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Optical Engineering

On the role of Ge-doping concentration in the refractive index rollover and thermal annealing characteristics of type IIa fiber Bragg gratings
Author(s): Jitendra Kumar; Om Prakash; Ramakant Mahakud; Sachin Kumar Agrawal; Sudhir K. Dixit; Shankar V. Nakhe
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Paper 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.

Paper Details

Date Published: 6 November 2014
PDF: 7 pages
Opt. Eng. 53(11) 117103 doi: 10.1117/1.OE.53.11.117103
Published in: Optical Engineering Volume 53, Issue 11
Show Author Affiliations
Jitendra Kumar, Raja Ramanna Ctr. for Advanced Technology (India)
Om Prakash, Raja Ramanna Ctr. for Advanced Technology (India)
Ramakant Mahakud, Raja Ramanna Ctr. for Advanced Technology (India)
Sachin Kumar Agrawal, Raja Ramanna Ctr. for Advanced Technology (India)
Sudhir K. Dixit, Raja Ramanna Ctr. for Advanced Technology (India)
Shankar V. Nakhe, Raja Ramanna Ctr. for Advanced Technology (India)


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