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基于直接序列扩频(DSSS)的时域编码是目前光码分多址(OCDMA)系统中常用的编码方式。报道了利用带有等效相移(EPS)的超结构光纤布拉格光栅(SSFBG)对重复频率为2.5 GHz,宽度为7 ps的超短光脉冲串进行编/解码的实验,实验中所用码为31位的m序列。正确解码和不正确解码信号的对比度为5∶1,与理论计算结果相符。实验结果表明,等效相移光栅能够代替相移光栅作为光码分多址系统的编/解码器。且当入射脉冲宽度小于码片持续时间时,能获得良好的编/解码效果。
Time-domain coding based on direct sequence spread spectrum (DSSS) is a commonly used coding method in optical code division multiple access (OCDMA) systems. An experiment was carried out on the encoding / decoding of ultrashort optical pulse trains with a repetition frequency of 2.5 GHz and a width of 7 ps by using superstructured Fiber Bragg Grating (SSFBG) with equivalent phase shift (EPS). The code used in this experiment is 31-bit m-sequence. The contrast between the correctly decoded and incorrectly decoded signals is 5: 1, which is in good agreement with the theoretical calculation. The experimental results show that the equivalent phase shift grating can replace the phase shift grating as a coder of optical code division multiple access system. And when the incident pulse width is less than the chip duration, good coding / decoding can be obtained.