Through studying the basic principle of super-fluorescent fiber source and combining with internal and external gain flattening technique, the spectral flatness of erbium-doped fiber amplified spontaneous emission (ASE) source with two-stage double-pass configuration pumped by two laser diodes (LDs) is improved. By optimizing the lengths of two-stage erbium-doped fiber (EDF) and adjusting the pump power of two LDs,the powers of C-band and L-band are matching, and the spectral flatness is superior to 0.5dBm from 1535 to 1610 nm. Utilizing the long period fiber grating (LPFG)-based thermally-insensitive gain flattening filter (GFF) fabricated by ourselves, the spectral protrusion is flattened near the peak of absorption wavelength of EDF, which make the spectrum not only cover the range of C-band and L-band, also realize the spectral flatness is better than 0.8dBm in the range of 3dB bandwidth. Application of the fiber ASE source in fiber Bragg grating sensing system could decrease the multi-signal peak power imbalance.
