Abstract

In recent high WDM capacity demonstrations, the addition of WDM channels in the S-band to the C-band and L-band channels was reported to improve considerably the total throughout of optical fiber.^1,2 In that perspective, the thulium-doped fiber amplifier (TDFA) is a promising candidate for allowing the use of this band by providing amplification with high efficiency. In a first step, the TDFA efficiency has been addressed with a single-wavelength up-conversion pump located near 1.05 µm.^3,4 The related gain band lies, in that case, around λ = 1.47 µm. Different techniques were proposed to enhance the power conversion efficiency of the amplifier and to shift the gain band towards higher wavelengths, where the attenuation of link fiber is lower. These methods can be classified into two main groups. The use of high-concentration thulium-doped fiber was shown as being a straightforward technique to shift the gain spectrum^5,6 and a power conversion efficiency of 42% has been reported with this technique.⁶ The second approach is the simultaneous launch into the doped fiber of two pump wavelengths.

© 2002 Optical Society of America