We first demonstrate that by inserting an appropriate long period grating in an Er-doped superfluorescent fiber source (SFS) of double-pass backward (DPB) configuration, the output spectrum can be broadened up to 40 nm. The characteristics of a long period grating (LPG) are then shown to have marked effects on the properties of the SFS. Both measured and simulated results agree well in the trend. The spectrum broadening using an LPG is shown effective over a large pump power range, especially for a single-humped DPB SFS. After the analysis of three types of output spectra, the tolerances of LPG's characteristics are found larger for a single-humped DPB SFS having the dominant band in 1558 nm.
C. D. Su and L. A. Wang, "Effect of Adding a Long Period Grating in a Double-Pass Backward Er-Doped Superfluorescent Fiber Source," J. Lightwave Technol. 17, 1896- (1999)