Scanning optical system

A scanning optical system, comprising:

• a laser source unit that emits a plurality of laser beams;
• a deflector that dynamically deflects the plurality of laser beams incident on a reflection surface in a main scanning direction, the plurality of laser beams being incident on the reflection surface along different paths in an auxiliary scanning direction which is perpendicular to the main scanning direction;
• and
• an imaging optical system that converges the dynamically deflected plurality of laser beams on a plurality of surfaces, which correspond to the plurality of laser beams, respectively,
• wherein the imaging optical system includes:
• a scanning lens group having at least one anamorphic aspherical surface on which the dynamically deflected plurality of laser beams are incident, a cross sectional shape, in the main scanning direction, of the anamorphic aspherical surface being defined as a function of a distance in the main scanning direction from a reference axis thereof, a cross sectional shape, in the auxiliary scanning direction, of the anamorphic aspherical surface being defined, independent of the cross sectional shape in the main scanning direction, as a function of a distance from the reference axis thereof;
• and
• a plurality of long lenses on which the plurality of laser beams passed through the scanning lens group being incident, respectively, all of the plurality of long lenses having the same optical surfaces, at least one surface of each of the plurality of long lenses being a two-dimensional polynomial aspherical surface, cross sectional shapes, in the main scanning direction and auxiliary scanning direction, of the two-dimensional polynomial aspherical surface being defined by a polynomial regarding a distance from a reference axis thereof, and
• wherein the plurality of long lenses are arranged such that the reference axes of the plurality of long lenses are inclined with respect to the reference axis of the scanning lens group at different angles depending on the incident angles, in the auxiliary scanning direction, of the laser beams that pass through the plurality of long lenses, respectively.