Fabrication of the high-Q Si3N4 microresonators for soliton microcombs
Shuai Wan, Rui Niu, Jin-Lan Peng, Jin Li, Guang-Can Guo, Chang-Ling Zou, and Chun-Hua Dong
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.
  • Jan. 11, 2022
  • Chinese Optics Letters
  • Vol.20 Issue, 3 032201 (2022)
  • DOI:10.3788/COL202220.032201
Third-order nonlinear phenomenon generated on the inner surface of bulk lithium niobate crystals with magnesium doping
Xiaojing Wang, Xiaobo Li, Hui Xu, Longhui He, Xuelei Li, Yulan Dong, and Xianfeng Chen
When two synchronized laser beams illuminate the inner surface of bulk lithium niobate crystals with magnesium doping (5%/mol MgO:LiNbO3) under the condition of total reflection, semi-degenerate four-wave mixing (FWM) is generated. On this basis, a more sophisticated frequency conversion process on the interface of nonlinear crystal has been researched. The generation mechanism of FWM is associated with the fundamental waves reflected on the inner surface of the nonlinear crystal. Analysis of the phase-matching mechanism confirms that the FWM is radiated by the third-order nonlinear polarized waves, which are stimulated by the third-order nonlinear susceptibility coefficient of the nonlinear crystal. Theoretically calculated and experimentally measured corresponding data have been presented in this article. These results are expected to provide new inspiration for further experimental and theoretical research on frequency conversion in nonlinear crystals.
  • Jan. 14, 2022
  • Chinese Optics Letters
  • Vol.20 Issue, 3 031901 (2022)
  • DOI:10.3788/COL202220.031901
Megapixel X-ray ghost imaging with a binned detector in the object arm
Haipeng Zhang, Ke Li, Feixiang Wang, Hong Yu, Changzhe Zhao, Guohao Du, Zhongliang Li, Biao Deng, Honglan Xie, Shensheng Han, and Tiqiao Xiao
  • Jan. 21, 2022
  • Chinese Optics Letters
  • Vol.20 Issue, 3 033401 (2022)
  • DOI:10.3788/COL202220.033401
Large area patterning of ultra-high thermal-stable structural colors in transparent solids
Jie Zhang, Dezhi Tan, Kaiqiang Cao, Tianqing Jia, and Jianrong Qiu
Printing stable color with a lithography-free and environment-friendly technique is in high demand for applications. We report a facile strategy of ultrafast laser direct writing (ULDW) to produce large-scale embedded structural colors inside transparent solids. The diffraction effect of gratings enables effective generation of structural colors across the entire visible spectrum. The structural colors inside the fused silica glass have been demonstrated to exhibit excellent thermal stability under high temperature up to 1200°C, which promises that the written information can be stable for long time even with unlimited lifetime at room temperature. The structural colors in the applications of coloring, anti-counterfeiting, and information storage are also demonstrated. Our studies indicate that the presented ULDW allows for fabricating large-scale and high thermal-stability structural colors with prospects of three-dimensional patterning, which will find various applications, especially under harsh conditions such as high temperature.
  • Jan. 14, 2022
  • Chinese Optics Letters
  • Vol.20 Issue, 3 030501 (2022)
  • DOI:10.3788/COL202220.030501
Quasi-resonant cavity enhanced photodetector with a subwavelength grating
Gongqing Li, Xiaofeng Duan, Weifang Yuan, Yongqing Huang, Kai Liu, and Xiaomin Ren
We designed a tunable wavelength-selective quasi-resonant cavity enhanced photodetector (QRCE-PD) based on a high-contrast subwavelength grating (SWG). According to simulation results, its peak quantum efficiency is 93.2%, the 3 dB bandwidth is 33.5 GHz, the spectral linewidth is 0.12 nm, and the wavelength-tuning range is 28 nm (1536–1564 nm). The QRCE-PD contains a tunable Fabry–Perot (F-P) filtering cavity (FPC), a symmetrical SWG deflection reflector (SSWG-DR), and a built-in p-i-n photodiode. The FPC and the SSWG-DR form an equivalent multi-region F-P cavity together by multiple mutual mirroring, which makes the QRCE-PD a multi-region resonant cavity enhanced photodetector. But, QRCE-PD relies on the multiple-pass absorption enhanced effect to achieve high quantum efficiency, rather than the resonant cavity enhanced effect. This new photodetector structure is significant for the application in the dense wavelength division multiplexing systems.
  • Jan. 11, 2022
  • Chinese Optics Letters
  • Vol.20 Issue, 3 031301 (2022)
  • DOI:10.3788/COL202220.031301
Impact of p-AlGaN/GaN hole injection layer on GaN-based vertical cavity surface emitting laser diodes [Invited]
Lei Han, Yuanbin Gao, Sheng Hang, Chunshuang Chu, Yonghui Zhang, Quan Zheng, Qing Li, and Zi-Hui Zhang
The hole injection capability is essentially important for GaN-based vertical cavity surface emitting lasers (VCSELs) to enhance the laser power. In this work, we propose GaN-based VCSELs with the p-AlGaN/p-GaN structure as the p-type hole supplier to facilitate the hole injection. The p-AlGaN/p-GaN heterojunction is able to store the electric field and thus can moderately adjust the drift velocity and the kinetic energy for holes, which can improve the thermionic emission process for holes to travel across the p-type electron blocking layer (p-EBL). Besides, the valence band barrier height in the p-EBL can be reduced as a result of usage of the p-AlGaN layer. Therefore, the better stimulated radiative recombination rate and the increased laser power are obtained, thus enhancing the 3 dB frequency bandwidth. Moreover, we also investigate the impact of the p-AlGaN/p-GaN structure with various AlN compositions in the p-AlGaN layer on the hole injection capability, the laser power, and the 3 dB frequency bandwidth.
  • Jan. 11, 2022
  • Chinese Optics Letters
  • Vol.20 Issue, 3 031402 (2022)
  • DOI:10.3788/COL202220.031402
High performances of diode-end-pumped Nd:SrAl12O19 lasers operated in continuous-wave and passively Q-switched regimes
Jun Guo, Jian Liu, Jie Xu, Bin Xu, Yuchong Ding, Xiaodan Wang, Xiaodong Xu, and Jun Xu
A good thermo-optic property of strontium dodeca-aluminum oxide (SrAl12O12, SRA) host material is very advantageous to the development of high-performance lasers by doping rare-earth ions for gain medium. In this work, we report on diode-end-pumped high-performance continuous-wave and passively Q-switched Nd:SRA lasers. For continuous-wave operation, a maximum output power of 6.45 W is achieved at 1049 nm with a slope efficiency of about 41.6%. Using a Y3Al5O12 (YAG) etalon, we have firstly achieved a 1066 nm laser with a maximum output power of 4.15 W and a slope efficiency of about 27%, to the best of our knowledge. For passively Q-switched operation, with Cr4+:YAG as a saturable absorber, a maximum average output power of 1.82 W was achieved with the shortest pulse width of 18.2 ns at pulse repetition rate of 22.9 kHz. The single-pulse energy and pulse peak power were 79.4 μJ and 4.3 kW. This work has further verified that the Nd:SRA crystal is very promising for high-performance laser generation.
  • Dec. 24, 2021
  • Chinese Optics Letters
  • Vol.20 Issue, 3 031401 (2022)
  • DOI:10.3788/COL202220.031401