A 2D optoelectronic diffraction grating based on PLZT ceramic material for optical switching and reconfigurable optical interconnect applications is demonstrated. Integrable chips are fabricated consisting of numerous fine interleaved transparent indium-tin oxide electrodes on a polycrystalline PLZT ceramic substrate. The chips measure one centimeter square. Electrode features are scales and measure from 12.5 micrometers to 100 micrometers . Reported here are chip material and fabrication details.

Multiple quantum well (MQW) electro-optic modulators grown on both GaAs and InP substrates have been designed and characterized. Strained-layer (In,Ga)As/GaAs p-i-n diodes grown on (100) GaAs substrates were found to have a differential absorption coefficient of 3.7 X 10³ cm^-1 for an applied electric field of 6.6 X 10⁴ V/cm. These devices were also grown on (110) GaAs substrates and exhibited polarization sensitive electroabsorption. In addition, InGaAs/InAlAs asymmetric coupled MQWs were designed and fabricated. Real charge transfer kinetics between the coupled MQWs were exhibited by these devices.

Diffractive optical elements have been proposed for many applications. One of the principal limitations of these lenses is abundant chromatic aberration that prohibits broadband use without design compensation. I am working on a novel configuration that exploits this typically unwanted effect to provide information into a third dimension of current 2D IR detection systems, meanwhile gaining additional information about the target. Possible parameters of interest are the target's direction and velocity vectors relative to the detector and its spectral signature, which will aid in target identification. This paper will focus on the design, fabrication techniques, and characterization of the DOE for this system.

This paper presents an overview of work performed in the analog optical signal processing group at the Photonics Center, Rome Laboratory, in the area of automated optical target recognition. The research encompasses optical correlator filter development, optical image remapping, optical image segmentation, and optical neural networks. While the focus of the work is on military applications, we also present potential commercial uses for many of these systems.

We present the history and progress of the Anti-Jamming Optical Beam-forming (AJOB) program at Rome Laboratory's Photonics Center. The main objective of this program is near- real-time active noise cancellation applied to radar signal processing. All efforts mentioned here were Rome Lab in-house efforts conducted at the Photonics center, unless other noted. The United States Air Force funded all work described here.

The use of photorefractive crystals as optically addressed time integration spatial light modulators in acousto-optic signal processing discussed. An example utilizing BSO is presented.

A microwave variable delay line has been demonstrated based on the dispersive properties of optical fibers. This processor offers high bandwidth and tunability with the stability that fiber optics offers. A two-tap processor has been demonstrated with a 1.3 ns spacing.

A 16-channel plane-to-plane optical interconnect suitable for a multilayer multichip module computer system was demonstrated. a single diffractive optic element was used to focus the outputs from a 4 X 4 array of LEDs son one plane to a corresponding array of photodetectors on a second plane. This architecture can be used to overcome the speed, interconnect number and density, and power limitations of traditional electronic interconnects.

A novel concept for a high-speed signal routing holographic switching system for long-haul communications is proposed. A 1 X 2 optical switch is used to split transmitting optical signals so that part of it can be used to control the state of the photonic switches after it had been converted to the electrical domain. The routing controller then matches a given address to a specific frequency that is used to modulate a spatial light modulator (SLM). As a result, a reference beam is produced that in turn is used to write a grating on a transmission volume hologram. Meanwhile the information remains in the optical domain where it travels through the optical delay line and priority sorter. The delay time is equivalent to the total processing time of the holographic grating. The grating is changed by changing wavelengths. This wavelength tunability provides a method for free-space reconfigurable optical interconnections with high connection density.

We report on the development of a transparent optical node at 1.3 micrometers wavelength for an ATM packet switch operating at 1.24416 Gbit/s header recognition rates. The node takes advantage of the high-speed performance of optoelectronic components to alleviate potential bottlenecks resulting from optical to electrical conversion experience in nontransparent packet switching architectures. The node is intended for use in two-connected, slotted networks, is self-clocking, and has drop/add multiplexing, buffering, and routing capabilities.

A new single-element broad-area laser has been designed, fabricated, and tested for use as an integrated optical memory element or logic gate. The design incorporates a square gain section and an intracavity saturable absorber for each of the two orthogonal cavities. The devices lases in two spatially orthogonal modes that can be independently modulated by the two saturable absorbers.

Cr⁴⁺ doped in forsterite and YAG form broadly tunable lasers in the 1.2-1.6 micrometers region. These lasers can operation cw with output powers up to 2W, they re both pumped with the 1.06 micrometers output of a Nd:YAG laser, and they can both be modelocked to produce femtosecond pulses. We report on the latest results from these lasers, including self-modelocked operation of the Cr:YAG laser at 1.52 micrometers , with 120 femtosecond pulses, and with 480 mW output power. Both lasers are significantly affected by temperature: output power decreases with increasing temperature. Attempts to find a new host lattice for Cr⁴⁺ which does not have the deleterious temperature sensitivity of forsterite of YAG have not led to any breakthroughs.

The operating characteristics of a simple self-starting mode-locked erbium fiber ring laser based on a commercial optical fiber gain module are described. The laser produces pulses of the order of 50 mW. In contrast to earlier lasers of the same type, no polarizing element was needed in the ring to initiate mode locking. the implications of this fact relative to possible mechanisms for mode locking are discussed.

In this work, the desirability of a true time-delay beamformer is briefly discussed. Experimental results are reviewed and fundamental systems calculations are reported. Results for both optical and radar performance specifications were obtained, based upon a mathematical model of the photonic delay line developed by the author. These results address the use of the photonic delay line in a standard radar beamformer. Future work will evaluate the performance of the photonic beamformer in adaptive processing.

Fibers containing nonlinear optical material have large interaction length. Therefor it is possible to use small amounts of nonlinear material in the fiber and obtain large nonlinear effects. One of the easiest methods of placing a nonlinear material into a fiber is to surround the core of the fiber with a thin cylinder of nonlinear optical materials. We investigate such a fiber in this paper.

The characterization of components for optical interconnect technology presents a unique opportunity for Martin Marietta Laboratory - Syracuse (MML) and Rome Laboratory (RL) to expand on their collaborative research in photonics. Under a pending agreement, MML and RL propose to evaluate optical components and related technology that have potential applications for avionics subsystems on aircraft, high-speed communications between supercomputers, and high-resolution digital television. This paper describes the evaluation of one such optical component, the vertical cavity surface emitting laser (VCSEL). These VCSELs are employed in the directly modulated transmitters of an optical interconnect being developed by the Optoelectronics Technology Consortium (OETC) to relieve the inevitable bottleneck created by the advancing computer clock speeds and conductor densities.

We used the statistical techniques of factor analysis to design binary and ternary optical correlation filters to identify objects in the same class as, but outside, the training set by identifying spatial frequencies that were invariant across the training set. We provided general expressions for performance measures as a function of training set imagery.

Vertical cavity surface emitting lasers (VCSELs) have been fabricated and studied as the optical sources in a vertical optical interconnect application. The VCSELs are to replace LEDs that are currently used in a proof-of-concept demonstration. The advantages of VCSELs ares better power efficiency as sources, higher optical powers, focused beam output, monochromatic operation, and higher modulation bandwidth. The VCSELs used in this project are the first to implement continuously sinusoidally graded interface mirrors grown by molecular beam epitaxy. material parameters, device results, and interconnect implications are presented.

Four- and eight-level diffractive optical elements (DOES) are fabricated in silicon using electron beam lithography and reactive ion etching. An f/1.9. 1-mm diameter, four-phase level, reflective off-axis, imaging DOE is fabricated for use in a free-space optical interconnect. The absolute first-order efficiency of the DOE is 73%. Eight-level linear gratings are fabricated to determine processing tolerances for DOEs with first order-diffraction efficiencies greater than 90%.

The effective phase modulation of cascaded Kerr-birefringent fibers have been modeled numerically. the results indicate increased modulation for multistage structures. These structures are used to design low-power interferometric switches showing noncyclic transfer characteristics and having stable ON/OFF states.

A reconfigurable variable delay line is presented. The approach uses a Bragg cell and electro- optic beam deflector to achieve up to 100 ns of time delay. The system, which is similar to those using a Bragg cell and segmented mirror device, demonstrated the general nature of the beam deflector. this suggests that a broader class of spatial light modulators may be used as the beam steering device. An interpretation is developed based on geometrical optics considerations. Experimental results are discussed and compared with theory.

It is shown that by applying spatial frequency dependent optical phase compensation in an optical heterodyne process, variable RF delay can be achieved over a prescribed frequency band. Experimental results that demonstrate the performance of the delay line with regard to both maximum delay and resolution over a broad bandwidth are presented. Additionally, a spatially integrated optical system is proposed for control of phased array antennas, providing mechanical stability, essentially eliminating the drift problems associated with free-space optical systems, and providing high packing density. This approach uses a class of SLM known as a deformable mirror device and leads to a steerable arbitrary antenna radiation pattern of the true time-delay type. Also considered is the ability to utilize the delay line as a general photonic signal processing element in an adaptive (reconfigurable) transversal frequency filter configuration. Such systems are widely applicable in jammer/noise canceling systems, broadband ISDN, spread spectrum secure communications and the like.

With the advent of new government policies regarding technology transfer from government institutions to the commercial sector, we have had much attention drawn to Cooperative Research and Development Agreements (CRADA) with federal laboratories for process and product development. I would like to relate the generally positive experiences Corning Incorporated has had in creating a CRADA with the Photonics Center at Rome Laboratory. Because our CRADA is still on-going, I cannot point out as yet any particular successful application of technology, as we're still working on it! However, I can describe some of our experiences in going through the CRADA process.

We report the first demonstration of all-optical address recognition and self-routing of photonic packets for a case where the packet bit period is only 4 ps, corresponding to a 0.25- Tb/s bandwidth optical network. An ultrafast all-optical devices, known as a terahertz optical asymmetric demultiplexer (TOAD), was used to read the address information encoded in a packet header, which in turn was used to route the packet. The bit-error rate at the switch output was measured to be less than 10^-9.

In the fabrication of an overcoupled 2 X 2 fused taper coupler, the light cycles back and forth between the output fibers as a function of the optical path length of the coupling region between the waveguides. This cycling (beat frequency) becomes extremely rapid for highly overcoupled couplers as the number of cycles per unit length of pull increases exponentially. We have fabricated couplers with several thousand cycles that are extremely sensitive to small changes in the interaction length or the refractive index. We propose the use of these overcoupled fused taper couplers as optical switches or electro-optic modulators.

The Brillouin threshold in PM fiber is measured and compared with calculated values as well as previous cited results on standard SM fiber. Factors affecting it are identified, and methods of working around the limitations posed to fiber signal levels are briefly discussed.

We have constructed a harmonically modelocked laser that includes an electronically driven modulator and an intracavity Fabry-Perot etalon. We use experimentally observed performance of this laser, and number simulations based on the operating parameters of this laser, to examine strategies for generating stable synchronized trains of ultrashort duration solitons at multi-GHz repetition rates. Introduction of a saturable absorber based on a mechanism that both saturates and recovers promptly is examined. This strategy provides means of generating stable trains of solitons, where the soliton durations are of the order of a few ps or less, as well as synchronizing those trains with optical pulsewidth precision. We identify a rapidly saturating and rapidly recovering saturable absorber with a shorter pathlength as a potentially useful improvement on the nonlinear loop mirror. Significant work remains, but generation and distribution of these synchronized ultrashort duration soliton trains over networks on a scale of km or more appear feasible.

A compact optical image correlator using orthogonal, wavelength-multiplexed Fourier transform holograms recorded in a photorefractive crystal is demonstrated. Cross-correlation and autocorrelation measurements were obtained using randomly selected test image against the set of reference images stored in the orthogonal data storage volume hologram. Over 20 holograms were recorded in the 645- to 651-nm wavelength range with >2% autocorrelation efficiency and 3-angstrom wavelength separation. A low-power tunable external cavity semiconductor laser was used for readout, further demonstrating the portability of this approach. The translation invariance of the input images was also investigated.