Optical CDMA Spectral-Amplitude Codecs Capable of Reducing Multiple-Access and Optical Beat Interferences

Jen-Fa HUANG  Yao-Tang CHANG  Song-Ming LIN  

IEICE TRANSACTIONS on Communications   Vol.E87-B   No.11   pp.3195-3202
Publication Date: 2004/11/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Transmission Systems and Transmission Equipment for Communications
spectral-amplitude coding (SAC),  optical code-division multiple-access (OCDMA),  fiber bragg gratings (FBGs),  multiple-access interference (MAI),  optical beat interference (OBI),  

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Spectral-amplitude coding (SAC) techniques in fiber-Bragg-grating (FBG)-based optical code-division multiple-access (OCDMA) systems were investigated in our previous work. This paper adopts the same network architecture to investigate the simultaneous reductions of multiple-access interference (MAI) and optical beat interference (OBI). The MAI is caused by overlapping wavelengths from undesired network coder/decoders (codecs) while the OBI is induced by interaction of simultaneous chips at adjacent gratings. It is proposed that MAI and OBI reductions may be obtained by use of: 1) a source spectrum that is divided into equal chip spacing; 2) coded FBGs characterized by approximately the same number of "0" and "1" code elements; and 3) spectrally balanced photo-detectors. With quasi-orthogonal Walsh-Hadamard coded FBGs, complementary spectral chips is employed as signal pairs to be recombined and detected in balanced photo-detectors, thus achieving simultaneous suppression of both MAIs and OBIs. Simulation results showed that the proposed OCDMA spectral-amplitude coding scheme achieves significant MAI and OBI reductions.