Fig. 1. Schematic of point-by-point fabrication of FBG based on beam shaping by small aperture

Fig. 2. Waist radius and Rayleigh length versus aperture of diaphragm

Fig. 3. Focal field energy distributions. (a) Aperture of 10.0 mm; (b) aperture of 1.0 mm

Fig. 4. Test method for FBG transmission spectrum. (a) Test of light source transmission spectrum; (b) pretest of FBG transmission spectrum

Fig. 5. Microscopic images of FBG fabricated with different apertures and corresponding transmission spectra

Fig. 6. Insertion loss and short-wavelength loss values of FBG fabricated with different apertures

Fig. 7. Schematics of cladding mode coupling. (a) Circular grating fringe; (b) filamentous grating fringe

Fig. 8. FBG transmission spectra in air and matching liquid

Fig. 9. FBG transmission spectra oscillating at short wavelength side. (a) FBG prepared on coated fiber; (b) low reflection