Optical see-through free-form head-mounted display
A see-through free-form head-mounted display including a wedge-shaped prism-lens having free-form surfaces and low F-number is provided.
1. A free-form prism-lens for use in an optical see-through head-mounted display, comprising:
a first free-form surface configured to receive light from a micro-display and configured to transmit the received light into the body of the prism-lens;
a second free-form surface configured to receive the light transmitted into the body of the prism-lens from the first free-form surface and configured to totally internally reflect the received light at the second surface; and
a third free-form surface configured to receive the light reflected by the second free-form surface and configured to reflect the light out of the prism-lens,
wherein the prism-lens has an f-number less than 3.5 and an effective focal length of 21 mm or less, wherein the exit pupil diameter is at least 6 mm.
2. The free-form prism-lens according to claim 1 , wherein the first free-form surface is described by
z
=
c
(
x
2
+
y
2
)
1
+
sqrt
(
1
-
(
1
+
k
)
c
2
(
x
2
+
y
2
)
)
+
∑
j
=
2
66
C
j
x
m
y
n
,
j
=
[
(
m
+
n
)
2
+
m
+
3
n
]
/
2
+
1
,
where the z is the sag of the first free-form surface measured along the z-axis of a local x, y, z coordinate system, c is the vertex curvature (CUY), k is the conic constant, and C j is the coefficient for x m y n .
3. The free-form prism-lens according to claim 2 , wherein the second free-form surface is described by
z
=
c
(
x
2
+
y
2
)
1
+
sqrt
(
1
-
(
1
+
k
)
c
2
(
x
2
+
y
2
)
)
+
∑
j
=
2
66
C
j
x
m
y
n
,
j
=
[
(
m
+
n
)
2
+
m
+
3
n
]
/
2
+
1
,
where the z is the sag of the second free-form surface measured along the z-axis of a local x, y, z coordinate system, c is the vertex curvature (CUY), k is the conic constant, and C j is the coefficient for x m y n .
4. The free-form prism-lens according to claim 3 , wherein the third free-form surface is described by
z
=
c
(
x
2
+
y
2
)
1
+
sqrt
(
1
-
(
1
+
k
)
c
2
(
x
2
+
y
2
)
)
+
∑
j
=
2
66
C
j
x
m
y
n
,
j
=
[
(
m
+
n
)
2
+
m
+
3
n
]
/
2
+
1
,
where the z is the sag of the third free-form surface measured along the z-axis of a local x, y, z coordinate system, c is the vertex curvature (CUY), k is the conic constant, and C j is the coefficient for x m y n .
5. The free-form prism-lens according to claim 1 , wherein at least one surface of the free-form prism-lens is described by
z
=
c
(
x
2
+
y
2
)
1
+
sqrt
(
1
-
(
1
+
k
)
c
2
(
x
2
+
y
2
)
)
+
∑
j
=
2
66
C
j
x
m
y
n
,
j
=
[
(
m
+
n
)
2
+
m
+
3
n
]
/
2
+
1
,
z
=
c
x
x
2
+
c
y
y
2
1
+
sqrt
(
1
-
(
1
+
k
x
)
c
x
x
2
-
(
1
+
k
y
)
c
y
y
2
)
+
∑
j
=
1
37
C
j
x
2
m
y
n
2
m
+
n
≤
10
,
m
=
0
,
1
,
2
,
3
,
4
,
5
,
n
=
0
,
1
,
…
,
10
where the z is the sag of the at least one surface measured along the z-axis of a local x, y, z coordinate system, c x is the radius of curvature of the at least one surface in the sagittal direction, c y is the radius of curvature of at least one surface in the tangential direction, and C j is the coefficient for x 2m y n .
6. The free-form prism-lens according to claim 1 , wherein the third free-form surface is partially mirrored to permit the internally reflected light to be reflected by the second free-form surface and to permit light from a real-world view to be transmitted through the third free-form surface to the exit pupil.
7. The free-form prism-lens according to claim 1 , wherein second and third free-form surfaces are configured to provide a wedge-shaped prism lens.
8. The free-form prism-lens according to claim 1 , wherein the z-axis is parallel to the optical axis at the exit pupil, and the prism lens is symmetric about the y-z plane and asymmetric about the x-z plane.
9. The free-form prism-lens according to claim 1 , wherein the diagonal field of view is at least 40 degrees.
10. The free-form prism-lens according to claim 1 , wherein the modulation transfer function is at least 10%×30 lps/mm.
11. The free-form prism-lens according to claim 1 , wherein the eye clearance is at least 16 mm.
12. The free-form prism-lens according to claim 1 , comprising an auxiliary lens disposed proximate the third free-form surface, the auxiliary lens configured to minimize the shift and distortion of rays from a real-world scene by the second and third surfaces of the prism-lens.
13. The free-form prism-lens according to claim 12 , wherein the auxiliary lens has a surface with the same shape as the third free-form surface of the prism-lens and is disposed in optical contact with the third free-form surface of the prism-lens.
14. The free-form prism-lens according to claim 13 , wherein at least one surface of the auxiliary lens is described by
z
=
c
(
x
2
+
y
2
)
1
+
sqrt
(
1
-
(
1
+
k
)
c
2
(
x
2
+
y
2
)
)
+
∑
j
=
2
66
C
j
x
m
y
n
,
j
=
[
(
m
+
n
)
2
+
m
+
3
n
]
/
2
+
1
,
where the z is the sag of the at least one free-form surface measured along the z-axis of a local x, y, z coordinate system, c is the vertex curvature (CUY), k is the conic constant, and C j is the coefficient for x m y n .
15. The free-form prism-lens according to claim 14 , wherein the modulation transfer function is at least 10%×30 lps/mm across the entire visual field.
16. The free-form prism-lens according to claim 12 , wherein at least one surface of the auxiliary lens is described by
z
=
c
(
x
2
+
y
2
)
1
+
sqrt
(
1
-
(
1
+
k
)
c
2
(
x
2
+
y
2
)
)
+
∑
j
=
2
66
C
j
x
m
y
n
,
j
=
[
(
m
+
n
)
2
+
m
+
3
n
]
/
2
+
1
,
z
=
c
x
x
2
+
c
y
y
2
1
+
sqrt
(
1
-
(
1
+
k
x
)
c
x
x
2
-
(
1
+
k
y
)
c
y
y
2
)
+
∑
j
=
1
37
C
j
x
2
m
y
n
2
m
+
n
≤
10
,
m
=
0
,
1
,
2
,
3
,
4
,
5
,
n
=
0
,
1
,
…
,
10
where the z is the sag of the at least one surface measured along the z-axis of a local x, y, z coordinate system, c x is the radius of curvature of the at least one surface in the sagittal direction, c y is the radius of curvature of at least one surface in the tangential direction, and C j is the coefficient for x 2m y n .
17. The free-form prism-lens according to claim 16 , wherein the modulation transfer function is at least 10%×30 lps/mm across the entire visual field.
18. The free-form prism-lens according to claim 1 , wherein the prism-lens has an f-number less than 2.