Fiber dispersion effect on envelope detection of intensity modulated signals in Suppressed Carrier (SC) Subcarrier Modulated (SCM) systems

Abstract

In optical transmission systems fiber dispersion can have a significant effect over medium or long distance transmission lines. This is also true for Carrier Suppressed (SC) Subcarrier Modulated (SCM) systems, where several frequency components are involved in transmission. Since the transfer medium - the fiber - is dispersive, signal detection can be degraded, if the transmitted frequency components have a phase difference at the detector. This phase difference arises from the frequency dependent delay time, caused by dispersion. The effect of fiber dispersion on baseband modulation content was analysed and reported in several articles [1,2] also taking into account the distortion of harmonic frequencies [3]. However, dispersion effect on subcarrier modulated signals have not been investigated deeply yet. In this paper fiber dispersion effect considering a subcarrier modulated system with suppressed carrier is analysed. Calculations are given for the case, when the modulation content on the subcarrier is a sinus. A phase delay between the sideband subcarriers is also taken into account. This will give the theoretical background of the simulations, where a whole transmission system is taken into account. Fiber dispersion is simulated through an allpass filter with special phase characteristic, modulation contents are PRBS signals both in the baseband of the optical carrier and of the subcarriers, and effect of imperfect carrier suppression is also taken into account.