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We report a new technique for fabricating fibre edge filters with arbitrary spectral response based on tilted fibre chirped gratings. The dependence of the spectral response on the tilt angle, chirp rate, fibre type and grating strength has been studied in detail. The near-linear wavelength response with tailorable slope efficiency has been demonstrated over the filtering ranges from 2 nm to 20 nm.

We report the observation of abnormal spectral evolution in regenerated fiber Bragg gratings in hydrogenated B -Ge-codoped and standard telecom fiber with UV overexposure. The behavior of this new type of regenerated grating, which we have designated type IA, contrasts with that of the previously reported type IIA grating in nonhydrogenated fiber by exhibiting a large redshift in Bragg wavelength with increasing exposure of as much as 18 nm from a strong (16-dB) In all observations reported to date, the type IIA gratings were formed in nonhydrogenated fibers. However, the introduction of hydrogen into the fiber to increase photosensitivity is a commonly adopted procedure. In seeking to clarify FBG growth with UV overexposure in hydrogenated standard telecom and B-Ge-codoped f ibers we have observed, for the f irst time to our knowledge, regenerated grating growth with an abnormal, i.e., contrary to the behavior expected on the basis of previously reported observation, spectral evolution that is quite distinct from that of type IIA. We have designated this new grating type IA and found it to exhibit less temperature sensitivity than the type I grating.We inscribed the FBGs reported here by two-beam holographic exposure, using a cw 244-nm laser with 8-mm beam width and 60-mW power. For reference, we produced a type I FBG in nonhydrogenated B-Ge-codoped fiber: a maximum 2.2-dB ref lectivity was obtained in ϳ2 min of UV exposure, as shown in Fig. 1(a); the ref lectivity decreased with subsequent exposure and fell to zero after 7 min. A maximum redshift of ϳ2.0 nm in the Bragg wavelength was recorded. As the UV exposure was maintained, the grating ref lectivity increased from zero, accompanied by a blueshift in the Bragg wavelength that is characteristic of the type IIA grating and a negative induced refractive-index change. Limited by the UV wavelength and power, the type IIA grating attained 8.7-dB ref lectivity and 0.66-nm blueshift after 37-min exposure. Subsequent annealing of the grating for 12 h at 70 ± C induced a further blueshift of 0.55 nm owing to relaxation of the photoinduced positive index change; the ref lectivity remained unchanged, indicating good thermal stability, as shown in Fig. 1(b).This fabrication procedure was repeated with a hydrogenated sample of the same fiber. Type I grating formation and complete erasure were again observed; however, with continued UV exposure a quite different behavior emerged that included formation of an

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