Zhaocheng Liu

Emergent Functionality and Controllability in Few‐Layer Metasurfaces

Recent progress in metamaterial research has successfully exceeded the limitations imposed by conventional materials and optical devices, enabling the manipulation of electromagnetic waves as desired. The distinct characteristics and controlling abilities of metamaterials make them ideal candidates for novel photonics devices not only in traditional optics but also for biological detection, medical science, and metrology. However, the controllability and functionality of both single-layer metasurfaces and bulk metamaterials are not sufficient to meet the requirements of emerging technologies; hence, new solutions must be found. As such technologies advance, new functionalities will emerge as different or identical single-layer metasurfaces are combined. Thus, innovation in few-layer metasurfaces will become an increasingly important line of research. Here, these metasurfaces are classified according to their functionalities and the few-layer metasurfaces that have been proposed up to now are presented in a clear sequence. It is expected that, with further development in this area, few-layer metasurfaces will play an important role in the family of optical materials.

Generation of vector beams with arbitrary spatial variation of phase and linear polarization using plasmonic metasurfaces.

A novel method is proposed to generate vector beams with arbitrary spatial variation of phase and linear polarization at the nanoscale using compact plasmonic metasurfaces with rectangular nanoapertures. The physical mechanism underlying the simultaneous control of light polarization and phase is explained. Vector beams with different spiral phasefronts are obtained by manipulating the local orientation and geometric parameters of the metasurfaces. In addition, radially and azimuthally polarized vector beams and double-mode vector beams are achieved through completely compensating for the Berry phase, which provides additional degrees of freedom for beam manipulation.

Broadband diodelike asymmetric transmission of linearly polarized light in ultrathin hybrid metamaterial

We present the underlying theory, the design specifications, and the experimental demonstration of the broadband diodelike asymmetric transmission of linearly polarized light in the near-infrared regime. This result is achieved through the use of a two-layer hybrid metamaterial, composed of an L-shaped metallic particle and a double nano antenna. The experimental results are shown to agree well with the theoretical predictions and the simulated transmission spectra. The realization of the diodelike asymmetric transmission can be attributed to the combination of two independently functioning metallic structures, which are shown to perform their respective function even when shifted away from perfect alignment. This work offers a further step in developing broadband diodelike asymmetric transmission for use in electromagnetic devices.

Controllable optical activity with non-chiral plasmonic metasurfaces

Optical activity is the rotation of the plane of linearly polarized light along the propagation direction as the light travels through optically active materials. In existing methods, the strength of the optical activity is determined by the chirality of the materials, which is difficult to control quantitatively. Here we numerically and experimentally investigated an alternative approach to realize and control the optical activity with non-chiral plasmonic metasurfaces. Through judicious design of the structural units of the metasurfaces, the right and left circular polarization components of the linearly polarized light have different phase retardations after transmitting through the metasurfaces, leading to large optical activity. Moreover, the strength of the optical activity can be easily and accurately tuned by directly adjusting the phase difference. The proposed approach based on non-chiral plasmonic metasurfaces exhibits large optical activity with a high controllable degree of freedom, which may provide more possibilities for applications in photonics.

High Performance Broadband Asymmetric Polarization Conversion Due to Polarization-dependent Reflection

We present the underlying theory, the design specifications, and the simulated demonstration of a high performance broadband asymmetric polarization conversion composed of an L-shaped gold particle and a gold nanoantenna array for the near-infrared regime. It can transform linearly polarized light to its cross polarization in the transmission mode for one propagation direction and efficiently reflect the light for the opposite propagation direction. The broadband asymmetric polarization conversion can be attributed to the polarization-dependent reflection of the nanoantenna array, which enhances the polarization conversion efficiency of the L-shaped particle and makes it asymmetric and devisable. This work offers a further step in the development of a high efficiency broadband optical activity device.

Fully interferometric controllable anomalous refraction efficiency using cross modulation with plasmonic metasurfaces.

We present a method of fully interferometric, controllable anomalous refraction efficiency by introducing cross-modulated incident light based on plasmonic metasurfaces. Theoretical analyses and numerical simulations indicate that the anomalous and ordinary refracted beams generated from two opposite-helicity incident beams and following the generalized Snells law will have a superposition for certain incident angles, and the anomalous refraction efficiency can be dynamically controlled by changing the relative phase of the incident sources. As the incident wavelength nears the resonant wavelength of the plasmonic metasurfaces, two equal-amplitude incident beams with opposite helicity can be used to control the anomalous refraction efficiency. Otherwise, two unequal-amplitude incident beams with opposite helicity can be used to fully control the anomalous refraction efficiency. This Letter may offer a further step in the development of controllable anomalous refraction.

Interferometric Control of Signal Light Intensity by Anomalous Refraction with Plasmonic Metasurface

We propose a new method of controlling signal light intensity by changing the polarization direction of pump light that is incident on a phase-gradient metasurface. Theoretical analyses and simulations demonstrate that, when the incident angles for signal and pump light sources conform to a certain relationship, the anomalous refraction of the pump light superposes with the signal light. The intensity of the signal light can be fully tuned across a broadband range by varying the polarization direction of the pump light. Our methods will contribute to the development of promising techniques to be used in photonics devices such as amplitude modulators and photoswitches.

Study on Z-Scan Characteristics for Light–Tunneling Heterostructures Composed Of One-Dimensional Photonic Band Gap Material and Metallic Film

The transmitted and reflected Z-scan characteristics for light-tunneling heterostructures composed of one-dimensional photonic bandgap material and metallic film are theoretically investigated. An apparent Z-scan signal will appear around the light-tunneling even if the incident peak intensity is very low. Both of the transmitted and reflected Z-scan signals from left incidence are much larger than those from right incidence, demonstrating the nonreciprocal for two incident directions. The variation of the reflected Z-scan curve shape is opposite to that of transmitted Z-scan curve shape as light wavelength increases. Moreover, the reflected Z-scan signals from left incidence will show a very sharp peak around the light-tunneling.