The Technology Of Encoded-Decoded For Optical Code Division Multiple-Access And

With the rapid development of internet,the communication capacity is sharply expanded. the space of wavelength gradually reducing,there is stern requirement in selecting laser source and filter. Furthermore,the intensity of laser become higher and the nonlinearity severer in fiber due the increasing number of multiplexing wavelength. Consequently, the wavelength resource in mainstream WDMA network becomes exhausted;It is difficult in realizing OTDMA technique because the optical pulse compression,optical pulse time delay,optical equalizing amplifier,optical dispersion compensation and optical regeneration technique is needed to adopted,which can not be easily realized; OCDMA system employed spreading spectrum sequence on the same wavelength. Spectrum efficiency is high. In tandem with WDM and OTDM it can increase the capacity of system greatly.It is important to select spreading spectrum code for OCDMA communication. The type, the length and the rate of spreading spectrum code will directly influence the realization of encoding, the capability of switching address and anti-jamming, and system capacity. So it is necessary to select the appropriate code sequence for enhancing the performance of OCDMA system. An arbitrary code among many codes applying to OCDMA is required to fit for corresponding encoded/decoded scheme. Therefore, the paper will firstly investigate spreading spectrum code in OCDMA system.Subsequently,the paper analyzes several important encoding/decoding techniques, which are a main technique in OCDMA system.Finally, the scheme of the encoder/decoder based upon FBG technique in spectral domain is proposed which is originated from traditional free-space grating-pair encoder and decoder. By mapping Walsh sequence ,the paper bring forward a method which implement the encoder and decode of OCDMA system utilizing step chirped fiber grating. Numerical simulation indicates the encoder/decoder has good correlation. Finally, the performanc of the OCDMA system is analyzed.