Abstract

We have constructed a hybrid electronic/electrooptic digital adder based on a system suggested by Arazi¹ which uses an optical-carry for fully parallel operation. The philosophy of the system is to rely on optics for operations which are difficult to do in parallel electronically. Here, electronic logic is used for summing the addend and carry bits, while the carries are generated optically. The optical-carry is based on a multistage optical path, with sources which add light to the path if a carry is generated, and with modulators which allow light to pass if a carry is propagated, at the corresponding column of the addition. The signals which set the light sources and modulators are derived from the addends simultaneously, so the addition is completed as soon as detected light signals reach the summing logic. With small changes in the driving logic, the device operates as a parallel subtractor, with optical borrow propagation. This system reduces the number of gate delays associated with electronic addition of long addends. For long addends, the system speed is limited by light loss through the carry path. Our bulk-optic breadboard system has six acoustooptic modulators as optical switches, with a single He-Ne laser source. It adds two 4-bit words at 10 MHz with a 200-ns pipeline delay.

© 1986 Optical Society of America