Nitrogen-Doped Silicon Germanium Matching Layer for Optical Filter Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Near-infrared narrow-band optical filters used in systems like face recognition and laser radar face challenges in maintaining optimal optical filter properties, particularly when light is incident at oblique angles, leading to issues with imaging quality due to shifts in passband center wavelength and reduced transmittance.
Innovation Solution
The optical filter design incorporates a substrate with a first set of films comprising high refractive index, low refractive index, and matching film layers, where the matching film layer is made of a nitrogen-doped silicon germanium mixture, ensuring a stable refractive index and minimal drift in passband center wavelength across varying incident angles, with an average transmittance of at least 93% within the specified wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multilayer film structure is used on the substrate, then the optical filter can block non-passband light, but the passband center wavelength drifts significantly when light incident angle changes from 0° to 30°
Solution Approach 1:
The patent changes the material parameter of the matching film layer by using nitrogen-doped silicon germanium mixture (SixGe1-xNy) with specific composition ratios (0<x≤1, 0<y≤1) and nitrogen doping concentration (0<z≤0.5), which has a refractive index between 2.5 and 3.5. This parameter optimization minimizes the drift of passband center wavelength when incident angle changes from 0° to 30°, resolving the contradiction between reliability and manufacturing precision.
2Illumination intensity
If the refractive index of film layers is optimized for normal incidence, then the transmittance at 0° is high, but the optical filter properties deteriorate at oblique angles (30° incidence)
Solution Approach 1:
The patent applies local quality by creating a matching film layer with specific nitrogen doping concentration and composition (SixGe1-xNy) that has intermediate refractive index properties. This local optimization of the film structure between the high refractive index layer and substrate ensures high transmittance at normal incidence while maintaining stable optical properties at oblique angles up to 30°, resolving the contradiction between illumination intensity and adaptability.
3Device complexity
If a simple multilayer structure is used, then the device complexity is low, but the imaging quality is insufficient due to large wavelength drift
Solution Approach 1:
The patent uses composite materials by combining silicon, germanium, and nitrogen in a doped mixture (SixGe1-xNy) for the matching film layer. This composite material structure provides the optimal balance between device simplicity and wavelength accuracy, achieving drift of not more than 16 nm at 30° incidence while maintaining a manageable film structure complexity.
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 maintains high signal-to-noise ratio and improves imaging quality by minimizing the drift of the passband center wavelength and enhancing the optical filter's performance even at oblique light incidence, providing a higher design margin for devices and circuits.
Implementation Method 1
the matching film layer is made of a nitrogen-doped silicon germanium mixture having a chemical formula SixGe1-xNy... ensuring a stable refractive index and minimal drift in passband center wavelength across varying incident angles
Data Source
AI summary
An optical filter that includes a substrate and a first set of films disposed on a first surface of the substrate, wherein the first set of films includes a high refractive index film layer, a low refractive index film layer, and a matching film layer. A material of the matching film layer includes a nitrogen-doped silicon germanium mixture having a chemical formula SixGe1-xNy, where 0≤x≤1, and 0<y≤0.1. In a wavelength range of 780 nm to 3000 nm, a refractive index of the high refractive index film layer is greater than a refractive index of the low refractive index film layer, and a refractive index of the matching film layer is not equal to a refractive index of its adjacent film layer.