WPAT, P.C.
Two-element fθ lens with short focal distance for laser scanning unit
A two-element fθ lens with short focal distance is used for a laser scanning unit with a polygon mirror and the two-element fθ lens comprises a first lens and a second lens. The first lens is a positive power meniscus lens and the second lens is a negative power meniscus lens in the main scanning direction. The first lens has a first and a second optical surface, the second lens has a third and a fourth optical surface. Concave surfaces of the first, second and third optical surfaces are disposed on the polygon mirror side. The fourth optical surface has an inflection point in SAG counted from the optical axis to peripheral portion and its paraxial portion is convex that is disposed on the polygon mirror side. The two-element fθ lens satisfies an optical condition of 0.4557≦tan(β)≦0.7265, wherein β is a maximum effective window angle.
E-Pin Optical Industry Co., Ltd.
G G H
G02B G02B H04N
inventional inventional inventional
San-Woei Huang-Chang Chih-Peng
Shyu Chen Wang