1/F FREQUENCY NOISE EFFECTS ON SELF-HETERODYNE LINEWIDTH MEASUREMENTS

The effects of 1/f frequency noise on self-heterodyne detection are described and the results are applied to the problem of laser diode linewidth measurement. Laser diode linewidths determined by self-heterodyne methods are not adequate predictors of coherent communication system performance because these measurements often include significant broadening due to 1/f frequency noise. In this paper the self-heterodyne autocorrelation function and power spectrum are evaluated for both the white and the 1/f components of the frequency noise. From numerical analysis, the power spectrum resulting from the 1/f frequency noise is shown to be approximately Gaussian and an empirical expression is given for its linewidth. These results are applied to the problem of self-heterodyne linewidth measurements for coherent optical communications and the amount of broadening due to 1/f frequency noise is predicted. Two methods are then provided for estimating the portion of the measured self-heterodyne linewidth due to the white and 1/f components of the frequency noise spectrum.