Curved waveguide-based augmented reality device, method for operation of said device, augmented reality glasses based on said device
A curved waveguide-based augmented reality device is provided. The device includes a projector, and a curved waveguide. The waveguide has a shape of a concentric cylindrical meniscus and includes an in-coupling diffractive optical element and an out-coupling diffractive optical element, a grating period of a diffraction grating of the in-coupling diffractive optical element at each point of the in-coupling diffractive optical element is such that rays from one point of an initial image are input into the curved waveguide in each point of the in-coupling diffractive optical element at the same angle relative to a normal to a surface of the curved waveguide at a point of ray incidence, and at least at one point on each of the diffractive optical elements a diffraction grating period of the in-coupling diffractive optical element is equal to a diffraction grating period of the out-coupling diffractive optical element.
1 . An augmented reality display device comprising
a projector forming an initial image; and
a curved waveguide having a shape of a concentric cylindrical meniscus and comprising an in-coupling diffractive optical element and an out-coupling diffractive optical element,
wherein a grating period of the in-coupling diffractive optical element at each point of the in-coupling diffractive optical element is such that rays emanating from one point of the initial image undergo diffraction at the in-coupling diffractive optical element at a same angle relative to a normal to a surface of the curved waveguide at a point of incidence, and
wherein, when a point radiation source corresponding to the one point of the initial image is located at a finite distance Z LGT from a concave surface of the curved waveguide, the grating period of the in-coupling diffractive optical element in the cross-section under consideration is defined by an expression:
T
YOZ
OUT
(
L
out
)
=
λ
…
sin
(
L
out
/
R
1
)
+
λ
/
T
0
,
where Lin is a linear coordinate along a concave surface of the curved waveguide with an origin in the center of the in-coupling diffractive optical element,
R1 is a curvature radius of the concave surface of the curved waveguide,
λ is an incident radiation wavelength corresponding to the initial image, and
T o is a diffraction grating period of the in-coupling diffractive optical element in the point where ray with a wavelength λ falling on the in-coupling diffractive optical element along the normal to the surface of the curved waveguide undergoes diffraction into a −1st diffraction order by the in-coupling diffractive optical element.
2 . The device of claim 1 ,
wherein the curved waveguide is configured to propagate rays of the initial image from the in-coupling diffractive optical element to the out-coupling diffractive optical element based on total internal reflection from surfaces of the curved waveguide,
wherein, when propagating the rays of the initial image, angles of incidence on and of reflection from a concave surface of the curved waveguide inside the curved waveguide are equal to each other and constant, and angles of incidence on and of reflection from a convex surface of the curved waveguide inside the curved waveguide are equal to each other and constant.
3 . The device of claim 1 , wherein the out-coupling diffractive optical element is configured to form a virtual image on a user retina by converting the rays passed through the curved waveguide and falling on the out-coupling diffractive optical element into parallel beams of rays.
4 . The device of claim 1 , wherein at least at one point on each of diffractive optical elements, a diffraction grating period of the in-coupling diffractive optical element is equal to a diffraction grating period of the out-coupling diffractive optical element.
5 . The device of claim 4 , wherein the diffraction grating period of the in-coupling diffractive optical element is equal to the diffraction grating period of the out-coupling diffractive optical element in a center of the in-coupling diffractive optical element and in the center of the diffraction grating of the out-coupling diffractive optical element.
6 . The device of claim 5 , wherein the center of the initial image lies on the normal to a waveguide surface in the center of the in-coupling diffractive optical element, and the center of an image formed by the out-coupling diffractive optical element lies on the normal to the waveguide surface in the center of the out-coupling diffractive optical element.
7 . The device of claim 5 ,
wherein, when the projector forms an image at infinity, for each point of the in-coupling diffractive optical element with coordinates x in and L in its period is defined by an expression:
T
IN
(
x
i
n
,
L
i
n
)
=
λ
sin
(
L
i
n
R
1
)
+
λ
T
0
,
xin is a linear coordinate of the point on the waveguide surface on which the ray falls along an OinXin axis in a coordinate system OinXinYinZin,
wherein a center Oin of a coordinate system is disposed at the center of the in-coupling diffractive optical element, a Zin axis is directed along the normal to the surface of the curved waveguide, a Yin axis is directed tangentially to the surface of the curved waveguide in a point Oin along a length of the curved waveguide and perpendicularly to the Zin axis, an Xin axis is directed along a generatrix of a cylindrical surface of the curved waveguide in the point Oin across a width of the curved waveguide and perpendicularly to the Zin axis;
Lin is a linear coordinate along the concave surface of the curved waveguide with an origin in the center Oin of the in-coupling diffractive optical element,
R1 is a curvature radius of the concave surface of the curved waveguide,
λ is an incident radiation wavelength corresponding to the initial image,
T0 is a diffraction grating period of the in-coupling diffractive optical element in the point where ray with a wavelength λ falling on the in-coupling diffractive optical element along the normal to the surface of the curved waveguide undergoes diffraction into a −1st diffraction order by the in-coupling diffractive optical element, and
wherein grating grooves of the in-coupling diffractive optical element are parallel to a common axis of the cylindrical surface of the curved waveguide.
8 . The device of claim 1 ,
wherein, when the out-coupling diffractive optical element forms an image at infinity, a variation of a period of the out-coupling diffractive optical element is equal to:
T
YOZ
OUT
(
L
out
)
=
λ
-
sin
(
L
out
/
R
1
)
+
λ
/
T
0
,
Lout is a linear coordinate along the concave surface of the curved waveguide in a cross-section YoutOoutZout with an origin in a center Oout of the out-coupling diffractive optical element, where the period of the out-coupling diffractive optical element is equal to T0, a Zout axis is directed along the normal to the surface of the curved waveguide, a Yout axis is directed tangentially to the surface of the curved waveguide in a point Oout along a length of the curved waveguide and perpendicularly to the Zout axis, an Xout axis is directed tangentially to the surface of the curved waveguide in the point Oout across a width of the curved waveguide and perpendicularly to the Zout axis,
R1 is a curvature radius of the concave surface of the curved waveguide,
λ is an incident radiation wavelength corresponding to the initial image, and
wherein grating grooves of the out-coupling diffractive optical element are parallel to a common axis of the cylindrical surface of the curved waveguide.
9 . The device of claim 1 , further comprising:
two flat waveguides disposed between the projector and the in-coupling diffractive optical element,
wherein each of the flat waveguides has a constant-period diffraction grating of the flat waveguide, and
wherein grooves of the diffraction grating of each flat waveguide are perpendicular to an axis of the cylindrical surface of the curved waveguide.
10 . A method of operating an augmented reality device, the method comprising:
forming, by a projector, an initial image; and
inputting, by an in-coupling diffractive optical element, rays of the initial image into a curved waveguide,
wherein rays emanating from one point of the initial image undergo diffraction at the in-coupling diffractive optical element at a same angle relative to a normal to a surface of the curved waveguide at a point of incidence,
wherein the rays inputted into the curved waveguide propagate within the curved waveguide based on total internal reflection from surfaces of the curved waveguide; and
transforming, based on an out-coupling diffractive optical element, the rays passed through the curved waveguide into parallel beams of rays to form a virtual image on a user retina,
wherein, when a point radiation source corresponding to the one point of the initial image is located at a finite distance Z LGT from a concave surface of the curved waveguide, the grating period of the in-coupling diffractive optical element in the cross-section under consideration is defined by an expression:
T
TOZ
IN
(
L
i
n
)
=
λ
sin
(
tan
-
1
(
R
1
·
sin
(
L
i
n
/
R
1
)
Z
LGT
-
R
1
·
cos
(
L
i
n
/
R
1
)
+
R
1
)
+
L
i
n
R
1
)
+
λ
T
0
.
where Lin is a linear coordinate along a concave surface of the curved waveguide with an origin in the center of the in-coupling diffractive optical element,
R1 is a curvature radius of the concave surface of the curved waveguide,
λ is an incident radiation wavelength corresponding to the initial image, and
T o is a diffraction grating period of the in-coupling diffractive optical element in the point where ray with a wavelength λ falling on the in-coupling diffractive optical element along the normal to the surface of the curved waveguide undergoes diffraction into a −1st diffraction order by the in-coupling diffractive optical element.
11 . The method of claim 10 ,
wherein the augmented reality device includes augmented reality glasses comprising an element for left eye and an element for right eye, and
wherein each of the elements for left and right eye is an augmented reality display device.
12 . The method of claim 11 , wherein a distance between centers of an out-coupling diffractive optical elements corresponds to a user interpupillary distance.
13 . The method of claim 11 , wherein the normal to a waveguide surface in a center of the out-coupling diffractive optical element for right eye is parallel to the normal to the waveguide surface in the center of the out-coupling diffractive optical element for left eye.
14 . The method of claim 11 , wherein at least at one point on each of diffractive optical elements, a diffraction grating period of the in-coupling diffractive optical element is equal to a diffraction grating period of the out-coupling diffractive optical element.
15 . The method of claim 14 ,
wherein the diffraction grating period of the in-coupling diffractive optical element is equal to the diffraction grating period of the out-coupling diffractive optical element in the center of the in-coupling diffractive optical element and in the center of the diffraction grating of the out-coupling diffractive optical element, and
wherein the center of the initial image lies on the normal to the waveguide surface in the center of the in-coupling diffractive optical element, and the center of an image formed by the out-coupling diffractive optical element lies on the normal to the waveguide surface in the center of the out-coupling diffractive optical element.