JPS59197016A - Acoustooptic element - Google Patents

Abstract

PURPOSE:To simplify the constitution by providing the second electrode in a corresponding positon on a transducer provided on the first electrode and connecting both electrodes so that plural electrostatic capacities formed between both electrodes are connected in series. CONSTITUTION:An insulating layer 11 is provided on one-side face of an acoustooptic medium 1, and electrodes 5a and 5b which are divided equally are provided on this layer 11. A transducer 2 is fixed onto the insulating layer 11, and electrodes 4a and 4b are provided in positions corresponding to electrodes 5a and 5b on the transducer 2. The electrode 4a on the transducer 2 and the electrode 5b on the acoustooptic medium 1 are conneted electrically by a lead wire 10, and a high frequency electric signal is applied between the electrode 4b on the transducer 2 and the electrode 5a on the acoustooptic medium 1 through leads 6 and 7 for electric input. A sound absorbing body 3 is fixed to the bottom of the acoustooptic medium 1. When electrodes on the transducer are extended and the number of divisions of electrodes is increased, a large-diameter incident laser light can be used for the acoustooptic element operated by the high frequency electric signal.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an acousto-optic device.

Configuration of a conventional example and its problems FIG. 1 shows an acousto-optic element using Ge as an acousto-optic medium as a conventional example. In the figure, 1 is an acousto-optic medium made of Ge, 2 is a transducer (piezoelectric transducer) adhered to the acousto-optic medium 1, 3 is a sound absorber, 4 is an electrode provided on the transducer 2, and 5 are electrodes provided on the acousto-optic medium 1; 6 and 7 are electrical input leads connected to the electrodes 4 and 5, respectively; 8 is a high-frequency electrical signal generator;
9 is a slope provided on the acousto-optic medium 1.

From the high-frequency electrical signal generator 8, electrical input ports 6 and 7
When a high frequency electrical signal is applied between the transducer 2
An electro-mechanical conversion takes place at , and the ultrasound signal propagates from the transducer 2 into the acousto-optic medium 1 .

At this time, when the laser beam A is made incident at a certain Bragg angle, the laser beam A is diffracted by the ultrasonic signal propagating within the acousto-optic medium 1 and separated into undiffracted light B and diffracted light C. Here, the direction of the diffracted light C is determined by the frequency of the high frequency electrical signal from the high frequency electrical signal generator 8, and the intensity of the diffracted light C is determined by the amplitude of the same high frequency electrical signal. In this way, the high frequency electrical signal applied between the electrical input leads 6 and 7 is converted into an optical signal. On the other hand, the ultrasonic signal diffracted by the laser beam is reflected downward from the slope of the acousto-optic medium 1 and absorbed by the sound absorber 3.

In the above-mentioned conventional acousto-optic device, when using the laser beam A with a large diameter, the width of the electrode 4 provided on the transducer 2 is increased to increase the width of the ultrasonic wave propagating in the acousto-optic medium 1. must be made larger than the aperture of laser beam A. That is, as shown in FIG. 2, if the thickness of the transducer 2 is T, and the width and length of the electrode 4 are H and L, respectively, then the width H is determined from the aperture of the nine lasers. It is necessary to set it large so that the propagating ultrasonic waves hit the entire laser beam A.

However, conventionally, the width H of the electrode 4 has been limited due to impedance matching between the acousto-optic element and the high frequency electric signal generator 8. This will be explained in detail below.

As is generally known, in order to supply electrical signals from a high-frequency electrical signal generator to a piezoelectric transducer without causing loss, the input impedance of the piezoelectric transducer and the output impedance of the high-frequency electrical signal generator must be adjusted. It is necessary to match.

In FIG. 1, the output impedance Z of the high frequency electrical signal generator 8. u''+ is approximately 50Ω, and the input impedance of the piezoelectric transducer is expressed by the following equation (2L).

Z: Lnヱ 1/2πra o -- (a) Here, f is the frequency of the high-frequency electric signal, and co is the capacitance (clamp capacitance) formed at the electrode 40 portion.

Furthermore, in the above equation (?L), the capacitance C6 changes depending on the shape LXH of the electrode 4 and the thickness T of the transducer 2, and is expressed by the following equation (b>).

H Co ok □ ・・・・
...(b) Obtain the following equation using equations (b) and e).

According to the above formula (C), Zin is the output impedance Z of the high frequency electric signal generator 8. In order to make it equal to ut (=50Ω), the vertical length of the electrode 4, the width @H''!l: and the thickness T of the transducer 2 should be appropriately determined for a certain frequency f. However, the thickness T is constrained by the frequency f, and the length L is constrained by the 16 inch constant Q, which is well known in the theory of Bragg diffraction. I can't take it.

In Fig. 3, the horizontal axis is the electrical input p input from the high frequency electrical signal generator 8 through the electrode 4 to the piezoelectric transducer.
The vertical axis is the intensity of the diffracted light C diffracted by the ultrasonic wave. This figure shows the intensity of the p-diffracted light C. It can be seen that in order to set IC,maX to the maximum value, it is better to supply electric power Pπ of a specific magnitude from the high frequency electric signal generator 8. However, when the electrical input Pπ is supplied from the electrode 4, if the area (LxH) of the electrode 4 is small, the electrical input per unit area becomes large and the piezoelectric transducer deteriorates rapidly due to heat generation.
A limit is added to the area (LXH).

Considering the above, the input input turns zi
In order to match n with the output impedance of 2.degree. ut (-60.OMEGA.), it is necessary to adjust the size of the width H within a certain heavy envelope.

The following table shows the frequency f of the high frequency electrical signal = 100MHz.

In the case of laser beam A having a wavelength of 10.6 μm (infrared rays), the input inbeak is relative to the width H.

It shows how the performance changes.

From this table, input impedance Zin 7! l2so
Ω, the output impedance Z. ut and matching force; it can be taken in the case of 1 = = 3π shoulder, H - 0, 6ff1m, and the aperture of the laser beam cannot be made larger than 0.6''. Also, if the frequency f becomes higher, formula(
As can be seen from C), in order to achieve impedance matching, the area (LxH) of the electrode 40 must not be made small, and the electric power Pπ sufficient to obtain the diffracted light C of sufficient intensity must be
If input to

In order to overcome the above conventional drawbacks, as shown in Figure 4,
Two-divided electrodes 4a and 4b are provided on the transsteuser 2, two-divided electrodes 5a and 5bl are provided on the acousto-optic medium 1 in correspondence with these electrodes 4a and 4b, and furthermore, an electrode 4a and 4b on the transsteuser 2 is provided. and electrode 5 on acousto-optic medium 1
b electrically connected with the lead wire 10, and the optical medium 1
An acousto-optic element has been invented which applies a high frequency electric signal between the electrodes Si2.

When the acousto-optic element is configured in this way, the capacitance C8' seen from the input side of the piezoelectric transducer is formed at the electrodes 4a and 4b on the transducer 2, respectively, as shown in FIG. Capacitance C? As the capacitance becomes a composite capacitance of L and Cb, its capacitance value becomes smaller. For this reason, the electrode 4 shown in FIG. The width H' of L and 4b can be set larger than that of the electrode 4 in FIG.

This can be explained concretely as follows.

Assuming that the electrodes 4a and 4b are divided into two equal parts, and the vertical length is L/, the horizontal width is H', and the thickness of the transducer 2 is T', the following equation holds. .

1 1 1 □N□+□ Co'C2LCb T'T' Za □+-- L'H'L'H'2T' Cdo □ L'H'L'-- (Electrode 40 in Figure 1 half), T'= T(
If the thickness is the same as that of the transducer in Figure 1), then LH'C' -□
... (6) T.

In order to make the electrostatic quantity on the input side of the piezoelectric transducer in Fig. 4 the same value as that in Fig. 1 (i.e., C8-0,7), equations (b) and (e) must be used. In comparison, 1-H is good, so H':4H, and electrode 4 in Figure 4.
The width H' of a and 4b can be made four times that of electrode 4 in FIG.

As shown in FIG. 5, the equivalent circuit of the conventional acousto-optic element described above is a capacitance Ca formed between electrodes 4a and 5a.
and the capacitance Cb formed between the electrodes 4b and 5b are connected in series, and the capacitances Cyu and Cb are connected in parallel to resistors RB and RB, respectively. Tokode r,
is the resistance of the acousto-optic medium 1 between the electrodes 5a and 5b, and r
b is the resistance of the transducer 2 between electrodes 4a and 4b.

Incidentally, since the specific resistance of the transducer 2 is sufficiently large, rb is close to infinity, so there is no problem. However, the resistivity of the acousto-optic medium 1 is, for example, G. When sucking from the air, the specific resistance is around 1ΩOn, and the resistance r2L becomes smaller, so that the electrodes 5a and 5b are almost in a short-circuited state. Therefore, the input impedance Zln of the acousto-optic element shown in FIG. 4 is different from a predetermined value, and there is a drawback that impedance matching with the high frequency electric signal generator 8 cannot be achieved.

SUMMARY OF THE INVENTION It is an object of the invention to provide an acousto-optic device which eliminates the drawbacks of the above-mentioned conventional examples and is capable of modulating and deflecting incident light with a large diameter.

Structure of the Invention In order to achieve the above object, the present invention provides an insulating layer on one surface of an acousto-optic medium, a plurality of first electrodes on the insulating layer, and a transducer on the first electrode. - a second electrode is provided on the transducer at a position corresponding to each of the first electrodes, and a plurality of capacitances formed between the first electrode and the second electrode are provided. They are connected in series.

DESCRIPTION OF EMBODIMENTS FIG. 6 shows an acousto-optic element according to an embodiment of the present invention, and the same parts as in FIG. 4 showing a conventional example are given the same numbers. An insulating layer 11 is provided, and electrodes 5a and 5b equally divided into two are provided on this insulating layer 11.

Further, the transducer 2 is fixed onto the insulating layer 11, and electrodes 4a and 4b are provided on the transducer 2 at positions corresponding to the electrodes 5a and 5b. '3. In addition, the electrode 4a on the transducer 2 and the electrode 6b on the acousto-optic medium 1 are electrically connected by a lead wire 10, and the electrode 4b on the transducer 2 and the electrode 5a on the acousto-optic medium 1 are connected electrically. A high-frequency electrical signal is applied through electrical input ports 6 and 7. A sound absorber 3 is fixed to the bottom surface of the acousto-optic medium 1.

Note that as the insulating layer 11, an optical antireflection film such as magnesium fluoride can be deposited and used. A feature of the present invention is that an insulator 11 is interposed between the acousto-optic medium 1 and the electrodes 5a and 5b, so that the resistance r? between the electrodes 6a and 5b in FIG. Lk can be made very large, and the equivalent circuit seen from the input side of the acoustic wave element shown in Fig. 6 is the capacitance Ca and Cb formed between electrodes 4a and 5a and between electrodes 4b and 5b, as shown in Fig. 7. are connected in series.

In this example, as shown in the explanation of FIG. 4, the capacitance seen from the input side of the acousto-optic element is 10.
When operating an acousto-optic device with a high frequency electric signal of 0 MHz, the vertical length L of the electrode on the transducer is 3πm.
, the width H can be made approximately 2.4 mm, and the aperture of the incident laser beam can be quadrupled.

Furthermore, by increasing the number of electrode divisions on the transducer, it becomes possible to use a larger diameter incident laser beam for an acousto-optic element operated by an even higher frequency electrical signal. Further, since the area of the electrode on the transducer can be increased four times when divided into two, the durability of the acousto-optic transducer against high-frequency electrical input can be improved.

As described in detail, the acousto-optic element according to the present invention has a simple structure, is highly effective, and has high industrial value.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a conventional acousto-optic element, Fig. 2 is an enlarged view of the main parts of the acousto-optic element, Fig. 3 is a diagram showing the relationship between electrical input and the intensity of diffracted light in the acousto-optic element, 4 is a perspective view of another conventional acousto-optic device, FIG. 5 is an equivalent circuit diagram of the acousto-optic device seen from the input side, and FIG. 6 is a perspective view of an acousto-optic device according to an embodiment of the present invention. FIG. 7 is an equivalent circuit diagram of the acousto-optic device seen from the input side. 1...Acousto-optic medium, 2...Transducer, 4a, 4b--(second) electrode, ia, 5
b=,,,. (first) electrode, 11...insulating layer. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 3 Figure 4 h 6δ Figure 5 May

Claims (2)

[Claims] (1) An insulating layer is provided on one surface of the acousto-optic medium, a plurality of first electrodes are provided on this insulating layer, a transducer is provided on this first electrode, and the above-mentioned an acousto-optic element in which a second electrode is provided at a position corresponding to each electrode of the first electrode, and a plurality of capacitances formed between the first electrode and the second electrode are connected in series. . (2) Claim 1 in which the acousto-optic medium is made of Ge
The acousto-optic device described in .