JPH06334818A - Light beam scanner - Google Patents

Abstract

PURPOSE:To obtain a light beam scanner capable of narrowing an angle between optical axes to the extent that optical performance such as color aberration is not lost. CONSTITUTION:Since a semiconductor laser 14 is arranged at the center part so as to be inserted between SHGs 16, 18, each included angle theta of each optical axis of a laser beam provided as an output from the semiconductor laser 14 and the SHGs 16, 18 is made narrowest. Since an AOM 20 arranged at the center is offset along an optical axis in a direction parted from the semiconductor laser 14, AOMs 20 are not interfered with each other. Since a concave lens 86R, a slit 38R, a convex lens 40R and a cylindrical lens 42R are offset along the optical axis, the optical axis is not interfered with B and G light side optical system 32. Thus, a defect due to arrangement of the semiconductor layer 14 between the SHGs 16, 18 in the light source section is not caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device for scanning a light beam to record or read an image.

[0002]

2. Description of the Related Art Conventionally, in an image recording apparatus as a scanning apparatus using a light beam, for example, a semiconductor laser or a laser beam output device (SHG) in which a semiconductor laser and an internal modulation function are integrated is provided in parallel. Laser beams emitted from these are externally modulated by an AOM (acousto-optical element) as needed through an optical system, and the modulated laser beam is applied to a polygon mirror (rotating polygon mirror) rotating at high speed. As a result, the light is deflected in the main scanning direction. The laser beam deflected in the main scanning direction is guided to the recording surface of the image recording material by the optical system, and the main scanning is performed on the recording surface.
With this main scanning, one image can be recorded by conveying the image recording material in the sub-scanning direction at a constant speed.

In this case, the respective optical axes are incident on the polygon mirror at different angles (see Japanese Patent Laid-Open No. 1-77018).
There may be a deviation between the colors in the main scanning direction on the image recording material. Note that this shift can be recognized by the human eye as being a shift of 30 μm.

The above-mentioned misalignment between the respective colors may be adjusted (corrected) at the exposure timing or the like. However, in consideration of optical performance (for example, field curvature, surface tilt correction, chromatic aberration, etc.), the different angle incidence is performed. The angle between the optical axes is preferably small.

By the way, at present, the wavelength of a semiconductor laser applicable without using internal modulation is R light (about 680 nm), and SHG is applied to the other (B light, G light).
Therefore, a combination of one semiconductor laser and two SHGs has a general structure (see Japanese Patent Laid-Open No. 63-141051). Further, as the configuration of SHG, Japanese Patent Application No. 5-10
No. 0844.

[0006]

However, the SHG
Has a large outer shape, and in the case of a scanning optical system using an external modulator such as AOM, mutual mutual components interfere with each other and it is limited to reduce the angle between the optical axes of the respective lights. It cannot be installed at an angle that does not hinder. In addition, the oscillation of the semiconductor laser may become unstable due to the return light from the AOM.

In consideration of the above facts, an object of the present invention is to obtain a light beam scanning device capable of narrowing the angle between the optical axes of respective colors to the extent that the optical performance such as chromatic aberration is not impaired.

[0008]

According to a first aspect of the present invention, at least one set comprises a semiconductor laser and the other set comprises a second high frequency output means (AHG), and a light source section which emits light from this light source section. A light beam scanning device for scanning or scanning an optical beam to record or read an image, the semiconductor laser and a second high frequency output device (SH).
G) and G) are alternately arranged so that the included angle of each optical axis is minimized.

The invention described in claim 2 is characterized in that the semiconductor laser is directly modulated.

According to a third aspect of the present invention, a light source section in which three semiconductor lasers outputting wavelengths corresponding to the three primary colors are arranged in parallel, and a light beam emitted from the light source section is scanned to record an image or A light beam scanning device comprising a scanning means for reading, characterized in that when one of the semiconductor lasers is directly modulated, the directly modulated semiconductor laser is arranged in the center.

According to a fourth aspect of the present invention, the optical components of the light source section or the scanning means corresponding to the light source section are arranged offset from each other along the optical axis.

According to a fifth aspect of the present invention, when the light from the semiconductor laser is externally modulated by the acousto-optic device (AOM), the incident surface of the acousto-optic device (AOM) is set with respect to the incident optical axis. It is characterized by having an angle larger than the Bragg angle.

[0013]

According to the first aspect of the invention, for example, the light source section is composed of one semiconductor laser and two second high frequency laser beam output means (SHG), and the light is output from the light source section. External modulator of light beam (eg acousto-optic device)
Intensity or pulse width modulation by to obtain maximum diffracted light,
Two SHGs in the case of scanning by the scanning means
The semiconductor lasers are arranged so as to be sandwiched by, that is, in the center (an example of alternate arrangement).

By arranging in this way, SHG
It is possible to narrow the included angle of each optical axis as compared with the case where the two are arranged adjacent to each other. As a result, it is possible to reduce field curvature, surface tilt correction, chromatic aberration, etc., which are caused by the optical components in the scanning means.

According to the invention described in claim 2, in the structure of the invention described in claim 1, for example, when the semiconductor laser is directly modulated, the semiconductor laser for direct modulation is arranged in the center. This makes it possible to further narrow the included angle of each optical axis, as compared with the case where the external modulators are arranged adjacent to each other.

According to the third aspect of the present invention, even when three semiconductor lasers are used as the light source section, by arranging the semiconductor laser for direct modulation in the center, the angle between the optical axes can be further narrowed. be able to.

According to the fourth aspect of the present invention, the optical components such as lenses arranged on the optical axis output from the light source section are offsetly arranged along the respective optical axes.
The included angle between the optical axes can be further narrowed.

According to the invention described in claim 5, the reflected light from the acousto-optic element (AOM) does not return to the semiconductor laser, and it is possible to prevent the oscillation of the semiconductor laser from becoming unstable.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a scanning optical system 10 of an image recording apparatus using a laser beam according to this embodiment. The scanning optical system 10 is provided on the optical surface plate 12. The optical surface plate 12 is covered with a dust cover (not shown) to prevent intrusion of dust that adversely affects the optical system.

As a light source unit corresponding to the three primary colors of this embodiment, one semiconductor laser 14 (for R light; wavelength 680n) is used.
m) and two SHG16 (for B light; wavelength 473n)
m) and 18 (for G light; wavelength 532 nm) are applied. The arrangement of the semiconductor laser 14 and the SHGs 16 and 18 is
The semiconductor lasers 14 are arranged side by side in the center.
Therefore, the two SHGs 16 and 18 are arranged relatively close to each other. The width dimension W _{SHG of the} SHGs 16 and 18 is
It is about 70 mm.

AOMs (acousto-optic elements) 20 are arranged on the output sides of the semiconductor laser 14 and the SHGs 16 and 18, respectively, and are modulated. Here, the AOM 20 applied to the semiconductor laser 14 is offset in the direction away from the semiconductor laser 14 along each optical axis, and the three AOMs 20 are arranged so as to overlap each other when viewed from the optical axis direction. . With such an arrangement, the AOMs 20 can be prevented from interfering with each other and can be placed close to each other. The width dimension W _AOM of the _{AOM 20} is about 50 mm.
It is a degree.

Convex lenses 22 (focal length 30.5 mm) and 24 are provided between the SHGs 16 and 18 and the AOM 20, respectively.
(Focal length 30.2mm) is interposed, SHG16, 1
The laser beam output from 8 is imaged by the AOM 20.

A collimator lens 26 (focal length 8 mm) and a convex lens 28 (focal length 81.2 m) are arranged between the semiconductor laser 14 and the AOM 20 in this order from the semiconductor laser 14 side.
m) and a concave lens 30 (focal length -15.2 mm) are provided, and the collimator lens 26 and the convex lens 28 are used to
The image is formed at M20, and the concave lens 30 performs waveform shaping to approximate the beam to a perfect circle.

That is, by using lenses having different focal lengths, regardless of the offset of the AOM 20, the AO
An image can be formed at M20.

The primary light output from the AOM 20 is incident on the reflection mirror 34 via the optical system 32. The optical system 32 has the same configuration for both BGR light and
The concave lens 36, the slit 38, and the convex lens 4 are sequentially arranged from the side.
0, a surface tilt correction cylindrical lens 42 (in FIG. 1, the symbols B, G, and R of the respective colors are added to the end of the symbols). The focal lengths of the lenses of each color are as shown in the table below.

[0026]

[Table 1]

Here, the optical system 32 is offset corresponding to the arrangement position of the AOM 20, for example, it is prevented that the concave lenses 36 are adjacent to each other, and the SHGs 16 and 18 are arranged close to each other and the AOM 20 is arranged. It is an arrangement that does not limit the close arrangement.

The light reflected by the reflecting mirror 34 is made to enter the reflecting mirror surface 44A of the polygon mirror 44.

The polygon mirror 44 has a rotating shaft 44B.
Is connected to a rotating shaft of a motor (not shown) and is rotated at high speed by the driving force of the motor. Therefore, the reflected light of the laser beam incident on the reflecting mirror surface 44A of the polygon mirror 44 is deflected as the polygon mirror 44 rotates (main scanning).

An fθ lens 46, a lens group 48 such as a cylindrical lens, and a cylindrical mirror 50 are arranged on the optical axis of the light reflected by the reflecting mirror surface 44 A of the polygon mirror 44. The laser beam is focused in the main scanning direction and is guided by a cylindrical mirror 50 onto a recording paper (not shown).

The recording paper is conveyed at a constant speed in the direction orthogonal to the main scanning direction of the laser beam by the driving force of a driving means (not shown) (sub scanning). As a result, a plurality of main scanning lines are continuously recorded on the recording paper to record an image.

The operation of this embodiment will be described below. As shown in FIG. 1, since one semiconductor laser 14 and two SHGs 16 and 18 that form the light source unit are arranged in the central portion so that the semiconductor laser 14 is sandwiched between the SHGs 16 and 18, The included angle θ between the optical axes of the laser beams output from the laser 14 and the SHGs 16 and 18 can be minimized.

Further, among the three AOMs 20, the AOM 20 arranged at the center is offset along the optical axis in the direction away from the light source, that is, the semiconductor laser 14, so that the combination (arrangement) of the light source units causes the optical axis of the optical axis to change. Even if the included angle is narrowed, the AOMs 20 do not interfere with each other.

Since the three optical axes are oriented so as to gradually converge to one point, in the optical system 32, the respective parts are arranged close to each other. However, depending on the offset amount of the AOM 20, the concave lens 36R and the slit 38
Since R 1, the convex lens 40 R, and the cylindrical lens 42 R are also offset along the optical axis, they do not interfere with the optical system 32 on the B light and G light sides.

Therefore, in the light source section, the semiconductor laser 1
There is no problem caused by placing 4 between the SHGs 16 and 18.

The light reflected by the reflecting mirror 34 is incident on the reflecting mirror surface 44A of the polygon mirror 44. The light reflected by the reflecting mirror surface 44A of the polygon mirror 44 is
Lens group 4 including fθ lens 46 and cylindrical lens
By passing through 8, the polygon mirror 44 focuses the laser beam in the main scanning direction, and the cylindrical mirror 50 guides the laser beam onto the recording paper.

Since the recording paper is conveyed at a constant speed in the direction orthogonal to the main scanning direction of the laser beam, a plurality of main scanning lines are continuously recorded on the recording paper,
The image is recorded.

In this embodiment, the semiconductor lasers 14 and S of the light source section are used as a structure for narrowing the included angle of the three optical axes.
The configuration in which the arrangement order of the HGs 16 and 18, the arrangement position of the AOM 20, and the arrangement position of the optical system 32 are combined is shown.
The object of the present invention can also be achieved by these independent configurations.

That is, as shown in FIG. 2, even if the light source unit only has one semiconductor laser 14 arranged between two SHGs 16 and 18, the downstream AOM 20 and the optical form 32 do not interfere with each other. If they are arranged close to each other, the included angle θ ₁ can be narrowed.

Further, as shown in FIG. 3, the semiconductor laser 1
When directly modulating 4, the semiconductor laser 14 for direct modulation can be arranged closer to the center to bring them closer. As a result, the included angle θ ₂ of each optical axis can be further narrowed compared to the case where the AOMs 20 are arranged adjacent to each other.

Although the wavelength of the semiconductor laser 14 is becoming shorter, the response to modulation becomes slower as the wavelength becomes shorter, so that an external modulator may be required. Even when three semiconductor lasers 14 are used as such a light source unit, as shown in FIG. 4, by arranging the semiconductor laser 14 for direct modulation in the center, the sandwiching angle θ ₃ of the optical axis is further increased. Can be narrowed.

The beam emitted from the semiconductor laser 14 is reflected by the convex lens 28, the concave lens 30, etc.
When the image is formed at 0, the reflected light from the incident surface of the AOM 20 may pass through the concave lens 30, the convex lens 28, etc. in the opposite direction, and the oscillation of the semiconductor laser 14 may become unstable (mode competition due to return light). .

In such a case, A is incident on the incident surface of the AOM 20.
The solution may be solved by applying an R coat, but if this is still unstable, the following measures are effective.

Normally, the incident surface of the AOM 20 is tilted by the Bragg angle with respect to the optical axis of the incident beam, but by further increasing this angle, the reflected light from the AOM 20 hardly returns to the semiconductor laser 14. be able to. Further, the reflected light is a concave lens 30 and a convex lens 28.
In order to forcibly prevent the laser beam from returning to the semiconductor laser 14, it is also effective to provide a light-shielding means at a position slightly downstream of the closest concave lens 30 of the AOM 20.

The closer the incident beam to the AOM 20 is to the parallel beam, the easier it is to separate the reflected light from the incident end of the AOM 20 from the incident beam.

The reflectance of the emission end face of the semiconductor laser 14 is increased to make the internal resonance state of the semiconductor laser 14 less likely to be affected by the returning light. Usually, in order to obtain a high light output, a method of lowering the emission end face reflectance is used, but this makes the light susceptible to the return light. The emission facet reflectance is preferably 30% or more.

When the single-mode semiconductor laser 14 is used, it is affected by the returning light. Therefore, it is effective to prevent this by performing high-frequency superimposition (several hundred MHz) and making it multi-mode. If the response of the semiconductor laser 14 is slow and does not follow the high frequency, the singleness can be reduced by switching at a lower frequency, and the influence of the returning light can be reduced.

[0048]

As described above, the light beam scanning device according to the present invention has an excellent effect that the angle between the optical axes of respective colors can be narrowed to the extent that the optical performance such as chromatic aberration is not impaired. .

[Brief description of drawings]

FIG. 1 is a schematic diagram of a scanning optical system according to the present embodiment.

FIG. 2 is a schematic diagram showing a basic configuration of a light source section.

FIG. 3 is a schematic diagram of an optical system showing a modified example of the present embodiment.

FIG. 4 is a schematic diagram of an optical system showing a modified example of the present embodiment.

[Explanation of symbols]

10 Scanning Optical System 14 Semiconductor Lasers 16 and 18 SHG (Second High Frequency Laser Beam Output Means) 20 AOM 32 Optical System

Claims (5)

[Claims] 1. A light source section comprising at least one set of semiconductor lasers and another set of second high frequency laser beam output means (SHG), and a light beam emitted from this light source section for scanning to record an image. Or a scanning means for reading, wherein the semiconductor laser and the second high frequency laser beam output means (SHG) are alternately arranged so that the included angle of each optical axis is minimized. A light beam scanning device characterized by: 2. The light beam scanning device according to claim 1, wherein the semiconductor laser is directly modulated. 3. A light source section in which three semiconductor lasers that output wavelengths corresponding to the three primary colors are arranged in parallel, and a scanning unit for scanning or scanning an optical beam emitted from the light source section to record or read an image. A light beam scanning device comprising: a semiconductor laser that is directly modulated when one of the semiconductor lasers is directly modulated. 4. The optical component of the light source unit or the scanning means corresponding to the light source unit is arranged so as to be offset from each other along the optical axis, according to any one of claims 1 to 3. Light beam scanning device. 5. When the light from the semiconductor laser is externally modulated by an acousto-optic device (AOM), the incident surface of the acousto-optic device (AOM) has an angle larger than the Bragg angle with respect to the incident optical axis. Claim 1 characterized in that
The light beam scanning device according to claim 4.