# US 12,181,673 B2 · Propagation optical system and virtual image display device

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- Number: US 12,181,673 B2
- Document ID: US12181673B2
- Status: Granted
- Kind: B2
- Application number: 17/378,812
- Filed: 2021-07-19
- Published: 2022-01-27
- Granted: 2024-12-31
- Earliest claimed: 2020-07-22
- Assignees: Ricoh Company, Ltd.
- Applicants: Yoshifumi Sudoh; Naoki Nakamura; Masahiro Itoh; Susumu Momma; Shun Okazaki; Shigenobu Hirano; Yasuo Katano; Kenji Kameyama; Norikazu Igarashi; Aino Hasegawa; Takashi Maki; Masamichi Yamada; Takemasa Tsutsui
- Inventors: Yoshifumi Sudoh; Naoki Nakamura; Masahiro Itoh; Susumu Momma; Shun Okazaki; Shigenobu Hirano; Yasuo Katano; Kenji Kameyama; Norikazu Igarashi; Aino Hasegawa; Takashi Maki; Masamichi Yamada; Takemasa Tsutsui
- Web page: https://patentgrep.com/patent/US12181673B2

## CPC

- G02B 27/0172: {characterised by optical features}
- G02B 3/06: with cylindrical or toric faces
- G02B 6/003: {Lens or lenticular sheet or layer}
- G02B 9/64: having more than six components
- G02B 13/16: for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV}
- G02B 2027/0145: {creating an intermediate image}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A propagation optical system includes: a first optical system; an intermediate optical element; and a second optical system. The first optical system, the intermediate optical element, and the second optical system being sequentially arranged in a direction from the image display element toward the light guide member along an optical axis. The intermediate optical element has a non-rotationally symmetric curved surface, of which shape is non-rotationally symmetric about the optical axis. A cross-sectional shape, of the non-rotationally symmetric curved surface, in a first plane including the optical axis is non-arc shape. The first plane is a plane in which the non-rotationally symmetric surface has a strongest positive power among planes including the optical axis. The propagation optical system is configured to form, between the first optical system and the second optical system, an intermediate image corresponding to an image displayed on the image display element.

## Claims

### Claim 1

A propagation optical system incorporated in a virtual image display device, to propagate light emitted from an image display element to a light guide member to display a virtual image, the propagation optical system comprising:
the image display element configured to emit light to display an image;
a first optical system;
an intermediate optical element; and
a second optical system,
the first optical system, the intermediate optical element, and the second optical system being sequentially arranged in a direction from the image display element toward the light guide member along an optical axis,
wherein the intermediate optical element has a non-rotationally symmetric curved surface, of which shape is non-rotationally symmetric about the optical axis,
wherein, a cross-sectional shape, of the non-rotationally symmetric curved surface, in a first plane including the optical axis is a non-arc shape,
wherein the first plane is a plane in which the non-rotationally symmetric surface has a strongest positive power among planes including the optical axis,
wherein the propagation optical system is configured to form, between the first optical system and the second optical system, an intermediate image corresponding the image displayed on the image display element,
wherein the first optical system is composed of a first front group and a first rear group each having positive power, sequentially arranged in the direction form the image display element toward the light guide member,
wherein the first front group has a plurality of lenses,
wherein the first rear group has a plurality of lenses, and
wherein a distance between the first front group and the first rear group along the optical axis is longest among distances along the optical axis between any neighboring two lenses within the first optical system.

### Claim 2 (depends on 1)

The propagation optical system according to claim 1,
wherein the non-arc shape has a decreasing positive power with an increase in distance from the optical axis.

### Claim 3 (depends on 2)

The propagation optical system according to claim 2,
wherein conditional expression (1) is satisfied:
0.02<Sag/H<0.25 (1)
where
Sag is a maximum value of difference in sag amount between the non-arc shape and an arc having a paraxial curvature of the non-arc shape in a specific plane, and
H is an effective ray height from the optical axis in the specific plane.

### Claim 4 (depends on 1)

The propagation optical system according to claim 1,
wherein the non-rotationally symmetric curved surface is an anamorphic aspherical surface.

### Claim 5 (depends on 4)

The propagation optical system according to claim 4,
wherein conditional expression (11) is satisfied:
−0.9<(Rp+Rn)/(Rp−Rn)<−0.3 (11)
where
Rp is a paraxial radius of curvature of the anamorphic aspherical surface in the first plane, and
Rn is a paraxial radius of curvature of the anamorphic aspherical surface in a second plane that includes the optical axis and orthogonal to the first plane.

### Claim 6 (depends on 4)

The propagation optical system according to claim 4,
wherein the anamorphic aspherical surface has a shape, in the first plane, having a decreasing positive power with an increase in distance from the optical axis.

### Claim 7 (depends on 6)

The propagation optical system according to claim 6,
wherein conditional expression (12) is satisfied:
0.6<Sagp/Sag_rp<1.0 (12)
where
Sagp is a maximum value of a sag amount of the anamorphic aspherical surface in the first plane, and
Sag_rp is a sag amount defined by a circle, in the first plane, having a paraxial curvature of the anamorphic aspherical surface at a height which provides maximum value of the sag amount of the anamorphic aspherical surface.

### Claim 8 (depends on 4)

The propagation optical system according to claim 4,
wherein conditional expression (13) is satisfied:
0.6<Sagn/Sag_rn<1.0 (13)
where
Sagn is a maximum value of a sag amount of the anamorphic aspherical surface in a second plane that includes the optical axis and is orthogonal to the first plane, and
Sag_rn is a sag amount defined by a circle, in the second plane, having a paraxial curvature of the anamorphic aspherical surface at a height which provides maximum value of the sag amount of the anamorphic aspherical surface.

### Claim 9 (depends on 1)

The propagation optical system according to claim 1,
wherein the second optical system is composed of a negative lens and a positive lens sequentially arranged in the direction from the image display element to the light guide member.

### Claim 10 (depends on 1)

The propagation optical system according to claim 1,
wherein conditional expression (2) is satisfied:
0.4<TLRa/TLR<0.7 (2)
where
TLR is a total length of the first optical system along the optical axis, and
TLRa is a distance along the optical axis between the first front group and the first rear group.

### Claim 11 (depends on 1)

The propagation optical system according to claim 1,
wherein the first front group is composed of three lenses of a positive lens, a negative lens, and a positive lens sequentially arranged in the direction from the image display element to the light guide member.

### Claim 12 (depends on 1)

The propagation optical system according to claim 1,
wherein the first rear group is composed of two lenses of a positive lens and a negative lens sequentially arranged in the direction from the image display element to the light guide member.

### Claim 13 (depends on 1)

The propagation optical system according to claim 1,
wherein conditional expression (3) is satisfied:
0.1<TLA/TL<0.5 (3)
where
TLA is a distance along the optical axis between the non-rotationally symmetric curved surface of the intermediate optical element and a surface closest to the light guide member within the second optical system, and
TL is a distance along the optical axis between a surface closest to the image display element within the first optical system and a surface closest to the light guide member within the second optical system.

### Claim 14 (depends on 1)

The propagation optical system according to claim 1,
wherein conditional expression (4) is satisfied:
0.3<TLC/TLR<0.6 (4)
where
TLC is a total length of the second optical system along the optical axis, and
TLR is a total length of the first optical system along the optical axis.

### Claim 15 (depends on 1)

The propagation optical system according to claim 1,
wherein conditional expression (5) is satisfied:
−3.0<β_relay<−1.0 (5)
where
β_relay is a lateral magnification of the first optical system.

### Claim 16 (depends on 1)

The propagation optical system according to claim 1,
wherein the intermediate optical element is a cylindrical lens.

### Claim 17 (depends on 1)

The propagation optical system according to claim 1,
wherein conditional expression (6) is satisfied:
−0.5<Pos1/Y<0.5 (6)
where
Pos1 is a position of the intermediate image with reference to a position of the non-rotationally symmetric curved surface on the optical axis, and
Y is a diagonal length of an image display area of the image display element.

### Claim 18 (depends on 1)

The propagation optical system according to claim 1,
wherein conditional expression (7) is satisfied:
0.4<f_r/f_rf<0.8 (7)
where
f_r is a focal length (>0) of the first optical system, and
f_rf is a focal length of the first front group.

### Claim 19 (depends on 1)

A virtual image display device comprising:
an image display element configured to emit light to display an image;
the propagation optical system according to claim 1 configured to propagate light from the image display element to a light guide member; and
the light guide member configured to guide and output the light from the propagation optical system to display a virtual image corresponding to the image displayed by the image display element.

### Claim 20

A propagation optical system incorporated in a virtual image display device, to propagate light emitted from an image display element to a light guide member to display a virtual image, the propagation optical system comprising:
a first optical system;
an intermediate optical element; and
a second optical system,
the first optical system, the intermediate optical element, and the second optical system being sequentially arranged in a direction from the image display element toward the light guide member along an optical axis,
wherein the intermediate optical element has a non-rotationally symmetric curved surface, of which shape is non-rotationally symmetric about the optical axis,
wherein, a cross-sectional shape, of the non-rotationally symmetric curved surface, in a first plane including the optical axis is non-arc shape,
wherein the first plane is a plane in which the non-rotationally symmetric surface has a strongest positive power among planes including the optical axis,
wherein the propagation optical system is configured to form, between the first optical system and the second optical system, an intermediate image corresponding to an image displayed on the image display element, and
wherein the second optical system is composed of a negative lens and a positive lens sequentially arranged in the direction from the image display element to the light guide member.