Kim Junhyeong, Kim Jae-Yong, Yoon Jinhyeong, Yoon Hyeonho, Park Hyo-Hoon, Kurt Hamza
School of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea.
Nanophotonics. 2022 Sep 9;11(20):4581-4590. doi: 10.1515/nanoph-2022-0443. eCollection 2022 Sep.
The on-chip optical power splitter is a common and important device in photonic integrated circuits (PICs). To achieve a low insertion loss and high uniformity while splitting the guided light, multi-mode interferometer-based structures utilizing a self-imaging principle are widely used mainly in the form of a 1 × 2 configuration. Recently, an inverse design method for nanophotonic devices has emerged to overcome the limited capability of the conventional design methods and make it possible to explore the vast number of design parameters. Because of the non-intuitive shape of inverse-designed structures, they allow us to discover interesting and complex optical responses which are almost impossible to find with conventional design methods. Here, we report two kinds of inverse-designed 1 × 4 optical power splitters composed of silicon bars of different lengths, which are fabricated with a standard CMOS-compatible process. The particle swarm optimization method was used to minimize the insertion loss and divide the power evenly into each output port with finite-difference time-domain method simulation. The first optical power splitter has a compact size of 8.14 × 12 μm and the second optical power splitter has an even more compact size of 6.0 × 7.2 μm. With the inverse designed structures, we fabricated the chip with a CMOS-compatible fabrication process. Experimental verification of the structures is provided and good agreement with the numerical results is obtained. The first 1 × 4 optical power splitter has a low insertion loss of less than 0.76 dB and uniformity of less than 0.84 dB, and the second more compact optical power splitter has a low insertion loss of less than 1.08 dB and uniformity of less than 0.81 dB. As the complexity of on-chip photonic systems has steadily increased, the inverse design of photonic structures holds great potential to be an essential part of advanced design tools.
片上光功率分配器是光子集成电路（PIC）中一种常见且重要的器件。为了在分束导波光时实现低插入损耗和高均匀性，基于自成像原理的多模干涉仪结构主要以1×2配置的形式被广泛使用。最近，一种用于纳米光子器件的逆向设计方法出现了，以克服传统设计方法能力有限的问题，并使得探索大量设计参数成为可能。由于逆向设计结构的形状不直观，它们使我们能够发现有趣且复杂的光学响应，而这些响应几乎不可能通过传统设计方法找到。在此，我们报告了两种由不同长度硅条组成的逆向设计的1×4光功率分配器，它们采用标准的CMOS兼容工艺制造。使用粒子群优化方法，通过时域有限差分法模拟来最小化插入损耗并将功率均匀分配到每个输出端口。第一个光功率分配器的紧凑尺寸为8.14×12μm，第二个光功率分配器尺寸更紧凑，为6.0×7.2μm。利用逆向设计的结构，我们采用CMOS兼容制造工艺制作了芯片。提供了对这些结构的实验验证，并获得了与数值结果的良好一致性。第一个1×4光功率分配器具有小于0.76dB的低插入损耗和小于0.84dB的均匀性，第二个更紧凑的光功率分配器具有小于1.08dB的低插入损耗和小于0.81dB的均匀性。随着片上光子系统的复杂性稳步增加，光子结构的逆向设计作为先进设计工具的重要组成部分具有巨大潜力。
