Effect of the spatial coherence of ultraviolet radiation (255nm) on the fabrication efficiency of phase mask based fiber Bragg gratings

Analysis on the saturation of refractive index modulation in fiber Bragg gratings (FBGs) written by partially coherent UV beams

“…The degrees of coherence at center of reversal interferograms of UV 1 and UV 2 beam are 0.3 and 0.42 respectively, which are much less than the theoretical value of unity due to the partial coherence of the beams. The fiber position at a distance of 0.8 mm behind the phase mask is well below the maximum affordable phase mask fiber distance related to beam spatial coherence width [21] for both beams. The measured visibility of the fringe pattern of a 2°apex angle biprism at a distance of 10 mm from the apex of the prism were 0.32 and 0.7 for the UV 1 and UV 2 beams respectively [18].…”

“…The optical fiber was mounted about 0.8 mm behind the phase mask. The details of the writing procedure are reported elsewhere [21]. The real-time growth of FBG grating was monitored by recording the wavelength transmission dip by an optical spectrum analyzer (Agilent 86142B).…”

“…For these general cases, Iz is to be substituted from Eq. (21) to Eq. (9) to find the expression of δnz, resulting in…”

Enhanced Temperature $({\sim}{800}^{\circ}{\rm C})$ Stability of Type-IIa FBG Written by 255 nm Beam

“…About 300 mW average power UV beam obtained from SHG of CVL, was used [12] to write FBG in high photosensitive Ge doped (∼10 mole %, CGCRI) single mode fiber. These fibers were not hydrogen loaded.…”

“…Thus the temperature stability of the FBG depends on the type of fiber, writing beam characteristics and pre/post treatment of FBGs. Using high repetition rate (hence high fluence) 255 nm UV source, fast writing of type-I FBGs was demonstrated [11], [12]. Low pulse energy also leads to higher fiber strength/lifetime [11].…”