Optical wideband source of L-band amplified spontaneous emission (ASE) from erbium doped fiber has extensive application in fiber sensors and device testing; here the pump power conversion is one of the key technique. In this work, based on the secondary pumping mechanism by C-band power for L-band signal, a Sagnac loop is used to feed-back the output of C-band ASE, the reflected C-ASE propagates along single direction in the fiber and is amplified in expending inversion population, so that the utility of pump power for L-band ASE is increased. Experimentally, the total output power was 14 dBm at 125 mW 980 nm pumping i.e. pump power conversion efficiency up to 20% was achieved. Without gain flatten filter, the 1 dB bandwidth was 31.1 nm (1568.9～1600 nm), so that high pump conversion efficiency and broad L-band ASE source was demonstrated.