电调谐液晶波导型光滤波器的理论分析

ANALYSIS OF TUNABLE WAVELENGTH FLTER WITH A LIQUID CRYSTAL WAVEGUIDE RESONATOR

近年来，液晶光滤波器已成为频分复用和高密度波分复用光纤通信系统中的一种重要选频器件。传统液晶光滤波器的谐振腔一般由向列相液晶和镀有高反膜的两块中行介质镜形成，单模光纤与谐振腔之间由自聚焦透镜进行耦合，基模间耦合效率低．并且谐振腔内的大量高阶横模的存在严重影响了腔的选频特性。本文提出了一种液晶波导型谐振腔结构的滤渡器，谐振腔由两个自聚焦透镜的端面和液晶波导形成，这种谐振腔结构简单紧凑，在满足模式匹配条件时，可以大大减小谐振腔与自聚焦透镜间的模式转换损耗，并能有效地抑制腔内的高阶横模。本文着重分析了液晶光滤波器的调谐、滤波原理，推导出了液晶波导谐振腔与自聚焦透镜之间的模式耦合系数和模式最佳匹配条件。

Tunable Liquid crystal wavelength filters are key components in FDM and HD WDM systems.In this paper,a novel tunable wavelength filter with a nematic liqual crystal waveguide resonator has been proposed.The resonator of the filter is devised to have a short liqual crystal waveguide whose end face s are coupled with GRIN rods.The paper has analyzed the operation prindple of the filter,deduced the coupling coefficient and modes matching con ditions between the modes of the liquid crystal waveguide and the GRIN rods.The modes metching conditions are necessary that the filter has a narrow baedwidth and low loss.