Optical device and display apparatus with same images for left and right eyes

An optical device comprising a waveguide plate, wherein the waveguide plate comprises:

• an entrance pupil grating unit, wherein an input light is diffracted by the entrance pupil grating unit to form a first left guided light and a first right guided light;
• a left pupil-expanding grating unit, located on a left side in a horizontal direction of the entrance pupil grating unit, wherein the first left guided light is diffracted by the left pupil-expanding grating unit to form a second left guided light;
• a right pupil-expanding grating unit, located on a right side in the horizontal direction of the entrance pupil grating unit, wherein the first right guided light is diffracted by the right pupil-expanding grating unit to form a second right guided light;
• a left exit pupil grating unit, located below in a vertical direction of the left pupil-expanding grating unit, wherein the second left guided light is diffracted by the left exit pupil grating unit to form a left output light;
• a right exit pupil grating unit, located below in a vertical direction of the right pupil-expanding grating unit, wherein the second right guided light is diffracted by the right exit pupil grating unit to form a right output light,
• wherein the left pupil-expanding grating unit and right pupil-expanding grating unit are bilaterally symmetric about the entrance pupil grating unit, the left exit pupil grating unit and the right exit pupil grating unit are bilaterally symmetric about the entrance pupil grating unit, and the input light, the left output light, and the right output light are in a same direction, a virtual image received by a left eye and a virtual image received by a right eye are exactly same.