Patent ID: 8596093

Claim:
A method for manufacturing an optical element having an upper molded-surface, a lower molded-surface, and a side molded-surface by pressure-molding a molten glass drop using a molding die having an upper molding die for molding the upper molded-surface, a lower molding die for molding the lower molded-surface, and a side molding die for molding the side molded-surface, the method comprising, in order: supplying the lower molding die with the molten glass drop of a predetermined volume and a temperature higher than a temperature of the upper molding die; leaving the molten glass drop on the lower molding die for a predetermined waiting time as to lower the temperature of the molten glass drop; and pressure-molding the molten glass by lowering the upper molding die to a molding position so as to form the upper molded-surface by contact of the glass with the upper molding die, the lower molded-surface by contact of the glass with the lower molding die, the side molded-surface by contact of the glass with the side-molding die, and to form a free surface of the glass, between the upper molded-surface and the side molded-surface, wherein the free surface of the glass is solidified while the upper molding die is at the molding position and while said free surface is apart from the upper and side molding dies, and wherein the predetermined volume of the molten glass drop is set to be 0.8 times or more and 0.97 times or less a volume of a space defined, when the upper molding die is at the molding position, by 1) an extended theoretical upper molded-surface generated by extrapolating the upper molded-surface, formed when the upper molding die is at the molding position, to an extended theoretical side molded surface defined by and coincident with the side molded-surface, 2) the extended theoretical side molded surface is generated by extrapolating the side molded-surface to the extended theoretical upper molded-surface that is defined by and coincident with the upper molded-surface formed when the upper molding die is at the molding position, and 3) the lower molded-surface, and wherein the predetermined volume is also set so that the free surface has the predetermined size.