Search for: All records

We demonstrate the use of plasmonic gradient metasurfaces to tailor the angular response of generic planar photodetectors. The resulting devices are promising for a wide range of computational imaging applications with enhanced miniaturization and functionality. 

We use a generative deep learning method based on denoising diffusion probabilistic model to design plasmonic phase-imaging sensors for broadband operation. This flexible method enables optimized inverse design for a wide range of nanophotonic devices. 

Angle-sensitive photodetectors are a promising device technology for many advanced imaging functionalities, including lensless compound-eye vision, lightfield sensing, optical spatial filtering, and phase imaging. Here we demonstrate the use of plasmonic gradient metasurfaces to tailor the angular response of generic planar photodetectors. The resulting devices rely on the phase-matched coupling of light incident at select geometrically tunable angles into guided plasmonic modes, which are then scattered and absorbed in the underlying photodetector active layer. This approach naturally introduces sharp peaks in the angular response, with smaller footprint and reduced guided-mode radiative losses (and therefore improved spatial resolution and sensitivity) compared to analogous devices based on diffractive coupling. More broadly, these results highlight a promising new application space of flat optics, where gradient metasurfaces are integrated within image sensors to enable unconventional capabilities with enhanced system miniaturization and design flexibility. 

We report a new technique for single-shot quantitative phase retrieval from transparent objects, based on plasmonic metasurface photodetectors featuring an asymmetric angular response around normal incidence combined with a particularly simple optical setup. 

Abstract The visualization of pure phase objects by wavefront sensing has important applications ranging from surface profiling to biomedical microscopy, and generally requires bulky and complicated setups involving optical spatial filtering, interferometry, or structured illumination. Here we introduce a new type of image sensors that are uniquely sensitive to the local direction of light propagation, based on standard photodetectors coated with a specially designed plasmonic metasurface that creates an asymmetric dependence of responsivity on angle of incidence around the surface normal. The metasurface design, fabrication, and angle-sensitive operation are demonstrated using a simple photoconductive detector platform. The measurement results, combined with computational imaging calculations, are then used to show that a standard camera or microscope based on these metasurface pixels can directly visualize phase objects without any additional optical elements, with state-of-the-art minimum detectable phase contrasts below 10 mrad. Furthermore, the combination of sensors with equal and opposite angular response on the same pixel array can be used to perform quantitative phase imaging in a single shot, with a customized reconstruction algorithm which is also developed in this work. By virtue of its system miniaturization and measurement simplicity, the phase imaging approach enabled by these devices is particularly significant for applications involving space-constrained and portable setups (such as point-of-care imaging and endoscopy) and measurements involving freely moving objects. 

We report the development of angle-sensitive photodetectors based on specially designed metasurfaces that can map the phase distribution of the incident light and visualize transparent phase objects without any external spatial-filtering elements. Pixel arrays of these devices can provide quantitative phase reconstruction in a single shot with state-of-the-art sensitivity. 

We report plasmonic metasurface photodetectors featuring a strong asymmetric angular response around normal incidence that can visualize transparent phase objects with high sensitivity in a simple and compact imaging setup. 

Graphene is a promising materials platform for metasurface flat optics at terahertz wavelengths, with the important advantage of active tunability. Here we review recent work aimed at the development of tunable graphene metasurfaces for THz wavefront shaping (including beam-steering metamirrors and metalenses) and light emission. Various design strategies for the constituent meta-units are presented, ranging from metallic phase-shifting elements combined with a nearby graphene sheet for active tuning to graphene plasmonic resonators providing the required phase control or radiation mechanism. The key challenge in the development of these devices, related to the limited radiative coupling of graphene plasmonic excitations, is discussed in detail together with recently proposed solutions. The resulting metasurface technology can be expected to have a far-reaching impact on a wide range of device applications for THz imaging, sensing, and future wireless communications. 

Graphene plasmonics provides a powerful means to extend the reach of metasurface technology to the terahertz spectral region, with the distinct advantage of active tunability. Here we introduce a comprehensive design platform for the development of THz metasurfaces capable of complex wavefront manipulation functionalities, based on ribbon-shaped graphene plasmonic resonators combined with metallic antennas on a vertical cavity. Importantly, this approach is compatible with the electrical characteristics of graphene grown by chemical vapor deposition (CVD), which can provide the required mm-scale dimensions unlike higher-mobility exfoliated samples. We present a single device structure that can be electrically reconfigured to enable multiple functionalities with practical performance metrics, including tunable beam steering and focusing with variable numerical aperture. These capabilities are promising for a significant impact in a wide range of THz technologies for sensing, imaging, and future wireless communications. 

We use specially designed plasmonic photodetectors to develop a new method for image differentiation that can produce edge-enhanced images without external optical elements and under incoherent illumination, unlike traditional optical spatial filters.