The Study Of Photonic Crystal Fiber Sensor Based On Sagnac Interferometer

Sensing Technology which is the world's rapid development of high-tech has become the focus of international research since 1980 s.The optic fiber sensor based on Sagnac interferometer is widely used in the field of torsion,temperature,stress,pressure and other sensing,as it has high sensitivity and easy to fabricate.With the development of photonic crystal fiber,the photonic crystal fiber sensor based on Sagnac interferometer become more flexible and can measure more physical quantities,which lead to so many people do much research on.In this paper,two novel structure of photonic crystal fiber are designed and fabricated to use in torsion and temperature sensor based on the Sagnac interferometer.In addition,the influence of sensor sensitivity is investigated after post-processing of the photonic crystal fiber.The principle and development of optical fiber sensing technology and the classification of optical fiber sensor is introduced in this paper.The phase modulation principle of the type of interference fiber optic sensor is analyzed,and the interference spectra of Sagnac effect and Sagnac interferometer are analyzed theoretically.Moreover,the influence of external physical quantity on Sagnac interference is analyzed and the process of preparing photonic crystal fiber in laboratory is briefly introduced.An optical fiber twist sensor is proposed by employing a Sagnac interferometer based on polarization-maintaining photonic crystal fiber(PM-PCF)doped germanium in core,And periodically twisted with heating by carbon dioxide laser to increase the torsion sensitivity.Experimental results demonstrate that the length of PM-PCF using in Sagnac loop have a huge impact on the torsion sensitivity,the torsion sensitivity of the sensor is to 3.75 nm/(rad/m)when the length of PM-PCF is 13 mm.After heating-twist the fiber torsion sensitivity increase more or less.When the length of PM-PCF is 20 mm and the heating-twist length is 15 mm,the torsion sensitivity can increase from 1.85 nm/(rad/m)to 3.65 nm/(rad/m)nearly raised by 2 times.Contrast experiment shows that the birefringence will be obviously reduced after heating-twist,due to the birefringence which caused by internal stress and geometry cancel out.The PM-PCF Torsion sensor was experimentally demonstrated to be low sensitivity to temperature,and the temperature sensitivity decrease deeply after heating-torsion,this may be an effective way to improve the performance of fiber optic sensing.A boron-doped double hole polarized photonic crystal fiber is designed and fabricated.The simulation analysis shows the birefringence of this fiber is composed of stress birefringence and geometric birefringence.The temperature sensor is proposed by employing a Sagnac interferometer based on this boron-doped polarization PCF.The experiments show that the interference spectrum moves in the short wavelength direction with the temperature rise above,and the temperature sensitivity is 1.1nm/?,the drift of the wavelength is linearly related to the change in temperature.Furthermore,the alcohol filling experiment is also conducted using boron-doped polarization PCF,the result shows the sensitivity of the sensor to the temperature after filling with alcohol is the same as the sensitivity before filling,the structure is not complete when the PCF is fabricated may be the reason that experimental phenomena caused.However,experimental results show that the birefringence of boron-doped PCF also changes linearly with temperature after alcohol filling.