Application of PT-symmetry in metasurfaces for measuring the inclination angle

The purpose of this study is to develop an optical inclination angle sensor using a metasurface as a scale. We propose to use the dependence of the reflection or transmission spectrum of the metasurface on the direction of light incident on it to measure the inclination angle. The disadvantages of this approach when using the simplest completely passive metasurfaces are considered. In particular, the use of bulky devices to scan the spectrum of the structure. As an alternative, the possibility of using metasurfaces with parity-time-symmetry properties to measure the inclination angle is proposed and investigated. Then no spectrum scanning of the metasurface is required to perform inclination angle measurements. As an example, a metastructure formed by two optically coupled subwavelength diffraction gratings (one of which is characterized by losses, and the other by gain) with a rectangular stroke profile is considered. The study is based on computer modeling by the finite element method.