Method for manufacturing grin lens
[Object] In manufacturing a GRIN lens by a sol-gel method, an operation for preparing a wet gel is facilitated and cracking in a base material during sintering and foaming during drawing are prevented. [Solution] The object is achieved by obtaining a GRIN lens by producing a wet gel from an alcohol solution containing a silicon alkoxide, a dopant alkoxide, and a boron alkoxide as the main ingredients, leaching the same, drying the same to form a dry gel, and sintering and drawing the same.
1. A method for manufacturing a GRIN lens, comprising:
a step of producing a wet gel from an alcohol solution containing a silicon alkoxide, a dopant alkoxide, and a boron alkoxide as the main ingredients having a concentration of a boron simple substance of 1 to 15 mol % relative to that of a silicon simple substance, a dopant simple substance, and a boron simple substance;
a step of eluting a dopant simple substance and a boron simple substance from an outer surface of the wet gel by leaching to give a refractive index distribution and to give the wet gel increased porosity by eluting almost all the boron;
a step of drying the wet gel to produce a dry gel having a decreased bulk density equal to or less than 0.830 (g/cm 3 );
a step of sintering the dry gel to form a glass base material; and
a step of drawing the base material,
wherein the concentration of the boron simple substance remaining in the dry gel after leaching is lower than 0.1 mol % relative to that of a silicon simple substance, the dopant simple substance, and the boron simple substance.
2. The method for manufacturing a GRIN lens according to claim 1 , wherein the dopant alkoxide is one or more alkoxide(s) of Ti, Ta, Sb, or Zr.
3. The method for manufacturing a GRIN lens according to claim 2 , wherein the step of producing a wet gel from an alcohol solution containing a silicon alkoxide, a dopant alkoxide, and a boron alkoxide as the main ingredients comprises stirring an alcohol solution containing a silicon alkoxide and a boron alkoxide for 10 to 150 minutes, adding an alcohol solution containing a dopant alkoxide to the stirred alcohol solution thereby producing a mixture, and further stirring the mixture.
4. The method for manufacturing a GRIN lens according to claim 1 , wherein the step of producing a wet gel from an alcohol solution containing a silicon alkoxide, a dopant alkoxide, and a boron alkoxide as the main ingredients comprises stirring an alcohol solution containing a silicon alkoxide and a boron alkoxide for 10 to 150 minutes, adding an alcohol solution containing a dopant alkoxide to the stirred alcohol solution thereby producing a mixture, and further stirring the mixture.
5. The method for manufacturing a GRIN lens according to claim 1 , wherein the step of drying the wet gel to produce a dry gel produces a dry gel with a bulk density bulk density between 0.750 and 0.830 (g/cm 3 ).