
Femtosecond laser direct-written fiber Bragg gratings with high reflectivity and low loss at wavelengths beyond 4 µm
Author(s) -
Gayathri Bharathan,
Toney Teddy Fernandez,
Martin Ams,
Jean Yves Carrée,
Samuel Poulain,
Marcel Poulain,
Alexander Fuerbach
Publication year - 2020
Publication title -
optics letters/optics index
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.524
H-Index - 272
eISSN - 1071-2763
pISSN - 0146-9592
DOI - 10.1364/ol.399329
Subject(s) - materials science , analytical chemistry (journal) , algorithm , computer science , chemistry , chromatography
We report on the fabrication of, to the best of our knowledge, the first highly reflective fiber Bragg gratings for the 4 µm wavelength range. A second-order grating with a coupling coefficient ( κ ) of 230 m -1 , losses <0.25 d B / c m , and a bandwidth of approximately 3 nm was inscribed into the core of a passive indium fluoride ( I n F 3 ) fiber using a femtosecond (fs) laser. Thermal annealing of this grating at a temperature of 150°C for 90 min resulted in the enhancement of κ to 275 m -1 . Further, we show that I n F 3 fibers respond very differently to irradiation with fs laser pulses as compared to ZBLAN fibers and that this difference manifests itself in a significantly larger process window for inscription and in the formation of a more complex refractive index profile that is believed to be caused by the larger nonlinearity of I n F 3 . This Letter paves the way to the development of new wavelength stabilized all-fiber mid-infrared lasers beyond 4 µm.