High-temperature stable π-phase-shifted fiber Bragg gratings inscribed using infrared femtosecond pulses and a phase mask

• Published in: Optics express Vol. 26; no. 18; p. 23550
• Main Authors: Hnatovsky, Cyril, Grobnic, Dan, Mihailov, Stephen J
• Format: Journal Article
• Language: English
• Published: United States OSA 03.09.2018
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.26.023550

NRC publication: Yes
Type II π-phase-shifted Bragg gratings stable up to ~1000°C are written inside a standard single mode silica optical fiber (SMF-28) with infrared femtosecond pulses and a special phase mask. Inscription through the protective polyimide fiber coating is also demonstrated. The birefringence of the Bragg gratings and, as a result, the polarization dependence of their spectra are strongly affected by the femtosecond laser polarization. Using optimized writing conditions, the full width at half maximum of the π-phase-shifted passband feature can be ~30 pm in transmission, while the polarization-dependent shift of its central wavelength can be less than 8 pm, for a 7 mm long grating structure. This makes such gratings a unique tool for high-resolution measurements of temperature, load and vibration in extreme temperature environments.