Abstract: A low-loss single mode fiber with low total dispersion within the wavelength range 1.25-1.385 .mu.m and low added cabling loss is disclosed. The fiber has relatively high .DELTA. to assure low cabling loss. The high .DELTA. is obtained, however, without paying a cost in high material dispersion by providing at least 20 percent of the .DELTA. by down-doping of the fiber cladding.

Abstract: A low-loss single mode fiber with low total dispersion within the wavelength range 1.25-1.385 .mu.m and low added cabling loss is disclosed. The fiber has relatively high .DELTA. to assure low cabling loss. The high .DELTA. is obtained, however, without paying a cost in high material dispersion by providing at least 20 percent of the .DELTA. by down-doping of the fiber cladding.

Abstract: Local transmission loss of optical fibers can be measured in "real time" with the disclosed non-destructive technique. Similarly, the technique allows determination of the presence and location of structural defects. It can be used to monitor the fiber drawing process, to adjust the process in response to the information derived by use of the technique, and to monitor and adjust the cabling process. It is based on the launching of light pulses into the fiber through the reservoir of material from which the fiber is being drawn, and the analysis of the light scattered back through the fiber and the reservoir. The back-scattered light is detected, and the time elapsed between launching of the light pulse and detecting light is used to determine the location of the scatterer.