Ultra-broadband spatial light modulation with dual-resonance coupled epsilon-near-zero materials

It has been found that the dielectric constants of transparent conductive oxides(TCOs)can be adjusted in an extremely large range by tuning the carrier density.Due to the remarkable light confinement property of the epsilon-near-zero(ENZ)effect of TCOs,it has attracted extensive interests of light modulation.However,the operation wavelength bandwidth is usually limited by optical resonance that is applied to enhance the light-TCOs interaction.In this work,a dual-resonance light coupling scheme is proposed to expand the modulation depth-bandwidth product with almost one order-of-magnitude improvement.In a metallic subwavelength grating structure with deep trenches backed by a ground plane,the ENZ mode can be coupled to both magnetic resonance and Fabry-Perot resonance respectively by tuning the bias.Decent light modulation can be obtained in a large operation wavelength band covering two resonances by optimizing the dual-resonance configuration.Such a reconfigurable efficient broadband modulation is important for robust communication link and possesses remarkable capacity for wavelength division multiplexing.

Titanium-nitride-based integrated plasmonic absorber/emitter for solar thermophotovoltaic application

Titanium nitride(TiN) as a refractory plasmonic material is proposed to be used as an angle-insensitive integrated broadband solar absorber and narrowband near-infrared(NIR) emitter for solar thermo-photovoltaic(STPV) application. By constructing TiN-nanopatterns/dielectric/TiN stack metamaterial, approximately 93% light absorption in a wavelength range of 0.3–0.9 μm and near unit narrowband(Δλ∕λ～0.3) emission in NIR(～2 μm) were demonstrated by numerical simulation. Keeping the excellent light absorption in the visible band, the emission wavelength can be easily tuned by patterning the top TiN layer into various subwavelength structures. This dual function attributes to the intrinsic absorption and plasmonic property of TiN. In such an integrated structure,broadband absorption and narrowband emission need to be balanced for an optimized power efficiency conversion. Detailed analysis has demonstrated that the STPV system based on this integrated absorber/emitter canexceed the Shockley–Queisser limit at 1000 K.