Sonya L. Walker

Five-stage free-space optical switching network with field-effect transistor self-electro-optic-effect-device smart-pixel arrays

The design, construction, and operational testing of a five-stage, fully interconnected 32 × 16 switching fabric by the use of smart-pixel (2, 1, 1) switching nodes are described. The arrays of switching nodes use monolithically integrated GaAs field-effect transistors, multiple-quantum-well p-i-n detectors, and self-electro-optic-device modulators. Each switching node incorporates 25 field-effect transistors and 17 p-i-n diodes to realize two differential optical receivers, the 2 × 1 node switching logic, a single-bit node control memory, and one differential optical transmitter. The five stages of node arrays are interconnected to form a two-dimensional banyan network by the use of Fourier-plane computer-generated holograms. System input and output are made by two-dimensional fiber-bundle matrices, and the system optical hardware design incorporates frequency-stabilized lasers, pupil-division beam combination, and a hybrid micro-macro lens for fiber-bundle imaging. Optomechanical packaging of the system ut lizes modular kinematic component positioning and active thermal control to enable simple rapid assembly. Two preliminary operational experiments are completed. In the first experiment, five stages are operated at 50 Mbits/s with 15 active inputs and outputs. The second experiment attempts to operate two stages of second-generation node arrays at 155 Mbits/s, with eight of the 15 active nodes functioning correctly along the straight switch-routing paths.

Six-stage digital free-space optical switching network using symmetric self-electro-optic-effect devices

We describe the design and demonstration of an extended generalized shuffle interconnection network, centrally controlled by a personal computer. A banyan interconnection pattern is implemented by use of computer-generated Fourier holograms and custom metallization at each 32 × 32 switching node array. Each array of electrically controlled tristate symmetric self-electro-optic-effect devices has 10,240 optical pinouts and 32 electrical pinouts, and the six-stage system occupies a 9 in. × 12.5 in. (22.9 cm × 31.7 cm) area. Details of the architecture, optical and mechanical design, and system alignment and tolerancing are presented.

Experimental investigation of a free-space optical switching network by using symmetric self-electro-optic-effect devices.

A prototype digital free-space photonic switching fabric is demonstrated. It consists of three cascaded 16 x 8 arrays of symmetric self-electro-optic-effect devices that are used as logic gates that implement part of a multistage interconnection network. We discuss architecture, device tolerancing, optical system design, and optomechanical design. This optical circuit is successfully configured as a fully operational array of 32 independent 2 x 2 nodes and operates at 100 kHz.

Beam array generation and holographic interconnections in a free-space optical switching network

Free-space photonic switching systems that optically interconnect large arrays of simple processing elements have already been demonstrated [IEEE Photon. Technol. Lett. 2, 438,600 (1990); Appl. Opt. 31, 5431 (1992); Electron. Lett. 27, 1869 (1991)]. In these system experiments, diffractive optical elements served as critical components that provided functionality not easily assumed by conventional optics. In the latest optical switching network, binary phase gratings were used to generate arrays of uniformintensity beams to illuminate modulators in the processor array. In addition, space-invariant binary phase grating designs were integral in forming the Banyan interconnection network used to link arrays in the system. Here we discuss the function, design, and performance of these diffractive elements.

Fabrication of fiber bundle arrays for free-space photonic switching systems

We describe a technique for assembling fiber bundle arrays as needed in optical computing and photonic switching systems. Two 4 x 4 arrays with single-mode and multimode optical fibers were manufactured. Fiber ends were located to within 3 μm of their ideal position and to a pointing precision of 30 arcmin. A third 4 x 8 array was manufactured with single-mode fibers, and fiber ends were located to within 1.5 μm of their ideal position.

Optomechanics of a free-space photonic switching fabric: the system

Parts of a multistage switching network were implemented by optically interconnecting arrays of symmetric self electro-optic effect devices. In an experiment completed last Spring, three 16 X 8 arrays of S-SEEDs, all operating as logic gates, were optically connected. A fully-interconnected switching fabric using six 32 X 32 S-SEED arrays is currently being tested. These are the latest in a series of experiments to investigate and develop this technology, and they substantially involve optomechanics. The practical realization of this technology represents a challenge to modern optomechanics due to the required precision, stability, and number of components involved. An overview of free-space photonic switching and the required experimental hardware subsystems is presented, followed by details of the optical systems to interconnect the switching device arrays and the mechanical systems which locate and position the optics and devices. The tolerancing analysis used in these systems is reviewed and comparisons between the two systems are made.

Parallel operation of a 32*16 symmetric self-electrooptic effect device array

Free-space optics for digital optical computing or for electrooptic interconnections is considered. Results of an experiment are presented in which 512 symmetric self-electrooptic effect devices (S-SEEDs) were simultaneously operated. In this experiment, simultaneous continuous bistable operation was shown for the 32*16 array of S-SEEDs, as well as simultaneously optical latching of optical data in a random access manner onto the array.<<ETX>>

Free space cascaded optical logic demonstration

We demonstrate a prototype digital free-space photonic switching fabric consisling of three cascaded 16x8 arrays of Symmetric Self Electro-optic Effect Devices used as logic gates. 1.

Practical applications of diffractive optics in free-space photonic switching networks

Free-space digital optical systems represent a novel interconnection technology that exploits the volume surrounding an electronic circuit substrate. The potential advantage of free-space optical systems is the creation of high density, energy efficient, parallel, high bandwidth interconnections. A photonic switching network, whose function is to connect high bandwidth channels, is a natural vehicle for exploring and developing this technology. Diffractive optical components play critical roles in these free-space systems as optical power array generators and interconnection holograms. In this paper, we will examine how these diffractive elements have served in realized photonic switching demonstration systems and explore some of the issues that determine their successes and limitations.

EGS switching networks based on free-space digital optics

Designers of future switching networks (both packet and circuit switches) will encounter many packaging and interconnection problems as data rates and network sizes continue to increase. Free-space digital optics is a new interconnection technology that may circumvent many of these predicted problems by using beams of light to transmit information between integrated circuits. The technology is described, and its advantages are outlined. New network architectures, such as the extended generalized shuffle (EGS) networks, that capitalize on the features of optics are described. A description of the current generation of prototype systems is given to illustrate the current state of the art.<<ETX>>