Abstract

Erbium-doped fibres suffer from quenching at high Er-concentrations [1, 2]. We have found that cryo-cooling to liquid-nitrogen temperature (LNT) substantially improves both the threshold and slope efficiency of a heavily doped, partly quenched, erbium-doped fibre laser (EDFL). The fibre is fabricated in-house by a heated-frit method, a technique suitable for gas-phase deposition of rare-earth doped fibre. It has an Er-concentration of ~8300 ppm (wt.) in a 10 µm diameter, 0.13 NA aluminosilicate core. It was characterised in a ring laser setup with an outcoupled signal of 3 dB. In the outcoupling we include the loss of an attenuator, two tap couplers, an extra isolator, and a connector pair inserted into the cavity for experimental convenience. The 1 m doped fibre was counter-pumped in the core at 1480 nm with negligible pump leakage. Figure 1 shows the resulting laser power at LNT and RT (room temperature), calculated as the difference between the circulating power after and before amplification in the EDF. The LNT case shows clear improvements in both threshold and slope efficiency, the latter reaching 38.6%. The emission wavelength shifts from 1592 nm at RT to1572 nm at LNT.

© 2011 Optical Society of America