JPH02222932A - Method and device for reducing light intensity variation of optical deflector - Google Patents

Abstract

PURPOSE:To reduce variation in the light intensity of a deflected light due to variation in the intensity of surface acoustic waves, etc., by reading the correcting value-to-frequency relation of an alternating voltage, applied to an inter-digital electrode couple, out of a storage means and correcting the value of the alternating voltage according to the relation when waveguide light is diffracted and deflected. CONSTITUTION:The optical deflector 10 has an optical waveguide 12 which is formed on a substrate 11, a converting diffraction grating(FGC) 13 for light beam incidence which is formed on the optical waveguide 12, an FGC 14 for light beam projection, etc. Further, a correction part 31 which constitutes the light intensity variation reducing device together with a controller 30 is provided between a high-frequency amplifier 19 and a sweeper 20. Then when the optical deflector 10 is operated, the controller 30 reads data out of a table stored on a table memory 35 and inputs a signal S7 which carries correcting values by frequencies (f) to a D/A converter 34. Consequently, the light intensity of a light beam L becomes nearly constant over the entire frequency range of the surface acoustic waves 15 and 16.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides an optical deflector that generates surface acoustic waves in an optical waveguide and deflects guided light by the diffraction action of the surface acoustic waves. The present invention relates to a method and apparatus for reducing light intensity fluctuations in a beam.

(Prior Art) Conventionally, as shown in Japanese Patent Application Laid-Open No. 81-183 [i2B], light is incident on an optical waveguide made of a material that allows surface acoustic waves to propagate, and propagates within this optical waveguide. By generating a surface acoustic wave in a direction that intersects the guided light, the surface acoustic wave causes Bragg diffraction of the guided light, and by continuously changing the frequency of the surface acoustic wave, the diffraction angle (deflection angle) of the guided light can be changed. An optical deflection device that continuously changes the amount of light is known.

On the other hand, as shown in Japanese Patent Application Laid-Open No. 1-25015, for example, the wavelength of the light beam is determined by ΔFJ by propagating a surface acoustic wave whose frequency changes continuously in an optical waveguide, similar to the above-mentioned optical deflection device. Optical spectrum analyzers have also been proposed. This optical spectrum analyzer
When a light beam guided through an optical waveguide is diffracted by a surface acoustic wave, the diffraction angle changes according to the surface acoustic wave frequency as described above, and also changes according to the wavelength of the light beam. , the wavelength of the light beam is determined based on the surface acoustic wave frequency when the light beam is diffracted at a predetermined angle.

As described above, in an optical deflector that continuously deflects a light beam or an optical deflector that constitutes an optical spectrum analyzer, the surface acoustic wave generating means is usually a pair of interdigitated electrodes (intersection) in which the spacing between electrode fingers changes. -D 1g1
tal transducer (hereinafter referred to as IDT) and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the IDT. I
More specifically, the DT is a Tilted-Flnger Chir I DT in which the interval between electrode fingers changes stepwise and the direction of each electrode finger changes stepwise.
ped IDT), so-called curved finger IDTs in which the electrode finger spacing changes continuously and each electrode finger forms an arc, and even multiple IDTs in which multiple IDTs with different electrode finger spacings are arranged at different inclinations. Fist Tilted ID
T (Multiple Tilted I DT) etc. are used. Further, the above-mentioned driver is generally composed of a high frequency amplifier, a frequency sweeper, and the like.

(Problem to be solved by the invention) By the way, when using the IDT or driver as described above, periodic intensity fluctuations (
It is recognized that fluctuations are likely to occur. That is, since the IDT and high frequency amplifier used for the above purpose are designed for a high frequency band, the impedance may deviate greatly from the impedance (50Ω) of a normal high frequency system. Therefore, reflection of the high frequency signal occurs between the high frequency cable and the IDT, and the reflected wave returns to the high frequency amplifier. Since this amplifier is also designed for a high band as described above, several percent to several tens of percent of the high frequency signal is reflected and propagated to the IDT side again. Therefore, the reflected wave toward the IDT interferes with the high frequency signal (progressive wave) originally output from the high frequency amplifier, and the high frequency intensity fluctuates.

When the high frequency intensity input to the IDT fluctuates in this way, the intensity of the surface acoustic wave emitted from the IDT similarly fluctuates, and the diffraction efficiency of guided light by the surface acoustic wave fluctuates. If this happens, the amount of diffracted light, that is, the intensity of the deflected light beam will fluctuate.

In addition to being caused by the reflected waves mentioned above, due to the uneven frequency characteristics of the high frequency amplifier and sweeper,
The light intensity of the deflected beam often fluctuates. In other words, I
This is because if the value of the alternating voltage applied to the DT changes depending on its frequency, the diffraction efficiency of the guided light will change in the same way as described above.

If the light intensity of the deflected beam fluctuates in this way, for example, when an optical deflector is used in an optical scanning recording device or an optical scanning reading device, problems such as density unevenness in the recorded image and a decrease in reading accuracy may occur. On the other hand, in the optical spectrum analyzer described above, the accuracy of spectrum analysis is reduced.

In order to prevent the intensity fluctuations of the surface acoustic waves mentioned above, it has been considered to insert an isolator, which is a non-reciprocal element, between the IDT and the driver, as shown in Japanese Patent Application Laid-open No. 83-53516, for example. It is being However, variations in the light intensity of the deflected beam due to causes other than the reflected waves cannot be reduced even by providing the above-mentioned isolator.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for reducing light intensity fluctuations in an optical deflector, which can reduce light intensity fluctuations of a deflected beam due to the various causes described above.

(Means and effects for solving the problem) As described above, the first method for reducing light intensity fluctuation according to the present invention includes an optical waveguide formed of a material that allows surface acoustic waves to propagate, surface acoustic wave generating means for generating in the optical waveguide a surface acoustic wave that propagates in a direction intersecting the optical path of the guided light and diffracts and deflects the guided light, the surface acoustic wave generating means comprising: When using an optical deflector consisting of an IDT and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the IDT, the intensity of the deflected light beam is determined by each of the above alternating voltages. /jlJ for each frequency, and based on the difference between the measured light intensity and a constant reference intensity, the correction value to be added to the alternating voltage value to eliminate this difference is determined for each frequency of the alternating voltage. The relationship between the correction value and the alternating voltage frequency is stored in a storage means, and then when the guided light is diffracted and deflected, the above-mentioned relationship is read out from the storage means and the value of the alternating voltage is corrected according to this relationship. It is characterized by this.

Further, a second method for reducing light intensity fluctuations according to the present invention, when using an optical deflector similar to the above, allows the intensity of the light beam incident on the optical waveguide to be modulated by an optical modulation means, and after deflection. The intensity of the light beam is measured for each frequency of the alternating voltage, and based on the difference between the measured light intensity and a certain reference intensity, the modulation that should be applied to the light modulation means to eliminate this difference is determined. A control signal is obtained for each frequency of the alternating voltage, the relationship between the modulation control signal and the alternating voltage frequency is stored in a storage means, and the above relationship is read from the storage means when the guided light is subsequently diffracted and deflected. Furthermore, the light modulation means is characterized in that its operation is controlled according to this relationship.

On the other hand, the first light intensity fluctuation reducing device according to the present invention, in an optical deflector having the same configuration as described above, adds a correction value to be added to the value of the alternating voltage in order to make the intensity of the deflected light beam constant. a storage means that stores information for each frequency of the alternating voltage; and a correction that reads out the relationship between the correction value and the alternating voltage frequency from the storage means and corrects the value of the alternating voltage according to this relationship when diffracting and deflecting the guided light. means.

The relationship between the correction value and the alternating voltage frequency to be stored in the storage means may be determined, for example, as in the first method.

Further, a second light intensity fluctuation reducing device according to the present invention is an optical deflector having a configuration similar to that described above, and includes an optical modulation means for modulating the intensity of the optical beam entering the optical waveguide, and an optical deflector for modulating the intensity of the optical beam after being deflected. A storage means stores a modulation control signal to be applied to the light modulation means for each frequency of the alternating voltage in order to make the intensity constant; and a storage means stores a modulation control signal pair from the storage means when diffracting and deflecting the guided light Modulation control means is provided for reading out the relationship between alternating voltages and frequencies and controlling the operation of the light modulation means in accordance with this relationship.

In this second device as well, the relationship between the modulation control signal and the alternating voltage frequency to be stored in the storage means may be determined, for example, in the same manner as in the second method.

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

FIG. 1 shows an optical deflector 10 equipped with a light intensity fluctuation reducing device according to a first embodiment of the present invention.

This optical deflector IO includes an optical waveguide 12 formed on a substrate 11 and a condensing grating for light beam incidence formed on this optical waveguide I2.
ng Coupler (hereinafter referred to as FCC) 13
, F G C14 for light beam emission, and these F G
First and second inclined finger chirp IDTi7.18 each generate a surface acoustic wave 15.1B that travels in a direction intersecting the optical path of the guided light traveling between C13 and C14, and the surface acoustic wave 15.16. A high-frequency amplifier 19 applies a high-frequency alternating voltage to the inclined finger chirp IDT 17, 18 to generate the voltage, and a high-frequency amplifier 19 that continuously changes the frequency of the voltage (
It has a sweeper 20 for sweeping. A correction section 31 is provided between the high frequency amplifier 19 and the sweeper 20, and together with a controller 30, constitutes a light intensity fluctuation reducing device.

In this embodiment, as an example', LiNb is used on the substrate 11.
The optical waveguide 12 is formed by using an O3 wafer and providing a Ti diffusion film on the surface of this wafer. Note that other crystalline substrates made of sapphire, Si, etc. may also be used as the substrate 11. Moreover, the optical waveguide 12 is also made of the above-mentioned Ti.
In addition to diffusion, other materials can be sputtered onto the substrate.
It can also be formed by vapor deposition or the like. However, this optical waveguide 12 is formed from a material such as the above-mentioned Ti diffusion film that allows surface acoustic waves to propagate, which will be described later. Further, the optical waveguide may have a laminated structure of two or more layers.

The deflected light beam L is emitted toward the FGCH from a light source 21 such as a semiconductor laser, for example.

This light beam L (divergent beam) is made into a parallel beam by the FGC 13 and then taken into the optical waveguide 12,
Wave is guided within the optical waveguide 12. This guided light L1 is
Due to the acousto-optic interaction with the first surface acoustic wave 15 emitted from the inclined finger chirp IDT 17, it is diffracted (B rag diffraction) as shown in the figure.

The guided light L1 diffracted and deflected in this way is converted into a second surface acoustic wave 1B emitted from the second inclined finger chirp IDTlB.
Due to the acousto-optic interaction with the beam, it is diffracted in a direction that further amplifies the above-mentioned deflection (see Figure 2). As described above, since the frequency of the alternating voltage applied to the first inclined finger chirp IDT 17 changes continuously, the frequency of the first surface acoustic wave 15 changes continuously. As is well known,
Since the deflection angle of the guided light LZ diffracted by the surface acoustic wave 15 is approximately proportional to the frequency of the surface acoustic wave 15, by changing the frequency of the surface acoustic wave 15 as described above, the guided light L2 changes as shown by arrow A. Continuously deflect as shown. This guided light L2 is then deflected by the second surface acoustic wave 16, but since the frequency of this second surface acoustic wave 1B also changes continuously like the first surface acoustic wave 15, the second The guided light L3 after passing through the surface acoustic wave IB is continuously and largely deflected as shown by arrow B. This guided light L3 is F
The light is emitted to the outside of the optical waveguide 12 by the GCI 4, and is focused at one point by its focusing action.

As described above, in this device, the guided light L1 is diffracted and deflected twice, so the deflection angle range Δδ of the guided light L3 can be extremely large. In other words,
When the frequency of surface acoustic wave 15.1B is the maximum frequency and the minimum frequency, the traveling directions of the guided light beam diffracted twice are as shown by ■ and ■° in Figure 2, respectively, and the difference between them is the deflection angle. The range is Δδ. The deflection angle range obtained when the guided light is diffracted and deflected twice in this way is described in, for example, Japanese Patent Application Laid-Open No. 83-136021! Detailed information is provided in the publication.

Here, IDT! ? The high frequency signal (alternating voltage) input to the high frequency amplifier 19 and the sweeper 20 may have intensity fluctuations due to the influence of the reflected waves mentioned above and due to the uneven frequency characteristics of the high frequency amplifier 19 and the sweeper 20. There is. Hereinafter, the method of suppressing this intensity variation and reducing the light intensity variation of the deflected beam L° will be explained. FIG. 3 shows a configuration related to this reduction of light intensity fluctuations, and will be described below with reference to FIG. 3. As shown in the figure, the correction section 31
includes a mixer 32, an amplifier 33, and a D/A converter 34 provided between the high frequency amplifier 19 and the sweeper 20.
and a table memory 35.

As mentioned above, prior to actually using the optical deflector lO,
A photodetector (for example, a photomultiplier tube) 36 having a wide light-receiving surface that detects the intensity of the deflected light beam L is arranged, and the sweeper 20 is operated based on a sweep control signal S1 from the controller 30. . At this time, the mixer 32 is first brought into a state in which the frequency-swept high-frequency signal S2 output from the sweeper 20 is input to the high-frequency amplifier 19 as it is. Thereby, the light beam L' is continuously deflected in the same manner as described above. This deflected light beam L° is received by the photodetector 36, and the output signal S3 indicating the light intensity is A
/D converter 37. The signal S4 digitized in this way is input to the controller 30.

The controller 30 consisting of a microcomputer etc.
As mentioned above, the frequency sweep timing of the surface acoustic waves 15.16 is also controlled, and based on this timing, the light intensity indicated by the signal S4 and the frequency of the high frequency signal S2 (that is, of the surface acoustic waves 15.16) are controlled. Find the relationship with f. If this relationship is shown continuously, it will be as shown by the solid line in FIG. 4, for example. The controller 30 uses this measured light intensity P and a preset constant reference intensity P.
A process is performed for each frequency f in which the frequency f is compared with r for each frequency f, and if there is a difference between the two, a small correction value ΔV is given in the correction table formed in the internal memory. Note that the setting value of the reference intensity Pr is the measurement light intensity P.
Anywhere is fine.

Then, the controller 30 outputs the frequency-swept high-frequency signal S2 from the sweeper 20 again to generate surface acoustic waves 15.16, but at this time, the signal S5 carrying the correction value for each frequency f is controlled by the sweep control. It is output after being synchronized with the signal S1. This signal S5 is D of the correction section 31.
After being converted into analog by the /A converter 34, the signal is amplified by the amplifier 33 and input to the mixer 32. This mixer 32 has a function of increasing or decreasing the amplitude of the high frequency signal S2 using a correction signal S6 (corresponding to the signal S5) consisting of a DC component sent from the amplifier 33. Therefore, the correction signal S6 corresponding to a certain frequency f increases or decreases the high frequency signal S2 of the same frequency f.

As described above, when the high frequency signal S2 is increased or decreased by the correction signal S6 and the surface acoustic wave 15.16 is frequency swept, the intensity of the deflected light beam L' becomes as follows when compared with the previous deflection.
It becomes closer to the reference intensity Pr. controller 30
At this time, the light intensity P determined by nj and the reference intensity Pr are compared for each frequency f, and if there is a difference between the two, the minute correction value is set in the table stored in the internal memory. A process of further adding ΔV is performed for each frequency f. Thereafter, the controller 30 increases or decreases the frequency of the surface acoustic waves 15 and 16 by using the correction signal S6 based on the table and the high frequency signal S2, as described above, to sweep the surface acoustic waves 15 and 16 in frequency.

By repeating the deflection of the light beam L° and changing the table several times in this way, the actually measured light intensity P will eventually converge to the reference intensity Pr over the entire frequency range of the surface acoustic waves 15.16. become. In other words, in this case, the correction section using the correction signal S6 is, as shown by the broken line in FIG. Become. In this embodiment, the correction signal S6 is generated based on the correction value as described above, but since this correction signal S6 corrects the amplitude of the high frequency signal S2, the above correction value is It can be said that it indirectly serves as a voltage correction mirror to be added to the IDT17.18.

When the above-mentioned state is reached, the controller 30 next transfers the table of correction value versus frequency f stored in its internal memory to the table memory 35 and stores it there. When this process is completed, the photodetector 3B and A/D converter 37 are removed. And after that, the optical deflector 10
When operating the controller 30, the controller 30 reads out the table data stored in the table memory 35 and inputs the signal S7 carrying the correction value for each frequency f to the D/A converter 34. Therefore, in this case, the light intensity P of the light beam L' is approximately constant over the entire frequency range of the surface acoustic waves 15 and lθ.

As described above, in this apparatus, when the optical deflector 10 is actually used, the high-frequency signal S2 is corrected while simply reading the correction data from the table memory 35, so that, for example, the deflected beam L' during actual use is Compared to a device that suppresses fluctuations in light intensity through feedback control while detecting the light intensity of , it is possible to set the sweep speed higher.

Note that the correction value versus frequency f to be stored in the table memory 35
Naturally, it is preferable that the table has correction values defined for more frequencies f. In other words, if the number of correction values is large enough, the analogized correction signal S6 can more accurately have an opposite phase to the output S3 of the photodetector 36 when no light intensity fluctuation correction is performed. .

Next, a second embodiment of the present invention will be described with reference to FIG. Note that in FIG. 5, elements equivalent to those in FIG. 3 are given the same numbers, and explanations thereof will be omitted unless particularly necessary.

In this embodiment, the light beam L emitted from the light source 21 is passed through an optical modulator 40 such as an AOM (acousto-optic modulator) or an EO,M (electro-optic modulator), and then passed through an optical deflector 10. It is designed to be incident on . The operation of this optical modulator 40 is controlled by a modulation circuit 41. On the other hand, the high frequency signal S2 outputted from the sweeper 20 is input to the high frequency amplifier 19 as it is without being corrected.

Prior to the actual use of the optical deflector IO, when the optical beam L is deflected several times in order to create data to be stored in the table memory 35, the controller 30 sends information about the surface elasticity as in the first embodiment. A signal S5 that takes a value corresponding to the difference between the measurement light intensity P and the reference intensity P is output for each wave frequency f. The modulation control signal S6
The signal is input to the modulation circuit 41 as .degree. This modulation control signal S6' is applied to the optical modulator 408 when the reference intensity Pr is set to be lower than the actually measured optical intensity P, for example.
This value is used to control the modulation circuit 4L so as to reduce the intensity of the light beam L received by M. The opposite is true if the reference intensity P is set to exceed the actual light intensity P.

When the operating state of the optical modulator 40 is changed to $111 based on the above modulation control signal S6° and the surface acoustic wave 15.18 is frequency swept, the intensity of the deflected light beam L° is the same as that of the previous deflection. When compared with the reference intensity Pr, it is closer to the reference intensity Pr. The controller 30 compares the measured light intensity P and the reference intensity Pr for each frequency f, and if there is a difference between the two, further adds a small correction amount ΔV' in the table stored in the internal memory. , is performed for each frequency f.

By repeating the deflection of the light beam L° and changing the table several times in this way, the actually measured light intensity P will eventually converge to the reference intensity Pr over the entire frequency range of the surface acoustic wave 15.1B. become.

When the above-mentioned state is reached, the controller 3° next transfers the table of modulation control signal versus frequency f stored in its internal memory to the table memory 35 and stores it there. When this process is completed, the photodetector 36 and the
/D converter 37 is removed.

Thereafter, when operating the optical deflector 10, the controller 30 reads out the table data stored in the table memory 35, and transmits the signal S7° carrying the modulation state for each frequency f to the D/A converter. 34. Therefore, in this case as well, the light intensity P of the light beam L° is
It remains approximately constant over the entire frequency range of the surface acoustic wave 15S113.

In the second embodiment, the light beam L is modulated by the optical modulator 40, but if the light source 21 is composed of, for example, a semiconductor laser, this light source 21
may be directly modulated based on the modulation control signal S6°.

(Effects of the Invention) As described above in detail, in the present invention, when diffracting and deflecting guided light, the relationship between the correction value of the alternating voltage applied to the IDT and the frequency is read out from the storage means, and the value of the alternating voltage is is corrected according to this relationship, or the intensity of the light beam entering the optical waveguide can be modulated by the optical modulation means, and when the guided light is diffracted or deflected, the optical modulation means Since the relationship between the modulation control signal to be applied and the alternating voltage frequency is read from the storage means and the operation of the optical modulation means is controlled according to this relationship, fluctuations in the optical intensity of the deflected beam due to fluctuations in the intensity of surface acoustic waves, etc. are reliably reduced. It becomes possible to do so.

Therefore, according to the present invention, for example, when an optical deflector is used in an optical scanning recording device or an optical scanning reading device, it is possible to prevent problems such as density unevenness in a recorded image and a decrease in reading accuracy. In a spectrum analyzer to which a waveguide type optical deflector is applied, it is possible to improve the precision of spectrum analysis.

Furthermore, in the light intensity fluctuation reducing device according to the present invention, when deflecting the light beam, data is simply read from the storage means and the light intensity fluctuation is corrected based on this data. Compared to the case where fluctuations are suppressed, it is possible to set the sweep speed higher.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a device according to a first embodiment of the present invention, FIG. 2 is an enlarged plan view of a part of the device according to the embodiment, and FIG. 3 is an electrical circuit of the device according to the embodiment described above. FIG. 4 is an explanatory diagram illustrating the effect of reducing light intensity fluctuations in the device of the above embodiment, and FIG. 5 is a block diagram showing a device of a second embodiment of the present invention. 10... Optical deflector 11... Substrate 12
...Optical waveguide 13...FCC for light beam incidence 14...FCC for light beam output 15...First surface acoustic wave 16...Second surface acoustic wave 17...First Inclined finger chive IDT18...
Second tilted finger chirp IDT19...high frequency amplifier
20...Sweeper-2I...Light source
30... Controller 31... Correction section
32...Mixer 33...Amplifier 3
4...D/A converter 35...Table memory 3
B... Photodetector 37... A/D converter 40.
... Optical modulator 41 ... Modulation circuit construction ... Guided light before entering the first surface acoustic wave,
... Guided light L3 that has passed through the first surface acoustic wave... Guided light L' that has passed through the second surface acoustic wave... Deflected beam Figure 1 Figure 3 Figure 2 Figure 4 Surrounding dryness f

Claims (4)

[Claims] (1) An optical waveguide formed from a material that allows surface acoustic waves to propagate, and a surface acoustic wave that propagates in a direction intersecting the optical path of the guided light traveling in the optical waveguide and diffracts and deflects the guided light. The surface acoustic wave generating means includes a pair of intersecting comb-shaped electrodes and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the pair of interdigitated electrodes. When using an optical deflector composed of Then, in order to eliminate this difference, a correction value to be added to the value of the alternating voltage is determined for each frequency of the alternating voltage, the relationship between the correction value and the alternating voltage frequency is stored in a storage means, and then the guided light is A method for reducing light intensity fluctuations in an optical deflector, comprising reading out the relationship from the storage means and correcting the value of the alternating voltage according to the relationship when diffracting and deflecting. (2) An optical waveguide formed of a material that allows surface acoustic waves to propagate; and a surface acoustic wave that propagates in a direction intersecting the optical path of the guided light traveling in the optical waveguide and diffracts and deflects the guided light. The surface acoustic wave generating means includes a pair of intersecting comb-shaped electrodes and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the pair of interdigitated electrodes. When using an optical deflector consisting of the following, the intensity of the optical beam entering the optical waveguide can be modulated by an optical modulation means, and the intensity of the optical beam after deflection is adjusted to each frequency of the alternating voltage. Based on the difference between the measured light intensity and a constant reference intensity, a modulation control signal to be applied to the light modulation means to eliminate this difference is determined for each frequency of the alternating voltage; This relationship between the modulation control signal and the alternating voltage frequency is stored in a storage means, and then when the guided light is diffracted and deflected, the relationship is read out from the storage means and the operation of the light modulation means is controlled according to this relationship. A method for reducing light intensity fluctuations in an optical deflector, characterized by: (3) An optical waveguide formed from a material that allows surface acoustic waves to propagate, and a surface acoustic wave that propagates in a direction intersecting the optical path of the guided light traveling in the optical waveguide and diffracts and deflects the guided light. The surface acoustic wave generating means includes a pair of intersecting comb-shaped electrodes and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the pair of interdigitated electrodes. An optical deflector comprising: a storage means that stores, for each frequency of the alternating voltage, a correction value to be added to the value of the alternating voltage in order to make the intensity of the deflected light beam constant; and the guided light. and a correction means for reading out the relationship between the correction value and the alternating voltage frequency from the storage means and correcting the value of the alternating voltage according to this relationship when diffracting and deflecting the light. Strength fluctuation reduction device. (4) An optical waveguide formed from a material that allows surface acoustic waves to propagate, and a surface acoustic wave that propagates in a direction intersecting the optical path of the guided light traveling in the optical waveguide and diffracts and deflects the guided light. The surface acoustic wave generating means includes a pair of intersecting comb-shaped electrodes and a driver that applies a high-frequency alternating voltage whose frequency changes continuously to the pair of interdigitated electrodes. An optical deflector comprising: an optical modulating means for modulating the intensity of the optical beam incident into the optical waveguide; and an optical modulating means to be added to the optical modulating means to uniform the intensity of the optical beam after deflection. a storage means that stores a modulation control signal for each frequency of an alternating voltage; and when diffracting and deflecting the guided light, the relationship between the modulation control signal and the alternating voltage frequency is read out from the storage means, and the light modulation means and modulation control means for controlling the operation according to this relationship.