Abstract

Previous theories of intermodulation distortion (IMD) in semiconductor lasers are based on the single-mode rate equation and small-signal analysis and are limited to frequencies above 2 GHz. These models do not adequately describe N-channel IMD. Recent measurements show that because of longitudinal-mode competition, low-frequency (≤2 GHz) third-order IMD can be substantially increased in Fabry-Perot lasers.¹ This effect, which seriously degrades system performance at low frequencies, is very important in subcarrier-multiplexed (SCM) transmission systems.² In this paper, for the first time to our knowledge, we adequately model the laser’s IMD over the frequency range from 50 MHz to 10 GHz by performing a large-signal analysis of the general multimode rate equations.³ This analysis explains the low-frequency enhancement of IMD, including all third- order IMD’s for 60-channel signals. Additionally, we show that fiber dispersion further increases third-order IMD.

© 1993 Optical Society of America