Temporary Brillouin Grating Acoustic Sensing via Pump Probe Pulse Timing
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Solution Overview
Problem
Conventional Brillouin-based fiber sensors are slow and lack sufficient bandwidth for acoustic sensing, with weak strain dependence that limits their sensitivity for detecting acoustic changes.
Innovation Solution
The system generates temporary Brillouin gratings within an optical fiber by injecting a longer pump laser pulse and a shorter probe laser pulse, allowing for the creation of multiple sensing regions along the fiber, enabling quicker detection of acoustic signals through the reflection of the pump laser pulse without measuring the Brillouin frequency shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional Brillouin-based fiber sensors measure the Brillouin frequency shift to detect acoustic signals, then the measurement can be performed, but the sensing bandwidth is insufficient and the response speed is slow
Solution Approach 1:
The patent extracts only the necessary component of Brillouin scattering - the acoustic grating formation and pump beam reflection - while discarding the frequency shift measurement aspect. By using a continuous pump beam and short probe pulses to create temporary gratings that reflect the pump beam, the system achieves acoustic sensing without measuring Brillouin frequency shift, thereby increasing bandwidth and response speed.
2Measurement precision
If conventional Brillouin-based fiber sensors are used for acoustic detection, then the system can detect strain and temperature, but the sensitivity for acoustic detection is insufficient due to weak strain dependence
Solution Approach 1:
The patent extracts the acoustic grating formation mechanism from conventional Brillouin sensing and separates it from temperature and strain measurement functions. By focusing solely on the acoustic wave-induced grating that reflects pump beam intensity, the system achieves high sensitivity for acoustic detection while simplifying the sensing mechanism.
3Speed
If the pump laser pulse duration is made longer than the probe laser pulse duration, then temporary Brillouin gratings can be created for acoustic sensing, but the conventional Brillouin frequency shift measurement approach becomes incompatible
Solution Approach 1:
Instead of measuring the Brillouin frequency shift of scattered light as in conventional approaches, the patent inverts the measurement approach by detecting the reflection of the continuous pump beam from temporary gratings created by short probe pulses. This inversion enables acoustic sensing with high bandwidth while avoiding frequency shift measurement limitations.
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 sensitivity and speed of acoustic sensing by utilizing the decay of temporary Brillouin gratings to detect external sources along the fiber, providing a higher bandwidth and improved sensitivity compared to traditional methods.
Implementation Method 1
Brillouin scattering is where light is scattered by an acoustic wave. While Brillouin scattering can occur spontaneously, in sensing applications Brillouin scattering is stimulated by design.
Implementation Method 2
At the point where the pump laser 104 and the probe laser 106 meet an acoustic grating 108 is generated. The acoustic grating 108 will propagate through the optical fiber 102 in the direction of travel of the pump laser 104 at the acoustic velocity of the medium.
Implementation Method 3
Due to the Doppler effect the frequency (freflected) of the reflected pump beam 112 is decreased and will match the frequency of the probe.
Data Source
AI summary
Method and apparatuses for acoustic sensing using an optical fiber are provide. An optical fiber sensor for acoustic sensing includes an optical fiber, a laser, a pump laser pulse generator, a probe laser pulse generator, a controller, and a detector. The pump laser pulse generator is configured to receive a laser beam, from the laser, and generate a pump laser pulse. Similarly, the probe laser pulse generator is configured to receive the laser beam and generate a plurality of probe laser pulses. The controller is constructed to control the pump laser pulse generator and the probe laser pulse generator to inject the pump laser pulse and the plurality of probe laser pulses, respectively, into the optical fiber at specific timings so as to generate a plurality of Brillouin gratings at a predetermined spacing. The detector is configured to receive reflected pump laser pulses from the plurality of Brillouin gratings, respectively, and provide the reflected pump laser pulses to the controller. The duration of the pump laser pulse is greater than a duration of a probe laser pulse.