Fig. 1. Experimental setup of the single stage BPDF amplifier. Points 1 and 2 are fusion splicing joints between BPDF and WDMs.

Fig. 2. (a) Background loss and (b) absorption spectrum of the BPDF.

Fig. 3. ASE spectra of the BPDF at 1240 and 1280 nm pumping.

Fig. 4. Gain characteristics of three pumping configurations, bidirectional pumping with the fiber length of 190 m and forward and backward pumping with the fiber length of 170 m.

Fig. 5. Gain characteristics under different pump wavelength combinations at fixed pump and signal power as well as fiber length.

Fig. 6. Gain and NF characteristics under bidirectional pumping with two 1240 nm LDs. (a) Gain versus fiber length with the pump power of 415 mW and the input signal power of −30 dBm. (b) Gain or NF versus signal power with the fiber length of 190 m and the pump power of 870 mW. (c) Gain or NF versus pump power with the fiber length of 190 m and the input signal power of −30 dBm.