Sensitivity-enhanced two-dimensional bending sensor based on single-mode fiber measurement

A sensitivity-enhanced two-dimensional bending sensor using four-core fiber (FCF) transition to realized singlechannel demodulation of seven-core fiber Bragg grating (FBG) is proposed. A section of FCF was added between the single-mode fiber (SMF) and the seven-core fiber (SCF), and the thermal diffusion technology (TDT) was used so that the signal of the SMF could be transmitted to the three side cores of the SCF through the FCF. Then, a 45 degrees reflective circular cone (45 degrees RCC) is fabricated at the end of the SCF, enabling the coupling of the symmetrical side core signals of the SCF. By inscribing the FBGs with different reflection wavelengths on the side cores of the SCF, the signals of each side core can be distinguished during single-channel demodulation. Monitoring the reflection wavelength shifts of the FBGs on the SCF can realize two-dimensional bending measurements. Furthermore, through the differential operation of the symmetrical side cores, the bending sensitivity can be enhanced while eliminating temperature crosstalk. The proposed sensor with high integration, high sensitivity, and reduced crosstalk, is expected to be applied in the field of structural inspection or interventional medical treatment.