Diffractive optical elements with optical power

A head-mounted display system comprising:

• an image projector;
• a camera;
• an eyepiece configured, during operation of the system, to receive light from the image projector and direct the light along a first optical path to a user's eye, and to direct light reflected from the user's eye along a second optical path to the camera located on a world side of the eyepiece;
• wherein the eyepiece comprises:
• (i) a waveguide having a first surface facing the user's eye,
• (ii) a first in-coupling optical element on the first surface in the first optical path configured to in-couple light from the image projector into the waveguide,
• (iii) a second in-coupling optical element on the first surface in the second optical path configured to in-couple light reflected from the user's eye into the waveguide such that the in-coupled infrared light that reflected from the user's eye travels via total internal reflection within the waveguide, and
• (iv) an out-coupling optical element on the first surface in the second optical path configured to out-couple the light reflected from the user's eye and guided within the waveguide out of the waveguide and direct the out-coupled light to the camera;
• a light source located on a user side of the eyepiece opposite the camera and arranged to illuminate the user's eye with infrared light, the user side being opposite the world side;
• and
• a reflector configured to direct the infrared light reflected from the user's eye toward the second in-coupling optical element.