A team from Universidade Federal de Pernambuco in Recife, Brazil, CETUC-PUC Rio in Rio de Janeiro, Brazil, and Acreo AB in Stockholm, Sweden, presented its findings on a dual-wavelength pumping technique for Tm:fiber amplifiers in the February issue of IEEE Photonics Technology Letters. Using optical frequency domain reflectometry, the group also examined the effects of fiber length on gain.

The pumping scheme featured an Yb:fiber laser emitting at 1050 nm in the forward direction and a Ti:sapphire at approximately 800 nm in the backward direction to depopulate the lower laser level and to directly populate the upper level, respectively, which boosted the population inversion. In tests with a 15-m fiber amplifier, 180 mW of total pump power produced a small-signal gain of 27 dB. Reflectometry data taken on an 18-m amplifier indicated that a 16-m length would be sufficient for the same performance in the counterpropagation configuration.