OPTICAL WAVEGUIDE TESTING SYSTEM WITH STANDOFF

A waveguide display test system. The system includes a plurality of projectors, a mounting assembly, and a camera. The mounting assembly is covered to hold a waveguide under test. In an image quality configuration a single projector is used with an optical relay that provides a standoff distanced between a virtual pupil and the single projector, and the virtual pupil is located at a walk off distance from the waveguide. In an modulation transfer function (MTF) tester configuration, the single projector is replaced with a plurality of projectors. And each of the plurality of projectors includes a respective relay system that is configured to place a virtual pupil of the projector at an input to the waveguide while having at least a threshold standoff distance between the plurality of projectors and the waveguide. Regardless of configuration, light (e.g., test pattern) from one or more projectors are incoupled to the waveguide, light propagates through the waveguide and is outcoupled to the camera. Images captured by the camera are analyzed to characterize optical properties of the waveguide

Higher-order Topology of Axion Insulator EuIn2_2As2_2

Based on first-principles calculations and symmetry analysis, we propose that EuIn$_2$As$_2$ is a long awaited axion insulator with antiferromagnetic (AFM) long range order. Characterized by the parity-based invariant $\mathbb Z_4=2$, the topological magneto-electric effect is quantized with $\theta=\pi$ in the bulk, with a band gap as large as 0.1 eV. When the staggered magnetic moment of the AFM phase is along $a/b$ axis, it's also a TCI phase. Gapless surface states emerge on (100), (010) and (001) surfaces, protected by mirror symmetries (nonzero mirror Chern numbers). When the magnetic moment is along $c$ axis, the (100) and (001) surfaces are gapped. As a consequence of a high-order topological insulator with $\mathbb Z_4=2$, the one-dimensional (1D) chiral state can exist on the hinge between those gapped surfaces. We have calculated both the topological surface states and hinge state in different phases of the system, respectively, which can be detected by ARPES or STM experiments