# US 11,310,448 B2 · Imaging apparatus and optical low-pass filter

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- Number: US 11,310,448 B2
- Document ID: US11310448B2
- Status: Granted
- Kind: B2
- Application number: 16/718,947
- Filed: 2019-12-18
- Published: 2020-07-16
- Granted: 2022-04-19
- Earliest claimed: 2019-01-11
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Yutaka Yamaguchi; Kazuhiko Momoki
- Web page: https://patentgrep.com/patent/US11310448B2

## CPC

- G02B 5/3083: {Birefringent or phase retarding elements (G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001)}
- H10F 39/8053: {Colour filters}
- H04N 25/615: involving a transfer function modelling the optical system, e.g. optical transfer function [OTF], phase transfer function [PhTF] or modulation transfer function [MTF]
- H10F 39/806: {Optical elements or arrangements associated with the image sensors}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

An imaging apparatus includes an optical low-pass filter that includes first, second, third, and fourth optical anisotropic elements configured to separate an incident ray into a plurality of rays, and a retardation plate disposed between two optical anisotropic elements adjacent to each other among the first to fourth optical anisotropic elements, and an image sensor configured to photoelectrically convert an optical image formed by light that has passed the optical low-pass filter. A predetermined condition is satisfied.

## Claims

### Claim 1

An imaging apparatus comprising:
an optical low-pass filter that includes first, second, third, and fourth optical anisotropic elements each configured to separate an incident ray into a plurality of rays, and a retardation plate disposed between two optical anisotropic elements adjacent to each other among the first to fourth optical anisotropic elements; and
an image sensor configured to photoelectrically convert an optical image formed by light that has passed the optical low-pass filter,
wherein the following condition is satisfied:
−0.20≤I≤0.20
I
=
∫
λ
max
λ
min
⁢
s
⁡
(
λ
)
·
cos
⁡
(
2
⁢
π
/
λ
·
δ
⁡
(
λ
)
)
⁢
d
⁢
⁢
λ
where λ is a wavelength of the light, δ(λ) is a phase difference of the retardation plate, S(λ) is a normalized spectral sensitivity spectrum of the image sensor, and λmax and λmin are the longest wavelength and the shortest wavelength in an integration range that is 10% or more of a peak intensity of the S(λ), respectively.

### Claim 2 (depends on 1)

The imaging apparatus according to claim 1, wherein the peak intensity is a peak intensity in a green band of the light.

### Claim 3 (depends on 1)

The imaging apparatus according to claim 1, wherein the image sensor includes a plurality of pixels arranged in a first direction and a second direction orthogonal to each other, and
wherein the first optical anisotropic element separates the ray in the first direction, the second optical anisotropic element separates the ray in the second direction, the third optical anisotropic element separates the ray in a direction that forms an angle of 45° relative to the first direction, and the fourth optical anisotropic element separates the ray in a direction that forms an angle of 45° relative to the second direction.

### Claim 4 (depends on 1)

The imaging apparatus according to claim 1, wherein a ray separation width by the third optical anisotropic element is wider than that by the first optical anisotropic element.

### Claim 5 (depends on 1)

The imaging apparatus according to claim 1, wherein a ray separation width by the fourth optical anisotropic element is wider than that by the first optical anisotropic element.

### Claim 6 (depends on 1)

The imaging apparatus according to claim 1, wherein a ray separation width by the third optical anisotropic element is wider than that by the second optical anisotropic element.

### Claim 7 (depends on 1)

The imaging apparatus according to claim 1, wherein a ray separation width by the fourth optical anisotropic element is wider than that by the second optical anisotropic element.

### Claim 8 (depends on 1)

The imaging apparatus according to claim 1, wherein the following condition is satisfied:
Dx<Dp and Dy<Dn, or
Dx<Dp,Dx<Dn,Dy<Dp and Dy<Dn
where Dx is a ray separation width by the first optical anisotropic element, Dy is a ray separation width by the second optical anisotropic element, Dp is a ray separation width by the third optical anisotropic element, and Dn is a ray separation width by the optical anisotropic element is Dn.

### Claim 9 (depends on 1)

The imaging apparatus according to claim 1, wherein a fast axis of the retardation plate is parallel or orthogonal to the first direction.

### Claim 10 (depends on 1)

The imaging apparatus according to claim 1, wherein an angle formed by ray separation directions of the two optical anisotropic elements adjacent to each other is 120° or higher and 150° or lower.

### Claim 11 (depends on 1)

The imaging apparatus according to claim 1, wherein the first to fourth optical anisotropic elements have the same ray separation widths.

### Claim 12 (depends on 1)

The imaging apparatus according to claim 1, wherein among the first to fourth optical anisotropic elements, one that is closest to an image side and one that is closest to an object side are made of quartz, and remaining optical anisotropic elements are made of quartz or lithium niobate.

### Claim 13 (depends on 1)

The imaging apparatus according to claim 1, wherein the first optical anisotropic element, the second optical anisotropic element, the retardation plate, the third optical anisotropic element, and the fourth optical anisotropic element are arranged in this order from an object side to an image side.

### Claim 14 (depends on 1)

The imaging apparatus according to claim 1, wherein the first and fourth optical anisotropic elements are made of quartz, and the second and third optical anisotropic elements are made of lithium niobate.

### Claim 15 (depends on 1)

The imaging apparatus according to claim 1, wherein the retardation plate is made of quartz having a thickness of 0.1 mm or more and 0.3 mm or less.

### Claim 16

An optical low-pass filter used for an imaging apparatus that includes an image sensor, the optical low-pass filter comprising:
first, second, third, and fourth optical anisotropic elements each configured to separate incident ray into a plurality of rays; and
a retardation plate disposed between two optical anisotropic elements adjacent to each other among the first to fourth optical anisotropic elements
wherein the following condition is satisfied:
−0.20≤I≤0.20
I
=
∫
λ
max
λ
min
⁢
s
⁡
(
λ
)
·
cos
⁡
(
2
⁢
π
/
λ
·
δ
⁡
(
λ
)
)
⁢
d
⁢
⁢
λ
where λ is a wavelength of the light, δ(λ) is a phase difference of the retardation plate, S(λ) is a normalized spectral sensitivity spectrum of the image sensor, and λmax and λmin are the longest wavelength and the shortest wavelength in an integration range that is 10% or more of a peak intensity of the S(λ), respectively.

### Claim 17

An optical low-pass filter comprising, in order from the light incident side to the light emitting side, first, second, third, and fourth optical anisotropic elements configured to separate an incident ray into a plurality of rays,
wherein the first and fourth optical anisotropic elements made of quartz, and the second and third optical anisotropic elements are made of lithium niobate.

### Claim 18 (depends on 17)

The optical low-pass filter according to claim 17, further comprising a fifth optical anisotropic element disposed between the second and third optical anisotropic elements.

### Claim 19 (depends on 18)

The optical low-pass filter according to claim 18, wherein the fifth optical anisotropic element is a retardation plate having an optical axis parallel to an optical surface of the fifth optical anisotropic element.

### Claim 20 (depends on 18)

The optical low-pass filter according to claim 18, wherein the fifth optical anisotropic element is made of quartz.

### Claim 21 (depends on 18)

The optical low-pass filter according to claim 18, wherein the optical low-pass filter is used with an image sensor configured to photoelectrically convert an optical image formed by light that has passed through the optical low-pass filter, and
wherein where a first direction and a second direction are two pixel arrangement directions orthogonal to each other in the image sensor, one of the first and second optical anisotropic elements separates the ray in the first direction, and the other separates the ray in a direction that forms an angle of 45° relative to the first direction, and
wherein one of the third and fourth optical anisotropic elements separates the ray in the second direction, and the other separates the ray in a direction that forms an angle of 45° relative to the second direction.

### Claim 22 (depends on 17)

An imaging apparatus comprising:
an optical low-pass filter according to claim 17; and
an image sensor configured to photoelectrically convert an optical image formed by light that has passed through the optical low-pass filter.