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(a) Metagrating as beam splitter and reflective mirror with the function switchable by the incident angle. (b) Bi-layer metagrating optimized for selective transmission and reflection. The lattice supercell is shown on top of the field plot. The top and bottom bar layers are separated by 200 nm spacer with the bar thickness of 600 nm and 400 nm, respectively.
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Synthesization of multiple functionalities over a flat metasurface platform offers a promising approach to achieving integrated photonic devices with minimized footprint. Metasurfaces capable of diverse wavefront shaping according to wavelengths and polarizations have been demonstrated. Here we propose a class of angle-selective metasurfaces, over...
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... further verify the flexible and versatile capability of the proposed method in angle-selective wavefront engineering, additional designs are incorporated in Fig. 5. Figure 5(a) shows a single layer grating with two switchable performances as beam splitter and reflective mirror according to the incident angle. Coming from normal direction, the beam splits into two beams along −50° and 45° with splitting ratio of 50:50, whereas the beam is totally reflected if the excitation comes from 30°. This ...
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... further verify the flexible and versatile capability of the proposed method in angle-selective wavefront engineering, additional designs are incorporated in Fig. 5. Figure 5(a) shows a single layer grating with two switchable performances as beam splitter and reflective mirror according to the incident angle. Coming from normal direction, the beam splits into two beams along −50° and 45° with splitting ratio of 50:50, whereas the beam is totally reflected if the excitation comes from 30°. ...
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... the optimization method is not limited to the reflection mode. The same angle-selective multifunctionality can be achieved in the transmission mode by optimizing the transmission matrix similarly. One can even engineer the reflection and transmission matrices simultaneously to control reflection and transmission according to angles. In Fig. 5(b), by removing the back mirror and using bi-layer grating design, with one layer embedded in the substrate and the other layer in air, we gain even larger flexibility to engineer the wavefront in both reflection and transmission modes. The normal excitation directly goes through with the transmission angle steerable ( . The efficiencies ...
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Citations
... More recently, gradient metasurfaces have been investigated for flexible wavefront manipulation, with multiple subwavelength cells combined to create a unit supercell. This unit supercell functions as the unit cell [17,18], wherein a desired phase change occurs from one constituent subwavelength cell to the next in order [19][20][21] to enable deflection to a desired direction. ...
... Meta-atom components made of a PCM play a crucial role in tunable and reconfigurable metasurfaces, because they may enable on-off switchable or gradually tunable functionalities. Moreover, not only on-off switching of a selected functionality but also switching between two different functionalities can be achieved for multifunctional operation [19,40,48,49]. Merging wavefront manipulation with the dynamic controllability provided by one or more of the aforementioned materials is attractive. ...
The planewave-response characteristics of simple lamellar metagratings exhibiting thermally mediated transmission-mode deflection (blazing) were numerically investigated, the unit cell of each metagrating containing a phase-change material chosen to be indium antimonide (InSb). Thermal control arises from the use of InSb in its insulator phase and the vicinity of the vacuum state. Metagratings of type A comprise parallel rods of InSb on silicon-dioxide substrate, whereas the substrate is also made of InSb in metagratings of type B . Both types exhibit thermally controllable deflection and asymmetric transmission, which occur when the real part of the relative permittivity of InSb is high. Narrowband features in the sub-diffraction regime may appear in a wide frequency range which involves the vicinity of the vacuum state, the real part of the relative permittivity of InSb being low then.
... 13 This prohibits the inverse design of large multichannel systems. There are many such multichannel systems including photonic circuits 14 and aperiodic meta-structures for applications in wide-field-of-view lenses, 13,15−20 beam combiners, 21,22 angle-multiplexed holograms, 23,24 concentrators, 15,25 thermal emission control, 26−28 image processing, 29−35 optical computing, 36,37 space compression, 38−40 etc. The inverse design of these systems remains challenging. ...
Computer-automated design and discovery have led to high-performance nanophotonic devices with diverse functionalities. However, massively multichannel systems such as metasurfaces controlling many incident angles and photonic-circuit components coupling many waveguide modes still present a challenge. Conventional methods require Min forward simulations and Min adjoint simulations—2Min simulations in total—to compute the objective function and its gradient for a design involving the response to Min input channels. Here, we develop a formalism that uses the recently proposed augmented partial factorization method to obtain both the objective function and its gradient for a massively multichannel system in a single or a few simulations, achieving over 2 orders of magnitude speedup and reduced memory usage. We use this method to inverse design a metasurface beam splitter that separates the incident light to the target diffraction orders for all incident angles of interest, a key component of the dot projector for 3D sensing. This formalism enables efficient inverse design for a wide range of multichannel optical systems.
... In the area of diffractive devices, including metasurfaces that permit local control of optical wavefronts such as lenses, beam deflectors, and holograms, a significant characteristic emerges. These devices often exhibit a fixed response when lit from varying incident angles, often resulting in distortions and reduced efficiency at angles deviating from the original design value [40][41][42]. This associated behavior derives from the consistent location of Fresnel zone boundaries, acting as the underlying grating period that controls device operation regardless of the incident angle [43,44]. ...
The potential of metasurface holography holds significant promise for revolutionary breakthroughs and groundbreaking advancements in imaging, chip-integrated AR/VR technology, and flat optical displays. Traditional diffractive systems, including metasurfaces, display fixed angular behavior due to the grating period defining incidence angles and diffraction limited response. To break this limit, we offer spin-encoded spatially multiplexed metaholograms designing technique facilitating efficient modulation of geometric phases. The proposed technique gives independent control over polarization states, permitting separate optical modifications for different oblique incident angles. Our suggested metasurface illustrates a multifunctional design method using traditional single-resonator geometry, effectively generating three high-fidelity far-field holographic images. Due to simple geometry and dense information multiplexing proposed approach holds potential for different applications, such as holographic optical elements (HOEs), enhanced optical storage, and anti-counterfeiting techniques.
... Currently, forward prediction typically relies on time-consuming numerical simulations to solve Maxwell's system of equations, nevertheless, especially as the complexity of the design grows and an increasingly finer spatial discretization is required, this approach incurs expensive computational costs [6,7]. In inverse design, traditional optimization algorithms are used to find optimal designs, but the process is very time-consuming and in most cases only results in a locally optimal solution rather than a global optimum [8][9][10][11][12][13][14]. As consequence, there is an urgent need to find a new method to simplify or even replace the traditional design approach. ...
Chiral plasmonic metamaterials can amplify chiral signals, resulting in circular dichroism (CD) responses that are several orders of magnitude far beyond those of nature. However, the design process of chiral plasmonic metamaterials based on conventional methods is time-consuming. In recent years, the combination of deep learning (DL) and nanophotonics have accelerated the design of nanophotonic devices. Here, we construct the fully connected neural network (FC-NN) model for the forward prediction and inverse design of chiral plasmonic metamaterials structures and introduce the permutation importance approach to optimize the model and increase its interpretability. Our experimental results show that using the peak magnitude of CD and the corresponding wavelength instead of the entire spectrum as the output in the forward prediction improves the accuracy of the peak magnitude of CD prediction, avoids the introduction of auxiliary networks, and simplifies the network structure; The permutation importance analysis shows that the gold length of the resonator is the most critical structural parameter affecting the CD response. In the inverse design, the permutation importance method helps us to make feature selections for the input of the network. By reducing 251 inputs (the whole CD spectrum) to 4 inputs (the peak magnitude of CD and the corresponding wavelength), the network can still maintain a good prediction performance and decrease the training time of the network. Our proposed method can be extended not only to other DL models to study the CD response of chiral metamaterials but also to other areas where DL is combined with metamaterials to accelerate the system optimization and design process of nanophotonic devices.
... Owing to the fast response of the TN-LC, the two focuses can be switched within tens of milliseconds. The most prevalent method requires bold design of the metasurface relying on local periodic approximation [17][18][19], which considers the unit cell individually. Such an approximation is on the condition that each nanostructure has a high locality. ...
This Letter describes the design procedure and process optimization of the electrically bifocal metalens. In our design, horizontal and vertical polarization is manipulated by applying a suitable voltage to a twisted nematic liquid crystal (TN-LC) cell. Each nanostructure is designed to be a rectangular prism, making different polarizations of light experience various phase delays, thus causing bi-focus. We selected lithographical methods to fabricate our metalens because of the minimum physical size, which can be as small as 50 nm, and the maximum aspect ratio, which is as high as 15. Furthermore, to increase the tolerance and make the sidewall vertical and smooth, we coated different characteristics of photoresist sensitivity to the upper and lower layers. After the development, the mushroom-type photoresist makes Ni easier to strip while in the lift-off process, thus increasing the quality of the whole metalens. Our experiment shows that the focal lengths and focusing efficiencies corresponding to the two polarizations are similar to the simulation results. The proposed electrically modulated bifocal metalens can be utilized in different applications and combined with other optical components.
... Phase gradient metasurfaces provide an alternative approach to the design of optical systems [30,31]. In particular, thin metasurface films allow a highly agile manipulation of optical fields, including polarization [32], phase [33], spectral [34] and direction-dependent [35] selectivity. The ability of metasurfaces for near-arbitrary control over light scattering is also of great interest for radiation pressure management in the context of laser [36] and solar sailing [16][17][18]. ...
Harnessing solar radiation pressure is key to transforming space exploration with multiple low cost sunlight propelled spacecraft to outer reaches of space. By controlling the direction of sunlight momentum transfer new missions and better maneuvering in space can be accessed. Here, we discuss design principles for taming in-plane radiation pressure under ambient sunlight. We propose and study theoretically ultra-wideband polarization insensitive metasurfaces for anomalous light reflection. Our design based on segmented tapered patch nanoantenna arrays allows reflection of >60% into one diffraction orders over a 400 nm band across larger part of the solar spectrum. Owing to a wideband nature and polarization insensitivity, our structures convert incident radiation into in-plane radiation pressure force with almost 30% efficiency. We discuss applications of our design to controlling solar sail spin. Beyond solar sailing, we envision that such anomalous metasurfaces for ambient sunlight will find use in solar concentration, spectrum splitting, and solar fuels.
... This prohibits the inverse design of large multi-channel systems. There are many such multi-channel systems including photonic circuits [9] and aperiodic meta-structures for applications in wide-field-of-view metalenses [8,[10][11][12], beam combiners [13,14], angle-multiplexed holograms [15,16], concentrators [10,17], thermal emission control [18][19][20], image processing [21][22][23][24][25][26][27], optical computing [28,29], space compression [30][31][32], etc. The inverse design of these systems remains challenging. ...
Computer-automated design and discovery have led to high-performance nanophotonic devices with diverse functionalities. However, massively multi-channel systems such as metasurfaces controlling many incident angles and photonic-circuit components coupling many waveguide modes still present a challenge. Conventional methods require $M_{\rm in}$ forward simulations and $M_{\rm in}$ adjoint simulations -- $2M_{\rm in}$ simulations in total -- to compute the objective function and its gradient for a design involving the response to $M_{\rm in}$ input channels. By generalizing the adjoint method and the recently proposed augmented partial factorization method, here we show how to obtain both the objective function and its gradient for a massively multi-channel system in a single simulation, achieving over-two-orders-of-magnitude speedup and reduced memory usage. We use this method to inverse design a metasurface beam splitter that separates the incident light to the target diffraction orders for all incident angles of interest, a key component of the dot projector for 3D sensing. This formalism enables efficient inverse design for a wide range of multi-channel optical systems.
... Different approaches to SF [33,[55][56][57][58][59][60][61][62][63] and demultiplexing [64][65][66][67][68] were suggested, but only a part of them is connected with wideband and simultaneously wide-angle blazing. At the same time, diverse scenarios of multifunctional operation attracted a lot of attention [69][70][71]; among them, the ones enabled by wideband/wide-angle blazing [40,45]. ...
This paper investigates diffractions by gratings made of a dispersive material in an epsilon-near-zero (ENZ) regime and having one-side corrugations, and those by two-component dielectric-ENZ gratings with the inner corrugations and flat outer interfaces. The goal is to achieve wideband and simultaneously wide-angle ${-}1$ − 1 st order blazing (deflection) that may enable wideband spatial filtering and demultiplexing in reflection mode. Several typical scenarios are discussed, which differ in the maximum magnitude of the blazed wave and size of the blazing area observed on the frequency-incidence angle plane, as well as the contribution of the ranges of positive and negative permittivity in the vicinity of zero. The high capability of ENZ and dielectric-ENZ gratings in asymmetric reflection is demonstrated for three different levels of losses for the dispersive material.
... Huygens' [24]- [25], asymmetric [26], supercell [27], [28], and metagrating [29]- [30] approaches. Both local and quasi-local metasurfaces, however, suffer from limited spectral control: for instance, the response away from the design frequency is generally suboptimal and poorly controllable. ...
... Inspection of Eqn. (27) shows that this closely matches the form predicted by TCMT, and ...
Symmetry-driven phenomena arising in nonlocal metasurfaces supporting quasi-bound states in the continuum (q-BICs) have been opening new avenues to tailor enhanced light-matter interactions via perturbative design principles. Geometric phase concepts - observed in many physical systems - are particularly useful in nonlocal metasurfaces, as they enable to locally pattern the q-BIC scattering rate and phase across the metasurface aperture without affecting the delocalized nature of the q-BIC resonance. However, this control typically comes with stringent limitations in terms of efficiency and/or of polarization operation. Here, we unveil a new form of geometric phase control, accumulated along a continuous contour of geometric perturbations that parametrically encircle a singularity associated with a bound state. This response is obtained regardless of the chosen polarization state, which can be rationally specified by a judicious choice of the perturbation geometry. Our findings extend geometric phase concepts to arbitrary polarizations, including linear and elliptical states, with near-unity scattering efficiency. This polarization-agnostic geometric phase offers new opportunities for wavefront manipulation, multifunctional operation and light emission, with applications in augmented reality, secure communications, wireless systems, imaging, lasing, nonlinear and quantum optics.
... Conventionally, diffraction gratings and total internal reflection in prisms have been widely used for angle-selective beam control or precise measurement of angular properties. However, angle-multiplexed metasurfaces can possess even more degrees of freedom for transmission phase engineering and have been realized with several different physical principles, such as localized resonance [15], high-order diffraction [16], guided wave excitations [17], near-field coupling between neighboring nanostructures [18], and surface plasmon polaritons [19]. Despite these pioneering studies, two difficult hurdles should be overcome before wide applications of the concept: namely, low angular sensitivity (required incident angle difference is larger than ∼10 • in many cases) [15,16,18,19] or low optical efficiency (as low as 10% even in recent papers) [17]. ...
... However, angle-multiplexed metasurfaces can possess even more degrees of freedom for transmission phase engineering and have been realized with several different physical principles, such as localized resonance [15], high-order diffraction [16], guided wave excitations [17], near-field coupling between neighboring nanostructures [18], and surface plasmon polaritons [19]. Despite these pioneering studies, two difficult hurdles should be overcome before wide applications of the concept: namely, low angular sensitivity (required incident angle difference is larger than ∼10 • in many cases) [15,16,18,19] or low optical efficiency (as low as 10% even in recent papers) [17]. It appears even more challenging to achieve high efficiency and high sensitivity at the same time, especially for optical beams with near-zero incidence angles. ...
Optical metasurfaces have great potential to overcome the functional limitations of conventional optical devices. In addition to polarization- or wavelength-multiplexed metasurfaces, angle-multiplexed metasurfaces can provide new degrees of freedom, enabling previously unrealized complex functionality in diverse applications such as LiDAR, augmented reality glasses, and imaging. However, there have been fundamental trade-offs in transmission efficiency and angular sensitivity for practically important paraxial rays. In this paper, we overcome this limitation by breaking mirror symmetries of single-layer metasurface structures. Based on an effective medium theory, we intuitively explain which material parameters affect the sensitivity and efficiency and prove that high sensitivity and high efficiency can be achieved simultaneously by breaking the mirror symmetry. Based on this, we propose optimized metasurfaces for two applications: an angle-multiplexed beam-steering device with up to 93% relative efficiency and an angle-multiplexed metalens array that can break the fundamental resolution–density trade-off of microlens arrays with high efficiency. The proposed angle-selective designs could pave the way for the development of new classes of compact optical devices with novel functions.
