High-performance vector torsion sensor based on high polarization-dependent in-fiber Mach-Zehnder interferometer

Area of Science:

• Optical Fiber Sensors
• Interferometry
• Nanofabrication

Background:

• Fiber optic sensors are crucial for various monitoring applications.
• Existing torsion sensors often lack vector measurement capabilities or require complex fabrication.
• In-fiber devices offer miniaturization and enhanced robustness.

Purpose of the Study:

• To propose and demonstrate a novel in-fiber Mach-Zehnder interferometer (MZI) for vector torsion sensing.
• To achieve high sensitivity and robustness in a compact and rapidly fabricated sensor.
• To enable vector torsion demodulation by controlling incident light polarization.

Main Methods:

• Fabrication of an in-fiber MZI by inscribing a straight waveguide in a single-mode fiber (SMF) core-cladding boundary using a femtosecond laser.
• Characterization of the device's transmission spectrum and polarization dependence.
• Investigation of the sensor's response to torsion, strain, and temperature.

Main Results:

• A 5 mm long in-fiber MZI was fabricated in under 1 minute.
• The asymmetric structure induced high polarization dependence, with a strong polarization-dependent dip in the transmission spectrum.
• Torsion sensitivity reached 5763.96 dB/(rad/mm) via intensity modulation, with weak responses to strain and temperature.
• Vector torsion sensing was achieved by manipulating incident light polarization.

Conclusions:

• The proposed in-fiber MZI is a high-performance, robust, and rapidly fabricated sensor for vector torsion measurement.
• The device's sensitivity and stability make it suitable for demanding applications.
• The integrated fiber coating ensures structural integrity and practical usability.