As the two most representative operation
modes in an optical imaging
system, bright-field imaging and phase contrast imaging can extract
different morphological information on an object. Developing a miniature
and low-cost system capable of switching between these two imaging
modes is thus very attractive for a number of applications, such as
biomedical imaging. Here, we propose and demonstrate that a Fourier
transform setup incorporating an all-dielectric metasurface can perform
a two-dimensional spatial differentiation operation and thus achieve
isotropic edge detection. In addition, the metasurface can provide
two spin-dependent, uncorrelated phase profiles across the entire
visible spectrum. Therefore, based on the spin-state of incident light,
the system can be used for either diffraction-limited bright-field
imaging or isotropic edge-enhanced phase contrast imaging. Combined
with the advantages of planar architecture and ultrathin thickness
of the metasurface, we envision this approach may open new vistas
in the very interdisciplinary field of imaging and microscopy.
Monochromatic light can be characterized by its three fundamental properties: amplitude, phase, and polarization. In this work, we propose a versatile, transmission-mode all-dielectric metasurface platform that can independently manipulate the phase and amplitude for two orthogonal states of polarization in the visible frequency range. For proof-of-concept experimental demonstration, various single-layer metasurfaces composed of subwavelength-spaced titanium-dioxide nanopillars are designed, fabricated, and characterized to exhibit the ability of polarization-switchable multidimensional light-field manipulation, including polarization-switchable grayscale nanoprinting, nonuniform cylindrical lensing, and complex-amplitude holography. We envision the metasurface platform demonstrated here to open new possibilities toward creating compact multifunctional optical devices for applications in polarization optics, information encoding, optical data storage, and security.
The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications. Since the radius of a Poincaré beam conventionally depends on the topological charge number, it is difficult to generate a stable and high-quality Poincaré beam by two optical vortices with different topological charge numbers, as the Poincaré beam formed in this way collapses upon propagation. Here, based on an all-dielectric metasurface platform, we experimentally demonstrate broadband generation of a generalized perfect Poincaré beam (PPB), whose radius is independent of the topological charge number. By utilizing a phase-only modulation approach, a single-layer spin-multiplexed metasurface is shown to achieve all the states of PPBs on the hybrid-order Poincaré Sphere for visible light. Furthermore, as a proof-of-concept demonstration, a metasurface encoding multidimensional SAM and OAM states in the parallel channels of elliptical and circular PPBs is implemented for optical information encryption. We envision that this work will provide a compact and efficient platform for generation of PPBs for visible light, and may promote their applications in optical communications, information encryption, optical data storage and quantum information sciences.
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