Study On Evanescent Field Enhancement And Spectral Sensing Of Optical Microfiber

Because of its small size,simple fabrication process,low loss and strong evanescent field,the optical microfiber has been paid more and more attention in recent years and widely used in a variety of optical microfiber sensors.Strong evanescent field brings strong interaction with the outside material or environment,the optical microfiber are used as temperature and stress sensor which based on the refractive index change.For further processing or modification in the structure of optical microfiber,it has caused the extensive concern in gas sensing and biosensing.At present,most of the optical microfiber sensors are mainly used to detect the physical parameters of the environment,there is a great space for the development of spectrum sensing.Interaction between light and material is the key of spectrum sensing,the strong evanescent field ensure the strong interaction between light and material,therefore this article use the combination of optical microfiber with Raman spectrum sensing and absorption spectrum sensing to do the research.This article first studied the optical microfiber Raman spectrum sensing.In the previous studies of optical fiber Raman sensing,researchers usually modified metal nanoparticles on the ordinary optical fiber surface which was corroded or tapered,then performed the Raman detecting use the principle of surface enhanced Raman scattering.However,this method is tedious and complicated.This paper made a new attempt in optical fiber Raman sensing applications.Under the action of strong evanescent field of optical microfiber and the induction effect of substrate,we have detected the Raman signal of R6 G solution at lowest concentration of 1 x 10-7M,successfully realized the application of optical microfiber in the Raman sensor.In addition,a new type of I-shaped optical microfiber was fabricated and studied with absorption spectroscopy.Due to its special structure,the optical microfiber breaks the circular symmetry of the light field distribution,and it can obtain a stronger evanescent field.In this article,this characteristic was used to design and making of new optical microfiber absorption spectral sensor.Compared with the same type of circular optical microfiber absorption sensor,it has been greatly improved thatthe I-shaped optical microfiber absorption sensor is more sensitive.In this article,the simulation model of the optical microfiber structure was established.The finite element method was used to simulate the electric field distribution of the optical microfiber.The simulation results show that the addition of the PDMS substrate will affect the evanescent field distribution in the optical microfiber Raman sensor.In the I-shaped optical microfiber absorption sensing,special structure breaks the circular symmetry of the electric field,the near circular symmetry Gauss distribution become the two deformation near Gauss field distribution,it enhance the proportion of evanescent field.The simulation data of this article will provide a better theoretical guidance for the development and optimization of subsequent optical microfiber spectrum sensor.