Patent ID: 8014257

Claim:
An extraction optical system extracting, from a light bundle in which a signal light component and stray light components are mixed, said signal light component, said light bundle being supplied through a light focus optical device focusing said light bundle and astigmatism adding means adding astigmatism to said light bundle, the extraction optical system comprising: a first phase element including: a first phase change area generating a phase difference of (+¼) times of a wavelength to polarization components of said light bundle which are in an orthogonal relationship; and a second phase change area generating a phase difference of (−¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship; a second phase element including: a third phase change area generating a phase difference of (+¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship; and a fourth phase change area generating a phase difference of (−¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship; and a separation element allowing only said signal light component among said signal light component and said stray light components which have passed through said first phase element to pass therethrough, or absorbing or reflecting only said stray light component thereamong in accordance with polarization directions thereof, wherein: said first phase element is divided into said first phase change area and said second phase change area by a first boundary, the first boundary being parallel to a first focal line in which said signal light component forms an image into a line shape on a side closer to said light focus optical device than a first focal point position on an optical axis of said light focus optical device at which said signal light component focused by said light focus optical device is formed into a smallest circle of confusion by said astigmatism adding unit, and being orthogonal to the optical axis of said light focus optical device; said second phase element is divided into said third phase change area and said fourth phase change area by a second boundary parallel to said first boundary; said first phase change area and said third phase change area are disposed to be symmetrical with respect to said first focal line; said second phase change area and said fourth phase change area are disposed to be symmetrical with respect to said first focal line; said first phase element is disposed between said first focal point position and said first focal line; and said second phase element is disposed between said first focal line and a second focal line in which said stray light components form an image into a line shape on a side closer to said light focus optical device than a second focal point position at which said stray light components form a smallest circle of confusion on the side closer to said light focus optical device than said first focal point position.