nm, and low dependence on optical polarization. The optics package was contained in a portable enclosure 12 inches wide, 6 inches in height, and 16 inches in length.

A method is described by which adaptive beamforming can be accomplished in transmit mode with a photonic true time delay beamformer. Performance predictions for a radar line array using this beamformer are also presented.

We present the continuing development of an anti-jamming optical beamformer (AJOB) at Rome Laboratory's Photonics Division. Developments include live radar tests and new system designs. The purpose of the AJOB system is the cancellation of multipath jamming interference in advanced surveillance radars. AJOB is a multichannel adaptive optical system which performs cancellation of multiple wideband (10 MHz) interference sources in the presence of multipath. The live radar test consisted of using a downconverted 80 MHz received signal from the main and subarrays of a C-band radar to correlate jamming signals produced by stationary jammers. The correlation parameters fed a tapped delay line filter to form an estimate of the noise, which was subtracted from the main antenna signal. For the scenarios tested, the long integration time for the correlation data provided accurate estimates of the jammer delays, and therefore single-step convergence was achieved.

We present dynamic range and time delay results for a multichannel acousto-optic (AO) correlator using an in-line interferometric time- integrating architecture. This novel design demonstrates improved performance compared to the dual-path Mach-Zehnder interferometric correlator. The design provides control of the correlation spatial frequency to match that of the detector elements. The simplicity of the design, improved dynamic range, and increased stability make the in-line interferometric time integrating correlator an attractive alternative for applications in radar signal processing and spectrum analysis.

We present an overview of continuing research on a dynamic optical system for producing variable delays of radio frequency (RF) signals. Our approach utilizes both a 16 & 64 tap programmable delay line. The approach uses a microlaser diode array to tap an acousto-optic (AO) cell at various spatial positions along the acoustic channel. This generates multiple delayed versions of the input signal to the AO cell. The use of the laser diode array allows for a programmable time delay, programmable weighting of each delay, a large number of delays equal to the number of elements in the diode array, and multiple delays at one time. This architecture, upon completion of future compatibility testing will replace an existing multi AO cell tap delay line as part of an adaptive optical processor for side lobe jamming cancellation.

Future imaging sensors for the aerospace and commercial video markets will depend on low cost, high speed analog-to-digital (A/D) conversion to efficiently process optical detector signals. Current A/D methods place a heavy burden on system resources, increase noise, and limit the throughput. This paper describes a unique method for incorporating A/D conversion right on the focal plane array. This concept is based on Sigma-Delta sampling, and makes optimum use of the active detector real estate. Combined with modern digital signal processors, such devices will significantly increase data rates off the focal plane. Early conversion to digital format will also decrease the signal susceptibility to noise, lowering the communications bit error rate. Computer modeling of this concept is described, along with results from several simulation runs. A potential application for direct digital conversion is also reviewed. Future uses for this technology could range from scientific instruments to remote sensors, telecommunications gear, medical diagnostic tools, and consumer products.

A photorefractive crystal can be used as a three-dimensionally parallel array of multipliers. In writing the photorefractive gratings, the crystal performs the operation of multiplying the inputs and integrating the resulting products. In readout the photorefractive crystal multiplies the inputs with the stored gratings. The three dimensional array of multipliers is only accessible from the two-dimensional faces. This restricts us to using the photorefractive crystal for outer- products in writing to the full three dimensions of parallelism and inner products in reading out the three dimensions, when we are using a single wavelength system. We have explored issues in using the full three dimensions of parallelism in the real time volume holograph for signal processing applications. These issues are illustrated with our successful implementation of a high-bandwidth large phased-array radar processing system. This example system leads to a new algorithm for processing phased-array-radar data, which has a great advantage in hardware complexity over the classic Widrow algorithm and leads to a significant hardware savings for true-time-delay phased-array-radar control systems.

A partially asymmetric quantum-well Fabry Perot uses unequal partial reflections from front and back interfaces and balances destructive interference upon reflection by relying on intrinsic absorption in the quantum wells. The antireflection condition produces large modulation contrast ratios for reflected beams, while the partial reflections simultaneously allow transmission through the device. When the device is operated as a holographic optical element by incorporating a photorefractive quantum well structure in the Fabry Perot, output diffraction efficiencies can approach 100%. These holographic devices are optically addressed and electrically switched. In this paper we present theoretical calculations of the properties of partially asymmetric Fabry-Perot quantum wells.

Photorefractives, in general, are among the most promising materials solutions to real time optical correlation. Applications include military target recognition and civilian robotic vision. Crystals of sillenite structure photorefractives, Bi₁₂XO₂₀, where X equals Si, Ge, or Ti, have been grown by melt techniques and in the case of bismuth silicon oxide (BSO) and bismuth titanium oxide (BTO) by the hydrothermal method of high-temperature/high-pressure solution growth. The two growth methods are discussed and crystals grown by the two methods are compared in this paper. Optical absorption and TSC studies show that hydrothermal BSO is essentially free of the native antisite Bi defect which usually acts as a donor. These studies also show that the trap density is greatly reduced in hydrothermal material. Preliminary experiments show that hydrothermal BTO crystals have improved properties over melt grown samples. Al and P act as donors and acceptors respectively and can be used to compensate the native antisite bismuth defect. Initial spectroscopy studies show that they can be used to alter the valence state of transition element dopants. This result may aid in 'tailoring' these materials.

Photorefractive ZnTe and CdTe crystals doped with vanadium and/or manganese were grown and characterized in the wavelength range of 0.63 micrometers to 1.52 micrometers . The highest gain was observed in ZnTe:Mn:V (1.5 cm^-1 at 0.63 micrometers ). Through the use of both dopants the effective trap density was increased over an order of magnitude to 4.8 X 10¹⁵ cm^-3. The wavelength sensitivity range of cadmium telluride photorefractives was extended to less than 0.6 micrometers in CD_0.55Mn_0.45Te:V.

Twin-free single crystals of iron doped indium phosphide (InP:Fe) have been grown with different concentrations of iron dopants and shallow donor impurities using several techniques: magnetic liquid encapsulated Kyropoulos (MLEK), liquid encapsulated Czochralski (LEC), and vertical gradient freeze (VGF). Iron in InP falls into one of two defect states, and thus can be used as an infrared photorefractive (PR) material for amplifying coherent optical signals. The crystals above were compared in PR experiments at room temperature to measure two-wave mixing gain. The two defect states where then measured by independent means to determine a relationship between PR gain and defect concentration. From an analysis of these data the PR gain can be optimized by growing crystals under conditions which result in InP:Fe with an optimum Fe³⁺ concentration, optimum Fe³⁺/Fe²⁺ ratio, uniform dopant distribution, and low defect density.

Photonic excitations of the electronic spin system in doped sillenite phase Bismuth Silicon Oxide (BSO) Bi₁₂SiO₂₀ are presented. Dynamic metastability is explained using a Two Level system (TLS) model for photonic perturbation of the spin Hamiltonian.

We report enhanced electroabsorption in selectively doped (Ga,In)As/(Al,In)As Asymmetric Double Quantum Wells (ADQWs) by the use of real space electron transfer. The electron concentration in both the wide and narrow wells is investigated by field dependent absorption and photoluminescence spectroscopy. Additionally, a study of carrier dynamics in these ADQW structures indicates that electrons tunnel between the coupled wells on picosecond time-scales.

The finite-difference time-domain (FD-TD) numerical solver for Maxwell's equations is used to model problems in nonlinear optics. Since FD-TD makes no assumptions about pulse bandwidth or preferred direction of scattering, and can account for frequency-dependent material properties that vary on a submicron scale, it can provide optical design engineers with an unprecedented level of detailed field information, including pulse dynamics. This paper presents FD-TD computed results for a variety of passive and active optical microstructures.

A novel switch is introduced which has the capability of interconnecting 1 input channel to N output channels in a single device, without crosstalk. It is based on the unique properties of spatial solitons which propagate without diffracting in space and create index channels which can be used to guide signals at the same or different frequencies. Angular scanning of the soliton channels is achieved by chirping the phase of the input wavefront. Some properties of the switch and the initial demonstration of soliton scanning in an AlGaAs planar waveguide at 1550 nm are discussed.

Broadly tunable solid state lasers in the near infrared can be created using Cr⁴⁺ ions doped in various host lattices. Cr:forsterite and Cr:YAG span much of the spectral region between 1.2 and 1.56 micrometers . New hosts are required for powerful operation at 1.32 micrometers . Novel laser structures may be possible using optical nanocrystals embedded in refractive-index matched hosts. Waveguides with net gain are possible using Cr-doped nanocrystals.

One of the major problems with both Semiconductor Cylinder Fibers (SCF) and semiconductor Micro Crystals (MC) in glass is surface states at the semiconductor glass interface. We here make a model for the surface states, analyze their effect and the effect ofbarrier layers. Both, the fact that no shift in energy due to a quantum size effect is observed in the SCF and that the recombination of optically excited charge carriers seems to be by non radiative processes is, probably, due to surface states at the semiconductor glass interfaces. In order to investigate the effect of surface states we model the surface states

Selective area disordering of multiquantum well structures is used to fabricate an optical switch that consists of an overmoded undisordered section integrated with disordered input and output branching waveguides.

Cadmium sulfide (CdS) layers were deposited from aqueous solutions of thiourea, cadmium sulfate, and ammonia on (100) InP, InGaAs, and InAlAs. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and atomic force microscopy (AFM) were used to investigate the structural and chemical nature of the deposited CdS layer and the CdS/semiconductor interface. XPS showed that the deposition process effectively removes existing native oxides on InP and InAlAs before CdS growth occurs. Capacitance-voltage measurements of metal-insulator- semiconductor (MIS) capacitors were used to investigate the interface- state density of samples with and without CdS films between InP and a deposited insulator. CdS interlayers were found to reduce both the hysteresis and the interface-state density of the MIS capacitors. Applications of CdS interlayers for various photonic devices will be discussed.

We describe the characterization and development of semiconductor quantum well electroabsorption modulators (EAMs) for insertion into high-performance photonic links intended for analog applications. Limitations of existing approaches are described, motivating the potential of EAMs for exploiting the flexibility of semiconductor bandgap engineering. Relationships are established between basic modulator device characteristics and the RF system performance measures of link gain (insertion loss), bandwidth, noise figure, and dynamic range; results are then presented that have established the viability of EAMs for wideband, low-loss, linear analog photonic links.