AMPLITUDE PHASE DECORRELATION - A METHOD FOR REDUCING INTENSITY NOISE IN SEMICONDUCTOR-LASERS

By the method of amplitude-phase decorrelation, the fundamental intensity noise floor of semiconductor laser light can be reduced over a wide bandwidth by the ratio 1/(1 + alpha-2), where alpha is the linewidth enhancement factor. The method uses a dispersive element to convert phase noise into intensity noise. We recently demonstrated this technique by reducing intensity noise from a DFB laser as much as 7 dB below its intrinsic level [1], [2]. In this paper, we extend these results by characterizing the frequency dependence of the noise reduction. Optimum reduction is achieved in the flat region of the spectrum and diminishes at higher frequencies approaching the relaxation resonance. The correlation properties of the fluctuations are also investigated. The cross-spectral density of the fluctuations shows they are decorrelated when noise is maximally reduced. Parallels between this technique and "detuned loading" [17] will also be established.