Page 411 - Fiber Bragg Gratings

388 Chapter 8 Fiber Grating Lasers and Amplifiers

Figure 8.26: Radiation loss spectrum of eight STG filters written at an exter-
nal blaze angle of 8° in a fiber with a core diameter of —12 microns [122].

The use of multiple STG filters allows tailoring complex gain spectra
with a greater degree of accuracy. The peak deviation over 3 dB from a
fixed gain of 13.7 dB across the bandwidth of the amplifier is conveniently
reduced to ±0.3 dB by the use of in-line STGs [122] and is shown in
Fig. 8.27. The required loss spectrum is deconvolved into a number of
contributions from individual gratings, prior to fabrication of the filter.

Figure 8.27: The ASE spectrum of a saturated erbium amplifier without and
with a composite STG gain equalizing filter [122].