Akonia Holographics, an AR optical component manufacturer under Apple, has been exploring the use of skew mirrors to reflect light without the limitations of the surface normal. The reflection angle of the skew mirrors remains constant for multiple wavelengths at a given angle of incidence, allowing for reflection outside of the surface normal. This overcomes the constraints of traditional media mirrors.
The patent application describes a reflective device that includes a grating medium with holographic or other grating structures. The physical properties of the grating structures allow the medium to diffract light around the reflective axis. The reflective device maintains a constant diffraction angle/reflection angle for multiband light at various angles of incidence. The grating structures can be designed to reflect light with specific wavelengths within a certain range of incident angles.
The application provides examples of the reflective device's configuration, materials, and performance. The described skew mirrors can reflect light with different wavelengths and angles of incidence, making them suitable for various applications such as headsets and devices utilizing total internal reflection.
The patent application, titled "Skew mirrors, methods of use, and methods of manufacture," was initially submitted by Akonia Holographics in June 2021 and recently published by the US Patent and Trademark Office.