Optics Letters ( IF 3.866 ) Pub Date : 2020-01-10 , DOI: 10.1364/ol.381111
Nurmemet Abdukerim, Dan Grobnic, Cyril Hnatovsky, and Stephen J. Mihailov

Bragg gratings with ultrastrong cladding modes are inscribed in a standard telecom optical fiber (i.e., SMF-28) using the phase mask technique and an infrared femtosecond laser. 1000°C-resistant fiber Bragg gratings (FBGs) whose cladding modes exceed 30 dB in transmission and spectrally span more than 250 nm can be produced with only a few (i.e., less than five) laser pulses, provided that the light intensity in the fiber core is kept at the level of ${\sim}{6} \times {{10}^{13}}\;{\rm W}/{{\rm cm}^2}$. The use of FBGs fabricated under the above conditions for refractometry is demonstrated.

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