Abstract: Optical waveguide having a fused silica core and a fluorine doped fused silica cladding is made by depositing particulate core silica onto a support tube and then drying and densifying the silica. Further particulate cladding silica is deposited and is heated in a fluorine containing gas to effect drying, fluorine diffusion into and sintering the cladding silica. The support tube is etched away and the resulting tubular preform is heated to collapse it into a rod from which waveguide is drawn, the waveguide having a fluorine doped silica cladding.

Abstract: To improve pulse dispersion of a multimode fiber transmission line, it is spliced to a short length of fiber adapted to strongly attenuate mode groups propagating near the core center.

Abstract: The fundamental-mode field radius `w` is a key parameter in characterizing optical fibers. `w` is a function of P, .theta. and .lambda. where P is the far-field power passing through a circular aperture subtending a solid angle of 2.theta. at the fiber end face and .lambda. is the center wavelength of transmitted length. `w` is derived by moving a fixed diameter aperture along an axis extending between the test fiber end surface and a photodetector so as effectively to vary .theta.. At each location the power P incident on the photodetector and the corresponding acceptance angle .theta. are measured. A microprocesor is programmed to compute from the range of measured values of .theta. and P, the value of mode field radius for a particular transmission wavelength .lambda..

Abstract: The chromatic dispersion of an optical fiber such as a 10 to 50 km length of single mode fiber is measured by launching into the fiber the outputs of at least three commonly modulated semiconductor lasers having output wavelengths close to a region of minimum chromatic dispersion of the fiber. At a remote end of the fiber the relative phases of the signals from the three lasers are determined and a chromatic dispersion profile of the fiber is derived from the measured relative phases and the output wavelenghts of the lasers by assuming a parabolic relationship between signal propagation times and wavelength. The profile can be determined by defferentiating a parabolic function fitted to the three date points derived using said three lasers or by directly generating a linear relationship between chromatic dispersion and wavelength on the basis of two values of chromatic dispersion derived from these three data points.