JPH02222931A - Optical deflector - Google Patents

Abstract

PURPOSE:To prevent a deflected light beam having varying in light intensity owing to variation in the intensity of surface acoustic waves which are excited by an inter-digital electrode couple by interposing a resistance attenuator between the inter-digital electrode couple and a driver which applies a high-frequency AC voltage to the electrode couple. CONSTITUTION:An optical deflector 10 has an optical waveguide 12 which is formed on a substrate 11, a converging diffraction grating(FGC) 13 for light beam incidence which is formed on the optical waveguide 12, an FGC 14 for light beam projection, and 1st and 2nd tilted finger chirped IDTs 17 and 18 which generate the surface acoustic waves 15 and 16 traveling crossing the optical path of waveguide light traveling between the FGCs 13 and 14. Then, the resistance attenuator 22 is interposed between a high-frequency amplifier 19 and tilted finger chirped IDTs 17 and 18. In this case, a reflected wave which returns to the high-frequency amplifier 19 of the lowest order and passes through the resistance attenuator 22 twice in total, so the wave is attenuated greatly. Consequently, fluctuations of the surface acoustic waves due to the reflected light are securely reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical deflector that generates surface acoustic waves in an optical waveguide and deflects guided light by the diffraction action of the surface acoustic waves. be.

(Prior Art) Conventionally, as shown in Japanese Patent Application Laid-open No. 81-183828, light is incident on an optical waveguide made of a material capable of propagating surface acoustic waves, and the guide propagates within the leading waveguide. A surface acoustic wave is generated in the direction intersecting the wave light, the guided light is Bragg diffracted by the surface acoustic wave, and the diffraction angle (deflection angle) of the guided light is continuously changed by continuously changing the frequency of the surface acoustic wave. A light deflection device that changes the direction of the light is known.

On the other hand, as shown in Japanese Unexamined Patent Publication No. 1-25015, for example, similar to the above-mentioned optical deflection device, a surface acoustic wave whose frequency changes continuously is propagated in a leading waveguide to measure the wavelength of a light beam. Spectrum analyzers have also been proposed. In the future, the Subekdrum Analyzer will be able to detect that when a light beam guided through a leading waveguide is diffracted by a surface acoustic wave, the diffraction angle changes depending on the surface acoustic wave frequency as described above, and also changes depending on the wavelength of the light beam. The wavelength of the light beam is determined based on the surface acoustic wave frequency when the light beam is diffracted at a predetermined angle.

As described above, in an optical deflector that continuously deflects a light beam or an optical deflector that constitutes an optical spectrum analyzer, the surface acoustic wave generating means is usually a pair of interdigitated electrodes (intersection) in which the spacing between electrode fingers changes. -D 1g1
tal transducer (hereinafter referred to as IDT) and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the IDT. I
More specifically, as a DT, a tilted finger chirp I DT (Tilted-Fb+ger Chir
ped I DT), so-called curved finger EDT in which the electrode finger spacing changes continuously and each electrode finger has an arc shape,
Furthermore, multiple tilted IDTs have a plurality of IDTs with different electrode finger spacings arranged at different inclinations.
DT (Multfple Tilted I DT) or the like is used. Further, the above-mentioned driver is generally composed of a high frequency amplifier, a frequency sweeper, and the like.

(Problem to be solved by the invention) By the way, when using the IDT or driver as described above, periodic intensity fluctuations (
It is recognized that fluctuations are likely to occur. That is, since the IDT and high frequency amplifier used for the above purpose are designed for a high frequency band, the impedance may deviate greatly from the impedance (50Ω) of a normal high frequency system. Therefore, reflection of the high frequency signal occurs between the high frequency cable and the IDT, and the reflected wave returns to the high frequency amplifier. Since this amplifier is also designed for a high band as described above, several percent to several tens of percent of the high frequency signal is reflected and propagated to the EDT side again. Therefore, the reflected wave heading toward the EDT interferes with the high frequency signal (progressive wave) originally output from the high frequency amplifier, causing the high frequency intensity to fluctuate.

When the high frequency intensity input to the IDT fluctuates in this way, the intensity of the surface acoustic wave emitted from the IDT similarly fluctuates, and the diffraction efficiency of guided light by the surface acoustic wave fluctuates. If this happens, the amount of diffracted light, that is, the intensity of the deflected light beam will fluctuate. Therefore, for example, when an optical deflector is used in an optical scanning recording device or an optical scanning reading device, problems such as uneven density in the recorded image and a decrease in reading accuracy occur. This will lead to a decrease in the accuracy of spectrum analysis.

In order to prevent the above-mentioned fluctuations in the surface acoustic waves, it has been considered to insert an isolator, which is a non-reciprocal element, between the IDT and the driver, as shown in Japanese Patent Application Laid-Open No. 83-53516, for example. ing. However, in the optical deflector described above, the frequency of the surface acoustic wave, that is, the frequency of the alternating voltage applied to the IDT, is approximately several hundred MHz to 2 GH2, so the wavelength of the microwave passing through the isolator is relatively long. Therefore, it is inevitable that the isolator becomes larger. In addition, isolators in the above frequency bands are rarely used, so
It is expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical deflector that can be formed compactly and inexpensively and that can prevent the above-mentioned fluctuation from occurring.

(Means for Solving the Problems) An optical deflector according to the present invention includes a leading wavepath as described above and a surface acoustic wave generating means, and the surface acoustic wave generating means is an ED in which the spacing between electrode fingers is changed.
An optical deflector comprising a T and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the IDT, characterized in that a resistive attenuator is inserted between the driver and the IDT. It is something to do.

(Function) When a resistive attenuator as described above is provided, even the lowest-order reflected wave returning to the high-frequency amplifier passes through the resistive attenuator twice in total, and is therefore significantly attenuated. Therefore, fluctuations in the surface acoustic waves caused by this reflected wave are significantly reduced.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an optical deflector 10 according to an embodiment of the present invention. This optical deflector 1O includes an optical waveguide 12 formed on a substrate 11, and a condensing diffraction grating for light beam incidence formed on this leading waveguide 12.
rating coupler (hereinafter referred to as FGC) 13, a light beam output FGC 14, and these FGs.
first and second inclined finger chirve IDTs 17.18 that respectively generate surface acoustic waves 15.1B that travel in a direction intersecting the optical path of the guided light that travels between C13 and C14, and the surface acoustic waves 15.16. It has a high frequency amplifier 19 that applies a high frequency alternating voltage to the inclined finger chirp IDTs 17 and 18 to generate the voltage, and a sweeper 20 that continuously changes (sweeps) the frequency of the voltage. and the high frequency amplifier 19 and the first and second inclined finger chirve IDs.
A resistance attenuator 22 is inserted between T17.1g.

In this embodiment, as an example, the substrate 11 has LiNb0
．． The leading waveguide 12 is formed by using a wafer and providing a Ti diffusion film on the surface of the wafer. Note that substrate 1
Other than that, a crystalline substrate made of sapphire, Sl, etc. may be used as the material. Further, the guide waveguide 12 is not limited to the above-mentioned Ti diffusion, but may also be formed by sputtering, vapor depositing, or the like other materials on the substrate 11. However, this guide wave path 12 is formed from a material such as the above-mentioned Ti diffusion film that allows surface acoustic waves to propagate, which will be described later. Further, the guiding waveguide may have a laminated structure of two or more layers.

The deflected light beam L is emitted toward the FCC 13 from a light source 21 such as a semiconductor laser, for example.

This light beam L (divergent beam) is made into a parallel beam by the FGC 13 and then taken into the optical waveguide 12,
The wave is guided within the guide wavepath 12. This guided light L1 is
Due to the acousto-optic interaction with the first surface acoustic wave 15 emitted from the inclined finger chirp IDT 17, the light is diffracted (Bragg diffraction) as shown.

The guided light L1 diffracted and deflected in this way is converted into a second surface acoustic wave 18 emitted from the second tilted finger chirp IDT 18.
Due to the acousto-optic interaction with the beam, it is diffracted in a direction that further amplifies the above-mentioned deflection (see Figure 2). As described above, since the frequency of the alternating voltage applied to the first inclined finger chirp IDT 17 changes continuously, the frequency of the first surface acoustic wave 15 changes continuously. As is well known,
Since the deflection angle of the guided light L2 diffracted by the surface acoustic wave 15 is approximately proportional to the frequency of the surface acoustic wave 15, as the frequency of the surface acoustic wave 15 changes as described above, the guided light L2 changes as shown by arrow A. Continuously deflect as shown. This guided light L2 is then deflected by the second surface acoustic wave te, but since the frequency of the second surface acoustic wave 1B also changes continuously like the first surface acoustic wave 15, the second surface acoustic wave te The guided light L3 after passing through the surface acoustic wave 1G is continuously and largely deflected as shown by arrow B. This guided light L3 is F
The light is emitted to the outside of the leading waveguide 12 by the GC 14, and is focused at one point by its condensing action.

As described above, in this device, the guided light L1 is diffracted and deflected twice, so the deflection angle range Δδ of the guided light L3 can be extremely large. In other words,
When the frequencies of the surface acoustic waves 15 and 16 are the maximum frequency and the minimum frequency, the traveling directions of the guided wave L3 diffracted twice are the directions shown by ■ and ■゛ in Fig. 2, respectively, and the difference between them is the deflection angle range. Δδ. The deflection angle range obtained when the guided light is diffracted and deflected twice in this way is described in detail in, for example, Japanese Patent Application Laid-Open No. 138028/1982.

Next, the function of the resistance attenuator 22 will be explained.

High frequency signal (alternating voltage) input to 1DT17.18
In this case, fluctuation occurs due to the influence of the reflected waves mentioned above.

However, in this device, a resistive attenuator 22 is inserted between the IDTs 17 and 18 and the high frequency amplifier 19, so for example, if this resistive attenuator 22 has an attenuation rate of 6 dB, first the IDT1? , 18, passes through the resistive attenuator 22 again, and returns to the high frequency amplifier 19 side, resulting in a total isolation of 12 dB. Therefore, from the high frequency amplifier 19 to the IDT1
7.18 The intensity fluctuation (fluctuation) caused by the interference of the reflected wave with the high frequency signal (traveling wave) that excites the surface acoustic wave, which is directly input to the surface acoustic wave, becomes extremely low level.
Naturally, the intensity fluctuations of the surface acoustic waves 15,18 are also reduced. If the intensity fluctuation of surface acoustic wave 15.1B is suppressed in this way,
The diffraction efficiency of the guided light by the surface acoustic waves 15 and I6 is also stabilized, and fluctuations in the amount of light of the deflected output beam L° are suppressed.

Note that in order to suppress the occurrence of the above-mentioned fluctuation to a level that causes no practical problems, it is generally sufficient to ensure isolation of about 10 dB.

In addition, FIG. 3 shows how the waveguide light diffraction efficiency changes due to the surface acoustic waves 15 or 16 using the resistive attenuator 2 described above.
2 is schematically shown using a solid line and a broken line, respectively. When the resistance attenuator 22 is provided,
The reason why the diffraction efficiency decreases overall is that the traveling wave is also attenuated by passing through the resistive attenuator 22.

Therefore, in order to keep the diffraction efficiency high even after providing the resistive attenuator 22, the gain of the high-frequency amplifier 19 should be set high in consideration of the attenuation caused by the resistive attenuator 22.

In the embodiment described above, the guided light is diffracted twice, but the present invention is also applicable to cases where the guided light is diffracted only once or three times.

Further, in the above embodiment, the inclined finger chirve I DT
17.18 is used, but the present invention is applicable to curved finger IDTs and multiple tilted IDTs as described above.
The present invention is similarly applicable to the case where surface acoustic waves are generated using T.

(Effects of the Invention) As explained in detail above, in the optical deflector of the present invention,
By inserting a resistance attenuator between the intersecting comb-shaped electrode pair and a driver that applies a high-frequency alternating voltage to it, the surface acoustic waves excited from the intersecting comb-shaped electrode pair fluctuate in intensity, causing the light of the deflected beam to change. Fluctuations in strength can be reliably prevented. Therefore, when the optical deflector of the present invention is applied to, for example, an optical scanning device, precise scanning becomes possible, and when applied to the aforementioned optical spectrum analyzer,
Accuracy of spectrum analysis can be improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic perspective view showing an embodiment of the device of the present invention, Fig. 2 is a plan view showing an enlarged part of the above-mentioned embodiment device, and Fig. 3 is the effect of diffraction efficiency-chemotaxis in the present invention. FIG. lO... Optical deflector 11... Substrate 12
...Optical waveguide 13...FCC for light beam incidence 14...FCC for light beam output 15...'th surface acoustic wave 1B...Second surface acoustic wave 17...t? 41 inclined finger chirve IDT18・
...Second inclined finger chirp IDT19...High frequency amplifier 20...Sweeper 21...Light source
22... Resistance attenuator L1... Guided light L2 before entering the first surface acoustic wave... Guided light L3 that has passed through the first surface acoustic wave... Second surface acoustic wave Passed waveguide light 5L cane

Claims (1)

[Claims] An optical waveguide formed of a material through which surface acoustic waves can propagate, and a surface elastic material that propagates in a direction intersecting the optical path of the guided light traveling within the optical waveguide and diffracts and deflects the guided light. surface acoustic wave generating means for generating waves in the optical waveguide; the surface acoustic wave generating means includes a pair of intersecting comb-shaped electrodes in which the electrode finger spacing changes; and a frequency in the electrode pair that changes continuously. What is claimed is: 1. An optical deflector comprising: a driver for applying a high-frequency alternating voltage; and a resistive attenuator inserted between these drivers and a pair of interdigitated electrodes.