JPH02930A - Optical deflecting device - Google Patents

Abstract

PURPOSE:To obtain a wide deflection angle range by further diffracting a light beam which is diffracted once with a surface acoustic wave by using another surface acoustic wave. CONSTITUTION:A converging diffraction grating (FGC) 13 for light beam incidence, an FGC 14 for light beam projection, and 1st and 2nd curved interdigital electrode couples (curved finger IDT) 17 and 18 are formed on an optical waveguide 12. Further, this device has a high frequency amplifier 19 which applies a high-frequency AC voltage to the curved finger IDTs 17 and 18 so as to generate the surface acoustic waves 15 and 16 and a voltage-controlled oscillator 20 which varies (sweeps) the frequency of the voltage. Consequently, the waveguide light which is deflected with the 1st surface acoustic wave 15 is deflected again with the 2nd surface acoustic wave 16, so the wide deflection angle range is obtained on the whole without setting the frequency bands of the 1st and 2nd surface acoustic waves so wide.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical deflection device that generates surface acoustic waves in an optical waveguide and deflects guided light by the diffraction action of the surface acoustic waves. The present invention relates to an optical deflection device that cancels the cylindrical lens effect of the surface acoustic waves and obtains a wide deflection angle range by deflecting the guided light twice by two surface acoustic waves.

(Prior Art) Conventionally, as shown in Japanese Patent Application Laid-Open No. 183828, light is incident on an optical waveguide made of a material through which surface acoustic waves can propagate, and the guide propagates within the optical 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. Such optical deflection devices include, for example, mechanical optical deflectors such as galvanometer mirrors and polygon mirrors, EOD (electro-optic optical deflectors), and A
Compared to optical deflectors that use optical deflection elements such as OD (acousto-optic optical deflectors), they have the advantage of being smaller and lighter, and are highly reliable as they do not have mechanical moving parts. .

(Problem to be solved by the invention 'XJ) By the way, when the frequency of the surface acoustic wave is continuously changed as described above, the surface acoustic The wavelength of the wave 41 is no longer constant across the beam width direction. In other words, Figure 4 (1
In the example shown in ), the surface acoustic wave wavelength is the minimum at the guided light end on the upper side of the figure, and the surface acoustic wave wavelength becomes larger toward the lower side. The opposite is true in the example of FIG. If the magnitude of the wave number vector is 1×1, then IK I −2π/A (Δ is the wavelength of the surface acoustic wave). Therefore, the smaller the wavelength of the surface acoustic wave, the larger the diffraction angle of the guided light. Therefore, in the example of FIG. 4(1), the diffracted waveguide light 40 converges, and in the example of FIG. 4(2), the diffracted waveguide light 40 diverges.

The above is called a cylindrical lens effect (especially static cylindrical lens effect) caused by surface acoustic waves, but there are also lens effects caused by other factors. In other words, as a means to generate surface acoustic waves whose frequency changes continuously in an optical waveguide, a pair of crossed comb-shaped electrodes (
IDT: Intcr D Igltal Tra
nsducer) and a voltage controlled oscillator (VCO: Voltag) that applies a frequency-swept alternating voltage to the IDT.
e Controlled 0scillat.

r) and a high frequency amplifier, etc., but this VC
Since the input terminal versus output frequency characteristic of O cannot be completely linear, the frequency change characteristic of the surface acoustic wave becomes nonlinear. The diffraction angle of the guided light varies in its width direction also due to this nonlinearity, resulting in a cylindrical lens effect. This lens effect is generally referred to as a dynamic cylindrical lens effect, and is local compared to the static cylindrical lens effect described above, and both of these cylindrical lens effects appear in a superimposed form in the guided light after deflection.

When the cylindrical lens effect caused by surface acoustic waves as described above occurs, the deflected light beam becomes a converging beam or a diverging beam, so various methods have been proposed to correct this lens effect. .

One such method is to optically correct the diffracted and deflected light beam by passing it through a correction lens such as a waveguide lens, but in this case, the deflection speed of the previous beam is Since a correction lens is designed accordingly, there is a problem in that the deflection speed cannot be changed. Furthermore, in this case, it is extremely difficult to design a correction lens that can also correct the dynamic cylindrical lens effect described above.

Furthermore, a method of electrically correcting the dynamic cylindrical lens effect described above has also been considered. In this method, the nonlinearity of the input voltage vs. output frequency characteristic of vCO mentioned above is investigated in advance, and a characteristic that cancels out this nonlinearity is found in VCO.
It is applied to the input voltage signal to the CO. However, the circuit that performs this electrical correction is expensive, so
If such correction is performed, the cost of the optical deflection device will increase significantly.

On the other hand, the above-described optical deflection device also has a problem in that it is difficult to obtain a large deflection angle.

In other words, in an optical deflection device using this optical waveguide, the optical deflection angle is approximately proportional to the frequency of the surface acoustic waves, so in order to obtain a large deflection angle, it is necessary to increase the frequency of the surface acoustic waves to an extremely high value. It will be necessary to change. Furthermore, in addition to changing the frequency of the surface acoustic waves over a wide band in this way, in order to satisfy the Bragg condition, the traveling direction of the surface acoustic waves is continuously changed (steering). It is necessary to control the angle of incidence on the

In order to meet the above requirements, for example,
-183ft26, multiple interdigitated electrode pairs (IDT: InterD 1g1L) generate surface acoustic waves whose frequencies change in different bands.
An optical deflection device has been proposed in which IDTs (transducers) are arranged so that the surface acoustic waves are generated in different directions, and each IDT is operated by switching.

However, the optical deflection device with the above configuration has a problem in that the diffraction efficiency decreases around the crossover frequency of the surface acoustic waves emitted by each IDT, so the amount of light of the deflected light beam fluctuates depending on the deflection angle. occurs.

Even with the above configuration, the IDT having a portion with a high deflection angle must be configured to generate surface acoustic waves of extremely high frequency. This point will be explained below using a specific example. When the incident angle of the guided light with respect to the traveling direction of the surface acoustic wave is θ, the deflection angle δ of the guided light due to the acousto-optic interaction between the surface acoustic wave and the guided light is δ−2θ. If the wavelength and effective refractive index of the guided light are λ and Ne, and the wavelength, frequency, and velocity of the surface acoustic wave are A and fSv, respectively, then 2θ-25ln-1 (λ/2Ne-A) λ/Ne ・
Δ−λ・f/Ne−■・・・(1). Therefore, the deflection angle range Δ(2θ) is Δ(2θ)・−・
Δ f λ /Ne ・V. Here, for example, λ-0.78 μm, Ne ” 2.2, v =
Deflection angle range Δ(2θ)−1 as 3500TrL/s
To obtain o', the frequency range of the surface acoustic wave, that is, the frequency band of the high frequency applied to the IDT, Δf = 1.
72 GHz is required. If this frequency band is set to one octave so as not to be affected by the second-order diffracted light, the center frequency fo = 2.57 GHz.

The maximum frequency is f2-3.43 GHz. The period of IDT that obtains this maximum frequency f2 is A-1.02 am,
The line width of the IDT electrode finger is W-Δ/4-0.255 μm.

In the photolithography method and electron beam lithography, which are common techniques for forming IDTs, the current line width limits are approximately 0.8 μm and 0.5 μm, respectively, and therefore IDTs with extremely small line widths as described above. is difficult to realize. Furthermore, even if such a fine IDT could be formed in the future, a driver that generates a high frequency of about 3.43 GHz would be difficult to manufacture and extremely expensive, and such a fine IDT would require a high voltage. becomes difficult to apply. Furthermore, if the frequency of the surface acoustic wave is increased as described above, the wavelength will naturally become shorter, so the surface acoustic wave will be more easily absorbed by the optical waveguide, resulting in a decrease in diffraction efficiency.

On the other hand, the literature
son on C1rcuits and 5yst
eIIls, vol, CAS-2[i, N
.

12, p1072 [Gulded-Wave
AcoustoopticBragg Module
ators f'or Wide-Band Int
egrated 0ptic Communicat
ions and Signal Pr.

ecssing] by C,S,TSA
As described above, in I, a plurality of IDTs are not operated by switching, but one IDT is configured as a curved finger IDT in which the electrode finger line width changes continuously and each electrode finger has an arc shape. An optical deflection device is shown in which the frequency and traveling direction of surface acoustic waves are continuously changed over a wide range using an IDT. In such a configuration, the problem of the amount of light beam fluctuating depending on the deflection angle as described above can be solved, but the problem remains that the frequency of the surface acoustic wave must be set extremely high. , which causes exactly the same problem as described above.

Therefore, the present invention does not cause the above-mentioned fluctuations in the light intensity of the light beam, can obtain a wide deflection angle range without setting the frequency of the surface acoustic wave extremely high, and can achieve the above-mentioned cylindrical lens effect with a simple configuration. It is an object of the present invention to provide an optical deflection device that can be corrected and also has a variable deflection speed.

(Means and Effects for Solving the Problems) The optical deflection device according to the present invention allows guided light to travel within an optical waveguide formed of a material through which surface acoustic waves can propagate, as described above. In an optical deflection device configured to diffract and deflect using elastic waves, a first surface acoustic wave that generates in an optical waveguide a first surface acoustic wave that propagates in a direction intersecting the optical path of the guided light and diffracts and deflects the guided light; a surface acoustic wave generating means, and a second surface acoustic wave that travels in a direction intersecting the optical path of the guided wave diffracted as described above and diffracts and deflects the guided light in a direction that further amplifies the deflection due to the diffraction. and second surface acoustic wave generating means for generating in the optical waveguide, and these first and second surface acoustic wave generating means are arranged such that their respective surface acoustic wave generating portions are opposite to each other with the guided light in between. The wave number vectors of the guided light before and after being diffracted by the first surface acoustic wave are lkl and Ik2, respectively, and the wave number vector of the guided light diffracted by the second surface acoustic wave is 3. When the wave number vectors of the first and second surface acoustic waves are IK, , IK2, the frequency and traveling direction of the first and second surface acoustic waves are continuously changed while satisfying the following conditions. It is characterized in that it is formed so as to

The above-mentioned first and second surface acoustic wave generating means are, for example, curved interdigitated comb-shaped electrode pairs in which the electrode finger interval changes stepwise and the direction of each electrode finger changes stepwise.
-Finger Chirped I DT) and a driver which is composed of the above-mentioned VCO, high frequency amplifier, etc. and applies an alternating voltage whose frequency changes continuously to this electrode pair. In that case, the inclined finger chirve IDT corresponds to the above-mentioned surface acoustic wave generation portion, and these IDTs are arranged on opposite sides of the guided light.

In the above configuration, since the guided light that has been deflected by the first surface acoustic wave is deflected again by the second surface acoustic wave, the frequency bands of each of the first and second surface acoustic waves are set to be very wide. Even without this, a wide deflection angle range can be obtained as a whole.

Further, in the above configuration, in order to satisfy the above-mentioned (2), the frequencies of the first and second surface acoustic waves are controlled so that they both gradually increase or both gradually decrease. If the surface acoustic wave generating parts of the second surface acoustic wave generating means are arranged on opposite sides of the guided light, one of these surface acoustic waves will be generated as shown in (1) in FIG. The wavelength of the other surface acoustic wave changes as shown in (2) in Figure 4.In other words, one of the first and second surface acoustic waves is a cylindrical wave that converges the guided light. One exhibits a lens effect, and the other exhibits a cylindrical lens effect that diverges the guided light, so the respective static lens effects cancel each other out.

When the first and second surface acoustic wave generating means are composed of the above-mentioned inclined finger chirp IDT and a driver that applies a frequency-swept alternating voltage to this IDT, both IDTs are driven by a common driver. It is preferable to do so. Then, by appropriately determining the installation positions of both IDTs with respect to the guided light, the wavelength distribution state of the first surface acoustic wave in the width direction of the guided light and that of the second surface acoustic wave can be adjusted. A substantially opposite relationship can be established in the wave width direction. If this is the case, the static cylindrical lens effect described above will be almost completely canceled out, and the guided light after being diffracted twice will become almost completely parallel light.

Also, if both IDTs are driven by a common driver,
The respective dynamic cylindrical lens effects caused by the first and second surface acoustic waves are also almost turned over in the waveguide width direction, and this dynamic cylindrical lens effect can also be canceled out.

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

FIG. 1 shows an optical deflection device according to an embodiment of the present invention. This optical deflection device 10 includes an optical waveguide 12 formed on a substrate n, and a focusing diffraction grating for light beam incidence formed on the optical waveguide 12.
(hereinafter referred to as FGC) 13, a light beam output FGC 14, and a surface acoustic wave 15, 16 that travels in a direction intersecting the optical path of the guided light that travels between these FGCs 13 and 14. The first and second curved interdigital comb-shaped electrode pairs (T
ilted -Finger Chirped I
nter Digital Transducer
, hereinafter referred to as curved finger IDTs) 17.18, a high frequency amplifier 19 that applies a high frequency alternating voltage to these curved finger IDTs 17.18 in order to generate the surface acoustic waves 15.1B, and VC02G, which is continuously changed (backward), is shown in white.

In this embodiment, as an example, the substrate 1
The optical waveguide 12 is formed by using three wafers and providing a Ti diffusion film on the surface of the wafer. Note that substrate 1
1 may also be a crystalline substrate made of sapphire, Si, or the like. Furthermore, the optical waveguide 12 is not limited to the above-mentioned Ti diffusion, but can also be formed by sputtering, light blue coating, or the like with other materials on the substrate 11. Regarding optical waveguides, for example, T. Tamir (T, Tam1r)
“Integrated Obtics” (ed.)
rated 0ptics ) J (Topics in Applied Physics
in ApplIed Physlcs) Volume 7)
Sbringer Fehrlag (Springe "-V"
erlag) (1975); Nishihara, Haruna, and Suhara, ``Optical Integrated Circuits,'' published by Ohmsha (1985). can also be used.

However, this optical waveguide 12 must be formed of a material such as the above-mentioned Ti diffusion film that can propagate surface acoustic waves, which will be described later. Further, the optical waveguide may have a laminated structure of two or more layers.

The curved finger IDTs 17 and 18 are made by, for example, applying a positive electron beam resist to the surface of the optical waveguide 12, and then applying Au to the surface of the optical waveguide 12.
A conductive thin film is vaporized and an electrode pattern is drawn with an electron beam.1.
After peeling off the Au thin film, development was performed, and then C "thin film, AI
It can be formed by depositing a thin film and then performing lift-off in an organic solvent. In addition, curved finger IDT17.
When the substrate 11 and the optical waveguide 12 are made of a piezoelectric material, the reference numeral 18 is inserted directly into the optical waveguide 12 or into the substrate l.
Surface acoustic waves 15, 16 can be generated even if the surface acoustic waves are placed on the substrate 11 or the optical waveguide 12, but if the substrate 11 or the optical waveguide 12 is not placed on the substrate 11, a piezoelectric thin film made of, for example, ZnO is coated on a part of the substrate 11 or the optical waveguide 12 by evaporation tube, sputtering, etc. and there I DT1
7.18 should be installed.

The light beam L to be deflected is emitted from a light source 21, such as a semiconductor laser, toward the FGC13.

This light beam L (divergent beam) is made into a parallel beam by the FGC 13 and then taken into the optical waveguide 12,
Wave is guided within the optical waveguide 12. This waveguide light 1 is the first
Due to the acousto-optic interaction with the first surface acoustic wave 15 emitted from the curved finger IDT+7 of
Bragg diffraction). As described above, since the frequency of the alternating voltage applied to the first curved finger IDT 17 changes continuously, the frequency of the first surface acoustic wave 15 changes continuously. As is clear from the above equation (1), the deflection angle of the guided light Lz diffracted by the surface acoustic wave 15 is approximately proportional to the frequency of the surface acoustic wave 15, so as described above, the frequency of the surface acoustic wave 15 is By changing,
The guided light L2 is continuously deflected as shown by arrow A.

This guided light L2 is then deflected by the second surface acoustic wave 16, but since the frequency of this second surface acoustic wave 1B also changes continuously like the first surface acoustic wave 15, the second
The guided light L3 after passing through the surface acoustic wave 1B of
Continuously deflect as shown in .

In this way, the guided light L3 directed in the IQ direction by the first and second surface acoustic waves 15, 16 is emitted to the outside of the optical waveguide 12 by the FGCI 4, and is focused at one point by its condensing action.

Next, regarding the deflection angle range 2Δ (2θ) of the guided light L3,
This will be explained with reference to FIG. FIG. 2 shows the detailed shape and arrangement of the first curved finger IDT17 and the second curved finger DT18. As shown, the first curved finger IDTl? And the second curved finger IDT 18 is formed such that the interval between the electrode fingers changes stepwise at a constant rate of change, and the direction of each electrode finger also changes stepwise at a constant rate of change. The first curved finger IDT17 and the second curved finger IDTl8 are located on opposite sides of the optical path of the guided light beams L1 to L3, and the one with the narrower spacing between the electrode fingers is located on the guided light side. By sweeping the frequency of the applied voltage as described above,
The maximum frequency fz -2GHz at the end on the guided light side
, the end far from the guided light has the minimum frequency f1-
IGHz surface acoustic waves! 5.1B is generated. The first curved finger IDT 17 has a shape in which the electrode fingers at the upper end and the lower end are inclined by 3'' to each other, so that the guided light L
The electrode fingers at the upper end are arranged at an angle of 6'' with respect to the direction of movement of the arrow L, and the electrode fingers at the lower end are arranged at an angle of 3°.On the other hand, the second curved finger IDT18 The electrode fingers at the lower end and the lower end are inclined by 9 inches to each other, and the guided light L
The electrode fingers at the lower end are arranged at an angle of 18'' with respect to the direction of movement of the curved finger IDT 1, and the electrode fingers at the upper end are arranged at an angle of 90''. They may be integrated with each other.Furthermore, as for the inclined finger chirve IDT as described above, for example, the above-mentioned C and S
A detailed explanation is given in the literature by TSAI.

When a 2 GHz surface acoustic wave 15.16 is emitted from each of the first curved finger IDT+7 and the second curved finger IDT18, the diffraction state of the light beam becomes the state shown by ■ in FIG. That is, in this case, the guided light L1 enters the surface acoustic wave 15 of 2 GHz at an incident angle of 6 degrees, and this angle satisfies the Bragg condition. In other words, guided light! , the wave number vector of the guided light L2 after diffraction is 1klSlk, respectively.
2. Surface acoustic waves] If the wave number vector of 5 is IK, then
As shown in FIG. 3(1), 1k l + IK 1 -1k Z.

In other words, the traveling direction of the diffracted waveguide light L2 is the vector l
The direction is k2 (deflection angle -26-12'). Also, at this time, the surface acoustic wave 16 of 2GH7 is transmitted to the second curved finger ID.
Electrode finger (first curved finger IDT) at the lower end of T18 in FIG.
Since the surface acoustic wave 16 forms an angle 12@ with the upper end of the surface acoustic wave 17 and travels in a direction perpendicular to the electrode finger, the incident angle of the guided light L2 with respect to the surface acoustic wave 16 is also 6°, and the surface acoustic wave [6 Since it has the same wavelength as the surface acoustic wave 15,
Satisfies the Bragg condition. That is, if the wave number vector of the guided light L3 after diffraction by the surface acoustic wave 16 is Ik3, and the wave number vector of the surface acoustic wave 16 is IK2, then FIG.
), it is uc2+IK2-■3. At this time, the guided light L3 with respect to the guided light Ll
Letting the deflection angle of δ3 be δ3''-24''.

From the above state, the frequency of surface acoustic wave 15.16 is IGH
It is gradually lowered to z. Size IIK of each wave number vector lK1 and IK2 of surface acoustic waves 15.18.

Since IK21 is 2π/A when its wavelength is 8, it is ultimately proportional to the frequency of the surface acoustic wave 15.16. Therefore, when the frequency of the surface acoustic wave 15.16 is IGHz, the wave number vector IKt 5I of the surface acoustic wave 15.18
The magnitude of K2 is 172 when the frequency is 20H2. Further, in this case, the traveling directions of the surface acoustic waves 15 and 16, that is, the directions of the wave number vectors IK1 and IK2, are as follows:
As described above, the electrode finger portions of the first curved finger IDT 17 and the second curved finger IDT 18 that excite the IGHz surface acoustic wave 15.16 are different from the electrode finger portion that excites the 2 GHz surface acoustic wave 15.16. Since they are tilted by 3" and 9 degrees, respectively, the directions of the wave number vectors IKI and IK2 of the 2 GHz surface acoustic wave 15.l[i change by 3" and 9 degrees, respectively. Also, since a = b in Fig. 3 (1), the wave number vector IK! when the frequency of the surface acoustic wave 15.18 is IGHz! , IK2 are as shown in FIG.
If the deflection angle of 3 is 62, it is δ2-12''.

As explained above, even when the frequency of the surface acoustic wave 15.113 is IGHz, the above equation (2), that is, lk,
The following relationship is established: +lKl -■2 ■2 +1K2-■3.

The size of the wave number vector lk, 1lktl, is n·2π/λ (n is the refractive index), where λ is the wavelength of the guided light L1.
Since this wavelength is the same for the guided lights L2 and L3, it is always lkl 1 ''l lkz l -l lk3, and - the magnitude of the wave number vector lK1 of the blade surface acoustic wave 15, IIKII, is 8 times the wavelength. Then, it is 2π/Δ, and this wavelength is always equal to the wavelength of surface acoustic wave 16, so
l IKt l -I IKz. In addition, the directions of the wave number vectors IKI and IK2 change as the frequency of surface acoustic waves 15.16 changes from 2 GHz to IGHz, as explained earlier.
When changing, each changes at its own fixed rate of change. Therefore, while the frequency of the surface acoustic wave 15.16 changes from 2 GHz to IGHz as described above, the relationship of the above-mentioned ('2J equation) always holds true, and the Bragg conditions of the guided light beam and the surface acoustic wave 15, The Bragg condition between the wave light L2 and the surface acoustic wave 16 is always satisfied.

As is clear from the above explanation, surface acoustic waves15.16
When the frequencies of are 2 GHz and IGHz, the traveling direction of the guided wave L3 diffracted twice is the direction of the vector ■3 in FIG. 3 (1), and the direction of the vector Ik3 in FIG. 3 (2) (in FIG. 2, ■The direction indicated by °), and the difference is 24-12-1
It is 2'. In other words, a wide deflection angle range of 12° is obtained by diffraction of the guided light twice by the surface acoustic waves 15 and 16. By the way, when deflecting a light beam using only one surface acoustic wave whose frequency changes from IGHz to 2GHz (the frequency band is set to one octave so as not to be affected by the second-order diffracted light), the deflection angle range is 6. ”.

Next, correction of the cylindrical lens effect will be explained with reference to FIG. In FIG. 5, the wavelengths of the surface acoustic waves 15 and 16 are schematically indicated by the spacing between horizontal lines perpendicular to their propagation direction. IDT17
．． The frequency of the alternating voltage applied to 18 is swept down gradually as described above. Therefore, the wavelength distribution state of the surface acoustic wave 15 in the width direction of the guided light is such that the wavelength gradually becomes smaller toward the upper side in the figure, as shown in the figure. Therefore, as explained above, the guided light L2 after passing through the surface acoustic wave 15 becomes divergent due to the cylindrical lens effect.

On the other hand, the wavelength distribution of the surface acoustic wave 16 in the width direction of the guided light is such that the wavelength gradually decreases toward the bottom in the figure, as shown in the figure. Therefore, the guided light L2 in a divergent state is incident on the surface acoustic wave 16.
is focused by the cylindrical lens effect of the surface acoustic wave 16, so the guided light L3 after passing through the surface acoustic wave 16 becomes a parallel beam. As described above, the static cylindrical lens effect caused by the first surface acoustic wave 15 and the static cylindrical lens effect caused by the second surface acoustic wave I6 cancel each other out, so in this device, this cylindrical lens effect There is no need to provide a correction lens or the like to correct this. Further, even if the deflection speed is reduced, the above-mentioned canceling relationship always holds, so that the cylindrical lens effect is always corrected accurately.

In the optical deflection device of the above embodiment, since the VCO 20 for applying a high frequency alternating voltage to the IDTs 17 and 18 is commonly used, the dynamic cylindrical lens effect caused by the nonlinearity of the VCO 20 is caused by the surface elastic Since the waves 15 and 16 appear in a reverse relationship with respect to the waveguide width direction, their dynamic cylindrical lens effects also cancel each other out.

In the above description, the frequency of the surface acoustic waves 15.16 is continuously changed from 2 GHz to IGHz, but on the contrary, it may be changed from IGHz to 2 GHz. In this case, the direction of deflection of the light beam L° is reversed. In this case, contrary to the above embodiment, the guided light L2 is converged by the static cylindrical lens effect (convex lens effect) of the first surface acoustic wave 15, and then the static cylindrical lens effect (convex lens effect) of the second surface acoustic wave 16 converges. The guided light L3 is converted into a parallel beam by the cylindrical lens effect (concave lens effect). Also, change the above frequency to 2-l-2-IG
If the frequency is changed to Hz, the light beam L° will be deflected back and forth, making it possible to scan the light beam back and forth.

Furthermore, in the embodiment described above, the incident angle of the guided light Ll with respect to the surface acoustic wave 15 with a frequency of 2 GHz (that is, the angle of incidence of the guided light Ll with respect to the electrode finger that excites 2 GHz of the first curved finger IDT 17)
The angle formed by the direction of movement of the first curved finger ID is 6 degrees.
The angle between the electrode finger that excites IGHz of T17 and the traveling direction of the guided light Ll is 3° - the curved finger IDT1g of the force tube 2
The angles formed by the electrode fingers that excite 2GH2 and IGHz with the above-mentioned direction of travel are 18'' and 9@, respectively, but in general, the minimum and maximum frequencies of surface acoustic waves!5.1G are fl and fl.
(fz = 2fx), if the angles set as 6°, 3″, !8@, and 9″ in the above example are respectively θ, θ/2.3θ, and 3θ/2, then In any case, it is possible to always satisfy the above-mentioned Bragg condition. This will be obvious by referring to FIGS. 3(1) and (2).

Note that even when the shape of the curved finger IDT 17.18 is defined by the above θ, the surface acoustic wave 15.1G (
7) Minimum and maximum frequency rt, "It is not necessarily necessary to set 2 to be f'2 - 2r1. For example, the maximum frequency r2 may be set slightly smaller than the value 2f1. However, Curved finger I in the shape above
As long as DT17.18 is formed, this IDT shape should be utilized to the fullest to obtain the maximum deflection angle range without the second-order diffracted light generated at the minimum frequency r1 entering the deflection angle range from rl to r2-2r. It is preferable to change the surface acoustic wave frequency between .

Furthermore, in the present invention, the minimum and maximum frequencies f1%f2 of the surface acoustic waves 15.16 are set to be fl-2fl, and the frequencies of the surface acoustic waves 15.16 are always changed so that they are equal to each other. This is not necessarily necessary, and even if the frequency and traveling direction of the surface acoustic waves 15.16 are changed individually, the first and second curved finger IDTs 17.1
It is possible to satisfy the relationship of the above-mentioned equation (2) by the shape and arrangement state of 8.

However, as in the above embodiment, surface acoustic waves 15.
If the 1G frequency is changed in the same way, it is possible to drive two curved finger IDTs with a common driver, which is convenient because only one expensive driver is required and the cylindrical lens effect can be corrected well and easily. It is.

(Effects of the Invention) As explained in detail above, in the optical deflection device of the present invention, a light beam that has been diffracted once by a surface acoustic wave is further diffracted by another surface acoustic wave, so that an extremely wide deflection can be achieved. The angular range is obtained. Therefore, by using the optical deflection device of the present invention, it is possible to shorten the distance from the optical deflection device to the surface to be scanned, thereby achieving miniaturization of the optical scanning recording device and the reading device.

In addition, in the device of the present invention, it is possible to achieve a wide deflection angle as described above without setting the frequency of each surface acoustic wave to be extremely high.
Since the range can be obtained, when using an IDT as a surface acoustic wave generating means, there is no need to set the line width extremely small, and this IDT can be easily manufactured using currently established technology. becomes. Further, as described above, there is no need to set the frequency of the alternating voltage applied to the IDT to be extremely high, and therefore the driver of the IDT can be easily and inexpensively formed.

Furthermore, the device of the present invention can easily correct the cylindrical lens effect of the surface acoustic waves by arranging the two surface acoustic wave generators on opposite sides of the guided light. This eliminates the need for an expensive correction circuit or special correction lens, and can be formed at a lower cost than conventional devices that correct the cylindrical lens effect using such means. Furthermore, since the device of the present invention is not limited in deflection speed due to the above correction, it can be highly versatile.

[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 explains the mechanism of light beam deflection in the present invention. FIG. 4 is an explanatory diagram illustrating the cylindrical lens effect of surface acoustic waves according to the present invention. FIG. 5 is an explanatory diagram illustrating correction of the cylindrical lens effect according to the present invention. lO... Light deflection device 11... Substrate 12.
...Optical waveguide 13...FGC for light beam incidence
4... FCC for light beam emission 5... First surface acoustic wave 16... Second surface acoustic wave 7... First curved finger IDT 8... Second curved finger IDT 9 ...High frequency amplifier 20...vCO21...
・Light source L! ... Guided light L2 before entering the first surface acoustic wave
... Guided light L3 that has passed through the first surface acoustic wave... Guided light Ikl that has passed through the second surface acoustic wave... Guided light L
1 wave number vector ■2... Wave number vector of guided light L2 ■3... Wave number vector of guided light L3 ■! ...Wave number vector of the first surface acoustic wave ■2...
Wave number vector of second surface acoustic wave Figure 1 Figure 3 Figure 2 Figure 1

Claims (2)

[Claims] (1) An optical waveguide formed of a material through which surface acoustic waves can propagate, and a first surface elastic member 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. a first surface acoustic wave generating means for generating a wave in the optical waveguide, and diffracting the guided light in a direction that travels in a direction intersecting the optical path of the diffracted guided light to further amplify the deflection due to the diffraction; and a second surface acoustic wave generating means for generating a second surface acoustic wave to be deflected in the optical waveguide, wherein the first and second surface acoustic wave generating means each have a surface acoustic wave generating portion. The wave number vectors of the guided light located on opposite sides of the guided light before and after being diffracted by the first surface acoustic wave are respectively _1
, ■_2, When the wave number vector of the guided light diffracted by the second surface acoustic wave is ■_3, and the wave number vectors of the first and second surface acoustic waves are ■_1 and ■_2, ■_1+■_1= ■_2 ■_2+■_2=■_3 An optical deflection device characterized in that it is formed so as to continuously change the frequency and traveling direction of each of the first and second surface acoustic waves while satisfying the following condition. (2) The first and second surface acoustic wave generating means each have a curved intersecting finger as the surface acoustic wave generating portion in which the interval between electrode fingers changes stepwise and the direction of each electrode finger changes stepwise. 2. The optical deflection device according to claim 1, further comprising a pair of interdigitated electrodes, wherein the crossed interdigitated electrode pairs are driven by a common driver.