Infrared Transparent Backlight for HMD Eye Tracking
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Solution Overview
Problem
Conventional spatial light modulators in head-mounted displays (HMDs) are opaque and scatter infrared light, making it difficult for eye tracking systems to achieve high image quality due to the scattering of IR light caused by the backlight assembly, which complicates the placement of tracking optics and expands field of view requirements.
Innovation Solution
A transparent backlight device that emits light in a first optical band towards the display panel while being transparent to a second optical band, allowing an eye tracking system to view a user's eye through the backlight device, using a mirror assembly and light sources to direct light towards an eyebox and a camera assembly to capture high-resolution images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional opaque backlight assembly is used, then the display can provide sufficient visible light, but it scatters infrared light and prevents high-quality eye tracking images
Solution Approach 1:
The backlight assembly is designed with spatially varying properties: certain regions contain infrared-transmissive materials that allow IR light to pass through without scattering, while other regions maintain conventional opaque structures for visible light emission. This local differentiation enables simultaneous optimization of both visible display performance and infrared eye tracking capability.
Solution Approach 2:
The backlight assembly incorporates composite structures combining materials with different optical properties - specifically, materials that are transparent to infrared wavelengths while maintaining visible light emission characteristics. This composite approach allows the single assembly to fulfill both display illumination and eye tracking transparency requirements.
2Measurement precision
If the backlight assembly is made transparent to infrared light, then eye tracking image quality improves, but the complexity of the optical system increases
Solution Approach 1:
The backlight assembly is designed to perform multiple functions simultaneously: it provides visible light illumination for the display while also serving as an infrared-transmissive window for eye tracking. This multi-functionality eliminates the need for separate infrared-transmissive components, thereby reducing overall system complexity despite the advanced material requirements.
Solution Approach 2:
The patent merges the backlight illumination function with the infrared transmission function into a single integrated assembly. By combining these previously separate functions into one component, the design reduces the number of parts and simplifies the optical path, even though the assembly itself has more complex material properties.
3Device complexity
If conventional backlight assemblies are used, then the display structure remains simple, but the field of view must be expanded to scan facial features which complicates tracking optics placement
Solution Approach 1:
The invention changes the optical parameters of the backlight assembly by introducing infrared transmissivity. This parameter change enables the system to accommodate expanded field of view requirements for facial feature scanning, as the infrared camera can now receive light through the backlight assembly, providing additional viewing angles and tracking capabilities without complicating the physical display structure.
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
The solution enables high-resolution eye tracking with improved image quality by allowing infrared light to pass through the backlight device, enabling accurate eye tracking and expanded field of view without compromising the display's functionality.
Implementation Method 1
The backlight device is configured to emit light in a first optical band through the second surface toward a display panel of a head-mounted display (HMD). The backlight device is transparent to light in a second optical band that is different than the first optical band.
Implementation Method 2
The backlight device is transparent to light in a second optical band that is different than the first optical band, allowing an eye tracking system to view a user's eye through the backlight device in the second optical band
Data Source
AI summary
A backlight device includes a first surface and a second surface that is opposite to the first surface. The backlight device is configured to emit light in a first optical band through the second surface toward a display panel of a head-mounted display (HMD). The display panel is configured to convert the light from the backlight device to image light. The backlight device is transparent to light in a second optical band that is different than the first optical band. An eye tracking system illuminates an eyebox with light in the second optical band. A camera assembly positioned adjacent to the first surface of the backlight device. The camera assembly is configured to capture images of the eye in the second optical band through the backlight device, the display panel. The eye tracking system determines eye tracking information based at least in part on the captured images.