Tunable wavelength-selective asymmetrical single-mode fibre directional couplers with an intermediate layer

Abstract

The power-transfer function of asymmetrical directional couplers consisting of two polished single-mode fibres with different core diameters and refractive-index differences has a band-pass behaviour over the wavelength. The fixed centre wavelength of the bandpass is determined by the fibre parameters only. Theoretical calculations show that, by inserting an intermediate dielectric layer with suitable thickness and shape between the fibres, the centre wavelength can be shifted easily over a range of ±30 nm. Experimental results are in good agreement with theory.