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.