Position tracking system for head-mounted display systems
Systems and methods for tracking the position of a head-mounted display (HMD) system component. The HMD component may carry a plurality of angle sensitive detectors that are able to detect the angle of light emitted from a light source. The HMD component may include one or more scatter detectors that detect whether light has been scattered or reflected, so such light can be ignored. Control circuitry causes light sources to emit light according a specified pattern, and receives sensor data from the plurality of angle sensitive detectors. The processor may process the sensor data and scatter detector data, for example using machine learning or other techniques, to track a position of the HMD component. An angle sensitive detector may include a spatially-varying polarizer having a position-varying polarizing pattern and one or more polarizer layers that together are operative to detect the angle of impinging light.
1. An angle sensitive detector, comprising:
a first polarizer operative to receive and filter light from a light source;
a spatially-varying polarizer optically aligned with the first polarizer, the spatially-varying polarizer including a polarization pattern configured to uniquely differentiate incident light by its incidence angle relative to the angle sensitive detector;
a second polarizer optically aligned with the spatially-varying polarizer to receive and filter light received from the spatially-varying polarizer; and
a photodetector positioned to receive light from the second polarizer, the photodetector operative to output at least one intensity signal that is indicative of the incidence angle of the incident light relative to the angle sensitive detector.
2. The angle sensitive detector of claim 1 wherein the spatially-varying polarizer comprises a liquid crystal material.
3. The angle sensitive detector of claim 1 wherein the spatially-varying polarizer comprises a multi-twist retarder.
4. The angle sensitive detector of claim 1 wherein the spatially-varying polarizer is operative to be switched off and, when the spatially-varying polarizer is switched off, the spatially-varying polarizer is operative to cease changing the polarization of the incident light.
5. The angle sensitive detector of claim 1 wherein the spatially-varying polarizer comprises a phase retarder.
6. The angle sensitive detector of claim 1 wherein the spatially-varying polarizer provides linear polarization at a first end, and gradually increases the retardance toward a second end opposite the second end.
7. The angle sensitive detector of claim 6 wherein the spatially-varying polarizer provides quarter wave retardance at the second end.
8. The angle sensitive detector of claim 1 wherein the first polarizer and the second polarizer each comprise linear polarizers.
9. The angle sensitive detector of claim 1 wherein the first polarizer and the second polarizer each comprise linear polarizers having the same polarization orientation.
10. An angle sensitive detector, comprising:
a first polarizer configured to:
receive light;
filter the light; and
output a first component of the filtered light;
a spatially-varying polarizer having a position-varying polarizing pattern that defines a plurality of polarization conversion properties respectively associated with a plurality of positions, the plurality of polarization conversion properties being operative to change a polarization of the first component differently depending on a position where the first component impinges on the spatially-varying polarizer, the spatially-varying polarizer being configured to:
receive the first component at a first position of the plurality of positions;
change the polarization of the first component in accordance with a first polarization conversion property, associated with the first position, of the plurality of polarization conversion properties; and
output a polarization-converted first component;
a second polarizer configured to:
receive the polarization-converted first component;
filter the polarization-converted first component; and
output a second component of the polarization-converted first component;
and
a photodetector configured to:
receive the second component;
detect the intensity of the second component; and
output data representative of the intensity of the second component, the data representative of the intensity of the second component usable to determine the first position.
11. The angle sensitive detector of claim 10 wherein the spatially-varying polarizer comprises a liquid crystal material.
12. The angle sensitive detector of claim 10 wherein the spatially-varying polarizer comprises a multi-twist retarder.
13. The angle sensitive detector of claim 10 wherein the position-varying polarizing pattern comprises a linear polarizer at a first end, a circular polarizer at a second end opposite the first end, and a gradual change between the linear polarizer and the circular polarizer between the first end and the second end.
14. The angle sensitive detector of claim 10 , wherein the first polarizer uniformly filters the light irrespective of where the light impinges on the first polarizer.
15. The angle sensitive detector of claim 10 , wherein the second polarizer uniformly filters the polarization-converted first component irrespective of where the polarization-converted first component impinges on the second polarizer.
16. The angle sensitive detector of claim 10 , wherein the spatially-varying polarizer is operative to be switched off and, when the spatially-varying polarizer is switched off, the spatially-varying polarizer is operative to cease changing the polarization of the first component.
17. The angle sensitive detector of claim 10 , wherein the photodetector is a single-cell photodiode.
18. The angle sensitive detector of claim 10 , wherein the photodetector is a multi-cell photodiode having a plurality of cells operative to detect a respective intensity of the second component in each cell of the plurality of cells.
19. The angle sensitive detector of claim 10 , wherein the light is emitted by a base station or a mobile object.
20. The angle sensitive detector of claim 10 , wherein the first polarizer and the second polarizer have the same light filtering properties.