Optical Diffuser for Helmet Display Etendue Expansion
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Solution Overview
Problem
Projection display technologies, such as helmet-mounted display devices, face challenges due to restricted Etendue, which limits the ability to fully illuminate the exit pupil, necessitating complex optical geometries to direct image-bearing light around obstacles.
Innovation Solution
An optical diffuser is employed to increase the Etendue by projecting the display image onto a diffuser with an input diffraction grating that diffracts light into a predominantly one angular direction, and an output diffraction grating further diffuses the beam into a rotationally symmetrical pattern, enhancing the effective Etendue of the optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a restricted Etendue optical system is used to fit around helmet obstacles, then the optical geometry can be compact, but the exit pupil cannot be fully illuminated
Solution Approach 1:
The patent transforms the light propagation from a restricted angular range to an expanded angular range by introducing a diffuser that redistributes light in additional angular dimensions. The diffuser converts a narrow angular input into a wide angular output, effectively adding angular dimensionality to the optical path without increasing the physical volume of the system.
Solution Approach 2:
The patent changes the angular distribution parameter of the light beam by using a diffuser with specific optical properties. The diffuser modifies the angular spread of light rays, transforming a collimated or narrow-angle beam into a wide-angle divergent beam that can fully illuminate the exit pupil while maintaining the compact optical geometry.
2Adaptability or versatility
If complex optical geometries are used to direct light around helmet obstacles, then the light path can be routed, but the system complexity increases
Solution Approach 1:
The patent introduces a diffuser as an intermediary optical element that simplifies the overall optical geometry. Instead of using multiple mirrors, prisms, or complex lens arrangements to route light around obstacles, the diffuser acts as a mediator that redistributes light angularly, enabling flexible light path routing with a single compact component.
3Illumination intensity
If the Etendue is increased using a diffuser, then the exit pupil illumination is improved, but the optical path length increases
Solution Approach 1:
The patent segments the optical function into two distinct parts: a compact imaging section that forms the image, and a diffuser section that expands the angular range. This segmentation allows the illumination enhancement function to be separated from the imaging function, enabling the use of a thin diffuser layer that increases Etendue without significantly extending the optical path length.
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 effectively increases the Etendue of the optical system, allowing a small image generation device to illuminate a large exit pupil, ensuring comfortable viewing and efficient light diffusion with minimal loss of image information.
Implementation Method 1
The input diffraction grating 2. is arranged to diffract incident light in principally, predominantly or mostly into one angular direction relative to the grating (i.e. the first order of diffraction) for entry into the fibre-optical piece
Implementation Method 2
Because the fibres act to project those oblique angles in a substantially rotationally symmetrical output beam, the oblique input angle of the rays relative to the optical axes of the optical fibres will substantially increase the effective Etendue of the optical system
Implementation Method 3
the optical diffuser may comprise an output optical diffraction grating positioned adjacent to the second plate face to extend over at least a part thereof such that light output by the optical fibres of the plurality of optical fibres is diffracted thereby in a direction oblique to said optical axes
Data Source
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AI summary
An optical diffuser (1) including a fibre-optical piece comprising: a first face (2) and a second face (3); a plurality of substantially parallel optical fibres (4) each extending along a respective optical axis (13) from an input end of the optical fibre exposed at the first face of the fibre-optical piece to an output end of the optical fibre exposed at the second face of the fibre-optical piece; an input optical diffraction grating (10A) positioned adjacent to the first face of the fibre- optical piece to extend over at least a part thereof such that light diffracted by the input optical diffraction grating is directed into optical fibres of the plurality of optical fibres in a direction oblique to said optical axes.