Fig. 1. CFBG inscription system with small dispersion

Fig. 2. Measurement system for small dispersion CFBG

Fig. 3. Simulation of CFBG reflection spectra. (a) Simulation of reflection spectra under different grating area lengths; (b) simulation of reflection spectra under different apodization functions; (c) simulation of reflection spectra under different refractive index modulation depths; (d) simulation of reflection spectra after adjusting appropriate parameters

Fig. 4. Transmission and reflection spectra of small dispersion CFBG

Fig. 5. CFBG dispersion measurements. (a) Small dispersion CFBG interferometric spectra; (b) cos［φ（f ）］ after removing two interferometer arms; (c) phase fitting of interferometric signals; (d) comparison of interferometric spectrum with fitted result

Fig. 6. Dispersion results and errors under different wavelengths. (a) Dispersion results under different wavelengths; (b) dispersion measurement error bar

Fig. 7. Simulated interference spectra and measured dispersion values . (a) Simulated interference spectra under different R';

Fig. 8. Spectra in case of poor fusion quality. (a) Interference spectrum after combining two interferometer arms; (b) interference spectrum after masking CFBG arm