Reflective Illumination Source for HMD Eye Tracking
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Solution Overview
Problem
Conventional methods for determining a user's focal point in head-mounted displays (HMDs) become increasingly difficult as fields of view expand and distances between the user's eyes and the display decrease, due to light scattering and refraction issues with conventional backlights used in liquid crystal displays.
Innovation Solution
Incorporating a reflective illumination source coupled to a partially transparent circuit board and a compound mirror positioned behind the display, which emits light onto the mirror to reflect and transmit suitable wavelengths for eye tracking, allowing for improved pupil identification and focal point determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional backlights are used in liquid crystal displays, then the display is illuminated, but light scattering and refraction prevent accurate eye tracking
Solution Approach 1:
The patent extracts the illumination function from the display structure by using a separate reflective illumination source positioned behind the display. This separates the backlighting function from the display panel, allowing the illumination source to be optimized for eye tracking without compromising display performance. The illumination source is taken out from the conventional backlight position and repositioned to reflect off the compound mirror.
Solution Approach 2:
The patent introduces a compound mirror as an intermediary between the illumination source and the display. This mirror reflects illumination light onto the display while being transparent to the imaging device's infrared light. The compound mirror acts as a mediator that enables both display illumination and eye tracking functionality without direct interference between the two systems.
2Area of stationary object
If the field of view increases and distance between user's eyes and display decreases, then more content is visible, but pupil identification becomes increasingly difficult
Solution Approach 1:
The patent replaces the mechanical/optical constraint of positioning an imaging device behind the display with a reflective illumination system. Instead of trying to position sensors optimally, the system uses a compound mirror to redirect illumination light, allowing the imaging device to capture clear pupil images even when the display is positioned close to the user's eyes for wide field of view.
3Measurement precision
If imaging device is positioned behind the display, then eye tracking is enabled, but conventional backlights scatter and refract light preventing suitable image capture
Solution Approach 1:
The patent inverts the conventional illumination approach by using a reflective illumination source instead of a transmissive backlight. Instead of light passing through the display from behind, the illumination source reflects light onto the display through the compound mirror. This inversion allows the imaging device positioned behind the display to capture clear pupil images without interference from scattered backlight light.
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 configuration enhances the ability to accurately track eye position and focus within HMDs, even with increased fields of view and reduced distances, by minimizing light scattering and refraction effects.
Implementation Method 1
The compound mirror is a mirrored surface having curvature in two orthogonal axes... the compound mirror reflects visible light incident on the compound mirror
Implementation Method 2
the compound mirror transmits certain wavelengths of light incident on the compound mirror, while reflecting other wavelengths of light incident on the compound mirror. For example, the compound mirror reflects visible light incident on the compound mirror, but transmits at least 50% of infrared light (e.g., light having a wavelength of 850 nm) incident on the compound mirror
Implementation Method 3
The illumination source is configured to emit light onto the compound mirror. In different embodiments, any type of illumination source may be used. Example illumination sources 310 include a light emitting diode (LED), an organic light emitting diode (OLED), a laser diode
Implementation Method 4
The illumination source is coupled to the partially transparent circuit board, which is nearer to the display than the illumination source. The partially transparent circuit board includes a transparent substrate, such as glass or plastic, and circuit traces coupling components
Data Source
AI summary
A head-mounted display (HMD) includes a display illuminated by one or more illumination sources. An illumination source is coupled to a partially transparent circuit board and is configured to emit light onto a compound mirror. The compound mirror is farther from an exit pupil of the HMD than the display and reflects light from the illumination source back towards the exit pupil of the HMD. Light reflected by the compound mirror is transmitted through the partially transparent circuit board onto the display, illuminating the display.