Abstract

The use of integrated optics to perform logic and computation was proposed earlier by Taylor¹ based on interconnected directional coupler switches and intensity Mach-Zehnder modulators. We apply the principle of polarization conversion and discrimination in integrated optical format to perform various logic functions. The principal components of the proposed logic gates are a polarization converter (TE ↔ TM) and polarizer. An illustration of the various logic gates that can be implemented by this concept is shown in Fig. 1. The logic input to these devices is an electrical voltage, equivalent to that which rotates the polarization by 90°, and the output is an optical intensity. The optical input is a linearly polarized light, and all waveguides are single mode in the TE and TM polarizations. From Fig. 1, it can be seen that logic gates such as AND, OR, NAND, NOR, EXCLUSIVE-OR, and NOT can be realized by properly arranging and cascading the polarization converters and polarizers along the waveguide pattern. Based on this concept, we report on the fabrication and demonstration of an integrated optical EXCLUSIVE-OR logic gate in Ti:LiNbO₃. As shown in Fig. 2, the device consists of a single-mode straight channel waveguide along which two polarization converters are cascaded and followed by a polarizer. The principle of operation can be understood by tracking the light polarization and transmission on the application of voltages to the two converters. Consider the case where both inputs A and B are ON. Assuming that the input light is in the TE polarization, the light is converted into TM past converter A and back to TE past converter B. If the polarizer is designed to pass the TM and attenuate the TE, the output is zero consistent with the truth table requirement of an EXCLUSIVE-OR gate. Other input–output combinations can be verified following the same reasoning.

© 1986 Optical Society of America