Multi-beam scanning optical apparatus and image forming apparatus using the same

Abstract

A multi-beam scanning optical apparatus includes an incident optical system for making a plurality of light beams emitted from light source means having a plurality of light emitting portions incident on a deflector, and a scanning optical system for forming images of the plurality of light beams deflected by the deflector on a surface to be scanned. The scanning optical system has at least one scanning optical element made of a resin. The scanning optical element made of the resin has birefringence due to a stress distribution generated upon cooling in a molding process thereof such that the directions of principal axes of birefringence at one end portion of the scanning optical element are different from those at the other end portion, opposite to the one end portion with respect to an optical axis thereof in a main scanning direction, of the scanning optical element. An interval between adjacent scanning lines formed on the scanning surface by the plurality of light beams whose images are formed on the scanning surface through the scanning optical element made changes in the main scanning direction in an effective scanning region. In the apparatus, a sub-scanning interval error between the scanning lines due to a polarization angle difference between the light beams emitted from the plurality of light emitting portions is so set as to be not more than ⅕ of a desired scanning line interval.

1 .- 18 . (canceled)  
   
   
       19 . An image forming apparatus comprising: 
 a multi-beam scanning optical apparatus according to any one of claims  38  or  39 ;    a photosensitive member disposed in the scanned surface;    a developer for developing, as a toner image, an electrostatic latent image formed on said photosensitive member by light beams scanned by said multi-beam scanning optical apparatus;    a transfer device for transferring the developed toner image onto a recording medium; and    a fixing device for fixing the transferred toner image on the recording medium.    
   
   
       20 . An image forming apparatus comprising: 
 a multi-beam scanning optical apparatus according to any one of claims  38  or  39 ; and    a printer controller for converting code data received from an external device into an image signal and inputting the image signal to said scanning optical apparatus.    
   
   
       21 .- 37 . (canceled)  
   
   
       38 . A multi-beam scanning optical apparatus comprising: 
 light source means having a plurality of light emitting portions, the light emitting portions emitting a plurality of light beams whose polarization directions are neither parallel nor orthogonal with each other;    incident optical means for carrying the plurality of light beams emitted from the light emitting portions of said light source means onto deflection means; and    scanning optical means for forming images of the plurality of light beams deflected by deflection means on a surface to be scanned, said scanning optical means having at least one scanning optical element made of a resin; and    polarized light limiting means inserted into an optical path between said light source means and the scanning optical element.    
   
   
       39 . A multi-beam scanning optical apparatus comprising: 
 light source means having a plurality of light emitting portions to emit a plurality of light beams;    incident optical means for carrying the plurality of light beams emitted from the light emitting portions of said light source means onto deflection means; and    scanning optical means for forming images of the plurality of light beams deflected by deflection means on a surface to be scanned, said scanning optical means having at least one scanning optical element made of a resin; and    adjustment means for independently adjusting polarization directions of the light beam emitted from the plurality of light emitting portions.