On the role of Ge-doping concentration in the refractive index rollover and thermal annealing characteristics of type IIa fiber Bragg gratings

Jitendra Kumar; Om Prakash; Ramakant Mahakud; Sachin Kumar Agrawal; Sudhir K. Dixit; Shankar V. Nakhe

doi:10.1117/1.OE.53.11.117103

6 November 2014 On the role of Ge-doping concentration in the refractive index rollover and thermal annealing characteristics of type IIa fiber Bragg gratings

Jitendra Kumar, Om Prakash, Ramakant Mahakud, Sachin Kumar Agrawal, Sudhir K. Dixit, Shankar V. Nakhe

Author Affiliations +

Optical Engineering, Vol. 53, Issue 11, 117103 (November 2014). https://doi.org/10.1117/1.OE.53.11.117103

Abstract

This paper presents studies on the role of Ge-doping concentration (6 to 18 mol. %) in the refractive index rollover fluence and thermal annealing characteristics of type IIa fiber Bragg gratings (FBGs). A 255 nm UV beam of low-pulse energy density (∼2.2 mJ/cm²), nanosecond (∼30 ns) duration, and high-repetition rate (∼5.5 kHz) was used for FBG inscription. It is observed that the UV fluence needed for refractive index rollover was higher for fiber having low Ge-doping (∼6 mol.%). The temperature sustainability of these gratings has been studied in a multistep thermal annealing process up to 800°C. It was observed that the higher the total UV fluence required for refractive index rollover, the higher the temperature sustainability of a type IIa grating. The temperature rise of the fiber for a single UV pulse and at the maximum cumulative UV fluence was estimated for different Ge-doping concentrations. The thermal stability of the grating is linked to the amount of Ge-doping concentration of the fiber. These observations may be due to the fact that a high cumulative fluence resulted in a larger stress relaxation, leading to enhanced FBG temperature stability.

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Jitendra Kumar, Om Prakash, Ramakant Mahakud, Sachin Kumar Agrawal, Sudhir K. Dixit, and Shankar V. Nakhe "On the role of Ge-doping concentration in the refractive index rollover and thermal annealing characteristics of type IIa fiber Bragg gratings," Optical Engineering 53(11), 117103 (6 November 2014). https://doi.org/10.1117/1.OE.53.11.117103

Published: 6 November 2014

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