A broadband achromatic metalens array for integral imaging in the visible

Integral imaging is a promising three-dimensional(3D)imaging technique that captures and reconstructs light field information.Microlens arrays are usually used for the reconstruction process to display 3D scenes to the viewer.However,the inherent chromatic aberration of the microlens array reduces the viewing quality,and thus,broadband achromatic imaging remains a challenge for integral imaging.Here,we realize a silicon nitride metalens array in the visible region that can be used to reconstruct 3D optical scenes in the achromatic integral imaging for white light.The metalens array contains 60×60 polarization-insensitive metalenses with nearly diffraction-limited focusing.The nanoposts in each high-efficiency(measured as 47%on average)metalens are delicately designed with zero effective material dispersion and an effective achromatic refractive index distribution from 430 to 780 nm.In addition,such an achromatic metalens array is composed of only a single silicon nitride layer with an ultrathin thickness of 400 nm,making the array suitable for on-chip hybrid-CMOS integration and the parallel manipulation of optoelectronic information.We expect these findings to provide possibilities for full-color and aberration-free integral imaging,and we envision that the proposed approach may be potentially applicable in the fields of high-power microlithography,high-precision wavefront sensors,virtual/augmented reality and 3D imaging.

Meta-objective with sub-micrometer resolution for microendoscopes

Microendoscopes are vital for disease detection and clinical diagnosis. The essential issue for microendoscopes is to achieve minimally invasive and high-resolution observations of soft tissue structures inside deep body cavities.Obviously, the microscope objective is a must with the capabilities of both high lateral resolution in a wide field of view(FOV) and miniaturization in size. Here, we propose a meta-objective, i.e., microscope objective based on cascaded metalenses. The two metalenses, with the optical diameters of 400 μm and 180 μm, respectively, are mounted on both sides of a 500-μm-thick silica film. Sub-micrometer lateral resolution reaches as high as 775 nm in such a naked meta-objective, with monochromatic aberration correction in a 125 μm full FOV and near diffraction limit imaging. Combined with a fiber bundle microscope system, the single cell contour of biological tissue(e.g., water lily leaf) can be clearly observed, compared to the indistinguishable features in other conventional lens-based fiber bundle systems, such as plano–convex and gradient refractive index(GRIN) cases.

In-plane excitation of a topological nanophotonic corner state at telecom wavelengths in a cross-coupled cavity

In silicon photonics,the cavity mode is a fundamental mechanism to design integrated passive devices for on-chip optical information processing.Recently,the corner state in a second-order topological photonic crystal(PC)rendered a global method to achieve an intrinsic cavity mode.It is crucial to explore such a topological corner state in silicon photonic integrated circuits(PICs)under in-plane excitation.Here,we study both theoretically and experimentally the topological nanophotonic corner state in a silicon-on-insulator PC cavity at a telecommunications wavelength.In theory,the expectation values of a mirror-flip operation for the Bloch modes of a PC slab are used to characterize the topological phase.Derived from topologically distinct bulk polarizations of two types of dielectric-vein PCs,the corner state is induced in a 90-deg-bend interface,localizing at the corner point of real space and the Brillouin zone boundary of reciprocal space.To implement in-plane excitation in an experiment,we fabricate a cross-coupled PC cavity based on the bend interface and directly image the corner state near 1383 nm using a far-field microscope.Finally,by means of the temporal coupled-mode theory,the intrinsic Q factor of a cross-coupled cavity(about 8000)is retrieved from the measured transmission spectra.This work gives deterministic guidance and potential applications for cavity-mode-based passive devices in silicon PICs,such as optical filters,routers,and multiplexers.