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Register a new userOne-shot ultraspectral imaging with reconfigurable metasurfaces
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One-shot spectral imaging that can obtain spectral information from different points in space at one time has always been difficult to achieve, and is extremely important for both fundamental scientific research and various practical applications. In this study, one-shot ultraspectral imaging by fitting thousands of micro-spectrometers on a chip, is proposed and demonstrated. Exotic light modulation is achieved by using a reconfigurable metasurface supercell, which enables 155,216 image-adaptive micro-spectrometers, simultaneously guaranteeing the spectral-pixel density and reconstructed spectral quality. By constructing a compressive-sensing algorithm, the device can reconstruct ultraspectral imaging ($Deltalambda$/$lambda$~0.001) covering a 300-nm-wide visible spectrum with an ultra-high center-wavelength accuracy of 0.04-nm standard deviation and spectral resolution of 0.8 nm. This scheme can be extended to almost any commercial camera with different spectral bands to seamlessly switch between image and spectral image, and opens up a new space for the application of spectral analysis combining with image recognition and intellisense.
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Multispectral imaging plays an important role in many applications from astronomical imaging, earth observation to biomedical imaging. However, the current technologies are complex with multiple alignment-sensitive components, predetermined spatial and spectral parameters by manufactures. Here, we demonstrate a single-shot multispectral imaging technique that gives flexibility to end-users with a very simple optical setup, thank to spatial correlation and spectral decorrelation of speckle patterns. These seemingly random speckle patterns are point spreading functions (PSFs) generated by light from point sources propagating through a strongly scattering medium. The spatial correlation of PSFs allows image recovery with deconvolution techniques, while the spectral decorrelation allows them to play the role of tune-able spectral filters in the deconvolution process. Our demonstrations utilizing optical physics of strongly scattering media and computational imaging present the most cost-effective approach for multispectral imaging with great advantages.
Fluorescence imaging is indispensable to biology and neuroscience. The need for large-scale imaging in freely behaving animals has further driven the development in miniaturized microscopes (miniscopes). However, conventional microscopes / miniscopes are inherently constrained by their limited space-bandwidth-product, shallow depth-of-field, and the inability to resolve 3D distributed emitters. Here, we present a Computational Miniature Mesoscope (CM$^2$) that overcomes these bottlenecks and enables single-shot 3D imaging across an 8 $times$ 7-mm$^2$ field-of-view and 2.5-mm depth-of-field, achieving 7-$mu$m lateral resolution and better than 200-$mu$m axial resolution. Notably, the CM$^2$ has a compact lightweight design that integrates a microlens array for imaging and an LED array for excitation in a single platform. Its expanded imaging capability is enabled by computational imaging that augments the optics by algorithms. We experimentally validate the mesoscopic 3D imaging capability on volumetrically distributed fluorescent beads and fibers. We further quantify the effects of bulk scattering and background fluorescence on phantom experiments.
Based on point spread function (PSF) engineering and astigmatism due to a pair of cylindrical lenses, a novel compressed imaging mechanism is proposed to achieve single-shot incoherent 3D imaging. The speckle-like PSF of the imaging system is sensitive to axial shift, which makes it feasible to reconstruct a 3D image by solving an optimization problem with sparsity constraint. With the experimentally calibrated PSFs, the proposed method is demonstrated by a synthetic 3D point object and real 3D object, and the images in different axial slices can be reconstructed faithfully. Moreover, 3D multispectral compressed imaging is explored with the same system, and the result is rather satisfactory with a synthetic point object. Because of the inherent compatibility between the compression in spectral and axial dimensions, the proposed mechanism has the potential to be a unified framework for multi-dimensional compressed imaging.
Metasurfaces offer the potential to control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. Existing metasurfaces frequently utilize metallic polaritonic elements with high absorption losses, and/or fixed geometrical designs that serve a single function. Here we overcome these limitations by demonstrating a reconfigurable hyperbolic metasurface comprising of a heterostructure of isotopically enriched hexagonal boron nitride (hBN) in direct contact with the phase-change material (PCM) vanadium dioxide (VO2). Spatially localized metallic and dielectric domains in VO2 change the wavelength of the hyperbolic phonon polaritons (HPhPs) supported in hBN by a factor 1.6 at 1450cm-1. This induces in-plane launching, refraction and reflection of HPhPs in the hBN, proving reconfigurable control of in-plane HPhP propagation at the nanoscale15. These results exemplify a generalizable framework based on combining hyperbolic media and PCMs in order to design optical functionalities such as resonant cavities, beam steering, waveguiding and focusing with nanometric control.
Motivated by the recent growing demand in dynamically-controlled flat optics, we take advantage of a hybrid phase-change plasmonic metasurface (MS) to effectively tailor the amplitude, phase, and polarization responses of the incident beam within a unique structure. Such a periodic architecture exhibits two fundamental modes; pronounced counter-propagating short-range surface plasmon polariton (SR-SPP) coupled to the Ge2Sb2Te5 (GST) alloy as the feed gap, and the propagative surface plasmon polariton (PR-SPP) resonant modes tunneling to the GST nanostripes. By leveraging the multistate phase transition of alloy from amorphous to the crystalline, which induces significant complex permittivity change, the interplay between such enhanced modes can be drastically modified. Accordingly, in the intermediate phases, the proposed system experiences a coupled condition of operational over-coupling and under-coupling regimes leading to an inherently broadband response. We wisely addressing each gate-tunable meta-atom to achieve robust control over the reflection characteristics, wide phase agility up to 315? or considerable reflectance modulation up to 60%, which facilitate a myriad of on-demand optical functionalities in the telecommunication band. Based on the revealed underlying physics and electro-thermal effects in the GST alloy, a simple systematic approach for realization of an electro-optically tunable multifunctional metadevice governing anomalous reflection angle control (e.g., phased array antenna), near-perfect absorption (e.g., modulator), and polarization conversion (e.g., wave plate) is presented. As a promising alternative to their passive counterparts, such high-speed, non-volatile MSs offer an smart paradigm for reversible, energy-efficient, and programmable optoelectronic devices such as holograms, switches, and polarimeters.
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