We introduce a gradient refractive index profile into water wave manipulation and design a novel waveguide isolator device. It functions similarly to an electrical diode, allowing water waves to pass in one direction while blocking them in the opposite direction. Moreover, its waveguide-like hollow structure enables it to block water waves without hindering the passage of vessels. We elucidate the wave-blocking mechanism through mode analysis and numerical simulations, and experimentally validated the device, observing a significant “water wave diode effect.” This effect effectively blocks water waves in one direction while allowing passage in the other. This is the first time that blocking water waves without hindering vessel passage has been realized in the experiment, showing great potential for applications in maritime ports and ocean freight transport.

We conduct theoretical calculations and simulations on the metagrating and derive the equivalent anisotropic model of the metagrating. This model provides evidence that the metagrating has the capability to control water waves and achieve unidirectional surface water wave. It is the first time that the unidirectional propagation of water waves has been seen in water wave metagrating experiment.  By combining complex gratings with real bridges, we explore the physics embedded in the ancient building — Luoyang Bridge, which are of great significance for the water wave metagrating design and provide a new method for analyzing the effects of water waves on bridges. At the same time, this discovery also provides a new idea for ocean cargo transportation, ocean garbage cleaning, and the development and protection of ancient bridges.

We  stack two X-cut lithium niobate layers together, proposing a novel inverted and twisted bilayer lithium niobate structure. By precisely twisting the upper layer of lithium niobate to the magic angle of 111°, the effective electromechanical coupling coefficient of one of the two lowest-order modes reaches 85.5%, while the other approaches zero, overcoming the inherent mutual limitations within single-crystal lithium niobate. Theoretical calculations, numerical simulations, and experimental results are highly consistent, verifying its accuracy. This work opens up new avenues for flexibly controlling multiphysical fields using the magic angle, advancing broadband acousto-electric and acousto-optic devices, and holds great potential in fields such as wireless communications, sensing, and hybrid integrated photonics.

In this paper, based on the combination of Brewster effect and complex structured fields, such as vortex waves, the reflection interface of traditional Brewster effect can be widened to two-dimensional space (e.g., cylindrical surface), namely angular Brewster effect. In addition, tunable reflection and absorption and broadband asymmetric acoustic vortices can be achieved by introducing additional degrees of freedom, i.e., the rotation angle and intrinsic losses of the anisotropic materials and the topological charge of vortex waves.

In this paper, a new paradigm is presented for realizing anomalous wave tunnelling through a general effective double-barrier model constructed by dispersion engineering, while preserving mode information. The observed tunnelling mechanism is corroborated well by experimental results in the microwave realm.

In this paper, we propose a novel construction method of dual-layer metasurfaces to achieve a double-conversion process for the waveform reshaping and differentiated focusing of two-dimensional vortex sources with different OAMs. Specifically, by utilizing a concise formula, a one-to-one correspondence is established between the OAM of incident vortex waves and different imaging points.

In this work, we report that an anomalous optical whispering-gallery mode (WGM) emerges with self-focusing field patterns in a nearly spherical cavity of ultrahigh- Q factor, driven by rotational symmetry breaking and positive surface curvature.

In this work, we propose a new paradigm of extremely anisotropic acoustic metasurface (AM) to achieve the efficient conversion from 2D vortex waves with arbitrary orbital angular momentum (OAM) to plane waves.

In this work, we explore the anisotropic polaritons on the spherical surface based on Maxwell’s fish-eye metric through stereographic projection.

In this work, a multiband elastic waveguide cloak that uses metamaterials and does not require active components or complex designs is introduced. By converting flexural waves to waveguide-trapped waves, a cloaking region with negligible vibration can be created.

In this work, it is demonstrated that in-plane optical vortex waves can exhibit transverse shift through DNM, and such a phenomenon is also called vortex Hall effect. From numerical calculations, a linear relationship is observed between the transverse shift and the topological charge l for a fixed wavelength.

In this work, by creating p -orbital topological acoustic metamaterials with disclination-induced conic and hyperbolic surfaces, we demonstrate the rich emergent bound states arising from the interplay among the real-space geometry, the bulk band topology, and the p -orbital physics.

In this work, a method is proposed to design a real-imaging magnifying lens with ultrabroadband super-resolution real-time imaging capability based on conformal transformation optics.

In this work, we propose and demonstrate an optical black hole (OBH) cavity based on transformation optics. The radiation loss of all WGMs in the ideal OBH cavity is completely inhibited by an infinite wide potential barrier.

In this work, the method based on Fabry-Perot resonances offers a feasible solution for achieving three-dimensional (3D) omnidirectional passive acoustic illusion. We theoretically demonstrate 3D acoustic illusion via Mie theory, a reduced version is further designed numerically and implemented experimentally.

In this work, we report tunable topological transitions in biaxial crystals enabled by interface engineering. We theoretically demonstrate such tailored polaritons at the interface of heterostructures between graphene and α-phase molybdenum trioxide (α-MoO3). The interlayer coupling can be modulated by both the stack of graphene and α-MoO3 and the magnitude of the Fermi level in graphene enabling a dynamic topological transition.

In this work, we find that a one-dimensional groove array can be equivalent to a negative water depth and excite unidirectional surface polaritons for water waves. We explain this phenomenon through theoretical analysis, numerical simulations, and experiments. This phenomenon shows that the propagation direction of water waves can be manipulated through such simple structures, which will be very important in offshore transportation and environmental protection.

In this work, we report that a MFEL embedded in an exterior coating, inspired by the solid immersion concept, can realize super-resolution imaging without a drain. Such a solution mitigates and bypasses the corresponding criticisms and debates of the past decades. We find that the total reflection at the outer solid-immersion interface and the native perfect focusing of MFEL synthetically contribute to a super-resolution image formed in the air

In this paper, by combining transformation optics and van der Waals layered materials, an invisibility concentrator with a thin layer of α-MoO3 wrapping around a cylinder is proposed. It inherits the effects of invisibility and energy concentration at Fabry–Pérot resonance frequencies, with tiny scattering.

In this paper, we implement a big metamaterial superscatterer, and experimentally demonstrate its superscattering effect at microwave frequencies by field-mapping technology. We confirm that superscattering is originated from the excitation of surface plasmons. Integrated with superscatterer, we experimentally display that an invisible gateway could stop electromagnetic waves in an air channel with a width much larger than the cutoff width of the corresponding rectangular waveguide.

In this paper, we find that the analog of de Sitter space is the Poincaré disk, while anti–de Sitter space is equivalent to Maxwell's fish-eye lens. In particular, we prove that the optical black hole actually has infinite number of photon spheres, while our black hole only has a single one, which is closer to the real black hole.

In this paper, manipulation of evanescent waves in a waveguide with gradient-index metamaterials is analyzed. It is shown that evanescent waves excited by a cutoff waveguide can be efficiently transmitted over a long distance by a mode-conversion mechanism. The experimental results are in good agreement with simulated results, and the manipulation is of broadband frequencies.

In this paper, we theoretically and experimentally study a new type of photonic interface (namely a hyperinterface) inside an optical metamaterial made of a zigzag alternating multilayer structure [namely structuredmetamaterials (SMMs)] in the deep-subwavelength regime. It is found that the subwavelength hyperinterfaces play a great role in the optical properties of such SMMs, and the electromagnetic properties of the hyperinterfaces can be effectively manipulated in a feasible way.

In this paper, we demonstrate that a flat gradient index optical thin-film waveguide is equivalent to a curved homogenous optical thin film waveguide for light rays by utilizing conformal equivalence. Such a relationship provides us an alternative method to design optical devices with either an inhomogeneous medium or equivalently curved surfaces made from only a homogeneous material, leading to applications on on-chip optical devices.

In this paper, we propose a bioinspired semianalytical conformal acoustics that can predict the evolution of acoustic functions strictly. Based on this method, we design a series of acoustic steering and collimation models. The proposed bioinspired conformal acoustics may bridge the gap between an animal’s biosonar and artificial materials, which show potential application value in underwater acoustics, medical ultrasonography, and other related applications.

In this article, we propose transformation caustics by applying coordinate transformation to the caustic effect. The limit boundaries of caustics can be used to design devices with asymmetric light propagation or light confinement, thus providing an alternative degree of freedom for metamaterials.

We demonstrate that light rays confined on geodesic lenses form closed trajectories, and that for optical waves, the spectrum of a geodesic lens is (at least approximately) degenerate and equidistant with the numerical method. Moreover, we fabricate two geodesic lenses in micrometer and millimeter scale and observe curved light rays along geodesics.

Inspired by electromagnetic waveguide cloaks with gradient index metamaterials, we fabricated a broadband cloak with simply a gradient depth profile on the bottom and without any other structures on the top to confine water waves in a certain area for cloaking regions. Being easy to construct, this design is potentially of significance for port applications.

In this article, we proposed the "inverse transformation optics", and found that a conformal singularity of a refractive-index profile, with either zero or infinity resulting from a power mapping w=z^a, is equivalent to a topological defect with positive charge or negative charge. We fabricated a "hat" shape device with such a topological defect with positive charge in experiments and its related light-bending functionality with laser beams.

We demonstrate for the first time a universal multimode waveguide star crossing based on transformation optics, which can handle in principle any number of waveguide modes and any number of crossing channels as well. The structure is transformed from a Maxwell’s fisheye, which could realize aberration-free imaging for each waveguide mode. A grayscale E-beam lithography is adopted to fabricate it on commercial silicon-on-insulator wafer. The proposed multimode waveguide star crossing has little loss and low crosstalk throughout an ultra-broad wavelength range of ~400 nm. Our study paves the way for realizing highly integrated and large capacity on-chip multimode routing and communication systems.

In the letter, we have proposed a method to construct new types of absolute instruments by combining the Mikaelian lens together with conformal mappings. There will be self-imaging and imaging effect along closed conformal curves. If the scaling parameter in Mikaelian lens is an irrational number, the imaging effect will be maintained along the curves forever while there will be no self-imaging effect. If we choose other orthogonal directions for the Mikaelian lens, e.g., the radial directions, the hyperbolic directions, or the parabolic directions from parabolic coordinates, the imaging effect will precisely happen along those predesigned open curves. Our method is very general and could be used on special waveguide design, microcavity design, and even cloaking designs in future.

Transformation optics has been used to propose various novel optical devices. With the help of metamaterials, several intriguing designs, such as invisibility cloaks, have been implemented. However, as the basic units should be much smaller than the working wavelengths to achieve the effective material parameters, and the sizes of devices should be much larger than the wavelengths of illumination to work within the light-ray approximation, it is a big challenge to implement an experimental system that works simultaneously for both geometric optics and wave optics. In this Letter, by using a gradient-index microstructured optical waveguide, we realize a device of conformal transformation optics (CTO) and demonstrate its self-focusing property for geometry optics and the Talbot effect for wave optics. In addition, the Talbot effect in such a system has a potential application to transfer digital information without diffraction. Our findings demonstrate the photon controlling ability of CTO in a feasible experiment system.

In this work, a waveguide structure is designed by employing gradient-index metamaterials, supporting strong Fano resonances with extremely sharp spectra. As the changes in the transmission spectrum originate from the interaction of guided modes from different channels, instead of resonance structures or metamolecules, the Fano resonances can be observed for both transverse electric and transverse magnetic polarizations.

In this work, we demonstrate an one-dimensional cloak consisting of parallel-plated waveguide with two slabs of gradient index metamaterials attached to its metallic walls. In it objects are hidden without limitation of polarizations, and good performance is observed for a broadband of frequencies. The experiments at microwave frequencies are carried out, supporting the theoretical results very well. The essential principle behind the proposed cloaking device is based on mode conversion, which provides a new strategy to manipulate wave propagation.

In this article, Fabry-Pe´rot resonances in materials of extreme anisotropy are used to design various transformation optical devices that are not only easy to realize but also work well for a set of resonant frequencies (multiple frequencies). As an example, a prototype of a cylindrical concentrator is fabricated for microwaves.

We design a new class of gradient index lenses from multivalued optical conformal mapping. Such lenses can make one active source appear omnidirectionally as two (or many) in-phase sources, each interfering with others. As a self-interference phenomenon, this has not been discussed before. Meanwhile, they can transform multiple in-phase sources into one.

We employ the recent concept of gradient index metamaterials to demonstrate a waveguide with asymmetric propagation of light, independent of polarization.

The device blocks both transverse electric and magnetic polarized modes in one direction but transmits them in the other for a broadband spectrum. Unlike previous works using chiral properties of metamaterials, our device is based on the principle of momentum symmetry breaking at interfaces with phase discontinuities. Experiments in the microwave region verify our findings, which may pave the way to feasible passive optical diodes.

We report an experiment on an inside-out Eaton lens fabricated using H-fractal metamaterials, copper printed on printed circuit boards in H-fractal patterns. The lens can perform good imaging functionality with both sources and images inside the vacuum core. The H-fractal metamaterials also provide design technique to achieve refractive index ranging in [0,1] with little loss in microwave spectrum. Excellent agreements between numerical and experimental results have been demonstrated.

We experimentally demonstrate the first metamaterial "illusion optics" device—an "invisible gateway" by using a transmission-line medium. The device contains an open channel that can block waves at a particular frequency range. We also demonstrate that such a device can work in a broad frequency range.

We extend the transformation media concept to the linear liquid surface waves. A mapping is introduced to generate an anisotropic depth parameter that corresponds to the anisotropic permittivity tensor in electromagnetic waves. A device that can rotate the liquid wave front is introduced, which is an analog of the metamaterial electromagnetic wave field rotator. The structure is based on a layered design. Simulation results are compared with experimental measurements.

We designed a metamaterial field rotator that can rotate electromagnetic wave fronts. Our starting point was the transformation-media concept. Effective medium theories and full simulations facilitated the actual design process. We created at a very simple structure comprising of an array of identical aluminum metal plates. We made and measured a sample and we experimentally demonstrated the field rotation effect as well as the broadband functionality at microwave frequencies.