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Silica-based optical fibres are a workhorse of nonlinear optics, providing ready access to a range of nonlinear phenomena including solitons and self-phase modulation. However, they have one fundamental limitation: due to the amorphous nature of silica, they do not exhibit second-order nonlinearity, except for negligible contributions from surfaces. Here we demonstrate second-harmonic generation in functionalized optical fibres by using a monolayer of highly nonlinear MoS2 directly grown on the fibre’s core. The MoS2-functionalized fibre exhibits a second-order susceptibility (χ(2)) value of 44 pm V–1 and a second-harmonic generation conversion efficiency of 0.2 × 10–3 m−2 W−1. This approach is scalable and can be generalized to other transition metal dichalcogenides and a wide range of waveguide systems. Our results demonstrate a new approach towards efficient in-fibre second-harmonic generation sources and may establish a platform for χ(2)-based nonlinear fibre optics, optoelectronics, photonics platforms, integrated optical architectures and active fibre networks.

The capability of tailoring the resonance wavelength of metasurfaces is important as it can alleviate the manufacturing precision required to produce the exact structure according to the design of the nanoresonators. Tuning of Fano resonances by applying heat has been theoretically predicted in the case of silicon metasurfaces. Here, we experimentally demonstrate the permanent tailoring of quasi-bound states in the continuum (quasi-BIC) resonance wavelength in an a-Si:H metasurface and quantitatively analyze the modification in the Q-factor with gradual heating. A gradual increment in temperature leads to a spectral shiftin the resonance wavelength. With the support of ellipsometry measurements, the spectral shift resulting from the short-duration (ten minutes) heating is identified to be due to refractive index variations in the material rather than a geometric effect or amorphous/polycrystalline phase transition. In the case of quasi-BIC modes in the near-infrared, resonance wavelength could be adjusted from T = 350 °C to T = 550 °C without affecting the Q-factor considerably. Apart from the temperature-induced resonance trimming, large Q-factors can be attained at the highest analyzed temperature (T = 700 °C) in the near-infrared quasi-BIC modes. Resonance tailoring is just one of the possible applications of our results. We expect that our study is also insightful in the design of a-Si:H metasurfaces where large Q-factors are required at high temperatures.

We report for the first time the direct growth of molybdenum disulfide (MoS2) monolayers on nanostructured silicon-on-insulator waveguides. Our results indicate the possibility of utilizing the Chemical Vapour Deposition (CVD) on nanostructured photonic devices in a scalable process. Direct growth of 2D material on nanostructures rectifies many drawbacks of the transfer-based approaches. We show that the van der Waals material grow conformally across the curves, edges, and the silicon–SiO2 interface of the waveguide structure. Here, the waveguide structure used as a growth substrate is complex not just in terms of its geometry but also due to the two materials (Si and SiO2) involved. A transfer-free method like this yields a novel approach for functionalizing nanostructured, integrated optical architectures with an optically active direct semiconductor.

In theDrosophilaolfactory system most odorants are encoded in the antennal lobe in a combinatory way, activating several glomerular circuits. However, odorants of particular ecological role for the fly are encoded through activation of a single specialized olfactory pathway. Comparative analyses of densely reconstructed connectomes of one broadly tuned glomerulus (DL5) and one narrowly tuned glomerulus (DA2) gained detailed insight into the variations of synaptic circuitries of glomeruli with different computational tasks. Our approach combined laser-branding of glomeruli of interest with volume based focused ion beam-scanning electron microscopy (FIB-SEM) to enable precise targeting and analysis of the two glomeruli. We discovered differences in their neuronal innervation, synaptic composition and specific circuit diagrams of their major cell types: olfactory sensory neurons (OSNs), uniglomerular projection neurons (uPNs) and multiglomerular neurons (MGNs). By comparing our data with a previously mapped narrowly tuned glomerulus (VA1v), we identified putative generic features of narrowly tuned glomerular circuits, including higher density of neuronal fibers and synapses, lower degree of OSN lateralization, stronger axo-axonic connections between OSNs, dendro-dendritic connections between many uPNs, and lower degree of presynaptic inhibition on OSN axons. In addition, this work revealed that the dendrites of the single uPN in DL5 contain a substantial amount of autapses interconnecting distant regions of the dendritic tree. The comparative analysis of glomeruli allows to formulate synaptic motifs implemented in olfactory circuits with different computational demands.

Quantum ghost imaging (QGI) is an intriguing imaging protocol that exploits photon-pair correlations stemming from spontaneous parametric down-conversion (SPDC). QGI retrieves images from two-path joint measurements, where single-path detection does not allow us to reconstruct the target image. Here we report on a QGI implementation exploiting a two-dimensional (2D) single-photon avalanche diode (SPAD) array detector for the spatially resolving path. Moreover, the employment of non-degenerate SPDC allows us to investigate samples at infrared wavelengths without the need for short-wave infrared (SWIR) cameras, while the spatial detection can be still performed in the visible region, where the more advanced silicon-based technology can be exploited. Our findings advance QGI schemes towards practical applications.

Metasurfaces are 2D planar lattices of nanoparticles that allow the manipulation of incident light properties. Because of that attribute, metasurfaces are promising candidates to replace bulky optical components. Traditionally, metasurfaces are made from a periodic arrangement of identical unit cells. However, more degrees of freedom are accessible if an increasing number of structured unit cells are combined. The present study explores a type of dielectric metasurface with complex supercells composed of Mie-resonant dielectric nanocylinders and nanoscale rings. We numerically and experimentally demonstrate the signature of an optical response that relies on the structures sustaining staggered optically induced magnetic dipole moments. The optical response is associated with an optical antiferromagnetism. The optical antiferromagnetism exploits the presence of pronounced coupling between dissimilar Mie-resonant dielectric nanoparticles. The coupling is manipulated by engineering the geometry and distance between the nanoparticles, which ultimately enhances their effective magnetic response. Our results suggest possible applications in resonant nanophotonics by broadening the modulation capabilities of metasurfaces.

We propose a quantum ghost imaging scheme based on biphotons, which, by using a collimated pump beam of the right size for biphoton generation, obviates the need for lenses to achieve imaging. The scheme is found to be analogous to the classical pinhole camera, where we show that the equivalent to the classical pinhole size depends not only mainly on the width of the pump beam but also on the thickness of the nonlinear crystal and the wavelengths of the biphoton.

Optical fibers equipped with plasmonic flow sensors at their tips are fabricated and investigated as photothermomechanical nanopumps for the active transport of target analytes to the sensor surface. The nanopumps are prepared using a bottom-up strategy: i.e., by sequentially stacking a monolayer of a thermoresponsive polymer and a plasmonic nanohole array on an optical fiber tip. The temperature-dependent collapse and swelling of the polymer is used to create a flow-through pumping mechanism. The heat required for pumping is generated by exploiting the photothermal effect in the plasmonic nanohole array upon irradiation with laser light (405 nm). Simultaneous detection of analytes by the plasmonic sensor is achieved by monitoring changes in its optical response at longer wavelengths (∼500-800 nm). Active mass transport by pumping through the holes of the plasmonic nanohole array is visualized by particle imaging velocimetry. Finally, the performance of the photothermomechanical nanopumps is investigated for two types of analytes, namely nanoscale objects (gold nanoparticles) and molecules (11-mercaptoundecanoic acid). In the presence of the pumping mechanism, a 4-fold increase in sensitivity was observed compared to the purely photothermal effect, demonstrating the potential of the presented photothermomechanical nanopumps for sensing applications.

We theoretically study the generation of photon pairs via spontaneous four-wave mixing (SFWM) in a liquid-filled microstructured suspended-core optical fiber. We show that it is possible to control the wavelength, group velocity, and bandwidths of the two-photon states. Our proposed fiber structure shows a large number of degrees of freedom to engineer the two-photon state. Here, we focus on the factorable state, which shows no spectral correlation in the two-photon components of the state, and allows the heralding of a single-photon pure state without the need for spectral post-filtering.

The growing maturity of nanofabrication technology has recently enabled the deployment of high-quality subwavelength nanostructures on photonic chips. A combination of existing photonic waveguide technology with nanophotonics and paradigms adapted from the field of optical metamaterials opens new avenues towards photonic integrated circuits providing unprecedented control of guided light waves. However, developing new functionalities while preserving both compatibility with current technology and the efficiencies required by existing and emerging applications remains a major challenge in on-chip nanophotonics. Here, we propose and demonstrate a radically new type of silicon nanophotonic waveguide consisting of a chain of resonantly forward scattering nanoparticles empowered by spectrally overlapping electric and magnetic dipolar Mie-type resonances. The propagation loss of the realized meta-waveguides in the telecom spectral range is as low as 0.4 dB/mm, exceeding the current record for Mie-resonant waveguides by more than an order of magnitude. Furthermore, the meta-waveguides support a negative group index over a broad spectral range of 60 nm and several millimeters of propagation distance, as well as regions of vanishing and anomalous dispersion within the transmission band. Finally, we show that meta-waveguide architectures composed of resonantly forward scattering nanoparticles can implement sharp bends with bending radii below 3 µm, and efficiently split the input signal within just 315 nm propagation length. Our work does not only contribute to addressing the challenges of miniaturization, dispersion and scattering control in on-chip photonics, but furthermore opens up completely new opportunities for enhanced light-matter interactions, interfacing with nanophotonic components, as well as nonlinear, ultrafast and quantum optics in resonant integrated light-guiding architectures.

The control of plasmon-nanoemitter interactions at the nanoscale enables the tailored modulation of optical properties, namely, the photoluminescence (PL) intensity of the nanoemitters. In this contribution, using a nanometer-thick poly[(2-diethylamino) ethyl methacrylate] (39 to 74 nm) as pH responsive spacer layer (p

All-dielectric optical metasurfaces are a workhorse in nano-optics, because of both their ability to manipulate light in different degrees of freedom and their excellent performance at light frequency conversion. Here, we demonstrate first-time generation of photon pairs via spontaneous parametric-down conversion in lithium niobate quantum optical metasurfaces with electric and magnetic Mie-like resonances at various wavelengths. By engineering the quantum optical metasurface, we tailor the photon-pair spectrum in a controlled way. Within a narrow bandwidth around the resonance, the rate of pair production is enhanced up to 2 orders of magnitude, compared to an unpatterned film of the same thickness and material. These results enable flat-optics sources of entangled photons - a new promising platform for quantum optics experiments.

Optical metasurfaces are currently an important research area all around the world because of their wide application opportunities in imaging, wavefront engineering, nonlinear optics, quantum information processing, just to name a few. The feature issue “Optical Metasurfaces: Fundamentals and Applications” in Photonics Research allows for archival publication of the most recent works in optical metasurface and provides for broad dissemination in the photonics community.

The coupling of two-dimensional materials with optical metasurfaces is a promising avenue to enhance the advantageous properties of both platforms. Here we integrate an ultrathin monolayer of the t...

Lithium niobate is an excellent and widely used material for nonlinear frequency conversion due to its strong optical nonlinearity and broad transparency region. Here, we report the fabrication and experimental investigation of resonant nonlinear metasurfaces for second-harmonic generation based on thin-film lithium niobate. In the fabricated metasurfaces, we observe pronounced Mie-type resonances leading to enhanced second-harmonic generation in the direction normal to the metasurface. We find the largest second-harmonic generation efficiency for the resonance dominated by the electric contributions because its specific field distribution enables the most efficient usage of the largest element of the lithium niobate nonlinear susceptibility tensor. This is confirmed by polarization-resolved second-harmonic measurements, where we study contributions from different elements of the nonlinear susceptibility tensor to the total second-harmonic signal. Our work facilitates establishing lithium niobate as a material for resonant nanophotonics.

Three-dimensional chiral plasmonic metasurfaces were demonstrated to offer enormous potential for ultrathin circular polarizers and applications in chiral sensing. However, the large absorption losses in the metallic systems generally limit their applicability for high-efficiency devices. In this work, we experimentally and numerically demonstrate three-dimensional chiral dielectric metasurfaces exhibiting multipolar resonances and examine their chiro-optical properties. In particular, we demonstrate that record high circular dichroism of 0.7 and optical activity of 2.67 × 10

During the past decade, optical metasurfaces consisting of designed nanoresonators arranged in a planar fashion were successfully demonstrated to allow for the realization of a large variety of flat optical components. However, in common implementations of metasurfaces and metasurface-based devices, their flat nature is thwarted by the presence of a substrate of macroscopic thickness, which is needed to mechanically support the individual nanoresonators. Here, we demonstrate that carbon nanomembranes (CNMs) having nanoscale thicknesses can be used as a basis for arranging an array of plasmonic nanoresonators into a metamembrane, allowing for the realization of genuinely flat optical devices. CNMs belong to the family of two-dimensional materials, and their thicknesses and mechanical, chemical, and electrical properties can be tailored by the choice of the molecular precursors used for their fabrication. We experimentally fabricate gold split-ring-resonator (SRR) metasurfaces on top of a free-standing CNM, which has a thickness of only about 1 nm and shows a negligible interaction with the incident light field. For optical characterization of the fabricated SRR CNM metasurfaces, we perform linear-optical transmittance spectroscopy, revealing the typical resonance structure of an SRR metasurface. Furthermore, numerical calculations assuming free-standing SRR arrays are in good overall agreement with corresponding experimental transmittance spectra. We believe that our scheme offers a versatile solution for the realization of ultrathin, ultra lightweight metadevices, and may initiate various future research directions and applications including complex sensor technologies, conformal coating of complex topographies with functional metasurfaces, fast prototyping of multilayer metasurfaces, and studying the optical properties of effectively free-standing nanoparticles without the need for levitation schemes.