JPH02111914A - Scanning type optical device - Google Patents

Abstract

PURPOSE:To decrease the shift of a reflected luminous flux and to allow plotting with higher accuracy by putting a deflecting element for correction which deflects the luminous flux emitted from a light source slightly in a sub-scanning direction and a deflector for scanning which deflects the luminous flux emitted from the deflecting element for correction in a main scanning direction in a nearly conjugated state. CONSTITUTION:The laser light emitted from an argon laser 10 is bisected by a half mirror 12 of 5% reflection via a pin hole 11. The laser light transmitted through the mirror 12 is rotated 90 deg. in the polarization direction by a 1st half wavelength plate 13 and is adjusted in light quantity by a variable filter 14. This light is further bisected by a 1st beam splitter 15 of 50% reflection and 50% transmission. The two split luminous fluxes are used as the luminous fluxes for plotting forming two spaced spots on a plotting plane. An AO modulator (deflecting element for correction) 22 for correction which corrects the influence by the surface inclination of a polygon mirror (deflector for scanning) PM is provided on the side before the condensing point by a 1st lens system 50. The positional deviation of the luminous flux on a reflecting surface is prevented in this way and the plotting is more exactly executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a scanning optical device used in a laser exposure device etc. that draws a precise pattern with a laser beam, and more specifically, relates to a scanning optical device that scans a beam. The present invention relates to a scanning optical device having a surface tilt correction function of a deflector such as a polygon mirror.

[Prior Art and Problems to be Solved by the Invention] In an ideal polygon mirror, the reflecting surface is parallel to the rotation axis, and the spot scans the same line when reflected from any reflecting surface. However, in reality, due to problems such as processing errors, the reflective surface is tilted with respect to the rotation axis, that is, surface inclination error occurs, and the scanning line for each reflective surface is aligned in the direction perpendicular to the spot scanning direction (main scanning direction). (sub-scanning direction).

It is technically difficult to eliminate this surface inclination error by improving the processing accuracy of the polygon mirror, and this leads to an increase in costs.

For this reason, conventional methods have been proposed to remove the influence of this surface tilt by providing an optical correction system.

JP-A-59-15216 discloses a method for reducing the influence of the fall of the reflective surface by converging a light beam so as to form a line image in the main scanning direction on the reflective surface of a polygon mirror. .

However, even with this method, complete correction is difficult. In addition, when using this method, an anamorphic lens system with different powers in the main scanning plane and sub-scanning plane is required to form a line image, so the manufacturing of the lens system itself is compared to a spherical lens. In particular, it has been difficult to manufacture anamorphic lens systems suitable for devices that require highly accurate drawing.

When correcting tilt while using a spherical lens as a lens system, an AO modulator (ultrasonic optical modulator) is installed between the light source and the deflector, as shown in Japanese Patent Laid-Open No. 56-107212, for example. There is a configuration in which the angle of incidence in the sub-scanning direction is slightly deflected by providing a.

Although not disclosed in this publication, a beam expander system is actually provided because it is necessary to increase the diameter of the beam incident on the scanning lens in order to narrow down the spot on the drawing surface.

In addition, since the response frequency of the AO probe is inversely proportional to the diameter of the beam on the element, in order to have a modulation function, it is necessary to place it at a position where the diameter of the beam is small. It will be provided in a parallel light beam closer to the light source side.

Figures 5(A) and 5(B) show an example in which an AO modulator is installed in a parallel beam of light on the light source side (left side in the figure) from the beam expander system. Type, (B)
shows an example using a Kevlar type beam expander. Note that the solid line in the figure shows the optical path before deflection by the AO modulator, and the broken line shows the optical path after deflection.

The focus distance of the lens L1 in the figure is fl, and the second lens L
When the focal length of 2 is fa, the magnification H of the beam expander system is L-f2/f+, and when the tilt angle of the light beam for tilt correction is θP, the deflection angle θ of the AO probe is ■The formula is as follows.

θ, nid θP...■ Next, the distance wound from the AO element to the second lunula L1 is
When the distance from the lens L2 to the polygon mirror is d, the deviation fiS of the light beam is expressed by the following equation.

S: (M2111+M(f++f2)+d)・θP・
・・■For example, f+:lo, fa:200. M=-20
, 9+=100 and a beam expander system that expands a 1φ beam to 20φ, and if the surface inclination of the reflecting surface of the polygon mirror is lO", the correction angle θP of the luminous flux is 20".
Therefore, from formula (■), the deflection angle of the AO element is θ, = -0
, 11".

In addition, the deviation of the light beam on the reflective surface of the polygon mirror is
Assuming that d2 is 100, S=3.5 from the formula 0.

Therefore, although the angular shift of the reflected light beam due to the surface tilt can be corrected, this correction causes a parallel shift in the reflected light beam. This shift causes the scanning line formed on the drawing surface to slightly deviate from its ideal position.
This becomes a problem when performing highly accurate drawing.

There is also the problem that it is difficult to control AO$$ in order to obtain a minute angle of θ=−0.11°.

FIG. 6 shows an example in which an AO probe is provided within the focused light in the beam expander.

In the figure, the distance Aff from the focal position of the second lens L2 with focal length AItf+ to the AOi element is 9, the focal length of the second lens is fa, the magnification of the beam expander system is H1, and the light flux for tilt correction is Assuming that the tilt angle is θp and the deflection angle of the AO element is θ, the following relationship holds true.

θs unit f2/11)・θP S”−h・(1+ −)・θp+d・θP Here, for example, f+”100. fa:2000. H knee 20.
Assuming a beam expander system that expands a beam of lφ to 20φ with Q = 20, and assuming that the surface tilt of the reflective surface of the polygon mirror is lO'', the deflection angle of the AO element to correct this is θ, = -0.56',5=-19,6, and the amount of deviation of the light beam on the polygon mirror becomes very large.

Therefore, in order to maintain drawing accuracy, a high-precision polygon mirror with less tilting is required.

Furthermore, in Japanese Patent Application Laid-Open No. 62-568918, two AO elements are provided, one AO element corrects the surface inclination, and the other AO element corrects the shift of the luminous flux due to the surface inclination correction. A configuration is disclosed. However, in this configuration, since two AO elements are provided, the degree of freedom in designing the optical system is reduced, and electrical control is also complicated.

[Object of the invention] This invention was made in view of the above problems, and
It is an object of the present invention to provide a scanning optical device that enables more accurate drawing by reducing the shift of the reflected light beam that occurs when correcting the angular deviation of the reflected light beam due to surface tilt.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a correction deflection element that minutely deflects the light beam emitted from the light source in the sub-travel direction, and a correction deflection element that slightly deflects the light beam emitted from the correction deflection element. It is characterized in that the scanning deflector for deflecting in the main scanning direction is optically substantially conjugate.

Being optically conjugate does not necessarily mean that there is an imaging relationship, but if only the principal ray is considered, it can be understood that no positional shift occurs even if there is an angular shift in the light beam.

Being optically conjugate means that the optical characteristic matrix Rp of the optical system between the AO element and the reflective surface of the polygon mirror is expressed as follows. However, m is the magnification of this optical system, and f is the focal length.

Here, the optical property matrix is the transfer function of the paraxial ray, and the height hl and angle α1 in the input plane are as follows:
This means converting into h2 and α2 on the output plane.

Furthermore, since the beam expander system is an afocal system with a magnification H as a whole, it has a matrix as follows. Here, K is a constant corresponding to a distance of 9° from the light source to the second lens L1.

The optical characteristic matrix of the entire beam expander system shown in FIGS. 5(A) and 5(B) has a solution as follows, and can be conjugate.

Further, the relationship between the inclination angle θP of the light beam for surface tilt correction and the deflection angle θ of the AO strand is expressed as follows.

Furthermore, the relationship between the AO element and the polygon mirror in the figure is such that the AO element is located in front of the beam expander system, so the magnification M knee f2μ! The condition for the AO element and the polygon mirror to be conjugated is f++h+Mll+(d/M)=0. In this system, 11)0. Since d>O is i-possible, Fig. 5 (
A) fl (O) cannot be conjugated.

In the case of fl)0 in FIG. 5(B), 11 (-(1/M)・(f1+h) Only when the d=-M”　9-M・([1+h) Therefore, θP is given by (1/M)·θ.

In the system shown in FIG. 5(B), as described above, 9
Therefore, the conjugate condition cannot be ensured unless f2 is set large.

Next, the optical characteristic matrix for the entire beam expander system in FIG. 6 is as follows, and the relationship between the inclination angle θP and the deflection angle θ is θρanyyyuzumi/f2)·θ.

is given by When an AO element is provided inside the beam expander system in this way, the relationship between the AO element and the polygon mirror is expressed by the following matrix, and the conjugate condition is g + f2 -
(II d/f2)=0. ', d=f, + (f, 27Q), and in this case, the relationship 1-(d/f2);-f2/II =lll holds true, where m is the relationship between the AO modulator and the polygon mirror. The magnification is between .

In this system, d must be very large in order to satisfy the conjugation condition.

By the way, in the systems shown in FIG. 5(B) and FIG. 6, there is a problem that the values of 9 and d are limited in order to satisfy the conjugate condition.
As shown in the figure, the problem can be solved by arranging a relay lens LR at the focal point of the laser beam.

FIG. 7 shows an example in which a relay lens LR of focal path if is provided in the configuration of FIG. f+fp/f
o); becomes 0. By adding the term -f+h/f-, the condition regarding 9 disappears.

In addition, the relay lens LR does not function as a beam expander system, and the optical characteristic matrix of the entire system is expressed as follows.What is the relationship between the tilt angle θP and the deflection angle θ?
P; θ, given by /M.

Next, FIG. 8 shows an example in which a relay lens LR is provided in the optical system of FIG. 6, and the relationship between the AO element and the polygon mirror can be expressed as follows.

The conjugate condition is as follows, and the conjugate condition at this time is expressed by , which increases the degree of freedom in design. In addition, the matrix of the entire system is as follows, and the relationship between the tilt angle θP and the deflection angle θ is θP=
−9・θ, given by /f2.

Note that it is preferable that the relay lens LR in FIGS. 7 and 8 not be placed at the convergence point of the laser beam, considering shadows caused by dust and scratches on the lens surface.
When the principal point position of the relay lens is shifted as shown in FIG. 9, the above-mentioned problems are avoided and the degree of freedom in design is improved.

Incidentally, in order to improve the magnification of the beam expander, a beam expander system may be further placed behind the optical system shown in FIGS. 5 to 8. In this case, the optical characteristic matrix of the beam expander system in the subsequent stage is R1...RN, and RP'=RII-RN-
Bi...The optical property matrix Rρ° as a whole is obtained from R1·Rp, and the conjugate condition is obtained from this.

The configuration in which the beam expander systems are stacked is physically based on the conjugate point of the reflective surface of the polygon mirror formed by the subsequent beam expander system and the AO modulator formed by the first beam expander system. It is equivalent to matching the conjugate point.

In such a case, 1 as shown in Figures 5 to 8
The degree of freedom is increased by the stage beam expander system compared to forming a conjugate relationship, and the above-mentioned relay lens is not necessarily required.

Figure 10 shows +R with a two-stage beam expander system.
This shows the results. Focal path tuft f+
, f2, and the distance between the conjugate point of the AO modulator formed by the first beam expander system consisting of the first and second lenses L+ and L2 and the second lens L2 is a. The optical property matrix between the conjugate points is expressed as, and from the conjugate condition, f++f2+? L19 + (a/MI): 0a Knee-M+
(f++fa+M+ 11 ) is given.

On the other hand, the third and fourth lenses L3. with focal apertures fs and fa.
The conjugate point of the polygon mirror formed by the second beam expander system consisting of L4 and the third lens L! Assuming that the distance is b, the optical property matrix between this conjugate point and the polygon mirror is given by:

Furthermore, FIG. 11 shows an example in which a beam expander system is superimposed on the rear of the optical system of FIG. 8.

If the distance between the conjugate point of the AO modulator formed by the optical system of FIG. 8 and the second lens L2 is a, then the optical characteristic matrix between the ^0 modulator and this conjugate point is expressed as follows. Then, from the conjugate condition, fs+f4+Mab+(d
2/M2)=Ob=-(1/M2)・(fa+f4+(
d2/H2)) is calculated by tj.

Here, if f3 is 0, then b(O) since M2>0, and a conjugate point is created inside the beam expander.

Furthermore, if the distance d1 between the second lens L2 and the third lens L3 is set to d as a+b, the AO modulator and the polygon mirror become conjugate, and the matrix between them is expressed as,
The following relationship holds from the conjugate condition.

On the other hand, the focal hole! ! ! ff f 3. The conjugate point of the polygon mirror formed by the second beam expander system consisting of the third and fourth lenses L3+L4 of f4 and the third
Assuming that the distance to the lens L is b, the optical characteristic matrix between this conjugate point and the polygon mirror is divided by k. Then, from the conjugate condition, f3 sat fa+M
2b+(da/H2)=Ob=-(1/M2)・(f
s+f4+(d2/M2)) is obtained.

Here, the distance d between the second lens L2 and the third lens L3.

If dl = a + b, the AO modulator and the polygon mirror become conjugate, and the matrix of these columns is Rp:
Rp2HRp+ M+; -b/f+, expressed as follows. Therefore, the overall optical characteristic matrix of the first and second beam expander systems is:

Rp: RP2°Rr+, and the relationship between the tilt angle θρ and the deflection angle θ is given by θ, knee M2·θp−b/II.

Note that M2 is a double beam expander system in the latter stage, and M2 knee fa/f3.

In addition, the optical characteristic matrix of the entire system of the first beam expander consisting of the first and second lenses L + * L 2 is expressed by the magnification H1 of the first beam expander system, and the beam expander -The magnification of the entire system is MI82.

In addition, in the explanation of Figs. 5 to 11, paraxial analysis was performed by using an optical characteristic matrix with a thin lens, but the actual lens system is composed of multiple thick lenses, and the Because it is also affected by this, it may be placed slightly offset from the paraxially analyzed position.

[Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4.

FIG. 1 is an explanatory diagram of the arrangement of an optical system of a photoplotter according to an embodiment, and FIGS. 2 and 3 are schematic explanatory diagrams of a part thereof developed along the optical axis.

This photoplotter splits the laser beam emitted from the argon laser 10 as a light source into three beams, two of which form two spots on the drawing surface, and the remaining one to accurately position the spot. It is used as a monitor light to detect. The spots on the drawing surface simultaneously scan adjacent scanning lines at predetermined intervals in the main scanning direction by rotation of the polygon mirror PM.

The reason for providing the interval in the main scanning direction is that the interval between adjacent scanning lines is set smaller than the spot diameter in order to perform precision drawing, and if the interval is not provided, the two spots will partially overlap and cause interference. This is because there is a possibility that the drawing performance may become unstable.

In order to combine two light beams into the same optical path, it is common to make the polarization directions of the two light beams orthogonal to each other and to combine them using a polarizing beam splitter. In order to divide the light beam emitted from the light source into three parts, combine them again, and scan them by the same deflector, it cannot be achieved by adjusting only the deflection direction.

Therefore, in this optical system, the light beam for drawing and the light beam for monitoring are distinguished using deflection, and the two light beams for drawing and the monitor are incident on the same lens from different directions, so that they are on the same optical path. It is synthesized into This combination method is permissible because, as described above, the drawing spot is formed by shifting it in the main scanning direction.

Next, the configuration of each part of this device will be explained along with its operation.

The laser beam emitted from the argon laser 10 is split into two by a 5% half mirror 12 through a pinhole 11. The laser beam reflected by this half mirror 12 is used as a monitor light beam 9. .

On the other hand, the laser beam that has passed through the half mirror 12 has its polarization direction rotated by 90 degrees by the first 1/2 wavelength plate 13, and the light ffi is adjusted by the barrier pull filter 14 so that 50% of the laser beam is reflected.
The beam is further divided into two by a first beam splitter 15 with 50% transmission.

The two divided beams are shown in Figure 4. It is used as a drawing light beam that forms two spots spaced apart by M on the III plane.

The first drawing light beam g1 transmitted through the first beam splitter 15 passes through the lens 16 to the first drawing AO modulator 1.
Focus the light on position 7.

This AO modulator 17 diffracts laser light incident from a direction that satisfies the Bragg condition by inputting ultrasonic waves to a transducer.
By performing 10FF, the laser beam can be switched to zero-order light and first-order light, and the first-order light is used as a drawing light beam. The AO modulator 17 is controlled by a write signal which is dot-by-dot exposure information for the drawing surface.

The primary light, which is the modulated ON light, is made into a parallel light beam again by a lens 18 provided behind the AO modulator 17, and then passed through a mirror 19 to a first light beam direction adjusting device 40 consisting of four prisms. is deflected at a predetermined angle by mirror 2.
0, the light enters the lun system 50.

On the other hand, the second beam reflected by the first beam splitter 15
The drawing light beam 22 is made into a convergent light via the lens 16', is reflected by the mirror 21, and is transmitted to the second drawing AO modulator 17'.
Enter the room. AO modulation i1j; 8N capability of 17° is similar to the first drawing AO modulator 17 described above. However, the signal that drives this second drawing river AO modulator 17' is as follows:
The signal input to the first drawing AO modulator 17 is a signal for scanning a line shifted by l line.

The primary light emitted from the second drawing AO modulator 17' passes through a lens 18' and is deflected at a predetermined angle by a second beam direction adjusting device 40° made up of four prisms, and enters the lens system 50 Q4. .

The lens 16.18' has a configuration as shown in Table 1 on page 24, and the lens 18.18' has a configuration as shown in Table 2. Hereinafter, C of the philtrum is the focal hole A1 of the entire system.
, rl is the radius of curvature of the first surface of the lens system, di is the distance between the first surface and the i+1th surface (lens thickness and air gap), and ni is the refractive index of the medium between the first surface and the i+1th surface, respectively. It represents.

The first and second beam direction adjusting devices each include a first prism group P having two prisms as shown in FIG.
1 and a second prism group P2. The configurations of these prisms are shown in Table 3 on the next page.

Here, in FIG. 4, an X axis parallel to the direction of incidence of the light beam and y and z axes perpendicular to this are set. x in Figure 4 (A)
-y plane is a cross section in the main scanning direction, x-2 in FIG. 4(B)
The plane shows a cross section in the sub-scanning direction.

The first prism group P+ includes first and second prisms 41.42
are arranged so that each person's output end is parallel to the y-axis, and the first
The prism 41 is rotatably adjustable around a rotation axis parallel to the y-axis.

Then, the third and fourth prisms 4 of the second prism group P2
3.44 is also the first Bunozum 1 in these relative relationships! They are arranged in the same way as PL, but the output end of each person is parallel to the Z-axis, and the third prism 43 can be rotated around the rotation axis parallel to the Z-axis. .

Table 1 Table 2 Table 3 In this device, by rotating and adjusting the first prism 41 and the third prism 43, the direction of the emitted light beam can be finely adjusted according to the relationship between the incident angle and the declination angle. In this example, the first and second drawing light beams 9g2 have their central axes at an angle of 0.27° in the main scanning direction and 0.034" in the sub-scanning direction, and 3.8mm,
The light is configured to enter the second lens system 70 from a position separated by 0.48 mm in the sub-scanning direction.

Moreover, the first prism group P+ and the second prism group P2 are
They are only involved in fine-tuning the direction of the light beam in the x-z plane and in the circle on the x-y plane, and do not interfere with other directional adjustments, so adjustments in each direction are performed independently. be able to.

Now, the lens system 50 into which the light beam emitted from the light beam direction adjustment device W140, 40' is incident has a three-piece configuration of "+-+" as shown in FIGS. 3 and 4. It is a positive lens and converges the incident laser light. A correction AO modulator 22 for correcting the chromatic tube due to the surface tilt of the polygon mirror PM is provided 62 mm in front of the light condensing point of the first lens system 50.

The drawing laser beam emitted from the correction AO modulator 22 and reflected by the mirror 23 passes through the two-lens relay lens system 60 labeled "-10", and passes through the two-lens relay lens system 60 labeled "-10". 2
The light enters the lens system 70.

The laser beam for drawing, which is made into a parallel beam by the second lens system 70, is reflected by the mirror 24 and combined with the monitor light by the first polarizing beam splitter 25. In other words, the monitor light g divided by the half mirror 12
I is reflected by the mirrors 26 and 27, enters the first polarizing beam splitter 25 as S-polarized light, and is reflected.

On the other hand, the two drawing light beams are made to have a polarization direction different from that of the monitor light by the first half-wave plate 13, and are incident as P-polarized light, so that they are transmitted as they are.

The two drawing light fluxes and the monitor light flux are the second 1/2
The polarization directions are each rotated by 90 degrees by the wave plate 28, and are transmitted to a third lens system 80 consisting of four lenses r -+-+ J and a fourth lens system 90 consisting of two lenses "++" via the mirror 29. incident.

The first lens system 50 and the second lens system 70 have a magnification of 1.67.
It constitutes the first beam expander system of 0.0
．． Expand the 7φ beam to 1.17φ. And the third
The lens system 80 and the fourth lens system 90 constitute a second beam expander system with a magnification of 21.4 times, and the two drawing light beams are expanded from 1.17φ to 25φ.

The two drawing light beams and the monitoring light beam are directed to a polygon mirror PM via two mirrors 30 and 31, and are reflected and deflected by this polygon mirror PM.

The relay lens system 60 connects these beam expanders.
It has a function of making the correction AO modulator 22 and the polygon mirror PM conjugate without being involved in the operation of the system, and correcting the deviation of the light beam on the polygon mirror due to surface tilt correction.

The configuration of the fourth to fourth lens systems described above is the 28th lens system.
, as shown in Tables 4 to 8 on page 29.

(Leaving space below) Table 4 Luns system 50 (3 groups, 3 elements) f = 179.99 Converted distance is 54.67, air equivalent distance between the focal point and AO modulation surface by the Luns system is 61 It is .95.

Table 5 Relay lens system 60 (2 groups, 2 lenses) The distance M when f=56.18 is 140.38.

Table 6 Second lens system 70 (2 elements in 2 groups) f=299.99 It is 76.55.

It is 298.94 in Table 7 and Table 8, and the distance from the fourth surface of the fourth lens system 90 to the polygon mirror PM is 1261.00.

The light beam reflected by the polygon mirror PM is converged by the fθ lens 100 with a focal length of 5151 mm, and the drawing light beam passes through the second polarizing beam splitter 32 to form two spots with a diameter of 5 μm on the 1111 screen.

On the other hand, the monitor light is reflected by this beam splitter 32.
]-1 and enters the light receiving optical system 34 via the scanning correction scale 33 having a striped pattern perpendicular to the scanning direction. The light receiving optical system 34 outputs a pulse having a frequency proportional to the scanning speed based on a change in the amount of transmitted light of the beam scanning the scale 33.

The two spots formed on the drawing surface are spaced apart by 20 μm AL in the main scanning direction and 2.5 μm AL, which is one line interval, in the sub-scanning direction.

Incidentally, the detection of surface inclination is described, for example, in Japanese Patent Application Laid-Open No. 57-84440.
As shown in the publication, this can be done from the outputs of a plurality of charging conversion elements provided outside the drawing range near the drawing surface.

[Effect] As explained above, according to the present invention, even when the angle of the light beam is changed to correct the surface tilt error of the reflection surface of the deflector, the positional deviation of the light beam on the reflection surface can be corrected. It can be corrected and more accurate drawing can be performed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the arrangement of an optical system showing one embodiment of the scanning optical device according to the present invention, FIG. 2 is a sectional view in the main scanning direction showing a part of the optical system of FIG. 1, and FIG. This figure is a cross-sectional view in the sub-scanning direction similar to FIG. 2, and FIGS. 4(A) and 4(B) are explanatory views showing cross-sections of the light beam direction adjusting device. 5 to 10 are explanatory diagrams showing the relationship between the beam expander system, the AO modulator, and the polygon mirror.
Figures (A) and (B) show a beam expander system with an AO modulator installed in the parallel beam, Figure 6 shows a beam expander system with an AO modulator installed in the convergent beam, and Figure 7 shows a beam expander system with an AO modulator installed in the convergent beam. Diagram (B)
8 is a system in which a relay lens is provided at the condensing point of FIG. 6, FIG. 9 is a modification of the relay lens shown in FIG. 7, and 10th The figure shows an example in which two stages of beam expander systems are provided, and FIG. 11 shows an example in which a beam expander is provided at the rear of the system in FIG. 8. 10... Argon laser (light source) 22... AO modulator for correction (deflection element for correction) 50.
60,70,80.90...Lens system P polygon mirror (scanning deflector) 1L" Figure Polygon mirror 2146 Figure 7 Polygon mirror Q:l, -□f, O→
Figure polygon mirror number! ! Figure polygon mirror-fl---f2

Claims (1)

[Claims] (1) A light source, a correction deflection element that minutely deflects a light beam emitted from the light source in a sub-scanning direction, and a correction deflection element that deflects a light beam emitted from the correction deflection element in a main-scanning direction perpendicular to the sub-scanning direction. a scanning deflector; a lens system that is provided between the correction deflection element and the scanning deflector to make them almost optically conjugate; and a lens system that deflects the light beam deflected by the scanning deflector. a scanning lens for condensing light onto a drawing surface; and a correction deflection element for keeping the direction of deflection of the light beam by the scanning deflector constant in accordance with the inclination of the deflection surface of the scanning deflector in the sub-scanning direction. 1. A scanning optical device comprising: a control means for controlling a deflection angle of a light beam.