High-efficiency ultraviolet inscription of Bragg gratings in microfibers

In this paper, we demonstrate high-efficiency inscription of Bragg gratings in microfiber. Strong Bragg gratings are easily inscribed using a 193-nm excimer laser and phase mask in microfiber drawn from the 62.5/125- μm standard multimode fiber (MMF) with no additional photosensitization treatment. The enlarged photosensitive core offered by the MMF provides a sufficient overlap between the fundamental mode and the induced refractive index modulation region, which significantly enhances the grating inscription efficiency. The grating inscription in the microfiber is even more efficient than that in the original MMF because the multibeam interference-induced fringe fuzziness in the normal size fiber does not occur as the fiber diameter down to the scale that is comparable with the Talbot length of the ultraviolet (UV)-writing light. The proposed method is beneficial for sensing and device applications of microfiber Bragg grating (mFBGs) because of the ease of fabrication, high coupling strength, and large wavelength separation between individual resonant dips.