Fig. 1. FBG reflection spectra corresponding to different UV irradiation distribution functions F(z) and their 3 dB bandwidth, 25 dB bandwidth, side band steepness N trend analysis. (a),(b) Different linear UV irradiation distribution functions F(z); (c),(d) corresponding FBG reflection spectra simulated under different F(z) functions; (e),(f) corresponding change trend analysis for 3 dB bandwidth, 25 dB bandwidth and side band steepness N of FBG reflection spectra under different F(z) functions

Fig. 2. Point-by-point writing of FBG by solid-state laser

Fig. 3. Possible irradiation inhomogeneity caused during UV irradiation. (a) Irradiation inhomogeneity introduced by scanning spot in solid-state laser scanning; (b) irradiation inhomogeneity introduced by misalignment between optical fiber and phase mask

Fig. 4. Adjustment of optical fiber tilt angle

Fig. 5. Reflection spectra and change trends of grating parameters of FBGs written at different fiber tilt angles with UV irradiation distribution function shown in Fig. 1(a). (a) Reflection spectra of FBGs written at different fiber tilt angles; (b) change trends of 3 dB bandwidth, 25 dB bandwidth and side band steepness N for spectra of FBGs written at different fiber tilt angles

Fig. 6. Reflection spectra and change trend of grating parameters of FBGs written at different fiber tilt angles with UV irradiation distribution function shown in Fig. 1(b). (a) Reflection spectra of FBGs written at different fiber tilt angles; (b) change trends of 3 dB bandwidth, 25 dB bandwidth and side band steepness N for spectra of FBSs written at different fiber tilt angles

Fig. 7. Measured non-uniform distribution of UV irradiation and effect of compensation. (a) Measured non-uniform distribution of UV irradiation and fitted non-uniform function F(z); (b) reflection spectra of FBGs written before and after correction