Theoretical And Applicational Research On Pressure Sensing Fiber Gratings Within Side-hole Fiber And Side-hole Structure For Sensitivity Enhancement

One of the main obstacles for practical application of measuring hydrostatic pressure with fiber grating is the pressure and temperature cross-sensing problem.The pressure sensitivity coefficient of single-mode fiber grating is only 13pm/MPa,but its temperature sensitivity coefficient is as large as 10 pm/℃,while the side-hole fiber grating has a pressure sensitivity coefficient of 6 pm/MPa and a temperature sensitivity coefficient of 0.05 pm/℃.Therefore,it is the low pressure sensitivity that restricts the application of fiber grating for measuring hydrostatic pressure in the low and medium range.Using analyses and numerical simulation,this dissertation has investigated the sensitivity characters of different kinds of fiber gratings,especially the side-hole fiber grating.A new sealing technology of side-hole structure has been presented as solution for enhancing pressure sensitivity and reducing temperature sensitivity.With this new sealing structure,the pressure and temperature characters of single-mode fiber grating,PANDA fiber grating and side-hole fiber grating are analyzed and compared in detail.Theoretical analyses suggest that,with a side-hole sealing structure,the wavelength span of the two peaks in the reflection spectra of single-mode fiber grating has a pressure sensitivity coefficient which is two orders larger than that of side-hole fiber grating,but with a temperature sensitivity coefficient that is one order lower than that of side-hole fiber grating.The detection system for fiber grating has been designed,which can separate the two peaks in the reflection spectra of birefringence fiber grating.With numerical interpolation method,the precision of detecting the span of the two polarization peaks is improved greatly.Therefore,the wavelength span of the two peaks in the reflection spectra of birefringence fiber grating can be detected with high precision.Fiber grating sensor with side-hole sealing structure has been developed and its reflection spectra has been investigated.Experiments show that this kind of fiber grating sensor has a pressure sensitivity coefficient of 145 pm/mH₂O,while its temperature sensitivity coefficient is lower than 0.008 pm/℃.Therefore,this new sensor can measure hydrostatic pressure within low and medium range successfully.