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（TiLiNbO3）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25 dB。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.