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.
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 any one of the preceding claims, 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 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 .
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 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 .
5 . 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.
6 . 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.
7 . 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.
8 . The free-form prism-lens according to claim 1 , wherein the diagonal field of view is at least 40 degrees.
9 . The free-form prism-lens according to claim 1 , wherein the exit pupil diameter is at least 6 mm.
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 12 or 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 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 .