Abstract

Optical memories are indispensable to time-division and self-routing photonic switching systems. Currently, optical fiber delay lines are commonly used as memory cells in such switching systems. These delay lines are fixed in length and not applicable to switching systems requiring flexible delays. To provide flexible delays, a directional coupler may be used in conjunction with a fiber delay line to form a reentrant delay-line memory.¹ However, this delay-line memory has drawbacks too. First, the front portion of an optical pulse may escape from the delay-line fiber undesirably before the rear portion enters it, resulting in loss of part of the optical pulse and causing crosstalk between adjacent time slots. Second, changes of the directional coupler operation states must be precisely controlled; otherwise the loss and crosstalk mentioned above occur again. We propose a photonic shift register. It is designed using directional couplers, optical fibers, and passive optical combiners. A single-bit shift register may be used as an optical memory cell with flexible delay. A multibit register may be used as a photonic serial-to-parallel converter, a photonic parallel-to-serial converter, or a time slot interchanger. Design and operation of this photonic shift register are elucidated.

© 1988 Optical Society of America