Fig. 1. Schematic diagram of femtosecond laser fabrication system.

Fig. 2. Schematic diagram of the paths of the femtosecond laser point-by-point method and the transversal-scanning method.

Fig. 3. SEM images of the fiber cross section inscribed with different methods: (a) point-by-point method, (b) transversal-scanning method.

Fig. 4. Transmission spectra of LPFGs fabricated by two different methods (LPFG-I with transversal-scanning method and LPFG-II with point-by-point method).

Fig. 5. (Color online) (a) Transmission spectra of LPFG-II with temperature increases; (b) resonant wavelength and attenuation change as a function of temperature change.

Fig. 6. (Color online) (a) Transmission spectra of LPFG-I with temperature increases; (b) resonant wavelength and peak attenuation change as a function of temperature change.

Fig. 7. (Color online) Changes of Δn variations for LPFG-I and LPFG-II as the temperature increases.

Fig. 8. (Color online) Transmission spectra of (a) LPFG-II and (b) LPFG-I before heating at 20°C and cooling down to 20°C, respectively.