JPH08334711A - Multi-beam optical scanning device - Google Patents

Abstract

(57) [Summary] [Object] In a multi-beam optical scanning device using a plurality of polarizing prisms, a plurality of polarizing prisms are used, and a half-wave plate is arranged between the polarizing prisms. Provided is a high-resolution optical scanning device in which the number of beams for scanning the body is four or more. [Structure] A laser beam 2 is emitted from a laser light source 1, passes through a polarizing prism 3, a half-wave plate 12, and a polarizing prism 13, and becomes four beams. The four beams are focused by the spherical lens 4, modulated by the multi-channel acousto-optic light modulator 5, converted into parallel light by the spherical lens 6, and arranged into a predetermined beam by the Dove prism 7, and the cylindrical lens 8
And the rotary polygon mirror 9 optically scans the photosensitive drum 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam optical scanning device which divides laser light into a plurality of beams and processes a plurality of beams in parallel to realize high speed.

[0002]

2. Description of the Related Art Optical scanning with a plurality of laser beams can reduce the number of rotations of a polygon mirror.
It is well known that it is effective in a high-speed laser beam printer because it can increase the irradiation time of dots. The configuration of the conventional multi-beam optical scanning device,
This will be described with reference to FIG. First, the laser light 2 emitted from the laser light source 1 is incident on the polarization prism 3. In the polarization prism 3, the laser light 2 is split into two beams whose polarization components are orthogonal to each other. The two beams generated by the polarization prism 3 pass through the spherical lens 4 and enter the multi-channel acousto-optic light modulator 5. The multi-channel acousto-optic light modulator 5 modulates each of the two beams according to the print signal. The two modulated beams are reflected by the spherical lens 6
, And a predetermined beam array is formed by the Dove prism 7. After that, the photosensitive drum 10 is optically scanned by the rotary polygon mirror 9 through the cylindrical lens 8. The lens 11 is for making the beam diameters and scanning speeds of the two beams for scanning the photosensitive drum 10 uniform.

[0003]

Conventional polarization prism 1
In a multi-beam optical scanning device using two beams, one polarizing prism generates two beams whose polarization directions are orthogonal to each other, so that only two beams can scan the photosensitive member. An object of the present invention is to provide an optical scanning device for high resolution in which the number of beams scanning the recording material is four or more.

[0004]

The above-mentioned object is to use a plurality of polarizing prisms, to arrange a half-wave plate between the polarizing prisms, and to set the optical axis direction of the half-wave plate to the former stage. 0 ° with respect to the polarization direction of the beam emitted from the polarizing prism
Alternatively, it is achieved by arranging so as not to be 90 °.

[0005]

In the mechanism configured as described above, the laser light is split into the beam polarized perpendicularly to the optical axis of the polarizing prism and the beam polarized parallel to the optical axis of the polarizing prism. Even if the two beams thus polarized are directly incident on the polarizing prism of the next stage, which has the same optical axis direction as the polarizing prism of the preceding stage, the respective beams cannot be separated into two beams.
By using a half-wave plate, the polarization direction of the beam can be changed so that the beam enters the polarizing prism of the next stage, and four circular spots can be arranged in a straight line on the image plane. When the half wave plate and the polarization prism are further continued, each beam can be separated into two beams by the polarization prism at the next stage, and the number of beams can be further increased.

[0006]

EXAMPLE An example of the present invention will be described with reference to FIG. The laser light 2 emitted from the laser light source 1 in FIG.
Incident on. In the polarizing prism 3, the laser light 2 is split into a beam polarized perpendicularly to the optical axis of the polarizing prism 3 and a beam polarized parallel to the optical axis. Next, the optical axis is 22.5 ° or 67.5 with respect to the polarization direction of the beam.
When two beams are passed through the half-wave plate 12 arranged so that the angle becomes 0, the polarization direction of each beam is 1.
45 ° or 13 with respect to the polarization direction before passing through the 1/2 wavelength plate
Rotate 5 °. After that, the two beams are directed to the polarizing prism 3
And the polarizing prism 1 arranged so that their optical axes are the same.
When the beam enters the polarization prism 13,
A beam polarized perpendicularly to the optical axis of and a beam polarized parallel to the optical axis are separated into four beams. These four beams are focused by the spherical lens 4 and enter the multi-channel acousto-optic modulator 5. The multi-channel acousto-optic light modulator 5 modulates each of the four beams according to the print signal. The modulated multi-beam becomes parallel light by the spherical lens 6, and becomes a predetermined beam arrangement by the Dove prism 7. After that, the light is narrowed down again by the cylindrical lens 8, and the photosensitive drum 10 is optically scanned by the rotary polygon mirror 9. The lens 11 is for making the beam diameter and scanning speed of the multi-beam scanning the photosensitive drum 10 uniform.

In order to make the diffraction efficiency in the multi-channel acousto-optic light modulator and the reflectance in the mirror uniform for a plurality of beams, a 1/2 wavelength plate is provided after the polarizing prism at the final stage, and its optical axis is set. 22.5 ° or 6 with respect to the polarization direction of the beam emitted from the polarizing prism at the final stage
Set it to be 7.5 °. When a quarter wave plate is used, the direction of the optical axis is set to 45 ° with respect to the polarization direction of the beam emitted from the polarizing prism at the final stage.

The above describes the case where the laser light is circularly polarized. However, the laser light incident on the first-stage polarizing prism is not circularly polarized, but at an angle other than 45 ° with respect to the polarization direction of the beam emitted from the first-stage polarizing prism. When polarized, the light intensities of the two beams emitted from the first-stage polarization prism are not equal. Therefore, in order to equalize the light intensities of the two beams emitted from the first-stage polarizing prism, a quarter-wave plate is provided in front of the first-stage polarizing prism, and the polarization direction of the beam emitted from the first-stage polarizing prism 45 to the direction
To be When a half-wave plate is used, it may be provided so that the optical axis direction is 22.5 ° or 67.5 ° with respect to the polarization direction of the beam emitted from the first-stage polarization prism.

[0009]

According to the present invention, a plurality of polarizing prisms are used, a half-wave plate is arranged between the polarizing prisms, and the optical axis of the half-wave plate is in the preceding stage. 0 ° or 9 with respect to the polarization direction of the beam emitted from
Since it is arranged so as to be other than 0 °, four or more beams can be generated. In this embodiment, since two polarizing prisms are used and the half-wave plate is arranged between them,
Although the number of beams is four, 2n beams can be generated by using n polarizing prisms and disposing a ½ wavelength plate between the polarizing prisms. Also,
The direction of the optical axis of the half-wave plate is 22.5 ° or 6 with respect to the polarization direction of the beam emitted from the polarizing prism in the preceding stage.
By arranging them at 7.5 °, two beams having mutually perpendicular polarization directions are incident on the next-stage polarizing prism in a state of being inclined at 45 ° with respect to the optical axis of the next-stage polarizing prism, It is branched into four spots having equivalent light intensities. Using a Wollaston prism as a polarizing prism,
A lens is placed between the final stage Wollaston prism and the multi-channel acousto-optic light modulator, the final stage Wollaston prism is located at the front focal point of the lens, and the multi-channel acousto-optic modulator is located at the rear focal point of the lens. When it is placed at a position, the light from the Wollaston prism is focused and is capable of high-speed modulation when it enters the multi-channel acousto-optic light modulator.

A half-wave plate is provided after the final-stage polarizing prism so that the direction of the optical axis is 22.5 ° with respect to the polarization direction of the beam emitted from the final-stage polarizing prism or 67.
When the angle is set to 5 °, the diffraction efficiency in the multi-channel acousto-optic light modulator and the reflectance in the mirror can be made uniform for each of a plurality of beams. When a quarter-wave plate is used, the same effect can be obtained by providing it so that the direction of the optical axis is 45 ° with respect to the polarization direction of the beam emitted from the polarizing prism at the final stage.

Although the above description has been made for the case where the laser light is circularly polarized light, the laser light incident on the first-stage polarization prism is not circularly polarized light, and the polarization direction of the beam emitted from the first-stage polarization prism is 45 °. When polarized at an angle other than, the quarter-wave plate is installed in front of the first-stage polarizing prism so that the optical axis direction is 45 ° with respect to the polarization direction of the beam emitted from the first-stage polarizing prism. By setting the values, the light intensities of the two beams emitted from the first-stage polarization prism can be made equal. Similarly, a 1/2 wavelength plate is installed in front of the first-stage polarizing prism, and the optical axis direction is 22. with respect to the polarization direction of the beam emitted from the first-stage polarizing prism.
The same effect can be obtained by providing it at 5 ° or 67.5 °.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a multi-beam optical scanning device according to the present invention.

FIG. 2 is a schematic diagram showing an example of a conventional multi-beam optical scanning device.

[Explanation of symbols]

1 ... Laser light source, 2 ... Laser light, 3 ... Polarizing prism, 4
... spherical lens, 5 ... multi-channel acousto-optic light modulator, 6 ... spherical lens, 7 ... Dove prism, 8 ... cylindrical lens, 9 ... rotating polygon mirror, 10 ... photosensitive drum, 11 ... lens, 12 ... 1/2 wavelength Plate, 13 ... Polarizing prism

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Yoji Hirose, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture, Hitachi Koki Co., Ltd. (72) Inventor, Yukio Oo, Yukio 1060, Takeda, Hitachinaka City, Ibaraki (72) Keiji Kataoka, Inventor, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture, Hitachi Koki Co., Ltd.

Claims (7)

[Claims] 1. A laser beam is split into a plurality of beams by a polarizing prism, and each beam is modulated in light intensity by a multi-channel acousto-optic light modulator. After rotating the array direction angle by the dove prism, one rotating polygon mirror is used to rotate multiple beams.
In a multi-beam optical scanning device that scans a recording material over a recording material, a plurality of polarizing prisms are arranged in the laser optical path so that the directions of their optical axes are the same, and a half-wave plate is arranged between the polarizing prisms. The multi-beam light is characterized in that the optical axis of the half-wave plate is oriented at an angle other than 0 ° or 90 ° with respect to the polarization direction of the beam emitted from the polarizing prism in the preceding stage. Scanning device. 2. The multi-beam optical scanning device according to claim 1, wherein the direction of the optical axis of the half-wave plate is 22.5 with respect to the polarization direction of the beam emitted from the polarizing prism of the preceding stage.
A multi-beam optical scanning device, characterized in that a half-wave plate is arranged at an angle of 6 ° or 67.5 °. 3. The multi-beam optical scanning device according to claim 1, wherein a Wollaston prism is used as a polarizing prism, and a lens is disposed between the Wollaston prism at the final stage and the multi-channel acousto-optical modulator. The Wollaston prism is arranged at the front focal position of the lens, and the multi-channel acousto-optical modulator is arranged at the rear focal position of the lens. 4. The multi-beam optical scanning device according to claim 2, wherein after the polarizing prism at the final stage, the direction of the optical axis of the half-wave plate is the polarization direction of the beam emitted from the polarizing prism at the final stage. On the other hand, a multi-beam optical scanning device characterized in that a half-wave plate is provided so as to have an angle of 22.5 ° or 67.5 °. 5. The multi-beam optical scanning device according to claim 2, wherein after the polarizing prism at the final stage, the direction of the optical axis of the quarter wavelength plate is the polarization direction of the beam emitted from the polarizing prism at the final stage. On the other hand, a multi-beam optical scanning device characterized in that a quarter-wave plate is provided so as to have an angle of 45 °. 6. The multi-beam optical scanning device according to claim 2, wherein the direction of the optical axis of the half-wave plate in front of the first-stage polarization prism is relative to the polarization direction of the beam emitted from the first-stage polarization prism. A multi-beam optical scanning device, characterized in that a half-wave plate is provided at an angle of 22.5 ° or 67.5 °. 7. The multi-beam optical scanning device according to claim 2, wherein the direction of the optical axis of the quarter-wave plate is in front of the polarization prism of the first stage with respect to the polarization direction of the beam emitted from the polarization prism of the first stage. , A multi-beam optical scanning device characterized in that a quarter-wave plate is provided so that the angle becomes 45 °.