Asymmetric taper scrambler for improved pump homogeneity and absorption in side-pumped double-clad fibre lasers
Abstract
A multimode optical fiber scrambler (MOFS) based on an asymmetric taper is demonstrated. The MOFS contains an adiabatic down-taper transition and an abrupt up-taper transition made into a double cladding fiber. This device improves the pump power absorption by two principal effects which adapt the side-coupled cladding light. The first one is to homogenize the ring-shaped light distribution from a side pump combiner before being launched into an active double-clad fiber. Secondly, provided the conservation of etendue, the low NA of that multimode beam is transformed during its propagation through the longer taper transition of the MOFS device. Then, a net NA increment occurs, so that it fills the full input NA of this fiber at the taper waist. The up-taper transition is non-adiabatic for the multimode beam so that it exits from the taper with the transformed NA. The MOFS was inserted into a >200 W fiber laser cavity and significantly improved the effective pump absorption from 0.6 dB m-1 to 1.8 dB m-1.
- Publication:
-
Laser Physics Letters
- Pub Date:
- August 2019
- DOI:
- 10.1088/1612-202X/ab2805
- Bibcode:
- 2019LaPhL..16h5105T
- Keywords:
-
- optical fibre;
- tapered fibre;
- fibre laser