Study Of Sensing Principle And Performance On Whispering Gallery Mode Optical Microresonator

In recent years,the detections for chemical and biological substances have become more and more important in the fields of environmental protection,disease monitoring and drug discovery.Whispering gallery mode(WGM)excited by the tapered fiber coupled with the optical microresonator owns ultra-high quality factor and small mode volume,which enables detect small changes in the environment,and obtain a higher sensitivity and a lower detection limit than traditional micro-nano optical sensors,so WGM has caused more attention.In addition,the Fano resonance combined with the WGM microresonator can further improve the sensitivity and reduce the detection limit due to its asymmetric and high-slope line shape,and the excitation method of Fano resonance only needs to introduce a continuous state to interfere with WGM,which has also been widely studied.In order to promote the WGM optical microresonator-based bio-chemical sensor from the experimental research to the commercial application as soon as possible,the better sensing performance and the higher working stability are required.In order to improve the performance of the WGM microresonator combined with the Fano resonance,a more stable and efficient way for exciting the Fano resonance needs to be proposed;Besides,it is necessary to solve the problem that the mode splitting induced by a very small particle is hard to be identified.In addition,the problem of unstable working state also needs to be settled which caused by the disturbance of the liquidphase detection environment on the tapered fiber.Therefore,this paper focuses on the factors limiting the performance improvement of the WGM bio-chemical sensor and the disturbance of the tapered optical fiber in liquid-phase environment.The detailed research methods and results are as follows:(1)By constructing an add-drop structure coupled with the WGM microresonator,and at the same time,the WGM microresonator coupled with a fiber Mach Zehnder interferometer(FMZI)system,due to the interference between the fiber arm and the transmission light at the Drop port,we successfully proposed a stable and efficient method for exciting the Fano resonance without the wide interference fringe background.And it has been proved that the high slope of the line shape provided by the Fano resonance can enhance the sensitivity by 9 times.(2)By constructing the interference between the transmission light of the Add drop and the fiber arm in the WGM microresonator coupled with the FMZI system.We have proved that the Fano resonance can modulate the spectrum of the mode splitting which is not easy to be identified.By fitting the double Fano line shape with multiple feature points,the information about the refractive index and the size of any small particle can be obtained.The proposed methods successfully solved the problem of the detection limitations for the particle detection with ultra-small size.(3)By proposing the axial separation detection method that describes the separation between the coupling region where the tapered fiber locates and the sensing region filled with the liquid,we achieve the axial position detection for the heavy-water liquid level and the fiber-taper-type particle based on the cylindrical WGM microresonator,and the sensitivity is up to 40pm/mm.Besides,we also realized the detection for the Goat immunoglobulin G(G-Ig G)and the carcinoembryonic antigen(CEA)solutions with different concentrations based on the cylinder-cone WGM microresonator,and the sensitivity is about 0.4pm/(ng/m L).The proposed method not only extends the axial position detection ability based on the cylindrical and cylindercone WGM microresonators,but also solves the problem for the stable coexistence of the tapered fiber and the liquid-phase environment.