Self electro-optic effect devices and their use in optical switching and communications systems

This thesis concerns itself with the optimisation and potential use of the symmetric self electro-optic effect device (S-SEED), a bistable optoelectronic logic device. The SEED utilises the change in absorption of light, of semiconductor multiple quantum wells, when an electric field is applied perpendicularly to their layers (ie. the quantum confined Stark effect). These multiple quantum wells, incorporated into the intrinsic region of a pin diode type structure, can be used to modulate an incident light beam by varying an applied electric field. Under certain conditions, the SEED can be operated under positive feedback and is bistable in the intensity of its input beams. By using the modulation enhancing characteristics of an asymmetric Fabry-Perot cavity, these devices can exhibit very high switching contrasts for low operating voltages. A high contrast SEED is demonstrated. These devices can also operate as linear modulators or optical 'taps' in which the tap absorbs only sufficient incident optical power to satisfy a current drive, with the remainder of the optical power reflected. An high contrast linear modulator and its functionality as an optical tap is demonstrated. This device's application for use in a self-adjusting, optical to electronic, serial to parallel convertor is also proposed. A limitation of current optical switching devices is that they are either relational devices with high bandwidth and no bit-sensitivity, or they are purely logic devices with bit-sensitivity but much lower bandwidth. A new way of operating the S-SEED is shown which combines the advantages of both groups of optical switching device. This 'enhanced intelligence' S-SEED can be operated in such a way as to yield functionality similar to that required in self-routeing optical packet switches. A discussion is also made of optimum SEED device characteristics and limitations with respect to speed and signal tolerances in S-SEED systems applications