| Recently,the research of micro/nano-optical devices has become a hot spot in optics.The photon states in micro/nano-device structures can be adjusted in an integrated way,which has extremely important applications in the fields of communication and computing.As an excellent optical resonator structure in micro/nano-devices,whispering gallery mode(WGM)optical microcavity has become an important research direction in the field of micro nano devices.Microcavity can limit the light field to a very small area.When there is a gain medium in the microcavity,the light wave will interact with the gain medium when it propagates in the cavity,which makes the light intensity increase continuously and form stable standing wave oscillation.Compared with Fabry-Perot microcavity or photonic crystal microcavity,WGM microcavity has the advantages of high quality(Q)factor and small mode volume.It has become a new type of photonic device with good application prospects.In this thesis,we start from the background of the research on the WGM microcavity,systematically review the development process of the WGM microcavity,introduce the current research hotspots in the field of microcavity,and its application in different fields,and summarize the application of WGM microcavity in high sensitivity sensing and low threshold laser research status,and in view of the existing problems in the current application,the research work and significance of this thesis are put forward.The main research achievements of this thesis are as follows:(1)From the perspective of geometrical optics,the theoretical model of WGM microcavity is established,and it is extended to the electromagnetic field theory.The electromagnetic field model of WGM microcavity is deduced in detail.Several important parameters,including quality factor,mode volume,resonant wavelength and free spectrum range,are described.Although the light can be well confined in the WGM microcavity and a high Q factor can be achieved,the interaction between light and surrounding materials in the microcavity is very weak.By combining the surface plasmon with WGM microcavity,the trade-off between the high Q factor and the sensitivity of the microcavity is maximized.In this thesis,a plasmonic diamond nanoring structure is proposed,which combines both advantages of plasmonic layer and diamond WGM microcavity by using the stable physical and chemical properties of diamond,such as high thermal conductivity,biocompatibility,durability,chemical inertia,mechanical hardness and wide optical transparent window from vacuum ultraviolet to infra-red.The plasmonic diamond microcavity has the special sensitivity of the plasmonic WGM resonance to the change of the environment refractive index,and combines the unique physical characteristics of diamond,which has great potential in the field of sensing application.We find that the plasmonic diamond microcavity can detect the refractive index of surrounding media with high sensitivity and can realize high sensitivity sensor in a smaller scale.Moreover,the size reduction of the device will reduce the sample size required for detection so as to reduce the detection cost.With the recently developed large-scale manufacturing methods of cheap and highly pure diamond crystals,they will greatly promote their new applications in compact microcavity sensors.(2)A kind of notched elliptical microdisk made of polymer with low refractive index is proposed.By introducing a wavelength level notch at the edge of the microdisk,WGM with a high Q factor is realized to spread out from the notch with very small divergence angle to the far-field.The effects of the notch,microcavity deformation parameters and microcavity size on the unidirectional emission are further studied.It is proved that the notched elliptical microdisk made of the polymer has good stability and robustness and is not sensitive to the small manufacturing errors.The notched elliptical microdisk not only solves the problem of the isotropic output in the plane in the perfect circular symmetric WGM microcavity,but also causes the extremely low collection efficiency in free space.It overcomes the traditional deformed microcavity by using the advantages of high hardness,high glass transfer temperature and excellent corrosion resistance to acid and alkali solution The disadvantage of poor adaptability of the system,for example,only suitable for the shortage of high refractive index materials with refractive index between 2.7 and 3.9 is overcomed.In addition,the elliptical microcavity is extended from two-dimensional plane structure to three-dimensional structure by bending and rotating.The far-field divergence angle is smaller,the efficiency is higher,and the performance is better.The unidirectional emission with adjustable resonance wavelength is realized,which lays the foundation for the local light field regulation in the deformed microcavity.(3)Based on the above researches,we consider that more and more attention has been recently paid to the applications of multi-wavelength lasers in wavelength division multiplexing communication system,optical signal processing and biomedical research.Traditional multi-wavelength lasers are usually made of several electrically pumped cascaded microdisks coupled to waveguides.However,in these multi-wavelength lasers,the gap between the microdisks and the waveguide must be precisely controlled,otherwise it is difficult to adjust the optical coupling efficiency.In addition,due to the coupling loss between the microdisks and the waveguide,the lasing intensities of different wavelengths are also uneven.The traditional way to solve these problems is to apply different bias currents to the microcavity,but with the increase of the quantity of microdisks,it may be difficult for multi-wavelength lasers with a large number of wavelength channels.In addition,the size and space of the multi-wavelength laser are relatively large,which is also a major obstacle to the realization of compact devices.How to design high integration,easy control and high performance multi wavelength output micro resonator is an urgent problem.Therefore,in this thesis,we propose an innovative crossed structure of multiple notched elliptical microcavities with unidirectional emissions.Without increasing the original size of the device,we realize a universal and scalable multi-wavelength device.Its main advantages are highly integrated and easy to control.Multiple wavelengths can be emitted separately without interference.By analyzing the resonant wavelength,far-field emission,emission efficiency and scalability of the multi-wavelength microcavity,the rationality and feasibility of the structure are proved.This kind of multi-crossed microdisks structure is expected to become a compact three-dimensional WGM multi-wavelength laser source,which can be used in biomedicine,environmental monitoring,optical communication and other fields.To sum up,the basic theory of WGM microcavity is explained in detail,and a comprehensive exploration of WGM microcavity with different shapes and structures through abundant device design and theoretical analysis are also analysed.The specific innovations of this thesis are as follows:(1)A detailed analysis of the sensing theory of the plasmonic WGM microcavity is made in this thesis.And a surface plasmon diamond nanoring structure is proposed,which can be used to detect the refractive index of surrounding media with high sensitivity and solve the trade-off between the high Q factor and the sensitivity of WGM microcavity.This structure can not only be used as an excellent platform for photon localization researches,but also improve the shortage of photon interaction with other systems to a great extent and provide theoretical guidance for the future researches and applications of the plasmonic WGM microcavity.(2)A symmetrical elliptical microcavity and an asymmetric oval microcavity with notches are designed to enlarge the research scope of WGM deformed microcavities.By adding a notch and breaking the circular symmetry of traditional microcavity,an excellent unidirectional emission is achieved on the opposite boundary of the notch and the far-field divergence angle is reduced to one order of magnitude smaller than that of the traditional microcavities,which is favorable to the efficient collection of light in free space.These deformed microcavities can be expected to be a high-quality micro/nano-laser sources through properly doping gain mediums.(3)A design idea of a general-purpose,scalable multi-wavelength microresonator is proposed,which is not only easy to configure,but also economical and practical.It is expected to become a new type of photonic device with good application prospects.(4)By bending and rotating,the elliptical microcavity is extended from two-dimensional planar structure to three-dimensional structure,and the far-field divergence angle is smaller.The three-dimensional WGM microcavity allows the vertical degree of freedom of the microcavity photons and realizes the single wavelength unidirectional emission with adjustable resonant wavelength.The overall structure has strong robustness and is insensitive to relative manufacturing errors.This kind of microcavity is expected to become a promising platform for the study of exciton polarized condensates and quantum optics in three-dimensional orbits,providing new technical solutions for the researches of microcavity physics and microcavity photonics. |
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