Abstract
AbstractMetasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi-directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi-directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add-on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface-sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full-wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing.
Highlights
Conventional optical devices made of natural materials have weak optical properties and they are usually bulky to achieve noticeable effects
The response for the asymmetric transmission phase (ATP) can be much larger than that of the asymmetric transmission (AT) for the complementary double-layer metasurface. These results demonstrate the advantage of using the add-on sapphire slab to control the chiral properties of metasurfaces/metamaterials. (Detailed discussion about the application of our approach to achiral metasurfaces can be found in Section 7 of the Supplementary Material.)
We propose a novel approach in the characterization of planar chiral metasurface with a controllable asymmetric transmission phase using a simple interference technique by adding a birefringent crystal, here a uniaxial a-cut sapphire slab, to the metasurface
Summary
Conventional optical devices made of natural materials have weak optical properties and they are usually bulky to achieve noticeable effects. Chiral metamaterials have surpassed ordinary natural chiral materials in applications as they have much stronger chiral effects [25, 26] These chiral metamaterials, especially the two-dimensional versions labeled as chiral metasurfaces, have great potentials in wave controls and manipulations as they, in addition to the handedness, are sensitive to the direction of the incident light, known as asymmetric transmission [27, 28]. Metasurfaces/metamaterials with tunable chirality such as controllable optical activity (OA) [32], circular dichroism (CD) [33], circular conversion dichroism (CCD) [34], and asymmetric transmission (AT) [35] have been reported Despite these efforts, it is still challenging to fabricate tunable chiral metasurfaces/metamaterials for the optical range due to technical limitations. Our approach is nondestructive and can be applied remotely to samples fabricated on ordinary substrates, opening up new opportunities in optical communication, imaging, and remote sensing applications
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