Dichroic Mirror Embedded Eye Tracker for AR
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Solution Overview
Problem
Augmented reality (AR) eye trackers face challenges in achieving accurate eye tracking due to their compact form factor, which limits the placement of cameras and mirrors, leading to off-axis views and increased susceptibility to damage.
Innovation Solution
Incorporating a dichroic mirror into the optical element of AR devices, angled to reflect non-visible light towards a camera embedded in the frame, allowing for more on-axis eye tracking while maintaining visibility and protection from the user's perspective.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a camera is placed far from the optical axis in the frame to avoid disrupting the user's view, then the camera is protected from damage, but the eye tracking accuracy deteriorates due to off-axis view
Solution Approach 1:
A dichroic mirror is introduced as an intermediary optical element between the eye and the camera. The mirror reflects non-visible light (infrared) from the eye to the camera while allowing visible light to pass through, enabling the camera to capture eye reflections from a protected position in the frame while maintaining on-axis optical path for accurate eye tracking
Solution Approach 2:
The optical path is redirected from a lateral (x-axis) arrangement to a depth (z-axis) arrangement by using the dichroic mirror to reflect light at an angle. This dimensional change allows the camera to be positioned in the frame plane while maintaining an effective on-axis view of the eye through the reflected optical path
2Volume of moving object
If the form factor of AR device is reduced to resemble eyeglasses, then the device becomes more wearable and compact, but the placement of mirrors and cameras becomes difficult
Solution Approach 1:
The dichroic mirror serves multiple functions simultaneously: it acts as a beam splitter to separate visible and non-visible light paths, provides the optical interface for the eye tracking camera, and maintains the compact form factor by integrating into the existing optical element structure rather than requiring separate mirror mounting space
Solution Approach 2:
The eye tracking optical path is merged with the existing waveguide or lens optical element by incorporating the dichroic mirror into the optical element itself. This integration combines the display optics and eye tracking optics into a single unified structure, eliminating the need for separate mirror assemblies and reducing overall device complexity
3Measurement precision
If a mirror is placed behind the lens in VR systems, then the eye tracking function is achieved, but the device form factor increases and is not suitable for compact AR devices
Solution Approach 1:
Instead of placing the mirror behind the lens along the optical axis (z-axis), the dichroic mirror is positioned in the frame plane and redirects light at an angle, utilizing the lateral dimension (x-axis) for camera placement while maintaining compact device dimensions. This dimensional reconfiguration eliminates the need for extended device depth
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 accuracy of eye tracking by providing a more on-axis view of the eye and protects the camera from damage, ensuring reliable operation in compact AR devices.
Implementation Method 1
The dichroic mirror is reflective in the first band of light, is transmissive in a second band of light, and is configured to direct light in the first band that is reflected from the portion of the eye toward a first position
Implementation Method 2
The one or more sources emit light in a first band of light, and the one or more sources are configured to illuminate a portion of an eye of a user of the eyewear device
Implementation Method 3
The camera is configured to capture one or more images of the light in the first band reflected by the dichroic mirror
Data Source
AI summary
An eyewear device has an optical element, a source, a dichroic mirror, and a camera. The optical element has a front surface, a back surface, a rim, and an angled portion of the rim. The source emits light in a first band of light and is configured to illuminate a portion of an eye of a user of the eyewear device. The dichroic mirror is arranged proximate to the angled portion of the rim, is reflective in the first band of light, is transmissive in a second band of light, and is configured to direct light in the first band reflected from the portion of the eye toward a first position. The camera is located in the first position that is located in a plane of the optical element, and the camera is configured to capture images of the light in the first band reflected by the dichroic mirror.