Optical beam scanning device restraining beam position error due to temperature change with diffraction grating and image forming apparatus using the same

An optical beam scanning device that shapes a diverging ray from a light source to be a light beam having a predetermined sectional shape in a pre-deflection optical system including plural optical elements and deflects the light beam shaped by the pre-deflection optical system with a rotating deflector to cause the light beam to scan in a main scanning direction, wherein

• the pre-deflection optical system has optical elements arranged between the light source and reflecting surfaces of the rotating deflector in a light beam traveling direction and having negative power,
• among the plural optical elements forming the pre-deflection optical system, in at least one optical element in which a principal ray of the light beam from the light source is made incident on a position of incidence different from an optical path of an optical axis of the pre-deflection optical system in a sub-scanning direction orthogonal to the main scanning direction, a diffraction grating is formed on at least one of a plane of beam incidence and a plane of beam exit in the optical element, and
• the optical element having the diffraction grating formed therein has a curvature radius of a plane of incidence set larger than a curvature radius of a plane of exit.

An optical beam scanning device that shapes respective diverging rays from plural light sources to be light beams having a predetermined sectional shape in a pre-deflection optical system including plural optical elements and deflects the light beams shaped by the pre-deflection optical system with a rotating deflector to cause the light beams to scan in a main scanning direction, wherein

• the pre-deflection optical system has optical elements arranged between the light source and reflecting surfaces of the rotating deflector in a light beam traveling direction and having negative power acting on all light beams,
• among the plural optical elements forming the pre-deflection optical system, in at least one optical element in which principal rays of respective light beams from the plural light sources are made incident on positions of incidence different from each other in a sub-scanning direction orthogonal to the main scanning direction, a diffraction grating is formed on at least one of a plane of beam incidence and a plane of beam exit in the optical element, and
• the optical element having the diffraction grating formed thereon has a plane of incidence formed as a convex surface and a plane of exit formed as a concave surface.

An optical beam scanning device that shapes respective diverging rays from plural light sources to be light beams having a predetermined sectional shape in a pre-deflection optical system including plural optical elements and deflects the light beams shaped by the pre-deflection optical system with a rotating deflector to cause the light beams to scan in a main scanning direction, wherein

• the pre-deflection optical system has optical elements arranged between the light source and reflecting surfaces of the rotating deflector in a light beam traveling direction and having negative power acting on all light beams,
• among the plural optical elements forming the pre-deflection optical system, in at least one optical element in which principal rays of respective light beams from the plural light sources are made incident on positions of incidence different from each other in a sub-scanning direction orthogonal to the main scanning direction, a diffraction grating is formed on at least one of a plane of beam incidence and a plane of beam exit in the optical element, and
• the optical element having the diffraction grating formed thereon has a curvature radius of a plane of incidence set larger than a curvature radius of a plane of exit.