Pixel size in cameras and other refractive imaging devices is typically limited by the free-space diffraction. However, a vast majority of semiconductor-based detectors are based on materials with substantially high refractive index. We demonstrate that diffractive optics can be used to take advantage of this high refractive index to reduce effective pixel size of the sensors below free-space diffraction limit. At the same time, diffractive systems encode both amplitude and phase information about the incoming beam into multiple pixels, offering the platform for noise-tolerant imaging with dynamical refocusing. We explore the opportunities opened by high index diffractive optics to reduce sensor size and increase signalto- noise ratio of imaging structures.
Optical characterization of subwavelength objects is important for biology, nanotechnology, chemistry, and materials science. Unfortunately, the information about interaction of an isolated subwavelength object with light is contained in evanescent waves that exponentially decay away from the source. Numerous techniques have been proposed to access or restore this information. In interscale mixing microscopy (IMM), a diffraction grating positioned in the near field proximity of the object is used to convert the originally-evanescent waves into propagating modes that can be detected with far-field measurements. However, far-field signal needs to be post-processed to un-couple the diffraction-limited and subwavelength responses. Several techniques, based on multiple measurements, have been previously proposed. Here, we show that with simple Fourier-transform based post processing can be used to characterize position, and optical size of the object based on a single measurement. To verify the proposed formalism, three finite diffraction gratings were fabricated. Two of these gratings contained pre-engineered “defects” that played the role of “unknown objects”, while the remaining grating was used as a reference. We demonstrate that we can identify the position and size of ~wavelength/10 object with far-field characterization. The same measurement provides a platform to analyze optical spectrum of the object. Although demonstrated in this work on example of 1D grating, IMM can be extended to 2D subwavelength imaging
Optical metasurfaces are periodic or graded pattern arrays of ultra-thin plasmonic and/or dielectric nanostructures, which are intended to scatter light in manners that cannot be achieved with conventional stratified media. Recent advancements in the theoretical knowledge and fabrication methods of two-dimensional materials, such as graphene, have provided the opportunity to scale down the principles of metasurfaces to atomic dimensions and to offer graded pattern meta-sheets. We present here engineered nanostructures to tailor the beaming pattern of light scattered through such meta-sheets. We obtain designs to precisely control both the in-plane scattering of surface waves associated with the sheets and also out-of-plane scattered far-field beams into a desired direction. We then determine a set of conductivity-balancing conditions to completely confine the surface waves to the meta-sheets at highly scattering sites and demonstrate that under such criterion the propagation of guided surface waves can be described simply using Fresnel equations of plane waves. Furthermore, we cascade three sinusoidally modulated reactance surfaces to realize a broad-beam leaky-wave antenna to completely scatter the surface waves to far-field and also control the steering direction. In addition, conformal patterned 2D sheets will be explored for the first time and how to successfully design and manipulate the light wavefront. For fast and accurate designs of the flat and conformal meta-sheets, we take advantage of our superior auxiliary differential equation finite-difference time-domain (ADE-FDTD) method. Also, an integral equations (IE) model will be applied for large-area system platforms design investigation.