Near-infrared ITO-based photonic hypercrystals with large angle-insensitive bandgaps.

The angle-sensitive photonic bandgap (PBG) is one of the typical features of one-dimensional photonic crystals. Based on the phase-variation compensation effect between the dielectric and hyperbolic metamaterials (HMMs), angle-insensitive PBGs can be realized in photonic hypercrystals. However, since hypercrystals are usually constructed using metal components, these angle-insensitive PBGs are mostly limited to narrow bandwidths in visible range. Here, we replace metal with indium tin oxide (ITO) to construct HMMs in the near-infrared range. In these ITO-based HMMs, we experimentally demonstrate the negative refraction of light in transverse magnetic polarization. With this HMM component, we realize a photonic hypercrystal with an angle-insensitive PBG in the wavelength range of 1.15-2.02 µm. These ITO-based hypercrystals with large angle-insensitive PBGs can find applications in near-infrared reflectors or filters.

Nonreciprocal Tamm plasmon absorber based on lossy epsilon-near-zero materials.

Contrary to conventional Tamm plasmon (TP) absorbers of which narrow absorptance peaks will shift toward short wavelengths (blueshift) as the incident angle increases for both transverse magnetic (TM) and transverse electric (TE) polarizations, here we theoretically and experimentally achieve nonreciprocal absorption in a planar photonic heterostructure composed of an isotropic epsilon-near-zero (ENZ) slab and a truncated photonic crystal for TM polarization. This exotic phenomenon results from the interplay between ENZ and material loss. And the boundary condition across the ENZ interface and the confinement effect provided by the TP can enhance the absorption in the ENZ slab greatly. As a result, a strong and nonreciprocal absorptance peak is observed experimentally with a maximum absorptance value of 93% in an angle range of 60∼70°. Moreover, this TP absorber shows strong angle-independence and polarization-dependence. As the characteristics above are not at a cost of extra nanopatterning, this structure is promising to offer a practical design in narrowband thermal emitter, highly sensitive biosensing, and nonreciprocal nonlinear optical devices.