Research On Key Technologies Of Optical CDMA Systems

Optical Code Division Multiple Access (OCDMA) Systems have many applications in the access network and confidential communications. Fiber Bragg grating (FBG) is one of the most promising options of OCDMA encoders/decoders, due to its flexible structure, low-cost advantages.In this paper, a testing bed for OCDMA systems is structured and verified by a series of experiments. Furthermore, detailed studies on chromatic dispersion, performance of encoders/decoders, phase compensation, two-dimensional coding design, are listed as follows:First, with respect to the chromatic dispersion, inherent characteristics between dispersion and receiving device have been studied in terms of exploring OCDMA system dispersion on the impact of signal reception. As for asynchronous, coherent, phase-encoded, direct-sequence OCDMA systems, a criterion, fmaxLmaxD = 102, is proposed to judge the maximum fiber access distance, within which chromatic dispersion can be neglected.Second, with respect to the performance of encoders/decoders, pulse width variation due to source chirp, chromatic dispersion, chip length of en/decoders and its corresponding impact on electrical power at receiving device is analyzed in this paper. The result shows that system performance is limited by not only the code length and pulse width, but also the chip length.Third, with respect to the phase compensation, the use of reconstruction equivalent chirp (REC) technology for long-term phase error is originally proposed in OCDMA field. The experiment results show that, the application of REC technology is so effective that phase compensation is well-done.Fourth, with respect to the two-dimensional code design, compared to conventional FBG array, this kind of OCDMA encoders/decoders has the advantage of integrated structure. Meanwhile, it is coherence, which holds a better signal to noise ratio (SNR) performance. In addition, through the phase adjustment, it can expand its code capacity.Lastly, the prospects of FBG technology for OCDMA system and the practical problems around this paper are introduced.