电光可调谐有限脉冲响应滤波器设计

Design of Electro-Optic Tunable Finite Impulse Response Filter

为得到高矩形度、低旁瓣、电光调谐逆向可导及通带带宽可调的电光可调谐滤波器,在x切y传的钛扩散铌酸锂(Ti∶LiNbO3)波导上,对周期性分布的N级叉指电极组提供分立电压V,产生周期性电场,实现似TE模与似TM模的偏振转换,进而实现滤波功能。该结构构成有限脉冲响应(FIR)网络,网络传输矩阵H(z)与电压V具有一一对应关系。利用z变换原理,运用待定系数法求解H(z),从而推导所需电压值V,实现了电光调谐逆向可导。加入不同电压,可以实现自由光谱范围(FSR)内不同通带宽度的可调谐滤波特性。通过仿真验证,该算法是可行的。当N为17时,边模抑制比(SMSR)可达到25dB。并且滤波曲线的矩形度随着叉指电极组级联级数N的增大而增大。

In order to realize the electro-optic tunable filter with high rectangular degree,low sidelobe,electro-optic tuning reverse derivation and passband width tuning,the N-stage interdigital electrodes distributed periodically are provided with independent voltages V on the x-cut,y-propagation Ti-diffused LiNbO3.The induced periodic electrical field could achieve conversion of the quasi-TE mode and the quasi-TM mode and also the wavelength filtering.The finite impulse response（FIR） digital filter network is composed of this optical path.And there is a one to one correspondence between the transmission function H（z） and the voltage matrix V.Using z-transform and method of undetermined coefficients,the voltage matrix V is derived to realize the electro-optic tuning reverse derivation.The tunable passband width in the free spectrum range（FSR） can be realized with different voltage matrices V.This method is proved to be feasible through the simulation.When N is equal to 17,side mode suppression ratio（SMSR） could reach 25 dB.Also,the rectangular degree of the filtering increases with the increase of cascading stage N.