Some Useful Formulas for Analysis of Interferometric Noise

It is well known that phase noise fluctuations at the output of a semiconductor laser can produce intensity noise fluctuations upon transmission through a fiber-optic link due to interferometric phase-to-intensity conversion [1-4]. In a single-mode fiber link, the interferometric conversion occurs when multiple reflections occur between a pair of fiber interfaces (Figure 1). Even in the absence of such fiber discontinuities, Rayleigh scattering in a sufficiently long piece of fiber can cause similar effects [5]. In an optical network using passive couplers, interferometric noise might occur if the difference between the two signal paths at the receiving node is small enough. The nature of the interferometric noise has been studied in [1-3]. It was shown that this excess noise can cause bit-error-rate floors [6], and the system performance has been evaluated as a function of the number and magnitude of the reflections [7].