Kurt H, Oner B B, Turduev M, Giden I H
Nanophotonics Research Laboratory Department of Electrical and Electronics Engineering TOBB University of Economics and Technology, Ankara 06560, Turkey.
Opt Express. 2012 Sep 24;20(20):22018-33. doi: 10.1364/OE.20.022018.
We present a novel design of two dimensional graded index medium that provides coupling of light with high coupling efficiency between two planar dielectric waveguides of different widths (15.46 μm vs. 2.21 μm). Poor light coupling performance of butt-coupler can be mitigated by implementing tapered coupler at the expense of long coupler section. In order to reduce coupling losses, a new coupling device approach based on graded index (GRIN) concept is proposed. The refractive index distribution is in the form of modified version of the Maxwell fish-eye lens. The inhomogeneous refractive index distribution is approximated by photonic crystals (PCs) such that the positions of each PC rods are appropriately arranged. Strong electric field focusing ability of the designed GRIN PC medium provides relatively high coupling efficiency that is around 90%. Spectral region corresponding to coupling efficiency over 75% has a bandwidth of Δω = 18.56% (284 nm). Finally, we discuss the durability of the proposed coupler against the lateral displacement and angular misalignment of output waveguides.
我们提出了一种新型的二维渐变折射率介质设计，该设计可在两个不同宽度（15.46μm对2.21μm）的平面介质波导之间实现高光耦合效率的光耦合。对接耦合器较差的光耦合性能可通过采用渐变耦合器来缓解，但代价是耦合器部分较长。为了降低耦合损耗，提出了一种基于渐变折射率（GRIN）概念的新型耦合装置方法。折射率分布采用麦克斯韦鱼眼透镜的改进形式。非均匀折射率分布由光子晶体（PC）近似，使得每个PC棒的位置得到适当排列。所设计的GRIN PC介质的强电场聚焦能力提供了约90%的相对较高的耦合效率。耦合效率超过75%的光谱区域带宽为Δω = 18.56%（284nm）。最后，我们讨论了所提出的耦合器对输出波导横向位移和角度失准的耐久性。
