ULTRAFAST ALL-OPTICAL SIGNAL-PROCESSING WITH MODE-LOCKED SEMICONDUCTOR-LASERS

The novel application potential of modelocked laser diodes (MLLDs) in ultrafast optical signal processing in addition to coherent optical pu lse generation is described. As the most fundamental function of MLLDs , we show that the generation of ultrashort (similar to 2 ps) coherent optical pulses with low timing jitter (<0.5 ps) at precisely controll ed wavelength and repetition frequency can be achieved by employing a rigid module configuration for an external-cavity MLLD. We then discus s new aspects of MLLDs which are functions of ultrafast all-optical si gnal processing such as optical clock extraction and optical gating. A ll-optical clock extraction is based on the timing synchronization of MLLD output to the injected optical data pulse. When the passive mode- locking frequency of an MLLD is very close to the fundamental clock pu lse frequency of optical data, the former frequency is pulled into the latter frequency by optical data injection. We show that same-frequen cy and subharmonic-frequency optical clock pulses can successfully be extracted from optical data pulses al bit rates of up to 80 Gbit/s wit h very simple configurations and very low excess timing jitter (<0.1 p s). On the other hand, optical gating is due to absorption saturation and the following picosecond absorption recovery in a saturable absorb er (SA) in an MLLD structure incorporating optical gate-pulse amplific ation. Here, MLLDs are anti-reflection coated and used as traveling wa ve devices instead of laser oscillators: and small saturation energy ( <1 pJ) and ultrafast recovery time (<8 ps) are demonstrated. By combin ing all these MLLD Functions, we successfully demonstrated an experime nt with 40- to 10-Gbit/s all-optical demultiplexing processing.