Long-Period Fiber Grating Based on Side-Polished Optical Fiber and Its Sensing Application

Abstract

A novel side-polished long-period fiber grating (LPFG) sensor was proposed and experimentally validated. Side-polished can provide a stronger evanescent field than traditional grating and bring superior sensitivity. The greater the side-polished depth, the higher the refractive index (RI) sensitivity. When d = 44 μm, the refractive index sensitivity reached 466.85 nm/RIU in the range of 1.3330 -1.3580, which is four-fold higher than LPFG prepared by electric-arc discharge (EAD) method. A graphene oxide (GO) nano-film is coated on the LPFG to make it realize high sensitivity relative humidity (RH) sensing. Humidity sensitivity reached -0.193 nm/%RH in the range of 40 -80% RH. In addition, sidepolished breaks the symmetry of the distribution of the crosssectional light field, which determines the ability to achieve vector curvature measurement. It shows good sensing performance in the same/opposite bending direction as the side polished surface. When the input light polarization is 90°, the average sensitivity reaches 5.03 and -5.9 nm/m -1 in the range of 0 -19.67 m -1 , respectively. This strongly indicates that the fabricated sensors show high sensitivity, low-cost materials, and robust performance and break the limitations of the EDA method to prepare gratings, which have good application potential for biomedicine and the field of construction.

Self‐Calibrated Flexible Holographic Curvature Sensor

“…However, they typically require high beam coherence, which limits their range, precise alignment, and time-consuming measurements. [9] When embedded in fibers, curvature sensors use either photonic crystals, [10,11] Bragg gratings, [12][13][14] or longperiod diffraction gratings [15,16] with a known lattice constant, and extract information on the curvature by tracking the intensity or wavelength of the spectral features of the transmitted or reflected light. [17] Alternatively, curvature sensors that track the light scattered by diffraction gratings can be realized on thick flexible substrates.…”