Hardened Optical Window Coatings for Scratch-Resistant LiDAR Sensing
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Solution Overview
Problem
LIDAR systems are vulnerable to damage from impacts, which cause window scratches and impair the effectiveness of the system by scattering emitted and reflected laser beams.
Innovation Solution
A layered film is applied to the window, comprising alternating layers of materials with different refractive indices, providing hardness and scratch resistance, configured for high transmissivity at 1550 nm and low reflection of visible light, with a hardness of at least 8 GPa.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a window is placed to protect the laser and sensor from impact, then protection from rocks and objects is improved, but scratches and damage occur causing beam scattering
Solution Approach 1:
A hardened layered film is applied to the window surface before use to prevent scratches and damage from occurring during operation. The film provides preemptive protection against rocks and objects, maintaining optical clarity and preventing beam scattering throughout the system's operational life.
Solution Approach 2:
The window incorporates a composite layered film structure combining multiple materials with different properties: a hardened top layer (such as silicon nitride or diamond-like carbon) for scratch resistance, intermediate layers for stress management, and adhesive layers for bonding. This composite structure provides both protection and optical performance.
2Strength
If a hardened film is applied to provide scratch resistance, then durability is improved, but optical transmissivity and reflectivity control become challenging
Solution Approach 1:
The protective coating is divided into multiple discrete layers, each with a specific function: the top layer provides hardness and scratch resistance, intermediate layers manage stress and provide transition, and bottom layers ensure adhesion. This segmentation allows each layer to be optimized for its specific purpose while collectively achieving both mechanical strength and optical performance.
Solution Approach 2:
Different layers of the film have different local properties tailored to their specific functions. The top surface layer has high hardness for scratch resistance, while underlying layers have optimized refractive indices for anti-reflective or reflective optical performance. Each layer's properties are locally optimized to meet the requirements of that specific position in the structure.
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 layered film enhances the durability of the window, reducing damage from impacts and maintaining the effectiveness of the LIDAR system by minimizing beam scattering.
Implementation Method 1
the layered film further includes alternating layers of materials having different indices of refraction (including the material providing the hardness and scratch resistance), such that the number of alternating layers and their thicknesses can be configured so that the window has high transmissivity and low reflection of the 1550 nm wavelength
Implementation Method 2
Further, the layered film can include one or more layers that absorb visible light wavelengths, if desired
Data Source
AI summary
A window for a sensing system is provided. The window includes a substrate, a layered film disposed on a first surface of the substrate, the layered film including alternating layers of higher refractive index materials and lower refractive index materials, wherein the refractive index of the higher refractive index materials is greater than the refractive index of the lower refractive index materials, and a maximum hardness, measured at the layered film and by the Berkovich Indenter Hardness Test, of at least 8 GPa. The window has: an average percentage transmittance of greater than 75% for electromagnetic radiation having a wavelength of 1550 nm at normal or near normal incidence; and an average percentage reflectance of less than 10% for electromagnetic radiation having a wavelength of 1550 nm at any angle of incidence within the range of 0° to 8°.