A mechanically reconfigurable metasurface that can continuously tune the wavefront is demonstrated in the visible frequency range by changing the lattice constant of a complex Au nanorod array ...fabricated on a stretchable polydimethylsiloxane substrate. It is shown that the anomalous refraction angle of visible light at 632.8 nm interacting with the tunable metasurface can be adjusted from 11.4° to 14.9° by stretching the substrate by ∼30%. An ultrathin flat 1.7× zoom lens whose focal length can continuously be changed from 150 to 250 μm is realized, which also demonstrates the potential of utilizing metasurfaces for reconfigurable flat optics.
We demonstrate strong exciton–plasmon coupling in silver nanodisk arrays integrated with monolayer MoS2 via angle-resolved reflectance microscopy spectra of the coupled system. Strong exciton–plasmon ...coupling is observed with the exciton–plasmon coupling strength up to 58 meV at 77 K, which also survives at room temperature. The strong coupling involves three types of resonances: MoS2 excitons, localized surface plasmon resonances (LSPRs) of individual silver nanodisks and plasmonic lattice resonances of the nanodisk array. We show that the exciton–plasmon coupling strength, polariton composition, and dispersion can be effectively engineered by tuning the geometry of the plasmonic lattice, which makes the system promising for realizing novel two-dimensional plasmonic polaritonic devices.
The manipulation of light-matter interactions in two-dimensional atomically thin crystals is critical for obtaining new optoelectronic functionalities in these strongly confined materials. Here, by ...integrating chemically grown monolayers of MoS2 with a silver-bowtie nanoantenna array supporting narrow surface-lattice plasmonic resonances, a unique two-dimensional optical system has been achieved. The enhanced exciton–plasmon coupling enables profound changes in the emission and excitation processes leading to spectrally tunable, large photoluminescence enhancement as well as surface-enhanced Raman scattering at room temperature. Furthermore, due to the decreased damping of MoS2 excitons interacting with the plasmonic resonances of the bowtie array at low temperatures stronger exciton–plasmon coupling is achieved resulting in a Fano line shape in the reflection spectrum. The Fano line shape, which is due to the interference between the pathways involving the excitation of the exciton and plasmon, can be tuned by altering the coupling strengths between the two systems via changing the design of the bowties lattice. The ability to manipulate the optical properties of two-dimensional systems with tunable plasmonic resonators offers a new platform for the design of novel optical devices with precisely tailored responses.
We explore the shape-dependent light scattering properties of silicon (Si) nanoblocks and their physical origin. These high-refractive-index nanostructures are easily fabricated using planar ...fabrication technologies and support strong, leaky-mode resonances that enable light manipulation beyond the optical diffraction limit. Dark-field microscopy and a numerical modal analysis show that the nanoblocks can be viewed as truncated Si waveguides, and the waveguide dispersion strongly controls the resonant properties. This explains why the lowest-order transverse magnetic (TM01) mode resonance can be widely tuned over the entire visible wavelength range depending on the nanoblock length, whereas the wavelength-scale TM11 mode resonance does not change greatly. For sufficiently short lengths, the TM01 and TM11 modes can be made to spectrally overlap, and a substantial scattering efficiency, which is defined as the ratio of the scattering cross section to the physical cross section of the nanoblock, of ∼9.95, approaching the theoretical lowest-order single-channel scattering limit, is achievable. Control over the subwavelength-scale leaky-mode resonance allows Si nanoblocks to generate vivid structural color, manipulate forward and backward scattering, and act as excellent photonic artificial atoms for metasurfaces.
Multi-color holography using metasurface is being studied in various ways to overcome the limitations of conventional optical holography. In this paper, we propose and numerically demonstrate an ...efficient method to generate multi-color holographic images from metasurface based on the depth-division multiplexing technique. The proposed metasurface consists of two-dimensional array of single-sized TiO
2
nanofins controlling the phase of transmitted light with cross-circular polarization based on wavelength-independent geometric phase. The meta-atom structure is optimized using systematic finite-difference time-domain simulations and high cross-polarization transmission efficiency of > 82% is simultaneously achieved at all three primary colors. Based on the optimized metasurface structure, a multi-color meta-hologram is designed by applying depth-division multiplexing technique. The holographic images generated by three-dimensional finite-difference time-domain simulations and numerical reconstruction based on Fresnel transformation agreed well with each other, demonstrating that the proposed method is effective in generating multi-color holographic images.
Optical vortex trapping can allow the capture and manipulation of micro- and nanometre-sized objects such as damageable biological particles or particles with a refractive index lower than the ...surrounding material. However, the quest for nanometric optical vortex trapping that overcomes the diffraction limit remains. Here we demonstrate the first experimental implementation of low-power nano-optical vortex trapping using plasmonic resonance in gold diabolo nanoantennas. The vortex trapping potential was formed with a minimum at 170 nm from the central local maximum, and allowed polystyrene nanoparticles in water to be trapped strongly at the boundary of the nanoantenna. Furthermore, a large radial trapping stiffness, ~0.69 pN nm(-1) W(-1), was measured at the position of the minimum potential, showing good agreement with numerical simulations. This subwavelength-scale nanoantenna system capable of low-power trapping represents a significant step toward versatile, efficient nano-optical manipulations in lab-on-a-chip devices.
Nanowires (NWs) and nanobelts (NBs) have been widely studied and fabricated into a variety of nanoscale devices such as light emitting diodes (LEDs), lasers and biosensors. These unique materials ...have attracted sustained attention due to their novel properties, ease of growth, and the ability to fabricate highly engineered devices. However, their widespread application remains hindered due to the difficulty in integrating multiple NWs or NBs together for more complex devices. Integration of multiple NWs and NBs together on the same chip can enable the coupling of different devices to help realize complex on-chip architectures such as photonic integrated circuits or nanoscale diagnostic tools, which currently require outcoupling using larger components. In this letter we report the coupling of on-chip NB LEDs and photodetectors using a single, precisely self-aligned, cadmium sulfide (CdS) NB fabricated on a silicon-on-insulator (SOI) substrate. Electroluminescence generated by the CdS NB is waveguided and measured across the self-aligned device and demonstrates an on/off ratio of 102–103. This work describes a new method for fabricating and integrating more complex nanoscale devices that can enable advances in areas such as on-chip optical computational components and nanoscale optical biodiagnostics.
We propose a full three-dimensional subwavelength surface-plasmon-polariton cavity based on a metal-coated dielectric nanowire with an axial heterostructure. Surface plasmon-polaritons are strongly ...confined at the nanowire-metal interface sandwiched by an effective plasmonic mirror that consists of lower-index nanowire core and metal shell. Numerical simulations show for a cavity <50 × 50 × 40 nm3 (mode volume, V ∼ 10−5 μm3) that a quality factor, Q, >36000 is achieved at 20 K. This ultrasmall plasmonic cavity can be used as a plasmonic emitter or laser device coupled to a plasmonic waveguide with a high coupling efficiency in deep-subwavelength photonic systems.
Structural colors generated by optical micro‐ or nanostructures have attracted much attention for replacing pigment colors due to their tunability and semipermanency. The advantages of structural ...colors are now ready to be extended to the spectral range outside that of visible wavelengths. Here, bright structural colors are demonstrated in the near‐ultraviolet (near‐UV) wavelength range based on the plasmonic resonance of an aluminum nanodisk array. Collective plasmonic oscillation of the aluminum nanodisks selectively reflects the near‐UV light with a high reflectance and narrow linewidth. The color of the reflected light is tuned over the full near‐UV range, depending on the structural parameters of the nanodisk array. In particular, aluminum nanodisk arrays can be used as structural color pixels that demonstrate printing of near‐UV images with a high resolution of ≈10 000 pixels per inch. The demonstrated near‐UV structural colors show significant progress toward UV filtering and imaging, anticounterfeit, color multiplexing, and photocatalysis.
The plasmonic resonance of an aluminum nanodisk array generates bright reflective structural color over the full near‐ultraviolet range. Eight different arrays show distinct colors with brightness >30% and a full‐width at half‐maximum ≈0.17 of the resonance wavelength. Additionally, printing of near‐UV images with a high resolution of ≈10 000 pixels per inch is demonstrated.
The realization of nonlinear photonic circuits to achieve the control of light-by-light is contingent upon a strong nonlinear response that can be captured in a guided-wave geometry. There remains a ...need to further scale down waveguides while maintaining a strong nonlinear response. In this study, we report second-harmonic generation and optical parametric generation using the second-order nonlinear response in an 80 nm thick CdS nanowire subwavelength waveguide. Moreover, our three-dimensional finite-difference time-domain (FDTD) simulations demonstrate that it is possible to enhance the coherence length due to the very nature of the subwavelength geometry. Nonlinear mixing in a nanowire subwavelength waveguide represents an advance toward all-optical processing and all-optical switching in integrated photonic circuits.
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