JPH0283517A - Laser beam scanner - Google Patents

Abstract

PURPOSE:To form high-grade images having no ghosts by depositing 2nd and 3rd multilayered dielectric films on the respective exit faces of a beam splitter which is formed by crimping a 1st multilayered dielectric films with two optical glasses and having high mechanical strength, thereby forming a dichroic mirror. CONSTITUTION:The laser beam emitted from one semiconductor laser 2 is transmitted through the 1st multiolayered dielectric films 20 by the beam splitter 11 and is emitted from the exist face 23. The laser beam is turned back by a mirror 12 and is guided to an object 4 to be irradiated. The laser beam emit ted from the other semiconductor laser 3 is reflected by the 1st multilayered dielectric films 20 and is emitted from the exist face 24 so as to be introduced to the object 4 to be irradiated. The complete sepn. of the laser beam in the beam splitter 11 is not possible. The 2nd multilayered dielectric films 13 and the 3rd multilayered dielectric films 14 are, thereupon, provided by utilizing the surface of the beam splitter 11 in order to prevent the beams a2, b2 failed to be separated in the beam splitter 11 which is the cause for the generation of the ghosts from arriving at the object 4 to be irradiated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser beam scanning device that deflects a laser beam whose brightness is modulated by an image signal in a main scanning direction and irradiates it onto an irradiated object. , for example, is provided in an image forming apparatus such as a laser printer, and is used as an exposure means for a photoreceptor.

[Conventional technology]

2. Description of the Related Art Imaging devices such as printers and displays incorporate a scanning device that modulates the brightness of light using a signal and irradiates it onto an irradiated object such as a photoreceptor, photographic film, or screen.

In this scanning device, a laser light source capable of obtaining a minute spot is used as a light source, and a polygon mirror (multifaceted Some examples include those that rotate a mirror (mirror), those that vibrate a galvano mirror, and those that rotate a hologram, but those that use a polygon mirror are the most popular because they have a simpler configuration than others.

When a laser beam is deflected by a polygon mirror, the scanning speed is proportional to the rotation speed of the polygon mirror, so in order to perform high-speed scanning, the rotation speed of the polygon mirror can be increased, but this depends on the durability of the motor and the rotation speed of the polygon mirror. There are restrictions such as the material of the polygon mirror.

Similarly, other deflection means must overcome various problems in order to operate at high speed.

Therefore, especially in high-speed printers, multiple laser beams modulated by different signals are used, and these beams are deflected at the same time to scan multiple parts of the irradiated object at the same time, effectively achieving several times faster scanning. It has been realized.

On the other hand, pull-color printers or two-color printers (e.g. black and red)
Scanning devices installed in printers also produce multicolor images by irradiating different parts of a single photoconductor or multiple photoconductors with two or more laser beams modulated with signals corresponding to images of each color. is formed.

In such a scanning device using multiple laser beams,
In order to achieve miniaturization and cost reduction, some laser beams are constructed so that each laser beam is deflected by one deflection means.

Among those that share the same deflection means, there are those in which the angle of incidence of each laser beam on the deflection means is different, and there are those in which the laser beams are separated from each other and incident on the deflection means. The uniform velocity linearity of the trajectory is poor, the latter requires a large deflection means with a large incident surface of the deflection means, and the linearity of the scanning trajectory is poor.

For this reason, conventional laser beam scanning devices prepare multiple laser beams each with different characteristics (wavelength, polarization direction, etc.), combine them into a single laser beam, and then After deflecting the beam in the main scanning direction, the laser beam is separated into multiple laser beams each with its own characteristics based on its characteristics, and each separated laser beam irradiates a different part of the object. I have to.

For example, in Japanese Patent Application Laid-open No. 60-32019, high-speed scanning is 1? In order to do this, two laser beams with different polarization directions are combined and deflected by a polygon mirror, and then separated by a polarizing beam splitter.
0-201319 discloses a scanning device for a color printer that combines and separates three laser beams with different wavelengths.

[Problem to be solved by the invention]

In general, a beam splitter that deflects a combined laser beam and then separates it based on its characteristics has a partially reflective film that transmits the laser beam of a certain characteristic and reflects the laser beam of another characteristic. It uses a guichroic mirror.

A gicroic mirror is a partially reflective film made of a dielectric multilayer film or a metal-dielectric multilayer film deposited on the surface of a transparent material such as optical glass, and has selectivity to wavelength or polarization direction. .

However, even if a partially reflective film with excellent selectivity is used, it is not possible to completely separate the laser beams, and laser beams with different characteristics are mixed in the transmitted beam and the reflected beam of the partially reflective film.

For this reason, when images are created by irradiating separate laser beams onto different parts of an irradiated object, a so-called ghost occurs, which is a phenomenon in which the desired image is combined with an image that should be formed on another part. There was a problem.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a laser beam scanning device that can create high-quality images without ghosts without increasing the number of parts.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention includes a plurality of laser light sources that emit laser beams modulated by image signals and each having different characteristics, and converts the laser beam emitted from each laser light source into one laser beam. a beam combining means for combining the combined laser beams into the main scanning direction, a deflection means for deflecting the combined laser beams in the main scanning direction, and a beam splitter for separating the deflected laser beams based on their characteristics. A laser beam scanning device configured to irradiate different parts of an irradiated object, wherein the beam splitter transmits a laser beam having specific characteristics and reflects a laser beam having other characteristics. The prism is composed of a prism in which two optical glasses are adhered to each other through a dielectric multilayer film, and each exit surface of the laser beam transmitted through the first dielectric multilayer film and the laser beam reflected by the first dielectric multilayer film. The structure is characterized by being coated with a second or third dielectric multilayer film that selectively transmits each laser beam.

[For production]

Laser beams having different characteristics are emitted from the plurality of laser light sources, and these laser beams are combined into one laser beam by a beam combining means.

The combined laser beam is deflected in the main scanning direction by the deflection means, and then enters the -beam splitter.

The first dielectric multilayer film of the beam splitter transmits a laser beam having specific characteristics in the combined laser beam, and
Laser beams having other characteristics are reflected, and the combined laser beam is separated into a plurality of laser beams, each of which irradiates a different part of the irradiated object.

The second or third dielectric multilayer film deposited on the exit surface of the beam splitter selectively transmits each separated laser beam.

As a result, each part of the object to be irradiated is irradiated with a laser beam having a high characteristic purity.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing a laser beam scanning device 1 according to an embodiment of the present invention, FIGS. 2 and 3 are sectional views showing an enlarged beam splitter 11.30, and FIGS.
The figure is a graph showing the optical characteristics of a gicchroic mirror.

In order to obtain two laser beams, the laser beam scanning bag W1 has oscillation wavelengths of 810 ns and 150 ntm, respectively.
Two semiconductor lasers 2.3 are installed as laser light sources. These semiconductor lasers 2.3 are luminance-modulated based on respective image signals by a control circuit (not shown).

Note that the oscillation wavelength is selected in consideration of the spectral sensitivity of the irradiated object 4, the stability of the oscillation characteristics, and the like.

The diverging laser beam emitted from the semiconductor laser 2.3 is
Each of the beams passes through a collimator lens 5.6 to become a parallel beam and enters a dichroic prism 7 as beam combining means.

The dichroic prism 7 uses a dielectric multilayer film (partially reflective film) that has the optical properties shown in FIG. It consists of two right-angled prisms glued together.

The dichroic prism 7 allows the semiconductor laser 2 to
．． The laser beams emitted from 3 are combined into one laser beam with their optical axes substantially aligned.

The combined laser beams enter the polygon mirror 9 through a cylindrical lens 8 for correcting the surface tilt of the polygon mirror 9.

The polygon mirror 9 rotates at high speed in the direction of the arrow and repeatedly deflects the incident laser beam in the main scanning direction. The fθ lens 10 is for keeping the scanning speed of the laser beam on the irradiated object 4 constant.

The laser beam passing through the fθ lens 10 is separated into two laser beams by a beam splitter 11.

Referring also to FIG. 2, the beam splitter 11 is constructed using a first dielectric multilayer film 20 having wavelength selection characteristics similar to those of the dichroic prism 7, that is,
The beam splitter 11 has two right-angle prisms 21 and 22 made of optical glass laminated together via a first dielectric multilayer film 20 that transmits most of the laser beam with a wavelength of 810 ns and reflects most of the laser beam with a wavelength of 750 rv. It is a guichroic prism.

By this beam splitter 11, the laser beam emitted from one of the semiconductor lasers 2 passes through the first dielectric multilayer film 20, exits from the emission surface 23, is reflected by the mirror 12, and is directed to the irradiated object 4. The laser beam guided and emitted from the other semiconductor laser 3 is reflected by the first dielectric multilayer film 20, emitted from the emission surface 24, and guided to the irradiated object 4.

The irradiated body 4 may be independent for each part to be irradiated with each laser beam.

However, the beam splitter 11 cannot completely separate the laser beams. In other words, if we look at the laser beam with a wavelength of 810n- as seen from the graph in Figure 4, 94% of the intensity is transmitted, but some absorption is ignored. Then, the remaining 6% becomes the poorly separated beam a2 with wavelength 7.
It is reflected together with the 50 nm laser beam. vice versa,
For a laser beam with a wavelength of 750 nm, 95%
is reflected, but the remaining 5% is transmitted as a poorly separated beam b2 together with the laser beam with a wavelength of 810 ns.

Therefore, the beam splitter 1, which causes ghosts,
In order to prevent the poorly separated beams a2 and b2 from reaching the irradiated object 4, a second dielectric multilayer film 13 and a third dielectric multilayer film 14 are provided using the surface of the beam splitter 11. .

As shown in FIG. 2, in the beam splitter 11,
The second dielectric multilayer film 13 is located on the exit surface 23 of the laser beam a that has passed through the first dielectric multilayer film 20, and the exit surface 24 of the laser beam b that has been reflected by the first dielectric multilayer film 20 is A third dielectric multilayer 14 is deposited respectively.

The second dielectric multilayer film 13 has the same characteristics as the first dielectric multilayer film 20, and on the contrary, the third dielectric multilayer film 14 has the same characteristics as the first dielectric multilayer film 20, and conversely, as shown in FIG. It has a wavelength selection characteristic of transmitting 95% of a laser beam with a wavelength of 810 nm and reflecting 95% of a laser beam with a wavelength of 810 nm.

Therefore, the intensity of the laser beam with a wavelength of 750n− mixed in the transmitted beam of the first dielectric multilayer film 13 is 0.25% (0°) of the intensity of the laser beam with a wavelength of 750rv when it enters the beam splitter 11. 05 Xo, 0
5), and the wavelength of 810 nm is mixed with the laser beam of wavelength 750 nm that passes through the second dielectric multilayer film 14.
The intensity of the n- laser beam is 0.3% (0.06Xo, 05) of the intensity of the laser beam of wavelength 810n- when it enters the beam splitter 11.

A dielectric multilayer film 13, 14 selectively transmits each laser beam separated by the beam splitter 11 on its optical path toward the irradiated object 4.
By installing this, the intensity of the poorly separated beam mixed with each laser beam that irradiates each part of the object 4 to be irradiated is reduced to a value that is undetectable.

Note that the installation angle of the beam splitter 11 is adjusted so that the laser beam reflected by the second or third dielectric multilayer film 13, 14 does not irradiate the object 4 to be irradiated.

Also, instead of the beam splitter 11, a beam splitter 30 shown in FIG. 3 can be used.

The beam splitter 30 is made by laminating a flat optical glass 31 and an optical glass rectangular prism 32 through a first dielectric multilayer film 33 that transmits a laser beam a with a wavelength of 810 nw and reflects a laser beam b with a wavelength of 750 nw. It is a guichroic prism.

Each exit surface 3 of the separated laser beams a and b
4.35 are provided with second and third dielectric multilayer films 36 and 37 having selective characteristics for the characteristics of each of the laser beams a and b.

The second dielectric multilayer film 36 has the same characteristics as the first dielectric multilayer film 33, and the third dielectric multilayer film 37 has the same wavelength 81
It has the selectivity of inverting the laser beam a of 0 nm and transmitting the laser beam b of wavelength 750 nm, and prevents the transmission of the poorly separated beams a2 and b2, respectively.

In addition, in order to prevent the scattered beams from affecting the outside, these beam splitters 11 and 30 may be coated with light-shielding paint on the surfaces other than the optical path of the laser beam, or may be provided with light-shielding members at necessary locations. good.

In the first and second embodiments described above, two laser light sources are used and the wavelengths of the laser beams emitted from each are made different to combine and separate the laser beams. This can be done with different laser beams. In addition, when using three or more laser beams, the characteristics of each laser beam should be adjusted appropriately, such as using two laser beams with the same wavelength and different polarization directions, and one laser beam with a different wavelength. Can be set. In that case, the selection characteristics can be selected by changing the material, thickness, and number of laminated layers of the dielectric layer that constitutes the partial reflection film of each part according to the characteristics of the laser beam used. In addition to semiconductor lasers, other solid lasers, gas lasers, and liquid lasers can be used.

〔Effect of the invention〕

According to the present invention, the second and third dielectric multilayer films are coated on each exit surface of a beam splitter with high mechanical strength, in which the first dielectric multilayer film is sandwiched between two pieces of optical glass. Since a loic mirror is formed, absorption loss is extremely small, and even with a low-power laser light source, a sufficient amount of light is ensured for the irradiated object. The purity of the features in the laser beam is increased, making it possible to create high-quality images without ghosts.

In addition, the first dielectric multilayer film and the second dielectric multilayer film of the beam splitter are
The angle at which the third dielectric multilayer film faces is fixed, and the first
The light selection characteristics of each laser beam separated by the dielectric multilayer film are stabilized.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a perspective view showing a laser beam scanning device of the invention, FIGS. 2 and 3 are enlarged sectional views showing an embodiment of a beam splitter, and FIG.
FIG. 5 and FIG. 5 are graphs showing the optical characteristics of the guichroic mirror. DESCRIPTION OF SYMBOLS 1... Laser beam scanning device, 2.3... Semiconductor laser (laser light source), 4... Irradiated object, 7... Dichroic prism (beam combining means), 9... Polycon mirror ( deflection means), 11...beam splitter, 13...second dielectric multilayer film, 14...third dielectric multilayer film, 20...first dielectric multilayer film, 21.
22... Optical glass, 23.24... Output surface, 3o
... Beam splitter, 31.32... Optical glass, 33... First dielectric multilayer film, 34.35... Exit surface, 36... Second dielectric multilayer film, 37. ...Third
dielectric multilayer film. Figure 2 Figure 3 Applicant Minolta Camera Co., Ltd. Agent Patent Attorney Yukio Kubo

Claims (1)

[Claims] (1) A plurality of laser light sources that emit laser beams modulated by image signals and each having different characteristics; a beam combining means that combines the laser beams emitted from each laser light source into one laser beam; The laser beam is provided with a deflecting means that deflects the deflected laser beam in the main scanning direction, and a beam splitter that separates the deflected laser beam based on its characteristics, and each separated laser beam irradiates a different part of the object to be irradiated. In the laser beam scanning device, the beam splitter connects two optical glasses via a first dielectric multilayer film that transmits a laser beam having specific characteristics and reflects a laser beam having other characteristics. The prism is formed in close contact with each other, and each laser beam is selectively transmitted through the exit surface of the laser beam transmitted through the first dielectric multilayer film and the laser beam reflected by the first dielectric multilayer film. 1. A laser beam scanning device comprising a second or third dielectric multilayer film.