Micro-fiber Fabry-perot Strain And Refractive Index Sensor

As a very important one of fiber optic sensors (FOS), FP fiber optic sensor is attractive to researchers. It is also one of the mutrurest and most widely used FOS because of its distinct advantages in resolution,precision,dynamic range and realization in comparison with other FOS.The principle and multiplexing of FP fiber optic sensor are summaried in detail firstly. This paper explores demodulation algorithm to improve the demodulation precision and multiplexing ability in order to establish the foundation for the application of FP fiber optic sensor. The main works and results are listed as follow:1. Frequency correction,CZT and ARMA harmonic recovery are employed in demodulation to a single FP fiber optic sensor, and they are compared with FFT in many different aspects. Frequency correction is based on FFT, so it is easy to calculate while remains big error. ARMA recovery has high precision and stable effect, but it is hard to calculate. CZT is a excellect demodulation method because of its high precision and small amount of calculation. The linearity of demodulation result is 0.9994 in micro-strain test.2. The sensing characteristics of fiber optic F-P refractive index sensor produced by 157nm excimer laser micromachining system in normal single-mode optical fiber are analysed. This sensor has a simple structure and is easy to operate. The reflective spectrum interferometic fringe count of this F-P sensor, which can avoid the fluctuation of optical power of the measurement system, is employed, and it can lead to a large refractive index measurement range. The length variation of a F-P cavity with about 25um length is 6.25nm when the temperature varies from 0oC to 70oC , which equates the refractive index variation of the cavity ².46×10^-4 . Glycerin solution with the refractive index range of 1.33—1.427 is measured in normal temperature, and the correlation coefficient of fitting curve of experiment results is 0.9951 and the resolution is ³.70×10^-4.3. Several algorithms for parallel FDM of FP fiber optic sensors are analysed. The relationship between the resolution of cavity length and the central wavelength and waveband of light source is calculated. We compared CZT-MUSIC, Root-MUSICand AR algorithms with CZT. CZT-MUSIC with biased and bigger autocorrelation matrix can get better performance and stabler effect. Besides, CZT-MUSIC,Root-MUSIC and AR algorithms are compared in many aspects, and Root-MUSIC can get the minimal crosstalk of 0.78%. At last, parallel FDM demodulation program is finished with LabVIEW.