Bimodal fibre coupler for spectral filtering and dispersion compensation

Abstract

A directional coupler made of step-index single-mode and dual-mode fibres and operating based on coupling of power between LP₀₁ and LP₁₁ modes is proposed for applications as narrowband spectral filter and as mode converter. With appropriate choice of parameters, couplers are designed such that the LP₀₁ mode of the single-mode fibre is phase matched with the LP₁₁ mode of the dual-mode fibre at a desired wavelength, allowing significant exchange of power between these two modes. Transmission properties of the coupler are investigated using the coupled-mode theory of parallel dielectric waveguides. Design data and spectral characteristics for two cases corresponding to peak transfer of power at 1 · 33 μm and 1 · 55 μm wavelengths are presented. Applications of the proposed coupler in wavelength division multiplexing and dispersion compensation are addressed.