We demonstrate subwavelength scale color pixels in a CMOS compatible platform based on anti-Hermitian metasurfaces. In stark contrast to conventional pixels, spectral filtering is achieved through structural color rather than transmissive filters leading to simultaneously high color purity and quantum efficiency. The subwavelength anti-Hermitian metasurface sensor is able to sort three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration opens a new door to subwavelength pixelated CMOS sensors and promises future high-performance optoelectronic systems.
One major hurdle in the progress of hyperbolic metamaterials (HMMs) is their lossy nature due to the metal constituent. In this work, we design a gain-assisted active HMM utilizing the recently emerged, solution-processed perovskite gain material. Our HMM is consisted of MAPbI3 perovskite and Au subwavelength multi-layer. We theoretically and experimentally investigate the strong emission polarization anisotropy that is unique to HMMs. Our work opens the way towards applications such as high-speed light emission, super resolution imaging and lithography, electro-optical modulators and perfect light absorbers.
We propose modification to gain spectra of semiconductor quantum heterostructures by incorporation of nanostructured metal, paving the way for tailor made “meta-gain” media. We show that the wavelength dependence of the principal direction of energy propagation in media with hyperbolic dispersion leads to blue-shifting of peak photoluminescence (PL), and thereby optical gain, relative to emission from the bare semiconductor. Additionally we show that emission spectra from metal-semiconductor hyperbolic metasurfaces depends strongly upon the polarization of an external optical pump. The simultaneous co-optimization of pump properties and optical and electronic densities of states provides a platform for not only compensating losses in metallic metamaterials, but also designing emission spectra beyond that provided by the constituent quantum heterostructures.
The majority of plasmonic and metamaterials research utilizes noble metals such as gold and silver which commonly operate in the visible region. However, these materials are not well suited for many applications due to their low melting temperature and polarization response at longer wavelengths. A viable alternative is aluminum doped zinc oxide (AZO); a high melting point, low loss, visibly transparent conducting oxide which can be tuned to show strong plasmonic behavior in the near-infrared region. Due to it’s ultrahigh conformality, atomic layer deposition (ALD) is a powerful tool for the fabrication of the nanoscale features necessary for many nanoplasmonic and optical metamaterials. Despite many attempts, high quality, low loss AZO has not been achieved with carrier concentrations high enough to support plasmonic behavior at the important telecommunication wavelengths (ca. 1550 nm) by ALD. Here, we present a simple process for synthesizing high carrier concentration, thin film AZO with low losses via ALD that match the highest quality films created by all other methods. We show that this material is tunable by thermal treatment conditions, altering aluminum concentration, and changing buffer layer thickness. The use of this process is demonstrated by creating hyperbolic metamaterials with both a multilayer and embedded nanowire geometry. Hyperbolic dispersion is proven by negative refraction and numerical calculations in agreement with the effective medium approximation. This paves the way for fabricating high quality hyperbolic metamaterial coatings on high aspect ratio nanostructures that cannot be created by any other method.
Using established nanofabrication techniques, we realize deeply subwavelength multilayer metal-dielectric nanostructures composed of silver and indium gallium arsenide phosphide (InGaAsP). In contrast to most, if not all, subwavelength multilayer metal-dielectric systems to date, the Bloch vector of the fabricated structure is parallel to the plane of the substrate, making it suitable for waveguide integration. InGaAsP multiple quantum wells (MQWs) are epitaxially grown on InP normal to the Bloch vector of the resulting multilayer. The associated carrier population of the MQWs allows for active control of the behavior of the nanostructure via external optical pumping. Individual layer thicknesses of 30nm are repeatedly achieved via electron-beam lithography, reactive ion etching of InGaAsP, and sputter deposition of silver. Resulting 60nm periods of the one-dimensional periodic structure are 25 times smaller than telecommunication wavelengths in vacuum. The realized multilayer nanostructures hold promise as a platform for active and tunable hyperbolic metamaterials at telecommunication frequencies.
Using effective medium theory (EMT), Bloch’s theorem (BT), and the transfer matrix method (TMM), we analyze the possibility of gain-enhanced transmission in metamaterials with hyperbolic dispersion at telecommunication frequencies. We compare different combinations of dissipative metals and active dielectrics, including noble metals, transparent conducting oxides (TCO), III-V compounds, and solid-state dopants. We find that both indium gallium arsenide phosphide (InGaAsP) and erbium-doped silica (Er:SiO2), when combined with silver, show promise as a platform for demonstration of pump-dependent transmission. On the other hand, when these active dielectrics are combined with aluminum-doped zinc oxide (AZO), a low-loss TCO, gain-enhanced transmission is negligible. Results based on EMT are compared to the more accurate BT and TMM. When losses are ignored, quantitative agreement between these analytical techniques is observed near the center of the first Brillouin zone of a one-dimensional periodic structure. Including realistic levels of loss and gain, however, EMT predictions become overly optimistic compared to BT and TMM. We also discuss the limitations to assumptions inherent to EMT, BT, and TMM, and suggest avenues for future analysis.
Metal nanocavity-based lasers show promise for dense integration in nanophotonic devices, thanks to their compact size and lack of crosstalk. Thermal considerations in these devices have been largely overlooked in design, despite the importance of self-heating and heat dissipation to device performance. We discuss the sources of self-heating in electrically-pumped wavelength-scale nanolasers, and the incorporation of these heat sources into a heat dissipation model to calculate laser operating temperature. We apply this thermal model to an example electrically-pumped nanolaser operating at room temperature.
We perform two analyses on temperature effects in Metal-Clad Subwavelength Semiconductor Lasers (MCSELs).
Firstly, we analyze the temperature dependence of the threshold gain in the infinite waveguide approximation. We show
that the dielectric layer of the semiconductor-dielectric-metal composite waveguide (CWG) becomes increasingly
important as temperature increases. However, we further show that the optimal geometry of the CWG is nearly invariant
with the temperature. Secondly, we relax the infinite waveguide assumption with the fully 3D finite element method,
and analyze the temperature dependence of the spontaneous emission factor, β. We identify a cavity geometry that
mitigates detuning between the dominant cavity mode and emission spectra. Ignoring coupling to freespace modes, we
explain that the modified cavity may lead to a MCSEL with large β (~0.5) for all temperatures.
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