Design Of Taper Micro Nano Fiber Sensing System And Its Sensing Characteristics

Micro-nano fiber sensor has many advantages such as small size and compact structure.Because of the diameter in the micron scale,micro-nano fiber sensors are sensitive to external environmental factors,and them present high sensing sensitivity.The higher-order mode light will appear when the core coupes into the clad in the tapering fiber.The interfering sensors could be designed taking the advantages of the characteristics,and the sensitivity can be further improved.The sensing for different parameters could be achieved when the tapering zone coated with the related sensitive material.Therefore,the micro-nano fiber sensors have attracted increasing attentions recent years.In this thesis,a taper micro nano fiber sensor with Mach-Zehnder interference structure was designed based on the characteristics of taper micro nano fiber,and the sensing experiments of temperature,humidity and refractive index were carried out.The numerical analysis of taper micro nano fiber were carried out by the beam propagation method and the theoretical feasibility of the sensor was verified.The tapers with different parameters were analyzed numerically.It is found that the transmission energy and taper waist energy is positively correlated with the radius of the linear taper.For the nonlinear taper,the transmission energy and taper waist energy is proportional to the radius of the taper.The transmission energy of the taper micro nano fiber decreases with the increase of the environmental refractive index.The symmetrical,asymmetric and graphene-coated taper micro nano fiber sensors were fabricated through arc discharge taper and flame taper technology.A symmetrical linear taper optical fiber sensing system based on temperature was built up to study the temperature characteristics of different distance of tapers,and it was proved that the temperature sensitivity was irrelevant to the distance of tapers.Then,the refractive index sensing system of micro nano fiber was set up.The obtained refractive index sensitivity of symmetrical linear taper fiber and asymmetric nonlinear taper micro nano fiber is 0.446/RIU and 0.658/RIU.In addition,a graphene-coated asymmetric micro nano fiber of humidity sensing system was builtup.The humidity experiment of symmetrical linear taper fiber and asymmetric nonlinear taper micro nano fiber was carried out.The obtained humidity sensitivity(1545~1555nm)of symmetric nonlinear taper micro nano fiber is 68.73pm/%RH under the ambient temperature of 25?,1atm of ambient pressure.And we also found that the interference spectra have blue shift with the increase of relative humidity.The symmetrical sensor is insensitive to humidity.