First-order fiber Bragg grating inscription in indium fluoride fiber using a UV/Vis femtosecond laser and two-beam interferometry
Ismael Chiamenti, Tino Elsmann, Aaron Reupert, Oğuzhan Kara, Martin Becker, Lothar Wondraczek, Maria Chernysheva
Abstract
Fiber gratings are among key components in fiber-based photonics systems and, particularly, laser cavities. In the latter, they can play multiple roles, such as those of mirrors, polarizers, filters, or dispersion compensators. In this Letter, we present the inscription of highly reflective first-order fiber Bragg gratings (FBGs) in soft indium fluoride-based ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">I</mml:mi> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">F</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> ) fibers using a two-beam phase-mask interferometer and a femtosecond laser. We demonstrate an enhanced response of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">I</mml:mi> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">F</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> -based fiber to a visible (400 nm) inscription wavelength compared to ultraviolet irradiation at 266 nm. In this way, FBGs with a reflectivity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>></mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>99.7</mml:mn> </mml:mrow> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> were inscribed at around 1.9 µm with the bandwidth of 2.68 nm. After thermal annealing at 393K, the Bragg wavelength demonstrates stable thermal shift of 20 pm/K in the temperature range 293–373K. These observations suggest a potential extension of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">I</mml:mi> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">F</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> fiber-based laser components to an operational range of up to 5 µm.