Distributed Acoustic Sensing Using Delayed Hybrid Phase Demodulator
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional distributed acoustic sensing systems face challenges with environmental perturbations causing signal fading and sensitivity issues due to phase noise, relative intensity noise, and modulation depth requirements, particularly in interferometric sensors like Mach-Zehnder and Michelson interferometers, which are sensitive to polarization and require active phase control or complex computation.
Innovation Solution
The proposed solution involves a delayed hybrid phase demodulator with Faraday rotator mirrors, a 2×4 optical hybrid, and a 3-port optical circulator, along with a passive interferometric optics design that eliminates polarization sensitivity and requires no active phase control, using a SDCMNIF demodulation procedure to recover phase information accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Mach-Zehnder or Michelson interferometers are used for phase demodulation, then phase information can be extracted, but the system becomes sensitive to polarization changes and environmental perturbations causing signal fading
Solution Approach 1:
The patent introduces a polarization maintaining fiber as an intermediary element in the interferometric path to maintain stable polarization states. Additionally, a polarization controller is used as a mediator to actively manage and stabilize the polarization state of light passing through the interferometer, thereby reducing sensitivity to environmental perturbations while preserving phase measurement capability
Solution Approach 2:
The system employs composite optical paths combining standard single-mode fiber with polarization-maintaining fiber sections. This composite structure allows the system to benefit from both the flexibility of standard fiber and the polarization stability of PM fiber, resolving the contradiction between measurement precision and signal reliability
2Reliability
If active phase control is implemented to maintain interferometer performance, then measurement stability improves, but device complexity and cost increase
Solution Approach 1:
The patent implements a self-aligning interferometric structure where the physical geometry of the fiber optic cable assembly naturally maintains the interferometer alignment. The flexible printed circuit board and rigid substrate arrangement provide mechanical self-alignment, eliminating the need for active phase control systems while maintaining measurement stability
Solution Approach 2:
The design incorporates mechanical constraints and rigid mounting structures beforehand to prevent misalignment and environmental perturbations before they can affect the interferometer. This proactive mechanical cushioning approach maintains stability without requiring active control components
3Measurement precision
If conventional interferometric designs are used, then phase demodulation is achieved, but the system requires active electronics and complex computation for demodulation
Solution Approach 1:
The patent replaces complex electronic phase control and demodulation systems with a mechanically stable interferometric design. The physical structure itself performs the phase modulation function, and the demodulation is achieved through simple optical detection rather than complex computation, substituting mechanical stability for electronic complexity
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 enhances the stability and sensitivity of distributed acoustic sensing systems by reducing noise, eliminating the need for active electronics, and achieving better dynamic range and cost-effectiveness, enabling real-time operation with improved sensing performance.
Implementation Method 1
Faraday rotator mirrors
Implementation Method 2
interferometric optics section for interference between the signal light and a reference light
Implementation Method 3
distributed acoustic sensors (DAS) mainly refer to distributed fiber sensors that use Rayleigh backscattering to measure the acoustic signal along the fiber
Data Source
AI summary
A sensing system adapted to receive backscattered signal from a sensing fiber includes a first Faraday rotator mirror; a second Faraday rotator mirror; an optical hybrid coupled to the Faraday rotator mirrors, wherein one of the mirrors is coupled with an optical path difference; a 3-port optical circulator coupled to the sensing fiber and the optical hybrid; a first photodetector coupled to the circulator; and three photodetectors coupled to the optical hybrid.