The Research On Fabry-perot Optical Fiber Displacement Sensor

With the advent of the era of Internet of things, the application range of the sensor is more and more widely, and the optical fiber sensor get a very fast development with its unique advantages. Optical fiber sensor has high sensitivity and resolution, and has the advantages of simple structure,stable performance, small size, bended, high temperature resistant. It is able to adapt to a variety of environment. It is widely used on the measurement of various physical quantities such as displacement, acceleration, pressure, sound, vibration, temperature, stress and deformation and so on. In many optical fiber sensors, Fabry-Perot (F-P) optical fiber displacement sensor which based on F-P cavity, is an important branch. This paper make a deep study on the working principle, demodulation circuit design, the experiments and simulation comparison etc. on the F-P optical fiber displacement sensor. The research content mainly includes:First of all, the Fabry-Perot cavity model was set up, the modeling and simulation were also made based on the multiple-beam interference principle. By changing the wavelength,numerical aperture of fiber parameters, to determine the factors that influence the sensitivity of the sensor and the linear range. Finally, determined the appropriate optical fiber and optical fiber probe, and provided a theoretical basis for the design of the overall scheme.Second, the design of the whole sensor system was made, and the detail design of signal processing circuit of F-P optical fiber displacement sensor was also made based on the weak signal detection theory and the phase locked technique. The circuit design of the light source part was including: the signal generator module, the amplitude processing of the signal module, the driver laser module, over-current protection module and temperature control module and so on; The circuit design of the signal processing was including: the conversion of photoelectric signal module, the amplification of weak signal module, the band pass filter module, the phase sensitive detection module, the low pass filter module, the zero adjustment module and the amplifier of DC module.Third, the design of data acquisition and transmission circuit for F-P optical fiber displacement sensor was made. This part set the FPGA control module as the core, and it mainly includes the digital to analog conversion module, the analog to digital conversion module, USB data transmission module and PC data processing and storage module. In addition, made program designs for DAC,ADC and USB data transmission module,in order to realize the functions of data acquisition system.After the laser module, signal processing module and data acquisition module has been debugged, the nanometer level displacement micro platform and fiber loop structure was set up to make a test on the displacement detection. The testing included the stability of the laser light source, the intensity of light varies with displacement characteristic test, the sensitivity test of the sensor, the system stability and repeatability test etc.. After the test, it proves that the sensitivity of the sensor can reach 38mV/nm, and basically meet the design requirements.