US 7,554,708 B2
Optical scanning device and image forming apparatus
Kohji Sakai, Tokyo (Japan); Yoshinori Hayashi, Kanagawa (Japan); and Daisuke Ichii, Kanagawa (Japan)
Assigned to Ricoh Company, Ltd., Tokyo (Japan)
Filed on Aug. 22, 2008, as Appl. No. 12/230,077.
Application 12/230077 is a division of application No. 11/714162, filed on Mar. 06, 2007, granted, now 7,443,558.
Claims priority of application No. 2006-067323 (JP), filed on Mar. 13, 2006; and application No. 2006-074457 (JP), filed on Mar. 17, 2006.
Prior Publication US 2009/0002792 A1, Jan. 01, 2009
Int. Cl. G02B 26/08 (2006.01)
U.S. Cl. 359—205 11 Claims
OG exemplary drawing
 
1. An optical scanning device comprising:
a first optical element that converts a cross-section shape of a light beam from a semiconductor laser to a desired shape;
a second optical element that guides the light beam output from the first optical element to an optical deflector that deflects the light beam; and
a third optical element that gathers the light beam deflected by the optical deflector onto a surface to be scanned to form a light spot thereby optically scanning the surface, wherein
at least one of lenses forming the first optical element and the second optical element includes a resin-made lens, at least one of resin-made lenses satisfies conditions (1) to (4):
(1) only one surface of the resin-made lens has a diffracting surface
|P3|≧|P1+P2|  (2)
|P1|>|P1+P2|and |P2|≧|P1+P2|  (3)
P1ΔP3>0   (4 )
where P1 is a power in any of a main scanning direction and a sub-scanning direction of a diffracting portion on a diffracting surface of the resin-made lens, P2 is a power of a refractive portion on the diffracting surface in the direction defined in P1, and P3 is a power on a surface other than the diffracting surface of the resin-made lens in the direction defined in P1.