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• Photonics Research
• Vol. 9, Issue 8, 08001423 (2021)
Xin-Tao He1、2、†, Meng-Yu Li1、2、†, Hao-Yang Qiu1、2, Wen-Sheng Ruan1、2, Li-Dan Zhou1, Lin Liu1, Xiao-Dong Chen1、2, Wen-Jie Chen1、2, Fu-Li Zhao1、2, and Jian-Wen Dong1、2、*
Author Affiliations
• 1State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, China
• 2School of Physics, Sun Yat-sen University, Guangzhou 510275, China
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Abstract

In silicon photonics, the cavity mode is a fundamental mechanism to design integrated passive devices for on-chip optical information processing. Recently, the corner state in a second-order topological photonic crystal (PC) rendered a global method to achieve an intrinsic cavity mode. It is crucial to explore such a topological corner state in silicon photonic integrated circuits (PICs) under in-plane excitation. Here, we study both theoretically and experimentally the topological nanophotonic corner state in a silicon-on-insulator PC cavity at a telecommunications wavelength. In theory, the expectation values of a mirror-flip operation for the Bloch modes of a PC slab are used to characterize the topological phase. Derived from topologically distinct bulk polarizations of two types of dielectric-vein PCs, the corner state is induced in a 90-deg-bend interface, localizing at the corner point of real space and the Brillouin zone boundary of reciprocal space. To implement in-plane excitation in an experiment, we fabricate a cross-coupled PC cavity based on the bend interface and directly image the corner state near 1383 nm using a far-field microscope. Finally, by means of the temporal coupled-mode theory, the intrinsic $Q$ factor of a cross-coupled cavity (about 8000) is retrieved from the measured transmission spectra. This work gives deterministic guidance and potential applications for cavity-mode-based passive devices in silicon PICs, such as optical filters, routers, and multiplexers.
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Xin-Tao He, Meng-Yu Li, Hao-Yang Qiu, Wen-Sheng Ruan, Li-Dan Zhou, Lin Liu, Xiao-Dong Chen, Wen-Jie Chen, Fu-Li Zhao, Jian-Wen Dong. In-plane excitation of a topological nanophotonic corner state at telecom wavelengths in a cross-coupled cavity[J]. Photonics Research, 2021, 9(8): 08001423