| In 1990s,the world's first Photonic Crystal Fiber(PCF)was published.Compared with conventional fiber,It is a kind of special fiber which has a variety of different arrangement forms in the cross section.which has a unique and tunable characteristic,which can be easily combined with sensitive material to obtain some new properties,which provides new opportunity for the development of fiber sensing technology.In this paper,several novel and practical photonic crystal fiber sensing technologies based on Sagnac and Mach-Zehnder interference principle is studied,and the main research contents and results are as follows:1.The mode field distribution of single solid core PCF with 5 layers air hole and double hole HiBi-PCF with 7 layers air hole is simulated by finite element theory and the perfectly matched layers is used as boundary conditions.The characteristics of PCF are calculated and analyzed,and the effective refractive index,effective mode area,nonlinear coefficient and dispersion coefficient are obtained.2.A kind of combination interference structure is proposed,and the core and cladding mode field is coupled in the Sagnac loop by using fusion splicing collapse method and HiBi-PCF long period grating inscribed with fiber Bragg grating cascade method.In the Sagnac loop,HiBi-PCF is sensitive to external refractive index and curvature as sensitive unit.The system is designed for the measurement of refractive index,curvature,and the simultaneous measurement of temperature and refractive index.The principle analysis,technological research and experimental measurement were carried out.The refractive experimental results show that the resonance wavelength of the sensor output signal is blue shifted with the increase of the refractive index of glycerol solution,and the law is linear.The sensitivity of refractive index measurement is 306.6nm/RIU,and the measurement error caused by temperature change can be neglected.The curvature experimental results show that the measurement sensitivity of curvature is 10.171 dB/m-1 in the range of 0m-1?0.48m-1,and the maximum temperature error is 0.97dB,which can be neglected in practical application.The refractive and temperature experimental results show that the resonant wavelength of high birefringence photonic crystal fiber loop mirror is blue shifted with the increase of the refractive index of glycerol solution.The sensitivity of refractive index measurement is-21.0714nm/RIU,and the effect of refractive index on the central wavelength of fiber Bragg grating can be neglected.The resonant wavelength of fiber Bragg grating is red shifted with the increase of temperature,and the sensitivity is 9.7pm/?.The effect of temperature on the high birefringence photonic crystal fiber loop mirror can be neglected.3.A kind of reflective Sagnac interferometer is proposed.A high sensitivity temperature sensing system with independent probe is formed with ethanol filled HiBi-PCF.It provides important scientific basis for the formation of distributed sensing network.Jones matrix method is used to analyze the interference spectrum equation.The polarization mode distribution of HiBi-PCF is simulated based on the finite element theory,and the perfectly matched layers is used as boundary conditions.The birefringence of the model was analyzed and increased with temperature,and the sensitivity is 0.00139/?.The variation of resonant wavelength shift with temperature,and temperature measurement sensitivity with HiBi-PCF length,and the interference spectrum period with HiBi-PCF length,and the relative output intensity with temperature are obtained.In the study of experiment,the HiBi-PCF temperature sensitive probe is made based on the filling process of the pressure injection method and the multiple discharge method,and the temperature sensing system based on wavelength demodulation and intensity demodulation is established.Wavelength demodulation experiments show that the wavelength of resonance wavelength increases linearly with the increase of temperature,and the linear fitting degree is 0.9986.The temperature measurement sensitivity is 9.14nm/? at 25?-27.5?.With the increase of temperature,the output optical power is changed with sine.The linear fitting degree of the output optical power is 0.9774,and the temperature measurement sensitivity is 0.1213mW/?.The optical power meter with a resolution of 0.001dB is used,so the temperature resolution of the sensing system is better than 0.01?.4.A kind of reflective Mach Zehnder interferometer is proposed,which is based on the unique process of collapse of intensified fusion splicing,collapse of intensified fusion splicing and taper,and cryptophane molecules sensitive film coating.The liquid refractive index and methane gas concentration sensing system with an independent probe is designed,and the principle analysis,technology and experiment are carried out.The experimental results show that the resonant wavelength shift of PCF-MZI based on transmission and probe is linearly increasing with the refractive index of NaCl,which were fabricated by the process of collapse of intensified fusion splicing,and the fitting degree are 0.9878 and 0.9825 respectively,and the sensitivity are 111.2nm/RIU and 122.6nm/RIU at 1.3333 to 1.3656.The resonant wavelength shift of PCF-MZI with probe is linearly increasing with the refractive index of NaCl,which were fabricated by the process of collapse of intensified fusion splicing and taper,and the fitting degree is 0.9700,and the sensitivity is 181.3nm/RIU at 1.3333 to 1.3737.The temperature sensitivity is 0.0009nm/? at 20?-50?,and it can be neglected.Methane gas concentration measurement results show that the resonant wavelength shift of PCF-MZI with probe is linearly decreasing with the Methane gas concentration,which were fabricated by the process of collapse of intensified fusion splicing and cryptophane molecules A sensitive film coating.The fitting degree is 0.999,and the sensitivity is 106.63nm/persent at 0%?5%.Substituting for cryptophane molecules E in the sensitive film,the fitting degree is 0.9853,and the sensitivity is 129.91nm/persent at 0%?5%.Compared with the PCF-MZI based on cryptophane molecules A sensitive film coating,the sensitivity of the sensor is improved,which is related to the film quality and the size of the cryptophane cavity. |
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