Optical Stack With Embedded Diffuse Surface for IR Sensor Protection
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Solution Overview
Problem
Conventional IR windows used in imaging devices to protect optical sensors and filter out ambient light often compromise on aesthetics and performance, leading to reduced modulation transfer function (MTF), dynamic range, and increased ghosting and flare, especially in high dynamic range (HDR) imaging applications.
Innovation Solution
An optical stack comprising a polymeric layer, a matching index layer, a bumpy diffuse surface, and a partially reflective layer is used, which is optically transparent to specific bandwidths of interest while diffusely reflecting ambient light, maintaining high transmission efficiency and reducing ghosting and flares.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external window is used to protect the optical sensor and filter out ambient light, then the optical sensor is protected and filtering performance is improved, but the modulation transfer function (MTF) is reduced and ghosting and flare increase
Solution Approach 1:
The optical window is segmented into multiple functional layers: a polymeric layer for basic protection and filtering, a bumpy diffuse surface for light scattering control, and a partially reflective layer for selective wavelength reflection. Each layer performs a specific function, collectively achieving both protection and high MTF performance.
Solution Approach 2:
The optical window uses a composite structure combining polymeric material with a bumpy diffuse surface and partially reflective coating. This composite design integrates the protective properties of the polymer with the optical control properties of the diffuse surface and reflective layer, achieving both sensor protection and high MTF.
2Object-affected harmful factors
If a conventional optical window is used to filter ambient light, then filtering performance is improved, but dynamic range is reduced
Solution Approach 1:
The optical window applies different optical properties to different layers: the polymeric layer provides broad-spectrum filtering, the bumpy diffuse surface selectively scatters ambient light while transmitting structured light, and the partially reflective layer reflects specific wavelengths. This local differentiation of optical properties achieves effective ambient light filtering while preserving dynamic range.
3Reliability
If an optical window is used to protect the optical sensor, then protection is improved, but ghosting and flare increase
Solution Approach 1:
The bumpy diffuse surface introduces controlled curvature and scattering centers that redirect stray light away from the optical sensor. This curved, diffuse surface structure prevents stray light from creating ghosting and flare artifacts while maintaining sensor protection.
4Shape
If the optical sensor is hidden behind a window, then aesthetic appearance is improved, but light transmission efficiency is reduced
Solution Approach 1:
The optical window is designed with specific parameter optimizations: the polymeric layer uses materials with high transmission coefficients for structured light wavelengths, the bumpy diffuse surface uses controlled scattering parameters to minimize overall light loss, and the partially reflective layer is tuned to reflect only ambient wavelengths while transmitting structured light. These parameter optimizations achieve aesthetic appearance while maintaining high light transmission efficiency.
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 configuration allows for high-efficiency light transmission while hiding the optical sensor, maintaining or enhancing the performance of IR machine vision systems by reducing the impact on MTF and transmission efficiency, and providing customizable appearances.
Implementation Method 1
a polymeric layer configured to be optically transparent to at least the one or more bandwidths of interest
Implementation Method 2
the matching index layer and polymeric layer having refractive indexes within a threshold similarity
Implementation Method 3
a bumpy diffuse surface embedded between the polymeric layer and the matching index layer
Implementation Method 4
a partially reflective layer positioned in between the bumpy diffuse surface and the matching index layer, the partially reflective layer configured to at least partially reflect at least some wavelengths outside the one or more bandwidths of interest
Data Source
AI summary
An optical system comprises an optical sensor configured to receive light within one or more bandwidths of interest and an optical stack placed optically in front of the optical sensor. The optical stack comprises a polymeric layer optically transparent to at least the one or more bandwidths of interest, and a matching index layer positioned optically in front of the polymeric layer, the matching index layer and polymeric layer having refractive indexes within a threshold similarity. The optical stack further includes a bumpy diffuse surface embedded between the polymeric layer and the matching index layer, and a partially reflective layer positioned in between the bumpy diffuse surface and the matching index layer, the partially reflective layer configured to at least partially reflect at least some wavelengths outside the one or more bandwidths of interest.