Core glass in the alkali-zinc-silicate glass system for an fiber-optic light guide and fiber-optic light guide made with said core glass

1. A core glass in the alkali-zinc-silicate system for a step index fiber, which contains, in Mol % on an oxide basis:

SiO 2

54.5-65

ZnO

18.5-30

Σ alkali metal oxides

  8-20

La 2 O 3

0.5-3

ZrO 2

  2-5

HfO 2

0.02-5 

Σ ZrO 2 + HfO 2

2.02-5 

TiO 2

  0-0.5

BaO

0.4-6

SrO

  0-6

MgO

  0-2

CaO

  0-2

Σ alkaline earth metal oxides

0.4-6

Li 2 O

0.5-3

Σ SiO 2 + ZrO 2 + HfO 2

>58.5;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1, but with the proviso that the core glass contains said Li 2 O in an amount that is not more than 25% of a sum total amount, in Mol % on said oxide basis, of said alkali metal oxides present in the core glass.

2. The core glass as defined in claim 1 , containing from 2 to 4.08 Mol % of said ZrO 2 , from 0.02 to 3.3 Mol % of said HfO 2 , and from 2.02 to 4.1 Mol % of said Σ ZrO 2 +HfO 2 .

3. A core glass in the alkali-zinc-silicate system for a step index fiber, as defined in claim 1 and which contains, in Mol % on an oxide basis:

SiO 2

55-61

ZnO

20-25

Σ alkali metal oxides

11-16

La 2 O 3

1.5-2.9

ZrO 2

  2-4.08

HfO 2

0.02-3.3 

Σ ZrO 2 + HfO 2

2.02-4.1 

TiO 2

 0-0.5

BaO

0.4-5  

SrO

0.4-5  

Σ alkaline earth metal oxides

0.4-5  

Li 2 O

1-2.5

Σ SiO 2 + ZrO 2 + HfO 2

>59.

4. The core glass as defined in claim 1 , wherein said alkali metal oxides comprise Na 2 O and K 2 O and a molar ratio of said Na 2 O to said K 2 O is from 1:1.1 to 1:0.3.

5. The core glass as defined in claim 1 , wherein said alkali metal oxides comprise Na 2 O and K 2 O and a molar ratio of said Na 2 O to said K 2 O is from 1:0.95 to 1:0.4.

6. The core glass as defined in claim 1 , wherein said molar ratio of said ZnO:said Σ alkaline earth metal oxides >4:1.

7. The core glass as defined in claim 1 , containing from 0 to 5 Mol % of B 2 O 3 and/or from 0 to 0.5 Mol % of P 2 O 5 , from 0 to 5 Mol % of GeO 2 and/or from 0 to 6 Mol % of Rb 2 O and/or from 0 to 6 Mol % of Cs 2 O.

8. The core glass as defined in claim 1 , containing from 0.2 to 2 Mol % of said B 2 O 3 .

9. The core glass as defined in claim 1 , containing from 0.05 to 0.4 Mol % of Sb 2 O 3 .

10. The core glass as defined in claim 9 , containing from 0.1 to 0.2 Mol % of said Sb 2 O 3 .

11. The core glass as defined in claim 1 , containing from 0.05 to 0.5 Mol % of Bi 2 O 3 and/or from 0.05 to 0.5 Mol % of TiO 2 and/or from 0.05 to 0.35 Mol % of WO 3 .

12. The core glass as defined in claim 11 , containing from 0.1 to 0.3 Mol % of said Bi 2 O 3 and/or from 0.1 to 0.4 Mol % of said TiO 2 and/or from 0.1 to 0.3 Mol % of said WO 3 .

13. The core glass as defined in claim 3 , wherein said alkali metal oxides comprise Na 2 O and K 2 O and a molar ratio of said Na 2 O to said K 2 O is from 1:1.1 to 1:0.3.

14. The core glass as defined in claim 3 , wherein said alkali metal oxides comprise Na 2 O and K 2 O and a molar ratio of said Na 2 O to said K 2 O is from 1:0.95 to 1:0.4.

15. The core glass as defined in claim 3 , wherein said molar ratio of said ZnO:said Σ alkaline earth metal oxides >4:1.

16. The core glass as defined in claim 3 , containing from 0 to 5 Mol % of B 2 O 3 and/or from 0 to 0.5 Mol % of P 2 O 5 , from 0 to 5 Mol % of GeO 2 and/or from 0 to 6 Mol % of Rb 2 O and/or from 0 to 6 Mol % of Cs 2 O.

17. The core glass as defined in claim 3 , containing from 0.2 to 2 Mol % of said B 2 O 3 .

18. The core glass as defined in claim 3 , containing from 0.05 to 0.4 Mol % of Sb 2 O 3 .

19. The core glass as defined in claim 18 , containing from 0.1 to 0.2 Mol % of said Sb 2 O 3 .

20. The core glass as defined in claim 3 , containing from 0.05 to 0.5 Mol % of Bi 2 O 3 and/or from 0.05 to 0.5 Mol % of TiO 2 and/or from 0.05 to 0.35 Mol % of WO 3 .

21. The core glass as defined in claim 20 , containing from 0.1 to 0.3 Mol % of said Bi 2 O 3 and/or from 0.1 to 0.4 Mol % of said TiO 2 and/or from 0.1 to 0.3 Mol % of said WO 3 .

22. A step index fiber comprising a core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

54.5-65

ZnO

18.5-30

Σ alkali metal oxides

  8-20

La 2 O 3

0.5-3

ZrO 2

  2-5

HfO 2

0.02-5 

Σ ZrO 2 + HfO 2

2.02-5 

TiO 2

  0-0.5

BaO

0.4-6

SrO

  0-6

MgO

  0-2

CaO

  0-2

Σ alkaline earth metal oxides

0.4-6

Li 2 O

0.5-3

Σ SiO 2 + ZrO 2 + HfO 2

>58.5;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1, but with the proviso that said core glass contains said Li 2 O in an amount that is not more than 25% of a sum total amount, in Mol % on said oxide basis, of said alkali metal oxides present in said core glass.

23. A step index fiber comprising a core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

54.5-65

ZnO

18.5-30

Σ alkali metal oxides

  8-20

La 2 O 3

 0.5-3

ZrO 2

  2-5

HfO 2

0.02-5

Σ ZrO 2 + HfO 2

2.02-5

BaO

 0.4-6

SrO

  0-6

MgO

  0-2

CaO

  0-2

Σ alkaline earth

 0.4-6

metal oxides

Li 2 O

 0.5-3,

but not more than 25% of a

sum total amount, in Mol %

on said oxide basis, of said

alkali metal oxides.

Σ SiO 2 + ZrO 2 + HfO 2

>58.5;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1; and

wherein the cladding comprises a cladding glass and the cladding glass contains, in Mol % on an oxide basis:

SiO 2

70-78

Al 2 O 3

 0-10

B 2 O 3

 5-14

Li 2 O

0

Na 2 O

 0-10

K 2 O

 0-10

MgO

0-1

CaO

0-2

SrO

0-1

BaO

0-3

F

 0-1.

24. A step index fiber comprising core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

54.5-65

ZnO

18.5-30

Σ alkali metal oxides

  8-20

La 2 O 3

 0.5-3

ZrO 2

  2-5

HfO 2

0.02-5

Σ ZrO 2 + HfO 2

2.02-5

BaO

 0.4-6

SrO

  0-6

MgO

  0-2

CaO

  0-2

Σ alkaline earth

 0.4-6

metal oxides

Li 2 O

 0.5-3,

but not more than 25% of a

sum total amount, in Mol %

on said oxide basis, of said

alkali metal oxides.

Σ SiO 2 + ZrO 2 + HfO 2

>58.5;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1, and

wherein the cladding comprises a cladding glass and the cladding glass contains, in Mol % on an oxide basis:

SiO 2

62-70

B 2 O 3

>15

Li 2 O

>0.1

Na 2 O

 0-10

K 2 O

 0-10

MgO

0-5

CaO

0-5

SrO

0-5

BaO

0-5

ZnO

0-5

F

 0-1.

25. A step index fiber comprising core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

54.5-65

ZnO

18.5-30

Σ alkali metal oxides

  8-20

La 2 O 3

 0.5-3

ZrO 2

  2-5

HfO 2

0.02-5

Σ ZrO 2 + HfO 2

2.02-5

BaO

 0.4-6

SrO

  0-6

MgO

  0-2

CaO

  0-2

Σ alkaline earth

 0.4-6

metal oxides

Li 2 O

 0.5-3,

but not more than 25% of a

sum total amount, in Mol %

on said oxide basis, of said

alkali metal oxides.

Σ SiO 2 + ZrO 2 + HfO 2

>58.5;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1, and

wherein the cladding comprises a cladding glass and the cladding glass contains, in Mol % on an oxide basis:

SiO 2

75-85

Al 2 O 3

1-5

B 2 O 3

10-14

Na 2 O

2-8

K 2 O

 0-1.

26. A step index fiber comprising a core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

55-61

ZnO

20-25

Σ alkali metal oxides

11-16

La 2 O 3

1.5-2.9

ZrO 2

  2-4.08

HfO 2

0.02-3.3 

Σ ZrO 2 + HfO 2

2.02-4.1 

TiO 2

 0-0.5

BaO

0.4-5  

SrO

0.4-5  

Σ alkaline earth metal oxides

0.4-5  

Li 2 O

1-2.5

Σ SiO 2 + ZrO 2 + HfO 2

>59;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1.

27. A step index fiber comprising core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

  55-61

ZnO

  20-25

Σ alkali metal oxides

  11-16

La 2 O 3

 1.5-2.9

ZrO 2

  2-4.08

HfO 2

0.02-3.3

Σ ZrO 2 + HfO 2

2.02-4.1

BaO

 0.4-5

SrO

 0.4-5

Σ alkaline earth

 0.4-5

metal oxides

Li 2 O

  1-2.5

Σ SiO 2 + ZrO 2 + HfO 2

>59;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1 and

wherein the cladding comprises a cladding glass and the cladding glass contains, in Mol % on an oxide basis:

SiO 2

70-78

Al 2 O 3

 0-10

B 2 O 3

 5-14

Li 2 O

0

Na 2 O

 0-10

K 2 O

 0-10

MgO

0-1

CaO

0-2

SrO

0-1

BaO

0-3

F

 0-1.

28. A step index fiber comprising a core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO2

  55-61

ZnO

  20-25

Σ alkali metal oxides

  11-16

La 2 O 3

 1.5-2.9

ZrO 2

  2-4.08

HfO 2

0.02-3.3

Σ ZrO 2 + HfO 2

2.02-4.1

BaO

 0.4-5

SrO

 0.4-5

Σ alkaline earth

 0.4-5

metal oxides

Li 2 O

  1-2.5

Σ SiO 2 + ZrO 2 + HfO 2

>59;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides >3.5:1, and

wherein the cladding comprises a cladding glass and the cladding glass contains, in Mol % on an oxide basis:

SiO 2

62-70

B 2 O 3

>15

Li 2 O

>0.1

Na 2 O

 0-10

K 2 O

 0-10

MgO

0-5

CaO

0-5

SrO

0-5

BaO

0-5

ZnO

0-5

F

 0-1.

29. A step index fiber comprising a core and a cladding, wherein the core comprises a core glass and said core glass contains, in Mol % on an oxide basis:

SiO 2

  55-61

ZnO

  20-25

Σ alkali metal oxides

  11-16

La 2 O 3

 1.5-2.9

ZrO 2

  2-4.08

HfO 2

0.02-3.3

Σ ZrO 2 + HfO 2

2.02-4.1

BaO

 0.4-5

SrO

 0.4-5

Σ alkaline earth

 0.4-5

metal oxides

Li 2 O

  1-2.5

Σ SiO 2 + ZrO 2 + HfO 2

>59;

wherein a molar ratio of ZnO:Σ alkaline earth metal oxides 3.5:1; and

wherein the cladding comprises a cladding glass and the cladding glass contains, in Mol % on an oxide basis:

SiO 2

75-85

Al 2 O 3

1-5

B 2 O 3

10-14

Na 2 O

2-8

K 2 O

 0-1.