JPH0693069B2 - Surface acoustic wave optical deflector - Google Patents

Description

The present invention relates to a plurality of electron beams that can be independently driven in order to deflect light propagating in a thin film optical waveguide by surface acoustic waves. The present invention relates to a surface acoustic wave optical deflector using an electron beam generator having a light source.

[Prior Art] A surface acoustic wave optical deflector is an acousto-optic device that uses a technique capable of deflecting a light beam propagating through a thin film optical waveguide by a surface acoustic wave generated in the optical waveguide. Its importance is increasing.

FIG. 9 is a schematic configuration diagram showing an example of a surface acoustic wave optical deflector that has been conventionally used. The thin film optical waveguide WG is provided on the optical waveguide substrate SUB, and the interdigital transducer IDT for surface acoustic wave excitation is provided on the thin film optical waveguide WG. A piezoelectric single crystal such as LiNbO ₃ (lithium niobate) is used as the substrate SUB, and the thin film optical waveguide WG is used.
For example, a thin film having a thickness of about several μm, which is formed by depositing Ti on the surface of a piezoelectric single crystal and thermally diffusing it inside, and has a higher refractive index than the substrate SUB is used. Alternatively, a non-piezoelectric single crystal such as Si can be used as the substrate SUB. In this case, as the thin film optical waveguide WG, it is possible to use, for example, a thin film formed by adhering a piezoelectric material such as ZnO (zinc oxide) on a non-piezoelectric single crystal and having a higher refractive index than the substrate SUB. As the interdigital electrode IDT for surface acoustic wave excitation, for example, a conductive material such as Al formed in a pattern by vapor deposition is used.

A surface acoustic wave SAW is excited from the IDT IDT, and the laser light Li propagating in the thin film optical waveguide WG is a surface acoustic wave SA.
It intersects the wavefront of W at an angle θ. When the wavelength of the surface acoustic wave SAW is Λ and the wavelength of the laser light Li is λ, the relation of θ = sin ⁻¹ (λ / 2Λ) holds, the laser light Li is the surface acoustic wave.
Bragg diffraction is caused by SAW, and a part of the light becomes diffracted light L1 and propagates in the optical waveguide WG, and the rest becomes non-diffracted light LO and propagates in the optical waveguide WG.

Since the wavefront of the surface acoustic wave SAW is used as a diffraction grating in the diffraction of the laser light Li, the emission direction of the diffracted light L1 can be changed by changing the wavelength Λ of the surface acoustic wave SAW. Excitation of surface acoustic wave SAW is usually a comb-shaped electrode I
It is performed by applying a high-frequency signal to the DT from the outside, so by changing the frequency of the high-frequency signal,
The emission direction of L1 can be changed.

In such a conventional surface acoustic wave optical deflector, since the surface acoustic wave is excited by the IDT electrode IDT, it has the following drawbacks.

I. Since the IDT of the interdigital transducer has an operating frequency bandwidth depending on its shape, the wavelength of the surface acoustic wave that can be generated is limited and the deflection angle range cannot be widened.

II. Since the wavefront of the generated surface acoustic wave is limited to the direction parallel to the IDT IDT, the angle between the incident laser beam Li and the surface acoustic wave SAW is constant as is clear from FIG. Therefore, the frequency that completely satisfies Bragg's condition is only 1.
Point, and even within the operating band of the IDT electrode,
At frequencies other than that frequency, the diffraction efficiency decreases due to the deviation from the Bragg condition.

[Object of the Invention] An object of the present invention is to control a plurality of intensity-modulated electron beams from an electron beam generator individually and irradiate the optical waveguide substrate, and generate a desired surface acoustic wave to generate an optical beam. An object of the present invention is to provide a surface acoustic wave optical deflector capable of deflecting a light beam in a waveguide in a wide angle range.

[Summary of the Invention] The gist of the present invention for achieving the above object is to provide a thin film optical waveguide substrate for propagating a light beam to be deflected, and a plurality of electron beams which are arranged adjacent to the substrate and can be independently driven. An electron beam generator in which the sources are two-dimensionally arranged and a plurality of intensity-modulated electron beams are individually generated from the electron beam generator, and a surface acoustic wave is excited on the substrate by irradiating the substrate. A surface acoustic wave optical deflector having a control means.

[Embodiment of the Invention] The present invention will be described in detail below based on the embodiment shown in FIGS. 1 to 8.

FIG. 1 is a schematic configuration diagram showing an embodiment of a surface acoustic wave optical deflector according to the present invention. A thin film optical waveguide WG is provided on a substrate SUB, and an ultrasonic transducer EAT that generates a surface acoustic wave using an electron beam generator is installed on the optical waveguide WG. The optical waveguide WG is made of the same material as that described in the above-mentioned conventional technique. The surface acoustic wave SAW excited by the ultrasonic transducer EAT is
It intersects with the laser light Li propagating in the optical waveguide WG and causes the laser light Li to undergo Bragg diffraction.

The ultrasonic transducer EAT used in the present invention can excite a surface acoustic wave SAW in a very wide frequency band, and can excite a surface acoustic wave SAW propagating in an arbitrary direction. 2 to 6 are explanatory views of the operation of the ultrasonic transducer EAT, and the surface acoustic wave SA will be described with reference to these drawings.
The method of generating W will be described. FIG. 2 shows the principle of an ultrasonic transducer EAT using an electron beam generator. An electron beam source EBS is two-dimensionally arranged at equal intervals on the lower surface of the solid-state electron beam generator EBH. The substrate SUB is arranged so as to face the solid-state electron beam generator EBH.
The acceleration voltage VAC is applied between the substrate and the substrate SUB. The acceleration voltage is applied to the surface of the electron beam generator EBH facing the substrate SUB.
An electrode MAC for applying VAC is formed. on the other hand,
The optical waveguide WG is formed on the surface of the substrate SUB, but since the optical waveguide WG is usually an electrical insulator, the electrode MS
Are formed. Then, the acceleration voltage VAC is applied between the electrodes MAC and MS.

As an electron beam source EBS, for example, Japanese Examined Patent Publication No. 54-30274,
JP-A-54-111272, JP-A-56-15529, JP-A-57-3
A structure as disclosed in Japanese Patent No. 8528 can be used. This is a method in which a reverse voltage is supplied to the pn junction to cause electron avalanche multiplication (avalanche multiplication) to generate electrons in the semiconductor substrate and release the electrons from the semiconductor substrate.
According to this, the electron beam source EBS arranged two-dimensionally in such an electron beam generator EBH is driven independently by appropriately controlling the application of the reverse voltage for each electron beam source EBS. It is possible to

FIG. 3 is a sectional view showing an example of the operation of the ultrasonic transducer EAT shown in FIG. As described above, the two-dimensionally arranged electron beam sources EBS can individually generate the electron beams CEB, but in the example of FIG. 3, all the electron beam sources EBS are intermittently connected at the same time. Electron beam CEB
Is generated. The intermittent frequency of the electron beam CEB can be in the range of several KHz to several 100 MHz, and the intermittently generated electron beam CEB is accelerated by the acceleration voltage VAC and collides with the surface of the substrate SUB, and Generates ultrasonic waves with a frequency equal to the intermittent frequency of the electron beam CEB.

Generation of ultrasonic waves in a substrate by collision of a single intermittent electron beam is described in, for example, “Ikoma, Morizuka,“ Electron Beam Acoustic Microscope ”, Applied Physics Vol. 51, No. 2 (1982), 205 (95). )page"
Are detailed in. According to this, most of the energy of the electron beam that is accelerated and collides with the substrate surface becomes heat, and a heat wave is generated in the substrate. This heat wave becomes an ultrasonic wave that propagates in the substrate due to the thermoelastic effect, and the frequency of the ultrasonic wave becomes equal to the intermittent frequency of the electron beam. When such a single electron beam is used, the ultrasonic wave is generated at one point, and the ultrasonic wave generated from the ultrasonic wave becomes a substantially spherical wave.

On the other hand, in the surface acoustic wave generator EBH shown in FIG. 3, since the electron beams CEB are two-dimensionally arranged and collide with the surface of the substrate SUB, the heat waves TW are also two-dimensionally arranged and serve as an ultrasonic wave generation source.
Since all the electron beam sources EBS are interrupted at the same time, the heat wave TW and the ultrasonic waves generated thereby all have the same phase. In this way, the ultrasonic waves generated in the same phase from the two-dimensionally arranged sources are superposed into a plane wave APW, and the substrate SUB
It will propagate in the direction DP perpendicular to its surface.

Although FIG. 3 shows an operation example in which the ultrasonic wave APW is generated in a direction perpendicular to the surface of the substrate SUB, such an ultrasonic transducer EAT can also generate a surface acoustic wave. As described above, the electron beam sources EBS that are two-dimensionally arranged in the electron beam generator EBH can be independently driven. In FIG. 4, surface acoustic waves are excited by utilizing such features. In FIG. 4, the distance between adjacent electron beam sources EBS is represented by p, the velocity of the surface acoustic wave propagating through the substrate SUB is represented by Vsaw, and the wavelength is represented by Λ. At this time, the adjacent electron beam sources EBS are alternately turned on and off at the frequency f,
If the relationship of 2p = Λ Vsaw = f · Λ is satisfied, the electron beam CEB intermittently generated from the adjacent electron beam source EBS is generated on the substrate as shown in FIGS. 4 (a) and 4 (b). Heat wave TW generated by collision with SUB
Is converted into ultrasonic waves by satisfying the boundary conditions of surface acoustic waves, and surface acoustic waves SAW are excited.

In FIG. 4, for the sake of explanation, the interval p between the electron beam sources EBS is equal to 1/2 of the wavelength of the surface acoustic wave SAW, and the electron beam sources EBS are adjacent to each other.
We have shown a special situation in which an electron beam CEB that is alternately intermittently generated is generated.
The occurrence of W will be described. FIG. 5 (a) is a sectional view when the substrate SUB is cut along a plane including the propagation direction of the surface acoustic wave SAW and the normal line of the surface of the substrate SUB, and CEB1 and CEB2 are discontinuous in this plane. Electron beam, P1 and P2 are electron beam CEB on the surface of substrate SUB
1, the point where CEB2 is irradiated. The distance between points P1 and P2 is d,
The ultrasonic velocity is represented by Vsaw and the wavelength is represented by Λ.

FIG. 5 (b) shows the interruption of the electron beam CEB applied to the points P1 and P2, and the electron beam is interrupted at the point P2 with a delay of time τ from P1. The intermittent frequency at this time is f,
At this time, the interruption of the electron beam CEB at the points P1 and P2 is caused by the substrate S
Since the condition of having the same effect on the surface acoustic wave SAW in UB is τ / (1 / f) = d / Λ, the following equation is obtained using f · Λ = Vsaw.

τ = d / Vsaw That is, the surface acoustic wave SAW is generated by driving two electron beam sources EBS whose distance is d along the propagation method of the surface acoustic wave SAW with a delay of τ = d / Vsaw. It

FIG. 5 shows the traveling direction of the surface acoustic wave SAW as described above,
It is a cross-sectional view of a surface including a normal to the surface of the substrate SUB,
It is not necessary that one axis of the two-dimensionally arranged electron beam source EBS is in this plane. FIG. 6 is a plan view of the electron beam generator EBH for explaining such a situation. In FIG. 6, white circles represent electron beam sources EBS arranged two-dimensionally. The propagation direction of the surface acoustic wave SAW is the x-axis, the direction orthogonal to it is the y-axis, and one origin is arbitrarily selected. The electron beam source is EBS0. At this time, if the position of an arbitrary electron beam source EBSi is represented by (xi, yi), the delay time τi of driving the electron beam source EBSi with respect to the electron beam source EBS0 at the origin is set to τi = x / Vsaw, The surface acoustic wave SAW propagating in the x direction is excited.

Therefore, by appropriately selecting the x-axis and setting the delay time τ of the drive of each electron beam source EBS so as to satisfy the above equation, it is possible to excite the surface acoustic wave SAW on the substrate SUB in any direction. it can.

Thus, the ultrasonic transducer EA used in the present invention
T can generate a surface acoustic wave SAW having a frequency in any direction of the substrate SUB. Due to this feature, in the surface acoustic wave optical deflector according to the present invention, incident light can be deflected over a wide angle. Describing these operations with reference to FIG. 7, FIG. 7 shows that in the embodiment shown in FIG. 1, the surface acoustic wave SAW can be generated so as to always satisfy the Bragg condition. FIG. 7 (a) shows a case where the laser light Li is deflected by a high-frequency surface acoustic wave. In this case, since the wavelength Λ of the surface acoustic wave SAW becomes small, it is necessary to satisfy the laser condition in order to satisfy the Bragg condition. The incident angle θ of the light Li must be large. That is, the surface acoustic wave SAW is generated so as to propagate while being inclined to the incident side of the laser light Li,
The SAW wavefront and the incident laser beam Li can satisfy the Bragg condition.

FIG. 7 (b) shows a case where a light beam is deflected by a surface acoustic wave SAW having a low frequency. In this case, since the wavelength Λ of the surface acoustic wave SAW becomes large, in order to satisfy the Bragg condition, laser light Li The incident angle θ of should be small. Therefore, by generating the surface acoustic wave SAW so that it propagates while being inclined to the side opposite to the incident side of the laser light Li, the angle formed between the wave front of the surface acoustic wave SAW and the incident laser light Li is also defined as the Bragg angle. It can be set to your satisfaction.

In the conventional example shown in FIG. 9 described above, the surface acoustic wave SAW is used.
The angle θ between the wavefront of and the incident laser light Li is fixed at a preset value, and since the Bragg condition is satisfied only at a single frequency, the diffraction efficiency was reduced at frequencies other than this frequency. In the present invention, as described with reference to FIG. 7, the light can be deflected while always satisfying the Bragg condition. Further, as described above, since the ultrasonic transducer EAT used in the present invention has no frequency band limitation due to the shape, it is possible to perform such Bragg diffraction in a wide band, and it is possible to make the deflection angle extremely wide. Is.

In the description of the embodiments, the method of intermittently generating an electron beam to generate a surface acoustic wave is illustrated, but to generate an ultrasonic wave, the electron beam may be intensity-modulated, for example, a sinusoidal intensity modulation. It is possible to use pulse modulation with a duty ratio other than 1: 1.

Further, the electron beam sources EBS arranged two-dimensionally can be driven independently, and the embodiment has been described under such conditions. However, it is also possible to drive any one of the electron beam sources EBS independently by forming electrodes for driving in a matrix, and such a driving method is used when the number of electron beam sources EBS is large. Also, it is effective in reducing the complexity of wiring and driving. FIG. 8 is a circuit diagram of such a drive. Common electrodes X1, X2 ..., Y1, Y2 ... Are connected in a matrix in the vertical and horizontal directions to the electron beam source EBS. X2 ... Are connected to the control circuit CONT1, and electrodes Y1, Y2 ... are connected to the control circuit CONT2. For example, control circuit CON
The electron beam source EBS34 can be selected and driven by selecting the electrode X3 at T1 and the electrode Y4 at the control circuit CONT2.

It is also possible to apply the present invention in combination with such a driving method and ultrasonic wave generation by pulse modulation of an electron beam with the above-mentioned duty ratio being appropriately selected. That is, by making the pulse width for driving the electron beam source EBS narrower than the delay time τ between the electron beam sources EBS in the embodiment, only one electron beam source EBS can be driven at the same time. it can.

As the electron beam generator EBM in these examples, the one disclosed in Japanese Patent Publication No. 54-30274 is used as described above, but in the surface acoustic wave optical deflector according to the present invention, the electron beam is used. It is not essential that it can drive the source independently. Therefore, the same effect can be obtained by using a known pn junction negative work function as an electron beam source or a field emission type solid-state electron beam source.

Further, in the embodiment, the electron beam sources EB arranged at equal intervals in the following two
Although S is shown as an example, it is obvious that the present invention can be applied even if the intervals are not even.

[Advantages of the Invention] As described above, the surface acoustic wave optical deflector according to the present invention is generated by irradiating the optical waveguide substrate with an electron beam generated from an electron beam source that is two-dimensionally arranged and can be individually controlled. By deflecting the light beam in the optical waveguide substrate by the desired surface acoustic wave, it is possible to realize diffraction that always satisfies the Bragg condition in a wide frequency range, and maintain a good diffraction efficiency while maintaining a wide angle range. It enables light deflection.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a surface acoustic wave optical deflector according to the present invention, FIG. 2 is a schematic configuration diagram of an ultrasonic transducer, and FIGS. 3 to 6 are operation explanatory diagrams of the ultrasonic transducer. FIG. 7 is an operation explanatory view of a surface acoustic wave optical deflector, and FIG.
FIG. 9 is a circuit diagram for easily driving an electron beam source, and FIG. 9 is a schematic configuration diagram of a conventional surface acoustic wave optical deflector. SUB is a substrate, WG is an optical waveguide, EAT is an ultrasonic transducer, EBH is an electron beam generator, EBS is an electron beam source, MAC, M
S is an electrode.

 ─────────────────────────────────────────────────── (72) Inventor Masanori Takenouchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Isamu Shimoda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Masahiko Okunuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A thin-film optical waveguide substrate for propagating a light beam to be deflected, an electron beam generator arranged adjacent to the substrate and having a plurality of electron beam sources which can be independently driven two-dimensionally arranged, and the electron beam generator. Surface acoustic wave optical deflection, comprising: a control unit for individually generating a plurality of intensity-modulated electron beams from a beam generator and irradiating the substrate to excite surface acoustic waves on the substrate. vessel. 2. The electron beam generator is provided with at least one (x, y) Cartesian coordinate system on the same plane as the two-dimensional array of the electron beam sources, and the position of any electron beam source is set to the coordinate system. When expressed by (x, y), the control means assumes that Vsaw is the surface acoustic wave velocity in the x direction on the substrate with respect to the electron beam source located at the origin (0, 0). The surface acoustic wave optical deflector according to claim 1, wherein the surface acoustic wave optical deflector is controlled so as to be driven with a delay of about τ = x / Vsaw.