Research On Microcavity Optical Frequency Comb And Its Application On Microwave Signal Generation

With the rapid development of optical microcavity fabrication technology,the quality factor has been constantly improved,which greatly promoted the field enhancement effect in the microcavity and created favorable condition for the generation of optical frequency comb with low pump threshold.Researchers have firstly realized the Kerr frequency comb with broadband optical spectrum via the silica microcavity in 2007,which opened the door of the field of microcavity optical frequency comb.Microcavity optical frequency comb breaks the many limitations of optical frequency comb based on mode-locked laser,which can achieve the high repetition rate from GHz to THz and exhibit the advantages of small size and low power consumption.It has great potential in the fields of precision measurement,spectroscopy,optical communication and microwave photonics.This dissertation presents the theoretical and experimental research of microcavity optical frequency comb based on a micro-ring resonator fabricated in high-index doped silica glass platform.We have demonstrated soliton frequency comb generation via auxiliary laser scheme and breather soliton frequency comb generation via single pump scheme.The physical phenomenon of periodic oscillation in time domain of breather soliton has been explored by the energy sampling and RF spectrum measurement in the cavity.The time domain and dynamic evolution process of the microcavity optical frequency comb are measured and analyzed based on the dual-comb sampling and time-lens technique,respectively.Based on the stable generation of microcavity optical frequency comb,the experimental research of microwave signal generation has been explored.Besides,quantum frequency comb has also been explored based on the spontaneous four wave mixing of the microcavity.The main research contents and achievements of this dissertation are following:1.Soliton optical frequency comb based on microcavity is explored by auxiliary laser scheme.The conversation of modulation instability to multiple soliton microcavity optical frequency comb has been realized in a microcavity with a FSR of49 GHz by reasonably setting the frequency of the pump and auxiliary laser.And a soliton optical frequency comb with a spectral bandwidth greater than 80 nm has been generated by adjusting the microcavity resonance peak.Furtherly,soliton crystal with a spectral bandwidth of 180 nm has been realized via single pump scheme.Besides,the breather soliton has been found in a microcavity with a FSR of 200 GHz and the physical phenomenon of periodic oscillation in time domain has been demonstrated by the measurement of the RF spectrum and the energy evolution of the pump sweeping over the resonance peak.2.Based on the spontaneous four wave mixing in the microcavity,quantum frequency comb is explored and the coincidence counting is investigated under the pump power of 20,40,60 m W,respectively.The coincidence to accidental ratio is about 3 to 5 under the pump power from 20 to 60 m W,which demonstrates the quantum correlation of the generated photon pairs.It is demonstrated that low pump power could effectively reduce the noise and improve the quality of the quantum frequency comb by the experimental results of the negative correlation between pump power and coincidence to accidental ratio,which contributes to a conclusion that the quality factor of microcavity is an important impact factor of the quality of quantum frequency comb.3.Based on dual-comb sampling scheme,we have explored the pulse distribution in time domain of the soliton frequency comb.Using a micro-ring resonator to generate a stable soliton frequency comb as the reference source,the direct measurement of soliton,dual-soliton,three-soliton and four-soliton state generated by another micro-ring resonator is realized.The pulse distribution in time domain has been characterized and described by the beat signal of two sets of optical frequency combs,which breaks the bandwidth limit of photodetector and can achieve the measurement of optical frequency comb with high repetition rate.4.Time-lens technique is demonstrated to be an effective method for various signal processing via numerical simulation.In experimental work,providing a temporal magnification for 18× via time imaging system,the pulses in time domain have been real-time observed via normal photodetector and oscilloscope.For opticalfrequency comb generated by the micro-ring resonator with FSR about 49 GHz,the solitons in the cavity are sampling by the period of 20.4 ps,which is used for describing the evolution of light field by capturing the real-time displacement of solitons,the transient behaviors including collision,annihilation and generation of solitons.This method solves the difficulty of real-time measurement of optical frequency comb with high repetition rate and provides a new research thought and an effective technical measure to explore the complex transient process of optical frequency comb generation.5.Based on microcavity soliton optical frequency comb,the microwave signal of48.97 GHz with a signal-to-noise ratio of 60 d B is successfully obtained.In addition,the time jitter and phase noise of microwave signal are analyzed in detail,respectively.The time jitter value is 533 fs and the phase noise is-110 d Bc/Hz at offset frequency of 1MHz.After adding frequency divider to the scheme,the tunable microwave signal is realized.Besides,we have also explored the research on RF signal generation based on dual-comb by the cascaded and parallel microcavities,respectively.And the linewidths of the optical signal of two schemes are measured and analyzed by the well-known delayed self-heterodyne method.