Analysis Of Modal Field Characteristics Of Micro-nano Fiber And Its Application In Sensing

In the field of small-sized photonics,the research on micro-nano fiber technology has received high heat attention.Micro-nano fiber,which has the advantage of lower optical transmission loss,the unique strong evanescent wave transmission and high coupling efficiency is widely used in the field of optical fiber sensing,optical fiber communication and optoelectronic devices.The work done in this dissertation is as follows:The first,the finite element analysis software COMSOL Multiphysics is used to analyze the micro-nano fiber.The distribution and coupling effect of the micro-nano fiber under the parameters of core diameter,transmission wavelength and the difference of cladding and core refractive index and so forth.The simulation results show that the fiber parameters such as the diameter of the micro-nano fiber,the distance between the optical fiber and the difference of the refractive index between fiber core and cladding can change the coupling between the fibers.Second,the fused taper fiber coupler is fabricated by the improved one-step stretching method.The relationship between the additional loss and the insertion loss deviation of the fused taper fiber coupler,which the length of it in the range of 10 mm to 35 mm,is studied.At the same time,the energy distribution of the optical power between the optical fibers is simulated by the beam propagation method,then the regular of the output optical power of the fiber coupler under different tensile length is obtained.Theoretical simulation and experimental data shows that the optical properties of the coupler are relatively good when the tensile length is about 20 mm.Finally,The optical power distribution of fused taper fiber coupler which under in the different optical fiber parameters is obtained by beam propagation method,then an experimental system for detecting the sensitivity of the used taper fiber coupler on temperature and solution refractive index is devised and established.From the experimental results,it concludes that with the temperature or solution refractive index increases,the transmission spectrum as a whole is linearly drifted to the short wavelength.However,the resonant peak energy values remain essentially unchanged.A simultaneous measurement sensing system for refractive index and temperature is studied using the long period fiber grating and fused tapered optical fiber coupler.Selected a resonant peak as the detection object,then experimental results show that the wavelength of the dip varies with temperature and the intensity of the dip changes with refractive index.Combine with the sensitivity coefficient matrix,it can obtain the sensitive oftemperature and refractive index at the same time.