JPH0785153B2 - Acousto-optic device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acousto-optical 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-optical device that uses a technique of deflecting a light beam propagating in a medium having an acousto-optic effect by an ultrasonic wave generated in the medium, and is used as an element in light control. In recent years, its importance is increasing.

FIG. 10 is a schematic configuration diagram showing an example of a conventionally used ultrasonic optical deflector, and FIG. 11 is an operation explanatory diagram thereof. First
In FIG. 10, electrodes D1 and D2 are provided on a medium SUB having an acousto-optic effect so as to sandwich the piezoelectric body P, and a high frequency signal source SG is provided between these electrodes D1 and D2. The high-frequency signal generated by the high-frequency signal source SG is applied between the electrodes D1 and D2, and the piezoelectric body P converts the electric signal into mechanical vibration to generate ultrasonic waves.
Then, the ultrasonic wave is transmitted into the medium SUB, becomes a plane wave APW of a volume wave (bulk wave), and propagates in the medium SUB in a direction DP perpendicular to the surface thereof. The wavefront of the ultrasonic wave thus generated acts as a diffraction grating on the incident light Li and causes Bragg diffraction. As a result, the incident light Li
Part is diffracted light L1 and the rest is non-diffracted light L0
Emit from SUB.

The spacing of the Bragg diffraction grating, that is, the wavelength of the ultrasonic wave propagating in the medium SUB is determined by the frequency of the high frequency signal applied to the electrodes D1 and D2. Therefore, by changing the frequency of the signal generated from the high-frequency signal source SG, the diffraction angle of the diffracted light L1 changes, and the diffracted light L1 can be swung in the Z direction as shown by Tz.

FIG. 11 is a cross-sectional view for explaining such a change in diffraction angle. FIG. 11A shows the case where the electrodes D1 and D2 are driven at a high frequency, and the diffracted light L1 is diffracted at an angle T1 with respect to the non-diffracted light L0. FIG. 11 (b) shows the case where the electrodes D1 and D2 are driven at a low frequency, and the diffraction angle is T2 (T1> T2).
Is.

Such a conventional ultrasonic optical deflector has the following drawbacks because the ultrasonic wave is generated using the ultrasonic transducer using the piezoelectric body P.

I. Since the transducer has a limited operating frequency bandwidth depending on its shape, the wavelength of ultrasonic waves that can be generated is limited, and the range of the deflection angle cannot be widened.

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

[Object of the Invention] An object of the present invention is to generate a desired ultrasonic wave by irradiating a medium having an acousto-optic effect by individually generating a plurality of intensity-modulated electron beams from an electron beam generator. Accordingly, it is an object of the present invention to provide an acoustooptic device capable of deflecting a light beam propagating through a medium in a wide angle range.

[Summary of the Invention] The gist of the present invention for achieving the above-described object is to provide an electron beam generator in which a plurality of electron beam sources that can be independently driven are two-dimensionally arranged, and an electron beam in which an intensity-modulated electron beam is individually emitted. An acousto-optic device comprising: a control unit that individually emits from a radiation source and irradiates a medium having an acousto-optic effect to generate an ultrasonic wave.

[Embodiment of the Invention] A detailed description will be given below based on an embodiment shown 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 SUB having an acousto-optic effect characteristic, and a medium S
Incident light Li enters the UB. Ultrasonic wave APW generated from ultrasonic transducer EAT in medium SUB
The wave front of propagates through the medium SUB in the DA direction. Ultrasonic APW
The wave front of acts as a diffraction grating for the incident light Li and causes Bragg diffraction. As a result, part of the incident light Li is L1.
And the rest becomes non-diffracted light L0, which is emitted from the medium SUB. The ultrasonic transducer EAT can arbitrarily control the direction of the wavefront of the generated ultrasonic wave APW, and does not limit the frequency band due to the shape of the transducer.

2 to 6 are explanatory views of the operation of the ultrasonic transducer EAT. FIG. 2 is a schematic configuration diagram of an ultrasonic transducer EAT using an electron beam generator. Electron beam sources EBS are 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, and the substrate of the electron beam generator EBH is arranged.
Electrode MAC for applying accelerating voltage to the surface facing SUB
Are formed. On the other hand, the substrate SUB is an arbitrary solid, and the DC acceleration voltage VAC is applied between the substrate SUB and the electrode MAC. If the substrate SUB is an electrical insulator, a metal electrode can be formed on the surface to apply the voltage VAC.

Examples of the electron beam source EBS include Japanese Patent Publication No. 54-30274, Japanese Patent Laid-Open No. 54-111272, Japanese Patent Laid-Open No. 56-15529, and Japanese Patent Laid-Open No. 57-38528.
It is possible to use a structure as disclosed in Japanese Patent Publication No. This is because electrons are generated in the semiconductor substrate by supplying a reverse voltage to the pn junction and causing electron avalanche multiplication (avalanche multiplication).
The semiconductor substrate is made to emit electrons. According to this, the electron beam source EBS arranged two-dimensionally on such an electron beam generator BH, by independently controlling the application of the reverse voltage for each electron beam source EBS, independently. It is possible to drive.

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 be individually controlled to generate the electron beam CEB, but in the example of FIG. 3, 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 range from several K Hz to several 100 MHz.
The electron beam CEB generated intermittently is accelerated by the acceleration voltage VAC and collides with the surface of the substrate SUB, and the electron beam CEB is absorbed in the substrate SUB.
Generates ultrasonic waves with a frequency equal to the intermittent frequency of.

The generation of ultrasonic waves in a substrate by the collision of a single intermittent electron beam is described in, for example, “Ikoma Akatsuka,“ 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, the ultrasonic transducer EA shown in FIG.
At T, the electron beams CEB are arranged two-dimensionally and collide with the surface of the substrate SUB, so that the heat wave TW also becomes two-dimensionally aligned and becomes an ultrasonic wave generation source, and all electron beam sources EBS are interrupted at the same time. The 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 and become a plane wave APW, which propagates in the substrate SUB in the direction DP perpendicular to the surface thereof.

FIG. 4 is a sectional view showing another operation example of the ultrasonic transducer EAT of FIG. As mentioned above, the electron beam source EB
Each S can be driven independently. Fourth
In the figure, electron beam sources EBS1, EBS2,
The electron beam CEB having the same intermittent frequency is irradiated while sequentially delaying the ... As described above, these electron beams CEB collide with the substrate SUB and serve as ultrasonic wave generation sources, but since the electron beam CEBs generated from the respective electron beam sources EBS1, EBS2, ... The spherical wave of the ultrasonic wave generated from the generation source has a phase delay. Therefore, due to the principle of wave field synthesis, these spherical waves are superposed to form a plane wave APW propagating in the direction DS determined by this delay time.

The propagation direction DS of the ultrasonic wave APW generated in the substrate SUB is determined by the delay time of the intermittent electron beam CEB generated from the electron beam source EBS as described above. FIG. 5 is an explanatory view of such a relationship between the delay time and the propagation direction DS. Fifth
Figure (a) shows the substrate SUB from the propagation direction DS of the ultrasonic APW to the substrate SU.
It is a cross-sectional view when cut by a plane formed by a perpendicular line hung on the B surface, CEB1 and CEB2 are intermittent electron beams in this plane, P1 and
P2 is a point where the electron beams CEB1 and CEB2 on the surface of the substrate SUB are irradiated. The distance between points P1 and P2 is d, the ultrasonic wave propagation direction DS and the substrate
The angle formed by the perpendicular to the SUB surface is θ, and the ultrasonic velocity is V
a, the wavelength is represented by λ.

FIG. 5 (b) shows the interruption of the electron beam CEB irradiated to the points P1 and P2. At the point P2, the electron beam CE is delayed by a time τ from P1.
The case where B is intermittent is shown, and the intermittent frequency is f. Further, when the electron beam CEB2 reaches the point P2, the position in the substrate SUB where the point P1 reaches is defined as P1 ′, and the distance between the points P1 and P1 ′ is defined as h. Therefore, after the time τ, the electron beam CEB1 has moved by the distance τ · λ / (1 / f), and at this time, the interruption of the electron beam CEB at the points P1 and P2 causes the ultrasonic wave in the substrate SUB. The conditions that have the same effect on APW are: τ / (1 / f) ・ λ = h Therefore, τ / (1 / f) = h / λ = d / (λ / sinθ), so f ・ λ = Va, the propagation direction DS of the ultrasonic wave is given by sin θ = τ · Va / d (1). Alternatively, the substrate SUB
In order to generate ultrasonic waves in the desired direction, the formula (1) is modified and the generation of the electron beam CEB is delayed by using the time τ obtained from τ = d · sin θ / Va (2) You can do it.

FIG. 5 shows the substrate SU from the ultrasonic wave propagation direction DS as described above.
It is a cross-sectional view of a plane formed by a perpendicular line to the surface of B, but it is not necessary that one axis of the two-dimensionally arranged electron beam source EBS exists in this plane. FIG. 6 is a plan view of an electron beam generator EBH for explaining such a situation. In FIG. 6, white circles are electron beam sources arranged two-dimensionally.
Represents EBS. The x-axis is the oblique line of the ultrasonic wave propagation direction DS to the surface of the substrate SUB, and the y-axis is the direction orthogonal thereto, and the origin is an electron beam source EBS0 arbitrarily selected. At this time,
When the position of an arbitrary electron beam source EBSi is represented by (xi, yi), the delay time τi of the electron beam source EBSi with respect to the electron beam source EBS0 at the origin is
Is set as τi = x · sin θ / Va (3), the ultrasonic wave APW generated in the substrate SUB has a diagonal line to the surface of the substrate SUB in the traveling direction that coincides with the x axis, and a perpendicular line to the surface. The angle between and is θ. Therefore, the ultrasonic wave APW can be generated in any direction within the substrate SUB by appropriately selecting the x-axis and setting the relative delay of each electron beam source EBS so as to satisfy the expression (3). . Since the generation of such ultrasonic waves does not use the piezoelectricity of the SUS substrate,
It is possible to generate ultrasonic APW for any substrate.

Thus, the ultrasonic transducer EA used in the present invention
T is an ultrasonic wave APW of any frequency in any direction of the substrate SUS
Can occur. Due to this feature, in the acoustooptic device of the present invention, the incident light Li can be two-dimensionally deflected over a wide angle. These operations will be described with reference to FIGS. 7 and 8. FIG. 7 shows that in the embodiment shown in FIG. 1, ultrasonic waves can always be generated so as to satisfy the Bragg condition. Figure 7 (a)
Is the case where the incident light Li is deflected by the high-frequency ultrasonic wave APW. In this case, the wavelength Λ of the ultrasonic wave APW becomes small. Therefore, in order to satisfy the Bragg condition,
The incident angle θ of Li must be large. That is, the ultrasonic wave APW is generated so as to propagate while being inclined toward the incident side of the incident light Li with respect to the normal line of the surface of the substrate SUB.
The wavefront of W and the incident light Li can be made to satisfy the Bragg condition.

FIG. 7B shows a case where the light beam is deflected by the ultrasonic wave APW having a low frequency. In this case, since the wavelength Λ of the ultrasonic wave APW becomes large, in order to satisfy the Bragg condition,
The incident angle θ of the incident light Li must be small. Therefore, in this case as well, the ultrasonic wave APW is generated so as to propagate while being inclined opposite to the incident side of the incident light Li.
The angle θ between the wavefront of APW and the incident light Li can be set so as to satisfy the Bragg angle.

In the conventional example shown in FIG. 11 described above, the angle between the wavefront of the ultrasonic wave APW and the incident light Li is fixed at a preset value, because the Bragg condition can be satisfied only at the first frequency, There was a decrease in diffraction efficiency at frequencies other than this frequency,
In the present invention, the light deflection can be performed while always satisfying the Bragg condition as described with reference to FIG. Further, as described above, since the ultrasonic transducer EAT used in the present invention does not have a 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 there.

FIG. 8 shows that the acousto-optic device according to the present invention can perform two-dimensional deflection instead of one-dimensional deflection as in the conventional case. As is apparent from FIGS. 8 (a) and 8 (b), by tilting the wavefront of the ultrasonic wave APW in the direction perpendicular to the incident light Li, the incident light Li becomes in the direction perpendicular to the deflection direction due to the frequency change of the ultrasonic wave APW. Is also deflected, and by combining these two deflection directions, two-dimensional deflection is possible.

In the above description of the embodiments, in order to intermittently generate an ultrasonic wave by generating an ultrasonic wave, the electron beam may be intensity-modulated. For example, a sinusoidal intensity modulation or a duty ratio other than 1: 1 may be used. It is possible to use pulse modulation.

Further, the electron beam sources EBS arranged two-dimensionally can be driven independently, and the description has been given in the embodiment under such conditions. However, it is possible to independently drive any one of the two-dimensionally arranged electron beam sources EBS by commonly connecting the driving electrodes in a matrix to each electron beam source EBS. Such a driving method is effective when there are a large number of electron beam sources EBS and in order to reduce the complexity of wiring and driving. FIG. 9 is a circuit diagram of such a drive. Common electrodes X1, X2, ..., Y1, Y2 ... Are connected in a matrix to the electron beam source EBS in the vertical and horizontal directions, respectively. , X2, ... are connected to the control circuit CONT1 by electrodes
Y1, Y2 ... Are connected to the control circuit CONT2. For example,
The electron beam source EBS34 can be selected and driven by selecting the electrode X3 by the control circuit CONT1 and the electrode Y4 by the control circuit CONT2.

It is also possible to apply the present invention by combining such a driving method and ultrasonic wave generation by pulse modulation of an electron beam in which the above-mentioned duty ratio is 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 is driven at the same time. You can

In these examples, the electron beam generator EBH disclosed in Japanese Patent Publication No. 54-30274 was used as described above, but in the acoustooptic device according to the present invention, the electron beam source is independent. It is not an essential matter as long as it can be driven. Therefore, the same effects can be obtained by the present invention even if a negative work function using a pn junction, which is known as an electron beam source, or a solid-state electron source such as a field emission type is used.

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

EFFECTS OF THE INVENTION As described 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 arrayed individually controllable electron beam source. By deflecting the incident light by the desired ultrasonic wave generated, it becomes possible to always perform diffraction satisfying the Bragg condition in a wide frequency range, and it is possible to deflect light in a wide angle range. Further, by controlling the wavefront of the ultrasonic wave, the ultrasonic wave can be deflected by a frequency change and can be deflected in a direction perpendicular to the ultrasonic wave, so that two-dimensional optical deflection can be realized.

[Brief description of drawings]

1 is a schematic configuration diagram of an embodiment of an acousto-optic device 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.
7 and 8 are diagrams for explaining the operation of the acousto-optic device, FIG. 9 is a circuit diagram for simply driving the electron beam source, and FIGS. 10 and 11 are schematic configuration diagrams of a conventional ultrasonic optical deflector. Is. SUB is a medium having an acousto-optic effect, EAT is an ultrasonic transducer, EBH is an electron beam generator, EBS is an electron beam source,
SG is a high frequency signal source, D1 and D2 are electrodes, and MAC is an accelerating 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. An electron beam generator in which a plurality of electron beam sources that can be independently driven are two-dimensionally arranged, and a medium having an acousto-optic effect by individually generating intensity-modulated electron beams from each electron beam source. An acousto-optic device comprising: 2. The acousto-optic device according to claim 1, wherein the control means allows the individual electron beam sources to be driven and controlled with a delay of a desired time.