Optical Filter Aperture Size Plasmon Resonance

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Solution Overview

Problem

Conventional optical filters with thin metal films suffer from low transmissivity and instability in optical characteristics, especially when trying to achieve desired optical characteristics across a wide wavelength range, due to heating issues and limited design freedom caused by matching aperture periods with surface plasmon wavelengths.

Innovation Solution

An optical filter design featuring a light-shielding conductive layer with apertures on a substrate and a dielectric layer, where the aperture size is less than or equal to the wavelength, and a surface area ratio of the conductive layer to the substrate surface is between 36% and 74%, utilizing localized surface plasmons to enhance transmissivity and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the aperture arrangement period is matched with the surface plasmon wavelength to increase transmissivity, then light transmissivity is improved, but design freedom is reduced and it becomes difficult to achieve desired optical characteristics across a wide wavelength range

Engineering Contradiction:

Improvelight transmissivityVSAvoiddesign freedom for optical characteristics

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

The patent changes the fundamental parameter from aperture period to aperture size as the controlling factor for plasmon resonance. By making aperture size (not period) the dominant parameter, the filter achieves wavelength selectivity without requiring periodic arrangement matching, thereby maintaining design freedom while achieving high transmissivity through localized surface plasmon resonance in sub-wavelength apertures.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using periodic aperture arrangements to couple with propagating surface plasmons (conventional approach), the patent inverts the approach by using isolated sub-wavelength apertures to generate localized surface plasmons. This inversion eliminates the need for periodic matching while achieving enhanced transmissivity through localized resonance effects.

Inventive Principle:

Principle #13The other way round (Inversion)

2Use of energy by moving object

If incident light intensity is increased to achieve desired transmitted light intensity in filters with low transmissivity, then transmitted light intensity is improved, but the thin metal film is heated and structural changes occur

Engineering Contradiction:

Improvetransmitted light intensityVSAvoidthin metal film temperature

Core Design Contradiction:

Use of energy by moving objectVSTemperature

Solution Approach 1:

The patent changes the aperture size parameter to be equal to or less than the light wavelength, which enables localized surface plasmon resonance. This resonance effect dramatically enhances the transmitted light intensity without requiring high incident light intensity, thereby avoiding film heating and structural changes while achieving the desired transmitted light level.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If a thin metal film structural body is used to increase transmissivity through surface plasmons, then light transmissivity is improved, but stability and endurance of the optical filter are reduced

Engineering Contradiction:

Improvelight transmissivityVSAvoidstability and endurance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent employs a composite structure combining a metal film with dielectric materials (substrate and coating layers). This composite configuration provides the plasmonic effects needed for high transmissivity while the dielectric components enhance structural stability and chemical endurance, preventing metal oxidation and degradation.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies dielectric coating layers on the metal film surface beforehand to protect against oxidation and environmental degradation. This protective layering ensures long-term stability and endurance of the optical filter while maintaining the plasmonic transmission enhancement.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 design achieves a maximum transmissivity of at least 50% at the resonance wavelength while maintaining spectral contrast, providing a stable and efficient optical filter with improved endurance and reduced energy loss, suitable for miniaturized light-receiving elements like CCD sensors.

Implementation Method 1

A transmissivity of the first wavelength is increased by surface plasmons induced in the apertures by light falling on the conductive layer

Methodology Applied

Scientific EffectLocalized surface plasmons: Surface Acoustic Wave

Data Source

PatentUS8067723B2Optical filter

Publication Date: 2011.11.29 CANON KK

AI summary

An optical filter includes a light-shielding conductive layer provided with a plurality of apertures on a substrate surface that selectively transmits light of a first wavelength, and a dielectric layer in contact with the conductive layer. A size of the apertures is a size equal to or less than the first wavelength, and a ratio of a surface area of the conductive layer to a surface area of the substrate surface is within a range of equal to or greater than 36% and equal to or less than 74%. A transmissivity of the first wavelength is increased by surface plasmons induced in the apertures by light falling on the conductive layer.