Towards the performance limit of catenary meta-optics via field-driven optimization

Catenary optics enables metasurfaces with higher efficiency and wider bandwidth,and is highly anticipated in the imaging system,super-resolution lithography,and broadband absorbers.However,the periodic boundary approximation without considering aperiodic electromagnetic crosstalk poses challenges for catenary optical devices to reach their performance limits.Here,perfect control of both local geometric and propagation phases is realized through field-driven optimization,in which the field distribution is calculated under real boundary conditions.Different from other optimization methods requiring a mass of iterations,the proposed design method requires less than ten iterations to get the efficiency close to the optimal value.Based on the library of shape-optimized catenary structures,centimeter-scale devices can be designed in ten seconds,with the performance improved by ~15%.Furthermore,this method has the ability to extend catenary-like continuous structures to arbitrary polarization,including both linear and elliptical polarizations,which is difficult to achieve with traditional design methods.It provides a way for the development of catenary optics and serves as a potent tool for constructing high-performance optical devices.

一种用于大视场成像和偏振光谱探测的微型可重构超构光学系统

Wide-angle imaging and spectral detection play vital roles in tasks such as target tracking,object classification,and anti-camouflage.However,limited by their intrinsically different architectures,as determined by frequency dispersion requirements,their simultaneous implementation in a shared-aperture system is difficult.Here,we propose a novel concept to realize reconfigurable dual-mode detection based on electrical-control tunable metasurfaces.As a proof-of-concept demonstration,the simultaneous implementation of wide-angle imaging and polarization-spectral detection in a miniature sharedaperture meta-optical system is realized for the first time via the electrical control of cascaded catenary-like metasurfaces.The proposed system supports the imaging(spectral)resolution of approximately 27.8 line-pairs per millimeter(lp·mm^(-1);~80 nm)for an imaging(spectral)mode from 8 to 14 μm.This system also bears a large field of view of about 70°,enabling multi-target recognition in both modes.This work may promote the miniaturization of multifunctional optical systems,including spectrometers and polarization imagers,and illustrates the potential industrial applications of meta-optics in biomedicine,security,space exploration,and more.

Crosstalk-free achromatic full Stokes imaging polarimetry metasurface enabled by polarization-dependent phase optimization

Imaging polarimetry is one of the most widely used analytical technologies for object detection and analysis.To date,most metasurface-based polarimetry techniques are severely limited by narrow operating bandwidths and inevitable crosstalk,leading to detrimental effects on imaging quality and measurement accuracy.Here,we propose a crosstalkfree broadband achromatic full Stokes imaging polarimeter consisting of polarization-sensitive dielectric metalenses,implemented by the principle of polarization-dependent phase optimization.Compared with the single-polarization optimization method,the average crosstalk has been reduced over three times under incident light with arbitrary polarization ranging from 9μm to 12μm,which guarantees the measurement of the polarization state more precisely.The experimental results indicate that the designed polarization-sensitive metalenses can effectively eliminate the chromatic aberration with polarization selectivity and negligible crosstalk.The measured average relative errors are 7.08%,8.62%,7.15%,and 7.59%at 9.3,9.6,10.3,and 10.6μm,respectively.Simultaneously,the broadband full polarization imaging capability of the device is also verified.This work is expected to have potential applications in wavefront detection,remote sensing,light-field imaging,and so forth.

All‐metallic wide‐angle metasurfaces for multifunctional polarization manipulation

Optical camouflage is a magical capability of animals as first noticed in 1794 by Erasmus Darwin in Zoonomia,but current biomimetic camouflage strategies cannot be readily applied in complex environments involving multispectral and in particular multi-polarization detection.Here we develop a plasmonic approach toward broadband infrared polarimetric crypsis,where the polarized thermal emission near the pseudo-Brewster angle is the main signal source and no existing polarizing camouflage technique has been discovered in nature.Based on all-metallic subwavelength structures,an electrodynamic resistance-reduction mechanism is proposed to avoid the significant polarization-dependent infrared absorption/radiation.It is also found that the structured metal surface presents giant extrinsic anisotropy regarding the phase shift between orthogonal polarization states,which helps to realize ultrahigh-efficiency and tunable polarization conversion in an unprecedented manner.Finally,we note that the catenary optical theory may provide a useful means to explain and predict these unusual performances.

Off-axis multi-wavelength dispersion controllingmetalens for multi-color imaging

Dispersion control is crucial in optical systems,and chromatic aberration is an important factor affecting imaging quality in imaging systems.Due to the inherent property of materials,dispersion engineering is complex and needs to trade off other aberration in traditional ways.Although metasurface offers an effective method to overcome these limits and results in well-engineered dispersion,off-axis dispersion control is still a challenging topic.In this paper,we design a single-layer metalens which is capable of focusing at three wavelengths(473 nm,532 nm,and 632 nm)with different incident angles(0°,-17°and 17°)into the same point.We also demonstrate that this metalens can provide an alternative for the bulky color synthetic prism in a 3-chips digital micromirror device(DMD)laser projection system.Through this approach,various off-axis dispersion controlling optical devices could be realized.

Perfect electromagnetic and sound absorption via subwavelength holes array

Broadband sound absorption at low frequency is notoriously difficult because the thickness of the absorber should be proportional to the working wavelength. Here we report an acoustic metasurface absorber following the recent theorydeveloped for electromagnetics. We first show that there is an intrinsic analogy between the impedance description of sound and electromagnetic metasurfaces. Subsequently, we demonstrated that the classic Salisbury and Jaumann ab-sorbers can be realized for acoustic applications with the aid of micro-perforated plates. Finally, the concept of coherent perfect absorption is introduced to achieve ultrathin and ultra-broadband sound absorbers. We anticipate that the ap-proach proposed here can provide helpful guidance for the design of future acoustic and electromagnetic devices.

Physics-data-driven intelligent optimization for large-aperture metalenses

Metalenses have gained significant attention and have been widely utilized in optical systems for focusing and imaging,owing to their lightweight,high-integration,and exceptional-flexibility capabilities.Traditional design methods neglect the coupling effect between adjacent meta-atoms,thus harming the practical performance of meta-devices.The existing physical/data-driven optimization algorithms can solve the above problems,but bring significant time costs or require a large number of data-sets.Here,we propose a physics-data-driven method employing an“intelligent optimizer”that enables us to adaptively modify the sizes of the meta-atom according to the sizes of its surrounding ones.The implementation of such a scheme effectively mitigates the undesired impact of local lattice coupling,and the proposed network model works well on thousands of data-sets with a validation loss of 3×10^(−3).Based on the“intelligent optimizer”,a 1-cm-diameter metalens is designed within 3 hours,and the experimental results show that the 1-mm-diameter metalens has a relative focusing efficiency of 93.4%(compared to the ideal focusing efficiency)and a Strehl ratio of 0.94.Compared to previous inverse design method,our method significantly boosts designing efficiency with five orders of magnitude reduction in time.More generally,it may set a new paradigm for devising large-aperture meta-devices.

Inversely engineered metasurfaces for independent manipulation of transmitted and reflected light fields

Independent manipulation of transmitted and reflected light fields is a key technology for the realization of multifunctional optical applications,which can be implemented based on multilayered plasmonic or supercell subwavelength structures.However,the former is not suitable for the optical bands,while the latter is insufficient in generating large phase gradients.Here,an adjoint-optimization-based inverse design methodology is proposed,which utilizes the polarization-selective local interference between individual meta-atoms and enables monolayer dielectric metasurfaces to decouple the wavefront of transmitted and reflected optical fields.Moreover,this methodology serves to mitigate the aperiodic electromagnetic crosstalk inherent between adjacent meta-atoms,consequently leading to a significant enhancement in the performance of meta-devices.We analyzed the physical mechanism of adjoint optimization and proposed the concept of phase factors,highlighting their importance in the rapid inverse design of meta-devices—an aspect often overlooked in previous research.To demonstrate the feasibility and robustness of our method,we optimize monolayer metasurfaces with different initial structures.These devices efficiently focus and deflect x-linearly and y-linearly polarized incident light in transmission and reflection spaces,respectively.Overall,this methodology holds immense potential for designing multifunctional,high-performing metasurfaces that meet multiple constraints,opening up broad prospects for applications.

Snapshot multi-dimensional computational imaging through a liquid crystal diffuser

Multi-dimensional optical imaging systems that simultaneously gather intensity,depth,polarimetric,and spectral information have numerous applications in medical sciences,robotics,and surveillance.Nevertheless,most current approaches require mechanical moving parts or multiple modulation processes and thus suffer from long acquisition time,high system complexity,or low sampling resolution.Here,a methodology to build snapshot multi-dimensional lensless imaging is proposed by combining planar-optics and computational technology,benefiting from sufficient flexibilities in optical engineering and robust information reconstructions.Specifically,a liquid crystal diffuser based on geometric phase modulation is designed to simultaneously encode the spatial,spectral,and polarization information of an object into a snapshot detected speckle pattern.At the same time,a post-processing algorithm acts as a special decoder to recover the hidden information in the speckle with the independent and unique point spread function related to the position,wavelength,and chirality.With the merits of snapshot acquisition,multi-dimensional perception ability,simple optical configuration,and compact device size,our approach can find broad potential applications in object recognition and classification.

Solvent-free carbon sphere nanofluids towards intelligent lubrication regulation

By simply switching the electrical circuit installed on steel/steel contact,the tribological behaviors of nanofluids(NFs)can be regulated in real time,thereby achieving the desired performance of friction reduction and wear resistance.Herein,solvent-free carbon spherical nanofluids(C-NFs)were successfully prepared for intelligent lubrication regulation.C-NFs with excellent lubrication performance can immediately reduce the coefficient of friction(COF)despite applying a weak electric potential(1.5 V).Moreover,polyethylene glycol 400(PEG400)containing 5.0 wt%C-NFs remained responsive to electrical stimulation under the intermittent voltage application with an average coefficient of friction(ACOF)reduction of 20.8%over PEG400.Such intelligent lubrication regulation of C-NFs under an external electric field(EEF)mainly depends on the orderly arranged double-electric adsorption film of ion canopy-adsorbed carbon spheres(CSs).The intermittent electrical application can continuously reinforce the adsorption film and its durability for real-time controlling the sliding interfaces.Electrical-stimulation-responsive intelligent lubricants provide a new technical support for realizing intelligent stepless control of devices.

Tailoring active color rendering and multiband photodetection in a vanadium-dioxide-based metamaterial absorber

Metamaterials have demonstrated exotic electromagnetic properties, which offer a good platform for realizing light absorption, photodetection, filtering, and so on. However, broadband multifunctional metamaterial absorbers are restricted in cascaded structures. Here, broadband multifunctional properties were realized by introducing vanadium dioxide into a metamaterial absorber. Through the modified design and highly efficient utilization of multiple resonant modes, both plasmonic tunable color filters and near-infrared photodetectors can be simultaneously achieved by this construction. Meanwhile, active color and a photodetection band in the near-infrared range can become tunable with the insulating-metallic transition of vanadium dioxide. Thus, the variations of rendering colors could correspondingly indicate shifts of the near-infrared photodetection bands. This method theoretically confirms the feasibility of designing multifunctional devices via a terial absorber, which holds great promise for future versatile utilization of vanadium-dioxide-based metamamultiple physical mechanisms to achieve numerous functionalities in a simple nanostructure or device.

Dual-band and ultra-broadband photonic spin-orbit interaction for electromagnetic shaping based on single-layer silicon metasurfaces

Achieving electromagnetic wave scattering manipulation in the multispectral and broad operation band has been a long pursuit in stealth applications. Here, we present an approach by using single-layer metasurfaces composed of space-variant amorphous silicon ridges tiled on a metallic mirror, to generate high-efficiency dual-band and ultra-wideband photonic spin-orbit interaction and geometric phase. Two scattering engineered metasurfaces have been designed to reduce specular reflection;the first one can suppress both specular reflectances at 1.05–1.08 μm and 5–12 μm below 10%. The second one is designed for an ultra-broadband of 4.6–14 μm, which is actually implemented by cleverly connecting two bands of 4.6–6.1 μm and 6.1–14 μm. Furthermore, the presented structures exhibit low thermal emission at the same time due to the low absorption loss of silicon in the infrared spectrum, which can be regarded as an achievement of laser–infrared compatible camouflage.We believe the proposed strategy may open a new route to implement multispectral electromagnetic modulation and multiphysical engineering applications.

Classical and generalized geometric phase in electromagnetic metasurfaces

The geometric phase concept has profound implications in many branches of physics,from condensed matter physics to quantum systems.Although geometric phase has a long research history,novel theories,devices,and applications are constantly emerging with developments going down to the subwavelength scale.Specifically,as one of the main approaches to implement gradient phase modulation along a thin interface,geometric phase metasurfaces composed of spatially rotated subwavelength artificial structures have been utilized to construct various thin and planar meta-devices.In this paper,we first give a simple overview of the development of geometric phase in optics.Then,we focus on recent advances in continuously shaped geometric phase metasurfaces,geometric–dynamic composite phase metasurfaces,and nonlinear and high-order linear Pancharatnam–Berry phase metasurfaces.Finally,conclusions and outlooks for future developments are presented.

High-fidelity mode scaling via topologicaloptimized on-chip metalens for compact photonic interconnection

Photonic integrated circuits(PICs)have attracted significant interest in communication,computation,and biomedical applications.However,most rely on highly integrated PICs devices,which require a low-loss and high-integration guided wave path.Owing to the various dimensions of different integrated photonic devices,their interconnections typically require waveguide tapers.Although a waveguide taper can overcome the width mismatch of different devices,its inherent tapering width typically results in a long length,which fundamentally limits the efficient interconnection between devices with a high scaling ratio over a short distance.Herein,we proposed a highly integrated on-chip metalens that enables optical interconnections between devices with high width-scaling ratios by embedding a free-form metasurface in a silicon-on-insulator film.The special geometric features endow the designed metalens with high coupling efficiency and high integration.The device has a footprint of only 2.35μm in the longitudinal direction and numerical aperture of 2.03,enabling beam focusing and collimation of less than 10μm between devices with width-scaling ratio of 11.For the fundamental transverse electric field(TE0)mode,the relative transmittance is as high as 96%for forward incidence(from wide to narrow waveguides),whereas the metalens can realize wavefront shaping for backward incidence,which can be used in optical phase arrays.This study provides new ideas for optical interconnect design and wavefront shaping in high-integration PICs.Our design approach has potential applications in directional radiators,LiDAR,on-chip optical information processing,analogue computing,and imaging.

Synthetic vector optical fields with spatial and temporal tunability

As an intrinsic nature of light,polarization plays a critical role in the vectorial characteristic of optical fields.Vector optical fields with an inhomogeneous polarization distribution show many exotic phenomena and applications not existing in scalar optical fields.Existing polarization optics,however,mainly focuses on the manipulation of polarization distribution on a single transverse plane.Here,we propose a synthetic approach to realize polarization manipulation with spatial and temporal degrees.The underlying mechanism relies on decoupling two orthogonal polarization states through asymmetric photonic spin-orbit interactions to obtain customer-tailored phase and amplitude difference in both transverse and longitudinal space,thereby changing the resulting polarization distribution at will in three-dimensional(3 D)space.Remarkably,a longitudinally varied cylindrical vector field is experimentally demonstrated by a monolayer metasurface,in which the polarization distribution switches continuously and periodically between radial and azimuthal polarization.Furthermore,the vector field can be dynamically tuned by rotating the incident polarization state.Our work extends polarization optics from two-dimensional space to 3 D space,allowing the arbitrary generation and manipulation of 3D vector optical fields with temporal tunability.

Synergistic lubrication of few-layer Ti_(3)C_(2)T_(x)/MoS_(2) heterojunction as a lubricant additive

The few-layer Ti_(3)C_(2)T_(x)/MoS_(2) heterostructure was successfully prepared via vertically growing of MoS_(2) nanosheets on the few-layer Ti3C2Tx matrix using hydrothermal method.The tribological properties as additive in mineral oil(150N)were evaluated in detail.The 0.3 wt% of few-layer Ti_(3)C_(2)T_(x)/MoS_(2) heterostructure addition amount can reduce the friction and wear of 150N by 39% and 85%,respectively.Moreover,the enhancement effect of few-layer Ti_(3)C_(2)T_(x)/MoS_(2) on tribological properties of 150N is superior to that of few-layer Ti_(3)C_(2)T_(x),MoS_(2) nanosheets,and their mechanical mixture.Based on the characterization and analysis of wear debris and wear track,such excellent tribological properties of the few-layer Ti_(3)C_(2)T_(x)/MoS_(2) heterostructure derive from its structural advantage toward good dispersion,the synergistic lubrication of Ti_(3)C_(2)T_(x) and MoS_(2) nanosheets during the rubbing process,and the formation of tribo-film.

Broadband high-efficiency polymerized liquid crystal metasurfaces with spin-multiplexed functionalities in the visible

Traditional optical components are usually designed for a single functionality and narrow operation band,leading to the limited practical applications.To date,it is still quite challenging to efficiently achieve multifunctional performances within broadband operating bandwidth via a single planar optical element.Here,a broadband high-efficiency polarization-multiplexing method based on a geometric phase polymerized liquid crystal metasurface is proposed to yield the polarization-switchable functionalities in the visible.As proofs of the concept,two broadband high-efficiency polymerized liquid crystal metalenses are designed to obtain the spin-controlled behavior from diffraction-limited focusing to sub-diffraction focusing or focusing vortex beams.The experimental results within a broadband range indicate the stable and excellent optical performance of the planar liquid crystal metalenses.In addition,low-cost polymerized liquid crystal metasurfaces possess unique superiority in large-scale patterning due to the straightforward processing technique rather than the point-by-point nanopatterning method with high cost and low throughput.The high-efficiency liquid crystal metasurfaces also have unrivalled advantages benefiting from the characteristic with low waveguide absorption.The proposed strategy paves the way toward multifunctional and high-integrity optical systems,showing great potential in mobile devices,optical imaging,robotics,chiral materials,and optical interconnections.

High-efficiency multi-wavelength metasurface with complete independent phase control

As a consequence of Kramers–Kronig relations, the wavelength-dependent behavior of the metasurface is one of the critical limitations in existing metasurface structures, which reduces the design freedom among different wavelengths. Here, we present an approach to construct a high-efficiency multi-wavelength metasurface with independent phase control by coding different wavelengths into orthogonal polarizations. As proof of the concept, two dual-band metasurfaces have been proposed and numerically demonstrated by multiple vortex beam generation in near-field and polarization multiplexing achromatic beam deflection. Furthermore, simulated results show that the proposed metasurface exhibits high transmission efficiency at both wavelengths, which may find widespread applications in subwavelength electromagnetics.