JP2005308807A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce variations in the scanning position in the subscanning direction of a face to be scanned with respect to the variations in the tilt angle in a subdirection of respective deflection and reflection faces and to reduce cost by improving energy utility rate in an optical scanner of an overfilled type. <P>SOLUTION: A first imaging optical system is composed by arranging in the order from a semiconductor laser 1 side to a polygon mirror 7 side: a collimate lens 3 which transforms a laser beam 2 emitted from the semiconductor laser 1 into a parallel luminous flux; a second optical system 5 having a function which transforms the intensity distribution in a main scanning direction of the leaser beam 2 on the deflection and reflection faces of the polygon mirror 7 into a substantially uniform intensity distribution having a width larger than the width in the main scanning direction of one of the the deflection and reflection faces of the polygon mirror 7; a first optical system 4 which converges the laser beam 2 in the subscanning direction; and a third optical system 6 having a function which aligns the phases of the disturbed laser beam 2 by the second optical system 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical scanning device used for image writing or the like in an image forming apparatus such as a laser beam printer, a laser facsimile, or a digital copying machine.

  Many optical scanning devices used in laser beam printers are arranged between a semiconductor laser as a light source, a polygon mirror as a rotary polygon mirror (optical deflector), and between the semiconductor laser and the polygon mirror. An adjustment optical system that adjusts the beam diameter, divergence angle, and the like of the laser light from the semiconductor laser, and guides the light flux from the polygon mirror to the surface to be scanned, thereby forming a uniform spot on the surface to be scanned at a constant speed. And an imaging optical system that forms an image.

  Many conventional optical scanning apparatuses are of the underfill type in which an effective aperture in the main scanning direction is arranged in front of the polygon mirror so as to illuminate a part of the deflecting reflection surface of the polygon mirror. However, in the underfill type optical scanning device, in order to increase the number of deflecting and reflecting surfaces of the polygon mirror in order to increase the scanning speed, it is necessary to increase the diameter of the inscribed circle of the polygon mirror. If the diameter of the inscribed circle of the polygon mirror is increased, the size of the polygon mirror is increased, and a large force is required for rotational driving of the polygon mirror. There was a certain limit. Therefore, the underfilled type optical scanning device has a problem that it is difficult to increase the scanning speed. Therefore, in recent years, an overfilled type optical scanning device has been proposed in which the deflection reflection surface of the polygon mirror is completely illuminated and the deflection reflection surface of the polygon mirror is an effective aperture in the main scanning direction.

  In this overfilled type optical scanning device, the size of the deflecting / reflecting surface of the polygon mirror required to generate a spot of a desired size on the surface to be scanned is very small, and the underfilled type optical scanning device. It is possible to provide more deflecting reflection surfaces by using a polygon mirror having the same inscribed circle as the polygon mirror used in the above. Therefore, in the overfilled type optical scanning device, the polygon mirror can be operated at a relatively low rotational speed, and a motor drive device with smaller power can be used. However, in an overfilled type optical scanning device, generally, the intensity distribution of the laser light that irradiates the deflecting / reflecting surface of the polygon mirror is a Gaussian distribution, so that it is formed on the surface to be scanned depending on the position of the surface to be scanned. There is a problem that the light amount of the spot to be changed changes, that is, the peripheral light amount ratio is bad. Therefore, a proposal for improving the peripheral light amount ratio has been made with respect to the overfilled type optical scanning device (see, for example, Patent Document 1).

  Hereinafter, a technique for improving the peripheral light amount ratio in the conventional overfilled type optical scanning device will be described with reference to FIG. FIG. 10 is a main part configuration diagram showing an optical scanning device in the prior art (Patent Document 1). As shown in FIG. 10, the laser diode 101 emits a collimated laser beam 102. The collimated laser beam 102 is expanded by a beam expander composed of two lenses 103 and 104. The expanded laser beam 102 has a Gaussian intensity distribution, enters a linear opening, that is, a slit 105, and is emitted in the form of a sheet. Next, the laser beam 102 passes through an aspheric lens system 108 composed of two aspheric lenses 106 and 107. The aspherical lens system 108 converts the intensity distribution of the collimated sheet-like laser light 102 in the main scanning direction on the deflection reflection surface of the polygon mirror 109 into a uniform intensity distribution. Here, the sag amount sag of the aspheric surfaces of the aspheric lenses 106 and 107 is given by the following (Equation 1).

[Equation 1]
sag = y ² / 2r + ay ⁴ + by ⁶ + cy ⁸ + dy ¹⁰

  Here, r is the radius of curvature at the apex of the aspheric surface, y is the distance from the optical axis, and a, b, c, and d are the 4th, 6th, 8th and 10th aspherical coefficients, respectively.

Next, the laser beam 102 is reflected by each deflecting / reflecting surface of the polygon mirror 109 that rotates in the direction indicated by the arrow, and the second imaging optical system (not shown here, but at least one curved lens or An image is formed on the surface to be scanned by a curved mirror. In this case, the laser beam 102 hits the deflecting / reflecting surface of the polygon mirror 109 from the front in the center of the scanning and hits the scanning end with a certain angle. Therefore, the illumination light caused by the change in the effective area of the deflecting / reflecting surface of the polygon mirror 109 is detected. Except for the decrease, the laser beam 102 is irradiated onto the surface to be scanned with uniform intensity.
Japanese Patent Laid-Open No. 3-80214

  However, since the optical scanning device disclosed in Patent Document 1 has a configuration in which a part of the energy of the laser light is blocked by the slit, there is a problem that the energy utilization rate is poor. Further, since the optical scanning device disclosed in Patent Document 1 does not have a function of converging the laser beam on the deflecting / reflecting surface of the polygon mirror in the sub-scanning direction, the sub-scanning of each deflecting / reflecting surface of the polygon mirror is performed. If there is variation in the tilt angle of the direction, there is also a problem that the scanning position in the sub-scanning direction on the surface to be scanned varies. Furthermore, the optical scanning device disclosed in Patent Document 1 has a problem that it is difficult to reduce the cost because the beam expander and the aspherical lens system are separately arranged. It was.

  The present invention has been made in order to solve the above-described problems in the prior art, and is an overfilled type optical scanning device that can improve the energy utilization rate and tilt the deflecting reflecting surfaces in the sub-direction. An object of the present invention is to provide an optical scanning device that can reduce the variation in the scanning position in the sub-scanning direction on the surface to be scanned with respect to the variation in corners, and can reduce the cost.

In order to achieve the above object, a first configuration of an optical scanning device according to the present invention includes a light source unit that emits a light beam,
A rotary polygon mirror that has a plurality of deflection reflection surfaces and scans the light beam from the light source unit in the main scanning direction;
Main scanning of one of the deflecting and reflecting surfaces of the rotating polygon mirror is arranged between the light source unit and the rotating polygon mirror, and the light beam from the light source unit is projected onto the deflecting and reflecting surface of the rotating polygon mirror. A first imaging optical system that forms a line image having a width larger than the width in the direction;
An optical scanning device including a second imaging optical system that is disposed between the rotary polygon mirror and the surface to be scanned and forms an image of the light beam from the rotary polygon mirror on the surface to be scanned;
The first imaging optical system includes:
A collimating lens that is disposed between the light source unit and the rotating polygon mirror and converts the light beam from the light source unit into a parallel light beam;
A first optical system that is disposed between the collimating lens and the rotary polygon mirror and converges the light beam with respect to a sub-scanning direction;
The intensity distribution in the main scanning direction of the light beam on the deflection reflection surface of the rotation polygon mirror is arranged between the collimating lens and the rotation polygon mirror, and the intensity distribution of one deflection reflection surface of the rotation polygon mirror is determined. A second optical system having a function of converting into a substantially uniform intensity distribution having a width larger than the width in the main scanning direction;
A third optical system disposed between the second optical system and the rotary polygon mirror and having a function of aligning the phases of the light beams disturbed by the second optical system; To do.

  According to the first configuration of the optical scanning device of the present invention, the intensity distribution of the light beam on the deflecting reflection surface of the rotary polygon mirror can be converted into a substantially uniform intensity distribution while forming an image in the sub-scanning direction. As a result, the peripheral light quantity ratio can be improved, the energy utilization rate can be improved, and the sub-scanning on the surface to be scanned with respect to the variation in the tilt angle in the sub-direction of each deflection reflection surface of the rotary polygon mirror Variation in the scanning position in the direction can be reduced. In addition, since the second optical system has a beam expanding function, it is not necessary to provide a separate beam expander, so that the cost of the optical scanning device can be reduced.

In addition, a second configuration of the optical scanning device according to the present invention includes a light source unit that emits a light beam,
A rotary polygon mirror that has a plurality of deflection reflection surfaces and scans the light flux from the light source unit in a main scanning direction;
Main scanning of one of the deflecting and reflecting surfaces of the rotating polygon mirror is arranged between the light source unit and the rotating polygon mirror, and the light beam from the light source unit is projected onto the deflecting and reflecting surface of the rotating polygon mirror. A first imaging optical system that forms a line image having a width larger than the width in the direction;
An optical scanning device including a second imaging optical system that is disposed between the rotary polygon mirror and the surface to be scanned and forms an image of the light beam from the rotary polygon mirror on the surface to be scanned;
The first imaging optical system includes:
A collimating lens that is disposed between the light source unit and the rotating polygon mirror and converts the light beam from the light source unit into a parallel light beam;
A first optical system that is disposed between the collimating lens and the rotary polygon mirror and converges the light beam with respect to a sub-scanning direction;
The intensity distribution in the main scanning direction of the light beam on the deflection reflection surface of the rotation polygon mirror is arranged between the collimating lens and the rotation polygon mirror, and the intensity distribution of one deflection reflection surface of the rotation polygon mirror is determined. A second optical system having a width larger than the width in the main scanning direction, gradually increasing from the center to the end, and having a function of converting to an intensity distribution having a peak at the end;
A third optical system disposed between the second optical system and the rotary polygon mirror and having a function of aligning the phases of the light beams disturbed by the second optical system; To do.

  According to the second configuration of the optical scanning device of the present invention, the same operational effect as the first configuration can be obtained, and the second optical system can transmit the light beam on the deflecting reflection surface of the rotary polygon mirror. The intensity distribution in the main scanning direction gradually increases from the center to the end and also has a function of converting to an intensity distribution having a peak at the end. Since the decrease in the amount of light due to the change in the effective area can be corrected, the light beam can be irradiated onto the surface to be scanned with a completely uniform intensity.

  In the first or second configuration of the optical scanning device of the present invention, each of the second and third optical systems includes at least one lens having a non-arc shape in the main scanning direction. Preferably it is.

  In the first or second configuration of the optical scanning device of the present invention, each of the optical systems of the second and third optical systems has a shape in which one surface is non-circular in the main scanning direction, Preferably, the other surface is a single lens. In this case, it is preferable that the one surface has no refractive power in the sub-scanning direction.

  In the first or second configuration of the optical scanning device of the present invention, the second optical system includes at least one lens having a non-arc shape in the main scanning direction, and the third optical system. Is preferably composed of at least one lens having an arc shape in the main scanning direction. In this case, it is preferable that the third optical system is composed of a cylindrical lens. According to these preferable examples, the third optical system can be manufactured inexpensively and easily, and the third optical system can be formed into a shape that can be easily measured.

  In the first or second configuration of the optical scanning device of the present invention, the second optical system has one surface having a non-arc shape in the main scanning direction and the other surface being a flat surface. It is preferable that the third optical system includes a single lens having one surface having an arc shape in the main scanning direction and the other surface being a flat surface. In this case, it is preferable that the third optical system is a cylindrical lens. In this case, it is preferable that the one surface of each of the second and third optical systems has no refractive power in the sub-scanning direction.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the material of the second optical system is a resin and the material of the third optical system is glass. According to this preferable example, it is possible to prevent deterioration of performance due to temperature change.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the first optical system is disposed between the collimating lens and the second optical system.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the second optical system is disposed between the collimating lens and the first optical system.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the collimating lens and the first optical system are integrally formed.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the collimating lens and the second optical system are integrally formed.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the first optical system and the second optical system are integrally formed.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the collimating lens, the first optical system, and the second optical system are integrally formed.

  In the first or second configuration of the optical scanning device of the present invention, it is preferable that the first optical system and the third optical system are integrally formed.

  According to the preferable example in which these are integrally formed, the cost of the optical scanning device can be reduced.

  According to the present invention, in the overfilled type optical scanning device, the first result of converting the intensity distribution of the light beam on the deflecting reflecting surface of the rotary polygon mirror into a substantially uniform intensity distribution while forming an image in the sub-scanning direction. By using the image system, the peripheral light quantity ratio can be improved, the energy utilization rate can be improved, and scanning with respect to the variation in the tilt angle in the sub-direction of each deflection reflection surface of the rotary polygon mirror can be performed. Variations in the scanning position in the sub-scanning direction on the surface can be reduced. In addition, by using the second optical system having both the beam expansion function and the intensity distribution conversion function, the number of optical systems can be reduced, so that the cost of the optical scanning device can be reduced. Further, by using a glass material lens having an arc shape in the main scanning direction as the third optical system, it is possible to realize an optical scanning device that is inexpensive and has little performance deterioration with respect to temperature change.

  Hereinafter, the present invention will be described more specifically using embodiments.

[First Embodiment]
FIG. 1 is a main part configuration diagram showing an optical scanning device according to a first embodiment of the present invention. As shown in FIG. 1, the optical scanning device of the present embodiment has a semiconductor laser 1 as a light source unit that emits laser light 2 having a wavelength of 780 nm, a plurality of deflecting reflection surfaces, and rotates in the direction of an arrow. However, the polygon mirror 7 serving as a rotary polygon mirror that scans the laser beam 2 emitted from the semiconductor laser 1 in the main scanning direction, and the semiconductor laser 1 and the polygon mirror 7 are disposed, and emitted from the semiconductor laser 1. A first imaging optical system that forms an image of the laser light 2 on the deflection reflection surface of the polygon mirror 7 as a line image having a width larger than the width of one deflection reflection surface of the polygon mirror 7 in the main scanning direction. And a curved mirror 8 as a second imaging optical system that is disposed between the polygon mirror 7 and the scanned surface 9 and forms an image of the laser beam 2 from the polygon mirror 7 on the scanned surface 9. ing. Here, the laser beam 2 emitted from the semiconductor laser 1 has a Gaussian distribution of intensity, and has different divergence angles in the horizontal direction and the vertical direction. The width in the main scanning direction of the deflecting / reflecting surface of the polygon mirror 7 is set to 6.70 mm.

  In FIG. 1, the axes of the xyz orthogonal coordinate system are defined. The traveling direction of the laser beam 2 emitted from the semiconductor laser 1 is defined as the z axis, and the direction included in the paper surface of FIG. 1 and perpendicular to the z axis is defined as the y axis. When the axes of the xyz orthogonal coordinate system are defined in this way, the y-axis direction matches the main scanning direction, and the x-axis direction matches the sub-scanning direction.

  The first imaging optical system includes a collimator lens 3 that converts laser light 2 emitted from the semiconductor laser 1 into a parallel light beam, which is arranged in order from the semiconductor laser 1 side to the polygon mirror 7 side, and a polygon mirror 7. The intensity distribution in the main scanning direction of the laser beam 2 on the deflection reflection surface is converted into a substantially uniform intensity distribution having a width larger than the width of one deflection reflection surface of the polygon mirror 7 in the main scanning direction. A second optical system 5 having a function, a first optical system 4 for converging the laser light 2 in the sub-scanning direction, and a third having a function for aligning the phases of the laser light 2 disturbed by the second optical system 5. And the optical system 6.

  The first optical system 4 is composed of a single lens having a positive refractive power only in the sub-scanning direction. More specifically, the first optical system 4 is composed of a single lens, the incident surface is a cylindrical surface having an arc outline on the xz plane, and the output surface is a flat surface. The second optical system 5 includes a single lens having a refractive power only in the main scanning direction (not having a refractive power in the sub-scanning direction). More specifically, the second optical system 5 includes a single lens, and the incident surface 5a has a flat surface and the output surface 5b has a non-arc contour on the yz plane (that is, non-circular in the main scanning direction). It has a toroidal surface (having an arc shape). The material of the second optical system 5 is PMMA (acrylic), and the refractive index is 1.486169 for light having a wavelength of 780 nm. In the xyz orthogonal coordinate system defined as described above, when the intersection point of the optical axis and the exit surface 5b of the second optical system 5 is the origin, the sag amount sag (mm) of the exit surface 5b is Is given by equation 2).

[Equation 2]
sag = (CUy ² / (1 + sqrt (1- (1 + k) CU ² y ² )))
+ Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰

Here, “sqrt” means taking a square root. Further, CU (mm ⁻¹ ) represents the curvature at the apex, k represents the conic constant, A, B, C, and D represent the fourth, sixth, eighth, and tenth aspheric coefficients, respectively, and the exit surface 5b The values at are as follows.

CU = 0.0753691
k = −49.204918
A = -0.11678e-02
B = 0.100975e-03
C = -0.466279e-05
D = 0.895117e-07
In all the embodiments of the present invention, the signs of the curvature and the radius of curvature are positive when the center of curvature is in the light traveling direction with respect to the curved surface.

  The third optical system 6 is composed of a single lens having a refractive power only in the main scanning direction (not having a refractive power in the sub-scanning direction). More specifically, the third optical system 6 is composed of a single lens, the incident surface 6a is a toroidal surface having a non-arc contour in the yz plane, and the exit surface 6b is a flat surface. The material of the third optical system 6 is PMMA (acrylic), and the refractive index is 1.486169 for light having a wavelength of 780 nm. In the xyz orthogonal coordinate system defined as described above, when the intersection of the optical axis and the incident surface 6a of the third optical system 6 is defined as the origin, the sag amount sag (mm) of the incident surface 6a is expressed as ( The values given by Equation 2) are as follows at the entrance surface 6a.

CU = 6.55781e-3
k = -3.978513
A = -0.141439e-6
B = −0.624058e-9
C = 0.274282e-11
D = −0.24706e-13
Hereinafter, the operation of the optical scanning apparatus configured as described above will be described with reference to FIGS. FIG. 2 is a diagram showing the intensity distribution of the laser beam on the incident surface of the third optical system in the first embodiment of the present invention, and FIG. 3 shows the optical scanning device in the first embodiment of the present invention. FIG. 4 is a diagram showing an intensity distribution of laser light incident on a polygon mirror (rotating polygonal mirror) in the first embodiment of the present invention.

First, the laser beam 2 having a wavelength of 780 nm emitted from the semiconductor laser 1 enters the collimating lens 3 and is converted into a parallel light beam by the collimating lens 3. Next, the laser beam 2 converted into a parallel light beam enters the second optical system 5. The beam width of the laser beam 2 at the position of the second optical system 5 (twice the distance from the optical axis to the position where the intensity becomes 1 / e ² times the peak value in the intensity distribution of the laser beam 2) is the main scanning. 3.88 mm in the direction and 13.67 mm in the sub-scanning direction. The second optical system 5 converts the intensity distribution in the main scanning direction of the laser light 2 into a uniform intensity distribution at the position of the third optical system 6.

  FIG. 2 shows the intensity distribution in the main scanning direction of the laser beam 2 at the position of the third optical system 6. For the calculation of the intensity distribution, the following (Equation 3) in which the influence of the phase shift by the lens is added to the Kirchhoff square approximation formula was used.

  Here, the coordinates of the exit surface 5b of the second optical system 5 are (x1, y1), and the coordinates of the entrance surface 6a of the third optical system 6 are (x2, y2). In the above (Equation 3), I2 (x2, y2) is the light intensity of the laser beam 2 on the incident surface 6a of the third optical system 6, and U1 (x1, y1) is the emission of the second optical system 5. The amplitude of the laser beam 2 on the surface 5 b, k is the wave number, z is the distance from the exit surface 5 b of the second optical system 5 to the entrance surface 6 a of the third optical system 6, and n is the second optical system 5. It represents the refractive index of the material PMMA (acrylic). In the present embodiment, the distance from the exit surface 5b of the second optical system 5 to the entrance surface 6a of the third optical system 6 is set to 287.71 mm. The distance between the third optical system 6 and the polygon mirror 7 is set to about 100 mm.

  As can be seen from FIG. 2, the second optical system 5 causes a Gaussian distribution with a beam width of 3.88 mm in the main scanning direction to have a width of 26.0 mm (from the width of the deflecting reflection surface of the polygon mirror 7 in the main scanning direction). Is also expanded to a uniform intensity distribution with a large width). In the prior art, a laser beam is expanded using a beam expander and an aspheric lens system, and the intensity distribution is converted. In the present embodiment, one lens, that is, Only the second optical system 5 is used to expand the laser beam 2 and convert its intensity distribution. As described above, according to the present embodiment, since the second optical system 5 has a beam expanding function, it is not necessary to separately provide a beam expander, so that the cost of the optical scanning device can be reduced. Can do.

  The laser beam 2 that has passed through the second optical system 5 enters the first optical system 4. Then, the first optical system 4 focuses the laser beam 2 incident on the first optical system 4 only in the sub-scanning direction and forms an image on the deflection reflection surface of the polygon mirror 7. Thereby, it is possible to reduce the variation in the scanning position in the sub-scanning direction on the surface to be scanned with respect to the variation in the tilt angle in the sub-direction of each deflection reflection surface of the polygon mirror 7.

  The laser beam 2 that has passed through the first optical system 4 is incident on the third optical system 6. The wavefront of the laser beam 2 incident on the third optical system 6 has a distortion (that is, a phase disturbance) in the main scanning direction because it has passed through the second optical system 5. The incident surface 6a of the third optical system 6 removes the distortion of the wavefront, and makes the wavefront of the laser light 2 that has passed through the incident surface 6a a quadratic curved surface or a flat surface. In the present embodiment, the wavefront of the laser beam 2 that has passed through the third optical system 6 is a plane. This is because the incident surface 6a of the third optical system 6 is a toroidal surface having a non-arc contour in the yz plane.

  The first optical system 6 forms an image of the laser beam 2 that has passed through the third optical system 6 on the deflection reflection surface of the polygon mirror 7 as a line image extending in the main scanning direction. At this time, the width of the laser beam 2 in the main scanning direction is larger than the width of the deflecting / reflecting surface of the polygon mirror 7 in the main scanning direction. That is, as shown in FIG. 4, the laser beam 2 is incident on the deflection reflection surface 7a of the polygon mirror 7 in a so-called overfilled state. On the other hand, without using a slit or the like, the first optical system 4 is used to converge only in the sub-scanning direction, and the width of the laser beam 2 in the sub-scanning direction is set in the sub-scanning direction of the deflection reflection surface of the polygon mirror 7. Since the width is smaller than the width, the energy utilization rate can be improved as compared with the prior art. In the present embodiment, since the distance between the third optical system 6 and the polygon mirror 7 is set to about 100 mm, it is converted into a uniform intensity distribution at the position of the third optical system 6. The laser beam 2 propagates to the polygon mirror 7 while maintaining almost the same intensity distribution except for a slight influence of diffraction.

  As shown in FIG. 3, the laser light 2 from the first imaging optical system (collimating lens 3 to third optical system 6) is incident on the polygon mirror 7 obliquely within the cross section in the sub-scanning direction. The laser beam 2 deflected and reflected by the deflection reflection surface of the polygon mirror 7 is incident on the curved mirror 8 at an angle. The laser beam 2 deflected and reflected by the deflecting / reflecting surface of the polygon mirror 7 is subjected to an image forming action by the curved mirror 8 and forms an image on the surface 9 to be scanned across the entire scanning width. In this case, except for a decrease in the amount of light caused by the change in the effective area of the deflecting / reflecting surface with respect to the laser beam 2 due to the deflection angle at the deflecting / reflecting surface of the polygon mirror 7, the laser beam 2 is covered with a uniform intensity. The scanning surface 9 is irradiated.

  As described above, in the overfilled type optical scanning device, the intensity distribution of the laser beam 2 on the deflecting reflection surface of the polygon mirror (rotating polygon mirror) 7 is made substantially uniform while forming an image in the sub-scanning direction. By using the first image-forming optical system that converts the light into the peripheral light, the peripheral light quantity ratio can be improved, the energy utilization rate can be improved, and each deflected reflection of the polygon mirror (rotating polygon mirror) 7 can be improved. It is possible to reduce the variation in the scanning position of the surface 9 to be scanned in the sub-scanning direction with respect to the variation in the inclination angle of the surface in the sub-direction. In addition, since the number of optical systems can be reduced by using the second optical system 5 having both the beam expansion function and the intensity distribution conversion function, the cost of the optical scanning device can be reduced.

  Incidentally, by slightly modifying the second and third optical systems 5 and 6 in the present embodiment, the intensity distribution of the laser beam 2 on the deflection reflection surface 7a of the polygon mirror 7 as shown in FIG. The intensity distribution gradually increases from the center to the end and can be converted into an intensity distribution having a peak at the end. Specifically, the correction of the second optical system 5 means that the following design correction is performed. That is, the second optical system 5 of the present embodiment causes the laser light 2 having a Gaussian distribution with a beam width of 3.88 mm to be uniformly distributed with a width of 26.0 mm at the position of the third optical system in the main scanning direction. While the laser beam 2 is designed to be converted into a laser beam 2 having an intensity distribution, the laser beam 2 incident on the second optical system is assumed to be a Gaussian distribution with a beam width smaller than 3.88 mm, and the laser beam That is, the second optical system is subjected to design modification so that 2 is converted into laser light 2 having a uniform intensity distribution with a width of 26.0 mm at the position of the third optical system. In actual use, laser light 2 having a Gaussian distribution with a beam width of 3.88 mm is incident on the second optical system. As the design correction is performed assuming that the beam width of the laser beam 2 incident on the second optical system is small, the third laser beam 2 having a beam width of 3.88 mm is incident on the second optical system. The intensity distribution converted at the position of the optical system can be an intensity distribution in which the difference between the intensity at the center and the intensity at the end is large. On the other hand, the third optical system 6 may be modified so that the wavefront of the laser beam 2 disturbed by the second modified optical system 5 is adjusted. As a result, the decrease in the amount of light caused by the change in the effective area of the deflecting / reflecting surface 7a of the polygon mirror 7 associated with the scanning can be corrected, so that the surface 9 to be scanned is irradiated with the laser light 2 with completely uniform intensity. It becomes possible to do.

  Further, in the present embodiment, the second optical system 5 is constituted by a single lens, and the incident surface 5a is a plane, and the exit surface 5b is a toroidal surface having a non-arc contour on the yz plane. However, the second optical system 5 is disposed between the collimating lens 3 and the polygon mirror (rotating polygon mirror) 7, and the intensity distribution in the main scanning direction of the laser light 2 on the deflection reflection surface of the polygon mirror 7. That has a function of converting one of the deflecting and reflecting surfaces of the polygon mirror 7 into a substantially uniform intensity distribution having a width larger than the width in the main scanning direction, the shape and the number of lenses constituting the same are limited. Not.

  Further, in the present embodiment, the third optical system 6 is constituted by a single lens, the incident surface 6a is a toroidal surface having a non-arc outline on the yz plane, and the exit surface 6b is a plane. However, the third optical system 6 is disposed between the second optical system 5 and the polygon mirror (rotating polygonal mirror) 7 and functions to align the phases of the laser beams 2 disturbed by the second optical system 5. The shape and number of lenses constituting the lens are not limited.

  In the present embodiment, the second optical system 5 is arranged between the collimating lens 3 and the first optical system 4. However, the first optical system 4 is arranged with the collimating lens 3 and the first optical system 4. It may be arranged between the second optical system 5.

  In the present embodiment, the collimating lens 3, the first optical system 4, the second optical system 5, and the third optical system 6 are provided separately. For example, the collimating lens 3 and the first optical system 6 are provided separately. The optical system 4 is integrated into a single lens, the collimator lens 3 and the second optical system 5 are integrated into a single lens, or the first optical system 4 and the second optical system 5 are integrated. One lens is formed by molding, the collimating lens 3, the first optical system 4 and the second optical system 5 are integrated into one lens, or the first optical system 4 and the third optical system 6. May be formed into a single lens by integral molding. With the above configuration, the cost of the optical scanning device can be reduced.

[Second Embodiment]
FIG. 6 is a main part configuration diagram showing an optical scanning device according to a second embodiment of the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The configuration of the optical scanning device of the present embodiment is different from the configuration of the optical scanning device of the first embodiment in that an aperture 10 is provided and the third optical system 6 of the first embodiment is provided. The third optical system 66 having a different shape and material is used.

  As shown in FIG. 6, an aperture 10 having a circular opening is provided between the collimating lens 3 and the second optical system 5, and the diameter of the circular opening of the aperture 10 is 7.8 mm. . The third optical system 66 having the function of aligning the phases of the laser beams 2 disturbed by the second optical system 5 has a refractive power only in the main scanning direction (no refractive power in the sub-scanning direction). It consists of a lens. More specifically, the third optical system 66 is composed of one lens, the incident surface 66a is a cylindrical surface having an arc contour in the yz plane, and the output surface 66b is a flat surface. That is, the third optical system 66 is composed of a cylindrical lens. The material of the third optical system 66 is glass (BK7), and the refractive index is 1.511183 for light with a wavelength of 780 nm.

  Hereinafter, the operation of the optical scanning apparatus configured as described above will be described with reference to FIGS. FIG. 7 is a main part configuration diagram in the sub-scanning direction cross section showing the optical scanning device according to the second embodiment of the present invention.

First, the laser beam 2 having a wavelength of 780 nm emitted from the semiconductor laser 1 enters the collimating lens 3 and is converted into a parallel light beam by the collimating lens 3. Next, the laser beam 2 converted into a parallel light beam passes through the aperture 10. Next, the laser beam 2 that has passed through the aperture 10 enters the second optical system 5. The beam width of the laser beam 2 at the position of the second optical system 5 (twice the distance from the optical axis to the position where the intensity becomes 1 / e ² times the peak value in the intensity distribution of the laser beam 2) is the main scanning. The direction is 3.88 mm, and the sub-scanning direction is 13.67 mm. However, the aperture is limited by the aperture 10. The second optical system 5 converts the intensity distribution of the laser light 2 in the main scanning direction into a uniform intensity distribution at the position of the third optical system 66. In the present embodiment, the distance from the exit surface 5b of the second optical system 5 to the entrance surface 66a of the third optical system 66 is set to 287.71 mm. The distance between the third optical system 66 and the polygon mirror 7 is set to about 100 mm. In the optical scanning device of the present embodiment, the configuration other than the aperture 10 and the third optical system 66 is the same as that of the optical scanning device of the first embodiment. The intensity distribution of the laser beam 2 in the main scanning direction is the same as that shown in FIG. The laser beam 2 that has passed through the second optical system 5 enters the first optical system 4. Then, the first optical system 4 focuses the laser beam 2 incident on the first optical system 4 only in the sub-scanning direction and forms an image on the deflection reflection surface of the polygon mirror 7. The laser light 2 that has passed through the first optical system 4 enters the third optical system 66. The wavefront of the laser beam 2 incident on the third optical system 66 is distorted in the main scanning direction because it has passed through the second optical system 5. Unlike the third optical system 6 of the first embodiment, the third optical system 66 is composed of a cylindrical lens having an arcuate contour on the yz plane. Although the distortion of the wavefront in the main scanning direction cannot be completely removed, the incident surface 6a is a toroidal lens having a non-arc contour in the yz plane. Compared with the optical system 6, there is an advantage that it can be manufactured inexpensively and easily. In the present embodiment, the second optical system 5 is made of resin (PMMA (acrylic)), and the third optical system 66 is made of glass (BK7). The change in the combined refractive power of the optical system 5 and the third optical system 66 is small, and as a result, the increase in the width of the spot of the laser beam 2 formed on the scanned surface 9 due to the temperature change can be suppressed. The operation after the laser beam 2 passes through the third optical system 66 is the same as that in the first embodiment. The laser beam 2 that has passed through the third optical system 66 is formed as a line image extending in the main scanning direction on the deflection reflection surface of the polygon mirror 7. At this time, the width of the laser beam 2 in the main scanning direction is larger than the width of the deflecting / reflecting surface of the polygon mirror 7 in the main scanning direction. That is, as shown in FIG. 4, the laser beam 2 is incident on the deflection reflection surface of the polygon mirror 7 in a so-called overfilled state. On the other hand, without using a slit or the like, the first optical system 4 is used to converge only in the sub-scanning direction, and the width of the laser beam 2 in the sub-scanning direction is set in the sub-scanning direction of the deflection reflection surface of the polygon mirror 7. Since the width is smaller than the width, the energy utilization rate can be improved as compared with the prior art. In the present embodiment, since the distance between the third optical system 66 and the polygon mirror 7 is set to about 100 mm, it is converted into a uniform intensity distribution at the position of the third optical system 66. The laser beam 2 propagates to the polygon mirror 7 while maintaining almost the same intensity distribution except for a slight influence of diffraction.

  As shown in FIG. 7, the laser light 2 from the first imaging optical system (collimating lens 3 to third optical system 66) is incident on the polygon mirror 7 obliquely within the cross section in the sub-scanning direction. The laser beam 2 deflected and reflected by the deflection reflection surface of the polygon mirror 7 is incident on the curved mirror 8 at an angle. The laser beam 2 incident on the curved mirror 8 is converged by the optical power of the curved mirror 8 and forms an image on the surface to be scanned 9 (that is, the laser deflected and reflected by the deflecting reflecting surface of the polygon mirror 7). The light 2 is imaged by the curved mirror 8 and is imaged across the entire scanning width on the scanned surface 9). In this case, the laser beam 2 is scanned at a uniform intensity except for a decrease in the amount of light caused by a change in the effective area of the deflecting / reflecting surface with respect to the laser beam 2 due to the deflection angle at the deflecting / reflecting surface of the polygon mirror 7. The surface 9 is irradiated. In FIG. 7, T1, T2, and T3 represent the center thickness of the second optical system 5, the center thickness of the first optical system 4, and the center thickness of the third optical system 66, respectively. , D3 is the distance between the second optical system 5 and the first optical system 4, the distance between the first optical system 4 and the third optical system 66, and the distance between the third optical system 66 and the polygon mirror 7. Each interval is shown. D4 represents the distance between the deflecting / reflecting surface of the polygon mirror 7 and the curved mirror 8, and D5 represents the distance between the curved mirror 8 and the surface 9 to be scanned. ΘP is an angle formed by the optical axis of the laser beam 2 from the first imaging optical system and the normal line of the deflecting / reflecting surface of the polygon mirror 7 (the optical axis of the laser beam 2 incident on the deflecting / reflecting surface of the polygon mirror 7). The angle formed by (incident optical axis) and the optical axis (reflected optical axis) of the laser beam 2 reflected by the deflecting / reflecting surface of the polygon mirror 7 represents 2 · θp), and θM is from the deflecting / reflecting surface of the polygon mirror 7. The angle between the optical axis of the laser beam 2 and the normal line at the apex of the curved mirror 8 (the optical axis of the laser beam 2 incident on the curved mirror 8 (incident optical axis) and the optical axis of the laser beam 2 reflected by the curved mirror 8 The angle formed by (reflecting optical axis) represents 2 · θM).

  Here, in order to explain the effect of the third optical system 66 being a cylindrical lens made of glass (BK7), the wavefront aberration and the spot size of the optical scanning device of the present embodiment are calculated. For comparison, the wavefront aberration and spot size of an optical scanning device using a toroidal lens having a non-arc shape in the main scanning direction as the third optical system are also calculated. In this toroidal lens, the material is PMMA (acrylic), the shape of the incident surface is the same as that of the third optical system 6 of the first embodiment, and the shape of the emission surface is positive in the main scanning direction. It has a cylindrical surface with a refractive radius of -586.058 mm. The surface shape of the curved mirror 8 is the sub-scanning direction coordinate with the vertex of the surface as the origin, the main scanning direction coordinate is x (mm), and the sag amount from the vertex at the position of y (mm) is Z (mm) (however, It is defined by the following (Equation 4) to (Equation 7) as the positive direction of the incident light beam.

[Equation 6]
g (y) = RDx (1 + BCy ² + BDy ⁴ + BEy ⁶ + BFy ⁸ + BGy ¹⁰ )

[Equation 7]
θ (y) = ECy ² + EDy ⁴ + EEy ⁶

  Here, the above (Equation 5) is an equation indicating a non-circular arc that is a shape on the generatrix, the above (Equation 6) is an equation indicating the radius of curvature in the sub-scanning direction (x direction) at the y position, and the above (Equation 7) is It is a formula which shows the amount of twist in y position. Note that RDy (mm) is a radius of curvature in the main scanning direction at the apex, RDx (mm) is a radius of curvature in the sub-scanning direction, K is a conic constant indicating a busbar shape, and AD, AE, AF, and AG are high values indicating a busbar shape. The next constants BC, BD, BE, BF, and BG are constants that determine the radius of curvature in the sub-scanning direction at the y position, and EC, ED, and EE are twist constants that determine the amount of twist at the y position. The surface shape of the curved mirror 8 is designed so that the main field curvature, the sub field curvature, and the fθ error can be corrected by satisfying the above (Formula 4) to (Formula 7). . That is, the curved mirror 8 has a non-arc shape in the cross section in the main scanning direction and a radius of curvature in the sub scanning direction corresponding to each image height so that the main field curvature, sub field curvature, and fθ error can be corrected. In order to correct the scanning line curvature, the torsion amount of the surface at a position corresponding to each image height of the curved mirror 8 is determined.

  The following (Table 1) shows specific numerical examples of the curved mirror 8. The number of deflection reflecting surfaces of the polygon mirror 7 is Np, the radius of a circle inscribed in the polygon mirror 7 is rp, the maximum image height is Ymax, and the rotation angle of the corresponding polygon mirror 7 is αmax.

  The following (Table 2) shows specific numerical examples of the first imaging optical system adapted to the second imaging optical system. The focal length of the collimating lens 3 is fc, the radius of curvature of the incident surface (cylindrical surface) of the first optical system 4 comprising a cylindrical lens is Rx4, and the radius of curvature of the exit surface 66b of the third optical system 66 is Ry66. did.

  In the present embodiment, the wavefront aberration and the spot size were calculated at a design temperature of 25 ° C. and a temperature of 55 ° C., which is 30 ° C. higher than the design temperature of 25 ° C. Note that when the temperature reaches 55 ° C., the calculation is performed assuming that the optical scanning device and the components constituting it will thermally expand uniformly from the design shape and that the refractive index will change for the transmission system. It was.

  Further, the wavelength shift of the laser beam 2 due to temperature was also taken into consideration. Here, the linear expansion coefficient of the material constituting the collimating lens 3 is 8.6e-6 (/ ° C), the refractive index change with temperature is 5.3e-6 (/ ° C), and the material constituting the first optical system 4 is The linear expansion coefficient is 7.0e-6 (/ ° C), the refractive index change with temperature is 2.4e-6 (/ ° C), and the linear expansion coefficient of the material constituting the second optical system 5 is 8.0e-5 (/ ° C). ), The refractive index change with temperature is -1.0e-4 (/ ° C), the linear expansion coefficient of the material constituting the third optical system 66 is 7.0e-6 (/ ° C), and the refractive index change with temperature is 2.4e. −6 (/ ° C.), the linear expansion coefficient of the material constituting the curved mirror 8 is 7.0e-5 (/ ° C.), and the linear expansion coefficient of the material constituting the stage (not shown) on which the optical system is arranged is It was 2.6e-5 (/ ° C). For comparison, when the third optical system is made of PMMA (acrylic), the linear expansion coefficient is 8.0e-5 (/ ° C), and the refractive index change with temperature is -1.0e-4 (/ ° C). ). In addition, it is assumed that the wavelength of the laser beam 2 fluctuates to 788 nm at a temperature of 55 ° C.

  FIG. 8A shows the RMS (root mean square) value of wavefront aberration for each scanning position at a design temperature of 25 ° C. and a temperature of 30 ° C. higher than the design temperature of 25 ° C. in the optical scanning apparatus of the present embodiment. A graph is shown. For comparison, FIG. 8B shows a design temperature in an optical scanning apparatus using a toroidal lens in which the material having a non-arc shape in the main scanning direction is PMMA (acrylic) as the third optical system described above. The graph of the RMS value of the wavefront aberration for every scanning position in 25 degreeC and the temperature 55 degreeC 30 degree higher than design temperature 25 degreeC is shown. 8A and 8B, the case where the design temperature is 25 ° C. is indicated by a solid line, and the case where the temperature is 55 ° C. is indicated by a broken line. As can be seen from FIGS. 8A and 8B, since the optical scanning device of the present embodiment uses a cylindrical lens as the third optical system 66, the wavefront aberration at the design temperature of 25 ° C. is scanned. Although it is as bad as about 40 mλ in the vicinity of the end of the position, since glass (BK7) is used as the material of the third optical system 66, the synthesis of the second optical system 5 and the third optical system 66 due to temperature change. The change in refractive power is small, and as a result, the degradation of wavefront aberration at a temperature of 55 ° C. is very small.

Next, FIG. 9A shows the main scanning direction and the sub-scanning direction for each scanning position at a design temperature of 25 ° C. and a temperature of 55 ° C. that is 30 ° C. higher than the design temperature of 25 ° C. shows a graph of spot size (intensity of 1 / e length connecting to become a point ^twice the peak value of the intensity distribution). For comparison, FIG. 9B shows a design temperature in an optical scanning apparatus using a toroidal lens in which the material having a non-arc shape in the main scanning direction is PMMA (acrylic) as the third optical system described above. A graph of the spot size in the main scanning direction and the sub-scanning direction for each scanning position at 25 ° C. and a temperature of 55 ° C. which is 30 ° C. higher than the design temperature 25 ° C. is shown. 9A and 9B, the spot size in the main scanning direction when the design temperature is 25 ° C. is the solid line, the spot size in the main scanning direction when the temperature is 55 ° C. is the one-dot chain line, and the design temperature is 25 ° C. The spot size in the sub-scanning direction is indicated by a fine broken line, and the spot size in the sub-scanning direction at a temperature of 55 ° C. is indicated by a rough broken line. As can be seen from FIGS. 9A and 9B, since the optical scanning device of the present embodiment uses glass (BK7) as the material of the third optical system 66, the second optical due to temperature changes. The change in the combined refractive power of the system 5 and the third optical system 66 is small, and as a result, the spot size in the main scanning direction hardly deteriorates (increases). In addition, since the optical scanning device of the present embodiment uses a cylindrical lens as the third optical system 66, the wavefront aberration at the design temperature of 25 ° C. is about 40 mλ near the end of the scanning position. The size hardly deteriorates (increases) in both the main scanning direction and the sub-scanning direction. Therefore, according to the present embodiment, by using an inexpensive cylindrical lens as the third optical system 66, it has almost the same imaging performance as when using an aspherical toroidal lens as the third optical system, In addition, an optical scanning device can be realized at a lower cost than when an aspherical toroidal lens is used as the third optical system.

  As described above, by using a cylindrical lens made of glass (BK7) as the third optical system 66, it is possible to realize an optical scanning device that is inexpensive and has little performance deterioration with respect to temperature change.

FIG. 1 is a main part configuration diagram showing an optical scanning device according to a first embodiment of the present invention. The figure which shows intensity distribution of the laser beam in the entrance plane of the 3rd optical system in the 1st Embodiment of this invention FIG. 1 is a main part configuration diagram in a sub-scanning direction cross section showing an optical scanning device according to a first embodiment of the present invention. The figure which shows intensity distribution of the laser beam which injects into the polygon mirror (rotating polygonal mirror) in the 1st Embodiment of this invention The figure which shows the other example of intensity distribution of the laser beam which injects into the polygon mirror (rotating polygonal mirror) in the 1st Embodiment of this invention The principal part block diagram which shows the optical scanning device in the 2nd Embodiment of this invention. The principal part block diagram in the subscanning direction cross section which shows the optical scanning device in the 2nd Embodiment of this invention. (A) is a graph of the RMS value of wavefront aberration for each scanning position at a design temperature of 25 ° C. and a temperature of 55 ° C. that is 30 ° C. higher than the design temperature of 25 ° C. in the optical scanning device of the second embodiment of the present invention; b) is a third optical system having a non-arc shape in the main scanning direction and a temperature that is 30 ° C. higher than the design temperature 25 ° C. in the optical scanning device using a PMMA (acrylic) toroidal lens. Graph of RMS value of wavefront aberration for each scanning position at 55 ° C (A) is a spot in the main scanning direction and the sub-scanning direction for each scanning position at a design temperature of 25 ° C. and a temperature of 55 ° C. higher than the design temperature of 25 ° C. in the optical scanning device of the second embodiment of the present invention. Graph of size, (b) is a design temperature of 25 ° C. and a design temperature of 25 ° C. in an optical scanning device using a PMMA (acrylic) toroidal lens having a non-arc shape in the main scanning direction as a third optical system. Graph of spot size in main scanning direction and sub-scanning direction for each scanning position at a temperature of 55 ° C, which is 30 ° C higher Main part block diagram which shows the optical scanning device in a prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Laser beam 3 Collimating lens 4 1st optical system 5 2nd optical system 5a Incident surface of 2nd optical system 5b Outgoing surface of 2nd optical system 6 3rd optical system 6a 3rd optics System entrance surface 6b exit surface of third optical system 7 polygon mirror (rotating polygon mirror)
7a Deflection / reflection surface 8 Curved mirror 9 Scanned surface 10 Aperture 66 Third optical system 66a Third optical system entrance surface 66b Third optical system exit surface

Claims (17)

A light source that emits a luminous flux;
A rotary polygon mirror that has a plurality of deflection reflection surfaces and scans the light beam from the light source unit in the main scanning direction;
Main scanning of one of the deflecting and reflecting surfaces of the rotating polygon mirror is arranged between the light source unit and the rotating polygon mirror, and the light beam from the light source unit is projected onto the deflecting and reflecting surface of the rotating polygon mirror. A first imaging optical system that forms a line image having a width larger than the width in the direction;
An optical scanning device including a second imaging optical system that is disposed between the rotary polygon mirror and the surface to be scanned and forms an image of the light beam from the rotary polygon mirror on the surface to be scanned;
The first imaging optical system includes:
A collimating lens that is disposed between the light source unit and the rotating polygon mirror and converts the light beam from the light source unit into a parallel light beam;
A first optical system that is disposed between the collimating lens and the rotary polygon mirror and converges the light beam with respect to a sub-scanning direction;
The intensity distribution in the main scanning direction of the light beam on the deflection reflection surface of the rotation polygon mirror is arranged between the collimating lens and the rotation polygon mirror, and the intensity distribution of one deflection reflection surface of the rotation polygon mirror is determined. A second optical system having a function of converting into a substantially uniform intensity distribution having a width larger than the width in the main scanning direction;
A third optical system disposed between the second optical system and the rotary polygon mirror and having a function of aligning the phases of the light beams disturbed by the second optical system; Optical scanning device. A light source that emits a luminous flux;
A rotary polygon mirror that has a plurality of deflection reflection surfaces and scans the light flux from the light source unit in a main scanning direction;
Main scanning of one of the deflecting and reflecting surfaces of the rotating polygon mirror is arranged between the light source unit and the rotating polygon mirror, and the light beam from the light source unit is projected onto the deflecting and reflecting surface of the rotating polygon mirror. A first imaging optical system that forms a line image having a width larger than the width in the direction;
An optical scanning device including a second imaging optical system that is disposed between the rotary polygon mirror and the surface to be scanned and forms an image of the light beam from the rotary polygon mirror on the surface to be scanned;
The first imaging optical system includes:
A collimating lens that is disposed between the light source unit and the rotating polygon mirror and converts the light beam from the light source unit into a parallel light beam;
A first optical system that is disposed between the collimating lens and the rotary polygon mirror and converges the light beam with respect to a sub-scanning direction;
The intensity distribution in the main scanning direction of the light beam on the deflection reflection surface of the rotation polygon mirror is arranged between the collimating lens and the rotation polygon mirror, and the intensity distribution of one deflection reflection surface of the rotation polygon mirror is determined. A second optical system having a width larger than the width in the main scanning direction, gradually increasing from the center to the end, and having a function of converting to an intensity distribution having a peak at the end;
A third optical system disposed between the second optical system and the rotary polygon mirror and having a function of aligning the phases of the light beams disturbed by the second optical system; Optical scanning device. 3. The optical scanning device according to claim 1, wherein each of the second and third optical systems includes at least one lens having a non-arc shape in the main scanning direction. The optical system of each of the second and third optical systems comprises a single lens having one surface having a non-arc shape in the main scanning direction and the other surface being a flat surface. The optical scanning device according to 1. The optical scanning device according to claim 4, wherein the one surface has no refractive power in the sub-scanning direction. The second optical system includes at least one lens having a non-arc shape in the main scanning direction, and the third optical system includes at least one lens having an arc shape in the main scanning direction. The optical scanning device according to claim 1. The second optical system includes a single lens having one surface having a non-arc shape in the main scanning direction and the other surface being a plane, and the third optical system has one surface The optical scanning device according to claim 1 or 2, comprising a single lens having an arc shape in the main scanning direction and the other surface being a flat surface. The optical scanning device according to claim 7, wherein the one surface of each of the second and third optical systems has no refractive power in the sub-scanning direction. The optical scanning device according to claim 6, wherein the third optical system includes a cylindrical lens. The optical scanning device according to claim 1, wherein the material of the second optical system is a resin, and the material of the third optical system is glass. The optical scanning device according to claim 1, wherein the first optical system is disposed between the collimating lens and the second optical system. The optical scanning device according to claim 1, wherein the second optical system is disposed between the collimating lens and the first optical system. The optical scanning device according to claim 1, wherein the collimating lens and the first optical system are integrally formed. The optical scanning device according to claim 1, wherein the collimating lens and the second optical system are integrally formed. The optical scanning device according to claim 1, wherein the first optical system and the second optical system are integrally formed. The optical scanning device according to claim 1, wherein the collimating lens, the first optical system, and the second optical system are integrally formed. The optical scanning device according to claim 1, wherein the first optical system and the third optical system are integrally formed.

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