Transverse Optical Switching and Scanning in Twin-stripe Semiconductor Laser Amplifiers

Abstract

Semiconductor lasers and laser amplifiers have intrinsic nonlinearities which, while often undesirable for optical communication and data storage, show considerable promise for optical switching, modulation and bistable logic. These functions will be limited by nanosecond carrier lifetimes whenever it is necessary to change the carrier numbers in the active region, as in switching of the gain or absorption. However, phenomena such as nonlinear waveguiding which redistribute existing carriers over short distances may be much faster [1]. Here we consider theoretically the use of nonlinear waveguiding based on the well-known dependence of the refractive index on local carrier density, to produce transverse mode switching and beam scanning in closely-coupled twin-stripe laser amplifiers. Light from an external source is coupled into one of the guides, and is propagated numerically through the structure without imposition of cavity end losses or boundary conditions. The paraxial wave equation is solved using a Crank-Nicholson algorithm with small variations in implicitness for numerical stability. The effects of carrier diffusion and amplifier gain saturation are included, and the results are checked by solving the scalar wave equation in the transverse plane. Several regimes of behavior, including bistable switching and gradual beam scanning, are identified.