Multiple Cladding Fiber Bragg Gratings Inscribed by Femtosecond Laser Point-by-Point Technology

Femtosecond laser point-by-point (PbP) technology can be used as a direct writing method to inscribe fiber Bragg gratings (FBGs) into the cladding of optical fibers. When the refractive index modulated area of cladding FBGs (CLFBGs) is close to the corecladding interface, the CLFBGs exhibit characteristics similar to conventional core-based FBGs. When bending was applied, the reflected power of the CLFBGs changed significantly and showed an orientation dependence on the fiber bending direction. The CLFBG inscription method provides a new opportunity to fabricate vector sensing devices, which can be realized by parallelly inscribed multiple CLFBGs. Compact CLFBGS with a low insertion loss (less than 0.05 dB) have application value in the fields of optical fiber sensors, communications, and lasers.