System for monitoring laser luminous power and method, and collimating lens thereof

A collimating lens for receiving a divergent beam and converting it to a collimated beam, wherein the collimating lens comprises a lens main body and the lens main body includes:

• a light-incident surface into which the divergent beam is input;
• a first light exit surface from which the collimated beam is output;
• a second light exit surface;
• a reflective surface which reflects a certain proportion of a light beam to the second light exit surface for output;
• a cylindrical section;
• and
• a truncated cone section,
• wherein a free end of the cylindrical section forms the light-incident surface and a free end of the truncated cone section forms the first light exit surface;
• a protruding portion is formed along an optical axis direction at the free end of the truncated cone section, and the reflective surface is formed by plating the protruding portion with a reflective film;
• and a part of another end of the truncated cone section that protrudes from a side of the cylindrical section forms the second light exit surface.