Ergonomic Head Mounted Display Device And Optical System

• US 20120162549A1
• Filed: 12/22/2011
• Published: 06/28/2012
• Est. Priority Date: 12/24/2010
• Status: Active Grant

• Current Assignee: Magic Leap, Inc.
• Original Assignee: Magic Leap, Inc.
• Inventors: Hua, Hong, Gao, Chunyu, Lin, Yuxiang
• Granted Patent: US 9,348,143 B2
• Time in Patent Office: Days
• US Class Current: 349/11
• CPC Class Codes: G02B 2027/011 comprising device for correcting geometrical aberrations, distortion
• CPC Class Codes: G02B 2027/0123 comprising devices increasing the field of view
• CPC Class Codes: G02B 2027/013 comprising a combiner of particular shape, e.g. curvature
• CPC Class Codes: G02B 2027/0178 Eyeglass type eyeglass details G02C
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 27/0176 characterised by mechanical features
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02B 5/30 Polarising elements light-modulating devices with active elements G02F1/00
• CPC Class Codes: G02B 6/003 Lens or lenticular sheet or layer

Abstract

This invention concerns an ergonomic optical see-through head mounted display device with an eyeglass appearance. The see-through head-mounted display device consists of a transparent, freeform waveguide prism for viewing a displayed virtual image, a see-through compensation lens for enabling proper viewing of a real-world scene when combined together with the prism, and a miniature image display unit for supplying display content. The freeform waveguide prism, containing multiple freeform refractive and reflective surfaces, guides light originated from the miniature display unit toward a user'"'"'s pupil and enables a user to view a magnified image of the displayed content. A see-through compensation lens, containing multiple freeform refractive surfaces, enables proper viewing of the surrounding environment, through the combined waveguide and lens. The waveguide prism and the see-through compensation lens are properly designed to ergonomically fit human heads enabling a wraparound design of a lightweight, compact, and see-through display system.

Claims

1. A freeform waveguide prism comprising at least three physical surfaces each of which contains a plurality of reflective and refractive freeform optical surfaces disposed upon the physical surfaces, where the interior space of the physical surfaces is filled by a refractive medium having an index (n) greater than 1, where the plurality of reflective surfaces folds and extends the optical path length so that the waveguide can be fit to an eyeglass shape, which enables an image display unit to be placed at the side of the head, and which enables a wide see-through field of view of up to 90°

relative to a straight ahead view in the temple directions, and 60°

in the nasal direction, and up to 60°

above and below relative to a straight ahead view, where the inner and outer surfaces are designed, within the constraint of fitting an eyeglass form factor and a maximum thickness, so that the plurality of freeform reflective surfaces guide light towards a pupil of a user without distorting the image,

the physical and optical surfaces comprising;

a. a physical inner surface 115, disposed towards the pupil of the user, where the physical inner surface is constrained to approximate a pre-designated curved surface for an eyeglass form factor, where the inner surface contains a plurality of freeform reflective surfaces optimized to reflect an image to the eyeball of the user with a minimum amount of distortion, and at least one refractive surface;

b. a physical outer surface 125, disposed towards an external scene, where the physical outer surface contains a plurality of freeform reflective surfaces optimized to reflect an image to the pupil of the user with a minimum amount of distortion, where the physical outer surface is within a maximum distance of the inner surface at all points, where the physical outer surface contains at least one refractive surface to allow light from the external scene to pass through the waveguide and reach the eyeball of the user;

c. a physical edge surface 120, which optionally contains a refractive surface for light from an image display unit to enter the waveguide;

d. a refractive input surface 130, disposed on one of the physical surfaces, that allows light from an image display unit to enter the waveguide;

e. a refractive output surface 135 that allows light to exit the waveguide, disposed upon the physical inner surface, near the pupil of the user;

f. a plurality of three (3) or more freeform reflective surfaces, disposed upon the physical inner and outer surfaces, where each reflection is produced by either satisfying the Total Internal Reflection criterion, or by the application of a semi-transparent, partially reflective coating to the surface of the waveguide;

where these reflections are optimized to guide the light along the interior of the prism with a minimum of distortion, where the plurality of reflections extends the optical path length such that the prism enables a wide see-through field of view, and a size suitable to fitting to the human head;

whereupon light 140 from an image display unit 105 enters the waveguide, through a first refractive surface 130;

whereupon the light 140 follows a path 145 along the waveguide that comprises a plurality of reflections upon the plurality of reflective surfaces, from the first refractive surface 130 to the second refractive surface 135, where each reflection is produced either by satisfying conditions of Total Internal Reflection, or by a semi-transparent coating applied to the surface;

whereupon light 140 passes through the second refractive surface 135 beyond which where the user places his or her pupil 150 to view the image;

whereupon light 198 from the real-world scene is refracted through the physical outer surface 125 of the waveguide 100 and the physical inner surface 115 of the waveguide before reaching the pupil 150, where the see-through field of view through the waveguide is up to 90°

in the temple direction, up to 60°

in the nasal direction, and up to 60°

above and below a straight ahead'"'"'view.

2. The waveguide of claim 1, where the plurality of reflections extends the optical path length so that the waveguide has a width of greater than 25 mm, from pupil to temple.

3. The waveguide of claim 1, where the constraints upon the inner surface comprise:

a. a first reference curved surface 230, which approximates the shape of an average human head, where the inner surface is constrained to lie outside of the first reference surface;

b. a second reference surface 240, which limits the extent to which the waveguide projects out from a face of a user, where the inner surface is constrained to lie inside of the second reference surface;

c. a maximum distance between the inner physical surface 115 and outer physical surface 225;

d. an upper and lower bound on the width 244 of the prism from a pupil to a temple in the horizontal dimension, so that the prism reaches the side of the head and is sufficiently wide to yield the designated see-through field of view set by the upper extent 290a, but does not stick out too far beyond the side of the head;

e. an upper and lower bound on the width 246 of the prism from pupil to a nose in the horizontal dimension, so that the prism is sufficiently wide to yield the designated see-through field of view set by the lower extent 290b, but does not interfere with the nose bridge;

f. a lower bound on the height of the prism from pupil in the vertical dimension, so that the prism is sufficiently wide to yield the designated see-through field of view set by the upper 290c or lower 290d extents;

g. a surface segment 215a, where the inner surface is constrained to fit an eyeglass form factor, where the width of the surface segment is bounded by the upper 290a and lower 290b extent of the designated see-through field of view in the horizontal direction, and the height of the surface segment is bounded by the upper 290c and lower 290d extent of the see-through field of view in the vertical direction, projected on the inner surface, where the local radius of curvature of the surface segment is bounded by a range dependent on the eyeglass form factor;

whereupon the shape of the inner and outer prism surfaces are optimized to minimize optical distortion from the entry point of the waveguide to the exit point of the waveguide within these constraints.

4. The waveguide of claim 3, where the specific constraints:

a. the center of the first reference curved surface is defined by reference dimensions Y_ref1, the distance between the midline of the head and the center of the reference surface to the temple side of the head, Z_ref1, the distance between the pupil and the center of the reference surface from front to back of the head, and Y_HIPD, where Y_HIPD is the distance from the pupil to the midpoint of the head, where typically Y_ref1 is in the range of 0 to 40 mm, Z_ref1 is in the range of 30 to 90 mm, and Y_HIPD is in the range of 20 to 40 mm;

the radius of curvature of the first reference surface is in the range of 40 to 100 mm in the horizontal dimension;

b. the position of the second reference surface is defined by reference dimension Z_ref2, the distance from the pupil to the reference surface, where typically Z_ref2 is less than 40 mm;

c. the maximum distance between the inner physical surface and outer physical surface is less than 40 mm;

d. the upper bound on the width of the prism in the temple direction is 80 mm;

e. the lower bound on the width of the prism in the temple direction is 15 mm;

f. the upper bound on the width of the prism from pupil to nose is 40 mm;

g. the lower bound on the width of the prism from pupil to nose is 8 mm.

5. The waveguide of claim 3, where the shape of the inner surface is constrained by approximating the appearance of a designated eyeglass form factor, where this eyeglass form factor is any of a number of industry standard form factors, including but not limited to 2-base, 3-base, 4-base, 5-base, 6-base, 7-base, 8-base, and 9-base.

6. The waveguide of claim 3, where the shape of the inner surface segment in the horizontal dimension approximates a curve with a radius between 50 mm and 100 mm to approximate the appearance of 8-base eyeglass form factor.

7. The waveguide of claim 3, the shape of the inner surface segment in the horizontal dimension approximates a curve with a radius between 100 mm and 500 mm to approximate the appearance of 4-base eyeglass form factor.

8. The waveguide of claim 1, where each physical surface of the waveguide contains one or more freeform surface segments, where each surface segment is described by a unique set of parameters.

9. The waveguide of claim 8, where multiple surface segments are connected by intermediate segments that are designed to maintain first order continuity with the adjoining segments.

10. The waveguide of claim 8, where any intersection points between surface segments are constrained to lie outside the upper boundary 290a of the see-through field of view 290.

11. The waveguide of claim 8, where the position of the intersection points are constrained such that there is a minimum 1 mm ray-free gap around the intersection points, where light entering the prism at the first refractive surface does not reach.

12. The waveguide of claim 1, where a semi-transparent coating is applied to surfaces that satisfy conditions of total internal reflection, a dielectric semi-transparent coating is applied so that they continue to satisfy this condition.

13. The waveguide of claim 1, where a mirror coating is applied to portions of the outer surface of the waveguide that are outside of the upper boundary 290a of the see-through field of view 290.

14. The waveguide of claim 1, where the surfaces are designed to refocus rays entering the waveguide at an intermediate point inside the waveguide, producing an intermediate image, a consequence of which is an increased optical power of the waveguide with an extended optical path length.

15. The optical waveguide of claim 1-2, where the waveguide contains five (5) reflective surfaces;

wherein light entering the waveguide is reflected consecutively five times (R1-R5) by the reflective surfaces before exiting through a refractive surface 435;

where the outer reflective surfaces are part of a single smooth outer surface 425 with the same surface parameters, and the inner surfaces are part of another single smooth inner surface 415 with the same surface parameters;

where the inner surface is constrained according to an 8-base eyeglass form factor;

where ray bundles 440a, 440b, and 440c enter the prism through a refractive surface 430 that lies along the edge of the prism, where the first (R1) and second (R2) reflections after entering the prism satisfy conditions of total internal reflection, where the third (R3), fourth (R4), and fifth (R5) reflections do not satisfy conditions of total internal reflection and instead have a semi-transparent coating applied.

16. The optical waveguide of claim 1-2, where the inner physical surface of the waveguide is segmented into two separate freeform surfaces with distinct parameters, where the waveguide contains five (5) reflective surfaces, wherein light entering the waveguide is reflected five times by the reflective surfaces (R1-R5) before exiting through a refractive surface 535;

where the outer reflective surfaces are part of a single smooth surface 525 with the same surface parameters;

where the inner is broken into two surface segments 515a and 515b, each of which is a single smooth surface with a set of unique parameters, where the first refractive surface 530 and the first inner surface segment 515a are described by the same set of freeform surface parameters;

where the second inner surface segment 515b is constrained to fit an 8-base eyeglass form factor, where the first and second inner surface segments are connected by an intermediate segment 515c;

where light enters the prism through the first refractive surface 530 and exits through the second refractive surface 535, whereupon it is projected into the users eyeball;

where the first and last reflections along the light'"'"'s path do not satisfy the total internal reflection criterion, and these surfaces have a semi-transparent coating applied, where the second, third and fourth reflections satisfy the total internal reflection criterion and the third reflection has a dielectric coating applied.

17. The waveguide of claim 16, where the intermediate surface segment 515c is designed to maintain first order continuity with the first or second inner surface segments 515b 515c.

18. The waveguide of claim 16, where a mirror coating is applied to the outer physical surface 525 outside the upper boundary of the see-through field of view 590a, in order to facilitate the first reflection (R1).

19. The waveguide of claim 1-2, where the waveguide is shaped for a flat design, where the waveguide comprises five (5) reflective surfaces, where light enters the first refractive surface 630, where the rays are reflected five times by the reflective surfaces;

where the outer reflective surfaces are part of a single smooth outer surface 625 with the same surface parameters;

where the inner surface 616 is another single smooth surface with the same surface parameters, but separate from the refractive surface 630;

where the rays are refracted out of the waveguide to the exit pupil 650 where they comprise a color image;

where the first and last reflections do not satisfy the total internal reflection criterion and have a semi-transparent coating applied, where the second, third and fourth surfaces satisfy the total internal reflectance criterion and the third reflection has a dielectric coating applied, where a mirror coating is applied to the outer surface 626a of the waveguide beyond the upper bound 690a of the see-through field of view 690.

20. The waveguide of claims 1-2, where the optical properties of the waveguide are designed so that a coupling lens is not necessary, as the waveguide itself is sufficient to correct for optical aberration.

21. The waveguide of claims 1-2 where the outer surface is broken into two segments 725a 725b, where the two segments are connected by a third segment 725c;

where the inner surface 715 is constrained to meet a 4-base eyeglass form factor;

where the segmentation of the outer surface facilitates meeting the optical requirements within the eyeglass form factor constraints.

22. The waveguide of claim 21, where the intermediate outer surface segment 725c is designed to maintain first order continuity with the first or second outer surface segments 725a and 725b.

23. The waveguide of claims 1-2, where the waveguide comprises five (5) reflective surfaces, where both the inner and outer physical surfaces are segmented into distinct segments;

where the first inner surface 815a contains the first refractive surface and the second reflective surface, the second inner surface segment 815b contains the fourth reflective surface and the second refractive surface 835, where the first outer surface segment 825a contains the first reflective surface, and the second outer surface segment 825b contains the third and fifth reflective surfaces;

where a third inner surface segment 815c connects the first and second inner surface segments, where a third outer surface segment 825c connects the first and second outer surface segments and is designed to maintain first order continuity with them;

where the inner surface segment 815b is constrained to approximate an 8-base eyeglass form factor;

whereupon light enters the first refractive surface of the waveguide 830, and is reflected five times (R1-R5) before exiting the waveguide at the second refractive surface 835;

24. The waveguide of claim 23, where the inner physical surface of the waveguide 915, is constrained to approximate a 4-base form factor instead of an 8-base form factor.

25. The waveguide of claim 1-2, where the waveguide comprises three (3) reflective surfaces, where light enters the first refractive surface 1030 of the waveguide, where the rays are reflected three times by the reflective surfaces;

where the outer reflective surfaces are part of a single smooth surface 1025 with the same surface parameters;

where the first refractive surface 1030 is not part of the inner surface 1015 of the waveguide, where the light is projected out of the refractive surface 1035 before reaching the exit pupil 1050;

where the first and second reflections (R1-R2) satisfy conditions of total internal reflection, and the third reflective surface R3 does not satisfy conditions of total internal reflection and has a semi-transparent coating applied to the outer surface 1025, where a dielectric coating is applied to the outer surface, where the inner surface is constrained to fit an 8-base form factor, and the surfaces are jointly designed to provide a wide see-through field of view.

26. The waveguide of claim 1, where surfaces satisfying the total internal reflectance criterion, which are part of the same physical surface as surfaces not satisfying total internal reflectance, also have a semi-transparent coating applied;

where the surfaces that satisfy the total internal reflectance criterion have a dielectric semi-transparent coating applied so that they continue to meet the total internal reflectance criterion.

27. The waveguide of claim 1, where rays from the same pixel of an image display unit 105 intersect at least once inside the waveguide 100, producing an intermediate image at this intermediate point.

30. The apparatus of claim 29, where the waveguide 100 and compensation lens 160 surfaces are jointly optimized for a maximum see through field of view with a minimum of distortion, under the constraint that the total thickness of the waveguide 100 and compensation lens 160 be no more than a maximum thickness, and the size of the air gap 195 be no more than a maximum thickness, in addition to the constraints listed for the waveguide in claim 2.

28. A compensation lens 160, to be used for viewing an external world in series with the waveguide prism, which corrects for optical distortion caused by viewing the world through the waveguide prism;

where the compensation lens comprises;

i. a refractive outer surface 170, disposed towards an external scene, that allows light 198 from the external scene to enter the compensation lens,

ii. a refractive inner surface 165, disposed towards the outer surface 125 of the waveguide prism 100, which allows light to exit the compensation lens and enter into the waveguide prism 100,

where the refractive inner and outer surfaces of the compensation lens 165 are designed to compensate for the effect of ray shift and distortion caused by the waveguide so that the user maintains a clear see-through view when observing the world through both lenses;

where the refractive inner surface 165, is typically constrained to approximate the shape of the outer surface 125 of the waveguide prism 100,

whereupon light 198 from the real-world scene is refracted through the refractive outer surface 170 and the refractive inner surface 165 of compensation lens 160, before reaching the waveguide 100.

29. An image display system which projects displayed virtual image into a pupil of a user through a waveguide prism, allowing the user to see displayed content overlaid upon a real world scene, where the system has a wide see-through field of view, of up to 90°

in the temple direction, 60°

in the nasal direction, and 60°

above and below a straight-ahead view, and where the system fits into the shape of an eyeglass form factor, the system comprising;

a. An image display unit 105, disposed towards the temple side of a users head, which projects light into a waveguide, where the image display unit is constrained to be outside of a reference curved surface defined by the shape of an average human head;

b. an optional coupling lens group 110, disposed between the image display unit and a waveguide, composed of one or more lenses, which guide light from the image display unit 105 into the waveguide 100 and corrects for optical aberration;

c. a transparent optical waveguide prism 100, which accepts the light from the image display unit and propagates the light until the image is projected into the field of view of the user;

where the waveguide has a physical inner surface 115, physical edge surface 120 and physical outer surface 125, a first refractive surface 130, and a second refractive surface 135, and a plurality of reflective surfaces, where the waveguide has a shape that fits into an eyeglass form factor and has a wide see-through field of view of up to 90°

in the temple direction, 60°

in the nasal direction, and 60°

above and below a straight-ahead view;

d. a compensation lens 160, secured to the physical outer surface 125 of the waveguide 100, which corrects for optical distortion caused by viewing the world through the waveguide prism;

where the inner surface of the compensation lens 165 approximates the shape of the outer surface 125 of the waveguide;

where a small air gap 195 is maintained between the compensation lens and the waveguide on surfaces where the total internal reflection criterion is satisfied for the outer surface 125 of the waveguide;

whereupon the image display unit 105 transmits light 140 into the optional coupling lens 110 followed by the waveguide 100, or into the waveguide directly, through a first refractive surface 130;

whereupon the light 140 follows a path 145 along the waveguide that comprises a plurality of reflections from the first refractive surface 130 to the second refractive surface 135;

whereupon light 140 passes through the second refractive surface 135 beyond which where the user places his or her pupil 150 to view the image;

whereupon light 198 from the real-world scene passes through the compensation lens 160 and the waveguide 100 before reaching the pupil 150, where the see-through field of view of the real-world scene is up to 90°

in the temple direction, 60°

in the nasal direction, and 60°

above and below a straight-ahead view.

31. The apparatus of claim 29, where the maximum thickness constraint of the joint waveguide and compensation lens is 40 mm and the maximum thickness of the air gap is 6 mm.

32. The apparatus of claim 29-31 where an index matching glue is used, between the outer physical surface of the waveguide 125 and the inner surface 165 of the compensation lens, on portions of the waveguide outer surface 125 where the total internal reflection criterion is not used to produce a reflection, to cement the compensation lens 160 to the waveguide 100, and where an air gap 195 is otherwise maintained.

33. The apparatus of claim 29, where the image display unit 405 is disposed facing the waveguide first refractive surface 430, which lies on an edge surface of the waveguide, where there is a coupling lens 410 between the image display unit and the waveguide prism 400 which corrects for optical aberration and improves the image quality;

where the image display unit 405 emits ray bundles 440a 440b 440c which enter the waveguide through a first refractive surface 430, are reflected five times by the reflective surfaces before exiting through a second refractive surface 435, before reaching the user'"'"'s pupil 450;

34. The apparatus of claim 29, where the image display unit 505 is disposed facing the inner surface of the waveguide, where the image display unit emits three ray bundles 540a 540b 540c which enters the first inner refractive surface 530 of the waveguide, where the rays are reflected five times by the reflective surfaces (R1-R5);

before reaching the exit pupil 550 where they comprise a virtual image, where there is a coupling lens 510 between the image display unit and the waveguide prism which corrects for optical aberration and improves the image quality;

35. The apparatus of claim 29, where there is a coupling lens 610 between the image display unit 605 and the waveguide prism 600 which corrects for optical aberration and improves the image quality;

36. The apparatus of claim 29, where the image display unit 105 is based on a reflective-type illuminated pixel array such as Liquid Crystal on Silicon (LCOS) microdisplay technology, Ferroelectric Liquid Crystal on Silicon (FLCoS), or other similar microdisplays, where the image display unit 805 comprises:

a. A reflective-type illuminated pixel array micro-display panel 806a

b. A field lens 805b

c. A polarized beam splitter 805c

where the field lens 805b enforces telecentricity of light on the display surface,

where the beam splitter 805c acts as a beam combiner to merge the illumination light path.