Optical glass, preform for precision press molding, optical element and method of manufacturing thereof

摘要

The optical glass of the present invention has a refractive index n_d of 1.70 or greater and an Abbé number of 50 or greater. Given as mole percentages, it comprises: B₂O₃ 20 to 80 percent, SiO₂ 0 to 30 percent, Li₂O 1 to 25 percent; ZnO 0 to 20 percent, La₂O₃ 4 to 30 percent, Gd₂O₃ 1 to 25 percent, Y₂O₃ 0 to 20 percent, ZrO₂ 0 to 5 percent, MgO 0 to 25 percent, CaO 0 to 15 percent, SrO 0 to 10 percent, with the combined quantity of the above components being 97 percent or greater. The molar ratio of {ZnO/(La₂O₃+Gd₂O₃+Y₂0₃)} is 0.8 or less and the molar ratio of {+SrO+BaO)/(La₂O₃+Gd₂O₃+Y₂0₃)} is 0.8 or less. Ta₂O₅ may be incorporated as an optional component, with the molar ratio {(ZrO₂+Ta₂O₅)/(La₂O₃+Gd₂O₃+Y₂O₃)}being 0.4 or less. The present invention further relates to a preform for precision press molding comprised of this glass, an optical element comprised of this glass, and methods of manufacturing the same.