Research On The Characteristics And Sensing Technologies Of Photonic Crystal Fiber Filled Magnetic Fluid

Photonic crystal fiber has developed 17 years from birth to now, and its unprecedented superiority has brought more opportunities for the next generation of optical communications, optical transmission and optical sensing. The photonic crystal fiber filled material showed greater development opportunities and development space. The selection of materials is wide, and different materials have different properties, which lead to the photonic crystal fiber filled material has more excellent characteristics.In this thesis, the photonic crystal fiber was selected as the research object, and the new functional materials magnetic fluid sensitive to temperature and magnetic field was selected as filling material, the characteristics and sensing technologies of photonic crystal fiber filled magnetic fluid (MF-PCF) were researched based on exploring new fiber optic sensor. The main contents are as follows:(1) The relationships between magnetic fluid refractive index and temperature/magnetic field were measured using face reflection method, which provides the basis for theoretical and experimental research of the MF-PCF.(2) The relationships between the characteristics of the MF-PCF different air holes (the mode field distribution, the normalized frequency Veff, the fundamental mode effective refractive index neff, the fundamental mode effective mode area Aes and confinement loss F(λ)) and temperature T/horizontal magnetic field H were researched theoretically under wavelength λ=1550nm. And the cross impacts of temperature and magnetic field on the characteristics of the MF-PCF were analyzed. The results show that the air holes are the greater; the characteristics of the MF-PCF are more sensitive to T/H. Under the same magnetic field, the Veff increases gradually and the neff, Aeff, and F(λ) decrease when the T increases from 20℃ to 80℃. Under H=60Oe, the sensitivities of the MF-PCF characteristics changing with T improve greatly, and does not affect the linearity. Under the same T, the Veff increases gradually and the neff,Aeff, and F(λ) decrease when H increases from 20Oe to 300Oe. The sensitivities of the MF-PCF characteristics changing with H reduce as the t T increasing.(3) The characteristics of the photonic crystal fiber filled selectively magnetic fluid (SFMF-PCF) were researched theoretically. Firstly, the characteristics of the SFMF-PCF with different filling modes (one-line air holes parallel to x-axis, two-line air holes parallel to y-axis, and three-line air holes parallel to x-axis,) were analyzed. The results showed that the birefringence of the SFMF-PCF filling one-line air holes parallel to x-axis was better than the other modes. Then, the relationships between the characteristics of the SFMF-PCF filling one-line air holes parallel to x-axis (the mode field distribution, polarization effective refractive index neff, phase birefringence B and confinement loss F(λ)) and T/H were researched theoretically And the cross impacts of the T and the H on the characteristics of the SFMF-PCF were analyzed. The results show that the air holes are the greater; the characteristics of the SFMF-PCF are more sensitive to the T and the H. Under the same H, the B of the SFMF-PCF decreases gradually when the T increases from 20℃ to 80℃, and the sensitivities of the B changing with T improves as the H increasing. Under the same T, the B of the SFMF-PCF increases gradually when H increases from 20Oe to 300Oe, and the sensitivities of the B changing with the H improves as the T increasing.(4) According to the theoretical analysis results, the temperature and magnetic field measuring system based on light intensity detection was set up, using the MF-PCF as sensing element. Under H=60Oe, the sensitivity measured experimentally of the total loss changing with temperature is-0.317dBm/"C when the temperature ranges from 20℃～80℃. Under T=20℃, the sensitivity measured experimentally of the total loss changing with magnetic field is 0.042dBm/Oe when the magnetic field ranges from 20Oe-300Oe.(4) According to the theoretical analysis results, the temperature and magnetic field measuring system based on light intensity detection was set up, using the MF-PCF as sensing element. Under H=60Oe, the sensitivity measured experimentally of the total loss changing with temperature is-0.317dBm/"C when the temperature ranges from 20℃～80℃. Under T=20℃, the sensitivity measured experimentally of the total loss changing with magnetic field is 0.042dBm/Oe when the magnetic field ranges from 20Oe-300Oe.The temperature and magnetic field measuring system based on fiber loop mirror was set up, using the SFMF-PCF as sensing element. The temperature sensitivity and magnetic field sensitivity were measured experimentally. And the scheme of simultaneous measurement temperature and magnetic field based on the SFMF-PCF fiber loop mirror was proposed. Under H=0Oe and H=T80Oe, the sensitivities measured experimentally of the spacing between two adjacent resonators valley changing with temperature are 0.868nm/℃and 0.771nm/℃ respectively. The sensitivities of resonant valley drift with temperature are-12.92nm/℃ and-32.204nm/℃ respectively. Under T=20℃, the sensitivity measured experimentally of the spacing between two adjacent resonators valley changing with magnetic field is 2.189nm/Oe. The sensitivity of resonant valley drift with magnetic field is-0.199nm/Oe.According to the difference in the sensitivities, the temperature and magnetic field can be measured simultaneously based on two-parameter matrix method. For the spectrometer with 0.02nm resolution, the resolutions of the temperature and the magnetic field are 0.07℃ and 0.41Oe respectively.(5) Two kinds of core doped germanium MF-PCF with different structures were designed, and were written Bragg gratings. One has a resonance peak (MF-PCFBG1), and another has double resonance peaks (MF-PCFBG2).Firstly, the resonant peaks drift of the MF-PCFBG1 with temperature/magnetic field was calculated theoretically. The temperature/magnetic field can be measured based on resonant peak sensitive to temperature and magnetic field. According to this theory, the temperature and magnetic field measuring system based on MF-PCFBGlwas set up. The sensitivities measured experimentally of resonance peak shift with temperature/magnetic field was consistent with theoretical calculation.Then, the resonant peaks drift of the MF-PCFBG2 with temperature/magnetic field was calculated theoretically. The results show that the sensitive coefficients of the resonant peaks changing with temperature/magnetic field were different. According to this theory, the system of temperature and magnetic field measuring simultaneously based on MF-PCFBG2 was set up. The sensitivities measured experimentally of resonance peaks shift with temperature/magnetic field was consistent with theoretical calculation. For the spectrometer with 0.02nm resolution, the resolutions of the temperature and the magnetic field are 0.82℃ and 4.98Oe respectively.