Optical Fiber Sensor Based On Open Cavity Fabry-Perot Interferometer

Optical fiber sensors have made considerable progress,due to its compact,lightweight,anti-electromagnetic interference and anti-corrosion properties.Phase-modulation fiber optic sensors have high detection sensitivity because of the use of interference techniques,and light interference in fiber optic sensors achieved by various fiber-optic interferometers.The fiber optic sensor based on Fabry-Perot interferometer structure has been widely used due to its simple structure,small size,high reliability,high sensitivity,fast time response,single fiber signal transmission and other advantages.In this paper,we have made three kinds of open fiber Fabry-Perot sensors with different structures.Based on this,we have studied the refractive index,gas pressure and temperature measurement.The main work is as follows:The relationship between the interference fringe contrast of single-mode EFPI optical fiber sensor and the length of air FP cavity was studied by theoretical simulation.The interference fringe contrast gradually decreased with the increase of gap length.We proposed the structure of an open cavity EFPI fiber-optic sensor with a thick capillary.We used glass flux to weld the open cavity capillary and the two single-mode fibers together,and the overall gel-free sensor realized.In addition,we constructed a sensing system based on the SM125 fiber sensor demodulator.By using cross-correlation signal processing technology can achieve an absolute measurement of the refractive index of liquid can be achieved.The difference between the sensor and Abbe refractometer measurement results is within 0.001 RIU.The resolution of the sensor can reach 10-5RIU level,and the refractive index sensitivity is about 105 nm/RIU.The temperature stability test of the sensor shows that the temperature sensitivity is 39.59nm/°C.We used femtosecond laser microfabrication to create an open cavity EFPI fiber sensor,and realized the detection of refractive index and pressure.The measured pressure and cavity length have excellent linearity,and the sensor has a very high cavity length/pressure sensitivity of 1.02 nm/k Pa.In addition,we introduced the open cavity EFPI fiber sensor welded by grapefruit PCF,capillary and single-mode fiber.It can realize high-sensitivity detection of low gas pressure,and the sensitivity of cavity length/pressure is 0.468nm/k Pa.The sensitivity of the two sensors is almost the same as the previous theoretical simulation results.The greater the cavity length,the higher the sensitivity.