Optical beam scanning device, optical beam scanning method

An optical beam scanning device configured to shape a divergent light from a light source into a light flux having a specified sectional shape by a pre-deflection optical system and to guide the light flux, which is shaped by the pre-deflection optical system and is deflected and scanned in a main scanning direction by a rotation deflector, to a photosensitive surface of a photosensitive body by a post-deflection optical system, wherein

• the pre-deflection optical system includes a first optical element which is an optical element including a diffraction grating formed on at least one of a light flux incident surface and a light flux outgoing surface and in which a main light beam of the light flux guided in the pre-deflection optical system passes along an optical axis of the optical element, and
• the post-deflection optical system includes at least one second optical element which is an optical element including a diffraction grating formed on at least one of a light flux incident surface and a light flux outgoing surface and in which a main light beam of the light flux from the pre-deflection optical system is incident on an incident position different from an optical path of an optical axis of the post-deflection optical system in a sub-scanning direction orthogonal to the main scanning direction.

An optical beam scanning method to shape a divergent light from a light source into a light flux having a specified sectional shape by a pre-deflection optical system and to guide the light flux, which is shaped by the pre-deflection optical system and is deflected and scanned in a main scanning direction by a rotation deflector, to a photosensitive surface of each of a plurality of photosensitive bodies by a post-deflection optical system, wherein

• the light flux is guided in the pre-deflection optical system by a first optical element which is an optical element including a diffraction grating formed on at least one of a light flux incident surface and a light flux outgoing surface and in which a main light beam of the light flux guided in the pre-deflection optical system passes along an optical axis of the optical element, and
• the light flux is guided in the post-deflection optical system by at least one second optical element which is an optical element including a diffraction grating formed on at least one of a light flux incident surface and a light flux outgoing surface and in which main light beams of light fluxes to be guided to the respective plurality of photosensitive bodies are incident on incident positions different from each other in a sub-scanning direction orthogonal to the main scanning direction.