Plastic optical element and optical scanner and imaging forming device including the same

Abstract

A plastic optical element for an optical system of an optical scanner includes a plurality of optical effective portions through which a plurality of light beams transmit, respectively, formed on at least one of an incidence surface and an exit surface in a sub scan direction, and an optical ineffective portion formed between neighboring optical effective portions not to allow the light beams to transmit therethrough, and including an area in which a local contraction occurs at a time of resin molding.

1 . A plastic optical element for an optical system of an optical scanner comprising:
 a plurality of optical effective portions through which a plurality of light beams transmit, respectively, formed on at least one of an incidence surface and an exit surface in a sub scan direction; and   an optical ineffective portion formed between neighboring optical effective portions not to allow the light beams to transmit therethrough, and including an area in which a local contraction occurs at a time of resin molding,   wherein the optical ineffective portion is set to have a length in the sub scan direction to satisfy the following relation:
     Y> 0.3*( a*b )/( a+b )−1.1
 
   where Y is the length of the optical ineffective portion in the sub scan direction, a is a thickness of the plastic optical element in the sub scan direction, and b is a thickness of the plastic optical element along an optical axis.   
     
     
         2 . (canceled) 
     
     
         3 . The plastic optical element according to  claim 1 , wherein
 the optical ineffective portion is formed by surface processing to have a reflectivity lower than that of the optical effective portions.   
     
     
         4 . The plastic optical element according to  claim 1 , further comprising:
 a concave portion on at least either of two edge surfaces in the sub scan direction.   
     
     
         5 - 7 . (canceled)