Abstract: A display may include a waveguide. An input coupler may couple image light into the waveguide and an output coupler may couple the image light out of the waveguide. A surface relief grating on the waveguide may couple infrared light into the waveguide and may couple the infrared light out of the waveguide. The surface relief grating may additionally or alternatively couple reflected infrared light into the waveguide and out of the waveguide and towards an infrared sensor. The surface relief grating may also form a cross-coupler for the image light. The infrared sensor may gather infrared sensor data based on the reflected infrared light. Control circuitry may perform gaze tracking operations based on the infrared sensor data. The input and output couplers may also be formed from surface relief gratings or may include other optical components.

Abstract: An eye tracking system for detecting position and movements of a user's eyes in a head-mounted display (HMD). The eye tracking system includes at least one eye tracking camera, an illumination source that emits infrared light towards the user's eyes, and diffraction gratings located at the eyepieces. The diffraction gratings redirect or reflect at least a portion of infrared light reflected off the user's eyes, while allowing visible light to pass. The cameras capture images of the user's eyes from the infrared light that is redirected or reflected by the diffraction gratings.

Abstract: An eye tracking system for detecting position and movements of a user's eyes in a head-mounted display (HMD). The eye tracking system includes at least one eye tracking camera, an illumination source that emits infrared light towards the user's eyes, and diffraction gratings located at the eyepieces. The diffraction gratings redirect or reflect at least a portion of infrared light reflected off the user's eyes, while allowing visible light to pass. The cameras capture images of the user's eyes from the infrared light that is redirected or reflected by the diffraction gratings.

Abstract: An electronic device may have a display that provides image light to a waveguide. First and second liquid crystal lenses may be mounted to opposing surfaces of the waveguide. An coupler may couple the image light out of the waveguide through the first lens. The second lens may convey world light to the first lens. Control circuitry may control the first lens to apply a first optical power to the image light and the world light and may control the second lens to apply a second optical power to the world light that cancels out the first optical power. Each lens may include two layers of liquid crystal molecules having antiparallel pretilt angles. The pretilt angles and rubbing directions of the first lens may be antiparallel to corresponding pretilt angles and rubbing directions of the second lens about the waveguide.

Abstract: An electronic device may have a display that emits image light, a waveguide, and an input coupler that couples the image light into the waveguide. Beam splitter structures may be embedded within the waveguide. The beam splitter structures may partially reflect the image light multiple times and may serve to generate replicated beams of light that are coupled out of the waveguide by an output coupler. The beam splitter structures may replicate the beams across two dimensions to provide an eye box with uniform-intensity light from the display across its area. The beam splitter structures may include stacked partially reflective beam splitter layers, sandwiched transparent substrate layers having different indices of refraction, a thick volume hologram interposed between substrate layers, or combinations of these or other structures. The reflectivity of the beam splitter structures may vary discretely or continuously across the lateral area of the waveguide.

Abstract: A display may include a waveguide, a diffractive input coupler, and an output coupler. The input coupler may diffract image light into the waveguide. The output coupler may diffract the image light out of the waveguide and towards an eye box. The output coupler may include a first volume hologram with a first grating vector and a second volume hologram with a second grating vector. The first and second grating vectors may be oriented at the same angle from opposing sides of an axis. The input coupler may have a first pitch. The first and second volume holograms may have a second pitch. The second pitch may be constant across the output coupler. In order to mitigate dispersion by the input coupler, the second pitch may be equal to twice the first pitch times a cosine of the angle.

Abstract: An electronic device may have a display system that produces images. The display system may have one or more pixel arrays such as liquid-crystal-on-silicon pixel arrays. Images from the display system may be coupled into a waveguide by an input coupler and may be coupled out of the waveguide using an output coupler. The input and output couplers may be formed from volume phase holographic gratings. An additional grating may be used to shift light that would otherwise pass above or below the user's field of view towards the viewer. Holographic gratings in the waveguide may have fringes with constant pitch and variable period. The period at a given portion of the grating may be Bragg-matched to maximize diffraction efficiency for light of a given incident angle.

Abstract: An electronic device may have a reflective display with a pixel array that generates images. The reflective display may be illuminated by an illumination system. Light from the illumination system may be reflected by the pixel array as image light. The image light may be provided to a viewer using a waveguide with diffractive input and output couplers. The illumination system may have a waveguide. The illumination system may also have a light source such as one or more light-emitting diodes. Light from the light source may be coupled into the waveguide of the illumination system by a diffractive coupler such as volume hologram that serves as an input coupler. Light from the light source may be routed to the display to illuminate the display using the waveguide in the illumination system and a diffractive coupler such as a volume hologram that serves as an output coupler.

Abstract: An eye tracking system for detecting position and movements of a user's eyes in a head-mounted display (HMD). The eye tracking system includes at least one eye tracking camera, an illumination source that emits infrared light towards the user's eyes, and diffraction gratings located at the eyepieces. The diffraction gratings redirect or reflect at least a portion of infrared light reflected off the user's eyes, while allowing visible light to pass. The cameras capture images of the user's eyes from the infrared light that is redirected or reflected by the diffraction gratings.

Abstract: An eye tracking system for detecting position and movements of a user's eyes in a head-mounted display (HMD). The eye tracking system includes at least one eye tracking camera, an illumination source that emits infrared light towards the user's eyes, and diffraction gratings located at the eyepieces. The diffraction gratings redirect or reflect at least a portion of infrared light reflected off the user's eyes, while allowing visible light to pass. The cameras capture images of the user's eyes from the infrared light that is redirected or reflected by the diffraction gratings.

Abstract: An electronic device may include a display that generates light for an optical system that redirects the light towards an eye box. The optical system may include a waveguide, a non-diffractive input coupler, a cross coupler, and an output coupler. The cross coupler may expand the light in a first direction. The cross coupler may perform an even number of diffractions on the light and may couple the light back into the waveguide at an angle suitable for total internal reflection. The output coupler may expand the light in a second direction while coupling the light out of the waveguide. The cross coupler may include surface relief gratings or holographic gratings embedded within the waveguide or formed in a separate substrate. The optical system may direct the light towards the eye box without chromatic dispersion and while supporting an expanded field of view and optical bandwidth.

Abstract: An electronic device may include an emissive display panel that emits light. The light may propagate along an optical path extending to an eye box. A waveguide with an input coupler and an output coupler may be interposed on the optical path. An angle-selective transmission filter (ASTF) may be interposed on the optical path and may filter the emitted light as a function of angle to remove high-angle light from the optical path before the light is provided to the output coupler. The ASTF may include diffractive grating structures such as thin-film holograms, volume holograms, or surface relief gratings, louvered mirrors, multi-layer coatings, or a pinhole array. This ASTF may serve to minimize stray light within the display, thereby optimizing the contrast and the modulation transfer function (MTF) of the display.

Abstract: An eye tracking system for detecting position and movements of a user's eyes in a head-mounted display (HMD). The eye tracking system includes at least one eye tracking camera, an illumination source that emits infrared light towards the user's eyes, and diffraction gratings located at the eyepieces. The diffraction gratings redirect or reflect at least a portion of infrared light reflected off the user's eyes, while allowing visible light to pass. The cameras capture images of the user's eyes from the infrared light that is redirected or reflected by the diffraction gratings.

Abstract: An electronic device may have a light source such as a laser light source. The light source may emit light into a waveguide. A phase grating may diffract the light that is emitted into the waveguide to produce diffracted light. The diffracted light may be oriented parallel to a surface normal of an angled edge of the waveguide and parallel to a surface normal of a microelectromechanical systems mirror element in a two-dimensional scanning microelectromechanical systems mirror that is coupled to the edge of the waveguide. A wave plate may be interposed between the mirror and the edge of the waveguide to change the polarization state of light reflected from the mirror element relative to incoming diffracted light from the phase grating. The phase grating may be configured so that the reflected light is not diffracted by the phase grating.

Abstract: An electronic device may have a display system that produces images. The display system may have one or more pixel arrays such as liquid-crystal-on-silicon pixel arrays. Images from the display system may be coupled into a waveguide by an input coupler and may be coupled out of the waveguide using an output coupler. The input and output couplers may be formed from volume phase holographic gratings. An additional grating may be used to shift light that would otherwise pass above or below the user's field of view towards the viewer. Holographic gratings in the waveguide may have fringes with constant pitch and variable period. The period at a given portion of the grating may be Bragg-matched to maximize diffraction efficiency for light of a given incident angle.

Abstract: An electronic device may include a display that produce images. The display may generate light for an optical system that redirects the light towards an eye box. The optical system may include a waveguide that propagates the light in a first direction towards the output coupler. The output coupler may couple the light out of the waveguide towards the eye box while inverting a parity of the light about the first direction. The coupler may include a first element such as a set of partial mirrors or diffractive gratings that redirects a first portion of the light in a second direction. The coupler may include a second element that redirects a second portion of the light in a third direction opposite the second direction. The first element may redirect the second portion and the second element may redirect the first portion towards the eye box.

Abstract: An electronic device may have a display that emits image light, a waveguide, and an input coupler that couples the image light into the waveguide. Beam splitter structures may be embedded within the waveguide. The beam splitter structures may partially reflect the image light multiple times and may serve to generate replicated beams of light that are coupled out of the waveguide by an output coupler. The beam splitter structures may replicate the beams across two dimensions to provide an eye box with uniform-intensity light from the display across its area. The beam splitter structures may include stacked partially reflective beam splitter layers, sandwiched transparent substrate layers having different indices of refraction, a thick volume hologram interposed between substrate layers, or combinations of these or other structures. The reflectivity of the beam splitter structures may vary discretely or continuously across the lateral area of the waveguide.

Abstract: An electronic device may have a reflective display with a pixel array that generates images. The reflective display may be illuminated by an illumination system. Light from the illumination system may be reflected by the pixel array as image light. The image light may be provided to a viewer using a waveguide with diffractive input and output couplers. The illumination system may have a waveguide. The illumination system may also have a light source such as one or more light-emitting diodes. Light from the light source may be coupled into the waveguide of the illumination system by a diffractive coupler such as volume hologram that serves as an input coupler. Light from the light source may be routed to the display to illuminate the display using the waveguide in the illumination system and a diffractive coupler such as a volume hologram that serves as an output coupler.

Abstract: An electronic device may have a display that provides image light to a waveguide. First and second liquid crystal lenses may be mounted to opposing surfaces of the waveguide. An coupler may couple the image light out of the waveguide through the first lens. The second lens may convey world light to the first lens. Control circuitry may control the first lens to apply a first optical power to the image light and the world light and may control the second lens to apply a second optical power to the world light that cancels out the first optical power. Each lens may include two layers of liquid crystal molecules having antiparallel pretilt angles. The pretilt angles and rubbing directions of the first lens may be antiparallel to corresponding pretilt angles and rubbing directions of the second lens about the waveguide.

Abstract: An electronic device may include a display system for presenting images close to a user's eyes. The display system may include a display unit that directs light and an optical system that redirects the light from the display unit towards a user's eyes. The optical system may include an input coupler and an output coupler formed on a waveguide. The input coupler may redirect light from the display unit so that it propagates in the waveguide towards the output coupler. The output coupler may redirect the light from the input coupler so that it exits the waveguide towards the user's eyes. A light-redirecting element may be used to redirect edge light that would otherwise be outside of the user's field of view towards the user's eyes.