A linewidth broadening and high efficiency erbium-doped superfluorescent fiber source (SFS) by using the cascaded dual-backward pumped configuration is proposed. The effects of fiber length arrangement and pump power ratio on the output characteristics of the L-band SFS are investigated by simulation. The simulational results show that the linewidth broadening L-band SFS can be achieved by the proposed design.The spectral linewidth is over 15 nm broader compared with the conventional L-band SFS, up to 60 nm. Further more, the design gives the highest pump efficiency at pump power ratio of 0.5. An L-band SFS of 62 mW output power, 30.1% pump efficiency and 56.6 nm linewidth is experimentally achieved with 206 mW pump power of a 980 nm LD.