JPH03132714A - Light beam scanner - Google Patents

Abstract

PURPOSE:To easily multiplex a demultiplex light beams by1st and 2nd plarization beam splitters and to apply light of 0th order as a synchronizing signal with simple structure by making the plane of polarization of the light of 0th order different from an exposure beam for scanning. CONSTITUTION:The light of 0th order which is outputted from an acoustooptic element (AOM) 18 has its plane of polarization changed by 90 deg. through a 1/2lambda plate 80 and is reflected by a mirror 82 to reach a polarization beam splitter 84. The polarization beam splitter 84 multiplexes the scanning laser beam which is refracted by the AOM 18 and the light of 0th order, and consequently the light of 0th order is outputted from a lens 29 after passing through the same optical path with said scanning laser beam. The light of 0th order outputted by the lens 29 is deflected by a polarization beam splitter 86 by 90 deg. and separat ed from the scanning laser beam. The light of 0th order which is separated by the polarization beam splitter 86 is detected by a photoelectric detector 96 and applied as the synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device that performs two-dimensional plane scanning by performing main scanning and sub-scanning of a light beam using a scanning optical system.

[Prior art]

Generally, a light beam emitted from a laser is irradiated onto the image,
In a light beam scanning device such as a light beam reader that reads the transmitted or reflected light, or a light beam recording device that irradiates a recording material with a light beam and records an image, the light beam from the laser is transferred to a rotating polygon mirror. ), a galvanometer mirror, etc., performs main scanning and sub-scanning to perform two-dimensional plane scanning.

That is, the light beam is reflected by the reflective surface of a polygon mirror that rotates at high speed to perform main scanning, and then this reflected light beam is reflected by a galvanometer that is tilted at a constant pitch at a predetermined timing. This eliminates the need for sub-scanning.

By the way, in the above-mentioned light beam scanning device, in order to keep the main scanning recording position constant, a light beam for forming a synchronization signal is required in addition to the scanning light beam.

By setting the time of input of this synchronization signal or the time when a predetermined time has elapsed since the time of input as the main scanning recording time, it is possible to synchronize each main scanning line.

In order to generate such a synchronization signal, conventionally, a synchronization signal light beam has been used in addition to a scanning light beam. In this case, it is necessary to combine the synchronization signal light beam before the scanning optical system so that the optical path matches the scanning light beam, and then separate the synchronization signal light beam to the encoder for synchronization signal generation. . This synthesis and separation is performed using a color separation prism (
Since this is performed using a mirror), lasers with different wavelengths are required for the synchronizing signal light beam and the scanning light beam.

[Problem to be solved by the invention]

However, in the above configuration, two lasers with different wavelengths are used.
It is necessary to install a plurality of lasers, and a plurality of drive sources are also required to drive these lasers, so the number of parts is large and the assembly workability is poor.

In particular, currently, laser recording devices have been developed that can perform multiple main scans simultaneously by splitting a single laser into multiple light beams manually powered by an acousto-optic device. It is not preferable to provide another laser to the Note that zero-order light is not used when the light beam is split by the acousto-optic element. Even if an attempt was made to apply this zero-order light as a synchronization signal, the light beams were output from the same laser, and the optical system for combining and separating them from the scanning light beam was complicated, making it impractical.

The present invention has been made in consideration of the above facts, and an object of the present invention is to provide a light beam scanning device that has a simple structure and can easily use the zero-order light of a light beam obtained by an acousto-optic element as a synchronization signal.

[Means to solve the problem]

The light beam scanning device according to the present invention includes an acousto-optic element that splits an incident light beam into a plurality of parts and performs optical modulation, and performs main scanning and sub-scanning of the light beam by a scanning optical system to scan a two-dimensional plane. A light beam scanning device that scans an image, the changing means being disposed on the optical path extension of the zero-order light passing through the acousto-optic element and changing the polarization plane of the zero-order light by a predetermined angle, and the changing means an optical member that guides the zero-order light whose polarization plane has been changed by the optical member to the optical path of the scanning light beam;
a first polarizing beam splitter that combines the zero-order light and the scanning light beam with different polarization planes; a second polarization beam splitter that separates the optical path of the combined zero-order light and the scanning light beam; It has a synchronization signal creation means for creating a synchronization signal using the zero-order light separated by the second polarization beam splitter.

[Effect]

According to the present invention, among the output lights split by the acousto-optic element, the zero-order light, which is not used as a scanning light beam and accounts for most of the output intensity, has its polarization plane changed by a predetermined angle by the changing means. The zero-order light whose polarization plane has been changed is guided again to the optical path of the scanning light beam by the optical member, and is combined with the scanning light beam by the first polarization beam splitter.

As a result, the optical path of the 0th-order light coincides with the scanning light beam, and main scanning is performed.

In this way, the zero-order light combined with the scanning light beam is
Separate with a polarizing beam splitter. This is because the zero-order light and the scanning light beam have different planes of polarization, so they can be easily separated. Using this separated zero-order light, a synchronization signal is created by a synchronization signal creation means. This synchronization signal makes it possible to control the scanning start timing of the scanning light beam. Further, the writing light separated by the second polarizing beam splitter is sub-scanned and guided to the writing surface.

That is, in the present invention, by making the polarization plane of the zero-order light different from that of the scanning exposure beam, it becomes possible to easily combine and separate the zero-order light with the first and second polarizing beam splitters, and the zero-order light can be easily combined and separated with a simple structure. can be applied as a synchronization signal.

〔Example〕

FIG. 2 shows a laser beam recording device 10 according to this embodiment.
It is shown.

The laser 12 outputs a laser beam in response to an on/off signal from a laser power source 14.
This laser beam is input through a lens 16 to an acousto-optic device (hereinafter referred to as AOM) 18 that constitutes a part of a simultaneous multi-beam optical modulator.

AOM 18 is controlled by AOM driver 20. An optical modulation circuit 22 that together with the AOM 18 constitutes a simultaneous multi-beam optical modulation device is connected to the AOM driver 20 . This optical modulation circuit 22 has the role of controlling the AOM driver 20 and changing the intensity of optical modulation by the AOMI 8, and its configuration will be described later.

In this embodiment, the laser beam output from the AOM 18 is divided into eight laser beams and is manually applied to a polygon mirror 28 via a lens 24 and a mirror 26.

Furthermore, as shown in FIG. 1, in addition to the eight laser beams mentioned above, the AOM 18 outputs laser beams that are not used for scanning. This is zero-order light that is not diffracted by the AOM 18 and passes through the AOM 18 in a straight line. The zero-order light that has passed through the AOM 18 is manually inputted to a 1/2λ plate 80 arranged on the extension of the optical path.

This 1/2λ plate 80 is configured to change the polarization plane of the 0th-order light by 90° and output it. The 0th-order light output from the 1/2λ plate 80 is inputted to a polarizing beam splitter 84 via a mirror 82. The polarizing beam splitter 84 is disposed on the optical path of the scanning laser beam output from the AOM 18, and as a result, the 0th order light is combined with this scanning laser beam (1st to 8th order lights). It is designed to reach a polygon mirror 28.

The polygon mirror 28 is rotated at high speed by a polygon driver 30, and is configured to perform main scanning by reflecting the input laser beam on its reflecting surface. The laser beam reflected by the reflective surface of the polygon mirror 28 enters the scanning lens 29, and after exiting from the scanning lens 29, it passes through the polarizing beam splitter 86 to the mirror 32,
The light enters the relay lens 33. In addition, the relay lens 33
The laser beam that reaches the polarizing beam splitter 86
It is a scanning laser beam that passes linearly through the 0
The secondary laser beam is polarized at right angles by a polarizing beam splitter 86. That is, since the polarization plane of the zero-order light has been changed by the 1/2λ plate 80, it is separated from the scanning laser beam by the polarization beam splitter 86.

The laser beam reflected by the polarizing beam splitter 86 is directed to the galvanometer 36 via the mirror 34.

The galvanometer 36 has a reflecting surface that is movable in the sub-scanning direction by a galvanometer driver 37, and moves in the sub-scanning direction every time one main scanning of the laser beam is completed to change the direction of reflection of the laser beam. . The laser beam reflected by the galvanometer 36 is reflected by a mirror 38,
It is designed to reach a stage 42 via a lens 40.

A recording material 44 is placed on the stage 42, and the laser beam is irradiated onto the recording material 44, so that an image can be recorded on the recording material 44.

The recording material 44 is wound in layers on reels 46 and 48 at both ends in the longitudinal direction, and when recording of one image is completed, the recording material 44 is wound from one reel 46 to the other reel 48.
This is the configuration that will be moved to.

As shown in FIG. 3, the AOM1 is connected to the optical modulation circuit 22.
A signal line 50 for propagating image data signals corresponding to the number of laser beams divided by 8 is input. The signal lines 50 are each connected to a modulator 64.

Although not shown, the signal lines 50 are branched, one being sent to a delay circuit, and the other recognizing the number of on-state image data signals. Here, by changing the light intensity of the image data signal that is delayed and output by the delay circuit in accordance with the number of recognized image data signal ONs, output fluctuations due to so-called competition for light are prevented.

Note that the delay circuit is set in consideration of the time required to recognize the number of on-states of the image data signal.

An oscillator 66 is connected to each of these modulators 64, and modulates each signal to a predetermined frequency for division by the AOM 18. The modulator 64 is
Each is connected to a mixer 68 via an amplifier 67. The mixer 68 mixes the image data signals output from the respective modulators 64 and outputs the mixed signal to the AOM driver 20.

As shown in FIG. 1, an encoder grating 88 is disposed on the optical path extension of the zero-order light that is polarized at right angles by the polarizing beam splitter 86.

The encoder grating 88 has a plurality of slit holes 90 along the main scanning direction of the 0th order light, and when the 0th order light is moved in the main scanning direction, a predetermined pulsed light is emitted to the back side of the encoder grating 88. It has become so. Note that the main scanning width Ws of the zero-order light is approximately 5Qmm, and the slit hole 90
The number of is also provided corresponding to this width.

On the back side of the encoder grating 88, a pair of mirrors 92.
94 are arranged facing each other. These mirrors 92.94
One end of each abuts an encoder grating 88 . Further, the distance between these mirrors 92 and 94 is inclined so that it gradually becomes narrower toward the other end. Therefore, the distance WM at the other end of these mirrors 92, 94 is approximately 29 mm.

A photodetector 96 is attached to the other end of the mirrors 92,94. In this photoelectric detector 96, the entire area between the mirrors 92 and 940 in the width direction is a photodetection surface.
The rise time is 15 nsec, and the photoelectric detector has performance that can sufficiently correspond to the scanning time of the laser beam. That is, the distance between the mirrors 92 and 940 was gradually narrowed to 29 mm, making the photoelectric detector 96 applicable.

The photoelectric detector 96 converts the detected light into a current value, and when this current value exceeds a predetermined threshold, it is applied as a synchronization signal to control the output timing of the scanning laser beam. It has become.

The operation of this embodiment will be explained below.

First, the image data signal is input to the delay circuit 52, delayed for a predetermined time, and then output. On the other hand, the number of on-states of the branched image data signal is recognized, and the light intensity of the image data signal output from the delay circuit 52 is controlled according to this number, thereby reducing the light intensity due to so-called competition for light. Fluctuations are prevented.

The image data signals are modulated by respective modulators 64, mixed by mixer 68, and output to AOM driver 20. In synchronization with the output from this AOM driver 20 to the AOM 18, the laser power supply 14 outputs the laser 12.
Turn on to output a laser beam.

The laser beam output from the laser 12 passes through the lens 16
The laser beam reaches the AOM 18 via the AOM 18, and is divided into a plurality of (eight in this embodiment) laser beams in the sub-scanning direction. The divided laser beam reaches the polygon mirror 28 via the polarizing beam splitter 84, the lens 24, and the mirror 26, and as the polygon mirror 28 rotates, the direction of reflection is changed and the laser beam is main-scanned.

The laser beam reflected by the reflective surface of the polygon mirror 28 is incident on the galvanometer 36 via mirrors 32 and 34. In the galvanometer 36, its reflecting surface is tilted in the sub-scanning direction for each main scanning of the laser beam. In this embodiment, since eight main scans are performed simultaneously, the tilt angle in the sub-scanning direction by the galvano makeup 36 is every nine pitches.

The laser beam reflected by the galvanometer 36 is irradiated onto the recording material 44 on the stage 42 via the mirror 38, lens 40, and deflection beam splitter 86, and an image is recorded.

Here, the laser beam recording apparatus 10 of this embodiment uses the zero-order light output from the AOM 18 as a synchronization signal that determines the main scanning recording timing.

That is, the 0th order light output from the AOM 18 is first
The plane of polarization is changed by 90° by the 1/2λ plate 80 , and then reflected by the mirror 82 to reach the polarizing beam splitter 84 . In the polarized beam splinter 84, A
The scanning laser beam diffracted by the OM 18 and the zero-order light are combined, and as a result, the zero-order light passes through the same optical path as the scanning laser beam and is output from the lens 40.

The zero-order light output from the lens 40 is deflected in a right angle direction by a polarizing beam splitter 86 and separated from the scanning laser beam. This is because the polarization plane of the zero-order light is changed by 90 degrees from the polarization plane of the scanning laser beam, and even laser beams having the same wavelength can be easily separated.

The zero-order light separated by the polarizing beam splitter 86 passes through the encoder grating 88, and pulsed light is output on the back surface thereof. The pulsed light, either directly or reflected by mirrors 92.94, reaches a photodetector 96 where it is detected and applied as a synchronization signal.

The photoelectric detector 96 converts the manually input light amount into a current value, and outputs it when this current value exceeds a predetermined threshold value, thereby controlling the main scanning recording timing by the scanning laser beam. can.

Here, the photoelectric converter 96 of this embodiment is a photoelectric detector whose rise time is 15 nsec, and this rise time can correspond to the scanning time of the laser beam. By the way, the width Ws of the zero-order light in the main scanning direction
is about 5Q+nm, and even if the photoelectric detector 96 is placed directly on the back side of the encoder grating 88, full-width detection cannot be ensured. Therefore, the encoder grid 9
Since the mirrors 92 and 94 are arranged so that the distance between the mirrors 92 and 94 gradually narrows toward the back side of the mirror 6, it is possible to correspond to the detectable width of the photoelectric detector 96, and a synchronization signal can be reliably obtained.

In this way, in this embodiment, the 0 output from the AOM18
Since the polarization direction of the secondary light is changed and used for generating a synchronization signal, there is no need to separately provide a laser with a different wavelength, and the number of parts can be reduced. In addition, 1/2λ plate 80
Since the polarization plane of the 0th-order light was changed by 90 degrees with respect to the scanning laser beam, the polarization beam splitter 84.8
By using 6, it is easy to connect the scanning laser beam and 0
It is possible to combine and separate the following light.

Furthermore, since the pair of mirrors 92 and 94 are arranged so that the distance between them gradually narrows toward the back side of the encoder grating 88, the photoelectric detector has a rise time that can sufficiently correspond to the scanning time of the scanning laser beam. 96 can be applied. Therefore, fluctuations in the amount of light due to main scanning can be reduced, and the S/N ratio of the detection signal can also be improved.

In addition, the pulsed light obtained by passing through the encoder grating 88 is reflected directly or by mirrors 92 and 94 to the photoelectric detector 9.
6, the efficiency of using pulsed light can be greatly increased. In other words, when the conventional acrylic rond is injected from the circumferential surface and the pulsed light is detected at the axial end of the acrylic rond, the utilization efficiency of the pulsed light is 1.
Compared to the 5%, the utilization efficiency of this pulsed light can be 80 to 100% in this embodiment.

In this example, the 1/2 λ plate 80 was used to change the polarization plane of the 0th-order light by 90°, but 1/4 λ plates were provided on the incident side and the reflective side of the mirror to convert the polarized light once into circularly polarized light. After that, the plane of polarization may be changed by 90°.

In addition, the light that has passed through the encoder grating 88 is guided to the photoelectric converter 96 either directly or by being reflected by a mirror 92.94, but as shown in FIG. A box body 98 may be arranged.

In this case, the side surface 98A of the box body is connected to the mirror 92.94.
It needs to be tilted as well.

〔Effect of the invention〕

As explained above, the light beam scanning device according to the present invention has a simple structure and has the excellent effect that the zero-order light of the light beam obtained by the acousto-optic element can be easily used as a synchronization signal.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of the scanning optical system according to this embodiment, and FIG.
3 is a block diagram of a light modulation circuit, and FIG. 4 is an enlarged view showing a modified example of a photoelectric converter for detecting a synchronizing signal and its surroundings. DESCRIPTION OF SYMBOLS 10... Laser beam recording device, 12... Laser, 18... AOM (acousto-optic device), 28... Polygon mirror 36... Galvanometer, 80... 1/2λ plate (changing means) , 82... mirror (optical member), 84... (first) polarizing beam splitter, 86...
... (second) polarizing beam splitter.

Claims (1)

[Claims] (1) A light beam that is equipped with an acousto-optic element that splits the incident light beam into multiple parts and performs optical modulation, and that scans a two-dimensional planar image by performing main scanning and sub-scanning of the light beam using a scanning optical system. A scanning device, comprising: a changing means disposed on the optical path extension of the zero-order light passing through the acousto-optic element and changing the polarization plane of the zero-order light by a predetermined angle, and the polarization plane being changed by the changing means. an optical member that guides the zero-order light to the optical path of the scanning light beam; a first polarizing beam splitter that combines the zero-order light and the scanning light beam with different polarization planes;
a second polarizing beam splitter that separates the optical path of the combined zero-order light and the scanning light beam; and a synchronization signal creation means that creates a synchronization signal using the zero-order light separated by the second polarization beam splitter. A light beam scanning device having .