Relationship between low-frequency fluctuations of the intensity of radiation and fluctuations of the voltage in semiconductor lasers

An experimental investigation was made of fluctuations of the radiation intensity and of fluctuations of the voltage across a laser at frequencies in the range from 0.5 Hz to 600 kHz. These low-frequency fluctuations were found to be correlated and their spectra were of the 1/f^a form, where a ≈ 0.8–1.1. A change in the sign of the correlation of these fluctuations was observed on passage across the lasing threshold. The relationship between the fluctuations was derived analytically for different types of noise. A comparison of the calculated relationship with the experimental data made it possible to determine that parameter the fluctuations of which predominated and were responsible for the observed low-frequency noise in injection lasers.