Retinal Projection Device Holographic Diffraction Stray Light
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Solution Overview
Problem
Existing retinal projection devices struggle to correctly recognize images when the user moves their eyes, due to issues with stray light caused by chromatic aberration, especially when using wide-band elements that widen the allowable range of incident angles.
Innovation Solution
A retinal projection device is designed with a notch filter and holographic diffraction layers to extract and separate circularly polarized light by wavelength, reducing stray light due to chromatic aberration. The device includes a projector module, a switching unit, a combiner, and a controller to ensure accurate image recognition despite eye movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a wide-band element with wide allowable range of incident angle is used to expand the eye box, then the allowable range of wavelength is widened, but stray light due to chromatic aberration occurs
Solution Approach 1:
The combiner is divided into multiple holographic diffraction layers, each layer being responsible for diffracting a specific wavelength range (red, green, or blue). This segmentation allows each layer to have a narrow wavelength range, preventing chromatic aberration while collectively covering the full visible spectrum and maintaining a wide eye box.
Solution Approach 2:
Each holographic diffraction layer is designed with specific local properties tailored to its designated wavelength range. The first layer has properties optimized for red light, the second for green light, and the third for blue light. This local optimization ensures that each layer only diffracts its target wavelength, eliminating stray light from other wavelengths while contributing to the overall wide eye box.
2Area of stationary object
If the allowable range of wavelength is widened to expand the eye box, then the incident angle range is widened, but image recognition accuracy deteriorates due to chromatic aberration
Solution Approach 1:
The wavelength range is segmented into three distinct bands (red, green, blue), each handled by a dedicated holographic diffraction layer. This segmentation prevents the mixing of wavelengths that causes chromatic aberration, thereby maintaining image recognition accuracy while allowing the eye box to be expanded through the combined effect of all three layers.
Solution Approach 2:
The notch filter acts as an intermediary component that selectively transmits only the desired circularly polarized light for each wavelength while blocking unwanted polarizations. This intermediary function ensures that only纯净 light reaches the holographic layers, preventing chromatic aberration and maintaining image accuracy across the expanded eye box.
3Area of stationary object
If circularly polarized light of both polarities is transmitted across all wavelengths, then the eye box is expanded, but chromatic aberration causes stray light
Solution Approach 1:
The notch filter extracts only the desired circularly polarized light component for each wavelength, removing the unwanted polarization components. This extraction process prevents stray light generation while maintaining the wide eye box, as each wavelength range is cleanly separated and transmitted only in its intended polarization state.
Solution Approach 2:
Each holographic diffraction layer is designed with local quality specific to its wavelength range and polarization state. The first layer diffracts only left-handed circularly polarized red light, the second layer diffracts only right-handed circularly polarized green light, and the third layer diffracts only left-handed circularly polarized blue light. This localized specificity eliminates stray light while maintaining the expanded eye box.
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 effectively reduces stray light caused by chromatic aberration, allowing for correct image recognition even when the user moves their eyes, thereby expanding the eye box without compromising image quality.
Implementation Method 1
a notch filter provided between the projector module and the combiner, the notch filter that: passes circularly polarized light having a first polarity in light having the red wavelength; reflects circularly polarized light having a second polarity different from the first polarity in the light having the red wavelength; passes circularly polarized light having the second polarity in light having the green wavelength; reflects circularly polarized light having the first polarity in the light having the green wavelength; passes circularly polarized light having the first polarity in light of the blue wavelength; and reflects circularly polarized light having the second polarity in the light of the blue wavelength
Implementation Method 2
The combiner includes: a first holographic diffraction layer that diffracts circularly polarized light having the first polarity in a first wavelength range including the red wavelength; a second holographic diffraction layer that diffracts circularly polarized light having the second polarity in a second wavelength range including the green wavelength; and a third holographic diffraction layer that diffracts circularly polarized light having the first polarity in a third wavelength range including the blue wavelength
Data Source
AI summary
A retinal projection device includes: a switching unit capable of switching an optical path of a beam; a combiner that converts the beam into parallel light; and a notch filter that passes circularly polarized light with a first polarity in light of the red wavelength, passes circularly polarized light with the second polarity in light of the green wavelength, and passes circularly polarized light with the first polarity in light of the blue wavelength. The combiner includes: a first holographic diffraction layer that diffracts circularly polarized light with the first polarity in a first wavelength range including the red wavelength; a second holographic diffraction layer that diffracts circularly polarized light with the second polarity in a second wavelength range including the green wavelength; and a third holographic diffraction layer that diffracts circularly polarized light with the first polarity in a third wavelength range including the blue wavelength.