Wavelength Variable Interference Filter Silver Bulge Prevention
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Solution Overview
Problem
Wavelength variable interference filters using silver or silver alloys face degradation due to thermal loads, leading to the generation of bulges on reflective film surfaces, which affects optical characteristics and reliability.
Innovation Solution
A wavelength variable interference filter design incorporating a quartz substrate with controlled hydroxyl group concentrations (500 ppm or less or 1000 ppm or more) and a protective indium gallium oxide film to suppress silver cohesion and bulge formation, ensuring stable optical performance over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver or silver alloy reflective films are used in wavelength variable interference filters, then high reflectance and optical performance are achieved, but the chemical stability is lower and atoms move easily under thermal load causing bulge generation and cohesion
Solution Approach 1:
A protective film made of inorganic material (such as silicon oxide, silicon nitride, or aluminum oxide) is introduced as an intermediary layer between the silver reflective film and the external environment. This protective film acts as a barrier that prevents direct contact between oxygen and the silver film, thereby suppressing oxidation and cohesion while maintaining the optical performance of the underlying silver reflective film.
Solution Approach 2:
The reflective film structure is transformed from a single silver layer into a composite structure consisting of multiple layers: a silver reflective film layer and a protective inorganic film layer. This composite structure combines the high reflectance properties of silver with the chemical stability and protective characteristics of inorganic materials, resolving the contradiction between optical performance and chemical stability.
2Ease of operation
If thermal load is applied to the wavelength variable interference filter, then operational functionality is maintained, but transformation occurs in the silver reflective film leading to bulge generation on the surface
Solution Approach 1:
The protective inorganic film is applied beforehand to the silver reflective film to create a cushioning barrier against thermal and environmental stresses. This pre-applied protective layer absorbs and distributes the thermal load, preventing direct thermal damage to the silver film and suppressing bulge generation during operation.
Solution Approach 2:
The inorganic protective film serves as a mediator between the thermal environment and the silver reflective film. It allows the filter to withstand thermal loads during operation while protecting the silver film from direct thermal exposure, thereby maintaining surface flatness and preventing transformation.
3Ease of manufacture
If the reflective film is exposed to the external environment, then ease of manufacture is maintained, but oxidation and cohesion occur leading to degradation of optical characteristics over time
Solution Approach 1:
The manufacturing process incorporates the deposition of an inorganic protective film as an additional step in forming the composite reflective film structure. This composite approach maintains ease of manufacture through standard deposition techniques while providing long-term protection against oxidation and cohesion, ensuring stable optical characteristics over time.
Solution Approach 2:
The inorganic protective film is deposited as an intermediary layer during the manufacturing process. This protective barrier is introduced in a controlled manufacturing environment, providing oxidation resistance and preventing cohesion while maintaining the ease of manufacture through conventional film deposition techniques.
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 solution effectively prevents bulge formation and maintains the optical characteristics and reliability of the wavelength variable interference filter, enhancing its durability and accuracy in wavelength resolution.
Implementation Method 1
retrieves a desired wavelength of light through multiple interference of the reflective film gap
Implementation Method 2
regulates an interval between a pair of reflective films that are disposed facing one another using an electrostatic attractive force
Data Source
AI summary
A wavelength variable interference filter includes a fixed substrate, a movable substrate that faces the first substrate, a fixed reflective film that is disposed between the fixed substrate and the movable substrate, and a movable reflective film that is disposed between the fixed reflective film and the movable substrate, in which the fixed substrate transmits light, the fixed reflective film includes silver, and a concentration of a hydroxyl group that the fixed substrate includes is 500 ppm or less or 1000 ppm or more.