S-band amplifier with variable gain tilt control

We present a method of variable gain tilt control for a thulium doped fiber amplifier (TDFA) using a mid-stage attenuator, together with measurements of the amplifier performance. The addition of tilt control allows S-band amplifiers to be used with a wide array of fibers and channel configurations since the effect of both Raman interactions and the O-H absorption peak can be compensated at installation. This is particularly important when adding amplifiers to an existing system, which may not be fully characterized in the S and S+ bands. The simplicity of using a variable attenuator to produce gain tilt, combined with the very short active-fiber lengths, allows manufacture at similar costs to erbium amplifiers.