Fiber Optic Particle Motion Sensor Using Unbalanced Interferometer
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Solution Overview
Problem
Current fiber optic sensors for dynamic acceleration and acoustic velocity measurements are costly, difficult to manufacture, and lack sufficient sensitivity, often requiring complex equipment and skilled labor, with existing technologies limiting sensitivity to around 1 mg, whereas many applications require sensitivities of 30-50 ng.
Innovation Solution
The development of a fiber optic sensor system using ultra-narrow band gratings coupled with an unbalanced fiber interferometer for high-speed interferometric interrogation, which translates wavelength shifts into phase shifts for demodulation, achieving significantly higher sensitivity and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional FBG accelerometers with spectroscopic interrogation are used, then manufacturing is simplified, but sensitivity is limited to about 1 mg
Solution Approach 1:
The patent replaces traditional spectroscopic interrogation methods with an interferometric detection system. Instead of using complex spectral analysis equipment, the invention uses an unbalanced fiber interferometer to convert wavelength shifts into phase shifts, which are then detected by a simple photodetector. This substitution of the detection mechanism achieves ultra-high sensitivity (30-50 ng level) while avoiding the complexity of spectroscopic equipment.
Solution Approach 2:
The invention changes the detection parameter from direct wavelength measurement (spectroscopy) to phase shift measurement (interferometry). By coupling the FBG with an unbalanced interferometer, the system translates wavelength shifts into phase modulations of the optical carrier, enabling detection at the 30-50 ng sensitivity level through phase demodulation rather than spectral analysis.
2Reliability
If fiber optic sensors are used in harsh environments, then reliability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the FBG sensor element with an unbalanced fiber interferometer into a single integrated package. The FBG is inscribed directly into the fiber that forms one arm of the interferometer, eliminating the need for separate coupling components and reducing assembly complexity. This integrated design maintains the reliability advantages of fiber optics in harsh environments while simplifying manufacturing compared to previous multi-component fiber optic sensor systems.
Solution Approach 2:
The interferometric structure uses the FBG's own reflected light as the measurement signal, eliminating the need for separate light sources or complex optical alignment. The FBG reflects light back through the interferometer, and the system self-demodulates the wavelength shift information through the interferometric phase modulation, reducing the need for external equipment and skilled assembly.
3Measurement precision
If unbalanced fiber interferometer with ultra-narrow band gratings is used, then sensitivity reaches 30-50 ng level, but device complexity increases
Solution Approach 1:
The invention extracts only the essential functional elements needed for high-sensitivity detection: an unbalanced fiber interferometer with a single FBG and a photodetector. By removing unnecessary components from more complex fiber optic sensor designs and focusing on the core interferometric measurement principle, the system achieves 30-50 ng sensitivity with a relatively simple structure that can be manufactured with standard fiber optic techniques.
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 system provides sensitivity several orders of magnitude higher than prior technologies, achieving a minimum detectable acceleration of about 33 ng, comparable to electronic geophones, but with 10,000 times better resolution than traditional FBG accelerometers.
Implementation Method 1
The unbalanced interferometer functions to translate the FBG wavelength shift into a phase shift, which is easily demodulated by the interrogator
Implementation Method 2
acceleration, acoustic velocity, or displacement (vibration) cause a corresponding shift in the center wavelength of the FBG reflection (or transmission) spectrum
Data Source
AI summary
An optical sensor in which acceleration, acoustic velocity, or displacement (vibration) causes a corresponding shift in the center wavelength of the sensor output. The sensor can be coupled to a high-speed interferometric interrogator through an unbalanced fiber interferometer. The unbalanced interferometer functions to translate optical wavelength shift into phase shift, which is easily demodulated by the interrogator. A method of measuring acceleration uses the sensor.