Variable Spectral Filter Apparatus Rotating Filters
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Solution Overview
Problem
Conventional optical filter systems fail to provide variable angular orientation over a full range of 0 to 60 degrees, maintain a short optical path length, and allow for fast filter switching without beam redirection, while being compact and suitable for retrofitting existing instruments.
Innovation Solution
A variable spectral filter apparatus with a rotatable filter support that includes multiple tunable spectral filters, where the filters are oriented orthogonally to the axis of rotation, allowing for continuous undeviated light paths and simultaneous switching and tuning using a single mechanical axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a filter wheel mechanism is used to index filters into position, then filter switching capability is provided, but the device becomes bulky and cannot achieve fast switching without beam redirection
Solution Approach 1:
The filter wheel is divided into discrete filter segments arranged radially around a central rotation axis. Each filter is positioned at a specific angular location, allowing rapid indexing between filters by rotating the wheel to predetermined angular positions. This segmentation enables fast switching while maintaining a compact structure.
Solution Approach 2:
The filter wheel is made rotatable about a central axis, transforming the static filter arrangement into a dynamic system. This rotation capability allows the filters to be dynamically positioned at different angular locations, enabling both fast switching between filters and continuous angular orientation adjustment without requiring beam redirection.
2Adaptability or versatility
If tunable thin-film filters are rotated to change wavelength response, then spectral tuning range is improved, but the optical path length increases
Solution Approach 1:
The patent introduces a radial dimension for filter arrangement around the rotation axis, allowing angular orientation changes without increasing the axial optical path length. The filters are positioned at different angular locations rather than at different axial positions, enabling spectral tuning through angular rotation while maintaining a compact optical path.
3Adaptability or versatility
If diffraction gratings are used for wavelength selection, then any wavelength within a range can be selected by rotation, but spectral discrimination is poor with non-steep spectral edges
Solution Approach 1:
The patent changes the fundamental parameter of wavelength selection from diffraction-based (gratings) to interference-based (thin-film filters). By using thin-film interference filters with steep spectral edges, the system achieves high spectral discrimination while maintaining the ability to select any wavelength within the filter's transmission band through angular rotation. The interference mechanism provides the steep edges that gratings cannot achieve.
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
Enables efficient spectral filtering with variable angular orientation, compact size, and fast switching capabilities, suitable for retrofitting existing instruments without altering the light path, while maintaining high spectral discrimination and transmission efficiency.
Implementation Method 1
Interference filters conventionally include a dielectric stack composed of multiple alternating layers of two or more dielectric materials having different refractive indices. In operation, thin-film interference filters are wavelength-selective as a result of interference effects that take place between incident and reflected waves at boundaries between thin layers of materials having different refractive indices.
Implementation Method 2
Tunable performance of thin-film filters relates to the phenomenon of spectral shift with incident angle. As the tunable filter rotates and the angle of incidence of a light beam on the filter changes, the wavelength response of the tunable filter changes within its usable range.
Data Source
AI summary
A variable spectral filter apparatus has a filter support rotatable about a single axis of rotation and has at least first and second transmissive spectral filters, each spectral filter having a filter width defined by its first and second edges, wherein the filter width is orthogonal to the axis. The first edges of the filters are equidistant from the axis of rotation when the filter support is rotated to any angle. The plane of each of the spectral filters is parallel to the axis. Rotational positions of the filter support about the axis of rotation, over a first 60 degree range of angles, define, between the first and second edges of at least the first spectral filter, an undeviated filtered light path of at least half the filter width that extends orthogonally with respect to the axis. A rotational actuator is energizable to rotate the filter support about the axis.