# US 2017/0285352 A1 · Illumination optical system and image projection apparatus with the same

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- Number: US 2017/0285352 A1
- Document ID: US20170285352A1
- Status: Published application
- Kind: A1
- Application number: 15/623,745
- Filed: 2017-06-15
- Published: 2017-10-05
- Earliest claimed: 2014-04-01
- Assignees: Canon Kabushiki Kaisha
- Applicants: Canon Kabushiki Kaisha
- Inventors: Takashi Sudo; Yuuki Maeda
- Web page: https://patentgrep.com/patent/US20170285352A1

## CPC

- G03B 21/208: {Homogenising, shaping of the illumination light}
- G02B 19/0014: {at least one surface having optical power}
- G02B 27/0927: {Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat}
- G02B 27/0961: {Lens arrays (lens arrays per se G02B3/0006)}
- G02B 19/0047: {for use with a light source (G02B19/009, G02B19/0095 take precedence; details of lighting devices in general F21V; non-semiconductor lasers having optical devices external to the laser cavity H01S3/005)}
- G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An illumination optical system illuminates an image display element and includes a first lens array configured to divide light emitted from a light source, a second lens array configured to receive light from the first lens array, and a condenser optical system configured to guide light from the second lens array to the image display element, and a conjugate point of the image display element is located between an incident surface of the first lens array and an incident surface of the second lens array.

## Claims

### Claim 1

An illumination optical system which illuminates an image display element, the illumination optical system comprising:
a first lens array configured to divide light emitted from a light source;
a second lens array configured to receive light from the first lens array; and
a condenser optical system configured to guide light from the second lens array to the image display element,
wherein a conjugate point of the image display element is located between an incident surface of the first lens array and an incident surface of the second lens array.

### Claim 2 (depends on 1)

The illumination optical system according to claim 1,
wherein the incident surface of the first lens array is a refracting surface of the first lens array.

### Claim 3 (depends on 1)

The illumination optical system according to claim 1,
wherein an emitting surface of the first lens array is a refracting surface of the first lens array, and
wherein the conjugate point of the image display element is located between the emitting surface of the first lens array and the incident surface of the second lens array.

### Claim 4 (depends on 1)

The illumination optical system according to claim 1,
wherein a following expression is satisfied:
0.010<(A(in air)−F2)/A(in air)<0.300,
where A(in air) is an air conversion length from the incident surface of the first lens array to the incident surface of the second lens array in an optical axis direction, and F2 is a focal length of the second lens array.

### Claim 5 (depends on 1)

The illumination optical system according to claim 1,
wherein a following expression is satisfied:
A(in air)−F2>t1A/n1,
where A(in air) is an air conversion length from the incident surface of the first lens array to the incident surface of the second lens array in an optical axis direction, F2 is a focal length of the second lens array, t1A is a thickness of a lens cell part of the first lens array, and n1 is a refractive index of the first lens array.

### Claim 6 (depends on 1)

The illumination optical system according to claim 1,
wherein the first lens array, the second lens array, and the condenser optical system are arranged in this order from the light source along an optical axis direction of the condenser optical system.

### Claim 7 (depends on 1)

The illumination optical system according to claim 1,
wherein a following expression is satisfied:
0.7<F2/F1<1.0,
where F1 is a focal length of the first lens array, and F2 is a focal length of the second lens array.

### Claim 8 (depends on 1)

The illumination optical system according to claim 1,
wherein the first lens array includes a plurality of cells and a cell boundary part formed between the plurality of cells, and
wherein the cell boundary part has a negative refractive power.

### Claim 9 (depends on 8)

The illumination optical system according to claim 8,
wherein the condenser optical system is configured to condense light from the cell boundary part of the first lens array on a position between the condenser optical system and the image display element.

### Claim 10 (depends on 1)

The illumination optical system according to claim 1,
wherein the first lens array and the second lens array are configured such that a center of curvature of each cell of the first lens array and the second lens array is displaced from a center position of each cell in a predetermined direction in a plane orthogonal to an optical axis of the condenser optical system.

### Claim 11 (depends on 10)

The illumination optical system according to claim 10,
wherein the first lens array is configured such that the center of curvature of each cell of the first lens array is displaced close to the optical axis of the condenser optical system relative to the center position of each cell in the predetermined direction, and
wherein the second lens array is configured such that the center of curvature of each cell of the second lens array is displaced away from the optical axis relative to the center position of each cell in the predetermined direction.

### Claim 12 (depends on 10)

The illumination optical system according to claim 10,
wherein the predetermined direction is a short side direction of the image display element.

### Claim 13 (depends on 12)

The illumination optical system according to claim 12,
wherein a distance between the conjugate point of the image display element for the short side direction and the image display element is shorter than a distance between the first lens array and the image display element, and
wherein a distance between the conjugate point of the image display element for a long side direction and the image display element is longer than the first lens array and the image display element.

### Claim 14 (depends on 13)

The illumination optical system according to claim 13,
wherein the second lens array has a toric surface and is configured such that radii of curvature of each cell in the short side direction and the long side direction are different from each other.

### Claim 15 (depends on 14)

The illumination optical system according to claim 14,
wherein each cell of the second lens array is configured such that the radius of curvature in the long side direction is greater than the radius of curvature in the short side direction.

### Claim 16

An image projection apparatus comprising:
an image display element; and
an illumination optical system configured to illuminate the image display element,
wherein the illumination optical system includes:
a first lens array configured to divide light emitted from a light source,
a second lens array configured to receive light from the first lens array, and
a condenser optical system configured to guide light from the second lens array to the image display element, and
wherein a conjugate point of the image display element is located between an incident surface of the first lens array and an incident surface of the second lens array.