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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 obtain high squareness, low sidelobe, electrooptic tuning inversely guided and tunable bandwidth of the tunable electro-optic tunable filter, in x cut y pass of titanium lithium niobate (Ti: LiNbO3) waveguide, the periodic The distributed N-level interdigital electrode sets provide a discrete voltage V, generate a periodic electric field, and realize the polarization conversion like TE mode and TM mode, thus realizing the filtering function. The structure constitutes a finite impulse response (FIR) network, and the network transmission matrix H (z) has a one-to-one correspondence with the voltage V. Using the principle of z-transform, the undetermined coefficient method is used to solve H (z) to deduce the required voltage value V, which makes the electro-optical tuning inversely definable. With different voltages, tunable filter characteristics with different pass-band widths in the free spectral range (FSR) can be achieved. Through simulation, this algorithm is feasible. When N is 17, the side mode suppression ratio (SMSR) can reach 25dB. And the squareness of the filter curve increases as the number N of interdigitated electrode group cascades increases.