Interference Filter Module with Orthogonal Rotation Axes
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Solution Overview
Problem
Conventional interference filter modules require precise film thickness control and fixed light incident angles, leading to increased manufacturing costs and difficulty in achieving target wavelength selection characteristics due to polarization dependence and polarization mode dispersion.
Innovation Solution
An interference filter module with 2n filters arranged on the optical axis, where each pair of filters is held rotatably with orthogonal rotation axes, allowing adjustable light incident angles to reduce polarization dependence and dispersion, and the filters are positioned to minimize divergence angles for improved wavelength selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the light incident surface of the interference filter is inclined with respect to the optical axis to prevent optical feedback, then optical feedback is reduced, but polarization dependence and polarization mode dispersion increase
Solution Approach 1:
The interference filter is divided into multiple independent filter units (first, second, third, fourth interference filters) arranged in series. Each filter unit can be independently inclined at different angles, allowing the system to prevent optical feedback while distributing and reducing the overall polarization dependence and mode dispersion through the combined effect of multiple filters with different orientations
Solution Approach 2:
The four interference filters are inclined at different asymmetric angles relative to the optical axis (first and fourth filters at a first angle, second and third filters at a second angle different from the first). This asymmetric arrangement breaks the symmetry that causes polarization mode dispersion while still preventing optical feedback through inclination
2Manufacturing precision
If two interference filters are arranged in series to improve wavelength selection characteristic, then wavelength selection characteristic is improved, but polarization dependence and polarization mode dispersion increase
Solution Approach 1:
The wavelength selection function is distributed across four interference filters rather than two, with each filter contributing to the overall wavelength selection. The segmentation into multiple filters with different inclination angles allows achieving better wavelength selection while reducing polarization effects through the combined optical path
Solution Approach 2:
The inclination angles of the interference filters are varied (first and fourth filters at one angle, second and third at another angle) to change the optical parameters of each filter. This parameter variation allows the system to maintain sharp wavelength selection characteristics while reducing the cumulative polarization dependence and mode dispersion that would occur with identical filters
3Manufacturing precision
If film thickness control with extremely high accuracy is required for interference filters to achieve target wavelength selection characteristic, then wavelength selection characteristic is improved, but manufacturing cost increases
Solution Approach 1:
Instead of requiring extremely precise film thickness control, the invention changes the approach by controlling the inclination angles of the filters and using multiple filters with different angles. This parameter change from thickness precision to angular arrangement allows achieving target wavelength selection characteristics with more relaxed manufacturing tolerances and lower cost
Solution Approach 2:
The system uses adjustable inclination angles for the interference filters rather than relying solely on fixed film thickness. This dynamic adjustment capability allows compensating for film thickness variations and achieving the desired wavelength selection characteristic without requiring extremely high initial manufacturing precision
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 module achieves reduced polarization dependence and polarization mode dispersion while maintaining excellent wavelength selection characteristics at a lower cost, without the need for precise film thickness control or fixed light incident angles.
Implementation Method 1
An interference filter serving as an optical element has a structure in which a thin film made of, for example, a dielectric is laminated on a substrate made of, for example, glass. This interference filter transmits light in a specific wavelength band and reflects light in other wavelength bands.
Implementation Method 2
when light unidirectionally traveling from one of the optical fibers is incident on the interference filter, so-called 'optical feedback', specifically, a phenomenon that a part of the light is specularly reflected to be incident on this optical fiber again is prevented
Data Source
Figure 1(A)~1(B)
Figure 2(A)~2(B)
Figure 3(A)~3(B)
AI summary
Provided is an interference filter module (1) including a pair of optical fiber collimators (3a, 3b) arranged on an optical axis (60) so as to be opposed to each other, an even number of interference filters (5a, 5b), and a casing (2) including a main body portion (21) having a cylindrical shape and filter holding portions (4a, 4b) to be mounted into the main body portion, which are configured to hold the interference filters. Two interference filters including a k-th interference filter when counted from a front end and a k-th interference filter when counted from a rear end are determined as a k-th set. The two interference filters of the k-th set are accommodated in two filter holding portions, which are a k-th filter holding portion when counted from the front end and a k-th filter holding portion when counted from the rear end. The two filter holding portions, which are the k-th filter holding portion when counted from the front end and the k-th filter holding portion when counted from the rear end, have rotation axes (46a, 46b) in directions orthogonal to a fore-and-aft direction and are configured so as to be rotatable in a state of being mounted in the casing. At the same time, the rotation axes of the filter holding portions are orthogonal to each other.