Abstract: A centrifugal fan introducing air via an inlet port in a direction of a rotation axis and discharging the air via an outlet port in the a direction of a centrifugal force produced by rotation includes: an impeller having a plurality of vanes around the rotation axis; and a housing including the inlet port and supporting the impeller such that the impeller is allowed to freely rotate in the housing. An inclined portion is formed at least at a part of edge portion of the inlet port, the inclined portion widening to the side that the impeller is disposed.

Abstract: An optical device comprises a light source unit comprising a plurality of light sources, a light mixing unit that is formed on the light source unit and comprises a light guiding part guiding light emitted from each light source, and a light mixing part mixing the guided light. A supporter supports the light mixing unit to be spaced from the light source unit. A small-sized optical device is provided having an enhanced light efficiency and a projection system having the same.