Abstract

With the development of high-data-rate optical communication networks, there is a growing interest in processing some highspeed operations optically. Among these, clock extraction is critical because of its function in more complex operations, such as signal regeneration. A novel optical clock recovery circuit is demonstrated that uses the periodic oscillations resulting from the astable behavior of a bistable optical device with finite feedback delay.¹ The novel optical clock recovery circuit is based on a hybrid electrooptic bistable system and consists of an integrated-optic Mach-Zehnder interferometer with a feedback loop that introduces a time delay τ. We consider a return-to-zero (RZ) optical data signal with a bit rate I/(2τ) and a pulse width τP (τP ≤ τ), which rides on an optical bias. We show that when this signal enters the clock recovery circuit, the optical signal at the modulator output is a continuous square-wave pattern with a period of 2τ. This signal corresponds to the clock of the incoming optical data signal. The time-dependent behavior of the modulator output intensity arises from the periodic instabilities in bistable systems, which are caused by a finite feedback time delay.² Clock extraction from an intensity-modulated, 13.6 Mbit/s, 2²³-1 pseudorandom RZ bit sequence is demonstrated. Jitter performance of the recovered clock for various input data patterns, the effect of long strings of data-bit 0s, and the speed limitations of the circuit are investigated. The inclusion of this clock recovery circuit into an optical regenerator is also discussed.

© 1990 Optical Society of America