In the realm of intensive research on metamaterials, particularly, the two-dimensional analogue, known as metasurfaces have attracted researchers due to their lower losses, high efficiencies and low cost as compared to plasmonic metasurfaces. Dielectric metasurfaces (DMs) have been widely reported to experience magnetic and electric dipole Mie type resonances, in which, upon tuning these two resonances, dielectric metasurfaces can exhibit spatially varying optical responses, phases and polarizations of scattered fields. Recently, dielectric metasurfaces have been used for color printing application with very high color vibrancy. However, the fundamental building blocks essential for the realization of optical metasurfaces are designed with uniform dimension nano structures, resonating at particular wave length, thus printing image only with particular color. In order to be able to cover the whole optical regime, the metasurface needs to be designed with tunable optical response to be able to print images with multiple colors. In this work, we report a cubic TiO<sub>2</sub> metasurface which experience magnetic and electric dipole resonances in the optical regime. We are able to tune the reflection peak of both resonances using Nematic liquid crystal (LCs). LCs are anisotropic materials with controlled orientation based upon different applied voltages. Changing the orientation of the LC allows for tuning the resultant of the electric field component of the LC and thus the reflection peak of the metasurface can be tuned across the optical regime. We report a tunable DM for optical filters application using single dimension designed metausrfcae with efficiency close to 99 % covering three colors in the visible range: red, orange and green.
Using all-dielectric metasurfaces has be the interest of the scientific community recently. This is because the conventionally used plasmonic resonator-based metasurfaces have high ohmic losses in the optical domain. On the other hand, dielectric materials have minimal losses in the optical regime. Dielectric metasurfaces are based on dielectric resonators, periodic sub-wavelength structures that exhibit electric and magnetic resonance near the operation wavelength. In this work a novel all-dielectric metasurface design is studied using Electro-optic polymers. Applying an electric potential over the electro-optic polymer can change the steering angle of the metasurface. This study is done using finite difference time domain simulation for the optical behavior of this structure. This structure is CMOS compatible contrary to plasmonic metasurfaces.
Metamaterials (MMs) are composite structures that exhibit non-conventional optical properties. Conventional threedimensional MMs are rather bulky, usually require complicated fabrication techniques and are not CMOS technology compatible. On the other hand, there has been a great ongoing interest in two-dimensional Metamaterials (Metasurfaces). Metasurfaces are two dimensional periodic structures that allow controllable change in the amplitude and phase of the incoming wave upon interaction that allows for designing ultrathin optical components with various functionalities. This can be achieved through optical resonances through the metasurface. These resonances can be achieved either through plasmonic antennae or dielectric resonators. Due to their lossy nature in the optical domain, plasmonic and metallic based metasurfaces can lead to inefficient operation and limit the applicability of such structures. In this work we discuss an all silicon metasurface design using cross-shaped unit cells. This cross design in addition to being polarization insensitive is capable of achieving phase difference from 0 to 2π by optimizing two degrees of freedom and thus offers a promising platform for various metasurface applications. We show through numerical simulations the properties of this polarization independent design and how it can be used for mid-infrared beam steering and lensing applications.
In this work, we present a novel and simple optical solution for MEMS LiDARs. The idea is based on increasing the collection optics throughput by removing the MEMS mirror from the path of the collected light, while inserting a multi-segment tapered structure to collect the light from a wide angle. The tapered also converts the large size optical spot captured to a small area compatible with the requirement of low detector noise dimensions. The expected improvement in the collected power is analyzed versus the tapering angle of a single tapered structure. A multi-segment optical system, or multiple tapered structure arranged in parallel, is also introduced allowing for the optimization of the acceptance angle and the power improvement ratio. Using a 3-segment mirror, the expected improvement is about 15x with an acceptance angle of ±30 degrees. The design of a single element taper section is fabricated using aluminum-coated acrylic and tested experimentally showing an improvement of about 7x in the coupled power through an angle of ±10 degrees in good agreement with the theoretical expectations.