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Nanophotonic platforms such as metasurfaces, achieving arbitrary phase profiles within ultrathin thickness, emerge as miniaturized, ultracompact and kaleidoscopic optical vortex generators. However, it is often required to segment or interleave independent sub-array metasurfaces to multiplex optical vortices in a single nano-device, which in turn affects the device’s compactness and channel capacity. Here, inspired by phyllotaxis patterns in pine cones and sunflowers, we theoretically prove and experimentally report that multiple optical vortices can be produced in a single compact phyllotaxis nanosieve, both in free space and on a chip, where one meta-atom may contribute to many vortices simultaneously. The time-resolved dynamics of on-chip interference wavefronts between multiple plasmonic vortices was revealed by ultrafast time-resolved photoemission electron microscopy. Our nature-inspired optical vortex generator would facilitate various vortex-related optical applications, including structured wavefront shaping, free-space and plasmonic vortices, and high-capacity information metaphotonics.

Nanostructured metasurfaces demonstrate extraordinary capabilities to control light at the subwavelength scale, emerging as key optical components to physical realization of multitasked devices. Progress in multitasked metasurfaces has been witnessed in making a single metasurface multitasked by mainly resorting to extra spatial freedom, for example, interleaved subarrays, different angles. However, it imposes a challenge of suppressing the cross-talk among multiwavelength without the help of extra spatial freedom. Here, we introduce an entirely novel strategy of multitasked metasurfaces with noninterleaved single-size Si nanobrick arrays and minimalist spatial freedom demonstrating massive information on 6-bit encoded color holograms. The interference between electric dipole and magnetic dipole in individual Si nanobricks with in-plane orientation enables manipulating six bases of incident photons simultaneously to reconstructed 6-bit wavelength- and spin-dependent multicolor images. Those massively reco...

Compact and miniaturized devices with flexible functionalities are always highly demanded in optical integrated systems. Plasmonic nanosieve has been successfully harnessed as an ultrathin flat platform for complex manipulation of light, including holography, vortex generation, and nonlinear processes. Compared with most of the reported single-functional devices, multifunctional nanosieves might find more complex and novel applications across nanophotonics, optics, and nanotechnology. Here, a promising roadmap for nanosieve-based helical devices is experimentally demonstrated, which achieves full manipulations of optical vortices, including its generation, hybridization, spatial multiplexing, focusing and nondiffraction propagation, etc., by controlling the geometric phase of spin light via over 121 thousands of spatially rotated nanosieves. Thanks to such spin-conversion nanosieve helical elements, it is no longer necessary to employ the conventional two-beam interferometric measurement to characterize optical vortices, while the interference can be realized natively without changing any parts of the current setup. The proposed strategy makes the far-field manipulations of optical orbital angular momentum within an ultrathin interface viable and bridges singular optics and integrated optics. In addition, it enables more unique extensibility and flexibility in versatile optical elements than traditional phase-accumulated helical optical devices.

The dielectric metasurface hologram promises higher efficiencies due to lower absorption than its plasmonic counterpart. However, it has only been used, up to now, for controlling linear-polarization photons to form single-plane holographic images in the near-infrared region. Here, we report a transmission-type metahologram achieving images in three colors, free from high-order diffraction and twin-image issues, with 8-level modulation of geometric phase by controlling photon spin via precisely patterned Si nanostructures with varying orientations. The resulting real and virtual holographic images with spin dependence of incident photons natively enable the spin degeneracy removal of light, leading to a metahologram-enabled spin Hall effect of light. Low-absorption dielectrics also enable us to create holograms for short-wavelength light down to 480 nm, thus spanning the three primary colors. It possesses the potential for compact color-display chips using mature semiconductor processes, and holds significant advantages over previous metaholograms operating at longer wavelengths.

With the recent burgeoning advances in nano-optics, ultracompact, miniaturized photonic devices with high-quality and spectacular functionalities are highly desired. Such devices' design paradigms often call for the solution of a complex inverse nonanalytical/semianalytical problem. However, currently reported strategies dealing with amplitude-controlled meta-optics devices achieved limited functionalities mainly due to restricted search space and demanding computational schemes. Here, we established a segmented hierarchical evolutionary algorithm, aiming to solve large-pixelated, complex inverse meta-optics design and fully demonstrate the targeted performance. This paradigm allows significantly extended search space at a rapid converging speed. As typical complex proof-of-concept examples, large-pixelated meta-holograms are chosen to demonstrate the validity of our design paradigm. An improved fitness function is proposed to reinforce the performance balance among image pixels, so that the image quality is improved and computing speed is further accelerated. Broadband and full-color meta-holograms with high image fidelities using binary amplitude control are demonstrated experimentally. Our work may find important applications in the advanced design of future nanoscale high-quality optical devices.

Nanostructured metasurfaces demonstrate extraordinary capabilities to control light at the subwavelength scale, emerging as key optical components to physical realization of multitasked devices. Progress in multitasked metasurfaces has been witnessed in making a single metasurface multitasked by mainly resorting to extra spatial freedom, for example, interleaved subarrays, different angles. However, it imposes a challenge of suppressing the cross-talk among multiwavelength without the help of extra spatial freedom. Here, we introduce an entirely novel strategy of multitasked metasurfaces with noninterleaved single-size Si nanobrick arrays and minimalist spatial freedom demonstrating massive information on 6-bit encoded color holograms. The interference between electric dipole and magnetic dipole in individual Si nanobricks with in-plane orientation enables manipulating six bases of incident photons simultaneously to reconstructed 6-bit wavelength- and spin-dependent multicolor images. Those massively reconstructed images can be distinguished by pattern recognition. It opens an alternative route for integrated optics, data encoding, security encryption, and information engineering.

A key recent advance in nanophotonics field has been the emergence of tunable, switchable and reconfigurable metasurfaces offering “optical properties on demand”. With these devices, light propagation does not have to be static, as traditionally assumed, but may be changed at will at any point in space and/or moment in time. Various approaches have been developed to realize optical components made from metadevices reconfigurable by mechanical, electrical, or optical means. In general, however, most of the existing reconfigurable metasurfaces tune the properties over the entire device homogeneously when stimulated. The ability to tailor the optical properties of individual meta-molecules in planar metasurfaces promises to open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping and adaptive optics. In this work, we pioneered the novel single-meta-molecule addressable digitally reconfigurable metadevices using the emerging paradigms of tunable metasurfaces - functional matter structured on the sub-wavelength scale, and by engaging new ideas of phase-change material integrated with nanostructures for dynamic light control. In our design, low loss dielectric nanostructures (amorphous Si nanorods) are patterned on top of phase-change foundation structures to form the hybrid meta-molecule. As for the phase-change medium, we use the chalcogenide glasses (e.g. germanium-antimony-telluride), which is widely exploited in rewritable optical disk storage technology and non-volatile electronic memories due to its good thermal stability, high switching speed, large number of achievable rewriting cycles and pronounced contrast of dielectric properties observed between two phases. The phase-change process in chalcogenide glasses is a material reaction to the photothermal effects. Using tightly-focused low-energy fs laser pulses to excite the phase transition results in a sharp border between the amorphous background and crystallized spots, allowing individual single meta-molecules to be addressed. The reconfiguration of meta-molecules will be accomplished by re-amorphization of the phase-change material with a high-energy single optical pulse. The preliminary simulation results demonstrated the reconfigurable metasurfaces for phase and resonance frequency modulation of light based on the innovative platform of digitally and individually reconfigurable meta-molecules for applications in active beam shape and hologram display. This development will progress photonic technology enabling increased information flow, while reducing power consumption and achieving new levels of miniaturization for photonic devices.

A key recent advance in nanophotonics field has been the emergence of tunable, switchable and reconfigurable metasurfaces offering “optical properties on demand”. Various approaches have been developed to realize optical components made from metadevices reconfigurable by mechanical, electrical, or optical means. In general, however, most of the existing reconfigurable metasurfaces tune the properties over the entire device homogeneously when stimulated. In this work, we pioneered single-meta-molecule addressable digitally reconfigurable metadevices using the emerging paradigms of tunable metasurfaces - functional matter structured on the sub-wavelength scale, and by engaging new ideas of phase-change material integrated with nanostructures for dynamic light control. In our design, low loss dielectric nanostructures (amorphous Si nanorods) are patterned on top of phase-change foundation structures to form the hybrid meta-molecule. As for the phase-change medium, we use the chalcogenide glasses (e.g. germanium-antimony-telluride), which have pronounced contrast of dielectric properties observed between two phases. The laser-induced submicron-sized phase-change footprint allows us to address single meta-molecules individually. The reconfiguration of meta-molecules will be accomplished by re-amorphization of the phase-change material with a high-energy single optical pulse. The preliminary simulation results demonstrated the reconfigurable metasurfaces for phase and resonance frequency modulation of light based on the innovative platform of digitally and individually reconfigurable meta-molecules for applications in active beam shape and hologram display

Metasurfaces, two-dimensional versions of metamaterials, retain the great capabilities of three-dimensional counterparts in manipulating electromagnetic wave behaviors, while reducing the challenges in fabrication. By judiciously engineering parameters of individual building blocks (such as geometry, size, and material) and selecting specific design algorithms, metasurfaces are promising to replace conventional electromagnetic elements in nanoplasmonic/photonic devices. Significantly, such concept can be readily promoted to other disciplines, such as acoustics, thermal physics, and seismology. In this article, the latest advances in full control of electromagnetic waves with metasurfaces are briefly reviewed from a functionality perspective. A broad avenue towards real-life applications of metamaterials has been opened up, although they are still at their infant stage. At the end, several promising approaches are suggested to extend the applications of metasurfaces.

A multifocus optical vortex metalens, with enhanced signal-to-noise ratio, is presented, which focuses three longitudinal vortices with distinct topological charges at different focal planes. The design largely extends the flexibility of tuning the number of vortices and their focal positions for circularly polarized light in a compact device, which provides the convenience for the nanomanipulation of optical vortices.

Quantum entanglements between integer-order and fractional-order orbital angular momentums (OAMs) have been previously discussed. However, the entangled nature of arbitrary rational-order OAM has long been considered a myth due to the absence of an effective strategy for generating arbitrary rational-order OAM beams. Therefore, we report a single metadevice comprising a bilaterally symmetric grating with an aperture, creating optical beams with dynamically controllable OAM values that are continuously varying over a rational range. Due to its encoded spiniform phase, this novel metagrating enables the production of an average OAM that can be increased without a theoretical limit by embracing distributed singularities, which differs significantly from the classic method of stacking phase singularities using fork gratings. This new method makes it possible to probe the unexplored niche of quantum entanglement between arbitrarily defined OAMs in light, which could lead to the complex manipulation of microparticles, high-dimensional quantum entanglement and optical communication. We show that quantum coincidence based on rational-order OAM-superposition states could give rise to low cross-talks between two different states that have no significant overlap in their spiral spectra. Additionally, future applications in quantum communication and optical micromanipulation may be found.

Optical manipulation by dielectric waveguides enables the transportation of particles and biomolecules beyond diffraction limits. However, traditional dielectric waveguides could only transport objects in the forward direction which does not fulfill the requirements of the next generation lab-on-chip system where the integrated manipulation system should be much more flexible and multifunctional. In this work, bidirectional transportation of objects on the nanoscale is demonstrated on a rectangular waveguide made of the phase change material Ge2Sb2Te5 (GST) by numerical simulations. Either continuous pushing forces or pulling forces are generated on the trapped particles when the GST is in the amorphous or crystalline phase. With the technique of a femtosecond laser induced phase transition on the GST, we further proposed a reconfigurable optical trap array on the same waveguide. This work demonstrates GST waveguide's potential of achieving multifunctional manipulation of multiple objects on the nanoscale with plausible optical setups.

The orbital angular momentum (OAM) of light can be taken as an independent and orthogonal degree of freedom for multiplexing in an optical communication system, potentially improving the system capacity to hundreds of Tbits per second. The high compactness and miniaturization of devices required for optical communications impose strict requirements on discriminating OAM modes of light at a small (micro- or even nano-meter) scale for demultiplexing; these requirements represent a challenge for traditional OAM sorting strategies. Here, we propose a semi-ring plasmonic nanoslit to directly and spatially sort various OAM modes of light into ∼120 nm-spaced mode intervals on the metallic surface. Making use of the constructive interference of a helical-phase modulated surface wave excited by a vortex beam, this on-chip interval can be stably demonstrated both theoretically and experimentally with a quasi-linear dependence on the plasmonic wavelength. Furthermore, its immunity to semi-ring geometry (i.e., the radius and number of rings) is verified by simulations. As a result, OAM discriminating is guaranteed by this stable sorting function. This technique shows a viable solution to discriminate the OAM of light at the nano-scale and might lead to broad benefits across the fields of optical communications, plasmonic physics and singular optics.

Two highly coupled plasmonic metasurfaces exhibit much higher conversion efficiency and extinction ratio than individual ones., Metasurfaces operating in the cross-polarization scheme have shown an interesting degree of control over the wavefront of transmitted light. Nevertheless, their inherently low efficiency in visible light raises certain concerns for practical applications. Without sacrificing the ultrathin flat design, we propose a bilayer plasmonic metasurface operating at visible frequencies, obtained by coupling a nanoantenna-based metasurface with its complementary Babinet-inverted copy. By breaking the radiation symmetry because of the finite, yet small, thickness of the proposed structure and benefitting from properly tailored intra- and interlayer couplings, such coupled bilayer metasurface experimentally yields a conversion efficiency of 17%, significantly larger than that of earlier single-layer designs, as well as an extinction ratio larger than 0 dB, meaning that anomalous refraction dominates the transmission response. Our finding shows that metallic metasurface can counterintuitively manipulate the visible light as efficiently as dielectric metasurface (~20% in conversion efficiency in Lin et al.’s study), although the metal’s ohmic loss is much higher than dielectrics. Our hybrid bilayer design, still being ultrathin (~λ/6), is found to obey generalized Snell’s law even in the presence of strong couplings. It is capable of efficiently manipulating visible light over a broad bandwidth and can be realized with a facile one-step nanofabrication process.

We propose an algorithm for jointly designing two phase-only masks (POMs) that allow for the encryption and noise-free retrieval of triple images. The images required for optical retrieval are first stored in quick-response (QR) codes for noise-free retrieval and flexible readout. Two sparse POMs are respectively calculated from two different images used as references for authentication based on modified Gerchberg-Saxton algorithm (GSA) and pixel extraction and are then used as support constraints in a modified double-phase retrieval algorithm (MPRA), together with the above-mentioned QR codes. No visible information about the target images or the reference images can be obtained from each of these authenticated POMs. This approach allows users to authenticate the two POMs used for image reconstruction without visual observation of the reference images. It also allows user to friendly access and readout with mobile devices.

The development of metasurface, capable of controlling wave-fronts through interfacial phase discontinuity, offers a fascinating methodology for designing two dimensional miniaturized optical devices. Owing to an additional advantage of the enhanced useful transmission via Bainet-inverted matasurface, we exploit them to demonstrate an intriguing concept of merging the phase-profiles of two distinct optical devices, a lens and a spiral phase plate, to realize an ultrathin nanostructured optical vortex lens. The proposed device can has multiple focal planes along the longitudinal direction; whereas the number of focal plans, corresponding topological charges and focal lengths can readily be tailored to meet any desired requirements. Meanwhile, the dual-polarity feature of the optical vertex metalens exhibits spin controlled real and virtual focal plans, while dispersionless aptitude of nanobars enables its working over the broadband. The concept unveils a novel way of employing metasurface, to engraft the phase profiles of multiple bulk devices, to achieve unique functionalities for promising applications in integrated photonics.

Metasurfaces that consist of a monolayer of photonic artificial atoms are emerging as attractive materials for optical wavefront-shaping and polarization-control devices. By integrating nanophotonics with a phase-encoding technique, we demonstrate theoretically an information authentication method using dielectric metasurfaces that can be verified without information disclosure at visible wavelengths. The required secured diffraction pattern can be simply achieved by a metasurface hologram with a small number of pixels, which means increased efficiency and lower costs of production. Although the decrypted image is noisy, it can be authenticated by recognition algorithms where the primary image is used as a reference. The results show that the dielectric metasurface approach, providing great flexibility in the design of the wavefront of light and compatible with the CMOS technology, can be potentially applied in optical information security.

An orthogonal dispersive spectral-domain optical coherence tomography (SDOCT) system based on a spectrometer consisting of a high spectral resolution virtually-imaged phased array (VIPA) and a low resolution diffraction grating is developed. Two-dimensional (2D) dispersion generated by the combination of the VIPA and the grating in conjunction with a 2D CCD leads to an improved performance of the spectrometer. Ultrahigh spectral resolution of 0.002 nm within a free spectrum range of 50 nm is realized, providing the spectrometer with a spectral sampling rate up to ~10(5). The developed SDOCT realizes an imaging depth over 80 mm, which is the longest depth range ever achieved by SDOCT. The increased spectral sampling rate also results in a high signal-to-noise ratio of the SDOCT system. The application of the developed system is further illustrated by quantitative phase imaging of a glass plate and an optical lens.