Patent ID: 7839753

Claim:
An optical system for extracting signal light components from a beam including the signal light components and stray light components, the optical system comprising: a condensing optical element situated on an optical path of the beam for condensing the beam, the condensing optical element condensing the signal light components at a first focus point and the stray light components at a second focus point; a first polarization changing element positioned between the condensing optical element and the second focus point that is situated closer to the condensing optical element than the first focus point, the first polarization changing element including first and second areas that are divided by a line perpendicularly intersecting with the optical axis of the condensing optical element, the first polarization changing element having an optical characteristic of changing the polarization direction of the beam incident on the first area to an angle of 90 degrees; a first separating element positioned between the first and second focus points, the first separating element being operable to reflect or absorb the stray light components condensed more toward the condensing optical element than the first focus point; a second separating element positioned between the first focus point and a third focus point at which the stray light components transmitted through the first separating element are condensed, the second separating element being operable to reflect or absorb the stray light components transmitted through the first separating element; and a second polarization changing element including first and second areas that are divided by a line perpendicularly intersecting with the optical axis of the condensing optical element, the second polarization changing element having an optical characteristic of changing the polarization direction of the beam incident on at least one of the first area and the second area of the second polarization changing element to an angle of 90 degrees.