Research On Nonlinear Reconfiguration Technologies Of Si₃N₄ Microresonator-Based Optical Frequency Combs

Silicon nitride（Si₃N₄）microresonator-based optical frequency combs has the characteristics of small volume,low power consumption,high repetition rate and CMOS-compatible fabrication.It has shown great application and research values in the fields of high-speed photonic signal processing and nonlinear physics.In this dissertation,we take the Si₃N₄ microresonators fabricated by the photonic Damascene process as the experimental platform,and focus on the stable generation and nonliear reconfiguration of the modelocked microcombs.The main innovative achievements of this dissertation are as follows:The stable generation of soliton microcombs in Si₃N₄ microresonators is studied.The study utilizes the electro-optic fast frequency sweeping method,and realizes the stable generation of single soliton microcombs with repetition rate of 100 GHz,spectral range of 240 nm and 3-dB bandwidth of 4.5 THz.In addition,the defect soliton crystal microcombs are observed for the first time in Si₃N₄ microresonators based on the mode coupling effect.The dynamic reconfigurable technology based on dual-coupled microresonators is proposed.The bidirectional reconfigurability and stable region extension of dissipative cnoidal waves（DCWs）microcomb is analyzed under the dual-coupled system.The comb line spacing of DCWs microcombs can be reconfigured from 8～22 times of the free spectral range.This study provides a theoretical support for the fabrication of dual-coupled microresonators for realizing monochromatically pumped reconfigurable microcomb.The single-mode and red-blue dual-pump scheme is proposed.In the experiment,the soliton-crystal-like breathing microcombs and the solitonmolecular-like breathing microcombs are observed for the first time.The comb line spacing of the novel breathing microcombs can be reconfigured from 2～17 times of the free spectral range based on the double parametric gain matching effect.The coexistence of multiple microcombs based on modes overlapping effect is proposed.The coexistence state of TE-polarized soliton microcomb and TM-polarized Turing rolls microcomb is observed for the first time in monochromatically pumped microresonators.In a Si₃N₄ microresonator with free spectral range of 100 GHz,the comb line spacing can be reconfigured from 21.6 GHz to 27.6 GHz.Moreover,0.1 THz and 23 GHz signal can be extracted simultaneously based on the multiple microcombs.The phase noise of 0.1 THz signal is reduced to-78 dBc/Hz@10 kHz through "quiet point" optimization.Lastly,combining the passive thermal compensation and mode coupling effect,the existence range of soliton state is extended to 12 GHz,and the deterministic generation of single soliton microcomb is realized,which improves the robustness of the soliton microcomb system.