Fabrication And Characteristic Research Of Non-uniform Fiber Grating

Compared with the traditional sensors,fiber-optic grating sensors have a wide application in the field of fiber sensing on account of the inherent advantages such as compact size,anti-interference and resistant to the high-temperature and high-pressure environments and so forth.Especially,the uniform fiber Bragg gratings(FBG)have been applied to the field of grating sensing owing to its experienced inscription technologies.However,the non-uniform fiber gratings,let us say,phase-shift fiber grating(PSFG),superstructure fiber grating(SFG)and Moire fiber grating,etc,which are not put into generally use due to complex periodic changes and limit of inscription technologies.In this paper,the sensing mechanisms of PSFG and SFG have been analyzed firstly.Then,we fabricated some non-uniform fiber gratings with the merits of small size and multi-function including PSFGs?SFGs and structural phase-shift grating based on the manufacture method of FBG through adjusting light path,changing material and cascading with FP cavity.Subsequently,the sensing characteristics of the non-uniform fiber gratings mentioned above have also been investigated responding to the measurands of temperature,pressure,refractive index and strain.The major research contents and results of this paper are as follows:(1)The characteristics of light wave propagating of fiber gratings,such as FBG?PSFG?SFG and structural phase-shift grating are analyzed theoretically using the method of Transfer Matrix method.Then,all of the fiber gratings' reflectance spectra(or transmission spectra)mentioned above are simulated by setting appropriate parameters using the software of MATLAB.The sensing characteristics of the fiber gratings aforementioned responding to temperature,pressure,strain and refractive index also are investigated.(2)We fabricated phase-shift grating sensors and investigated its sensing characteristics.Firstly,inscribed PSFG sensor by means of screen method.Experimental results shown that the temperature sensitivity and strain sensitivity of PSFG are 0.010 nm/? and 1.361 nm/N,respectively.Secondly,fabricated grating-photosensitive adhesive cavity sensor and then the sensing characteristics of temperature and pressure also are tested.Experimental results shown that the temperature sensitivity of photosensitive adhesive cavity is 223.4 pm/? with the temperature increasing from 30? to 110? and the FBG also exhibits response sensitivity as 11.6 pm/?;the pressure sensitivity of photosensitive adhesive cavity is 25.0 nm/MPa with the pressure changed from 0 MPa to 0.7 MPa and the FBG is insensitive to pressure.Therefore,according to the temperature compensation method,the grating-photosensitive adhesive cavity sensor can realize simultaneous measurement of temperature and pressure.And the resolutions of this integrated sensor in measuring temperature and pressure are 0.086 ? and 0.730 MPa,respectively.Thirdly,in order to fabricate non-uniform fiber gratings,the grating-photosensitive adhesive cavity sensor was further optimized,and to fabricate a structural phase-shift grating sensor,which can realize sensing temperature,pressure,refractive index.Experimental results shown that the temperature sensitivity of photosensitive adhesive cavity is 0.3076 nm/? with the temperature increasing from 25? to 50? and the grating also exhibits response sensitivity as 6.2 pm/? and-0.2299 dB/? over the whole measurement range;the pressure sensitivity of photosensitive adhesive cavity is 0.81 nm/MPa with the pressure changed from 0 MPa to 1.2 MPa and the grating barely shift,and the RI sensitivity of photosensitive adhesive cavity is 355.03 nm/RIU corresponding to a series of RI values and the grating response sensitivity as 319.82 dB/nm,respectively.And the resolutions of this integrated sensor in measuring temperature,pressure and RI are 0.16 ?,0.1245 MPa and 0.0001 RIU,respectively.(3)We inscribed the SFGs with different period's single mode fiber(SMF)and seven-core fiber(SCF)and then,SFGs are also subjected respectively to temperature and strain to research the sensing characteristics.Obtained the temperature sensitivity and strain sensitivity of SMF-SFG are 10.5 nm/?and 1.3263 nm/N,respectively,and the response sensitivities of SCF-SFG are 10.6 nm/? and 0.9113 nm/N.All in all,we investigated the light transmission characteristics and sensing theory of non-uniform fiber Bragg grating,and then successfully made some non-uniform fiber grating sensors based on the inscription light path of FBG characterizes via adjusting the light path,replacement of fiber material,and fusion of many technologies such as,the beam modulation technology,fiber-optic microstructure production and special fiber-optic inscribing.Then the sensing characteristics of the non-uniform fiber grating sensors mentioned above are studied.The study of non-uniform grating theory and writing technology will be of great significance to its application in optical fiber communication and sensor detection.