Experimental and numerical investigations on asymmetric fused fibre couplers consisting of different single-mode fibres

Fused fibre couplers (FFCs) are essential components in fibre-based laser and amplifier systems for combining the pump and signal wavelengths into one fibre. Typically, identical fibres are employed in FFCs, which limits the combinable wavelengths to above the cutoff of the fibre. An approach for coupling two widely separated wavelengths is the use of different fibres with single mode guidance for the respective wavelength [1]. Due to the asymmetry introduced by the different fibres a special technique is necessary, for example pre-tapering one fibre before coupler fabrication, in order to achieve a high coupling ratio.