High Sensitivity Sensing Of Optical Fiber And Optical Microcavity System

In recent years,in addition to transmitting optical signals and measuring the changes of measured object parameters,optical fiber sensors also have the characteristics of small size,large bandwidth,anti-electromagnetic interference and good robustness,and can realize multiplex detection and multi-parameter distributed sensing.The relevant applications are more and more extensive,especially the measurement of strain and refractive index.With the continuous optimization and improvement of the structure of optical fiber sensors by researchers,many new strain sensors and refractive index sensors have also begun to be used in the health monitoring of bridge buildings and biological sensors in the medical field.Based on the principle of multimode interference,using the multi-interface reflection and plasma polaron effect,two types of interferometric optical fiber sensors are designed,and the theoretical calculation,simulation and experiment of the designed structure are carried out,showing the excellent sensitivity of the two new sensor structures.The main contents are as follows:1.In this paper,a U-shaped core offset optical fiber structure sensor is designed.Only 4 segments of offset optical fiber segments are needed to realize the high sensitivity and large strain range of the microstructure strain sensor.Based on the simulation of three-dimensional beam propagation by RSoft,the beam propagation form in the structure is analyzed,and it is verified that the U-shaped core offset fiber structure has a large propagation loss in the core offset area.The reflection spectrum is mainly formed by the interaction of three reflected beams on the core axis,which causes strong multimode interference.At the same time,comparing the results of the beam passing through the actual U-shaped core offset fiber sample with the results of calculation and simulation,the three images are almost identical.Due to the large transverse bending radius,core offset period and strong optical interference of the Ushaped asymmetric microstructure,the strain sensitivity of the structure can reach 20.75 pm/με,and the strain accuracy can reach 0.5 με.Due to the reduction of the effective Young’s modulus of the asymmetric U-shaped structure,the tensile strain range can reach up to 35 mε.This Ucore offset optical fiber has excellent application potential in special strain applications such as bridges,subways,oil and gas pipeline structure health monitoring,which require high strain sensitivity,large strain range and combined compression and tension.2.In this paper,a simple sensor structure of MIM waveguide side-coupled Taiji resonator is designed,in which the MIM waveguide is embedded with a silver-air-silver groove(SASG).Through theoretical analysis of the transfer matrix and transmission amplitude of the MIM waveguide side-coupled Tai Chi resonator,the interference between the narrow discrete mode of the Tai Chi resonator and the wide continuous mode of the S ASG in this structure can cause multiple Fano resonances.At the same time,the finite element method is proposed by using COMSOL software to simulate the MIM waveguide side-coupled Taiji resonator structure with SASG embedded,which proves that the S-type cross branch in the Taiji resonator can increase the propagation mode of the beam in the structure,and finally realize the sevenfold Fano resonance.Moreover,the structure can adjust the Fano resonance frequency controllable by changing the rotation angle and inner and outer radius of the Taiji resonator,so that it can realize the multi-band controllable spectral line shaping in the visible-near infrared region.When the structure is applied to the exploration experiment of refractive index sensing characteristics,the maximum Q factor of the MIM waveguide side-coupled Taiji resonator structure is 317,and the modulation depth reaches 24.1 dB.The maximum sensitivity of refractive index sensing is 2016 nm/RIU,and the FOM value is 345.In addition,the structure can also be used to detect the concentration of glucose solution,with the highest sensitivity of 0.245 nm·L/g.MIM waveguide side-coupled Taiji resonator has multiple adjustable Fano resonances and excellent sensing sensitivity.Through the corresponding conversion relationship,this structure can also be applied to the frontier applications of biosensors.