Patent ID: 7921672

Claim:
A method for manufacturing a GRIN lens comprising: forming a wet gel including a refractive index distribution imparting metal, the wet gel having a concentration distribution of the refractive index distribution imparting metal which varies in a radial direction; drying the wet gel to form a dry gel with a bulk density ρ of at least 0.6 g/cm 3 ; sintering the dry gel to form a GRIN lens base material; and stretching the GRIN lens base material while heating the GRIN lens base material, wherein during the sintering operation, partial pressures of oxygen during sintering at 800° C. or higher are 10 −1 Pa or lower, and wherein during the sintering operation, the relationship between a rate of temperature increase v in degrees Celsius per hour and the bulk density ρ in g/cm 3 of the dry gel during sintering at 1,000 to 1,150° C. is given by v≦10 5 *EXP(−12ρ).