# US 2025/0093568 A1 · Systems and methods for light recycling using polarization at an incoupler and a reflective structure

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2025/0093568 A1
- Document ID: US20250093568A1
- Status: Published application
- Kind: A1
- Application number: 18/728,360
- Filed: 2022-07-21
- Published: 2025-03-20
- Earliest claimed: 2022-01-11
- Assignees: Google Inc.
- Applicants: Google LLC
- Inventors: Daniel Adema; Shreyas Potnis; Timothy Paul Bodiya
- Web page: https://patentgrep.com/patent/US20250093568A1

## CPC

- G02B 6/0018: {Redirecting means on the surface of the light guide}
- G02B 6/0016: {Grooves, prisms, gratings, scattering particles or rough surfaces}
- G02B 6/0056: {for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements}
- G02B 27/0172: {characterised by optical features}
- G02B 27/283: {used for beam splitting or combining}
- G02B 27/286: {for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another (G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

The present disclosure describes techniques for reflecting light incoupled into a waveguide in a direction away from the outcoupler back toward the outcoupler. The waveguide includes an incoupler to incouple light of a first polarization state, and a reflective structure to receive incoupled light of the first polarization state and reflect it with a second polarization state toward the outcoupler. The reflective structure is on an opposite side of the incoupler as the outcoupler. In some embodiments, a polarization beam splitter or other polarization-selective layer is included at an interface of the incoupler and a waveguide substrate of the waveguide to transmit light of the first polarization state and reflect light of the second polarization state.

## Claims

### Claim 1

A waveguide comprising:
an incoupler to incouple light of a first polarization state; and
a reflective structure to receive incoupled light of the first polarization state and reflect it with a second polarization state toward an outcoupler.

### Claim 2 (depends on 1)

The waveguide of claim 1, wherein the reflective structure is on an opposite side of the incoupler as the outcoupler.

### Claim 3 (depends on 1)

The waveguide of claim 1, wherein the incoupler transmits light of the first polarization state and reflects light of the second polarization state.

### Claim 4 (depends on 1)

The waveguide of claim 1, further comprising a polarization beam splitter layer at an interface between the incoupler and a waveguide substrate of the waveguide.

### Claim 5 (depends on 4)

The waveguide of claim 4, wherein the polarization beam splitter layer transmits light of the first polarization state and reflects light of the second polarization state.

### Claim 6 (depends on 1)

The waveguide of claim 1, wherein the reflective structure comprises a diffractive grating with a fractional pitch of a grating of the incoupler.

### Claim 7 (depends on 6)

The waveguide of claim 6, wherein the fractional pitch is half of a pitch.

### Claim 8 (depends on 6)

The waveguide of claim 6, wherein the reflective structure comprises a waveplate to convert light of the first polarization state to the second polarization state.

### Claim 9 (depends on 6)

The waveguide of claim 6, wherein the diffractive gating is on a same surface of a waveguide substrate of the waveguide as the incoupler.

### Claim 10 (depends on 1)

The waveguide of claim 1, wherein the reflective structure comprises a prism.

### Claim 11 (depends on 10)

The waveguide of claim 10, wherein the prism is a right-angle prism with mirrored internal surfaces.

### Claim 12 (depends on 10)

The waveguide of claim 10, wherein the reflective structure comprises a waveplate to convert light of the first polarization state to the second polarization state.

### Claim 13 (depends on 1)

The waveguide of claim 1, wherein the reflective structure comprises a mirror.

### Claim 14 (depends on 13)

The waveguide of claim 13, wherein the reflective structure comprises a waveplate to convert light of the first polarization state to the second polarization state.

### Claim 15 (depends on 1)

The waveguide of claim 1, wherein the incoupler comprises a binary diffractive incoupler grating.

### Claim 16

A method comprising:
incoupling, via an incoupler, light of a first polarization state into a waveguide; and
receiving, at a reflective structure, incoupled light of the first polarization state and reflecting it with a second polarization state toward an outcoupler.

### Claim 17 (depends on 16)

The method of claim 16, wherein the reflective structure is on an opposite side of the incoupler as the outcoupler.

### Claim 18 (depends on 16)

The method of claim 16, further comprising converting the incoupled light of the first polarization state to the second polarization state via a waveplate in the reflective structure.

### Claim 19 (depends on 18)

The method of claim 18, further comprising reflecting light of the second polarization state at an interface of the incoupler and a waveguide substrate of the waveguide.

### Claim 20 (depends on 16)

The method of claim 16, wherein the incoupler comprises a binary diffractive incoupler grating.