级联光子晶体Mach-Zehnder干涉仪的可调谐滤波特性

基于液晶的电控双折射特性和光子晶体自准直特性,在二维光子晶体引入复合缺陷提出一种可调谐Mach-Zehnder 干涉(MZI)滤波器结构,应用液晶系统的自由能理论,推导了外加电压与液晶有效折射率的关系,并结合MZI 相位调制原理和光子晶体等效折射率理论,得到液晶的电控双折射特性与MZI 滤波器的输出光谱间的数学关系,运用时域有限差分法(FDTD)对滤波器的输出进行仿真模拟,并根据仿真结果对结构进行一级级联的优化设计。结果表明:通过控制外加电压的大小可以改变输出端的透射波长,达到可调谐滤波的效果,并且一级级联后的滤波效果比级联前有很大的改善,滤波的半波带宽从20 nm 减小为7 nm,可调谐范围从15 nm 增大为40 nm,因此可以通过进一步级联的方式使滤波器结构更加的优化,以便运用到光波分复用系统中。

Tunable filtering characteristics of cascaded photonic crystal Mach-Zehnder interferometer

Based on the electrically controlled birefringence of the liquid crystal and the photonic crystal self-collimation effect, a tunable Mach-Zehnder interferometer filter structure was designed by introducing complex defects in the two-dimensional photonic crystal. The mathematical model was established between the applied voltage and the effective refractive index of the liquid crystal with applying free energy theory of the liquid crystal. Based on the phase modulation principle of Mach-Zehnder interferometer and the theory of the equivalent refractive index of the photonic crystal, the effect of the electrically controlled birefringence of the liquid crystal on output spectra of Mach-Zehnder interferometer filter was theoretical analyzed, and the output spectra of the filter was simulated with finite difference time domain method. And according to the simulation results, the cascaded optimization of the structure was designed. The results show that by controlling the applied voltage can change the transmission wavelength of output and achieve the effect of tunable filter. After level cascaded, the filter effect has a significant improvement. The filter bandwidth of a half-wave reduced from 20 nm to 7 nm, and the tuning range was increased from 15 nm to 40 nm. Therefore, the filter can more optimization by means of further cascading of the structure, in order to used in the optical wavelength division multiplexing system.