Research On Manipulations And Applications Of Terahertz Ring Resonators

As a region in the electromagnetic spectrum that has not been fully exploited,terahertz waves,which have unique characteristics such as abundant frequency resources,fingerprinting property,and low energy in a terahertz photon,have attracted much attention in the fields of communications,detection and security.Based on the frequency-selective absorption and enhancement of terahertz matter interaction,terahertz resonators play important roles in both terahertz fundamental physics and real-world applications.From the perspective of the device structure,ring resonators possess ultrahigh quality(Q)factors,small mode volumes,and the potential for device integration,which has unprecedentedly promoted the developments of fields such as sensing with high sensitivity,optical communications,and nonlinear optics.In contrast,the research of terahertz whispering gallery mode resonators is still an emerging field.Reported works mainly focused on the verification of the devices and the optimization of the Qs.To meet the requirements of practical applications,the manipulations and functional applications of terahertz resonators are critical,but related studies are still needed more discussion.In this thesis,focuses lie on the study of terahertz ring resonators.Methods for designing,modeling and measuring the terahertz ring resonators are firstly summarized and explored.The manipulations of terahertz ring resonators based on mode coupling and magnetic-optical effect are studied,and functional applications such as tunable Fano resonances and integrated terahertz isolators are experimentally demonstrated.Generally,the specific research results are summarized as follows:(1)Mode coupling effect for the manipulation of performances in a multimode ring resonator is systematically studied.A multimode terahertz ring with an intrinsic Q around1040 is designed and demonstrated,and performances in different coupling states are observed.Mode coupling effects are discussed and reproduced with the help of mode analysis and an extended transfer matrix model.Then different properties such as dual resonances and single resonance are observed and comprehensively analyzed,moreover,mode splitting in the ring is discussed.Based on the experiments,mode coupling can be introduced to design different transmission properties based on a compact structure,which is helpful in demonstrating different kinds of filters.(2)Manipulations on the transmission property based on controllable mode coupling effects in coupled rings are discussed in detail,and tunable high Q Fano resonances are generated.Based on the coupled ring system which consists of a low Q silica ring and a high Q silicon ring,a terahertz Fano resonance with a Q of 2095 is designed and demonstrated.With the help of the thermoelectric tuning scheme on the resonances of the silicon ring,the manipulations of central frequencies and line shapes of Fano resonances can be continuously adjusted.By controlling the coupling strength between rings,the tunability of resonant intensities is realized.Finally,the Fano resonances hold the ability to realize a continuously tunable group delay in the range of-0.4～0.15 ns in theory.(3)The manipulations on a ring resonator based on the magneto-optical effect are explored,then a nonreciprocal ring resonator is realized and a tunable on-chip terahertz isolator is designed and demonstrated.By combining the magnetic material Indium Antimonide and on-chip ring resonators,the magnetic field will determine the state of reciprocity and nonreciprocity,and therefore isolation functions with high isolation ratios are theoretically analyzed based on nested ring structure and racetrack ring structure.Then an isolator based on a racetrack ring is designed and fabricated,and an isolation ratio up to52 d B is experimentally measured.Meanwhile,the chip has a tunable range of 2.8 GHz and tunable isolation functions in the range of 0.405～0.495 THz based on different modes,which proves the tunability and wide applicable frequency range.Finally,the working environment of the device is room temperature and a magnetic field below 0.8 T,which is proper for various practical applications.