Technology Of The Linked Dual Femtosecond Fiber Frequency Combs And Theoretical Analysis On The Microresonator Frequency Combs

In recent years,because of the advantage of the high frequency stability,high phase stability and low phase noise,the frequency combs are used in the precision measurement widely.Howerever,with the development of the precision measurement,the stability,reliability and environmental suitability of the frequency combs are needed to be increased.To enhance the stability and reliability,the technology of the all polarization-maintaining fiber frequency comb is studied experimentally.The polarization-maintaining characteristic is beneficial to restrain the influence of the external environment on the system stability.Moreover,the Kerr frequency combs based on the microresonator are the international research focus.The spacing between the teeth of the frequency comb can be increased by use of the Kerr frequency combs,which are also significant for the optical integration.The frequency comb based on all polarization-maintaining femtosecond fiber lasers is studied in this paper.The key technologies are experimented,and the prototype of the frequency comb is constructed.Perfect linkage of dual frequency combs based on all polarization-maintaining femtosecond fiber lasers is demonstrated.Moreover,the Kerr frequency combs based on the microresonator is investigated theoretically.The research work and results are summarized as follows:1.The frequency comb based on all polarization-maintaining femtosecond fiber lasers is constructed.With the aid of the optical delay line,the repetition frequency(fr)is tunable in a large range(~1 MHz).By use of the proportion integration differentiation controller,the fr and the carrier-envelope offset frequency(fceo)are both locked to the stable microwave referenced oscillator.The standard deviations of the fr and fceo are 213 ?Hz and 2.43 mHz(the gatetime is 1s).The phase noise power spectra densities of the fr and fceo is measured,and the corresponding integrated phase noises are 1 mrad(the integrating range is 10Hz~10MHz)and 0.75 rad(the integrating range is 100Hz~100MHz)respectively.2.The linkage of the dual frequency combs based on all polarization-maintaining femtosecond fiber lasers is realized.As for the absolute distance measurement,the linkage of the dual frequency combs is needed and studied experimentally.By employing two independent tracking feedback controlling circuits,the ?fr and the ?fceo between the dual frequency combs arelocked to the stable microwave referenced oscillator simultaneously.Thus,while the fr of one frequency comb varies,the other frequency comb's fr tracks immediately,as well as the fceo.The correlation coefficient is employed to evaluate the linkage capability of the dual frequency combs.The correlation coefficients of the dual fr's and the dual fceo's are up to 0.99 and 0.98,which indicate an ideal linkage between the dual frequency combs.Moreover,the frequency linkage characteristic is studied in different circumstances,when the frequency of the master frequency comb is varied by various methods.The perfect linkage is demonstrated in the experiment,when the master frequency comb's frequency is changed automatically and manully.The relative jitter between the dual frequency combs is reduced because of the linkage.Thus,the stability of the distance measurement is increased.At present,the linked dual frequency combs is used in the abosulate distance measurement successfully,and the precision is less than 1 ?m.3.The generation of the Kerr frequency combs based on the microresonator is demonstrated,and influences of the microresonator properties and the pump parameters on the field profile are analyzed theoretically.By use of the split-step Fourier algorithm,the Lugiato-Lefever Equation is introduced to describe the evolution of the field inside the microresonator.The simulation results indicate that,in the anomalous dispersion regime,when the initial field envelope is set as a Gaussian pulse,the suitable parameters are available for the generation of the soliton.The corresponding spectrum is spaced by the FSR.Both the increase of the frequency detuning and dispersion parameter can result in the powerful pulses in the microresonator.In the normal dispersion regime,only the dark soliton can exist in the microresonator.With the raising of the dispersion parameter,the pulse width of the dark soliton is increased.And the shape of the dark soliton is varied when the frequency detuning is increased.The theoretical analysis is significant to select the microresonator parameter and the pump for the Kerr combs generation.4.The spatiotemporal evolution of the electromagnetic field inside the microresonator pumped by the continuous wave and periodical pulse train simultaneously based on the Lugiato-Lefever Equation.The theoretical analysis results demonstrate that the synthetical pump can compensate for the drawback that the bright solitons cannot be generated in the normal dispersion regime.Moreover,the influences of the microresonator and the pump parameters on the field evolution and electromagnetic field profile are analyzed in either the normal or anomalousdispersion regime.It is concluded that,in the normal dispersion regime,the high amplitude of the pump pulses leads to the pulse split,and the pulse stretching occurs when the loss of the microresonator rises.In the anomalous dispersion regime,increasing the frequency and the amplitude of the pump pulses both result in multiple peaks in the cavity.A series of equidistant pulses can be generated by raising the CW pump power.The study is important for the selections of the microresonator parameter and the pump under the synthetical pump.