Tunable Optical Filter With Bonded Glass Mirrors for Compact Devices
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Solution Overview
Problem
Existing tunable optical filter devices face challenges with large volume, high driving voltage, and complex substrate processing, particularly in devices with limited space such as handheld hyperspectral cameras and mobile phones.
Innovation Solution
A tunable optical filter device utilizing glass films with bonded mirrors and a driving unit to adjust the gap between them, employing capacitive or piezoelectric driving for tunable filtering, with glass films of specific thicknesses and silicon structures for improved flexibility and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external piezo actuators are used to assemble FPI modules, then the optical filtering function is achieved, but the device volume becomes large and driving voltage becomes high
Solution Approach 1:
The patent integrates the piezo actuator directly into the substrate, merging the actuation function with the structural component. This eliminates the need for external piezo actuators and reduces overall device volume while maintaining the optical filtering function through direct coupling of the actuator and mirror assembly.
Solution Approach 2:
The piezo actuator is nested within the substrate structure, with the mirror assembly positioned on top of the actuator. This nested configuration allows the actuator to be hidden within the device footprint, reducing the external volume required while maintaining full functionality.
2Reliability
If optical glass substrate is used for FPI devices, then optical performance is maintained, but substrate processing becomes difficult with slow etching speed
Solution Approach 1:
The patent changes the substrate material from optical glass to semiconductor material (such as silicon). This parameter change enables the use of standard semiconductor fabrication processes including photolithography and plasma etching, which provide much higher etching speeds and better processing control while maintaining optical performance through precise mirror layer deposition.
Solution Approach 2:
The patent replaces chemical etching (mechanical/chemical process) with semiconductor fabrication processes. Instead of using chemical solutions to etch glass substrates, the invention uses photolithography patterns and plasma etching on semiconductor substrates, achieving faster processing and finer feature sizes.
3Reliability
If bulk-processed devices with cantilever beam structure are used, then movable mirrors are created, but device complexity increases and processing cost increases
Solution Approach 1:
The patent extracts the spring component from the bulk-processed cantilever beam structure. Instead of creating a complex three-dimensional cantilever beam with integrated spring, the invention uses a simple planar mirror assembly supported by the substrate, with the piezo actuator providing the necessary mechanical compliance and movement capability.
4Device complexity
If spring and mirror are provided by the same substrate in bulk-processed devices, then structure is simplified, but mirror deformation is affected by inherent stress
Solution Approach 1:
The patent segments the device into distinct functional layers: the substrate provides structural support, the piezo actuator provides actuation, and separate mirror layers are deposited on top. This segmentation allows each component to be optimized independently, with the mirror layers being deposited with high precision control to ensure flatness is not affected by substrate stress.
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 device achieves smaller size, lower driving voltage, simpler processing, and lower cost, making it suitable for devices with limited space while maintaining high optical filtering performance.
Implementation Method 1
the surfaces of the first glass film and the second glass film on which the mirrors are located are bonded to each other at the periphery through a bonding compound to form a cavity between the mirrors
Implementation Method 2
the first glass film or the second glass film are provided with a driving unit for directly driving deformation of the first glass film and/or the second glass film and thereby creating a movement thereof
Implementation Method 3
employing capacitive or piezoelectric driving for tunable filtering
Implementation Method 4
a first mirror and a second mirror, and the surfaces of the first glass film and the second glass film on which the mirrors are located
Implementation Method 5
Substrate of Fabry-Perot interferometer (FPI) devices in the near-infrared and visible-range
Data Source
AI summary
Disclosed is an adjustable optical filter device. The device comprises a first glass thin film provided with a first mirror and a second glass thin film provided with a second mirror. The peripheries of the surfaces of the first glass thin film and the second glass thin film that have a mirror are bonded to each other by means of a bond to form a cavity between the mirrors. The first glass thin film or the second glass thin film is provided with a driving unit for controlling the relative displacement of the first glass thin film and/or the second glass thin film. The tunable optical filter device has better optical filtering performance than existing filter devices, has the performance of small size and lower driving voltage, and can be applied to devices having a limited size, such as miniature spectrometers, small or even mini hyperspectral cameras or mobile phones.