| Hollow core pure quartz optical fiber has important research and application value in the fields of high temperature and high pressure measurement,gas and microfluid sensing with its excellent high temperature resistance and unique air hole microfluidic channel structure.Temperature and pressure are important parameters that reflect the health of engineering structures,and their measurement is crucial in the field of engineering.With the development of science and technology and the advancement of industrial technology,the measurement of high temperature and high pressure is becoming more and more important in the fields of aerospace,petrochemical industry,deep sea exploration,metallurgical industry and so on.Optical fiber sensors are widely used in temperature,pressure,and other physical,chemical,and biomass sensing due to their compact structure,high sensitivity and integration,and online distributed measurement.Among many optical fiber sensing technologies,optical fiber microcavity white light interferometry is not only not affected by the fluctuation of light source power,but also can perform absolute measurement of parameters,which is one of the research hotspots.The selected topic of the thesis comes from the National Natural Science Foundation of China "Aero-engine high-temperature materials/advanced manufacturing and fault diagnosis scientific basis" major research project: "High-temperature dynamic optical fiber sensing mechanism and key technology research for aero-engine condition monitoring and fault diagnosis",Systematic research on hollow-core optical fiber microcavity interferometric hightemperature and high-pressure sensing technology,including: design and preparation of hollowcore optical fiber microcavity interferometer,high-temperature and high-pressure sensing principle and signal demodulation technology,high-temperature and high-pressure integrated sensing and high-temperature dynamics Research on pressure sensing and other aspects.The main contents of this paper are as follows:1.Systematically studied the preparation technology of hollow-core fiber microcavity interferometer.Overcame the low-loss fusion of hollow-core photonic bandgap fibers and ordinary single-mode fibers,precision cutting of different types of hollow-core fibers,the preparation of hollow-core fiber single cavity / composite microcavity,hollow-core fiber microcavity Mach-Zehnder interferometer(MZI: Mach-Zehnder Interferometer)and closed or open microcavity Fabry-Perot Interferometer(FPI: Fabry-Perot Interferometer)preparation and femtosecond laser preparation of hollow fiber side microfluidic channel array and other key technologies.Explores and summarizes a complete set of hollow fiber processing based on arc discharge thermal processing and femtosecond laser micromachining technology and the preparation methods of multiple microcavity(single cavity / composite cavity,closed cavity / open cavity)sensors.2.The signal demodulation technology of fiber-optic microcavity interferometric sensors is studied,including three different methods of white light interference wavelength demodulation,phase demodulation and laser interference dynamic demodulation.The relationship between the wavelength demodulation accuracy,detection limit,Q value of white light interference spectrum,and signal-to-noise ratio is analyzed.Several white light interference phase demodulation methods including Fourier phase method,Fourier main frequency method,wave number domain Fourier transform phase method,phase shift measurement method and stepped phase shift measurement method are introduced,and various phases are compared.The advantages and disadvantages of the demodulation method.The method of dynamic demodulation of fiber-optic microcavity laser interference is preliminarily studied.3.Proposed and realized a hollow fiber MZI high temperature sensor.Experiments have studied the high-temperature response and flame-retardant characteristics of the sensor.In order to eliminate the stress introduced during the preparation of the MZI hollow fiber microcavity,an FPI probe-type high-temperature sensor with hollow fiber microcavity was proposed.Experiments show that the sensor has a very high temperature in the temperature range of 1100 ? without high temperature flame.Measure linearity(0.99)and repeatability.4.Proposed and implemented a high-pressure sensing technology based on open gas microcavity FPI.The linear relationship between gas refractive index and air pressure overcomes the shortcomings of poor stability,low linearity and poor preparation repeatability of the closed cavity air pressure sensor.In the range of 0-10 MPa air pressure measurement,the sensor achieves high wavelength sensitivity(4.17 nm / MPa)and high measurement linearity(above 0.9999).Further,the ultra-long open microcavity FPI was prepared by using low-loss hollow-core photonic bandgap fiber,combined with phase demodulation to achieve the sensor phase sensitivity of 134.05 ?m / MPa,proving that the characteristic of phase sensitivity is proportional to the cavity length and is weak Pressure detection and dynamic sound pressure detection provide a new way.5.Designed and prepared a quartz / air composite microcavity FPI high temperature and high pressure integrated sensor,combined with phase demodulation algorithm to achieve high temperature and high pressure simultaneous measurement.By cascading hollow core optical fibers with different inner diameters,a composite microcavity of quartz cavity(closed cavity)and air cavity(open cavity)is formed,and high temperature measurement is realized by using the large thermo-optic coefficient of quartz material and the insensitivity of air pressure,and gas refraction is used The pressure-sensitive and temperature-insensitive characteristics of the rate enable high-pressure measurement.By performing fast Fourier transform and band-pass filtering on the composite microcavity interference spectrum,the spectral separation of the two sets of microcavity interference signals is achieved,and the demodulated interference spectra are phase demodulated respectively to achieve high temperature(800 ?)and high pressure(10 MPa)Integrated measurement.6.Preliminary research on laser interference dynamic pressure sensing technology.A preliminary sound pressure sensing experiment was conducted to prove the feasibility of this open microcavity for dynamic sound pressure sensing.The concept of realizing high-frequency acoustic wave sensing by increasing the opening degree of the air microcavity is further proposed.The thesis combines theory with experiments,and conducts research in accordance with the ideas of “theoretical design device preparation sensing test signal demodulation optimization and promotion application development”.Interference high-temperature,highpressure and high-temperature and high-pressure integrated sensing technology has been studied in detail and comprehensively.In the future,we will further study the application of aircore fiber microcavity interferometric sensors in the fields of high-speed dynamic barometric pressure sensing,ultra-high temperature barometric pressure sensing,and gas composition detection,and will actively explore air-core fiber microcavity interferometric high-temperature high-pressure sensors in aerospace Applications in other fields. |
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