9 research outputs found
Advanced concepts and functionalities for symmetry-broken photonic bound states in the continuum
Adaptive method for quantitative estimation of glucose and fructose concentrations in aqueous solutions based on infrared nanoantenna optics
In life science and health research one observes a continuous need for new concepts and methods to detect and quantify the presence and concentration of certain biomolecules-preferably even in vivo or aqueous solutions. One prominent example, among many others, is the blood glucose level, which is highly important in the treatment of, e.g., diabetes mellitus. Detecting and, in particular, quantifying the amount of such molecular species in a complex sensing environment, such as human body fluids, constitutes a significant challenge. Surface-enhanced infrared absorption (SEIRA) spectroscopy has proven to be uniquely able to differentiate even very similar molecular species in very small concentrations. We are thus employing SEIRA to gather the vibrational response of aqueous glucose and fructose solutions in the mid-infrared spectral range with varying concentration levels down to 10 g/l. In contrast to previous work, we further demonstrate that it is possible to not only extract the presence of the analyte molecules but to determine the quantitative concentrations in a reliable and automated way. For this, a baseline correction method is applied to pre-process the measurement data in order to extract the characteristic vibrational information. Afterwards, a set of basis functions is fitted to capture the characteristic features of the two examined monosaccharides and a potential contribution of the solvent itself. The reconstruction of the actual concentration levels is then performed by superposition of the different basis functions to approximate the measured data. This software-based enhancement of the employed optical sensors leads to an accurate quantitative estimate of glucose and fructose concentrations in aqueous solutions
High-Q Nanophotonics over the Full Visible Spectrum Enabled by Hexagonal Boron Nitride Metasurfaces
All-dielectric optical metasurfaces with high quality (Q) factors have been hampered by the lack of simultaneously lossless and high-refractive-index materials over the full visible spectrum. In fact, the use of low-refractive-index materials is unavoidable for extending the spectral coverage due to the inverse correlation between the bandgap energy (and therefore the optical losses) and the refractive index (n). However, for Mie resonant photonics, smaller refractive indices are associated with reduced Q factors and low mode volume confinement. Here, symmetry-broken quasi bound states in the continuum (qBICs) are leveraged to efficiently suppress radiation losses from the low-index (n approximate to 2) van der Waals material hexagonal boron nitride (hBN), realizing metasurfaces with high-Q resonances over the complete visible spectrum. The rational use of low- and high-refractive-index materials as resonator components is analyzed and the insights are harnessed to experimentally demonstrate sharp qBIC resonances with Q factors above 300, spanning wavelengths between 400 and 1000 nm from a single hBN flake. Moreover, the enhanced electric near fields are utilized to demonstrate second-harmonic generation with enhancement factors above 10(2). These results provide a theoretical and experimental framework for the implementation of low-refractive-index materials as photonic media for metaoptics
Permittivity-asymmetric quasi-bound states in the continuum
Broken symmetries lie at the heart of nontrivial physical phenomena. Breaking
the in-plane geometrical symmetry of optical systems allows to access a set of
electromagnetic states termed symmetry-protected quasi-bound states in the
continuum (qBICs). Here we demonstrate, theoretically, numerically and
experimentally, that such optical states can also be accessed in metasurfaces
by breaking the in-plane symmetry in the permittivity of the comprising
materials, showing a remarkable equivalence to their geometrically-asymmetric
counterparts. However, while the physical size of atoms imposes a limit on the
lowest achievable geometrical asymmetry, weak permittivity modulations due to
carrier doping and electro-optical Pockels and Kerr effects, usually considered
insignificant, open up the possibility of infinitesimal permittivity
asymmetries for on-demand, and dynamically tuneable optical resonances of
extremely high quality factors. We probe the excitation of
permittivity-asymmetric qBICs (-qBICs) using a prototype
Si/TiO metasurface, in which the asymmetry in the unit cell is provided
by the refractive index contrast of the dissimilar materials, surpassing any
unwanted asymmetries from nanofabrication defects or angular deviations of
light from normal incidence. -qBICs can also be excited in 1D
gratings, where quality-factor enhancement and tailored interference phenomena
via the interplay of geometrical and permittivity asymmetries are numerically
demonstrated. The emergence of -qBICs in systems with broken
symmetries in their permittivity may enable to test time-energy uncertainties
in quantum mechanics, and lead to a whole new class of low-footprint optical
and optoelectronic devices, from arbitrarily narrow filters and topological
sources, biosensing and ultrastrong light-matter interaction platforms, to
tuneable optical switches.Comment: Manuscript and Supplementary Information, 27 pages, 4 Figures
manuscript + 4 Supplementary Figure
Optically addressable spin defects coupled to bound states in the continuum metasurfaces
Van der Waals (vdW) materials, including hexagonal boron nitride (hBN), are
layered crystalline solids with appealing properties for investigating
light-matter interactions at the nanoscale. hBN has emerged as a versatile
building block for nanophotonic structures, and the recent identification of
native optically addressable spin defects has opened up exciting possibilities
in quantum technologies. However, these defects exhibit relatively low quantum
efficiencies and a broad emission spectrum, limiting potential applications.
Optical metasurfaces present a novel approach to boost light emission
efficiency, offering remarkable control over light-matter coupling at the
sub-wavelength regime. Here, we propose and realise a monolithic scalable
integration between intrinsic spin defects in hBN metasurfaces and high quality
(Q) factor resonances leveraging quasi-bound states in the continuum (qBICs).
Coupling between spin defect ensembles and qBIC resonances delivers a 25-fold
increase in photoluminescence intensity, accompanied by spectral narrowing to
below 4 nm linewidth facilitated by Q factors exceeding . Our findings
demonstrate a new class of spin based metasurfaces and pave the way towards
vdW-based nanophotonic devices with enhanced efficiency and sensitivity for
quantum applications in imaging, sensing, and light emission.Comment: 13 pages, 4 Figures + 4 Supplementary Figure
Adaptive Method for Quantitative Estimation of Glucose and Fructose Concentrations in Aqueous Solutions Based on Infrared Nanoantenna Optics
Radial bound states in the continuum for polarization-invariant nanophotonics
All-dielectric nanophotonics underpinned by bound states in the continuum
(BICs) have demonstrated breakthrough applications in nanoscale light
manipulation, frequency conversion and optical sensing. Leading BIC
implementations range from isolated nanoantennas with localized electromagnetic
fields to symmetry-protected metasurfaces with controllable resonance quality
(Q) factors. However, they either require structured light illumination with
complex beamshaping optics or large, fabrication-intense arrays of
polarization-sensitive unit cells, hindering tailored nanophotonic applications
and on-chip integration. Here, we introduce radial quasi bound states in the
continuum (rBICs) as a new class of radially distributed electromagnetic modes
controlled by structural asymmetry in a ring of dielectric rod pair resonators.
The rBIC platform provides polarization-invariant and tunable high-Q resonances
with strongly enhanced near-fields in an ultracompact footprint as low as 2
m. We demonstrate rBIC realizations in the visible for sensitive
biomolecular detection and enhanced second-harmonic generation from monolayers
of transition metal dichalcogenides, opening new perspectives for compact,
spectrally selective, and polarization-invariant metadevices for
multi-functional light-matter coupling, multiplexed sensing, and high-density
on-chip photonics
Optically addressable spin defects coupled to bound states in the continuum metasurfaces
Abstract Van der Waals (vdW) materials, including hexagonal boron nitride (hBN), are layered crystalline solids with appealing properties for investigating light-matter interactions at the nanoscale. hBN has emerged as a versatile building block for nanophotonic structures, and the recent identification of native optically addressable spin defects has opened up exciting possibilities in quantum technologies. However, these defects exhibit relatively low quantum efficiencies and a broad emission spectrum, limiting potential applications. Optical metasurfaces present a novel approach to boost light emission efficiency, offering remarkable control over light-matter coupling at the sub-wavelength regime. Here, we propose and realise a monolithic scalable integration between intrinsic spin defects in hBN metasurfaces and high quality (Q) factor resonances, exceeding 102, leveraging quasi-bound states in the continuum (qBICs). Coupling between defect ensembles and qBIC resonances delivers a 25-fold increase in photoluminescence intensity, accompanied by spectral narrowing to below 4 nm linewidth and increased narrowband spin-readout efficiency. Our findings demonstrate a new class of metasurfaces for spin-defect-based technologies and pave the way towards vdW-based nanophotonic devices with enhanced efficiency and sensitivity for quantum applications in imaging, sensing, and light emission
Unlocking the out-of-plane dimension for photonic bound states in the continuum to achieve maximum optical chirality
Abstract The realization of lossless metasurfaces with true chirality crucially requires the fabrication of three-dimensional structures, constraining experimental feasibility and hampering practical implementations. Even though the three-dimensional assembly of metallic nanostructures has been demonstrated previously, the resulting plasmonic resonances suffer from high intrinsic and radiative losses. The concept of photonic bound states in the continuum (BICs) is instrumental for tailoring radiative losses in diverse geometries, especially when implemented using lossless dielectrics, but applications have so far been limited to planar structures. Here, we introduce a novel nanofabrication approach to unlock the height of individual resonators within all-dielectric metasurfaces as an accessible parameter for the efficient control of resonance features and nanophotonic functionalities. In particular, we realize out-of-plane symmetry breaking in quasi-BIC metasurfaces and leverage this design degree of freedom to demonstrate an optical all-dielectric quasi-BIC metasurface with maximum intrinsic chirality that responds selectively to light of a particular circular polarization depending on the structural handedness. Our experimental results not only open a new paradigm for all-dielectric BICs and chiral nanophotonics, but also promise advances in the realization of efficient generation of optical angular momentum, holographic metasurfaces, and parity-time symmetry-broken optical systems