Fig. 1. The measured spectrum of the CTFBG fabricated for the following experiments.

Fig. 2. Experimental configuration for the mitigation of SRS in a bi-directional pumping fiber amplifier. HR: high reflection FBG, OC: output coupler FBG, LD: laser diode, YDF-$20/400$: LMA-YDF-$20/400$-M by Nufern, CLS: cladding light stripper.

Fig. 3. Changing spectra of output as the pump power increases (a) without and (b) with CTFBG inserted, (c) comparison spectra at pump power of 2069 W, (d) signal ratio and (e) output power versus pump power with and without CTFBG.

Fig. 4. Changing spectra of output as the pump power increases (a) without and (b) with CTFBG inserted, (c) comparison spectra at pump power of 3569 W, (d) signal ratio and (e) output power versus pump power with and without CTFBG.