"Ray theory of graded non-circular optical fibres"@en . . . . "Abstract. Both bound and tunnelling rays exist in multimode graded fibres which do not have circular symmetry; however, the fraction of energy in the tunnelling rays is generally less than that in a similar circular fibre, especially for near-parabolic profiles. For a large class of non-symmetric profiles, no tunnelling rays can propagate."@en . . . "BF00620105" . . . "1979" . . . . .