Eye-tracking system positioning diffractive couplers on waveguide

A method of illuminating an eye of a user with an eye-tracking system, the method comprising:

• configuring an at least partially transparent visible light waveguide having a visible light display region to emit visible light to impinge upon the eye of the user;
• emitting at least infrared (IR) light from a light source, the IR light traveling along an IR light path to impinge upon the eye of the user;
• directing the IR light along the IR light path with a microelectromechanical system (MEMS) projector positioned in the IR light path and configured to direct the IR light from the light source;
• coupling at least a portion of the IR light directed by the MEMS projector with at least one diffractive input coupler on an input end of the IR light path downstream of the MEMS projector;
• coupling the portion of the IR light with at least one diffractive output coupler positioned in the IR light path downstream of the at least one diffractive input coupler to receive the portion of the IR light from the at least one diffractive input coupler and direct the portion of the IR light along the IR light path toward the eye;
• and
• receiving a portion of the IR light reflected from the eye of the user via at least one sensor configured to receive IR light.

An eye-tracking system, comprising:

• an at least partially transparent visible light waveguide having a visible light display region configured to emit visible light to impinge upon an eye of a user;
• a light source being configured to emit at least infrared (IR) light that travels along an IR light path to impinge upon the eye of the user;
• a microelectromechanical system (MEMS) projector positioned in the IR light path and configured to direct the IR light along the IR light path;
• at least one diffractive input coupler on an input end of the IR light path downstream of the MEMS projector to diffract at least a portion of the IR light directed by the MEMS projector;
• at least one diffractive output coupler positioned in the IR light path downstream of the at least one diffractive input coupler to receive the portion of the IR light from the at least one diffractive input coupler and direct the portion of the IR light along the IR light path toward the eye;
• and
• at least one sensor configured to receive the IR light after being reflected by the eye, wherein
• the at least one diffractive input coupler is configured to decrease a cross-sectional area of an IR light beam directed by the MEMS projector as the IR light beam passes through the diffractive input coupler, and
• the at least one diffractive output coupler is narrower than a step size of the IR light path in the visible light waveguide in a direction parallel to the visible light waveguide.