TRANSFER OF ORBITAL ANGULAR-MOMENTUM FROM A STRESSED FIBEROPTIC WAVE-GUIDE TO A LIGHT-BEAM

A stressed fiber-optic waveguide is used to impart orbital angular mom entum to a Hermite-Gaussian (HG(10)) laser mode. The transmitted beam has an annular intensity profile and a well-defined azimuthal phase de pendence. We confirm the phase structure of the beam by observing the interference pattern produced between it and a plane wave. The transfe r of the angular momentum to the light occurs because of a difference in phase velocity within the fiber for two orthogonal modes that compr ise the input beam. This represents a mechanism for the transfer of or bital angular momentum to a light beam that has not hitherto been iden tified. (C) 1998 Optical Society of America.