Solid-State Etalon Filter Assembly for Solar Telescopes
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Solution Overview
Problem
Solar telescopes face challenges in maintaining the stability and optical quality of narrow bandpass filters due to environmental changes and high background noise, requiring advanced filtering technologies that balance light throughput and stray light rejection while being cost-effective.
Innovation Solution
The combination of lower transmittance etalons with higher transmittance filters, including a circular polarizer and a blocker/trimmer filter, along with direct heating of the etalon to stabilize the bandpass, and the use of antireflective coatings to reduce stray reflections, achieves the necessary throughput and rejection of stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If air-gapped etalons are used to achieve narrow bandpass filtering, then spectral selectivity is improved, but stability against environmental changes deteriorates
Solution Approach 1:
The patent applies parameter changes by transitioning from air-gapped to solid-state etalons, fundamentally changing the physical state of the spacer material. This eliminates the sensitivity to pressure and temperature variations that plague air-gapped designs, while maintaining the narrow bandpass filtering capability through precise control of the solid spacer thickness and refractive index.
Solution Approach 2:
The patent employs lower quality, less expensive solid spacer materials (such as glass or plastic) instead of requiring extremely high precision optical flats. While these materials have higher absorption losses, the invention compensates through the combination with high-transmittance filters, achieving overall system performance without the cost and complexity of premium optical materials.
2Stability of the object's composition
If solid-state etalons with high quality materials are used to improve stability, then spectral position stability is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent applies local quality by assigning different functional requirements to different components of the optical system. The solid-state etalon uses modest quality materials where stability is achieved through design rather than material perfection, while the accompanying filters use high-transmittance materials to compensate for absorption losses. This localized optimization reduces overall system cost while maintaining performance.
3Object-affected harmful factors
If multiple filters are combined to achieve necessary stray light rejection, then stray light blocking is improved, but light throughput deteriorates
Solution Approach 1:
The patent employs composite materials by combining multiple filter types with complementary transmission characteristics. The system integrates solid-state etalons, high-transmittance interference filters, and absorptive filters in a composite arrangement where each component addresses specific portions of the spectral range, achieving high stray light rejection while preserving maximum light throughput in the desired bandpass region.
4Stability of the object's composition
If active control systems are added to stabilize air-gapped etalons, then spectral position stability is improved, but device complexity increases
Solution Approach 1:
The patent extracts the active control system entirely from the design by adopting solid-state etalons. This passive stabilization approach eliminates the need for temperature control mechanisms, pressure regulation systems, or active feedback loops, achieving spectral position stability through the inherent mechanical stability of solid materials rather than through complex active control.
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 solution provides stable and selective light transmission, enhancing the ability to observe solar events by reducing stray light and maintaining the integrity of the narrow bandpass, while being cost-effective and compact.
Implementation Method 1
Narrow bandpass filters are often made by thin film technologies that combine multilayer stacks of coatings to create constructive or destructive interference with the light impinging on the filter
Implementation Method 2
The circular polarizer is produced by combining a quarter-wave plate with a linear polarizing element
Implementation Method 3
The linear polarizing element is an absorptive-type or reflective-type linear polarizer
Implementation Method 4
the use of antireflective coatings to reduce stray reflections
Implementation Method 5
direct heating of the etalon to stabilize the bandpass
Data Source
AI summary
The invention relates to the combination of lower transmittance etalons with higher transmittance filters, including use of a single circular polarizer with high efficiency and optical performance for its filtered polarization, to achieve necessary throughput of a narrow bandpass region. The lower transmittance etalons can be achieved by using lower transmittance solid-state etalon materials, or by control of the coatings on the etalon. Alternate configurations are described that reduce the optical assembly's footprint, and/or include additional filters to remove stray light. An innovative option to heat the etalon directly is disclosed to actively stabilize and maintain the etalon's bandpass.