as measured over a domain from 1 0 to 1 65 micrometers for an embodiment of the invention over all lowest loss is at a wavelength of approximately 1 57 micrometers and such wavelength is conveniently adopted for comparison purposes the loss reducing benefit of the presence of germania or phosphorus pentoxide in accordance with the invention may be attributable to the existance of stable suboxides of germanium and phosphorus at temperatures of approximately 1600 degrees c and above as a result oxygen may become free especially at elevated processing temperatures of approximately 1900 degrees and above during sintering and collapsing since such high temperature processing of silica may result in the formation of reduced silica defects of the form sio 2 x and since such defects are believed to be the cause of increasd intrinsic loss minute but significant amounts of oxygen given off by germania or phosphorus pentoxide may oxidize the reduced silica defects to silica sio 2 thereby contributing to reduced intrinsic optical loss the following examples are of silica based single mode optical fiber waveguides having reduced intrinsic loss by doping in accordance with the invention in all of the examples waveguiding results from a fluorine doped cladding fluorine.