Experimental Investigation On The Coupling Between Microtoroidal Resonators And Tapered Nanofibers

Optical resonator is an important optical device.It has a wide range of applications in the laser,precision measurement,spectral measurement,quantum optics and other fields.With the development of optical resonators,optical resonators are developing toward miniaturization and integration.The size of the traditional F-P cavity is too large,and the control system is complex.Therefore,it's difficult to achieve multi-cavity system.With the development of semiconductor micro-nano processing technology,whispering gallery mode resonators have a rapid development.Microtoroidal resonators have a small mode volume,an ultrahigh quality factor and a simple mode.Besides,they are very easy to product and integrate.Microtoroidal resonators are one of the most promising multi-cavity models.The goal of this paper is for the application of microtoroidal resonators in cavity quantum electrodynamics.We carried out experimental research related the critical coupling between microtoroidal resonators and tapered nanofibers.This research provided an experimental basis for achieving the strong coupling between microtoroidal resonators and cesium atoms.The main research work is as follows:1.Built a tapered nanofiber fabricated systemTapered nanofibers are used as external coupling devices for exciting the modes of microtoroidal resonators.Tapered nanofibers are heated by hydrogen and oxygen flame and are stretched from ordinary single mode fiber by precise pulling stage.The minimum diameter of the tapered nanofiber was about 600 nm and the transmission was 93%.2.Completed the coupling system of microtoroidal resonators and tapered nanofibersThe system comprised a laser input optical system,two microscopes,a coupling adjustment section and a detection device.The relative position of the microtoroidal resonator and the tapered nanofiber could be viewed in real time by the horizontal and vertical microscopes,and the relative position was controlled by the high-precision translation stages.We could adjust the pitch of the tapered nanofiber,polarization and other parameters.The coupling efficiency between the microtoroidal resonator and the tapered nanofiber was more than 99%.3.The critical coupling between the microtoroidal resonator and the tapered nanofiber was realizedBy scanning the laser wavelength,the transmission line of the microtoroidal resonator was obtained.When the gap distance between the microtoroidal resonator and the tapered nanofiber was 0.6?m,the microtoroidal resonator and the tapered nanofiber reached the critical coupling.At this time,the transmission of the microtoroidal resonator was 0.3% ± 0.3% and the coupling efficiency was 99.7% ± 0.3%.4.When the microtoroidal resonator and the tapered nanofiber reached different coupling,we investigated the variation of the minimum transmission,the linewidth and the resonant frequency of the microtoroidal resonator with the gap distance between the microtoroidal resonator and the tapered nanofiber.With the decrease of the gap distance,the minimum transmission of the microtoroidal resonator decreased first,and decreased to a minimum of 0.3% ± 0.3% at the critical coupling,and then increased.With the decrease of the gap distance,the linewidth gradually increased and the resonant frequency of the microtoroidal resonator lay at a redshift of 19.2 ± 0.1GHz.5.Measured the parameters of the microtoroidal resonatorThe free spectral range of the microtoroidal resonator was 1067 ± 5GHz and the linewidth was 2.9 ± 0.1GHz.The effective diameter of the microtoroidal resonator was 71 ± 1?m.The intrinsic quality factor of microtoroidal resonator was(2.0 ± 0.2)×10~5.