Abstract
Chiral mirrors are a class of metamaterials that reflect circularly polarized light of a certain helicity in a handedness-preserving manner, while absorbing circular polarization of the opposite handedness. However, most absorbing chiral mirrors operate only in a narrow frequency band, as limited by the causality principle. Instead of absorbing the undesired waveform, here we propose a transparent chiral mirror that allows undesired waves to pass through. In particular, the handedness-preserving band of the transparent chiral mirror is free of the causality limit, thus enabling broadband functionality. Furthermore, since electromagnetic waves outside the handedness-preserving band may transmit through the proposed chiral mirror, the reflected wave contains only circular polarization components of a certain handedness over a wide frequency range, which is favored in many applications. Moreover, the scheme is lossless and scalable. To realize the proposed transparent chiral mirror, we apply an array of helical microstructures in a two-dimensional square lattice. Traditionally, this kind of structure has been used as a circular polarizer but we apply it instead in a reflective mode. Our work provides a bandwidth analysis of chiral mirrors, and paves the way to new opportunities for creating broadband chiral metamaterials with handedness-preserving properties.
Highlights
Artificial chiral structures, especially those in the emerging field of chiral metamaterials, have been highly effective for applications involving polarization selectivity.1,2 Researchers have realized a variety of two- and three-dimensional chiral metamaterials composed of structures that are non-superimposable on their own mirror image, giving rise to a series of applications in polarization manipulation, imaging, chemical and biological detection, and nonlinear optics.3–10Conventional mirrors will reverse the handedness of circularly polarized electromagnetic waves upon reflection (Fig. 1a)
Chiral mirrors are a class of metamaterials that reflect circularly polarized light of a certain helicity in a handedness-preserving manner, while absorbing circular polarization of the opposite handedness
Since electromagnetic waves outside the handedness-preserving band may transmit through the proposed chiral mirror, the reflected wave contains only circular polarization components of a certain handedness over a wide frequency range, which is favored in many applications
Summary
Artificial chiral structures, especially those in the emerging field of chiral metamaterials, have been highly effective for applications involving polarization selectivity. Researchers have realized a variety of two- and three-dimensional chiral metamaterials composed of structures that are non-superimposable on their own mirror image, giving rise to a series of applications in polarization manipulation, imaging, chemical and biological detection, and nonlinear optics.. Conventional mirrors will reverse the handedness of circularly polarized electromagnetic waves upon reflection (Fig. 1a). To preserve the handedness of the reflected wave, Eric and Nikolay proposed a type of chiral mirror (Fig. 1b). In the handedness-preserving band, the mirror reflects one circular polarization without changing its handedness while absorbing the other. This type of chiral mirror brings new functionalities that go beyond the conventional mirrors.. This type of chiral mirror brings new functionalities that go beyond the conventional mirrors.16–21 These absorbing chiral mirrors suffer from a narrow handedness-preserving band, because the absorption bandwidth of any passive layer with a fixed thickness is limited by the causality. Principle. To design a broadband chiral mirror requires a different design methodology
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