Scanning optical system using parallel plate to eliminate ghost images
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorJunji Kamikubo
Life of this patent
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Abstract
A scanning optical system includes a polygonal mirror, enclosed in a housing, which deflects light. The housing is provided with a transparent plane-parallel plate, parallel to a reflecting surface of the polygonal mirror, through which a laser light source emits a laser beam into the housing. An image forming optical system, provided between the polygonal mirror and an objective surface to be scanned, has a power at least in a main scanning direction. The laser beam is made incident on the polygonal mirror in a direction inclined toward a sub-scanning direction, with respect to a direction perpendicular to the reflecting surface of the polygonal mirror.
Claims2
A reflection type scanning optical system, comprising:
- a deflector which deflects light;
- a housing in which said deflector is enclosed, said housing having a transparent plane-parallel plate;
- a laser light source which emits a laser beam onto said deflector through said transparent plane-parallel plate at a predetermined incident angle in a sub-scanning direction;
- and
- a curved mirror having a curvature at least in a main scanning direction to reflect said light deflected by said deflector at a predetermined reflection angle with respect to a direction of incidence of said light,
- wherein said laser beam is made incident on said deflector at an angle "a" with respect to a center scanning line in a main scanning plane;
- said plane-parallel plate of said housing being inclined so that a line normal to said plane-parallel plate defines an angle "b", with respect to an incident direction of the light in said main scanning plane;
- and
- the following relationships are satisfied:
- .vertline.a+2 b .vertline.>.theta. (1)
- .theta.>.vertline.a.vertline.>0 (2)
- wherein .theta. represents a half scanning angle in said main scanning direction.
Dependencies are inferred from the claim text.