Distributed gain in a Tm-doped silica fiber - experiment and modeling

This paper investigates for the first time the distributed gain of the silica-based thulium-doped fiber amplifiers (TDFA) using coherent optical frequency domain reflectometry (COFDR). Gain spectra and distributed gain are reported for the various pump schemes. Results show that the 805 nm pump has a more pronounced effect when added to 1050 nm than when added to 1426 nm, with a peak gain increase of 0.9 dB (~4% pump power increase gives -20% more gain). This paper also observes that for the 1426-nm upconversion pump, the 805-nm auxiliary pump resulted in a slight gain shift, increasing gain at longer wavelengths (>1470 nm) while reducing at lower wavelengths.