Optical device having reduced diffraction artifacts for eye-tracking
A system is provided. The system includes a light source configured to emit an infrared light to illuminate an eye of a user. The system includes a grating disposed facing the eye and including a birefringent material film configured with a uniform birefringence lower than or equal to 0.1. The grating is configured to diffract the infrared light reflected from the eye, and transmit a visible light from a real world environment toward the eye, with a diffraction efficiency less than a predetermined threshold. The system includes an optical sensor configured to receive the diffracted infrared light and generate an image of the eye based on the diffracted infrared light.
1. A system, comprising:
a light source configured to emit an infrared light to illuminate an eye of a user;
a grating disposed facing the eye and including a polarization volume hologram (“PVH”) film configured with a uniform birefringence lower than or equal to 0.1, wherein the grating is configured to diffract the infrared light reflected from the eye, and transmit a visible light from a real world environment toward the eye with a diffraction efficiency of less than 0.5% for the visible light; and
an optical sensor configured to receive the diffracted infrared light and generate an image of the eye based on the diffracted infrared light.
2. The system of claim 1 , wherein the diffraction efficiency is less than 0.1%.
3. The system of claim 1 , wherein the diffraction efficiency is less than 0.05%.
4. The system of claim 1 , wherein the diffraction efficiency is less than 0.01%.
5. The system of claim 1 , wherein the PVH film is a reflective PVH film.
6. The system of claim 1 , wherein the PVH film includes molecules configured with in-plane molecular reorientations that change in a linearly repetitive pattern from a center to an edge of the PVH film.
7. The system of claim 1 , further including a display system configured to project a virtual image into a display window in a predetermined field of view.
8. The system of claim 7 , wherein the grating is configured to optically combine the virtual image and a real image formed by the visible light from the real world environment in the predetermined field of view.
9. The system of claim 1 , wherein the grating reduces a rainbow effect in a see-through view observed caused by a diffraction of the visible light from the real world environment toward the eye.
10. The system of claim 1 , wherein the PVH film is configured to converge or diverge the infrared light while diffracting the infrared light.
11. The system of claim 1 , wherein the PVH film is a transmissive PVH film.