Formation of enhanced regenerated grating in few-mode fiber by CO_2 laser pretreatment

Influence of Internal Stresses in Few-Mode Fiber on the Thermal Characteristics of Regenerated Gratings

“…Yang et al demonstrated the RG inscribed in new glass composition-based photosensitive fiber with temperature resistance up to 1400℃ [9]. Our earlier investigation [10] has proven that the pre-treatment process has a profound impact on the performance of the RG in terms of temperature resistant and durability. However, in line with the advancement that has been made, there are still unresolved questions and difficulties in characterization of real mechanism in regeneration process.…”

“…When the fiber subjects to the high temperature (approaching transition temperature (~1200℃) [25]), the fiber glass viscosity decreases drastically which allows stress relaxation to take place in the non-treated fiber. The gradual decay in the frozen-in stresses with increasing temperature leads to an increase in resultant material refractive index in the fiber core [10]. In combination with the thermo-optic effect, the fiber glass material refractive index also increases with temperature increment, which explains the higher thermal sensitivity of non-treated fibers as depicted in Fig.…”

“…The grating reflectivity gradually increases, and it reaches the optimum level at t = 150 min. In this work, the efficiency of the regeneration of grating is indicated by the regeneration ratio [10]. The regeneration ratio denotes the ratio of the acquired maximum grating strength of the RG to the initial grating strength of the seed FBG.…”