Diffraction optical element, optical scanner, and image forming apparatus

Abstract

To reduce a defect in the shape of a diffraction surface along with release of a mold, in a diffraction optical element in which the direction of a reference axis of the diffraction surface and a release direction are different from each other.SOLUTION: A diffraction optical element is manufactured by a manufacturing method including a step of molding resin material by using a mold to obtain a diffraction surface, and a step of releasing the resin material from the mold in a first direction. The diffraction surface includes a plurality of lattice planes contributing to diffraction, and a plurality of lattice wall surfaces each provided between the lattice planes adjacent to each other, and a reference axis of the diffraction surface is not parallel to the first direction. On a section including the reference axis, when the angle formed by the reference axis and the first direction is defined as α, and the angle formed by the reference axis and the lattice wall surface is defined as β, the condition of |α|<β<|α|+20° is satisfied.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a diffractive optical element.

Background Art

[0002] A diffractive optical element can produce an optical action such as that of an aspherical lens by changing the period of its periodic structure (diffraction grating). Patent Document 1 discloses a diffractive optical element used in an imaging optical system of an optical scanning device.

[0003] By the way, by manufacturing a diffractive optical element by injection molding of resin, a low-cost and lightweight product can be produced. However, there is a problem that the shape of the diffractive surface is likely to be distorted due to the release resistance from the mold in injection molding. Patent Documents 2 and 3 disclose the shape of a diffraction grating for reducing the release resistance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the shape of the diffraction grating disclosed in Patent Documents 2 and 3 is used for a diffractive optical element in which the direction of the reference axis (optical axis) of the diffractive surface and the release direction are different, as shown in FIG. 7, the structure of the mold becomes an undercut. For this reason, shape defects such as "flash" and "peeling" occur on the diffractive surface, and these shape defects reduce the diffraction efficiency or increase ghost light.

[0006] The present invention provides a method for manufacturing a diffractive optical element capable of reducing the shape defect of a diffractive surface caused by demolding in a diffractive optical element in which the direction of the reference axis of the diffractive surface is different from the demolding direction, the diffractive optical element, an optical scanning device using the same, and an image forming device.

Means for Solving the Problems

[0007] The method for manufacturing a diffractive optical element according to one aspect of the present invention includes a step of obtaining the diffractive surface by molding a resin material with a mold, and a step of demolding the resin material from the mold in a first direction. The diffractive surface includes a plurality of grating surfaces contributing to diffraction and a plurality of grating wall surfaces respectively provided between adjacent grating surfaces. The reference axis of the diffractive surface is non-parallel to the first direction. In a cross section including the reference axis, when the angle formed by the reference axis and the first direction is α and the angle formed by the reference axis and the grating wall surface is β, |α| < β < |α| + 20° It is characterized by satisfying the condition.

[0008] Further, the method for manufacturing a diffractive optical element according to another aspect of the present invention includes a step of obtaining the diffractive surface by molding a resin material with a mold, and a step of demolding the resin material from the mold in a first direction. The diffractive surface includes a plurality of grating surfaces contributing to diffraction and a plurality of grating wall surfaces respectively provided between adjacent grating surfaces. The reference axis of the diffractive surface is non-parallel to the first direction. In a cross section including the reference axis, when the angle formed by the reference axis and the first direction is α and the angle formed by the reference axis and the grating wall surface is β, in the grating wall surface where the positive directions of the angle α and the angle β are the same among the plurality of grating wall surfaces, α < β < α + 20° The condition is satisfied, In the grating wall surface where the positive directions of the angle α and the angle β are different from each other among the plurality of grating wall surfaces, β = 0 It is characterized by satisfying the condition.

[0009] In addition, an optical scanning device using each of the above diffraction optical elements and an image forming device using the optical scanning device also constitute another aspect of the present invention.

Advantages of the Invention

[0010] According to the present invention, in a diffraction optical element in which the direction of the reference axis of the diffraction surface is different from the demolding direction (first direction), it is possible to reduce the shape defect of the diffraction surface associated with demolding.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the shape of the diffraction optical element in the drawings is shown at a different scale from the actual one.

Examples

[0013] FIG. 1 and FIG. 2 respectively show the configurations in the main scanning direction and the sub-scanning direction cross-sections (main scanning cross-section and sub-scanning cross-section) of the optical scanning device of Example 1. The sub-scanning direction is a direction parallel to the rotation center axis of the optical deflector described later, and the main scanning direction is a direction in which the light beam deflected and scanned by the optical deflector is projected onto the main scanning cross-section. The main scanning cross-section is a cross-section with the sub-scanning direction as the normal, and the sub-scanning cross-section is a cross-section with the main scanning direction as the normal.

[0014] The light sources 11 and 12 are each composed of a semiconductor laser (wavelength λ = 790 nm) or the like, and emit first and second light beams modulated according to image information. The first apertures 21 and 22 each have a rectangular opening, and shape the beam shape by restricting the beam width in the sub-scanning direction of the first and second light beams emitted from the light sources 11 and 12 and passing through the opening.

[0015] The collimator lenses 31 and 32 as condenser lenses each convert the first and second light beams as divergent light beams emitted from the light sources 11 and 12 into parallel light beams. The cylindrical lenses 41 and 42 as the first optical systems each condense the parallel light beams from the collimator lenses 31 and 32 within the sub-scanning cross-section and form a line image on the deflection surface (reflective surface) 10a of the optical deflector 10 as a deflection element.

[0016] FIG. 8 shows the cylindrical lens 41. The cylindrical lens 42 is formed in the same manner. The cylindrical lenses 41 and 42 of this embodiment are integrally formed as one optical element (cylindrical lens unit 4) and are manufactured by injection molding of resin. The manufacturing method of the cylindrical lenses 41 and 42 includes a step of obtaining a diffractive surface by molding a resin material with a mold, and a step of demolding the resin material from the mold in a first direction. Note that the material of the cylindrical lenses 41 and 42 is not limited to resin, and may be a non-resin material (such as inorganic fine particles) whose main component is resin.

[0017] The incident surfaces 41a and 42a of the cylindrical lenses 41 and 42 have refractive power only in the sub-scanning cross-section (sub-scanning direction). Also, the exit surfaces 41b and 42b of the cylindrical lenses 41 and 42 have a diffractive surface 300 that compensates for the deterioration of optical performance due to wavelength changes of the light sources 11 and 12 caused by fluctuations in the ambient temperature and the like.

[0018] The second apertures 51 and 52 (only the second aperture 51 is shown in FIG. 1) shape the beam by restricting the beam widths of the first and second light beams from the cylindrical lenses 41 and 42 in the main scanning direction.

[0019] The light deflector 10 has a deflection surface 10a formed by a four-sided polygon mirror (rotating polygon mirror) and rotates at a constant speed in the direction of arrow A in FIG. 1 by a motor (not shown). Note that, as the deflection element, a galvanometer mirror or the like that deflects the light beam by sinusoidal vibration can also be used.

[0020] The imaging optical system 61 as the second optical system has a condensing function and fθ characteristics and is composed of first and second imaging lenses (fθ lenses) 61a and 61b as optical elements. Both the first and second imaging lenses 61a and 61b are anamorphic optical elements having aspherical lens surfaces in the main scanning cross-section. The imaging optical system 61 forms the first and second light beams reflected and deflected by the deflection surface 10a of the light deflector 10 on the photosensitive drum surfaces 71 and 72 (only the photosensitive drum surface 71 is shown in FIG. 1) as the scanned surfaces, respectively. At this time, skew correction is performed by making the deflection surface 10a and the photosensitive drum surfaces 71 and 72 conjugate in the sub-scanning cross-section.

[0021] Between the imaging optical system 61 and the photosensitive drum surfaces 71 and 72, dust-proof glasses 81 and 82 (only the dust-proof glass 81 is shown in FIG. 1) are provided to prevent dust, toner, etc. from entering the optical scanning device from the photosensitive drum side.

[0022] The first aperture 21, the collimator lens 31, the cylindrical lens 41, and the second aperture 51 constitute an incident optical system LA1 that guides the first light beam emitted from the light source 11 to the optical deflector 10. Similarly, the first aperture 22, the collimator lens 32, the cylindrical lens 42, and the second aperture 52 constitute an incident optical system LA2 that guides the second light beam emitted from the light source 12 to the optical deflector 10.

[0023] In the optical scanning device having the above components, the first and second light beams emitted from the light sources 11 and 12 have their beam widths in the sub-scanning direction restricted by the first apertures 21 and 22, are converted into parallel light beams by the collimator lenses 31 and 32, and are incident on the cylindrical lenses 41 and 42. The first and second light beams incident on the cylindrical lenses 41 and 42 are emitted as they are within the main scanning cross-section, and the beam width in the main scanning direction is restricted by the second aperture 51. Also, within the sub-scanning cross-section, they are converged by the cylindrical lenses 41 and 42, pass through the second apertures 51 and 52, and the beam width in the main scanning direction is restricted, and they form a line image (a line image long in the main scanning direction) on the deflection surface 10a of the optical deflector 10.

[0024] The plurality of light beams reflected and deflected by the deflection surface 10a of the optical deflector 10 are mainly incident on the first imaging lens 61a having positive power in the main scanning direction, and further incident on the second imaging lens 61b having positive power mainly in the sub-scanning direction. Then, the plurality of light beams that have passed through the second imaging lens 61b form spot-like images on the photosensitive drum surfaces 71 and 72. By rotating the optical deflector 10 in the direction of arrow A, the plurality of light beams scan the photosensitive drum surfaces 71 and 72 at a constant speed in the main scanning direction indicated by arrow B. Thereby, a plurality of scanning lines can be simultaneously formed on the photosensitive drum surface, which is the recording medium, to perform image recording.

[0025] Also, in the present embodiment, in the sub-scanning cross-section shown in FIG. 2, the optical axes of the incident optical systems LA1 and LA2 have a configuration of sub-scanning oblique incidence with an angle with respect to the main-scanning cross-section. With such a configuration of sub-scanning oblique incidence, light beams emitted from a plurality of light sources can be deflected by a single light deflector 10. In the present embodiment, the case where two light sources 11 and 12 are deflected by a single light deflector 10 is shown, but the number of light sources is not limited to this.

[0026] Note that the collimator lens and the cylindrical lens provided for each light source may be configured as one optical element, or the collimator lens may be configured by a plurality of lenses instead of a single lens.

[0027] Also, as described above, the cylindrical lenses 41 and 42 formed integrally may be arranged at different positions in the main-scanning cross-section. Also, the cylindrical lenses 41 and 42 may be separate optical elements from each other. Further, the diffractive surface may be a surface other than the exit surfaces of the respective cylindrical lenses.

[0028] FIG. 3 shows the shape of the diffractive surface 300 provided on the exit surfaces 41b and 42b of the cylindrical lenses 41 and 42. Note that in FIG. 3, a part of the diffractive surface 300 is shown enlarged. FIG. 3 shows a cross-section including the reference axis of the diffractive surface 300 (the central axis of the base surface or the normal line erected at the center of the base surface: referred to as the optical axis in the following description). The optical axis of the diffractive surface 300 coincides with the optical axes of the respective incident optical systems indicated by the dashed-dotted line in FIG. 2. In the present embodiment, the cylindrical lenses 41 and 42 correspond to diffractive optical elements in which the diffractive surface is formed with their exit surfaces 41b and 42b as the base surfaces.

[0029] The diffraction surface 300 has a plurality of grating surfaces (diffraction power portions contributing to diffraction) 301 each having a diffraction power (diffraction effect) inclined by an angle (blaze angle) θ with respect to the base surface, and a plurality of grating wall surfaces (step portions not contributing to diffraction) 302 respectively provided between adjacent grating surfaces. Each grating wall surface 302 has a planar wall surface 302a. A diffraction grating portion is formed by one grating surface 301 and one adjacent grating wall surface 302. A plurality of such diffraction grating portions are formed on the diffraction surface 300 so as to form a blaze shape (sawtooth shape). In this embodiment, as shown in FIG. 8, the diffraction surface 300 has diffraction power only in one of two directions (a direction corresponding to the above-described sub-scanning direction) orthogonal to each other and orthogonal to the optical axis. Also, as shown in FIG. 3, in the diffraction surface 300 of this embodiment, a plurality of grating surfaces 301 are formed such that the periodic interval of the grating surfaces becomes narrower as the distance from the center of the diffraction surface 300 increases. However, since an effect similar to that of an aspherical lens can be obtained on the diffraction surface by changing the period of the diffraction grating, the period of the diffraction grating may be appropriately changed for aberration correction.

[0030] As shown in FIG. 2, in the configuration of sub-scanning oblique incidence in which the optical axes of the incident optical systems LA1 and LA2 have different angles with respect to the deflection surface 10a, the optical axes of the cylindrical lenses 41 and 42 (that is, the respective diffraction surfaces 300) are inclined with respect to each other. Further, in the injection molding of the cylindrical lens unit 4 in which these cylindrical lenses 41 and 42 are integrally formed, the mold release direction (first direction) and the direction in which the optical axis of each diffraction surface extends (hereinafter referred to as the optical axis direction) are different from each other. That is, the diffractive optical element provided in the cylindrical lens unit 4 has two diffraction surfaces with different optical axis directions.

[0031] In the cross-section shown in FIG. 3 of the diffractive optical element in which the release direction and the optical axis direction are different from each other as described above, let the angle α be the acute angle formed by the optical axis direction of the diffraction surface 300 with respect to the release direction, and the positive direction is the direction from the optical axis direction toward the release direction. Also, in the same cross-section, let the angle β be the angle formed by the wall surface 302 of the grating wall surface 302 with respect to the optical axis direction, and the positive direction is the direction in which the angle on the resin side (diffraction grating portion side), in other words, the angle at the tip of the diffraction grating portion, increases. In FIG. 3, the positive directions of the angles α and β are indicated by arrows.

[0032] At this time, the diffraction surface 300 satisfies the condition represented by the following formula (1).

[0033] |α| < β < |α| + 20° (1) The angle β and the lower limit value in formula (1) indicate the relationship between the optical axis direction and the release direction of the diffraction surface 300. When the angle β is less than the lower limit value of formula (1), the grating wall surface 302 (wall surface 302a) becomes an undercut with respect to the mold, so the shape of the grating wall surface 302 is likely to collapse, resulting in a decrease in diffraction efficiency and an increase in ghost light. In order to suppress these, by setting an angle β larger than the absolute value of the angle α, it is possible to avoid an undercut with respect to the mold. That is, in a diffractive optical element in which the optical axis direction and the release direction of the diffraction surface 300 are different, it is possible to reduce the shape defect of the diffraction surface associated with release.

[0034] The upper limit value of formula (1) is determined by the diffraction efficiency of the diffraction surface 300. By increasing the angle β, the angle formed by the grating wall surface 302 and the release direction increases, reducing the release resistance and enabling stable molding. However, since the area of the grating surface 301 becomes smaller, the diffraction efficiency decreases.

[0035] FIG. 4 shows the results of calculating the diffraction efficiency by changing the angle β of the grating wall surface 302. Here, the transfer matrix method was used for the calculation of the diffraction efficiency. Also, the blaze angle θ of the diffraction grating portion is θ = tan -1 {mλ / p(n - 1)} It was set to satisfy the following. Here, m is the order of diffraction used, λ is the wavelength used, p is the pitch of the diffraction grating section (grating plane 301), and n is the refractive index of the resin at the wavelength λ used. Here, m = 1, λ = 790 nm, p = 80 μm, and n = 1.5287 were used.

[0036] As shown in FIG. 4, as the angle β increases, the diffraction efficiency at the order of diffraction used decreases. When the diffraction efficiency at the order of diffraction used decreases, the diffraction efficiency at the unnecessary order of diffraction increases and ghost light increases. When the angle β exceeds the upper limit value of the formula (1), the optical performance deteriorates due to the decrease in diffraction efficiency and the increase in ghost light, which is not preferable.

[0037] Note that the blaze angle θ may be set to satisfy the following conditions.

[0038] θ = sin -1 {mλ / p(n - 1)} In addition, in this embodiment, the case where the diffraction surface 300 has a blaze shape has been described. However, the diffraction surface may have a shape other than the blaze shape, for example, a stepped shape in which the inclined surface of the blaze shape is approximated by stepped steps, or an uneven shape in which grooves are dug in the base surface.

Example

[0039] Next, Example 2 will be described. In Example 1, the angle β of the grating wall surface 302 was set to avoid an undercut with respect to the mold, whereas in Example 2, the angle β is set according to the relationship between the optical axis direction and the mold release direction of the diffraction surface.

[0040] Specifically, for the grating wall surface in which the positive directions of the angles α and β are the same as shown in FIG. 5(a) among the plurality of grating wall surfaces 302, the angle β is set to satisfy the following condition of formula (2).

[0041] α < β < α + 20° (2) When the positive directions of the angles α and β are the same, it is preferable to satisfy the condition of formula (2) for the same reason as the condition of formula (1) described in Example 1.

[0042] On the other hand, for the lattice wall surfaces among the plurality of lattice wall surfaces 302 where the positive directions of the angles α and β are different from each other as shown in FIG. 5(b), the angle β is set so as to satisfy the condition of the following formula (3).

[0043] β = 0 (3) As shown in FIG. 4, the closer the angle β of the lattice wall surface 302 is to 0 (the closer it is to being parallel to the optical axis direction), the larger the area of the lattice surface 101 with respect to the light beam can be increased, and the diffraction efficiency can be improved. When the positive directions of the angles α and β are different, as shown in FIG. 5(b), by setting the angle β to be parallel to the optical axis direction (β = 0), it is possible to obtain a diffraction surface shape that does not result in undercut while improving the diffraction efficiency.

[0044] The shapes of the other diffraction surfaces are the same as those in the first embodiment.

Embodiment

[0045] Next, Example 3 will be described. This example is an image forming apparatus including the optical scanning apparatus described in Example 1 or 2, and is a laser beam printer, a digital copier, a multifunction printer (multifunctional printer), etc. having an electrophotographic process.

[0046] FIG. 6 shows a specific configuration of the image forming apparatus 100 of this example. The image forming apparatus 100 includes a printer controller 153, the optical scanning apparatus 110 of Example 1 or 2, photosensitive drums 121, 122, 123, 124 as image carriers, developing devices 131, 132, 133, 134, a conveyance belt 151, and a fixing device 154.

[0047] Color signals of R (red), G (green), and B (blue) are input to the printer controller 153 from an external device 152 such as a personal computer. As the external device 152, for example, an image reading device equipped with a CCD sensor may be used. A digital copier is configured by the image reading device and the image forming apparatus 100.

[0048] The printer controller 153 converts the R, G, and B color signals into color image information (dot data) of C (cyan), M (magenta), Y (yellow), and B (black). These color image information are input to the optical scanning device 110.

[0049] The optical scanning device 110 forms the light beams (beams) 141, 142, 143, 144 modulated according to the color image information on the photosensitive surfaces (scanned surfaces) of the photosensitive drums 121, 122, 123, 124 and scans the photosensitive surfaces in the main scanning direction. Thereby, electrostatic latent images corresponding to the color image information of C, M, Y, and B are recorded (formed) on the photosensitive drums 121, 122, 123, 124. The developing devices 131, 132, 133, 134 develop the electrostatic latent images of C, M, Y, and B with toner. The developed toner images of each color are transferred to a sheet of paper as a transfer material conveyed by the conveyance belt 151. The sheet of paper with the unfixed toner image transferred thereon is conveyed to the fixing device 154.

[0050] The fixing device 154 is composed of a fixing roller having a fixing heater (not shown) and a pressure roller, and fixes the toner image on the paper by heating while pressing the paper with the unfixed toner image transferred thereon between the fixing roller and the pressure roller. The paper with the toner image fixed thereon is discharged to the outside of the apparatus by a paper discharge roller (not shown).

[0051] The above embodiments include the following configurations.

[0052] (Configuration 1) A method for manufacturing a diffractive optical element having a diffractive surface, a step of obtaining the diffractive surface by molding a resin material with a mold, and a step of demolding the resin material from the mold in a first direction, wherein the diffractive surface includes a plurality of grating surfaces contributing to diffraction and a plurality of grating wall surfaces respectively provided between the adjacent grating surfaces, and a reference axis of the diffractive surface is non-parallel to the first direction, In a cross section including the reference axis, when the angle formed by the reference axis and the first direction is α and the angle formed by the reference axis and the lattice wall surface is β, |α| < β < |α| + 20° A method for manufacturing a diffractive optical element, characterized by satisfying the above conditions. (Configuration 2) A method for manufacturing a diffractive optical element having a diffractive surface, comprising: a step of obtaining the diffractive surface by molding a resin material using a mold; a step of releasing the resin material from the mold in a first direction; and the diffractive surface includes a plurality of grating surfaces contributing to diffraction and a plurality of grating wall surfaces respectively provided between the adjacent grating surfaces; the reference axis of the diffractive surface is non-parallel to the first direction; In a cross section including the reference axis, when the angle formed by the reference axis and the first direction is α and the angle formed by the reference axis and the lattice wall surface is β, among the plurality of grating wall surfaces, on the grating wall surface where the positive directions of the angle α and the angle β are the same, α < β < α + 20° satisfying the above conditions; among the plurality of grating wall surfaces, on the grating wall surface where the positive directions of the angle α and the angle β are different from each other, β = 0 A method for manufacturing a diffractive optical element, characterized by satisfying the above conditions. (Configuration 3) the diffractive surface has a blazed shape with a blaze angle of θ, when the number of diffraction orders to be used is m, the wavelength to be used is λ, the pitch of the grating surface is p, and the refractive index of the resin at the wavelength λ to be used is n, θ = tan -1 {mλ / p(n - 1)} A method for manufacturing a diffractive optical element according to Configuration 1 or 2, characterized by satisfying the above conditions. (Configuration 4) the diffractive surface has a blazed shape with a blaze angle of θ, When the number of diffraction times used is m, the wavelength used is λ, the pitch of the grating surface is p, and the refractive index of the resin at the wavelength λ used is n, θ = sin -1 {mλ / p(n - 1)} A method for manufacturing a diffractive optical element according to Configuration 1 or 2, characterized by satisfying the condition. (Configuration 5) A method for manufacturing a diffractive optical element according to any one of claims 1 to 4, characterized in that the diffractive surface has at least two diffractive surfaces whose directions of the reference axis are different from each other. (Configuration 6) A method for manufacturing a diffractive optical element according to any one of Configurations 1 to 5, characterized in that the diffractive surface is orthogonal to the reference axis and has the diffractive power only in one of two directions orthogonal to each other. (Configuration 7) A light source, An incident optical system including the diffractive optical element manufactured by the manufacturing method according to any one of Configurations 1 to 6, and into which a light beam from the light source is incident, A light deflector that deflects the light beam from the incident optical system toward the surface to be scanned, An imaging optical system that forms an image of the deflected light beam on the surface to be scanned, and a light scanning device characterized by having the same. (Configuration 8) The light scanning device according to Configuration 7, A developing device that develops an electrostatic latent image formed on the surface to be scanned by the light scanning device to form a toner image, An image forming apparatus characterized by having a fixing device that fixes the toner image transferred to the material to be transferred on the material to be transferred. (Configuration 9) The light scanning device according to Configuration 7 or 8, An image forming apparatus characterized by having a controller that converts a color signal input from an external device into color image information and inputs the color image information to the light scanning device.

[0053] Each of the embodiments described above is merely a representative example, and various modifications and changes can be made to each embodiment when implementing the present invention.

Explanation of Signs

[0054] 11, 12 light sources 41, 42 cylindrical lenses 300 diffraction surface 301 grating surface 302 grating wall surface 302a wall surface

Claims

1. A method for manufacturing a diffractive optical element having a diffractive surface, comprising: a step of obtaining the diffractive surface by molding a resin material with a mold; a step of demolding the resin material from the mold in a first direction; and having, the diffractive surface includes a plurality of grating surfaces contributing to diffraction and a plurality of grating wall surfaces respectively provided between the adjacent grating surfaces; a reference axis of the diffractive surface is non-parallel to the first direction; in a cross section including the reference axis, when an angle formed by the reference axis and the first direction is α and an angle formed by the reference axis and the grating wall surface is β, ｜α｜＜β＜｜α｜＋２０° A method for manufacturing a diffractive optical element, characterized by satisfying the following conditions.

2. A method for manufacturing a diffractive optical element having a diffractive surface, comprising: a step of obtaining the diffractive surface by molding a resin material with a mold; a step of demolding the resin material from the mold in a first direction; and having, the diffractive surface includes a plurality of grating surfaces contributing to diffraction and a plurality of grating wall surfaces respectively provided between the adjacent grating surfaces; a reference axis of the diffractive surface is non-parallel to the first direction; in a cross section including the reference axis, when an angle formed by the reference axis and the first direction is α and an angle formed by the reference axis and the grating wall surface is β, in the grating wall surface where the positive directions of the angle α and the angle β are the same among the plurality of grating wall surfaces, α＜β＜α＋２０° satisfying the following conditions, in the grating wall surface where the positive directions of the angle α and the angle β are different from each other among the plurality of grating wall surfaces, β＝０ A method for manufacturing a diffractive optical element, characterized by satisfying the following conditions.

3. The diffractive surface has a blazed shape with a blazed angle of θ, when the number of diffraction orders in use is m, the wavelength in use is λ, the pitch of the grating surface is p, and the refractive index of the resin at the wavelength λ in use is n, θ = tan －１ {mλ / p(n - 1)} The method for manufacturing a diffractive optical element according to claim 1 or 2, characterized by satisfying the following conditions.

4. The diffractive surface has a blazed shape with a blazed angle of θ, when the number of diffraction orders in use is m, the wavelength in use is λ, the pitch of the grating surface is p, and the refractive index of the resin at the wavelength λ in use is n, θ = sin －１ {mλ / p(n - 1)} The method for manufacturing a diffractive optical element according to claim 1 or 2, characterized by satisfying the following conditions.

5. The method for manufacturing a diffractive optical element according to claim 1 or 2, characterized in that the diffractive surface has at least two diffractive surfaces with different directions of the reference axis.

6. The method for manufacturing a diffractive optical element according to claim 1 or 2, wherein the diffractive surface has diffractive power only in one of two directions orthogonal to the reference axis and orthogonal to each other.

7. A light source, including the diffractive optical element manufactured by the manufacturing method according to claim 1 or 2, an incident optical system into which a light beam from the light source is incident, a light deflector that deflects the light beam from the incident optical system toward a surface to be scanned, and an imaging optical system that forms an image of the deflected light beam on the surface to be scanned. A light scanning device characterized by comprising:

8. The light scanning device according to claim 7, a developing device that develops an electrostatic latent image formed on the surface to be scanned by the light scanning device to form a toner image, and a fixing device that fixes the toner image transferred to a material to be transferred to the material to be transferred. An image forming apparatus characterized by comprising:

9. The light scanning device according to claim 7, and a controller that converts a color signal input from an external device into color image information and inputs the color image information to the light scanning device. An image forming apparatus characterized by comprising:

Images