Scanning Mirror Eyebox Expansion in Head-Mounted Displays
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Solution Overview
Problem
Conventional near-to-eye optical systems in head-mounted displays (HMDs) suffer from limited field of view and eyebox size, leading to a degraded user experience due to small eyebox dimensions, which can cause the image to disappear with minor shifts in the optical apparatus.
Innovation Solution
The implementation of whole image scanning using a scanning mirror and actuator, combined with real-time eye tracking and diffraction gratings, to project a two-dimensional array of image pixels simultaneously and dynamically adjust the image position to enlarge the eyebox area, allowing the image to be viewed from a larger range of locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional near-to-eye optical systems are used in HMDs, then the system structure is simple, but the eyebox size is limited and the field of view is restricted
Solution Approach 1:
The patent employs a scanning mirror that dynamically moves to redirect the projected image across different angular positions. This dynamic repositioning allows a single static optical path to serve multiple viewing angles, effectively enlarging the eyebox area without requiring multiple fixed optical paths or complex multi-element optical systems.
Solution Approach 2:
The scanning mirror introduces an angular dimension to the optical system by rotating the reflected beam across a range of angles. This adds a temporal/dimensional aspect where the image is scanned through different positions over time, transforming a two-dimensional static optical path into a three-dimensional dynamic viewing solution that expands the effective eyebox volume.
2Area of stationary object
If conventional optical systems are used, then the device size is compact, but the field of view is limited
Solution Approach 1:
The scanning mirror dynamically adjusts the angular position of the reflected beam to sweep across a wide field of view. This dynamic scanning mechanism allows a single compact optical path to deliver images across extended angular ranges, effectively expanding the field of view without requiring multiple fixed optical paths or complex multi-element systems.
Solution Approach 2:
The scanning mirror performs periodic angular movements to cycle through different viewing angles, creating a time-varying optical path that systematically covers the entire desired field of view. This periodic scanning action allows a compact static optical system to achieve extended field of view coverage through temporal multiplexing.
3Reliability
If conventional optical systems are used, then the alignment is straightforward, but minor shifts cause the image to disappear
Solution Approach 1:
The scanning mirror dynamically compensates for minor optical misalignments and user head movements by actively adjusting the beam direction. This dynamic adaptation ensures the image remains within the user's field of view even when optical alignment shifts occur, significantly improving image visibility stability and reducing sensitivity to alignment variations.
Solution Approach 2:
The system incorporates eye tracking to monitor user eye position and provides feedback to the scanning mirror control system. This feedback mechanism allows real-time adjustment of the scanning mirror position to maintain proper image alignment with the user's eye, compensating for optical shifts and head movements to keep the image visible.
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 solution significantly increases the eyebox area, relaxing optical alignment constraints and improving user experience by maintaining the image visibility even with minor movements, thereby enhancing the field of view and user interaction.
Implementation Method 1
uses a scanning mirror to redirect the projected image
Implementation Method 2
uses a diffraction grating to extend an eyebox
Data Source
AI summary
An optical apparatus includes an image source, a scanning mirror, an actuator, and a scanning controller. The image source outputs an image by simultaneously projecting a two-dimensional array of image pixels representing a whole portion of the image. The scanning mirror is positioned in an optical path of the image to reflect the image. The actuator is coupled to the scanning mirror to selectively adjust the scanning mirror about at least one axis. The scanning controller is coupled to the actuator to control a position of the scanning mirror about the at least one axis. The scanning controller includes logic to continuously and repetitiously adjust the position of the scanning mirror to cause the image to be scanned over an eyebox area that is larger than the whole portion of the image.