Numerical investigations of off-resonant pumped Er3+:Yb3+-codoped fibre amplifiers

Abstract

Single-frequency Er3+:Yb3+-codoped fibre amplifiers in MOPA configuration are promising candidates to fulfil the challenging requirements of laser sources operating at 1.5 μm for the third generation of interferometric gravitational wave detectors (GWDs) [1]. However, their output power is limited by amplified spontaneous emission (ASE) of the Yb3+ ions between 1.0 μm and 1.1 μm and stimulated Brillouin scattering (SBS). Recently, it has been shown that the Yb3+-ASE can be significantly supressed by pumping the amplifier off-resonant at around 940 nm [2]. The low absorption cross-section prevents the bottlenecking of the Yb3+-to-Er3+ energy transfer process, which is responsible for the generation of excessive Yb3+-ASE. However, the lower absorption cross-section also requires a longer total fibre length to ensure sufficient pump light absorption, hence lowering the SBS threshold and making this approach less attractive.