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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。
Based on the electronically controlled birefringence of liquid crystal and the self-collimation of photonic crystals, a tunable Mach-Zehnder interference (MZI) filter structure is introduced into the two-dimensional photonic crystal. By using the free energy theory of liquid crystal system, The relationship between the electronically controlled birefringence of the liquid crystal and the output spectrum of the MZI filter is obtained by combining the MZI phase modulation principle and the photonic crystal equivalent refractive index theory with the applied voltage and the effective refractive index of the liquid crystal. (FDTD) to simulate the output of the filter, and the structure of a cascade optimization based on the simulation results. The results show that the output wavelength can be changed by controlling the applied voltage to achieve the tunable filtering effect. The filtering efficiency after the first cascade is greatly improved compared with that before cascaded. The half-wave bandwidth of the filter is increased from 20 nm Reduced to 7 nm and the tunable range is increased from 15 nm to 40 nm. Therefore, the filter structure can be further optimized by further cascading so as to be applied to the optical wavelength division multiplexing system.