Optical Filter for Ambient Light Sensor with Angle-Stable NIR Blocking

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Solution Overview

Problem

Ambient light sensors in information terminal devices face challenges in accurately detecting illuminance and color tones due to reduced visible light incidence caused by the need for a blackish appearance and high incident angles, leading to decreased detection accuracy and malfunction.

Innovation Solution

An optical filter with a base member containing near-infrared absorbing fine particles and a dielectric multilayer film is designed to maintain high visible-light transmittance and near-infrared blocking performance, even at oblique angles, by optimizing transmittance and optical density across various wavelengths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a multilayer metal film near-infrared cut filter is used on a glass plate, then near-infrared blocking performance is improved, but the optical properties change greatly with incident angle, causing detection accuracy to decrease

Engineering Contradiction:

Improvenear-infrared blocking performanceVSAvoiddetection accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent combines a base member containing near-infrared absorbing fine particles with a dielectric multilayer film to create a composite optical filter. This composite structure integrates the broadband near-infrared absorption capability of the particle-containing base member with the angle-stable optical properties of the dielectric multilayer film, resolving the contradiction between near-infrared blocking performance and detection accuracy at oblique angles.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes specific parameters including the average particle diameter of near-infrared absorbing fine particles (1 nm to 200 nm), the wavelength range for near-infrared blocking (800 nm to 1,200 nm with optical density ≥1.7), and visible light transmittance characteristics (45%-85% at 400 nm to 650 nm). These parameter optimizations ensure stable spectral properties across various incident angles while maintaining effective near-infrared blocking.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If a larger amount of near-infrared absorbing particles is added to achieve sufficient near-infrared blocking performance, then near-infrared blocking performance is improved, but visible light transmittance decreases

Engineering Contradiction:

Improvenear-infrared blocking performanceVSAvoidvisible light transmittance

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

The patent applies local quality by using near-infrared absorbing fine particles with specific size ranges (1 nm to 200 nm average diameter) that selectively absorb near-infrared wavelengths while being transparent to visible light. The dielectric multilayer film is designed with specific optical characteristics to block near-infrared rays. This localized functional differentiation allows the base member to provide broadband near-infrared absorption without significantly affecting visible light transmittance, which is then fine-tuned by the dielectric multilayer film to achieve the target range of 45%-85%.

Inventive Principle:

Principle #3Local quality

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 optical filter ensures excellent sensor sensitivity and color-tone sensing properties independently of incident angles, preventing sensor malfunctions and maintaining effective near-infrared blocking performance.

Implementation Method 1

a base member including a layer containing near-infrared absorbing fine particles

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Implementation Method 2

a dielectric multilayer film provided on at least one side of the base member

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11226442B2Optical filter and ambient light sensor including optical filter

Publication Date: 2022.01.18 JSR CORPORATION

AI summary

An optical filter including a base member having a layer containing near-infrared absorbing fine particles and a dielectric multilayer film, the optical filter satisfying a requirement that, in a wavelength range of 400 nm to 650 nm, an average of transmittance of any of light incident from a direction perpendicular to the optical filter, light obliquely incident at an angle of 30 degrees, and light obliquely incident at an angle of 60 degrees is 45% or higher and lower than 85%; and a requirement that, in a wavelength range of 800 nm to 1,200 nm, an average of optical density (OD value) of any of light incident from the direction perpendicular to the optical filter, light obliquely incident at an angle of 30 degrees with respect to the perpendicular direction, and light obliquely incident at an angle of 60 degrees with respect to the perpendicular direction is 1.7 or higher.