Correlation Function Method for Semiconductor Laser Optical Noise Investigation and Fluctuations of Directivity Diagram of Laser Radiation

Correlation function method was used for the optical noise investigation in InGaAsP/InP multiple-quantum-well lasers. It was observed that correlation factor between laser optical noises measured by two photodetectors decreases with laser current increasing above threshold. It is found that this correlation factor decrease is determined by fluctuations of directivity diagram of laser radiation in free space. These excess fluctuations can be eliminated using aperture near the laser emission facet that passes only central part of the beam.