Transition and pure bending losses in multimode and single-mode bent optical fibres

The total radiation losses from both multimode and single-mode bent slabs are quantified on the basis of ray theory. These losses are divided, for infinitely thick cladding, into transition and pure bending losses. Approximate numerical and analytic results are derived for the transition losses, which are due to refraction over the initial part of the bend. Bending losses, in contrast, are mainly due to tunnelling, and become dominant at large bend angles. Experimental confirmation is provided for multimode and single-mode fibres