Narrow Linewidth CW Laser Phase Noise Characterization Methods for Coherent Transmission System Applications

Several techniques for phase noise PSD measurement of continuous wave (CW) lasers to be used in coherent transmission systems are analyzed. Between them, we evaluate two novel techniques. The first employs a homodyne optical phase-locked loop, while the second uses a signal source analyzer. Experimental results obtained by these two methods are compared with classical linewidth measurement methods like self-heterodyne and Michelson interferometer. Limits and accuracy of each method are discussed. Furthermore, the comparison shows that, for coherent transmission system applications, only a subset of the analyzed methods is useful for laser phase noise characterization.