| With the improvement of living standards,our demand for large communication capacity and fast communication speed is increasing.The development of traditional electronic technology is limited by the electronic bottlenecks such as electromagnetic interference.In the context of such demand,optical communication technology and microwave photonics technology emerged.In these fields,the miniaturization of integrated optical components is the focus of research.Optical microcavities have extremely high-quality factor and minimal mode volume,they are enormous potential in many fields such as optoelectronic devices(ultra-narrow bandwidth filters,optical isolators,optical modulators,etc.),high sensitivity sensors and basic physics research.In the field of digital signal processing and microwave communication,the ultra-narrow filters are desired to realize fast and precise control of the signal.Although the performance of the traditional electric filter is well,the influence of the electronic bottleneck has certain influences in application.Meanwhile,the traditional optical filters often fail to achieve ultra-narrow filter bandwidth and high peak rejection ratio due to their generation mechanism.Therefore,there is a great need of a novel filter method that can be independent of the electronic bottleneck and has excellent filter performance,including narrow filter bandwidth,high mode rejection ratio,and good frequency tuning capability.In view of the above problems,this paper explores some solutions.The content of the thesis can be divided into research background,theoretical basis,device preparation and experiment.The main contents are briefly introduced as follows,Firstly,the research background and basic characteristics of the optical whispering-gallery mode cavity are briefly introduced.At the same time,the research progress in the field of microcavity is introduced,and the application aspects are also shown via several published examples.Secondly,based on the classical electromagnetic theory,the mode distribution equation in the microsphere cavity is derived according to Maxwell's equation,and the corresponding mode distribution has been analyzed.At the same time,the basic characteristics of the microsphere cavity such as quality factor,mode volume and free spectral range are analyzed.The radial mode distribution and angular pattern distribution of the microspheres were studied theoretically by the finite element simulation software COMSOL Miltiphysics.The mode distribution of the tapered fiber is also solved and analyzed according to the mode distribution model of conventional single mode fiber.Combined with the mode distribution of the microsphere cavity,the basic features of the coupling between the microsphere cavity and the tapered fiber are studied.Thirdly,under the guidance of the basic theory of microsphere cavity and tapered fiber,the fabrication of microsphere cavity and tapered fiber were carried out.Two different microsphere fabrication methods were introduced,and the advantages and disadvantages of the two fabrication methods were compared and analyzed.A tapered fiber was prepared by an oxyhydrogen flame melting method,and the state of the tapered fiber was monitored by monitoring its transmission power.Finally,a microwave photonic filter with narrow bandwidth and high rejection ratio based on the microsphere cavity is realized.Firstly,the performance characterization of the optical cavity mode of the microsphere is realized by the frequency sweep method.Then,four modulation methods for implementing microwave photonic filter are introduced.The modulation characteristics of DP-MZM are analyzed theoretically.Based on the microsphere cavity,the microwave photonic filter with relative narrow bandwidth is realized by the single sideband modulation scheme.Then,to further improve the peak rejection ratio of the filter,the double-band modulation scheme is applied.The experimental results show that the proposed method can realize the microwave photonic filter with excellent performances. |
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