Reflective Pupil Relay Optics for Large-Pupil MEMS Scanning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing laser scanning projectors face challenges in generating a larger pupil size for improved waveguide efficiency and performance, particularly in augmented reality systems, where a larger pupil size enhances the mixing of ambient light with additional visual information.
Innovation Solution
An optical system comprising a RGB laser source, fast and slow axis MEMS micromirrors, and an Offner mirror relay, along with optical surface magnification mirrors, to scan and magnify the laser beam, increasing the pupil size and improving waveguide efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical modules are used with standard pupil size, then device complexity is reduced, but waveguide efficiency and performance deteriorate due to insufficient pupil size for effective light mixing
Solution Approach 1:
The optical module is segmented into multiple functional components: fast axis MEMS mirror for horizontal scanning, slow axis MEMS mirror for vertical scanning, Offner relay for beam expansion, and diffractive waveguide for light mixing. Each component performs a specific function, allowing the system to achieve large pupil size and high waveguide efficiency while maintaining manageable complexity through modular design
Solution Approach 2:
The patent implements nested optical paths where the fast axis MEMS mirror scans the laser beam horizontally, which is then further scanned vertically by the slow axis MEMS mirror. The Offner relay nested within this path expands the beam to create a large output pupil that feeds into the diffractive waveguide, creating a compact nested structure that achieves large pupil size without proportionally increasing device volume
2Reliability
If pupil size is increased to improve waveguide efficiency, then waveguide performance is improved, but optical path complexity and distortion increase
Solution Approach 1:
The Offner relay acts as an intermediary optical system between the MEMS mirrors and the diffractive waveguide. It receives the scanned laser beam and transforms it into a large, well-collimated output pupil with minimal distortion. The relay's dual-mirror design with precise curvature radii (R1 and R2) serves as a mediator that converts the complex scanned beam into a simplified large pupil format suitable for waveguide coupling
Solution Approach 2:
The patent changes key optical parameters to achieve large pupil size: the Offner relay uses specific curvature radii (R1 and R2) and separation distance (d) to achieve the desired beam expansion ratio. The fast and slow axis MEMS mirrors are driven at different frequencies and amplitudes to create the required scanning patterns. These parameter optimizations enable large pupil generation while controlling optical path complexity
3Reliability
If pupil size is increased for better light mixing, then waveguide efficiency improves, but power requirements increase
Solution Approach 1:
The patent replaces traditional mechanical beam expansion mechanisms (such as moving lenses or mirrors) with a stationary Offner relay configuration. The beam expansion is achieved through the fixed geometric arrangement of the relay mirrors rather than mechanical movement, eliminating the need for additional actuators and reducing power consumption while maintaining large pupil size for efficient waveguide coupling
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 enhances waveguide performance by increasing pupil size, reducing distortion, and lowering power requirements, enabling high brightness applications and expanded field of view in augmented reality systems.
Implementation Method 1
an Offner mirror relay receiving the combined RGB laser beam as it is scanned along the slow axis and reflecting the combined RGB laser beam along a second path toward an exit aperture of the optical module
Implementation Method 2
The diffractive waveguide has an input diffractive grating defined therein and is positioned such that the combined RGB laser beam passes from the exit aperture of the optical module into the input diffractive grating
Implementation Method 3
three optical surface magnification mirrors receiving the combined RGB laser beam as it is scanned along the fast axis and magnifying a diameter of the combined RGB laser beam
Data Source
AI summary
An optical module includes a fast-axis mirror that scans a laser beam along a fast-axis, a magnification mirror set formed by three discrete mirrors shaped to magnify the laser beam as it is scanned along the fast-axis and reflect the laser beam after magnification toward a slow-axis mirror that scans the laser beam along the slow-axis, and an Offner mirror relay that receives the laser beam as it is scanned along the slow-axis and reflects the laser beam out an exit aperture. The laser beam as output from the exit aperture is received at an input diffractive grating of a diffractive waveguide, with a user's eye being positioned adjacent an output diffractive grating of the waveguide such that the user's eye views ambient light entering the waveguide from objects within the user's field of view as well as light from the laser beam as it exits the output diffractive grating.