Patent ID: 7330293

Claim:
An optical scanning unit comprising: a light source that produces and emits at least one beam; a beam deflector that deflects and scans the beam emitted by the light source in a main scanning direction of an exposed object; and a planar optical system (POS) comprising an entrance face and an exit face that is disposed in an optical path between the light source and the exposed object and is adapted to secure an optical path length of an incident beam and to reduce the space occupied by the optical scanning unit, by reflecting the incidence beam in a plane a plurality of times in a different direction from that in which the beam is emitted from the light source, such that a difference between a first width (W 1 ) between front and rear edges of the scanned beam entering the entrance face of the POS and a second width (W 2 ) between front and rear edges of the scanned beam exiting the exit face of the POS is increased.