Research On Theoretical Properties Of The Coated LPFG

Coated fiber grating sensor is one of the fast developing passive fiber devices in recent years. Theory and technology research on coated fiber grating has been developed very swiftly home and abroad. Many technological workers produced have a wide variety of coated fiber grating for different purposes. Due to its excellent optical properties and flexible design for adjusting allow it to be widely used in the field of optical communications and optical sensors. In the communication field, the coated fiber grating is widely used in filters and tuning techniques, which showed great superiority; in the sensing field, the coated fiber grating is commonly applied in the liquid concentration sensors, chemical sensors, biosensors, gas sensors, temperature sensors and humidity sensors. With the coated fiber grating theory getting better and the development of coating technology, coating fiber grating is bound to become a major force in all walks of life, and it will demonstrate a wider application and development prospects.This paper attempts a detailed study of the working mechanism and the sensing application of coating fiber grating in four parts:(1) General coating methods of coated LPFG, its application and development in recent years at home and abroad is introduced in detail.(2) Based on a triple-clad numerical model, the effective refractive index of the core guided mode and cladding modes can be obtained while the distribution of the electromagnetic field equations and boundary continuity conditions are used to derive the dispersion equation of the core guided mode and cladding modes, with the Graphic method and the dichotomy. With numerical simulation, the transmission spectrum of the coated LPFG is acquired after analyzing its spectral characteristics.(3) The thin-film parameters of the coated LPFG and the influence of environmental refractive index on LPFG cladding refractive index are studied. Then a detailed analysis on the cladding mode reorganization is made when the thin-film thickness reaching a certain thickness.(4) The impact of the film parameters and environmental refractive index on the coated LPFG resonant wavelength is the focus. In analyzing the influence of film thickness on the coated LPFG resonant wavelength, the optimum overlay thickness (OOT) is obtained. It has great significance in guiding the development of coating technology.