Patent ID: 8336333

Claim:
A method of manufacturing a diffractive optical element comprising stacked first and second diffraction gratings made of different materials, wherein the materials of the first and second diffraction gratings are glass, wherein the first and second diffraction gratings have grating surfaces contacted to each other, wherein the materials satisfy the following conditions, Tg2≦600° C., and Tg3≦600° C. wherein the materials satisfy one of the following conditions, Tg3>At2, and Tg2>At3, where Tg2 and At2 are a transformation point temperature and a yield point temperature of the material of the first diffraction grating respectively, and Tg3 and At 3 are a transformation point temperature and a yield point temperature of the material of the second diffraction grating respectively, the method comprising: molding the second diffraction grating using a metal mold at a molding temperature of At3 or higher; cooling the second diffraction grating to Tg3 or lower while being contacted to the metal mold, and removing the metal mold; molding the first diffraction grating using the molded second diffraction grating as a glass mold at a molding temperature in a range from Tg3 or lower At2 or higher of the material; and cooling the first and second diffraction gratings while being contacted to each other.