Abstract: A display may include illumination optics (36), a spatial modulator (40) and a waveguide (26). The illumination optics may produce illumination that is modulated by the spatial modulator to produce image light. The waveguide may direct the image light towards an eye box. The illumination optics may include light sources (58) an X-plate (44), and at least one Fresnel lens (60) interposed between the light sources and the X-plate. The Fresnel lenses may minimize the size of the illumination optics while still exhibiting satisfactory optical performance. The spatial light modulator may include a reflective display panel (50) and a powered prism (48) with a reflective coating on a curved reflective surface. The powered prism may optimize f-number while minimizing the volume of the spatial light modulator. The collimating optics may include a diffractive optical element (56) that compensates for thermal effects and chromatic dispersion in the display.

Abstract: A head-mounted display may include a display system and an optical system in a housing. The display system may have displays that produce images. Positioners may be used to move the displays relative to the eye positions of a user's eyes. An adjustable optical system may include tunable lenses such as tunable cylindrical liquid crystal lenses. The displays may be viewed through the lenses when the user's eyes are at the eye positions. A sensor may be incorporated into the head-mounted display to measure refractive errors in the user's eyes. The sensor may include waveguides and volume holograms, and a camera for gathering light that has reflected from the retinas of the user's eyes. Viewing comfort may be enhanced by adjusting display positions relative to the eye positions and/or by adjusting lens settings based on the content being presented on the display and/or measured refractive errors.

Abstract: A display may include a reflective display panel, an infrared image sensor and a waveguide. The panel may be operated in a first operating mode in which the panel reflects image light towards the waveguide and a second operating mode in which the panel reflects infrared light from the waveguide towards the infrared image sensor. The panel may also reflect infrared light from an infrared emitter towards the waveguide. If desired, the infrared image sensor may be mounted adjacent a reflective surface of a reflective input coupling prism on the waveguide. The infrared image sensor may receive the infrared light through the reflective surface. If desired, a world-facing camera may receive world light through the waveguide. The display module and the world-facing camera may be operated using a time multiplexing scheme to prevent the image light from interfering with images captured by the world-facing camera.

Abstract: An electronic device may include a display module that produces light having an image, a lens that directs the light to a waveguide, and a waveguide that directs the light to an eye box. The lens may produce a foveated image in the light by applying a non-uniform magnification to the image in the light. The non-uniform magnification may vary as a function of angle within a field of view of the lens. This may allow the foveated image to have higher resolution within the central region than in the peripheral region. Performing foveation using the lens maximizes the resolution of images at the eye box without increasing the size of the display module. Control circuitry on the device may apply a pre-distortion to the image that is an inverse of distortion introduced by the lens in producing the foveated image.

Abstract: A head-mounted display may include a display system and an optical system in a housing. The display system may have displays that produce images. Positioners may be used to move the displays relative to the eye positions of a user's eyes. An adjustable optical system may include tunable lenses such as tunable cylindrical liquid crystal lenses. The displays may be viewed through the lenses when the user's eyes are at the eye positions. A sensor may be incorporated into the head-mounted display to measure refractive errors in the user's eyes. The sensor may include waveguides and volume holograms, and a camera for gathering light that has reflected from the retinas of the user's eyes. Viewing comfort may be enhanced by adjusting display positions relative to the eye positions and/or by adjusting lens settings based on the content being presented on the display and/or measured refractive errors.

Abstract: An electronic device may include a display module that produces light having an image, a lens that directs the light to a waveguide, and a waveguide that directs the light to an eye box. The lens may produce a foveated image in the light by applying a non-uniform magnification to the image in the light. The non-uniform magnification may vary as a function of angle within a field of view of the lens. This may allow the foveated image to have higher resolution within the central region than in the peripheral region. Performing foveation using the lens maximizes the resolution of images at the eye box without increasing the size of the display module. Control circuitry on the device may apply a pre-distortion to the image that is an inverse of distortion introduced by the lens in producing the foveated image.

Abstract: The display may include a display module and a waveguide. The module may produce first light of first wavelengths during first time periods and may produce second light of second wavelengths during second time periods interleaved with the first time periods. Diffractive gratings or a dichroic wedge may redirect the first light into the waveguide at a first angle and may redirect the second light into the waveguide at a second angle separated from the first angle by a separation angle. The separation angle may be equal to half the angle subtended by the projection of a pixel in the module. The first and second time periods may alternate faster than the response of the human eye. This may configure the first and second image light to collectively provide images at an eye box with an increased effective resolution without increasing the space or power consumed by the display module.

Abstract: An electronic device may include a display module that produces foveated images having high and low resolution regions. The module may include a reflective display panel that produces first reflected light during first time periods and second reflected light during second time periods. The first reflected light may reflect off of a beam splitter to form the low resolution region of the foveated image. The second reflected light may be transmitted by the beam splitter, de-magnified by a lens, and redirected by an optical steering element to produce the high resolution region at a desired, adjustable, location in the foveated image. The reflective display panel may be replaced by sets of emissive display panels that concurrently display the high and low resolution regions in the foveated image. The sets of emissive display panels may be replaced by front-lit reflective display panels.

Abstract: A display may have display layers that form an array of pixels. An angle-of-view adjustment layer may overlap the display layers. The angle-of-view adjustment layer may include an array of adjustable light blocking structures formed from electrochromic material. The electrochromic material may be interposed between first and second electrode layers. When it is desired to operate the display in a private viewing mode, control circuitry may apply a current to the first and second electrodes that causes the electrochromic material to become more opaque, thereby restricting the angle of view of the display. When it is desired to operate the display in a public viewing mode, control circuitry may apply a current to the first and second electrodes that causes the electrochromic material to become more transparent, thereby opening up the angle of view of the display.

Abstract: An electronic device such as a head-mounted display may have a display system that produces images. The display system may have one or more pixel arrays (26-1, 26-2) such as liquid-crystal-on-silicon pixel arrays. Images from the display system may be coupled into a waveguide (116) by an input coupler system (114X, 114Y) and may be coupled out of the waveguide in multiple image planes using an output coupler system (120X, 120Y). The input and output coupler systems may include single couplers, stacks of couplers, and tiled arrays of couplers. Multiplexing techniques such as wavelength multiplexing, polarization multiplexing, time-division multiplexing, multiplexing with image light having different ranges of angular orientations, and/or tunable lens techniques may be used to present images to a user in multiple image planes.

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 provide foveated images at an eye box. The device may have a first display module that produces a low resolution portion of the image and a second display module that produces a high resolution portion of the image. A reflective input coupling prism may be mounted to a waveguide. A steering mirror may overlap the prism. The mirror may receive the high resolution portion through the waveguide and the prism. The mirror may reflect the high resolution portion back into the waveguide and may be adjusted to shift a location of the high resolution portion within the image. For example, the steering mirror may adjust the position of the high resolution portion to align with the gaze direction at the eye box. A reflective surface of the prism may reflect the low resolution portion of the image into the waveguide.

Abstract: A display may include illumination optics, a spatial modulator, and a waveguide. The illumination optics may produce illumination that is modulated by the spatial modulator to produce image light. The waveguide may direct the image light towards an eye box. The illumination optics may include light source sets that produce the illumination. Each set may include a low power light source and a high power light source. In a first state, the high and low power light sources may be active. In a second state, the low power light sources may be active. Control circuitry may adjust between the first and second states based on image data. The second state may be used when virtual objects in the image data are confined to a peripheral region of the field of view of the eye box.

Abstract: A display may include a waveguide for providing light to an eye box. The display may include polarization recycling structures having a polarizing beam splitter and a prism. The polarizing beam splitter may transmit a first portion of unpolarized light as first image light having a first polarization and may reflect a second portion of the unpolarized light as second image light having a second polarization. One or more waveplates may be mounted to the prism for transmitting the second image light. Upon transmission by the waveplate(s), the second image light may have the same polarization as the first image light. An input coupler may couple the first and second image light into the waveguide. Providing polarized light to the waveguide may maximize the optical efficiency of the waveguide. The polarization recycling structures may maximize the amount of the image light that is coupled into the waveguide.

Abstract: An electronic device may provide image light to an eye box. The display may include a light source panel that emits the image light. A waveguide may direct the image light towards the eye box. An input coupler may couple the image light into the waveguide and an output coupler may couple the image light out of the waveguide. A color filter may be optically interposed between the light source panel and the output coupler. The color filter may filter the image light using a steep cutoff characteristic. The color filter may allow the image light to exhibit a desired color point while also allowing the light source panel to use light emitters having peak emission wavelengths that maximize the efficiency of the light emitters and thus the power efficiency of the device.

Abstract: An electronic device may have a pixel array. A light source may illuminate the pixel array to produce image light. The image light may pass through a multi-element lens and may be coupled into a waveguide using an input coupler such as a prism. An output coupler such as a diffraction grating may couple the image light out of the waveguide and towards a user. The user may view the image light and may observe real-world objects through the waveguide. The waveguide may have locally modified portions that define an aperture stop at a distance from an exit surface of the multi-element lens. The multi-element lens may have first and second achromatic doublets and first and second singlets between the first and second achromatic doublets. The lens elements of the multi-element lens may include lens elements with aspheric surfaces.

Abstract: An electronic device may include a display module that generates light and an optical system that redirects the light towards an eye box. The system may include an input coupler that couples the light into the waveguide. The input coupler may include a prism on the waveguide and a scanning mirror. The scanning mirror may receive the light through the waveguide and the prism and may reflect the light into the waveguide through the prism while being rotated over a set of orientations. The scanning mirror may fill a relatively large field of view eye box with a corresponding image frame despite the limited field of view of the image light produced by the display module. The orientation of the scanning mirror may be adjusted based on gaze tracking data.

Abstract: A display may have display layers that form an array of pixels. An angle-of-view adjustment layer may overlap the display layers. The angle-of-view adjustment layer may include an array of adjustable louvers that move from a first position in which the angle of view of the display is restricted for a private viewing mode and a second position in which the angle of view of the display is not restricted for a normal viewing mode. The louvers may contain electrophoretic particles. The louvers may be tapered and may have a width at one end that is less than ten microns. The electrophoretic particles may form isolated clusters on a lower substrate in normal viewing mode to increase the transmittance of the display in normal viewing mode. The angle-of-view adjustment layer may be a second liquid crystal display layer that is used to block off-axis light.

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 include a waveguide with an input coupler and an output coupler. The input coupler may receive the image light from imaging optics. The input coupler may be an input coupling prism and the imaging optics may include lens elements. World light may be viewable at an eye box through the output coupler. Biasing, compensation, and/or prescription lenses may overlap the output coupler. The input coupling prism, the lens elements in the imaging optics, and/or one or more of the biasing, compensation, and prescription lenses may be formed from gradient index (GRIN) material. The GRIN material may have a gradient refractive index that varies in one or more gradient directions. Use of GRIN materials may minimize the volume required to form the device without sacrificing optical performance. In addition, the GRIN materials may compensate for dispersion and aberrations in the device.