Abstract

Typically, a passively mode-locked semiconductor laser was implemented with a saturable absorber, which provided pulse-narrowing mechanism. In this paper, we demonstrate numerically a passively mode-locked semiconductor laser based on nonlinear directional coupling in a coupler consisting of two parallel traveling-wave semiconductor amplifiers. In such a nonlinear directional coupler, the coupler length is chosen to be nearly a coupling length (one-half of a beat length) so that the efficient linear coupling can occur. When a high-power signal appears, the induced gain saturation breaks the phase-matching condition and stops the coupling of energy into the other amplifier. This process may lead to pulse narrowing and, hence, possible mode-locking.

© 1996 Optical Society of America