Research On Sensing Properties Of Twin-Hole Fiber

Optical fiber sensors are widely used in many fields such as petrochemical,defense military and artificial intelligence,because of anti-electromagnetic interference,small size and high precision.Special optical fibers with air holes inside,such as photonic crystal fibers and hollow core fibers,can realize new characteristics.The twin-hole fiber(THF),as one kind of special optical fiber,is composed of two symmetrical air holes and quartz cladding.The light directly enters the cladding of THF from single-mode fiber(SMF)to excite the multimodes and form multimode interference at the output end.It is used for sensing of refractive index(RI),temperature and curvature,which is useful in many practical applications.In this thesis,theoretical and experimental research on the sensing characteristics of THF is carried out.The main work is as follows:Firstly,the basic theory and analysis method of optical wave transmission in optical fiber are expounded.The internal mode field of THF is simulated.The sensor structure of THF are designed and fabricated.The light field in THF and at the junction with single-mode fiber(SMF),and the transmission spectrum of the incident light of different wavelengths are simulated and analyzed.Next,the simulations and experiments of RI sensing of THF sensors were carried out.Three THF sensors with different lengths were designed,and the simulation and measurement analysis of RI sensing were carried out respectively for comparison.The measurement results show that the sensors based on THF has high RI sensitivity as 1351 nm/RIU when RI range is from 1.43 to 1.445,which exhibit linear response in the low RI and nonlinear response in the high RI.Finally,sensing characteristics of the THF sensor on the temperature and curvature were studied.Through the simulation and measurement analysis of temperature sensing,the sensor was found to be insensitive to temperature of range from 30 to 80 ℃.Curvature sensing experiments show that the sensor has high curvature sensitivity and linearity,and the measured sensitivity is-101.487 nm/m-1.The sensor based on THF has the advantages of simple structure,high sensitivity and temperature insensitivity.It has a good application prospects in the field of RI sensing and curvature sensing.