Patent ID: 8480235

Claim:
An illumination optical system for illuminating a surface to be illuminated comprising: a lens array system configured to split a light beam from a light source in a first plane which is parallel to an optical axis of the illumination optical system, a plurality of first light source images are formed in a first light source image zone with the use of the thus split light beams, and light beams from the plurality of first light source images are led to the surface to be illuminated, the lens array system further configured to split the light beam from the light source in a second plane which is parallel to the optical axis of the illumination optical system and which is perpendicular to the first plane, a plurality of second light source images are formed in a second light source image zone with the use of the thus split light beams, and light beams from the plurality of second light source images are led to the surface to be illuminated, and a polarization separation surface which is arranged at an inclination to the optical axis of the illumination optical system, wherein the width of the first light source image zone in the first plane is larger than that of the second light source image zone in the second plane, and wherein the second plane is parallel with a normal line to the polarization separation surface and the optical axis of the illumination optical system.