SCANNING OPTICAL APPARATUS

摘要

In a scanning optical apparatus, an illumination optical system has a diffractive power φdM and a refractive power φnM in a main scanning direction, and a ratio φnM/φdM in the main scanning direction for a focal length fi in a range of 10-22 mm satisfies: g2(fi)≦φnM/φdM≦g1(fi), where A(Z)=(1.897×107)Z2+6744Z+0.5255, B(Z)=(2.964×107)Z2+5645Z+0.6494, C(Z)=(3.270×107)Z2+3589Z+0.5250, D(Z)=(5.016×107)Z2+4571Z+0.8139, g1(fi)=fi{D(Z)−B(Z)}/12−5D(Z)/6+11B(Z)/6, g2(fi)=fi{C(Z)−D(Z)}/12−5C(Z)/6+11A(Z)/6.

主权项

1. A scanning optical apparatus comprising:
a light source; a deflector configured to deflect a beam of light from the light source in a main scanning direction; an illumination optical system disposed between the light source and the deflector and configured to convert the beam of light emitted from the light source into a beam of light slightly converging in the main scanning direction and focused near the deflector in a sub-scanning direction; and a scan lens configured to cause the beam of light deflected by the deflector to be focused into a dot-like image on a target surface to be scanned, wherein the scan lens satisfies:
0.2≦1−s′/fm≦0.5where s′ is a distance from an image-space principal point in the main scanning direction to an image point, and fm is a focal length in the main scanning direction,
wherein the illumination optical system has at least one rotation-symmetric diffractive surface and at least one anamorphic refractive surface, the illumination optical system having a focal length fi [mm] in the main scanning direction, which satisfies:
10≦fi≦22; wherein a ratio mM/mS of a lateral magnification mM in the main scanning direction to a lateral magnification mS in the sub-scanning direction, of an entire optical system which includes the illumination optical system and the scan lens, satisfies:
mM/mS≧1.38; wherein a holding member provided to retain a distance between the light source and the illumination optical system has a coefficient Z of linear expansion [1/K] which satisfies:
3.05×10−5≦Z≦9.50×10−5; wherein the illumination optical system has a refractive power φnM in the main scanning direction and a diffractive power φdM in the main scanning direction, and a ratio φnM/φdM of the refractive power φnM to the diffractive power φdM in the main scanning direction satisfies:
g2(fi)≦φnM/φdM≦g1(fi)where A(Z)=(1.897×107)Z2+6744Z+0.5255, B(Z)=(2.964×107)Z2+5645Z+0.6494, C(Z)=(3.270×107)Z2+3589Z+0.5250, D(Z)=(5.016×107)Z2+4571Z+0.8139, g1(fi)=fi{D(Z)−B(Z)}/12−5D(Z)/6+11B(Z)/6, g2(fi)=fi{C(Z)−D(Z)}/12−5C(Z)/6+11A(Z)/6.