JPS6353516A - Transducer array for surface acoustic wave - Google Patents

Abstract

PURPOSE:To obtain uniform surface acoustic wave intensity in a wide frequency range with low power consumption, by respectively connecting isolators to the high-frequency signal input sides of transducers. CONSTITUTION:High-frequency signals produced by a variable frequency oscillator 11 are distributed by a power distributor 13 after they are amplified to desired electric power by means of an amplifier 12 and inputted to transducers (IDT) 3-6 through isolators 17-20 and variable phase shifters 14, respectively. Since each IDT has its own center frequency and natural frequency band width, only one or, to the utmost, only two IDTs among the four are driven and caused to produce surface acoustic waves (SAW). From the IDTs 3, 5, and 6, from which no SAW is excited, signals are respectively reflected to the isolators 20, 18, and 17 through the variable phase shifters 14, but the isolators absorb the signals without transmitting them to the distributor 13 side. Therefore, appearance of ripples is eliminated and characteristic deterioration hardly takes place.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to optical waveguide acousto-optic technology.
.

Surface acoustic wave (Su
rface acoustic wave', hereinafter S
The present invention relates to transducer arrays (abbreviated as AW), and in particular to surface acoustic wave transducer arrays with improved drive circuits.

[Prior Art] Broadband transducers are increasingly required to be used as components of optical waveguide type AO devices such as optical deflectors, spectrum analyzers, and correlators. Several methods are already known for making broadband SAW transducers. Among them, there are multiple comb-shaped transducers with different center frequencies.
A multi-tilted SAW transducer array (MT
The advantage of the S array is that it is simple in structure and allows electrical vA adjustment after the transducer is fabricated.

Such an MTS array excites surface acoustic waves in an optical waveguide, and creates a desired AO between the guided light propagating in the optical waveguide.
In order to produce the effect, it is necessary to apply a high frequency signal with a specific frequency and power to each T. Such a high frequency signal is generally generated and amplified by an electric circuit before being input to the EDT. These electric circuits are called IDT drive circuits.

FIG. 2 is a schematic diagram showing an example of a configuration including an IDT drive circuit of a circulating surface acoustic wave transducer array.

In Fig. 2, 1 is an optical waveguide made of Ti-expanded Fh LiNbO3, etc., 2 is guided light (incident light) propagating through the optical waveguide, and 3, 4, 5, and 6 have different center frequencies. In addition, the IDTs are arranged at different inclination angles with respect to the guided light 2, 7 is a SAW that is excited from the IDT and propagates through the optical waveguide 1, and 8 is the SAW that is excited from the IDT and propagates through the optical waveguide 1.
This is the diffracted light generated by diffracting the incident light 2 by W, and 9 is the undiffracted light.

The high frequency signal generated by the variable frequency oscillator 11 is amplified to a desired power by an amplifier 12, and then distributed by a power divider 13, and then distributed by a variable phase shifter 14.
and is input to EDTs 3.4 and 5.6 via matching circuit IS. Since each strand T has a different center frequency and natural frequency bandwidth, effectively only one or at most two of the four IDTs are driven to generate a SAW. FIG. 2 depicts the case where the driving frequency of the transducer array is such that the SAW is excited only from the EDT 4. E
The 5AW7 excited by the DT4 acts as a moving diffraction grating for the incident light 2, and part of the incident light 2 undergoes Bragg diffraction and becomes the diffracted light 8, while a part passes through as is and becomes the non-diffracted light. The zero-diffracted light 8, which is 9, is separated from the undiffracted light 9 and used for signal processing, recording, and the like.

The variable phase shifter 14 compensates for the phase difference between the diffracted lights by each IDT at the crossover frequency of two adjacent IDTs, and adjusts the phase of each SAW so that the SAWs from the two IDTs strengthen each other. This is to adjust the By appropriately setting the arrangement of each IDT, the same effect can be obtained by omitting the variable phase shifter as described above (see Japanese Patent Laid-Open No. 117527/1983).

[Problem to be solved by the invention 1 In the conventional transducer array as described above,
In order to reduce the power consumption of the drive circuit, it is sufficient to reduce the insertion loss of the variable phase shifter and matching circuit, and also to reduce the rD
Regarding T, it is sufficient to reduce the electrode finger resistance and match the impedance within the specific pass frequency band with the signal source side.

However, if the electrode finger resistance in the IDT is reduced and the impedance within the pass frequency band is matched with the signal source side, the EDT
has a high impedance, and the high frequency signal input to the IDT is reflected back to the signal source side with almost no loss. The N
The radiation signal passes through the matching circuit 15 and the variable phase shifter 14, but since passive reciprocal circuits are generally used as these electrical circuits, when the insertion loss of these circuits is reduced as described above, the EDT The reflected high frequency signal from the side passes through with almost no loss and returns to the power divider 13 again, and is then sent to the amplifier 1.
2 to the distributor 13.

For example, as shown in FIG.
If the high frequency signals from the IDTs are near the center frequency of the EDT 4, the high frequency signals are outside the frequency band of the EDTs 3.5.6, so the high frequency signals reflected by these IDTs return to the power divider 13. , amplifier 12 to the distributor 1
Since the phase of the high-frequency signal that is reflected by each IDT and returns to the power divider 13, which interferes with the input signal to EDT 3, differs depending on the frequency, the frequency characteristics of the high-frequency signal that interferes with these and input to EDT 4 will be severely affected. −, a pull occurs.

FIG. 3 is a graph showing the simulation results of ripple occurrence as described above. In this simulation, there are three IDTs that make up the transducer, each IDT has five pairs of electrode fingers, and the center frequency is 360 MHz for the first IDT and 360 MHz for the second (7) IDT. 400MHz, the third IDT is 440MHz,
It is assumed that each IDT is matched to a signal source of 50Ω using an inductor, and the same effect can be obtained by omitting the use of a variable phase shifter by appropriately setting the IDT arrangement.

In FIG. 3, #l, #2. #3 is the first above
, the second and third IDTs. The broken lines show the results when the three IDTs are driven individually, and the solid lines show the results when the three IDTs are driven in parallel in the same manner as shown in FIG. 2 above. The results are shown below. From FIG. 3, it can be seen that with the drive circuit configuration as shown in FIG. 2, significant ripples occur within the frequency band due to the reflected high frequency signals from other IDTs.

When such ripples occur in the frequency characteristics of the high-frequency signal input to the IDT, the intensity of the SAW for diffracting the guided light 2 shown in FIG. 2 varies depending on the frequency, and as a result, the intensity of the diffracted light 8 It will vary depending on the frequency. Therefore, in the conventional transducer array as shown in Fig. 2, if you try to reduce the loss of each circuit part and reduce power consumption, it is difficult to respond to changes in the frequency of the high-frequency signal used to excite the 5AW7. Therefore, there was a problem that the intensity of the diffracted light 8 could not be made uniform.

Therefore, the present invention solves the problems in the conventional surface acoustic wave transducer array as described above, and provides a surface acoustic wave transformer that can obtain a similar surface acoustic wave intensity in a wide frequency range with low power consumption. The purpose of the present invention is to provide a deuser array.

[Means for Solving the Problems] According to the present invention, in order to achieve the above objects, in a surface acoustic wave transducer array comprising a plurality of surface acoustic wave transducers, A surface acoustic wave transducer array is provided, characterized in that an isolator is connected to the high frequency signal input side of each transducer.

[Example] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of a surface acoustic wave transducer array according to the present invention.

In FIG. 1, 1 is an optical waveguide made of T] diffused L 1Nb03, etc., and 2 is a guided light (
incident light). 3, 4, 5.6 are IDTs each having a different center frequency and arranged at different inclination angles with respect to the guided light 2, 7 is a SAW excited from the IDT and propagating through the optical waveguide 1, and 8 is an The SAW
9 is a diffracted light generated by diffracting the incident light 2, 9 is a undiffracted light, and 12 is an amplifier.

Isolators 17, 18, 19, and 20 are interposed between the power divider 13 and each variable phase shifter 14. The isolator is a two-opening passive circuit element that transmits electromagnetic waves traveling in one direction with almost no attenuation and absorbs most of the IT electromagnetic waves traveling in the opposite direction. (Published by Ohm Publishing), page 759].

The high frequency signal generated by the variable frequency oscillator 11 is amplified to a desired power by the amplifier 12, and then
The power is distributed by the power divider 13 and transmitted to the IDT 3 via the isolators 17 to 20 and the variable phase shifter 14, respectively.
~6 will be input. Since each IDT has a different center frequency and natural frequency bandwidth, the four IDTs
Only one or at most two IDTs of T are driven to generate a SAW. In FIG. 1, similar to FIG. 2 above, the drive frequency of the transducer array is SA.
The case where W is a frequency that is excited only from the IDT 4 is depicted. 5 excited by IDT4
The AW 7 acts as a diffraction grating that moves with respect to the incident light 2, and a part of the incident light 2 undergoes Bragg diffraction and becomes the diffracted light 8, and a part passes through as is and becomes the undiffracted light 8, which becomes the undiffracted light 8.
is separated from the undiffracted light 9 and used for No. 48 processing, recording, etc.

In the above-mentioned tree embodiment, variable phase shifters 1 are connected to IDTs 3, 5, and 6 that are not excited in the SAW, respectively.
4, the signal is reflected to isolator 20.18.17, but as mentioned above, the isolator is connected to power divider 1.
The signal is absorbed without being transmitted to the third side. Therefore, the appearance of ripples such as the solid line in the frequency characteristic graph of FIG. 3, as explained with reference to FIG.

In the above embodiments, a variable phase shifter is used to make the SAWs from the two IDTs mutually strengthen at the crossover frequency, but in the present invention, such a variable phase shifter is not used. It is also possible to achieve the same effect by appropriately setting the arrangement of each T as described in the above-mentioned Japanese Patent Application Laid-Open No. 58-117527. In this case, in the above embodiment, the arrangement may be determined in consideration of the amount of phase shift in each of the isolators 17 to 20 so that the diffracted lights are strengthened at the crossover frequency of each IDT.

Furthermore, although the above embodiment shows a transducer array with four IDTs, in the present invention
Of course, the number of T's is not limited to four, and the present invention can be similarly applied to any transducer array having a plurality of IDTs.

Further, although FIG. 1 above shows an embodiment in which a variable phase shifter is provided between an isolator and an IDT, the variable phase shifter may also be provided between a power divider and an IDT. .

Furthermore, although FIG. 1 above shows a configuration in which the IDT and the variable phase shifter are directly connected, if the output impedance of the drive circuit and the input impedance of the IDT are different, the configuration shown in FIG. 2 above may be used. It is also possible to insert a matching circuit to reduce the irregular gold phase.

[Effects of the Invention] According to the present invention as described above, even when a high frequency signal with a frequency outside the fixed frequency band of the IDT is input to the IDT, the reflected signal from the IDT is absorbed by the isolator and other Since there is no interference with the input high-frequency signal to the IDT, it is possible to suppress the appearance of ripples in the frequency characteristics of the SAW excited from the IDT, and thus the SAW intensity can be reduced over a wide frequency range with low power consumption.
A similar surface acoustic wave transdeuser array can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a surface acoustic wave transducer array according to the present invention. FIG. 2 is a schematic diagram showing an example of a conventional surface acoustic wave transducer array. FIG. 3 is a graph showing simulation results of ripple occurrence in a surface acoustic wave transducer array. 1: Optical waveguide, 2 Bi-infrared light, 3-6: IDT, ? ': SAW, 8: Diffracted light, 9: Non-diffracted light, 12: Amplifier, 17-20 Core isolator-0 Agent Patent attorney Johei Yamashita Figure 1 Figure 2

Claims (4)

[Claims] (1) A surface acoustic wave transducer array comprising a plurality of surface acoustic wave transducers, characterized in that an isolator is connected to the high frequency signal input side of each transducer. Array. (2) The surface acoustic wave transducer array according to claim 1, wherein a high frequency signal emitted from a single variable frequency oscillator and distributed by a distribution means is inputted to each isolator. (3) The surface acoustic wave transducer array according to claim 1, which has a variable phase shifter before or after each isolator. (4) The surface acoustic wave transducer array according to claim 1, wherein impedance matching means is interposed between each transducer and its driving means.