Light quantity control apparatus

Light quantity control apparatus comprising first, second and third birefringence elements having substantially parallel incident planes and emitting planes and aligned along an axis;

• said first birefringence element dividing incident light into two light components;
• a polarization converter disposed between said first and second birefringence elements for polarizing said two light components and sending the same to the second birefringence element;
• said second birefringence element separating said polarized two light components into light converted by said polarization converter and light not converted and said second birefringence element operating to synthesize first output light waves and to emit the other one of the separated light waves as second and third output light waves,
• means disposed between said second and third birefringence elements for changing direction of the first output light wave emitted by said second birefringence element, said direction changing means comprising a mirror for reflecting said first output light back to said second birefringence element;
• said third birefringence element operating to synthesize the second and the third light waves supplied from said second birefringence element so as to emit one output light wave, thereby controlling quantity of light derived out from said third birefringence element by said polarization converter, said apparatus further comprising another mirror disposed on an incident face of said first birefringence element, and wherein the light reflected by said first mentioned mirror is separated into two light components by said second birefringence element and then synthesized by said first birefringence element after transmitting through said first birefringence element, said another mirror reflecting the synthesized light components back to said first birefringence element.