We present a photosensitive three-hole microstructured optical fiber specifically designed to improve the refractive index sensitivity of a standard fiber Bragg grating (FBG) sensor photowritten in the suspended Ge-doped silica core. We describe the specific photowriting procedure used to realize gratings in such a fiber. We then determine their spectral sensitivity to the refractive index changes of material filling the holes surrounding the core. The sensitivity is compared with that of standard FBGs photowritten in a six-hole fiber with a larger core diameter. We demonstrate an improvement in the sensitivity by two orders of magnitude and reach a resolution of $3\times {10}^{-5}$ and $6\times {10}^{-6}$ around mean refractive index values of 1.33 and 1.40, respectively.

A compact upconversion fiber laser operating around 810 nm is proposed using thulium-doped silica-based fiber with locally modified thulium environment by high alumina codoping. Using a comprehensive numerical model of thulium doped fiber we investigate performance of the proposed laser. Comparison with two other thulium hosts, fluoride glass and standard silica, is presented. Efficient lasing can be expected even for silica based fiber for specific ranges of the fiber and laser cavity parameters, especially when ³H₄ lifetime is enhanced. With moderate pump power of 5 W at wavelength of 1064 nm, the predicted output power of the upconversion laser is about 2 W at 810 nm.

A singlemode optical fibre exhibiting a very high negative chromatic dispersion (–1800 ps/(nm.km)) at 1.55 µm is realised and characterised for dispersion compensation applications.