A double-pass bi-directional(DP-BD) pump configuration is proposed for the high efficiency Lband ASE. A L-band ASE of 13.7 dBm output power and 38nm bandwidth of 1566～1604 nm where the ASE power intensity is higher than－16 dBm is obtained by selecting 1480 nm LD and heavily doped erbium fiber with optimized length simultaneously. The DP-BD ASE source has a pump conversion efficiency of 23.4% which is larger than that by double-pass forward(DPF) configuration of 11.8%.