为进一步增强加密或存储器件的实用性与安全性，设计并实现了一种多通道偏振复用的相变全息超表面，通过在多通道全息超表面设计中引入相变介质，实现了动态的可擦除功能。当耦合相变介质层处于非晶态时，所构造的编码超表面可以产生两个独立成像的全息通道。当相变介质变为晶态时，决定相位调控的交叉偏振被关闭，对应的相位编码“被擦除”。 

双通道偏振复用可擦除介质型全息超表面

Abstract Recently, the multifunctional terahertz metasurface holography (meta-holography) has garnered significant attention and sparked wide discussions due to its capacity for carrying a large amount of information. However, traditional multifunctional meta-holography, achieved by integrating metasurfaces with active materials or MEMS technology, have exhibited distinct shortcomings due to their intrinsic properties, such as slow response, complex structure, or low reliability. Herein, we propose a transmissive metasurface platform composed of anisotropic all-dielectric meta-atoms including three parts: the elliptical silicon pillars (Si-pillars), circular Si-pillars, and a quartz substrate sandwiched between them. This platform enables the implementation of dual-channel holographic images by utilizing linear polarization (LP) multiplexing and circular polarization (CP) decoupling. As proof of concept, two transmissive anisotropic metasurfaces (MS-1 and MS-2) are designed and created. When illuminated with two orthogonal LP-polarization waves, the MS-1 can produce holographic images of the letters ‘X’ and ‘Y’ in the corresponding co-polarized channel. Additionally, the MS-2 is illuminated by the left-circularly polarized (LCP) wave, two holographic images with different patterns (‘L’ and ‘R’) are reconstructed in the co-polarized and cross-polarized channels respectively. Therefore, the proposed metasurfaces allowing for polarization-multiplexing or polarization-decoupling can exhibit considerable potential for applications in multifunctional integration and high information capacity. 

Transmissive all-dielectric metasurfaces for reconstructing terahertz holographic images via polarization-multiplexing and polarization-decoupling

The interplay between two paradigms, artificial intelligence (AI) and optical metasurfaces, nowadays appears obvious and unavoidable. AI is permeating literally all facets of human activity, from science and arts to everyday life. On the other hand, optical metasurfaces offer diverse and sophisticated multifunctionalities, many of which appeared impossible only a short time ago. The use of AI for optimization is a general approach that has become ubiquitous. However, here we are witnessing a two-way process—AI is improving metasurfaces but some metasurfaces are also improving AI. AI helps design, analyze and utilize metasurfaces, while metasurfaces ensure the creation of all-optical AI chips. This ensures positive feedback where each of the two enhances the other one: this may well be a revolution in the making. A vast number of publications already cover either the first or the second direction; only a modest number includes both. This is an attempt to make a reader-friendly critical overview of this emerging synergy. It first succinctly reviews the research trends, stressing the most recent findings. Then, it considers possible future developments and challenges. The author hopes that this broad interdisciplinary overview will be useful both to dedicated experts and a general scholarly audience.

Synergy between AI and Optical Metasurfaces: A Critical Overview of Recent Advances

Electromagnetic metasurfaces have been playing exotic roles in the construction of ultracompact and versatile metadevices for wave–matter interactions. So far, multiple metasurfaces cascaded with intercouplings have been intensively investigated for extraordinary wavefront control and broadband spectral regulations. However, most cases face high structural complexity and little attention is paid to cascaded metasurfaces without interlayer couplings. In this paper, we demonstrate one type of terahertz Bragg mirror with ideally high reflectivity and ultra-broad bandwidth by simply resorting to decoupled metasurfaces. Cascaded metasurfaces with decoupled mode control prove practically straightforward for analytical design and easy to fabricate for engineering purpose in our scheme. Essentially, by flexibly tuning the decoupled metasurface mode, the middle Fabry–Perot mode that behaves like a defect mode inside the reflective passband can be eliminated for substantial band expanding. Fundamental analyses and rigorous calculations are performed to confirm the feasibility of our metasurface-based THz Bragg mirror with scalable bandgap. In comparison, our meta-mirror provides superior spectral performance of a larger bandgap and higher in-band reflectivity over that composed by ten layers of alternate dielectrics (Rogers 3003 and 3005). Finally, our analytical methodology and numerical results provide a promising way for the rapid design and fabrication of a Bragg mirror in the optical regime. 

Terahertz Meta-Mirror with Scalable Reflective Passband by Decoupling of Cascaded Metasurfaces

Stacked lightweight metasurfaces for wider stopband in X-K band

Electromagnetic metasurfaces have been intensively used as ultra-compact and easy-to-integrate platforms for versatile wave manipulations from optical to terahertz (THz) and millimeter wave (MMW) ranges. In this paper, the less investigated effects of the interlayer coupling of multiple metasurfaces cascaded in parallel are intensively exploited and leveraged for scalable broadband spectral regulations. The hybridized resonant modes of cascaded metasurfaces with interlayer couplings are well interpreted and simply modeled by the transmission line lumped equivalent circuits, which are used in return to guide the design of the tunable spectral response. In particular, the interlayer gaps and other parameters of double or triple metasurfaces are deliberately leveraged to tune the inter-couplings for as-required spectral properties, i.e., the bandwidth scaling and central frequency shift. As a proof of concept, the scalable broadband transmissive spectra are demonstrated in the millimeter wave (MMW) range by cascading multilayers of metasurfaces sandwiched together in parallel with low-loss dielectrics (Rogers 3003). Finally, both the numerical and experimental results confirm the effectiveness of our cascaded model of multiple metasurfaces for broadband spectral tuning from a narrow band centered at 50 GHz to a broadened range of 40~55 GHz with ideal side steepness, respectively.

/pdf/intercoupling-of-cascaded-metasurfaces-for-broadband-2uzkpbra.pdf

Intercoupling of Cascaded Metasurfaces for Broadband Spectral Scalability

We experimentally measured the ultra-narrow momentum width of an optical trapped Bose-Einstein condensate (BEC) in situ based on matter-wave interference, which validates our previous theoretical work [arXiv: 2205.02416v2]. By sweeping the interval of double stand-wave pulses, the BEC wave packet was splitted into diﬀerent diﬀraction orders and then we counted the oscillation curve of the population of zero-momentum state to calibrate the momentum width. Compared with our simpliﬁed theory, we observed an accelerated evolution of interference fringes in time-domain. We evaluated this interference process minutely by numerically calculating the Gross-Pitaevskii equation and using Wigner function to intuitively demonstrate the inﬂuence of the external potential and nonlinear term. We conﬁrmed that the reduction of interference fringe evolution period actually originates from the synergistic cooperation of the mean-ﬁeld interaction of the BEC and spatial density modulation caused by the interference between diﬀerent momentum states. Our approach could be generalized to other ultra-cold atomic gases with diﬀerent momentum distributions, and in principle a single shot can obtain the result. This quantum thermometry is particularly suitable for momentum width calibration in practical deep cooling experiments, while for atomic samples at pK level the mean-ﬁeld interaction can be safely ignored.

Calibrating the momentum width of a trapped Bose-Einstein condensate by one-dimensional optical lattice pulse sequences

The Efimov effect and its universal property are of paramount importance in quantum few-body physics. Despite this, the predicted ground state Efimov resonance has not yet been observed in 39,40,41K-87Rb mixtures within the currently available observation window. Cooling atoms in the microgravity environment of outer space might overcome this limitation, whereas the residual curvature of the strong magnetic fields may result in significant atom leakage. In this work, we propose an optical method based on far-detuned time-averaged dipole potential to counteract the three-dimensional inhomogeneous field. The target intensity distribution can be conveniently obtained by modulating the central position of the quasi-1D print beam using acoustic optical modulators. Within a volume of 300 × 300 × 400 µm3, the residual potential fluctuations can be reduced by two orders of magnitude to less than 100 pK. The proposed approach offers a realistic prospect of investigating the Efimov-type resonance in the 40K-87Rb Bose-Fermi mixture.

Compensating three-dimensional field inhomogeneity in cold atom Efimov-state search by a time-averaged optical potential.

Designing precision measurement of the gravitational Aharonov-Bohm effect in microgravity

The unprecedented capability of metasurfaces in pixel-wise-level accurate light manipulation has enabled the realization of polarization-multiplexed metasurface holograms in a single or multiple channel. However, most metasurfaces are static and unable to realize active or tunable wave control in many scenarios. We introduce an erasable functionality for multi-channel metasurface holograms based on active phase tuning, which is realized using the nonvolatile chalcogenide phase change alloy of GeSbSeTe (GSST). Upon the incidence of linearly or circularly polarized waves, polarization-dependent holograms constructed using amorphous GSST (a-GSST) elliptical pillars are achieved because of the complete phase control. The a-GSST holograms feature a subwavelength spatial resolution for all elliptical pillars, with local transmittances ranging from 66% to 90%. Benefiting from the amorphous-to-crystalline phase transition of GSST, the hologram functionality can be completely erased because the crystallized pillars cannot provide the effective propagation modes required by the anisotropic phase modulations in the operating wavelength range. The unique properties of the proposed polarization-multiplexed holograms with erasable functionality offer more degrees of freedom and have potential applications in many fields, such as anti-counterfeiting, encryption, and holographic sources.

Polarization-multiplexed metaholograms with erasable functionality

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