Ultrathin Metalens Research Articles

Broadband varifocal metalens via dielectric spin-decoupled metasurface

Ultrathin metalens with a large varifocal range and broadband spectral response play an important role in diverse optical applications. In this paper, we numerically demonstrate a broadband varifocal metalens in the near-infrared band based on two cascaded all-dielectric spin-decoupled metasurfaces. The spin-dependent phase profiles are introduced by combining the geometric phase and propagation phase. At the designed wavelength of 1550 nm, when the second metasurface is rotationally actuated with respect to the first metasurface, the left-circularly polarized (LCP) or right-circularly polarized (RCP) focal lengths of metalens can be continuously adjusted with the corresponding highest focusing efficiency of 32% and 50%, respectively. More importantly, the varifocal metalens with bifocal characteristics is realized under the excitation of linearly polarized (LP) light, and the total highest focusing efficiency of two focal spots is up to 48%. The proposed varifocal metalens is anticipated to find applications in miniaturized polarization detection, imaging devices, and wearable displays.

Design of a dielectric ultrathin near-infrared metalens based on electromagnetically induced transparency

A transmissive metasurface lens thinner than a wavelength promises a potential way to replace conventional bulky components for wavefront and polarization control of incident light. Here we propose a novel approach for an ultrathin metasurface lens at the working wavelength of 1550 nm composed of silicon cuboids on the silica substrate. Taking advantage of the ‘slow-light’ effect of the electromagnetically induced transparency (EIT) phenomena, the thickness of the proposed transmissive metalens has been reduced to 130 nm (∼1/12λ0), and it can focus incident light to a near diffraction-limited spot. The focusing efficiency of the ultrathin metalens is about 2 times larger than its peer without EIT effect. One key advantage of this metalens design is the reduction of the aspect ratio down to about 1, making this approach significantly degrade the difficulty of metalens manufacturing.

Through-Wall Wireless Communication Enabled by a Metalens

Getting wireless signals around obstacles or passing them through walls is proven to be challenging for electromagnetic waves with a short wavelength and some energy-efficient buildings due to thick insulating materials. Here, we propose a scheme of through-wall wireless communication by applying purposely designed passive metalenses for an asymmetric background medium of the wall. An ultrathin metalens consisting of three layers of metallic patterns is applied to focus the incoming waves to the other side of the wall with high efficiency. The focusing effect is verified by scanning the spatial distribution of electric fields. Due to the focusing effect, the wireless signal strength is significantly enhanced while propagating through the wall. To validate its use in the 5-GHz Wi-Fi environment, we demonstrate that the metalens can reconnect a network channel that is otherwise broken due to weak signal strength, and thus, significantly increase the data transmission rate. Our work opens an unobstructive and retrofitting approach for sustaining wireless communication in future eco-friendly buildings beyond 5G and 6G.

On-chip optical levitation with a metalens in vacuum

Optical levitation of dielectric particles in vacuum is a powerful technique for precision measurements, testing fundamental physics, and quantum information science. Conventional optical tweezers require bulky optical components for trapping and detection. Here, we design and fabricate an ultrathin dielectric metalens with a high numerical aperture of 0.88 at 1064 nm in vacuum. It consists of 500-nm-thick silicon nano-antennas, which are compatible with an ultrahigh vacuum. We demonstrate optical levitation of nanoparticles in vacuum with a single metalens. The trapping frequency can be tuned by changing the laser power and polarization. We also transfer a levitated nanoparticle between two separated optical tweezers. Optical levitation with an ultrathin metalens in vacuum provides opportunities for a wide range of applications including on-chip sensing. Such metalenses will also be useful for trapping ultracold atoms and molecules.

Ultrahigh numerical aperture meta-fibre for flexible optical trapping

Strong focusing on diffraction-limited spots is essential for many photonic applications and is particularly relevant for optical trapping; however, all currently used approaches fail to simultaneously provide flexible transportation of light, straightforward implementation, compatibility with waveguide circuitry, and strong focusing. Here, 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. The unique capabilities of this flexible, cost-effective, bio- and fibre-circuitry-compatible meta-fibre device were demonstrated by optically trapping microbeads and bacteria for the first time with only one single-mode fibre in combination with diffractive optics. Our study highlights the relevance of the unexplored but exciting field of meta-fibre optics to a multitude of fields, such as bioanalytics, quantum technology and life sciences.

Numerical simulation research of wide-angle beam steering based on catenary shaped ultrathin metalens

In this paper, a bilayer ultrathin (≈0.153λ) metalens is presented by exploring the advantage of the metasurface with catenary shape and symmetry transformation. The simulation results show that the proposed metalens has high polarization conversion efficiency (>90% even when the incidence angle is 60°), and the wide-angle beam steering ability is beyond ± 70°. Compared with the previous beam steering lens with transmitted array, the metalens in this paper exhibits obvious advantages. Moreover, the longitudinal local catenary fields existing in this metalens can ensure the wide-angle operation for this structure.

Ultrathin Metalenses: High‐Efficiency and Wide‐Angle Beam Steering Based on Catenary Optical Fields in Ultrathin Metalens (Advanced Optical Materials 19/2018)

Ultrathin Metalenses: High‐Efficiency and Wide‐Angle Beam Steering Based on Catenary Optical Fields in Ultrathin Metalens (Advanced Optical Materials 19/2018)

High‐Efficiency and Wide‐Angle Beam Steering Based on Catenary Optical Fields in Ultrathin Metalens

AbstractRecent advances in artificial subwavelength structures promise the realization of ultrathin, lightweight, and flat metalens, providing a potential candidate for traditional bulky and curved lens. Nevertheless, most metalenses are generally suffering from serious off‐axis aberration, resulting in a limited field‐of‐view (FOV). Here, a methodology to extend the FOV of metalens is presented by exploring the local catenary optical fields and symmetry transformation from rotational symmetry to transversal symmetry. As a proof of the concept, a high efficiency (>80% even when the incidence angle is titled by 60°) and ultrathin (≈0.127 λ) metalens consisting of bilayer geometric metasurface is designed, fabricated, and characterized. The wide FOV of metalens benefiting from local catenary fields and symmetry transformation is numerically demonstrated by full‐wave simulation and ray tracing method. Moreover, the wide‐angle beam steering ability beyond ± 60° is experimentally demonstrated, which exhibits obvious advantages compared with previous beam steering transmitarrays. The novelty of the proposed methodology lies at the fact that both transversal and longitudinal local catenary fields are excited in a single component: the transversal catenary field is utilized for high efficiency spin–orbit interaction and phase modulation, while the longitudinal catenary field and symmetry transformation ensure wide‐angle operation.

Arbitrary focusing lens by holographic metasurface

In this paper, an ultrathin metalens has been proposed based on a holographic metasurface that consists of elongated apertures in 40 nm gold film, which exhibit intriguing properties such as on- and off-axis focusing and also can concentrate light into multiple, discrete spots for circularly polarized incident lights. First, the spatial transmission phase distributions of the designed metalens with arbitrary focusing can be obtained by computer-generated holography. Then, the discrete phase distributions can be continuously encoded by subwavelength nanoapertures with spatially varying orientations in gold film. The simulation results show that our designed metalens can work efficiently for different types of focusing. Finally, our metasurface shows superior broadband characteristics between 670 and 810 nm, and the corresponding focal lengths of the designed lenses also can be efficiently modulated with the incident lights at different wavelengths.