Method for manufacturing an optical fibre

A method for manufacturing an optical fiber comprising the steps of,

• a. forming a fused silica glass core rod containing dopant by heating a rotatable and movable refractory mandrel by means of an irradiation of a carbon dioxide gas laser beam at a high temperature and by ejecting a mixed gas of oxygen and oxidizable silicon compound vapor and a vapor of an oxidizable compound forming dopant to the refractory mandrel while rotating and moving said refractory mandrel so as to deposit silicon oxide and an oxide of said dopant thereon and by fusing the deposited oxides,
• b. forming a fused silica glass cladding layer containing dopant on said glass core rod by heating the surface of the glass core rod by means of an irradiation of a carbon dioxide gas laser beam at a high temperature and by ejecting a mixed gas of oxygen and an oxidizable silicon compound vapor and a vapor of an oxidizable compound forming dopant to said glass core rod while rotating and moving the glass core rod and by gradually decreasing the concentration of dopant in the mixed gas so as to deposit silicon oxide and an oxide of said dopant on the glass core rod initially and depositing dopant in gradually less concentration and finally depositing silicon oxide and by fusing the deposited oxides, and
• c. forming the optical fiber by heating a preform consisting of said glass core rod and said glass cladding layer at a temperature above the softening point of said preform and by spinning the heated preform.

A method for manufacturing an optical fiber comprising the steps of,

• a. forming a glass core rod by heating a rotatable and movable silica rod arranged in a silica glass vessel preheated by an electric furnace by means of an irradiation of a carbon dioxide gas laser beam at a temperature of 1,600.degree.-1,800.degree.C and by ejecting a mixed gas of oxygen and pure silicon tetrachloride vapor and pure aluminum trichloride vapor to said silica rod so as to deposit silicon dioxide and aluminum oxide thereon while rotating the silica rod and moving it at a speed corresponding to the speed of growth of the deposited oxides and by fusing the deposited oxides,
• b. forming a fused silica glass cladding layer on said glass core rod by heating the glass core rod by means of an irradiation of a carbon dioxide gas laser beam at a temperature of 1,600.degree.-1,800.degree.C while rotating and moving said glass core rod and by ejecting a mixture of gas of oxygen and pure silicon tetrachloride vapor and pure aluminum trichloride vapor, wherein concentration of the aluminum trichloride in the mixed gas is gradually decreased until the concentration of silicon tetrachloride becomes 100% finally so as to form a fused silica glass cladding layer having a varying aluminum oxide concentration in the direction of thickness of the cladding layer, and
• c. forming the optical fiber by heating a preform consisting of said glass core rod and said glass cladding layer at a temperature above the softening point of said preform and by spinning the heated preform.

A method for manufacturing an optical fiber comprising the steps of,

• a. forming a SiO.sub.2.Al.sub.2 O.sub.3 glass core rod by heating the surface of a rotatably and movably arranged silica rod in a silica glass vessel suited for evacuation and preheated to about 1,000.degree.C by means of an irradiation of a first carbon dioxide gas laser beam at a temperature of 1,600.degree.-1,800.degree.C and by ejecting a mixed gas of oxygen and pure silicon tetrachloride vapor and pure aluminum trichloride vapor to said silica rod so as to deposit silicon dioxide and aluminum oxide on the rod while rotating and moving said silica rod at a speed corresponding to the speed of growth of the deposited oxides,
• b. forming a fused SiO.sub.2 glass cladding layer on said SiO.sub.2.Al.sub.2 O.sub.3 glass core rod continuously with the above step by simultaneously heating said glass core rod rotating and moving in the above step by means of an irradiation of a second carbon dioxide gas laser beam to heat the surface of the glass core rod at a temperature of 1,600.degree.-1,800.degree.C and by ejecting a mixed gas of oxygen and high purity silicon tetrachloride vapor so as to deposit silicon dioxide on the glass core rod and by fusing thereof, and
• c. forming the optical fiber by heating a preform consisting of said SiO.sub.2.Al.sub.2 O.sub.3 glass core rod and said SiO.sub.2 glass cladding layer at a temperature above the softening point of said preform and by spinning the heated preform.

A method for manufacturing an optical fiber comprising the steps of,

• a. forming a SiO.sub.2.Al.sub.2 O.sub.3 glass core rod by heating the surface of a rotatably and movably arranged silica rod in a silica glass vessel suited for evacuation and preheated to about 1,000.degree.C by means of an irradiation of a first carbon dioxide gas laser beam at a temperature of 1,600.degree.-1,800.degree.C and by ejecting a mixed gas of oxygen and pure silicon tetrachloride vapor and pure aluminum trichloride vapor to said silica rod so as to deposit silicon dioxide and aluminum oxide on the rod while rotating and moving said silica rod at a speed corresponding to the speed of growth of the deposited oxides.
• b. forming an SiO.sub.2.Al.sub.2 O.sub.3 glass cladding layer on said SiO.sub.2.Al.sub.2 O.sub.3 glass core rod continuously with the above step by simultaneously heating said glass core rod rotating and moving in the above step by means of an irradiation of a second carbon dioxide gas laser beam to heat the surface of the glass core rod at a temperature of 1,600.degree.-1,800.degree.C and by ejecting a mixed gas of oxygen and high purity silicon tetrachloride vapor and high purity aluminum trichloride, so as to deposit silicon oxide and aluminum oxide, wherein the mole ratio of the silicon tetrachloride and the aluminum trichloride in the mixed gas is so controlled as to deposit 100% of silicon oxide at a final stage of deposition and to form the deposited silicon oxide and aluminum oxide layer in which the concentration of aluminum oxide is different in the direction of the thickness of the layer and by fusing the deposited oxide layer, and
• c. forming the optical fiber by heating a preform consisting of said glass core rod and fused silica cladding layer containing a varying concentration of the aluminum oxide content in the direction of thickness at a temperature above the softening point of said preform and by spinning the heated preform.