Simultaneous directional curvature and temperature sensor based on a tilted few-mode fiber Bragg grating

Area of Science:

• Fiber optics sensing
• Optical metrology
• Nanophotonics

Background:

• Fiber Bragg gratings (FBGs) are widely used for sensing applications.
• Few-mode fiber Bragg gratings (FM-FBGs) offer enhanced sensing capabilities due to multiple propagating modes.
• Directional curvature sensing remains a challenge in optical fiber technology.

Purpose of the Study:

• To develop and demonstrate a directional curvature sensor.
• To investigate the performance of tilted FM-FBGs for curvature sensing.
• To evaluate the sensor's capability for simultaneous curvature and temperature measurement.

Main Methods:

• Fabrication of tilted few-mode fiber Bragg gratings (FM-FBGs) using UV laser inscription.
• Simulation of LP01 and LP11 eigenmodes under fiber bending.
• Experimental measurement of curvature sensitivity at different directions (0° and 90°).
• Analysis of temperature influence on the LP11 mode resonance.

Main Results:

• The sensor utilizes the LP11 mode resonance in the tilted FM-FBG for directional curvature detection.
• Measured curvature sensitivities are -2.67 dB/m⁻¹ at 0° and 0.128 dB/m⁻¹ at 90° for a curvature range of 4.883 to 7.625 m⁻¹.
• Temperature variations showed minimal impact on the LP11 mode resonance depth.
• Demonstrated simultaneous measurement resolutions of 9.15×10⁻⁴ m⁻¹ for curvature and 0.952°C for temperature.

Conclusions:

• The proposed tilted FM-FBG sensor effectively measures directional curvature.
• The sensor exhibits potential for simultaneous directional curvature and temperature sensing with high resolution.
• This technology offers a promising solution for advanced structural health monitoring and other applications requiring precise directional strain and temperature measurements.