Research On Sensing Characteristics Based On Tilted Fiber Grating

Optical fiber devices are a unique category of optoelectronic devices,and fiber Bragg grating has been widely used in communication,sensing and other fields in recent years.Different from ordinary fiber Bragg gratings(FBG),tilted fiber Bragg gratings(TFBG)have a unique structure of grating plane and fiber core axial Angle,which makes the mode coupling in fiber core and cladding more diversified and transmission spectrum more complex.Therefore,TFBG has broader application potential in sensing,demodulation and other aspects.This paper focuses on the sensing characteristics of TFBG,analyzes the optical waveguide transmission in TFBG with theory,and focuses on the refractive index and temperature sensing characteristics of TFBG and the edge filtering and demodulation technology of TFBG with the combination of simulation and experiment.The work done is as follows:1.The development history,different types and applications of fiber Bragg grating in various fields are summarized,and the innovation achievements,writing methods and applications of TFBG are introduced emphatically.2.The structure of TFBG is analyzed,and the coupled mode theory and transmission matrix theory used to analyze TFBG are introduced.The coupled mode equation and spectral parameter formula of TFBG are derived by using these two theories.3.OptiGrating software was used to simulate and analyze the characteristics of TFBG transmission spectrum,and control variable method was used to study the influence on the resonant wavelength and transmittance of core mode and cladding mode of transmission spectrum of TFBG structure parameters such as Angle,period and gate area length.The temperature and refractive index sensing characteristics of TFBG were studied respectively.4.The refractive index sensing characteristics of TFBG are simulated and experimentally studied.Firstly,the refractive index sensing system using only one TFBG is simulated and tested.It is found that from the resonant peak of the high-order cladding mode,the transmittance gradually attenuates and disappears with the increase of the ambient refractive index,and the overall optical power of the transmission spectrum of TFBG decreases.A novel refractive index sensing system based on TFBG cascade fiber ring mirror is designed.The simulation results show that the transmittance of each mode is doubled,and the experimental sensitivity is 1.418mw/RIU higher than that without cascade.5.The edge filter demodulation technology of TFBG is studied to convert wavelength shift into power change,and the FBG encapsulated by plexiglass is taken as the sensor grating to carry out experiments on the temperature sensor demodulation system of FBG based on TFBG edge filter.The sensitivity of the four sensor gratings is 0.1072 n W/℃,0.1937 n W/℃,0.2323 n W/℃ and0.2987 n W/℃,respectively.On this basis,the system is improved.By cascaded TFBG and fiber ring mirror,the depth of edge filtering transfer function is increased exponentially.The sensitivity of four sensor gratings is 0.1756 n W/℃,0.4468 n W/℃,0.4988 n W/℃ and 0.7318 n W/℃,respectively.Compared with the uncascaded optical fiber ring mirror,the system temperature sensitivity is greatly improved.