Observation of valley-dependent beams in photonic graphene

Abstract

Valley-dependent propagation of light in an artificial photonic hexagonal lattice, akin to electrons in graphene, is investigated in microwave regime. Both numerical and experimental results show that the valley degeneracy in the photonic graphene is broken when the frequency is away from the Dirac point. The peculiar anisotropic wave transport property due to distinct valleys is analyzed using the equifrequency contours. More interestingly, the valley-dependent self-collimation and beam splitting phenomena are experimentally demonstrated with the armchair and zigzag interfaces, respectively. Our results confirm that there are two inequivalent Dirac points that lead to two distinct valleys in photonic graphene, which could be used to control the flow of light and might be used to carry information in valley polarized beam splitter, collimator or guiding device.

Topological Valley Transport in Two-dimensional Honeycomb Photonic Crystals

“…Such properties give us methods to determine the excited valley state. Valley-dependent bulk excitation and wave transport were reported based on the distinct iso-frequency contour shapes at different frequencies 36 , 37 . Here we introduce a different mechanism.…”

“…The upward propagation Φ I II mode is which carries the positive orbital angular momentum and thus can be effectively excited by a source with m = 1 optical vortex index. Similar sources were used to experimentally excite topological valley interface states 30 , 37 . We perform the finite-element simulations to visualize the topological interface states.…”

Narrow electromagnetic beam transmission associated to the Dirac cones in a graphenelike photonic crystal

“…This provides an alternative way for wave propagation control and beam manipulation. Studies on K-valley dependent EM beam propagation, associated to the lower Dirac cones in dielectric photonic crystals [5,16] and to the upper cones in analogous situations of electron beams in atomic graphenes [17,18], are both carried out. Beam splitting and self-collimation are obtained for the zigzag and armchair edge incidences.…”

Dispersion tuning and route reconfiguration of acoustic waves in valley topological phononic crystals

“…T opological materials that exhibit a valley degree of freedom (DOF) enable a way to transport information and energy [1][2][3][4][5][6][7][8][9][10][11] and are attracting a growing interest in condensed matter physics 6 . Recently, the concept of valley topological phases has been extended to classical bosonic systems, inspiring various ways of manipulating classical waves using periodic structures, such as electromagnetic waves with photonic crystals [12][13][14][15][16][17][18] or acoustic/elastic waves with phononic crystals (PCs) [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . The valley Hall phases for classical waves are generally realized by creating a periodic lattice that breaks a mirror [19][20][21][22][23] or inversion [25][26][27][28][29][30][31] symmetry of a two-dimensi...…”