JP2000267030A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning device of a small over field type, in which the distance from a rotary polygonal mirror to a scanned face is short without changing a system focal distance and whose ability is high, by making the reciprocal of the synthesis focal distance of plural scanning lenses in a deflection face to be smaller than that of the system focal distance of an optical scanning device. SOLUTION: In an optical scanning device 10, the reciprocal (lens power of system) of an optical scanning device system focal distance (f) and the reciprocal (lens power of scanning lens 24) of the synthesis focal distance f1 of a scanning lens are set like 1/f1<1/f. A laser beam which is media incident on the scanning lens 24 is not bent in the optical axis direction of the scanning lens 24 and an angle which optical beams and an optical axis make after the scanning lens is prevented from being narrowed by the scanning lens 24. Thus, the distance from a rotary polygonal mirror 22 to a scanned face 30 can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly to an optical scanning device used in an image recording device such as a laser printer or a digital copying machine. The present invention relates to a so-called overfilled optical scanning device in which the width of a light beam incident on the rotary polygon mirror along a direction corresponding to the main operation direction is increased.

[0002]

2. Description of the Related Art As an optical scanning device that deflects a light beam in a main scanning direction by a rotating polygon mirror and scans a surface to be scanned, the width of the reflecting surface of the rotating polygon mirror along the rotation direction (hereinafter, referred to as a surface width). ) Is generally larger than the width of the light beam incident on the rotary polygon mirror along the main scanning direction, that is, a so-called underfilled type.

[0003] In image recording apparatuses such as laser printers and digital copiers, there is a constant demand for faster image recording and higher resolution. In the above-described underfilled optical scanning device, there are a method of increasing the rotation speed of the rotary polygon mirror and a method of increasing the number of surfaces of the rotary polygon mirror in order to respond to a demand for high speed or the like. However, it is not easy to increase the rotation speed of the motor that drives the rotary polygon mirror. In addition, increasing the number of surfaces of the rotary polygon mirror while maintaining the surface width causes an increase in the diameter of the rotary polygon mirror, and it is difficult to rotate the polygon mirror with a large load. Therefore, there is known a so-called overfilled type optical scanning device in which the width of each reflecting surface is made smaller than the width of a light beam in order to prevent the rotating polygon mirror from increasing in size and increase the number of reflecting surfaces. .

In such an optical scanning device, a deflector such as a rotary polygon mirror for deflecting an incident light beam at a constant angular velocity in a direction corresponding to the main scanning direction, and an fθ lens as an optical scanning lens are used. ing. The fθ lens converges a laser beam deflected by a deflector, mainly using a semiconductor laser or the like as a light source, as a light spot on a surface to be scanned such as a photosensitive drum or a photosensitive belt, and scans the light spot with the light spot. It has two functions of moving at substantially constant speed on a surface.

Further, the fθ lens has a conjugate relationship between the position of the deflecting point on the deflector and the position of the light spot on the surface to be scanned in a plane orthogonal to the plane formed by the deflected laser beam. Along with a cylindrical lens which is arranged on the laser beam incident side of the deflector and has a lens power in a direction corresponding to the sub-scanning direction, the inclination of the reflection surface of the deflector can be optically controlled. And a surface tilt correction optical system for making the light spot substantially circular.

An fθ lens used in an overfilled type optical scanning device is disclosed in Japanese Patent Application Laid-Open No. 8-171070.
And Japanese Patent Application Laid-Open No. 9-96773 disclose an optical system including a set of two fθ lenses and a cylindrical mirror arranged near a surface to be scanned.

[0007]

However, the overfilled type optical scanning device is an optical scanning device suitable for high speed and high resolution. However, since the number of rotating polygon mirrors is increased, the underfilled type optical scanning device is used. When compared with, the angle of view that can be scanned is narrow, and an optical system with a long system focal length is required to scan the same scanning width, and accordingly the optical path from the rotating polygon mirror to the surface to be scanned such as a photoconductor Becomes longer. Since the optical path is long, there is also a problem that the stability of the position of the light beam becomes insufficient and it is difficult to maintain the performance. Further, in order to reduce the size of the overfilled type, it is necessary to increase the number of mirrors that bend the optical path. However, a plurality of scanning lenses described in Japanese Patent Application Laid-Open Nos. 8-177070 and 9-96773 are disclosed. The scanning imaging system composed of a mirror has a problem that the structure is complicated, the degree of freedom in arranging components for miniaturization is small, and the cost is high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has a high performance compact overfilled type in which the distance from the rotary polygon mirror to the surface to be scanned is short without changing the system focal length of the optical scanning device. It is an object of the present invention to provide an optical scanning device.

[0009]

According to one aspect of the present invention, a light source for emitting a light beam, a plurality of reflecting surfaces parallel to a rotation axis, and the light beam A rotating polygon mirror that deflects the light at a constant angular velocity in a predetermined direction by the reflecting surface, and a principal ray of a light beam deflected by the rotating polygon mirror from the light source so as to extend over the plurality of reflecting surfaces of the rotating polygon mirror. Imaging means for forming an image as a long line image in a direction corresponding to the deflection surface formed by the light source, and forming a light beam converging toward the rotary polygon mirror in the deflection surface; the rotary polygon mirror and the surface to be scanned Are converged on the deflecting surface on which the light spot is incident so as to be scanned at a substantially constant speed, and converge on the surface to be scanned, which is a divergent light beam in a direction orthogonal to the deflecting surface. Two scans Comprising lenses and, the reciprocal of the combined focal length of the deflection plane of the two scanning lenses, and being smaller than the reciprocal of the system focal length of the optical scanning device.

According to the first aspect of the present invention, a light beam is emitted from the light source, and the light beam from the light source is deflected by the reflection surface of the rotating polygon mirror rotating at a constant angular velocity. In the imaging means, the light beam from the light source is imaged as a long line image in a direction corresponding to the deflection surface formed by the principal ray of the light beam deflected by the rotating polygon mirror so as to span the plurality of reflection surfaces of the rotating polygon mirror. And a light beam converging toward the rotary polygon mirror in the deflection plane is formed. Further, the scanning lens is disposed between the rotary polygon mirror and the surface to be scanned, and an overfilled for correcting a surface tilt constituted by a so-called fθ lens that scans the surface to be scanned with a light beam at a substantially constant speed. It is a type of optical scanning device.

Here, the characteristics of the fθ lens are generally h
= F × θ (h: position of light spot on scanned surface,
θ: angle of the light beam deflected by the rotating polygon mirror, f:
(System focal length of the optical scanning device). Further, the light beam deflected by the rotating polygon mirror usually has a parallel light or a shape close to the parallel light within the deflection plane due to ease of design and stability of performance. Further, since the scanning lens is designed so that the light beam becomes a small light spot on the surface to be scanned, the focal length fl of the scanning lens in the deflection plane is almost equal to the focal length f of the system in the optical scanning device. Are identical. However, in order to shorten the optical path, it is disadvantageous that the focal length fl of the scanning lens and the focal length f of the system are substantially the same. That is, since the scanning lens having the focal length f has a finite positive power (the reciprocal of the focal length), the light beam deflected by the rotary polygon mirror is bent in the optical axis direction by the scanning lens. Therefore, the angle between the light beam after the scanning lens and the optical axis becomes narrow, and it is necessary to increase the distance between the scanning lens and the surface to be scanned.

Therefore, the scanning lens in the optical scanning device of the present invention uses a combined lens power of the two scanning lenses so that the light beam reaches a desired image height position from the rotary polygon mirror to the scanning lens at a short distance. Is smaller. That is, the reciprocal of the focal length of the scanning lens (lens power of the scanning lens) is made smaller than the reciprocal of the system focal length of the optical scanning device (lens power of the system).

By doing so, the scanning lens does not bend in the direction of the optical axis, and a shorter optical path can be realized as compared with a conventional overfilled type optical scanning device.

Further, by using two scanning lenses, it is possible to obtain a high-performance short-path overfilled optical scanning device.

According to a second aspect of the present invention, in the first aspect of the present invention, in the two scanning lenses, a focal length in a deflection plane of a lens arranged on a rotary polygon mirror side is negative, and It is characterized in that the lens disposed on the scanning surface side has a positive focal length in the deflection plane.

According to the invention described in claim 2, according to claim 1
In the invention described in the above, in the two scanning lenses, the focal length of the lens disposed on the rotating polygon mirror side in the deflection surface is negative (light beam divergence), and the lens disposed on the scanning surface side By setting the focal length in the deflecting surface to be positive (light beam convergence), fθ characteristics can be satisfied as in a general fθ lens.

According to a third aspect of the present invention, in the second aspect of the invention, in the two scanning lenses, all four lens shapes near the optical axis in the deflection surface are convex toward the rotary polygon mirror. It is characterized by having a shape.

According to the invention described in claim 3, according to claim 2,
In the invention described in (1), the fθ characteristic can be satisfied by making the lens shape near the optical axis in the deflection plane of the two scanning lenses all convex toward the rotating polygon mirror.

According to a fourth aspect of the present invention, in the third aspect of the present invention, in the lens shape of the two scanning lenses, a rotationally symmetric aspherical surface is arranged in order from the rotating polygon mirror side.
It is characterized by being a lens composed of a toric aspheric surface, a toric aspheric surface, and an anamorphic aspheric surface.

According to the fourth aspect of the present invention, the third aspect is provided.
In the invention described in the above, by forming the lens shapes of the two scanning lenses as a rotationally symmetric aspherical surface, a toric aspherical surface, a toric aspherical surface, and an anamorphic aspherical surface in order from the rotating polygon mirror side, It is possible to obtain imaging performance, that is, so-called surface tilt correction performance.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 4, the optical scanning device 10 of this embodiment includes a semiconductor laser 12 as a light source, and the semiconductor laser 12 emits and diverges from the semiconductor laser 12 on the laser beam emission side. A collimator lens 14 for forming a laser beam into a converged laser beam and an aperture 16 are sequentially arranged. Note that an aspheric glass lens is used for the collimator lens 14.

On the laser beam emitting side of the collimator lens 14, a cylindrical lens 18 for converging a converged laser beam as a long linear image in the main scanning direction and a reflecting mirror 20 are arranged in order in the sub-scanning direction. . The laser beam is reflected so that the reflection surface 26 of the rotary polygon mirror 22 is located at or near the image forming position of the line image, and is deflected at a constant angular velocity in a direction corresponding to the main scanning direction. The rotating polygon mirror 22 to be rotated is arranged. The number of the reflecting surfaces 26 of the rotary polygon mirror 22 is one having 12 reflecting surfaces 26 as an example. The rotating polygon mirror 22
The beam width in the direction corresponding to the main scanning direction of the beam incident on the rotating polygon mirror 22 is about 3
It is configured to perform an overfilled type scan in which a double beam is incident.

On the laser beam reflecting side of the rotary polygon mirror 22, there is arranged a scanning lens 24 composed of two lenses that converge a substantially circular light spot on the surface 30 to be scanned so as to be scanned at a constant speed. I have.

A laser beam emitted from the semiconductor laser 12 is converted into convergent light by a collimator lens 14 which is a pre-polygon system disposed on the incident side of a rotary polygon mirror 22, and is converged via a cylindrical lens 18 and a reflecting mirror 20. The image is formed on the reflection surface 26 of the rotary polygon mirror 22 as a long line image in a direction corresponding to the main scanning direction. The laser beam is deflected by the rotary polygon mirror 22 at a constant angular velocity in a direction corresponding to the main scanning direction, and is scanned on the surface 30 to be scanned 30 by the scanning lens 24 at a constant speed in the main scanning direction. The scanning lens 24 performs surface tilt correction to correct pitch unevenness in the sub-scanning direction. Further, the beam spot on the scanned surface 30 is made substantially circular by the cylindrical lens 18.

Here, the optical scanning device 1 according to the present embodiment
In the case of 0, the reciprocal of the system focal length f of the optical scanning device (the lens power of the system) and the reciprocal of the combined focal length fl of the scanning lens (the lens power of the scanning lens 24) are set as follows.

1 / fl <1 / f Thus, by setting the lens power of the system and the lens power of the scanning lens, the laser beam incident on the scanning lens 24 is bent in the optical axis direction of the scanning lens. Is eliminated, and the angle formed between the light beam after the scanning lens and the optical axis is not narrowed by the scanning lens 24. Therefore, the distance from the rotary polygon mirror 22 to the surface to be scanned 30 can be reduced.

Next, the scanning lens 24 of the present embodiment will be described. FIG. 1 shows a lens shape and a plane orthogonal to the deflection (including the optical axis of the lens and orthogonal to the deflection plane) in the deflection plane of the scanning lens 24 (the plane formed by the principal ray of the laser beam deflected by the rotating polygon mirror 22). Plane).

The surface S1 of the scanning lens 24 on the rotating polygon mirror 22 side, that is, the deflecting means side of the lens 24a disposed on the deflecting means side is formed of an axisymmetric aspheric surface.
Surface S2 is formed of a toric aspherical surface, and the surface to be scanned 3
The surface S3 on the deflection means side of the scanning lens 24b on the 0 side is formed of a toric aspherical surface, and the surface S4 on the side of the surface to be scanned 30 is formed of an aspherical surface having an asymmetric rotational axis (referred to as an anamorphic aspherical surface).

Hereinafter, the radius of curvature RM near the optical axis in the deflection plane of the lens surface, the radius of curvature near the optical axis in the plane orthogonal to the deflection of the lens surface is RS, and the sign of the radius of curvature is the side on which the incident light beam is incident. Is positive when it is convex, and negative when it is convex on the side where the incident light beam travels.

When the distance from the optical axis to the aspheric surface of the lens surface S1 is h, the position Z of the surface in the optical axis direction has a shape expressed by the following equation (1).

[0032]

(Equation 1)

Where c is the curvature on the optical axis, K is the conic constant, and A, B, C, D, E, F, G, H, and J are higher-order coefficients.

As shown in FIG. 2 (a), the toric aspherical surface of the lens surfaces S2 and S3 has a ZY plane with the origin 0 at the intersection of the optical axis A and the lens surface S and the Z axis in the optical axis direction. Assuming the deflection plane, and assuming the X axis in the plane orthogonal to the deflection,
As the position Z of the surface in the optical axis direction, a straight line parallel to the Y axis, which is separated from the origin by RS from a curve expressed by the following equation (2), is obtained as the rotation axis R. FIG. 2B shows the position of the rotation axis R.

[0035]

(Equation 2)

Here, K is a conical constant, and A, B, C, and D are higher-order coefficients.

As shown in FIG. 3 (a), the aspheric surface of the lens S4 has a deflecting surface defined by a ZY plane whose origin is the intersection point of the optical axis A and the lens surface S and whose optical axis is the Z axis. Assuming,
When the X axis is assumed to be within the plane orthogonal to the deflection, the position Z of the surface in the optical axis direction is a curved surface represented by the following equation (3).

[0038]

(Equation 3)

Where KX is a non-arc shaped conical constant in the plane of deflection orthogonal to the optical axis, KY is a non-arc shaped conical constant in the plane of deflection including the optical axis, AR, BR, CR, D
R, AP, BP, CP, and DP are higher-order coefficients.

This plane is within the deflection plane, that is, within the plane of X = 0.

[0041]

(Equation 4)

Similarly, in the plane orthogonal to the deflection, that is, in the plane of Y = 0,

[0043]

(Equation 5)

Can be expressed as follows. Each is in the form of an expression that represents a normal aspheric surface.

The shape in the plane of X = 0 and Y = 0 is X = Rcos when considered in the direction of the cross section shown in FIG.
It can be expressed by substituting θ, Y = Rsin θ, and Z = Z and converting to cylindrical coordinates.

[0046]

(Equation 6)

When R is put out and organized

[0048]

(Equation 7)

The equation (4) is a normal aspherical surface in the cross section in the R direction.

Next, the operation of the present embodiment will be described.

The laser beam emitted from the semiconductor laser 12 is converted into convergent light by the collimator lens 14, and has a predetermined beam diameter by the aperture 16. The laser beam having a predetermined beam diameter is condensed in the sub-scanning direction by the cylindrical lens 18, converted into a long line image in the main scanning direction, and formed on the reflection surface 26 of the rotary polygon mirror 22 by the reflection mirror 20. You.

The laser beam imaged on the reflecting surface 26 of the rotating polygon mirror 22 is subjected to main scanning by the rotation of the rotating polygon mirror 22, and the laser beam reflected on the reflecting surface 26 enters the scanning lens 24. Then, a substantially circular light spot is formed on the scanned surface 30 by the scanning lens 24 so as to be scanned at a constant speed.

At this time, the optical scanning device 10 of the present embodiment
In an optical system that converges a laser beam in the main scanning direction for forming an image as a light spot on the surface 30 to be scanned, the power of the scanning lens 24 is smaller than the reciprocal of the system focal length of the optical scanning device. , Scanning lens 24
This reduces the amount of bending of the laser beam in the optical axis direction. Or, it will not be bent. That is,
The angle formed between the light beam after the scanning lens and the optical axis can be increased, and the distance between the rotary polygon mirror 22 and the scanned surface 30 can be reduced.

[0054]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of a scanning lens and a scanning device suitable for scanning in the short direction (297 mm) of A3 paper will be described below.

Table 1 shows the dimensions of each part of the scanning lens 24 of Example 1 prepared using the optical glass BK7, the combined focal length in the deflection plane, and the system focal length. In Table 1, n is the refractive index of the optical glass, and d0 is the rotating polygon mirror 22.
Is the distance on the optical axis from the reflection surface 26 of the scanning lens 24 to the lens surface S1 of the scanning lens 24 on the side of the rotating polygon mirror 22;
The distance on the optical axis between 1 and S2, d4 is the lens surface S2, S3
D3 is the distance on the optical axis between the lens surfaces S3 and S4, and d4 is the distance on the optical axis from the lens surface S4 of the scanning lens 24 on the scanned surface 30 side to the scanned surface 30. (D
0, d1, d2, and d4, see FIG. 1), fl (f
(ocal length) is the focal length of the scanning lens 24 in the deflection plane, θ is the maximum angle of view, and λ is the wavelength of the laser beam. The unit of the dimensions of each part is the conic coefficient K, K
Y, KX, coefficients A, B, C, D, E, F, G, H, J,
AR, BR, CR, DR, AP, BP, CP, DP, refractive index n, maximum angle of view θ, and mm excluding wavelength λ.

From the center of rotation of the rotating polygon mirror 22 to the reflecting surface 26
Is 14 mm, and the angle between the light beam incident on the rotary polygon mirror 22 and the optical axis is 60 degrees. The incident light beam is a light beam that converges in the vicinity of the reflection surface 26 in the plane orthogonal to the deflection, and is a convergent light in the deflection surface. In the first embodiment, 170.
The collimator lens 14 generates convergent light that converges at a point 4 mm away from the reflection surface 26 of the rotary polygon mirror 22 in the direction of the scanning lens 24. Note that the specifications of the collimator lens 14 and the cylindrical lens 18 can be appropriately determined based on system requirements such as a laser light amount and a spot size.

FIG. 5A shows the field curvature of the scanning lens 24 shown in Table 1, and FIG. 5B shows the fθ characteristic in terms of the amount of positional deviation from ideal. The broken line in FIG. 5A indicates the field curvature in the main scanning direction, and the solid line indicates the field curvature in the sub-scanning direction. The system focal length as a reference for the fθ characteristic is 3
32.3155 mm.

As described above, in this embodiment, the reciprocal of the combined focal length in the deflection plane is smaller than the reciprocal of the system focal length. The focal length of the first lens is negative,
The second focal length is positive.

In this embodiment, the distance from the reflecting surface 26 of the rotary polygon mirror 22 to the surface to be scanned is 305 mm.

In a conventional ordinary scanning device combining a plano-concave lens and a plano-convex lens, the main plane is on the scanning surface side with respect to the scanning lens, and the distance from the rear side of the second lens to the scanning surface is 332. It was longer than 3155 mm, and the distance from the rotating polygon mirror 22 to the surface to be scanned was about 437 mm. Therefore, a size reduction of about 3/4 has been achieved. As for the performance, as shown in FIGS. 5A and 5B, the curvature of field is well corrected. Further, the deviation from the ideal showing the fθ characteristic is within 0.5%, and good results can be obtained.

As another example, Table 2 shows Examples 2 and 3
The configuration of the third embodiment is shown in FIG. The reference numerals are the same as those described in Table 1.

FIGS. 6 and 7 schematically show the shapes of the scanning lenses in the examples shown in Tables 2 and 3. FIG. All of these can achieve a short optical path, and the performance can be almost the same as that of the first embodiment. In the example of Table 2, the incident light beam is a convergent light beam that converges at a point away from the reflection surface 26 of the rotary polygon mirror 22 in the direction of the scanning lens by 195.5 mm. In the example of Table 3, the incident light beam is 194.8 mm.
Convergent light that converges at a point separated by mm from the reflecting surface 26 of the rotary polygon mirror 22 in the direction of the scanning lens is used.

In the above embodiment, the optical glass BK
7, the optical glass BK7 is used.
Since a has a low refractive index, a person skilled in the art can easily design a scanning lens using a plastic material also having a low refractive index, such as acrylic, polycarbonate, or amorphous polyolefin. It is also possible to use glass having a high refractive index. As a manufacturing method, since there are many aspherical shapes, molding is desirable.

[0064]

[Table 1]

[0065]

[Table 2]

[0066]

[Table 3]

[0067]

As described above, according to the present invention, a high-performance, compact overfilled optical scanning device in which the distance from the rotary polygon mirror to the surface to be scanned is short without changing the system focal length of the optical scanning device. There is an effect that the device can be provided. Further, since the second scanning lens has low power, even if a plastic material is used, the second scanning lens is less affected by a change in the refractive index due to a change in temperature, and has an effect of exhibiting stable performance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a shape of a scanning lens according to the present embodiment in a deflection plane and a deflection orthogonal plane.

FIG. 2 is a diagram for explaining the surface shapes of S2 and S3 of the scanning lens of the present embodiment.

FIG. 3 is a diagram for explaining a surface shape of a scanning lens S4 according to the present embodiment.

FIG. 4 is a perspective view showing an optical scanning device according to the embodiment.

5A is an aberration diagram illustrating curvature of field, and FIG. 5B is an aberration diagram illustrating fθ characteristics.

FIG. 6 is a diagram illustrating a scanning lens shape according to a second embodiment.

FIG. 7 is a diagram illustrating a scanning lens shape according to a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical scanning device 12 Semiconductor laser 14 Collimator lens 16 Aperture 18 Cylindrical lens 20 Reflection mirror 22 Rotating polygon mirror 24 Scanning lens 26 Reflection surface 30 Scanning surface

Claims (4)

[Claims] A light source that emits a light beam; a rotating polygon mirror having a plurality of reflecting surfaces parallel to a rotation axis and deflecting the light beam at a constant angular velocity in a predetermined direction by the reflecting surface; A light beam from the light source is imaged as a long line image in a direction corresponding to a deflecting surface formed by a principal ray of the light beam deflected by the rotating polygon mirror so as to extend over the plurality of reflecting surfaces of the polygon mirror, and Image forming means for forming a light beam converging toward the rotary polygon mirror within the deflection surface, and disposed between the rotary polygon mirror and the surface to be scanned, and the light spot is incident so as to be scanned at a substantially constant speed. Two scanning lenses that converge a light beam that is a convergent light beam within the deflecting surface and a divergent light beam in a direction orthogonal to the deflecting surface to the surface to be scanned. Composite focus on Reciprocal of release is, the optical scanning device, characterized in that less than the reciprocal of the system focal length of the optical scanning device. 2. In the two scanning lenses, the focal length of the lens disposed on the rotating polygon mirror side in the deflection surface is negative, and the focal length of the lens disposed on the scanning surface side in the deflection surface is negative. The optical scanning device according to claim 1, wherein the focal length is positive. 3. The optical scanning device according to claim 2, wherein, in the two scanning lenses, the lens shape in the vicinity of the optical axis in the deflecting surface is a convex shape on the rotating polygon mirror side for all four surfaces. apparatus. 4. The lens shape of the two scanning lenses, characterized in that the lens is composed of a rotationally symmetric aspherical surface, a toric aspherical surface, a toric aspherical surface, and an anamorphic aspherical surface in order from the rotating polygon mirror side. The optical scanning device according to claim 3.