Ergonomic head mounted display device and optical system

• US 9,348,143 B2
• Filed: 12/22/2011
• Issued: 05/24/2016
• Est. Priority Date: 12/24/2010
• Status: Active Grant

• Current Assignee: Magic Leap, Inc.
• Original Assignee: Magic Leap, Inc.
• Inventors: Gao, Chunyu, Hua, Hong, Lin, Yuxiang
• Primary Examiner(s): Stahl, Mike
• Application Number:
  US13/335,884
• Publication Number:
  US 20120162549A1
• Time in Patent Office: 1,615 Days
• Field of Search: None
• US Class Current: 1/1
• 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 comprising at least three physical surfaces, at least one of which contains a plurality of reflective and refractive freeform optical surfaces disposed thereon, where an interior space defined by the physical surfaces is filled by a refractive medium having an index (n) greater than 1, where the plurality of reflective and refractive surfaces folds and extends an optical path length so that the waveguide can be fit to an eyeglass shape, which enables an image display unit to be placed at a side of a head, and which enables a wide see-through field of view of up to 90°

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

in a nasal direction, and up to 60°

above and below relative to a straight ahead view, where inner and outer surfaces thereof are designed, within a constraint of fitting an eyeglass form factor and a maximum thickness, so that the plurality of freeform reflective and refractive optical 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 is configured to reflect an image to an eyeball of the user with a minimum amount of distortion;

(b) a physical outer surface 125, disposed towards an external scene, where the physical outer surface is configured 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; and

(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 a Total Internal Reflection criterion, or by 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 waveguide with a minimum of distortion, where a plurality of reflections extends the optical path length such that the waveguide enables a wide see-through field of view, and a size suitable to fitting to a human head;

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

whereupon the light 140 follows a path 145 along the waveguide that comprises the plurality of reflections upon the plurality of reflective and refractive surfaces, from the refractive input surface 130 to the refractive output 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 refractive output surface 135 beyond which the user places the pupil 150 to view the image;

whereupon light 198 from the external 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 directions, 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 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 curved surface;

(b) a second reference surface 240, which limits an 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 a width 244 of the waveguide from a pupil to a temple in a horizontal dimension, so that the waveguide reaches the side of the head and is sufficiently wide to yield a designated see-through field of view set by an upper extent 290a thereof;

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

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

(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 a horizontal direction, and a height of the surface segment is bounded by the upper 290c and lower 290d extent of the see-through field of view in a vertical direction, projected on the inner surface, where a 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 waveguide surfaces are optimized to minimize optical distortion from an entry point of the waveguide to an exit point of the waveguide within these constraints.

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

(a) the center of the first reference curved surface is defined by reference dimensions Y_ref1, the distance between a midline of the head and the center of the reference surface to a 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 a 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;

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

(b) a position of the second reference surface is defined by reference dimension Z_ref2, the distance from the pupil to the reference surface, where 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 waveguide in the temple direction is 80 mm;

(e) the lower bound on the width of the waveguide in the temple direction is 15 mm;

(f) the upper bound on the width of the waveguide from pupil to nose is 40 mm; and

(g) the lower bound on the width of the waveguide 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 an upper boundary 290a of a see-through field of view 290.

11. The waveguide of claim 8, where the position of intersection points are constrained such that there is a minimum 1 mm ray-free gap around the intersection points, where light entering the waveguide at the refractive input 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.

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 an upper boundary 290a of a 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 waveguide of claim 1 or 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; and

where ray bundles 440a, 440b, and 440c enter the waveguide through a refractive surface 430 that lies along the edge of the waveguide, where the first (R1) and second (R2) reflections after entering the waveguide 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 occur at regions where a semi-transparent coating has been applied.

16. The waveguide of claim 1 or 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 surface is broken into first and second inner surface segments 515a and 515b, each of which is a single smooth surface with a set of unique parameters, where the refractive input 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 inner surface segment 515c;

where light enters the waveguide through the refractive input surface 530 and exits through the refractive output surface 535, whereupon it is projected into the user'"'"'s eyeball; and

where the first and last reflections along the light'"'"'s path do not satisfy the total internal reflection criterion, and occur at regions where a semi-transparent coating has been applied, where the second, third and fourth reflections satisfy the total internal reflection criterion and the third reflection occurs at a region where a dielectric coating has been applied.

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

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

19. The waveguide of claim 1 or 2, where the waveguide is shaped for a flat design, where the waveguide comprises five (5) reflective surfaces, where light enters the refractive input surface 630, where 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 an exit pupil 650 where they comprise a color image; and

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

20. The waveguide of claim 1 or 2, where 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 claim 1 or 2, where the outer surface is broken into first and second outer surface segments 725a and 725b, where the two segments 725a and 725b are connected by a third outer surface segment 725c;

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

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

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

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

where a first inner surface 815a contains the refractive input surface and a second reflective surface, a second inner surface segment 815b contains a fourth reflective surface and the refractive output surface 835, where a first outer surface segment 825a contains the first reflective surface, and a second outer surface segment 825b contains 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 second inner surface segment 815b is constrained to approximate an 8-base eyeglass form factor; and

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

24. The waveguide of claim 1, where the inner physical surface of the waveguide 915, is constrained to approximate a 4-base form factor.

25. The waveguide of claim 1 or 2, where the waveguide comprises three (3) reflective surfaces, where light enters the refractive input 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 refractive input 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; and

where 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.

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.