Fabrication And Strain Sensing Characteristics Of Fiber Optic F-P Microcavities

Fiber optic sensors have attracted wide attention from total number of researchers because of their high sensitivity,compact structure,fast response time and strong resistance to electromagnetic interference.In strain measurement Fabry-Perot interferometers(FPIs)have a small coefficient of thermal expansion in the microcavity present in the optical fiber,which makes them insensitive to ambient temperature and further leads to their low temperature-strain cross-sensitivity,and thus have good strain measurement performance compared with other sensors.In this paper,the feasibility of FPIs for strain sensing is demonstrated by combining simulation with experiment,and the effects of its model parameters on the performance of microcavity sensing are investigated.Two kinds of fiber optic strain sensors based on FPIs are designed,the microcavity structure is optimized,and the performance indexes of sensor strain sensitivity,repeatability,and temperature-strain cross response are analyzed.(1)The sensing characteristics of fiber-optic FPIs are investigated using the time-domain finite-difference method.The reflection spectrum of the simulation model showes a significant red-shift with increasing applied strain,and the strain sensitivity of this model is1.53 pm/με in the range of 0 με-8000με.The interference contrast could be increased from 4.9d B to 12.3 d B as the reflective surfaces of the two thin walls of the inner cavity of the microcavity tended to be parallel.The circular microcavity is prepared by the scheme of arc discharge using a fusion splicer,and the reflectance spectral test optical path is built,and the fit of its spectral results with the simulation results is obtained as high as 98%.(2)A circular rectangular microcavity strain sensor with high interference contrast is designed and prepared,and the unique circular rectangular structure of the sensor provided an interference contrast of up to 25 d B.Through experimental tests,the strain sensitivity of the sensor is obtained as 8 pm/με in the strain range of 0 με-1200 με;the sensitivity of the released stress of the sensor is derived as 7.79 pm/με,and the applied strain and released strain had basically no effect on the sensor;in the range of 20°C-80°C,the reflection spectrum of the sensor fluctuated in the range of ±2.4 nm with the increase of temperature,and the derived strain-temperature cross-response is only ～0.59 με/°C.(3)A cascaded dual circular microcavity strain sensor with high sensitivity is designed and prepared,which utilizes the multi-beam interference formed by two FPIs whose reflection spectra appear in the form of an envelope,greatly providing strain sensitivity in the strain range of 0 με-500 με of 17.48 pm/με,which is twice that of a single rounded rectangular microcavity structure;the derived The sensitivity of the sensor for releasing stress is 17.79pm/με,and the applied strain and released strain have essentially no effect on the sensor.