Research Of Tunable Filters Based On Special Fiber Bragg Grating Structures

On one hand fiber Bragg grating(FBG) is integrated in the fiber naturally, with the advantages of low insertion loss, immunity to electromagnetic interference, excellent filter characteristics, etc., thus there is a wide range of applications in optical fiber communication and optical fiber sensing field, especially with the development of all-optical systems, FBGs show more importance. On the other hand with the rapid development of WDM technology and tunable lasers, tunable filters have become indispensable in the fields of both optical communication and optical sensing, such as acousto-optic tunable filters, Fabry-Perot tunable filters and fiber grating tunable filters. Based on the above, this paper mainly studies two different kinds of tunable filters based on special fiber Bragg grating structures.The principle of the first kind tunable filter is the interference phenomenon between a micro-fiber Bragg grating and the Fresnel reflection of a fiber end face. Firstly, the inscribed process of a fiber Bragg grating with the aid of the phase mask is introduced. Then through drawing the common fiber into micro-fiber and cutting the end face of the fiber to a flat face, the final methodology of obtaining the wanted interferometer is determined. Furthermore, by adjusting and optimizing experimental parameters, the interferometer structure to be tuned is finally obtained and we can observe obvious interference effect. Finally, by adjusting the bearing capacity of the interference structure, the wavelength of the interference fringes were tuned, and we observe a total wavelength shift amount of 35 pm and obtain a good linear tuning characteristic, and the tuning efficiency of the wavelength shift changes to force changes is 0.165pm/μN.The second tunable filter is based on the interference phenomenon of a pair of fiber Bragg gratings, also referred to as Fabry-Perot cavity composed of fiber Bragg gratings(FBG F-P cavity). First, we select the methodology of producing the FBG F-P cavity structure. By observing the experimental phenomena step by step, finally we determine to produce two FBGs dependently, choose the similar ones according to their spectra and match them to a pair, then finally we get the FBG F-P cavity structure. Last, by adjusting the bearing stress to the FBG F-P cavity structure, the wavelength of the interference fringes of the structure is tuned, and we observe a total wavelength shift amount of 1.09 nm and obtain a good linear tuning characteristic, and the tuning efficiency of the wavelength shift changes to force changes is 1.09pm/με.