Correlation between 1/f fluctuations in the two output beams of a laser diode

The coherence function of 1/f noise fluctuations in the optical output from the two laser facets is derived from a simple model. At low power, the coherence is shown to be dependent on the optical absorption in thermal equilibrium. The coherence function can be used to determine the absorption coefficient. In the superradiation region, the coherence function increases strongly with power toward its maximum value of one. It remains one above threshold. Experimental findings on a channeled-substrate-planar laser are in good agreement with the author´s theory