Yurui Qu

Broadband optical absorption based on single-sized metal-dielectric-metal plasmonic nanostructures with high-ε″ metals

We propose a broadband, efficient, ultra-thin metal-insulator-metal (MIM) absorber with a simple single-sized disk configuration by utilizing metals with high imaginary part of permittivity (e″). The physics behind this is that field dissipation is remarkably enhanced in MIM absorbers with high-e″ metals, significantly extending the absorption bandwidths, which are conventionally limited by magnetic resonances of MIM absorbers with low-e″ metals. The experimentally demonstrated MIM absorber based on tungsten with high-e″ yields broadband absorption from visible to near-infrared range (400–1700 nm) with an average measured absorption of 84%. The ultra-thin and single-sized nanostructure with broadband efficient absorption facilitates the scalability to large-area photonic applications.

Thermal camouflage based on the phase-changing material GST

Camouflage technology has attracted growing interest for many thermal applications. Previous experimental demonstrations of thermal camouflage technology have not adequately explored the ability to continuously camouflage objects either at varying background temperatures or for wide observation angles. In this study, a thermal camouflage device incorporating the phase-changing material Ge2Sb2Te5 (GST) is experimentally demonstrated. It has been shown that near-perfect thermal camouflage can be continuously achieved for background temperatures ranging from 30 °C to 50 °C by tuning the emissivity of the device, which is attained by controlling the GST phase change. The thermal camouflage is robust when the observation angle is changed from 0° to 60°. This demonstration paves the way toward dynamic thermal emission control both within the scientific field and for practical applications in thermal information.Thermal camouflage: hidden in hot or coldThermal camouflage surfaces developed by Chinese researchers can be tailored to hide objects in front of different backgrounds. Traditional thermal camouflage comprises low-emissivity cloaks that lower the apparent temperature of vehicles or people to match their surroundings; however, objects can only be well-hidden when the background is one particular temperature. Qiang Li and co-workers at Zhejiang University in Hangzhou deposited a germanium-antimony-tellurium alloy onto gold film, before thermally annealing their samples at 200 °C. By varying the annealing time, the researchers prepared samples that were completely amorphous (randomly structured), completely crystalline (ordered), or intermediate states between the two. They found that the more crystalline samples had higher apparent temperatures, meaning the surfaces could be tailored to work at a range of background temperature. As well as benefitting military, such technology could allow better heat management during space travel.

Photothermal Switching Based on Silicon Mach-Zehnder Interferometer Integrated with Light Absorber

We present an all-optical switch based on photothermal effects in a silicon Mach-Zehnder interferometer (MZI) integrated with a light absorber. The metal-insulator-metal light absorber located near the longer arm of the asymmetric MZI efficiently converts infrared light to heat. Pumped by a continuous-wave 1064-nm laser, the spectral transmittance of the fully etched strip waveguide (half-etched rib waveguide) MZI can be tuned with an efficiency of 38 pm/mW (98.5 pm/mW). Dynamic switching experiments show that the rise/fall time constant of the output probe light is 11.45/10.98 μs (8.25/7.13 μs) for the fully etched (half-etched) MZI.

Enhanced Second Harmonic Generation in AU/AI2O3/AU absorber

A kind of metal-insulator-metal (MIM) metamaterial absorber for generating second harmonic signal is investigated. The absorbers exhibit high absorption efficiency at the dip and notably enhance the generated second harmonic signal by a factor of over 30, in contrast to an Au/alumina double-layer without Au disk on the top. This study demonstrates the potential of metamaterial absorber for nonlinear photonics.

Tunable dual-band thermal emitter consisting of single-sized phase-changing GST nanodisks

Thermal emission control has been attracting increased attention in both fundamental science and many applications including infrared sensing, radiative cooling and thermophotovoltaics. In this paper, a tunable dual-band thermal emitter including phase-changing material Ge2Sb2Te5 (GST) is experimentally demonstrated. Two emission peak wavelengths are at 7.36 μm and 5.40 μm at amorphous phase, and can be continuously tuned to 10.01 μm and 7.56 μm while GST is tuned to crystalline phase. Compared with other dual-band metamaterial emitters, this tunable dual-band thermal emitter is only composed of an array of single-sized GST nanodisks (on a gold film), which can greatly simplify the design and manufacturing process, and pave the way towards dynamical thermal emission control.

Chip-Scale Plasmonic Sum Frequency Generation

Plasmonics provides a promising candidate for nonlinear optical interactions because of its ability to enable extreme light concentration at the nanoscale. We demonstrate on-chip plasmonic sum frequency generation (SFG) with a metal—dielectric–metal nanostructure. The two cross-polarized pumps (800 and 1500 nm) are designed to match the two resonances of this plasmonic nanostructure to make the most of the electric field enhancement and spatial overlapping of the modes. Since these two resonances are predominantly determined by the sizes of the top metallic nanostructures in the same direction, the SFG (521 nm) can be independently controlled by each pump via changing these sizes. This study exerts the full strength of plasmonic resonance induced field enhancement, thereby paving a way toward using nanoplasmonics for future nonlinear nanophotonics applications, such as optical information processing, imaging, and spectroscopy.