JPH08194183A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning optical device having a scanning efficiency higher than a conventional device. SOLUTION: This scanning optical device 10 is formed of a curved support surface 14 for supporting a base to be scanned; a light source 36 for supplying a circular polarized beam; a scanning means 22 for scanning the beam from the light source to the curved support surface in main scanning direction; a scanning means driving means for moving either one of the scanning means 22 and the curved support surface to the other in the sub-scanning direction orthogonal to the main scanning direction; and a modulating means for modulating the beam from the light source according to a modulation control signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device.

[0002]

2. Description of the Related Art A raster type photoplotter (image generating apparatus) of a planar design or a cylindrical surface drum design is known. Devices of this kind are used, for example, in the manufacture of printed circuit boards. On the other hand, a scanner (image reading device) that reads data from a substrate has a structure similar to that of the raster type photoplotter. Planar-designed photoplotters, such as those disclosed in U.S. Pat. No. 4,851,656, have a planar surface that receives the substrate.
urface). In this photo plotter, the optical exposure head is movably supported by a guide device and scans the substrate during exposure. The photoplotter of the cylindrical surface drum design is characterized in that the surface for receiving (holding) the substrate is a substantially cylindrical surface. Beam light is emitted from the optical exposure head, and the emitted beam is scanned on the substrate by the rotary spinner. The optical exposure head of this photoplotter is moved along the axis of the cylindrical surface in order to scan the substrate thoroughly. A raster type photoplotter adopting a cylindrical surface drum design as disclosed in US Pat. No. 5,291,392 has a simple structure and a low manufacturing cost, and is superior to a planar type raster type photoplotter. There is.

As a raster type photoplotter of a typical cylindrical surface drum design, Gerber Scientifi of the United States is used.
c, Inc.), the Crescent 42 (the Crescent 4
2: There is a product name). In this photo plotter, the surface for receiving the substrate inside the drum is a curved surface of 180 °. This one
The 80 ° curved surface is a curved surface of the inner surface of the drum which is half the size of a perfect cylindrical shape in cross section. That is, it means that it is a perfect cylindrical surface at 360 °. The photoplotter also has a spinner whose center is located on the axis of the drum. This construction produces one scan line per revolution of this spinner with the scan mirror tilted at 45 ° to the drum axis by design. Therefore, in this structure, the scanning efficiency is about 50%. The scanning efficiency is the generation efficiency of the scanning line per one rotation of the spinner, and is 100 when the two scanning lines are generated per one rotation of the spinner.
% Scanning efficiency.

Image generation can be speeded up by improving the processing capability of the processing system for converting code information of characters and figures into scanning line information. However, increasing the image generation speed of a raster photoplotter with a cylindrical surface drum design presents some challenges. The rotation speed of the spinner is 20,000 to 24,000 considering the performance of the air bearing and the motor and the mirror deformation of the spinner.
Limited to rpm range. Another method for speeding up image generation is the use of multi-beams (multiple beam light). However, it is very difficult to use multiple beams due to the geometry of the scan plane of the drum. The scan plane geometry of this drum produces an undesired rotation in the image plane of the multi-beam so that it is never in a single plane with respect to its axis of movement. In order to solve this problem, a rotating prism device synchronized with the spinner is required, but this rotating prism device is a complicated device and the device becomes expensive.

Next, how to improve the time efficiency of the scanner or photoplotter will be described. As described above, the scanning efficiency of the above-mentioned conventional apparatus is 50% at the maximum.
For a photoplotter with a cylindrical surface drum design, the angle (size) of the surface of the drum inner surface that receives the substrate is increased (for example, 270
It is possible to improve the scanning efficiency by increasing the angle to 0 °), but there is a problem that the operability becomes very complicated. Poor scanning efficiency is not preferable in two respects. The first problem is that the lower the scanning efficiency is, the higher the scanning speed of the video device must be. The second point is that there is an exposure limitation in a device or the like for drawing an image directly on a printed circuit board. Increasing the scanning efficiency of scanners and photoplotters improves the ability to expose the substrate.

As a conventional device for improving the overall processing capability of a scanner or photoplotter, US Pat.
There is an apparatus disclosed in 7,606. This U.S. Patent discloses a scanning optical device having a light source for emitting a beam of light and a polygon mirror as a deflecting means having a plurality of mirror surfaces for deflecting the beam of light from the light source. Each mirror surface of the polygon mirror has a pair of reflecting surfaces. The pair of reflecting surfaces are inclined toward the rotation axis of the polygon mirror and are orthogonal to each other.
Further, the reflection mirror is fixed so as to face one surface of the pair of reflection surfaces. The fixed mirror is arranged so that the beam light deflected by the fixed mirror returns to the polygon mirror. When the device disclosed in this US patent is used, the width of the scanning angle of the laser beam is doubled as compared with the conventional device which uses the polygon mirror, thereby performing scanning without increasing the rotation speed of the polygon mirror. Increases speed. U.S. Pat. No. 4,44
Japanese Patent No. 5,126 discloses an image generating apparatus that scans a recording medium with a plurality of light beams. This device has a beam generation device that generates a plurality of light beams and irradiates the plurality of light beams simultaneously onto one surface of a rotating polygon mirror. This U.S. Pat. No. 4,445,1
The purpose of the image generating device disclosed in No. 26 is to generate a plurality of scan lines within a predetermined time during the operation of the device.

An image recording apparatus using a multi-beam is disclosed in, for example, US Pat. No. 4,506,275 and US Pat.
There is a device disclosed in Japanese Patent No. 517,608. This apparatus has a recording unit for recording or copying a halftone image on a photosensitive material. This recording unit
An acousto-optic light modulati comprising a plurality of ultrasonic wave exciting portions arranged side by side on a single acousto-optic medium.
ng element). The plurality of ultrasonic excitation parts are
Each independently modulates the incident light beam into a plurality of modulated light beams according to the image signal output from the photoelectric scanning means. This device has a diameter-reducing optical system that narrows the diameters of the plurality of modulated beam lights. The plurality of modulated beam lights are diameter-reduced by a plurality of beam light transmitting elements and are focused from the diameter-reducing optical system. It is sent to the lens and projected onto the film in the recording cylinder. In this device, a fixed scanning head is used as the scanning head. The substrate is arranged on the outer peripheral surface of the rotary drum.

US Pat. No. 5,251,057 discloses a multi-beam optical modulator. This device is used in a raster output scanner that uses one original beam of light and one side of a rotating polygon mirror to produce two consecutive scan lines. One original light beam is first split into two light beams by a beam splitter. The two light beams generated by this division are polarized by 90 ° to each other and sent to the acousto-optic light modulator. These two light beams are
The acousto-optic light modulators are sufficiently separated from each other that they can modulate their light beams with minimal interference. The two light beams output from the acousto-optic light modulator are combined by a beam recombining device, that is, a beam splitter installed upside down within a separation range of one scanning line. Since these two light beams are polarized by 90 ° with respect to each other, they can be combined (bundled) in close proximity without interfering with each other.

As described above, none of the above-mentioned conventional devices makes the scanning efficiency of the scanning device 100%.
Moreover, none of them can improve the processing capacity without complicated improvement of the optical and electronic parts of the device.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a scanning optical device having a scanning efficiency higher than that of the conventional device.

[0011]

SUMMARY OF THE INVENTION A scanning optical apparatus according to the present invention comprises a curved support surface for supporting a substrate to be scanned; a light source for supplying circularly polarized light beam; and a main scanning beam light from the light source for the curved support surface. Scanning means for scanning in one direction; scanning means driving means for moving one of the scanning means and the curved support surface in the sub scanning direction orthogonal to the main scanning direction with respect to the other; from a light source in response to a modulation control signal In a scanning optical device including: a modulation unit that modulates the beam light of; and a scanning unit that is driven to rotate about a rotation axis and reflects the beam light from the light source toward the substrate to perform scanning in the main scanning direction. A spinner provided; a spinner provided between the spinner and the light source, and rotating the circularly polarized light of the beam light from the light source from the light source in response to the circular polarization direction switching signal, the first direction being opposite to the first direction; Circular polarization that switches between two directions Direction switching means; a first encoder for outputting a signal according to the rotational angle position of the spinner; a modulation control signal given to the modulation means and a circular polarization direction given to the circular polarization direction switching means according to the signal of the first encoder. A control unit that outputs a switching signal; and a spinner that transmits the light beam emitted from the circular polarization direction switching unit.
A quarter-wave plate of; and when the linearly-polarized beam light transmitted through the first quarter-wave plate is polarized in the first polarization direction, the beam light is split by a splitter surface provided inside. A polarization beam splitter which reflects and transmits the linearly polarized beam light passing through the first quarter-wave plate and passing through the splitter surface when it is polarized in the second polarization direction orthogonal to the first polarization direction; The second 1 that transmits the light beam that has passed through the surface and transmitted through the polarization beam splitter.
/ 4 wavelength plate; reflects the beam light transmitted through the second ¼ wavelength plate, transmits the beam light again through the second ¼ wavelength plate, and returns it to the polarization beam splitter. And a reflecting plate which is incident on the splitter surface.

Further, the scanning optical apparatus of the present invention includes a laser light source for outputting a circularly polarized light beam; a modulation means for modulating the light beam according to drawing information; and a circle for switching the rotation direction of circularly polarized light of the light beam between normal and reverse directions. Polarization direction switching means; a deflector having a rotation axis for deflecting the beam light in the main scanning direction; receiving the beam light scanned in the main scanning direction by the deflector, and centering on the rotation axis of the deflector A deflector provided with an object to be scanned supported on the inner cylindrical surface; moving means for moving one of the object to be scanned and the deflector with respect to the other in a sub-scanning direction orthogonal to the main scanning direction. Is a polarization beam splitter that has a splitter surface that reflects the S-polarized beam light and transmits the P-polarized beam light, and is driven to rotate about the rotation axis that forms 45 ° with respect to the splitter surface; On the splitter, Means for converting the circularly polarized light of the laser light incident along the axis of rotation into linearly polarized light; and the linearly polarized light beam transmitted through this means and transmitted through the polarization splitter surface, in the direction of the linearly polarized light of the beam light. Is converted by 90 ° and reflected again toward the splitter surface. Further, each time the polarization beam splitter rotates 180 °,
The circular polarization direction switching means reverses the rotation direction of the circular polarization of the beam light, and the control means is provided to alternately emit the linearly polarized light beam from the polarization splitter surface.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. 1 and 2 show a raster type photoplotter 10 of a cylindrical surface drum design to which the present invention is applied. In each drawing, the entire photo plotter 10 is not shown, but only a part thereof is shown. The photoplotter 10 has a drum 12 including a drum surface (curved support surface; inner cylindrical surface) 14 that constitutes a part of a cylindrical surface. The drum surface 14 of the drum 12 is formed so that its cylindrical shape does not deform due to environmental changes such as temperature changes due to extremely high processing accuracy. This drum 12
Is preferably made by aluminum casting, and a plurality of reinforcing members are arranged along the circumference of the drum 12.

The drum surface 14 receives the substrate (scanned body) 21 on its inner surface and has a plurality of holes 16. The plurality of holes 16 communicate with a plurality of air passages 18 formed in the drum 12. The plurality of air passages 18 are connected to a known vacuum pump (not shown). Therefore, when this vacuum pump is operated, the substrate 21 can be sucked and held on the drum surface 14 through the plurality of air passages 18 and the plurality of holes 16. The vacuum pump is operated to hold the substrate 21 on the drum surface 14 while scanning the substrate 21 placed on the drum surface 14.

The photoplotter 10 has a guide rail 20 extending parallel to the axial direction (sub-scanning direction) of the drum 12.
A raster type scanner (scanning means) 22 is provided on the guide rail 20.
It is movably supported along 0. The scanner 22 is a device for scanning the light beam 24 on the substrate 21 according to a command signal received from the control means 26. The scanner 22 has a linear encoder (second encoder) 28. This linear encoder 28 is
When the scanner 22 moves along the guide rail 20, a signal indicating the position of the scanner 22 (position in the sub scanning direction) is generated. A signal indicating the position of the scanner 22 is output to the control means 26. Also photo plotter 1
Reference numeral 0 has driving means (not shown) for moving the scanner 22 along the guide rail 20. The drive means moves the scanner 22 along the guide rail 20 in response to a drive signal received from the control means 26. The driving means, the guide rail 20 and the like constitute a scanning means driving means.

The scanner 22 is a high-speed scanning device 3
Has 0. This high-speed scanning device 30 has a motor 32 and a spinner (deflecting means) 60. The spinner 60 has a rotating shaft 40.
Are coaxial with the central axis of the drum surface 14. The high-speed scanning device 30 causes the spinner 60 to reflect the beam light emitted from the laser light source 36, and the motor 32 drives the spinner 60 to rotate about a rotation axis 40 to form a series of scanning lines 38 on the substrate 21. Expose. The laser light source 36 outputs a circularly polarized light beam.
The rotation speed of the spinner 60 is usually 12,000 rpm. The scanner 22 has a rotary encoder (first encoder) 42 that generates a signal indicating an angular position with respect to the rotation axis 40 of the mirror surface 35 during scanning.
The light beam emitted from the laser light source 36 is incident on the spinner 60 along the rotation axis 40 so that the light beam is received at the center of the mirror surface 35.

3 and 4 show a photoplotter 44 as a conventional example of a raster type photoplotter having a cylindrical surface drum design. In FIG. 3, only the front half of the rotary drum substrate surface (drum surface) 46 is shown, and in FIG. 4, only the rear half of the rotary drum substrate surface 46 is shown. The rotating drum substrate surface 46 receives the beam light 48 reflected by the mirror surface 49 of the spinner 50. Spinner 50
The light beam 48 is rotated about the rotation axis 52 to move the light beam 48 from right to left in the drawing. Spinner 50 mirror surface 49
Are arranged so as to be inclined by about 45 ° with respect to the central axis of the rotary drum substrate surface 46. The mirror surface 49 is directed to the optical axis of the beam light emitted from the laser light source 36,
The beam light is reflected directly toward the rotary drum substrate surface 46. By rotating the spinner 50 once, the light beam 48 can be scanned from the starting end 46a to the ending end 46b of the rotary drum substrate surface 46.

An initial rotational position 54 is set on the spinner 50. When the spinner 50 is located at the initial rotation position 54, the beam light 48 is not projected onto the substrate (not shown) on the rotating drum substrate surface 46 and the rotating drum substrate surface 46.
It will be projected on. In FIG. 4, the second rotation position 56 following the initial rotation position 54 shown in FIG. 3 is shown. When the spinner 50 moves from the initial rotation position 54 to the second rotation position 56, the beam light 4 that scans on the substrate
8 comes to a position where it has completely moved to the end 46b. In FIG. 5, a rotation range from the initial rotation position 54 to the second rotation position 56 is shown by a curve 58. When the spinner 50 exceeds the second rotational position 56, the spinner 50 further rotates in the same direction before the control means 26 re-feeds the modulated beam light to the spinner 50 for the generation of the next scan line. Must return to the initial rotational position 54. In many conventional photoplotters of this type, the size (angle) of the drum surface that receives the substrate is at most 165 °, which is considerably smaller than the practically feasible upper limit of 180 °. Therefore, the scanning efficiency of this type of conventional photoplotter is 5
It was 0% or less.

6 and 7 are enlarged views of the spinner 60 of the present invention shown in FIG. This spinner 60
In the photo plotter 10 of the present invention using the
Two scan lines are generated each time 0 rotates once. The main feature of the spinner 60 is that the polarization direction of the incident beam light can be switched.

The spinner 60 has a polarization plane (splitter plane) 72 inside and has a polarization beam splitter (PBS: polarization beam) rotated about the rotation axis 40.
splitter) 70. The spinner 60 includes a first quarter-wave plate 64 fixed to the surface of the polarization beam splitter 70 that receives the light beam from the laser light source 36.
A second quarter-wave plate 78 fixed to a surface opposite to the surface to which the first quarter-wave plate 64 is fixed, and a polarization beam splitter of the second quarter-wave plate 78. It has a reflection plate 79 fixed to the surface opposite to the surface on the 70 side.

Further, the spinner 60 has a focus lens (first lens) fixed to the surface on the side where the light beam reflected by the polarization plane 72 is emitted to the outside of the polarization beam splitter 70.
74 and a focus lens (second lens) fixed to a surface facing the surface to which the focus lens 74 is fixed
Has 80.

In FIG. 6, the beam light that is incident on the spinner 60 and is a parallel light beam is circularly polarized light beam 62 that is clockwise when viewed from the spinner 60 side. The first quarter wave plate 64 is fixed on the first spinner surface 66. The beam light 62 is linearly polarized by being transmitted through the first quarter-wave plate 64 and is then S-polarized first beam light 68.
It is said. The S-polarized first beam light 68 is reflected by the polarization plane 72 in the polarization beam splitter 70 and is emitted to the outside of the polarization beam splitter 70 (on the right side in FIG. 6).
When the first beam light 68 is reflected by the polarization plane 72, the reflected beam light is emitted from the spinner 60 so as to follow the scanning rotation direction. The polarization plane 72 transmits incident light having a predetermined polarization angle such as P-polarized light and reflects incident light having another polarization angle such as S-polarized light. At the time of this reflection, the polarization plane 7
2 reflects approximately 100% of the linearly polarized first beam light 68. First beam light 68 reflected by the polarization plane 72
A focus lens 74 that focuses the first beam light 68 reflected by the polarization surface 72 onto the substrate is fixed to the surface of the polarization beam splitter 70 where is emitted.

Therefore, the first light beam 68 constitutes the initial light beam generated by the device of the present invention, as in the conventional device. The second following the scanning with this initial light beam
In the scanning of 1, the beam light that is incident on the spinner 60 and is a parallel light beam is a circularly polarized light beam 76 that is counterclockwise when viewed from the spinner 60 side. This light beam 7
6 is shown in FIG. This light beam 76 is the first 1 /
After passing through the four-wave plate 64, the second light beam 77 is P-polarized light whose polarization direction is orthogonal to that of the S-polarized light beam. Subsequently, the second beam light 77 is transmitted to the polarization beam splitter 70.
And is transmitted through the polarization plane 72. At the time of this transmission, the polarization plane 72 transmits substantially 100% of the second light beam 77.
After passing through the polarization beam splitter 70, the second beam light 77 has a phase of 90 by the second quarter wave plate 78.
It is shifted by ° and reflected in the opposite direction by the reflection plate 79. The beam light reflected by the reflection plate 79 is transmitted through the second quarter-wave plate 78 again and has a phase of 90 °.
The light beam is shifted to be S-polarized light beam similar to the first light beam 68. That is, the P-polarized second beam light 77 transmitted through the polarization beam splitter 70 is transmitted through the second quarter-wave plate 78 twice, and as a result, the direction of linearly polarized light is converted by 90 °, and the S-polarized beam is obtained. It becomes light and enters the polarization plane 72. The polarization plane 72 reflects the S-polarized beam light toward the focus lens 80. This focus lens 80
Is a focus lens similar to the focus lens 74, and focuses the S-polarized beam light that has passed through the focus lens 80 onto the substrate.

The raster type photoplotter 10 of the present invention having the spinner 60 having the above structure further has an acousto-optical modulator 81 between the spinner 60 and the laser light source 36. This acousto-optical modulator 81 is
Control means 2 for switching signal (circular polarization direction switching signal)
The beam light emitted from the laser light source 36 is switched between the clockwise and counterclockwise circular polarization directions. In addition, the acousto-optical light modulator 81 is used for the substrate 2
It has a modulation means for modulating the beam light from the laser light source 36 in accordance with the drawing information 1 and modulates the beam light according to the modulation control signal output from the control means 26.

The rotary encoder 42 has one spinner 60.
A signal generated each time it rotates is output to the control means 26.
Thereby, the control means 26 can irradiate the modulated beam light twice at a predetermined timing while the spinner 60 makes one rotation. Therefore, the raster type photoplotter 10 of the present invention can generate two scanning lines for each rotation of the spinner. Therefore, as compared with the conventional raster type photoplotter in which only one scanning line is generated for each rotation of the spinner, the scanning efficiency is double, that is, the scanning efficiency is 100.
%become. The efficiency of the raster type photoplotter 10 may be further improved by, for example, doubling the moving speed in the sub-scanning direction.

Although the scanning optical device has been described with reference to the raster type photoplotter 10 in the above embodiment, the present invention is not limited to the raster type photoplotter, and the present invention can be similarly applied to the raster type scanner.

Although the present invention has been described with reference to the above embodiments,
The invention is not limited to this embodiment, and various modifications and alternatives are possible without departing from the scope of the subject matter of the invention.

[0028]

As described above, according to the scanning optical device of the present invention, two scanning lines can be generated for each rotation of the spinner, and the scanning efficiency can be doubled as compared with the conventional device. .

[Brief description of drawings]

FIG. 1 is a schematic view showing a part of a raster type photoplotter having a cylindrical surface drum design including a spinner to which the present invention is applied.

FIG. 2 is a perspective view showing a relationship between scanning beam light and a spinner of the photoplotter shown in FIG.

FIG. 3 is an explanatory diagram showing a spinner and a front half of a drum surface of a conventional photoplotter.

4 is an explanatory view showing a spinner and a rear half of a drum surface of the photoplotter in FIG. 3. FIG.

FIG. 5 is a diagram illustrating the scanning efficiency of the conventional photoplotter shown in FIGS. 3 and 4.

FIG. 6 is a plan view showing a spinner to which the invention is applied, which receives a circularly polarized beam of light in a counterclockwise direction when viewed from the spinner side.

FIG. 7 is a plan view showing a spinner to which the present invention is applied, which receives a circularly polarized beam of light that is clockwise when viewed from the spinner side.

[Explanation of symbols]

 10 raster type photo plotter (scanning optical device) 12 drum 14 drum surface (curved supporting surface; inner cylindrical surface) 16 hole 18 air passage 20 guide rail 21 substrate (scanned object) 22 raster type scanner (scanning means) 24 beam light 26 control means 28 linear encoder (second encoder) 30 high-speed scanning device 32 motor 36 laser light source 38 scanning line 40 rotary shaft 42 rotary encoder (first encoder) 60 spinner 62 beam light 64 first quarter wave plate 70 polarization Beam splitter 72 Polarization plane 74 Focus lens (first lens) 78 Second quarter-wave plate 79 Reflector 80 Focus lens (second lens)

Claims (6)

[Claims] 1. A curved support surface for supporting a substrate to be scanned; a light source for supplying a circularly polarized light beam; a scanning means for scanning the curved support surface with the light beam in a main scanning direction; Scanning means driving means for moving one of the scanning means and the curved supporting surface in the sub-scanning direction orthogonal to the main scanning direction with respect to the other; modulating means for modulating the light beam according to a modulation control signal; In a scanning optical device provided with, is driven to rotate about an axis of rotation, the light beam from the light source is reflected toward the substrate to scan in the main scanning direction,
A spinner provided on the scanning means; provided between the spinner and the light source, wherein the rotation direction of the circularly polarized light of the beam light is the first direction and the first direction in response to the circular polarization direction switching signal. A circular polarization direction switching means for switching to the opposite second direction; a first encoder for outputting a signal according to the rotational angle position of the spinner; and a modulation given to the modulation means according to a signal from the first encoder. Control means for outputting a control signal and the circular polarization direction switching signal given to the circular polarization direction switching means; and the spinner transmits the beam light emitted from the circular polarization direction switching means. A quarter-wave plate; when the linearly-polarized beam light transmitted through the first quarter-wave plate is polarized in the first polarization direction, the beam light is reflected by a splitter surface provided inside. Let A polarization beam splitter that transmits the linearly polarized light beam that has passed through the first quarter-wave plate and has a second polarization direction that is orthogonal to the first polarization direction and that transmits the splitter surface; A second quarter-wave plate that transmits the beam of light that passes through the splitter surface and the polarization beam splitter;
A reflector that reflects the beam of light that has passed through the quarter-wave plate, transmits the beam of light again through the second quarter-wave plate, returns it into the polarization beam splitter, and makes it incident on the splitter surface; A scanning optical device comprising: 2. The scanning optical device according to claim 1, wherein the curved support surface is a drum surface of a raster type photoplotter. 3. The spinner according to claim 1, further comprising a first lens and a second lens fixed to surfaces of the polarization beam splitter facing each other.
A scanning optical device in which the beam light polarized in the first polarization direction and the beam light polarized in the second polarization direction emitted from the polarization beam splitter enter the lens and the second lens, respectively. 4. The apparatus according to claim 2, further comprising a second encoder that outputs a signal corresponding to a position of the scanning means with respect to the curved support surface in the sub-scanning direction, and the control means includes a second encoder. A drive signal is output in response to the signal, and the scanning means drive is a scan in which either the scanning means or the curved support surface is moved in the sub-scanning direction orthogonal to the main scanning direction with respect to the other in response to the drive signal. Optical device. 5. The scanning optical device according to claim 1, further comprising a second encoder that outputs a signal corresponding to a position of the scanning unit with respect to the curved support surface in the sub-scanning direction. 6. A laser light source for outputting a circularly polarized light beam; a modulation means for modulating the light beam according to drawing information; and a circular polarization direction switching means for switching the rotation direction of the circularly polarized light of the light beam between normal and reverse directions. A deflector having a rotation axis for deflecting the beam light in the main scanning direction; an inner cylinder having the rotation axis of the deflector as a center for receiving the beam light scanned in the main scanning direction by the deflector A deflector which is supported on the surface; and a moving means which moves one of the deflector and the deflector with respect to the other in a sub-scanning direction orthogonal to the main scanning direction. Is a polarization beam splitter that has a splitter surface that reflects the S-polarized light beam and transmits the P-polarized light beam, and is driven to rotate about the rotation axis that forms 45 ° with respect to the splitter surface; To the splitter A means for converting circularly polarized light of the laser light incident along the rotation axis into linearly polarized light; and linearly polarized beam light transmitted through this means and transmitted through the polarization splitter surface, Means for converting the direction by 90 ° and reflecting the light again toward the splitter surface, and each time the polarization beam splitter is rotated by 180 °, the circular polarization direction switching means changes the circular polarization of the beam light. The scanning optical device is provided with a control means for reversing the rotation direction of the beam splitter and alternately emitting linearly polarized beam light from the polarization splitter surface.