Optical glass, press-molding glass material, optical element and method of manufacturing the same, and bonded optical element

1. An optical glass, which comprises, denoted as weight percent,

2 to 37 percent of SiO 2 ,

0 to 25 percent of B 2 O 3 ,

0 to 10 percent of GeO 2 ,

18 to 55 percent of a combined content of Li 2 O, Na 2 O, K 2 O, CaO, SrO, and BaO, 33.78 to 55 percent of a combined content of TiO 2 , Nb 2 O 5 , and WO 3 , and

0 to 15 percent of La 2 O 3 ;

wherein the weight ratio of SiO 2 content relative to a combined content of SiO 2 and B 2 O 3 (SiO 2 /(SiO 2 +B 2 O 3 ) ranges from 0.1 to 1;

a weight ratio of the Li 2 O content to a combined content of Li 2 O, Na 2 O, K 2 O, CaO, SrO, and BaO (Li 2 O/(Li 2 O+Na 2 O+K 2 O+CaO+SrO+BaO) ranges from 0 to 0.4; and

a weight ratio of TiO 2 content relative to a combined content of TiO 2 , Nb 2 O 5 , and WO 3 (TiO 2 /(TiO 2 +Nb 2 O 5 +WO 3 ) ranges from 0.35 to 1;

a specific gravity being equal to or less than 4.3; and

which has a refractive index nd ranging from 1.87939 to 1.990 and an Abbé number νd ranging from 21 to 29.

2. The optical glass according to claim 1 , wherein a difference (Tx−Tg) between a peak crystallization temperature Tx and a glass transition temperature Tg is equal to or greater than 120° C.

3. The optical glass according to claim 1 , which has a liquidus temperature LT of equal to or lower than 1,300° C.

4. The optical glass according to claim 1 , which has an average coefficient of linear expansion α at 100 to 300° C. of equal to or greater than 85×10 −7 /° C.

5. The optical glass according to claim 1 , wherein the content of La 2 O 3 ranges from 0 to 11 weight percent.

6. An optical element, which is comprised of the optical glass according to claim 1 .

7. A bonded optical element, wherein an optical element comprised of the optical glass according to claim 1 is bonded to an optical element comprised of fluorophosphate glass.

8. A press-molding glass material, which is comprised of the optical glass according to claim 1 .

9. A method of manufacturing an optical element, which comprises:

preparing an optical element blank by press molding the press-molding glass material according to claim 8 in a heat-softened state; and

grinding and polishing the optical element blank that has been prepared to provide an optical element.

10. An optical glass, which comprises, denoted as weight percent,

2 to 37 percent of SiO 2 ,

0 to 25 percent of B 2 O 3 ,

0 to 10 percent of GeO 2 ,

18 to 55 percent of a combined content of Li 2 O, Na 2 O, K 2 O, CaO, SrO, and BaO, and

27 to 55 percent of a combined content of TiO 2 , Nb 2 O 5 , and WO 3 ; as well as comprises no La 2 O 3 ;

wherein the weight ratio of SiO 2 content relative to a combined content of SiO 2 and B 2 O 3 (SiO 2 /(SiO 2 +B 2 O 3 ) ranges from 0.1 to 1;

a weight ratio of the Li 2 O content to a combined content of Li 2 O, Na 2 O, K 2 O, CaO, SrO, and BaO (Li 2 O/(Li 2 O+Na 2 O+K 2 O+CaO+SrO+BaO) ranges from 0 to 0.4; and

a weight ratio of TiO 2 content relative to a combined content of TiO 2 , Nb 2 O 5 , and WO 3 (TiO 2 /(TiO 2 +Nb 2 O 5 +WO 3 ) ranges from 0.35 to 1; and

which has a refractive index nd ranging from 1.860 to 1.990 and an Abbé number νd ranging from 21 to 29.

11. An optical element, which is comprised of the optical glass according to claim 10 .

12. A bonded optical element, wherein an optical element comprised of the optical glass according to claim 10 is bonded to an optical element comprised of fluorophosphate glass.

13. A press-molding glass material, which is comprised of the optical glass according to claim 10 .

14. A method of manufacturing an optical element, which comprises:

preparing an optical element blank by press molding the press-molding glass material according to claim 13 in a heat-softened state; and

grinding and polishing the optical element blank that has been prepared to provide an optical element.