Tunable Fabry-Perot Filter With Angled Movable Reflectors
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Solution Overview
Problem
Existing Fabry-Perot filters face limitations in tuning range and finesse due to mirror spacing constraints, material choices, and structural issues such as warping and tilting, which affect their performance in infrared spectroscopy applications, especially for wavelengths greater than 8 µm.
Innovation Solution
A tunable Fabry-Perot filter design featuring two moveable reflector supports with elongated shapes arranged at an angle, allowing for variable mirror spacing and electrostatic attraction, integrated with volume micromechanics to minimize warping and tilting, and using dielectric layer stacks for high reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If surface micromechanics with sacrificial layers is used to produce Fabry-Perot filters, then the manufacturing process is simplified, but the mirror spacing is limited and cannot achieve wavelengths greater than 8 µm
Solution Approach 1:
The patent replaces the mechanical sacrificial layer release method with a chemical bonding approach. Two silicon wafers are bonded together using oxygen plasma treatment and silane coupling agents, eliminating the need for sacrificial layers and enabling much larger mirror spacings suitable for wavelengths greater than 8 µm while maintaining manufacturing simplicity
Solution Approach 2:
The patent uses composite material structures with alternating layers of polysilicon and silicon dioxide deposited on silicon carrier substrates. This composite structure provides both mechanical support and optical functionality, enabling the creation of thick membrane structures with large mirror spacings that maintain structural integrity
2Volume of moving object
If thin membranes are used for movable mirrors, then the device size is reduced, but warping occurs which limits the choice of layering materials and reduces finesse
Solution Approach 1:
The patent uses thin silicon dioxide layers (2-5 µm) as flexible membranes that can be deposited using standard semiconductor techniques. These thin films provide the necessary flexibility for micromechanical movement while maintaining sufficient structural stability to prevent warping when properly supported by the silicon carrier substrates
Solution Approach 2:
The patent changes the physical and chemical parameters of the membrane materials, specifically using silicon dioxide with controlled thickness and depositing polysilicon layers with specific doping concentrations. These parameter optimizations ensure the membranes remain stable and warp-free during operation
3Length of stationary object
If large mirror spacing is achieved for wavelengths greater than 8 µm, then the tuning range is extended, but the available materials for mirrors are limited
Solution Approach 1:
The patent employs composite material systems combining silicon carrier substrates with deposited polysilicon and silicon dioxide layers. This composite approach enables the creation of mirrors with large spacing for wavelengths greater than 8 µm while maintaining access to a wide range of materials through standard semiconductor deposition techniques
Solution Approach 2:
The patent creates a universal manufacturing platform using standard semiconductor fabrication techniques that can produce Fabry-Perot filters for multiple wavelength ranges. The same basic process can be adapted for different materials and wavelength ranges, providing versatility beyond just the 8 µm limit
4Device complexity
If fixed filter arrangements or filter wheel constructions are used, then the device is simple and robust, but the spectral resolution and measurement speed are limited
Solution Approach 1:
The patent transforms fixed, static filter arrangements into dynamic, continuously tunable filters using micromechanical actuators. The movable mirrors can be positioned continuously to scan through the spectrum, providing both the simplicity of a compact design and the high spectral resolution needed for precise measurements
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 design achieves a large tuning range with high finesse, stability under dynamic loads, and reduced excitation voltage requirements, enabling precise measurements across a wide wavelength range, including beyond 8 µm, while maintaining robustness and simplicity.
Implementation Method 1
portions of the first reflector support facing portions of the second support frame, and portions of the second reflector support facing portions of the first support frame, allowing for variable mirror spacing and electrostatic attraction
Data Source
AI summary
A tunable Fabry-Perot filter comprises a first part (10), which has a first reflector carrier (12) comprising a first reflector (34) and a first carrier frame (14) on which the reflector carrier (12) is spring-mounted. The tunable Fabry-Perot filter further comprises a second part (20), which has a second reflector carrier (22) comprising a second reflector (36) and a second carrier frame (24) on which the second reflector carrier (22) is spring-mounted. The first and second parts (10, 20) are connected to each other such that the first reflector (34) and the second reflector (36) lie opposite one another, wherein a distance between the first reflector and the second reflector is variable. Both the first reflector carrier and the second reflector carrier have an oblong shape and are arranged at an angle to each other such that the reflectors lie opposite one another in a region in which the oblong reflector carriers overlap. Regions of the first reflector carrier are located opposite of regions of the second carrier frame, and regions of the second reflector carrier are located opposite of regions of the first carrier frame.