Abstract: A platinum thin film having a thickness of 0.01 to 5 &mgr;m is formed by means of the sputtering method on a press face of a die based on the use of a cemented carbide base material. A nickel thin film having a thickness of 0.05 to 0.5 &mgr;m and a thin film made of an alloy of platinum and iridium are allowed to intervene between the cemented carbide base material and the platinum thin film, if necessary. Alternatively, an alloy thin film having a thickness of 0.01 to 5 &mgr;m, which contains 10 to 70% by weight of iridium and 30 to 90% by weight of one or more species of metals selected from metals of the platinum group except for iridium, may be allowed to intervene between the cemented carbide base material and the platinum thin film.

Abstract: There is provided a glass substrate having a V-groove portion for arranging an optical fiber core and a countersunk portion for containing an optical fiber coated portion, formed on the extension of the V-groove portion, on the surface thereof. The surface roughness of an inside side face of the countersunk portion is 1 &mgr;m or less in Rmax, or 0.2 &mgr;m or less in Ra at least at the connecting portion of the V-groove portion and the countersunk portion. The glass substrate is manufactured by a two-stage molding method in which a first molding step for forming a concave portion in the surface of a glass substrate molded body by grinding or pressing, and a second molding step for pressing the glass substrate molded body obtained by the first molding step from the top and bottom surfaces while reheating the molded body are performed.

Abstract: A press mold for glass substrate includes an upper mold and a lower mold, and a pressure apparatus for applying pressure to the upper mold and the lower mold, for molding a plate-shaped glass substrate having a predetermined thickness between the upper mold and the lower mold. An engaging projected piece is projectingly provided on the side portion of the upper mold, an engaging projected piece supporting portion for supporting the engaging projected piece is provided on the side portion of the lower mold, and an end portion of the upper mold is formed so as to be released from the lower mold with the engaging projected piece as a rotating shaft. Variance in pressure on mold surfaces between the upper mold and lower mold is detected, and a buffer made of material having lower compressive yield strength than material constituting the lower mold is inserted between the lower mold and the pressure apparatus in a position corresponding to the mold surface portion at lower pressure.