CURVED OPTICAL SEE-THROUGH THIN FREEFORM LIGHTGUIDE WITH LARGE FIELD OF VIEW IN EYEWEAR FORMFACTOR
1. An optical device comprising:
- a microdisplay configured to emit light of a computer generated image (CGI);
a lightguide having a curved first surface at a top of the lightguide for receiving the CGI from the microdisplay and a curved second surface for reflecting the CGI through an eye-side third surface to a user eye; and
a head mountable frame supporting the microdisplay and the lightguide, wherein the microdisplay is positioned at a top of the head mountable frame, and wherein the first curved surface of the lightguide is at a top side of the lightguide.
An optical device includes a frame supporting a lightguide, a microdisplay, and a field lens positioned therebetween that directs light from the microdisplay into a top surface of the lightguide. Four optical surfaces of the lightguide include: a curved surface where light from the microdisplay enters a top of the lightguide, curved eye-side and world-side surfaces providing total internal reflection, and a combiner surface. The eye-side surface is used twice. Once in total internal reflection, and a second time as a refractive surface when light is reflected from the combiner surface and is thereby refracted out of the lightguide and directed towards a user'"'"'s eye. The field lens has a curved first surface oriented toward the microdisplay and a curved second surface oriented toward the top of the lightguide. The combiner surface combines ambient light from a world-side of the lightguide with light from the microdisplay.
- 1. An optical device comprising:
a microdisplay configured to emit light of a computer generated image (CGI); a lightguide having a curved first surface at a top of the lightguide for receiving the CGI from the microdisplay and a curved second surface for reflecting the CGI through an eye-side third surface to a user eye; and a head mountable frame supporting the microdisplay and the lightguide, wherein the microdisplay is positioned at a top of the head mountable frame, and wherein the first curved surface of the lightguide is at a top side of the lightguide.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
- 16. An apparatus comprising:
a display positioned at a top of a head wearable frame; a display lens for receiving light from the display; and a lightguide positioned near to the display lens to guide light from the display to an eye-ward direction, the lightguide including; a transparent curved first surface on an eye-side of the lightguide; a transparent curved second surface on a world-side of the lightguide; a transparent third surface oriented toward the display lens for receiving display light, the display light reflecting inside the lightguide via total internal reflection; and a transparent curved fourth surface shaped to reflect light from the display to a user eye and to combine the display light with ambient light entering from the world-side through the transparent curved second surface of the lightguide.
- View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
The present application claims priority to U.S. Provisional Patent Application No. 62/751,008, titled “CURVED OPTICAL SEE-THROUGH THIN FREEFORM LIGHTGUIDE WITH LARGE FIELD OF VIEW IN EYEWEAR FORMFACTOR” and filed on Oct. 26, 2018, the entirety of which is incorporated by reference herein.
The present disclosure relates generally to design, placement, and use of a see-through lightguide as part of a head-mountable display (HMD) device for creating augmented vision.
HMD devices usually incorporate a near-to-eye optical system to create a virtual image placed a distance in front of a user. Single eye and dual eye displays are referred to as monocular and binocular HMDs, respectively. Some HMD devices display only a computer-generated image (CGI), while other types of HMD devices are capable of superimposing a CGI over a real-world view. This latter type of HMD typically includes some form of see-through eyepiece and can serve as a hardware platform for implementing augmented reality (AR). A scene of the world when looking through see-through eyewear is augmented with an overlaying CGI. Such an arrangement is also referred to as a heads-up display (HUD).
HMDs have practical and leisure applications. However, many applications are limited due to cost, size, weight, thickness, field of view, and efficiency of optical systems used to implement existing HMD devices. A narrow field of view is particularly restrictive. Use of conventional components yield a CGI of only a few degrees width and a few degrees of height, resulting in a poor user experience. Previous HMD designs have attempted to address these issues by employing curved lightguides and have positioned a microdisplay in a temple region of a head wearable frame similar to a conventional pair of glasses. However, based on the particular geometry and physical constraints of arrangement of these designs, the lightguide restricts a light path to include at least two bounces or reflections on an eye-side of the lightguide and two reflections on a world-side of the lightguide thereby restricting a size of a resulting visible image. In addition, conventional constraints in positioning the components of HMDs lead to low field of view (FOV) displays that are on the order of 10 degrees diagonal within user sight.
The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items.
Previous designs of lightguides placed a microdisplay at a temple position of a head-mountable display (HMD) device or apparatus or of a transparent heads up display (HUD) device or apparatus. This position can result in a lightguide length that is longer than desired. In particular, a microdisplay at the temple position can require a light path having two or more reflections on the eye-side surface of the lightguide and two or more reflections on the world-side surface of the lightguide before the light reaches a user'"'"'s eyes. In order to hide the microdisplay in the temple position, the lightguide was required to be tilted at approximately 18 degrees so as to facilitate total internal reflection (TIR) within the lightguide. All of these constraints yielded a low field of view (FOV) display on the order of approximately ten degrees diagonal in a viewable image emitted from the microdisplay.
Embodiments described herein relate to see-through HMD devices, such as glasses, helmets, and windshields which enable optical merging of computer generated and real-world scenes to form a combined view. To improve over previous geometries, according to certain embodiments, a microdisplay (“display”) is placed at a top of a curved lightguide as part of an HMD device to provide bilateral optic symmetry and extend a field of view from a few degrees to approximately 40 degrees horizontally and approximately 14 degrees vertically. The lightguide and microdisplay are positioned relative to one another to provide one reflection of total internal reflection on an eye-side, and one reflection on the world-side from surfaces of the lightguide. A projection from the microdisplay then outcouples with light from a world-side of the lightguide through a combiner region of the lightguide before reaching user eyes.
The placement of the microdisplay at the top of the lightguide is supported by various features of the lightguide such as having a curved eye-side surface and a curved world-side surface of the lightguide. According to certain embodiments, these curved surfaces are spherical, and each of these curved surfaces has a similar or approximately a same sized characteristic dimension (e.g., spherical dimension, radius) as each other. A first surface of the lightguide that first receives light from the microdisplay is curved, and, according to certain embodiments, is freeform, so as to correct for astigmatism, if any, with respect to the microdisplay. Another and final surface of the lightguide, providing a final reflection of light from the microdisplay toward the user eye, is also curved in a freeform manner. This final surface is referred to herein as a combiner or combiner surface. The image reflected therefrom is referred to as a light field. In other embodiments, the final surface of the lightguide is a rotationally symmetric aspherically-shaped surface, an anamorphic aspherically-shaped surface, a toroid-shaped surface, a Zernike polynomial-shaped surface, a radial basis function-shaped surface, an x-y polynomial-shaped surface, or a non-uniform rational b-spline-shaped surface.
A first lightguide is provided for a first (left) user eye, and a second lightguide is provided for a second (right) user eye. Each of the first and second lightguides is wrapped approximately five degrees from a view axis. According to some embodiments, a wrap angle is at least two degrees relative to the view axis. A frame maintains a surface of the lightguides at an approximately four degrees of tilt. An optical axis is oriented at approximately four degrees below a horizontal axis. An overall or combined pantoscopic tilt is thereby approximately eight degrees for the user eyes. A lightguide is approximately five mm or less in thickness. According to certain embodiments, a thickness is four mm or less in thickness. Spherical radii of curvature of spherical surfaces of the lightguide are designed such that the optical power thereof sums to zero (i.e., each light guide is a zero power shell). A see-through shell is maintained a small distance from the lightguide resulting in an aesthetically pleasing HMD device that provides a substantially enlarged image relative to conventional HMD devices and HMD image viewing systems.
Display light 303 from a display 305 and ambient light 304 from the world-side of the lightguide 301 are combined in the combiner aperture 302. The display light 303 travels a light path 350 within the lightguide 301. The combiner aperture 302 is a portion of the combiner surface 317 that reflects the display light 303 toward the eye-ward side of the lightguide 301. Display light 303 generated by the display 305 is directed by way of a field lens 307 into a top surface 304 of the lightguide 301. The display light 303 reflects inside the lightguide 301 at least one time from each of the world-side surface 313 and the eye-side surface 315. Preferably, the display light 303 reflects one time from each of the surfaces 313, 315 before exiting on the eye-ward side of the lightguide 301. The shapes of the surfaces of each component of the set of components 300, including the surfaces of the lightguide 301 and the filler piece 340, include a dimensional component along one or more of a first (x) axis 310, a second (y) axis 311, and a third (z) axis 312. For example, the combiner surface 317 is curved from a perspective relative to the first axis 310 and curved from a perspective relative to the second axis 311 as further shown in other figures and further described herein.
The lightguide 301 includes an outer groove 325 in an outer edge 326 and an inner edge 327. The outer groove 325 extends from a top side 345 to a bottom side 346. The outer groove 325 is also formed in the top side 345 and the bottom side 346 of the lightguide 301. The outer groove 325 along the edges 326, 327 and sides 345, 346 mate to a ridge of a frame (not illustrated) so as to hold the lightguide 301 fixed in the frame as shown in
Display light 303 generated by the display 305 is directed by way of the field lens 307 into the top surface 304 of the lightguide 301. Display light 303 from the display 305 and ambient light 304 from the world-side of the lightguide 301 are combined in the combiner aperture 302. The display light 303 travels the light path 350 within the lightguide 301. In certain embodiments, the display light 303 reflects inside the lightguide 301 one time from each of the world-side surface 313 and the eye-side surface 315 before exiting on the eye-ward side of the lightguide 301. In other embodiments, the display light 303 reflects inside the lightguide 301 more than one time from each of the world-side surface 313 and the eye-side surface 315 before exiting on the eye-ward side of the lightguide 301. The outer groove 325 is visible through the transparent lightguide 301 in the outer edge 326, the inner edge 327, and the bottom side 346. Passages 347 for receiving fasteners are visible near the top side 345 of the lightguide 301.
From the microdisplay 505, display light 503 first passes into a first surface 508 of the field lens 507. The first surface 508 is curved along a first axis, along a second axis (e.g., perpendicular to the page containing
Further, the field lens 507 is made of a first material and the lightguide 501 is made of a different second material. For example, the first material is a plastic material and the second material is a glass material, or a synthetic resin material such as Zeonex® E48R. According to some embodiments, a combination of the first material and the second material causes a color correction of the display light 503 by the time the display light 503 reaches the eye 531. While not illustrated, one or more of the components in the light path 550—the lightguide 501, the microdisplay 505, and the field lens 507—include one or more coatings for affecting a quality or a quantity of the display light 503 before reaching the eye 531.
The field lens 507 directs the display light 503 into a top surface 545 of the lightguide 501. The top surface 545 is curved such as being spherical or freeform in contour along a first axis, along a second axis, or along both a first axis and a second axis at a top position of the lightguide 501. The curvature of the top surface 545 corrects some or all of any astigmatism in the resulting CGI formed at the combiner surface 517. According to some embodiments, the resulting CGI, or field of view (FOV) thereof, is approximately 40 degrees horizontal and 14 degrees vertical relative to the eye 531 where the pupil has a nominal diameter or pupil size of 4 mm.
The lightguide 501 includes a world-side surface 513 having a world-side curvature 514 and an eye-side surface 515 having an eye-side curvature 516. The world-side surface 513 and the eye-side surface 515 are positioned relative to the top surface 545 so as to allow for total internal reflection of the display light 503 between the two surfaces 513, 515. Display light 503 enters the top surface 545 within approximately 24 degrees of a normal of the top surface 545. The display light 503 reflects from each of the two surfaces 513, 515 one time before reflecting from the combiner surface 517 toward the eye 531. The two surfaces 513, 515 are positioned within about five mm of each other. A lightguide thickness 510 is approximately five mm or less along a length from a top to a bottom of the lightguide 501. The lightguide thickness 510 as used herein is a distance between the world-side surface 513 and a closest point at the eye-side surface 515. According to some embodiments, along the world-side surface 513, the world-side curvature 514 includes a first spherical curvature 519 having a radius between 80-100 mm at the eye-ward side. Along the eye-side surface 515, the eye-side curvature 516 includes a second spherical curvature 520 having a radius between 80-100 mm at the eye-ward side. The first spherical curvature 519 is approximately 91.7 mm and the second spherical curvature 520 is approximately 90.0 mm.
The combiner surface 517 of the lightguide 501 is also positioned at a second angle 534, a pantoscopic tilt angle, relative to a vertical axis in front of the eye 531. According to some embodiments, the second angle 534 is measured from the vertical axis to a point within the CGI reflected from the combiner surface 517. For example, the second angle 534 is measured relative to a center of the CGI reflected from the combiner surface 517. As another example, the second angle 534 is measured relative to a center of the combiner surface 517. In some embodiments, the second angle 534 is approximately four degrees. A combined angle 537 including the first angle 533 and the second angle 534 relative to a vertical axis in front of the eye 531 is approximately eight degrees.
The combiner surface 317 reflects light from the display at the top side 114 of the lightguide 101 toward the eye-ward side 115 of the frame 110. The combiner surface 317 also allows light from the world-side 113 to pass therethrough and combine with light from the display thereby creating a composite image for an application of AR. The filler piece 340 is positioned within or below the lightguide 101 and generally below the combiner surface 317. Light is reflected to a user eye (not illustrated) at the combined angle 537 based on the geometries of the lightguide 101, the frame 114, and the combiner surface 317. A shell 601 that is approximately 1.45 mm thick is positioned in front of the lightguide 101 and the filler piece 340 across an entire front of the eyewear device 100 from the top side 114 to the bottom side 120. A thickness of 1.45 mm is a typical sunglass lens thickness. The shell 601 is generally of a uniform thickness from the top side 114 to the bottom side 120. According to a first embodiment, a transparent model of a five mm thick synthetic resin shell 601 having world-side radius of approximately 91.7 mm and an eye-side radius of approximately 90 mm yields almost no aberrations at a line of sight and yields two arcminutes of blur at approximately 30 degrees. A position at 30 degrees is close to a maximum comfortable eye motion. At 45 degrees, the blur is 7.5 arcminutes. According to other embodiments, the shell 601 includes a material, a component, a coating or a film (not illustrated) giving the shell 601 a darkened or a sunglass-type aspect such as altering a characteristic of inbound light from the world-side 113 of the eyewear device 100. The frame 110 maintains an air gap 602 of approximately 0.15 mm between a front or world-side surface of the lightguide 101 and the shell 601.
The lightguides 701-1, 701-2 are positioned an equal distance from a central axis 711 as evidenced by a respective visual axis 713 for each of the eyes 531, 707. A center 702 of the combiner aperture 302 is formed in each lightguide 701-1, 701-2 and positioned a first wrap angle 703 with respect to the respective eye 531, 707. The first wrap angle 703 is greater than a second wrap angle 712 of each of the lightguides 701-1, 701-2 where the second wrap angle 712 is relative to a normal taken from a front surface of the respective lightguides 701-1, 701-2. For example, the first wrap angle 703 is approximately five degrees while the second wrap angle 712 is approximately 0.9 degrees. An interpupillary distance 706 of approximately 63 mm is provided between the visual axis of each eye 531, 707. Each of the combiner apertures 302 includes a vertical field size 704 of approximately 14 degrees and a horizontal field size 705 of approximately 40 degrees relative to the pupils 532, 708 of the first and second eyes 531, 707 for a pupil size 714 of approximately four mm.
where m and n and x and y are integers, and where R is a length of a radius. For example, m=2 and n=0 corresponds to C2,0=x2. The first coefficient 803 corresponds to m=2 and n=0. For the first surface 801, x2 is approximately −0.015 and for the second surface 802, x2 is approximately 0.014. The second coefficient 804 corresponds to m=0 and n=2. The third coefficient 805 corresponds to m=3 and n=0. The fourth coefficient 806 corresponds to m=1 and n=2. The fifth coefficient 807 corresponds to m=4 and n=0. The values of the second through fifth coefficients 804-807 for the surfaces 801, 802 are as shown in
The illustrated embodiments in the figures are not drawn to scale. Not all of the activities or elements described above in the general description are required. A portion of a specific activity or a device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. The concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitation is intended for the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.