Influence of spontaneous frequency fluctuations on lineshape of semiconductor laser modulated by a pseudorandom pumping current

The lineshape of a single-mode semiconductor laser is studied numerically for fast pseudorandom current modulation. We analyze the contribution of frequency fluctuations originated from spontaneous emission to the laser spectrum. The expression is derived for the nonstationary phase increment determining the influence of frequency noise on the lineshape. The obtained results show that spectral characteristics of laser radiation substantially depends on the spontaneous emission factor as well as on parameters of modulation.