Long-range fiber-based laser Doppler vibrometer using Faraday rotator for polarization-rotation compensation

Area of Science:

• Optics and Photonics
• Sensing Technology
• Fiber Optic Systems

Background:

• Laser Doppler vibrometers (LDVs) are crucial for non-contact vibration measurement.
• Long-distance applications of fiber optic LDVs are limited by polarization state fluctuations in installed fibers.
• Existing methods to compensate for polarization changes can be complex and costly.

Purpose of the Study:

• To present a simple and effective method for extending the measurement distance of fiber optic laser Doppler vibrometer systems.
• To demonstrate the compensation of polarization rotation in long-range optical fibers using a Faraday rotator (FR).
• To achieve stable and reliable vibration measurements over kilometer-scale fiber optic links.

Main Methods:

• Integration of a Faraday rotator (FR) into the sensing head unit of the LDV system.
• Utilizing standard single-mode optical fibers of varying lengths (100 m and 10 km).
• Emulating polarization rotation within the installed optical fibers to simulate real-world conditions.

Main Results:

• The proposed system successfully compensated for polarization rotation in long-range optical fibers.
• Vibration measurement performance remained stable and reliable even with randomly rotated polarization states.
• The system's effectiveness was verified using both 100-m and 10-km fiber optic cables.

Conclusions:

• The addition of a Faraday rotator is a simple yet highly effective method to extend the operational distance of fiber optic laser Doppler vibrometers.
• This technique overcomes the limitations imposed by polarization fluctuations in installed long-range optical fibers.
• The proposed system offers a stable and reliable solution for remote vibration monitoring applications.