Multifocal lens
The invention relates to a multifocal lens 1 having several concentric diffractive zones 7, 8, 9, 10 on a lens surface 2 , wherein in each diffractive zone a diffraction phase structure is defined, which is expressible by the following function or by a smoothed version of the function: ϕ ( ξ ) = 2 π × { p 1 ξ , 0 ≤ ξ < w 1 p 2 ξ + q 2 , w 1 ≤ ξ < w 2 p 3 ξ + q 3 , w 2 ≤ ξ < 1 , wherein ξ indicates a position within the respective diffractive zone in a radial direction, φ(ξ) indicates a phase shift experienced by light passing through the position indicated by ξ, w 1 and w 2 define a spatial partitioning of the respective diffractive zone in the radial direction, p 1 , p 2 and p 3 indicate gradients and q 2 and q 3 are constants. The position ξ depends quadratically on a radial distance to the center of the lens surface and is normalized with respect to the radial width of the respective diffractive zone and the gradients p 1 , p 2 and p 3 are negative.
1 . A multifocal lens ( 1 ) having several concentric diffractive zones L 8 , 9 , 10 ) on a surface ( 2 ) of the lens, wherein in each diffractive zone ( 7 , 8 , 9 , 10 ) a diffraction phase structure is defined, which diffraction phase structure is expressible by the following piecewise function, which comprises three phase terms:
ϕ
(
ξ
)
=
2
π
×
{
p
1
ξ
,
0
≤
ξ
<
w
1
p
2
ξ
+
q
2
,
w
1
≤
ξ
<
w
2
p
3
ξ
+
q
3
,
w
2
≤
ξ
<
1
,
wherein ξ indicates a position within the respective diffractive zone ( 7 , 8 , 9 , 10 ) in a radial direction, φ(ξ) indicates a phase shift experienced by light passing through the position indicated by ξ, w 1 and w 2 define a spatial partitioning of the respective diffractive zone ( 7 , 8 , 9 , 10 ) in the radial direction in accordance with the three phase terms, p 1 , p 2 and p 3 indicate gradients of the three phase terms and q 2 and q 3 are constants, wherein ξ depends quadratically on a radial distance to the center of the surface ( 2 ) of the lens ( 1 ) and is normalized with respect to the radial width of the respective diffractive zone ( 7 , 8 , 9 , 10 ), and wherein the gradients p 1 , p 2 and p 3 are negative.
2 . The multifocal lens as defined by claim 1 , wherein the lens ( 1 ) is a trifocal lens with diffractive orders 0, +1 and +2.
3 . The multifocal lens as defined by claim 2 , wherein the constants q 2 and q 3 are positive.
4 . The multifocal lens as defined by claim 2 , wherein the gradient p is within a range from −1.2 to −0.4, the gradient p 2 is within a range from −1.0 to −0.1, the gradient p 3 is within a range from −1.2 to −0.4, the constant q 2 is within a range from −0.2 to 0.3 and the constant q 3 is within a range from 0.4 to 1.2.
5 . The multifocal lens as defined by claim 1 , wherein the constants q 2 and q 3 are positive.
6 . The multifocal lens as defined by claim 5 , wherein the gradient p 1 is within a range from −1.1 to −1.0, the gradient p 2 is within a range from −1.1 to −1.0, the gradient p 3 is within a range from −1.1 to −1.0, the constant q 2 is within a range from 0.3 to 0.4 and the constant q 3 is within a range from 1.0 to 1.1.
7 . The multifocal lens as defined by claim 5 , wherein the gradient p 1 is within a range from −1.2 to −1.0, the gradient p 2 is within a range from −1.3 to −1.2, the gradient p 3 is within a range from −1.2 to −1.0, the constant q 2 is within a range from 0.7 to 0.8 and the constant q 3 is within a range from 1.0 to 1.2.
8 . The multifocal lens as defined by claim 1 , wherein the gradient p 1 is within a range from −1.2 to −0.4, the gradient p 2 is within a range from −1.0 to −0.1, the gradient p 3 is within a range from −1.2 to −0.4, the constant q 2 is within a range from −0.2 to 0.3 and the constant q 3 is within a range from 0.4 to 1.2.
9 . The multifocal lens as defined by claim 1 , wherein the constant w 1 is 0.25 and the constant w 2 is 0.75 such that the radial width of the middle phase term is twice the radial width of the inner phase term.
10 . The multifocal lens as defined by claim 1 , wherein the outer border ( 11 ) of at least the innermost diffractive zone ( 7 ) is defined by
r
k
=
2
λ
k
p
+
k
2
λ
2
,
wherein k indicates the respective diffractive zone, λ is the wavelength of the light and p is a predefined value defining an add power.
11 . The multifocal lens as defined by claim 10 , wherein the equation of claim 9 defines the outer border of the innermost diffractive zone ( 7 ) and the outer border of the other diffractive zones ( 8 , 9 , 10 ) is defined by
r
k
(
r
k
-
1
2
+
λ
2
+
4
λ
2
p
2
+
4
λ
2
r
k
-
1
2
)
1
/
2
.
12 . The multifocal lens as defined by claim 1 , wherein the constants w 1 and w 2 are the same for all diffractive zones ( 7 , 8 , 9 , 10 ).
13 . The multifocal lens as defined by claim 1 , wherein the gradients p 1 , p 2 and p 3 , and the constants q 2 and q 3 are the same for all diffractive zones ( 7 , 8 , 9 , 10 ).
14 . The multifocal lens as defined by claim 1 , wherein the gradients p 1 , p 2 and p 3 , and the constants q 2 and q 3 are not the same for all diffractive zones ( 7 , 8 , 9 , 10 ).
15 . The multifocal lens as defined by claim 1 , wherein the gradients p 1 , p 2 and p 3 , and the constants q 2 and q 3 are different for all diffractive zones ( 7 , 8 , 9 , 10 ).
16 . A method for producing a multifocal lens ( 1 ) having several concentric diffractive zones ( 7 , 8 , 9 , 10 ) on a surface ( 2 ) of the lens, wherein the method comprises:
mathematically providing a diffraction phase structure for each diffractive zone ( 7 , 8 , 9 , 10 ) by providing for each diffractive zone ( 7 , 8 , 9 , 10 ) following piecewise function, which comprises three phase terms:
ϕ
(
ξ
)
=
2
π
×
{
p
1
ξ
,
0
≤
ξ
<
w
1
p
2
ξ
+
q
2
,
w
1
≤
ξ
<
w
2
p
3
ξ
+
q
3
,
w
2
≤
ξ
<
1
,
wherein ξ indicates a position within the respective diffractive zone ( 7 , 8 , 9 , 10 ) in a radial direction, φ(ξ) indicates a phase shift experienced by light passing through the position indicated by ξ, w 1 and w 2 define a spatial partitioning of the respective diffractive zone ( 7 , 8 , 9 , 10 ) in the radial direction in accordance with the three phase terms, p 1 , p 2 and p 3 indicate gradients of the three phase terms and q 2 and q 3 are constants, wherein ξ depends quadratically on a radial distance to the center of the surface ( 2 ) of the lens ( 1 ) and is normalized with respect to the radial width of the respective diffractive zone ( 7 , 8 , 9 , 10 ), and wherein the gradients p 1 , p 2 and p 3 are negative; and
forming the diffractive multifocal lens ( 1 ) such that the diffractive zones ( 7 , 8 , 9 , 10 ) have the mathematically provided diffraction phase structures.
17 . A multifocal lens ( 1 ) having several concentric diffractive zones ( 7 , 8 , 9 , 10 ) on a surface ( 2 ) of the lens, wherein in each diffractive zone ( 7 , 8 , 9 , 10 ) a diffraction phase structure is defined, which diffraction phase structure is expressible by a smoothed version of the following piecewise function, which comprises three phase terms:
ϕ
(
ξ
)
=
2
π
×
{
p
1
ξ
,
0
≤
ξ
<
w
1
p
2
ξ
+
q
2
,
w
1
≤
ξ
<
w
2
p
3
ξ
+
q
3
,
w
2
≤
ξ
<
1
,
wherein ξ indicates a position within the respective diffractive zone ( 7 , 8 , 9 , 10 ) in a radial direction, φ(ξ) indicates a phase shift experienced by light passing through the position indicated by ξ, w 1 and w 2 define a spatial partitioning of the respective diffractive zone ( 7 , 8 , 9 , 10 ) in the radial direction in accordance with the three phase terms, p 1 , p 2 and p 3 indicate gradients of the three phase terms and q 2 and q 3 are constants, wherein ξ depends quadratically on a radial distance to the center of the surface ( 2 ) of the lens ( 1 ) and is normalized with respect to the radial width of the respective diffractive zone ( 7 , 8 , 9 , 10 ), and wherein the gradients p 1 , p 2 and p 3 are negative.
18 . A method for producing a multifocal lens ( 1 ) having several concentric diffractive zones ( 7 , 8 , 9 , 10 ) on a surface ( 2 ) of the lens, wherein the method comprises:
mathematically providing a diffraction phase structure for each diffractive zone ( 7 , 8 , 9 , 10 ) by providing for each diffractive zone ( 7 , 8 , 9 , 10 ) a smoothed version of following piecewise function, which comprises three phase terms:
ϕ
(
ξ
)
=
2
π
×
{
p
1
ξ
,
0
≤
ξ
<
w
1
p
2
ξ
+
q
2
,
w
1
≤
ξ
<
w
2
p
3
ξ
+
q
3
,
w
2
≤
ξ
<
1
,
wherein ξ indicates a position within the respective diffractive zone ( 7 , 8 , 9 , 10 ) in a radial direction, φ(ξ) indicates a phase shift experienced by light passing through the position indicated by ξ, w 1 and w 2 define a spatial partitioning of the respective diffractive zone ( 7 , 8 , 9 , 10 ) in the radial direction in accordance with the three phase terms, p 1 , p 2 and p 3 indicate gradients of the three phase terms and q 2 and q 3 are constants, wherein ξ depends quadratically on a radial distance to the center of the surface ( 2 ) of the lens ( 1 ) and is normalized with respect to the radial width of the respective diffractive zone ( 7 , 8 , 9 , 10 ), and wherein the gradients p 1 , p 2 and p 3 are negative; and
forming the diffractive multifocal lens ( 1 ) such that the diffractive zones ( 7 , 8 , 9 , 10 ) have the mathematically provided diffraction phase structures.