Compact HMD Using Dichroic Element for Eye Tracking
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) are bulky, making them unsuitable for mixed reality applications where a lightweight form factor is desirable without compromising brightness or user experience.
Innovation Solution
A compact HMD design incorporating an electronic display, a pancake lens assembly, a dichroic element, an eye tracking system, and a depth camera assembly, which uses separate optical bands for image presentation and eye tracking, allowing for a reduced form factor and weight while maintaining brightness and enabling advanced user interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional display panels and optical assemblies are used, then image brightness is maintained, but device weight and form factor increase
Solution Approach 1:
The optical system is segmented into multiple functional layers: a waveguide layer for light propagation, a coupling layer for injecting image light, and a separate dichroic element for eye tracking illumination. This segmentation allows each component to be optimized independently, reducing overall weight while maintaining brightness performance.
Solution Approach 2:
The patent transitions from conventional bulk optical assemblies to a planar waveguide-based optical system. By confining light propagation to a two-dimensional waveguide plane, the optical path is compressed in the third dimension, dramatically reducing headset weight and form factor while preserving image brightness through efficient light coupling.
2Adaptability or versatility
If separate optical bands are used for image display and eye tracking, then device functionality is enhanced, but optical system complexity increases
Solution Approach 1:
The waveguide structure serves multiple functions simultaneously: it guides image light from the display to the user's eye, transmits infrared illumination light for eye tracking, and allows optical access for depth sensing cameras. This multi-functionality reduces the need for separate optical paths, simplifying the overall system despite enhanced capabilities.
Solution Approach 2:
The dichroic element acts as an optical intermediary that selectively reflects infrared light while transmitting visible light. This allows the system to handle multiple optical bands through a single integrated component rather than requiring separate optical paths for each function, reducing complexity.
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 compact HMD design effectively reduces the bulk and weight of the device while maintaining image brightness and enabling advanced eye tracking and depth sensing capabilities, enhancing the user experience in mixed reality applications.
Implementation Method 1
The dichroic element is transmissive to the image light in the first optical band, and is reflective to light in a second optical band (e.g., an infrared (IR) band) which is different from the first optical band.
Implementation Method 2
The pancake lens assembly directs the image light to an eyebox.
Implementation Method 3
The fold mirror further directs the light to the tracking camera.
Data Source
AI summary
A head-mounted display (HMD) includes a dichroic element, an eye tracking system, a controller, and an external focus camera. The dichroic element is transmissive to the light in a first optical band (e.g., visible light) but reflective to light in a second optical band (e.g., IR light). The eye tracking system includes a source assembly and a tracking camera. The source assembly projects light in the second optical band into an eyebox of the HMD. The tracking camera captures images of at least a portion of a user's eye in the eyebox. The controller of the HMD determines a gaze direction of the user based on the captured images. An orientation of the external focus camera corresponds to the gaze direction. The external focus camera captures image data of a portion of a local area surrounding the HMD at the orientation.