Clad glass composition and mother glass rod for gradient-index rod lens formed using the same, gradient-index rod lens and method of manufacturing the same, rod lens array, and image processor

Abstract

The present invention provides a clad glass composition that is excellent in devitrification resistance and that prevents the whole mother glass rod from devitrifying by preventing a core glass composition from devitrifying in forming a mother glass rod using a concentric crucible drawing method. The clad glass composition forms a clad of a mother glass rod for a gradient-index rod lens having a core/clad structure. The clad glass composition includes 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 the range of 5 to 35 mol %, the total of MgO+CaO+SrO+BaO is in the range of 2 to 20 mol %, the total of Li 2 O+Na 2 O+K 2 O+MgO+CaO+SrO+BaO is in the 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 the range of 0 to 15 mol %. In the clad glass composition, 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. The clad glass composition is substantially free from lead and has a refractive index in the range of 1.56 to 1.68.

1 . A clad glass composition that forms a clad of a mother glass rod for a gradient-index rod lens having a core/clad structure, 
 wherein the clad glass composition 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;    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.    
   
   
       2 . The clad glass composition according to  claim 1 , further comprising an oxide of at least one element selected from the group consisting of Fe, Co, Ni, Mn, Cr, and Cu, as a colorant.  
   
   
       3 . The clad glass composition according to  claim 2 , wherein the content by percentage of the colorant is 5 mol % or less.  
   
   
       4 . The clad glass composition according to  claim 1 , wherein the clad glass composition has devitrification resistance when maintained at a temperature in a range of 600° C. to 1000° C. for 120 hours.  
   
   
       5 . The clad glass composition according to  claim 1 , wherein the content by percentage of Bi 2 O 3  is in a range of 0.5 mol % to 5 mol %.  
   
   
       6 . The clad glass composition according to  claim 1 , wherein the total of the contents by percentage of MgO, CaO, SrO, and BaO is in a range of 2 mol % to 17 mol %.  
   
   
       7 . The clad glass composition according to  claim 6 , wherein the total of the contents by percentage of MgO, CaO, SrO, and BaO is in a range of 2 mol % to 12 mol %.  
   
   
       8 . The clad glass composition according to  claim 1 , wherein the total of the contents by percentage of CaO, SrO, and BaO is in a range of 2 mol % to 7 mol %.  
   
   
       9 . The clad glass composition according to  claim 8 , wherein the total of the contents by percentage of CaO, SrO, and BaO is in a range of 2 mol % to 6 mol %.  
   
   
       10 . 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 according to  claim 1 , and    a core glass composition that forms a core has a different composition from the clad glass composition.    
   
   
       11 . 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 according to  claim 1 ,    a core glass composition that forms a core 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% 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.    
   
   
       12 . The mother glass rod for a gradient-index rod lens according to  claim 11 , wherein a difference Δn (Δn=n 1 −n 2 ) between a refractive index n 1  of the core glass composition and a refractive index n 2  of the clad glass composition is in a range of −0.03 to 0.04.  
   
   
       13 . The mother glass rod for a gradient-index rod lens according to  claim 11 , wherein the mother glass rod has a diameter of 400 μm or smaller.  
   
   
       14 . A gradient-index rod lens obtained by providing a mother glass rod for a gradient-index rod lens according to  claim 11  with a refractive index distribution by an ion exchange method.  
   
   
       15 . A rod lens array comprising at least two gradient-index rod lenses according to  claim 14 , 
 wherein the rod lenses are arrayed and formed into one body, with their optical axes being substantially in parallel with each other.    
   
   
       16 . An image processor comprising a rod lens array according to  claim 15 , 
 wherein the rod lens array serves as an imaging optical system.    
   
   
       17 . A method of manufacturing a gradient-index rod lens, comprising: 
 charging an outer crucible of a concentric crucible with a melt of a clad glass composition having a composition (A);    charging an inner crucible of the concentric crucible with a melt of a core glass composition having a composition (B);    forming a mother glass rod for a gradient-index rod lens having a core/clad structure by a concentric crucible drawing method; and    providing the mother glass rod with a refractive index distribution by an ion exchange method in which the mother glass rod formed above is immersed in molten salt containing sodium,    wherein the clad glass composition having the composition (A) 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    wherein the core glass composition having the composition (B) 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% 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.