A Research Of Frequency Comb Excitation And Applications Based On Optical Fiber Microresonator

As a new type of light source,the optical frequency comb has received extensive attention in recent years.Different from the continuous light,it is an ultra-short pulse sequence with a certain time period in the time domain,and is composed of a series of equal frequency intervals in the frequency domain,while maintaining a highly coherent phase lock.Optical frequency combs have become by far the most effective absolute optical frequency measurement tools due to their unprecedented measurement capabilities,and has been intensively studied in the field of precision measurement,including precision spectroscopy,atomic clock,molecular fingerprint measurement,remote signal clock synchronization and satellite navigation,etc.Besides,with the development of photonic technology,optical frequency combs have also been applied in ultrafast laser,optical communication,ultrasensitive photon sensing and detection,and thus become an important cornerstone of modern science and technology.Under the above background,optical frequency comb devices with functional output and high integration have become a current research focus.However,the current optical frequency comb excitation schemes generally have problems in dynamic control,high loss,and difficulty in integration.And the realization of dual-optical frequency comb excitation with single-pump has become a major scientific problem.Therefore,based on the fiber Fabry–Pérot(F-P)microresonator,this thesis mainly explores the excitation and applications of frequency combs.Aiming at the requirements and implementation difficulties of functional frequency combs,a new structure of fiber microresonators and a new excitation mechanism of Kerr combs are proposed,which realizes output modulation and application expansion.At the same time,this fiber microcavity can be directly connected to the all-fiber system through butt coupling,which greatly reduces the system loss.The main research contents of this thesis are as follows:1.The frequency comb mode-locking mechanism based on graphene saturable absorption and the electrical modulation of graphene are systematically studied,then an innovative structure of fiber microresonator based on graphene is proposed,and The corresponding theoretical model is built up.The main innovations include:(1)The innovative high-Q optical fiber microresonator structure with graphene heterojunction are realized.Including the high-quality single-crystal graphene grown and fabrication to the end surface of the optical fiber microresonator by chemical vapor deposition(CVD)and wet transfer,and Au/Ti electrodes combination to form the graphene heterojunction.(2)Efficient control of graphene physical properties using external electrical modulation,and the theoretical simulation results are highly consistent with the experimental tests.The central wavelength of the optical frequency comb output under electrical control can be modulated from 1562 nm to 1594 nm,the mode locking state can be changed from fundamental mode locking to harmonic mode locking,with repetition rate from 10 GHz to 80 GHz.(3)Stabilize the frequency comb using graphene as a negative feedback unit,and broaden spectrum from 1300 nm to 2000 nm under different mode-locking states through supercontinuous amplification,the phase noise can reach to-120 d Bc/Hz @ 10 k Hz.2.The soliton mode-locking theory of optical frequency combs based on the Kerr effect is systematically studied,and analyzed the influence of Brillouin on it.Then,a new excitation mechanism for microresonator Kerr frequency combs is proposed and the related theory is established,more importantly,a new paradigm of soliton microcomb multiplexing is opened up.The specific innovations are as follows:(1)Based on the study of the birefringence effect in the optical fiber transmission process,a highly nonlinear fiber microresonator structure is designed,including the preparation of the distributed Bragg reflector and the selection of the optical fiber length,and a corresponding polarization controller,which can realize pressure modulation in two dimensions.The whole cavity can be temperature-controlled and stabilized through TEC.(2)The generation of Kerr dual-soliton based on orthogonal mode and Brillouin gain is realized.The frequency comb evolution and soliton generation are simulated based on the LLE(Lugiato-Lefever Equation)theory.And complete the characterization analysis of soliton spectrum,time-domain spectrum and frequency-domain spectrum(3)Leveraging the pressure sensitivity of the device and the fine stress adjustment of mechanical arm,achieving the detection of external force by combining the dual-comb beat note and lock-in amplification technology.The detect limit can down to 520 p N,and the sensing range can reach up to 7.3 m N.