Silica-air double-clad optical fiber

A new design of the silica-air double-clad optical fiber is proposed. The fiber was prepared from an MCVD preform inserted into a supporting silica tube with a fluorine-doped connective element with a lower refractive index (/spl Delta/n/spl sim/-4/spl times/10/sup -3/) and air as the second cladding. A numerical aperture as high as 0.3 was measured for the first cladding and for fiber lengths up to 50 cm. Although it is realized that the results are preliminary, the optimization of the fiber parameters promises a new all-glass design for double-clad optical fibers for high-power fiber laser applications.