| Optical microcavities,which confine light for a long time through the cyclic resonance effect,can greatly increase the optical power in the cavity,so it is widely used in basic physics research and the field of optoelectronic devices.Compared with other types of optical microcavities,the whispering gallery mode(WGM)optical microcavity has a very high quality factor and a smaller mode volume,which can greatly enhance the interaction between light and matter,so it has attracted great attention from researchers.In the past two decades,various materials and shapes of WGM optical microcavities have been invented and fabricated to meet different research and application requirements.Optical nonlinear effects based on WGM optical microcavities,especially optical frequency combs and stimulated Brillouin scattering,have been widely applied in the fields of narrow linewidth lasers and microwave signal generation.This dissertation takes the WGM microrod cavity as the research topic.Firstly,the fabrication,optimization,mode control and packaging technology of the microrod cavity were studied.On this basis,the generation and optimization technology of the Kerr optical frequency comb based on the microrod cavity were investigated.At the same time,the application of the Kerr optical frequency comb and stimulated Brillouin scattering based on microrod cavity in high-capacity optical communication system were explored.The main research contents and innovations of this thesis are summarized as follows:1.The fabrication,optimization,mode control and packaging technology of the microrod cavity were studied.By optimizing processing technology,the quality factor of the microrod cavity was improved and the free spectral range was optimized with high precision.On this basis,the WGM excitation control method of the microrod cavity was investigated,and the packaging of the microrod cavity and tapered fiber coupling system was realized.The main research contents are summarized as follows:(1)In response to the high performance requirements of the WGM microcavity,the WGM microrod cavity was fabricated and its performance parameters were optimized.Through the optimization of materials and fabrication technology,the quality factor(>10~9)exceeding the highest level reported for the same type of microcavity has been obtained.The laser annealing process was proposed for the first time to realize the high-precision optimization of the free spectral range of the microrod cavity(<5MHz),and the continuous tuning of the repetition frequency of the single soliton Kerr comb was realized,with a tuning accuracy of about 10MHz.(2)Aiming at the controllability requirements for the excitation mode of the microrod cavity,a simulation model of the microrod cavity and tapered fiber coupling system was established using the finite element method.Based on the simulation model,the number of excited WGMs and excitation efficiency control of WGMs,as well as the selective excitation control method of high-order WGMs were studied,and verified by experiments.(3)In response to the requirements of turning the microcavity coupling system into an available equipment,a stable and reliable packaging scheme of the microrod cavity and tapered fiber coupling system was designed.Compared with the traditional scheme,this scheme innovatively proposed a design for adjusting the coupling position after packaging,which realized the compensation of the coupling changes caused by the packaging process and the influence of the external environment,and realized the precise control of the coupling efficiency of the microcavity.Based on the packaging system,the stable single soliton Kerr comb was successfully generated.2.The generation and performance optimization technology of single soliton Kerr comb based on WGM microrod cavity were studied.A coherent laser-assisted heating method was proposed,and the single soliton Kerr comb was successfully generated.On this basis,the suppression effect of the auxiliary laser on the relative frequency noise of the laser injected into the cavity was studied,and the spectral envelope and intrinsic power of the single soliton Kerr comb were optimized.The main research contents are summarized as follows:(1)Aiming at the difficulty of generating soliton Kerr combs in microrod cavities with ultra-high Q values,a coherent assisted laser heating scheme was proposed.The pump laser and the auxiliary laser come from the same laser,thus their coherence can reduce the strict requirement for the stability of the laser in the process of soliton generation,and enhance the long-term stability of the generated soliton Kerr comb.The stable existence of the single soliton Kerr comb for up to 6 hours was achieved without feedback control of the pump laser wavelength,which was significantly improved compared to the stable time within 1 hour of the traditional scheme.At the same time,utilizing the high-precision tuning capability of the driving frequency of the pump laser,the tuning of the detuning frequency of the pump laser with a precision of several hertz was realized in the process of generating the soliton Kerr comb.(2)The suppression effect of the auxiliary laser on the relative frequency noise of the laser injected into the cavity was studied theoretically and verified by experiments.The research results show that a better suppression effect is obtained than the thermal effect.(3)By fine-tuning the relative coupling position of the microrod cavity and the tapered fiber,the flatness of the spectral envelope of the single soliton Kerr comb was optimized,and the energy conversion efficiency from the pump laser to the soliton Kerr comb was greatly increased.3.The applications of nonlinear effects based on WGM microrod cavity in high-capacity optical communication systems were studied,including Kerr optical frequency comb and stimulated Brillouin scattering.The main research contents are summarized as follows:(1)Aiming at the defect of low intrinsic power of Kerr combs,optical injection locking(OIL)technology was utilized to achieve low-noise and equalized amplification of soliton Kerr combs based on microrod cavities.The coherent optical communication experiment was carried out by using the optical comb teeth after power amplification as the carrier.Benefiting from the optical signal to noise ratio(OSNR)of up to 60d B,it achieved better communication quality than the traditional power amplification scheme of cascaded erbium-doped fiber amplifier(EDFA).(2)The stimulated Brillouin scattering effect based on the microrod cavity was utilized to realize the coherent carrier recovery of the high-order modulation signal,and the regenerated coherent carrier was used as the local oscillator for self-homodyne coherent detection.Compared with the traditional scheme which used an independent narrow linewidth laser as the local oscillator,it greatly reduced the consumption of digital signal processing at the receiving without sacrificing system performance.Through the research in this dissertation,a high-performance and controllable micro-rod cavity optical device was obtained.Based on this device,the Kerr optical frequency comb with good performance was generated and its application in the field of high-capacity optical communication was explored.In the future,the fabrication and packaging technology will continue to be improved to realize the stable and efficient preparation of the device to further promote its practical application.At the same time,the noise characteristics and power of the Kerr comb based on the device will be further optimized,and it will be extended to more application fields such as high-precision optical measurement and low-noise microwave signal generation. |
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