Spatial Splitting Optical MEMS Interferometer Design
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Solution Overview
Problem
Micromachined interferometers face performance degradation due to long optical propagation distances and absorption losses, especially in the near infrared and visible wavelength ranges, as well as dispersion issues caused by refractive index variations in silicon-based beam splitters, which are difficult to mitigate with anti-reflection coatings in optical MEMS systems.
Innovation Solution
The implementation of a spatial splitting-based optical MEMS interferometer (SSB-MI) that uses a spatial splitter and spatial combiner to split and combine interferometer beams within different propagation media, reducing absorption, dispersion, and Fresnel losses by eliminating propagation through silicon and employing various splitter and combiner configurations such as truncating, MMI, slotted, and Y-type designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional beam splitter using reflection and transmission by a dielectric interface is used, then the interferometer can be constructed with standard micromachining techniques, but the optical propagation distance becomes relatively long which degrades interferometer performance
Solution Approach 1:
The patent extracts the beam splitting function from a bulky dielectric beam splitter and implements it directly at the silicon wall interface. The silicon wall itself serves as the beam splitter through its inherent optical properties, eliminating the need for a separate dielectric beam splitter component and reducing the overall optical propagation distance.
Solution Approach 2:
The patent changes the optical path configuration to minimize propagation distance through the silicon medium. By using the silicon wall as the beam splitter and optimizing the interferometer geometry, the optical path length within silicon is reduced from millimeters to micrometers, significantly lowering absorption losses.
2Ease of manufacture
If metallization of the mirror is performed using shadow mask sputtering, then the mirror can be formed selectively on silicon side walls, but a relatively large distance must be maintained between the mirror and beam splitter which degrades performance
Solution Approach 1:
The patent merges the beam splitter and mirror functions into a more compact configuration. The silicon wall serves as both the structural element and the beam splitter, while the metallized mirror is positioned much closer to this interface, reducing the separation distance and improving optical coupling efficiency.
3Ease of manufacture
If the beam splitter is made of silicon or uses air/silicon interface, then the interferometer can be fabricated using DRIE on SOI wafers, but dispersion occurs due to refractive index variations with wavelength
Solution Approach 1:
The patent introduces an air gap as an intermediary medium between the silicon components. By configuring the interferometer to use air propagation paths rather than silicon propagation, the dispersive effects of silicon's wavelength-dependent refractive index are eliminated, improving phase accuracy across broad spectral ranges.
4Reliability
If compensating dielectric interfaces are added to address dispersion, then phase errors can be reduced, but Fresnel loss increases and anti-reflection coating becomes difficult
Solution Approach 1:
The patent removes the need for compensating dielectric interfaces by using air as the propagation medium. Since air has a nearly constant refractive index across wavelengths, dispersion is naturally minimized without requiring additional compensating interfaces that would introduce Fresnel losses.
5Loss of energy
If anti-reflection coating is applied to reduce Fresnel loss, then transmission efficiency can be improved, but the coating process is difficult in optical MEMS monolithic systems
Solution Approach 1:
The patent converts the inherent optical properties of air into a benefit by using air propagation to eliminate dispersion and minimize Fresnel losses at interfaces. This approach avoids the need for complex anti-reflection coating processes while achieving superior optical performance.
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 approach significantly reduces absorption and dispersion losses, enhances interferometer performance by minimizing propagation distances, and improves bandwidth and visibility of interference patterns, making it suitable for applications like FTIR Spectroscopy and Optical Coherence Tomography.
Implementation Method 1
The spatial splitter receives an input beam and spatially splits the input beam into first and second interferometer beams
Implementation Method 2
The spatial combiner receives the first and second interferometer beams and spatially combines them to produce an output
Implementation Method 3
The moveable mirror receives one of the first and second interferometer beams and reflects the received beam towards the spatial combiner
Implementation Method 4
The MEMS actuator is coupled to the moveable mirror to cause a displacement thereof to produce an optical path difference between the first interferometer beam and the second interferometer beam
Implementation Method 5
Each of the input beam, the first and second interferometer beams and the output beam propagate within a propagation medium that is different from the spatial splitter medium and the spatial combiner medium
Data Source
Figure 1
Figure 2A~2C
Figure 3A
AI summary
A spatial splitting-based optical Micro Electro-Mechanical Systems (MEMS) Interferometer includes a spatial splitter for spatially splitting an input beam into two interferometer beams and a spatial combiner for spatially combining the two interferometer beams. A MEMS moveable mirror is provided to produce an optical path difference between the first interferometer beam and the second interferometer beam.