Time-dependent simulation of a laser-modulator combination

Abstract

We present a computer model of an injection laser that is optically coupled to an on-chip electroabsorption modulator. The laser is assumed to be either of the distributed feedback type (DFB-laser) or of the cavity type with one of the mirrors formed by a diffraction grating (DBR-laser). Due to residual reflections at the output of the modulator there is coupling between the modulator and the laser so that the electrical signal that drives the modulator may affect the behavior of the laser. The temporal evolution of the laser is described by the usual rate equations which are solved numerically. At every step of the time integration the light distribution and oscillation frequency of the laser-modulator combination are obtained as solutions of an eigenvalue equation. In this initial study the modulator is driven by a sinusoidal electrical signal. The performance of the device is judged by how much frequency modulation is introduced by the coupling between the laser and the modulator. We find that DFB lasers are slightly more susceptible than DBR lasers to optical feedback between the modulator and the laser. The permissible end-facet reflectivities depend on the requirements of the system into which the laser-modulator is to be incorporated. For a specific DFB and DBR lasers, information relating length-bit rate products to permissible end-facet reflectivities are provided. >