Optical system and mixed reality device

A mixed reality device, comprising:

• a data processing module and an optical system;
• wherein the optical system comprises:
• a projection apparatus, which is configured to project two beams of image light;
• a substrate layer, which has two side surfaces and two planes, wherein each of the two side surfaces is configured to receive a respective one of the two beams of the image light from the projection apparatus, and the two planes are configured to totally reflect each of the two beams of the image light entering the substrate layer;
• and a diffraction grating layer, which is disposed on at least one plane of the substrate layer and configured to diffract, in a reflective manner or a transmissive manner, the two beams of the image light propagating in the substrate layer, wherein energy of target image light diffracted out of the diffraction grating layer is uniformly distributed;
• and wherein the data processing module is configured to transmit image information to be displayed to the projection apparatus of the optical system to display an image,
• wherein in a case where the diffraction grating layer is disposed on one plane of the substrate layer, grating fringes of the diffraction grating layer are distributed axisymmetrically with respect to a direction perpendicular to the diffraction grating layer and passing through a preset position point, wherein the preset position point is located on the diffraction grating layer,
• wherein in a case where the two beams of the image light are diffracted by the diffraction grating layer in the transmissive manner, in a direction from one edge of the diffraction grating layer to the preset position point, transmissive diffraction efficiency of the image light passing through the substrate layer gradually increases;
• and
• in a direction from the preset position point to the other edge of the diffraction grating layer, reflective diffraction efficiency of the image light passing through the substrate layer gradually decreases.