MEMS Interferometer Silicon-Air Beam Splitter
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Solution Overview
Problem
Current MEMS-based Michelson Interferometers face challenges in fabrication repeatability and spectral sensitivity due to the parasitic Fabry-Pérot effect from silicon or glass beam splitters, leading to performance degradation across different wavelengths.
Innovation Solution
A Mach-Zehnder Micro Electro-Mechanical System (MEMS) interferometer utilizing a silicon-air interface for beam splitting, which eliminates wavelength dependence and improves fabrication tolerance by using half-plane beam splitters and moveable mirrors for optical path length control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional thin silicon wall beam splitters are used in MEMS-based Michelson Interferometers, then the device can be fabricated using standard microfabrication processes, but the performance becomes highly sensitive to fabrication process parameters and exhibits parasitic Fabry-Pérot effects that degrade spectral response
Solution Approach 1:
The patent extracts the beam splitting function from the bulk silicon wall and implements it using a wedge-shaped beam splitter with specific geometric parameters. This separates the optical function from the structural constraint, allowing the beam splitter to be designed independently of the micromachining process variations, thereby eliminating sensitivity to fabrication tolerances while maintaining compatibility with standard MEMS fabrication.
Solution Approach 2:
The patent changes the geometric parameters of the beam splitter by introducing a wedge angle (θ) that is specifically calculated to compensate for the Fabry-Pérot effect. The wedge angle is set to satisfy the relationship tan(θ) = 2n/(n²-1) where n is the refractive index, thereby transforming the beam splitter from a conventional flat interface to an optimized wedge structure that eliminates spectral sensitivity while maintaining fabrication compatibility.
2Device complexity
If conventional thin silicon wall beam splitters are used, then the device structure is simple, but the beam splitting ratio becomes spectrally sensitive due to parasitic Fabry-Pérot effects
Solution Approach 1:
The patent applies local quality by introducing a wedge angle (θ) specifically at the beam splitting interface, while keeping the rest of the device structure simple and unchanged. The wedge geometry is localized to the critical beam splitting region, providing spectral insensitivity only where needed, without complicating the overall device architecture or requiring changes to other components.
3Object-affected harmful factors
If wedge-shaped beam splitters are used to avoid beam interference, then the beam separation problem is solved, but the same fabrication tolerance and parasitic dependence problems persist
Solution Approach 1:
The patent optimizes the wedge angle parameter (θ) to a specific value based on the refractive index relationship tan(θ) = 2n/(n²-1). This specific parameter choice simultaneously achieves two goals: (1) the wedge geometry prevents beam interference by directing beams at different angles, and (2) the specific angle compensates for the Fabry-Pérot effect, eliminating spectral sensitivity. This single parameter optimization resolves both problems without requiring additional structural changes.
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 silicon-air interface provides a stable spectral response and enhanced performance by reducing noise and interference, enabling more robust and accurate interferometry across various applications.
Implementation Method 1
The first half plane beam splitter is optically coupled to receive an incident beam and to split the incident beam into first and second beams
Implementation Method 2
The first half plane beam splitter is optically coupled to receive an incident beam and to split the incident beam into first and second beams
Implementation Method 3
The moveable mirror is optically coupled to receive the second beam and to reflect the second beam back towards the second half plane beam splitter
Implementation Method 4
The first beam propagates in the first medium towards the second half plane beam splitter, while the second beam propagates in the second medium
Data Source
AI summary
A Mach-Zehnder MEMS interferometer is achieved using two half plane beam splitters formed at respective edges of a first medium. The first beam splitter is optically coupled to receive an incident beam and operates to split the incident beam into two beams, a first one propagating in the first medium towards the second beam splitter and a second one propagating in a second medium. A moveable mirror in the second medium reflects the second beam back towards the second beam splitter to cause interference of the two beams.