Ultrafast All-Optical Signal Processing with Mode-Locked Semiconductor Lasers

Hisakazu KURITA  Ichiro OGURA  Hiroyuki YOKOYAMA  

IEICE TRANSACTIONS on Electronics   Vol.E81-C   No.2   pp.129-139
Publication Date: 1998/02/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Issue on Ultrashort Optical Pulse Technologies and their Applications)
Category: Mode-locked and Gain-switched Laser Diodes and High speed EA Modulators
ultrashort light pulses,  semiconductor lasers,  mode-locking,  clock extraction,  gate switch,  nonlinear optical effects,  

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The novel application potential of mode-locked laser diodes (MLLDs) in ultrafast optical signal processing in addition to coherent optical pulse generation is described. As the most fundamental function of MLLDs, we show that the generation of ultrashort (2 ps) coherent optical pulses with low timing jitter (<0. 5 ps) at precisely controlled wavelength and repetition frequency can be achieved by employing a rigid module configuration for an external-cavity MLLD. We then discuss new aspects of MLLDs which are functions of ultrafast all-optical signal processing such as optical clock extraction and optical gating. All-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 pulse frequency of optical data, the former frequency is pulled into the latter frequency by optical data injection. We show that same-frequency and subharmonic-frequency optical clock pulses can successfully be extracted from optical data pulses at bit rates of up to 80 Gbit/s with very simple configurations and very low excess timing jitter (<0. 1 ps). On the other hand, optical gating is due to absorption saturation and the following picosecond absorption recovery in a saturable absorber (SA) in an MLLD structure incorporating optical gate-pulse amplification. Here, MLLDs are anti-reflection coated and used as traveling wave devices instead of laser oscillators, and small saturation energy (<1 pJ) and ultrafast recovery time (<8 ps) are demonstrated. By combining all these MLLD functions, we successfully demonstrated an experiment with 40- to 10-Gbit/s all-optical demultiplexing processing.