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.

Quasiperiodic metamaterials empowered non-metallic broadband optical absorbers.

Realizing a polarization-insensitive broadband optical absorber plays a key role in the implementation of microstructure optoelectrical devices with on-demand functionalities. However, the challenge is that most of these devices involve the constituent metals, thus suffering from poor chemical and thermal stability and a complicated manufacturing process. In addition, the extreme contrast between the negative (metallic) and positive (dielectric) real parts of the constituent permittivities can cause additional problems in the design of structural devices. Based on these facts, this work proposes a design of planar broadband one-dimensional structure based on Fibonacci geometry. Experimental results show that the proposed planar structure exhibits high absorptivity behavior independent of polarization and angle in the wavelength range of 300-1000 nm. The absorptivity remains more than 80% when the incident angle is 60°. This proof-of-concept represents a new strategy for realizing non-metallic broadband optical absorbers with advantages of polarization-independence, low-cost, and wide-field-of-view and paves the way for light manipulation under harsh conditions.

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.

Enhanced Diffuse Reflectance and Microstructure Properties of Hybrid Titanium Dioxide Nanocomposite Coating.

In this research, we studied enhanced diffuse reflectance that can be achieved by excitations of multiple-scattering in a hybrid micro-structured titanium dioxide coating. Conventional approaches to obtain diffuse reflection structure rely heavily on exciting the scattering of randomly textured surface, whereas here, we reveal numerically and experimentally that, besides interface scattering, bulk scattering of ordered-disordered hybrid structure can be also employed to obtain highly efficient diffuse reflector. The diffuse reflectance over the measured wavelength region increases significantly with thickness, while angle and polarization-dependent specular reflections are suppressed. These results show the potential to be used as a highly efficient diffuse reflector or for applications in various advanced fields of photonics related to light extractions and diffusers.