Highly robust anisotropic zero refraction effects in semi-Dirac photonic crystals

Area of Science:

• Photonics
• Materials Science
• Condensed Matter Physics

Background:

• Epsilon-and-mu-near-zero (EMNZ) waveguides based on photonic crystals (PCs) offer ultra-low loss but are limited by high sensitivity to parameter variations.
• Anisotropic EMNZ effects are particularly prone to degeneration due to accidental semi-Dirac points, restricting practical applications.

Purpose of the Study:

• To report highly robust anisotropic zero refraction effects in novel two-dimensional symmetry-reduced PCs.
• To investigate the stability and tunability of EMNZ properties in these new structures.

Main Methods:

• Investigated two types of two-dimensional symmetry-reduced PCs: square-lattice with elliptical air holes and rectangular-lattice with circular air holes.
• Analyzed the emergence of semi-Dirac cones at the Brillouin zone center in C2-symmetric PCs.
• Examined the performance across a wide variation range of the background refractive index.

Main Results:

• Achieved robust anisotropic zero refraction and epsilon-and-mu-near-zero (EMNZ) behavior in C2-symmetric PCs.
• Demonstrated stable performance resembling EMNZ or impedance-mismatched materials in two perpendicular directions.
• Showcased consistent anisotropic EMNZ and zero-phase optical transmission over a wide background refractive index variation, with tunable working frequency.

Conclusions:

• Symmetry-reduced PCs provide a pathway to overcome the limitations of accidental zero refraction effects in photonic crystals.
• The reported structures exhibit robust anisotropic EMNZ properties with tunable frequencies, contrasting with single-frequency limitations of previous designs.