To provide a polarizing beam splitter having a film structure capable of reducing a ripple in a transmission bandpass of a P polarization.
This polarizing beam splitter has a multi-layer film (polarizing beam splitter film 4) formed by being alternatively laminated with high refractive films 2 and low refractive films 3 on an optical substrate 1, and it reflects a light of a 1st light source 6 incident to a surface having the multi-layer film from an air face and transmits a light of a 2nd light source 7 incident to an optical substrate surface opposite to the above surface having the multi-layer film. Further, the number of laminated layers N of the polarizing beam splitter film 4 is in the range of 16≤N≤40, and a distribution of a ratio of optical film thickness D/M (M: average thickness of optical films of all laminated layer films, D: thickness of optical film of each layer) is in the range of 0.5≤D/M≤2.5, and an average surface roughness is settled to ≤0.50nm, which is obtained by measuring such measuring points that a distance between the measuring points is ≤100nm with respect to a surface of the side arranging the polarizing beam splitter film 4 of the optical substrate 1 thereon.
MARO TAKESHI
MINAGAWA YOSHIAKI
