New patent for Google: head-mounted display with ultra-large field of view

At the Display Week 2018 held in late May 2018, Google released a head-mounted display with a wide field of view and high sensitivity for VR devices. The display is 4.3 inches in size, with a single-eye resolution of 18 million pixels, a pixel density of up to 1443ppi, and a refresh rate of up to 120Hz. It is an OLED display.

The head-mounted device uses a set of optical systems (mainly precision optical lenses) to magnify the image on the ultra-micro display screen, project the image onto the retina, and then present it as a large-screen image in the eyes of the viewer. To put it in a more vivid way, it is like looking at an object with a magnifying glass and presenting a magnified virtual object image.

The biggest feature of head-mounted displays is that they have advanced gaze tracking capabilities, which is a major breakthrough compared to before. The wearer can issue commands without moving his hands, for example, the page of a document can be automatically turned as the eyes move downward. Entertainment head-mounted displays also have very powerful entertainment functions, and major game developers around the world have begun to develop virtual and real games. With the advancement of technology, handheld entertainment devices that integrate games will become a hot research field.

On April 30, 2020, Google also announced an invention patent called "Curved Optical Transparent Thin Free-Form Light Guide" (publication number: US 2020/0132919 A1), and the applicant is Google.

Based on the information currently disclosed in the patent, let us take a look at how this enhanced head-mounted device uses light guidance to obtain an ultra-wide field of view.

As shown in the figure above, which is a perspective view of the eyeglass device of the patent invention, the device 100 includes a pair of light guides 101 installed in a frame 110. The frame fixes the light guide between its top side 114 and bottom side 120, and the frame is shaped like a normal pair of glasses.

Typically the light guides are transparent and each includes a dielectric mirror coating 102 which acts as a reflector, reflecting light 103 from the individual microdisplays 105 and allowing ambient light 104 from the world side 113 to pass through the rearward side 115 of the light guide and the dielectric mirror coating.

The frame includes two arms 111 extending from the frame's temples toward and above the user's ears, each arm housing a cord 112 for a respective microdisplay, each microdisplay receiving power and display signals from the computing device via its respective cable.

The frame supports display housings for individual microdisplays, each display housing enclosing a portion of its microdisplay, with display light leaving the microdisplay and entering a corresponding light guide from the top side of the frame. The display light is magnified by the user due to features of the light guide and the surface of the objective lens or display lens located between the microdisplay and the corresponding light guide. For example, the light guide acts as a magnifier and outputs a 40 degree horizontal by 14 degree vertical field of view for a pupil diameter of approximately 4 mm.

As shown in the exploded perspective view of the light guide, the assembly 300 of the eyeglass device 100 includes a light guide 301 and a matching filler 340, which is optional and included in the light guide to make the eyeglass device look like ordinary glasses. The surface of the filler is shaped to match the surface of the light guide, including the surface of the recess 341 in the light guide.

The combiner surface 317 is defined by top, bottom, outer and inner interface lines, each of which is located at the intersection of the respective surfaces of the light guide.On both sides of the filler, the second matching surface 343 is shaped to match the side curvature 314 of the side surface 313 of the light guide.

The display light reflects from the light guide at least once from the side surface and the eye side surface, and the display light reflects from each surface once and then exits from the eye side of the light guide. The surface shape of each component of a set of components includes the surface of the light guide and the filling member, and the light guide includes an outer groove 325 in the outer edge 326 and the inner edge 327.

The outer groove extends from the top side to the bottom side, and the outer groove is also formed in the top and bottom sides of the light guide, and cooperates with the outer groove and the ridge of the frame along the edge and side to fix the light guide in the frame.

Finally, let's take a look at the top view of this light guide and what the scene is like when it is actually used.

As shown in the figure above, two light guides are arranged in a binocular arrangement, one for each eye, to facilitate proper viewing of 3D content. The first light guide is located in front of the right eye and right pupil, and the second left light guide is located in front of the left eye and left pupil. Each light guide includes a plurality of grooves 709 in its edges for docking with the frame.

Visible on the eye-side surface of each light guide is an opening 710 corresponding to the back of the recess 341, with the housing 601 placed on the other side of each light guide. A plurality of channels 347 are formed in the light guide to facilitate directing other components thereto, with a top surface 344 for receiving display light from the display being centered at the top edge of the light guide.

The light guides are equidistant from the central axis 711 as evidenced by the respective visual axes of each eye, forming a center of a combiner aperture in each light guide, and positioning a first wrap angle relative to the eye, the first wrap angle being greater than a second wrap angle of each light guide, wherein the second wrap angle is taken relative to a normal from a front surface of each light guide.

The above is the new head-mounted device invented by Google. It is a head-mounted display that uses imaging light guides to transmit image light to the viewer. The imaging light guide combined with various types of waveguides relays the image light to the viewer in a narrow space, so as to guide the virtual image to the viewer's pupil and enable the user to have a more realistic feeling. This head-mounted display (HMD) will play an important role in military applications, commercial applications, industrial applications, fire fighting applications and entertainment applications!