Absorptive and dispersive bistability in semiconductor injection lasers

McLnerney, Heffernan

J.E. Carroll, Ian H. White

Abstract Absorptive, dispersive and modal bistabilities are considered in semiconductor injection lasers. Previous work is briefly reviewed and the discussion is concerned with experimental work with transverse modal bistability in twin stripe injection lasers. A simple circuit analogy indicates how modal bistability can arise and how it is possible to have stronger light output on the side where the current drive is weakest. Experimental results are reviewed for an optical flip-flop with the use of twin-stripe lasers with three such lasers coupled together in an optical logic circuit. Various mode patterns that have been observed by using different geometries of twin-stripe lasers are discussed. Use is foreseen for active bistable devices in front-end optical signal processing.

Guo-Qin Ge, Leung Pui Tang

Coherent transitions of charge carriers between the conduction and valence bands of a semiconductor medium are essential for the operation of a semiconductor laser. In this paper, we study how such interband coherence can be set up by an injection current and a coherent pump-field. In the absence of the pump-field, the injection current is the only source to establish the interband coherence in a semiconductor laser system. A laser threshold is obtained, which shows that a strongly coupled high-Q microcavity has a low threshold value. However, when an external pump-field serving as another mechanism to create the interband coherence is applied, the threshold value of the injection current can be lowered and it vanishes for sufficiently strong field. Besides, if the pump-field exceeds a threshold value, it is even possible to achieve a bistability in the inversionless region. Some fundamental macroscopic properties, including polarization, absorption and dispersion for the semicoductor system, are also obtained analytically.

Ian H. White

J.E. Carroll, Ian H. White

Rongqing Hui

Static and dynamic properties of dispersive optical bistability (OB) in semiconductor lasers biased from below to above threshold has been investigated both theoretically and experimentally. The OB result is found to be varied continuously from below to above threshold. Although conventionally the OB switch-off time in dispersive semiconductor laser amplifiers is limited by the effective carrier lifetime, a much faster OB switch-off can be obtained when a laser diode operates well above threshold in the injection-locked condition.>