Armstrong, Westerman, Hattori, McLeland & Naughton
Glass having refractive index distribution
 A process for producing a glass having a rod refractive index distribution, which includes pressing a glass at a temperature below the glass transition temperature to form a glass having a density increased towards the surface layer thereof, or alternatively includes heating a glass at a temperature around the transition temperature at the lowest to prepare glass having a uniformly enhanced density and heating the treated glass under a pressure lower than the applied pressure at a temperature below the glass transition temperature of the glass to prepare a rod glass having a density increased towards the central portion. 
Agency of Industrial Science and Technology
C C C
C03B C03B C03B
inventional inventional inventional
Isao Naoyuki Hiroshi Jun Kohei Makoto Saburo Kenichi
Kondoh Kitamura Yamashita Matsuoka Fukumi Kinoshita Kose Kinugawa