Influence of the Optical Fibre Dispersion on the Square Synchronizer Timing Jitter

Abstract

Very high bit rates are being increasingly used on direct detection optical systems. The influence of the clock recovery circuit (CRC) inaccuracies is of special significance in these systems since a small timing error may represent a high fraction of the bit period. Recently, we evaluated analytically the performance of the square synchronizer (a CRC employing a squarer as nonlinearity) in a direct detection optical receiver with the optical power incident on the photodetector modelled by a binary synchronous signal with equally likely symbol realizations: a general expression for the dynamic timing jitter (timing jitter root mean square) normalized by the bit period, E dyn /T, valid for any type of photodetector (PIN or APD), optical pulse shape, pulse shape at the input to the squarer, prefilter, narrow bandpass filter, noise type dominance and signal to noise ratio (S/N) was presented1. In2 the influence of the various types of noise on the square synchronizer performance in binary direct detection optical communications was analysed for a very narrow optical pulse shape (Dirac pulse shape). The generalization of this analysis to more realistic pulse shapes incident on the photodetector (which take into account the optical fibre dispersion) is the objective of this paper. In section 2, a summary of the dynamic timing jitter computation in the square synchronizer on direct detection optical communications is presented. In section 3, we present numerical results that descriUe the influence of the optical fibre dispersion on the square synchronizer performance and we provide a thorough physical explanation of these results for two noise dominant situations, the signal shot-noise and the circuit noise. In section 4, main conclusions are drawn.