Second-order dispersion in oscillating GaAs junction lasers

The frequency separation between adjacent longitudinal modes in semiconductor lasers varies from mode to mode over the laser spectrum because of the effects of dispersion in the laser medium. Because of the interest in mode locking and self-pulsing of GaAs lasers it is desirable to know the magnitude of this effect. We have measured this variation of mode separation by measuring the correlation function of the field amplitude in the output beam of an oscillating, diffused junction, stripe geometry GaAs laser operating CW at
\sim80\deg
K. The correlation function is measured with a Michelson interferometer and is facilitated by using a diode that simultaneously oscillates in two widely separated families of longitudinal modes. The significance of this measurement to mode locking and self-pulsing in GaAs lasers is discussed.