Waveguide Image Combiner for Night Vision Field of View
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Solution Overview
Problem
Existing night vision devices face challenges in reduced lighting conditions due to obstructions caused by reflective surfaces and support arms, which limit the field of view and require luminance reduction of symbology to prevent damage, leading to suboptimal performance in combining scene images with generated symbology.
Innovation Solution
A viewing device utilizing a waveguide with input and output diffraction gratings that separates green light for symbology and infra-red light for the scene, allowing minimal obstruction and a wide field of view by using a planar waveguide and diffraction gratings with varying diffraction efficiencies to combine images without obscuring the external scene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a reflecting prism and support arms are used to combine symbology with the outside scene view, then the field of view is limited and obstruction is created, but the symbology can be superimposed on the scene
Solution Approach 1:
The patent extracts the harmful obstructing elements (reflecting prism and support arms) from the optical path by replacing them with a waveguide-based system. The waveguide internally guides the symbology light through total internal reflection, eliminating the need for external reflective surfaces and support structures that block the view of the outside scene.
Solution Approach 2:
The waveguide acts as an intermediary medium that carries the symbology light from the display element to the user's eye without requiring direct line-of-sight reflection. The light is coupled into the waveguide, guided through its interior, and extracted at the exit surface, serving as a mediator that avoids obstructing the external scene view.
2Reliability
If the luminance of the symbology image is diminished to prevent damage to the intensifier, then the symbology visibility is reduced, but the intensifier is protected
Solution Approach 1:
The patent segments the optical system into separate wavelength channels: the symbology is displayed in the visible spectrum while the outside scene is captured in the infrared spectrum. This segmentation allows each channel to operate at its optimal intensity level without interfering with the other, enabling the symbology to remain bright without damaging the infrared intensifier.
Solution Approach 2:
The patent applies local quality by using wavelength-selective optical elements (diffraction gratings and filters) that allow different parts of the optical system to handle different wavelength ranges with appropriate intensity levels. The symbology path maintains high visible light intensity while the scene path handles infrared intensity, with each optimized for its specific wavelength range.
3Object-generated harmful factors
If a small prism is used to reduce obstruction, then the light obstruction is minimized, but the angular range of visible symbology is limited
Solution Approach 1:
The patent transitions from a two-dimensional reflective surface approach to a three-dimensional waveguide structure. The waveguide extends the symbology visibility across the entire exit surface area, providing a wide angular range without requiring large reflective surfaces that would cause obstruction. The light is distributed throughout the waveguide volume and extracted across the full exit aperture.
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 enables an unobstructed view of the external scene with superimposed symbology in reduced lighting, maintaining a wide field of view and preventing damage to the image intensifier, while ensuring the symbology does not obscure the scene image.
Implementation Method 1
an input diffraction grating for receiving radiation in the first range of wavelengths from the image projector and for directing the received radiation along the waveguide
Implementation Method 2
the output diffraction grating being arranged to couple the radiation in the first range of wavelengths out of the waveguide along a viewing direction
Implementation Method 3
a planar waveguide and diffraction gratings with varying diffraction efficiencies to combine images without obscuring the external scene
Implementation Method 4
an image intensifier arranged to receive the combined radiation via the inlet aperture and to render discernible to a viewer the radiation in the second, infra-red range of wavelengths
Data Source
Figure 1(a)~1(b)
Figure 2
AI summary
An image combiner for a viewing device, such as a night vision device, is disclosed. The combiner is arranged to combining a first image, such as generated symbology, with a second image, such as a view of an outside scene in reduced lighting conditions. The image combiner comprises a waveguide comprising means for capturing the first image from a first viewing direction and means for directing the first image in a second viewing direction, the second viewing direction being substantially coincident with a viewing direction of the second image, such that the first image can combine with the second image. At least a portion of the waveguide is arranged to substantially transmit the second image, such that the second image can pass substantially through the waveguide.