All-fibre single-mode small-signal amplifier operating near 0.976 μm

We have developed and demonstrated a polarisation-maintaining single-mode ytterbium-doped fibre for light amplification at a wavelength near 0.976 μm in an all-fibre configuration. A distinctive feature of the proposed fibre design is low losses due to fusion splices with standard single-mode fibre having a core diameter of 10 μm, which has made it possible to produce an all-fibre small-signal amplifier with a gain threshold near 3 W and a differential pump-to-signal conversion efficiency of 9.8 % in the saturation regime. The proposed amplifier has been shown to be well-suited for small-signal amplification. In particular, at an input signal power near 1 mW and a gain of 20 dB, the ratio of the amplified signal to the integrated luminescence intensity near 0.976 μm exceeds 20 dB. A 40-dB gain has been demonstrated for an ultrasmall signal of ∼10-μW power.