Apple has filed for a patent (number 20200117003) for an “optical system with dispersion compensation” that shows work continues on the rumored“Apple Glasses,” a head-mounted augmented reality/virtual reality (AR/VR) head-mounted display (HMD).
Such a device will arrive this year, next year, 2021, or 2022, depending on which rumor you believe. It may or may not have to be tethered to an iPhone to work. Other rumors say that Apple Glasses could have a custom-build Apple chip and a dedicated operating system dubbed “rOS” for “reality operating system.”
The goal of the newly filed patent is to improve image quality while Apple notes that dispersion may cause chromatic aberrations in optical devices such as an HMD. These chromatic aberrations can have a degrading effect on an image of an optical reflective device. Apple says that “improved methods for correcting the effects of dispersion and optical reflective devices that mitigate the degrading effects of dispersion on reflected images are desired.”
Here’s Apple’s summary of the invention: “Systems and methods of dispersion compensation in an optical device are disclosed. A holographic optical element may include a set of different holograms in a grating medium. Each hologram in the set may have a corresponding grating vector with a grating frequency and direction. The directions of the grating vectors may vary as a function of the grating frequency.
“Different holograms in the set may diffract light in a particular direction so that the light emerges from a boundary of the grating medium in a single given direction regardless of wavelength. A prism may be used to couple light into the grating medium. The prism may be formed using materials having dispersion properties that are similar to the dispersion properties of the grating material. The prism may have an input face that receives perpendicular input light. The prism may include multiple portions having different refractive indices.”