The Design And Experimental Study Of Interferometric Microstructure Fiber Optic Sensor

With high sensitivity,electromagnetic interference free,corrosion resistance,long service life,intrinsic safety and so on,optical fiber sensor plays an important role in the fields of mechanical vibration detecting,security monitoring,and structure safety monitoring,and other fields.Due to compact structure and high sensitivity,the optical fiber Fabry-Perot interferometer(FFPI)sensor has been a research hotspot in the field of optical fiber sensors field.Based on the requirements of the research project of the national important scientific research instrument and key projects of technical innovation of ministry of public security undertaken by the laboratory,this paper designs two kinds of intelligent FFPI sensors for the detection of acceleration and sound pressure.This paper proposes a design scheme about intrinsic optical fiber accelerometer based on optical fiber micro bubble cavity:use of hydrofluoric acid corrosion in the fiber core to form a groove,and then use the electrodes of fusion splicer to discharge making the groove closed and then expanding into a micro bubble in the end of the fiber optic.The FFPI is formed by using the Fresnel reflection on the first and second reflective surface of the micro bubble cavity.Through the extensive experiments on corrosion and discharge,the manufactured FFPI cavity is approximately 142 ?m,the wall thickness is about 1?m,and the extinction ratio of interference spectrum can reach 18 dB.After using an 8.9 g mass block,the resonant frequency is measured at 1520 Hz,and the 3dB bandwidth of frequency is 856 Hz.By the range of 1mg to 10mg vibration exciter,the voltage sensitivity is 14.16 V/g and the output signal linearity is 0.9992.When using 706 Hz and 2 mg acceleration excitation,the output signal-to-noise ratio(SNR)is greater than 40 dB,the minimum detectable acceleration is 20 ?g/(?).When the work temperature ranges of sensor from 20 ? to 100? the temperature sensitivity is 1.7 pm/?,which temperature has slight effect on the detection of acceleration.This paper also designs a kind of sound pressure sensor which is based on FFPI between optical fiber end and Aluminum-Polyimide(Al-PI)corrugated film:based on microlithography and magnetic control spluttering coating technology,Al-PI films with corrugated were fabricated.And it effectively reduced the residential stress in the thin film,and improved the acoustic pressure sensitivity of the film.The diameter of the sound pressure sensor probe is only 2 mm.The experimental results show that the output SNR of the sensor under 100 mPa and 2.6 kHz can reach 50 dB,and the minimum detectable sound pressure of the system is 0.32 mPa/(?)and linearity is 0.99981 within the sound pressure range of 10?1000 mPa.Finally,this paper develops an effective method for measuring the intensity and phase noise in double beam interferometric sensor system,only by using natural drift of the interferometer working point instead of using phase tracking technology.Experiments explore the effect of light source intensity noise suppression when use dual balanced detection technology in sensing system.The results show that 12 dB suppression effect can be reached by using dual balanced detection technology on testing the ring cavity fiber laser intensity noise,and the SNR of the sensor system also can be improved significantly.