Optical fiber of the graded index type and method of producing same

Claim 1

A graded index glass optical fiber having an axis and a circumference, said fiber consisting essentially of: 60 to 70 mole % silicon dioxide; 15 to 30 mole % of two or more alkali metal oxides, the quantity of lithium oxide not exceeding 15 mole %; and 10 to 25 mole % magnesium oxide in combination with at least one metal oxide having a cation which can be exchanged with the magnesium cation, said metal oxide being selected from the group consisting of CaO, SrO, BaO, and ZnO, the quantity of CaO not exceeding 15 mole %; wherein the fiber is substantially free of boron contains less than 0.01 parts per million of impurities which absorb radiation having a wavelength up to 1500 nanometers; and wherein the graded refractive index is caused by a decreasing exchangeable cation concentration and an increasing magnesium concentration in the fiber from the fiber axis to the fiber circumference.

Claim 5

A method of producing a graded index glass optical fiber, said method comprising the steps of: providing a double crucible having an inner crucible and an outer crucible; providing, in the inner crucible, a glass consisting essentially of 60 to 70 mole % silicon dioxide, 15 to 30 mole % of two or more alkali metal oxides, the quantity of lithium oxide not exceeding 15 mole %, and 10 to 25 mole % of at least one metal oxide having a cation which can be exchanged with a magnesium cation, said metal oxide being selected from the group consisting of CaO, SrO, BaO, and ZrO; providing, in the outer crucible, a glass consisting essentially of 60 to 70 mole % silicon dioxide, 15 to 30 mole % of two or more alkali metal oxides, the quantity of lithium oxide not exceeding 15 mole %, and 10 to 25 mole % of MgO; heating the glasses to a fiber drawing temperature; and drawing the glasses out of the crucibles with the glass from the outer crucible surrounding the glass from the inner crucible, to form an optical fiber; wherein the fiber is substantially free of boron and contains less than 0.01 parts per million of impurities which absorb radiation having a wavelength up to 1500 nanometers; and wherein the graded refractive index is caused by a decreasing exchangeable cation concentration and an increasing magnesium concentration in the fiber from the from axis to the fiber circumference.

Claim 6

A method of producing a graded index glass optical fiber, said method comprising the steps of: providing a double crucible having an inner crucible and an outer crucible; providing, in the inner crucible, a glass consisting essentially of 60 to 70 mole % silicon dioxide, 15 to 30 mole % of two or more alkali metal oxides, the quantity of lithium oxide not exceeding 15 mole %, and 10 to 25 mole % of at least one metal oxide having a cation which can be exchanged with a magnesium cation, said metal oxide being selected from the group consisting of CaO, SrO, BaO, and ZrO; providing, in the outer crucible, a glass consisting essentially of 60 to 70 mole % silicon dioxide, 15 to 30 mole % of two or more alkali metal oxides, the quantity of lithium oxide not exceeding 15 mole %, and 10 to 25 mole % of MgO; heating the glasses to a fiber drawing temperature; and drawing the glasses out of the crucibles with the glass from the outer crucible surrounding the glass from the inner crucible, to form an optical fiber; wherein the fiber is substantially free of boron and contains less than 0.01 parts per million of impurities which absorb radiation having a wavelength up to 1500 nanometers; and wherein the graded refractive index is caused by a decreasing exchangeable cation concentration and an increasing magnesium concentration in the fiber from the from axis to the fiber circumference.