Illumination optical system and a projector using the same

An illumination optical system comprising:

• a laser light source that generates an excitation light;
• a fluorescent substance that generates a fluorescent light in response to the excitation light;
• a light tunnel that outputs the excitation light input at one end thereof to said fluorescent substance from the other end thereof, and that outputs the fluorescent light generated by said fluorescent substance from the one end thereof;
• and a mirror that is placed within a light path between said laser light source and said light tunnel, and that reflects the fluorescent light, said mirror having an aperture formed thereon that allows the excitation light to pass through, the fluorescent light being reflected by a part of the mirror which is different than the aperture;
• wherein the part of the mirror which is different from the aperture prevents the excitation light from passing therethrough.