| The F-P interferometric fiber displacement sensor is based on a single F-P microcavity,and the free spectral range(FSR)of the sensor interference spectrum is narrow.Since the larger FSR can provide a larger F-P microcavity sensing range,the Vernier effect is introduced in this paper,causing a periodic envelope in the interference spectrum of the sensor,significantly widening the FSR of the interference spectrum.Since the extrinsic structure has a gauge length of the order of millimeters,which is close to the range of the length of the F-P microcavity required in this paper,the sensing probe of the present invention adopts an extrinsic structure.According to the research status of FP interferometric fiber-optic sensors,it is found that although the single-cavity sensing probe has many structures,the FSR of the interference spectrum is narrow,and with the introduction of multi-parameter measurement in the fiber sensor,the introduction of the Vernier effect,double-cavity mixing The structure has gradually received people's attention;due to the limitations of the cursor effect conditions,the optical sensor based on the Vernier effect has not been applied to the displacement measurement of the millimeter-scale dynamic range,thus determining the research topic of this paper.The focus of this paper is to apply the birefringence of liquid crystal,design the F-P interference type fiber displacement sensor based on the Vernier effect,and give the preparation method and experimental test method of the sensor;the main research contents are as follows:The spectral peak tracking method is used to analyze the measurement principle of the tracking spectral wavelength shift,which shows the significance of widening the FSR of the interference spectrum for displacement sensing.Spectra with periodic envelopes do not necessarily belong to the Vernier effect spectrum,thus explaining the reasons for this type of spectroscopy.Through the interference spectrum analysis of FP liquid crystal cavity,the possibility of generating the Vernier effect spectrum through a single FP liquid crystal cavity is proved.The calculation method of the envelope width of the periodic envelope and whether the spectrum belongs to the Vernier effect spectrum are given.In the sensing principle of FP liquid crystal cavity,the linear relationship between spectral wavelength shift and displacement and temperature is derivedAccording to the polarization state response of the incident light,the theoretical analysis of the interference spectrum of the F-P liquid crystal cavity is verified,and it is determined that the polarization direction of the incident light and the liquid crystal axis are 45°in the displacement response and temperature response test of the sensor.In the displacement response test of the sensor,the linear response of the experimental data proves that the displacement linear response of the sensor is good(linear fit is 0.99)and the maximum displacement sensitivity is 2.97 the experimental results are analyzed according to the displacement measurement range.The upper and lower limits of the measurement range(FP liquid crystal cavity length range)are selected to be 0.3 mm and 1.2 mm.In the temperature response test of the sensor,according to the temperature response near the clearing point of the liquid crystal,combined with the polarization state response of the incident light,it is determined that the Vernier effect spectrum is derived from the birefringence of the liquid crystal;taking the FP cavity of 0.4 mm length as an example,the FP liquid crystal cavity interference The FSR of the spectrum is 36 nm.This makes the dynamic measurement range of the uni-peak measurement eleven times larger than the displacement sensing without considering the temperature cross-sensitivity,which reduces the relative error of the sensor length measurement of the bimodal measurement by 11 times. |
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