| The whispering gallery mode(WGM)resonator has many characteristics,such as compact structure,ultra-high quality factor,high energy density.Many high-performance optoelectronic devices have been developed with it as the key component.In past decades,the optical frequency comb generated in the WGM resonator provides an optical frequency comb implementation with better performance,easier implementation,and more potential for miniaturization.Dissipative Kerr soliton optical frequency combs based on WGM resonators have shown great application value in the fields of spectroscopy,metrology,and ultra-precision measurement.In this paper,in order to solve some technical problems in manufacturing and applying process of WGM crystal resonators with large-size and ultra-high quality factor,we firstly studied the processing method,polishing process optimization and structure optimization of large-size crystal resonators.Then nonlinear effects,generation of optical frequency combs,and modulation of dispersion are investigated.Finally,the application of resonator optical frequency combs to distance measurement and stable coupling packaging were explored.The main research contents and innovative work of this paper are listed as follows:1.The processing method and polishing process optimization of large-scale resonator were studied.Through self-building equipments and self-developed processing technology,it is the first in China to develop a large-scale resonantor with ultra-high quality factor.The main research contents are:(1)A quartz rod-type resonator processing platform was built,and a processing method for preparing a quartz rod-type resonator on a high-purity quartz rod was explored.A rod-shaped quartz resonator with millimeter-scale size,ultra-high quality factor(>108)and good mechanical stability was made.(2)In view of the problem that it is difficult to purchase finished high-precision special polishing machine tools in China and the existing crystal polishing process is only suitable for plane polishing,a crystal resonator cavity processing equipment with independent intellectual property rights has been developed.After researching and analyzing the factors and the polishing mechanism,the ultra-smooth surface polishing process for curved surfaces was summarized,and a crystal resonator with a millimeter-scale size and a quality factor of more than 108 was successfully prepared.2.The excitation of nonlinear effects in a large-scale resonator and the generation of soliton state optical frequency combs are studied,which solves the problem of precisely controlling the size of the resonator in the process of generating cascaded Brillouin lasers.For the first time,Raman soliton optical frequency combs are generated in a quartz rod-type resonator.Through the combination of simulation and experiment,for the first time,the optimization of the edge structure of the crystal resonator is studied to control the total dispersion of the resonator and improve the performance of the crystal resonator optical frequency comb.The main research contents are:(1)The optical field evolution model in the WGM resonator and the coupling model between the waveguide and the resonator were constructed.Conditions and process of the state transition of the resonator optical frequency comb are analyzed from the simulation results,which provides theoretical guidance for generating the soliton state optical frequency comb.The coupling characteristic between the tapered fiber and the resonator was analyzed and the waveguide manufacturring equipment in the laboratory is improved to prepare a tapered fiber with a single-mode structure and a transmittance of more than 95%,which solved the instability problem of the coupling state caused by the waveguide.(2)A resonator performance detection system and a nonlinear experimental system were built.The Brillouin frequency shift was matched by the multi-mode resonance between the millimeter-scale CaF2 resonator and the tapered fiber,which solved the problem in the process of generating Brillouin scattered light that the resonator should has precise size,and the generated cascaded Brillouin lasers up to 5th order.Using the third harmonic effect in the resonator to generate visible green light or red light,it provides an experimental idea for converting the communication band laser to the visible light band.(3)The conversion process of Kerr optical frequency comb and Raman optical frequency comb was studied in the quartz rod cavity,and the Raman soliton optical frequency comb with a spectral range of 31 nm was effectively excited by increasing the pump power and detuning,providing a simple method for generating soliton state optical frequency combs.A fast frequency sweep method was used to generate a Kerr soliton optical frequency comb with low phase noise in a MgF2 crystal resonator,with a spectral range covering 1427 nm to 1617 nm,which provides a stable optical frequency comb source for subsequent resonator optical frequency comb applications.(4)Aiming at the basic requirement of anomalous dispersion in the process of resonator optical frequency comb generation,the control of the total dispersion of the resonator by changing the resonator structure was studied.By constructing the resonator structure models with different edge shapes,the total dispersion of the resonator was simulated and calculated by the finite element analysis method.A single-side bevel polishing device was added to the crystal cavity processing equipment,and the crystal cavity samples with different edge shapes were processed and the total cavity dispersion changing was experimentally verified.The change of the total cavity dispersion has the ability to control the performance of the optical frequency comb.The resonator of the wedge-shaped edge structure increases the spectral range of the optical frequency comb up to 110 nm and generates a dispersive wave than that excited with the edge plane resonator.3.For the first time,the crystal resonator optical frequency comb was applied to the absolute distance measurement.The experimental results show that the crystal resonator optical frequency comb can completely replace the traditional mode-locked optical frequency comb.For the first time,a new crystal cavity structure for multi-comb measurement was proposed.It was verified that this structure can fully meet the requirements of multi-comb measurement.It was the first time in China to realize the stable coupling package of crystal resonator and waveguide,which lays a solid foundation for the subsequent use of crystal resonator outside the laboratory environment.The main research contents are:(1)By designing and processing a precision coupling packaging platform and a coupling adjustment mechanism with anti-vibration performance,the stable coupling packaging of the crystal resonator can be realized,and the coupling state can keep unchanging for a long time.(2)The distance measurement experiment was carried out by combining the crystal cavity optical frequency comb with the dispersion interferometry method.The experimental results show that the ranging accuracy error is better than 5 μm and the repeatability is 1 μm,which proves that the crystal cavity optical frequency comb can completely replace the mode locking laser optical frequency comb in the application of absolute distance measurement.(3)In view of the requirements for the size of the crystal resonator in the multi-comb measurement,a new crystal resonator structure was designed to maintain the size consistency of the resonator during processing,and the coaxial cascade structure was successfully made by improving the processing equipment.The crystal cavity samples were experimentally verified to meet the needs of multi-comb measurements.In this paper,the research and pioneering achievements of large-scale resonator processing technology,resonator optical frequency comb generation and ranging applications,and resonator-coupled packaging devices,have demonstrated the unique physical properties of large-scale resonators and their potential application advantages in high-precision spectral measurement field.In future research,large-scale crystal resonators with ultra-high quality factor can be used to explore microwave photonics applications,develop resonator optical frequency combs in the infrared band and gas molecule detection applications.It can also develop multi-comb multi-target absolute distance measurement applications based on single-comb distance measurement in this paper. |
PDF Full Text Request