Yinghui Guo

Dispersion management of anisotropic metamirror for super-octave bandwidth polarization conversion.

Dispersion engineering of metamaterials is critical yet not fully released in applications where broadband and multispectral responses are desirable. Here we propose a strategy to circumvent the bandwidth limitation of metamaterials by implementing two-dimensional dispersion engineering in the meta-atoms. Lorentzian resonances are exploited as building blocks in both dimensions of the dedicatedly designed meta-atoms to construct the expected dispersion. We validated this strategy by designing and fabricating an anisotropic metamirror, which can accomplish achromatic polarization transformation in 4-octave bandwidth (two times of previous broadband converters). This work not only paves the way for broadband metamaterials design but also inspire potential applications of dispersion management in nano-photonics.

Merging plasmonics and metamaterials by two-dimensional subwavelength structures

As one of the major fields of photonics in the last few decades, plasmonics takes advantage of the coupling of light and free electrons in noble metals, and allows the localization of light beyond the diffraction limit. Recently, plasmonics has been introduced into the newly emerging metamaterials, which are artificially structured effective materials with unique physical properties that do not exist in natural materials. Based on the strong light–matter interaction below the diffraction limit, the plasmonic metamaterials have found important applications in various photonic devices, such as color filters, flat lenses and perfect absorbers. In this review article, we focus on the planar plasmonic metamaterials that rely on the patterned arrangement of metallic and dielectric inclusions in the two-dimensional (2D) space. The interesting optical effects, underlying physical principles and the practical applications in functional devices are outlined, with a brief discussion of their future development trends.

Dynamical manipulation of electromagnetic polarization using anisotropic meta-mirror.

Polarization control of electromagnetic wave is very important in many fields. Here, we propose an active meta-mirror to dynamically manipulate electromagnetic polarization state at a broad band. This meta-mirror is composed of a double-layered metallic pattern backed by a metallic flat plate, and the active elements of PIN diodes are integrated into the meta-atom to control the reflection phase difference between two orthogonal polarization modes. Through switching the operating state of the PIN diodes, the meta-mirror is expected to achieve three polarization states which are left-handed, right-handed circular polarizations and linear polarization, respectively. We fabricated this active meta-mirror and validated its polarization conversion performance by measurement. The linearly polarized incident wave can be dynamically converted to right-handed or left-handed circular polarization in the frequency range between 3.4 and 8.8u2009GHz with the average loss of 1u2009dB. Furthermore, it also can keep its initial linear polarization state.

Dispersion controlling meta-lens at visible frequency

Dispersion management is crucial in constructing spectrometers, superprisms, and achromatic lens systems. Unfortunately, the dispersion of natural materials is determined by the molecular energy levels with limited tunability, and thus conventional methods of dispersion controlling are complex and need to trade off other aberration. Metasurface offers an alternative method to overcome those limits via utilizing dedicatedly designed nanostructures that response to special wavelength, which results in well-engineered dispersions. As proof of the concept, we design a series of flat dielectric metasurface lenses, which are able to steer the dispersion arbitrarily for three wavelengths at visible frequency (473, 532, and 632.8 nm). Based on the unique dispersion engineering ability of metasurface, the achromatic meta-lens and the super-dispersion meta-lenses are realized. Furthermore, the light of different wavelengths can be focused on any desired spatial positions.

Super-resolution imaging with a Bessel lens realized by a geometric metasurface

In the super resolution imaging system, a lens and an axicon that can generate spherical wavefronts and non-diffracting Bessel beams respectively are both essential yet difficult to integrate using the traditional approach. We propose a new concept of a Bessel-lens to indicate unique optical elements that merge the functionalities of lenses and axicons simultaneously. The Bessel-lens is a mission that is extremely difficult if not impossible for state-of-the-art technology because of the exotic phase profile. Via the geometric phases in space-variant nanoslits, planar Bessel-lenses are designed and experimentally characterized for the first time to generate subdiffraction beams. Compared with a planar lens and axicon with the same dimensions and numerical aperture, the proposed Bessel-lens possesses a higher imaging resolution, which may find applications in microscopy, nanofabrication and dense data storage.

Nanoapertures with ordered rotations: symmetry transformation and wide-angle flat lensing

We report the experimental demonstration of a two-dimensional (2D) metasurface with ordered rotation of elements and show that it can be used to control the symmetry of light-matter interaction. A 2D lens is demonstrated in the visible region by transforming the rotational symmetry associated with the off-axis incident light to the translational symmetry, allowing an extraordinarily large field of view (FOV) as well as optical Fourier transformation. Furthermore, such a planar lens has a long focal depth, with polarization selectivity and subwavelength resolution. The scheme presented here may provide many new perspectives on the design of novel 2D optical devices.

Color display and encryption with a plasmonic polarizing metamirror

Abstract Structural colors emerge when a particular wavelength range is filtered out from a broadband light source. It is regarded as a valuable platform for color display and digital imaging due to the benefits of environmental friendliness, higher visibility, and durability. However, current devices capable of generating colors are all based on direct transmission or reflection. Material loss, thick configuration, and the lack of tunability hinder their transition to practical applications. In this paper, a novel mechanism that generates high-purity colors by photon spin restoration on ultrashallow plasmonic grating is proposed. We fabricated the sample by interference lithography and experimentally observed full color display, tunable color logo imaging, and chromatic sensing. The unique combination of high efficiency, high-purity colors, tunable chromatic display, ultrathin structure, and friendliness for fabrication makes this design an easy way to bridge the gap between theoretical investigations and daily-life applications.

Wide Field-of-view and Broadband Terahertz Beam Steering Based on Gap Plasmon Geodesic Antennas

Despite a plethora of applications ranging from wireless communications to sensing and spectroscopy, the current terahertz beam steering technologies suffer from tremendous insert loss, stringent control of electric bias, limited scanning angle, relatively complicated configuration and narrow operation bandwidth, preventing further practical application. We propose and demonstrate a conceptually new approach for terahertz beam steering by virtue of gap plasmon geodesic antennas. By adjusting the geometric dimension of the gap plasmon geodesic antennas, all gap plasmon modes add coherently along a peculiar direction that depends on the geodesic mean surface. Consequently, high directive beams are generated through the antenna, whose direction could be changed within a wide-angle range spanningu2009±45° by lateral motion of the feed. Furthermore, an assembled antenna structure consisting of four-element geodesic antennas array is proposed for full 360° beam steering, which can operate in a broadband range from 0.8u2009THz to 1.2u2009THz.

Meta-Chirality: Fundamentals, Construction and Applications

Chiral metamaterials represent a special type of artificial structures that cannot be superposed to their mirror images. Due to the lack of mirror symmetry, cross-coupling between electric and magnetic fields exist in chiral mediums and present unique electromagnetic characters of circular dichroism and optical activity, which provide a new opportunity to tune polarization and realize negative refractive index. Chiral metamaterials have attracted great attentions in recent years and have given rise to a series of applications in polarization manipulation, imaging, chemical and biological detection, and nonlinear optics. Here we review the fundamental theory of chiral media and analyze the construction principles of some typical chiral metamaterials. Then, the progress in extrinsic chiral metamaterials, absorbing chiral metamaterials, and reconfigurable chiral metamaterials are summarized. In the last section, future trends in chiral metamaterials and application in nonlinear optics are introduced.

Theory of microscopic meta-surface waves based on catenary optical fields and dispersion

Surface waves bounded by subwavelength-structured surfaces have many exotic electromagnetic properties different from those supported by smooth surfaces. However, there is a long-standing misconception, claiming that these waves must propagate along the macroscopic interface. In this paper, we describe in detail the microscopic meta-surface wave (M-wave) in artificial subwavelength structures. It is shown that the waves penetrating macroscopic surfaces share the essence of most surface waves (i.e., they spread along the microscopic interfaces, formed by adjacent constitutive materials). Equivalent circuit theory and transfer matrix method have been adopted to quantitatively describe these M-waves with high accuracy in the form of catenary optical fields and dispersion. Based on these analyses, novel omnidirectional band-stop filters and wide-angle beam deflectors are designed with operational angles up to 88°. We believe these results may provide many new perspectives for both the understanding and design of functional subwavelength structures.