Optical scanning device, optical scanning method, and image forming apparatus

A method of optical scanning comprising:

• providing an optical scanning device including
• a laser light source that emits a laser beam;
• a light deflector that deflects the laser beam;
• a scan-imaging optical system that focuses the laser beam deflected from the light deflector on a scanning surface to optically scan the scanning surface;
• a diffractive optical element receives the laser beam and diffracts a portion of the laser beam as a diffracted light;
• and
• a detecting unit that detects the diffracted light, wherein
• the laser light source is a surface-emitting laser light source,
• the diffractive optical element is made of plastic material having a linear expansion coefficient within a temperature variation range of the optical scanning device nearly equal to a rate of wavelength change of an emission wavelength of the laser light source within the temperature variation range;
• and
• optically scanning the scanning surface by using the optical scanning device such that a diffraction angle of a diffracted light that is detected by a light-detector for diffracted-light detection is not actually changed within a temperature variation range of the optical scanning device.

An image forming apparatus comprising an optical scanning device, the optical scanning device including

• a laser light source that emits a laser beam;
• a light deflector that deflects the laser beam;
• a scan-imaging optical system that focuses the laser beam deflected from the light deflector on a scanning surface to optically scan the scanning surface;
• a diffractive optical element receives the laser beam and diffracts a portion of the laser beam as a diffracted light;
• and
• a detecting unit that detects the diffracted light,
• wherein
• the laser light source is a surface-emitting laser light source,
• the diffractive optical element is made of plastic material having a linear expansion coefficient within a temperature variation range of the optical scanning device nearly equal to a rate of wavelength change of an emission wavelength of the laser light source within the temperature variation range.