Abstract

Measurements of the spectral line shape as a function of power have been carried out from room temperature down to 1.7 K in order to understand the influence of fundamental quantum fluctuations on the spectral characteristics of single-frequency cw (GaAl)As diode lasers. Previous measurements¹ of linewidth from such devices as a function of reciprocal power at 273,195, and 77 K agreed well with a model² for the linewidth in which spontaneous emission caused fluctuations in both the phase and amplitude of the laser field. A power-independent contribution to the laser linewidth was also observed³ whose magnitude increased from 1.9 MHz at 273 K to 8.4 MHz at 77 K and was consistent with a phenomenological model involving electron number fluctuations in the gain volume that produced fluctuations in the resonant frequency of the passive cavity. An alternative theory for this power-indepen dent broadening by Vahala and Yariv⁴ attributed the phenomenon to electron occupation fluctuations rather than number fluctuations.

© 1984 Optical Society of America