Abstract

In all-optical switching systems bistable distributed-feedback (DFB) amplifiers are being used experimentally as memory cells and signal regenerators. In this frame a single section DFB amplifier (with one AR coated facet) operating around threshold at 1549 nm is pumped by a similar laser with a carefully controlled frequency detuning. The polarization controlled pump beam is modulated by a Mach-Zehnder switch (2.5 GHz bandwidth) to avoid source frequency chirp. The measurement of a pump reference and of the beam reflected from the amplifier is performed through a fiber directional coupler inserted between the two DFB diodes. Optical bistability has been observed both in transmission and in reflection for a sinewave modulated input in the 1-200 MHz frequency range. The output square wave exhibits up and down switching times lower than 1 ns and about 2 ns, respectively. The latter figure is consistent with the carrier recombination time in InGaAsP active structures, which is the main limit to the recovery time of bistable amplifiers. Work is in progress to investigate this feature in other types of amplifiers (e.g., multisection DFBs and quantum well structures).

© 1992 Optical Society of America