Fiber-end antireflection method for ultra-weak fiber Bragg grating sensing systems

A novel fiber-end antireflection method for reducing the reflection noise in ultra-weak fiber Bragg grating (FBG) sensing systems is proposed in this study. The principle of fiber-end antireflection is analyzed and simulated theoretically, and then an antireflection structure is designed and fabricated. In this method, the fiber end is cut into an inclined surface and covered directly with an ellipsoid photosensitive ultraviolet (UV) glue drop, whose refractive index is similar to that of the fiber core. Under the online monitoring of the fiber-end reflection with the ultra-weak FBG interrogator, the refractive index of the glue drop is adjusted by controlling the UV curing time to achieve optimal reflection suppression. Results show that this method can reduce fiber-end reflection to less than -60 dB and effectively eliminate the influence of fiber-end reflection noise on the last sensor. The proposed method thus provides an excellent solution for the fiber-end processing of ultra-weak FBG sensing systems.