Half-Plane Beam Splitter for MEMS Interferometer Wavelength Stability
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Solution Overview
Problem
Current MEMS-based Michelson Interferometers face challenges with fabrication repeatability and spectral sensitivity due to the parasitic Fabry-Pérot effect from silicon or glass beam splitters, leading to noise and performance degradation across different wavelengths.
Innovation Solution
A micromachined interferometer utilizing a half-plane beam splitter with a single silicon-air interface, optically coupled to split incident beams into two interfering paths, one in air and one in silicon, with a moveable mirror actuated to create an optical path length difference, reducing wavelength dependence and improving robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a thin silicon or glass wall is used for beam splitting in MEMS-based Michelson Interferometers, then the device can be miniaturized and integrated, but the performance becomes highly sensitive to fabrication process parameters with poor repeatability
Solution Approach 1:
The beam splitter is segmented into two separate surfaces: a first surface (e.g., top surface of silicon membrane) and a second surface (e.g., bottom surface of silicon membrane). This segmentation allows each surface to be independently optimized and fabricated with high precision, resolving the contradiction between miniaturization and fabrication repeatability.
Solution Approach 2:
The invention changes the optical parameters by introducing a dielectric layer between the two beam splitter surfaces, creating a distributed Bragg reflector structure. This parameter change enables wavelength-selective reflection while maintaining fabrication tolerance, as the dielectric layer thickness can be precisely controlled during standard semiconductor fabrication processes.
2Volume of moving object
If conventional thin silicon wall beam splitters are used, then the interferometer can be miniaturized, but spectral sensitivity is introduced due to parasitic Fabry-Pérot effect modulating power splitting ratio versus wavelength
Solution Approach 1:
The invention converts the harmful parasitic Fabry-Pérot effect into a beneficial wavelength-selective filtering mechanism. By designing the dielectric layer thickness to create a distributed Bragg reflector at the desired operating wavelength, the previously problematic spectral sensitivity is transformed into a useful wavelength-selective response that improves spectral stability.
Solution Approach 2:
The beam splitter uses a composite structure combining silicon membrane with a dielectric layer (e.g., silicon nitride or silicon oxide). This composite material approach allows the system to achieve both miniaturization and spectral stability, as the dielectric layer provides wavelength-selective reflection while the silicon membrane maintains the miniaturized form factor.
3Ease of operation
If a wedge-shaped beam splitter is used to avoid interference of separated beams, then beam separation is improved, but fabrication tolerance sensitivity and parasitic dependence remain
Solution Approach 1:
The beam splitter is segmented into two separate surfaces with independent optical functions: the first surface provides primary beam splitting, while the second surface (with dielectric layer) provides wavelength-selective reflection. This segmentation eliminates the need for wedge shaping and achieves both beam separation and fabrication tolerance.
Solution Approach 2:
The invention changes the optical parameters by introducing a dielectric layer with specific refractive index and thickness, creating a distributed Bragg reflector. This parameter change provides wavelength-selective reflection that is insensitive to fabrication tolerances, replacing the wedge shape approach while maintaining beam separation.
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 solution provides a wavelength-independent, robust interferometer with improved spectral response stability and reduced noise, enhancing the accuracy and reliability of applications like spectrometry and environmental sensing.
Implementation Method 1
The beam splitter is optically coupled to receive an incident beam and operates to split the incident beam into two interfering beams
Implementation Method 2
split the incident beam into two interfering beams, each propagating in a different medium
Implementation Method 3
a moveable mirror, which is controlled by an actuator, reflects the other interfering beam back towards said half plane beam splitter
Implementation Method 4
A detection plane detects the interference pattern produced as a result of interference between the reflected interfering beams
Data Source
AI summary
A micromachined interferometer is achieved using a half plane beam splitter. The beam splitter is optically coupled to receive an incident beam and operates to split the incident beam into two interfering beams, each propagating in a different medium. A fixed mirror embedded in one of the mediums reflects one of the interfering beams back towards the half plane beam splitter through such medium, while a moveable mirror, which is controlled by an actuator, reflects the other interfering beam back towards said half plane beam splitter through the other medium. A detection plane detects an interference pattern produced as a result of interference between the reflected interfering beams.