JPWO2010001852A1 - Light modulator - Google Patents

Abstract

The optical modulator includes an acoustooptic medium 1 and surface acoustic wave generating means 2 that generates surface acoustic waves in the acoustooptic medium 1. In the acousto-optic medium 1, a surface acoustic wave traveling region 3 which is a region where the surface acoustic wave generated by the surface acoustic wave generating means 2 is made of the same material. The acousto-optic medium 1 includes first and second end faces that face each other across the surface acoustic wave traveling region 3 in a direction that intersects the traveling direction of the surface acoustic wave. First-order diffracted waves generated when incident light incident from the first end face passes through the surface acoustic wave traveling region 3 and light that propagates in the acousto-optic medium 1 with the surface acoustic wave generating means 2 stopped. Are emitted in different directions from the second end face.

Description

  The present invention relates to an optical modulator using an acousto-optic material.

  FIG. 1 shows the configuration of a bulk acousto-optic device described in Patent Document 1 (Japanese Patent Laid-Open No. 06-273705). This bulk acoustooptic device includes an acoustooptic medium 200, a piezoelectric vibrator 201 formed on an end surface of the acoustooptic medium 200, and a high-frequency power source 202 for driving the piezoelectric vibrator 201.

  When the high-frequency voltage is supplied to the piezoelectric vibrator 201, the piezoelectric vibrator 201 vibrates, thereby generating an ultrasonic traveling wave 203 in the acoustooptic medium 200. In the region where the ultrasonic traveling wave 203 in the acousto-optic medium 200 reaches, the refractive index changes periodically. When incident light 206 is incident on this refractive index changing region at a Bragg diffraction angle θ, first-order diffracted light 204 is generated. On the other hand, when the supply of the high-frequency voltage to the piezoelectric vibrator 201 is stopped, the refractive index change region is not formed, so that the incident light 206 passes through the acoustooptic medium 200 as it is and is emitted as non-diffracted light 205.

  In addition to the above, there is a waveguide type acoustooptic device for optical communication described in Non-Patent Document 1 (Japanese Journal of Applied Physics Vol. 46, No. 2, pp. 669-674). FIG. 2 shows the configuration of the waveguide type acoustooptic device.

  As shown in FIG. 2, an optical waveguide 301 and comb-shaped electrodes 302 and 303 are formed on the piezoelectric element 300. The optical waveguide 301 is formed by increasing the refractive index in a region of the wavelength of light by the pronto exchange method, and the height is 0.8 μm.

  The comb-shaped electrode 302 includes first and second electrode portions each having a plurality of linear electrodes arranged at equal intervals, and the first and second electrode portions are alternately arranged with linear electrodes. ing. The comb electrode 303 also has the same structure as the comb electrode 302. The comb electrodes 302 and 303 are formed on both sides of the optical waveguide 301 so as to face each other.

  When a high frequency voltage is applied to the comb electrodes 302 and 303, surface acoustic waves are generated near the surface of the piezoelectric element 300. Due to the surface acoustic waves from the comb electrodes 302 and 303, the refractive index of the central portion of the optical waveguide 301 (the region sandwiched between the comb electrodes 302 and 303) changes. When light propagating in the optical waveguide 301 enters the refractive index change region, diffracted light is generated.

  The waveguide acousto-optic device is used as a device for modulating single mode infrared light of 10 mW or less.

  However, the acoustooptic device described above has the following problems.

  In the bulk acoustooptic device described in Patent Document 1, the acoustooptic medium 200 and the piezoelectric vibrator 201 are large in size, and the cross-sectional size of the region where the ultrasonic traveling wave 203 is generated is about several millimeters. The supply voltage to the piezoelectric vibrator 201 is several tens of volts or more, and the power consumption of the bulk acoustooptic device is several tens of watts or more. As described above, the bulk acoustooptic device has a problem that the device size is large and the power consumption is large.

  In particular, in an image display device such as a laser display, it is desired to reduce the size and power consumption of an optical modulator, and it is difficult to apply the bulk acousto-optic element to such an image display device. is there.

  The waveguide acoustooptic device for optical communication described in Non-Patent Document 1 has the following problems.

  (1) Since the waveguide type acoustooptic device has a structure in which incident light is confined in a waveguide having a size approximately equal to the wavelength of the light, depending on the intensity of the incident light, the optical density in the waveguide becomes extremely high, The waveguide may be damaged. Thus, the optical damage resistance of the waveguide type acoustooptic device is low. On the other hand, in an image display device such as a laser display, light modulation is performed on high output light of, for example, 100 mW or more. It is difficult to apply a waveguide acousto-optic element having low light damage resistance to an image display device that performs such high-power light modulation.

When the waveguide acoustooptic element is applied to an image display device, visible light having a wavelength shorter than that of infrared light is modulated by the waveguide acoustooptic element. In this case, the thickness of the waveguide is further reduced, and optical damage is likely to occur. Moreover, the optical damage resistance of the LiNbO ₃ material used for the waveguide is two orders of magnitude lower than that of glass. In optical communication applications, since signal light is amplified and relayed by a fiber amplifier, a high light output is not always required, and thus the above optical damage problem has not been revealed.

  (2) The above optical damage problem can be avoided by enlarging the cross-sectional size of the waveguide to lower the light density. However, when the cross-sectional size of the waveguide is enlarged, the light propagating in the waveguide becomes multimode without maintaining the single mode, and the traveling direction of the diffracted light of each waveguide mode is changed by Bragg diffraction with the acoustic wave. It will be different from each other. For this reason, when the cross-sectional size of the waveguide is enlarged, there arises a problem that the diffraction efficiency is remarkably lowered.

  (3) A typical surface acoustic wave is distributed at a depth of that wavelength (typically about 20 μm). The region where light propagating in the waveguide interacts with the surface acoustic wave is a region that is at most as narrow as the wavelength of the light, and in other wide regions, the surface acoustic wave does not contribute to light diffraction. Thus, the energy utilization rate of the surface acoustic wave is small.

  In the waveguide type acoustooptic device, in order to obtain sufficient diffracted light, the interaction length (in this case, the same as the waveguide length) needs to be 2 mm or more. For this reason, it is difficult to reduce the size of the element.

  (4) The diameter of the light beam for image display is 500 μm or more, and in order to put it in a waveguide having a thickness of about 1 μm, various optical systems are required, and light loss is generated accordingly. As described above, there is a problem that the optical insertion loss when the light beam for image display is put into the waveguide is large. In addition, there is a disadvantage that the number of parts of the device increases. Furthermore, since the element itself is large and its structure is complicated, the manufacturing cost also increases.

  An object of the present invention is to provide a small-sized optical modulator that can solve the above-described problems and can modulate a high-power light beam.

In order to achieve the above object, an optical modulator of the present invention includes:
An acousto-optic medium;
An acoustic wave generating means for generating a surface acoustic wave or an interfacial acoustic wave in the acoustooptic medium,
In the acousto-optic medium, an elastic wave propagation region covered with a surface elastic wave or an interface elastic wave generated by the elastic wave generating means is formed of the same material,
First and second end faces facing each other across the elastic wave propagation region in a direction intersecting the traveling direction of the surface acoustic wave or the interfacial elastic wave, and incident light incident from the first end face is elastic The first-order diffracted wave generated when passing through the wave propagation region and the light propagating through the acousto-optic medium in a state where the elastic wave generating means is stopped are respectively in different directions from the second end face. Emitted.

It is a schematic diagram which shows the structure of a bulk type acoustooptic device. It is a schematic diagram which shows the structure of the waveguide type acoustooptic element for optical communications. It is a schematic diagram which shows the structure of the optical modulator which is the 1st Embodiment of this invention. It is a schematic diagram for demonstrating Bragg diffraction in the optical modulator shown in FIG. It is a schematic diagram for demonstrating the structure of the optical modulator which is the 2nd Embodiment of this invention. It is a characteristic view which shows the beam propagation distance dependence of the diameter of a light beam. It is a schematic diagram for demonstrating the structure of the optical modulator which is the 3rd Embodiment of this invention. It is a schematic diagram for demonstrating the structure of the optical modulator which is the 4th Embodiment of this invention. It is a schematic diagram for demonstrating the structure of the optical modulator which is the 5th Embodiment of this invention. It is a characteristic view which shows the relationship between the diameter of a light beam and a beam condensing distance according to wavelength. It is a characteristic view which shows the relationship between the diameter of a light beam, and a beam condensing distance according to beam waist. It is a schematic diagram which shows an example of an image display apparatus provided with the optical modulator of this invention.

DESCRIPTION OF SYMBOLS 1 Acousto-optic medium 2 Surface acoustic wave generating means 3 Surface acoustic wave traveling region

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 3 is a schematic diagram showing the configuration of the optical modulator according to the first embodiment of the present invention.

  Referring to FIG. 3, the optical modulator includes an acoustooptic medium 1 and surface acoustic wave generating means 2 formed on the surface of the acoustooptic medium 1. The acousto-optic medium 1 is a medium for causing the surface acoustic wave generated by the surface acoustic wave generating means 2 to interact with incident light. Such interaction between surface acoustic waves and incident light is generally called an acousto-optic effect. The acoustooptic medium 1 is made of a material capable of obtaining an acoustooptic effect, for example, an acoustooptic material doped with quartz or impurities. The impurity is, for example, Er (erbium), In (indium), or the like.

  The surface acoustic wave generating means 2 is composed of, for example, a plurality of linear electrodes arranged at equal intervals on the same plane, and an even-numbered linear electrode group and an odd-numbered linear electrode group counted from one side, A high frequency voltage is applied between the two. As an example of such an electrode structure, there is an electrode structure composed of first and second comb electrodes. In the first and second comb electrodes, linear electrodes corresponding to the comb teeth are alternately arranged, and the intervals between the linear electrodes are equal. Note that the intervals between the linear electrodes are not only in a state where the distances between the linear electrodes are completely matched, but also in a state where the spacing between the linear electrodes is shifted due to a manufacturing error or the like. Is also included.

  By applying a high frequency voltage between the comb electrodes, a surface acoustic wave is generated in the vicinity of the surface of the acoustooptic medium 1. The surface acoustic wave is a traveling wave that travels along the surface portion of the acousto-optic medium 1 along the alignment direction of the linear electrodes (the direction intersecting the length direction of the linear electrodes), and is refracted along the traveling direction. A periodic change in rate occurs.

  The surface acoustic wave traveling region 3, which is a region (surface acoustic wave propagation region) covered by the surface acoustic wave, is made of the same material, and the depth thereof is about the wavelength of the surface acoustic wave. For example, the depth of the region covered by the surface acoustic wave of wavelength Λ is the wavelength Λ. The wavelength Λ of the surface acoustic wave (or the depth of the region covered by the surface acoustic wave 3) is determined by the interval (period) of the linear electrodes and the frequency of the high-frequency voltage applied between the linear electrode groups (surface acoustic wave generation The driving frequency of the means 2). The width L of the surface acoustic wave traveling region 3 (the width in the length direction of the linear electrode) is an interaction length in which an acoustooptic effect is generated.

  Of the side surfaces of the acousto-optic medium 1, one of the side surfaces facing each other with the surface acoustic wave traveling region 3 interposed therebetween is an incident end surface, and the other is an output end surface. The surface on which the surface acoustic wave generating means 2 is formed is a plane that intersects with each of the incident end face and the exit end face.

  The incident angle of the light beam with respect to the incident end face of the acoustooptic medium 1 is set so that the light beam from the incident end face enters the surface acoustic wave traveling region 3 at a predetermined incident angle. Here, the predetermined incident angle is an angle satisfying a condition that the light beam from the incident end face is refracted when passing through the surface acoustic wave traveling region 3, and more preferably, the light beam is in the surface acoustic wave traveling region. The angle satisfies a condition such that Bragg diffraction occurs when passing through 3.

  FIG. 4 schematically shows diffraction in the optical modulator shown in FIG. The surface acoustic wave travels in the vicinity of the surface of the acoustooptic medium 1 from the near side toward the far side as viewed in the drawing. The light beam 4 is incident on the incident end face of the acoustooptic medium 1 from the left side as viewed in the drawing. When the incident light beam 4 passes through the surface acoustic wave traveling region 3, a first-order diffracted wave 4a is generated by Bragg diffraction. The first-order diffracted wave 4 a is emitted outward from the emission end face of the acousto-optic medium 1.

  When the supply of the high-frequency voltage to the surface acoustic wave generating means 2 is stopped, the surface acoustic wave traveling region 3 is not formed, so that the incident light beam 4 propagates through the acoustooptic medium 1 without being diffracted and exits. The light is emitted from the end face toward the outside. The traveling direction of light from the emission end face is the same as the traveling direction of zero-order light.

  The optical axis of the first-order diffracted wave 4a emitted from the emission end face when the high-frequency voltage is supplied is Bragg relative to the optical axis of light (zero-order light) emitted from the emission end face when the supply of the high-frequency voltage is stopped. It is tilted by the diffraction angle. Therefore, by controlling the supply of the high-frequency voltage to the surface acoustic wave generating means 2, the traveling direction of the output light from the emission end face can be switched, whereby the light beam 4 can be modulated. Usually, the first-order diffracted wave 4a is used as the output light of the optical modulator.

  The diameter of the light beam 4 is defined by the wavelength Λ of the surface acoustic wave (or the depth of the region covered by the surface acoustic wave 3). Although not shown in FIGS. 3 and 4, as an optical system for making the light beam 4 incident on the acousto-optic medium 1, an optical system comprising an antireflection film, a reflecting mirror, an aspheric lens, etc. provided on the incident end face Is used. The light beam 4 is a parallel light beam having an elliptical cross section, and the beam diameter of the light beam 4 is set so that most of the light beam 4 passes through at least a part of the surface acoustic wave traveling region 3.

Here, as shown in FIG. 4, in the cross-sectional shape of the light beam 4, the beam width in the depth direction (X direction) is the vertical beam width d _v (z), and the beam width in the horizontal direction (Y direction) is horizontal. Called the beam width d _h (z).

Considering the diffraction efficiency of the light beam, the vertical beam width d _v (z) is preferably about the depth Λ of the region (elastic wave propagation region) covered by the surface acoustic wave 3 or slightly smaller than Λ. This is because when the portion of the light beam that passes through the region where the surface acoustic wave 3 does not reach is increased, the light beam portion is not diffracted, so that the extinction ratio during modulation decreases. However, the area of the edge portion of the elliptical cross-sectional shape of the light beam is small, and the vertical beam width has a distribution that slightly spreads depending on the position in the Z direction. Considering this, it is desirable that the vertical beam width d _v (z) is smaller than 1.2 × Λ. By satisfying this condition, the degree of reduction in the extinction ratio can be suppressed to 5% or less, which is a normal specification for a display.

When the beam cross-sectional area is reduced, a high extinction ratio can be obtained, but the light density is increased, so that the intensity of the light beam that can be used is limited. Although details will be described later, the light beam intensity in the case of using quartz is about 200 mW at the maximum when the vertical beam width is Λ. The light beam intensity required for the display depends on the size and configuration of the screen, and is usually 20 mW to 200 mW. Therefore, it is desirable that the vertical beam width d _v (z) is larger than 0.1 × Λ.

Under these conditions, the surface acoustic wave traveling region 3 has a depth Λ (the depth Λ corresponds to the interval between the linear electrodes) and a width L (the width L corresponds to the width of the intersection of the linear electrodes). The vertical beam width d _v (z) satisfies the condition of 0.1 × Λ <d _v (z) <1.2 × Λ for an arbitrary z (0 ≦ z ≦ L). Fulfill. More preferably, the vertical beam width d _v (z) satisfies the condition of 0.7 × Λ <d _v (z) <Λ. Here, the width direction of the surface acoustic wave traveling region 3 is a direction (Z direction) perpendicular to the depth direction (X direction) and the traveling direction (Y direction). The depth Λ is, for example, about 30 μm.

The horizontal beam width d _h (z) in the Y direction is determined by setting the driving frequency f of the surface acoustic wave generating means (or the interfacial elastic wave generating means), which is the elastic wave generating means, to the propagation velocity v of the surface acoustic wave (or the interfacial elastic wave). A value W divided by (= v / f) or a smaller value. This is because if the horizontal beam width is larger than W, the individual modulation signals cannot be sufficiently separated, and the resolution of the display image is lowered.

The horizontal beam width d _h (z) must be greater than 2 × Λ. This is because if the number of surface acoustic waves that fall within the horizontal beam width (when counted as one at one wavelength) is less than 3, the diffraction efficiency decreases. In order to obtain high diffraction efficiency, it is necessary to make the modulation frequency f smaller than v / 2Λ.

After all, when the optical modulator is driven at the frequency f (MHz), the horizontal beam width d _h (z) in the Y direction is 2 × Λ <d _h (z) ≦ with respect to the propagation velocity v of the surface acoustic wave. The condition of W (= v / f> 2 × Λ) is satisfied.

In the present embodiment, since the first-order diffracted wave 4a is used as output light of the optical modulator, the extinction ratio can be increased by increasing the light amount (luminance) of the first-order diffracted wave 4a. The amount of light (luminance) of the first-order diffracted wave 4 a is proportional to the amount of light beam incident on the surface acoustic wave traveling region 3. By satisfying the above-mentioned conditions of the vertical beam width d _v (z) and the horizontal beam width d _h (z), most of the light beam 4 passes through the surface acoustic wave traveling region 3. Thereby, the extinction ratio can be increased.

  Further, by setting the beam diameter of the light beam 4 so as to satisfy the above conditions, most of the light beam 4 passes through the surface acoustic wave traveling region 3 even when the drive frequency f of the optical modulator is set high. Will do. Therefore, for example, even when modulation is performed in a high band of 30 MHz or higher, the extinction ratio can be increased.

  Further, unlike the waveguide type acoustooptic device described in Non-Patent Document 1, the optical modulator of this embodiment does not have a waveguide structure in the acoustooptic medium 1. In addition, the acousto-optic medium 1 is made of a material (crystal or acousto-optic material doped with impurities) having excellent optical damage resistance. For this reason, there is no problem that the acoustooptic medium 1 is damaged when a high-power light beam, for example, a light beam of 100 mW or more is modulated.

  In addition, when a single mode light beam enters the acoustooptic medium 1, the incident light passes through the surface acoustic wave traveling region 3 while maintaining the single mode. When the conditions for Bragg diffraction are satisfied, high-order diffracted waves other than the first-order diffracted wave 4a are small and can be ignored. Therefore, the single-mode primary diffraction wave 4a can be obtained. Thus, according to the optical modulator of this embodiment, single-mode output light can be obtained. In order to obtain the single-mode first-order diffracted wave 4a, it is desirable to use a Gaussian beam as the light beam.

  Furthermore, in the waveguide type acoustooptic device, the interaction length L needs to be 2 mm or more. However, according to the optical modulator of this embodiment, for example, the depth of the surface acoustic wave traveling region 3 (surface elasticity) (Corresponding to the wave wavelength) is 20 μm, the interaction length L is 400 μm. Thus, since the interaction length L can be reduced, the optical modulator can be miniaturized.

  In the waveguide acousto-optic device, the region where the interaction occurs is limited to the inside of the waveguide, and the region is a region that is at most as narrow as the wavelength of incident light. Therefore, for example, when a surface acoustic wave having a wavelength of 20 μm is generated, the depth of the region covered by the surface acoustic wave is 20 μm, but the interaction occurs only in a narrow region in the waveguide. The energy utilization rate is low. On the other hand, according to the optical modulator of the present embodiment, the beam diameter of the light beam 4 is set according to the depth of the surface acoustic wave traveling region 3 and the interaction length. In other words, it is possible to set conditions such that the light beam 4 is incident on the entire surface acoustic wave traveling region 3. Thereby, an interaction can be generated in a wide region in the surface acoustic wave traveling region 3, and the energy utilization rate of the surface acoustic wave can be improved.

  Further, by forming the surface acoustic wave generating means 2 with comb-shaped electrodes, the electrode area (capacitance) and the driving voltage can be reduced and the power consumption can be reduced as compared with the piezoelectric vibrator. Therefore, a small element with low power consumption can be provided. In addition, by using a comb electrode having a high driving frequency, an optical modulator capable of driving in a high band of, for example, 20 MHz or more can be provided.

(Second Embodiment)
In order to make the light beam efficiently enter the surface acoustic wave traveling region 3, it is desirable to reduce the diameter of the light beam using an optical system. Here, an embodiment including such an optical system will be described.

  FIG. 5 is a diagram for explaining a configuration of an optical modulator according to the second embodiment of the present invention, and a partial view indicated by an arrow 100A is a schematic diagram viewed from the upper surface side of the optical modulator. The partial view indicated by the arrow 100B is a schematic view seen from the side of the optical modulator. As shown in FIG. 5, a piezoelectric material 108 having comb-shaped electrodes 102 formed on the surface is formed on a support substrate 101. The piezoelectric material 108 is, for example, quartz. The material of the support substrate 101 is, for example, silicon (Si).

  The comb-shaped electrode 102 is a surface acoustic wave generating means, and includes first and second comb-shaped electrodes in which linear electrodes corresponding to each other's comb teeth are alternately arranged, and the intervals between the linear electrodes are equal. It is. By supplying a high-frequency voltage between the first and second comb electrodes, a surface acoustic wave 110 a is generated near the surface of the piezoelectric material 108. When the piezoelectric material 108 is made of quartz, the traveling speed of the surface acoustic wave 110a is 3157 m / s.

  The period of the first comb electrode (interval of the comb teeth) and the period of the second comb electrode (interval of the comb teeth) are the same. Here, the period of each of the first and second comb electrodes is Λ To do. Further, the interaction length of the comb electrode 102 is L. The region (surface acoustic wave propagation region) covered by the surface acoustic wave 110a is made of the same material, and the depth from the surface is the same as the period Λ.

  An ultrasonic wave absorbing portion 103 for absorbing the surface acoustic wave 110 a is formed in the traveling direction of the surface acoustic wave 110 a generated by the comb electrode 102 in the piezoelectric material 108. It is desirable that the cross-sectional area in the direction perpendicular to the surface acoustic wave traveling direction of the ultrasonic absorber 103 is equal to or larger than the cross-sectional area of the elastic wave propagation region. Any material or shape may be used as the ultrasonic absorber 103 as long as it can absorb ultrasonic waves (surface acoustic waves and sea surface acoustic waves).

  Of the end faces of the piezoelectric material 108, one of the end faces located in the direction intersecting with the traveling direction of the surface acoustic wave 110a is the incident end face, and the other is the exit end face. A front end antireflection film 106 is formed on the incident end face, and a rear end antireflection film 107 is formed on the output end face. On the support substrate 101, condensing lenses 105a and 105b are further provided via optical jigs 109a and 109b, respectively.

  The condensing lens 105 a condenses the incident light beam 104. The incident light beam 104 is a parallel light beam. The light beam condensed by the condenser lens 105 a enters the piezoelectric material 108 from the incident end face of the piezoelectric material 108. The incident light beam is incident on the region covered by the surface acoustic wave 110a at a predetermined incident angle. Here, the predetermined incident angle is an angle that satisfies a condition that causes Bragg diffraction.

The shape of the cross section of the light beam collected by the condensing lens 105a in the region covered by the surface acoustic wave 110a is an elliptical shape, and the vertical beam width d and horizontal beam width W in the cross section are the aforementioned vertical beam width d. Each condition regarding _v (z) and horizontal beam width d _h (z) is satisfied. The vertical beam width d and the horizontal beam width W can be adjusted by the position, focal length, direction (optical axis direction), etc. of the condenser lens 105a.

  The condensing lens 105b is provided in the traveling direction of the light beam (here, the diffracted light beam 104a) from the emission end face of the piezoelectric material 108. The diffracted light beam 104a is diffused light (first-order diffracted light), and the condenser lens 105b is used to make the diffracted light beam 104a a parallel light beam. A light ray passing through the center of the cross section of the diffracted light beam 104a in a direction intersecting the traveling direction (this light ray locus corresponds to the optical axis of the diffracted light beam 104a) coincides with the optical axis of the condenser lens 105b. The angle between the optical axis of the diffracted light beam 104a and the optical axis of the outgoing light beam 104b (0th-order light) emitted from the outgoing end face when the supply of the high-frequency voltage is stopped is 2θ. This angle 2θ is equal to the Bragg diffraction angle.

  Next, the operation of the optical modulator of this embodiment will be described.

  When a high-frequency voltage is supplied to the comb electrode 102, a surface acoustic wave 110a is generated near the surface of the piezoelectric material 108. Bragg diffraction occurs when the light beam obtained by condensing the incident light beam 104 by the condenser lens 105a passes through the region covered by the surface acoustic wave 110a. As a result, the diffracted light beam 104a is emitted from the emission end face of the piezoelectric material 108. Is done. The diffracted light beam 104a is converted into a parallel light beam by the condenser lens 105b. The diffracted light beam 104a formed into the parallel light beam is used as output light of the light modulator.

  When the supply of the high-frequency voltage to the comb-shaped electrode 102 is stopped, the surface acoustic wave 110a is not generated. Therefore, the light beam condensed by the condenser lens 105a propagates in the piezoelectric material 108 without being diffracted. Then, the emitted light beam 104b is emitted from the emission end face. The outgoing light beam 104b deviates from the optical path of the diffracted light beam 104a that is the output light of the optical modulator.

  Thus, by controlling the supply of the high-frequency voltage to the comb-shaped electrode 102, the on / off of the output light (diffracted light beam 104a) of the optical modulator can be controlled.

  The effects described in the first embodiment can also be obtained by the optical modulator of this embodiment.

  FIG. 6 shows the beam propagation distance dependence of the diameter of the light beam. The vertical axis represents the diameter r of the light beam, and the horizontal axis represents the beam propagation direction x. The point where the propagation direction x is 0 corresponds to the incident position of the light beam in the region covered by the surface acoustic wave. The graph of the R light beam (630 nm) is indicated by a one-dot chain line, the graph of the G light beam (530 nm) is indicated by a broken line, and the graph of the B light beam (470 nm) is indicated by a solid line. The depth Λ of the region covered with the surface acoustic wave is ˜20 μm.

  In any of the R light beam, G light beam, and B light beam, if the vertical beam width d is 15 μm, the interaction length L is 2 mm, and the depth Λ of the region covered by the surface acoustic wave is 20 μm. The light beam can be contained within a certain area.

  Note that the vertical beam width d and horizontal beam width W of the light beam, the depth Λ of the region covered by the surface acoustic wave, and the interaction length L take into account diffraction efficiency, light damage resistance, light density, element size, and the like. It is desirable to set appropriately. For example, when the vertical beam width d is 15 μm and the depth Λ is 20 μm, the interaction length L may be about 400 μm. Even in such a setting, the element size can be reduced without impairing the diffraction efficiency and light damage resistance.

  Further, when the vertical beam width d and the horizontal beam width W are reduced, a condensing lens having a short focal length is used. By using a condensing lens with a short focal length, the distance between the condensing lens and the piezoelectric material 108 can be reduced, and the size of the optical modulator can be reduced accordingly. The vertical beam width d and the horizontal beam width W are determined by the depth Λ and the interaction length L of the region covered by the surface acoustic wave.

  According to the optical modulator of this embodiment, for example, since the interaction length L can be reduced from 2 mm to 400 μm, the element size can be reduced.

Further, when the modulator is driven at a modulation frequency of 20 MHz, the depth Λ is 20 μm and the horizontal beam width W is 105 μm. The maximum allowable light density in the visible light of quartz is 100 W / mm ² or more, and the maximum allowable light output is

で与えられる。これは、大型ディスプレイ用のレーザ光源に必要なレベルの光出力を得ることが可能であることを意味する。すなわち、本実施形態の光変調器によれば、２００ｍＷ以上の大出力の可視光を３０ＭＨｚ以上の高帯域で変調するディスプレイ用の光ビーム変調器を提供することが可能である。

Given in. This means that it is possible to obtain a light output of a level necessary for a laser light source for a large display. That is, according to the light modulator of the present embodiment, it is possible to provide a light beam modulator for display that modulates high-power visible light of 200 mW or more in a high band of 30 MHz or more.

(Third embodiment)
By expanding the range in the depth direction of the region covered by the surface acoustic wave, it becomes possible to modulate a light beam with higher output. Here, a configuration of an optical modulator capable of modulating such a high-output light beam will be described.

  FIG. 7 is a schematic diagram for explaining the configuration of the optical modulator according to the third embodiment of the present invention. This optical modulator has the same configuration as that of the optical modulator of the second embodiment, except that surface acoustic wave generating means (comb-shaped electrodes) are provided on each of the front and back surfaces of the piezoelectric material.

  The front surface comb electrode 102 a is formed on the surface of the piezoelectric material 108, and the back surface comb electrode 102 b is formed on the back surface of the piezoelectric material 108. Each of the front comb electrode 102a and the back comb electrode 102b has the same configuration as the comb electrode 102 shown in FIG. 5, and the first and second linear electrodes corresponding to the comb teeth are alternately arranged. Composed of comb-shaped electrodes, the intervals between the linear electrodes are equal.

  The first and second comb electrodes of the front surface comb electrode 102a are disposed at positions facing the first and second comb electrodes of the back surface comb electrode 102b, respectively. The periods of the first and second comb electrodes constituting the front comb electrode 102a and the back comb electrode 102b are the same. Here, the period of the first and second comb electrodes is Λ.

  By applying a high-frequency voltage to the surface comb electrode 102a, a first surface acoustic wave having a wavelength Λ is generated near the surface of the piezoelectric material 108 on which the surface comb electrode 102a is provided. Similarly, by applying a high frequency voltage to the back comb electrode 102b, a second surface acoustic wave having a wavelength Λ is generated in the vicinity of the surface of the surface of the piezoelectric material 108 on which the back comb electrode 102b is provided. The traveling directions of the first and second surface acoustic waves are the same. The periodic change in the refractive index formed along the traveling direction of the first surface acoustic wave is the same as the periodic change in the refractive index formed along the traveling direction of the second surface acoustic wave. It is. Therefore, when the region covered by the first surface acoustic wave and the region covered by the second surface acoustic wave overlap each other in the depth direction, the first and second surface acoustic waves are integrated into one surface. It can be regarded as an elastic wave.

  The depth of the region covered with the first surface acoustic wave from the surface side on which the surface comb-shaped electrode 102a is formed is Λ, and the region covered with the second surface acoustic wave on which the back surface comb-shaped electrode 102b is formed. The depth from is also Λ. Therefore, if the distance between the surface on which the front surface comb-shaped electrode 102a is formed and the surface on which the rear surface comb-shaped electrode 102b is formed is 2Λ or less, the region covered by the first surface acoustic wave and the region covered by the second surface acoustic wave Overlap with each other in the depth direction. In the present embodiment, the thickness of the piezoelectric material 108 is set so that the region covered by the first surface acoustic wave and the region covered by the second surface acoustic wave overlap each other in the depth direction.

  In the present embodiment, the light beam collected by the condenser lens 105a is incident at a predetermined incident angle on the region covered by the first and second surface acoustic waves. Here, the predetermined incident angle is an angle that satisfies a condition that causes Bragg diffraction.

Further, the shape of the cross section of the light beam collected by the condensing lens 105a in the region where the first and second surface acoustic waves reach is an elliptical shape, and the vertical beam width d and the horizontal beam width W in the cross section are Each condition regarding the vertical beam width d _v (z) and the horizontal beam width d _h (z) is satisfied.

  According to the optical modulator of the present embodiment configured as described above, the range in the depth direction of the region covered by the surface acoustic wave is expanded by about twice as much as that of the second embodiment. Therefore, the output of the light beam that can be modulated can be increased accordingly. Specifically, in the second embodiment, when a 200 mW light beam can be modulated, in this embodiment, a light beam of about 400 W, which is twice that, can be modulated. In this way, it is possible to provide a light beam modulator for a display having a higher output.

(Fourth embodiment)
The optical modulators of the first to third embodiments use surface acoustic waves, but it is also possible to use interface acoustic waves instead of surface acoustic waves. Here, the configuration of an optical modulator that modulates a light beam using such an interfacial acoustic wave will be described.

  FIG. 8 is a diagram for explaining the configuration of the optical modulator according to the fourth embodiment of the present invention, and a partial view indicated by an arrow 200A is a schematic view seen from the upper surface side of the optical modulator. The partial view indicated by the arrow 200B is a schematic view seen from the side of the optical modulator. This optical modulator has the same configuration as that of the optical modulator of the second embodiment except that an interfacial acoustic wave generating means is provided in place of the surface acoustic wave generating means.

  As shown in FIG. 8, a buried comb-shaped electrode 112 that is an interfacial acoustic wave generating means is formed in the piezoelectric material 108. The embedded comb-shaped electrode 112 is composed of first and second comb-shaped electrodes in which linear electrodes corresponding to mutual comb teeth are alternately arranged, and the intervals between the linear electrodes are equal. The period of the first comb electrode (interval of comb teeth) and the period of the second comb electrode (interval of comb teeth) are the same. Here, each period of the first and second comb electrodes is Λ. Further, the interaction length of the comb electrode 102 is L.

  By supplying a high-frequency voltage between the first and second comb electrodes, an interfacial elastic wave 110b having a wavelength Λ is generated in the piezoelectric material 108. The propagation speed of the interfacial elastic wave 110b is faster than the propagation speed of the surface acoustic wave.

  The interfacial acoustic wave 110b travels in the vicinity of a plane (a plane intersecting with each of the incident end face and the exit end face) including each linear electrode in the piezoelectric material 108 in a direction intersecting with the longitudinal direction of the linear electrode. . A region (elastic wave propagation region) covered with the interfacial elastic wave 110b is made of the same material. In the direction perpendicular to the plane including each linear electrode (the depth direction of the piezoelectric material), the interfacial acoustic wave 110b exists in the vertical direction of the plane, and the depth of each is approximately the wavelength Λ. Accordingly, the range in the depth direction of the region covered by the interfacial elastic wave 110b is about 2Λ. As the interaction region between the light beam and the interfacial elastic wave, the entire region covered by the interfacial elastic wave 110b (depth 2Λ) can be used. Of these, the region (depth Λ) located below the plane including each linear electrode is used as the interaction region.

  An ultrasonic wave absorbing portion 103 for absorbing the interfacial elastic wave 110b is formed in the traveling direction of the interfacial elastic wave 110b in the piezoelectric material 108.

  The light beam condensed by the condenser lens 105 a enters the piezoelectric material 108 from the incident end face of the piezoelectric material 108. The incident light beam is incident on the region covered by the interfacial acoustic wave 110b at a predetermined incident angle. Here, the region covered by the interfacial acoustic wave 110b is a region located below the plane including each linear electrode. The predetermined incident angle is an angle that satisfies a condition that causes Bragg diffraction.

The shape of the cross section of the light beam collected by the condensing lens 105a in the region where the interfacial acoustic wave 110b reaches is an elliptical shape, and the vertical beam width d and horizontal beam width W in the cross section are the aforementioned vertical beam width d. Each condition regarding _v (z) and horizontal beam width d _h (z) is satisfied. The vertical beam width d and the horizontal beam width W can be adjusted by the position, focal length, direction (optical axis direction), etc. of the condenser lens 105a.

  The condensing lens 105b is provided in the traveling direction of the light beam (here, the diffracted light beam 104a) from the emission end face of the piezoelectric material 108. The diffracted light beam 104a is diffused light (first-order diffracted light), and the condenser lens 105b is used to make the diffracted light beam 104a a parallel light beam. A light ray passing through the center of the cross section of the diffracted light beam 104a in a direction intersecting the traveling direction (this light ray locus corresponds to the optical axis of the diffracted light beam 104a) coincides with the optical axis of the condenser lens 105b. The angle between the optical axis of the diffracted light beam 104a and the optical axis of the outgoing light beam 104b (0th-order light) emitted from the outgoing end face when the supply of the high-frequency voltage is stopped is 2θ. This angle 2θ is equal to the Bragg diffraction angle.

  Next, the operation of the optical modulator of this embodiment will be described.

  When a high frequency voltage is supplied to the embedded comb electrode 112, an interfacial elastic wave 110 b is generated inside the piezoelectric material 108. Bragg diffraction occurs when the light beam from the condenser lens 105a passes through the region covered by the interfacial acoustic wave 110b. As a result, the diffracted light beam 104a is emitted from the emission end face of the piezoelectric material 108. The diffracted light beam 104a is converted into a parallel light beam by the condenser lens 105b. The diffracted light beam 104a formed into the parallel light beam is used as output light of the light modulator.

  When the supply of the high-frequency voltage to the embedded comb electrode 112 is stopped, the interfacial acoustic wave 110b is not generated, so that the light beam from the condenser lens 105a propagates through the piezoelectric material 108 as it is without being diffracted. Then, the emitted light beam 104b is emitted from the emission end face. The outgoing light beam 104b deviates from the optical path of the diffracted light beam 104a that is the output light of the optical modulator.

  In this way, by controlling the supply of the high-frequency voltage to the embedded comb electrode 112, the on / off of the output light (diffracted light beam 104a) of the optical modulator can be controlled.

  The effects described in the second embodiment can also be obtained by the optical modulator of this embodiment.

  In addition, since the propagation speed of the interfacial acoustic wave 110b is faster than the propagation speed of the surface acoustic wave, an optical modulator that can be driven in a higher band can be provided as compared with a form using the surface acoustic wave. . According to the present embodiment, it is possible to provide an optical modulator that can be driven in a high band of, for example, 100 MHz or more. In order to realize a large high-definition display, an optical modulator capable of high-speed modulation is required. According to this embodiment, since high-speed modulation is possible, a large-sized high-definition display can be realized.

(Fifth embodiment)
By expanding the range in the depth direction of the region covered by the interfacial elastic wave, it becomes possible to modulate a light beam with higher output. Here, a configuration of an optical modulator capable of modulating such a high-output light beam will be described.

  FIG. 9 is a schematic diagram for explaining a configuration of an optical modulator according to the fifth embodiment of the present invention. This optical modulator has the same configuration as that of the optical modulator of the fourth embodiment, except that two interfacial acoustic wave generating means (comb-shaped electrodes) are provided in portions facing each other in the depth direction in the piezoelectric material. belongs to.

  Embedded comb electrodes 112a and 112b are formed inside the piezoelectric material 108 so as to face each other in the depth direction. The embedded comb electrodes 112a and 112b have the same configuration as the embedded comb electrode 112 shown in FIG. 8, and first and second comb electrodes in which linear electrodes corresponding to each other's comb teeth are alternately arranged. The intervals between the linear electrodes are equal.

  The first and second comb electrodes of the embedded comb electrode 112a are arranged at positions facing the first and second comb electrodes of the embedded comb electrode 112b, respectively. The periods of the first and second comb electrodes constituting the embedded comb electrode 112a and the embedded comb electrode 112b are the same. Here, the period of the first and second comb electrodes is Λ.

  By applying a high frequency voltage to the embedded comb electrode 112a, a first interfacial elastic wave having a wavelength Λ is generated inside the piezoelectric material 108. Similarly, when a high frequency voltage is applied to the embedded comb electrode 112b, a second interface elastic wave having a wavelength Λ is generated inside the piezoelectric material 108. The traveling directions of the first and second interfacial elastic waves are the same. Further, the periodic change in the refractive index formed along the traveling direction of the first interfacial elastic wave is the same as the periodic change in the refractive index formed along the traveling direction of the second interfacial elastic wave. It is. Therefore, when the region covered by the first interfacial elastic wave and the region covered by the second surface interfacial elastic wave overlap each other in the depth direction, the first and second interfacial elastic waves are integrated into one It can be regarded as an interfacial elastic wave.

  In the direction perpendicular to the plane including the respective linear electrodes constituting the embedded comb electrode 112a (the depth direction of the piezoelectric material), the first interfacial elastic waves are present in the vertical direction of the plane, respectively, and the depths thereof are both The wavelength is about Λ. Similarly, in the direction perpendicular to the plane including the linear electrodes constituting the embedded comb electrode 112b (the depth direction of the piezoelectric material), the second interfacial elastic wave exists in the vertical direction of the plane, Both depths are about the wavelength Λ. If the distance between the plane including each linear electrode constituting the embedded comb electrode 112a and the plane including each linear electrode constituting the embedded comb electrode 112b is 2Λ or less, the region covered by the first interfacial elastic wave and the second The region covered with the interfacial elastic wave overlaps with each other in the depth direction. In the present embodiment, the interval between the embedded comb electrodes 112a and 112b is set so that the region covered by the first interface acoustic wave and the region covered by the second interface acoustic wave overlap each other in the depth direction. .

  In the present embodiment, the light beam condensed by the condenser lens 105a is incident at a predetermined incident angle on the region covered by the first and second interface elastic waves. Here, the predetermined incident angle is an angle that satisfies a condition that causes Bragg diffraction.

Further, the shape of the cross section of the light beam collected by the condensing lens 105a in the region where the first and second interfacial elastic waves reach is an elliptical shape, and the vertical beam width d and the horizontal beam width W in the cross section are Each condition regarding the vertical beam width d _v (z) and the horizontal beam width d _h (z) is satisfied.

  According to the optical modulator of the present embodiment configured as described above, the range in the depth direction of the region covered by the interfacial acoustic wave is expanded by a maximum of about two times compared to the fourth embodiment. Therefore, the output of the light beam that can be modulated can be increased accordingly. Specifically, in the case of the third embodiment, when a 200 mW light beam can be modulated, in this embodiment, a light beam of about 400 W, which is twice that, can be modulated. In this way, it is possible to provide a light beam modulator for a display having a higher output.

  According to the optical modulators of the first to fifth embodiments described above, a compact optical modulator capable of modulating high-power visible light of 200 mW or more with a high bandwidth of 30 MHz or more and a high extinction ratio. Can be provided. Such a light modulator is most suitable as a light beam modulator for a laser display that modulates high-power visible light.

  The optical modulators according to the first to fifth embodiments are examples of the present invention, and the configuration thereof can be changed as appropriate. For example, it is desirable to design the piezoelectric material and the condensing lens in consideration of diffraction efficiency, light density, light damage resistance, and the like.

  For example, in each embodiment, by increasing the speed of the surface acoustic wave (or interfacial elastic wave), the diffraction efficiency during high-speed modulation can be increased and the light density can be decreased. Specifically, the propagation speed of surface acoustic waves when using quartz as the piezoelectric material is 3157 m / s, whereas the propagation of surface acoustic waves when using LN (lithium niobate) as the piezoelectric material. The speed is 4000 m / s. Therefore, by using LN as the piezoelectric material, it is possible to improve the diffraction efficiency and the light density.

In addition, since LiNbO ₃ crystal doped with several percent of impurities such as Er (erbium) and In (indium) has a light damage resistance more than three times that of quartz, LiNbO doped with such impurities as a piezoelectric material. By using _three crystals, a structure excellent in light damage resistance can be provided. In this case, a light beam of about 1 W can be modulated.

  In addition, when quartz is used as the piezoelectric material, impurities may be introduced into the quartz. By introducing impurities into the crystal, it is possible to improve light damage resistance.

  Further, a Gaussian beam may be used as the light beam.

  Further, the condensing distance of the condensing lens varies depending on the wavelength of the light beam. FIG. 10 shows the relationship between the diameter of the light beam and the beam focusing distance for each wavelength. The graph of the R light beam (630 nm) is indicated by a one-dot chain line, the graph of the G light beam (530 nm) is indicated by a broken line, and the graph of the B light beam (470 nm) is indicated by a solid line. As can be seen from this relationship, the condensing distance when condensing the R light beam having a diameter of 500 μm is 38 mm. Further, the condensing distance when condensing a B light beam having a diameter of 600 μm is 60 mm. Since the condensing distance varies depending on the wavelength as described above, the condensing lens of the optical modulator needs to be designed in consideration of the wavelength of the light beam to be modulated.

  FIG. 11 shows the relationship between the diameter of the light beam and the beam focusing distance for each beam waist. A graph of the beam waist of 10 μm is indicated by a solid line, a graph of the beam waist of 15 μm is indicated by a broken line, and a graph of the beam waist of 20 μm is indicated by a dashed line. From this relationship, it can be seen that if the beam waist is reduced, the focusing distance is shortened. By shortening the focusing distance, the element size can be reduced. However, in this case, since the light density increases, it is necessary to reduce the light intensity of the light beam to be modulated correspondingly. Thus, there is a trade-off relationship between element size and light intensity. Therefore, it is necessary to consider this trade-off relationship in the design of the condensing lens.

  The optical modulator of the present invention can be applied to an optical communication device, an image display device, an image forming device, and the like. The optical modulator of the present invention can be used as a deflector in addition to an optical switch.

  Hereinafter, an image display apparatus will be described as an application example of the optical modulator of the present invention.

  FIG. 12 is a schematic diagram illustrating an example of an image display device. This image display device includes laser light sources 402, 403, 404, collimator lenses 405, 406, 407, reflection mirror 408, dichroic mirrors 409, 410, horizontal scanning mirror 415, vertical scanning mirror 416, and light modulators 418, 419, A housing 400 containing 420 is included. The optical modulators 418, 419, and 420 are the optical modulators of the present invention.

  A collimator lens 405, an optical modulator 418, and a reflection mirror 408 are sequentially arranged in the traveling direction of the laser light from the laser light source 402. A parallel light beam from the collimator lens 405 enters the light modulator 418. The optical modulator 418 operates according to a control signal supplied from a control unit (not shown). During a period when the control signal is on (high-frequency voltage supply period), a high-frequency voltage is applied to the comb-shaped electrode in the optical modulator 418, and a surface acoustic wave or an interfacial acoustic wave is generated. As a result, Bragg diffraction occurs when incident light passes through a region where surface acoustic waves or interface acoustic waves are generated, and a first-order diffracted wave is output from the optical modulator 418 as output light. The output light goes to the reflection mirror 408. On the other hand, during the period in which the control signal is off (voltage supply stop period), no surface acoustic wave or interfacial acoustic wave is generated. The light transmitted through the light modulator 418 deviates from the optical path toward the reflection mirror 408.

  A collimator lens 406, an optical modulator 419, and a dichroic mirror 409 are sequentially arranged in the traveling direction of the laser light from the laser light source 403. A parallel light beam from the collimator lens 406 enters the light modulator 419. In the optical modulator 419, the same operation as that of the optical modulator 418 is performed. The output light of the light modulator 419 goes to the dichroic mirror 409.

  A collimator lens 407, an optical modulator 420, and a dichroic mirror 410 are sequentially arranged in the traveling direction of the laser light from the laser light source 404. A parallel light beam from the collimator lens 407 enters the light modulator 420. In the optical modulator 420, the same operation as that of the optical modulator 418 is performed. The output light from the light modulator 420 is directed to the dichroic mirror 410.

  The dichroic mirror 409 is provided at a position where the light beam from the light modulator 419 and the light beam reflected by the reflection mirror 408 intersect. The dichroic mirror 409 has a wavelength selection characteristic that reflects light from the light modulator 419 and transmits light from the reflection mirror 408.

  The dichroic mirror 410 is provided at a position where the light beam from the light modulator 420 and the light beam from the dichroic mirror 409 intersect. The dichroic mirror 410 has a wavelength selection characteristic that reflects the light from the light modulator 420 and transmits the light from the dichroic mirror 409.

  The horizontal scanning mirror 415 is arranged in the traveling direction of the light beam from the dichroic mirror 410, and its operation is controlled by a horizontal scanning control signal from a control unit (not shown). The vertical scanning mirror 416 is arranged in the traveling direction of the light beam from the horizontal scanning mirror 415, and its operation is controlled by a vertical scanning control signal from a control unit (not shown).

  As the laser light sources 402, 403, and 404, light sources that emit laser light of colors corresponding to the three primary colors R, G, and B are used. A color image can be displayed on the screen 417 by controlling the light modulators 418, 419 and 420 on and off and controlling the horizontal scanning mirror 415 and the vertical scanning mirror 416.

  According to the present invention described above, the depth of the elastic wave propagation region (direction perpendicular to the electrode surface including each linear electrode of the comb-shaped electrode constituting the elastic wave generating means) is the wavelength of the surface acoustic wave or the interfacial elastic wave. (It is the same as the period of each linear electrode of the comb electrode), and almost the entire range in the depth direction can be used as a region for modulating incident light. When incident light passes through the entire range of the acoustic wave propagation region in the depth direction, the range of the interaction region between the incident light and the surface acoustic wave or the interfacial elastic wave is sufficient compared to the waveguide acoustooptic device. Therefore, the light density can be lowered correspondingly, and the light damage resistance is also improved. As a result, it becomes possible to modulate a light beam with a high light output.

  Further, since the interaction region is enlarged, the energy utilization rate and diffraction efficiency of the surface acoustic wave or the interfacial elastic wave are improved.

  Furthermore, since the interaction region is enlarged, the focused beam diameter in the elastic wave propagation region can be increased. The configuration of the condensing optical system in this case is simpler than that of the condensing optical system in which the light beam is put into the waveguide.

  Furthermore, since the interaction region is expanded, sufficient diffraction efficiency can be obtained even if the width (interaction length) of the elastic wave propagation region is reduced. Therefore, the width (interaction length) of the elastic wave propagation region can be reduced as compared with the waveguide type acoustooptic device, and the device can be downsized accordingly.

  In addition, the power consumption of the elastic wave generating means composed of comb-shaped electrodes is smaller than that of a bulk acousto-optic device using a piezoelectric vibrator. Therefore, power saving can be achieved.

  In addition, since the size of the cross section of the elastic wave propagation region in the present invention is smaller than the cross section of the region where the ultrasonic traveling wave is generated in the bulk acoustooptic device, the device can be downsized accordingly.

  Further, according to the present invention, when the incident light is in the single mode, the emitted light also maintains the single mode. Thus, single mode output light can be obtained.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and operation of the present invention without departing from the spirit of the present invention.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2008-173537 for which it applied on July 2, 2008, and takes in those the indications of all here.

Claims (15)

An acousto-optic medium;
An acoustic wave generating means for generating a surface acoustic wave or an interfacial acoustic wave in the acoustooptic medium,
In the acousto-optic medium, an elastic wave propagation region covered with a surface elastic wave or an interface elastic wave generated by the elastic wave generating means is formed of the same material,
First and second end faces facing each other across the acoustic wave propagation region in a direction intersecting with the traveling direction of the surface acoustic wave or the interfacial acoustic wave, and incident light incident from the first end face is the elasticity The first-order diffracted wave generated when passing through the wave propagation region and the light propagating through the acoustooptic medium in a state where the elastic wave generating means is stopped are respectively in different directions from the second end face. An emitted light modulator.   The acousto-optic medium includes a first surface comprising a plane intersecting each of the first and second end surfaces, and the elastic wave generating means is formed on the first surface. The optical modulator according to item 1.   The acousto-optic medium includes a first surface composed of a plane intersecting each of the first and second end surfaces, and a second surface facing the first surface, and the elastic wave generating means includes The optical modulator according to claim 1, wherein the optical modulator is formed on each of the first and second surfaces.   The elastic wave generating means has first and second comb electrodes composed of a plurality of linear electrodes arranged in parallel on the same plane, and the first and second comb electrodes are linear with each other. The optical modulator according to any one of claims 1 to 3, wherein the electrodes are alternately arranged.   The optical modulator according to claim 1, wherein the elastic wave generating means is formed inside the acoustooptic medium.   The elastic wave generating means has first and second comb electrodes composed of a plurality of linear electrodes arranged in parallel on a first plane intersecting each of the first and second end faces, 6. The optical modulator according to claim 5, wherein the first and second comb-shaped electrodes are alternately arranged with linear electrodes. The elastic wave generating means includes first and second comb electrodes composed of a plurality of linear electrodes arranged in parallel on a first plane intersecting each of the first and second end faces; A third comb electrode and a fourth comb electrode composed of a plurality of linear electrodes arranged in parallel on a second plane opposite to the first plane;
The first and second comb electrodes are alternately arranged with linear electrodes, and the third and fourth comb electrodes are alternately arranged with linear electrodes. 7. The optical modulator according to item 6.   The light modulator according to any one of claims 1 to 7, further comprising a condensing lens for condensing a light beam on the elastic wave propagation region.   Perpendicular to the plane including each linear electrode of the beam diameter of the light focused on the elastic wave propagation region by the condenser lens with respect to the period Λ of each linear electrode of the comb-shaped electrode constituting the elastic wave generating means 9. The optical modulator according to claim 8, wherein a width in one direction is larger than 0.1 × Λ and smaller than 1.2 × Λ.   Perpendicular to the plane including each linear electrode of the beam diameter of the light focused on the elastic wave propagation region by the condenser lens with respect to the period Λ of each linear electrode of the comb-shaped electrode constituting the elastic wave generating means 9. The optical modulator according to claim 8, wherein a width in a simple direction is larger than 0.7 × Λ and smaller than Λ.   With respect to the period Λ of each linear electrode of the comb-shaped electrode constituting the elastic wave generating means, the driving frequency f of the elastic wave generating means, and the propagation velocity v of the surface elastic wave or the interfacial elastic wave, by the condenser lens The width in the direction perpendicular to the direction perpendicular to the plane including each linear electrode of the beam diameter of the light condensed on the elastic wave propagation region is greater than 2 × Λ and not more than v / f. The optical modulator according to any one of Items 8 to 10, wherein:   The light modulator according to any one of claims 8 to 11, wherein the light beam condensed by the condenser lens is a Gaussian beam.   The optical modulator according to any one of claims 1 to 12, further comprising an antireflection film on the first and second end faces.   The optical modulator according to any one of claims 1 to 13, wherein the acoustooptic medium is made of quartz.   The optical modulator according to any one of claims 1 to 13, wherein the acoustooptic medium is made of quartz containing impurities.

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