Unidirectional wave propagation in media with complex principal axes
Physical Review A
American Physical Society
©2018 American Physical Society
In an anisotropic medium, the refractive index depends on the direction of propagation. Zero index in a fixed direction implies a stretching of the wave to uniformity along that axis, reducing the effective number of dimensions by 1. Here we investigate two-dimensional gyrotropic media where the refractive index is 0 in a complex valued direction, finding that the wave becomes an analytic function of a single complex variable z. For simply connected media this analyticity implies unidirectional propagation of electromagnetic waves, similar to the edge states that occur in photonic “topological insulators.” For a medium containing holes the propagation is no longer unidirectional. We illustrate the sensitivity of the field to the topology of the space using an exactly solvable example. To conclude we provide a generalization of transformation optics where a complex coordinate transformation can be used to relate ordinary anisotropic media to the recently highlighted gyrotropic ones supporting one-way edge states.
The author acknowledges financial support from Royal SocietyTATAUniversity Research FellowshipNo. RPG-2016- 186. He is very grateful for the suggestions of C. G. King and T. G. Philbin.
This is the author accepted manuscript. The final version is available from American Physical Society via the DOI in this record.
Vol. 97 (2), 023834