Exceptional Points of Degeneracy in Coupled Chirowaveguides

Exceptional points of degeneracy are critical junctures wherein eigenvalues and eigenvectors coalesce, resulting in unique dispersion features. In coupled waveguides, they occur via co-directional or contra-directional coupling. The former requires gain-loss modulation, akin to $\mathcal{P} \mathcal{T}$-symmetric gratings, whilst the latter relies on negative phase velocity. We illustrate forks in modal dispersion arising due to negative refraction induced by giant chirality. Such an approach circumvents the manufacturing challenges of balancing photon creation and absorption, while not requiring simultaneous negativity of permittivity and permeability. Meta-media with giant and controllable chirality offer exciting opportunities for light manipulation.