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  • Received: Jan. 13, 2020

    Accepted: Feb. 27, 2020

    Posted: Feb. 28, 2020

    Published Online: Apr. 22, 2020

    The Author Email: Daoxin Dai (

    DOI: 10.1364/PRJ.387816

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    Long Zhang, Lanlan Jie, Ming Zhang, Yi Wang, Yiwei Xie, Yaocheng Shi, Daoxin Dai. Ultrahigh-Q silicon racetrack resonators[J]. Photonics Research, 2020, 8(5): 05000684

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Photonics Research, Vol. 8, Issue 5, 05000684 (2020)

Ultrahigh-Q silicon racetrack resonators 

Long Zhang1, Lanlan Jie1, Ming Zhang1,2, Yi Wang1, Yiwei Xie1, Yaocheng Shi1,2, and Daoxin Dai1,2,*

Author Affiliations

  • 1State Key Laboratory for Modern Optical Instrumentation, Center for Optical & Electromagnetic Research, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou 310058, China
  • 2Ningbo Research Institute, Zhejiang University, Ningbo 315100, China


An ultrahigh-Q silicon racetrack resonator is proposed and demonstrated with uniform multimode silicon photonic waveguides. It consists of two multimode straight waveguides connected by two multimode waveguide bends (MWBs). In particular, the MWBs are based on modified Euler curves, and a bent directional coupler is used to achieve the selective mode coupling for the fundamental mode and not exciting the higher-order mode in the racetrack. In this way, the fundamental mode is excited and propagates in the multimode racetrack resonator with ultralow loss and low intermode coupling. Meanwhile, it helps achieve a compact 180° bend to make a compact resonator with a maximized free spectral range (FSR). In this paper, for the chosen 1.6 μm wide silicon photonic waveguide, the effective radius Reff of the designed 180° bend is as small as 29 μm. The corresponding FSR is about 0.9 nm when choosing 260 μm long straight waveguides in the racetrack. The present high-Q resonator is realized with a simple standard single-etching process provided by a multiproject wafer foundry. The fabricated device, which has a measured intrinsic Q-factor as high as 2.3×106, is the smallest silicon resonator with a >106Q-factor.

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