Metallic metasurface for high efficiency optical phase control in transmission mode

High-Efficiency, Dual-Band Beam Splitter Based on an All-Dielectric Quasi-Continuous Metasurface

Metasurface-based beam splitters attracted huge interest for their superior properties compared with conventional ones made of bulk materials. The previously reported designs adopted discrete metasurfaces with the limitation of a discontinuous phase profile. In this paper, we propose a dual-band beam splitter, based on an anisotropic quasi-continuous metasurface, by exploring the optical responses under x-polarized (with an electric field parallel to the direction of the phase gradient) and y-polarized incidences. The adopted metasurface consists of two identical trapezoidal silicon antenna arrays with opposite spatial variations that lead to opposite phase gradients. The operational window of the proposed beam splitter falls in the infrared and visible region, respectively, for x- and y-polarized light, resulting from the different mechanisms. When x-polarized light is incident, the conversion efficiency and total transmission of the beam splitter remains higher than 90% and 0.74 within the wavelength range from 969 nm to 1054 nm, respectively. In this condition, each array can act as a beam splitter of unequal power. For y-polarized incidence, the maximum conversion efficiency and transmission reach approximately 100% and 0.85, while the values remain higher than 90% and 0.65 in the wavelength range from 687 nm to 710 nm, respectively. In this case, each array can be viewed as an effective beam deflector. We anticipate that it can play a key role in future integrated optical devices.

Ultra-broadband large-angle beam splitter based on a homogeneous metasurface at visible wavelengths

Metasurface-based beam splitters with high efficiency, large split angle, wide bandwidth and easy fabrication are highly desirable and still in pursuit. In this paper, we propose a heuristic scheme for designing an ultra-broadband high-efficiency power beam splitter based on a homogeneous metasurface. The conversion efficiency and total transmission intensity of the power splitter stays higher than 95% and 0.66 within the wavelength region from 604 nm to 738 nm, respectively. Particularly, the conversion efficiency can maintain greater than 99% in 58 nm bandwidth. The angle between two split beams can reach a maximum of 157.82° at the wavelength of 738 nm. In addition to simplified design and easy fabrication, the proposed power beam splitter possesses high robustness as well. We expect that our design can pave a new way for realizing high-performance metasurface-based beam splitters.

Metasurface Color Filters Using Aluminum and Lithium Niobate Configurations

Two designs of metasurface color filters (MCFs) using aluminum and lithium niobate (LN) configurations are proposed and numerically studied. They are denoted as tunable aluminum metasurface (TAM) and tunable LN metasurface (TLNM), respectively. The configurations of MCFs are composed of suspended metasurfaces above aluminum mirror layers to form a Fabry-Perot (F-P) resonator. The resonances of TAM and TLNM are red-shifted with tuning ranges of 100 nm and 111 nm, respectively, by changing the gap between the bottom mirror layer and top metasurface. Furthermore, the proposed devices exhibit perfect absorption with ultra-narrow bandwidth spanning the whole visible spectral range by composing the corresponding geometrical parameters. To increase the flexibility and applicability of proposed devices, TAM exhibits high sensitivity of 481.5 nm/RIU and TLNM exhibits high figure-of-merit (FOM) of 97.5 when the devices are exposed in surrounding environment with different refraction indexes. The adoption of LN-based metasurface can enhance FWHM and FOM values as 10-fold and 7-fold compared to those of Al-based metasurface, which greatly improves the optical performance and exhibits great potential in sensing applications. These proposed designs provide an effective approach for tunable high-efficiency color filters and sensors by using LN-based metamaterial.

Resonant cavity enhanced waveguide transmission for broadband and high efficiency quarter-wave plate

Existing transmission type optical quarter-wave plates based on metallic sub-wavelength structures can hardly realize transmission efficiency above 60%. And their working bandwidths are still very narrow. In this paper, we demonstrate a transmission type quarter-wave plate design with efficiency above 92% over a broad wavelength range (from 1260 nm to 1560 nm). The device proposed is based on a one-dimensional metal-insulator-metal waveguide array buried in silica. Phase difference between transmitted TE and TM components can be tuned continuously. At the same time, transmission efficiency can be kept above 90% in the same spectral range for both the TE and TM incidences. The broad bandwidth and remarkable efficiency are explained with the combination of low dispersion of waveguide modes and the resonant cavity enhanced transmission effect. To give a better understanding of the structure, we also propose a modified effective medium model. The optical response of the structure can be well reproduced with the semi-analytic effective medium model.

Metallic metasurfaces for high efficient polarization conversion control in transmission mode

A high efficient broadband polarization converter is an important component in integrated miniaturized optical systems, but its performances is often restricted by the material structures, metallic metasurfaces for polarization control in transmission mode never achieved efficiency above 0.5. Herein, we theoretically demonstrate that metallic metasurfaces constructed by thick cross-shaped particles can realize a high efficient polarization transformation over a broadband. We investigated the resonant properties of designed matesurfaces and found that the interaction between double FP cavity resonances and double bulk magnetic resonances is the main reason to generate a high transmissivity over a broadband. In addition, through using four resonances effect and tuning the anisotropic optical response, we realized a high efficient (> 0.85) quarter-wave plate at the wavelength range from 1175nm to 1310nm and a high efficient (> 0.9) half-wave plate at the wavelength range from 1130nm to 1230nm. The proposed polarization converters may have many potential applications in integrated polarization conversion devices and optical data storage systems.