JPH04264420A - Optical scanner - Google Patents

Abstract

PURPOSE:To correct the curvature of field an make a plane scan by utilizing an electrooptical lens which need not be moved mechanically and is fast in response speed. CONSTITUTION:The electrooptical lens 4 which provides converging operation is a subscanning direction is arranged a the beam waist position of a 1s cylinder lens 3 and used, and the incident beam from a laser light source 1 is made incident on the electrooptical lens after being converged in a main scanning direction by the 1st cylinder lens 3 so that the beam passes the square- distributed refractive index distribution area of the electrooptical lens 4. Consequently, the electrooptical lens 4 functions as a variable focus position lens which has a little aberration. For the purpose, the voltage impressed to the electrooptical lens 4 is controlled by a control power source 10 corresponding to the curvature of field to correct the curvature of field on the surface of a scanned medium 9 in the subscanning direction.

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 such as a laser printer or a digital copying machine that performs optical writing by deflecting and scanning a laser beam using a rotating polygon mirror.

0002

2. Description of the Related Art Generally, in this type of optical scanning device, an fθ lens is disposed after a rotating polygonal mirror to perform scanning, but there is a curvature of field in the scanning line on the surface of the scanned medium that is the object of image formation. This results in plane scanning with poor imaging characteristics. In order to correct such field curvature, for example, Japanese Patent Application Laid-Open No. 58-5710
According to Publication No. 8, the imaging characteristics of the optical system are improved without making the optical system complicated or expensive by making the positional relationship of each lens system movable without fixing it. It is shown. Specifically, the deviation from plane scanning that occurs within one scanning period is controlled by moving collimator lenses, condensing lenses, etc. in the optical axis direction using actuators to improve imaging characteristics and enable plane scanning. be.

0003

[Problem to be Solved by the Invention] However, according to such a publication method, the optical system has moving parts that must be precisely set and maintained, which may cause adverse effects such as vibration. Conceivable. Furthermore, since it is mechanically movable, the response speed is slow, and it is difficult to say that it is suitable for application to high-speed equipment such as laser printers.

0004

[Means for Solving the Problems] The invention according to claim 1 includes a collimating lens that converts a laser beam emitted from a laser light source into a parallel beam, and a first lens that converges the converted parallel beam in the main scanning direction. A cylinder lens, an electro-optic lens having a pair of electrodes disposed at the beam waist position of the first cylinder lens and shaped to have a convergence effect in the sub-scanning direction, and a laser beam emitted from the electro-optic lens. a second cylinder lens that has a convergence effect in the main scanning direction; a third cylinder lens that converges the laser beam emitted from the second cylinder lens in the sub-scanning direction; a rotating polygon mirror disposed near the beam waist position of the emitted laser beam and driven to rotate; an imaging optical system that forms an image of the deflected beam deflected by the rotating polygon mirror;
A control power supply that drives and controls the electro-optical lens to bring the beam waist position in the sub-scanning direction into alignment with the surface of the scanned medium in the sub-scanning direction within one scanning period, which is scanned by the laser beam that is deflected and imaged. and has been established.

In the invention as claimed in claim 2, in the invention as claimed in claim 1, the first cylinder lens and the second cylinder lens have a convergence effect in the sub-scanning direction, and the electro-optic lens has a convergence effect in the main-scanning direction. and a control power source for driving and controlling the electro-optical lens so that the beam waist position in the main scanning direction coincides with the surface of the scanned medium within one scanning period. did.

The invention set forth in claim 3 has a configuration in which the invention set forth in claim 1 and the invention set forth in claim 2 are combined.

[0007]

According to the invention as claimed in claim 1, an electro-optical lens having a convergence effect in the sub-scanning direction is disposed at the beam waist position of the first cylinder lens, and the incident beam from the laser light source is approximately 2 Since the first cylinder lens focuses the light in the main scanning direction so that the light passes through the power-law distribution refractive index distribution region, the light enters the electro-optic lens, which functions as an electro-optic lens with a variable focal position with almost no aberrations. Become,
It is possible to correct the curvature of field in the sub-scanning direction on the surface of the medium to be scanned and perform plane scanning. This correction operation can be electrically controlled using a control power source for the electro-optic lens, and the response speed is fast, so that sufficient correction can be performed within one scanning line period. Further, since the correction is based on a solid-state control method using an electro-optic lens, no mechanically movable parts are required in the optical system, and there is no adverse effect on the precisely set optical system.

According to the second aspect of the invention, an electro-optic lens having a convergence effect in the main scanning direction is disposed at the beam waist position of the first cylinder lens, so that the incident beam from the laser light source is approximately 2 Since the first cylinder lens focuses the light in the sub-scanning direction so that it passes through the power-law distribution refractive index distribution region, the light enters the electro-optic lens, which functions as an electro-optic lens with a variable focus position with almost no aberrations. Therefore, it is possible to correct the curvature of field in the main scanning direction on the surface of the scanned medium and perform plane scanning.

According to the invention set forth in claim 3, the combination of the invention set forth in claim 1 and the invention set forth in claim 2 provides an electro-optical lens having a convergence effect in the sub-scanning direction and an electro-optic lens having a convergence effect in the main-scanning direction. Since the curvature of field in each direction is corrected independently using an electro-optic lens, it is possible to correct the curvature of field in both the main scanning direction and the sub-scanning direction on the surface of the scanned medium and perform flat scanning. can.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention as claimed in claim 1 will be described with reference to FIGS. 1 to 4. Figure 1 shows the basic configuration of this embodiment. Figure 1(a) shows the planar configuration seen parallel to the scanning plane (main scanning direction), and Figure 1(b) shows the planar configuration in the direction perpendicular to the scanning plane (main scanning direction). The front configuration as seen in the sub-scanning direction is shown. Generally speaking,
A semiconductor laser 1 as a laser light source, a collimating lens 2, a first cylinder lens 3, an electro-optic lens 4, and a second
A cylinder lens 5, a third cylinder lens 6, a rotating polygon mirror 7, and a toroidal fθ lens 8 serving as an imaging optical system are disposed in this order, and are configured to scan a surface of a scanned medium 9. A control power source 10 is connected to the electro-optical lens 4, and is configured so that a high frequency voltage can be selectively applied by a control system and switching means (not shown).

First, the semiconductor laser 1 emits a laser beam 11 having a polarization plane in the sub-scanning direction as shown by the arrow in FIG. The light is incident on the cylinder lens 3. This first cylinder lens 3 has a convergence effect in the main scanning direction, and the electro-optical lens 4 is disposed at the beam waist position of the laser beam emitted from this first cylinder lens 3. Here, the electro-optic lens 4 is made of a rectangular electro-optic medium 12 whose end face is polished, for example, PLZT.
Based on an electro-optic crystal, an electrode pair 13 made up of a pair of electrode films 13a and 13b is provided on both sides in the sub-scanning direction with an optical path sandwiched therebetween, and a control power source 10 is connected to the electrode pair 13. There is. With this configuration, the details will be described later, but it has a convergence effect in the sub-scanning direction.
By changing the voltage applied by the control power source 10, the focal length can be varied.

The second cylinder lens 5 provided on the output side of the electro-optic lens 4 has a convergence effect in the main scanning direction, and focuses the laser beam emitted from the electro-optic lens 4 in the main scanning direction. It becomes a parallel beam. The third cylinder lens 6 has a convergence effect in the sub-scanning direction, and focuses this parallel beam in the sub-scanning direction. The rotating polygon mirror 7 is disposed near the beam waist of the laser beam focused in the sub-scanning direction and emitted from the third cylinder lens 6, and is rotated to direct the beam in the main scanning direction. This will cause deflection scanning. The toroidal fθ lens 8 has a different focal length in the main and sub-scanning directions, and forms an image of the laser beam deflected by the rotating polygon mirror 7 on the surface of the scanned medium 9. In the sub-scanning direction, this toroidal fθ lens 8 is arranged so that the reflecting surface of the rotating polygon mirror 7 and the surface of the scanned medium 9 have an almost conjugate relationship in terms of geometrical optics. This is designed to prevent misalignment of the scanning line due to

In such a configuration, first, when no voltage is applied to the electro-optic lens 4 by the control power supply 10, or when only a constant DC voltage is applied (when the electro-optic lens 4 1 (c), the curvature of field on the scanned medium 9 surface is as shown in Fig.
), the curvature of field M in the main scanning direction and the curvature of field S in the sub-scanning direction are in different states. Of these, in this embodiment, only the curvature of field S in the sub-scanning direction, which has a larger curvature of field, is corrected (the curvature of field M in the main-scanning direction is assumed to be within a tolerance value, and (The method for correcting the curvature of field in the main scanning direction will be explained in the embodiment described later).

Since the curvature of field S in the sub-scanning direction shown in FIG. 1(c) is determined by the imaging optical system and is fixed, the curvature of field S in the sub-scanning direction corresponds to the curvature of field S in the sub-scanning direction within one scanning period. This is corrected by changing the focal length of the electro-optical lens 4 in the sub-scanning direction. That is, this correction is performed by applying a high frequency voltage with a period corresponding to the curvature of field S to the electro-optic lens 4 by the control power supply 10, so that the beam waist position in the sub-scanning direction always matches the surface of the scanned medium 9. This is achieved by When the value of the applied high-frequency voltage increases, the convergence function of the electro-optic lens 4 becomes larger, and it functions as a composite lens with the imaging optical system, so that the beam waist position in the sub-scanning direction becomes a rotating polygon near the surface of the scanned medium 9. When the beam approaches the mirror 7 side, and conversely, the value of the high-frequency voltage decreases, the beam waist position in the sub-scanning direction moves away from the rotating polygon mirror 7. Therefore, by setting the high frequency voltage applied by the control power source 10 in accordance with the degree of the field curvature S, it can be corrected and plane scanning becomes possible.

By the way, the function of the electro-optic lens 4 used in this embodiment will be explained in detail with reference to FIGS. 2 to 4. First, the electrode films 13a and 13b are formed in the shape of straight strips with a relatively narrow electrode width d and length L at the center of both surfaces of the electro-optic medium 12 perpendicular to the sub-scanning direction. For example, Au is used as the material for the electrode films 13a and 13b, but other conductive materials may be used. The manufacturing method is based on the vacuum evaporation method. For example, the electro-optic crystal 12 is 9.0/6.
A PLZT electro-optic crystal with a composition of 5/35 is used.

First, when no voltage is applied to the electrode pair 13, the electro-optic lens 4 does not have a lens function, and the incident beam is emitted as is. Next, V1 is applied to the electrode pair 13.
When the voltage is applied, a broken line E in FIG. 2 appears in the electro-optic medium 12.
An electric field distribution as shown in 1 occurs, and the electrode part (electrode film 13a
, 13b) and becomes weaker near the center of the electro-optic medium 12. Based on such electric field distribution, a refractive index distribution occurs in the crystal due to the electro-optic effect (secondary electro-optic effect) of the PLZT electro-optic crystal. Now, the direction of the electric field and the light beam 1
When the polarization direction of is the z-axis direction, the traveling direction of the light beam 1 is the y-axis direction, and the z-axis component of the refractive index in the electric field is nZ,

[Equation 1] nZ = n0 (1-n02 R33EZ2 /2)
......(1). However, n0 is the refractive index of the PLZT electro-optic crystal at electric field E=0, and R33 is the matrix component of the second-order electro-optic constant.

From equation (1), the refractive index change ΔnZ due to the electric field EZ is:

[Math. 2] ΔnZ = -n03 R33EZ2 /2
......(2), which is proportional to the square of the electric field strength. And, since the refractive index is small where the electric field is strong,
The refractive index distribution is such that the refractive index is low near the electrode portions in the PLZT electro-optic crystal and becomes high near the center of the crystal. Therefore, a lensing effect occurs toward the center in the z-axis direction. This lens effect becomes more effective as the electrode length L becomes longer.

Therefore, when the laser beam 11 linearly polarized in the z-axis direction (sub-scanning direction) is incident on the electro-optic medium 12, the voltage V1 applied to the electrode pair 13 having the electrode width d and length L causes It is subjected to a converging lens action in the z-axis direction (sub-scanning direction).

FIG. 3 shows the results of the refractive index distribution in the electro-optic medium 12 according to this embodiment obtained by the finite element method. In FIG. 3, the coordinate origin 0 is the center position of the electro-optic medium 12, and x=0 mm (indicated by ■), x=0.25 mm (indicated by ■
), and the refractive index distribution in the z-axis direction at each position of x=0.5 mm (indicated by ■). However, n0
= 2.5, electric field strength EZ = 1000 V/mm, electrode width d = 1.1 mm, and thickness of the electro-optic medium in the z-axis direction is 1.
It was set to 4 mm. As a result, the refractive index distribution became a curved distribution as shown by ■■■. Based on such a refractive index distribution, ray tracing was performed using the Runge-Kutta-Zill method when the electrode length L = 8.0 mm, and the convergence characteristics were examined. It has been found that the beam 11 converges in each region of ■■■ due to different refractive index distributions, resulting in aberrations.

In this regard, in this embodiment, the linearly polarized laser beam 11 is not directly incident on the electro-optic medium 12 of the electro-optic lens 4, but is converged in the x-axis direction (main scanning direction) by the first cylindrical lens 3. The focused laser beam 11 is made incident at the beam waist position. That is, as shown in FIG. 4, the laser beam 11 enters the electro-optic medium 12 as a focused laser beam 11 that is flattened in the x-axis direction. As a result, near the center of the electro-optic medium 12 (x=0
mm), the refractive index distribution approaches a square distribution over the entire z-axis direction, as shown in FIG. The refractive index of the power law distribution is sensed and converged, and aberrations are improved. In other words, the convergent laser beam 11 converged by the first cylindrical lens 3
By appropriately setting the relationship between the incident position x and the electrode width d1, convergence characteristics with less aberration can be obtained.

Next, an embodiment of the invention according to claim 2 will be explained with reference to FIGS. 5 to 8. The same parts as those shown in the previous embodiment are indicated using the same reference numerals. In this example,
It is designed to correct field curvature in the main scanning direction, and instead of the cylinder lens 3 and electro-optic lens 4,
A first cylinder lens 15 having a convergence effect in the sub-scanning direction and an electro-optic lens 16 having a convergence effect in the sub-scanning direction are provided, the cylinder lens 5 is omitted, and the cylinder lens 6 is replaced by a second cylinder lens 15. It is a cylinder lens. Furthermore, instead of the toroidal fθ lens 8, an fθ lens 17 and a cylinder lens 18 that is long in the main scanning direction and has a convergence effect in the subscanning direction are provided as an imaging optical system. The reflecting surface of the rotating polygon mirror 7 and the surface of the scanned medium 9 are geometrically optically substantially conjugate with respect to the sub-scanning direction by the fθ lens 17 and the cylinder lens 18, and scanning due to the surface tilt of the rotating polygon mirror 7 is achieved. Line misalignment is prevented.

Here, the electro-optic lens 16 is disposed at the beam waist position of the laser beam emitted from the first cylinder lens 15, and is arranged on both sides of the rectangular electro-optic crystal 19 perpendicular to the sub-scanning direction. An electrode pair 20 is formed on the electrode and connected to a control power source 21. As will be described later in FIG. 6, the electrode pair 20 includes four straight strip-shaped electrode films 20a1, 20a2, 20b1, 20b2 formed on both sides with a gap g in the main scanning direction on each side.
Consisting of With this configuration, the details will be described later, but it has a convergence effect in the main scanning direction, and the control power supply 2
By changing the applied voltage according to No. 1, the focal length can be varied.

In such a configuration, when the electro-optical lens 19 does not exhibit a lens function, the curvature of field on the surface of the scanned medium 9 is caused by the image in the main scanning direction, as shown in FIG. 5(c). The curvature of field M in the sub-scanning direction and the curvature of field S in the sub-scanning direction are different from each other. In particular, the curvature of field S in the sub-scanning direction is approximately within the allowable value, but the curvature of field M in the main scanning direction is large. Therefore, correction is required. Therefore, in this embodiment, this curvature of field M is attempted to be corrected by the lens action of the electro-optic lens 19.

The curvature of field M in the main scanning direction shown in FIG. 5(c) is also determined by the imaging optical system and is fixed, so it corresponds to the curvature of field M in the main scanning direction within one scanning period. This is corrected by changing the focal length of the electro-optical lens 16 in the main scanning direction. That is, this correction is performed by applying a high frequency voltage with a period corresponding to the curvature of field M to the electro-optical lens 16 by the control power supply 21, so that the beam waist position in the main scanning direction is always adjusted to the scanned medium 9.
This is achieved by matching on the surface. When the value of the applied high-frequency voltage increases, the convergence function of the electro-optic lens 16 becomes larger, and it functions as a composite lens with the imaging optical system, so that the beam waist position in the main scanning direction becomes a rotating polygon near the 9th surface of the scanned medium. When the beam approaches the mirror 7 side, and conversely, the value of the high-frequency voltage decreases, the beam waist position in the main scanning direction moves away from the rotating polygon mirror 7. Therefore, by setting the high frequency voltage applied by the control power source 21 in accordance with the degree of field curvature M, it can be corrected and plane scanning becomes possible.

By the way, the operation of the electro-optic lens 16 used in this embodiment will be explained in detail with reference to FIGS. 6 to 8. Even in the electro-optical lens 16 of this example, when no voltage is applied to the electrode pair 20, it does not have a lens effect, and the incident beam is emitted as is. Then,
When a voltage V2 is applied to the electrode pair 20 by the control power supply 21, an electric field distribution as shown by a broken line E2 in FIG. 6 is generated in the electro-optic medium 19 due to the shape and arrangement of the electrodes. As a result, due to the electro-optic effect of the PLZT electro-optic crystal, x
- The refractive index distribution is such that the refractive index becomes high near x=0 (the origin is the center of the electro-optic medium 19 shown in FIG. 6) on the z plane. Such a refractive index distribution is given by equation (1). This results in a lensing effect towards the center in the x direction. Such a lens effect becomes larger as the electrode length becomes longer.

Therefore, when the laser beam 11 linearly polarized in the z-axis direction (sub-scanning direction) is incident on the electro-optic medium 19, the voltage V2 applied to the electrode pair 20 causes the convergent lens to be polarized in the x-axis direction (main-scanning direction). be affected.

Now, FIG. 7 shows the results of the refractive index distribution in the electro-optic medium 19 according to this embodiment obtained by the finite element method. In FIG. 7, the coordinate origin 0 is the center position of the electro-optic medium 19, and the positions of z = 0 mm (indicated by ■), z = 0.3 mm (indicated by ■), and z = 0.6 mm (indicated by ■) are shown. This figure shows the refractive index distribution in the x-axis direction (main scanning direction) at . However, n0=2.5, electric field strength EZ=1000V/m
m, the electrode gap g=1.5 mm, and the thickness of the electro-optic medium 19 in the z-axis direction was 1.4 mm. As a result, the refractive index distribution became a curved distribution as shown by ■■■. Based on this refractive index distribution, ray tracing was performed using the Runge-Kutta-Zill method when the electrode length was set to 8.0 mm, and the convergence characteristics were examined. It was found that No. 11 causes aberrations due to convergence due to different refractive index distributions in each region of ■■■.

In this regard, in this embodiment, the linearly polarized laser beam 11 is not directly incident on the electro-optic medium 19;
The laser beam 11 is made incident by a cylindrical lens 15 and converged in the z-axis direction (sub-scanning direction). That is, as shown in FIG. 8, the laser beam 11 enters the electro-optic medium 19 as a flattened laser beam 11 in the z-axis direction. As a result, near the center of the electro-optic medium 19 (z = 0 mm)
Compared to the refractive index distribution shown in FIG. 7, in which the refractive index distribution approaches a square distribution over the entire x-axis direction, the flat convergent light beam 18 has an approximately square distribution within the electro-optic medium 19. It will be converged by sensing the refractive index of
Aberrations are improved.

Further, the invention according to claim 3 will be explained with reference to FIG. This embodiment is a combination of the two embodiments described above so that both field curvatures M and S can be corrected. Specifically, the cylinder lens 3 is a first cylinder lens, the electro-optic lens 4 is a first electro-optic lens,
The cylinder lens 5 is a second cylinder lens, the cylinder lens 15 is a third cylinder lens, and the electro-optical lens 16
is a second electro-optical lens, the cylinder lens 6 is a fourth cylinder lens, the toroidal fθ lens 8 is an imaging optical system, the control power source 10 is a first control power source, and the control power source 21 is a second control power source. That is.

According to this embodiment, by controlling the control power supplies 10 and 21 independently, the curvature of field S in the sub-scanning direction and the curvature of field M in the main scanning direction are respectively adjusted according to the embodiments described above.
and can be corrected individually, making it possible to perform plane scanning with improved two-dimensional imaging characteristics.

[0031]

Effects of the Invention Since the present invention is configured as described above, according to the first aspect of the invention, the electro-optic lens having a convergence effect in the sub-scanning direction is positioned at the beam waist position of the first cylinder lens. The incident beam from the laser light source is focused in the main scanning direction by this first cylinder lens so that it passes through a refractive index distribution region with an approximately square distribution, and is made incident on the electro-optic lens. , the electro-optical lens can function as a variable focal position lens with almost no aberrations, and the curvature of field in the sub-scanning direction on the surface of the scanned medium can be corrected for plane scanning. The operation can be electrically controlled using a control power source for the electro-optical lens, and the response speed is fast.
It can be sufficiently corrected within one scanning line period, and
Since the correction is based on a solid-state control method using an electro-optic lens, no mechanically movable parts are required in the optical system, and there is no adverse effect on the precisely set optical system.

Similarly, according to the second aspect of the invention, an electro-optic lens having a convergence effect in the main scanning direction is disposed at the beam waist position of the first cylinder lens, and the incident beam from the laser light source is The electro-optic lens is focused in the sub-scanning direction by the first cylinder lens so that it passes through a refractive index distribution area with an approximately square-law distribution, and is incident on the electro-optic lens. It is possible to correct the curvature of field in the main scanning direction on the surface of the scanned medium and perform plane scanning.

Furthermore, according to the invention set forth in claim 3, by combining the invention set forth in claim 1 and the invention set forth in claim 2, an electro-optic lens having a convergence effect in the sub-scanning direction and a convergence function in the main-scanning direction are combined. Since the curvature of field in each direction can be corrected independently using an electro-optic lens that has a function, it is possible to correct the curvature of field in both the main scanning direction and the sub-scanning direction on the surface of the scanned medium. It is capable of plane scanning.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the invention according to claim 1, (a)
is a plan view, (b) is a front view, and (c) is a characteristic diagram showing a state of field curvature.

FIG. 2 is a cross-sectional view showing an electric field distribution state in an electro-optic lens.

FIG. 3 is a characteristic diagram showing the refractive index distribution depending on the position in the electro-optic medium.

FIG. 4 is a side view showing the shape of a beam incident on an electro-optic medium.

FIG. 5 shows an embodiment of the invention according to claim 2, (a)
is a plan view, (b) is a front view, and (c) is a characteristic diagram showing a state of field curvature.

FIG. 6 is a cross-sectional view showing the electric field distribution state in the electro-optic lens.

FIG. 7 is a characteristic diagram showing the refractive index distribution depending on the position in the electro-optic medium.

FIG. 8 is a side view showing the shape of a beam incident on an electro-optic medium.

FIG. 9 shows an embodiment of the invention according to claim 3, (a)
is a plan view, (b) is a front view, and (c) is a characteristic diagram showing a state of field curvature.

[Explanation of symbols]

1 Laser light source 2 Collimating lens 3
Cylinder lens 4 Electro-optic lenses 5, 6 Cylinder lens 7 Rotating polygon mirror 8 Imaging optical system 9 Scanned medium 10 Control power source 11 Laser beam 13 Electrode pair 15 Cylinder lens 16 Electro-optic lenses 17, 18 Imaging optical system 20 Electrode pair 21 Control power supply

Claims (3)

[Claims] 1. A laser light source, a collimating lens that converts a laser beam emitted from the laser light source into a parallel beam, a first cylinder lens that converges the converted parallel beam in the main scanning direction, and a first cylinder lens that focuses the converted parallel beam in the main scanning direction. An electro-optic lens having a pair of electrodes arranged at the beam waist position of the cylinder lens and shaped to have a convergence effect in the sub-scanning direction, and a convergence effect in the main-scanning direction on the laser beam emitted from this electro-optic lens. a third cylinder lens that converges the laser beam emitted from the second cylinder lens in the sub-scanning direction; and a beam waist of the laser beam emitted from the third cylinder lens. A rotating polygon mirror arranged near the position and driven to rotate, an imaging optical system that forms an image of the deflected beam deflected by the rotating polygon mirror, and a scanned medium that is scanned by the deflected laser beam. and a control power source that drives and controls the electro-optical lens to bring the beam waist position in the sub-scanning direction into alignment with the surface of the scanned medium within one scanning period. 2. A laser light source, a collimating lens that converts the laser beam emitted from the laser light source into a parallel beam, a first cylinder lens that converges the converted parallel beam in the sub-scanning direction, and a first cylinder lens that focuses the converted parallel beam in the sub-scanning direction. An electro-optic lens having a pair of electrodes arranged at the beam waist position of the cylinder lens and shaped to have a convergence effect in the main scanning direction, and a convergence effect in the sub-scanning direction on the laser beam emitted from this electro-optic lens. a second cylinder lens having a second cylinder lens, a rotating polygon mirror arranged near the beam waist position of the laser beam emitted from the second cylinder lens and driven to rotate, and a deflection deflected by the rotating polygon mirror. An imaging optical system that forms an image of the beam, a scanned medium that is scanned by the deflected and imaged laser beam, and a state in which the beam waist position in the main scanning direction is aligned with the surface of the scanned medium within one scanning period. and a control power source for driving and controlling the electro-optical lens. 3. A laser light source, a collimating lens for converting a laser beam emitted from the laser light source into a parallel beam, a first cylinder lens for converging the converted parallel beam in the main scanning direction, and a first cylinder lens for converging the converted parallel beam in the main scanning direction. a first electro-optic lens having a pair of electrodes disposed at the beam waist position of the cylinder lens and having a convergence effect in the sub-scanning direction; and a laser beam emitted from the first electro-optic lens. The second one has a convergence effect in the main scanning direction.
a cylinder lens, a third cylinder lens that converges the laser beam emitted from the second cylinder lens in the sub-scanning direction, and a third cylinder lens that is disposed at the beam waist position of the third cylinder lens and converges it in the main-scanning direction. a second electro-optical lens having a pair of electrodes shaped to have an effect; a fourth cylinder lens having a convergence effect in the sub-scanning direction on the laser beam emitted from the second electro-optic lens; a rotating polygon mirror arranged near the beam waist position of the laser beam emitted from the fourth cylinder lens and driven to rotate; an imaging optical system that forms an image of the deflected beam deflected by the rotating polygon mirror; Driving and controlling the first electro-optic lens so that the beam waist position in the sub-scanning direction coincides with the surface of the scanned medium that is scanned by the deflected and imaged laser beam within one scanning period. a first control power source; and a second control power source that drives and controls the second electro-optical lens to bring the beam waist position in the main scanning direction into alignment with the surface of the scanned medium within one scanning period. An optical scanning device characterized by: