Patent ID: 7185984

Claim:
An illumination optical system comprising: a light source; a beam splitting element including a plurality of lenses that splits light emitted from the light source into a plurality of sub-beams; a polarization conversion element including a polarization beam splitter array that splits each of the plurality of sub-beams into two types of polarized light, the polarization beam splitter array having a plurality of polarization splitting films and reflective films which are alternately arranged, and a phase element disposed on the emitting surface side of the polarization beam splitter array to align the light polarization directions of the two types of polarized light; and a light shielding member that adjusts a quantity of incident light on the polarization splitting films, the light shielding member being provided between the beam splitting element and the polarization beam splitter array; wherein the light shielding member is disposed movably along a light incident surface of the polarization beam splitter array so as to vary a quantity of incident light on portions of the light incident surface corresponding to the polarization splitting films.