Patent ID: 8777422

Claim:
An illumination optical system comprising: a light source device comprising: a red light-emitting device that emits red light; a blue light-emitting device that emits blue light; and a fluorescence plate comprising a green fluorescence region and a light transmission region, wherein the green fluorescence region is excited by the blue light to emit green light, and the light transmission region transmits the blue light; a light guide comprising a dichroic layer therein, wherein the dichroic layer is arranged so as to intersect a center axis of the light guide at about 45 degrees to transmit the blue light while reflecting the green light and the red light; and a mirror group and a lens group, which guide the red light, the blue light and the green light to the light guide, such that the blue light transmitted through the light transmission region is incident on an end surface of the light guide, and the red light and the green light are incident on a side surface of the light guide, wherein the blue light-emitting device is a blue laser diode, wherein the red-light emitting device is a red light-emitting diode, wherein a diffusing member is provided on the end surface of the light guide, wherein the blue light transmitted by the light transmission region is incident on the diffusing member, travels in the light guide along the center axis of the light guide, and then is transmitted by the dichroic layer, and wherein the red light and the green light are incident on the side surface of the light guide such that an optical axis of the red light corresponds to an optical axis of the green light, and then are reflected by the dichroic layer.