Fig. 1. 257 nm UV femtosecond laser + phase mask CFBG writing system

Fig. 2. Ultra-flat high reflectivity CFBG. (a) Packaged CFBG; (b) CFBG reflection spectrum

Fig. 3. Pulse stretching performance test of the CFBG. (a) Spectral comparison before and after stretching; (b) pulse waveform after stretching