Production method of optical element, optical element forming mold and optical element

A mold assembly for an optical element, comprising:

• a cavity die which is formed so as to define therein a recess, and
• a core die having a protruding part adapted to enter into the recess in the cavity die, for press-molding an optical element including a lens surface,
• wherein the protruding part of the core die has an external shape which is different from a cross-sectional shape of a recess in the cavity die corresponding to the protruding part, and the outer peripheral surface of the protruding part and the inner peripheral surface of the recess define therebetween a space in which the material flows when the material is pressed during die-fastening,
• the recess in the cavity die has a cross-sectional shape which is quadrangular, with respect to the die-fastening direction of the protruding part of the core die, and
• the protruding part of the core die has an external shape which is circular.

An optical element comprising:

• a prismatic body portion comprising a plurality of side surface parts, and bottom surface parts,
• a lens portion formed in either one of the bottom surface parts of the body portion, and
• protrusions which are formed respectively at corners of the body portion around the lens portion,
• wherein the optical element further comprises peripheral sides each of which extends between ones of the corners adjacent to each other circumferentially so that each of the peripheral sides forms a boundary between one of the side surface parts and one of the bottom surface parts, and each of the protrusions at the ones of the corners protrudes in a thickness direction of the lens portion with respect to an intermediate point of the peripheral side extending between the ones of the corners.

An optical element comprising:

• a prismatic body portion constituted by a plurality of side surface parts and two bottom surface parts,
• a lens portion formed in either one of the bottom surface parts,
• protrusions formed at corner parts of the body portion around the lens portion, and protruded in the thicknesswise direction of the lens portion, and
• a mark formed in a part of the body portion, other than the lens portion, for indicating a positional relationship of the lens portion with respect to the body portion,
• wherein the optical element further comprises peripheral sides each of which extends between ones of the corners adjacent to each other circumferentially so that each of the peripheral sides forms a boundary between one of the side surface parts and one of the bottom surface parts, and each of the protrusions at the ones of the corners protrudes in a thickness direction of the lens portion with respect to an intermediate point of the peripheral side extending between the ones of the corners.