Based on an integrated array of refractory titanium nitride (TiN), a metasurface perfect absorber (MPA) in the visible-to-near infrared (NIR) band is reported. The systematic and detailed simulation study of the absorption of the MPA is performed with the finite-different time-domain (FDTD) method. Tailoring the structure, the MPA realizes as high an average as 99.6% broadband absorption, ranging from 400 nm to 1500 nm. The broadband perfect absorption can be attributed to localized surface plasmonic resonance (LSPR), excited by the continuous diameter evolution from the apex to the base of the nanocone, and the gap plasmons excited among the nanocones, as well as in the spacer layer at longer wavelengths. Particularly, the coupling of the resonances is essentially behind the broadening of the absorption spectrum. We also evaluated the electric field intensity and polarization-dependence of the nanocone MPA to offer further physical insight into light trapping capability. The MPA shows about 90% average absorption even at an oblique incidence up to 50°, which improves the acceptance capability of light-harvesting system applications. This unique design with the TiN nanocone array/aluminium oxide (Al₂O₃)/TiN structure shows potential in imminent applications in light trapping and thermophotovoltaics.

In this paper, a thin metasurface perfect absorber based on refractory titanium nitride (TiN) is proposed. The size parameter of the metasurface is investigated based on the finite difference time domain method and transfer matrix method. With only a 15-nm-thick TiN layer inside the silica/TiN/silica stacks standing on the TiN substrate, the near-perfect absorption throughout the visible regime is realized. The cross-talk between the upper and lower dielectric layers enables the broadening of the absorption peak. After patterning the thin film into a nanodisk array, the resonances from the nanodisk array emerge to broaden the high absorption bandwidth. As a result, the proposed metasurface achieves perfect absorption in the waveband from 400 to 2000 nm with an average absorption of 95% and polarization-insensitivity under the normal incidence. The proposed metasurface maintains average absorbance of 90% up to 50-degree oblique incidence for unpolarized light. Our work shows promising potential in the application of solar energy harvesting and other applications requiring refractory metasurfaces.

To circumvent the hindrance to broad practical applications associated with uses of highly lossy metals in plasmonics, electrostatic modification-based low-loss structures are conceived and demonstrated in supporting surface plasmon polaritions (SPPs). Pairing a highly polar ${\mathrm{LiNbO}}_3$ (LN) slab with a nonpolar indium-tin-oxide (ITO) thin film, a subnanometer ITO layer was modified into visible SPPs supportive owing to electrostatic screening; yet a theoretical treatment of a sandwiched structure with a sub-nanometer interlayer and an anisotropic substrate is still missing. In this Letter, a hybridized SPP supporting picture was drawn in the ITO/LN system, which agrees well with the 2D diffraction patterns observed out of phase gratings written with two coherent laser beams either of pure-extraordinary, pure-ordinary, or mixed polarizations. This platform of ITO/LN is promising in designing hybridized SPP-based devices in which the parasitic scattering of surface waves may be suppressed greatly.

In this paper, we report a polarization-independent broadband metasurface perfect absorber based on tunable gap magnetic resonance and Fabry–Perot (FP) resonance in a structure with consecutive size variation. By using the finite-difference time-domain method, the effects of size parameters are investigated. Due to the coexistence of the FP-like resonance and gap magnetic resonance, the near-unit absorption reaches as high as 99.46% with nanocone morphology throughout the visible-to-near infrared regime where most solar radiation is located. The structure raised in this paper is less complex and more thermally stable due to abandoning the spacer layer in traditional tri-layer structures. This method can be developed for other refractory materials and has great potential in solar energy related optoelectronics applications.

Two dimensional electron gases (2DEGs) formed at interfaces between two oxides have been drawing growing attention for their intriguing magnetic, superconducting, and optical properties. Remarkable anisotropic transmission was observed from an indium-tin-oxide (ITO) coated lithium niobate (LN) slab, implying that a 2DEG is formed at one of the ITO/LN interfaces, and this is seemingly behind the anisotropic transmission. To optically probe 2DEG formation at one of the ITO/LN interfaces, the first reflected beam was monitored with one (two) laser beam(s). Reflective dynamics as large as 5%-15% were observed, pointing unambiguously to a subwavelength coupling and corresponding to, conservatively, exponential gain coefficients of −26 800 to +2700 cm⁻¹ with half a wavelength as the coupling range. All observations are far beyond the reach of conventional bulk photorefractive effects, but align well with a picture of surface plasmon polariton excitation based on 2DEG formation. The 2DEG proximal to the LN substrate is a promising candidate for designing nonlinear plasmonics based nanometric waveguides, rectifiers, modulators, and sensors, which are compatible with current photonic circuits.

Dynamic optical structural color is always desired in various display applications and usually involves active materials. Full-color generation, especially bi-directional full-color generation in both reflective and transmissive modes, without any active materials included, has rarely been investigated. Herein, we demonstrate a scheme of bi-directional full-color generation based on a plasmonic metasurface modulated by the rotation of the polarization angle of the incident light without varying the geometry and the optical properties of the materials and the environment where the metasurface resides. The metasurface unit cell consists of plasmonic modules aligning in three directions and is patterned in a square array. The metasurface structural color device is numerically confirmed to generate full colors in both reflection and transmission. Based on the proposed polarization-dependent structural color, the information encoding process is demonstrated for three multiplexed animal images and quick-responsive (QR) codes to verify the efficient information encoding and decoding of the proposed scheme. In the simulation, the animals can be seen under different polarization incidences, and the QR codes can be successfully decoded by the polarization rotation in transmission. The proposed bi-directional full-color generation metasurface has great potential in applications such as kaleidoscope generation, anti-counterfeiting, dynamic color display, and optical information encoding.