Polymer waveguides are considered to be good candidates for optical interconnects application due to their advantages such as flexibility, good compatibility, and versatility for realizing 3D and micro structures. However, constrained by the limited degrees of freedom provided by template-based design approaches, there lacks a satisfying solution which achieves small footprint and low loss simultaneously. Inverse design has been proposed to improve the performance. However, most inverse design methods target at silicon-based optical devices optimization which has a relatively high refractive index difference. In this paper, we demonstrate an ultra-compact low loss polymer wavelength (de)multiplexer with spot-size conversion structure to interposing Si and optical fiber using gradient-based topology optimization and downhill simplex method. The 2-channel wavelength (de)multiplexer displays an excess propagation loss of 0.84 dB and 1.06 dB at 1310 nm and 1550 nm, respectively, with a total footprint of 245 × 35 $\mu$ m $^2$ . The 4-channel wavelength (de)multiplexer for coarse wavelength division multiplexing applications with 20 nm spacing (1270, 1290, 1310, and 1330 nm) with an excess waveguide propagation loss of 1.72 dB within 271 × 50 $\mu$ m $^2$ has also been demonstrated and all the output ports of the polymer wavelength demultiplexing structure achieved a conversion efficiency over 90%.

中文翻译：

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具有拓扑优化的具有光点尺寸转换器的超紧凑型低损耗聚合物波长（De）多路复用器

聚合物波导由于具有诸如柔性，良好的兼容性以及用于实现3D和微结构的多功能性等优点，被认为是光学互连应用的良好候选者。然而，受基于模板的设计方法所提供的有限的自由度的约束，缺少令人满意的解决方案，该解决方案同时实现了小尺寸和低损耗。已经提出了反向设计以改善性能。但是，大多数逆设计方法都针对具有相对较高的折射率差的基于硅的光学设备优化。在本文中，我们演示了一种超紧凑型低损耗聚合物波长（de）多路复用器，它采用基于梯度的拓扑优化和下坡单纯形法，将光点尺寸转换结构插入到Si和光纤之间。$ \ mu $ 米 $ ^ 2 $ 。用于粗波分复用应用的4通道波长（de）多路复用器，间距为20 nm（1270、1290、1310和1330 nm），在271×50内的波导传播损耗为1.72 dB$ \ mu $ 米 $ ^ 2 $ 还已经证明了这一点，并且聚合物波长多路分解结构的所有输出端口都实现了超过90％的转换效率。