Signal analysis of self-pulsating semiconductor lasers

Abstract

A self-pulsating semiconductor laser (SPSL) exhibits inherent pulsation of light observed in its output. This self-induced pulsation shows promise for potential applications in telecommunications (optical communications) and signal processing, as well as in optical data storage applications. SPSL's have already been demonstrated in clock extraction and for optical clock distribution. SPSL's are used as CD lasers (with narrow stripe geometry) since self-sustained pulsation could be implemented to reduce optical-feedback noise. Self pulsations are attributed to two common reasons. One is through internal excitation of the laser resonance by the nonlinear interactions between various longitudinal modes of the semiconductor lasers. The other is caused by saturable absorbing effects that causes self induced and absorptive Q-switching in the laser. In the case of narrow stripe geometry SPSL's, the self-pulsation occurs because of the presence of saturable absorbers in the active material of the laser.
In this paper, signal analysis of the SPSL is studied based on a theoretical model of a laser diode of narrow-stripe geometry given in IEEE J. Quantum Electron. 35, 764 (1999). Saturable absorbing effects in the transverse dimension of the laser diode induce the self-pulsation. We present time traces of the relative intensity and study the dependence of self-pulsating frequency (SPF) on bias currents. Also, to the authors' knowledge, the on/off ratio of the self-pulsations as a function of bias current has been studied for the first time.