Fig. 1. Spectra of FBG pair written by femtosecond laser. (a) HRFBG; (b) LRFBG

Fig. 2. Spectrum of CTFBG written by femtosecond laser

Fig. 3. CTFBG testing system based on high-power fiber oscillator

Fig. 4. Output spectral experimental results. Output spectra at different pump powers (a) without and (b) with CTFBG; (c) comparison of output spectra at maximum power; (d) Raman suppression spectrum of CTFBG

Fig. 5. Experimental results of output power and time domain signal. (a) Output power variation curve, and insert is profile of output laser beam; (b) output power variation curve of local zooming; time domain signal of output laser (c) without and (d) with CTFBG, and insert is corresponding Fourier spectrum

Fig. 6. Experimental results of CTFBG temperature characteristics. (a) CTFBG temperature as function of output power; (b) CTFBG thermography at maximum output power