The Study On Optical Code Division Multiple-Access (OCDMA) Technology

With the expands of multimedia, Internet and B-ISDN, the increasing demand has been presented for higher communication capacities and more quickly optical communication, and all optical local area network is one of research issues of optical communication. In this paper, we introduce OCDMA technology in detail and research the performance of OCDMA by experimens:At first, the basic principle of OCDMA is introduced simply and compare this technology with other duplicate technologies.We introduce the pivotal technics for OCDMA: research of address codes and design of encoder/decoder.We discuss the performance of optical orthogonal codes (OOC) and prime-hop sequences. OOC is a classic signature sequences that satisfy the auto- and crosscorrelation properties. We investigated the probability density function for any two interfering OOC's. Furthermore, we derive the bit error rate of the proposed OCDMA system as a function of data rate, code lenth, code weight, number of users, and receiver threshold; and we discuss the performance characteristics for a variety system parameters. An optical CDMA concept using wavelength hopping and time spreading is described employing prime sequences for both hopping and the spreading pattern (prime-hop sequences), and proofs are given that the autocorrelation function has zero side lobes and the crosscorrelation function is at most 1. In such systems, the number of possible stations is greatly increased as is the number of simultaneous users. Code generation and correlation are described in detail and networks for efficient code generation are analysed. It is shown that the system offers increased security levels leading to a very secure transmission.A time/frequency encoding/decoding optical CDMA system with high quality Bragg grating arrays is developed , and transmission rates up to 1.4Gb/s per user are achieved in the system. It is proved that even if the distance between Bragger gratings is bigger than the critical value required by the prevention of code overlap, the performance of the system will not deteriorate obviously. We also design another encoder/decoder adapting to high rate transmission.The experimental results show that the system is a kind of access network with high security as well as low error rate.