讨论了一种新型光功能器件——光子晶体滤波器的工作机理，以带阻和带通滤波器构造多信道光子晶体滤波器，提出了能够用于光码分多址(OCDMA)系统编解码的基本原理。根据耦合模理论，缺陷谐振腔把光信号分成多个码片，完成对用户信号的频域编码。设计出中心波长分别为1527.70,1551.10和1570.00 nm的三通道滤波器作为OCDMA波导编解码器。为了保证码片的透射比，在主波导侧面附加缺陷介质构成带阻滤波器，使第二个码片透射比达到95%。谱宽为0.3 nm,信号基本上不会出现干扰，保证了用户发送和接收信号的准确性。该器件在整个编码过程中损耗的能量极少，这对于实现远距离通信很重要。

The mechanism of a new optical function device——photonic crystal (PC) filter is discussed. Subsequently, the basic theory for encoder/decoder in optical code division multiple access (OCDMA) system based on multiple channel PC filter consisting of band-pass filter and band-stop filter is proposed. Light signals are divided into several chips by the defect resonate cavity to encode/decode the user signals in frequency domain, according to the coupled-mode theory. Thus, the decoder in 2D-OCDMA can be performed. A waveguide decoder/encoder in OCDMA system consisting of three-channel photonic crystal filter, whose wavelength centered at 1527.70, 1551.10, 1570.00 nm is designed. To elevate the transmission efficiency, an extra defect is attached in at the sideway of the bus waveguide. As a results, the efficiency of the second chip is up to 95%. In emulation, the full width at half maximum is 0.3 nm, so there won′t be interference between signals in each channel. Also, energy loss in the process of decoding/encoding by PC waveguide encoder/decoder is small, which plays an important part in remote communication.