Reductions of multiple-access interference in fiber-grating-based optical CDMA network

A fiber Bragg grating (FBG) encoder/decoder scheme based on correlation subtractions of nearly orthogonal M-sequence codes is presented. With proper coder design, a receiver can reject interfering users and obtain quasi-orthogonality between optical code-division multiple-access (CDMA) users in the network. However, optical CDMA networks may be degraded by multiple-access interference (MAI) due to nonflattened incoherent sources and nonideal FBG coders. A compensating module is therefore proposed to compensate for such MAI effects. As a result, the MAI effects induced by nonideal FBG coders can be perfectly eliminated by the compensating module. With spectral width reduction on the incoherent source, the scheme can partly compensate the MAI effects induced by nonflattened sources and further reduce the average error probability in the system performance.

I. Introduction

In today's optical communications, fiber capacity has to keep pace with rapid traffic increases due to continuing growth in the use of phones, multimedia, and computer net-works. Wavelength-division multiple-access is a promising solution for increasing the transmission capacity on optical communication links. Motivated by the successful capacity improvement of code-division multiple-access (CDMA) techniques in wireless communications, many people have become interested in the development of optical CDMA systems.