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Perfect vortex (PV) beams possess a radial intensity profile independent of their topological charges, overcoming the defects of the regular vortex beams. However, the bulky optical elements used in conventional methods for generation of PV beams limit their potential applications. Metasurfaces are ultra-thin version of metamaterials with the flexible ability of controlling electromagnetic waves, promising great potential applications in many optical fields. Here, an all-dielectric metasurface based on a geometrical phase is demonstrated, featuring broadband and high efficiency in manipulation of circularly polarized light. We numerically simulate the performance of the unit-cell and metasurface for generating PV beams carrying integer and fractional topological charges. We hope the designed metasurface will provide an ultra-compact way for generation of high-quality PV beams. [ABSTRACT FROM AUTHOR]

• We proposed the high-performance dynamic beam all-direlectric coding metasurface converter based on phase change materials of GST in optical communication band. • We found the theoretical support for optimizing geometric parameters by multipole decomposition and field diagram characterization of amorphous and crystalline elements. The optimized units can achieve ultra-high transmittance and 2π phase coverage in amorphous state. • The large contrast in transmittance and phase between the two states enables us to switch the beam deflection without changing the structure. And further applied it to the design of beam focusing and holographic reconstruction. • We arrayed the units into coding metasurface, and with the help of Fourier method, we realized the beam deflection at any angle in the working band of 1.119um. Phase change materials, especially Ge 2 Sb 2 Te 5 (GST), play an important role in the design of dynamic all-dielectric metasurface due to its flexibility and adjustability. And its non-volatility makes it possible to form dynamic metasurfaces with complex functions. In this paper, we propose a cross-shaped all-dielectric metasurface based on GST interlayer, which can achieve ultra-high transmittance and complete 2π phase coverage in the near-infrared band when the interlayer material is in amorphous state. Through multipole decomposition and field distribution characterization, we have revealed the regulation principles of the unit cell before and after the switching. And thus, we designed the arrays of metasurface with switchable beam deflection, arbitrary coding and focusing functions. Holographic reconstruction based on GS algorithm is discussed and extended to independent control of the RGB channels in imaging applications. Our research can provide a reference for the design of compact multifunctional optical elements, optical encryption and dynamic metasurfaces. [ABSTRACT FROM AUTHOR]

• A waveguide chip that disperses light and focuses it directly onto a camera without any free-space elements. • Fine spectral resolution (0.42nm) and a large focal depth (>4mm) for precise spectral analysis with relaxed system alignment. • No need for customized detectors and electronic circuits. • The chip can be easily mounted to any commercial camera for fiber spectrum analysis. We propose and experimentally demonstrate a fiber spectrum analyzer based on a planar waveguide chip butt-coupled with an input fiber and aligned to a standard camera without any free-space optical elements. The chip consists of a single-mode waveguide to connect with the fiber, a beam broadening area, and a waveguide array in which the lengths of the waveguides are designed for both wavelength separation and beam focusing. The facet of the chip is diced open so that the outputs of the array form a near-field emitter. The far field are calculated by the Rayleigh-Sommerfeld diffraction integral. We show that the chip can provide a focal depth on the millimeter scale, allowing relaxed alignment to the camera without any fine-positioning stage. Two devices with 120 and 220 waveguides are fabricated on the polymer waveguide platform. The measured spectral width are 0.63 nm and 0.42 nm, respectively. This simple and practical approach may lead to the development of a spectrum analyzer for fiber that is easily mountable to any commercial camera, thereby avoiding the complication for customized detectors as well as electronic circuits afterwards. [ABSTRACT FROM AUTHOR]