JPH10148855A - Laser beam control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam control device which can hold a constant line interval between each laser beam on the image plane with small astigmatic differences even when the position of deflection of an acoustic optical element and the beam waist position near the position of deflection are made apart by a specified distance. SOLUTION: The laser beam control device 1 is composed from a semiconductor laser element 2, a waveguide-type acoustic optical element 3, a condenser lens 4, polygon-plane condenser lens 5, a polygon mirror 6 and a scanning lens group 7. The acoustic optical element 3 is placed so that the beam waist position shown by a two-dot chain line 11 is positioned at the roughly central position of the optical path inside the element 3. The position of deflection displayed by a two-dot chain line 12 is disposed apart by a specified distance Δr on the downstream side of the optical path of the beam waist position 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser beam control device, and more particularly to a laser beam control device using a waveguide type acousto-optic device.

[0002]

2. Description of the Related Art Conventional laser beam control devices include:
For example, IEICE Technical Report [TECHNICAL REPORT O
FIEICE] US92-51 (1992-09) is known. In this laser beam control device, a waveguide-type acousto-optic device is driven by multi-frequency to split a laser beam, and a beam waist position and a deflection position of the waveguide-type acousto-optic device coincide with each other.

Further, as disclosed in Japanese Patent Publication No. 59-42855, an apparatus for driving a crystal-type acousto-optic device at multiple frequencies to divide a laser beam into a plurality of laser beams and then simultaneously scanning the plurality of laser beams is known. Proposed. In this multiple beam simultaneous scanning device, the deflection position and the beam waist position near the deflection position are separated by a predetermined interval in order to adjust the interval between the multiple scanning lines. Here, since the crystal is expensive, the size of the crystal acousto-optic element is as small as about several millimeters. If the deflection position is set in the crystal acousto-optic element, the beam waist position near the deflection position will be crystal acousto-optic. It was outside the device.

[0004]

However, when the conventional laser beam control device described in the IEICE technical paper is used as a pseudo multiple light source of a laser beam scanning optical device, the beam waist position and the acousto-optic Since the deflection position of the element is the same, the inclination error of the polygon mirror of the laser beam scanning optical device (error for changing the angle of the laser beam in the direction perpendicular to the deflection direction of the polygon mirror for each polygon surface) is corrected. When the tilt correction function is added to the scanning lens group of the laser beam scanning optical device for the purpose of performing the laser beam scanning, the laser beam split by the waveguide type acousto-optic element is re-focused on a single point on the image plane, and a plurality of scanning lines are There was a problem that the interval could not be adjusted.

On the other hand, in the multiple beam simultaneous scanning device described in Japanese Patent Publication No. 59-42855, since a deflection position and a beam waist position are arranged separately, a scanning lens group is provided with a surface tilt correction function. Also, the problem that the laser beam split by the crystal-type acousto-optic element is re-focused on the image plane at one point can be solved. However, since the beam waist is arranged outside the crystal-type acousto-optic element, there are the following problems.

(1) If the acousto-optic element and other optical elements are displaced due to environmental (temperature) change or temporal change, the deflection position and the beam waist position are relatively displaced, and a plurality of scan lines are not detected. The interval could not be kept constant. (2) When a driving error of the acousto-optic element occurs due to an environmental change, a power supply variation, or the like, the emission angle variation amount of the laser beam emitted from the acousto-optic element having a high refractive index into the air is changed by each laser beam on the image plane. Are enlarged in the direction in which the scanning lines are arranged, and the beam waist position is liable to fluctuate in that direction.

(3) When there is a beam waist behind the deflection position, each laser beam is emitted from the acousto-optic device at a different angle, so that a different amount of astigmatic difference is generated for each laser beam. Because of the difference in the amount of astigmatism, the beam waist position (that is, the light source position of each beam viewed from the rear optical system) is set to a desired position for each laser beam when viewed from the optical system behind the acousto-optic element. , And each scan line on the image plane was non-uniform. However, when there is a beam waist in front of the deflection position, a certain astigmatic difference occurs in each laser beam, and correction can be performed. However, a new optical surface is required for correction, and for example, the dielectric crystal itself, which is an acousto-optical element, must be processed to add a correction function, or a cylindrical lens or prism for correction must be added. Was.

Therefore, an object of the present invention is to provide a line spacing between laser beams on an image plane even when a deflection position of an acousto-optic element and a beam waist position near the deflection position are separated by a predetermined distance. Can be kept constant, and
An object of the present invention is to provide a laser beam control device having a small astigmatic difference.

[0009]

In order to achieve the above object, a laser beam control apparatus according to the present invention comprises:
(A) a semiconductor laser element; (b) a waveguide-type acousto-optic element which is driven by multi-frequency to deflect a laser beam emitted from the semiconductor laser element to divide the laser beam into a plurality of laser beams; A deflector for deflecting the plurality of laser beams emitted from the waveguide-type acousto-optic element in the main scanning direction, and (d) a laser emitted from the semiconductor laser element in the waveguide-type acousto-optic element. A deflection position for splitting the beam into a plurality of laser beams and a beam waist position near the deflection position have a predetermined interval.

With the above-described structure, the difference between the refractive index at the beam waist position and the refractive index at the deflection position in the waveguide of the waveguide type acousto-optic device is different from the deflection position within the crystal of the acousto-optic device of the conventional laser beam controller. Since the difference in refractive index at the beam waist position outside the crystal (in air) is extremely small,
The characteristic difference between the laser beams split at the deflection position is significantly reduced.

Further, by adopting a configuration in which the waveguide type acousto-optic element has a plurality of ultrasonic transducers for generating surface acoustic waves, the ultrasonic transducer to which a high-frequency signal is applied can be arbitrarily switched. For example, the deflection position at which the laser beam emitted from the semiconductor laser element is divided into a plurality of laser beams is switched, so that the image density can be easily switched.

Further, in the laser beam control device according to the present invention, two adjacent laser beams of the plurality of laser beams are arranged such that D _m > 4λ · C · P _i / ｛π · (θ ₂ −θ ₁ ) · D _{v 満}足 is satisfied, and the air equivalent distance Δ from the deflection position to the beam waist position is Δ = π · D _o · (D _m ² −D _o ² ) ^1/2 / 4λ where D _{m is the} deflection position beam diameter at D _v: a plurality of beam diameter of the laser beam is aligned direction D _o on the surface to be scanned: the beam diameter at the beam waist position P _i: spacing theta ₁ of the laser beam to be adjacent on the surface to be scanned , Θ ₂ : deflection angles of two adjacent laser beams (θ ₂
> Θ ₁ ) C: a proportional constant (magnification) of the optical system λ: a wavelength of a laser beam is satisfied.

With the above configuration, the cross-sectional area of the laser beam incident / emitted to the optical waveguide is minimized,
Flatness (smoothness) required for each transmission surface of emission
Accuracy is reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a laser beam control device according to the present invention will be described with reference to the accompanying drawings. In each embodiment, the same components and the same portions are denoted by the same reference numerals. First Embodiment, FIGS. 1 to 4 As shown in FIGS. 1 and 2, a waveguide type acousto-optic device 3 used in a laser beam control device has a laminated structure of a substrate 31 and an optical waveguide 32. ing. As the substrate 31, a crystal plate such as sapphire or a thin plate such as silicon or glass is used. Since the substrate 31 may be a thin plate, it is less expensive than a rectangular crystal used for a crystal acousto-optic device.

The optical waveguide 32 is formed on the substrate 31 by, for example, a laser ablation method, a sputtering method, a vacuum evaporation method, a CVD method, a sol-gel method, or a method using ion exchange or proton exchange. Optical waveguide 32
The material is preferably a material having excellent piezoelectricity and having little attenuation with respect to the wavelength of the laser beam emitted from the semiconductor laser element 2 as a light source, in order to efficiently perform acousto-optic interaction. Specifically, ZnO or LiNbO
₃ , PbMoO ₄ , TeO ₂ , As ₂ O ₃ , GaAs and the like are used.

On the optical waveguide 32, an interdigital transducer 33, which is an ultrasonic vibrator, is formed at a position on the near right side of the center portion by a photolithography method, a lift-off method, an etching method, an electron beam drawing method, or the like. You. By appropriately setting the interval and width of the electrode fingers of the interdigital transducer 33, it is possible to increase the Bragg diffraction angle described later or to obtain a wide range of changes in the Bragg diffraction angle. Further, the entrance prism 35 and the exit prism 3 are provided on both left and right sides of the optical waveguide 32.
6 are provided. The incidence prism 35 transmits the laser beam L emitted from the semiconductor laser element 2 to the optical waveguide 3.
2 for the light to enter. Exit prism 36
Is for emitting a laser beam L traveling through the optical waveguide 32 to the outside.

In the waveguide type acousto-optic device 3 having the above configuration, the transducer 33 is provided with a high-frequency power source 37.
When the high-frequency signal generated in step (1) is applied, a surface acoustic wave 38 is excited in the optical waveguide 32. As the high frequency power supply 37, for example, a VCO (voltage controlled oscillator) is used. Surface acoustic wave 3
8 propagates through the optical waveguide 32 in the direction of arrow a in FIG. On the other hand, the laser beam L emitted from the semiconductor laser element 2
Enters the optical waveguide 32 via the incidence prism 35 and travels through the optical waveguide 32. In the optical waveguide 32, a synchronous change in the refractive index occurs due to the surface acoustic wave 38, and this serves as a diffraction grating for the laser beam L. Therefore,
When the laser beam L crosses the surface acoustic wave 38, the laser beam L and the surface acoustic wave 38 undergo acousto-optic interaction (Bragg diffraction), so that the laser beam L is deflected as shown in FIG.

Incidentally, the Bragg diffraction angle of the laser beam L depends on the period of the surface acoustic wave 38, and the period of the surface acoustic wave 38 depends on the frequency of the high-frequency signal applied to the transducer 33. So, transducer 3
The laser beam L is deflected at a plurality of different Bragg diffraction angles by applying high-frequency signals of a plurality of different frequencies to 3 to generate a plurality of surface acoustic waves 38 of different periods, as shown in FIG. , Into a plurality of intensity-modulated laser beams. The plurality of laser beams are respectively emitted through the emission prism 36.

FIG. 3 is a schematic configuration diagram of a laser beam control device 1 using the waveguide type acousto-optic device 3. The laser beam control device 1 applies high-frequency signals of a plurality of different frequencies to the waveguide-type acousto-optic device 3 (multi-frequency driving) to divide the laser beam emitted from the semiconductor laser device 2 into a plurality of laser beams. This is a device for simultaneously scanning the plurality of laser beams on the surface to be scanned. The laser beam control device 1 includes a semiconductor laser device 2, a waveguide type acousto-optic device 3, a condenser lens 4, a polygon surface condenser lens 5, a polygon mirror 6, and a scanning lens group 7. ing.

The semiconductor laser element 2 is modulated (ON / OFF) based on print data input to a drive circuit (not shown).
It is controlled and emits a laser beam when turned on. This laser beam L is converged by a condenser lens 4 and then divided into a plurality of intensity-modulated laser beams by a waveguide type acousto-optic device 3. The mirror 6 is reached.

Each laser beam is deflected at a constant angular velocity on each polygon surface based on the rotation of the polygon mirror 6 and enters the scanning lens group 7. Each laser beam transmitted through the scanning lens group 7 is condensed on the photosensitive drum 8 and simultaneously scans the photosensitive drum 8 in the direction perpendicular to the paper surface. The scanning lens group 7 corrects the laser beam deflected mainly by the polygon mirror 6 at a constant angular speed on the surface to be scanned (photosensitive drum 8) at a constant speed, that is, corrects distortion. Has a function. The photoconductor drum 8 is driven to rotate at a constant speed in the direction of arrow c, and an image (electrostatic latent image) is formed on the drum 8 by the main scanning in the direction perpendicular to the paper surface of the polygon mirror 6 and the sub-scanning of the drum 8 in the direction of arrow c. Is formed.

In the above arrangement, in order to correct the surface tilt error of each polygon surface of the polygon mirror 6, the scanning lens group is set so that the polygon surface of the polygon mirror 6 and the surface of the photosensitive drum 8 have a conjugate relationship. 7, a tilt correction function is added. As shown in FIG. 4, the waveguide-type acousto-optic device 3 is arranged such that the beam waist position indicated by the two-dot chain line 11 is located substantially at the center of the optical path length in the device 3, and the interdigital transducer The deflection position by 33 is indicated by the two-dot chain line 12. The deflection position 12 is arranged at a predetermined distance Δr on the downstream side of the optical path from the beam waist position 11.

[0023] Here, in order to up-modulation rate of the laser beam L (rising characteristics), below a predetermined value of the beam diameter D _m of the laser beam L in the deflection position 12, for example 85
It is desirable to set it to μm or less. Further, in designing an optical system lens using a semiconductor laser element, the beam diameter Do of the laser beam L at the beam waist position 11 and the beam diameter _Do of FIG. The relationship between the adjacent laser beam L at the beam waist position 11 and the distance _Po between the laser beam L is indicated by the direction in which a plurality of laser beams are arranged on the surface to be scanned (photosensitive drum 8), that is, in the sub-scanning direction. and the beam diameter D _v, proportional to the relation between the distance P _i of the laser beam to be adjacent on the surface to be scanned, it is desirable to satisfy the following relational expression (1).

P _o / D _o = C (P _i / D _v ) (1) where C is a proportional constant (magnification) of the optical system. On the other hand, the intensity of the laser beam L has a Gaussian normal distribution. Assuming that, the following relational expression (2) holds. Here, Δ is the air-equivalent distance of the distance Δr between the beam waist position 11 and the deflection position 12, and the relational expression of Δr = nΔ holds when the refractive index of the optical waveguide 32 at the wavelength λ is n.

D _m / D _o = [1+ {4λΔ / (πD _o ² )} ² ] ^1/2 (2) From the relational expression (2), the following relational expression (3) is obtained. Δ = πD _o (D _m ² −D _o ² ) ^1/2 / 4λ (3) By the way, the air conversion distance Δ and the deflection angles θ ₁ , θ ₂ (θ ₂ >
Between the interval P _o at the beam waist position 11 of the two laser beams diffracted by the θ _1), sinθ ₁ when the angle theta _1, theta ₂ is sufficiently small, sin [theta ₂ is substantially theta _1, theta because it is a _2, the following equation (4) is satisfied.

P _o = Δ (sin θ ₂ −sin θ ₁ ) = Δ (θ ₂ −θ ₁ ) (4) From the above relational expressions (3) and (4), the following relational expression is obtained. P _o / D _o = π (θ ₂ −θ ₁ ) (D _m ² −D _o ² ) ^1/2 / 4λ D _m ² −D _o ² = [4λ / {π (θ ₂ −θ ₁ )}] ² ( _Po / D
_o ) ² Further, using the relational expression (1), D _m ² −D _o ² = {4λCP _i / π (θ ₂ −θ ₁ )} ² (P _i /
D _v ) ² . Here, P _i and D _v are numerical values given by design according to scanning specifications, C and λ are numerical values given by design according to optical system specifications, and D _m , θ ₁ and θ ₂ are waveguide type acousto-optics. It is a numerical value given by design according to the element specification.

Accordingly, in the laser beam control device 1, the following relational expression (5) holds. _{^{D o 2 = D m 2 -}} [4λCP i / {π (θ 2 -θ 1)}] 2 (P i / D v) 2> 0 D m> 4λCP i / {π (θ 2 -θ 1) D _v ｝ (> 0) (5) Next, an example of calculating the air-equivalent distance Δ using specific numerical values will be described.

D _m = 85 μm, θ ₂ −θ ₁ = 0.8 °, P _{i
/ D v = 1, λ =} 0.78μm, When _{C = 1, D o = [} 0.085 2 - [(4 × 0.78 × 10 -3 × 1)
/ {(Π ² /180)×0.8}] ² × 1 ² ] ^1/2 = 46.
5 (μm) Therefore, if the condenser lens 4 is selected so that D _o = 46.5 (μm), the air-equivalent distance Δ at this time is calculated to be 3.33 mm from the relational expression (3). You. The actual distance Δr in the optical waveguide 32 is Δr = n × 3.3, where n is the refractive index of the optical waveguide 32 at the wavelength λ = 0.78 μm.
3 is calculated.

The laser beam control device 1 thus obtained
Since the beam waist position 11 is arranged in the acousto-optic element 3, each object point of the plurality of laser beams after division exists in the acousto-optic element 3. Therefore, even if the position of the acousto-optic element 3 is shifted with respect to the other optical elements 2, 4, 5, 6, and 7 due to environmental changes or changes over time, the object point of each laser beam is equally shifted. The relative positional relationship between the scanning line 11 and the deflection position 12 is not easily shifted, and the interval between a plurality of scanning lines on the photosensitive drum 8 can be kept constant.

Further, even if a driving error of the acousto-optic element 3 occurs due to environmental change or power supply fluctuation, the object point of each laser beam is within the acousto-optic element 3, so that the object point shifts by the deflection angle θ ₁ , θ corner only _two shift difference, not affected by the output angle variation of the laser beam emitted into the air from the acousto-optic element 3. As a result, the interval between a plurality of scanning lines on the photosensitive drum 8 can be kept constant.

Further, even in the waveguide type acousto-optic device 3, the astigmatic difference of the split laser beam is generated.
The processing technique for forming the astigmatic difference correction function of the refractive index distribution, the diffraction grating, the waveguide lens, and the like in the waveguide 32 is relatively easy, and has high productivity. From the above results, the photosensitive drum 8
The spacing between multiple scan lines above can be kept constant,
In addition, the laser beam control device 1 with a small astigmatic difference can be obtained.

Further, the laser beam control device 1 positions the beam waist position 11 substantially at the center of the optical path length in the acousto-optic device 3, and determines that the adjacent laser beam has a value of D _m > 4λC
P _i / {π (θ ₂ −θ ₁ ) D _v }, and the air-equivalent distance Δ satisfies Δ = πD _o (D _m ² −D _o ² ) ^1/2 / 4λ. Therefore, it is possible to minimize the cross-sectional area of the laser beam L incident on / emitted from the optical waveguide 32,
Flatness (smoothness) required for each transmission surface of emission
Can be relaxed.

[Second Embodiment, FIG. 5] As shown in FIG. 5, the waveguide type acousto-optic device 42 used in the laser beam control device 41 of the second embodiment is the same as the first embodiment except for an interdigital transducer 43. This is the same as the waveguide type acousto-optic device 3 of the first embodiment. An interdigital transducer 43 is formed on the optical waveguide 32 at a position on the left side of the center. Further, although not shown, an entrance prism and an exit prism are disposed at both left and right ends of the optical waveguide 32. Acousto-optic element 42
Are arranged such that the beam waist position 11 is located substantially at the center of the optical path length in the element 42. The deflection position 12 by the interdigital transducer 43 is located at a predetermined distance Δr and upstream of the beam waist position 11 on the optical path.

The laser beam control device 41 using the waveguide type acousto-optic device 42 having the above configuration has the same operation and effect as the laser beam control device 1 of the first embodiment.

[Third Embodiment, FIGS. 6 and 7] In the conventional laser beam controller, the deflection position is changed by moving the ultrasonic vibrator in the optical axis direction, thereby switching the image density. For this reason, there is a problem that switching of the image density is easily affected by a moving error of the ultrasonic transducer.
Therefore, a third embodiment describes a laser beam control device capable of reliably and stably switching the image density.

As shown in FIG. 6, the laser beam control device 51 comprises a waveguide type acousto-optic device 52 and switches S1 and S1.
2 except for the laser beam control device 1 of the first embodiment.
Is similar to The waveguide-type acousto-optic device 52 includes an optical waveguide 32 provided on a substrate, a low-density interdigital transducer 53 provided at a central portion on the optical waveguide 32 on the left side, and a high-density interdigital transducer 53 provided on the central portion on the right side. An interdigital transducer 54 is provided. Further, although not shown, an entrance prism and an exit prism are disposed at both left and right ends of the optical waveguide 32.

The acousto-optic device 52 is arranged such that the beam waist position 11 is located substantially at the center of the optical path length in the device 52. The deflection position 13 by the low-density interdigital transducer 53 is arranged at a predetermined distance Δr _{1 on} the optical path upstream side of the beam waist position 11. The deflection position 14 by the high-density interdigital transducer 54 is located at a predetermined distance Δr ₂ (see FIG. 7) at the downstream side of the optical path from the beam waist position 11.

Further, the beam diameter D _{m1 at the} deflection position 13 and the air-equivalent distance Δ ₁ from the deflection position 13 to the beam waist position 11 are represented by the relational expressions (3) and (5) described in the first embodiment, respectively. Are satisfied. Similarly, the beam diameter D _{m2 at the} deflection position 14 and the air-equivalent distance Δ ₂ from the deflection position 14 to the beam waist position 11 satisfy the relational expressions (3) and (5), respectively. Each of the interdigital transducers 53 and 54 is connected to the high-frequency power source 37 via switches S1 and S2, respectively.

When a low-density image is formed on the surface to be scanned in the laser beam control device 51 having the above configuration, the switch S1 is turned on and the switch S2 is turned off, as shown in FIG. The laser beam L emitted from the laser element 2 is split at the deflection position 13 to form a plurality of laser beams. In this case, the interval between the plurality of scanning lines on the surface to be scanned increases. Conversely, when forming a high-density image on the surface to be scanned, as shown in FIG.
1 is turned off, the switch S2 is turned on, and the laser beam L is split at the deflection position 14 to form a plurality of laser beams.
In this case, the interval between the plurality of scanning lines on the surface to be scanned becomes smaller.

As described above, the laser beam controller 51
Is to switch the deflection positions 13 and 14 by the switches S1 and S2, and to perform the switching of the image density reliably and stably with a simple configuration in addition to the operation and effect of the laser beam control device 1 of the first embodiment. Can be.

[Fourth Embodiment, FIGS. 8 and 9] A fourth embodiment describes another laser beam control device capable of reliably and stably switching the image density.

As shown in FIG. 8, a laser beam control device 61 is the same as the laser beam control device 51 of the third embodiment except for high-frequency power supplies 62 and 63. The high-frequency power supplies 62 and 63 generate high-frequency signals having different frequencies f ₁ and f ₂ , respectively, and are connected to the low-density interdigital transducer 53 and the high-density interdigital transducer 54 via switches S1 and S2. In the laser beam control device 61 having the above configuration, when forming a low-density image on the surface to be scanned,
As shown in FIG. 8, switch S1 is turned on and switch S2 is turned on.
Is turned off, and the laser beam L is split at the deflection position 13 to form a plurality of laser beams. In this case, the interval between the plurality of scanning lines on the surface to be scanned increases. Conversely, when forming a high-density image on the surface to be scanned, as shown in FIG. 9, the switch S1 is turned off, the switch S2 is turned on, and the laser beam L is divided at the deflection position 14, Laser beam. In this case, the interval between the plurality of scanning lines on the surface to be scanned becomes smaller.

This laser beam control device 61
In addition to the functions and effects of the laser beam control device 51 of the embodiment, by combining the switching of the deflection positions 13 and 14 and the switching of the frequencies f ₁ and f ₂ , the degree of freedom in switching the image density can be increased.

[Other Embodiments] The laser beam control device according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the gist.

For example, the incidence and emission of the laser beam to and from the optical waveguide can be performed not only by a prism but also by a diffraction grating (grating) formed in the optical waveguide, an end face of the optical waveguide utilizing end face coupling, or the like. Further, the beam waist position is desirably located near the interface between the optical waveguide and the outside. This is because the laser beam transmits through the interface between the optical waveguide and the outside in a smaller area range, so that the accuracy of the flatness of the transmission surface of the optical waveguide can be further relaxed.

In the second embodiment, when the beam waist position 11 is located at the right end of the acousto-optic device 3 (see FIG. 5), the laser beam can reach the optical waveguide 32 and the outside in a smaller area. Since the light passes through the interface, the accuracy of the flatness of the transmission surface of the optical waveguide 32 can be further reduced, and the effect of astigmatism can be further reduced.

[0047]

FIG. 10 shows a first and second embodiment manufactured by the inventors.
2 shows a waveguide type acousto-optic element used in the laser beam control device of the embodiment. An optical waveguide 101 made of LiNbO ₃ is formed on the rectangular ceramic substrate 100 from the left side to the right side. At the center of the optical waveguide 101, an interdigital transducer 102 for generating a surface acoustic wave and an interdigital transducer 103 for absorbing unnecessary surface acoustic waves are formed to face each other. On a ceramic substrate 100, an optical waveguide 101 is interposed, and electrodes 105 are provided on both sides thereof.
Is provided. The electrode 105 is used as a relay electrode when electrically connecting the interdigital transducers 102 and 103 to an external peripheral device (for example, a high-frequency power supply or the like).

[0048]

As is apparent from the above description, according to the present invention, in the waveguide type acousto-optic device, the deflection position at which the laser beam emitted from the semiconductor laser device is divided into a plurality of laser beams is determined. Since the beam waist position near the deflection position has a predetermined interval, the line interval between the laser beams on the image plane can be kept constant, and the astigmatic difference is small. A laser beam control device can be obtained.

Further, by providing a plurality of ultrasonic transducers in the waveguide type acousto-optic element, the deflection position can be switched, and a laser beam control device capable of stably and reliably changing the image density can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a waveguide type acousto-optic device used in a first embodiment of a laser beam control device according to the present invention.

FIG. 2 is a more detailed perspective view of the waveguide-type acousto-optic device shown in FIG.

FIG. 3 is a configuration diagram showing a laser beam control device according to the first embodiment.

FIG. 4 is an optical path diagram for explaining the operation of the laser beam control device shown in FIG.

FIG. 5 is an optical path diagram showing a second embodiment of the laser beam control device according to the present invention.

FIG. 6 is an optical path diagram showing a third embodiment of the laser beam control device according to the present invention.

FIG. 7 is an optical path diagram for explaining the operation of the laser beam control device shown in FIG.

FIG. 8 is an optical path diagram showing a fourth embodiment of the laser beam control device according to the present invention.

9 is an optical path diagram for explaining the operation of the laser beam control device shown in FIG.

FIG. 10 is a plan view showing a specific example of a waveguide type acousto-optic element used in the laser beam control device according to the present invention.

[Explanation of symbols]

1, 41, 51, 61 laser beam control device 2 semiconductor laser device 3, 42, 52 waveguide acousto-optic device 6 polygon mirror (deflector) 11 beam waist position 12, 13, 14 deflection position 33, 43, 53, 54 ... transducers (ultrasonic transducers) Δr, Δr ₁ , Δr ₂ ... distance

Claims (3)

[Claims] A semiconductor laser element; a waveguide-type acousto-optic element that is driven by multi-frequency to deflect a laser beam emitted from the semiconductor laser element and divides the laser beam into a plurality of laser beams; A deflector for deflecting the plurality of laser beams emitted from the element in a main scanning direction, wherein the laser beam emitted from the semiconductor laser element is converted into a plurality of laser beams within the waveguide-type acousto-optic element. A deflection position to be split and a beam waist position near the deflection position having a predetermined interval. 2. The laser beam control device according to claim 1, wherein the waveguide type acousto-optic device has a plurality of ultrasonic transducers for generating a surface acoustic wave. 3. Two adjacent laser beams of the plurality of laser beams satisfy D _m > 4λ · C · P _i / {π · (θ ₂ −θ ₁ ) · D _v }, and The air-equivalent distance Δ from the deflection position to the beam waist position is Δ = π · D _o · (D _m ² −D _o ² ) ^1/2 / 4λ where D _m : beam diameter at the deflection position D _v : beam diameter in the direction in which the plurality of laser beams on the scanned surface are aligned D _o: the beam diameter at the beam waist position P _i: spacing theta ₁ of the laser beam to be adjacent on the surface to be scanned, theta _2: two adjacent Angles of two laser beams (θ ₂
> Θ ₁ ) C: Proportion constant (magnification) of the optical system λ: The wavelength of the laser beam is satisfied.
The laser beam control device as described in the above.