Key Takeaways & Executive Findings
- •• The proposed single-layer chiral metasurface achieves a high circular polarization extinction ratio, overcoming the traditional trade-off between structural complexity and performance. • It directly converts circularly polarized incident light into linearly polarized light, enabling efficient and compact circular polarization detection. • The operating wavelength is tunable by adjusting geometric parameters, offering design flexibility for different applications. • Experimental demonstrations confirm strong circular dichroism with a simplified fabrication process compared to multi-layer or 3D chiral metasurfaces.
Abstract
Circular polarizers based on the metasurface suffer from a trade-off between the structural complexity and the polarization extinction ratio (ER). Herein, we present a single-layer chiral metasurface with strong circular dichroism. The structure turns a circularly polarized incident beam into a linearly polarized beam, achieving a high circular polarization ER. The operating wavelength of the proposed metasurface is tunable by changing the geometric parameters. The metasurface’s localized surface plasmon resonances between structures ensure strong chiral optical effects. We further experimentally demonstrate the circular dichroism of the fabricated metasurface.
1. Introduction
Polarization is critical for light. In particular, circularly polarized light (CPL) is widely used in holography (Wang Q et al., 2018; Wan et al., 2022), bioimaging, optical communication (Farshchi et al., 2011), and many other advanced optical technologies (Lin et al., 2004; Garcia et al., 2015). The detection of CPL has a high potential for the development of these optical technologies. Traditional optical CPL detection requires a quarter-wave plate (QWP), a linear polarizer (LP), and other mechanically rotating components. This causes substantial losses in sensitivity and resolution in light detection. However, the progress in optical metasurfaces provides opportunities for ultra-thin CPL detection and manipulation.
Optical metasurfaces are artificial electromagnetic media structured on the subwavelength scale that exhibit unprecedented properties. Over the past few years, optical metasurfaces have been employed for the design and fabrication of optical elements and systems with abilities that surpass the performance of conventional optical elements (Pendry et al., 2006; Soukoulis and Wegener, 2010; Yu et al., 2011; Frese et al., 2019). Specifically, for polarization applications, a three-dimensional (3D) chiral optical metasurface was first proposed to differentiate the handedness of CPL (Hentschel et al., 2017), performing a wider regulation bandwidth and a higher circular polarization extinction ratio (ER). For example, the gold helix achieves an ER of 20 over a wide wavelength range (Gansel et al., 2010). The spiral-type ramp-shaped metamaterial (Rajaei et al., 2019) and the L-shaped metallic strip can also achieve optical chirality (Dietrich et al., 2012). Three-dimensional structures achieve high ERs and broad bandwidths. However, the fabrication of these complicated nanostructures has a high requirement for the equipment and the fabrication procedure, which is a fatal limitation to mass production.
With the development of nanotechnology, planar lithography techniques, such as photolithography and electron-beam lithography, have become mature, and the multi-layer metasurface dominates the research on artificial nanostructures for CPL detection. Multi-layer metasurfaces realize circular dichroism by rotating components of each layer or combining diverse metasurfaces to form a 3D chiral structure (Zhao Y et al., 2012; Wang ZJ et al., 2016; Yun et al., 2017; Bai et al., 2019; Gorkunov et al., 2020; Cen et al., 2022; Zhao X et al., 2022). The ER of a multi-layer metasurface can reach 35 in experiments (Basiri et al., 2019). However, the multi-layer metasurface also suffers from fabrication challenges. For example, aligning vertically adjacent layers always requires a complex fabrication procedure involving multiple lithography and film deposition steps. Single-layer structures can also be chiral and present circular dichroism, providing an alternative that has a simplified fabrication procedure. However, they always suffer from relatively low ERs in simulations (below 20) (Li et al., 2015; Zhang et al., 2017; Ma et al., 2018). To resolve this dilemma, we develop a single-layer chiral metasurface that performs better circular dichroism and demonstrate it both in theory and through experiments. The operating wavelength of the proposed metasurface is tunable by changing geometric parameters.
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Xinjie SUN, Xin HE, Zixin CAI, Xiang HAO (2025). Single-layer chiral metasurface for circularly polarized light detection. Frontiers of Information Technology & Electronic Engineering. https://doi.org/10.1631/FITEE_2400081
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Frequently Asked Questions
What is a chiral metasurface?
A chiral metasurface is a subwavelength-structured artificial electromagnetic medium that exhibits chirality, meaning it responds differently to left-handed and right-handed circularly polarized light. This property enables applications such as circular polarization detection and manipulation.
How does this single-layer metasurface achieve circular polarization detection?
The proposed single-layer chiral metasurface converts a circularly polarized incident beam into a linearly polarized beam. By analyzing the resulting linear polarization, the handedness of the circular polarization can be determined, achieving a high circular polarization extinction ratio.
What is the polarization extinction ratio (ER)?
The polarization extinction ratio (ER) is a figure of merit that quantifies the ability of a device to distinguish between two orthogonal polarization states. A higher ER indicates better discrimination between left-handed and right-handed circular polarizations.
What are the advantages of a single-layer design compared to multi-layer or 3D structures?
Single-layer metasurfaces offer a simplified fabrication process, requiring fewer lithography and deposition steps, which makes them more suitable for mass production. This work demonstrates that a single-layer design can achieve high circular dichroism, overcoming the traditional limitation of low extinction ratios.
How is the operating wavelength of the metasurface tuned?
The operating wavelength can be adjusted by changing the geometric parameters of the metasurface structures, such as their size, shape, and period. This tunability allows the device to be optimized for specific wavelength ranges.
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