Today the US Patent & Trademark Office published a patent application from Apple that relates to optical systems and, more particularly, to optical systems for head-mounted displays. While augmented reality is mentioned, the priority in this patent is virtual reality. This head-mounted display system is to view virtual reality content, movies and specialty content that could include movies and games using Voxel technology. While Apple’s CEO said in an interview in the UK that AR glasses are a ways off, that statement didn’t apply to a VR headset.
Apple notes in their filing that head-mounted displays such as virtual reality glasses use lenses to display images for a user. A microdisplay may create images for each of a user’s eyes. A lens may be placed between each of the user’s eyes and a portion of the microdisplay so that the user may view virtual reality content.
If care is not taken, a head-mounted display may be cumbersome and tiring to wear. Optical systems for head-mounted displays may use arrangements of lenses that are bulky and heavy. Extended use of a head-mounted display with this type of optical system may be uncomfortable. Apple’s invention is designed to overcome the negatives of such systems.
Head-mounted displays may be used for virtual reality and augmented reality systems. For example, a pair of virtual reality glasses that is worn on the head of a user may be used to provide a user with virtual reality content.
An illustrative system in which a head-mounted display such as a pair of virtual reality glasses is used in providing a user with virtual reality content is shown in FIG. 1. As shown in FIG. 1, virtual reality glasses (head-mounted display) #10 may include a display system such as display system #40 that creates images and may have an optical system such as optical system #20 through which a user (e.g., user’s eyes #46) may view the images produced by display system by looking in direction #48.
Apple’s patent FIG. 1 also shows control circuitry #42 that may use display system to display visual content such as virtual reality content, pre-recorded video for a movie or other media, or other images.
Input-output devices #44 noted in fig. 1 above may be coupled to control circuitry #42. Input-output devices may be used to gather user input from a user, may be used to make measurements on the environment surrounding glasses #10, may be used to provide output to a user, and/or may be used to supply output to external electronic equipment. Input-output devices may include buttons, joysticks, keypads, keyboard keys, touch sensors, track pads, displays, touch screen displays, microphones, speakers, light-emitting diodes for providing a user with visual output, sensors (e.g., a force sensors, temperature sensors, magnetic sensor, accelerometers, gyroscopes, and/or other sensors for measuring orientation, position, and/or movement of the glasses, proximity sensors, capacitive touch sensors, strain gauges, gas sensors, pressure sensors, ambient light sensors, and/or other sensors). If desired, input-output devices may include one or more cameras (e.g., cameras for capturing images of the user’s surroundings, cameras for performing gaze detection operations by viewing eyes and/or other cameras).
Apple’s patent FIG. 2 noted above is a cross-sectional side view of glasses #10 showing how optical system #20 and display system #40 may be supported by head-mounted support structures such as housing #12 for the glasses. The Housing may have the shape and resemblance of a frame for a pair of glasses, may have the shape of a helmet, may have the shape of a pair of goggles, or may have any other suitable housing shape that allows the housing to be worn on the head of a user.
The housing may be formed from plastic, metal, fiber-composite materials such as carbon-fiber materials, wood and other natural materials, glass, other materials, and/or combinations of two or more of these materials.
The display system and the optical components of the glasses may be lightweight and compact. The optical system may, for example, be based on catadioptric lenses.
Apple’s patent FIGS. 8 and 9 are respectively top and side views of lens elements with cylindrical surfaces.
Apple notes that during assembly the of optical system, a planar piece of quarter wave film may be placed between lens elements #32 and #26 with optical adhesive on either side of the quarter wave film.
The lens elements may then be forced together to distribute the adhesive and bend the quarter wave film about axis Y (an axis parallel to axis Y). Providing a cylindrically curved shape for surfaces S6 and S7 can enable the thickness of lens elements to be reduced.
The use of cylindrically curved shapes for surfaces S6 and S7 can help make for a more uniform thickness across the lens elements and thereby improve lens element moldability.
When forming injection molded lens elements, uniformity of thickness in the mold cavity can help improve uniformity of flow of the molten plastic as it is being injected into the mold and the melt front flows across the mold cavity. The presence of a uniform flow during molding can be important for preventing flow lines in the molded lens, particularly when the lens element is thicker at the edge than the center.
More uniform flow can also result in a lower birefringence in the molded lens elements. For catadioptric optical systems, low birefringence in the lens elements helps to maintain control of the polarization state of the image light, so that stray light and ghosts are reduced so that the user is thereby provided with a high contrast image without stray light artifacts.
Other Notes about the Invention
The display system may have a pixel array that produces image light associated with the images. The display system may also have a linear polarizer through which image light from the pixel array passes and a quarter wave plate through which the light passes after passing through the linear polarizer.
The optical system may be a catadioptric optical system having one or more lens elements formed from clear materials such as glass or plastic and having reflective structures. The lens elements may include a plano-convex lens element and a plano-concave lens element. The plano-convex lens element may have a convex surface and an opposing planar surface. The plano-concave lens element may have a concave surface and an opposing planar surface that faces the planar surface of the convex lens element.
A partially reflective mirror may be formed on a convex surface of the plano-convex lens element. A reflective polarizer may be formed on the planar surface of the plano-convex lens or the concave surface of the plano-concave lens. An additional quarter wave plate may be located between the reflective polarizer and the partially reflective mirror.
Apple’s patent application was filed back in Q1 2017. Considering that this is a patent application, the timing of such a product to market is unknown at this time. Some of the engineers noted as the inventors include:
Mr. Border: Senior Optics Manufacturing Exploration Engineer
Mr. Cheng: Senior Process Engineer
Mr. Anderson: Senior Opto-Mechanical Exploration Engineer
Mr. Bollman: Hardware Engineering Manager
Mr. Myhre: Display Exploration Engineer
Mr. Zhu: Senior Optical Engineer
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