Analysis of couplers composed of a fibre half-block with a slab overlay: effects of curvature of the fibre and asymmetry of the slab waveguide

Light coupling between a single-mode fibre half-block and a single-mode asymmetric slab waveguide is analysed theoretically using coupled-mode theory. In comparison with previous work where the fibre is straight or the slab waveguide is symmetric, the characteristics of coupling are distributed along the direction of light propagation and are strongly dependent not only on the relative values of the refractive indices of the fibre core and the slab, but also on the asymmetry of the slab waveguide, that is, the relative values of the refractive indices of the claddings on both sides of the slab.