Theoretical Studies On The Soliton Optical Frequency Comb Via Phase-modulated Pumping Scheme

Optical frequency comb(OFC)has been widely used in science and technology for its close connection between microwave frequency and the optical signal generated in the process of atomic transition.Initially,OFCs were generated by mode-locked lasers.However,the corresponding comb spacing is limited by the length of the cavity,and the repetition frequency is generally difficult to beyond 10 GHz.In addition,the high cost and large volume of mode-locked laser are not favorable for the development trend of miniaturization and integration.In recent years,with the continuous development of technology and fabrication in the field of photonic integration,compared with the traditional mode-locked-laser-based OFC,OFC generated from the micro-cavity(microcomb)has shown unprecedented excellent performance.Microcomb is advantageous in integrability,low threshold,high repetition rate and wide spectral coverage have revolutionized the fields of timing,terabit level coherent optical communication and spectroscopy.Breakthroughs in high-Q microresonators enable the ultra-high repetition-rate soliton microcomb generation,triggering intense applications by holding the promise of taking frequency comb technology outside of the laboratory.Accessing and maintaining the high-coherence soliton state are usually technically challenging,with the requirement for delicate control of the pump power frequency detuning or operation temperature.Besides,the soliton repetition rate will also be affected by environmental fluctuations,such as temperature change,wavelength instability,etc.Based on the high-index-doped silica glass resonator,we numerically proposed phase-modulation pump scheme(PMS)and realized repetition-rate multiplicable soliton microcomb in a designed single resonator.By controlling the pumping conditions and modulation methods,the deterministic generation of multi-repetition-rate tunable optical frequency combs can be achieved.Simultaneously,It is found that the PMS have an effect on stabilizing the generated solitons with inhibited temporal drift caused by the Raman self-frequency shift effect.The main work and the conclusions obtained are as follows:Firstly,a high-index-doped silica glass micro-ring resonator with flat anomalous dispersion is carefully designed.Additionally,the dynamics are studied theoretically by solving the Lugiato-Lefever Equation.The physical conditions and mechanism based on four-wave mixing effect of optical frequency comb nonlinear evolution relating to continuous wave pump scheme are analyzed.Distinct from traditionally soliton generation scheme,the pump laser is modulated before pump coupling into the resonator.Stable soliton states are directly established in the absence of the primary comb and chaotic MI stage.Optimizing the pump power and the modulation frequency,one can realize deterministic generation and continuous dialing of repetition-rate multiplicable solitons(10?40GHZ)via the proposed method.On the basis of PMS scheme,the subharmonic phase modulation(SPS)method also investigated.By setting the modulation frequency to non-integer multiple FSR with precisely controlling the modulation depth,ultra-high repetition rate solitons(50?200GHz)can be obtained,which can solve the constraints of cavity length and high-frequency electrical devices.An extended Lugiato-Lefeve Equation including Kerr nonlinear phase modulation and Raman self-frequency shift(RSFS)is established and numerically studied.Correspondingly,the simulation results can give insights of soliton generation dynamics.PMS utilizing complex nonlinear effects against undesired soliton temporal drifts,and equally important,contribute to improving absolute soliton stability through inhibiting chronic temporal drifts,realizing soliton spacing equalization from disturbed positions and thus,offering an attractive approach for robust and controllable microcomb generation with improved stabilities.