Fundamental study on design and fabrication of photonic crystal bent waveguide

本文用数值方法分析了三角形阵列上由硅圆气孔二维光子晶体构成的急弯光波导的特性。高效弯曲波导是实现紧凑集成光电路的关键器件。求解方法是基于多维波数字滤波器原理的时域有限差分法（FD-TD）；该方法易于实现，且比传统的Yee算法精度更高。首先，我们检查了波导的色散关系，并确认了在高阶模式的截止频率下获得的单模传播性能。为了使单模区带宽最大化，我们计算了光子晶体的设计参数。接下来，我们提出了一种无反射的微腔急剧弯曲波导。我们已经证明，由于谐振隧道效应，来自锐角的反射波可以被微腔完全消除，并且可以通过改变微腔的结构来控制透射带。其次，我们还分析了带微腔的分支波导，证明了可以实现无损耗的功率分频。最后，我们在绝缘体上硅（SOI）晶圆上制作了光子晶体波导。用电子束书写器定义了波导图样。对波导图样的精度进行了检验，并对制作条件进行了优化。

We have analyzed the characteristics of sharply bent optical waveguides constructed by two-dimensional photonic crystal of circular air-holes in silicon on a triangular array numerically. The highly efficient bent waveguides are the key devices to realize compact integrated optical circuits. The method of solution is finite-difference time-domain(FD-TD) method based on the principles of multidimensional wave digital filters ; this method can easily be implemented and is more accurate than the conventional one, the Yee algorithm.First, we have checked the dispersion relation of the waveguides and confirm the performance of a single mode propagation that is attained in the cutoff frequencies of higher-order modes. We have calculated the design parameter of photonic crystal to maximize the bandwidth of single mode region. Next, we have proposed a reflection-free sharply bent waveguide with the microcavity. We have shown that reflected waves from the sharply corner can be completely eliminated by the microcavity due to resonant tunneling and shown that transmission bands can be controlled by changing structure of the microcavity. Next we have also analyzed the branching waveguide with the microcavity and shown that loss-less power dividing can be realized. Finally, we have fabricated the photonic crystal waveguide on a silicon-on-insulator(SOI) wafer. The waveguide patterns are defined by electron beam writer. We have checked the accuracy of waveguide pattern and optimized the fabrication condition.