We introduce high-resolution speckle-free holograms, created using polarization manipulating metasurfaces. The holograms enable clear projection of 2D and 3D images, in contrast to conventional holograms with significant speckle noise. The approach uses a simple non-iterative algorithm at a low computational cost. As a proof of concept, we demonstrate a reflective hologram composed of silicon nitride nanoposts on an aluminum layer that projects a high-resolution grayscale image. By implementing three holograms for primary colors, full-color far-field and 3D holograms become feasible, with potential applications in anticounterfeiting tags.
We present fully-reconfigurable photonic integrated circuits (PICs) based on liquid-crystal-cladded slab waveguides. Our design utilizes a single-mode slab waveguide with a thin nematic liquid crystal (LC) cladding layer. We achieve local effective index modulation by controlling the LC’s director’s direction through electrodes integrated beneath the slab. As a proof of concept, we demonstrate a straight waveguide at 1550nm with voltage-controlled activation. The reconfiguration time and the excess loss due to LC were measured as 0.1 ms and 7.3 dB/cm, respectively. The low-temperature fabrication process enables cost-effective PICs on CMOS chips for 3D sensing, telecommunications, and data processing applications.
Sophisticated techniques to accurately align patterns have been developed that predominantly address the overlay of proximal layers in layer-by-layer processes that are separated by short, micron-scale distances. However, in some applications such as in flat optics, accurate, 3D alignment of workpieces whose patterns may be separated by large distances is desirable. Here, we describe an alignment scheme based on the far-field of a cascade of metasurface elements suitable for accurately aligning patterns separated by millimeter-scale distances. By using an 850nm laser illumination, we demonstrate registration accuracies of 10nm laterally and 50nm axially for patterns separated by mm-scale distances.
On-chip integration of metasurfaces with optoelectronic components enables the manufacture of reliable and low-cost systems that do not require post-fabrication alignment and assembly. Here we present an on-chip miniature beam scanning metasystem by integrating a large 2D array of VCSELs and a metalens. The beam scanner measures 4 mm*4 mm*3 mm and scans a ~1 mW laser beam at 940 nm with <1 degree divergence angle over a 140 degree*140 degree field of view with <30 mW of power consumption. The scanner switches between two angles in <1 µs, enabling the realization of fully-integrated miniature imaging lidar systems.
We present a technique for designing efficient and robust metasurfaces that optimizes the metasurface design curves instead of individual metasurface elements and thus does not suffer from the size limitations of conventional optimization techniques. Spatially varying design curves are parametrized and optimized using the grating averaging technique. We present simulation and experimental results of highly efficient metasurface beam deflectors and lenses that are robust to fabrication errors. In particular, we present an 80° beam deflector with absolute efficiency of 75% and a metalens with NA of 0.8 and an efficiency of 86% that is robust to fabrication errors.
I will present different techniques developed to design and fabricate visible and near-infrared metasurface with large dimensions. In particular, I will present metasurface design using adjoint optimization and introduce a novel technique for designing arbitrarily large metasurfaces using optimized smaller metasurfaces. I will also discuss metasurface design using grating averaging and nonlinear optimization. Scalable and low-cost fabrication of large diameter visible metasurfaces using different nanoimprint techniques will also be presented.
The recent development of efficient dielectric metasurfaces has enabled practical optical components and systems composed of multiple cascaded metasurfaces. In this talk, I present an overview of our work on modeling, design, and implementation of cascaded metasurface components and systems. In particular, I present accurate system-level models for metasurfaces, techniques for designing efficient metasurfaces, multifunctional cascaded metasurfaces, and bilayer birefringent metasurfaces that provide the ultimate control over the wavefront and polarization of light. Furthermore, I will introduce a novel technique for engineering chromatic dispersion by cascading and briefly discuss a single-snapshot hyperspectral imager enabled by cascading multiple metasurfaces.
We present a new class of grating-integrated microdisk resonators that directly and efficiently couple to free space and can be excited by top illumination. We discuss the theory and design of such devices and present characterization results of 1530-nm-resonators with 0.8 µm to 1.2 µm radii, which are fabricated using amorphous silicon on glass. A 1.2-µm-radius resonator has a measured Q of ~16,000 and is efficiently excited by top illumination as evidenced by an observed thermally-induced bistability threshold of 0.7 mW. The small footprint and ease of coupling enable dense resonator arrays for applications in free space and flat optics.
Metasurfaces are attractive options for the realization of on-chip optical systems because of their flat form factor and their ability to modify the wavefront, amplitude, and polarization of light with high efficiency. Several metasurface platforms have been reported that provide different levels of control over the polarization and phase of light, and it has been shown that a single layer birefringent metasurface can implement symmetric and unitary Jones matrices. Optical components with such Jones matrices can convert any arbitrary input polarization to any desired output polarization or perform independent wavefront transformations for two orthogonal polarizations while changing their handedness. However, the Jones matrices that describe the most general polarization and phase transformations are not symmetric, and this limits the range of possible devices that single layer birefringent metasurfaces can implement. For example, a single layer birefringent metasurface cannot impart two different phase shifts to x- and y-polarized light while simultaneously converting their polarizations to right- and left-handed circularly polarized. Here we show that bi-layer birefringent metasurfaces do not suffer from such limitations and can implement the most general form of Jones matrices that describe loss-less and reciprocal optical components. By using the Poincare sphere representation and closed-form relations, we identify the degrees of freedom in the design and present a procedure that allows for the design of large-scale devices based on bi-layer metasurfaces. As a proof-of-concept, we demonstrate a chiral bi-layer metasurface that focuses left- and right-handed polarized waves to two different points without changing their polarizations.
Characteristic modes (c-modes) are a complete and orthogonal set of modes that can be used as a basis for the expansion of the waves scattered from electromagnetic and optical scatterers. In this talk, we present an introduction to the c-modes and discuss their applications in the analysis and design of 2D and 3D meta-structures. We present an equation for finding the c-modes and demonstrate that the c-modes and the natural (quasi-normal) resonances of meta-structures are related to each other. The relation between the c-modes and the natural mode leads to closed-form solutions for the transmission and reflection spectra of non-diffractive meta-structures that only depend on the complex-valued frequencies of the natural modes. As an example, we show that the wide bandwidth and high reflectivity of 1D high contrast gratings can be attributed to the alignment of two resonances associated with two different c-modes. In addition, using the c-modes concept, we present accurate expressions for the field enhancement and the Purcell factor in the presence of meta-structures and establish an upper bound on the number of degrees of freedom of meta-structures.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.