Compact assembly-free vector bend sensor based on all-in-fiber-core Mach-Zehnder interferometer

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Interferometry

Background:

• Optical fiber sensors are crucial for structural health monitoring.
• Existing sensors often face limitations in cost, assembly, or sensitivity.
• Developing compact, assembly-free, and sensitive sensors is an ongoing challenge.

Purpose of the Study:

• To present a novel, low-cost, compact, and assembly-free optical fiber curvature sensor.
• To demonstrate the sensor's high sensitivity and direction-dependent spectral shift.
• To evaluate the sensor's immunity to environmental factors for practical applications.

Main Methods:

• Fabrication of a positive refractive index modified zone (PRIMZ) in a single-mode fiber (SMF) core using a femtosecond laser.
• Transformation of the SMF section into a few-mode fiber (FMF), creating an "SMF-FMF-SMF" Mach-Zehnder interferometer.
• Analysis of the spectral shift in the interference pattern under varying bending conditions and orientations.

Main Results:

• Achieved high sensitivities of 2.53 nm/m⁻¹ (0°) and 2.24 nm/m⁻¹ (180°) over a wide bending range (0-4 m⁻¹).
• Demonstrated direction-dependent spectral shifts in response to bending.
• Confirmed immunity to surrounding refractive index changes and low-temperature crosstalk.

Conclusions:

• The developed optical fiber sensor is a cost-effective, compact, and assembly-free solution for precise curvature measurement.
• Its high sensitivity, directionality, and environmental robustness make it suitable for practical structural monitoring.
• This technology holds significant potential for enhancing safety and efficiency in various engineering applications.