Intensity fluctuations of injection lasers operated with high frequency modulation

Measurements of the noise properties of GaAlAs double heterostructure injection laser have shown that intensity fluctuations are much stronger when applying HF modulation than in CW operation. Measurements employed a frequency modulator with a center frequency of 35 or 70 MHz, a Smith trigger that converts FM signals into square-wave pulses and a driver amplifier. Using Langevin-noise sources, the spectrum of intensity fluctuations during turn-on of the laser is calculated. It is found that the center frequency of the signal or the pulse repetition frequency should be as low as possible to reduce turn-on effects.