Spectral lineshape and noise of semiconductor lasers under analog intensity modulation

Abstract

Intensity and frequency fluctuations of semiconductor lasers under analog intensity modulation are theoretically investigated in both time and frequency domains. The spectral properties of the relative intensity noise (RIN) and the frequency noise (FN) as well as the associated lineshape are examined as functions of the modulation frequency and strength. The study is based on a numerical solution of the stochastic rate equations of semiconductor lasers. Based on the time variation of the photon number and the phase portrait of the photon number versus the electron number, the modulation dynamics are classified into six distinct types. The results showed that the high-frequency regimes of both RIN and FN are higher and the lineshape is more broadened when the signal is pulsed than when it varies continuously with time. The low-frequency components of RIN and FN are considerably enhanced and the laser coherency is extremely deteriorated when the laser emits irregular spike-like pulses under low-frequency strong modulation.