Optical scanning device in image forming apparatus

An optical scanning device comprising:

• a light source that emits a light beam;
• a first optical system that guides the light beam emitted by the light source;
• an optical deflector that deflects the light beam guided by the first optical system;
• and
• a second optical system that converges the light beam deflected by the optical deflector on a surface to be scanned, wherein
• the first optical system includes at least one resin lens having a diffractive surface,
• the second optical system includes at least one resin optical element, and
• a beam diameter depth in a sub-scanning direction, Ws, that can have a maximum intensity of 1/e2, satisfies conditions
• Δs1+Δs2+Δs3−Δd1×(β1×β2)2<Ws/40 (4)
• Δd1>0 and Δs2+Δs2<0 (5)
• where, Δs1 is a beam waist position shift in the sub-scanning direction due to a change in the power in the refracting unit when the temperature in the first optical system rises by 1° C., Δs2 is a beam waist position shift in the sub-scanning direction due to a change in the power in the diffracting unit when the temperature in the first optical system rises by 1° C., Δs3 is a beam waist position shift in the sub-scanning direction when the temperature in the second optical system rises by 1° C., Δd1 is a shift in the distance between a forward principal point in a main scanning direction of the first optical system and the light source when the temperature in the first optical system rises by 1° C., β1 is a lateral magnification of the first optical system in the sub-scanning direction, and β2 is a lateral magnification of the second optical system in the sub-scanning direction.

An optical scanning device comprising:

• a light source that emits a light beam;
• a coupling lens that shapes the light beam into a beam pattern;
• an anamorphic optical element that guides the light beam shaped by the coupling lens;
• an optical deflector that deflects the light beam guided by the anamorphic optical element;
• and
• a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein
• the scanning optical system includes more than one resin lens,
• the anamorphic optical element is a resin lens having a first surface and a second surface, the first surface being rotationally symmetric having formed thereon a concentric circular power diffractive surface, the second surface having formed thereon a power diffractive surface that converts the light beam emitted from the light source into a parallel light beam in a main scanning direction and into a convergent light beam in a sub-scanning direction, and
• the power of the power diffractive surface is set so that a beam waist position shift in a main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.

An optical scanning device comprising:

• a light source that emits a light beam;
• a coupling lens that shapes the light beam into a beam pattern;
• an anamorphic optical element that guides the light beam shaped by the coupling lens;
• an optical deflector that deflects the light beam guided by the anamorphic optical element;
• and
• a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein
• the scanning optical system includes more than one resin lens,
• the anamorphic optical element is an anamorphic resin lens having a first surface and a second surface, the first surface being anamorphic refractive surface, the second surface bearing thereon a power diffractive surface having an axis in a main scanning direction, and
• the power of the power diffractive surface is set so that a beam waist position shift in the main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.

An image forming apparatus comprising an optical scanning device that includes a light source that emits a light beam;

• a first optical system that guides the light beam emitted by the light source;
• an optical deflector that deflects the light beam guided by the first optical system;
• and
• a second optical system that converges the light beam deflected by the optical deflector on a surface to be scanned, wherein
• the first optical system includes at least one resin lens having a diffractive surface,
• the second optical system includes at least one resin optical element, and
• a beam diameter depth in a main scanning direction, Wm, that can have a maximum intensity of 1/e2, satisfies conditions
• Δm1+Δm2+Δm3−Δd1×(f2/f1)2<Wm/40 (1)
• Δd1>0 and Δm2<0 (2)
• where, Δm1 is a beam waist position shift in the main scanning direction due to a change in the power in a refracting unit when the temperature in the first optical system rises by 1° C., Δm2 is a beam waist position shift in the main scanning direction due to a change in the power in the diffracting unit when the temperature in the first optical system rises by 1° C., Δm3 is a beam waist position shift in the main scanning direction when the temperature in the second optical system rises by 1° C., Δd1 is a shift in the distance between a forward principal point of the first optical system in the main scanning direction and the light source when the temperature in the first optical system rises by 1° C., f1 is a focal distance of the first optical system in the main scanning direction, and f2 is a focal distance of the second optical system in the main scanning direction.

An image forming apparatus comprising at least one image forming device that includes

• a photosensitive image bearing unit;
• an optical scanning unit that scan a surface of the image bearing unit with a light beam to thereby forming a latent image on the image bearing unit;
• and
• a developing unit that develops the latent image on the image bearing unit into a visual image, wherein
• the optical scanning unit includes
• a light source that emits a light beam;
• a coupling lens that shapes the light beam into a beam pattern;
• an anamorphic optical element that guides the light beam shaped by the coupling lens;
• an optical deflector that deflects the light beam guided by the anamorphic optical element;
• and
• a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein
• the scanning optical system includes more than one resin lens,
• the anamorphic optical element is a resin lens having a first surface and a second surface, the first surface being rotationally symmetric having formed thereon a concentric circular power diffractive surface, the second surface having formed thereon a power diffractive surface that converts the light beam emitted from the light source into a parallel light beam in a main scanning direction and into a convergent light beam in a sub-scanning direction, and
• the power of the power diffractive surface is set so that a beam waist position shift in a main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.

An image forming apparatus comprising:

• a photosensitive image bearing unit;
• an optical scanning unit that scan a surface of the image bearing unit with a light beam to thereby forming a latent image on the image bearing unit;
• and
• a developing unit that develops the latent image on the image bearing unit into a visual image, wherein
• the optical scanning unit includes
• a light source that emits a light beam;
• a coupling lens that shapes the light beam into a beam pattern;
• an anamorphic optical element that guides the light beam shaped by the coupling lens;
• an optical deflector that deflects the light beam guided by the anamorphic optical element;
• and
• a scanning optical system that converges the light beam deflected by the optical deflector on a surface to be scanned to form a laser spot, wherein
• the scanning optical system includes more than one resin lens,
• the anamorphic optical element is an anamorphic resin lens having a first surface and a second surface, the first surface being anamorphic refractive surface, the second surface bearing thereon a power diffractive surface having an axis in a main scanning direction, and
• the power of the power diffractive surface is set so that a beam waist position shift in the main scanning direction or a sub-scanning direction or both the main scanning direction and the sub-scanning direction, caused by mode hopping or temperature variation in the semiconductor laser device is substantially zero.