相移超结构光纤布拉格光栅OCDMA编/解码器及其相关特性研究

基于相移超结构光纤布拉格光栅(SSFBG)光码分多址(OCDMA)编/解码器由于具有产生超长光学码的能力成为了目前的研究热点，相关特性是衡量OCDMA编/解码器性能的主要特性。（目的）为了研究此类器件的实用特性，本文研究了基于SSFBG的OCDMA编/解码器的结构及实现双极性编/解码的原理，（方法）利用矩阵分析法仿真研究了器件的相关特性，推导了因光栅周期不同而导致的编/解码器之间布拉格波长偏差对器件相关特性的影响。（结果）结果表明随着码字长度的增加，器件的自相关和互相关的对比度增加；但是当保持码片间隔不变而增加码字长度时，编/解码器的相关特性对布拉格波长偏差更加敏感，对于长度为31的Gold序列，当码片间隔为6 ps时，为了得到编/解码器之间良好的相关特性，布拉格波长偏差应小于0.02 nm；（结论）同一码字可以在不同的布拉格波长下重复使用，此特性有望用于波分复用（WDM）型OCDMA系统中。

OCDMA Encoder/Decoder Based on Phase Shifted Superstructure Fiber Bragg Grating and there Correlation Property

Recently optical code division multiple access (OCDMA) encoder/decoder based on phase shifted superstructure fiber Bragg grating (SSFBG) have attracted more attention because of SSFBG can generate long optical codes. The correlation property is fatal to the performance of OCDMA encoder/decoder. To evaluate the practical value of this kind of encoder/decoder the structure and bipolar encoding/decoding principle for OCDMA system based on phase shifted SSFBG are studied. The correlation property is simulated using transmission matrix method. The correlation property versus Bragg wavelength deviation between encoder and decoder because of the deviation of grating period is derived theoretically. Results indicate that the ratio of auto-correlation and cross-correlation is improved with the code length is increased, but the correlation property is more sensitive to the deviation of Bragg wavelength between encoder and decoder with the code length is increased while holding the chip pulse width. To obtain good correlation property the deviation of Bragg wavelength between encoder and decoder using Gold sequences with length 31 and chip duration of 6 ps must less than 0.02 nm. A code can be used with different Bragg wavelengths to implement hybrid wavelength division multiple (WDM) OCDMA system.