以含各向异性介质的中心对称膜层结构为对象,通过对光束入射角及各介质层结构参数的分析,设计了一种应用于密集波分复用(DWDM)系统的TM和TE偏振光均透射的平顶多通道偏振滤波器。给出了100GHz信道间隔的平顶偏振滤波器设计实例,其TM、TE偏振光的透射率均在99.999%以上,半高全宽(FWHM)分别为17.70GHz和19.14GHz,截止度分别约为35.74dB和33.40dB,且两偏振光的各透射窗口的中心频率均符合ITU-T标准。利用光学薄膜设计软件TFCalc对本文设计的结构进行了性能模拟,所得结果与利用传输矩阵法的理论结果几乎完全一致,验证设计此结构的可行性。最后,讨论了各介质膜层折射率对滤波器性能参数的影响。本文设计结构简单,用较少的膜层数就能实现高透射率的偏振滤波。
A flat-top multi-channel polarization filter,which can transmit both TM and TE polarized lights,is designed based on the centrosymmetric structure containing an anisotropic medium.The paper analyzes the incident angle and the structural parameters.Then a detailed design example of a 100 GHz channel-spacing filter with excellent properties is given.The cutoff degrees of transmission spectra of TM-polarized light and TE-polarized light are 35.74 dB and 33.40 dB respectively.The FWHMs of them are 17.70 GHz and 19.14 GHz respectively.The transmittances of TM-polarized and TE-polarized lights are both higher than 99.999%.Their center frequencies of transmittance windows accord with the ITU-T standard.In addition,this design structure is also simulated by TFCalc.The simulation result is almost the same as that obtained by the transfer matrix method,which proves the feasibility of the design structure.At last,the influence of the dielectric layers′ refractive indices on performance parameters is studied.The proposed structure is simple and its good polarization filtering characteristics can be obtained with fewer thin film layers.