Near-threshold behavior of the intrinsic resonant frequency in a semiconductor laser

The excitation-dependence of the resonant frequency intrinsic to a semiconductor laser is analyzed in terms of a spatially uniform laser model which takes into account radiative and nonradiative recombination as well as spontaneous emission into the lasing modes. The analysis reveals that the frequency of the resonance excited by internal quantum noise approaches a minimum value as the excitation level approaches threshold in contradiction to the behavior expected from a small-signal analysis of the external modulation spectrum or the relaxation oscillations. This distinctly different behavior of the noise-excited resonance is shown to result from the presence of noise fluctuations in the optical field, which are sensed only by the noise-excited spectrum. Experimental observations made with a stripe-geometry (AlGa)As double-heterostructure laser confirm the predicted behavior of the noise-excited resonant frequency in the near-threshold regime.