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A method of fabricating a dispersion shifted optical fiber with a smooth annular ring refractive index profile has the steps of heating a quartz tube with an external oxygen or hydrogen burner and supplying the quartz tube with raw materials including SiCl.sub.4, GeCl.sub.4, POCl.sub.3 and CF.sub.4.

A method of fabricating a dispersion shifted optical fiber with a smooth annular ring refractive index profile has the steps of heating a quartz tube with an external oxygen or hydrogen burner and supplying the quartz tube with raw materials including SiCl.sub.4, GeCl.sub.4, POCl.sub.3 and CF.sub.4. O.sub.2 is later supplied. Then, the quartz tube is heated in nine passes of decreasing temperature from 1920.degree. C. to 1890.degree. C., so as to deposit a core section. In the nine passes, the quantity of SiCl.sub.4 feed flow decreases from 380 milligrams per minute to 260 milligrams per minute, the quantity of GeCl.sub.4 feed flow increases from 20 milligrams per minute to 195 milligrams per minute, and the quantity of O.sub.2 feed flow is kept constant at 1500 cubic centimeters per minute.

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[ What is claimed is:] [1.] A method of fabricating a dispersion shifted optical fiber, comprising the steps of:depositing a first clad by heating a quartz tube with an external burner to provide a temperature of said quartz tube increasing from 1875.degree. C. to 1903.degree. C. while supplying sai

[ What is claimed is:] [1.] A method of fabricating a dispersion shifted optical fiber, comprising the steps of:depositing a first clad by heating a quartz tube with an external burner to provide a temperature of said quartz tube increasing from 1875.degree. C. to 1903.degree. C. while supplying said quartz tube with raw materials including feed flow quantities of 5200 milligrams per minute of SiCl.sub.4, 430 milligrams per minute of GeCl.sub.4, 30 milligrams per minute of POCl.sub.3, and 9 cubic centimeters per minute of CF.sub.4 ;depositing an annular ring section by supplying raw materials including feed flow quantities of 3300 milligrams per minute of SiCl.sub.4, 1150 milligrams per minute of GeCl.sub.4, 20 milligrams per minute of POCl.sub.3, and 1500 cubic centimeters per minute of O.sub.2 while maintaining said temperature of said quartz tube at about a constant temperature of 1900.degree. C.;depositing a second clad by supplying raw materials including feed flow quantities of 3800 milligrams per minute of SiCl.sub.4, 430 milligrams per minute of GeCl.sub.4, 10 milligrams per minute of POCl.sub.3, and 7 cubic centimeters per minute of CF.sub.4 while heating said quartz tube to increase said temperature of said quartz tube from 1890.degree. C. to 1897.degree. C.;depositing a core section by heating said quartz tube in nine temperature-deceasing passes to provide said temperature at 1920.degree. C., 1916.degree. C., 1913.degree. C., 1909.degree. C., 1906.degree. C., 1901.degree. C., 1897.degree. C., 1894.degree. C., and 1890.degree. C., respectively, while supplying SiCl.sub.4 with respectively decreasing feed flow quantities of 380 milligrams per minute, 365 milligrams per minute, 350 milligrams per minute, 335 milligrams per minute, 320 milligrams per minute, 305 milligrams per minute, 290 milligrams per minute, 275 milligrams per minute, and 260 milligrams per minute in said nine passes, by supplying GeCl.sub.4 with feed flow quantities of respectively 20 milligrams per minute, 52 milligrams per minute, 82 milligrams per minute, 109 milligrams per minute, 134 milligrams per minute, 156 milligrams per minute, 175 milligrams per minute, 191 milligrams per minute, and 195 milligrams per minute in said nine passes, and by supplying O.sub.2 at a constant feed flow of 1500 cubic centimeters per minute in said nine passes;condensing said quartz tube by heating said quartz tube to provide said temperature in a temperature range from 2300.degree. to 2360.degree. C.while supplying CF.sub.4 at a feed flow from a range from 30 cubic centimeters per minute to 40 cubic centimeters per minute of CF.sub.4, to said quartz tube;etching by heating said quartz tube to provide said temperature in a temperature range from 2220.degree. to 2250.degree. C.; andsealing by supplying 100 cubic centimeters per minute of Cl.sub.2 to said quartz tube while heating said quartz tube to provide said temperature in a temperature range from 2350.degree. to 2370.degree. C. [20.] An optical fiber for lightwave communications, comprising:a first clad layer; anda core section disposed inside said first clad layer and includinga central axis,an external interface disposed at a first radial distance R.sub.1 from said central axis, anda plurality of deposited glass layers disposed concentrically about said central axis and including an innermost layer adjacent to said central axis and an external layer adjacent to said external interface, with each deposited glass layer having a corresponding layer refractive index;and wherein said core section has a core refractive index varying in accordance with a core refractive index profile providing a core refractive index value for each radial distance from said central axis not exceeding said first radial distance R.sub.1, with said core refractive index profile exhibiting, for each first and second deposited glass layers included in said plurality of deposited glass layers and adjacent to each other, a smooth transition between said layer refractive index of said first layer and said layer refractive index of said second layer.