Based on transformation optics, we introduce another set of generalized laws of reflection and refraction (differs from that of [Science 334, 333 (2011)]), through which a transformation media slab is derived as a meta-surface, producing anomalous reflection and refraction for all polarizations of incident light.

Generalized laws of reflection and refraction from transformation optics

Metasurfaces are planar photonic elements composed of subwavelength nanostructures, which can deeply interact with light and exploit new degrees of freedom (DOF) to manipulate optical fields. In the past decade, metasurfaces have drawn great interest from the scientific community due to their profound potential to arbitrarily control light. Here, recent developments of multiplexing and multifunctional metasurfaces, which enable concurrent tasks through a dramatic compact design, are reviewed. The fundamental properties, design strategies, and applications of multiplexing and multifunctional metasurfaces are then discussed. First, recent progress on angular momentum multiplexing, including its behavior under different incident conditions, is considered. Second, a detailed overview of polarization-controlled, wavelength-selective, angle-selective, and reconfigurable multiplexing/multifunctional metasurfaces is provided. Then, the integrated and on-chip design of multifunctional metasurfaces is addressed. Finally, future directions and potential applications are presented.

Metasurface‐Empowered Optical Multiplexing and Multifunction

Holography has numerous applications because of its capability of arbitrary wavefront modulation. Computer-generated holograms (CGHs) take it a big step forward. Conventional holography engineers the wavefront via phase accumulation, suffering from large size, low resolution, and small viewing angle. Metasurfaces, ultrathin two-dimensional metamaterials with subwavelength features, can manipulate the amplitude, phase, and polarization of the light, solving the above issues. In this review, advances of holography, CGH algorithms, and the principles of various metasurfaces are presented. Metasurface holography, realized by encoding the hologram in the metasurface, is investigated. Information multiplexing methods of metasurface holograms, including wavelength-multiplexed, polarization-multiplexed, complex amplitude modulated, nonlinear, and dynamic metasurfaces, are presented. The challenges and outlook of metasurface holograms are discussed.

When metasurface meets hologram: principle and advances

Polarization manipulation is a significant issue for artificial modulation of the electromagnetic (EM) wave, but general mechanisms all suffer the restriction of inherent symmetric properties between opposite handedness. Herein, a strategy to independently and arbitrarily manipulate the EM wave with orthogonal circular polarizations based on a metasurface is proposed, which effectually breaks through traditional symmetrical characteristics between orthogonal handedness. By synthesizing the propagation phase and geometric phase, the appropriate Jones matrix is calculated to obtain independent wavefront manipulation of EM waves with opposite circular polarizations. Two transmissive ultra-thin meta-deflectors are proposed to demonstrate the asymmetrical refraction of transmitted circularly polarized waves in the microwave region. Simulated transmitted phase front and measured far-field intensity distributions are in excellent agreement, indicating that the transmitted wave with different polarizations can be refracted into arbitrary and independent directions within a wide frequency band (relative bandwidth of 25%). The results presented in this paper provide more freedom for the manipulation of EM waves, and motivate the realizations of various polarization-independent properties for all frequency spectra.

Complementary transmissive ultra-thin meta-deflectors for broadband polarization-independent refractions in the microwave region

The optical vortex beam with an orbital angular momentum, featuring a doughnut intensity distribution and a helically structured wavefront, has received extensive attention due to its applications in nanoparticle manipulation and optical communications. In this paper, we propose high-efficiency polarization-independent vortex beam generators which are capable of transforming the arbitrarily polarized plane wave into a focusing optical vortex beam and an abruptly focusing airy vortex beam. Besides, based on holographic metasurfaces, we provide a general design scheme for detecting the topological charges. With such a design strategy, multichannel topological charge resolved devices are demonstrated, which successfully implement the detection of the topological charges from -2 to 2. The metasurfaces designed with a simple and effective method in light manipulation promise photonic applications in secure communications and other related areas.

High efficiency focusing vortex generation and detection with polarization-insensitive dielectric metasurfaces

Metasurfaces provide a compact, flexible, and efficient platform to manipulate the electromagnetic waves. However, chromatic aberration imposes severe restrictions on their applications in broadband polarization control. Here, we propose a broadband achromatic methodology to implement polarization-controlled multifunctional metadevices in mid-wavelength infrared with birefringent meta-atoms. We demonstrate the generation of polarization-controlled and achromatically on-axis focused optical vortex beams with diffraction-limited focal spots and switchable topological charge (L∥ = 0 and L⊥ = 2). Besides, we further implement broadband achromatic polarization beamsplitter with high polarization isolation (extinction ratio up to 21). The adoption of all-silicon configuration not only facilitates the integration with CMOS technology but also endows the polarization multiplexing meta-atoms with broad phase dispersion coverage, ensuring the large size and high performance of the metadevices. Compared with the state-of-the-art chromatic aberration-restricted polarization-controlled metadevices, our work represents a substantial advance and a step toward practical applications.

Mid-infrared polarization-controlled broadband achromatic metadevice.

Broadband Achromatic Metalens in Mid‑Wavelength Infrared

We propose a novel approach to designing an ultrathin polarization-independent metalens (PIM) by utilizing antennas without rotational invariance Two arrays of nanoblocks are elaborately designed to form the super cell of the PIM, which are capable of focusing right-handed circularly polarized and left-handed circularly polarized lights With such a strategy, the PIM is able to achieve polarization-independent focusing, since the light with any polarization can be treated as a combination of the two orthogonal ones A theoretical analysis based on the Jones vector is proposed to detailedly explore the underlying physics The polarization-independent characteristic of the designed PIM is also demonstrated by utilizing finite difference time domain simulations Moreover, polarization-independent focusing can be achieved within a wavelength range of 400 nm These results can deepen our understanding of polarization-independent focusing and provide a new method for designing ultrathin polarization-independent devices

Polarization-independent metalens constructed of antennas without rotational invariance.

Manipulating the polarization states of electromagnetic waves, a fundamental issue in optics, has attracted intense attention. However, most of the reported devices are either so bulky or with specific functionalities. Here we propose a conceptually new approach to design an ultra-thin meta-waveplate (MWP) with anomalous functionalities. By elaborately designing the structural units of the metasurface, the incident right circular polarized (CP) light carrying spin angular momentum can be coupled into two surface plasmon modes with opposite orbital angular momenta which interaction with each other in the near-field, degenerating to a linear polarized (LP) light in the far-filed. The incoming spin angular momentum is annihilated and the designed MWP can function as a quarter-waveplate. However, compared with the conventional quarter-waveplates, our designed MWP owns the unidirectional function (only converting CP light to LP light) with a certain output polarization angle, which provides an extra degree of freedoms in controlling the polarization. Moreover, the designed MWP can function as a chiral material and exhibiting optical rotation properties within a broad bandwidth.

Feilong Yu

Papers

High efficiency focusing vortex generation and detection with polarization-insensitive dielectric metasurfaces

Mid-infrared polarization-controlled broadband achromatic metadevice.

Broadband Achromatic Metalens in Mid‑Wavelength Infrared

Polarization-independent metalens constructed of antennas without rotational invariance.

Annihilating optical angular momentum and realizing a meta-waveplate with anomalous functionalities