Modeling Of Properties And Sensing Applications Of Microfiber Ring Resonators In Aqueous Solution

Because of microfibers' low optical loss, stronge evanescent field and low dimension, many types of microfiber ring resonators have been demonstrated with a high Q factor. One type, the knot resonator, can maintain its structure and resonant properties when immersed in water or when embedded in a polymer. This suggests that microfiber ring resonators can be used to fabricate stable devices for optical sensing and other application in aqueous solution. We mainly model the properties and sensing applications of microfiber ring resonators in aqueous solution.In this thesis, we first model the propagation properties of microfibers in aqueous solution. The results show that light guided along such a microfiber leaves a large fraction of the guided field outside the wire as evanescent waves, making it amenable to side coupling and highly sensitive to the index change of the surrounding medium. In the second part of this work, we simulate the resonance properties of microfiber ring resonators in aqueous solution by solving Maxwell's equation and the resonance equation. We find that the Q factor of microfiber ring resonators can reach values as high as 3.5×10~5. We find that loss is one of the most important parameters determining the Q factor. Therefore we also calculate the bend loss of microfiber ring, which strongly depends on the diameter of both the ring and the microfiber, and comes into play for miniaturizing resonators. In the third section, we proposed to use microfiber ring resonators for designing optical sensors, based on the propagation properties of microfibers and the resonance properties of microfiber rings. A sensor setup based on a microfiber ring is proposed and modeled. A detailed estimation of the sensor performance for refractive index and temperature sensing, including sensitivity and detection limit, is presented with the help of several examples. These simulations provide general guidelines for obtaining optimal microfiber ring geometries and for satisfying sensing requirements corresponding to a given application. The results show that microfiber ring sensors are promising for developing miniaturized opticalring sensors with high sensitivity and low detection limit.In conclusion, our simulation shows that, by using microfiber ring resonators, it is possible to obtain a high sensitivity for optical sensing by choosing suitable values forthe microfiber ring parameters (tipically a fiber diameter in excess of 1 μm and a ringdiameter of several hundred μm ). In addition, the reduced footprint of the proposedmicrofiber ring sensor may allow sensing in small scale environment, support integration of sensor arrays with high density, and require a reduced amount of analytes.