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摘要:
硅基片上功率分束器是光子集成电路的重要组成,具有广泛的应用,比如反馈电路、抽头功率监测和光学量化等。纳米光子器件的设计方法大致可以分为正向设计方法和逆向设计方法。本文概述了正向设计方法和逆向设计方法的区别与联系,并且对逆向设计算法进行了归纳分类,此外,总结了近年来具有代表性的逆向设计的硅基片上功率分束器,包括多通道功率分束器、任意分束比功率分束器、多模式功率分束器、宽带功率分束器和多功能功率分束器,最后对逆向设计算法以及逆向设计的功率分束器的发展趋势进行了总结与展望。
Abstract:The silicon-based on-chip power splitter, an important component of the photonic integrated circuits, has much wider scope of applications such as feedback circuits, tap-port power monitoring, and optical quantization. The design methods of the nanophotonic devices can be roughly divided into the forward design and inverse design methods. This review article outlines the differences and connections between the forward design and inverse design methods, and classifies the inverse design algorithms. In addition, the review article summarizes the representative inverse-designed silicon-based on-chip power splitters in recent years, including multichannel power splitters, arbitrary-split-ratio power splitters, multimode power splitters, broadband power splitters, and multifunction power splitters. Finally, the summary and outlook are made on the development trend of the inverse design algorithms and the inverse-designed power splitters.
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Overview: The photonic integrated circuits (PICs) have been widely accepted as a viable alternative to support futuristic data communication networks. Specifically, silicon photonics offer a more promising and attractive platform to address the growing demands for optical communications due to its unique combination of low fabrication costs, low power consumption, compact footprint, and compatibility with mature complementary metal oxide semiconductor processes. The silicon-based on-chip nanophotonic devices are becoming fundamental building blocks of the complex PICs. The device-design methods can be roughly divided into the forward design and inverse design methods. The forward design method, a mechanism-orientation method, relying on the intuition, experience, and physical effect, usually finds the good device performance by tuning small sets of the characteristic parameters. While remarkable success has been accomplished using the forward design method, the trial-and-error procedure of this method becomes computationally costly and time-inefficient due to the continuously increasing complexity of the nanophotonic devices. In addition, limited by the small parameter search space of the forward-designed nanophotonic device, the device generally occupies a large footprint and has a limited performance. Driven by the increasing demands for the high-density PICs in the practical applications, great progress has been made in the research of the inverse design method. The inverse design method, an objective-orientation method, has been proposed to overcome the shortcomings of the forward design method. The nanophotonic device with the compact footprint and low loss can be designed automatically by the inverse design method. The inverse design method provides a new avenue for the realization of photonic chips. The silicon-based on-chip power splitter has much wider scope of applications such as feedback circuits, tap-port power monitoring, and optical quantization. As a result, the power splitter has been attracting more and more attention in recent years. Although the forward-designed power splitters have good performances, their large footprints limit their further applications in the high-density and large-scale PICs. Inverse-designed silicon-based on-chip power splitters featuring compact footprint, low loss, multiple channels, and flexible functions, has become the key building block for realizing the high-density optical system. In this review, we outline the differences and connections between the forward design and inverse design methods, and classify the inverse design algorithms. In addition, we summarize the representative inverse-designed silicon-based on-chip power splitters in recent years, including multichannel power splitters, arbitrary-split-ratio power splitters, multimode power splitters, broadband power splitters, and multifunction power splitters. Finally, the summary and outlook are made on the development trend of the inverse design algorithms and the inverse-designed power splitters.
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图 1 逆向设计的功率分束器总结。A:4通道的功率分束器[62];B:分束比为1:2:1的功率分束器[63];C:三TE偏振模式的功率分束器[70];D:工作带宽为700 nm功率分束器[71];E:可调谐的功率分束器[72]
Figure 1. Summary of the inverse-designed power splitters. A: The power splitter with four channels [62]; B: The power splitter with a split ratio of 1:2:1 [63]; C: The power splitter for the TE0, TE1, and TE2 modes [70]; D: The power splitter with 700 nm working bandwidth [71]; E: The tunable power splitter [72]
图 4 组合的多通道功率分束器的结构与性能。(a)由三个具有不同输出方向的1×2功率分束器组成的1×4功率分束器[60];(b)由一个1×2功率分束器和两个1×3功率分束器组成的1×6功率分束器[86]
Figure 4. Structures and results of the assembled power splitters with multiple channels. (a) The 1 × 4 power splitter assembled by three 1 × 2 power splitters with different output directions [60]; (b) The 1 × 6 power splitter assembled by one 1 × 2 power splitter and two 1 × 3 power splitters [86]
图 5 任意分束比功率分束器的结构和性能。(a)分束比为1:2:1的1×3功率分束器[87];(b)分束比分别为1:1、1:2和1:3的1×2功率分束器[63];(c)分束比分别为9:1、8:2、7:3和6:4的1×2功率分束器[88]
Figure 5. Structures and results of the power splitters with arbitrary split ratios. (a) The 1 × 3 power splitter with a split ratio of 1:2:1 [87]; (b) The 1 × 2 power splitters with the split ratios of 1:1, 1:2, and 1:3 [63]; (c) The 1 × 2 power splitter with the split ratios of 9:1, 8:2, 7:3, and 6:4 [88]
图 7 单个多模式功率分束器的结构和性能。(a)双TE模式功率分束器[90];(b)三TE模式功率分束器[70]; (c)四模式双偏振功率分束器[93]
Figure 7. Structures and results of the single-device power splitters with multiple modes. (a) The two-TE-mode power splitter [90]; (b) The three-TE-mode power splitter [70]; (c) The four-mode and dual-polarization power splitter [93]
图 10 宽带功率分束器的结构和性能。(a) 300 nm带宽的1×4功率分束器[96];(b) 445 nm带宽的1×2功率分束器[97];(c) 550 nm带宽的1×2功率分束器[98];(d) 700 nm带宽的1×2功率分束器[71]
Figure 10. Structures and results of the broadband power splitters. (a) The 1×4 power splitter with 300 nm working bandwidth [96]; (b) The 1×2 power splitter with 445 nm working bandwidth [97]; (c) The 1×2 power splitter with 550 nm working bandwidth [98]; (d) The 1×2 power splitter with 700 nm working bandwidth [71]
图 11 组合功能功率分束器的结构和性能。(a)具有不同输出方向的功率分束器[86];(b)任意输入的功率分束器[100];(c)模式转换的功率分束器[101];(d)模式转化和波长解复用的功率分束器[102]
Figure 11. Structures and results of the combined-functional power splitters. (a) The power splitter with different output directions [86]; (b) The power splitter with the arbitrary input waveguides [100]; (c) The power splitter with the mode conversion [101]; (d) The power splitter with the mode conversion and wavelength demultiplexing [102]
图 12 可调谐功率分束器的结构和性能。(a)基于GSST的可调谐分束比的功率分束器[72];(b)基于GSST的可调谐的直通和分束功能的功率分束器[103];(c)基于Sb2Se3的可调谐分束比的功率分束器[104]
Figure 12. Structures and results of the tunable power splitters. (a) The GST-based power splitter with the reconfigured power ratios [72]; (b) The GSST-based power splitter with the straight passing and power splitting [103]; (c) The Sb2Se3-based power splitter with the reconfigured power ratios [104]
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