JP2000180805A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modular always and stably operating even under the environment that foreign matters such as dust, trash and vaporized chemicals exist. SOLUTION: The optical modulator 5 is constituted so that an acoustooptical medium 7 that a roughness/fineness wave of a refractive index generated by a sound wave forms a diffraction grating is interposed between an incident port 6A and an emission port 6B to be fixed in a casing 6 having the incident port 6A making incident a laser beam and the emission port 6B making emit the laser beam, and the incident port 6A and the emission port 6B are respectively sealed by transparent seal plates 8A, 8B made of a transparent member. Since the incident port 6A and the emission port 6B are sealed by the transparent seal plates 8A, 8B, it is prevented that the foreign matters enter into the casing 6 and the acoustooptical medium 7 in the casing 6 is protected always. Further, when the foreign matters are stuck to the optical modulator 5 outer surface by wiping the transparent seal plates 8A, 8B, or exchanging with the new transparent plates 8A, 8B, the optical state is restored easily and inexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator for modulating an incident laser beam, for example, an acousto-optic modulator (AOM) for modulating light with a sound wave.
dulator).

[0002]

2. Description of the Related Art Conventionally, an optical modulator has been used for controlling a laser beam in a scanning type drawing apparatus such as a laser photo plotter, a printed board exposure apparatus, a laser printer and the like. In particular, an acousto-optic light modulator is widely used. This type of optical modulator includes a transparent acousto-optic medium in which a compressional wave having a refractive index generated by a sound wave forms a diffraction grating, and a vibrator for applying ultrasonic waves to the acousto-optic medium. The laser light that has entered the acousto-optic medium emits light in different directions depending on whether the acousto-optic medium is provided with ultrasound or not.
It is possible to use one as signal light and block the other. Therefore, by controlling the vibrator, the laser light can be turned on / off at a desired timing.

FIG. 4 is a perspective view showing the structure of a conventional optical modulator. The housing 1 having a rectangular parallelepiped outer shape is
Slit-shaped entrances 1A and exits 1B are respectively symmetrically opened at the center of the pair of opposed wall surfaces.
The acousto-optic medium 2 is formed by cutting a transparent crystal in which a compressional wave having a refractive index generated by an acoustic wave forms a diffraction grating into a thin plate shape and coating the crystal surface. The acousto-optic medium 2 thus formed is housed and fixed in the housing 1 with one surface thereof facing the entrance 1A of the housing 1 and the other surface facing the emission opening 1B. Note that this acousto-optic medium 2
, A vibrator (not shown) for generating ultrasonic waves is brought into contact therewith.

[0004] For this optical modulator to be incident laser light L ₁₂ from its entrance 1. When an ultrasonic wave is applied to the acousto-optic medium 2 by a vibrator (not shown), the laser light L ₁₂ is diffracted by the acousto-optic medium 2 and emitted as laser light (signal light) L ₁₃ .
If no ultrasonic wave is given, it is cut off. That is, by whether to ultrasonic, signal light L ₁₃ may be ON / OFF. Thus, it is possible to utilize topped with desired data to the signal light L _13.

[0005]

However, in the above-mentioned conventional optical modulator, foreign matter such as dust, dirt, vaporized chemicals and the like existing in the atmosphere from the entrance 1A or the exit 1B of the housing 1 is not shown. 4), and the acousto-optic medium 2
There is a problem that carbonization, unnecessary light scattering and crystal alteration of the acousto-optic medium 2 are caused by adhering to the surface of the substrate. Each of these causes a decrease in the light transmittance of the optical modulator and a loss in the efficiency of the optical system.

Further, if the dust adhering to the crystal surface of the acousto-optic medium 2 is wiped off, the crystal is too soft to be damaged. Also, it is difficult to remove the chemicals attached to the crystal surface, and if it is intentionally wiped, the coating applied to the crystal surface may be altered.

Therefore, by protecting the acousto-optic medium 2 from foreign substances such as dust, dirt, and vaporized chemicals present in the atmosphere, an optical modulator that can always operate stably under various use conditions is provided. It is an object of the present invention to provide.

[0008]

An optical modulator according to the present invention employs the following configuration to solve the above-mentioned problems.

That is, in the optical modulator according to the first aspect of the present invention, a compression / dense wave having a refractive index generated by a sound wave forms a diffraction grating in a housing having an entrance through which laser light enters and an exit through which laser light exits. The acousto-optic medium to be formed is fixed by being interposed between the entrance and the exit of the housing, and the entrance and the exit are respectively sealed by a transparent sealing plate made of a transparent member. Features.

[0010] With such a configuration, no foreign matter enters from the entrance or exit of the optical modulator, so that the acousto-optic medium inside the housing is protected from the foreign matter. Also, since the transparent sealing plate is made of a transparent member, the laser light
The light passes through the transparent sealing plate, enters the inside of the housing from the entrance, is modulated by the acousto-optic medium, and is emitted from the exit while passing through the transparent sealing plate.

In addition, when a sound wave is given to the acousto-optic medium, the laser light transmitted through the acousto-optic medium may be used as the signal light. Conversely, when no sound wave is given, the laser light may be used. The laser light transmitted through the acousto-optic medium may be used as signal light.

Further, even if the laser light is incident on the acousto-optic medium at a fixed angle, if the frequency of the sound wave applied to the acousto-optic medium is different, the emitted laser light will be different for each frequency of the sound wave. Each go in a different direction. By using the characteristics of the acousto-optic medium and changing the frequency of the sound wave applied to the acousto-optic medium, the incident light may be emitted in a plurality of directions according to the frequency to perform signal switching.

According to a second aspect of the present invention, the optical modulator is characterized in that the transparent sealing plate of the first aspect is formed in a parallel plate shape.

According to a third aspect of the present invention, there is provided an optical modulator characterized in that the surface of the transparent sealing plate according to the first or second aspect is provided with an antireflection coat for preventing reflection of laser light. .

An optical modulator according to a fourth aspect is the optical modulator according to the first to third aspects.
In any of the configurations, it is possible to supply a sound wave to the acousto-optic medium, by switching the supply or stop of the sound wave,
This is specified by further including a vibrator that controls the laser beam incident from the entrance port to exit or exit the exit port. The vibrator only needs to be able to convert a signal into a sound wave, and may include a piezoelectric element or a magnetostrictive material.

According to a fifth aspect of the present invention, in the configuration of the fourth aspect, the entrance and the exit of the housing are formed in a slit shape so that a plurality of laser beams can be transmitted. The oscillator is specified by supplying a sound wave to the acousto-optic medium so that each of the plurality of laser beams incident from the entrance can be controlled.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. <Structure of Optical Modulator> An optical modulator 5 according to an embodiment of the present invention includes a housing 6 and an entrance 6A formed in the housing 6 with an opening.
And an emission port 6B, an acousto-optic medium 7 built in the housing 6, and transparent sealing plates 8A and 8B for sealing the entrance 6A and the emission port 6B, respectively. FIG. 1 is a perspective view showing a schematic configuration of the optical modulator 5.

The housing 6 has a rectangular parallelepiped shape, and a slit-shaped entrance 6 is formed at the center of a pair of opposed wall surfaces of the housing 6.
A and the emission port 6B are respectively formed with openings. The entrance 6A causes the transmitted laser beam L ₁₀ coming plurality parallel incident so as to be substantially perpendicular to the housing 6 wall having the entrance 6A, is guided to the casing 6. Further, the exit port 6B is formed symmetrically with the entrance port 6A, and the plurality of laser beams L ₁₁
Can be emitted in parallel in a direction substantially perpendicular to the wall surface of the housing 6 having the emission port 6B.

The acousto-optic medium 7 is obtained by cutting a transparent crystal (here, tellurium dioxide), in which a compression wave of a refractive index generated by a sound wave forms a diffraction grating, into a thin plate, and applying a coating to the crystal surface. Is formed. The acousto-optic medium 7 thus formed is housed and fixed in the housing 6 with one surface thereof facing the entrance 6A of the housing 6 and the other surface facing the emission opening 6B. The acousto-optic medium 7 is brought into contact with a vibrator (not shown) for generating ultrasonic waves.

The ultrasonic wave generated by the vibrator allows the acousto-optic medium 7 to turn on / off the laser light incident from the incident hole 6A of the housing 6. Hereinafter, the laser light ON / OFF control, that is, the laser light control by the acousto-optic effect will be described with reference to FIG. Note that FIG. 1 illustrates a multi-channel configuration in which eight laser beams are controlled, respectively, but FIG. 2 treats a single laser beam for simplicity.

In FIGS. 2A and 2B, reference numeral 9a denotes a vibrator, which is formed by a piezoelectric element for converting a high-frequency current into an ultrasonic wave. The vibrator 9a is connected to a drive circuit 9b that can supply a high-frequency current. FIG. 2A shows a case where the driving circuit 9b is turned off, and FIG. 2B shows a case where the driving circuit 9b is turned on.

As shown in FIG. 2A, when the driving circuit 9b does not apply a high-frequency current to the vibrator 9a, the vibrator 9a does not generate ultrasonic waves. In this state, the laser beam L ₁₀ incident on the transparent acoustooptic medium 7, the acousto-optic medium 7 is transmitted through and emitted as a laser beam (0-order light) L ₁₁ '. By arranging the blocking member K so as to block the optical path of the laser light L ₁₁ ′, the laser light L ₁₁ ′
₁₁ 'can be cut off.

As shown in FIG. 2B, when a high frequency current is applied to the vibrator 9a by the drive circuit 9b, the vibrator 9a generates an ultrasonic wave. This ultrasonic wave is applied to the acousto-optic medium 7
When it propagates through the inside, the compressional wave W of the refractive index due to the photoelastic effect
Occurs. Thus the compressional wave W acts as a diffraction grating, the laser beam L ₁₀ is diffracted laser light (primary light) emitted as L _11. Without interrupting the laser beam L _11, it is emitted from the exit 6B of the housing 6 shown in FIG.

Thus, the drive circuit 9b is turned on / off.
By, it is possible to ON / OFF of the laser beam L _11. Therefore, it is possible to use this laser light L ₁₁ as the signal light.

In order for the acousto-optic medium 7 that functions as described above to always operate normally, the acousto-optic medium 7 must be protected from dust, dust, vaporized chemicals, and the like existing in the atmosphere. For this reason, as shown in FIG. 1, transparent sealing plates 8A and 8B, which are parallel plates made of glass,
The entrance 6A and the exit 6B of the housing 6 are respectively sealed. Since the housing 6 has no opening other than the entrance 6A and the exit 6B, by sealing the entrance 6A and the exit 6B, the inside of the casing 6 is completely shut off from the outside air. .

The surfaces of the transparent sealing plates 8A and 8B are
An antireflection coat in the form of a transparent thin film is applied. The anti-reflection coat removes a light reflection component by interference of light in the thin film, and is effective for light near a specific wavelength corresponding to the film thickness. For this reason, the film thickness of the antireflection coat is determined according to the wavelength of the laser light to be used so that the reflected component of the laser light can be removed. With this antireflection coat, the light transmittance of the light modulator 5 can be increased.

<Scanning Drawing Apparatus with Light Modulator> The above-described light modulator 5 is used by being incorporated into a scanning drawing apparatus such as a laser photoplotter, a printed board exposure apparatus, and a laser printer. FIG. 3 is a perspective view showing a schematic configuration of a scanning type drawing apparatus provided with the light modulator 5.

This scanning type drawing apparatus includes a light source 10 and an optical table 11 which are fixedly provided, and a drawing table 12 which is slidably provided in the X direction in the drawing. Here, an argon laser is used as the light source 10, and the laser light emitted from the light source 10 is
A scanning line S in the Y direction orthogonal to the X direction is formed on the drawing surface 13 on the drawing table 12 via the scanning optical system arranged in 1.

The operator or robot must
On the drawing surface 13 of the drawing table 12, photographic paper, printed circuit board, paper, film or the like to be drawn is placed.
Keep it fixed. Then, a control circuit (not shown) of the scanning type drawing apparatus drives a motor (not shown) to drive the drawing table 12.
Is moved in the X direction in FIG. 3 so that the drawing target on the drawing surface 13 is set at a predetermined drawing start position.

The laser light emitted from the light source 10 disposed below the optical bench 11 is reflected by mirrors 20 and 21 and passes through an optical path hole 11a formed in the optical bench 11.
After being reflected by the mirror 22, the beam diameter is adjusted by the variable power lens system 23. This adjustment is performed to correct a change in the beam diameter originating from the light source 10. The laser light transmitted through the variable power lens system 23 is reflected by a half mirror 24 as a light splitting element, and is drawn by drawing light L ₁ (indicated by a solid line in FIG. 3) and transmitted monitor light L ₂ (one point in FIG. 3). (Indicated by a chain line).

The drawing light L ₁ is bisected by the half mirror 25, and the reflected drawing light enters the beam separator 26 a, and the transmitted drawing light enters the beam separator 26 b via the mirror 27. Each beam separator 26
a and 26b have a function of further separating each drawing light into a plurality of lines. In the example shown here, each drawing light is 8
Although they are separated into books, they are shown by three lines in FIG. 3 for convenience of illustration.

Each of the separated drawing lights is applied to a mirror 28.
The beam interval is narrowed by the first reduction optical systems 29a and 29b composed of a pair of lens groups disposed with the lenses a and 28b interposed therebetween, and the light is incident on the optical modulator 5 (a, b). In addition,
Since two optical modulators 5 are used, in FIG.
Reference numerals are attached to distinguish them from 5b.

First, one optical modulator 5a will be described. 8 of the drawing light incident from the transmission to the entrance 6A transparent sealing plate 8A shown in in the housing 6 1 (indicated as L ₁₀ in FIG. 1) is further incident on the acoustooptic medium 7. A vibrator and a drive circuit (not shown) independently control the eight drawing lights. That is, ON or OFF is individually switched for each drawing light at a predetermined timing. The driving circuit is O
In the case of N states, rendering light corresponding to the incident drawn light (shown as L ₁₁ in FIG. 1), the exit port shown in FIG. 1 6
B is transmitted through the transparent sealing plate 8B and is emitted.
In the state, the incident drawing light is blocked, and the corresponding drawing light is not emitted. Thus, only the drawing light turned ON is emitted from the optical modulator 5a, and the beam splitter 3
2 is incident.

Next, the other optical modulator 5b will be described. 8 of the drawing light incident on the transparent electrode and the transparent sealing plate 8A shown in FIG. 1 the housing 6 from the light inlet 6A (shown as L ₁₀ in FIG. 1) is further incident on the acoustooptic medium. A drive circuit connected to a vibrator (not shown) independently controls the eight drawing lights. That is, ON or OFF is individually switched for each drawing light at a predetermined timing. When the driving circuit is in the ON state, the drawing light corresponding to the incident drawn light (shown as L ₁₁ in FIG. 1), it is emitted through the transparent sealing plate 8B from the exit 6B shown in FIG. 1 But OF
In the F state, the incident drawing light is blocked, and the corresponding drawing light is not emitted. Thus, only the drawing light turned ON is emitted from the optical modulator 5b, reflected by the mirror 31, and then enters the beam splitter 32.

The beam splitter 32 is provided with the optical modulator 5
The drawing light modulated by a and the drawing light modulated by the light modulator 5b and reflected by the mirror 31 are combined. After that, the combined drawing light travels on the same optical path, is reflected by the mirror 33, and is then reduced in beam interval by the second reduction optical system 35 composed of a pair of lens groups disposed with the mirror 34 interposed therebetween. Rotator 36
Incident on. The image rotator 36 adjusts the direction so that a plurality of parallel drawing lights are properly arranged on the drawing surface.

The monitor light L ₂ transmitted through the half mirror 24 is reflected by the mirror 50, passes through the monitor light reduction optical system 51 and the monitor light magnification adjusting optical system 52, and is reflected by the mirror 53. Between the rear group lens of the second reduction optical system 35 and the image rotator 36, the light is reflected by a mirror 54 disposed outside the optical path of the drawing light and merges with the drawing light.

The drawing light and monitor light emitted from the image rotator 36 are reflected by mirrors 37 and 38, pass through a collimator lens 39, are reflected by a mirror 40, and enter a polygon mirror 41. Polygon mirror 4
1 is a substantially octagonal prism shape in which eight side surfaces are reflection surfaces,
It rotates counterclockwise in FIG. 3 around the central axis of the prism and reflects and deflects the drawing light and the monitor light simultaneously. Each reflection surface of the polygon mirror 41 corresponds to one scan. That is, eight scans are performed during one rotation of the polygon mirror 41.

The drawing light and monitor light reflected and deflected by the polygon mirror 41 are converged by the fθ lens 42 and directed to the drawing surface 13 via the mirror 43 and the condenser lens 44. The mirror 45 is disposed outside the optical path of the drawing light, and reflects only the monitor light toward the mirror 46.

The drawing light travels straight and reaches the drawing surface 13, and scans the drawing surface 13. There are a plurality of drawing lights, which scan the drawing surface 13 in parallel with S in a state where they are arranged in a direction orthogonal to the scanning lines S. Therefore, in the sub-scanning direction (FIG.
3 can be scanned in the Y direction in FIG. 3 along the scanning line S while simultaneously drawing a plurality of dots (16 dots in this case) arranged in the X direction in FIG.

The drawing light turned on by the light modulators 5a and 5b reaches the drawing surface 13 and sensitizes the corresponding portion to form dots, but is turned off by the light modulators 5a and 5b. Since the drawn drawing light does not reach the drawing surface 13, the corresponding portion of the drawing surface 13 is left unexposed. That is, a desired image can be drawn on the drawing surface by turning ON / OFF the optical modulators 5a and 5b at desired timing.

The monitor light separated from the drawing light by the mirror 45 is reflected by the mirror 46 and scans on the monitor scale 47. The monitor scale 47 is a transparent plate on the surface of which a large number of opaque lines are formed at equal pitches, and a monitor signal scans over the transparent plate, so that a pulse signal is generated from a light receiving element (not shown) that detects transmitted light. Is output. A control circuit (not shown) can detect which position on the drawing surface 13 the drawing light is currently scanning based on a signal from the light receiving element.

When one scan is completed, the drawing table 1
Reference numeral 2 moves 16 dots in the X direction (sub-scanning direction) in FIG. 3 to prepare for the next scan. At this time, the drawing light and the monitor light are applied to the boundary between the adjacent reflection surfaces of the polygon mirror 41, and the next scanning is started by further rotating the polygon mirror 41. The drawing light is
The scanning is performed again from the end of the scanning line S in the Y direction in FIG.

After the above-described operation is repeated to perform drawing on the entire drawing surface 13, a control circuit (not shown) moves the drawing table 12 in a direction opposite to the X direction in FIG. Then, the operator or the robot releases the object to be drawn from the drawing table 12 and picks it up.

As described above, when the scanning type drawing apparatus is operated, foreign matter D such as dust, dirt, and chemicals may adhere to the light modulator 5. Therefore, the foreign matter D does not enter the housing 6 because it is completely shut off from the outside air. Therefore, the foreign matter D does not adhere to the acousto-optic medium 7 inside the housing 6. When foreign matter D adheres to the transparent sealing plates 8A and 8B of the optical modulator 5, the transparent sealing plates 8A and 8B are simply wiped off or replaced with new transparent sealing plates 8A and 8B. Thus, the performance of the optical modulator 5 can be easily and inexpensively recovered, and the scanning type drawing apparatus can function normally again.

[0045]

According to the optical modulator of the present invention configured as described above, the acousto-optic medium in the housing is protected by sealing the entrance and exit of the housing with the transparent sealing plate. And can always function stably under various use conditions. In addition, even when foreign matter adheres to the optical modulator, the original state can be easily and inexpensively recovered by wiping the transparent sealing plate or replacing the transparent sealing plate.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of an optical modulator according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an acousto-optic effect.

FIG. 3 is a perspective view showing a schematic configuration of a scanning drawing apparatus.

FIG. 4 is a perspective view showing a schematic configuration of an optical modulator according to a conventional technique.

[Explanation of symbols]

 Reference Signs List 5 light modulator 6 housing 6A entrance 6B exit 7 acousto-optic medium 8A, 8B transparent sealing plate 9a vibrator 9b drive circuit

Claims (5)

[Claims] 1. An acousto-optical medium in which a compression wave having a refractive index generated by a sound wave forms a diffraction grating is provided in a housing having an entrance through which laser light is incident and an exit through which laser light is emitted. An optical modulator characterized in that the optical modulator is interposed and fixed between an entrance port and an exit port, and the entrance port and the exit port are respectively sealed by a transparent sealing plate made of a transparent member. 2. The optical modulator according to claim 1, wherein said transparent sealing plate is formed in a parallel plate shape. 3. An optical modulator according to claim 1, wherein an anti-reflection coating for preventing reflection of laser light is applied to a surface of said transparent sealing plate. 4. A laser beam can be supplied to the acousto-optic medium, and the supply or stop of the sound wave is switched so that the laser beam incident from the entrance is emitted to the exit.
4. The optical modulator according to claim 1, further comprising a vibrator that controls so as to cut off the light. 5. 5. An entrance and an exit of the housing are formed in a slit shape so that a plurality of laser beams can be transmitted, and the vibrator includes a plurality of laser beams incident from the entrance. 5. The optical modulator according to claim 4, wherein a sound wave is supplied to the acousto-optic medium so that each of the optical modulators can be controlled.