Effects of four-wave mixing on the noise characteristics of semiconductor lasers

Abstract

It is well known that four-wave mixing (FWM) couples the longitudinal modes of a semiconductor laser.1 Such a coupling, although not commonly included in the laser rate equations, can significantly affect the noise characteristics. Both interband and intraband contributions to FWM should be considered. The interband contribution is generally believed to be negligible because of a relatively slow response time (≈1 ns) and a large mode spacing (≈100 GHz). The intraband contribution has its origin in the nonlinear gain whose response is governed by the intraband relaxation time (≈ 0.1 ps). We study the effects of such FWM by numerical simulation of the appropriately modified stochastic rate equations. The equations incorporate not only FWM but also the coupling through self- and cross-saturation.