The emerging metasurfaces with the exceptional capability of manipulating an arbitrary wavefront have revived the holography with unprecedented prospects. However, most of the reported metaholograms suffer from limited polarization controls for a restrained bandwidth in addition to their complicated meta-atom designs with spatially variant dimensions. Here, we demonstrate a new concept of vectorial holography based on diatomic metasurfaces consisting of metamolecules formed by two orthogonal meta-atoms. On the basis of a simply linear relationship between phase and polarization modulations with displacements and orientations of identical meta-atoms, active diffraction of multiple polarization states and reconstruction of holographic images are simultaneously achieved, which is robust against both incident angles and wavelengths. Leveraging this appealing feature, broadband vectorial holographic images with spatially varying polarization states and dual-way polarization switching functionalities have been demonstrated, suggesting a new route to achromatic diffractive elements, polarization optics, and ultrasecure anticounterfeiting.

Carbon nanocoils (CNCs) are employed to fabricate fast, high-resolution, and reversible humidity sensor based on a flexible liquid crystal polymer (LCP) substrate. The humidity sensor displays fast-response (1.9 s) and recovery time (1.5 s), a broad relative humidity (RH) detection range (4−95%), linearity, repeatability, and stability. The rapid response and recovery are considered to benefit from the hydrophobic effect of the LCP substrate and high purity of the CNCs, which give rise to weak physical adsorption. Meanwhile, the high sensitivity results from both the unique helical structure of CNCs and the microporous structure of the LCP substrate. The distinctive structure-related properties enable the sensor to reliably perceive an extremely small RH variation of 0.8%, which is too small to be detected by most humidity sensors reported previously. These features allow the sensor to monitor a variety of important human activities, such as respiration, speaking, blowing, and noncontact fingertip sensation, accurately. Furthermore, different human physical conditions can be distinguished by recognizing the respiration response patterns. In addition, the long-term operation and mechanical bending do not adversely affect the sensing performance.

Metal heterostructures constructed surface plasmon polaritons (SPPs) Bragg reflectors and nanocavities on flat metallic surfaces are proposed and demonstrated numerically. A metal heterowaveguide structured by alternately stacking two kinds of metal gap waveguides (MGWs) shows periodically effective refraction index modulation to SPPs and produces SPP propagation on flat metallic surfaces a band gap in certain frequencies, known as plasmonic band gap, in which SPP propagation is forbidden. Changing the width of one MGW in the heterowaveguide, a SPP nanocavity with high quality factor can be created. Our results imply a broad possibility of constructed SPP-based Bragg reflectors, emitter, and filters, etc., on flat metallic surfaces for planar nanometeric photonic networks.

The emerging meta-holograms rely on arrays of intractable meta-atoms with various geometries and sizes for customized phase profiles that can precisely modulate the phase of a wavefront at an optimal incident angle for given wavelengths. The stringent and band-limited angle tolerance remains a fundamental obstacle for their practical application, in addition to high fabrication precision demands. Utilizing a different design principle, we determined that facile metagrating holograms based on extraordinary optical diffraction can allow the molding of arbitrary wavefronts with extreme angle tolerances (near-grazing incidence) in the visible–near-infrared regime. By modulating the displacements between uniformly sized meta-atoms rather than the geometrical parameters, the metagratings produce a robust detour phase profile that is irrespective of the wavelength or incident angle. The demonstration of high-fidelity meta-holograms and in-site polarization multiplexing significantly simplifies the metasurface design and lowers the fabrication demand, thereby opening new routes for flat optics with high performances and improved practicality.

We demonstrate an approach for easy fabrication of two-dimensional (2D) hexagonal and three-dimensional (3D) face-centered-cubic (fcc)-type photonic crystal (PhC) microstructures in a photosensitive polymer by applying a simple single refracting prism. This prism enables the splitting and recombining of a single incoming laser beam to form multiple-beam interference pattern simultaneously. Thus, antivibration equipment and complicated optical alignment system are not required, leading to a much more simple optical setup than previously reported laser holographic lithography techniques. Large-scale (over 1cm2) 2D hexagonal and 3D fcc-type PhCs have been produced. Reflection/transmission measurements performed on the fabricated 3D fcc-type PhC structures agree well with the corresponding band structure calculation.

Based on finite-difference time-domain simulation of the propagation characteristics of surface plasmon polaritons (SPPs) in optical circuits made from metal gap waveguides (MGWs) with nanometric gap widths, we theoretically demonstrate that two structures that consist of splitting and recombining MGWs and of coupling MGWs can be used as nanoscale Mach-Zehnder interferometers. MGW arrays show capabilities for array imaging and for controlling the flow of SPPs. Other potential applications of coupling MGWs, as SPP switches, directional couplers, and even as a nanoscale counterpart for observing linear and nonlinear dynamic behavior of electromagnetic fields, are also predicted and discussed. Our results point to an interesting way to manipulate optical signals and provide efficient sensing in nanophotonic architectures.

Strong vibrational coupling has been realized in a variety of mechanical systems. However, there have been no experimental observations of strong coupling of the acoustic modes of plasmonic nanostructures, due to rapid energy dissipation in these systems. Here we realized strong vibrational coupling in ultra-high frequency plasmonic nanoresonators by increasing the vibrational quality factors by an order of magnitude. We achieved the highest frequency quality factor products of f × Q = 1.0 × 10 13 Hz for the fundamental mechanical modes, which exceeds the value of 0.6 × 10 13 Hz required for ground state cooling. Avoided crossing was observed between vibrational modes of two plasmonic nanoresonators with a coupling rate of g = 7.5 ± 1.2 GHz, an order of magnitude larger than the dissipation rates. The intermodal strong coupling was consistent with theoretical calculations using a coupled oscillator model. Our results enabled a platform for future observation and control of the quantum behavior of phonon modes in metallic nanoparticles.

We analytically show that an incident light can be almost completely diffracted into the -1(st) order in wide-angle and broadband by suitably designed thin metallic nano-gratings with simple rectangular cross sections. Such extraordinary optical diffraction results from the excitation of localized cavity modes and exists even when the grating period is modulated in a broad range. By modulating the period with binary holography techniques, we can shape an incident wave into arbitrary wavefronts with near-unity conversion efficiencies. To show the efficacy of this approach, we demonstrate three reflection-type metasurfaces for achieving near-complete conversions from a Gaussian beam into a focused beam, Bessel beam, and vortex beam, respectively, with the complete suppression of the undesired specular reflection. Our findings provide a facile approach to build arbitrary wavefront-shaping metasurfaces with wide-angle, broadband, and high efficiency performance.