Patent ID: 8248695

Claim:
An illuminating device comprising an optical source emitting an unpolarized light beam, a polarizing beam splitter comprising a grid polarizer included between first faces of a first and of a second transparent prism, which prisms each have a second exit face both situated within one and the same plane, said first faces and second faces of each prism being perpendicular; the unpolarized light beam penetrating into the first prism through a third face of this first prism and reaching the polarizing beam splitter that transmits the light with a first polarization direction and that reflects the light with a second polarization direction; the light transmitted by the polarizing beam splitter being transmitted to a third face of the second prism that reflects it toward said second exit face of the second prism, and the light reflected by the polarizing beam splitter being transmitted to said third face of the first prism that reflects it toward said second exit face of the first prism, wherein the grid polarizer is formed on the first face of one transparent prism selected from the group including the first prism and the second prism, and wherein an antireflective coating is provided on the first face of the other transparent prism, which other transparent prism lacks the grid polarizer thereon, wherein an air gap is provided for cooling between the grid polarizer and the antireflective coating, and wherein the divergence of said light beam is greater than or equal to 5° on either side of the average direction of said beam.