Harvard Scott Hinton

Symmetric self-electrooptic effect device: optical set-reset latch, differential logic gate, and differential modulator/detector

The symmetric self-electrooptic-effect device (S-SEED), a structure consisting of two p-i-n diodes electrically connected in series and acting as an optically bistable set-reset latch, is discussed. Applications and extensions of this device are also discussed. The devices do not require the critical biasing that is common to most optically bistable devices and thus is more useful for system applications. They have been optically cascaded in a photonic ring counter and have been used to perform different NOR, OR, NAND, and AND logic functions. Using the same device, a differential modulator that generates a set of complementary output beams with a single voltage control lead and a differential detector that gives an output voltage dependent on the ratio of the two optical input powers have been demonstrated. >

Symmetric self‐electro‐optic effect device: Optical set‐reset latch

We demonstrate an integrated symmetric self‐electro‐optic effect device consisting of two quantum well p‐i‐n diodes electrically connected in series. The device acts as a bistable optical memory element with individual set (S) and reset (R) inputs and complementary outputs (optical S‐R latch). The switching point is determined by the ratio of the two inputs, making the device insensitive to optical power supply fluctuations when both power beams are derived from the same source. The device also shows time‐sequential gain, in that the state can be set using low‐power beams and read out with subsequent high‐power beams. The device showed bistability for voltages greater than 3 V, incident optical switching energy densities of ∼16 fJ/μm2, and was tested to a switching time of 40 ns.

Architectural considerations for photonic switching networks

Photonic technologies are reviewed that could become important components of future telecommunication systems. Photonic devices and systems are divided into two classes according to the function they perform. The first class, relational, refers to devices, that map the input channels to the output channels under external control. The second class, logic, perform some type or combination of Boolean logic functions. Some of the strengths and weaknesses of operating in the photonic domain are presented. Relational devices and their applications are discussed. Optical logic devices and their potential applications are reviewed. >

Optical Interconnections Using Microlens Arrays

Free-space interconnection of widely spaced pixels may be implemented using microlenses, rather than conventional imaging. Advantages, problems, and studies of system capacity are discussed.

Photonic switching fabrics

The strengths and limitations of the photonic technology are reviewed, beginning with the temporal bandwidth limitations of photonic devices and then focusing on spatial bandwidth, commonly referred to as the parallelism of optics, and how it can be used in photonic fabrics. Some of the proposed photonic switching fabrics that are based on guided-wave devices are discussed, comprising switching fabrics based on space channels, using directional couplers and optical amplifiers, and those based on time channels. The latter include active reconfigurable fabrics based on TDM, time-slot interchangers, and universal time slots, in addition to passive shared media fabrics. Some of the switching fabrics that have been proposed using wavelength channels are outlined, and multidimensional fabrics are briefly reviewed. Photonic switching fabrics based on free-space devices are described, covering free-space relational switching fabrics, the basic hardware required for digital free-space optical fabrics, and digital free-space switching fabrics.<<ETX>>

Free-space digital optical systems

Within the past 15 years there has been significant progress in the development of two-dimensional arrays of optical and optoelectronic devices. This progress has, in turn, led to the construction of several free-space digital optical system demonstrators. The first was an optical master-slave flip-flop using Hughes liquid-crystal light valves as optical logic gates and computer-generated holograms as the gate-to-gate interconnects. This was demonstrated at USC in 1984. Since then there have been numerous demonstrations of free-space digital optical systems including a simple optical computing system (1990) and five switching fabrics designated System/sub 1/ (1988), System/sub 2/ (1989), System/sub 3/ (1990), System/sub 4/ (1991) and System/sub 5/ (1993). The main focus of this paper will be to describe the five switching fabric demonstrators constructed by AT&T in Naperville, IL. The paper will begin with an overview of the SEED technology which was the device platform used by the demonstrators. This will be followed by a discussion of the architecture, optics, and optomechanics developed for each of the five demonstrators. >

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.

Photonic switching using directional couplers

May 1987-Voi. 25, No. 5 IEEE Communications Magazine I n the past few years the term photonic interconnection network (a photonic switch) has expanded and taken on several different meanings. In the most general case, a photonic switch refers to a system where both the inputs and outputs to an interconnection network are information encoded streams of photoris. An example of this would be a switching system that is used to interconnect a large collection of fiber-optic cables. In this general case a photonic switching system can be treated as a black box that operates on the inputs to connect them to the desired outputs. The fabric used within this black box can be divided into three classes. In the first class, this black box can include an optical-to-electrical conversion (o/e) followed by a conventional electronic switch, which is then followed by an electrical-to-optical conversion (e/o). Here there is a large inefficiency added by the o/e and e/o conversions in addition to imposing a rate constraint on the bit-rate of the photonic signal. T h e second class of switching fabric is an interconnection network that has the capability of switching the light entering the network without having to convert to the electrical domain. In this class, the control of the network remains in the electronic domain. A directional coupler, which is discussed in detail, is an example of an element in this fabric. The final class of switching fabric is similar to the previous class in that no ole or e/o conversions take place. The difference is that the control of this class of photonic switch is optical. This class of switch could be composed of optical logic that has been designed to perform switching functions. This article deals exclusively with the second class of switches based on an electro-optic device known as a directional coupler. Directional couplers can be fabricated in several materials but the focus of this article will be on LiNbOg based devices. T h e article begins by describing the basic principles behind the operation of the directional coupler. After the operation of directional couplers has been described, some of the current system design constraints are discussed. Finally, there is a brief description of the switching environment best suited for directional couplers along with some potential applications.

Reconfigurable intelligent optical backplane for parallel computing and communications.

A reconfigurable intelligent optical backplane architecture for parallel computing and communications is described. The backplane consists of a large number of reconfigurable optical channels organized in a ring with relatively simple point-to-point optical interconnections between neighboring smart-pixel arrays. The intelligent backplane can implement (l) dynamically reconfigurable connections between any printed circuit boards, (2) dynamic embeddings of classical interconnection networks such as buses, rings, multidimensional meshes, hypercubes, shuffles, and crossbars, (3) multipoint switching, (4) sorting, (5) parallel-prefix operations, (6) pattern-matching operations, (7) snoopy caches and intelligent memory systems, and (8) media-access control functions. The smart-pixel arrays can be enhanced to include more complex functions, such as queuing and routing, as the technologies mature. Descriptions of the architecture and the smart-pixel arrays and discussions of the system cost, availability, and performance are included.

Design and construction of an active alignment demonstrator for a free-space optical interconnect

An x-y active alignment system based on Risley beam steerers is described. The demonstrator features a quadrant detector which detects the misalignment error between the center of a spot of light and the center of the quadrant detector. This misalignment error is then used by a new algorithm to calculate the rotational displacement required for the two Risley beam steerers to steer the spot of light to the center of the quadrant detector. The experimental results indicate that any spot misaligned by up to 160 /spl mu/m on the quadrant detector will be systematically centered by the demonstrator system.<<ETX>>