No abstract

Photonic topological states have been exploited to give rise to robust optical behaviors that are quite insensitive to local defects or perturbations, which provide a promising solution for robust photonic integrations. Specifically, for example, optical coupling between waveguides is a universal function in integrated photonics. However, the coupling performance usually suffers from high structure‐sensitivity and challenges current manufacturing for massive production. Here, the topological edge state in a finite Su–Schriffer–Heeger modeled optical waveguide array is explored and robust optical coupling (e.g., directional coupling and beam splitting) is demonstrated, which is quite insensitive to structural variations. It is experimentally proved that even a large discrepancy (21–26% structural deviation) in silicon waveguides gaps has little influence on optical coupling (>90% performance), while conventional counterparts totally break down. Moreover, thanks to such a topological design, the devices show much broader working bandwidth (≈10 times performance improvement) than the conventional ones, greatly favoring the photonic integrations. This work would inspire new families of optical devices with robust and broadband properties that can excite more interesting and useful exploration in both fields, and possibly open a new avenue toward topological devices with unique properties and functionalities.

Self-imaging is an important function for signal transport, distribution, and processing in integrated optics, which is usually implemented by multimode interference or diffractive imaging process. However, these processes suffer from the resolution limit due to classical wave propagation dynamics. We propose and demonstrate subwavelength optical imaging in one-dimensional silicon waveguide arrays, which is implemented by cascading straight and curved waveguides in sequence. The coupling coefficient between the curved waveguides is tuned to be negative to reach a negative dispersion, which is an analog to a hyperbolic metamaterial with a negative refractive index. Therefore, it endows the waveguide array with a superlens function as it is connected with a traditional straight waveguide array with positive dispersion. With a judiciously engineered cascading silicon waveguide array, we successfully show the subwavelength self-imaging process of each input port of the waveguide array as the single point source. Our approach provides a strategy for dealing with optical signals at the subwavelength scale and indicates functional designs in high-density waveguide integrations.

Metasurfaces with local phase tuning by subwavelength elements promise unprecedented possibilities for ultrathin and multifunctional optical devices in which geometric phase design is widely used due to its resonant‐free and large tolerance in fabrications. By arranging the orientations of anisotropic nanoantennas, the geometric phase‐based metasurfaces can convert the incident spin light to its orthogonal state, and enable flexible wave front engineering together with the function of a half‐wave plate. Herein, by incorporating the propagation phase, another important optical device of quarter‐wave plate together with the wave front engineering as well, which is implemented by controlling both the cross‐ and copolarized light simultaneously with a singlet metasurface, is realized. Highly efficient conversion of the spin light to a variety of linearly polarized light is obtained for meta‐holograms, metalens focusing and imaging in the blue light region. This work provides a new strategy for efficient metasurfaces with both phase and polarization control, and enriches the functionalities of metasurface devices for wider application scenarios.

No abstract

Bin fang, chen chen, Shining Zhu & tao Li * Metasurfaces are made of subwavelength nanoantennas with a flat, ultrathin architecture, and strong capability in manipulating the propagation of light by flexible modulations on its phase, amplitude, and polarization. Conventional metallic metalenses always suffer from its low efficiencies due to large intrinsic loss. Here, we demonstrate a cavity enhanced bilayer metalens composed of aluminum nanobars and its complementary structures. The focusing and imaging experiments definitely show an improved efficiency of such kind of bilayer metalens compared with its single layer counterpart. Detailed theoretical analyses based on full-wave simulations are carried out with respect to different cavity lengthes and working wavelengths, which reveals that the improvement rightly attributes to enhanced cavity mode. Our design will not only improve the working efficiency for metalens with simplified manufacturing procedure, but also indicates more possibilities by employing the metal as electrodes.