Optoelectronic clocking system for testing RSFQ circuits up to 20 GHz

Abstract

Unlike coaxial cable optical fiber has a bandwidth commensurate with the clock rates of even the fastest rapid single flux quantum (RSFQ) circuits. Employing this advantage we have developed an optoelectronic clocking system in which optical pulses from a picosecond laser are delivered via fiber to a superconducting chip on which metal-semiconductormetal (MSM) photodiodes generate fast electrical pulses with subpicosecond timing accuracy. An optical pulse splitter constructed out of beamsplitters mirrors and half-wave plates permits selection of pulse pattern and clock rate from 80. 6 MHz up to 20. 6 GHz. With a sampling oscilloscope we have directly observed optical triggering of an RSFQ T flip-flop at frequencies up to 1. 3 GHz with a variety of bit patterns. Optical triggering of a Josephson transmission line (JTL) at frequencies up to 20. 6 GHz has been verified by precise measurement of the Josephson voltage; this result represents the highest clock rate ever reported for an optical interface for RSFQ circuits. © 1997 IEEE.