Silica-air double-clad optical fiber

A new design of the silica-air double-clad optical Liber is proposed. The f iber was prepared from an MCVD preform inserted into a supporting silica tu be with a fluorine-doped connective element with a lower refractive index ( Delta n similar to -4 x 10(-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 prelimina ry, the optimization of the fiber parameters promises a new all-glass desig n for double-clad optical fibers for high-power fiber laser applications.