Holographic Sight HOE Illumination Angles
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Solution Overview
Problem
Holographic weapon sights face issues with wavelength shift due to temperature changes, causing reticle position drift, and ambient light leads to visibility of reflected light and potential rainbow effects, making existing designs cumbersome and difficult to package compactly.
Innovation Solution
A compact holographic weapon sight design where a holographic optical element (HOE) is illuminated by a diverging beam, and the user views a reflection of the HOE in a non-diffractive element (NDE), with carefully selected beam angles to minimize visibility of reflected light and compensate for wavelength shifts, using a customized light source and adjustable mechanisms for windage and elevation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a holographic optical element (HOE) is used to reconstruct reticle image, then the reticle image can be viewed through the HOE, but ambient light causes reflected light visibility and rainbow effects
Solution Approach 1:
The optical system is segmented into distinct functional components: illumination beam path and viewing beam path are separated. The HOE is positioned at a 45-degree angle to reflect illumination light onto the target while allowing viewing light to pass through to the user's eye, preventing ambient light from causing rainbow effects in the user's field of view.
Solution Approach 2:
The harmful reflected light is extracted and redirected away from the user's eye. By positioning the HOE at 45 degrees and using appropriate beam angles, the reflected illumination light is directed toward the target rather than back to the user, eliminating the rainbow effect while maintaining reticle visibility.
2Reliability
If laser diode wavelength shifts due to temperature changes, then the reticle position drifts, but using achromat configuration with grating and HOE compensates for wavelength shift
Solution Approach 1:
The system uses a VCSEL with wavelength stability specifications (±2nm over temperature range) to control the wavelength parameter. By selecting a light source with inherent wavelength stability and optimizing the HOE reconstruction and viewing angles, the system achieves reticle position stability without requiring complex achromat configurations.
3Device complexity
If the HOE is illuminated by diverging beam, then the setup is simpler, but the image plane depth and reticle position drift
Solution Approach 1:
The system uses a diverging illumination beam which dynamically adapts to different viewing conditions. The VCSEL inherently produces a diverging beam that illuminates the HOE effectively. Combined with optimized reconstruction and viewing angles, this approach maintains image plane depth stability within acceptable limits while keeping the illumination setup simple and compact.
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 reduces the impact of wavelength shifts and ambient light issues, providing a compact and stable reticle image, minimizing parallax errors and allowing for effective aiming without the rainbow effect, while maintaining image quality and position stability across temperature variations.
Implementation Method 1
a light source, preferably a vertical-cavity surface-emitting laser diode (VCSEL), operable to project a diverging beam of light
Implementation Method 2
a holographic optical element (HOE) disposed in the path of the diverging beam of light such that the HOE is illuminated by the diverging beam of light... the HOE reconstructs an object beam
Implementation Method 3
a non-diffractive element (NDE) reflecting the image of the reticle, the non-diffractive element being disposed in the viewing path
Data Source
AI summary
A holographic gun sight has a housing with a viewing end and an opposing target end, a viewing path being defined from the viewing end to the target end. A light source projects a light beam along a path to illuminate a reflection-type holographic optical element (HOE). The HOE reconstructs an object beam with an image of a reticle. The absolute difference between the incidence angle of the light beam on the HOE and the object beam angle is greater than zero and less than or equal to 30 degrees.