Wavefront Control Research Articles

Multi‐Color Optical Quasiparticle Laser Source Formed of a Pr3+ Doped Fiber Laser with a Dual‐Output Coupling Geometry

AbstractThe generation of multicolor (523, 605, 637, and 719 nm) optical quasiparticles (bimerons and skyrmions with topologically protected polarization textures) from a diode‐pumped Pr3+‐doped fluoro‐aluminate glass (Pr3+: WPFG) fiber simply with intra‐cavity plano‐convex lens and wedge‐plate and without any wavefront control elements, such as a spatial light modulator is demonstrated. This robust and cost‐saving system efficiently produces Bloch‐, Néel‐, and anti‐quasiparticles with high mode purity. In particular, the green optical quasiparticles will have the potential to explore many applications in materials science and biotechnologies.

Polarization Volume Hologram for On‐Chip Wavefront Engineering

AbstractLiquid crystal (LC) planar optics have advanced wavefront engineering toward ultrathin designs, capturing widespread attention. However, most wavefront control in LC planar optics remains constrained to freespace due to limitations in the precision of freely controllable units. Here, LC on‐chip wavefront engineering is proposed and confirmed. By controlling the initial azimuth angle of the polarization grating, the initial phase can be engineered, as theoretically predicted by rigorous coupled‐wave analysis. Experimentally, the initial azimuth angle of a polarization volume hologram grating, used as a waveguide coupler, is ingeniously modulated using a holographic template. Consequently, several on‐chip optical elements, including lenses, vortex beam generators, and holograms, are demonstrated. Furthermore, exit pupil expansion and multiexposure technologies are adopted to enhance off‐chip functionality and enable multifunctional, highly integrated LC on‐chip photonic systems. The proposed LC on‐chip wavefront engineering may find applications in freeform optics, near‐eye displays, LIDAR, and integrated photonic systems.

Efficient wide-angle broadband blazed gratings enabled by metasurfaces

Metasurfaces composed of two-dimensional nanopillar arrays can manipulate light fields in desirable ways and exhibit the unique advantage of beam steering. Here, we experimentally demonstrate a metasurface-based wide-angle broadband all-dielectric blazed grating with an extreme incident angle of up to 80°, which is achieved by optimizing the wide-angle phase shifts and transmissivities of the unit cells. It exhibits a maximum diffraction efficiency of 72% and a high average efficiency of 64% over a wide range of incident angles from −80° to 45° at 1.55 μm. Moreover, the proposed grating has a broad bandwidth of 200 nm (1.45–1.65 μm), and average efficiencies of more than 50% can be achieved experimentally over the same incidence angles. Our results may pave the way for the creation of novel and efficient flat optical devices for wavefront control.

Laser-induced reconfigurable wavefront control with a structured Ge2Sb2Te5-based metasurface

Phase change materials have been widely exploited in active metasurfaces due to their large index contrast. Despite recent advances in phase-change metasurfaces, it remains a challenge to integrate diverse reconfigurable optical functionalities into a single metasurface. Here, we demonstrate an effective strategy to realize reconfigurable wavefront control by combining a Ge2Sb2Te5-rod array with laser writing technology. Through arbitrarily modifying the position and power of laser source, the laser writing process helps to realize site-selective and multi-level phase change of Ge2Sb2Te5 rods. Due to multi-level switching for optical properties of Ge2Sb2Te5 material, the Ge2Sb2Te5-rod array offers complete phase control and high amplitude modulation. Subsequently, various optical devices are designed in numerical simulation, including a phase-only hologram, dynamic meta-deflectors, a grayscale image and a perfect absorber. The structured Ge2Sb2Te5-based metasurface with the combination of laser writing technology offers an effective way to explore various types of optical functionalities in the same device.

Anomalous wavefront control of Lamb wave with metasurfaces via superposed prism resonance

As a special branch of metamaterials characterized by phase discontinuity, elastic metasurfaces have presented extraordinary capacity for elastic wave manipulation. This class of metamaterials has received extensive attention in recent years. In this paper, a subwavelength elastic metasurface with locally resonant prisms is employed to steer the propagation of the A0 Lamb wave. Based on the dispersion curve and transmission ratio, we establish that the resonant feature of prisms is influenced by the diagonal ratio of cross section. By gradually tuning the diagonal ratio of prism cross section, the pattern of resonance modes and the mechanism of resonance superposition are clarified. In this regard, two different resonant modes can be superimposed at a certain frequency. A complete 2 π phase shift that is crucial for redirecting wave propagation can therefore be realized. To have a broader working frequency range, the influence of prism height on the resonance superposed frequency and the effect of plate thickness on the incident flexural wave are explored. Based on the generalized Snell’s law, negative refraction is verified numerically through a metasurface assembled from unit cells with constant phase change. In addition, other wavefront modulations such as eccentric focusing, nonparaxial propagation are also demonstrated. This novel design introduces new degrees of freedom in many engineering applications such as seismic wave protection, structural health monitoring and energy harvesting.

Reconfigurable Multifunctional Metasurfaces for Full-Space Electromagnetic Wave Front Control

In order to implement multiple electromagnetic (EM) wave front control, a reconfigurable multifunctional metasurface (RMM) has been investigated in this paper. It can meet the requirements for 6G communication systems. Considering the full-space working modes simultaneously, both reflection and transmission modes, the flexible transmission-reflection-integrated RMM with p-i-n diodes and anisotropic structures is proposed. By introducing a 45°-inclined H-shaped AS and grating-like micro-structure, the polarization conversion of linear to circular polarization (LP-to-CP) is achieved with good angular stability, in the transmission mode from top to bottom. Meanwhile, reflection beam patterns can be tuned by switching four p-i-n diodes to achieve a 1-bit reflection phase, which are embedded in the bottom of unit cells. To demonstrate the multiple reconfigurable abilities of RMMs to regulate EM waves, the RMMs working in polarization conversion mode, transmitted mode, reflected mode, and transmission-reflection-integrated mode are designed and simulated. Furthermore, by encoding two proper reflection sequences with 13×13 elements, reflection beam patterns with two beams and four beams can be achieved, respectively. The simulation results are consistent with the theoretical method. The suggested metasurface is helpful for radar and wireless communications because of its compact size, simple construction, angular stability, and multi-functionality.

Origami multifunctional metagrating for a mechanically controlled electromagnetic wavefront

Metasurface or artificial electromagnetic (EM) structures offer viable options for manipulating EM waves with compact periodic structures. Tunable metasurfaces are ideal for many engineering and scientific applications because they can manipulate EM wavefronts. However, it is challenging to implement tunable metasurfaces that can achieve multiple functions for integration. In addition, integrated multifunctional metasurfaces are often structurally complicated and bulky. This paper proposes a simple spatial modulation mechanism that uses Miura origami reconfigurable one-dimensional metagrating to achieve multiple control of EM wavefront. Theoretical predictions, numerical simulations, and experiments confirm and validate the basic concepts. In particular, the continuous geometric deformation of the Miura-ori lattice is a promising method for compensating the dispersion of characters in gradient metasurfaces. Considering origami structures’ outstanding mechanical properties and strong deformation abilities, this discovery opens up another avenue for lightweight and deployable meta-devices.

Ultrathin metasurface for super multi-view 3D display with linear and circular polarization control

Multiview 3D display technologies are advantageous due to their smooth motion parallax, visual discomfort alleviation, and wide depth of focus. However, the potential applications of this technology are constrained by its bulky size and limited light modulation capability. Metasurfaces offer diverse wavefront control by manipulating the phase, amplitude, and polarization of light. They provide design freedom and high image quality for multiview 3D display technologies. Here, we propose an ultrathin metasurface-based super multiview 3D display that can effectively modulate the flexibility of linearly polarized (LP) and circularly polarized (CP) electromagnetic waves. Numerical results demonstrate that it can produce 24 views together for LP and CP waves and high-quality reconstructed 3D images are obtained. The suggested metasurface for super multiview 3D display is promising to underpin the advancement of meta-optics-based operations in 3D display, imaging and integrated optics.

Electrically switchable 2N-channel wave-front control for certain functionalities with N cascaded polarization-dependent metasurfaces.

Metasurfaces with tunable functionalities are greatly desired for modern optical system and various applications. To increase the operating channels of polarization-multiplexed metasurfaces, we proposed a structure of N cascaded dual-channel metasurfaces to achieve 2N electrically switchable channels without intrinsic loss or cross-talk for certain functionalities, including beam steering, vortex beam generation, lens, etc. As proof of principles, we have implemented a 3-layer setup to achieve 8 channels. In success, we have demonstrated two typical functionalities of vortex beam generation with switchable topological charge of l = -3 ~ +4 or l = -1 ~ -8, and beam steering with the deflection direction switchable in an 8×1 line or a 4×2 grid. We believe that our proposal would provide a practical way to significantly increase the scalability and extend the functionality of polarization-multiplexed metasurfaces. Although this method is not universal, it is potential for the applications of LiDAR, glasses-free 3D display, OAM (de)multiplexing, and varifocal meta-lens.

Optical characteristics and wavefront control of femtosecond laser pulses and their effect on the performance of diamond graphite electrodes

High purity diamond is an excellent material for making radiation hard detectors suitable for high-energy particle detection, cancer treatment and other fields. Electrodes are formed by the localized graphitization of the diamond bulk, where fine control of the manufacturing process is essential to the performance of the detector. The resistivity of the electrode formed by diamond graphitization significantly affects the performance of the detector. Femtosecond laser pulses interact with the material for a very short time (10-13 s), exhibiting a cold processing. In this paper, we utilize Spatial Light Modulators (SLM) to optimize the optical characteristics of the 800 nm femtosecond laser pulse and control the graphitization process. Our research focuses on the analysis of the influence exerted by the pulse characteristics on the diameter and resistivity of inscribed graphite structures. By examining these parameters, the study aims to refine the graphitization process, thereby optimizing the functional characteristics of the diamond-based detectors.

Full transmission of vectorial waves through 3D multiple-scattering media.

A striking prediction from the random matrix theory (RMT) in mesoscopic physics is the existence of "open channels": waves that use multipath interference to achieve perfect transmission across an opaque disordered medium even in the multiple-scattering regime. Realization of such open channels requires a coherent control of the complete incident wavefront and has only been achieved for scalar waves in two dimensions (2D) so far. Here, we utilize a recently proposed "augmented partial factorization" full-wave simulation method to compute the polarization-resolved scattering matrix from 3D vectorial Maxwell's equations and demonstrate the existence of open channels in 3D disordered media. We examine the spatial profile of such open channels, demonstrate the existence of a bimodal transmission eigenvalue distribution, and study the effects of incomplete polarization control and finite-area illumination. The simulations provide full access to all spatiotemporal properties of the complex wave transport in 3D disordered systems, filling the gap left by experimental capabilities.

Extension of Babinet’s relations to reflective metasurfaces: Application to the simultaneous control of wavefront and polarization

Extension of Babinet’s relations to reflective metasurfaces: Application to the simultaneous control of wavefront and polarization

Spin-Locked WS2 Vortex Emission via Photonic Crystal Bound States in the Continuum.

Owing to their strong exciton effects and valley polarization properties, monolayer transition-metal dichalcogenides (1L TMDs) have unfolded the prospects of spin-polarized light-emitting devices. However, the wavefront control of exciton emission, which is critical to generate structured optical fields, remains elusive. In this work, the experimental demonstration of spin-locked vortex emission from monolayer Tungsten Disulfide (1L WS2) integrated with Silicon Nitride (SiNx) PhC slabs is presented. The symmetry-protected bound states in the continuum (BIC) in the SiNx PhC slabs engender azimuthal polarization field distribution in the momentum space with a topological singularity in the center of the Brillouin zone, which imposes the resonantly enhanced WS2 exciton emission with a spin-correlated spiral phase front by taking advantage of the winding topologies of resonances with the assistance of geometric phase scheme. As a result, exciton emission from 1L WS2 exhibits helical wavefront and doughnut-shaped intensity beam profile in the momentum space with topological charges locked to the spins of light. This strategy on spin-dependent excitonic vortex emission may offer the unparalleled capability of valley-polarized structured light generation for 1L TMDs.

Multichannel full-space coding metasurface with linearly-circularly-polarized wavefront manipulation

Abstract Achieving independent multitasked wavefront control by using an ultrathin plate is a challenge to increase information capacity in integration optics and radar applications. Transmission-reflection-integrated metasurface provides an efficient recipe primarily for multifunctional meta-device, however it is challenging to synergize both linear polarization (LP) and circular polarization (CP) using a single meta-plate. Here, a multichannel full-space coding metasurface composed of interleaved shared-aperture meta-atom is proposed to achieve large information capacity by capsulating judiciously engineered high efficiency triple sub-elements (modes) in four-layer scheme. By rotating dual-gap split ring resonator and varying size of “L” type structure insulating by a metallic ring with electrostatic-analogue shielding effect, both Pancharatnam–Berry (PB) and dynamic phases are independently realized under CP and LP waves, respectively. Such an extraordinary insulating strategy completely suppresses crosstalk among three modes and unprecedentedly increases the capability in yielding kaleidoscopic wavefront control. To verify the significance, a proof-of-concept metadevice is devised and experimentally demonstrated with tri-channel wavefront manipulations, exhibiting reflective dual-vortex beam and Bessel beam for forward and backward CP wave, respectively at high frequency, while transmissive polarization beam splitting for 45°-LP wave at low frequency. Our finding in polarization-direction multiplexing is expected to generate great interest in electromagnetic integration with emerging degree of freedoms.

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

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.

Preserving a qubit during state-destroying operations on an adjacent qubit at a few micrometers distance

Protecting qubits from accidental measurements is essential for controlled quantum operations, especially during state-destroying measurements or resets on adjacent qubits, in protocols like quantum error correction. Current methods to preserve atomic qubits against such disturbances waste coherence time, extra qubits, and introduce additional errors. We demonstrate the feasibility of in-situ state-reset and state-measurement of trapped ions, achieving >99.9% fidelity in preserving an ‘asset’ ion-qubit while a neighboring ‘process’ qubit is reset, and >99.6% preservation fidelity while applying a detection beam for 11 μs on the same neighbor at a distance of 6 μm. This is achieved through precise wavefront control of addressing optical beams and using a single ion as both a quantum sensor for optical aberrations and an intensity probe with >50 dB dynamic range. Our demonstrations advance quantum processors, enhancing speed and capabilities for tasks like quantum simulations of dissipation and measurement-driven phases, and implementing error correction.

Circularly polarized plane terahertz waves radiated from a resonant tunneling diode integrated with a collimating metalens and quarter-wave plate

Terahertz flat optics based on metasurfaces can replace massive optical components with optically thin components. However, metasurfaces with unprecedented material properties frequently produce a specified function, and terahertz flat optics has yet to be commonly adopted in terahertz devices that require multiple functions. Here, we present a two-layer component composed of a collimating metalens and a quarter-wave plate that convert linearly polarized terahertz wide-angle radiation waves from a resonant tunneling diode to circularly polarized plane waves. Our findings would be applied to laminate structures with optical vortices, ultrahigh directivity and arbitrary wavefront control in 6 G wireless communications.

Terahertz wave regulation based on both geometry and propagation phase metasurface

By combining geometry phase with propagation phase, we designed a metasurface without change the pattern size and rotation direction to achieve multifunctional regulation of terahertz waves. By using different encoding arrangements, the designed metasurface can achieve functions including terahertz beam splitting, multi-vortex beam, and deflection focusing according to two decoupled circularly polarized channels. In addition, the metasurface generates opposite energy distributions for two orthogonal circularly polarized waves incidence in the frequency range of 1.25–1.60 THz, which can achieve imaging function and be used for information encryption. The functions achieved by metasurfaces can be flexibly switched by simply using external applied laser illumination. This feature provides a new method for achieving innovative terahertz wavefront control.

Unidirectional guided-wave-driven metasurfaces for arbitrary wavefront control

Metasurfaces are capable of fully reshaping the wavefronts of incident beams in desired manners. However, the requirement for external light excitation and the resonant nature of their meta-atoms, make challenging their on-chip integration. Here, we introduce the concept and design of a fresh class of metasurfaces, driven by unidirectional guided waves, capable of arbitrary wavefront control based on the unique dispersion properties of unidirectional guided waves rather than resonant meta-atoms. Upon experimentally demonstrating the feasibility of our designs in the microwave regime, we numerically validate the introduced principle through the design of several microwave meta-devices using metal-air-gyromagnetic unidirectional surface magneto-plasmons, agilely converting unidirectional guided modes into the wavefronts of 3D Bessel beams, focused waves, and controllable vortex beams. We, further, numerically demonstrate sub-diffraction focusing, which is beyond the capability of conventional metasurfaces. Our unfamiliar yet practical designs may enable full, broadband manipulation of electromagnetic waves on deep subwavelength scales.

Enhancement of piezoelectric energy harvesting for flexural waves by a metasurface-assisted phononic cavity

Piezoelectric energy harvesting of mechanical waves exhibits great potential applications in electricity generation for low-powered electronic devices. In this work, the metasurface-assisted phononic cavity is proposed for the enhancement of piezoelectric energy harvesting of elastic flexural waves. By employing the two-dimensional plate-type metamaterial, we construct a phononic cavity that possesses the ability to localize and amplify the flexural waves. On the other hand, for the purpose of flexural wave focusing, a sparse metasurface is inversely designed based on the interference theory through the particle swarm optimization algorithm. For collaborative wave manipulation, the sparse metasurface is set in front of the phononic cavity. Additionally, piezoelectric patches are attached within the phononic cavities. The wave characteristics of the metasurface-assisted phononic cavity are studied by using the finite element method. For comparison, a conventional phononic cavity (i.e., cavity without metasurface) and a reference bare plate are also considered. Due to the wavefront control ability of the metasurface, more flexural waves are guided into the phononic cavity region. Thus, compared with the reference plate, the power amplification ratios of the metasurface-assisted cavity and the conventional cavity are 102 and 7, respectively. The electrical outputs of the phononic cavity are remarkably boosted by the assistance of the sparse metasurface.