Harmonic and intermodulation distortion in semiconductor lasers (Invited Paper)

Abstract

Since the middle and late 1980s, there has been great interest in using subcarrier multiplexing for high capacity lightwave systems. While fiber optic systems are known to give superior performance with digital systems, the present cost of high-speed electronics for processing digital signals continues to make the subcarrier alternative attractive. For these systems, it is useful to have an a-priori knowledge of the distortion produced by a directly modulated laser diode. In this paper, we discuss the harmonic and intermodulation distortion arising from the inherent non-linearity of lasing action manifest in the rate equations. Only analytical techniques are considered. We point out the problem with an approximate harmonic balance technique reported earlier. The main emphasis is on the intermodulation products interfering with subcarriers, as only these products are of interest when the subcarriers are restricted to an octave bandwidth. Earlier analytical work was restricted to two subcarriers and required certain assumptions for determining multicarrier intermodulation distortion. We examine these assumptions in the light of our recent investigations.