Prism based light redirection system for eye tracking systems
A head-mounted device (HMD) contains a display, an optics block, a redirection structure, and an eye tracking system. The display is configured to emit image light and provide it to an eye of a user. The optics block is configured to direct the emitted light in order to allow it to reach the eye. The eye tracking system contains a camera, an illumination source, and a controller. The camera is configured to capture image data using infrared light reflected from the eye. The controller is configured to use this image data to determine eye tracking information. The illumination source is configured to illuminate the eye with infrared light for the purpose of taking eye tracking measurements. The redirection structure is configured to direct infrared light reflected from the eye to the eye tracking system. In multiple embodiments, redirection structures may comprise prism arrays, lenses, liquid crystal layers, or grating structures.
1. A redirection structure comprising:
a polarization interlace grating structure including an isotropic grating that is overmolded with a layer of birefringent material that forms a surface on a first side of the isotropic grating, the isotropic grating is such that it reflects light in an infrared band that is received from an eyebox to a first position, and
wherein the first position is occupied by a camera of an eye tracking system and light in the infrared band is reflected from an eye in the eyebox and redirected by the polarization interlace grating toward the first position,
wherein the redirection structure is located between a display element and the eyebox, the display element configured to emit image light in a visible band towards a second side of the redirection structure, wherein the second side is opposite the first side, and the first side is closer to the eyebox than the display element, and
the redirection structure further comprises:
a dichroic coating coupled to the second side of the redirection structure, and the dichroic coating is reflective in the infrared band and transmissive in the visible band.
2. The redirection structure of claim 1 , wherein the birefringent layer is linearly birefringent and light in the infrared band is linearly polarized.
3. The redirection structure of claim 1 , wherein the birefringent layer is circularly birefringent and light in the infrared band is circularly polarized.
4. The redirection structure of claim 1 , wherein the first side of the isotropic grating is located on an eyebox-facing side of the redirection structure.
5. The redirection structure of claim 1 , wherein the first side of the isotropic grating is located on a side opposite an eyebox-facing side of the redirection structure.
6. The redirection structure of claim 1 , wherein the birefringent layer is filled with photopolymerized liquid crystal.
7. The redirection structure of claim 1 , wherein the birefringent layer is filled with chiral liquid crystal.
8. The redirection structure of claim 1 , wherein the birefringent layer forms a grating.
9. The redirection structure of claim 1 , wherein the isotropic grating has a first refractive index, and the birefringent layer has an ordinary refractive index equal to the first refractive index.
10. The redirection structure of claim 9 , wherein the isotropic grating is composed a first material and the birefringent layer is composed of a second material, the first material being different from the second material.
11. The redirection structure of claim 1 , wherein the isotropic grating is a blazed grating with a blaze angle ranging from 20 to 60 degrees.
12. The redirection structure of claim 1 , wherein the redirection structure is a component of a head-mounted display device.
13. A head-mounted display (HMD) comprising:
a display element configured to output image light in a visible band of light through a display surface;
a redirection structure configured to direct light in an infrared band to a first position and to transmit light in the visible band from a first side of the redirection structure to a second side of the redirection structure, the redirection structure comprising:
a polarization interlace grating structure including an isotropic grating that is overmolded with a layer of birefringent material that forms a surface on a first side of the isotropic grating, the isotropic grating is such that it reflects light in the infrared band received from an eyebox to the first position, and
a dichroic coating coupled to the first side of the redirection structure, the dichroic coating is reflective in the infrared band and transmissive in the visible band; and
an illumination source configured to illuminate portions of the eyebox with the light in the infrared band; and
a camera located in the first position, the camera configured to capture the light in the infrared band that is reflected from an eye in the eyebox and redirected by the redirection structure to the first position.
14. The HMD of claim 13 , wherein the birefringent layer is linearly birefringent and light in the infrared band is linearly polarized.
15. The HMD of claim 13 , wherein the birefringent layer is circularly birefringent and light in the infrared band is circularly polarized.
16. The HMD of claim 13 , wherein the isotropic grating has a first refractive index, and the birefringent layer has an ordinary refractive index equal to the first refractive index.
17. The HMD of claim 13 , wherein the isotropic grating is composed a first material and the birefringent layer is composed of a second material, the first material being different from the second material.
18. A redirection structure comprising:
a polarization interlace grating structure including an isotropic grating that is overmolded with a layer of birefringent material that forms a surface on a first side of the isotropic grating, the isotropic grating is such that it reflects light in an infrared band that is received from an eyebox to a first position, and
wherein the first position is occupied by a camera of an eye tracking system and light in the infrared band is reflected from an eye in the eyebox and redirected by the polarization interlace grating toward the first position,
wherein the isotropic grating is a blazed grating with a blaze angle ranging from 20 to 60 degrees.
19. A head-mounted display (HMD) comprising:
a display element configured to output image light in a visible band of light through a display surface;
a redirection structure configured to direct light in an infrared band to a first position and to transmit light in the visible band from a first side of the redirection structure to a second side of the redirection structure, the redirection structure comprising:
a polarization interlace grating structure including an isotropic grating that is overmolded with a layer of birefringent material that forms a surface on a first side of the isotropic grating, the isotropic grating is such that it reflects light in the infrared band received from an eyebox to the first position, wherein the isotropic grating is a blazed grating with a blaze angle ranging from 20 to 60 degrees,
an illumination source configured to illuminate portions of the eyebox with the light in the infrared band; and
a camera located in the first position, the camera configured to capture the light in the infrared band that is reflected from an eye in the eyebox and redirected by the redirection structure to the first position.