Patent ID: 8193108

Claim:
A mother glass rod for a gradient index rod lens having a core/clad structure, wherein a clad glass composition that forms a clad is a clad glass composition that comprises the following components, indicated by mol %: 45 to 65% SiO 2 ; 0.5 to 10% TiO 2 ; 0 to 15% B 2 O 3 ; 0 to 7% Al 2 O 3 ; 0.1 to 10% Bi 2 O 3 ; 0 to 5% Li 2 O; 5 to 30% Na 2 O; 0 to 10% K 2 O; 0 to 15% MgO; 0 to 10% CaO; 0 to 10% SrO; 0.5 to 10% BaO; 0 to 10% Cs 2 O; 0 to 10% ZnO; 0 to 7% Y 2 O 3 ; 0 to 7% Nb 2 O 5 ; 0 to 7% In 2 O 3 ; 0 to 7% La 2 O 3 ; 0 to 10% Ta 2 O 5 ; 0 to 7% ZrO 2 ; and 0 to 1% Sb 2 O 3 , where the total of Li 2 O+Na 2 O+K 2 O is in a range of 5 to 35 mol %, the total of MgO+CaO+SrO+BaO is in a range of 2 to 20 mol %, the total of Li 2 O+Na 2 O+K 2 O+MgO+CaO+SrO+BaO is in a range of 7 to 50 mol %, and the total of Cs 2 O+ZnO+Y 2 O 3 +Nb 2 O 5 +In 2 O 3 +La 2 O 3 +ZrO 2 +Ta 2 O 5 is in a range of 0 to 15 mol %, at least two molar ratios selected from the group consisting of: MgO/(MgO+CaO+SrO+BaO); CaO/(MgO+CaO+SrO+BaO); SrO/(MgO+CaO+SrO+BaO); and BaO/(MgO+CaO+SrO+BaO) are at least 0.1, and the clad glass composition is substantially free from lead and has a refractive index in a range of 1.56 to 1.68, and a core glass composition that forms a core has a different composition from the clad glass composition, and comprises the following components, indicated by mol %: 40 to 65% SiO 2 ; 1 to 10% TiO 2 ; 0 to 20% B 2 O 3 ; 0 to 10% Al 2 O 3 ; 5 to 12% Li 2 O; 5 to 15% Na 2 O; 0 to 16% MgO; 0 to 15% CaO; 0.1 to 12% SrO; 0.1 to 12% SrO; 0.1 to 12% BaO; 0 to 3% Cs 2 O; 0 to 8% ZnO; 0 to 5% Y 2 O 3 ; 0 to 5% Nb 2 O 5 .; 0 to 5% In 2 O 3 ; 0 to 5% La 2 O 3 ; 0 to 5% Ta 2 O 5 ; 0 to 1% SnO 2 ; 0 to 1% Sb 2 O 3 ; and 0 to 1% As 2 O 3 , where the total of SiO 2 +TiO 2 +B 2 O 3 +Al 2 O 3 is in a range of 50 to 70 mol %, the total of Li 2 O+Na 2 O is in a range of 10 to 27 mol %, the molar ratio of Li 2 O/Na 2 O is in a range of 0.7 to 2, and the total of MgO+CaO+SrO+BaO is in a range of 5 to 36 mol %, at least two values selected from the contents by percentage of CaO, SrO, and BaO are in a range of 0.1 to 15 mol %, at least two molar ratios selected from the group consisting of: MgO/(MgO+CaO+SrO+BaO); CaO/(MgO+CaO+SrO+BaO); SrO/(MgO+CaO+SrO+BaO); and BaO/(MgO+CaO+SrO+BaO) are at least 0.1, and the core glass composition is substantially free from lead.