5 research outputs found
Temperature Invariant Metasurfaces
Thermal effects are well known to influence the electronic and optical properties of materials through several physical mechanisms and are the basis for various optoelectronic devices. The thermo-optic (TO) effect - the refractive index variation with temperature (dn/dT), is one of the common mechanisms used for tunable optical devices, including integrated optical components, metasurfaces and nano-antennas. However, when a static and fixed operation is required, i.e., temperature invariant performance - this effect becomes a drawback and may lead to undesirable behavior through drifting of the resonance frequency, amplitude, or phase, as the operating temperature varies over time. In this work, we present a systematic approach to mitigate thermally induced optical fluctuations in nanophotonic devices. By using hybrid subwavelength resonators composed from two materials with opposite TO dispersions (dn/dT0), we are able to compensate for TO shifts and engineer meta-atoms and metasurfaces with zero effective TO coefficient (dn/dT~0). We demonstrate temperature invariant resonant frequency, amplitude, and phase response in meta-atoms and metasurfaces operating across a wide temperature range and broad spectral band. Our results highlight a path towards temperature invariant nanophotonics, which can provide constant and stable optical response across a wide range of temperatures and be applied to a plethora of optoelectronic devices. Controlling the sign and magnitude of TO dispersion extends the capabilities of light manipulation and adds another layer to the toolbox of optical engineering in nanophotonic systems
Ultrawide Thermo-optic Tuning of PbTe Meta-Atoms
Subwavelength
Mie resonators have enabled new classes of optical
antenna and nanophotonic devices and can act as the basic meta-atom
constituents of low-loss dielectric metasurfaces. In any application,
tunable Mie resonances are key to achieving a dynamic and reconfigurable
operation. However, the active tuning of these nanoantennas is still
limited and usually results in sub-linewidth resonance tuning. Here,
we demonstrate the ultrawide dynamic tuning of PbTe Mie resonators
fabricated via both laser ablation and a novel solution-processing
approach. Taking advantage of the extremely large thermo-optic (TO)
coefficient and a high refractive index of PbTe, we demonstrate high-quality
factor Mie resonances that are tuned by several linewidths with temperature
modulations as small as Δ<i>T</i> ∼ 10 K. We
reveal that the origin for this exceptional tunability is due to an
increased TO coefficient of PbTe at low temperatures. When combined
into metasurface arrays, these effects can be exploited in ultranarrow
active notch filers and metasurface phase shifters that require only
a few kelvin modulation. These findings demonstrate the enabling potential
of PbTe as a versatile, solution-processable, and highly tunable nanophotonic
material that suggests new possibilities for meta-atom paints, coatings,
and 3D metamaterials fabrication
Widely Tunable Infrared Antennas Using Free Carrier Refraction
We
demonstrate tuning of infrared Mie resonances by varying the carrier
concentration in doped semiconductor antennas. We fabricate spherical
silicon and germanium particles of varying sizes and doping concentrations.
Single-particle infrared spectra reveal electric and magnetic dipole,
quadrupole, and hexapole resonances. We subsequently demonstrate doping-dependent
frequency shifts that follow simple Drude models, culminating in the
emergence of plasmonic resonances at high doping levels and long wavelengths.
These findings demonstrate the potential for actively tuning infrared
Mie resonances by optically or electrically modulating charge carrier
densities, thus providing an excellent platform for tunable metamaterials
High-Index Topological Insulator Resonant Nanostructures from Bismuth Selenide
Topological insulators (TIs) are a class of materials characterized by an insulting bulk and high mobility topologically protected surface states, making them promising candidates for future optoelectronic and quantum devices. Although their electronic and transport properties have been extensively studied, their optical properties and prospective photonic capabilities have not been fully uncovered. Here, we use a combination of far-field and near-field nanoscale imaging and spectroscopy, to study CVD grown Bi2Se3 nanobeams (NBs). We first extract the mid-infrared (MIR) optical constants of Bi2Se3, revealing refractive index values as high as n ~6.4, and demonstrate that the NBs support Mie-resonances across the MIR. Local near-field reflection phase mapping reveals domains of various phase shifts, providing information on the local optical properties of the NBs. We experimentally measure up to 2{\pi} phase-shift across the resonance, in excellent agreement with FDTD simulations. This work highlights the potential of TI Bi2Se3 for quantum circuitry, non-linear generation, high-Q metaphotonics, and IR photodetection
Switchable Plasmonic–Dielectric Resonators with Metal–Insulator Transitions
Nanophotonic resonators
offer the ability to design nanoscale optical
elements and engineered materials with unconventional properties.
Dielectric-based resonators intrinsically support a complete multipolar
resonant response with low absorption, while metallic resonators provide
extreme light confinement and enhanced photon–electron interactions.
Here, we construct resonators out of a prototypical metal–insulator
transition material, vanadium dioxide (VO<sub>2</sub>), and demonstrate
switching between dielectric and plasmonic resonances. We first characterize
the temperature-dependent infrared optical constants of VO<sub>2</sub> single crystals and thin-films. We then fabricate VO<sub>2</sub> wire arrays and disk arrays. We show that wire resonators support
dielectric resonances at low temperatures, a damped scattering response
at intermediate temperatures, and plasmonic resonances at high temperatures.
In disk resonators, however, upon heating, there is a pronounced enhancement
of scattering at intermediate temperatures and a substantial narrowing
of the phase transition. These findings may lead to the design of
novel nanophotonic devices that incorporate thermally switchable plasmonic–dielectric
behavior