# US 6,724,534 B2 · Diffractive optical element and scanning optical apparatus using the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,724,534 B2 - Document ID: US6724534B2 - Status: Granted - Kind: B2 - Application number: 09/871,643 - Filed: 2001-06-04 - Published: 2001-10-25 - Granted: 2004-04-20 - Earliest claimed: 1998-05-25 - Assignees: Canon Kabushiki Kaisha - Inventors: Manabu Kato - Web page: https://patentgrep.com/patent/US6724534B2 ## CPC - G02B 27/4227: {in image scanning systems} - G02B 13/0005: {having F-Theta characteristic (scanning systems employing movable or deformable optical elements G02B26/10)} - G02B 27/0037: {with diffracting elements (G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876)} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## 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. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) An element according to claim 1, wherein a 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. ### Claim 3 (depends on 1) An element according to claim 1, wherein a tilt angle θe of said wall portion of said diffraction grating with respect to the normal to the substrate surface continuously changes to increase as a distance from an optical axis of said diffractive optical element becomes large. ### Claim 4 (depends on 1) An element according to claim 1, wherein said diffraction grating is formed on a glass substrate by a replica process. ### Claim 5 (depends on 1) An element according to claim 1, wherein said diffractive optical element is manufactured by integrally forming said substrate and said diffraction grating from a plastic material by injection molding. ### Claim 6 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. ### Claim 7 (depends on 6) An apparatus according to claim 6, wherein the tilt angle θe changes to increase as a distance from the optical axis of said diffractive optical element becomes larger. ### Claim 8 (depends on 6) An apparatus according to claim 6, wherein the tilt angle θe changes to increase intermittently as a distance from the optical axis of said diffractive optical element becomes larger. ### Claim 9 (depends on 6) An apparatus according to claim 6, wherein said diffractive optical element has different powers in main scanning and sub-scanning directions. ### Claim 10 (depends on 6) An apparatus according to claim 6, wherein the diffraction grating is formed on a side of the surface to be scanned of said diffractive optical element. ### Claim 11 (depends on 6) An apparatus according to claim 6, wherein said diffractive optical element is manufactured by forming said diffraction grating on a glass substrate by a replica process. ### Claim 12 (depends on 6) An apparatus according to claim 6, wherein said diffractive optical element is manufactured by integrally forming the substrate and said diffraction grating from plastic material by injection molding. ### Claim 13 (depends on 6) An apparatus according to claim 6, further comprising a refractive optical element, wherein said refractive optical element comprises a toric lens made of plastic and has different powers in main scanning and sub-scanning directions. ### Claim 14 (depends on 6) An apparatus according to claim 6, wherein said substrate surface comprises a flat surface or a curved surface. ### Claim 15 (depends on 6, 7, 8, 9, 10, 11, 12, 13, 14) An image forming apparatus including a scanning optical apparatus as defined in any of claims 6-14. ### Claim 16 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. ### Claim 17 (depends on 16) An apparatus according to claim 16, wherein said diffraction grating is formed on a side of the surface to be scanned of said diffractive optical element. ### Claim 18 (depends on 16) An apparatus according to claim 16, wherein a 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. ### Claim 19 (depends on 16) An apparatus according to claim 16, wherein said diffractive optical element is manufactured by forming said diffraction grating on a glass substrate by a replica process. ### Claim 20 (depends on 16) An apparatus according to claim 16, wherein said diffractive optical element is manufactured by integrally forming the substrate and said diffraction grating from plastic material by injection molding. ### Claim 21 (depends on 16) An apparatus according to claim 16, further comprising a refractive optical element, wherein said refractive optical element comprises a toric lens made of plastic and having different powers in main scanning and sub-scanning directions. ### Claim 22 (depends on 16) An apparatus according to claim 16, wherein the substrate surface comprises a flat surface or a curved surface. ### Claim 23 (depends on 16, 17, 18, 19, 20, 21, 22) An image forming apparatus including a scanning optical apparatus as defined in any of claims 16-22. ### Claim 24 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. ### Claim 25 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.