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Topological edge state, a unique mode for manipulating electromagnetic waves (EMs), has been extensively studied in both fundamental and applied physics. Up to now, the work on topological edge states has focused on manipulating linearly polarized waves. Here, we realize chirality-dependent topological edge states in one-dimensional photonic crystals (1DPCs) to manipulate circularly polarized waves. By introducing the magneto-electric coupling term (chirality), the degeneracy Dirac point (DP) is opened in PCs with symmetric unit cells. The topological properties of the upper and lower bands are different in the cases of left circularly polarized (LCP) and right circularly polarized (RCP) waves by calculating the Zak phase. Moreover, mapping explicitly 1D Maxwell's equations to the Dirac equation, we demonstrate that the introduction of chirality can lead to different topological properties of bandgaps for RCP and LCP waves. Based on this chirality-dependent topology, we can further realize chirality-dependent topological edge states in photonic heterostructures composed of two kinds of PCs. Finally, we propose a realistic structure for the chirality-dependent topological edge states by placing metallic helixes in host media. Our work provides a method for manipulating topological edge states for circularly polarized waves, which has a broad range of potential applications in designing optical devices including polarizers, filters, and sensors with robustness against disorder.

Edge states in photonic heterostructures composed of metal layers and all-dielectric one-dimensional photonic crystals (1DPCs) will shift toward short wavelengths (blueshift) with the increase in the incident angle for both transverses magnetic (TM) and transverse electric (TE) polarizations. However, we achieve redshift edge states for TM polarization and blueshift edge states for TE polarization in heterostructures composed of metal layers and 1DPCs containing layered hyperbolic metamaterials. Owing to the opposite wavelength shift of the edge states for two orthogonal polarizations, the ellipsometric phase will change dramatically around the edge state wavelength in a broad angle range. Based on this wide-angle phase singularity property, we propose a biosensor which can work with high refractive index resolution in a broad angle range.

Quasiperiodic structures have recently been found to possess salient topological properties. In this Letter, we theoretically and experimentally demonstrate the topological edge states in a quasiperiodic Harper chain composed of split-ring resonators. In a finite-size Harper chain, we find that there is always a pair of edge states in the bandgaps, independent of the number of the resonators. Different from the topological edge states localized at both ends of a periodic chain, this pair of edge states is selectively localized at the left or right end of the quasiperiodic chain at different frequencies. These paired-edge states with asymmetric field distribution can be used for unidirectional propagation. Our results not only provide a versatile platform to study the topological physics beyond the periodic structures but also may be useful in some applications such as selective unidirectional power transfer.

One of the fascinating topological phenomena is the edge state in one-dimensional system. In this work, the topological photonics in the dimer chains composed by the split ring resonators are revealed based on the Su-Schrieffer-Heeger model. The topologically protected photonic edge state is observed directly with the in situ measurements of the local density of states in the topological nontrivial chain. Moreover, we experimentally demonstrate that the edge state localized at both ends is robust against a varied of perturbations, such as losses and disorder. Our results not only provide a versatile platform to study the topological physics in photonics but also may have potential applications in the robust power transfer.

Near-field coupling is a fundamental physical effect, which plays an important role in the establishment of classical analog of electromagnetically induced transparency (EIT). However, in a normal environment the coupling length between the bright and dark artificial atoms is very short and far less than one wavelength, owing to the exponentially decaying property of near fields. In this work, we report the realization of a long range EIT, by using a hyperbolic metamaterial (HMM) which can convert the near fields into high-k propagating waves to overcome the problem of weak coupling at long distance. Both simulation and experiment show that the coupling length can be enhanced by nearly two orders of magnitude with the aid of a HMM. This long range EIT might be very useful in a variety of applications including sensors, detectors, switch, long-range energy transfer, etc.

The generation and control of valley pseudospin currents are the core of valleytronics. Here, the photonic analogy for generation and control of valley pseudospin currents using the pseudomagnetic fields induced in strained graphene is investigated in a microwave regime. In photonic graphene with uniaxial distortion, photons in two different valleys experience pseudomagnetic fields with opposite signs, and valley-dependent propagations in bended paths are observed. The external-field-free photonic transportation behavior may be very useful in controlling the flow of light in future valley-polarized devices.