Performance analysis in time-gated spectral phase-encoded time spreading (SPECTS) OCDMA systems

In this paper we present a comprehensive analysis of the pulse width influence of the initial pulse and the nonlinear optical loop mirror (NOLM) control pulse on a spectral phase-encoded optical code division multiple access (SPECTS-OCDMA) system. The analysis accounts for the detection errors that occur due to multiple access interference (MAI) between the desired and undesired user signals within the NOLM time window. We also investigate by means of two different scenarios how some system parameters perform under the effect of MAI, using the bit error rate (BER) as the figure of merit. In the first scenario, we evaluate how the initial pulse width affects the overall system performance. Results indicate that the system performance does not depend directly on the initial pulse width, but rather on the NOLM´s control pulse width to the initial pulse width ratio, when the spectral resolution (number of points per chip in the spectral window) is kept constant. In the second scenario, results show that the increase of the bit rate transmission affects the system performance if the temporal spreading after the encoding process is greater than the bit period. When that is the case, part of the spread energy is within the NOLM´s temporal window of the adjacent bit transmitted (inter-symbol interference).