Wavefront shaping with disorder-engineered metasurfaces

Large area highly ordered monolayer composite microsphere arrays - fabrication and tunable surface plasmon linewidth

A route to produce highly ordered two-dimensional periodic composite microsphere/gel arrays by using a sol–gel coassembly method was proposed and demonstrated. The proposed semi-infiltrated ordered monolayer PS microsphere/gel array affords a flexible platform to produce versatile plasmonic structures through either adjusting the gel infiltration height or sputtered metal film thickness. Fabrication factors, such as environmental humidity, evaporation temperature, and tetraethyl orthosilicate solution concentration, that will affect the quality of the monolayer film were experimentally investigated. Pair correlation function was applied to evaluate the order degree of the experimental results, which reveals the high uniformity of the composite microsphere arrays (CSAs). By adjusting metal film thickness, the figures of merit of propagating surface plasmons excited on CSAs or concave arrays can be tuned under normal incidence.

Surface plasmons on co-assembled large area highly ordered monolayer composite sphere arrays exhibit tunable linewidth.

Wide-angular-range and high-resolution beam steering by a metasurface-coupled phased array

Optical beam steering has broad applications in lidar, optical communications, optical interconnects, and spatially resolved optical sensors. For high-speed applications, phased-array-based beam-steering methods are favored over mechanical methods, as they are unconstrained by inertia and can inherently operate at a higher speed. However, phased-array systems exhibit a tradeoff between angular range and beam divergence, making it difficult to achieve both a large steering angle and a narrow beam divergence. Here, we present a beam-steering method based on wavefront shaping through a disorder-engineered metasurface that circumvents this range-resolution tradeoff. We experimentally demonstrate that, through this technique, one can continuously steer an optical beam within a range of 160° (80° from normal incidence) with an angular resolution of about 0.01° at the cost of beam throughput.

Metasurface of deflection prism phases for generating non-diffracting optical vortex lattices

A functional metasurface of both transparent medium slices and multiple deflection prisms is proposed, where phase retardations for generating non-diffracting vortex lattices are integrated and encoded as rotation angles of nano-apertures. Under plane-wave illumination, the transmitted waves from the thin flat metasurface act analogously as multiple beams, each with a designed propagating direction and pre-scribed phase shift, that generate an optical lattice within their overlapping region of space. By altering the design parameters of the metasurface, lattice type and size can be controlled. Both numerical simulations and experiments were conducted, verifying the possibility of the proposed method and the non-diffracting properties of the generated vortex lattices.

Compact folded metasurface spectrometer

An optical design space that can highly benefit from the recent developments in metasurfaces is the folded optics architecture where light is confined between reflective surfaces, and the wavefront is controlled at the reflective interfaces. In this manuscript, we introduce the concept of folded metasurface optics by demonstrating a compact spectrometer made from a 1-mm-thick glass slab with a volume of 7 cubic millimeters. The spectrometer has a resolution of ~1.2 nm, resolving more than 80 spectral points from 760 to 860 nm. The device is composed of three reflective dielectric metasurfaces, all fabricated in a single lithographic step on one side of a substrate, which simultaneously acts as the propagation space for light. The folded metasystem design can be applied to many optical systems, such as optical signal processors, interferometers, hyperspectral imagers, and computational optical systems, significantly reducing their sizes and increasing their mechanical robustness and potential for integration.

Here, the authors introduce the folded metasurface optics architecture by demonstrating a compact high-resolution optical spectrometer made from a 1-mm-thick glass slab. The spectrometer has a resolution of 1.2 nm, resolving more than 80 spectral points in a 100-nm bandwidth centered at 810 nm.

Hyperuniformity in amorphous speckle patterns

Hyperuniform structures possess the ability to confine and drive light, although their fabrication is extremely challenging. Here we demonstrate that speckle patterns obtained by a superposition of randomly arranged sources of Bessel beams can be used to generate hyperunifrom scalar fields. By exploiting laser light tailored with a spatial filter, we experimentally produce (without requiring any computational power) a speckle pattern possessing maxima at locations corresponding to a hyperuniform distribution. By properly filtering out intensity fluctuation from the same speckle pattern, it is possible to retrieve an intensity profile satisfying the hyperuniformity requirements. Our findings are supported by extensive numerical simulations.

Metasurface-Based Polarimeters

The state of polarization (SOP) is an inherent property of light that can be used to gain crucial information about the composition and structure of materials interrogated with light. However, the SOP is difficult to experimentally determine since it involves phase information between orthogonal polarization states, and is uncorrelated with the light intensity and frequency, which can be easily determined with photodetectors and spectrometers. Rapid progress on optical gradient metasurfaces has resulted in the development of conceptually new approaches to the SOP characterization. In this paper, we review the fundamentals of and recent developments within metasurface-based polarimeters. Starting by introducing the concepts of generalized Snell’s law and Stokes parameters, we explain the Pancharatnam–Berry phase (PB-phase) which is instrumental for differentiating between orthogonal circular polarizations. Then we review the recent progress in metasurface-based polarimeters, including polarimeters, spectropolarimeters, orbital angular momentum (OAM) spectropolarimeters, and photodetector integrated polarimeters. The review is ended with a short conclusion and perspective for future developments.

MEMS-tunable dielectric metasurface lens

Varifocal lenses, conventionally implemented by changing the axial distance between multiple optical elements, have a wide range of applications in imaging and optical beam scanning. The use of conventional bulky refractive elements makes these varifocal lenses large, slow, and limits their tunability. Metasurfaces, a new category of lithographically defined diffractive devices, enable thin and lightweight optical elements with precisely engineered phase profiles. Here we demonstrate tunable metasurface doublets, based on microelectromechanical systems (MEMS), with more than 60 diopters (about 4%) change in the optical power upon a 1-μm movement of one metasurface, and a scanning frequency that can potentially reach a few kHz. They can also be integrated with a third metasurface to make compact microscopes (~1 mm thick) with a large corrected field of view (~500 μm or 40 degrees) and fast axial scanning for 3D imaging. This paves the way towards MEMS-integrated metasurfaces as a platform for tunable and reconfigurable optics.