Optical birefringence plays an important role in the manipulation of polarization states of light. However, the weak birefringence in common birefringent materials restricts the device thickness to tens of microns for desired phase retardation. Although recent advances in dielectric metasurfaces have enabled remarkable birefringence using structurally anisotropic nanostructures, the refractive index contrast between the dielectric and the air cladding fundamentally limits the thickness of metasurfaces to a fraction of a micron to obtain the required phase retardation. Here, birefringent resonances in high-index tungsten disulfide (WS2) metasurfaces are utilized to push the thickness limit down to the deep subwavelength scale. The inherent high-index property of WS2 enables birefringent resonances in WS2 metasurfaces which consist of anisotropic nanostructures with a thickness of only 50 nm. Such birefringent resonances enhance the light-matter interaction and produce an unprecedented birefringence (Δneff) about 4. As a result, it is experimentally realized that circular-to-linear polarization conversion with a normalized efficiency of ≈90% within an incident angle range up to ±10°. The results break the fundamental limit of birefringent devices and provide strategies for creating ultimate thin polarization optical devices. 相似文献
Origami metasurfaces have emerged as a versatile platform for dynamically manipulating electromagnetic waves due to their numerous advantages, including cost-effectiveness, lightweight nature, and diverse structural transformations. They are particularly well-suited for reconfigurable chiroptical responses that can find utility in various applications. However, current research has primarily focused on modulating spectral properties like optical chirality and resonant frequencies, which may limit their practical applications. Herein, an origami metasurface enabled by a simple yet highly effective deformation method is proposed to achieve simultaneous tunable chirality and wavefront manipulation, which expands the modulation freedom of mechanical deformation in chiral metasurfaces. The planar metasurface with spin-insensitive transmittance is bulked into 3D metasurfaces to break the mirror symmetry, thereby triggering pronounced chiral responses. Additionally, through the implementation of propagation phase design, two types of meta-atoms with distinct phase responses are interleaved to create a chiral anomalous reflector that spin-selectively modulates the reflection beam. The experimental results agree well with the simulation results and theoretical predictions, verifying the high quality of the proposed design that may offer untapped potential for applications such as reconfigurable photonics devices. 相似文献
Dielectric metasurfaces are two‐dimensional structures composed of nano‐scatterers that manipulate the phase and polarization of optical waves with subwavelength spatial resolution, thus enabling ultra‐thin components for free‐space optics. While high performance devices with various functionalities, including some that are difficult to achieve using conventional optical setups have been shown, most demonstrated components have fixed parameters. Here, we demonstrate highly tunable dielectric metasurface devices based on subwavelength thick silicon nano‐posts encapsulated in a thin transparent elastic polymer. As proof of concept, we demonstrate a metasurface microlens operating at 915 nm, with focal distance tuning from 600 μm to 1400 μm (over 952 diopters change in optical power) through radial strain, while maintaining a diffraction limited focus and a focusing efficiency above 50%. The demonstrated tunable metasurface concept is highly versatile for developing ultra‐slim, multi‐functional and tunable optical devices with widespread applications ranging from consumer electronics to medical devices and optical communications.
Optical dielectric metasurfaces composed of arrayed nanostructures are expected to enable arbitrary spatial control of incident wavefronts with subwavelength spatial resolution. For phase modulation, one often resorts to two physical effects to implement a 2π-phase excursion. The first effect relies on guidance by tall nanoscale pillars and the second one exploits resonant confinement by nanoresonators with two degenerate Mie resonances. The first approach requires high aspect ratios, while the second one, known as Huygens’ metasurfaces, is much flatter, and thus easier to manufacture. The two approaches are compared, more focusing on conceptual rather than technological issues, and fundamental limitations with the latter are identified. The origin of the limitations based on general arguments are explained, such as reciprocity, multimode/monomode operation, and symmetry breaking. 相似文献
Beam steering is one of the main challenges in energy-efficient and high-speed infrared light communication. To date, active beam-steering schemes based on a spatial light modulator (SLM) or micro-electrical mechanical system (MEMS) mirror, as well as the passive ones based on diffractive gratings, are demonstrated for infrared light communication. Here, for the first time to the authors' knowledge, an infrared beam is steered by 35° on one side empowered by a passively field-programmable metasurface. By combining the centralized control of wavelength and polarization, a remote passive metasurface can steer the infrared beam in a remote access point. The proposed system has the scalability to support multiple beams, flexibility to steer the beam, high optical efficiency, simple and cheap devices on remote sides, and centralized control (low maintenance cost), while it avoids disadvantages such as grating loss, a small coverage area, and a bulky size. Based on the proposed beam-steering technology, a proof-of-concept experiment system with a data rate of 20 Gbps is also demonstrated. 相似文献
A general strategy for the realization of electric and magnetic quasi-trapped modes located at the same spectral position is presented. This strategy's application makes it possible to design metasurfaces allowing switching between the electric and magnetic quasi-trapped modes by changing the polarization of the incident light wave. The developed strategy is based on two stages: the application of the dipole approximation for determining the conditions required for the implementation of trapped modes at certain spectral positions and the creation of the energy channels for their excitation by introducing a weak bianisotropy in nanoparticles. Since excitation of trapped modes results in a concentration of electric and magnetic energies in the metasurface plane, the polarization switching provides possibilities to change and control the localization and distribution of optical energy at the sub-wavelength scale. A practical method for spectral tuning of quasi-trapped modes in metasurfaces composed of nanoparticles with a preselected shape is demonstrated. As an example, the optical properties of a metasurface composed of silicon triangular prisms are analyzed and discussed. 相似文献
A perfect vortex beam (PVB) is a propagating optical field carrying orbital angular momentum (OAM) with a radial intensity profile that is independent of topological charge. PVBs can be generated through the Fourier transform of a Bessel–Gaussian beam, which typically requires a well-aligned optical setup consisting of a spiral phase plate, an axion, and a lens. Here, based on a single-layer dielectric metasurface, the broadband generation of PVBs across the entire visible spectrum is demonstrated. The metasurface is composed of TiO2 nanopillars acting as deep-subwavelength half-waveplates, and able to provide the desired geometric phase profile to an incident circularly polarized light for the generation of PVBs. Through rigorous optimization of the nanopillars’ structural parameters, the authors experimentally generate vortex beams carrying OAM with different topological charges that exhibit constant radial intensity profiles, verifying their “perfect” characteristics. Furthermore, it is also demonstrated that the ellipticity and diameter of a PVB can be simultaneously controlled by adjusting the structural parameters of the metasurface, which further increases the flexibility in their design. These results open a new route towards creating ultra-compact, flat, multifunctional nanophotonic platforms for efficient generation of structured light beams. 相似文献
Transmission–reflection-integrated metasurfaces (TRIMs) provide an effective avenue to realize functionality integration and miniaturization of imaging and communication systems. However, most of the previous works suffer from large chromatic aberrations due to the intrinsic dispersive properties of the resonators constituting metasurfaces, which results in the meta-devices working in a small operation bandwidth. Here, a broadband achromatic TRIM is proposed based on the frequency-multiplexing scheme and dispersion engineering in transmission and reflection mode, respectively. As a proof of the scheme, 1D achromatic transmission–reflection-integrated focusing metasurface and common-caliber transmitarray and reflectarray flat plate antenna are demonstrated over a broad frequency range. The achromatic focusing in transmission mode and reflection mode with simulated focusing efficiencies of 13.12–17.21% and 14.57–20.86% are simultaneously realized at 12–18 and 19–24 GHz, respectively. The radiation gains increase by an average of 17.53 and 23.57 dB for the transmission mode and reflection mode relative to the bare standard rectangle waveguides. The scheme for achromatic and independent electromagnetic manipulation in transmission and reflection mode can also be applied to other frequency ranges and promise unprecedented progress for optical imaging and wireless telecommunication. 相似文献
Nature has long inspired scientists and engineers to develop transparent surfaces via constructing anti-reflective surfaces. In absence of anti-reflection (AR) coating, silicon reflects about 35% of light for a single interface air−silicon. Here, inspired by jellyfish anti-reflective eyes, a man-made anti-reflective surface on the facet of the waveguide is proposed and demonstrated for waveguides transparency in near-infrared. The optimized metamaterial with unit cells of 560 × 560 nm shows transparency of 2.6 times better as compared to the waveguide with blank facet. Metasurfaces are milled on the waveguides facets with a focused ion beam. Silicon-on-insulator waveguides are tested with an inline set-up. Far-field scattering diagrams reveal that it is the special geometry of the unit cells of the engraved metamaterial, which can be associated with the directional scattering resulting in combined effect: on one hand the ultra-high transparency of the device and on the other hand the efficient coupling to the low-order modes due to the focusing dielectric nano-antennas effect. Reported here waveguide facets as AR metamaterials on a chip, opens up opportunities to engineer transparent on-chip devices with high coupling efficiency for diverse applications from sensing to quantum technologies. 相似文献
