LPG in Fluoride Optical Fiber via Micro-Tapering Technique: Mid-IR Mode Coupling

For the first time, micro-tapering of fluoride glass optical fibers is exploited as a feasible technique to obtain long period gratings. The spectral properties of the fabricated long period gratings are accurately predicted by means of finite element method modal analysis and coupled mode theory. An efficient optical grating inscription is performed by using a commercial glass processing system, based on graphite filament heating. The periodic tapering, obtained via heating and stretching technique, of a section of zirconium fluoride optical fiber, provides a measured transmission attenuation with a dip larger than 15 dB at the designed resonant wavelength. A good agreement between the simulation and the characterization is obtained. These results pave the way for a number of applications, among which notch filtering in fiber amplifiers and sensing in the Mid-Infrared spectral range.