Optical scanning apparatus

摘要

An optical scanning apparatus has a first scanning optical element having a negative power in a sub-scanning direction. A first light beam and a second light beam enter the first scanning optical element through points of an input surface on a same side of a reference surface, which includes an optical axis of the first scanning optical element and being parallel to a main-scanning direction. The second light beam makes a greater angle with the reference surface than the first light beam. A first angle between the reference surface and a principal ray of a first ghost light beam is greater than a second angle between the reference surface and a principal ray of a first normal light beam and is smaller than a third angle between the reference surface and a principal ray of a second normal light beam.

主权项

1. An optical scanning apparatus comprising:
a light source configured to emit a plurality of light beams including a first light beam and a second light beam; a deflector configured to deflect the plurality of light beams in a main-scanning direction; and a scanning optical element group configured to focus the deflected light beams on a plurality of surfaces to be scanned, wherein: the scanning optical element group includes a first scanning optical element having an input surface and an output surface and having a negative power in a sub-scanning direction, the plurality of light beams entering the first scanning optical element through the input surface and exiting the first scanning optical element through the output surface; the first light beam and the second light beam enter the first scanning optical element through points of the input surface on a same side of a reference surface including an optical axis of the first scanning optical element and being parallel to the main-scanning direction; when the first light beam and the second light beam entering through points of the incident surface located at a same position in the main-scanning direction are compared with each other, an angle between the reference surface and a principal ray of the second light beam is greater than an angle between the reference surface and a principal ray of the first light beam; and when the first light beam and the second light beam entering through points of the incident surface located at a same position in the main-scanning direction are compared with each other, a first angle between the reference surface and a principal ray of a first ghost light beam is greater than a second angle between the reference surface and a principal ray of a first normal light beam and is smaller than a third angle between the reference surface and a principal ray of a second normal light beam, the first ghost light beam being a part of the first light beam exiting through the output surface after being reflected by the output surface and the input surface, the first normal light beam being another part of the first light beam exiting through the output surface without being reflected by either of the input surface and the output surface, the second normal light beam being a part of the second light beam exiting through the output surface without being reflected by either of the input surface and the output surface.