Mode symmetry in microstructured fibres revisited.

Motivated by the recent development of hollow-core, microstructured optical fibres without a translationally-periodic cladding structure, an analysis of the symmetry-induced properties of the modes of a uniform fibre with CM point group symmetry is presented. Modes are classified according to the irreducible representations of the longitudinal components of the electric and magnetic fields; the radial component of the electric field and azimuthal component of the magnetic field share the symmetry of the longitudinal component of the electric field, while the radial component of the magnetic field and the azimuthal component of the electric field have the same symmetry as the longitudinal magnetic field. The symmetry class of the lowest order modes in fibres with point group CM with M from 1 to 10 is given. The work is closely related to previous analyses, but clarifies the symmetry relationship between the two orthogonal modes in a degenerate pair and how the different symmetries of the longitudinal electric and magnetic field components emerge from the governing equations.