Analysis of the Performance of a PAM/PPM/OOK System Operating with OCDMA, under Nonlinear Optical Effects in Optical Fiber Propagation

摘要

In this article, we present a numerical simulation study of encoding, decoding and propagation performance of short optical pulses and words with modulations OOK, PAM and PPM in OCDMA systems (Optical Code Division Multiple Access). The encoding and decoding of short pulses are obtained through fiber Bragg grating (FBG - FBG optical) devices, where the codes are inserted through discrete jumps in the optical phase (±π) where Gold codes were used. A figure of merit (SNR - Signal to Noise Ratio) was obtained to quantify the interference in propagation of short optical pulses. An increase in the temporal width was observed. For decoded pulses due to the nonlinearity effect, we observed an increase of 1.3 ps considering the propagation with y = 3 W~(-1) km~(-1) and y = 24 W~(-1) km~(-1). Analysis of coding and decoding words "a" and "w" was done. Considering the propagation (with y = 9 W~(-1) km~(-1)) of a word "w", an error occurred in all modulations except for simultaneous PPM/PAM modulation, which is associated to the better autocorrelation characteristics obtained with the OOK, PAM and PPM modulations alone, and could double the transmission rate. The nonlinear effects directly affect the process of the autocorrelation codes due to interference from adjacent chip components of the code.