SiGe Optical Filter Layers for Ambient Light Rejection in NIR Sensing
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Solution Overview
Problem
Ambient light interferes with near-infrared (NIR) light transmission and reception, reducing the accuracy of systems like gesture recognition and identity recognition by optical receivers.
Innovation Solution
An optical filter using silicon-germanium (SiGe) based high refractive index layers, alternating with low refractive index layers, is designed to block ambient light while allowing NIR light to pass through, with a reduced angle shift and improved manufacturability through hydrogenation and annealing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional optical filters are used to block ambient light, then ambient light interference is reduced, but the filter complexity and manufacturing difficulty increase
Solution Approach 1:
The patent uses silicon-germanium (SiGe) composite material with refractive index greater than 3 as the high refractive index layer in the optical filter. This composite material approach enables effective ambient light blocking while simplifying the overall filter structure compared to conventional multi-layer dielectric filters, directly resolving the contradiction between filtering performance and device complexity.
2Length of stationary object
If high refractive index materials are used to reduce filter thickness, then manufacturing difficulty increases due to stress control, but filter compactness improves
Solution Approach 1:
The patent modifies the refractive index parameter by using silicon-germanium (SiGe) material with refractive index greater than 3, which is higher than conventional silicon-based materials. This parameter change enables reduced filter thickness while the specific SiGe composition and deposition parameters are optimized to control internal stress, thereby achieving both compactness and manufacturability.
Solution Approach 2:
The patent applies different silicon-germanium compositions with optimized germanium content in different layers of the optical filter. By locally adjusting the material composition and refractive index within the SiGe system, the filter achieves reduced thickness while maintaining stress control through localized material property optimization.
3Ease of manufacture
If silicon-based optical filters are used, then manufacturing is relatively easy, but the refractive index is insufficient leading to larger angle shift
Solution Approach 1:
The patent transitions from pure silicon-based materials to silicon-germanium (SiGe) composite materials with refractive index greater than 3. This composite material approach maintains manufacturability through established semiconductor fabrication processes while achieving the higher refractive index needed to reduce angle shift and improve optical performance consistency.
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 SiGe-based filter effectively filters out ambient light, enhances NIR light transmission, and reduces manufacturing difficulties by minimizing stress and thickness, improving the accuracy and efficiency of optical systems.
Implementation Method 1
An optical filter may include a first set of layers of a silicon-germanium based material... The first refractive index may be greater than 3 at a spectral range of approximately 800 nanometers (nm) to approximately 1100 nm
Implementation Method 2
the set of optical filter layers may be arranged in at least one of: an (H-L) m order, an (H-L) m -H order, or an L-(H-L) m order, where m is a quantity of alternating H and L layers
Data Source
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AI summary
An optical filter may include a substrate. An optical filter may include a set of optical filter layers disposed onto the substrate. The set of optical filter layers including a first subset of optical filter layers. The first subset of optical filter layers may include a silicon-germanium (SiGe) with a first refractive index. An optical filter may include a second subset of optical filter layers. The second subset of optical filter layers may include a material with a second refractive index. The second refractive index being less than the first refractive index.