Color-separating and -recombining optical system and projection display using the same

A color-separating and -recombining optical system comprising:

• a light-beam separator having a separating plane to separate a light beam having a first, a second and a third beam component into the first, second and third beam components;
• a first polarization beam splitter having a first splitting plane and being provided as having a first gap between the first splitter and the separator, the seperated first component being incident in the first splitter via the first gap;
• a second polarization beam splitter having a second splitting plane and being provided as having a second gap between the second splitter and the separator, the separated second and third components being incident in the second splitter via the second gap;
• and
• a light-beam combiner having a combining plane and being provided as having a third gap between the combiner and the first splitter and a fourth gap between the combiner and the second splitter, the combiner combining the first component emitted from the first splitter and incident in the combiner via the third gap and the second and third components emitted from the second splitter and incident in the combiner via the fourth gap,
• wherein the separating plane, the first and second splitting planes and the combining plane intersect each other like a character-“X”;
• and one of the first to fourth gaps is an air gap whereas the remaining three gaps are filled with an optical joint material.