Phase-Step Diaphragm Sensor for Acoustic Sensing
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Solution Overview
Problem
Existing membrane-based fiber acoustic sensors, particularly interferometric Fabry-Perot sensors, are time-consuming to fabricate and require precise tuning of laser wavelength and cavity length, making them unwieldy for large arrays, while also being sensitive to wavelength changes, which limits their reproducibility and ease of assembly.
Innovation Solution
A phase-front-modulation (PFM) sensor utilizing a reflective diaphragm with a π/2 phase step microfabricated in a silicon wafer and a single-mode fiber, forming a simple interferometric sensor head that is easier and faster to assemble, with a broader and more reproducible operating wavelength range, and comparable minimum detectable pressure (MDP) performance to previous FP-based sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric Fabry-Perot sensors are used, then high sensitivity and low noise are achieved, but fabrication is time-consuming and requires precise tuning of laser wavelength and cavity length
Solution Approach 1:
The sensor is divided into two separate portions: a first portion (waveguide or fiber) and a second portion (reflector with diaphragm), which can be fabricated independently and then assembled. This segmentation eliminates the need for complex monolithic Fabry-Perot cavity fabrication and laser wavelength tuning, significantly reducing fabrication time while maintaining sensitivity through the preserved optical interference mechanism between the two portions.
Solution Approach 2:
The reflector portion is pre-fabricated with a specific phase-shift structure (e.g., π/2 phase step) during manufacturing, eliminating the need for post-fabrication laser wavelength and cavity length tuning. This preliminary structuring of the reflector ensures optimal interference conditions are achieved automatically upon assembly, reducing both fabrication time and operational complexity.
2Measurement precision
If interferometric Fabry-Perot sensors are used, then high sensitivity is achieved, but precise tuning of laser wavelength and cavity length is required, making them unwieldy for large arrays
Solution Approach 1:
By separating the sensor into independently fabricable portions with standardized interfaces, each unit can be manufactured and tested separately, then rapidly assembled into large arrays without requiring complex individual tuning of each sensor element. This modular approach dramatically reduces assembly complexity for large-scale deployments.
Solution Approach 2:
The reflector is designed with a fixed phase-shift parameter (e.g., π/2 phase step) that establishes optimal interference conditions across a broader wavelength range, eliminating the need for precise laser wavelength tuning. This parameter optimization makes the sensors more robust and easier to assemble in large arrays with consistent performance.
3Measurement precision
If membrane-based fiber acoustic sensors are used, then compact size and high sensitivity are achieved, but they are sensitive to wavelength changes, limiting reproducibility
Solution Approach 1:
The reflector is designed with a specific phase-shift parameter (e.g., π/2 phase step) that creates an interference pattern less sensitive to wavelength variations. This parameter optimization broadens the operational wavelength range and improves reproducibility across different manufacturing batches and operating conditions, while maintaining high sensitivity through the enhanced interference mechanism.
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 PFM sensor achieves a minimum detectable pressure (MDP) as low as 2.4 µPa/√Hz between 1 kHz and 30 kHz, with potential for further optimization to match or exceed the sensitivity of high-end commercial sensors, and is more straightforward to fabricate and assemble, offering improved reproducibility and reduced noise compared to previous FP-based sensors.
Implementation Method 1
The optical reflector is configured to reflect at least a portion of the light. The first portion of the optical reflector is configured to reflect a first portion of the light back to the at least one optical waveguide. The second portion of the optical reflector is configured to reflect a second portion of the light back to the at least one optical waveguide.
Implementation Method 2
The at least one optical waveguide is configured to emit light in a direction.
Implementation Method 3
The reflected second portion of the light differs in phase from the reflected first portion of the light by a phase difference that is not substantially equal to an integer multiple of π when the second portion of the optical reflector is in an equilibrium position in absence of the perturbation.
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A sensor and a method of fabrication are provided. The sensor includes at least one optical waveguide and an optical reflector. The optical reflector is optically coupled to the at least one optical waveguide and includes a first portion and a second portion. The first portion is configured to reflect a first portion of light back to the at least one optical waveguide. The second portion is configured to reflect a second portion of light back to the at least one optical waveguide. The reflected second portion of the light differs in phase from the reflected first portion of the light by a phase difference that is not substantially equal to an integer multiple of π when the second portion of the optical reflector is in an equilibrium position in absence of the perturbation.