Design of a 65-degree collimating lens for lightguide-based AR glasses

The collimating lens has a diagonal full field angle of 65°. The aperture stop is positioned on the first surface of the lens, with an aperture stop size of 10 mm and F-number of 2.046. The angular resolution is 45 PPD, and the spatial frequency is 60 cycles/mm. This design uses a 1.03-inch microdisplay with an equal aspect ratio. The active area of the microdisplay is 18.432 mm ´ 18.432 mm. The Seidel aberrations are zero for the lightguide, independent of the material index and thickness of the lightguide. The light-emitting surface of the microdisplay is located at the object focal plane of the collimating lens. The function of the collimating lens is to collimate and project the microdisplay image into the lightguide, eventually reaching the eye for viewing. The collimating lens in the AR system can be regarded as a magnifier, with an angular magnification of 12.22. The virtual image size is 225 mm ´ 225 mm at the distance of 250 mm ahead of the viewing eye. Two metrics are developed, the line resolution and the lateral color resolution, to evaluate the amount of line warping and lateral color. The line resolution and the lateral color resolution of the collimating lens design described in this paper are 0.407 arcmin and 0.675 arcmin, respectively, both of which are less than the human eye's angular resolution of 1 arcmin.