Fiber Acoustic Sensor With Phase-Front Modulation Alignment Tolerance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing fiber optic acoustic sensors based on Fabry-Perot interferometry suffer from high minimum detectable pressures due to high diaphragm stiffness and low FP finesse, and previous phase-front-modulation sensors face alignment challenges with large optical components and high sensitivity to angular misalignment.
Innovation Solution
A phase-front modulation sensor design using a reflective diaphragm with a π/2 phase step microfabricated in a silicon wafer, combined with an optical fiber, eliminates the need for an optical lens and relaxes alignment tolerances, achieving higher sensitivity and easier assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a Fabry-Perot interferometer with a single reflective diaphragm is used, then the device complexity is reduced, but the measurement precision deteriorates due to high diaphragm stiffness and low FP finesse resulting in high minimum detectable pressures
Solution Approach 1:
The reflective surface is segmented into two distinct portions: a first portion that remains stationary and a second portion (diaphragm) that moves in response to acoustic pressure. This segmentation allows the system to maintain simple device architecture while achieving high measurement precision through differential phase modulation of the two segments.
Solution Approach 2:
Different portions of the optical reflector are assigned different functional properties: the first portion provides a stable reference reflection while the second portion (diaphragm) provides the pressure-responsive variable reflection. This local differentiation enables precise acoustic measurement without requiring the entire device to be complex.
2Measurement precision
If phase-front modulation sensing is implemented, then the sensitivity is improved, but the ease of operation deteriorates due to alignment challenges with large optical components and high sensitivity to angular misalignment
Solution Approach 1:
The optical lens, which creates alignment challenges in conventional PFM sensors, is completely removed from the system. The phase-front modulation is achieved directly through the differential reflection from the two portions of the optical reflector, eliminating the need for precise lens alignment while maintaining high sensitivity.
Solution Approach 2:
The mechanical alignment system involving large optical components is replaced with a compact integrated structure where the phase modulation is achieved through the inherent geometry of the two-portion reflector. This substitution dramatically improves ease of operation by reducing sensitivity to angular misalignment.
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 sensor achieves a sensitivity about 3.9 times higher than previous PFM sensors with similar MDP at 1 kHz, and is less sensitive to alignment, temperature, and mode-field diameter variations, facilitating easier fabrication and alignment.
Implementation Method 1
the optical reflector configured to reflect at least a portion of the light, the optical reflector comprising: a first portion of the optical reflector configured to reflect a first portion of the light back to the at least one optical waveguide; and a second portion of the optical reflector configured to reflect a second portion of the light back to the at least one optical waveguide
Implementation Method 2
the reflected second portion of the light differing 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 includes at least one optical waveguide having a mode-field diameter greater than 11 µm and an optical reflector optically coupled to the at least one optical waveguide. The optical reflector includes a first substrate portion configured to reflect a first portion of a light beam back to the at least one optical waveguide and a diaphragm configured to reflect a second portion of the light beam back to the at least one optical waveguide. The diaphragm is responsive to a perturbation by moving relative to the first substrate portion. The light beam is centered on a region between the first substrate portion and the diaphragm.