Mid-infrared microfiber Bragg gratings.

We report mid-infrared (mid-IR) Bragg gratings fabricated on sub-wavelength-diameter chalcogenide glass (ChG) microfibers. ChG microfibers with diameters around 3 µm are tapered drawn from glass fibers, and the mid-IR microfiber Bragg gratings (mFBGs) are inscribed on microfibers using interference patterns of near bandgap light at a 532 nm wavelength. At a wavelength of about 4.5 µm, the mFBG has an extinction ratio of 15 dB and a positive photo-induced refractive index change of 2×10. The dependence of the grating formation on accumulated influence of exposure power density and time is investigated. The mid-IR mFBGs demonstrated here may be used as building blocks for micro-photonic circuits or devices in the mid-IR spectral range.