High thermal stability of ultra-low insertion loss type II cladding fiber Bragg grating based on femtosecond laser point-by-point technology

The insertion loss (IL) of the type II fiber Bragg grating (FBG) induced by the femtosecond laser limits its multiplexing performance. Femtosecond laser point-by-point (PbP) technology is used to directly write type II fiber gratings in the cladding of single-mode fibers that avoids short-wave loss and features a temperature resistance of up to 1100 °C. The cladding FBG is integrated in series along the fiber axis, and the IL of the eight cladding FBGs is less than 0.06 dB. Cladding FBGs with ultra-low IL has potential applications in the fields of optical fiber sensors and communications.