A new method is presented to tune Bragg wavelength slightly by using hydrofluoric acid to etch fiber cladding.The spectral characteristics before and after etching and the change properties of Bragg wavelength are studied.Cladding modes are reduced during the etching process.High-order cladding modes are converted into radiation modes,and energy of cladding modes is coupled to the outside.As the cladding radius decreases,the Bragg wavelength shifts to longer direction.Experimental results show that this method can tune Bragg wavelength slightly,and the tunable range is 0.002-0.120 nm.
A new method is presented to fabricate the triangular fiber Bragg grating(TFBG).The fabrication device is simple,only requires a single exposure and does not need to write complicated program.The transfer matrix method is used to design the fiber Bragg grating,and the grating resonant wavelength and the grating reflectivity can be controlled in order to achieve the triangular spectrum.With different fiber tilt angles,the available bandwidth of TFBG,the linearity and the oblique gradient are also different.In the experiment,the angles 1°,1.5° and 2° are chosen.The results show that the best angle value is 1.5°,and the TFBG has a good linearity,greater gradient and wider available bandwidth.
