Suppression and spectral splitting of the amplitude noise due to mode beatings in a single-frequency injection laser

Investigations of intensity fluctuations in a single-frequency injection laser showed that they are due to beatings between coherent field and superluminescent spontaneous emission. It has been experimentally found that in the region of developed laser emission, the level of fluctuations is decreased with an increase of the output power, and so the relative spectral shift of external cavity superluminescent mode frequenices is dependent on the laser output power. The explanation of this phenomenon was made on the basis of the mechanism of a nonlinear interaction of a field in the active region of a laser diode. It has been shown that the fluctuation level is over the shot noise level by less than 4 dB when the laser output power is sufficiently large, about 6 mW.