Optical element, metal die, and cutting tool

An optical element capable of transmitting light, comprising:

• an optical surface having an optical axis;
• diffractive grooves provided on at least a part of the optical surface and each of the diffractive grooves including
• a first surface capable of being approximated by a predetermined optical function;
• and
• a second surface extending in a direction to cross the first surface;
• wherein a surface roughness Rz of the first surface is not larger than {fraction (1/10)} of a using wavelength of a light source.

A metallic die for molding an optical element capable of transmitting light, wherein the optical element comprises an optical surface having an optical axis;

• diffractive grooves provided on at least a part of the optical surface and each of the diffractive grooves including a first surface capable of being approximated by a predetermined optical function and a second surface extending in a direction to cross the first surface;
• the metallic die comprising:
• a surface corresponding to the first surface of the optical element,
• wherein the surface is formed by a rotating cutting process with a cutting tool, and
• wherein a feed rate of the cutting tool in a radius direction is 0.1 μm to 1 μm per one rotation of the metallic die.

A cutting tool for cutting a metallic die for molding an optical element capable of transmitting light, wherein the optical element comprises an optical surface having an optical axis;

• diffractive grooves provided on at least a part of the optical surface and each of the diffractive grooves including a first surface capable of being approximated by a predetermined optical function;
• a second surface extending in a direction to cross the first surface;
• and a third surface to connect the first surface and the second surface, and wherein the at least a part of the metallic mold is formed by a rotating cutting process with the cutting tool,
• the cutting tool comprising:
• a rake face opposite to a rotation direction of the metallic die at the time of the rotating cutting process;
• the rake face formed by
• a first edge to cut a surface of the metallic die corresponding to the second surface of the optical element,
• a second edge extending in a direction to cross the first edge, and
• a third edge to connect the first edge and the second edge and to cut a surface of the metallic mold corresponding to the third surface of the optical element,
• wherein a first extending line from the first edge and a second extending line from the second edge cross at a crossing point and a distance between the crossing point and the third edge is 0.1 μm to 3 μm.

A cutting tool for cutting a metallic die for molding an optical element capable of transmitting light, wherein the optical element comprises an optical surface having an optical axis;

• diffractive grooves provided on at least a part of the optical surface and each of the diffractive grooves including a first surface capable of being approximated by a predetermined optical function;
• a second surface extending in a direction to cross the first surface;
• and a third surface to connect the first surface and the second surface, and wherein the at least a part of the metallic mold is formed by a rotating cutting process with the cutting tool,
• the cutting tool comprising:
• a rake face opposite to a rotation direction of the metallic die at the time of the rotating cutting process;
• the rake face formed by
• a first edge to cut a surface of the metallic die corresponding to the second surface of the optical element,
• a second edge extending in a direction to cross the first edge, and
• a third edge to connect the first edge and the second edge and to cut a surface of the metallic mold corresponding to the third surface of the optical element,
• wherein an angle α formed between the first edge and the second edge satisfies the following conditional formula:
• θmax≦(90−(α/2+S))
• where θmax is a maximum normal angle of the metallic die corresponding to the optical surface and S is a setting angle of the cutting tool to the optical axis of the optical surface.

A cutting tool for cutting a metallic die for molding an optical element capable of transmitting light, wherein the optical element comprises an optical surface having an optical axis;

• diffractive grooves provided on at least a part of the optical surface and each of the diffractive grooves including a first surface capable of being approximated by a predetermined optical function;
• a second surface extending in a direction to cross the first surface;
• and a third surface to connect the first surface and the second surface, and wherein the at least a part of the metallic mold is formed by a rotating cutting process with the cutting tool,
• the cutting tool comprising:
• a rake face opposite to a rotation direction of the metallic die at the time of the rotating cutting process, the rake face formed by
• a first edge to cut a surface of the metallic die corresponding to the second surface of the optical element,
• a second edge extending in a direction to cross the first edge, and
• a third edge to connect the first edge and the second edge and to cut a surface of the metallic mold corresponding to the third surface of the optical element,
• a first side surface forming the first edge with the rake face;
• and
• a second side surface forming the second edge with the rake face;
• wherein the first surface has a first inclination angle to the rake face, the second surface has a second inclination angle to the rake face, the first inclination angle is different from the second inclination angle, and a difference between the first inclination angle and the second inclination angle is 1° to 20°.

A cutting tool for cutting a metallic die for molding an optical element capable of transmitting light, wherein the optical element comprises an optical surface having an optical axis;

• diffractive grooves provided on at least a part of the optical surface and each of the diffractive grooves including a first surface capable of being approximated by a predetermined optical function;
• a second surface extending in a direction to cross the first surface;
• and a third surface to connect the first surface and the second surface, and wherein the at least a part of the metallic mold is formed by a rotating cutting process with the cutting tool,
• the cutting tool comprising:
• a rake face opposite to a rotation direction of the metallic die at the time of the rotating cutting process;
• the rake face formed by
• a first edge to cut a surface of the metallic die corresponding to the second surface of the optical element,
• a second edge extending in a direction to cross the first edge, and
• a third edge to connect the first edge and the second edge and to cut a surface of the metallic mold corresponding to the third surface of the optical element,
• a first side surface forming the first edge with the rake face;
• and
• a second side surface forming the second edge with the rake face;
• wherein at least one of the first surface and the second surface has a first inclination angle to the rake face, crossing lines of the first surface and the second surface form a first clearance angle, at least one of the first surface and the second surface has a second inclination angle to the rake face, at least the side surface having the second inclination angle and another side surface form crossing lines and the crossing lines form a second clearance angle.