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• Chinese Optics Letters
• Vol. 20, Issue 3, 032201 (2022)
Shuai Wan1、2, Rui Niu1、2, Jin-Lan Peng3, Jin Li1、2, Guang-Can Guo1、2, Chang-Ling Zou1、2, and Chun-Hua Dong1、2、*
Author Affiliations
• 1CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China
• 2CAS Center For Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
• 3Center for Micro and Nanoscale Research and Fabrication, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026, China
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Abstract

The microresonator-based soliton microcomb has shown a promising future in many applications. In this work, we report the fabrication of high quality (Q) $Si3N4$ microring resonators for soliton microcomb generation. By developing the fabrication process with crack isolation trenches and annealing, we can deposit thick stoichiometric $Si3N4$ film of 800 nm without cracks in the central area. The highest intrinsic Q of the $Si3N4$ microring obtained in our experiments is about $6×106$, corresponding to a propagation loss as low as 0.058 dBm/cm. With such a high Q film, we fabricate microrings with the anomalous dispersion and demonstrate the generation of soliton microcombs with 100 mW on-chip pump power, with an optical parametric oscillation threshold of only 13.4 mW. Our $Si3N4$ integrated chip provides an ideal platform for researches and applications of nonlinear photonics and integrated photonics.

1. Introduction

The optical frequency comb, which is a series of equidistant coherent optical lines in the frequency domain, has been greatly developed in the past two decades[13]. The conventional optical frequency comb is produced by the mode-locked laser and has played an important role in the precise measurement of time and frequency[46]. Based on the optical field enhancement of the microresonator, in 2007, the generation of the optical frequency comb was realized in the microresonator by continuous-wave (CW) laser pumping[7], which opens a new field of optical frequency combs based on the microresonator. Due to the emergence of noise in the generation process[8], the early microresonator frequency combs showed low coherence, and their application value was not expected. In recent years, with the discovery of dissipative Kerr solitons[9], stable and fully coherent soliton microcombs can be obtained in microresonators by simultaneously balancing gain and loss, as well as dispersion and nonlinearity[1013].