6 - Optical and mechanical issues in free-space digital optical logic systems

Summary

Introduction

This chapter discusses the issues involved in the design of a free-space digital optical logic system. The first section is an introduction to this field with an overview of the justification of pursuing this exciting and challenging course. The second section is a discussion of the basic characteristics of the devices that must be used in a system of this type with specific examples of the behavior of three of the most popular devices. Section 6.3 is a discussion of the optical and mechanical constraints involved in the design process. The fourth section is a design example using logic gates made from symmetric self electro-optic effect devices (S-SEEDs). The final section summarizes the likely future directions.

Background of digital optics

Two methods exist for communicating high bandwidth information: light and electricity. It is clear that the optimum choice for long distances (>1 km) is light; hence the adoption of fiber for telephony. It is equally clear that over short distances (<1 mm), the optimum choice is electricity hence its use for gate-to-gate interconnection in a chip. It has been shown that as the distance between the transmitter and receiver increases, the energy required by an electrical connection increases more rapidly than if optics is used (Miller, 1989). It is difficult to justify the use of optics over short distances and conversely, electrical connection is not ideal except over the shortest distances. The ultimate optimum choice for chip-to-chip and board-to-board interconnection is unclear.