Measurements of 1/f frequency noise reduction in semiconductor lasers using optical feedback with dispersive loss

The authors review the theoretical framework for linewidth reduction in semiconductor lasers using optical feedback with dispersive loss. These results are then applied to lasers having both white and 1/f frequency noise. Experimental confirmation of the dependence of frequency noise on feedback parameters is presented using optical feedback from an external cavity containing Cs vapor. It is shown that such feedback reduces the frequency noise spectrum uniformly within its operating bandwidth. It is also shown that where white noise is dominant, the linewidth is reduced by the same factor, 1/Q², as the frequency noise spectrum, but, when 1/f noise dominates, the linewidth is reduced only by 1/Q