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Register a new userTransmissive Metagrating for Arbitrary Wavefront Shaping Over the Full Visible Spectrum
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Metagratings have been shown to form an agile and efficient platform for extreme wavefront manipulation, going beyond the limitations of gradient metasurfaces. Previous approaches for transmissive metagratings have resorted on compound asymmetric inclusions to achieve single-channel near-perfect diffraction. However, such complex inclusions are sensitive to geometric parameters and lack the flexibility for arbitrary phase modulation, restricting applications to beam deflection. Here, we show perfect unitary diffraction in all-dielectric transmissive metagratings using rectangular inclusions by tailoring their multipole interferences. Using this principle, we experimentally demonstrate analog phase profile encoding of a hologram through displacement modulation of CMOS-compatible silicon nitride nanobars, manifesting broadband and wide-angle high diffraction efficiencies for both polarizations and across the entire visible range. Featured with extreme angle/wavelength/polarization tolerance and alleviated structural complexity for both design and fabrication, our demonstration unlocks the full potential of metagrating-based wavefront manipulation for a variety of practical applications.
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Converting spin angular momentum to orbital angular momentum has been shown to be a practical and efficient method for generating optical beams carrying orbital angular momentum and possessing a space-varying polarized field. Here, we present novel liquid crystal devices for tailoring the wavefront of optical beams through the Pancharatnam-Berry phase concept. We demonstrate the versatility of these devices by generating an extensive range of optical beams such as beams carrying $pm200$ units of orbital angular momentum along with Bessel, Airy and Ince-Gauss beams. We characterize both the phase and the polarization properties of the generated beams, confirming our devices performance.
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We study the three-dimensional (3D) spatially-resolved distribution of the energy density of light in a 3D scattering medium upon the excitation of open transmission channels. The open transmission channels are excited by spatially shaping the incident optical wavefronts. To probe the local energy density, we excite isolated fluorescent nanospheres distributed inside the medium. From the spatial fluorescent intensity pattern we obtain the position of each nanosphere, while the total fluorescent intensity gauges the energy density. Our 3D spatially-resolved measurements reveal that the local energy density versus depth (z) is enhanced up to 26X at the back surface of the medium, while it strongly depends on the transverse (x; y) position. We successfully interpret our results with a newly developed 3D model that considers the time-reversed diffusion starting from a point source at the back surface. Our results are relevant for white LEDs, random lasers, solar cells, and biomedical optics.
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