Band-rejection fibre filter using periodic core deformation

Grating-based all-fibre bandstop filters were fabricated by introducing periodic deformations in the core of the fibre with a CO₂ laser by first ablating the surface of the fibre and then annealing it. These devices, which can be tailored to any wavelength, have a broad bandwidth (10 nm), high peak wavelength rejection (>20 dB), low insertion loss (<0.3 dB), a very flat response outside the rejection band, and a short physical length (6 mm)