Study of Non-reciprocal Dichroism in Photonic Structures

Non-reciprocal phenomena are widely used in photonic devices. Important applications such as isolators and circulator waveguide structures depend on non-reciprocal effects. The basis of these phenomena is a difference in phase or refractive index for an electromagnetic wave of a given polarization as it travels through a medium in opposite directions. Generally this applies to the real part of the refractive index. The present report addresses a less studied phenomenon in non-reciprocal propagation, namely differences in optical absorption loss for a given polarization state in opposite propagation directions, a phenomenon we have termed non-reciprocal dichroism. Nonreciprocal dichroism can be defined as a difference in absorption between two opposite directions of wave traversal. In this report, we attempt to study the non-reciprocal dichroism in transversely magnetized optical waveguides. Further, we investigate the existence of frozen modes in waveguide structures. Such modes can give rise to conditions wherein a wave has neither velocity nor acceleration, and thus can be thought of as “frozen” in a medium. In the presence of absorption loss, this leads to large absorption levels and can be considered as an extreme case of non-reciprocal dichroism. Abbreviations TE : Transverse Electric TM : TransverseMagnetic