Fig. 1. Structure diagram of Bragg grating filter

Fig. 2. The transmission spectrum of the waveguide gratings with different grating numbers and relationship between transmission and grating numbers

Fig. 3. Transmission curves of bandwidth comparison between the first-order and the third-order Bragg grating filters

Fig. 4. Fixed groove refractive index and grating duty cycle，the filter spectrum changing with grating period of the first-/third- order gratings and the relations of period and filter wavelengths

Fig. 5. The filter spectrum changing with refractive index of the first-/third- order gratings and the relations of the refractive index and filter wavelengths

Fig. 6. Comparison of filtering spectral lines when the number of gratings of the third-order grating is 500 and 167

Fig. 7. The relationship between wavelength and grating transmittance under different duty cycle

Fig. 8. Fix the period of grating and refractive index of filled medium，the filtered spectrum and filtered light field with 0.4 duty cycle