Dual-path disparity sensor for waveguide display alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In near-eye display systems, particularly waveguide-based systems, it is challenging to detect boresight errors between the left and right images due to misalignments or relative movements, leading to undesired optical artifacts like illumination and color mismatch, which degrade the user experience. The existing designs face difficulties in coupling sufficient disparity test light signal to the disparity sensor, especially for shorter wavelengths like blue light, resulting in low intensity and inaccurate detection.
Innovation Solution
The implementation of a waveguide display system that uses a projector to project both display light and disparity test light, with a set of output gratings that direct the disparity test light along two different paths within the waveguide. This system includes first and second disparity gratings with different grating vectors, allowing the disparity test light to propagate along secondary paths with larger incident angles, reducing interactions and losses, and enhancing signal strength collected by the disparity sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If disparity test light is coupled into the waveguide using existing output gratings, then the system can detect boresight errors, but the signal strength is insufficient especially for shorter wavelengths like blue light
Solution Approach 1:
The output grating is divided into two separate gratings: a first output grating that directs display light to the user's eye, and a second output grating that directs disparity test light to the disparity sensor. This segmentation allows each grating to be optimized for its specific function, with the second grating specifically designed to enhance signal strength for detection wavelengths including blue light
Solution Approach 2:
The second output grating serves multiple purposes: it directs blue light (shorter wavelengths) to the disparity sensor with high efficiency, and also directs green and red light (longer wavelengths) to the disparity sensor. This multi-functionality ensures sufficient signal strength across the entire visible spectrum for accurate boresight error detection
2Ease of manufacture
If disparity test light propagates along the primary path in the waveguide, then it follows the standard optical path, but it experiences multiple interactions and losses reducing signal strength
Solution Approach 1:
The system introduces a secondary path that diverges from the primary propagation path at a different angle. The second output grating couples disparity test light into this secondary path, which directs light to the disparity sensor through a different geometric route. This dimensional change in the optical path reduces interactions with waveguide boundaries and minimizes losses, significantly enhancing signal strength
3Device complexity
If the waveguide uses a single layer structure, then the device complexity is reduced, but it cannot efficiently direct shorter wavelengths to the disparity sensor
Solution Approach 1:
The output coupler region of the waveguide is designed with local quality variations: the first output grating is optimized for directing display light (all wavelengths) to the user's eye, while the second output grating is specifically optimized for directing disparity test light (particularly shorter wavelengths like blue light) to the disparity sensor. This localized optimization at the output interface enables efficient wavelength-specific coupling without requiring complex multi-layer waveguide structures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly improves the signal strength of disparity test light detected by the sensor, particularly for shorter wavelengths, achieving up to 40 times higher intensity without modifying existing input and output gratings, thereby enabling accurate detection and compensation for misalignments, thus enhancing the user experience by reducing optical artifacts.
Implementation Method 1
The one or more output gratings may be configured to direct a first portion of the disparity test light coupled into the waveguide along a first path to the first disparity grating, and direct a second portion of the disparity test light coupled into the waveguide along a second path to the second disparity grating
Implementation Method 2
an input coupler on the waveguide and configured to couple disparity test light into the waveguide
Implementation Method 3
The first disparity grating may be configured to couple the first portion of the disparity test light out of the waveguide, and the second disparity grating may be configured to couple the second portion of the disparity test light out of the waveguide
Data Source
AI summary
A waveguide display system includes a waveguide transparent to visible light, a projector configured to project disparity test light onto the waveguide, an input coupler configured to couple the disparity test light into the waveguide, and a set of gratings on the waveguide. The set of gratings is configured to guide the disparity test light to propagate along two different paths in the waveguide, and couple the disparity test light propagating along the two different paths out of the waveguide at a peripheral region of the waveguide. The set of gratings includes two disparity gratings having different grating vectors or a two-dimensional grating having two different grating vectors. The disparity test light on a longer primary path includes the full color spectrum of the disparity test light, while the disparity test light on a shorter secondary path includes only disparity test light having shorter wavelengths.