Study On Kerr Optical Frequency Comb Based On Micro-ring Resonator

Since the first microresonator based optical frequency comb(microcomb)was reported in 2007 by Del'Haye,et.al.,microcombs have been realized in a variety of material platforms.By now,microcombs have been successfully used in optical communication systems,microwave photonics,optical frequency synthesis,optical clocks,dual-comb spectroscopy as well as dual-combs ranging measurement,et.al.,and present unprecedented performance.In this thesis,based on external injecting pump and“self-locked”schemes,the microcombs generation in a high-index doped silica glass micro-ring resonator(MRR)is experimentally and theoretically studied.The details of the researches and the achieved results are summarized as follows:1.The design and measurement methods of a MRR are systematically studied.For the demand of microcombs generation,the free spectral range(FSR),the quality factor and the waveguide dispersion of a MRR are carefully designed.Further,the designed MRR is fabricated based on high-index doped silica glass platform whose fabrication process is Complementary-Metal-Oxide-Semiconductor(CMOS)compatible.The main parameters of the MRR are measured under the assistance of a fiber ring resonator.The FSR of the MRR is~49GHz,the quality factor is in the range of 1.4~2.1×10~6 and the dispersion is~43ps~2/km at 1560nm.2.The MRR is successfully butterfly packaged.Soliton crystals(SCs)are stably generated by slowly tuning the resonance of the MRR through a thermoelectric cooler(TEC)based thermal-tuning approach for the first time.Analogy with the lattice structure of solid crystals,SCs can be classified to perfect,Schottky defects,Frenkel defects and superstructure defects,et.al.The SCs generation experiments provide an effective experimental method for the study of the interaction of solitons.The repetition rate stability during a short time is experimentally studied using delayed self-heterodyne interferometer(DSHI)method for the first time,to the best of our knowledge.In our experiments,the SCs are generated using a 100Hz linewidth laser as pump which is the narrowest linewidth pump laser in microcomb generation experiments to our knowledge.The repetition rate fluctuations are 53.24Hz and509.32Hz within 10?s and 125?s respectively.The effects of the pump frequency instability and the pump power variations to the repetition rate fluctuation of microcombs are theoretically analyzed.And our researches provide the theoretical foundation for realizing frequency stable microcombs in the future.3.The intrinsic mechanism of MRR based microcomb generation is analyzed and the evolution process of microcombs is theoretically studied based on Lugiato-Lefever equation(LLE).Along with the decrease of the pump detuning,primary comb(Turing pattern),sub-combs,modulational instability(MI)combs and soliton combs are theoretically obtained in sequence.Further,through sweeping the pump power and the pump-resonance detuning,the schematic of the comb evolution flow chart is obtained.And the generation condition of SCs is obtained for the first time.Furthermore,the steady solutions of different types of SCs are obtained based on the perturbation normalized LLE where the mode-crossing and non-uniform transmission loss effects are included by reducing the detuning at the mode of 102 and using the measured transmission loss parameters respectively.Finally,Raman self-frequency shift of soliton crystals is experimentally observed and theoretically studied using the perturbation LLE by introducing a Raman response expression.The Raman response time of high-index doped silica glass waveguide is speculated to be~3fs by comparing the theoretical and experimental results.4.Fiber ring cavity based phase-locked microcombs are experimentally obtained based on“self-locked”scheme for the first time when a MRR is embedded in a 1.9m length fiber gain cavity.While the optical phase is tuned using a polarization controller,single frequency laser,mode-locked state(“FD-DFWM”),sub-combs,stable microcombs,high noise combs and dual orthogonal combs are generated in sequence.And the mechanism of the optical field evolution in the MRR is detailedly analyzed.Further,dual-pump Kerr OFCs with varying FSR spacing are experimentally realized based on“self-locked”scheme.The dual pumps are self-oscillated in a fiber cavity.Over 180nm bandwidth OFCs are generated through the nondegenerate four-wave-mixing(FWM)in the MRR.The FSR of the dual-pump microcombs can be varied at range of 6~46 FSRs by tuning the central wavelengths of the dual-passband optical filter.5.Based on filter-driven dissipative four-wave-mixing(“FD-DFWM”)mode-locked technique,stable repetition rate multiplicable pulsed laser source is realized for the first time,to the best of our knowledge.The well-known“super-mode”instability of traditional“DFWM”mode-locked lasers is overcome by reducing the fiber cavity length using a high-Q factor MRR which not simply used as a filter but acts as a nonlinear element as well.Through tuning the laser cavity length,stable mode-locked lasers are experimentally realized with repetition rate tunable at range of 1~15 FSR(49~735 GHz).And the repetition rate tunable“FD-DFWM”laser is theoretically simulated based on nonlinear Schr?dinger equation(NLSE).