Illuminating optical system and projector

Abstract

The invention concerns improving the efficiency with which light being used in a polarization conversion optical system used in an illuminating optical system. An illuminating optical system includes a light source for emitting unpolarized light, a separation optical system for separating the light emitted from the light source into a plurality of partial light beams, and a polarization conversion optical system for substantially converting the unpolarized partial light beams into one type of linearly polarized light beams whose polarization directions are aligned and causing the one type of linearly polarized light beams to leave therefrom. In the illuminating optical system, the separation optical system includes a first lens array having an M column (M is an integer equal to or greater than 2) of small lenses, and a second lens array having an N column (N is an integer equal to or greater than 1 and less than M) of small lenses. In addition, the separation optical system is constructed such that the partial light beams formed in a plurality of columns at the plurality of small lens columns in the first lens array are collected in a smaller number of columns in order to strike the second lens array, whereby the partial light beams separated at the M column of small lenses in the first array are incident upon the N column of small lenses in the second lens array.