JP2007264101A - Inner drum exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inner drum type exposure apparatus in which scanning and exposure are performed with a plurality of light beams by dividing a light beam in a main scanning means and an appropriate circular-polarization light beam is made incident on the main scanning means. <P>SOLUTION: The problem is solved by arranging an optical member which reduces the light quantity in the long axis direction of an ellipse of a light beam which is transformed into an ellipse polarization light with a light beam optical system in a light beam optical system which allows the light beam incident on a main scanning means through a prescribed optical path. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inner drum type exposure apparatus that holds a scanning object such as a recording medium on an inner peripheral surface of an arc, and more specifically, a combined light beam or a single light beam is separated into a plurality of light beams. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner drum exposure apparatus that scans with a light beam, and that allows any light beam to enter a scanned object in an appropriate state.

The recording medium is two-dimensionally supported by a light beam that is main-scanned in the circumferential direction of the arc by a spinner (optical deflector) that supports the recording medium on an arc-shaped inner circumferential surface and rotates a reflecting surface around the center line of the arc. An inner drum exposure apparatus (cylindrical inner surface scanning exposure apparatus) that performs scanning exposure is known.
Further, in such an inner drum exposure apparatus, for example, light beams modulated independently of each other are combined and incident on a spinner, deflected / scanned, and the combined light beams are separated into multi-beams. An apparatus for performing exposure has been proposed.

As an example, Patent Document 1 discloses an inner drum exposure apparatus schematically shown in FIG.
This inner drum exposure apparatus 200 performs two-dimensional scanning exposure of a recording medium held on the inner surface of a cylindrical support 202 having an arcuate inner peripheral surface with two light beams L1 and L2. The support 202, the light source unit 204, the main scanning unit 206, and the light beam optical system 208 are configured.

  In the inner drum exposure apparatus 200 (hereinafter referred to as the exposure apparatus 200), the light source unit 204 emits a light beam 210 (for example, a semiconductor laser or an argon laser) that emits a P-polarized linearly deflected light beam to a mirror 222 described later, for example. Etc.) is split into two light beams L1 and L2 by a half prism 212, and each light beam is modulated by a modulator 214 (L1) such as an AOM (acousto-optic modulator) and a modulator 216 ( According to L2), modulation is independently performed according to the recorded image.

The light beam L2 modulated by the modulator 216 is reflected in a predetermined direction by the mirror 218 and enters the polarization beam splitter 220.
On the other hand, the light beam L 1 modulated by the modulator 214 is reflected in a predetermined direction by the mirror 222, and the polarization direction (polarization plane) is rotated by 90 ° by the half-wave plate 224, and then the polarization beam splitter 220. Is incident on. By the rotation of the polarization direction of the light beam L1 by the half-wave plate 224, the two light beams (L1 and L2) are linearly polarized light having polarization directions orthogonal to each other (for example, P polarization and S polarization). Become a beam.
The polarization beam splitter 220 multiplexes two linearly polarized light beams having polarization directions orthogonal to each other into an apparently one light beam (synthetic beam Lc) whose optical axes coincide with each other.

  The combined beam Lc then enters the quarter wave plate 226. The quarter-wave plate 226 is arranged with the crystal optical axis inclined by 45 ° with respect to the polarization direction of the light beam. Therefore, each light beam of the combined beam Lc incident / passed on the quarter-wave plate 226 becomes a circularly polarized light beam in different rotation directions (right rotation and left rotation with respect to the traveling direction).

The circularly polarized combined beam Lc emitted from the light source unit 204 (¼ wavelength plate 226) is then widened by the beam expander 230 in the light beam optical system 208 and has a certain thickness. Then, the light beam is incident on the main scanning unit 206 through a condenser lens 232 for condensing the light beam.
Here, the light beam optical system 208 makes the combined beam Lc incident on the main scanning unit 206 through a predetermined optical path that travels along the center line of the inner peripheral surface of the support 202 (hereinafter simply referred to as the center line).

The main scanning unit 206 includes a spinner mirror 234, a quarter-wave plate 236, and a Wollaston prism 238.
The spinner mirror 234 is a mirror that acts as a spinner (optical deflector), and the center of the reflection surface is located on the center line, is disposed at an angle of 45 ° with respect to the center line, and travels along the optical axis. Is deflected at a right angle and reflected toward the inner peripheral surface of the support 202.

The quarter-wave plate 236 and the Wollaston prism 238 are disposed on the optical path of the combined beam Lc reflected by the spinner mirror 234.
The combined beam Lc reflected by the spinner mirror 234 is first converted into a linearly polarized light beam by the quarter wavelength plate 236. Here, as described above, the combined beam Lc is a light beam formed by combining (synthesizing) the light beams L1 and L2 having different rotation directions, and thus the light beam converted by the quarter wavelength plate 236. L1 and L2 are linearly polarized light beams having polarization directions orthogonal to each other.
Next, the combined beam Lc is separated into individual light beams L1 and L2 by the Wollaston prism 238, and enters the inner peripheral surface of the support 202 (the recording medium held here).

The main scanning unit 206 is an integrated unit of a spinner mirror 234, a quarter-wave plate 236, and a Wollaston prism 238. As described above, the spinner mirror 234 is positioned on the center line and is driven by a drive source (not shown). Rotate around the center line. As a result, the light beams L1 and L2 traveling along the optical path on the center line, reflected by the spinner mirror 234, and separated by the Wollaston prism 238 are deflected / main scanned in the circumferential direction (main scanning direction) of the inner surface of the support 202. The
Although not shown, the exposure apparatus 200 includes sub-scanning means for moving the condenser lens 232 and the main scanning means 206 integrally in the center line direction (sub-scanning).
Therefore, the recording medium held on the inner peripheral surface of the support 202 by the main scanning of the light beam by the main scanning unit 206 and the sub scanning of the main scanning unit 206 (condensing lens 232) by the sub scanning unit is as follows. The entire surface is scanned and exposed two-dimensionally by the light beams L1 and L2.

As described above, the light beams L1 and L2 are modulated in the light source unit 204 according to the recorded image independently of each other.
Further, in the main scanning unit 206, the respective light beams L1 and L2 separated by the Wollaston prism 238 are incident on the same position in the main scanning direction and at different positions in the sub scanning direction. A half-wave plate 236 and a Wollaston prism 238 are arranged with the axis set.
Thereby, the exposure apparatus 200 performs image recording by exposure with two light beams (multi-beam).

Japanese Patent No. 27951551

In such an exposure apparatus that separates a light beam using the polarization of light, an element (such as a Wollaston prism 238) that separates the light beam is used in order to make the light beam incident at a predetermined position regardless of the scanning position. The positional relationship between the spinner mirror 234 and the spinner mirror 234 must always be kept constant. In addition, in order to perform proper light beam separation, it is necessary to always make the polarization direction of the light beam incident on the separation element constant with respect to the separation element. Therefore, in such an exposure apparatus, a main scanning unit in which a separation element and a spinner are integrally formed is used, and a circularly polarized light beam is incident on the main scanning unit.
Further, in order to properly separate the light beam, it is necessary to make the light beam having an appropriate circular polarization instead of the elliptical polarization incident on the main scanning unit.

Here, since FIG. 7 is a schematic diagram, the light beam optical system 208 makes the combined beam Lc incident on the main scanning unit 206 from the light source unit 204 along a straight optical path.
However, in an actual exposure apparatus, it is extremely rare that such a simple light beam optical path can be set. That is, in the exposure apparatus, in order to limit the design, such as the positional relationship with various components, and to reduce the size of the apparatus, a plurality of reflecting mirrors for deflecting the optical path are provided, and the optical path of the light beam is bent several times. Usually, the light beam is incident on the main scanning means through a predetermined optical path.

However, when a circularly polarized light beam is reflected by the reflection mirror, a phase shift (retardation) occurs between the S-polarized light component and the P-polarized light component, resulting in an elliptically polarized light beam. For example, as shown in FIG. 8, when the optical path of the light beam L is turned back by 180 ° with two reflection mirrors that deflect the optical path of the light beam L by 90 °, the light beam L that is circularly polarized becomes the S polarization direction. And an elliptically polarized light beam L having a major axis in the direction of 45 ° with respect to the P polarization direction.
When this phase shift occurs by 5 °, the circularly polarized light beam becomes an elliptically polarized light beam having a maximum ratio of the major axis to the minor axis of 1: 0.8. As described above, in a normal exposure apparatus, since a plurality of reflecting mirrors are arranged, this ratio increases.

In an exposure apparatus that performs scanning exposure by separating a light beam using polarized light as described above, if the elliptically polarized light beam is incident on the main scanning means, the light beam cannot be properly separated. Therefore, the intended exposure cannot be performed properly.
For example, in the case of the exposure apparatus 200 shown in FIG. 7, when the elliptically polarized combined beam Lc is incident on the main scanning means 206, it can be returned to a completely linearly deflected light beam by the quarter wavelength plate 236. Accordingly, stray light is generated in the light beam separated by the Wollaston prism 238. As a result, stray light of the light beam L2 rides on the light beam L1, and stray light of the other light beam rides on one light beam, resulting in a reduction in the extinction ratio.

In order to solve such a problem, a reflecting mirror that is coated so as not to cause a phase difference between the S-polarized component and the P-polarized component is required. However, it is very difficult to completely eliminate the phase difference, and the cost of the reflecting mirror is very high.
It is also conceivable to arrange a quarter-wave plate upstream of the main scanning means to make elliptically polarized light circularly polarized light. Here, at the time of entering the main scanning means, the light beam is usually of a certain thickness, and is also incident on the main scanning means 204 so as to be arranged in the exposure apparatus 200 of FIG. The light beam is often widened by a beam expander. For this reason, it is necessary to use an expensive quarter-wave plate having high transmission wavefront accuracy in a wide region, and as a result, the cost of the exposure apparatus becomes very high.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and an exposure apparatus that achieves high image quality by separating one light beam into equal amounts of light and forming a partially overlapping composite spot, A plurality of light beams, which are independently modulated and combined, are incident on the main scanning means and separated to perform scanning exposure by separating the light beams using the polarization of light, such as an exposure apparatus that performs multi-beam exposure. In the inner drum exposure apparatus, an appropriate circularly polarized light beam can be incident on the main scanning means, and thereby, an inner drum exposure apparatus capable of performing high-quality image recording with a plurality of appropriately separated light beams. Is to provide.

  In order to achieve the above object, an inner drum exposure apparatus of the present invention has a light source unit that emits a circularly polarized light beam and an arc-shaped inner peripheral surface, and a support that holds a recording medium on the inner peripheral surface. And a deflection surface that reflects the light beam toward the inner peripheral surface of the support, and the light beam is rotated by rotating the deflection surface about the center line of the inner peripheral surface of the support. Main scanning means comprising: a deflection element that scans in the main scanning direction that coincides with the circumferential direction of the inner peripheral surface of the support; and a separation element that rotates integrally with the deflection element and separates the light beam into a plurality of parts And at least a light beam emitted from the light source unit, and a sub-scanning unit that moves the main scanning unit and the support in a sub-scanning direction that coincides with a center line direction of an inner peripheral surface of the support. Deflection by one reflecting mirror and the main run in a predetermined optical path And a light beam optical system including at least one optical element that attenuates the amount of light in the long axis direction of the light beam converted from circularly polarized light to elliptically polarized light by being reflected by the reflecting mirror. An inner drum exposure apparatus is provided.

In such an inner drum exposure apparatus of the present invention, it is preferable that the optical element is a light-transmitting flat plate disposed with a normal line inclined with respect to the optical axis of the light beam. It is preferable that the flat plate is disposed with a normal line inclined at least in the minor axis direction. Further, the flat plate is formed by forming a dielectric film on a light beam incident surface. preferable.
In addition, the separation element uses a uniaxial crystal, and the light beam is an equal light amount and parallel, and further overlaps a part of the beam spot, and the ordinary ray separated in the sub scanning direction at the same position in the main scanning direction. Preferably, the light source unit multiplexes and emits two circularly polarized light beams modulated independently of each other and having different rotation directions, The main scanning means further includes a quarter-wave plate that rotates integrally with the deflection element and the separation element, and converts the circularly polarized light beam into a linearly polarized light beam. It is preferable that the two light beams linearly polarized by the wave plate travel at different angles or in parallel to each other and are separated into the two sub-scanning directions at the same position in the main scanning direction. .

According to the present invention having the above-described configuration, in the inner drum exposure apparatus that performs the scanning exposure by separating the light beam using the polarization of light, the spinner (deflection element) and the light beam separation element are integrated. A light beam optical system in which a circularly polarized light beam is incident on the main scanning means along a predetermined optical path is a long axis direction of the light beam that has become elliptically polarized light due to optical path deflection by a reflection mirror in the light beam optical system ( It has an optical element that attenuates the amount of light in the direction of the major axis of elliptical deflection.
As a result, even if the circularly polarized light beam becomes elliptically polarized light due to the reflection by the reflection mirror in the light beam optical system, the light amount in the major axis direction of this ellipse is attenuated, so that it becomes a circularly polarized light beam. It can be converted and incident on the main scanning means.

  Therefore, according to the inner drum exposure apparatus of the present invention, without using expensive optical components such as a reflective mirror with a coating that eliminates the phase difference and a quarter-wave plate for making elliptically polarized light into circularly polarized light, An appropriate light beam can be incident on the main scanning means, and high-quality image recording can be performed with a plurality of appropriately separated light beams.

  Hereinafter, the inner drum exposure apparatus of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

FIG. 1 shows a conceptual diagram of an example of an inner drum exposure apparatus of the present invention.
An inner drum exposure apparatus 10 (hereinafter referred to as an exposure apparatus 10) shown in FIG. 1 holds a photosensitive material A in an arc shape (cylindrical inner surface shape) and uses a light beam L scanned in the circumferential direction from the inside of the arc. The photosensitive material A is subjected to scanning exposure.
Such an exposure apparatus 10 basically includes a support 12 indicated by an imaginary line (two-dot chain line) in the drawing, a central control means 14, a laser driver 16, a spinner driver 18, a laser light source 20, A quarter wavelength plate (λ / 4 plate) 22, an optical flat plate 24, an optical path deflecting unit 26, a condenser lens 28, and a main scanning unit 30 are configured.

The central control unit 14 includes a CPU and the like, and controls the driving and operation of the entire exposure apparatus 10. Further, the central control means 14 supplies the laser driver 16 with a drive signal of the laser light source 20 corresponding to the image to be recorded, and further instructs the spinner driver 18 to rotate the spinner mirror 36 in the main scanning means 30 and to perform sub-scanning. Put out.
The laser driver 16 is a known laser driver corresponding to the laser light source 20, and drives the laser light source 20 in accordance with a drive signal supplied from the central control means 14, and modulates the light beam in accordance with the image to be recorded. L is emitted.
As will be described later, in the exposure apparatus 10, the main scanning unit 30 moves in the direction of the center line of the arc-shaped inner peripheral surface of the support 12 while rotating the spinner mirror 36 (sub-scanning in the sub-scanning direction). The spinner driver 18 rotates the motor 38 of the main scanning unit 30 and performs sub-scanning in response to an instruction from the central control unit 14.

The support (drum) 12 has an arc-shaped inner peripheral surface (cylindrical inner surface), and holds the photosensitive material A in close contact with the inner peripheral surface.
The photosensitive material A is held (fixed) on the support 12 by an inner drum type (cylindrical inner surface scanning) such as a method using suction, a method using static electricity, a method using a fixing member using a magnet or fitting. A known method used in a type exposure apparatus may be used. In addition, the supply and discharge of the photosensitive material A to the support 12 may be performed manually or automatically using a known method used in an inner drum type exposure apparatus.

The laser light source 20 is a laser light source that emits linearly polarized laser light. The laser light source 20 is modulated and driven by the laser driver 16 and emits a light beam L that is modulated according to an image to be recorded.
As the laser light source 20, various laser light sources capable of emitting a linearly polarized light beam L can be used. As an example, a single transverse mode semiconductor laser having a light intensity distribution in which the center light intensity is high and the light intensity gradually decreases with increasing distance from the center is exemplified.

  The quarter-wave plate 22 is disposed with the crystal optical axis inclined by 45 ° with respect to the linear polarization direction of the light beam L emitted from the laser light source 20. In the exposure apparatus 10, the linearly polarized light beam L emitted from the laser light source 20 passes through the ¼ wavelength plate 22 and is converted into a circularly polarized light beam.

  In the illustrated example, the light source unit is configured by the laser light source 20 and the quarter-wave plate 22. However, the present invention is not limited to this, and when the laser light source 20 is a light beam light source that emits a circularly polarized light beam, the quarter wavelength plate 22 is unnecessary.

The optical flat plate 24 is a light-transmitting flat plate disposed with its normal line inclined with respect to the optical axis of the light beam L. In the illustrated exposure apparatus 10, the optical flat plate 24, the optical path deflecting unit 26, and the condenser lens 28 constitute a light beam optical system that causes the light beam L to enter the main scanning unit 30 along a predetermined optical path. The
The circularly polarized light beam L is converted into elliptically polarized light by reflection by reflection mirrors 26a and 26b of the optical path polarization means 26 described later. However, by passing through the optical flat plate 24, the long axis component of the ellipse is converted. Since the amount of light is attenuated, the light can enter the main scanning unit 30 in the same state as the circularly polarized light beam L. The optical flat plate 24 will be described later in detail.

The optical path deflecting means 26 includes two reflecting mirrors 26a and 26b that form a pair. In this optical path deflecting means 26, the reflection mirror 26a and the reflection mirror 26b are both 45 ° with respect to the optical axis of the light beam L, and the angle formed by the extension surface of the reflection surface facing each other is 90 °. It is arranged to become. Accordingly, the light beam L is deflected by 90 ° by the two reflecting mirrors 26a and 26b of the light path deflecting means 26, thereby turning back the light path by 180 ° and in the direction opposite to that before the incidence. Proceed to.
As described above, the optical path deflecting unit 26 folds the optical path of the light beam L by 180 ° and condenses it as a predetermined optical path that travels along the center line (cylindrical center line) of the arcuate inner peripheral surface of the support 12. The light enters the main scanning means 30 through the lens 28.
In the following description, the center line of the arc-shaped inner peripheral surface is simply referred to as “center line”.

  The condensing lens 28 is arranged with its optical axis aligned with the center line, condenses the light beam L reflected on the optical path polarization means 26 and traveling on the center line, and has a predetermined size on the inner peripheral surface of the support 12. A beam spot.

The light beam L collected by the condenser lens 28 travels on the center line as described above, and then enters the main scanning unit 30.
FIG. 2 shows a schematic diagram of the main scanning unit 30. The main scanning means 30 includes a beam displacer 34, a spinner mirror 36, a motor 38, and a holder 40.

The beam displacer 34 uses a prism made of a uniaxial crystal, etc. and utilizes the polarization of light, and as shown schematically in FIG. It is an optical element that divides the light beam into two light beams, an ordinary ray Po and an extraordinary ray Pe.
In the illustrated example, the beam displacer 34 irradiates the light beam L with the ordinary ray Po so as to partially overlap two light beam spots (spots on the photosensitive material) of the ordinary ray Po and the extraordinary ray Pe. Divide into extraordinary rays Pe. In the exposure apparatus 10 shown in the drawing, the light beam incident on the photosensitive material A is thus combined with a steep rise in the amount of light at the edge of the beam spot and a shape close to a rectangle by the two light beams. As a beam spot, high-quality image recording is possible.

As an example, when the wavelength of the light beam is 405 nm and the shift amount (divided width between the ordinary ray Po and the extraordinary ray Pe) is 5.5 μm, quartz is used as the uniaxial crystal of the beam displacer 34, The thickness may be about 0.904 mm. Quartz has the advantages that it is stable in material and low in cost, and can accommodate a circle having a diameter of 30 mm.
For example, a Gaussian beam having a half-value width of 5 μm is used as the light beam L, and the light beam L is split into two light beams of an ordinary ray Po and an extraordinary ray Pe that are equal in quantity and parallel under the above conditions, so that the half-value width is 5 μm. Can be obtained by splitting one of the two light beams and shifting one of them by 5.5 μm, so that a part of the two light beams is overlapped. A beam spot with a sharp rise can be obtained.
In the present invention, the beam displacer 34 is not limited to the above-described one, and various known ones according to the intended light beam separation in the exposure apparatus can be used.

In the illustrated example, as shown in FIG. 3, the main scanning unit 30 includes a surface on which the light beam L is incident on the spinner mirror 36, a crystal optical axis in a uniaxial crystal of the beam displacer 34, and a normal line. The uniaxial crystal of the beam displacer 34 is arranged so that the planes to include are the same plane. In other words, the uniaxial crystal of the beam displacer 34 so that the crystal optical axis exists in the plane formed by the optical axis of the light beam L incident on the spinner mirror 36 and the optical axis of the light beam L reflected by the spinner mirror 36. Place.
Thereby, the light beam L can be made into two light beams obtained by separating the ordinary ray Po and the extraordinary ray Pe in the direction of the center line (sub-scanning direction). Therefore, the beam spot can be formed in a rectangular shape that is long in the sub-scanning direction, and it is possible to reliably prevent deterioration in image quality due to the separation of the scanning lines in the sub-scanning direction, resulting in a higher quality image. Recording is possible.

The two light beams split by the beam displacer 34 then enter a spinner mirror 36, which is an optical deflector, and are deflected / scanned.
The spinner mirror 36 is fixed to the tip of the rotating shaft 38a of the motor 38 at a 45 ° angle with respect to the center line, with a part of the reflecting surface (in the illustrated example, the center position of the reflecting surface) positioned at the center line. . The motor 38 rotates the rotating shaft 38a around the center line.
Therefore, the light beam incident on the spinner mirror 36 is reflected on the inner peripheral surface of the support by the spinner mirror 36, and is scanned in the circumferential direction of the inner peripheral surface indicated by the arrow b in the figure (the main scan is performed in the main scanning direction). )

A holder 40 indicated by an imaginary line (two-dot chain line) in the drawing is a cylindrical object fixed to the rotating shaft 38a of the motor 38, and holds the beam displacer 34 on the upstream side. Therefore, the beam displacer 34 and the spinner mirror 36 are rotated together, and their positional relationship does not change. Therefore, the two light beams are always separated in the sub-scanning direction.
In addition, an opening 40a through which the light beam L passes is formed in the reflection direction of the light beam L by the spinner mirror 36 of the holder 40 (the optical path of the two separated light beams).

Although not shown, in the exposure apparatus 10, the main scanning means 30 and the condenser lens 28 are integrated, and the sub-line moves in the extending direction of the center line (sub-scanning direction) indicated by the arrow c in the drawing. A scanning means is arranged. The sub-scanning unit performs sub-scanning of the main scanning unit 30 and the condenser lens 28 in accordance with an instruction from the spinner driver 18 as described above.
As described above, since the light beam is main-scanned in the circumferential direction of the inner peripheral surface of the support 12 by the spinner mirror 36 (main scanning means 30), the sub-scanning in the center line direction by this sub-scanning means. The entire surface of the photosensitive material A held on the inner peripheral surface of the support 12 can be two-dimensionally scanned and exposed.
The sub-scanning means is not particularly limited, and various known linear movement methods such as a screw transmission method can be used.

  As described above, the exposure apparatus 10 in the illustrated example separates the light beam L in the sub-scanning direction by the beam displacer 34 to obtain two light beams that are partially overlapped. By separating the light beam, the exposure apparatus 10 makes it possible to record a higher quality image by using a combined beam spot having a steep rise in the amount of light at the edge portion and a shape close to a rectangle elongated in the sub-scanning direction. Yes.

Here, in the exposure apparatus 10 of the illustrated example, the optical path of the light beam L that has been circularly polarized by the quarter wavelength plate 22 is turned back by 180 ° by the optical path deflecting means 26 composed of the two reflecting mirrors 26a and 26b. The light beam L is incident on the main scanning means 30 (and the condensing lens 28) along a predetermined optical path that travels along the center line.
However, as described above, when a circularly polarized light beam is reflected by a reflecting mirror, a phase difference (retardation) occurs between the S-polarized light component and the P-polarized light component, so that the light beam is converted into elliptically polarized light. .

In the exposure apparatus 10 of the illustrated example, when an elliptically polarized light beam L instead of circularly polarized light is incident on the beam displacer 34 of the main scanning unit 30, the crystal optical axis of the uniaxial crystal constituting the beam displacer 34 and the light The relationship with the polarization direction of the beam is not constant.
As a result, the light amounts of the two light beams (ordinary ray Po and extraordinary ray Pe) divided by the beam displacer 34 are equal to each other depending on the deflection direction (position of the light beam in the main scanning direction) by the main scanning unit 30. Accordingly, an inappropriate light amount distribution is generated in a combined beam spot formed by two overlapping light beams, which causes deterioration of image quality.

  Further, the exposure apparatus 200 shown in FIG. 7 described above that combines and circularly polarizes individually modulated linearly polarized light beams and separates them into individual light beams by a Wollaston prism or the like to perform multi-beam exposure. As described above, the stray light of the other light beam rides on the light beam separated by the Wollaston prism or the like and the extinction ratio deteriorates.

In order to eliminate such inconveniences, the inner drum exposure apparatus of the present invention has a light quantity in the major axis direction of an elliptically deflected light beam converted from circularly polarized light by a light beam optical system that makes the light beam incident on the main scanning means. An optical element for attenuating.
In the exposure apparatus 10 shown in the drawing, an optical flat plate 24 is disposed as the optical element between the quarter-wave plate 22 and the optical path deflecting means 26 (reflection mirror 26a). As described above, the optical flat plate 24 is a light-transmitting flat plate, which converts the light beam L by the reflection mirror 26a and the reflection mirror 26b of the optical path deflecting unit 26 into the elliptical deflection of the circularly deflected light beam L. The normal is inclined with respect to the optical axis of the light beam L according to the conversion state.

FIG. 4 shows the relationship between the angle with respect to the optical axis of the light beam (incident angle of the light beam) and the reflection characteristics in a general light-transmissive flat plate.
In FIG. 4, the vertical axis represents the reflectance, and the horizontal axis represents the inclination angle θ of the plane plate (the angle formed by the optical axis of the incident light and the normal line of the plane plate). Therefore, an inclination angle of 0 ° at the origin is normal incidence.

As shown in FIG. 4, when the tilt angle θ is 0 °, the reflectivity of the P-polarized component and the S-polarized component is the same, but the reflectivity of light according to the change of the tilt angle θ of the flat plate (that is, The change in transmittance differs between the P-polarized component and the S-polarized component.
The reflectance of the S-polarized light component increases (the transmittance decreases) as the tilt angle θ increases. On the other hand, the P-polarized component decreases in reflectivity as the tilt angle θ increases from normal incidence, and after the reflectivity becomes 0% (transmittance 100%) at a certain tilt angle θ, As the angle θ increases, the reflectance increases. When the tilt angle θ is other than 0 °, the reflectance of the S-polarized component is larger at all tilt angles θ.

  Therefore, such a flat plate is disposed in an optical path in which the light beam L in the optical path is circularly polarized, and the light beam is generated in a light beam optical system that enters the main scanning unit in a predetermined optical path. In accordance with the conversion of the light beam from circularly polarized light to elliptically polarized light, the S-polarization direction and the P-polarization direction of the flat plate are matched and inclined so as to attenuate the light quantity in the major axis direction of this ellipse (elliptical ellipse). By adjusting the angle θ, the light beam that has become elliptically polarized light can be made into a light beam equivalent to circularly polarized light (equivalent in terms of light component intensity for each polarization direction).

The exposure apparatus 10 in the illustrated example includes a circularly polarized light beam L emitted from a light source unit including a laser light source 20 and a quarter-wave plate 22, and includes an optical flat plate 24, an optical path deflecting unit 26, and a condenser lens 28. The light beam optical system causes the light beam to enter the main scanning unit 30 along a predetermined optical path traveling along the center line.
The optical flat plate 24 is a light that reduces the amount of light in the major axis direction of the ellipse according to the conversion of the circularly polarized light beam L generated by reflection by the reflection mirror 26a and the reflection mirror 26b of the optical path deflecting unit 26 into elliptically polarized light. They are arranged at an inclination angle with respect to the optical axis of the beam L.

As described above, in the exposure apparatus 10, the optical path polarization unit 26 turns the optical path of the light beam L 180 degrees by the reflecting mirror 26a and the reflecting mirror 26b that deflect the optical path of the light beam L by 90 degrees, as in FIG. This is an optical system.
That is, the reflection mirror 26a and the reflection mirror 26b have the same P-polarization direction and the S-polarization direction, and the circularly polarized light beam L has an angle of 45 ° with respect to the P-polarization direction (and the S-polarization direction). The elliptically polarized light having the long axis (and the short axis) is obtained.

Therefore, in the exposure apparatus 10 of FIG. 1, as an example, as schematically shown in FIG. 5A, the transmitted light amount is reduced (the reflected light amount is increased) in the major axis direction of this elliptically polarized light. The optical plane plate 24 is inclined in the minor axis direction with the major axis as the rotation axis so that the major axis direction of this ellipse is S-polarized light and the minor axis direction is P-polarized light (that is, with respect to P deflection in the optical path deflecting means). Then, the optical flat plate 24 is tilted around the 45 ° direction). Further, the light quantity in the long axis direction and the light quantity in the short axis direction can be adjusted by adjusting the inclination angle of the optical flat plate 24 in the short axis direction.
Thereby, as schematically shown in FIG. 5B, the elliptically polarized light beam (see FIG. 8) after the light beam deflecting means 26 reflects the light beam L transmitted through the optical flat plate 24. A light beam L having a light amount distribution such as elliptically polarized light inclined in the reverse direction can be obtained. That is, since the light beam L in which the light quantity in the major axis direction of the elliptically polarized light reflected by the optical path polarization means 26 is attenuated can be obtained, the light beams reflected by the reflection mirror 26a and the reflection mirror 26b of the optical path polarization means 26 are converted into circularly polarized light. Equivalent light beams (equivalent in light component intensity for each polarization direction) can be obtained.

  Therefore, according to the exposure apparatus 10 of the present invention, an appropriate light beam L equivalent to circularly polarized light can be incident on the main scanning means 30, and a high-quality image can be obtained by two appropriately divided light beams. Can be recorded.

The tilt direction and tilt angle of the optical flat plate 24 are not particularly limited. The state of elliptically polarized light generated in the light beam optical system (the reflecting mirrors 26a and 26b in the illustrated example), the light of the optical flat plate 24, and the like. In accordance with the relationship with the reflection characteristics (light transmission characteristics) and the like, the tilt direction and the tilt angle that can reduce the amount of light in the major axis direction of the elliptically polarized light may be appropriately determined.
Here, as in the previous example, the optical flat plate 24 is arranged in the minor axis direction of the elliptically polarized light generated in the light beam optical system in that the light quantity in the major axis direction and minor axis direction of the light beam can be suitably adjusted. It is preferable to arrange them with a certain degree of inclination.

In the present invention, the optical flat plate 24 is not particularly limited, and has various light transmission (transparency) and optical characteristics such as various glass plates and various resin flat plates used for optical members. If it has, the various light-transmitting board can be utilized altogether.
Further, a dielectric film is formed on the surface of the optical flat plate 24, and the reflection (transmission) characteristics of the optical flat plate as shown in FIG. 4 are adjusted to control the light quantity attenuation ratio of S-polarized light and P-polarized light. It is also preferable to do this.

In the exposure apparatus 10 of the present invention, the arrangement position of the optical flat plate 24 is limited to between the quarter wavelength plate 24 and the optical path deflecting means 26 in the illustrated example (upstream of the reflection mirror that converts circular deflection into elliptical deflection). If the position is upstream of the main scanning means 30 and the light beam is circularly polarized (elliptically polarized), it can be arranged at various positions. For example, in the case of the exposure apparatus 10 shown in the drawing, it may be between the reflection mirror 26a and the reflection mirror 26b, between the reflection mirror 26b and the condenser lens 28, downstream of the condenser lens 28, and the like.
The number of the optical flat plates 24 is not limited to one, and may be a plurality of optical flat plates 24, for example, one optical flat plate 24 is provided for one reflecting mirror.

As shown in FIG. 1, the present invention is not limited to an exposure apparatus 10 that forms a combined beam spot by two light beams obtained by separating one light beam to improve the image quality. The present invention is applicable to various inner drum type exposure apparatuses that perform exposure by separating beams.
For example, the linearly polarized light beams individually modulated as disclosed in the above-mentioned Patent Document 1 are combined / circularly polarized and separated into individual light beams by a Wollaston prism or the like of the main scanning means. The present invention can also be suitably used for an exposure apparatus that performs the above exposure.

  An example is shown in FIG. The example shown in FIG. 6 is the same as the exposure apparatus 200 of FIG. 7 except that it has the same optical path deflecting means 26 as before, and therefore the same members are given the same reference numerals and the description thereof is different. Mainly do the part.

  In the inner drum exposure apparatus 50 shown in FIG. 6, as described above, the light source unit 204 uses the modulators 214 and 216 to emit linearly polarized light beams L1 and L2 emitted from the light source 210 and divided by the half prism 212. After independent modulation, the polarization direction of the light beam L1 is converted by the half-wave plate 224 to obtain two linearly polarized light beams having polarization directions orthogonal to each other. Next, the two light beams are combined by the polarization beam splitter 220 to form an apparently one light beam (combined beam Lc) whose optical axes coincide with each other, and further rotated differently by the quarter wavelength plate 226. A circularly polarized light beam in the direction (right rotation and left rotation with respect to the traveling direction).

The circularly polarized combined beam Lc emitted from the light source unit 204 (quarter wave plate 226) is first widened by the beam expander 230 in the light beam optical system 52, and then optical path deflected. The optical path is deflected by the means 26 to be a predetermined optical path traveling along the center line of the support 202.
Here, in the light beam optical system 52, the optical flat plate 24 is disposed upstream of the optical path deflecting means 26, with the direction of 45 ° as the axis with respect to the P deflection in the optical path deflecting means 26 as in the previous example. It is arranged in an inclined state. The combined beam Lc is transmitted through the optical flat plate 26, so that the light quantity in the major axis direction of the elliptical deflection converted by the reflection at the reflection mirror 26a and the reflection mirror 26b of the optical path deflection means 26 is reduced. Therefore, the combined beam Lc deflected in the optical path by the optical path deflecting unit 26 becomes a combined beam Lc equivalent to circular deflection.

  The combined beam Lc having a predetermined optical path traveling along the center line of the support 202 by the optical path deflecting unit 26 enters the main scanning unit 206 through the condenser lens 232. The combined beam Lc incident on the main scanning unit 206 is reflected by the spinner mirror 234 toward the inner surface of the support 202, converted from circularly polarized light into a linearly deflected light beam by the quarter wave plate 236, and the Wollaston prism 238. Thus, the combined light beam Lc is separated into the individual light beams L 1 and L 2, and enters the photosensitive material A held on the support 202. In the illustrated example, the Wollaston prism 238 separates the light beam L1 and the light beam L2 and advances them at different angles. However, the present invention is not limited to this, and the separation element is a combined beam Lc. The light beam L1 and the light beam L2 separated from each other may travel in parallel.

  Here, since the main scanning unit 206 is rotated around the center line by a driving source (not shown), the light beam reflected by the spinner mirror 234 performs main scanning in the circumferential direction (main scanning direction) of the inner peripheral surface of the support 202. In addition, since the scanning unit 206 and the condenser lens 232 are sub-scanned in the center line direction (sub-scanning direction) by a sub-scanning unit (not shown), the photosensitive material A is two-dimensionally generated by the light beam L1 and the light beam L2. The entire surface is scanned.

  Also in this exposure apparatus 50, since the combined beam Lc equivalent to circularly polarized light can be incident on the main scanning means 206, the combined beam Lc is converted into appropriate linearly polarized light by the quarter wavelength plate 236, and the Wollaston prism is obtained. Since the light beam L1 and the light beam L2 can be appropriately separated without generating stray light in 238, multi-beam exposure can be performed with a good extinction ratio, and a high-quality image can be recorded.

Although the inner drum exposure apparatus of the present invention has been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements and modifications may be made without departing from the scope of the present invention. Of course.
For example, the exposure apparatus shown in FIG. 6 uses a Wollaston prism as a light beam (synthetic beam) separation element. However, the present invention is not limited to this, and a lotion prism, senalmon prism, light beam, and the like. Various known light beam separation elements for separating a light beam into a plurality of light beams, such as a beam displacer for separating the light beams in parallel, can be used.

It is a conceptual diagram of an example of the inner drum exposure apparatus of this invention. It is the schematic of the main scanning means of the inner drum exposure apparatus shown in FIG. It is a conceptual diagram for demonstrating the effect | action of the beam displacer arrange | positioned at the main scanning means shown in FIG. It is a graph which shows the light reflection characteristic of a light transmissive flat plate. (A) And (B) is a conceptual diagram for demonstrating the optical plane plate of the inner drum exposure apparatus shown in this FIG. It is a conceptual diagram of another example of the inner drum exposure apparatus of this invention. It is a conceptual diagram of an example of the conventional inner drum exposure apparatus. It is a conceptual diagram for demonstrating the change of the light beam by reflection.

Explanation of symbols

10, 50, 200 (Inner drum) Exposure device 12, 202 Support 14 Central control means 16 Laser driver 18 Spinner driver 20, 210 Light source 22, 226, 238 1/4 wavelength plate 24 Optical flat plate 26 Optical path deflecting means 26a, 26b, 218, 222 Reflecting mirror 28, 232 Condensing lens 30, 206 Main scanning means 34 Beam displacer 36, 234 Spinner mirror 38 Motor 40 Holder 52, 208 Light beam optical system 204 Light source unit 212 Half prism 214, 216 Modulator 220 Polarizing beam splitter 224 1/2 wavelength plate 230 Beam expander 238 Wollaston prism

Claims (6)

A light source that emits a circularly polarized light beam;
A support having an arc-shaped inner peripheral surface and holding a recording medium on the inner peripheral surface;
A deflection surface that reflects the light beam toward the inner peripheral surface of the support is provided, and the light beam is supported by rotating the deflection surface about a center line of the inner peripheral surface of the support. A main scanning means having a deflection element that scans in a main scanning direction that coincides with a circumferential direction of an inner peripheral surface of the body, and a separation element that rotates integrally with the deflection element and separates the light beam into a plurality of parts;
Sub-scanning means for relatively moving the main scanning means and the support in a sub-scanning direction coinciding with the direction of the center line of the inner peripheral surface of the support;
The length of the light beam converted from circularly polarized light to elliptically polarized light by reflection by the reflection mirror, which is deflected by at least one reflection mirror and incident on the main scanning means through a predetermined optical path by the light beam emitted from the light source unit An inner drum exposure apparatus comprising: a light beam optical system including at least one optical element that attenuates the amount of light in the axial direction.   The inner drum exposure apparatus according to claim 1, wherein the optical element is a light-transmitting flat plate arranged with a normal line inclined with respect to the optical axis of the light beam.   The inner drum exposure apparatus according to claim 2, wherein the flat plate is disposed with a normal line inclined at least in a minor axis direction.   4. The inner drum exposure apparatus according to claim 2, wherein the flat plate is formed by forming a dielectric film on a light beam incident surface.   The separation element uses a uniaxial crystal, the light beam is equal in quantity and parallel, and further overlaps a part of the beam spot. The inner drum exposure apparatus according to claim 1, wherein the inner drum exposure apparatus is a light beam. The light source unit multiplexes and emits two circularly polarized light beams modulated independently of each other and having different rotation directions;
The main scanning unit further includes a quarter-wave plate that rotates integrally with the deflecting element and the separating element, and uses a circularly polarized light beam as a linearly polarized light beam. 2. Two light beams that are linearly polarized by a four-wavelength plate travel at different angles or in parallel to each other and are separated into two sub-scanning directions at the same position in the main scanning direction. The inner drum exposure apparatus according to any one of 1 to 4.

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