Resolving the problem of cross sensitivity in fiber Bragg grating sensor based on the principle of polarized-light interference

The article introduces an advanced approach of fiber grating strain demodulation based on the principle of polarized-light interference.This method can solve the problem of cross sensitivity in fiber Bragg grating sensor.As for the yttrium vanadate(YVO4)crystal polarized-light interferometer,if there are two different fiber Bragg gratings that have a p rad phase difference,one is used for strain sensor and the other is used for temperature compensating.Then the problem of cross sensitivity can be overcome.The analyses of the strain demodulation resolution show that with a decrease in crystal thickness the resolution increases.The experiment shows that when the thickness of YVO_(4) crystal is 0.5 mm,the effect of cross-sensitivity will be reduced to 0.13μe/°C,which is 1.6%of the effect used by only one fiber Bragg grating for strain measure.And when the thickness is 0.1 mm the cross-sensitivity will be reduced to 0.0067μe/°C,which is less than 0.08%.Less thickness of crystal is beneficial for the resolution of strain measure,but the machining of small thickness crystal is difficult.To solve this problem,a new scheme of polarized-light interferometer with the structure of double layer crystal was analyzed.

Investigation of Strain-Temperature Cross-Sensitivity of FBG Strain Sensors Embedded Onto Different Substrates

The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating(FBG)sensors.In this work,a theoretical investigation of the strain-temperature cross-sensitivity has been performed using the temperature reference grating method.To experimentally observe and theoretically verify the problem,the substrate materials,the preloading technique,and the FBG initial central wavelength were taken as main parameters.And a series of sensitivity coefficients calibration tests and temperature compensation tests have been designed and carried out.It was found that when the FBG sensors were embedded on different substrates,their coefficients of the temperature sensitivity were significantly changed.Besides,the larger the coefficients of thermal expansion(CTE)of substrates were,the higher the temperature sensitivity coefficients would be.On the other hand,the effect of the preloading technique and FBG initial wavelength was negligible on both the strain monitoring and temperature compensation.In the case of similar substrates,we did not observe any difference between temperature sensitivity coefficients of the temperature compensation FBG with one free end or two free ends.The curves of the force along with temperature were almost overlapped with minor differences(less than 1%)gained by FBG sensors and pressure sensors,which verified the accuracy of the temperature compensation method.We suggest that this work can provide efficient solutions to the strain-temperature cross-sensitivity for engineering strain monitoring with the self-sensing element embedded with FBG sensors.

Tilted Fiber Bragg Gratings:Principle and Sensing Applications

In this paper,the mode coupling mechanism of tilted fiber Bragg gratings(TFBGs)is briefly introduced at first.And a general review on the fabrication,theoretical and experimental research development of TFBGs is presented from a worldwide perspective,followed by an introduction of our current research work on TFBGs at the Institute of Modern Optics,Nankai University(IMONK),including TFBG sensors for single-parameter measurements,temperature cross sensitivity of TFBG sensors,and TFBG-based interrogation technique.Finally,we would make a summary of the related key techniques and a remark on prospects of the research and applications of TFBGs.