Metasurfaces composed of planar arrays of subwavelength artificial structures show promise for extraordinary light manipulation. They have yielded novel ultrathin optical components such as flat lenses, wave plates, holographic surfaces, and orbital angular momentum manipulation and detection over a broad range of the electromagnetic spectrum. However, the optical properties of metasurfaces developed to date do not allow for versatile tunability of reflected or transmitted wave amplitude and phase after their fabrication, thus limiting their use in a wide range of applications. Here, we experimentally demonstrate a gate-tunable metasurface that enables dynamic electrical control of the phase and amplitude of the plane wave reflected from the metasurface. Tunability arises from field-effect modulation of the complex refractive index of conducting oxide layers incorporated into metasurface antenna elements which are configured in reflectarray geometry. We measure a phase shift of 180° and ∼30% change in the reflectance by applying 2.5 V gate bias. Additionally, we demonstrate modulation at frequencies exceeding 10 MHz and electrical switching of ±1 order diffracted beams by electrical control over subgroups of metasurface elements, a basic requirement for electrically tunable beam-steering phased array metasurfaces. In principle, electrically gated phase and amplitude control allows for electrical addressability of individual metasurface elements and opens the path to applications in ultrathin optical components for imaging and sensing technologies, such as reconfigurable beam steering devices, dynamic holograms, tunable ultrathin lenses, nanoprojectors, and nanoscale spatial light modulators.

Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They are poised to revolutionize optics by enabling complex low-cost systems where multiple metasurfaces are lithographically stacked and integrated with electronics. For imaging applications, metasurface stacks can perform sophisticated image corrections and can be directly integrated with image sensors. Here we demonstrate this concept with a miniature flat camera integrating a monolithic metasurface lens doublet corrected for monochromatic aberrations, and an image sensor. The doublet lens, which acts as a fisheye photographic objective, has a small f-number of 0.9, an angle-of-view larger than 60° × 60°, and operates at 850 nm wavelength with 70% focusing efficiency. The camera exhibits nearly diffraction-limited image quality, which indicates the potential of this technology in the development of optical systems for microscopy, photography, and computer vision.

In this paper, we propose a unified end-to-end trainable multi-task network that jointly handles lane and road marking detection and recognition that is guided by a vanishing point under adverse weather conditions. We tackle rainy and low illumination conditions, which have not been extensively studied until now due to clear challenges. For example, images taken under rainy days are subject to low illumination, while wet roads cause light reflection and distort the appearance of lane and road markings. At night, color distortion occurs under limited illumination. As a result, no benchmark dataset exists and only a few developed algorithms work under poor weather conditions. To address this shortcoming, we build up a lane and road marking benchmark which consists of about 20,000 images with 17 lane and road marking classes under four different scenarios: no rain, rain, heavy rain, and night. We train and evaluate several versions of the proposed multi-task network and validate the importance of each task. The resulting approach, VPGNet, can detect and classify lanes and road markings, and predict a vanishing point with a single forward pass. Experimental results show that our approach achieves high accuracy and robustness under various conditions in realtime (20 fps). The benchmark and the VPGNet model will be publicly available 1 .

Metamaterials are effectively homogeneous materials that display extraordinary dispersion. Negative index metamaterials, zero index metamaterials and extremely anisotropic metamaterials are just a few examples. Instead of using locally resonating elements that may cause undesirable absorption, there are huge efforts to seek alternative routes to obtain these unusual properties. Here, we demonstrate an alternative approach for constructing metamaterials with extreme dispersion by simply coiling up space with curled channels. Such a geometric approach also has an advantage that the ratio between the wavelength and the lattice constant in achieving a negative or zero index can be changed in principle. It allows us to construct for the first time an acoustic metamaterial with conical dispersion, leading to a clear demonstration of negative refraction from an acoustic metamaterial with airborne sound. We also design and realize a double-negative metamaterial for microwaves under the same principle.

We have studied the dispersion relations of multilayers of silver and a dye-doped dielectric using four methods: standard effective-medium theory (EMT), nonlocal-effect-corrected EMT, nonlinear equations based on the eigenmode method, and a spatial harmonic analysis method. We compare the validity of these methods and show that metallic losses can be greatly compensated by saturated gain. Two realizable applications are also proposed. Loss-compensated metal-dielectric multilayers that have hyperbolic dispersion relationships are beneficial for numerous applications such as subwavelength imaging and quantum optics.

Printable metalenses composed of a silicon nanocomposite are developed to overcome the manufacturing limitations of conventional metalenses. The nanocomposite is synthesized by dispersing silicon nanoparticles in a thermally printable resin, which not only achieves a high refractive index for high-efficiency metalenses but also printing compatibility for inexpensive manufacturing of metalenses. The synthesized nanocomposite exhibits high refractive index >2.2 in the nearinfrared regime, and only 10% uniform volume shrinkage after thermal annealing, so the nanocomposite is appropriate for elaborate nanofabrication compared to commercial high-index printable materials. A 4 mm-diameter metalens operating at the wavelength of 940 nm is fabricated using the nanocomposite and one-step printing without any secondary operations. The fabricated metalens verifies a high focusing efficiency of 47%, which can be further increased by optimizing the composition of the nanocomposite. The printing mold is reusable, so the large-scale metalenses can be printed rapidly and repeatedly. A compact near-infrared camera combined with the nanocomposite metalens is also demonstrated, and an image of the veins underneath human skin is captured to confirm the applicability of the nanocomposite metalens for biomedical imaging.

We report transmissive color filters based on subwavelength dielectric gratings that can replace conventional dye-based color filters used in backside-illuminated CMOS image sensor (BSI CIS) technologies. The filters are patterned in an 80-nm-thick poly-silicon film on a 115-nm-thick SiO 2 spacer layer. They are optimized for operating at the primary RGB colors, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 exhibit peak transmittance of 60-80%, and an almost insensitive response over a ±20 • angular range. This technology enables shrinking of the pixel sizes down to near a micrometer. KeywordsSubwavelength grating, high-index contrast, color filters, CMOS image sensor Scalability of complementary metal oxide transistor (CMOS) technology has improved the performance of CMOS image sensors (CIS) in the past decade. One of the trends in the CIS technology, driven mainly by portable devices with small form-factors, is to decrease the pixel size, which will lead to improved spatial resolution for digital imaging. 1 The scalability of CIS technology has enabled lateral pixel size to be reduced from more than 10 µm to less than 2 µm in the last decade. 2,3 Along with scaling of the pixel size, there have been considerable efforts to redesign color filters, 4-6 microlenses, 7 and infrared filters 8 to prevent the degradation of the optical performance. Dye-doped polymers have been conventionally used for RGB color filters in digital color imaging. However, when the pixel size gets smaller, the optical crosstalk among pixels becomes significant because of the small absorption coefficient of the organic dyes. Besides, the dye-doped polymers are essentially photoresists that degrade under ultraviolet illumination or high temperature environments. To address these issues, plasmonic color filters made of metallic thin films with subwavelength patterning have been studied for CIS technology. 5,9,10 The plasmonic color filters have several advantages such as flexible color tunability across visible spectrum and compatibility with CMOS processes. However, the absolute efficiency of the plasmonic color filters is relatively low (40-50% range) compared to conventional organic dye-doped filters. Here, we show that dielectric subwavelength gratings can be used to achieve highly efficient transmission color filters with close to angular insensitive properties. Furthermore, compared to dye-based filters, our dielectric-based filters possess better reliability under ultraviolet illumination and at high temperature. For the optimized filter designs, we take the advantage of the backside-illumination (BSI) CIS technologies, where the color filter layer can be placed in close proximity to the photodiodes 2 16 anti-reflection coating, 17,18 and reflective-transmission filters for displays. 19 In this letter, we demonstrate designs for polarizatio...

While there has been enormous progress in meta-surface designs, most meta-surfaces are constrained by Lorentz reciprocity. Breaking reciprocity, however, enables additional functionalities and greatly expands the applications of meta-surfaces. Here, we introduce a realistic nonreciprocal meta-surface that can achieve optical circulation and isolation. This device consists of a photonic crystal slab that supports two bands of guided resonances, and upon a temporal modulation in each unit cell with a spatially varying phase, an indirect photonic transition can be induced between the guided resonances, which breaks Lorentz reciprocity without the use of magneto-optic materials. We provide direct first-principle numerical simulations, using the multifrequency finite-difference frequency-domain method, to demonstrate that this device can achieve optical circulation and isolation with no back reflection under realistic modulation frequency and modulation strength.