Oblique Notch Filter for Laser Retro-Reflection Reduction
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Solution Overview
Problem
Optical devices, such as sniper scopes, are vulnerable to detection and harm from coherent electromagnetic radiation sources like lasers, which can cause detection and physiological damage to users.
Innovation Solution
An optical device equipped with a notch filter arranged at an oblique angle to the optical axis, which attenuates and reflects incident electromagnetic radiation away from the user, reducing detection likelihood and protecting the user from harmful radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a notch filter is arranged normally (perpendicular to optical axis) to attenuate specific wavelengths, then transmission of that wavelength is reduced, but retro-reflection of other wavelengths may still occur causing detection
Solution Approach 1:
The patent applies asymmetry by tilting the notch filter at an oblique angle (5-75 degrees) relative to the optical axis. This asymmetric arrangement causes incident electromagnetic radiation to be reflected away from the source direction rather than returning along the same path, thereby reducing retro-reflection while maintaining wavelength-specific attenuation functionality
Solution Approach 2:
The patent converts the potentially harmful retro-reflection effect into a beneficial directional reflection. By orienting the notch filter obliquely, the reflected radiation is redirected away from the source, transforming what would be a detection vulnerability into a protective feature that reduces detectability
2Object-affected harmful factors
If a filter is used to block specific wavelengths, then protection from harmful radiation is improved, but visibility and color accuracy may deteriorate
Solution Approach 1:
The patent applies local quality by using a notch filter that selectively attenuates only specific wavelength bands while allowing other wavelengths to pass through. This localized filtering approach provides protection from harmful radiation at specific wavelengths without compromising overall visibility and color accuracy across the visible spectrum
Solution Approach 2:
The patent utilizes parameter changes by adjusting the central wavelength and bandwidth of the notch filter to match specific threat wavelengths. This selective parameter tuning allows the filter to block harmful radiation at targeted wavelengths while maintaining high transmission and color fidelity for other wavelengths, thus preserving visibility
3Reliability
If the notch filter is arranged at a steep oblique angle to reduce retro-reflection, then detection risk is reduced, but the reflected radiation may redirect towards the user causing harm
Solution Approach 1:
The patent uses the obliquely arranged notch filter itself as an intermediary element that both attenuates specific wavelengths and redirects radiation away from harmful paths. The filter's angled orientation acts as a mediator that transforms the radiation path without requiring additional protective components, simultaneously addressing detection and protection concerns
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 notch filter effectively reduces retro-reflection and transmission of specific wavelengths of electromagnetic radiation, minimizing detection risks and protecting users from laser-induced harm while maintaining high visibility and color accuracy.
Implementation Method 1
a filter assembly comprising a first notch filter arranged to attenuate transmission of electromagnetic radiation having a first wavelength incident normally thereupon
Implementation Method 2
incident electromagnetic radiation having a predetermined wavelength propagating along the optical axis is reflected by the first notch filter away therefrom
Data Source
AI summary
An optical device 10 comprises an objective lens 11 defining a focal plane FP and an eyepiece 12 spaced apart therefrom, defining an optical axis OA therethrough. The optical device 10 comprises an optical member 13 having a first planar face 14, arranged on the optical axis OA proximal the focal plane FP, wherein the first planar face 14 is arranged to oppose the objective lens 11. The optical device 10 comprises a filter assembly 100 comprising a first notch filter 101 arranged to attenuate transmission of electromagnetic radiation having a first wavelength λ1, wherein the first notch filter 101 is arranged in front of the optical member 13. The first notch filter 101 is arranged at a first oblique angle θ1 to the optical axis OA whereby, in use, incident electromagnetic radiation having a predetermined wavelength λi propagating along the optical axis is reflected by the first notch filter 101 away therefrom, wherein the first wavelength λ1 and the predetermined wavelength λi are different. In this way, retro-reflection of the incident electromagnetic radiation towards a source thereof is reduced, thereby better detection of the optical device 10.