Elliptical normal modes and stop band reconfiguration in multimode birefringent one-dimensional magnetophotonic crystals

Abstract

This study examines photonic stop band reconfiguration upon magnetization reversal in multimode elliptically birefringent Bragg filter waveguides. Magnetization reversal in longitudinally magnetized magneto-optic waveguides affects the character of the local orthogonal elliptically polarized normal modes, impacting the filter's stop band configuration. Unlike the standard case of circular birefringence in magneto-optic media, opposite helicity states do not transform into each other upon magnetization reversal for a given propagation direction. Rather, helicity reversals yield new and different normal modes with perpendicularly oriented semimajor axes, corresponding to a north-south mirror reflection through the equatorial plane of the Poincar\'e sphere. For asymmetric contradirectional coupling between different-order waveguide modes in multimode magnetophotonic crystals, this symmetry breaking, namely, the obliteration of normal modes upon magnetization reversal, allows for strongly reconfigured stop bands, through the hybridization of the elliptically polarized states. The effect of Bloch mode reconfiguration on the stop band spectral profile contributes to the magnetic response of the filter. In such elliptically birefringent media, input polarization helicity reversal also becomes a powerful tool for optical transmittance control. Both magnetization and helicity reversals can thus serve as useful tools for the fabrication of on-chip magnetophotonic crystal switches.