Patent ID: 7690793

Claim:
An illumination optical system illuminating an illuminated plane with a luminous flux from a light source, comprising: a first beam splitter splitting the luminous flux from the light source and forming plural first light source images in a first light source image area using split luminous fluxes on a first section parallel to an optical axis of the illumination optical system; a second beam splitter splitting the luminous flux from the light source and forming plural second light source images in a second light source image area using split luminous fluxes on a second section parallel to the optical axis and orthogonal to the first section; a compression optical system disposed closer to the light source than the second beam splitter and compressing an incident luminous flux on the second section; a superposing system disposed closer to an illuminated plane than the first beam splitter and the second beam splitter and superposing the luminous fluxes from the first light source image and the second light source image on the illuminated plane; and an optical element disposed between the superposing system and the illuminated plane and having a polarization splitting surface, wherein a normal of the polarization splitting surface is parallel to the second section, a width of the first light source image area in a direction perpendicular to the optical axis of the first section is greater than a width of the second light source image area in a direction perpendicular to the optical axis on the second section, the compression optical system includes, in order from a light source side to an illuminated plane side, a first compression optical element having a positive refractive power and a second compression optical system having a negative refractive power, and an illuminated plane side surface of the second compression optical system having the negative refractive power is a concave surface.