# US 8,540,372 B2 · Waveplate compensation in projection polarization conversion systems

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- Number: US 8,540,372 B2
- Document ID: US8540372B2
- Status: Granted
- Kind: B2
- Application number: 13/710,356
- Filed: 2012-12-10
- Published: 2013-04-25
- Granted: 2013-09-24
- Earliest claimed: 2010-02-24
- Assignees: RealD Inc.
- Applicants: Reald, Inc.
- Inventors: David A. Coleman; Miller H. Schuck; Gary D. Sharp
- Web page: https://patentgrep.com/patent/US8540372B2

## CPC

- G02B 30/25: using polarisation techniques
- G02B 27/283: {used for beam splitting or combining}
- G03B 21/14: Details
- G03B 35/20: using two or more projectors
- G03B 35/26: using polarised or coloured light separating different viewpoint images
- H04N 13/363: using image projection screens (volumetric display H04N13/388)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- 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)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

Three dimensional projection systems may be single projector or multiple projector systems. These 3D projection systems may include a one or more polarization conversion systems (PCS). Each PCS may be designed for relatively small throw ratios and thus, may be designed to accommodate the small throw ratios. Each PCS may include a polarizing beam splitter, a first optical stack, a reflector and a second quarter wave retarder. The first optical stack may include a rotator, a polarizer, a polarization switch and a first quarter wave retarder. Each PCS may receive light from a respective projector, and the PBS in each PCS may direct the light toward the first optical stacks. The light may be converted to a different polarization state as it passes through the first optical stack. The converted light may then be re-directed by a reflecting element to a second quarter wave retarder. The second quarter wave retarder may convert linearly polarized light to circularly polarized light.

## Claims

### Claim 1

A multiple projector polarization conversion system comprising:
a first and second polarization conversion system, wherein each of the first and second polarization conversion system comprises:
a polarizing beam splitter (PBS) operable to receive incoming light and separate the incoming light into a first light bundle with a first state of polarization (SOP) and a second light bundle with a second state of polarization (SOP), wherein the first SOP is orthogonal to the second SOP;
a first optical stack operable to receive the first light bundle from the PBS, wherein the first optical stack comprises a rotator and a first polarization switch;
a reflector operable to receive the first light bundle from the first optical stack; and
a second optical stack operable to receive the second light bundle from the PBS, wherein the second optical stack comprises a second polarization switch and a second polarizer.

### Claim 2 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein each of the first and second polarization conversion system further comprises a lens set operable to receive the second light bundle from the PBS and operable to direct the second light bundle received from the PBS toward the second optical stack.

### Claim 3 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the first polarization switch and the second polarization switch are substantially synchronized to alternately project left and right eye images.

### Claim 4 (depends on 1)

The multiple projector polarization conversion system of claim 1, further comprising a controller operable to synchronize the left and right eye images.

### Claim 5 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the PBS is a cube PBS.

### Claim 6 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the first optical stack further comprises a first polarizer and a first quarter wave retarder, and wherein the first quarter wave retarder has an approximately +45 degree configuration relative to the optic axis of the first polarizer.

### Claim 7 (depends on 6)

The multiple projector polarization conversion system of claim 6, wherein each of the first and second polarization conversion systems further comprise a second quarter wave retarder operable to receive the first light bundle from the reflector, and wherein the second quarter wave retarder has an approximately −45 degree configuration relative to the optic axis of the first polarizer.

### Claim 8 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the first light bundle is S-polarized light and wherein the second light bundle is P-polarized light.

### Claim 9 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the PBS is a wire grid PBS.

### Claim 10 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the PBS is a retarder based PBS.

### Claim 11 (depends on 1)

The multiple projector polarization conversion system of claim 1, wherein the rotator is an achromatic half-wave plate.

### Claim 12 (depends on 1)

The multiple projector polarization conversion system of claim 1, further comprising a controller operable to synchronize the first and second polarization conversion systems.

### Claim 13

A waveplate compensation method for providing a multiple projector polarization conversion system, the method comprising:
receiving incoming light from a first projector at a first polarizing beam splitter (PBS) wherein the first PBS separates the incoming light from the first projector into a first light bundle and a second light bundle;
receiving the first light bundle from the first PBS at a first optical stack wherein the first optical stack comprises, a first rotator and a first polarization switch;
receiving the first light bundle from the first optical stack at a first reflecting element;
receiving the second light bundle from the first PBS at a second optical stack, wherein the second optical stack comprises a second polarization switch and a second polarizer;
receiving incoming light from a second projector at a second polarizing beam splitter (PBS), wherein the second PBS separates the incoming light from the second projector into a third light bundle and a fourth light bundle;
receiving the third light bundle from the second PBS at a third optical stack wherein the third optical stack comprises, a second rotator and a third polarization switch;
receiving the third light bundle from the third optical stack at a second reflecting element; and
receiving the fourth light bundle from the second PBS at a fourth optical stack, wherein the fourth optical stack comprises a fourth polarization switch and a fourth polarizer.

### Claim 14 (depends on 13)

The waveplate compensation method of claim 13, wherein the first and third light bundles have a first state of polarization (SOP) and the second and fourth light bundles have a second state of polarization (SOP), and further wherein the first SOP is orthogonal to the second SOP.

### Claim 15 (depends on 13)

The waveplate compensation method of claim 13, further comprising:
receiving the second light bundle from the first PBS at a first lens set and directing the second light bundle received from the first PBS toward the second optical stack; and
receiving the fourth light bundle from the second PBS at a second lens set and directing the fourth light bundle received from the second PBS toward the fourth optical stack.

### Claim 16 (depends on 13)

The waveplate compensation method of claim 13, wherein the first and third light bundles are S-polarized light and the second and fourth light bundles are P-polarized light.

### Claim 17 (depends on 13)

The waveplate compensation method of claim 13, further comprising:
rotating the first light bundle by 90 degrees relative to an optic axis at the first rotator; and
rotating the third light bundle by 90 degrees relative to an optic axis at the second rotator.

### Claim 18 (depends on 13)

The waveplate compensation method of claim 13, wherein the first optical stack further comprises a first quarter wave retarder and a first polarizer, wherein the third optical stack further comprises a third quarter wave retarder and a third polarizer, and wherein the first and third quarter wave retarders have an optic axis orientation of at least one of an approximately +45 degree orientation relative to the plane of incidence and an approximately −45 degree orientation relative to a plane of incidence.

### Claim 19 (depends on 13)

The waveplate compensation method of claim 13, further comprising:
receiving the first light bundle from the first reflecting element at a second quarter wave retarder;
converting the first light bundle from linearly polarized light to circularly polarized light at the second quarter wave retarder;
receiving the third light bundle from the second reflecting element at a fourth quarter wave retarder; and
converting the third light bundle from linearly polarized light to circularly polarized light at the fourth quarter waver retarder.

### Claim 20

A multiple projector polarization conversion system comprising:
a first projector operable to provide light in the direction of a projection screen;
a second projector operable to provide light in the direction of the projection screen; and
first and second polarization conversion systems operable to receive light from the first and second projectors respectively, wherein each of the first and second polarization conversion systems comprise:
a polarizing beam splitter (PBS) operable to receive incoming light and separate the incoming light into a first light bundle with a first state of polarization (SOP) and a second light bundle with a second state of polarization (SOP), wherein the first SOP is orthogonal to the second SOP;
a first optical stack operable to receive the first light bundle from the PBS, wherein the optical stack comprises, a rotator and a polarization switch;
a reflector operable to receive the first light bundle from the first optical stack; and
a second optical stack operable to receive the second light bundle from the PBS, wherein the second optical stack comprises a second polarization switch and a second polarizer.