Multilayer Optical Filter for Endoscope Polarization Control
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Solution Overview
Problem
Existing optical devices with thin-film filters face challenges in reducing angular dependence on S polarization and managing ripple in wavelength pass bands, particularly in dichroic and notch filters, which affect the separation of wavelength bands and polarization characteristics.
Innovation Solution
A multiple layer film section is introduced between two optical members with refractive indices nS, nL, and nH, where the thin film layers are stacked alternately, and the refractive indices and film thickness are optimized to satisfy specific conditional expressions, allowing for controlled reflection and passage of wavelength bands while minimizing polarization divergence and ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a dichroic filter or notch filter with 45 degree angle of incidence is used, then wavelength band separation is achieved, but angular dependence on S polarization occurs and ripple appears in pass bands
Solution Approach 1:
The patent changes the angle of incidence parameter from the conventional 45 degrees to 55-65 degrees, which fundamentally alters the optical path and reduces angular dependence on S polarization. This parameter change resolves the contradiction by maintaining wavelength separation while improving polarization stability
Solution Approach 2:
The patent employs a composite multilayer film structure combining high refractive index materials (Ta2O5, TiO2) and low refractive index materials (SiO2, MgF2) in alternating layers. This composite structure enables precise control of optical properties to achieve both wavelength separation and reduced polarization dependence simultaneously
2Manufacturing precision
If the refractive index and film thickness are optimized for wavelength separation, then filtering performance improves, but polarization divergence increases
Solution Approach 1:
The patent optimizes specific parameters including setting the angle of incidence to 55-65 degrees and configuring the multilayer film with alternating high (n=2.0-2.5) and low (n=1.4-1.7) refractive index materials with controlled thickness ratios. These parameter changes achieve both high filtering precision and reduced polarization divergence
Solution Approach 2:
The patent addresses polarization divergence by introducing angular dimension control through the 55-65 degree incidence angle range, which transforms the optical interaction in a way that reduces sensitivity to polarization state while maintaining wavelength selectivity
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 achieves a small separation of P and S polarizations, reduces ripple in pass bands, and enables effective filtering of specific wavelength bands, improving the performance of optical devices such as imaging instruments and endoscopes.
Implementation Method 1
A multiple layer film section which has a structure in which, at least two types of thin film layers namely a first thin film layer, and a second thin film layer which has a refractive index higher than a refractive index of the first thin film layer, are stacked alternately
Implementation Method 2
At the multiple layer film section, out of the light incident, a light of a first wavelength band is allowed to be reflected
Implementation Method 3
a multiple layer film section which is provided between an optical surface of the first optical member and an optical surface of the second optical member
Implementation Method 4
The first optical member and the second optical member are joined by an adhering means
Data Source
AI summary
An optical device includes a first optical member and a second optical member formed of a medium having a refractive index greater than 1, and a multiple layer film section. The multiple layer film section has a structure in which at least two types of thin film layers namely a first thin film layer and a second thin film layer which has a refractive index higher than a refractive index of the first thin film layer, are stacked alternately. The first optical member and the second optical member are joined by an adhering means (an adhesive), and satisfy a predetermined condition. At the multiple layer film section, from a light incident, a light in a first wavelength band is let to be reflected, and a light in a second wavelength band which is shorter than the first wavelength band, and a light in a third wavelength band which is longer than the first wavelength band is let to pass (to be transmitted).