Eyepiece for a personal display and personal display comprising such eyepiece

Abstract

The invention relates to personal display devices and in particular an eyepiece therefor. The eyepiece is adapted for projecting an image from an image plane on one side of the eyepiece through an exit pupil on the opposite side of the eyepiece and comprises at least one stationary lens group and at least two movable lens groups being movable with respect to the stationary lens group along an optical axis between the image plane and the exit pupil. According to the invention, the lens groups are arranged in positive-negative-positive configuration and the movable lens groups are arranged to move along the optical axis between a first state providing a first field-of-view and a second state providing a second field-of-view smaller than the first field-of-view to the image plane. The invention allows for improving optical performance and user experience of personal display devices.

Claims

1. An eyepiece for projecting an image from an image plane on one side of the eyepiece through an exit pupil on the opposite side of the eyepiece, comprising: a stationary lens group and two movable lens groups being movable with respect to the stationary lens group along an optical axis between the image plane and the exit pupil, wherein the lens groups are arranged in positive-negative-positive configuration and the movable lens groups are arranged to move along the optical axis between a first state providing a first field-of-view and a second state providing a second field-of-view smaller than the first field-of-view to the image plane wherein the eyepiece is adapted to provide an image of essentially equally sized area of the image plane at said exit pupil in said first and second states, wherein the lens groups comprise: a first movable positive lens group located closest to the exit pupil, a third stationary positive lens group located closest to the image plane, and a second movable negative lens group between the first lens group and the third lens group, whereby the first lens group and the second lens group are adapted to move farther from the third lens group and closer to each other when moving from the first state to the second state.

2. The eyepiece according to claim 1, wherein the second lens group is adapted to be in the vicinity of the third lens group in the first state and in the vicinity of the first lens group in the second state.

3. The eyepiece according to claim 1, wherein the first field-of-view is 100 degrees or more and the second field-of-view is 65 degrees or less.

4. The eyepiece according to claim 1, wherein each of the lens groups comprises at most two lens elements.

5. The display device according to claim 1, wherein the display element is configured so that the lens groups may be immobilized in any desired position between and including the first and second states.

6. The eyepiece according to claim 1, wherein at least two of the lens groups comprise only a single lens element.

7. A personal display device comprising: a display element, and an eyepiece for projecting an image from the display element to an eye of a viewer, the eyepiece comprising: a stationary lens group and two movable lens groups being movable with respect to the stationary lens group along an optical axis between the image plane and the exit pupil, wherein the lens groups are arranged in positive-negative-positive configuration and the movable lens groups are arranged to move along the optical axis between a first state providing a first field-of-view and a second state providing a second field-of-view smaller than the first field-of-view to the image plane wherein the eyepiece is adapted to provide an image of essentially equally sized area of the image plane at said exit pupil in said first and second states, wherein the lens groups comprise: a first movable positive lens group located closest to the exit pupil, a third stationary positive lens group located closest to the image plane, and a second movable negative lens group between the first lens group and the third lens group, whereby the first lens group and the second lens group are adapted to move farther from the third lens group and closer to each other when moving from the first state to the second state, whereby the display element is positioned at said image plane.

8. The display device according to claim 7, further comprising a processing unit functionally connected to the display element for displaying content on the display element.

9. The display device according to claim 7, further comprising two such eyepieces in binocular configuration.

10. The display device according to claim 7, wherein the device is a wearable device.

11. An eyepiece for projecting an image from an image plane on one side of the eyepiece through an exit pupil on the opposite side of the eyepiece, comprising: a stationary lens group and two movable lens groups being movable with respect to the stationary lens group along an optical axis between the image plane and the exit pupil, wherein the lens groups are arranged in positive-negative-positive configuration and the movable lens groups are arranged to move along the optical axis between a first state providing a first field-of-view and a second state providing a second field-of-view smaller than the first field-of-view to the image plane wherein the eyepiece is adapted to provide an image of essentially equally sized area of the image plane at said exit pupil in said first and second states, wherein the first field-of-view is 100 degrees or more and the second field-of-view is 65 degrees or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B show the optical configurations of the eyepiece according to one embodiment in a wide-angle state and tele state, respectively.

(2) FIGS. 2A and 2B illustrate schematically a personal display device comprising an eyepiece of the present kind in side and top views, accordingly.

(3) FIGS. 3A and 3B show distortion graphs of an exemplary eyepiece in tele and wide angle states, respectively.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) The term “eyepiece” generally refers to an optical device that is designed for projecting an image from an image plane on one side of the device through an exit pupil located on the opposite side of the device at a non-zero distance therefrom. An eyepiece of this kind allows for viewing a sharp and enlarged image of the image plane with a bare eye.

(5) The term “lens element” refers to a single optical lens in contrast with the term “lens group” that may comprise either a single lens or two or more lenses in a predefined mutual configuration.

(6) The term “wide angle” state (first state) here refers to a field of view of 100 degrees or more and the term “tele” or “zoomed” state (second state) to a field of view of 65 degrees or less.

(7) In FIGS. 1A and 1B, an outline of an exemplary lens system of an eyepiece is shown in wide-angle and narrow-angle viewing configurations, respectively. The image plane, such as a display surface, is herein denoted with reference numeral 14, whereas the exit pupil is denoted with reference numeral 10. A support structure of the lens system is not shown, but it is understood by a skilled person that some kind of a mechanical structure for holding the necessary lens groups and allowing for moving the movable lens groups must be provided to form an operational eyepiece. Various such structures are known per se.

(8) There is provided a negative middle lens group 12 (second lens group), which is surrounded by positive lens groups 11 (first lens group) and 13 (third lens group). The second lens group 12 acts as a variator lens group. The third lens group 13 is closest to and fixed with respect to a display 14, whereas the first and second lens groups 11 and 12 are moveable.

(9) In general, each lens group 11, 12, 13 can contain one or more lens elements, the refractive power being divided between the elements.

(10) According to one embodiment, the first lens group 11 comprises, preferably consists of, two lens elements 11A, 11B. According to one embodiment, the first lens element 11A, which comes closest to the eye, is a plano-convex lens with the planar surface facing towards the eye, whereas the neighboring second lens element 11B is a meniscus lens or the like. According to one embodiment, the second lens element 11B is a positive meniscus lens, although in some configurations it may also be a negative meniscus lens. Typically, the second lens element 11B is asperical like shown in FIGS. 1A and 1B. It should be noted that the lenses are not necessarily directly classifiable to any single category but have custom aspheric features.

(11) According to an alternative embodiment, the first lens group 11 comprises, in particular consists of, a single Fresnel lens element. However, a two-lens solution is preferred for image quality reasons.

(12) According to one embodiment, the second lens group 12 comprises, preferably consists of, a plano-concave lens element 12A, with the planar side facing the third lens group 13 and the display 14.

(13) According to one embodiment, the third lens group 13 comprises, preferably consist of, a wavefront corrector lens element 13A, which serves to correct the shape of the wavefront close to the image source. Typically, the third lens element 13A is aspheric. The third lens is static with respect to the display.

(14) According to one embodiment, the first and second lens groups 11 and 12 are movable between a first state (wide angle state) and second state (tele state) so that their distance from the third lens group is increased when moved from the first state towards the second state. In one embodiment, the first lens group travels a first distance and second lens group travels a second, longer distance from a first position in the vicinity of the third lens group to a second position in the vicinity of the first lens group.

(15) According to an alternative embodiment, the first lens group 11 is stationary and lens groups 12 and 13 movable. This will, however, also require the display to move, and in order to keep the binocular convergence calibration valid, it is not as preferred as the option where groups 11 and 12 are movable.

(16) The zoom factor is mainly limited by the increase of the system length. It may also be possible to design the system in a way of internal zooming principle, where the total length of the optical system does not change. The presented embodiment, with extendable structure is, however, preferred in applications where the shortest possible dimension of the eyepiece in the wide angle state is desired.

(17) In some embodiments, the exit pupil is located at a distance of at least 8 mm from the lens groups. This allows for convenient viewing and prevents eyelashes from hitting the eyepiece.

(18) There may also be provided diopter adjustment means, which are known per se, functionally connected to the eyepiece.

(19) FIG. 2A shows a personal display 23 according to one embodiment. The display 23 comprises a display element 24 and an eyepiece 26 of the present kind positioned so that the display element 24 covers the entire field-of-view α of the eyepiece 26 in wide angle state (and consequently also in the tele state). Thus, the viewer's eye 20, brought close to or at the exit pupil, will catch the image presented of at the display element.

(20) FIG. 2B shows an embodiment of a personal display device 23, where two eyepieces 26A, 26B of the present kind are provided in binocular configuration and targeted on different portions of a single display element 24 and for both eyes 20A, 20B of a user. Naturally, there may also be two display elements, one for each eyepiece. This way, by presenting suitably different image content at suitable positions of the display element(s) 24 or suitably positioned display elements 24 for each eye 20A, 20B, a three-dimensional experience can be provided for the user.

(21) The term personal display system, as herein used, refers to a display system intended to be viewed by a single person. Examples of personal display systems include various head-mounted displays (HMDs), such as virtual reality (VR) devices, augmented reality (AR) devices and so-called wearable smart display devices.

(22) The personal display system typically may contain all necessary components for producing, processing and displaying content for the user via the display element and the eyepiece or be adapted to function as a display unit only receiving the data to be displayed from an external source. Typically, in a minimum configuration, there is provided a processing unit functionally connected to the display element, the processing unit being capable of receiving a data signal representing the content to be displayed from an external or internal source, and controlling the display element accordingly to show the content thereon.

(23) According to one embodiment, the processing unit is adapted to apply a software-based geometric correction on the image to be displayed, taking into account the optical distortion characteristics of the eyepiece. In an alternative embodiment, the processing unit does not perform such correction. This is also possible with the present optical system, which performs well in particular in the tele state. Thus, the image seen by the user may geometrically essentially correspond to that displayed in the display element.

(24) The display element 24 may be opaque or at least partially transparent. In the latter case, a so called see-through display device can be provided where the display device is capable of passing, in addition to the image displayed at the display element, also ambient light to the user, who sees them simultaneously.

EXAMPLE

(25) An exemplary lens configuration that is schematically represented by FIGS. 1A and 1B is represented by the surface parametrization formula

(26) $z=\frac{{\mathrm{cr}}^2}{1+\sqrt{1-\left(1+k\right)c^2{r}^2}}+{\alpha }_1{r}^2+{\alpha }_2{r}^4+{\alpha }_3{r}^6+{\alpha }_4{r}^8+{\alpha }_5{r}^{10}+{\alpha }_6{r}^{12}+{\alpha }_7{r}^{14}+{\alpha }_8{r}^{16}.$
where r is the distance from optical axis, limited by semi-diameter; c is the surface curvature (inverse of surface radius of curvature); k is the conic constant and α is the aspherical coefficient.

(27) In one example, the surface data of the lenses are as listed in Table 1, starting from the exit pupil (STOP) and going towards the display (DISP). The term “Thickness” refers to a distance between centre points of successive surfaces comprising material having properties indicated in the “Refractive index” and “Abbe number columns” (which are empty for air).

(28) Exemplary aspherical coefficients of the surfaces are listed in Table 2.

(29) Exemplary design thicknesses are shown in Table 3.

(30) General properties of the exemplary eyepiece are given in Table 4.

(31) TABLE-US-00001 TABLE 1 Lens surface data Radius of Semi- curvature Thickness Refractive Abbe Diameter Surface # [mm] [mm] index n.sub.d number V.sub.d [mm] STOP PLANO 12.00 5.00 2 −269.18 5.87 1,720 34.7 20.50 3 −30.80 0.00 20.50 4 82.24 7.93 1,720 34.7 25.00 5 −267.21 Variable 25.00 6 −158.14 1.00 1,847 23.8 25.50 7 98.86 Variable 25.50 8 67.44 6.04 1,720 34.7 25.50 9 446.27 4.044 25.50 DISP PLANO 26.55

(32) TABLE-US-00002 TABLE 2 Aspherical coefficients of lens surfaces Conic Surface # constant k α1 α2 α3 α4 α5 2 0.00 0  2.260E−05 −3.374E−08 −7.406E−11  1.709E−13 3 0.00 0  2.662E−05 −1.529E−08  6.230E−11 −1.472E−13 4 0.00 0  4.485E−06  5.025E−10 −9.258E−13 −4.686E−15 5 0.00 0 −2.438E−07 −1.355E−09  2.454E−13 −2.076E−15 8 0.00 0 −7.238E−07 −1.720E−09 −2.296E−12  6.074E−17 9 0.00 0 −3.283E−06 −1.413E−09 −2.313E−13 −1.070E−15

(33) TABLE-US-00003 TABLE 3 Lens thicknesses Surface # Wide Tele 5 18,354 0.381 7 0 31.82

(34) TABLE-US-00004 TABLE 4 Eyepiece properties Property Wide Tele Focal length 32.14 44.86 F/# 3.18 4.47 FFOV [dgr] 110 60.5 Distortion % 41.9 4 Total length 69.06 55.27

(35) FIGS. 3A and 3B show distortion graphs of the exemplary eyepiece in tele and wide angle states, respectively (as seen when light is coming from the left in the configuration of FIGS. 1B and 1A).