Lithium niobate (LN) has been the material of choice for electro-optic modulators owing to its excellent physical properties. While conventional LN electro-optic modulators continue to be the ...workhorse of the modern optoelectronics, they are becoming progressively too bulky, expensive, and power-hungry to fully serve the needs of this industry. Here, we demonstrate plasmonic electro-optic directional coupler switches consisting of two closely spaced nm-thin gold nanostripes on LN substrates that guide both coupled electromagnetic modes and electrical signals that control their coupling, thereby enabling ultra-compact switching and modulation functionalities. Extreme confinement and good spatial overlap of both slow-plasmon modes and electrostatic fields created by the nanostripes allow us to achieve a 90% modulation depth with 20-μm-long switches characterized by a broadband electro-optic modulation efficiency of 0.3 V cm. Our monolithic LN plasmonic platform enables a wide range of cost-effective optical communication applications that demand μm-scale footprints, ultrafast operation and high environmental stability.
We report thorough measurements of surface plasmon polaritons (SPPs) running along nearly perfect air-gold interfaces formed by atomically flat surfaces of chemically synthesized gold monocrystals. ...By means of amplitude- and phase-resolved near-field microscopy, we obtain their propagation length and effective mode index at visible wavelengths (532, 594, 632.8, 729, and 800 nm). The measured values are compared with the values obtained from the dielectric functions of gold that are reported in literature. Importantly, a reported dielectric function of monocrystalline gold implies ∼1.5 times shorter propagation lengths than those observed in our experiments, whereas a dielectric function reported for properly fabricated polycrystalline gold leads to SPP propagation lengths matching our results. We argue that the SPP propagation lengths measured in our experiments signify the ultimate limit of optical losses in gold, encouraging further comprehensive characterization of optical material properties of pure gold as well as other plasmonic materials.
Anapole states associated with the destructive interference between dipole and toroidal moments result in suppressed scattering accompanied by strongly enhanced near fields. In this work, we ...comprehensively examine the anapole state formation in metal–insulator–metal configurations supporting gap surface-plasmon (GSP) resonances that are widely used in plasmonics. Using multipole decomposition, we show that in contrast to the common case of dielectric particles with out-of-phase superposition of electric and toroidal dipoles anapole states in GSP resonators are formed due to the compensation of magnetic dipole moments. Unlike anapole states in dielectric particles, magnetic anapole states in GSP resonator does not provide a pronounced suppression of scattering, but it features huge electric field enhancement, which we verify by numerical simulations and two-photon luminescence measurements. This makes the GSP resonator configuration very promising for use in a wide range of applications, ranging from nonlinear harmonic generation to absorption enhancement and sensing.
Stress-induced premature senescence program is known to be activated in cells by various genotoxic stressors, and oxidative stress is considered to be the main of those. To this end, many studies ...discover antioxidants as protective anti-aging agents. In the current study, we examined the effects of different antioxidants (Tempol, resveratrol, NAC, DPI) on the mesenchymal stem cells maintained in normal physiological conditions. We used high, but non-cytotoxic antioxidant doses which are widely used in laboratory practice to protect cells from oxidative damage. We show that these substances induce reversible block of cell proliferation and do not cause any genotoxic effects when applied to the quiescent cells. However, the same doses of the same substances, when applied to the proliferating cells, can induce irreversible cell cycle arrest, DNA strand breaks accumulation and DNA damage response activation. As a consequence, antioxidant-induced DNA damage results in the stress-induced premature senescence program activation. We conclude that high doses of antioxidants, when applied to the proliferating cells that maintain physiological levels of reactive oxygen species, can cause DNA damage and induce premature senescence which suggests to re-estimate believed unconditional anti-aging antioxidant properties.
Lithium niobate Mach–Zehnder modulators (MZMs) are present in a wide range of technologies and though fulfilling the performance and reliability requirements of present applications, they are ...becoming progressively too bulky, power inefficient, and slow in switching to keep pace with future technological demands. Here, we utilize plasmonics to demonstrate the most efficient (VπL = 0.23 Vcm) lithium niobate MZM to date, consisting of gold nanostripes on lithium niobate that guide both plasmonic modes and electrical signals that control their relative optical phase delay, thereby enabling efficient electro-optic modulation. For high linearity (modulation depth of >2 dB), the proposed MZM inherently operates near its quadrature point by shifting the relative phase of the signal in the interferometric arms. The demonstrated lithium niobate MZM manifests the benefits of employing plasmonics for applications that demand compact (<1 mm2) and fast (>10 GHz) photonic components operating reliably at ambient temperatures.
Black Hole Shadows Constrain Extended Gravity Prokopov, V. A.; Alexeyev, S. O.; Zenin, O. I.
Journal of experimental and theoretical physics,
07/2022, Volume:
135, Issue:
1
Journal Article
Peer reviewed
Open access
The first images of black hole shadows open new possibilities to constrain modern extended gravity theories. We present the method of shadow background calculation for black hole solutions in the ...form of Taylor series where
g
11
= –
. The method is extended to general nonrotating case
g
11
≠ –
. The results of the analysis are compared with the predictions of General relativity taking into account the Event Horizon Telescope data. The results for the Horndesky model with the Gauss–Bonnet invariant, loop quantum gravity, Bumblebee model and Gauss–Bonnet gravity are in full agreement with the observations of M87*. In conformal gravity, large values of
m
2
and
Q
s
must be excluded. In STEGR
f
(
Q
) gravity the observational limits on the parameter α are: –0.025 < α < 0.04. For an alternative generalization of the Bumblebee model with the Schwarzschild approximation: –0.3 <
l
< 0.45. These results demonstrate the maximum one can achieve without taking into account of the rotation of a black hole.
High-index dielectric nanostructures have recently become prominent forefront alternatives for manipulating light at the nanoscale. Their electric and magnetic resonances with intriguing ...characteristics endow them with a unique ability to strongly enhance near-field effects with minimal absorption. Similar to their metallic counterparts, dielectric oligomers consisting of two or more coupled particles are generally employed to create localized optical fields. Here we show that individual all-dielectric nanostructures, with rational designs, can produce strong electric fields with intensity enhancements exceeding 3 orders of magnitude. Such a striking effect is demonstrated within a Si nanodisk by fully exploiting anapole generation and simultaneously introducing a slot area with high-contrast interfaces. By performing finite-difference time-domain simulations and multipole decomposition analysis, we systematically investigate both far-field and near-field properties of the slotted disk and reveal a subtle interplay among different resonant modes of the system. Furthermore, while electric fields at anapole modes are typically internal, i.e., found inside nanostructures, our slotted configuration generates external hotspots with electric fields additionally enhanced by virtue of boundary conditions. These electric hotspots are thereby directly accessible to nearby molecules or quantum emitters, opening up new possibilities for single-particle enhanced spectroscopies or single-photon emission enhancement due to large Purcell effects. Our presented design methodology is also readily extendable to other materials and other geometries, which may unlock enormous potential for sensing and quantum nanophotonic applications.
Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes by reducing the cross sections of propagating modes far beyond ...the diffraction limit, that is, by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging, and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidence of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-Pérot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to ∼12000, with the enhanced field being evenly distributed over the gap volume of 30 × 30 × 10 nm3, and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing.
Anapole states associated with the resonant suppression of electric-dipole scattering exhibit minimized extinction and maximized storage of electromagnetic energy inside a particle. Using numerical ...simulations, optical extinction spectroscopy, and amplitude-phase near-field mapping of silicon dielectric disks, we demonstrate high-order anapole states in the near-infrared wavelength range (900–1700 nm). We develop the procedure for unambiguously identifying anapole states by monitoring the normal component of the electric near-field and experimentally detect the first two anapole states as verified by far-field extinction spectroscopy and confirmed with the numerical simulations. We demonstrate that higher-order anapole states possess stronger energy concentration and narrower resonances, a remarkable feature that is advantageous for their applications in metasurfaces and nanophotonics components, such as nonlinear higher-harmonic generators and nanoscale lasers.
Historically, the field of plasmonics has been relying on the framework of classical electrodynamics, with the local-response approximation of material response being applied even when dealing with ...nanoscale metallic structures. However, when the confinement of electromagnetic radiation approaches atomic scales, mesoscopic effects are anticipated to become observable, e.g., those associated with the nonlocal electrodynamic surface response of the electron gas. Here, we investigate nonlocal effects in propagating gap surface plasmon modes in ultrathin metal-dielectric-metal planar waveguides, exploiting monocrystalline gold flakes separated by atomic-layer-deposited aluminum oxide. We use scanning near-field optical microscopy to directly access the near-field of such confined gap plasmon modes and measure their dispersion relation via their complex-valued propagation constants. We compare our experimental findings with the predictions of the generalized nonlocal optical response theory to unveil signatures of nonlocal damping, which becomes appreciable for few-nanometer-sized dielectric gaps.
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