JPS6347739A - Acoustic-optical device - Google Patents

Abstract

PURPOSE:To deflect light beams transmitted in a medium within a wide angle range by generating plural electron beams whose intensity is modulated from an electron beam generator while individually controlling them and radiating the electron beams to a medium having an acoustic-optical effect to generate a required ultrasonic wave. CONSTITUTION:In case of deflecting incident light Li by ultrasonic waves APW with high frequency, the wavelength of the ultrasonic waves APW is reduced, so that the incident angle of the incident light Li should be set up to a large value to satisfy Bragg's condition. Namely, the ultrasonic waves APW are generated so as to be transmitted with an inclination to the incident side of the incident light Li from the normal on the surface of a substrate SUB and an angle formed by the wave surface of the ultrasonic waves APW and the incident light Li is set up so as to satisfy Bragg's condition. In case of deflecting light beams by ultrasonic waves with low frequency, the wavelength of the ultrasonic waves APW is increased, so that the incident angle of the incident light Li is reduced to satisfy the Bragg's condition, the ultrasonic waves APW are generated so as to be transmitted with an inclination to the opposite side against the incident side of the incident light Li and an angle formed by the wave surface of the ultrasonic waves APW and the incident light Li is set up so as to satisfy Bragg's condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acousto-optic device using an electron beam generator capable of independently driving a plurality of electron beam sources.

[Prior Art] An ultrasonic optical deflector is an acousto-optic device that uses a technology to deflect a light beam propagating in a medium with an acousto-optic effect using an ultrasonic wave generated in the medium, and is used as an element in optical control. Its importance has been increasing in recent years.

FIG. 10 is a schematic configuration diagram showing an example of a conventionally used ultrasonic optical deflector, and FIG. 11 is an explanatory diagram of its operation. In FIG. 10, a medium SUB having an acousto-optic effect
Above, electrodes 111.02 are installed to sandwich the piezoelectric body P, and a high frequency signal source SG is connected between these electrodes aiD1.02.
is provided. The high frequency signal generated by the high frequency signal source SG is applied between the electrode device and 02, and the piezoelectric body P converts the electric signal into mechanical vibration due to its piezoelectricity, thereby generating an ultrasonic wave. Then, the ultrasonic wave is transmitted into the medium SOB, and the plane wave AP of the bulk wave (bulk wave)
W in the medium SUB in the direction OP perpendicular to its surface.
propagates to. The wavefront of the ultrasonic wave thus generated acts as a diffraction grating for the incident light L.

Causes Bragg diffraction. As a result, part of the incident light Li becomes diffracted light L1 and the rest becomes undiffracted light LO, which is output from the medium SOB.

The spacing between the Bragg gratings, that is, the wavelength of the ultrasonic wave propagating in the medium SOB, is determined by the distance between the electrodes 01. It is determined by the frequency of the high frequency signal applied to D2. Therefore, by changing the frequency of the signal generated from the high-frequency signal source SG, the diffraction angle of the first diffracted light L1 changes, and the diffracted light L1 moves toward the Z direction T2.
It can be made to swing as shown in .

FIG. 11 is a cross-sectional view for explaining such a change in the diffraction angle. FIG. 11(a) shows the case where the electrodes D1 and D2 are driven at a high frequency, and the diffracted light L1 is the non-diffracted light L.
It is diffracted at an angle T1 with respect to O.

FIG. 11(b) shows the electrode D1. This is a case where D2 is driven at a low frequency, and the diffraction angle is T2 (TI>72).

In such a conventional ultrasonic optical deflector, since ultrasonic waves are generated using an ultrasonic transducer using a piezoelectric material P, the conventional ultrasonic optical deflector has the following drawbacks.

1. Since the transducer has a limited operating frequency bandwidth due to its shape, 5 the wavelength of the ultrasonic waves that can be generated is limited, and the range of deflection angles cannot be widened.

(2) The wavefront of the generated ultrasonic wave is limited to the direction parallel to the transducer, so as is clear from FIG. 11, the angle between the incident light beam and the wavefront is constant. Therefore, there is only one frequency that completely satisfies Bragg's condition, and even within the bandwidth of the ultrasonic transducer, at frequencies other than this, the diffraction efficiency decreases due to deviation from Bragg's condition.

[Objective of the Invention] An object of the present invention is to individually control and generate a plurality of intensity-modulated electron beams from an electron beam generator, and irradiate the medium with an acousto-optic effect to generate desired ultrasonic waves. An object of the present invention is to provide an acousto-optical device that can deflect a light beam propagating in a medium over a wide angular range by deflecting the light beam propagating in a medium.

[Summary of the Invention] The gist of the present invention to achieve the above-mentioned object is to provide an electron beam generator in which a plurality of independently driven electron beam sources are arranged in a two-dimensional manner, and an electron beam that is intensity-modulated to be generated by individual electron beams. This is an acousto-optic device characterized by comprising a control means for individually generating ultrasonic waves from a radiation source and irradiating a medium having an acousto-optic effect to generate ultrasonic waves.

[Embodiments of the Invention] A detailed description will be given below based on the embodiments illustrated in FIGS. 1 to 9.

FIG. 1 is a schematic configuration diagram, in which an ultrasonic transducer EAT using an electron beam generator is installed on a crystal or other medium SOB having acousto-optic effect characteristics.
Incident light Li is made to enter the medium SOB.

The wavefront of the ultrasonic wave APW generated from the ultrasonic transducer FAT in the medium SOB propagates in the medium SOB in the OA direction. The wavefront of the ultrasonic wave APW acts as a diffraction grating on the incident light Li, causing Bragg diffraction.

As a result, part of the incident light Li becomes Ll, and the rest becomes undiffracted light LO, which exits from the medium SUB. The ultrasonic transducer EAT can arbitrarily control the direction of the wavefront of the generated ultrasonic wave APW, and has no frequency band limitation due to the shape of the transducer.

2 to 6 are explanatory diagrams of the operation of the ultrasonic transducer EAT. FIG. 2 is a schematic diagram of an ultrasonic transducer FAT using an electron beam generator. On the lower surface of the solid-state electron beam generator EBH, electron beams rXEBS are arranged two-dimensionally at equal intervals. The substrate SOB is placed opposite the solid-state electron beam generator EBH, and an electrode MAC for applying an accelerating voltage is formed on the surface of the electron beam generator EBH that faces the substrate SOB. on the other hand,
The substrate SOB is any solid body, and a DC accelerating voltage VAC is applied between it and the electrode (IAC). In addition, the substrate S
If OB is an electrical insulator, a metal electrode can be formed on the surface and voltage VAC can be applied.

As an electron beam source EBS, for example, Japanese Patent Publication No. 54-3027
No. 4, JP-A-54-111272, JP-A-56-15
529, Japanese Unexamined Patent Publication No. 57-38528, and the like can be used. This is a device in which electrons are generated within a semiconductor substrate by supplying a reverse voltage to a pn junction to cause electron avalanche multiplication, and the electrons are emitted from the semiconductor substrate. According to this,
The electron beam sources EBS arranged two-dimensionally on such an electron beam generator EBH can be driven independently by appropriately controlling the application of reverse voltage to each electron beam source EBS. It is.

Figure 3 shows the ultrasonic transducer FAT shown in Figure 2.
FIG. 2 is a cross-sectional view showing an example of the operation. The two-dimensionally arranged electron beam sources EBS as described above can be individually controlled to generate the electron beam CEB, but the third
In the illustrated example, intermittent electron beams CEB are generated simultaneously from all the electron beam sources EBS. Note that the intermittent frequency of electron beam CEB is from several KHz to several 100 MHz.
A range of is possible! ! The continuously generated electron beam CEB is accelerated by the accelerating voltage VAC and collides with the surface of the substrate SOB, generating ultrasonic waves having a frequency equal to the intermittent frequency of the electron beam CEB in the substrate SBR.

The generation of ultrasonic waves in a substrate by the collision of a single intermittent electron beam is described, for example, in "Ikoma and Akatsuka, '°Electron Fj Ultrasonic Microscope #a," Applied Physics Vol. 51, No. 2 (1982),
205 (95) page”. According to it,
Most of the energy of the electron beam that accelerates and collides with the substrate surface becomes heat, generating heat waves within the substrate. This thermal wave becomes an ultrasonic wave due to the thermoelastic effect and propagates through the substrate, 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 source of the ultrasonic wave is one point, and the ultrasonic wave generated from that point becomes a substantially spherical wave.

On the other hand, the ultrasonic transducer E shown in FIG.
In A block, the electron beam CEB is two-dimensionally arranged and connected to the substrate SOB.
Because the heat wave T'll collides with the surface of the In this way, the ultrasonic waves generated with equal phases from two-dimensionally arranged sources are superimposed to form a plane wave APW, which propagates in the direction DP perpendicular to the surface of the substrate SBR.

FIG. 4 is a sectional view showing another example of the operation of the ultrasonic transducer EAT of FIG. 2. As described above, the electron beam sources EBS can be driven independently.

In Figure 4, we use these features to create an electron beam source EBS.
1, EBS2, . . . are sequentially delayed, and an electron beam CEB of the same intermittent frequency is irradiated. As mentioned above, these electron beams CEB collide with the substrate SOB and become an ultrasonic generation source, but each electron beam source EBSI, EBS2, .
Since there is a delay in the electron beam CEB generated from ..., a phase lag occurs in the spherical wave of the ultrasonic wave generated from the corresponding ultrasonic generation source. Therefore, according to the principle of wave field synthesis, these spherical waves are superimposed to form a plane wave APW that propagates in the direction OS determined by this delay time.

The propagation direction O of the ultrasonic wave APW generated in the substrate SBR
5 is determined by the delay time of the intermittent electron viCEB generated from the electron beam source EBS as described above.

FIG. 5 is an explanatory diagram of the relationship between such delay time and propagation direction O5. Figure 5(a) shows the substrate SUB being exposed to ultrasonic APW.
CEBI, CEB2
is the interrupted electron beam in this plane, Pi; P2 is the electron beam C on the surface of the substrate SOB; d is the distance between 0 point PI, which is the point where EBI and CEB2 are irradiated, and 22; and the ultrasonic propagation direction DS is The angle between the perpendicular line drawn on the surface of the substrate S [78] is θ
, the speed of the ultrasonic wave is expressed by Va, and the wavelength is expressed by In.

Figure 5(b) shows the electron beam CE irradiated to points P1 and P2.
At point P2, the electron beam CEB is intermittent with a delay of time from Pl, and the intermittent frequency is f in both cases. Also, electronic! When ICEB2 reaches point P2, the position in the substrate SBR where one point P1 reaches is set as PI', and the distance between points PI and PI' is set as h. Therefore, after time +1.'lτ, the electron beam CEBI is the distance τ・
This means that the electron beam CEB has moved by 1/(1/f), and at this time, the interruption of the electron beam CEB at points P1 and P2 causes the substrate S
The conditions that have the same effect on the ultrasonic APW in UB are τ/(1/f)・Input=h Therefore, τ/(1/f)=h/λ=d/(Input/sinθ) Therefore, using f・in=Va, sinθ= ?・Va/d-(
In 1), the propagation direction DS of the ultrasonic wave is given. Alternatively, to generate ultrasonic waves in a desired direction within the substrate SO3, (1
) by transforming the equation, r=d*sinθ/Va −(2)
The generation of the electron beam CEB may be delayed using the time τ obtained from .

As mentioned above, FIG. 5 is a cross-sectional view taken along the plane formed by the perpendicular line drawn from the ultrasonic propagation direction OS to the surface of the substrate SUB, and one axis of the two-dimensionally arranged electron beam source EBS is within this plane. FIG. 6 is a plan view of the electron beam generator EBH for explaining such a situation. In FIG. 6, the white circle symbols represent the two-dimensionally arranged electron beam sources EBS, with the oblique shadow of the ultrasonic propagation direction DS on the surface of the substrate S08 as the is one randomly selected electron beam source EBS
Let it be O. At this time, if the position of an arbitrary electron beam source EBS i is expressed as (xi, y+), then the delay time τi of the electron beam source EBS i with respect to the electron beam source EBSO at the origin is τ1=x
By setting asinθ/Va - (3), the oblique shadow of the ultrasonic wave APW generated in the substrate SUB on the surface of the substrate S08 in the traveling direction coincides with the X axis, and the angle formed with the perpendicular to the surface is θ. becomes. Therefore, by appropriately selecting the X-axis and setting the relative delay of each electron beam source EBS so as to satisfy equation (3), it is possible to generate ultrasonic waves APW in any direction within the substrate SUB. . Since such generation of ultrasonic waves does not use the piezoelectricity of the substrate SOS, it is possible to generate ultrasonic waves on any substrate.

In this way, the ultrasonic transducer E used in the present invention
The AT is capable of generating ultrasonic waves APW of any frequency in any direction of the substrate SUS. Due to this feature, the acousto-optic device of the present invention can two-dimensionally deflect the incident light Li over a wide angle. Figure 7,
These operations will be explained using FIG. 8. FIG. 7 shows that in the embodiment shown in FIG. 1, ultrasonic waves can always be generated so as to satisfy Bragg's condition.

FIG. 7(a) shows a case where the incident light Li is deflected by a high frequency ultrasonic wave APW, and in this case, the ultrasonic wave APW
Since the wavelength Δ of W becomes smaller, the angle of incidence θ of the incident light Li must be set larger in order to satisfy Bragg's condition. In other words, the ultrasonic wave APW must be set so that the angle of incidence θ of the incident light Li is greater than the normal to the surface of the substrate 5tlB. The wavefront of the ultrasonic wave APW and the incident light L are generated by tilting toward the incident side and propagating.
i can be made to satisfy Bragg's condition.

FIG. 7(b) shows a case where a light beam is deflected by a low frequency ultrasonic wave APW, and in this case, the wavelength Δ of the ultrasonic wave APW is
becomes large, so in order to satisfy Bragg's condition, the incident angle θ of the incident light L1 must be made small. Therefore, the ultrasonic wave APW should be propagated at an angle opposite to the incident side of the incident light Li. By generating, in this case as well, the angle θ between the wavefront of the ultrasonic wave APW and the incident light Li is
The Bragg angle can be set to satisfy.

In the conventional example shown in FIG. 11 described above, the ultrasonic APW
The angle between the wavefront and the incident light Li is fixed at a preset value, and the Bragg condition can only be satisfied at a single frequency, resulting in a decrease in diffraction efficiency at frequencies other than this.However, the present invention Now, as explained with reference to FIG. 7, light can be deflected while always satisfying the Bragg condition. Furthermore, as mentioned above, since the ultrasonic transducer FAT used in the present invention has no frequency band limitation due to its shape, such Bragg diffraction can be performed in a wide band.
It is possible to make the deflection angle extremely wide.

FIG. 8 shows that the acousto-optic device according to the present invention is capable of two-dimensional deflection, rather than one-dimensional deflection as in the prior art. As is clear from FIGS. 8(a) and (b), by tilting the wavefront of the ultrasonic APW in a direction perpendicular to the incident light Li, the incident light Li is directed in a direction perpendicular to the deflection direction due to the frequency change of the ultrasonic APW. are also deflected, and these two
By combining two deflection directions, two-dimensional deflection becomes possible.

In the above embodiment, in order to generate ultrasonic waves by intermittent electron beam, it is sufficient that the electron beam is intensity modulated, for example, sinusoidal intensity modulation or duty ratio other than 1:l is used. It is possible to use pulse modulation.

Furthermore, the two-dimensionally arranged electron beam sources EBS can be driven independently, and the examples have been described under such conditions. However, by commonly connecting electrodes for driving to each electron beam source EBS in a matrix, it is also possible to independently drive any one of the two-dimensionally arranged electron beam sources EBS. Such a driving method is effective when the number of electron beam sources EBS is large or for reducing the complexity of wiring and driving. FIG. 9 is a circuit diagram of such a drive, and the electron beam source EBS has common electrodes x1, x2, . . . , Yl, Y in the vertical and horizontal directions, respectively.
2... are connected in a matrix, and the electrodes x1,
x2, . . . are connected to the control circuit C0NTl, and the electrodes Y1, Y2
... is connected to the control circuit C0NT2. For example, the control circuit C0NTl TE electrode x3 is connected to the control circuit C0NT2.
By selecting electrode Y4, the electron beam source EB
S34 can be selected and driven.

It is also possible to apply a combination of such a driving method and ultrasonic wave generation by pulse modulation of an electron beam with a suitably selected duty ratio as described above to the present invention. That is, the delay time between the electron beam sources EB and EB in the embodiment is
By narrowing the pulse width for driving S, only one electron beam source EBS can be driven at the same time.

In these Examples, the electron beam generator EBH disclosed in Japanese Patent Publication No. 54-30274 was used as described above, but in the acousto-optic device according to the present invention, the electron beam source is independent. It's not a trivial matter as long as you can drive it.

Therefore, the present invention can obtain the same effect even if other known electron beam sources using a pn junction negative work function or solid state electron beam sources such as field emission type are used.

Furthermore, in the embodiment, electron beam sources E are arranged two-dimensionally at equal intervals.
Although BS is illustrated, it is clear that the present invention can be applied even if the BSs are not equally spaced.

[Effects of the Invention] As explained above, the acousto-optic device according to the present invention irradiates a medium having an acousto-optic effect with an electron beam generated from a two-dimensionally arranged individually controllable electron beam source. By deflecting incident light using the generated desired ultrasonic waves, it is possible to perform diffraction that always satisfies Bragg's conditions over a wide frequency range, making it possible to deflect light over a wide angular range. Furthermore, by controlling the wavefront of the ultrasonic wave, it becomes possible to deflect the ultrasonic wave by changing its frequency and to deflect it in a direction perpendicular to it, thereby realizing two-dimensional optical deflection.

[Brief explanation of drawings]

FIG.
Figures 3 to 6 are diagrams explaining the operation of the ultrasonic transducer; Figures 7 and 8 are diagrams explaining the operation of the acousto-optic effect; Figure 9 is a circuit diagram for simply driving the electron beam source; Figures 10 and 11
The figure is a schematic configuration diagram of a conventional ultrasonic optical deflector. Symbol SOB is a medium with an acousto-optic effect, FAT is an ultrasonic transducer, EBH is an electron beam generator, EBS
is an electron beam source, SC is a high frequency signal source, Dl and D2 are electrodes, and MAC is an accelerating electrode. Patent Applicant: Canon Corporation Figure 1 Figure 2 Figure 5 (b) Figure 6 Figure 7 (b) Figure N8 Figure 11 (b)

Claims (1)

[Claims] 1. An electron beam generator in which a plurality of independently driven electron beam sources are two-dimensionally arranged, intensity-modulated electron beams are individually generated from each electron beam source, and an acousto-optic effect is achieved. an acousto-optic device comprising: a control means for generating ultrasonic waves by irradiating a medium with the ultrasonic waves; 2. The acousto-optic device according to claim 1, wherein the control means is capable of controlling the drive of each of the individual electron beam sources with a delay of a desired time.