# US 11,994,689 B2 · Diffractive optical elements for large-field image display

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- Number: US 11,994,689 B2
- Document ID: US11994689B2
- Status: Granted
- Kind: B2
- Application number: 15/733,635
- Filed: 2019-10-18
- Published: 2021-10-21
- Granted: 2024-05-28
- Earliest claimed: 2019-10-18
- Assignees: Google Inc.
- Applicants: Google LLC
- Inventors: Khoa Nguyen
- Web page: https://patentgrep.com/patent/US11994689B2

## CPC

- G02B 27/4272: {having plural diffractive elements positioned sequentially along the optical path}
- G02B 5/1823: {in an overlapping or superposed manner}
- G02B 27/10: Beam splitting or combining systems (polarising systems G02B27/28; mixing and splitting light signals using optical waveguides G02B6/28; {beam shaping, e.g. changing the cross-sectional area, by dividing or superposing multiple light beams G02B27/0905})
- G02B 27/4205: {having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant}
- G02B 13/16: for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV}
- G02B 2027/0123: {comprising devices increasing the field of view}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

Techniques of generating a wavefront modulating element (WME) for imaging an object over a large image field include (i) designing a WME by breaking a large image into smaller sub-images and then applying an inverse imaging operation to find a segment of a plurality of segments (324-1 to-334-n) of a WME (in the from of DOE) producing a sub-image, and (ii) specifying an optical system to illuminate the WME resulting from each of the plurality of segments in such a way that the large image is reproduced as closely as possible. Along these lines, given a large target image in the far-field, a WME generation system decomposes the target image into sub-images. From this decomposition, the WME generation system then produces WME segments corresponding to the sub-images. The WME segments are then arranged in an optical system such that abeam of electromagnetic radiation (316) is reproduced into sub-beams that are normally incident on the WME segments (for example by gratings 332 diffracting light towards a DOE and back into a lightguide 320).

## Claims

### Claim 1

A method, comprising:
generating a wavefront modulating element (WME) based on a first image, the WME including a plurality of WME segments, each of the plurality of WME segments corresponding to a respective portion of the first image;
generating, by an illumination system, a beam of electromagnetic radiation; and
illuminating each of the plurality of WME segments with the beam of electromagnetic radiation at a specified angle of incidence, each of the plurality of WME segments being disposed upon a respective diffraction grating to produce a respective monolithic diffractive stack for that WME segment, the plurality of WME segments producing upon illumination a second image, a difference between the first image and the second image being less than a specified threshold.

### Claim 2 (depends on 1)

The method as in claim 1, wherein illuminating each of the plurality of WME segments includes coupling the beam of electromagnetic radiation into a light guide, the light guide including walls to which the WME is connected.

### Claim 3 (depends on 2)

The method as in claim 2, wherein the respective monolithic diffractive stack for each of the plurality of WME segments is configured to produce an approximation to the respective portion of the first image to which that WME segment corresponds, the respective monolithic diffractive stack for each of the plurality of WME segments being disposed on a wall of the light guide.

### Claim 4 (depends on 3)

The method as in claim 3, wherein the light guide includes walls, and
wherein illuminating each of the plurality of WME segments includes:
propagating the beam of electromagnetic radiation through the light guide via total internal reflection off the walls of the light guide; and
collecting stray light reflected by the respective monolithic diffractive stack back into the light guide to produce illumination having substantially the same brightness when incident on each of the plurality of WME segments of the WME.

### Claim 5 (depends on 2)

The method as in claim 2, wherein generating the beam of electromagnetic radiation includes expanding and homogenizing the beam using a beam expander prior to the coupling of the beam of electromagnetic radiation into the light guide.

### Claim 6 (depends on 1)

The method as in claim 1, wherein generating the WME based on the first image includes:
receiving intensity data representing the first image;
performing an image decomposition operation to produce a plurality of sub-images of the first image, each of the plurality of sub-images representing a portion of the first image; and
for each of the plurality of sub-images of the first image, performing an inverse imaging operation on that sub-image to produce a representation of a respective WME segment of a plurality of representations of WME segments.

### Claim 7 (depends on 6)

The method as in claim 6, wherein performing the inverse imaging operation on each of the plurality of sub-images of the first image includes:
applying a Gerchberg-Saxton algorithm to each of the plurality of sub-images.

### Claim 8 (depends on 6)

The method as in claim 6, wherein the WME includes a diffractive optical element (DOE) and each of the plurality of WME segments includes a respective DOE segment of the DOE, and
wherein each representation of a DOE segment of the plurality of WME segments includes a respective plurality of pixels, each of the respective plurality of pixels having one of a specified number of phase values.

### Claim 9 (depends on 8)

The method as in claim 8, wherein each of the respective plurality of pixels further includes an intensity value.

### Claim 10 (depends on 6)

The method as in claim 6, wherein generating the WME based on the first image further includes:
arranging the plurality of WME segments based on the image decomposition operation to form the WME.

### Claim 11

A system, comprising:
a DOE generation system including controlling circuitry configured to generate a diffractive optical element (DOE) based on a first image, the DOE including a plurality of DOE segments, each of the plurality of DOE segments corresponding with a respective portion of the first image;
an illumination system configured to generate a beam of electromagnetic radiation; and
an imaging system configured to produce a second image upon illumination with the beam of electromagnetic radiation by illuminating each of the plurality of DOE segments with the beam of electromagnetic radiation, each of the plurality of DOE segments being disposed upon a respective diffraction grating to produce a respective monolithic diffractive stack for that DOE segment, the plurality of DOE segments forming the DOE and producing upon illumination a second image, a difference between the first image and the second image being less than a specified threshold.

### Claim 12 (depends on 11)

The system as in claim 11, wherein the imaging system configured to illuminate each of the plurality of DOE segments is further configured to couple the beam of electromagnetic radiation into a light guide, the light guide including walls to which the DOE is connected.

### Claim 13 (depends on 12)

The system as in claim 12, wherein the respective monolithic diffractive stack for each of the plurality of DOE segments is configured to produce an approximation to the respective portion of the first image to which that DOE segment corresponds, the respective monolithic diffractive stack for each of the plurality of DOE segments being disposed on a wall of the light guide.

### Claim 14 (depends on 11)

The system as in claim 11, wherein the respective diffraction grating has a pitch based on a maximum length of a segment of the DOE.

### Claim 15 (depends on 13)

The system as in claim 13, wherein the respective diffraction grating is configured to reflect illumination back into the light guide, the illumination propagating in the light guide in at least two orthogonal directions.

### Claim 16 (depends on 12)

The system as in claim 12, wherein light guide includes a mirror surface to couple the beam of electromagnetic radiation into the light guide.

### Claim 17 (depends on 12)

The system as in claim 12, wherein light guide includes a diffraction grating to couple the beam of electromagnetic radiation into the light guide.

### Claim 18

A computer program product comprising a non-transitory storage medium, the computer program product including code that, when executed by processing circuitry of a computing device, causes the processing circuitry to perform a method, the method comprising:
receiving intensity data representing an image;
performing an image decomposition operation to produce a plurality of sub-images of the image, each of the plurality of sub-images representing a portion of the image;
for each of the plurality of sub-images of the image, performing an inverse imaging operation on that sub-image to produce a wavefront modulating element (WME) segment of a plurality of WME segments, each of the plurality of WME segments corresponding to a respective sub-image of the plurality of sub-images; and
arranging the plurality of WME segments based on the image decomposition operation to form a WME such that each of the plurality of WME segments is disposed upon a respective diffraction grating to produce a respective monolithic diffractive stack for that WME segment.

### Claim 19 (depends on 18)

The computer program product as in claim 18, wherein performing the inverse imaging operation on each of the plurality of sub-images of the image includes:
applying a Gerchberg-Saxton algorithm to each of the plurality of sub-images.

### Claim 20 (depends on 18)

The computer program product as in claim 18, wherein each representation of a WME segment of the plurality of WME segments includes a respective plurality of pixels, each of the respective plurality of pixels having one of a specified number of phase values.