Physical Review Letters
Disorder-Induced Topological State Transition in the Optical Skyrmion Family
Skyrmions endowed with topological protection have been extensively investigated in various platforms including magnetics, ferroelectrics, and liquid crystals. While the optical counterpart has been proposed and realized recently, the study of optical skyrmions is still in its infancy. Among the unexplored questions, the investigation of the topology induced robustness against disorder is of substantial importance on both fundamental and practical sides but remains elusive. In this Letter, we manage to generate optical skyrmions numerically in real space with different topological features at will, providing a unique platform to investigate the robustness of various optical skyrmions. A disorder-induced topological state transition is observed for the first time in a family of optical skyrmions composed of six classes with different skyrmion numbers.
Plasmonic bound states in the continuum to tailor light-matter coupling
Plasmon resonances play a pivotal role in enhancing light-matter interactions in nanophotonics, but their low-quality factors have hindered applications demanding high spectral selectivity. Here, we demonstrate the design and 3D laser nanoprinting of plasmonic nanofin metasurfaces, which support symmetry-protected bound states in the continuum up to the fourth order. By breaking the nanofins’ out-of-plane symmetry in parameter space, we achieve high-quality factor (up to 180) modes under normal incidence. The out-of-plane symmetry breaking can be fine-tuned by the nanofins’ triangle angle, opening a pathway to precisely control the ratio of radiative to intrinsic losses. This enables access to the under-, critical, and over-coupled regimes, which we exploit for pixelated molecular sensing.
Thin film surface phonon polariton dispersion
Surface phonon polaritons (SPhPs) are mixed light-matter states originating from strong coupling of photons with lattice vibrations. We retrieve the SPhP dispersion in silicon carbide free-standing membranes few hundreds of nanometers thick through near-field spectroscopy. We find several branches in the experimental dispersion, which we rationalize as multiple reflections of tip and edge launched SPhPs, in good agreement with theoretical predictions. Our work paves the way to employ large-area free standing membranes as a platform for phonon polaritonics, with foreseeable applications in the field of thermal management at the nanoscale.
Metasurface measuring twisted light in turbulence
We demonstrate the use of an ultrathin OAM mode-sorting metasurface for characterizing the OAM orthogonality breakdown under different turbulence conditions. Our approach allows the measurement of the whole OAM spectrum at the same time. This metasurface exhibits strong OAM selectivity with an average modal crosstalk below −42.4 dB for OAM modes with topological charges ranging from −15 to +15. Our results suggest that higher-order OAM modes are as robust as lower-order modes in particular turbulence environments, paving the way for future practical free-space OAM communications harnessing high-dimensional OAM multiplexing. We demonstrated that a flat optical device with a small form factor can be integrated with practical communication systems for compact, fast, and efficient generation and detection of twisted light.
Radial bound states in the continuum for polarisation-invariant nanophotonics
We introduce radial quasi-bound states in the continuum (radial BICs) as a new class of radially distributed electromagnetic modes controlled by structural asymmetry in a ring of dielectric rod pair resonators. The radial BIC platform provides polarization-invariant and tunable high-Q resonances with strongly enhanced near fields in an ultracompact footprint as low as 2 µm2. We demonstrate radial BIC 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.
Strong chiroptical effects from a chiral metasurface-coupled perovskite nanocrystal monolayer
Here we developed a hybrid system of a dielectric chiral nanoantenna array that was coated with a monolayer of cubic all-inorganic lead halide perovskite nanocrystals. By tuning the thickness of the perovskite film down to one monolayer of nanocrystals, we restricted the interactions exclusively to the near-field regime. The chiral surface built of z-shaped Si nanoantennas features pronounced chiral resonances in the visible to IR region. We demonstrate that the two-photon excited photoluminescence emission of the nanocrystals can be enhanced by up to one order of magnitude in this configuration.
An achromatic metafiber for focusing and imaging
We present the design and nanoprinting of a 3D achromatic diffractive metalens on the end face of a single-mode fiber, capable of performing achromatic and polarization-insensitive focusing across the entire near-infrared telecommunication wavelength band ranging from 1.25 to 1.65 μm. Furthermore, we demonstrate the use of our compact and flexible achromatic metafiber for fiber-optic confocal imaging, capable of creating in-focus sharp images under broadband light illumination. These results may unleash the full potential of fiber meta-optics for widespread applications including hyperspectral endoscopic imaging, femtosecond laser-assisted treatment, deep tissue imaging, wavelength-multiplexing fiber-optic communications, fiber sensing, and fiber lasers.
Optical Metasurfaces for Energy Conversion
Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light–matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.
Speical ISSUE IN Journal of Optics
Vectorial wavefront holography
Polarisation holography is underpinned by the Jones matrix method that uses birefringent holograms, including ultrathin metasurface holograms, limiting the polarisation control to orthogonal polarisation states. Here I introduce a novel concept of vectorial wavefront holography by exploiting the wavefront shaping of a structured vector beam. I will show that a phase hologram can be used to tailor the polarisation interference of a vector beam in momentum space, creating arbitrary polarisation states that include but not limited to the linear, circular, azimuthal, and radial polarisations.
Nanophotonic Materials for Twisted Light Manipulation
We summarize recent metasurface devices developed for OAM generation in both real and momentum space, presenting design principle and exemplary devices. We further discuss current challenges faced by the nanophotonic field for twisted light manipulation and future advances to meet these challenges. We believe twisted light manipulation in nanophotonics will continue to make significant impact on future development of ultracompact, ultrahigh-capacity, and ultrahigh-speed OAM systems-on-a-chip.
Advances in Optics and Photonics
Nanophotonic manipulation of optical angular momentum for high-dimensional information optics
This review aims to introduce the emerging concept of angular momentum (AM)-involved information optics and its implementation in nanophotonic devices.
Journal of Optics
Roadmap on multimode light shaping
This Roadmap highlights the common roots of these different techniques and thus establishes links between research areas that complement each other seamlessly. We provide an overview of all these areas, their backgrounds, current research, and future developments. We highlight the power of multimodal light manipulation and want to inspire new eclectic approaches in this vibrant research community.
OAM-controlled hybrid nanowire circuit
An orbital angular momentum-controlled hybrid nanowire circuit allows the use of different twisted light modes for selective excitation of semiconductor nanowires on-a-chip, unveiling the possibility of building orbital angular momentum-based optical switches, logic gates, and modulators with a potentially high capacity.
Optical vortices in nanophotonics (Invited)
Optical vortices carried by twisted light wavefronts have attracted a great deal of interest, providing not only new physical insights into light-matter interactions, but also a transformative platform for boosting optical information capacity. Here, we provide a mini review on recent achievements made in nanophotonics for the generation and detection of optical vortices and some of their applications.
Nanointerferometric detection of the spin–orbit Hall effect
We demonstrate a nanointerferometric scheme to map light’s spin and orbital angular momentum with a subwavelength resolution via the interferometric scattering signal from a plasmonic nanohole. Further, we demonstrate the application of the nanointerferometric method to discrimination of spin–orbit Hall effect on the hybrid-order Poincaré sphere.
Light science & applications
Ultrahigh-NA metafibre for flexible optical trapping
We demonstrate the design and 3D nanoprinting of an ultrahigh numerical aperture meta-fibre for highly flexible optical trapping. Taking into account the peculiarities of the fibre environment, we implemented an ultrathin meta-lens on the facet of a modified single-mode optical fibre via direct laser writing, leading to a diffraction-limited focal spot with a record-high numerical aperture of up to NA ≈ 0.9.
Topological insulator-based gap surface plasmon metasurfaces (Invited)
We numerically demonstrated the plasmonic capabilities of the topological insulator (TI) Bi2Te3 as a material for gap–surface plasmon (GSP) metasurfaces. Our work forms the basis for accurately controlling the far- and near-field responses of TI-based GSP metasurfaces in the visible spectral range.
Complex-amplitude metasurface for OAM holography
We demonstrate the use of a complex-amplitude metasurface hologram for orbital angular momentum holography that is capable of multiplexing up to 200 independent orbital angular momentum channels. Our metasurface can be three-dimensionally printed in a polymer matrix on SiO2 for large-area fabrication.
3D vectorial holography
We demonstrate 3D vectorial holography where an arbitrary 3D vectorial field distribution on a wavefront can be precisely reconstructed using the machine learning inverse design based on multilayer perceptron artificial neural networks.
We show that the monolithic integration of dielectric metasurfaces with VCSELs enables remarkable arbitrary control of the laser beam profiles, including self-collimation, Bessel and Vortex lasers, with high efficiency. Such wafer-level integration of metasurface through VCSEL-compatible technology simplifies the assembling process and preserves the high performance of the VCSELs.
OAM holography for high-security encryption
We demonstrate OAM holography by discovering strong OAM selectivity in the spatial-frequency domain without a theoretical helical mode index limit. As such, OAM holography allows the multiplexing of a wide range of OAM-dependent holographic images with a helical mode index spanning from −50 to 50, leading to a 10 bit OAM-encoded hologram for high-security optical encryption.
Metasurface OAM holography
We demonstrate metasurface orbital angular momentum holography by utilizing strong orbital angular momentum selectivity offered by meta-holograms consisting of GaN nanopillars with discrete spatial frequency distributions. The reported orbital angular momentum-multiplexing allows lensless reconstruction of a range of distinctive orbital angular momentum-dependent holographic images.
On-chip OAM nanometrology
We demonstrate angular-momentum nanometrology through the spatial displacement engineering of plasmonic angular momentum modes in a CMOS-compatible plasmonic topological insulator material. The generation and propagation of surface plasmon polaritons on the surface of an ultrathin topological insulator Sb2Te3 film with a thickness of 100 nm is confirmed, exhibiting plasmonic figures of merit superior to noble metal plasmonics in the ultraviolet-visible frequency range.
laser & photonics reviews
Angular momentum-controlled near-unity bisignate circular dichroism
Non-absorption-based bisignate circular dichroism is demonstrated through the nonresonant angular momentum mode-sorting sensitivity of a single nanoring slit enclosed by a concentric plasmonic nanogroove coupler. Quasi-flat bisignate circular dichroism with a near-unity magnitude is achieved in the visible and near-infrared wavelength range.
On-chip OAM multiplexing
We demonstrate noninterference angular momentum multiplexing by using a mode-sorting nanoring aperture with a chip-scale footprint as small as 4.2 micrometers by 4.2 micrometers, where nanoring slits exhibit a distinctive outcoupling efficiency on tightly confined plasmonic modes. The nonresonant mode-sorting sensitivity and scalability of our approach enable on-chip parallel multiplexing over a bandwidth of 150 nanometers in the visible wavelength range.
New Horizons Research Centre
Clayton, VIC 3800, Australia