Study On Microcavity Optical Fiber Refractive Index Sensor

All optical fiber interference sensors have broad application prospects in the detection of physical quantities such as refractive index and gas concentration due to its unique advantages such as high sensitivity,small size,low cost,etc.However,the sensor structure and the inherent material parameters of the optical fiber limit the effective refractive index range of the cladding mode participating in the sensing,which limits the application range of this kind of refractive index sensor.In recent years,in order to meet the needs of this type of sensor for low-concentration liquid refractive index and gas refractive index detection,there have been micro-nano optical fiber structures,optical fiber end-face open cavities,and optical fiber surface de-cladding to core sensing structures.Studies have shown that the above method can effectively improve the sensitivity of refractive index detection and expand the detection range.However,there are still many problems in the structure of existing sensors,and its sensing performance needs further study.This thesis is based on micro-cavity optical fiber interference sensor,which is developed by theoretical analysis and experimental research.In this paper,the refractive index and temperature sensing characteristics of the open and closed micro-cavity structure of optical fiber interference sensor are studied,and the concentration and pressure of ethanol gas are studied by using the closed-cavity sensing structure.The main research contents in this paper include:1.The development status of optical fiber interference sensors micro-cavity structure are briefly reviewed.The research status of refractive index sensing,temperature sensing,pressure sensing and gas concentration sensing based on micro-cavity optical fiber structure are discussed.2.Study on refractive index sensing characteristics of micro-cavity optical fiber structure.Firstly,the F-P interference theory model and the M-Z interference theory model are constructed,and the refractive index sensing theory is analyzed respectively.Then the interference light field distribution of the sensing structure is simulated.Finally,the refractive index experiment is carried out by using the micro-cavity optical fiber sensing structure.The experimental results show that the sensitivity of the refractive index sensing based on the open micro-cavity optical fiber structure is 50.001nm/RIU.When the fine core optical fiber with a length of 3cm is connected to the sensing structure,the sensitivity of low refractive index range reaches 565.22nm/RIU,and the sensitivity of high refractive index range reaches-655.55nm/RIU.The latter structure achieves refractive index sensitization.The refractive index sensitivity of the closed micro-cavity optical fiber sensing structure is-81.481nm/RIU.3.Study on temperature sensing characteristics of micro-cavity optical fiber structure.The optical fiber F-P temperature sensing model and the optical fiber M-Z temperature sensing model are established,and the theoretical analysis and experimental research on F-P temperature sensing characteristics and M-Z temperature sensing are carried out.The experimental results show that when the temperature detection range is from 35? to 95?,the temperature sensitivity of the open micro-cavity optical fiber structure is 0.0158nm/?.When the fine core optical fiber is connected,the temperature sensitivity is 0.0287nm/?.The sensitivity of the closed micro-cavity optical fiber sensing structure is 0.0439nm/?.4.Study on air pressure sensing characteristics of closed micro-cavity optical fiber structure.The closed micro-cavity pressure sensing model is established,and the F-P cavity pressure theory is analyzed.The air pressure sensing characteristics of the closed micro-cavity structure are studied in combination with experiments.The experimental test shows that the interference spectrum is red-shifted with the increase of the gas pressure of the ethanol gas.The pressure sensitivity is 1.2709nm/MPa.When the gas pressure exceeds 0.2MPa,the change of the wavelength tends to be slow,and the sensing structure can effectively detect the change of gas pressure.5.Study on ethanol gas concentration sensing characteristics of closed micro-cavity optical fiber structure.Firstly,the principle of closed microcavity gas concentration sensing of M-Z interference is analyzed.Then,the output spectrum simulation of different microcavity length sensing structures is carried out.Finally,the two cavity length structures are studied by experiments.The experimental results show that the sensing structure with a cavity length of 25.3?m is more sensitive to gas concentration sensing,and the sensitivity is-0.855nm/%.When the cavity is filled with graphene,the gas concentration sensitivity is as high as-1.0922nm/%.The linearity of the wavelength and the gas concentration is also improved compared with the previous one,and the linearity is 97.43%.