Copper-Phosphate Glass Optical Filter for Near-Infrared Shielding
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Solution Overview
Problem
Existing optical filters for solid-state image sensors in digital cameras suffer from incident angle dependence of spectral transmittance, leading to ghost and flare effects that deteriorate image quality, especially in visible light and long wavelength infrared regions. Additionally, current filters do not effectively manage transmittance in the short wavelength infrared region (1200 nm to 1600 nm).
Innovation Solution
A phosphate glass for optical filters is developed, incorporating Cu, with specific optical characteristics: a transmittance of 25% or more at 1550 nm, an average transmittance of 5% or less at 700 nm to 1200 nm, and tailored compositions to optimize transmittance in various wavelength regions while minimizing near-infrared transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dielectric multilayer film is used to reflect near-infrared rays, then near-infrared shielding is improved, but incident angle dependence of spectral transmittance occurs causing ghost and flare
Solution Approach 1:
The patent changes the fundamental parameter of near-infrared rejection mechanism from reflection (dielectric multilayer film) to absorption (copper ions in glass). This parameter change eliminates incident angle dependence because absorption is an intrinsic material property that does not vary with light angle, thereby resolving the ghost and flare issues while maintaining effective near-infrared shielding.
Solution Approach 2:
The patent creates a composite optical system by integrating copper-containing glass with dielectric multilayer films. The copper glass provides angle-independent near-infrared absorption, while the dielectric films provide additional spectral control. This composite approach combines the advantages of both materials to achieve superior overall performance.
2Object-affected harmful factors
If copper is added to glass to absorb near-infrared light, then near-infrared transmittance is reduced, but optical characteristics in short wavelength infrared region are not optimized
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: copper ion concentration (0.1-10 wt%), glass composition (phosphate, silicate, or borate base), and film thickness. By adjusting these parameters, the glass achieves selective absorption in the near-infrared region while maintaining high transmittance in the short wavelength infrared region (1200-1600 nm), thus resolving the contradiction between near-infrared blocking and short-wavelength infrared transmission.
3Adaptability or versatility
If solid-state image sensor is used for both visible and short wavelength infrared sensing, then sensor integration is improved, but near-infrared absorption sensitivity degrades color reproducibility
Solution Approach 1:
The copper-containing glass acts as an intermediary optical element positioned between the light source and the solid-state image sensor. It selectively absorbs near-infrared light before it reaches the sensor, preventing unwanted near-infrared signal generation that would otherwise degrade color reproducibility, while allowing visible and short wavelength infrared light to pass through for simultaneous sensing.
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 glass and optical filter achieve low near-infrared transmittance while maintaining high transmittance in the short wavelength infrared region, thereby improving image quality and sensing accuracy in both visible light and infrared regions.
Implementation Method 1
a glass added with Cu (copper) that is described in Patent Literature 2 can cut near-infrared light (wavelength of 700 nm to 1200 nm) by absorption of copper ions having absorption near a wavelength of 900 nm
Implementation Method 2
the glass having a transmittance of 25% or more at a wavelength of 1550 nm and an average transmittance of 5% or less at a wavelength of 700 nm to 1200 nm
Data Source
AI summary
A glass for an optical filter, the glass being a phosphate glass including Cu, in which the glass has: an average transmittance of 80% or more at a wavelength of 430 nm to 550 nm; an average transmittance of 2% or less at a wavelength of 800 nm to 950 nm; an average transmittance of 3% or less at a wavelength of 1000 nm to 1200 nm; an average transmittance of 5% or less at a wavelength of 700 nm to 1200 nm; a transmittance of 25% or more at a wavelength of 1550 nm; and a wavelength at which a transmittance is 50% of 615 nm or more in a wavelength range of 600 nm to 800 nm.