On fluctuations and transients in injection lasers

A new computer model of the semiconductor injection laser is described. The electron-photon interactions are introduced using a Monte Carlo technique in combination with multimode rate equations to compute laser output versus time and to compute output power probability density. Laser turn-on initially in a side mode, followed by evolution to the normal equilibrium modal power distribution, is shown to be intrinsic and a natural consequence of fluctuations in the modal powers at the moment the laser passes through threshold. Calculations of fluctuations in the equilibrium power levels show that occasional dropouts of the main-mode power are also a natural consequence of electron-photon interactions. Reduction in equilibrium fluctuations and in turn-on fluctuations can be achieved by increasing the laser power-output level, by increasing the mirror reflectivities, and by decreasing the laser length. This work indicates that conventional injection lasers must be operated at or above the 1 mW level in order to assure an error rate of 10
^-9
in digital systems. The well-known transition from thermal-noise statistics below threshold to Poisson statistics well above threshold is still evolving in the 0.5-2 mW region in the injection laser.