In this paper, the effect of UV exposure time on the thermal regeneration characteristics of fiber Bragg gratings (FBGs) inscribed using 255 nm laser radiation is presented for the first time. This effect is studied in terms of reflectivity, refractive index (RI) modulation and thermal stability of the gratings. TypeI FBGs of RI modulation varying from 2.03 × 10 −4 to 3.38 × 10 −4 were inscribed in hydrogenated SMF28 fiber by controlling UV exposure fluence from 0.9 kJ cm −2 to 28.8 kJ cm −2 . Thermally regenerated gratings were fabricated from typeI FBGs by applying a stepannealing schedule up to 900 °C. The reflectivity of the regenerated FBGs increases with UV fluence and after reaching a maximum value of 46.05%, it decreases. The different behavior of the thermal regeneration characteristics of FBGs is linked with the stress developed inside the fiber during the writing of FBGs and their relaxation during thermal annealing. The theoretical calculations using the defect center and densification model provided an indirect novel approach to estimate the contribution of stress relaxation in thermal regeneration. The work presented in this paper is significant for optimizing the thermal regeneration of FBGs with the final aim of developing a highly reflective regenerated grating for high temperature sensing applications.

No abstract

The Editors have retracted this conference paper "Design of Silicon-on-Insulator Based Mode Splitters with Asymmetrical Variation of Slots" because of substantial overlap with an earlier article published by others (1). Although the authors have cited the earlier study (1) and state that their work was an extension of it, the Editors concluded that because the design of the mode splitter reported is not original this conference paper is redundant.All Authors agree to this retraction.(1) Hada SL, Rahman BMA (2019) Design of compact mode splitters using identical coupled waveguides with slots. OSA Continuum 2:848-861

No abstract