JPH0320817Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multi-beam optical modulation device, and particularly to a multi-beam optical modulation device that reduces the temperature gradient in an ultrasound propagation medium during operation.

[Prior Art] It is already known that the phenomenon of light scattering caused by sound waves is a useful means for modulating laser beams, and multi-beam optical modulation is one of the acousto-optic devices that utilizes this phenomenon. There is an element.

As shown in FIGS. 5 and 6, such a multi-beam optical modulation element usually includes an ultrasonic propagation medium 101 made of glass or the like and a transducer 102 attached to one side of the ultrasonic propagation medium 101. It is configured.

The transducer 102 in this case is
A lower electrode 105 disposed on the side of the ultrasonic propagation medium 101, a piezoelectric element 103 disposed on the lower electrode 105, and a piezoelectric element 103 disposed at a constant interval on the upper surface of the piezoelectric element 103. Multiple upper electrodes 10
4 to form a three-layer structure.

Then, by applying an electric signal between each upper electrode 104 and lower electrode 105, the piezoelectric element 103 is excited separately, and the ultrasonic propagation medium 10
The ultrasonic waves propagate through each part separately.

At this time, the inside of the ultrasonic propagation medium 101 is in a state as if a diffraction grating is formed, and the incident beam 106 of each laser beam transmitted through the ultrasonic propagation medium 101 is deflected, and the diffracted light is The output beam 107 can be obtained as follows.

In this case, the plurality of upper electrodes 104 provided on the piezoelectric element 103 have a rectangular shape with the same area as shown in FIG. 5, or an elliptical or It was formed by arranging diamond-shaped objects at equal intervals.

[Problems to be solved by the invention] By the way, in the multi-beam optical modulation element configured as described above, the vibration energy of the ultrasonic wave during its operation is affected by the viscosity of the ultrasonic propagation medium 101 itself or the transducer. Ducer 10
2 and the ultrasonic propagation medium 101 causes conversion loss and heat generation, which heats the ultrasonic propagation medium 101 and generates heat. Further, the upper electrode 104 that is energized generates heat due to its resistance value, and heats the ultrasonic propagation medium 101 .

In this case, the ultrasonic propagation medium 101 traps heat in the center, which is the part with the worst heat dissipation, and becomes the highest temperature, and as it goes outward, the heat dissipation improves and the temperature decreases. Therefore, a temperature gradient as shown in FIG. 7 occurs in the ultrasonic propagation medium 101.

Such a temperature gradient causes a fluctuation distribution in the refractive index of the ultrasonic propagation medium 101 itself, which should originally be constant, and gives a lens-like effect, causing each emitted beam 107 to be distorted as shown in FIG. There was an inconvenience that it became difficult to maintain parallelism between the output beams 107 by condensing the beams toward the center or diffusing them.

An object of the present invention is to provide a multi-beam optical modulation element in which the temperature gradient in the ultrasonic propagation medium in the direction orthogonal to the transmission direction of each laser beam is minimized.

[Means for Solving the Problems] In order to achieve the above object, the present invention was constructed as follows.

That is, the present invention provides a multi-beam optical modulation device comprising an ultrasonic propagation medium and a transducer, the transducer comprising a piezoelectric element and
This piezoelectric element is formed by an upper electrode and a lower electrode that are arranged to sandwich the piezoelectric element from both the upper and lower sides, and the upper electrode is separately provided corresponding to the transmitting part of each laser beam, and The structural feature is that the transducer is deformed and formed so that the amount of heat generated by the transducer increases as the transducer is located.

[Function] For this reason, in the multi-beam optical modulation element of the present invention, the area increases toward the left and right sides of the ultrasonic propagation medium in the direction orthogonal to the laser beam transmission direction, or the thickness increases. By arranging the upper electrode, which is formed by thinning and deforming the Reduces temperature gradients within the ultrasound propagation medium in orthogonal directions,
It can be flattened.

Therefore, the refractive index in the ultrasonic propagation medium can be made constant and uniform, and each laser beam can be emitted as a highly parallel output beam.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a perspective view showing an embodiment of the present invention. In the figure, a transducer 2 is disposed on one side of an ultrasonic propagation medium 1 made of PbMoO ₄ or the like.

This transducer 2 consists of a piezoelectric element 3 made of LiNbO ₃ or the like whose crystal structure is a 36° rotated Y plate.
and an upper electrode 4 which is formed using a conductive material such as Au and which holds the piezoelectric element 3 from both upper and lower sides.
and a lower electrode 5.

Of these, for the upper electrode 4, the piezoelectric element 3
A plurality of upper electrodes 4 are arranged at regular intervals on the top, and each upper electrode 4 is deformed so that the amount of heat generated by the transducer 2 increases as it goes from the center toward both sides. .

That is, as shown in FIGS. 1 and 2,
Each of the upper electrodes 4 is formed so that the one located in the center has the smallest area, and thereafter the upper electrodes 4 are formed with a larger area while being symmetrical, and are successively arranged at predetermined intervals. .

In addition, as shown in FIG. 3, each upper electrode 4 has the same width and length, and the one located in the center is the thickest. It is also possible to arrange thinner parts one after another at predetermined intervals.

Since the multi-beam optical modulator according to the present invention is configured in this way, the ultrasonic propagation medium 1
In this case, the left and right sides in the direction perpendicular to the laser beam transmission direction are heated to the highest temperature.

That is, a pair of upper electrodes 4 located at the outermost side
is formed so that its area is maximized compared to the other upper electrodes 4, or even if the area is the same, its thickness is minimized, so that the heat generation of the transducer 2 is The amount is also large, and the ultrasonic propagation medium 1 located in this area is heated most intensely.

In this way, the amount of heat generated by the transducer 2 gradually decreases in the direction of the upper electrode 4 located in the center, so that the degree of heating of the ultrasonic propagation medium 1 etc. also decreases accordingly. To go.

Therefore, the amount of heat dissipated from each part of the ultrasonic propagation medium 1 can be made proportional to the amount of heating, and as shown in FIG. 4, by reducing the temperature gradient in the ultrasonic propagation medium 1, its flattening It is possible to aim for

Therefore, by reducing the occurrence of phenomena such as refraction of the incident beam 6 in the ultrasonic propagation medium 1 due to lenses, each output beam 7 is
It is possible to suppress the inconvenience that the distance between the beams is widened or narrowed, and it is possible to deflect and modulate each output beam 7 while maintaining a high degree of parallelism.

In order to confirm the effectiveness of the present invention, an experiment was conducted in the following manner.

i.e. 15mm (vertical) x 15mm using _PbMoO4
Form an ultrasonic propagation medium of (width) x 8 mm (height),
Au is used for the electrode, and a 36° rotated Y plate is used for the piezoelectric element.
Each was formed using LiNbO ₃ , and the piezoelectric element and the lower electrode were bonded and fixed with In interposed therebetween.

The upper electrodes are arranged in a total of 5 rows,
The standards are as follows.

Width × length (thickness is constant) Center row 1 × 15 (mm) 1 piece Both outer rows 1.3 × 15 (mm) 2 outermost row 1.6 × 15 (mm) 2 pieces Regarding the above upper electrode The width is 1 mm, the length is 15 mm, the thickness of the center row is 2 to 3 μm, and the thickness of the outermost row is 5000 Å. may be formed with a thickness of 1000 Å.

In this way, when each channel was driven with a power of 0.5W and the laser beam was transmitted, the divergence angle of each output beam was
While it was 0.5 mrad, that of the present invention was
It was only around 0.1 mrad, and it was confirmed that when using the present invention, an output beam with high parallelism could be obtained by reducing the temperature gradient and making the refractive index uniform.

[Effects of the invention] As described above, according to the invention, since the shape of each upper electrode constituting the transducer is changed, the amount of heat dissipated from each part of the ultrasonic propagation medium is Heating can flatten the temperature gradient.

Therefore, it is possible to make the refractive index in the ultrasonic propagation medium uniform, and it is possible to eliminate the disadvantage that the intervals between the emitted beams are not constant and become gradually narrower or wider. A multi-beam light modulator can be provided.

[Brief explanation of the drawing]

FIG. 1 is an overall perspective view showing an embodiment of the present invention;
Fig. 2 is a partially omitted front view of Fig. 1, Fig. 3 is a partially omitted front view of another embodiment, and Fig. 4 shows the temperature distribution in the ultrasonic propagation medium during operation of the present invention. Graph diagram, FIG. 5 is an overall perspective view showing a conventional example,
Fig. 6 is a partially omitted front view of Fig. 5, Fig. 7 is a graph showing the temperature distribution in the ultrasonic propagation medium during operation of the conventional example, and Fig. 8 is the position of each output beam in the conventional example. FIG. 3 is a plan view showing the relationship. DESCRIPTION OF SYMBOLS 1... Ultrasonic propagation medium, 2... Transducer, 3... Piezoelectric element, 4... Upper electrode, 5... Lower electrode, 6... Incident beam, 7... Outgoing beam.

Claims (1)

[Claims for Utility Model Registration] 1. In a multi-beam optical modulation device comprising an ultrasonic propagation medium and a transducer, the transducer includes a piezoelectric element and a structure in which the piezoelectric element is sandwiched from both upper and lower sides. The transducer is formed of an upper electrode and a lower electrode, and the upper electrode is individually provided corresponding to the transmission area of each laser beam, and the transducer's heat generation amount increases as the upper electrode is located on the outer side. A multi-beam light modulation element characterized in that it is formed by deforming it so that it becomes larger. 2. The multi-beam light modulation element according to claim 1, wherein the upper electrode has a larger area as it is located on the outer side. 3. The multi-beam light modulator according to claim 1, wherein the upper electrodes are thinner as they are located on the outer side.