Diffractive optical element and scanning optical apparatus using the same
AssigneeCanon Kabushiki Kaisha
InventorManabu Kato
Life of this patent
Estimating the term…
Abstract
Diffraction optical element used in a scanning optical apparatus as a scanning optical element has a diffraction grating formed on a substrate. The diffraction grating has a tilt portion for generating a power and a wall portion connecting one end portion of the tilt portion to the substrate. The wall portion is tilted within a predetermined range with respect to a normal of the substrate surface. The tilt angle of the wall portion of the diffraction grating with respect to the normal of the substrate continuously changes to increase as a distance away from an optical axis of the diffraction optical element becomes large.
Claims25
A diffractive optical element to be used in a scanning optical apparatus comprising:
- a diffraction grating formed on a substrate surface and having a tilt portion for generating power and a wall portion connecting one end portion of said tilt portion to the substrate, said wall portion being tilted with respect to a normal to the substrate surface toward such a direction that the diffraction efficiency in said wall portion is increased, and said diffractive optical element having different powers in main scanning and sub-scanning directions of the scanning optical apparatus.
A scanning optical apparatus comprising:
- a light source;
- a deflection element for deflecting a light beam emitted by said light source;
- and
- a scanning optical element for forming an image of the light beam deflected by said deflection element on a surface to be scanned,
- wherein said scanning optical element comprises at least one diffractive optical element having a diffraction grating, said diffraction grating being formed on a substrate surface and having a tilt portion for generating power and a wall portion connecting one end portion of said tilt portion to the substrate, said wall portion being tilted with respect to a normal to the substrate surface by a tilt angle θe, and the tilt angle being smaller near an optical axis of said diffractive optical element than in an off-axis region such that lowering of the diffraction efficiency in an off-axis region is alleviated.
A scanning optical apparatus comprising:
- a light source;
- a deflection element for deflecting a light beam emitted by said light source;
- and
- a scanning optical element for forming an image of the light beam deflected by said deflection element on a surface to be scanned,
- wherein said scanning optical element comprises at least one diffractive optical element having a diffraction grating, said diffraction grating being formed on a substrate surface and having a tilt portion for generating power and a wall portion connecting one end portion of said tilt portion to the substrate, said wall portion being tilted with respect to a normal to the substrate surface toward such a direction that the diffraction efficiency in said wall portion is increased, and said diffractive optical element having different powers in main scanning and sub-scanning directions.
A scanning optical apparatus comprising:
- a light source;
- a deflection element for deflecting a light beam emitted by said light source;
- and
- a scanning optical element for forming an image of the light beam deflected by said deflection element on a surface to be scanned,
- wherein said scanning optical element comprises at least one diffractive optical element having a diffration grating, said diffration grating being formed on a substrate surface and having a tilt portion for generating power and a wall portion connecting one end portion of said tilt portion to the substrate, said wall portion being tilted with respect to a normal to the substrate surface by a tilt angle θe, and the tilt angle being smaller near an optical axis of said diffractive optical element than in an off-axis region, and
- wherein a tilt angle θe of said wall portion of said diffration grating with respect to the normal to the substrate surface satisfies
- tan−1(h/P)≦θe≦tan−1(h/P)+10°
- where h is a depth of said diffraction grating, and P is a grating pitch.
A diffractive optical element having a diffraction grating, said diffraction grating being formed on a substrate surface and having a tilt portion for generating power and a wall portion connecting one end portion of said tilt portion to the substrate, said wall portion being tilted with respect to a normal to the substrate surface by a tilt angle θe, and the tilt angle being smaller near an optical axis of said diffractive optical element than in an off-axis region,
- wherein the tilt angle θe of said wall portion of said diffraction grating with respect to the normal to the substrate surface satisfies
- tan −1(h/P)≦θe≦tan−1(h/P)+10°
- where h is a depth of said diffraction grating, and P is a grating pitch.
Dependencies are inferred from the claim text.