JPS6353517A - Transducer array for surface acoustic wave - Google Patents

Abstract

PURPOSE:To obtain uniform surface acoustic wave intensity over a wide frequency range with low power consumption, by successively transmitting high-frequency signals to a transducer (IDT), whose natural frequency band matches the frequency of the signals, by means of circulators. CONSTITUTION:High-frequency signals produced by a variable frequency oscillator 11 are inputted to the 1st circulator 17 from an opening A of the circulator 17 after they are amplified by an amplifier 12 and further inputted to an IDT 6 from another opening B of the circulator 17 through the 1st variable phase shifter 14. When the frequency of the inputted high-frequency signals is within the natural frequency band of the IDT 6, surface acoustic waves (SAW) are excited from the IDT 6. When the frequency is outside the band, the signals are reflected by the IDT 6 and transmitted to the opening B of the circulator 17. Then the signals are inputted to the 2nd circulator 18 from the next opening C. Thus, the high-frequency signals from the amplifier 12 are transmitted to an IDT, whose natural frequency bands match the frequency of the signals, by means of the circulators in an almost no-loss state and converted into elastic surface waves.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an optical waveguide type combination! optical
.

Surface acoustic wave (Su
rface acoustic wave, hereinafter SA
The present invention relates to transducer arrays (referred to as W), 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. A plurality of comb-shaped transducers (with different center frequencies)
A multiple ◆tilted φSAW transducer array (MTS) is a multiple tilted φSAW transducer array (MTS
The advantage of this array is that it has a simple structure and allows for electrical 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 waveguide light propagating in the guide 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 high frequency signals are generally generated and amplified by an electrical circuit before being input to the IDT. These electric circuits are called IDT drive circuits.

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

In FIG. 2, 1 is a leading waveguide made of Ti-diffused LiNbO3, etc., 2 is a guided wave (incident light) propagating through the leading waveguide, and 3, 4, and 5.6 each have a different center frequency. 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 a diffracted light generated when the incident light 2 is diffracted by the SAW. and
9 is 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 the IDTs 3, 4, 5.6 via the matching circuit 15. Since each IDT has a different center layer wave number 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 drive frequency of the transducer array is such that the SAW is excited only from IDT 4. I
The 5AW7 excited by the DT4 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 9. The diffracted light 8 is separated from the undiffracted light 9 and used for signal processing, recording, etc.

Note that 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 changes the phase of each SAW so that the SAWs from the two IDTs strengthen each other. It is something to be adjusted. 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
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 rDT is reduced and the impedance within the pass frequency band is matched with the signal source side, the IDT
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 reflected signal passes through the matching circuit 15 and the variable phase shifter 14, but since passive reciprocal circuits are generally used as these electric circuits, when the insertion loss of these circuits is reduced as described above, the above The reflected high frequency signal from the IDT 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 signal from the IDT 4 is near the center frequency of the IDT 4, the high frequency signal is outside the frequency band of the IDT 3.5.6, so the high frequency signal reflected by these IDTs is transmitted to the power distribution device 3. Return, from the 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 IDT 3, differs depending on the frequency, the frequency characteristics of the high-frequency signal that interferes with these and input to IDT 4 has severe ripples. occurs.

FIG. 3 is a graph showing the simulation results of ripple occurrence as described above. In this simulation, there are three IDTs making up the transducer, each IDT has five pairs of electrode fingers, and the center frequency is 360 MHz for the first IDT and 400 MHz for the second IDT.
M)iz, the third IDT is 440MH2, and each ID
It is assumed that each T is matched to a signal source of 50Ω using an inductor, and that the same effect is 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 Problem E] According to the present invention, in order to achieve one or more of the following objects, in a surface acoustic wave transducer array comprising a plurality of surface acoustic wave transducers, A first opening of a circulator is connected to the high frequency signal input side of each transducer, and a second opening of each circulator following the first opening is connected to the next circulator. A third opening following the second opening of the circulator is connected to the second opening of the circulator.
The high frequency signal source side is connected to the third opening following the second opening of the circulator, and the first opening of the last circulator is connected to
A surface acoustic wave transducer array is provided, characterized in that a high frequency signal absorbing means is connected to a second aperture following the aperture of the surface acoustic wave transducer.

[Embodiment 1] Hereinafter, a specific embodiment 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 Ti-diffused LiNbO3, etc., 2 is guided light (incident light) propagating through the leading waveguide, and 3, 4, and 5.6 each have a different center frequency. 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 a diffracted light generated when the incident light 2 is diffracted by the SAW. and
9 is a undiffracted light, and 12 is an amplifier.

Circulators 17, 18 and 19, 20 are interposed between the amplifier 12 and each variable phase shifter 14. The circulator is generally a network having n apertures, from a first aperture to an n-th aperture, with an input aperture (the first I3
When a reflection-free end is connected to each aperture other than i1 port), the input signal from the input aperture is transmitted to the second aperture in the next order with almost no reflection or loss, and the input signal from the second aperture is similarly transmitted. The signal is transmitted to the third opening, and in the same manner (3rd opening → 43rd J1 opening), Kai-Kenken (3rd opening → 1t31 opening)
0) [See page 760 of "Electronic Communication Handbook J (Tg, edited by the Communication Society, published by Ohmsha, 1984)]" The above circulators 17 to 20 are all circulators with n=3.0 The SAW used in the surface acoustic wave optical deflector generally has a frequency of 100100-
According to the above literature, if a lumped constant circulator is used in this frequency band, it is possible to handle a power of several tens of W with an insertion loss of about 0.5 dB. It is fully effective.

The high frequency signal generated by the variable frequency oscillator 11 is amplified to a desired power by the amplifier 12, and then
The signal is inputted to the first circulator 17 from the opening A thereof, and is inputted from the next opening B of the circulator to the IDT 6 via the variable phase shifter 14. If the input high frequency signal is within the natural frequency band of the IDT 6, the SAW is excited from the IDT, but if not, the SAW is excited as shown in FIG.
is not excited, and the input signal is reflected by the IDT and passed through the variable phase shifter 14 to the circulator 17.
is transmitted to aperture B of. The signal is then inputted to the second circulator 18 from the next opening C of the circulator. Signal transmission is performed in the circulator 18 in the same manner as in the circulator 17, and the input signal is inputted to the IDT 5 via the variable phase shifter 14. The input high frequency signal is the I
If it is within the natural frequency band of DT5, the SAW is excited from the IDT; otherwise, as shown in FIG. 1, the SAW is not excited and the input signal is reflected by the IDT. The signal is transmitted to the circulator 18 via the variable phase shifter 14, and then input to the third circulator 19. Signal transmission is performed in the circulator 19 in the same manner as in the case of the circulator 17, and the input signal is transmitted to the variable phase shifter 1.
The data is input to the IDT 4 via step 4. When the input high frequency signal is within the natural frequency band of the IDT 4, the first
As shown in the figure, 5AW7 is excited from the IDT, but if not, the SAW is not excited and the input signal is reflected and returns to the circulator-19, and then to the fourth circulator-20. The same operation is performed in the circulator as well. Note that a resistor R is connected to the last opening of the fourth and final circulator 20. The resistor is for absorbing an input high frequency signal when the frequency of the signal is not within the natural frequency band of either IDT.

As described above, the high frequency signal from the amplifier 12 is transmitted by the circulator almost without loss to an IDT whose frequency falls within the natural frequency band, and is converted into a SAW at the IDT. In FIG. 1, similar to FIG. 2 above, the drive frequency of the transducer array is SAW.
The case where the frequency is such that it is excited only from the IDT 4 is illustrated. 5A excited by IDT4
W7 acts as a diffraction grating that moves with respect to the incident light 2, part of the incident light 2 undergoes Bragg diffraction and becomes diffracted light 8, and a part passes through as is and becomes undiffracted light 9.0 Diffracted light 8 becomes non-diffracted light 8. It is separated from the diffracted light 9 and used for signal processing, recording, etc.

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. A similar effect can also be achieved by appropriately setting the arrangement of each IDT as described in the above-mentioned Japanese Patent Laid-Open No. 58-117527. In this case, in the above embodiment, circulators 17 to 20 and ID
The arrangement may be determined in consideration of the amount of phase shift in each of T3 to T6, 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.

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, a high frequency signal is routed through a circulator up to an IDT whose frequency falls within the natural frequency band.
The SAW is excited from the IDT by being sequentially transmitted, and the reflected signal does not interfere with the input high-frequency signal, so it is possible to suppress the appearance of ripples in the frequency characteristics of the SAW excited from the IDT. I can,
Thus, the SAW can be used over a wide frequency range with low power consumption.
A surface acoustic wave transducer array with similar intensities 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. l: leading wavepath, 2: incident light, 3 to 6: IDT, 7: SAW, 8: diffracted light,
9: Non-diffracted light, 12: Amplifier. 17-20: Circulator. Agent Patent Attorney Yohei Yamacho Figure 2

Claims (3)

[Claims] (1) In a surface acoustic wave transducer array having a plurality of surface acoustic wave transducers, a first opening of a circulator is connected to the high frequency signal input side of each transducer, and the first opening of each circulator is connected to the high frequency signal input side of each transducer. The second opening following the first opening has a third opening following the second opening of the next circulator.
However, the high-frequency signal source side is connected to the third opening in the order following the second opening of the first circulator, and the third opening in the order following the second opening of the last circulator is connected. A surface acoustic wave transducer array, characterized in that a high frequency signal absorbing means is connected to the second opening of the surface acoustic wave transducer array. (2) The surface acoustic wave transducer array according to claim 1, wherein the circulator is a lumped constant circulator. (3) The surface acoustic wave transducer array according to claim 1, wherein impedance matching means is interposed between each transducer and its driving means.