The Application Of VT-DBR Laser In Tilted Fiber Bragg Gratings Measurement

In recent decades,electronic sensors play an important role in the field of industrial and scientific measurement.However,electronic sensors have certain limitations in specific applications,such as sensors are susceptible to electromagnetic interference,electrical signal transmission losses limit the use of distance,etc..The optical fiber sensor uses light instead of current and optical fiber instead of copper wire,which has greater advantages in antielectromagnetic interference and other aspects.Compared with electronic sensors,fiber optic sensors have a variety of different characteristics in terms of implementation and signal processing.In recent years,fiber optic sensors and many related optical measurement instruments have evolved from the laboratory research stage to the field engineering application stage.Fiber Bragg Grating(FBG)sensors are one of the most widely used fiber optic sensors.The wavelength of reflected light is easily influenced by ambient temperature or strain,which enables sensing of the corresponding parameters.Tilted Fiber Bragg Grating(TFBG),as a kind of fiber grating with special structure,can realize the coupling of cladding mode and core mode,and is more sensitive to the external environment refractive index parameter than FBG,which opens a new way for biochemical parameter sensing.This paper introduces the principle,development background,application status,preparation method and comparison of various traditional demodulation methods of TFBG,and proposes a demodulation method combining wavelength scanning laser light source and synchronous photodetector.In this paper,a TFBG demodulation system based on Vernier Tuned-Distributed Bragged Reflector(VT-DBR)is developed based on the current demand of TFBG in measurement field and the limitation of signal demodulation method,and the construction of this new demodulation system is highlighted.The principle of VT-DBR laser,the design of related configuration circuits,the communication method of the upper computer and the advantages of the system are introduced respectively,and the application of TFBG in refractive index measurement is done,and the experimental results verify the feasibility of wavelength scanning laser in the application field of TFBG measurement and demodulation.The system has the advantages of low cost,high reliability,and suitability for engineering field application measurements through highly integrated modular circuitry,and the use of independently designed logarithmic amplifiers to make photodetectors improves the input dynamic range of the system,and the current accuracy of the system for solution refractive index measurement is about 0.0003 RIU.The VT-DBR laser selected for the system has a wide tuning range(40nm),tiny The VT-DBR laser selected for the system has the advantages of wide tuning range(40 nm),small tuning interval(8 pm),and more than 40 d B of side mode rejection ratio.In this paper,the intensity and wavelength values of the resonance point in the TFBG transmission spectrum are studied in relation to the ambient refractive index by the wavelength demodulation method and intensity demodulation method respectively,and it is concluded that within a certain range,the drift of the resonance wavelength of the cladding mode has a linear increasing relationship with the ambient refractive index,and the sensitivity and dynamic range of different modes of the cladding mode to the ambient refractive index are different.The maximum sensitivity of the wavelength demodulation method in this experiment is about 37.4 nm/RIU.as the ambient refractive index gradually increases,the higher-order cladding mode cuts off first than the lower-order cladding mode,so the dynamic range of the response of the higher-order cladding mode to the ambient refractive index is smaller than that of the lower-order cladding mode.The intensity demodulation method yields that the intensity change of resonance point of an order cladding mode in a certain refractive index range has a linear increasing relationship with the ambient refractive index,but as the refractive index increases,the single cladding mode will tend to cut off,so the sensitivity of the curve will gradually increase.Finally,the fixed working point method is proposed and used to study the intensity value of a maximum slope wavelength point in the spectrum in relation to the change of refractive index,and it is concluded that when the intensity or wavelength of the resonance point of a certain low-order cladding mode cannot distinguish the change of the ambient refractive index,the fixed working point method can still respond to the change of the ambient refractive index with high linearity,and the maximum sensitivity of the fixed working point method in this experiment is about 1671 d Bm/RIU.