Tilt-Mirror Assembly for Waveguide Coupling in Image Projectors
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Solution Overview
Problem
Existing image projector configurations face challenges in efficiently coupling light from the projector into a waveguide, particularly in terms of optical path length and pupil imaging, which affect the quality and efficiency of image projection.
Innovation Solution
The image projector employs a tilt-mirror assembly with an illumination system, utilizing pupil imaging to efficiently direct illumination from the spatial light modulator into the waveguide, and incorporates scanning mirrors to adjust the optical path and ensure effective coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a diagonal approach is used to transmit light from projector to waveguide, then the optical path length is shortened, but the coupling efficiency into the waveguide is reduced
Solution Approach 1:
The patent employs a tilt-mirror assembly that can dynamically adjust the angle of the optical path. This allows the system to optimize between short optical path length and high coupling efficiency by tilting the mirror to the appropriate angle, making the optical path configurable rather than fixed in a diagonal arrangement
Solution Approach 2:
The patent changes the optical parameters by introducing a tilt-mirror assembly that modifies the angle of light transmission. By adjusting the tilt angle, the system can transform the fixed diagonal approach into a variable configuration that achieves both short optical path and effective waveguide coupling through optimized angular parameters
2Reliability
If a perpendicular approach is used to transmit light from projector to waveguide, then the coupling efficiency is improved, but the optical path length is increased
Solution Approach 1:
The tilt-mirror assembly provides dynamic adjustment capability, allowing the system to transition from a fixed perpendicular arrangement to a configurable optical path. By tilting the mirror, the system can shorten the optical path while maintaining the beneficial coupling characteristics of the perpendicular approach
3Productivity
If pupil imaging is used to direct illumination into the waveguide, then the optical efficiency is improved, but the device complexity increases
Solution Approach 1:
The tilt-mirror assembly serves multiple functions: it performs pupil imaging to optimize optical efficiency, simultaneously adjusts the optical path angle, and provides configurability for different waveguide coupling approaches. This multi-functionality achieves high optical efficiency without proportionally increasing device complexity
Solution Approach 2:
The tilt-mirror assembly acts as an intermediary element between the projector and waveguide, performing pupil imaging and optical path adjustment in a single component. This intermediary approach simplifies the overall system compared to using separate components for each function
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 achieves high optical efficiency and effective coupling of light into the waveguide, improving the quality and efficiency of image projection, while allowing for flexible optical designs such as diagonal and perpendicular coupling.
Implementation Method 1
The image projector employs a tilt-mirror assembly with an illumination system, utilizing pupil imaging to efficiently direct illumination from the spatial light modulator into the waveguide
Implementation Method 2
incorporates scanning mirrors to adjust the optical path and ensure effective coupling
Implementation Method 3
the projected image is typically introduced into a light guide along which the image propagates by internal reflection until being coupled out to the eye of the user
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A
AI summary
An image projector includes an illumination arrangement with a number of illumination sources and a tilt-mirror assembly, all operating under control of a controller. An optical arrangement directs illumination from the illumination sources towards the mirror and on to an image plane. A collimating arrangement collimates the illumination from the image plane to generate a collimated image directed to an exit stop. The controller (830) modulates an intensity of each of the illumination sources (808) synchronously with tilt motion of the mirror (814) according to the content of the digital image. In certain implementations, the illumination sources (808) are spaced apart. Although the tilt motion brings each illumination source to scans across only part of a dimension of the field of view, all of the illumination sources together scans across the entirety of the one dimension.