A novel three-dimensional (3D) metallic metamaterial structure with asymmetric transmission for linear polarization is demonstrated in the infrared spectral region. The structure was fabricated by direct laser writing and selective electroless silver coating, a straightforward, novel technique producing mechanically and chemically stable 3D photonic structures. The structure unit cell is composed of a pair of conductively coupled magnetic resonators, and the asymmetric transmission response results from interplay of electric and magnetic responses; this equips the structure with almost total opaqueness along one propagation direction versus satisfying transparency along the opposite one. It also offers easily adjustable impedance, 90° one-way pure optical activity and backward propagation possibility, resulting thus in unique capabilities in polarization control and isolation applications. We show also that scaling down the structure can make it capable of exhibiting its asymmetric transmission and its polarization capabilities in the optical region.

Recently, coherent control of the optical response of thin films in standing waves has attracted considerable attention, ranging from applications in excitation-selective spectroscopy and nonlinear optics to all-optical image processing. Here, we show that integration of metamaterial and optical fibre technologies allows the use of coherently controlled absorption in a fully fiberized and packaged switching metadevice. With this metadevice, which controls light with light in a nanoscale plasmonic metamaterial film on an optical fibre tip, we provide proof-of-principle demonstrations of logical functions XOR, NOT and AND that are performed within a coherent fibre network at wavelengths between 1530 and 1565 nm. The metadevice has been tested at up to 40 gigabits per second and sub-milliwatt power levels. Since coherent absorption can operate at the single-photon level and with 100 THz bandwidth, we argue that the demonstrated all-optical switch concept has potential applications in coherent and quantum information networks.

Coherent interconversion of signals between optical and mechanical domains is enabled by optomechanical interactions. Extreme light-matter coupling produced by confining light to nanoscale mode volumes can then access single mid-infrared (MIR) photon sensitivity. Here we utilise the infrared absorption and Raman activity of molecular vibrations in plasmonic nanocavities to demonstrate frequency upconversion. We convert 𝝀 ~10 μm incoming light to visible via surface-enhanced Raman scattering (SERS) in doubly-resonant antennas that enhance upconversion by >10 10 . We show >200% amplification of the SERS antiStokes emission when a MIR pump is tuned to a molecular vibrational frequency, obtaining lowest detectable powers ~1 μW/μm 2 at room temperature. These results have potential for lowcost and large-scale infrared detectors and spectroscopic techniques, and bring singlemolecule sensing into the infrared.

and by exploiting their acute response to their immediate environment, a variety of novel applications have been realized such as negative indices of refraction, [3,4] broadband circular polarization devices, [5] and strongly twisted local electromagnetic fields for sensitive detection of chiral molecules. [6][7][8][9][10] In chiral media, optical activity is a result of the cross-coupling between electric and magnetic fields. Two classical approaches have been proposed to model the mechanisms of optical activity: [11,12] (a) the coupled oscillator model system, where optical activity arises from the coupling of two separate, noncollinear oscillators, and (b) the one-electron model system, where an electron is bound on a helix, giving electric and magnetic character to the optical transitions. Recently, the plasmonic analogue of the coupled oscillator model system, which consists of a system of two cornerstacked gold nanorods, was experimentally demonstrated. [13] This system resembles two coupled, vertically displaced electrons that carry out orthogonal harmonic oscillation driven by an external light field. In this work, we experimentally and theoretically study the plasmonic version of the one-electron model system, which comprises a loop-wire structure, namely the so-called "twisted omega particle." In this case, the 3D plasmonic meta-atom combines a small electric dipole antenna (the metallic wire) and a split-ring resonator (the loop), which exhibits a magnetic dipole resonance leading to a different electromagnetic response to RCP light and the left-handed one (LCP). [14,15] Results and Discussion Fabrication and Optical Characterization Fabrication ApproachTwisted omega architectures have already been theoretically studied and discussed as prototype for plasmonic structures with strong chiro-optical far-field response. [16][17][18][19] To this end, Helgert et al. utilized a layer-by-layer approach to fabricate an architecture reminiscent of the twisted omega by placing two L-shaped gold nanoparticles on top of each other and connected in the vertical direction. [20] Based on a combined spectroscopicThe plasmonic version of a 3D chiral meta-atom which consists of a loopwire structure, namely the so-called twisted omega particle, is experimentally realized. The structure is fabricated by direct laser writing and subsequent electroless silver plating, a novel technique capable of producing truly 3D photonic nanostructures. In this case, the metallic wire of finite length supports an electric dipole resonance, whereas the loop acts as a split-ring resonator which exhibits a magnetic dipole resonance, leading to the separation of right-handed circularly polarized light and the left-handed one. The arising optical activity is discussed in terms of a single oscillator model system used classically to describe the generation of natural optical activity in chiral media, and it is shown that the twisted omega particle acts as its exact plasmonic analogue.

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Plasmonic nanoconstructs are widely exploited to confine light for applications ranging from quantum emitters to medical imaging and biosensing. However, accessing extreme near-field confinement using the surfaces of metallic nanoparticles often induces permanent structural changes from light, even at low intensities. Here, we report a robust and simple technique to exploit crystal facets and their atomic boundaries to prevent the hopping of atoms along and between facet planes. Avoiding X-ray or electron microscopy techniques that perturb these atomic restructurings, we use elastic and inelastic light scattering to resolve the influence of crystal habit. A clear increase in stability is found for {100} facets with steep inter-facet angles, compared to multiple atomic steps and shallow facet curvature on spherical nanoparticles. Avoiding atomic hopping allows Raman scattering on molecules with low Raman cross-section while circumventing effects of charging and adatom binding, even over long measurement times. These nanoconstructs allow the optical probing of dynamic reconstruction in nanoscale surface science, photocatalysis, and molecular electronics.

Plasmonic self-assembled nanocavities are ideal platforms for extreme light localization as they deliver mode volumes of <50 nm 3 . Here we show that high-order plasmonic modes within additional micrometer-scale resonators surrounding each nanocavity can boost light localization to intensity enhancements >10 5 . Plasmon interference in these hybrid microresonator nanocavities produces surface-enhanced Raman scattering (SERS) signals many-fold larger than in the bare plasmonic constructs. These now allow remote access to molecules inside the ultrathin gaps, avoiding direct irradiation and thus preventing molecular damage. Combining subnanometer gaps with micrometer-scale resonators places a high computational demand on simulations, so a generalized boundary element method (BEM) solver is developed which requires 100-fold less computational resources to characterize these systems. Our results on extreme near-field enhancement open new potential for single-molecule photonic circuits, mid-infrared detectors, and remote spectroscopy.

Large distance implementation of quantum communication technologies requires coherent control of single photons in optical fiber networks. Here we demonstrate the phenomenon of coherent perfect absorption of single photons in a fully fiberized ultrathin plasmonic metamaterial fabricated at the end facet of an optical fiber. Continuous control of single-photon absorption probability is achieved by driving the network between the regimes of coherent total absorption and coherent total transmission. To circumvent phase fluctuations inherent to optical fiber networks, we implemented a reference-based postselection technique which yielded interference fringe visibility comparable to that of free space experiments. Coherent absorption of quantum light in fiber environment provides new opportunities for dissipative single-photon switching, filtering, and measurement, as well as for manipulation of entangled, weak coherent, and NOON states in optical fiber networks.