Spin-encoded Wavelength-space Multitasking Janus Metasurfaces&nbsp;

doi:10.21203/rs.3.rs-120169/v1

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Spin-encoded Wavelength-space Multitasking Janus Metasurfaces

https://doi.org/10.21203/rs.3.rs-120169/v1

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The fruitful progress toward light manipulation in reflective (R) or transmissive (T) geometry (half-space) has facilitated strong aspiration to achieving full-space electromagnetic wave control in both R and T channels. Although it promises large-capacity and integrated functionality, yet imposes prohibitive difficulty and big challenging for extreme wave control (direction of arrival in full space) via an ultrathin flat device. As of today, very limited demonstrations were reported for single-band and linear-polarization operation, significantly limiting the exploitable degree of freedoms (DoFs) for real-world applications. Herein, we report for the first time a triple-layer wavelength-space multitasking scheme for wide-angle and large-capacity detection. Two anisotropic sub-meta-atoms are engineered with high quality factor and simultaneous in-plane and out-of-plane symmetry breaking, facilitating four R and two T spin-conversion channels with high efficiency and insulation. The chirality-assisted Fano effect gives rise to the wide-angle operation and boosted channels. Above features and released DoF would be extraordinary beneficial for large-capability and angle-engineered advanced device. Two proof-of-concept metadevices, i.e., large-scanning kaleidoscopic-beam generator and a wide-angle large-capacity reverser for multi-target tracking, are devised to verify the significance. Numerical and experimental results have approved predesigned advanced functions at six channels with measured efficiency over 75%. Our findings in multi-DoF multitasking of metasurfaces could stimulate great interest in radar applications with versatile beam generation and multi-channel integration.

Electrical Engineering

Chirality

Fano splitting

Janus metasurface

wavelength-space multitasking

spin wave control

FigS1.jpg
Figure S1 Illustration of the frequency ratio control over f1 and f2 by the asymmetry gap β.
To gain an insight into the principle of multiband operation, we afford FDTD calculated current distributions on the meta-atom, see Fig. S2. As can be inspected, the current is densely distributed around the left longer part of ASRR at f1, whereas it is strongly localized around the right shorter part at f2, accounting for the two reflective operation band. Moreover, the current intensity is mainly concentrated near the top-and-bottom evolved H patterns and centre annular slot at f3, indicating an ABA transmission response. The origin of above three operation modes gives us a clear guideline for individual control.
FigS1.jpg
Figure S1 Illustration of the frequency ratio control over f1 and f2 by the asymmetry gap β.
To gain an insight into the principle of multiband operation, we afford FDTD calculated current distributions on the meta-atom, see Fig. S2. As can be inspected, the current is densely distributed around the left longer part of ASRR at f1, whereas it is strongly localized around the right shorter part at f2, accounting for the two reflective operation band. Moreover, the current intensity is mainly concentrated near the top-and-bottom evolved H patterns and centre annular slot at f3, indicating an ABA transmission response. The origin of above three operation modes gives us a clear guideline for individual control.
FigS2.jpg
Current distributions on the meta-atom at three representative frequencies of f1, f2 and f3. Given the clear origin of three resonances, the key for meta-atom design is how to maintain the high efficiency of spin conversion. Fig. S3 plots the frequency spectrum of the composite meta-atom under x and y linearly-polarized (LP) EM wave excitation for both reflection and transmission, respectively. As is appreciated, high reflection rate (|ryy|≈|rxx|>0.88) and transmission (|tyy|≈|txx|≈1) rate are clearly observed at f1, f2, and f3 for both co-polarized components in two cases. Moreover, the phase difference (φyy-φxx) between them is around 180o across three bands. Therefore, we conclude that the high spin conversion efficiency can be well engineered by controling birefringent response of the anisotropic ASRR and evolved H structure under LP excitation.
FigS2.jpg
Current distributions on the meta-atom at three representative frequencies of f1, f2 and f3. Given the clear origin of three resonances, the key for meta-atom design is how to maintain the high efficiency of spin conversion. Fig. S3 plots the frequency spectrum of the composite meta-atom under x and y linearly-polarized (LP) EM wave excitation for both reflection and transmission, respectively. As is appreciated, high reflection rate (|ryy|≈|rxx|>0.88) and transmission (|tyy|≈|txx|≈1) rate are clearly observed at f1, f2, and f3 for both co-polarized components in two cases. Moreover, the phase difference (φyy-φxx) between them is around 180o across three bands. Therefore, we conclude that the high spin conversion efficiency can be well engineered by controling birefringent response of the anisotropic ASRR and evolved H structure under LP excitation.
FigS3.jpg
Figure S3 Illustration of the physics for the high efficiency of spin conversion under triple R and T channels. In the main text, we have shown clear evidence for the individual control at several target frequencies. Here, we afforded comprehensive results in full spectrum to further demonstrate our declaration. Figs. S4~S6 illustrates the effect of individual change of ψ1, ψ2 and ψ3 for each sub-atom to the total reflection and transmission properties. As is much appreciated from Figs. S4~S6, negligible mode shift and amplitude penalty is observed in all cases when altering ψ1, ψ2 and ψ3 within 0~150o in steps of 30o. Most importantly, individual changing of ψ1 and ψ2 only induces elegant reflection and transmission PB phase, respectively without significant phase distortion, indicating a satisfactory suppressed mutual impact. Moreover, the near-unity spin conversion efficiency is inspected in all reflection and transmission modes. Above good feature can also be inspected from the opposite side of the meta-atom (backward channel) in a completely independent manner. Such a proposal finds strong support from Fig. S4, where altering ψ2 does not pose any influence on the reflection and transmission response of observed side at f1, f2 and f3. Such an intriguing isolation is the key for engineering asymmetry forward and backward reflective functions of F1~F4 in both sides.
FigS3.jpg
Figure S3 Illustration of the physics for the high efficiency of spin conversion under triple R and T channels. In the main text, we have shown clear evidence for the individual control at several target frequencies. Here, we afforded comprehensive results in full spectrum to further demonstrate our declaration. Figs. S4~S6 illustrates the effect of individual change of ψ1, ψ2 and ψ3 for each sub-atom to the total reflection and transmission properties. As is much appreciated from Figs. S4~S6, negligible mode shift and amplitude penalty is observed in all cases when altering ψ1, ψ2 and ψ3 within 0~150o in steps of 30o. Most importantly, individual changing of ψ1 and ψ2 only induces elegant reflection and transmission PB phase, respectively without significant phase distortion, indicating a satisfactory suppressed mutual impact. Moreover, the near-unity spin conversion efficiency is inspected in all reflection and transmission modes. Above good feature can also be inspected from the opposite side of the meta-atom (backward channel) in a completely independent manner. Such a proposal finds strong support from Fig. S4, where altering ψ2 does not pose any influence on the reflection and transmission response of observed side at f1, f2 and f3. Such an intriguing isolation is the key for engineering asymmetry forward and backward reflective functions of F1~F4 in both sides.
FigS4.jpg
Figure S4 Effect of the rotation ψ1 to the (a, b) reflection rRL and (c, d) transmission tRL (a, c) amplitude and (b, d) phase properties.
FigS4.jpg
Figure S4 Effect of the rotation ψ1 to the (a, b) reflection rRL and (c, d) transmission tRL (a, c) amplitude and (b, d) phase properties.
FigS5.jpg
Figure S5 Effect of the rotation ψ2 to the (a, b) reflection rRL and (c, d) transmission tRL (a, c) amplitude and (b, d) phase properties.
FigS5.jpg
Figure S5 Effect of the rotation ψ2 to the (a, b) reflection rRL and (c, d) transmission tRL (a, c) amplitude and (b, d) phase properties.
FigS6.jpg
Figure S6 Effect of the rotation ψ3 to the (a, b) reflection rRL and (c, d) transmission tRL (a, c) amplitude and (b, d) phase properties.
FigS6.jpg
Figure S6 Effect of the rotation ψ3 to the (a, b) reflection rRL and (c, d) transmission tRL (a, c) amplitude and (b, d) phase properties.
FigS7.jpg
Figure S7 Layout of the triple-layer full-space kaleidoscopic-beam generator based on our chirality-assisted wavelength-space multitasking concept. The top row is the CAD model while the bottom row is the photograph of fabricated sample.
FigS7.jpg
Figure S7 Layout of the triple-layer full-space kaleidoscopic-beam generator based on our chirality-assisted wavelength-space multitasking concept. The top row is the CAD model while the bottom row is the photograph of fabricated sample.
FigS8.jpg
Figure S8 illustration of the angle-immune EM response of the meta-atom at large θi when EM wave is incident along xz plane. The total reflection rRL (a, b) and transmission tRL (c, d) amplitude (a, c) and phase (b, d) properties.
FigS8.jpg
Figure S8 illustration of the angle-immune EM response of the meta-atom at large θi when EM wave is incident along xz plane. The total reflection rRL (a, b) and transmission tRL (c, d) amplitude (a, c) and phase (b, d) properties.
FigS9.jpg
Figure S9 illustration of the angle-immune EM response of the meta-atom at large θi when EM wave is incident along yz plane. The total reflection rRL (a, b) and transmission tRL (c, d) amplitude (a, c) and phase (b, d) properties.
FigS9.jpg
Figure S9 illustration of the angle-immune EM response of the meta-atom at large θi when EM wave is incident along yz plane. The total reflection rRL (a, b) and transmission tRL (c, d) amplitude (a, c) and phase (b, d) properties.
FigS10.jpg
Figure S10 Illustration of the angle-sensitive EM response of the partial-symmetry meta-atom with symmetry split gap. (a) Amplitude and (b) phase response under different incident angles of θi=0o, 10o, 20o, 30o, 40o, and 60o, here ψ1=ψ2=ψ3=0o. (a) Amplitude and (b) phase response under different ψ1 of ψ1=0o, 30o, 60o, 90o, 120o, and 150o, here θi=20o and ψ2=ψ3=0o.
FigS10.jpg
Figure S10 Illustration of the angle-sensitive EM response of the partial-symmetry meta-atom with symmetry split gap. (a) Amplitude and (b) phase response under different incident angles of θi=0o, 10o, 20o, 30o, 40o, and 60o, here ψ1=ψ2=ψ3=0o. (a) Amplitude and (b) phase response under different ψ1 of ψ1=0o, 30o, 60o, 90o, 120o, and 150o, here θi=20o and ψ2=ψ3=0o.
FigS11.jpg
Figure S11 Layout of the triple-layer multitasking full-space retroreflector and negative refractor based on our chirality-assisted wavelength-space multitasking concept. The middle layer is the same with that of fabricated kaleidoscopic-beam generator.
FigS11.jpg
Figure S11 Layout of the triple-layer multitasking full-space retroreflector and negative refractor based on our chirality-assisted wavelength-space multitasking concept. The middle layer is the same with that of fabricated kaleidoscopic-beam generator.
FigS12.jpg
Figure S12 Illustration of the experimental setup for (a) NF and (b) FF measurements.
FigS12.jpg
Figure S12 Illustration of the experimental setup for (a) NF and (b) FF measurements.

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Spin-encoded Wavelength-space Multitasking Janus Metasurfaces

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