Antireflection Structure for Stray Light Control in Optical Units
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Solution Overview
Problem
Optical units that repeatedly reflect light to secure optical path length face challenges in minimizing stray light generation due to unnecessary reflections, which degrade the quality of the effective light flux, especially in compact devices like telescopes and cameras, where existing antireflection methods like the moth-eye structure are inefficient and prone to specular reflection.
Innovation Solution
An optical unit with an antireflection structure featuring convex portions with an average height and pitch larger than the maximum wavelength of light, arranged at an angle of 45 to 60 degrees relative to the optical path, effectively absorbs and attenuates stray light by multiple reflections, preventing it from becoming secondary stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a moth-eye structure is used as antireflection means, then the refractive index discontinuous interface is eliminated to reduce reflection, but specular reflection occurs at the vertex of protrusions and reflectance increases when incident direction deviates from the axial direction
Solution Approach 1:
Instead of using a moth-eye structure with fine protrusions that causes specular reflection at vertices, the patent inverts the approach by using a rough surface structure with larger-scale irregularities. This rough surface diffusely reflects stray light away from the optical path rather than creating concentrated specular reflection, thereby solving the reliability problem while maintaining antireflection effectiveness.
Solution Approach 2:
The patent changes the scale parameter of the surface structure from the sub-wavelength scale of moth-eye structures to a larger scale where the surface irregularities are comparable to or larger than the wavelength of light. This parameter change transforms the reflection mechanism from specular to diffuse, eliminating the vertex reflection problem while maintaining the ability to suppress stray light.
2Object-affected harmful factors
If black paint is applied to locations where unnecessary light collides, then stray light is suppressed, but gas and organic substances are generated over time and contaminate optical surfaces
Solution Approach 1:
Instead of using black paint that degrades over time and contaminates optical surfaces, the patent employs a rough surface structure that is inherently stable and maintenance-free. The rough surface provides continuous stray light suppression without generating contaminants, effectively replacing a short-lived solution with a permanent structural solution.
Solution Approach 2:
The patent replaces the chemical approach of using black paint with a physical structural approach using a rough surface. This substitution eliminates the chemical degradation and contamination issues associated with paint while maintaining the mechanical function of suppressing stray light through diffuse reflection.
3Volume of moving object
If the optical unit is miniaturized to reduce device size, then compactness is achieved, but the available inner space is limited making it difficult to freely arrange a diaphragm, causing unnecessary light to travel outside the effective light flux
Solution Approach 1:
The patent applies preliminary action by forming a rough surface structure in advance on the inner walls of the optical unit. This pre-configured surface structure proactively suppresses stray light before it can interfere with the effective light flux, eliminating the need for additional space-consuming diaphragms or light blocking structures.
Solution Approach 2:
The patent applies local quality by creating a rough surface structure specifically on the inner walls where stray light is generated, rather than uniformly treating the entire optical path. This localized approach effectively suppresses stray light at its source while maintaining the compact overall design of the optical unit.
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 significantly reduces stray light generation, enhancing the quality of the effective light flux and preventing performance deterioration in optical devices like spectroscopic analyzers, telescopes, and cameras by effectively managing reflections in compact designs.
Implementation Method 1
effectively absorbs and attenuates stray light by multiple reflections
Implementation Method 2
effectively absorbs and attenuates stray light by multiple reflections
Data Source
AI summary
An optical unit includes a reflective optical element and an antireflection structure having an average height and an average pitch larger than a maximum wavelength of light contained in an effective light flux. The antireflection structure is disposed outside an optical path of the effective light flux, and the antireflection structure has a plurality of convex portions extending in a predetermined direction. An angle formed between the predetermined direction and the optical path of the effective light flux is from 45 degrees to 60 degrees.