Comparison of distributed gain in 800 nm+1050 nm or 800 nm+1410 nm pumping schemes for thulium-doped fiber amplifiers using optical frequency domain reflectometry

Distributed gain in thulium-doped fiber amplifiers using 800 nm+1050 nm or 800 nm+1410 nm pumps was studied. We show that the former is advantageous over the later primarily due to ground state absorption.