High-sensitivity ultrasonic phase-shifted fiber Bragg grating balanced sensing system

Area of Science:

• Optoelectronics
• Materials Science
• Acoustics

Background:

• Traditional ultrasonic sensing systems often require signal amplification, which can introduce noise and limit sensitivity.
• Fiber Bragg gratings (FBGs) offer a robust platform for optical sensing, but achieving high sensitivity for ultrasonic detection remains a challenge.

Purpose of the Study:

• To develop and demonstrate a high-sensitivity ultrasonic sensing system capable of direct ultrasonic strain detection.
• To leverage the unique properties of phase-shifted fiber Bragg gratings (PS-FBGs) for enhanced sensing performance.
• To investigate the potential of the developed system for practical applications in non-destructive testing.

Main Methods:

• Utilizing a phase-shifted fiber Bragg grating (PS-FBG) as the core sensing element.
• Modulating the output of a tunable laser with the PS-FBG to directly detect ultrasonic strain.
• Employing a balanced photo-detector (BPD) to eliminate DC components, amplify AC signals, and reject laser intensity noise.

Main Results:

• Achieved a high sensitivity of 9 nε/Hz(1/2) for ultrasonic strain detection.
• Demonstrated broadband detection capabilities due to the PS-FBG.
• Identified the balanced photo-detector noise and laser frequency noise as the primary limitations to minimum detectable strain.

Conclusions:

• The proposed high-sensitivity ultrasonic sensing system, based on PS-FBG and BPD, offers significant advantages for direct strain detection.
• The system's high sensitivity and broadband detection capabilities make it suitable for acousto-ultrasonic testing and acoustic emission detection without signal amplification.
• Further research can focus on optimizing the BPD and laser source to further reduce noise and enhance detection limits.