Reducing ghost images

• US 9,766,464 B2
• Filed: 12/17/2015
• Issued: 09/19/2017
• Est. Priority Date: 12/17/2015
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Inventors: Poon, Yarn Chee, Nguyen, Ian, Glik, Eliezer, Levola, Tapani
• Primary Examiner(s): FONT, FRANK G
• Application Number:
  US14/973,150
• Publication Number:
  US 20170176745A1
• Time in Patent Office: 642 Days
• Field of Search: 35948907, 359630, 359633, 359900, 385 37, 345 8
• CPC Class Codes: G02B 2027/012 comprising devices for attenuating parasitic image effects
• CPC Class Codes: G02B 2027/0125 Field-of-view increase by wavefront division
• CPC Class Codes: G02B 2027/0174 holographic
• CPC Class Codes: G02B 2027/0178 Eyeglass type eyeglass details G02C
• CPC Class Codes: G02B 27/0018 with means for preventing ghost images anti-reflection coatings G02B1/11
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: 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
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces

Abstract

In a near-eye or heads-up display system including a display engine and an optical waveguide, a quarter-wave retarder (QWR) is positioned between a polarizing beam splitter (PBS) of the display engine and an input diffraction grating of the waveguide. Additionally, a linear polarizer can be positioned between the PBS and the QWR. Light corresponding to an image generated by a reflective microdisplay of the display engine is diffracted into the waveguide by the input diffraction grating, so it can travel by way of total internal reflection to an output coupler and viewed by a human eye. The QWR alone, or in combination with the linear polarizer, prevents a ghost image that may otherwise occur if a portion of the light corresponding to the image, that is diffracted into the waveguide by the input diffraction grating, is diffractively out-coupled by the input diffraction grating and thereafter reflects off the reflective microdisplay.

Claims

1. A near-eye or heads-up display system, comprising:

an optical waveguide including an input diffraction grating and an output coupler;

a display engine configured to produce an image and to direct light corresponding to the image and having a first linear polarization state toward the input diffraction grating of the optical waveguide;

the input diffraction grating of the optical waveguide configured to diffract light corresponding to the image, that is incident on the input diffraction grating, into the optical waveguide; and

a quarter-wave retarder (QWR) positioned within the display engine, or between the display engine and the input diffraction grating of the optical waveguide, so that linearly polarized light corresponding to the image and having the first linear polarization state, which is directed toward the input diffraction grating of the optical waveguide, is converted to circularly polarized light before being diffracted into the optical waveguide by the input diffraction grating;

wherein the QWR will change from circularly polarized light to linearly polarized light having a second linear polarization state that is orthogonal to the first linear polarization state, at least a portion of circularly polarized light corresponding to the image that after being diffracted into the optical waveguide by the input diffraction grating is diffracted out of the optical waveguide by the input diffraction grating.

2. The system of claim 1, wherein:

the display engine includes a reflective microdisplay that is used to produce the image; and

the display engine also includes a polarizing beam splitter (PBS) configured to transmit linearly polarized light having the first linear polarization state, and reflect linearly polarized light having the second linear polarization state that is orthogonal to the first linear polarization state; and

the PBS is positioned within the display engine and relative to the optical waveguide to reflect, in a direction away from the reflective microdisplay, at least a portion of light corresponding to the image that after being diffracted out of the optical waveguide by the input diffraction grating is converted by the QWR from circularly polarized light to linearly polarized light having the second linear polarization state that is orthogonal to the first linear polarization state.

3. The system of claim 2, wherein the system prevents a ghost image that may otherwise be caused if light corresponding to the image, after being diffracted out of the optical waveguide by the input diffraction grating, were reflected off of the reflective microdisplay.

4. The system of claim 1, further comprising:

a linear polarizer configured to transmit light having the first linear polarization state and absorb light having the second linear polarization state that is orthogonal to the first linear polarization state;

wherein the linear polarizer is positioned relative to the QWR to absorb at least a portion of light corresponding to the image that after being diffracted out of the optical waveguide by the input diffraction grating is converted by the QWR from circularly polarized light to linearly polarized light having the second linear polarization state that is orthogonal to the first linear polarization state.

5. The system of claim 4, wherein:

the display engine includes a reflective microdisplay that is used to produce the image; and

the display engine also includes a polarizing beam splitter (PBS) positioned within the display engine and relative to the optical waveguide to cause linearly polarized light corresponding to the image and having the first linear polarization state to be directed toward the input diffraction grating of the optical waveguide;

the QWR is positioned between the PBS of the display engine and the input diffraction grating of the optical waveguide; and

the linear polarizer is positioned between the PBS of the display engine and the QWR.

6. The system of claim 5, wherein the system prevents a ghost image that may otherwise be caused if light corresponding to the image, after being diffracted out of the optical waveguide by the input diffraction grating, were reflected off of the reflective microdisplay.

7. The system of claim 1, wherein the QWR comprises a quarter wave film, a quarter wave coating or a quarter wave plate.

8. The system of claim 1, wherein the first linear polarization state comprises P polarization, and the second linear polarization state comprises S polarization.

9. The system of claim 1, wherein the first linear polarization state comprises S polarization, and the second linear polarization state comprises P polarization.

10. The system of claim 1, wherein the optical waveguide is configured to cause at least a portion of light corresponding to an image, that is diffracted into the optical waveguide by the input diffraction grating, to travel by way of total internal reflection (TIR) to the output coupler where the portion of the light corresponding to the image is coupled out of the optical waveguide.

11. A method, comprising:

producing an image using a reflective microdisplay;

directing linearly polarized light corresponding to the image towards an input diffraction grating of an optical waveguide, the linearly polarized light having a first linear polarization state;

using a quarter wave retarder (QWR) to change the linearly polarized light corresponding to the image to circularly polarized light so that the light corresponding to the image that is diffracted into the optical waveguide by the input diffraction grating is circularly polarized;

using the optical waveguide to internally reflect a portion of the circularly polarized light corresponding to the image from the input diffraction grating to an output coupler of the optical waveguide where the portion of the light corresponding to the image is coupled out of the waveguide; and

using the QWR to change a further portion of the light corresponding to the image, which after being diffracted into the optical waveguide by the input diffraction grating is diffracted out of the optical waveguide by the input diffraction grating, from circularly polarized light to linearly polarized light having a second linear polarization state that is orthogonal to the first linear polarization state.

12. The method of claim 11, further comprising:

preventing the further portion of the light corresponding to the image, which has the second linear polarization state that is orthogonal to the first linear polarization state, and which is diffracted out of the optical waveguide by the input diffraction grating, from being reflected off the reflective microdisplay.

13. The method of claim 12, wherein:

the directing the linearly polarized light corresponding to the image towards the input diffraction grating of the optical waveguide is performed using a polarizing beam splitter (PBS); and

the preventing the further portion of the light corresponding to the image from being reflected off the reflective microdisplay is performed by using the PBS to reflect the further portion of the light corresponding to the image in a direction away from the reflective microdisplay.

14. The method of claim 12, wherein:

the directing the linearly polarized light corresponding to the image towards the input diffraction grating of the optical waveguide is performed using a polarizing beam splitter (PBS); and

the preventing the further portion of the light corresponding to the image from being reflected off the reflective microdisplay is performed using a linear polarizer that is configured to transmit light having the first linear polarization state and to absorb light having the second linear polarization state.

15. The method of claim 14, wherein:

the QWR is positioned between the PBS and the input diffraction grating of the optical waveguide; and

the linear polarizer is positioned between the PBS and the QWR.

16. A system, comprising:

a reflective microdisplay configured to produce an image;

a polarizing beam splitter (PBS);

an optical waveguide including an input diffraction grating and an output coupler;

the PBS positioned to cause linearly polarized light corresponding to the image and having a first linear polarization state to be directed toward the input diffraction grating of the optical waveguide;

a quarter-wave retarder (QWR) positioned between the PBS and the input diffraction grating of the optical waveguide so that linearly polarized light corresponding to the image and having the first linear polarization state, which is directed toward the input diffraction grating of the optical waveguide, is converted to circularly polarized light before being diffracted into the waveguide by the input diffraction grating of the optical waveguide; and

the optical waveguide configured to cause at least a portion of the circularly polarized light corresponding to the image, that is diffracted into the waveguide by the input diffraction grating, to travel by way of total internal reflection (TIR) to the output coupler where the portion of the light corresponding to the image is coupled out of the waveguide;

wherein the QWR, which is positioned between the PBS and the input diffraction grating, will change from circularly polarized light to linearly polarized light having the second linear polarization state that is orthogonal to the first linear polarization state, a further portion of the circularly polarized light corresponding to the image that after being diffracted into the optical waveguide by the input diffraction grating is diffracted out of the optical waveguide by the input diffraction grating.

17. The system of claim 16, wherein:

the PBS will reflect, in a direction away from the reflective microdisplay, light corresponding to the image that after being diffracted out of the optical waveguide by the input diffraction grating is converted by the QWR from circularly polarized light to linearly polarized light having the second linear polarization state that is orthogonal to the first linear polarization state, thereby preventing a ghost image that may otherwise occur due to the diffracted out light.

18. The system of claim 16, further comprising:

a linear polarizer positioned between the PBS and the QWR and configured to transmit light having the first linear polarization state and absorb light having the second linear polarization state that is orthogonal to the first linear polarization state;

wherein the linear polarizer will transmit the light corresponding to the image and having the first linear polarization state, that is directed toward the input diffraction grating of the optical waveguide, before the light corresponding to the image and having the first linear polarization state reaches the QWR; and

wherein the linear polarizer will absorb light corresponding to the image that after being diffracted out of the optical waveguide by the input diffraction grating is converted by the QWR from circularly polarized light to linearly polarized light having the second linear polarization state that is orthogonal to the first linear polarization state, thereby preventing a ghost image that may otherwise occur due to the diffracted out light.

19. The system of claim 16, wherein the reflective microdisplay comprises a liquid crystal on silicon (LCoS) microdisplay.

20. The system of claim 16, wherein the first linear polarization state comprises P polarization, and the second linear polarization state comprises S polarization.