Research And Application Of Ohmic Thermally Tuned Hybrid Microbubble Cavities

Whispering gallery mode(WGM)optical microcavity has the advantages of high quality factor(Q),small mode volume,high energy density and extremely narrow linewidth.It provides a good platform for basic research and application in chemistry,hylology,biology,biomedicine and other fields.In this paper,WGM silicon dioxide microbubble resonator(MBR)was used as the supporter.After we insreted an Au microwire into the MBR,a layer of polydimethylsiloxane(PDMS)was coated on the inner surface of that,fanilly we formed a new structure of hybrid MBR embedded an Au microwire.Based on the principle of different materials with opposite thermo-optic coefficients(TOC)compete with each other and the method of ohmic thermal tuning,the new structure of hybrid microbubble cavity can be developed in a series of researches such as electromagnetically induced transparency/absorption(EIT/EIA)and optical frequency comb(OFC).The main contents of this paper are as follows:1.We propsed a new structure of hybrid MBR embedded an Au microwire,which is based on an Au microwire through the microbubble and coated with a PDMS layer.The EIT/EIA effect was studied in the hybrid microbubble cavity,and the controllable EIT/EIA was realized by ohmic thermal tuning.Based on the Mie scattering four layers structure model,the relations of thermal sensitivity and the field distribution of different radial modes with the wall thickness in PDMS-coated MBR are analyzed theoretically.Because Si O₂ and PDMS have positive and negative TOCs respectively,the thermal sensitivities of different radial modes are different,or even opposite,so the frequency detuning between modes can be effectively controlled by changing the temperature of the microcavities.In the experiment,the thin-walled microbubble cavity was fabricated.Firstly,an Au microwire(20?m in diameter)was inserted into the microfluidic channel,and then a PDMS layer was coated on the inner surface of the microfluidic channel to form a hybrid microbubble cavity.Finally,the Au microwire was connected to the circuit,and the ohmic heat generated by the Au microwire was used to tune the resonance wavelength of adjacent and different radial modes.By selecting modes with different external coupling decay rates and intrinsic decay rates,and the controllable Fano,EIT and EIA were realized by changing the current in the Au microwire,.Through the coupled mode theories,the transmissions in different states were established numerically,and the experimental results were in good agreement with the theoretical results.2.We studied OFC in the anomalous dispersion region of WGM microbubble cavity,and the ohmic thermal tuning method was applied to tune the OFC.The Q-factor of WGM microbubble cavity can be up to 10⁸.In the case of high power laser pump,there are abundant nonlinear phenomena,such as Raman,frequency comb,Brillouin,etc.Among them,frequency comb has a wide range of applications,such as precision measurement,atomic clock,spectroscopy,broadband sensing,optical fiber communication,etc.The important premise of these applications is the resonant tunability of frequency comb.In theory,the relations between the mode dispersion and the size of the microbubble cavity are calculated by using the Mie scattering programs,and the anomalous dispersion region of mode is obtained.In the experiment,we fabricated the microbubble cavity in the anomalous dispersion region,and the communication band OFC was successfully realized by external laser pumping.Similarly,the ohmic thermal tuning of OFC can be realized by changing the current with the Au microwire in the hollow channel of microbubble cavity,and the tuning range was up to0.21nm.This method can provide an effective tuning method for WGM microbubble cavity OFC.