Determination of mode conversion coefficients in optical fibres

Abstract

A simple method has been devised for the experimental determination of mode conversion coefficients in multimode fibers and involves only the observation of the far-field output as the angle of incidence of a collimated input beam is changed. The normalized mode coupling coefficient in a liquid-core fiber is D = 3 x 10-6 rad2 / m and increases by as much as a factor of 10 when transverse pressure is applied. Values some 2 orders of magnitude larger are found in glass-core fibers. There is good agreement between the theory presented and experiment