Apparatus, and system of an optical lens

A Head Mounted Display (HMD) comprising:

• a display;
• a controller to control images to be displayed by the display;
• and,
• a catadioptric lens configured to direct light from the display to an eye of a user, the catadioptric lens comprising:
• a catadioptric folder configured to fold an optical path of the catadioptric lens, the catadioptric folder comprising:
• a first surface comprising a semi-reflective surface;
• a second surface comprising a reflective polarizer surface, the second surface opposite to the first surface;
• and
• a retarder between the first surface and the second surface, the retarder configured to convert a polarization of the light in a path between the first surface and the second surface,
• wherein the first and second surfaces are configured such that, over at least 10% of the catadioptric folder, an inter-surface distance of the catadioptric folder is monotonically decreasing with a distance from a central axis of the catadioptric lens.