JPH08201743A - Light modulation method and device - Google Patents

Abstract

(57) [Abstract] [Purpose] Optical modulation can be performed without applying a DC component to the electro-optical modulator, and deterioration of the electro-optical modulator can be avoided. [Structure] First KTP2 and electrode layer 4 as an electro-optical modulator provided with electrode layers 4a and 4b as electrodes
In an optical modulation device that applies a light modulation driving voltage to the second KTP 3 provided with c and 4d to modulate light incident on the electro-optical modulation element, for example, laser light, and is connected to each of the electrodes. , A power supply unit 1 as a voltage supply means for alternately switching the direction of the light modulation driving voltage applied between the electrodes between one direction and the opposite direction, and applies a DC voltage component to each of the KTPs. Light modulation can be performed without it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulation method for applying an optical modulation drive voltage to an electro-optical modulation element to modulate the light incident on the electro-optical modulation element, and an optical modulation method to which the above optical modulation method is applied. Regarding the device.

[0002]

2. Description of the Related Art As a laser light source for optical recording, there is known a laser light generator having a light source section having, for example, a semiconductor laser for excitation, a laser medium, and a nonlinear optical crystal element.

According to the above laser beam generator, the laser beam excited by the laser beam of the semiconductor laser and taken out is introduced as the fundamental wave laser beam into the nonlinear optical crystal element, and this nonlinear optical crystal element is introduced. From
For example, high power density can be obtained with low power consumption, such as extracting a harmonic laser beam such as a second high frequency laser beam.

When the above laser light generator is used as a laser light source for optical recording, an external light modulator for modulating the intensity and phase of the output laser light from this laser light source, a so-called light modulator is required.

An electro-optic modulator as the above optical modulator is
The electro-optical modulation device is provided with an electro-optical modulation element for modulating the phase and intensity of incident light, and a voltage for performing light modulation, that is, a so-called light-modulation drive voltage is applied to the electro-optical modulation element. The phenomenon that the refractive index in the element changes,
That is, the electro-optic effect is used.

In the electro-optic modulator, an electrode layer is formed on an appropriate side surface of the electro-optic modulator, and the light modulation driving voltage is applied through the electrode layer. Also,
In an electro-optical intensity modulator that modulates the intensity of incident light, two electro-optical modulation elements are arranged so that their optical axes are orthogonal to each other, and in an electro-optical phase modulator that modulates the phase of incident light, Only one optical modulator is used.

In recent years, KTiOPO ₄ (KTP) which is an electro-optic crystal has been widely used as an electro-optic modulator. This is because this KTP has a large electro-optic effect and high durability against optical damage to visible light.

[0008]

By the way, in order to obtain a large electro-optical effect using KTP, it is necessary to apply an optical modulation drive voltage in the c-axis direction of the KTP crystal. When applied, the KTP crystal is colored black and deteriorates.

In this phenomenon, ions inside the KTP crystal are c
It has a structure that makes it easy to move in the axial direction.
When a direct current voltage of about 0 V / cm is applied in the c-axis direction, an ion-conducting current flows, and titanium ions are converted to Ti
It is considered that a reduction reaction of ^{4 +} → Ti ³⁺ occurs, and this trivalent titanium ion Ti ³⁺ is colored black.

Therefore, the black colored KTP crystal is annealed at high temperature, for example, so-called annealing.
ing), an oxidation reaction is performed to regenerate colorless KTP crystals, but this operation is not possible at room temperature and is troublesome.

Similarly, with respect to other electro-optical modulators, the phenomenon of deterioration occurs when a DC voltage is applied.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and an optical modulation method capable of avoiding deterioration of an electro-optical modulation element, and the application of this optical modulation method. An object of the present invention is to provide a preferable light modulator.

[0013]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an optical modulation method in which an optical modulation drive voltage is applied to an electro-optical modulation element to modulate light incident on the electro-optical modulation element. In the above, the direction of the light modulation drive voltage applied to the electro-optical modulator is alternately switched between one direction and the opposite direction.

Further, it can be mentioned that the light modulation drive voltage is a voltage in which the time applied in the one direction is equal to the time applied in the opposite direction.

Here, it can be mentioned that the light modulation driving voltage is an AC voltage which switches between the one direction and the opposite direction at a constant cycle. The light modulation driving voltage may be a voltage that switches between the one direction and the opposite direction according to one value of binary data of a digital signal.

As the electro-optical modulator, K
An example is a TiOPO ₄ crystal element.

Further, in order to solve the above-mentioned problems, the present invention applies an optical modulation drive voltage to an electro-optical modulation element provided with an electrode to modulate light incident on the electro-optical modulation element. The device is provided with a voltage supply means that is connected to the electrodes and that alternately switches the direction of the light modulation driving voltage applied between the electrodes between one direction and the other direction.

Further, the voltage supply means is for generating and outputting a light modulation drive voltage between the respective electrodes in which the time applied in the one direction is equal to the time applied in the opposite direction.

Here, it can be mentioned that the voltage supply means outputs an AC voltage that switches between the one direction and the opposite direction at a constant cycle. Further, a data supply means for supplying digital data is provided, and the voltage supply means can output a voltage that switches between the one direction and the opposite direction according to one value of the binary data of the digital signal. Can be mentioned.

As the electro-optic modulator, K
An example is a TiOPO ₄ crystal element.

[0021]

According to the optical modulation method of the present invention, when the light incident on the electro-optical modulation element in accordance with the input electric signal, that is, the incident light is modulated, that is, the so-called optical modulation is performed, the electro-optical modulation element is used. By alternately switching the direction of the optical modulation driving voltage as the electric signal applied to the one direction and the opposite direction, even if a DC power source is used to generate the electric signal, the DC component has the electro-optical modulation. Not applied to the element. Further, it is possible to control the DC component of the intensity of the incident light without supplying a DC voltage as an electric signal to be supplied to the electro-optical modulator.

Further, when the light modulation drive voltage is applied to the electro-optical modulator, the application time in the one direction and the application time in the opposite direction are made equal to each other, so that the electric signal is transmitted. Even if a DC power supply is used to generate it, no DC component is applied to the electro-optic modulator.
Further, it is possible to control the DC component of the intensity of the incident light without supplying a DC voltage as an electric signal to be supplied to the electro-optical modulator.

Here, by setting the light modulation driving voltage to an AC voltage, the direction of the light modulation driving voltage applied to the electro-optical modulator can be switched between the one direction and the opposite direction at a constant cycle. . Therefore, it is possible to prevent the direct current component from being applied to the electro-optical modulator, and it is possible to control the direct current component of the intensity of the incident light without supplying the direct current component.

Further, the light modulation drive voltage is set to a voltage that switches between the one direction and the opposite direction according to one value of binary data of the digital signal, for example, data of "1", whereby the digital signal is obtained. Optical modulation can be performed by applying an electric signal based on the above binary data to the electro-optical modulator. At the time of performing this light modulation, it is possible to avoid applying a DC component to the electro-optic modulator, and to control the DC component of the intensity of the incident light without supplying the DC component. You can

As the electro-optic modulator, KTi is used.
Light modulation can be efficiently performed by using the OPO ₄ crystal element.

According to the optical modulator of the present invention,
Light that is incident on the electro-optical modulation element in accordance with an input electric signal, that is, light modulation driving as the electric signal applied to each electrode of the electro-optical modulation element when performing so-called light modulation when modulating the incident light By alternately switching the direction of the voltage between the one direction and the opposite direction, even if a DC power source is used to generate the electric signal, a DC component is not applied to each electrode. Further, it is possible to control the DC component of the intensity of the incident light without supplying a DC voltage as an electric signal to be supplied to the electro-optical modulator.

Further, a DC power supply is used to generate the electric signal by equalizing the time when the light modulation drive voltage is output in one direction by the voltage supply means and the time when the light modulation drive voltage is output in the opposite direction. However, the direct current component is not applied to the electrodes. Further, it is possible to control the DC component of the intensity of the incident light without supplying a DC voltage as an electric signal to be supplied to the electro-optical modulator.

Here, by setting the light modulation drive voltage to an alternating voltage, the voltage supply means can switch the direction of the light modulation drive voltage between the one direction and the opposite direction at a constant cycle. Therefore, it is possible to prevent the direct current component from being applied to the electro-optical modulator, and it is possible to control the direct current component of the intensity of the incident light without supplying the direct current component.

Further, by setting the light modulation drive voltage to a voltage that switches between the one direction and the opposite direction according to one value of binary data of the digital signal, for example, "1" data, the voltage is changed. The supply means can output an electric signal based on the binary data of the digital signal, can prevent the direct current component from being applied to the electro-optical modulation element, and can supply the direct current component without supplying the direct current component. Can also control the DC component of the intensity of the incident light.

As the electro-optical modulator, KTi is used.
Light modulation can be efficiently performed by using the OPO ₄ crystal element.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical modulation method and device of the present invention will be described in detail below with reference to the drawings.

Here, FIG. 1 shows an example of an optical modulation device to which the optical modulation method of the present invention is applied.

In the above light modulator, the electrode layer 4 as an electrode is used.
a and 4b are provided as a first KTP2 as an electro-optic modulator and a second KT is provided with electrode layers 4c and 4d.
In the optical modulation device for applying a light modulation driving voltage to P3 to modulate the light incident on the electro-optical modulation element, for example, laser light, the light connected to the electrodes and applied between the electrodes. Power supply unit 1 as voltage supply means for alternately switching the direction of the modulation drive voltage between one direction and the other direction
It comprises.

The above first KTP2 and second KTP3
Are cut in the respective crystal axis directions, and the surface on the incident light side or the incident surface 5 and the surface on the outgoing light side or the outgoing surface 6 are optically polished. In addition, each of the electrode layers 4a, 4b, 4c, 4d
Is composed of a metal layer having a thickness of, for example, 20 nm of titanium and 500 nm of gold, and is deposited on the surface of the predetermined KTP shown in FIG. 1, for example.

Further, in each KTP, the optical axis of the first KTP2 and the optical axis of the second KTP3 are orthogonal to each other with the same direction as the incident light optical path Y as the optical axis of each KTP so that they are in series. It is arranged.

Further, in the power supply unit 1, the output terminal 7
Is connected to the electrode layer 4b of the first KTP2 and the electrode layer 4d of the second KTP3, and the output terminal 8 is connected to the electrode layer 4a of the first KTP2 and the electrode layer 4c of the second KTP3. .

By connecting in this way, for example, a positive voltage as an optical modulation driving voltage having a positive polarity is output from the output terminal 7, and a negative voltage as an optical modulation driving voltage having a negative polarity is output from the output terminal 8. By outputting the voltage of
In KTP2, from the electrode layer 4b to the electrode layer 4a,
Further, in the second KTP3, a voltage is applied from the electrode layer 4d to the electrode layer 4c. When the output from the output terminal 7 and the output from the output terminal 8 are switched, the first K
A voltage is applied in the opposite direction between TP2 and the second KTP3. In the present embodiment, the output terminal 7
Is referred to as the first voltage, and the optical modulation drive voltage that outputs the negative voltage from the output terminal 8 is referred to as the first voltage. The negative voltage is output from the output terminal 7 and the positive voltage is output from the output terminal 8. The light modulation drive voltage that outputs the signal is called a second voltage.

The light modulation drive voltage is, for example, a voltage at which the first voltage and the second voltage are output for the same time within a predetermined time, that is, the average voltage of 0V.
Further, the intensity I of the output laser light emitted from the emission surface 6
Changes depending on the magnitude V of this light modulation drive voltage,
This transfer function is shown in equation (1). In equation (1), V
_s is a switching voltage, which is a value that can be arbitrarily set.

I [V] = sin ² (πV / 2V _s ) ... (1) Here, as the power supply unit 1, a voltage such that the first voltage and the second voltage can be alternately switched. An example using a power supply device for generating will be described. The relationship between the light modulation drive voltage (V) output from the power supply unit 1 and the time (t) is represented by a curve R, as shown in FIG. Further, the relationship between the intensity (I) of the output laser light and the voltage V represented by the equation (1) is the curve P.
It is represented by.

According to FIG. 2, in the above optical modulator, the power supply unit 1 is connected to the first voltage and the second voltage as described above.
Assuming that the power supply device generates a voltage that can be switched alternately with the voltage of, the point on the curve P where the value of the intensity I of the output laser light has a minimum value, for example, the point A is set as an operating point, so-called bias. That is, the light modulator outputs an output laser beam having an intensity I of 0 when the voltage supplied by the power supply unit 1 is 0V. Further, the power supply unit 1 supplies each KTP with a voltage indicated by a curve R having an amplitude V _S centering on the point A. And the first KTP2
The intensity of the output laser light obtained by modulating the intensity of the laser light incident on the two KTPs maintains a value corresponding to B.
Note that it is possible to set a value according to any value of B as the value of V _S. In this way, each of the above K
Optical modulation can be performed without supplying a DC voltage component to TP.

Next, an example will be described in which a data supply unit for outputting binary data as a digital signal relating to the light modulation operation is provided and the data supply unit is connected to the power supply unit 1.
Each bit of the binary data is “0” or “1”
When the data "1" is input, the power supply unit 1 changes the first voltage or the second voltage according to the binary data from the data supply unit. Output. However, the average voltage is 0 V, that is, the first and second voltages are output the same number of times. Further, the power supply unit 1 stops voltage output when "0" data is input. That is, the power supply unit 1
The relationship between the light modulation drive voltage (V) output from the device and the time (t) is shown in FIG.
1001101 ″, it is represented by a curve S. Further, similarly to FIG. 2, the relationship between the intensity (I) of the output laser light and the voltage V represented by the equation (1) is represented by a curve P. The above bit pattern is represented by T. When two "1" s are consecutive, voltages of the same polarity are output, but between these two consecutive "1s". The polarity may be inverted, and the voltage may be output when the data “0” is input.

According to FIG. 3, in the above optical modulator,
When a data supply unit is provided and the data supply unit is connected to the power supply unit 1, first, the optical modulator sets the point A as a bias. In addition, as described above, the power supply unit 1 supplies each of the KTPs with the voltage represented by the curve S having the amplitude V _S centering on the point A in accordance with the binary data. . Then, the intensity of the output laser light obtained by modulating the intensity of the laser light incident on the first KTP2 by the two KTPs is a value corresponding to B when data of "1" is sent, and "0". When the data of "is sent, it takes a value corresponding to 0. That is, the light modulation device operates like a shutter based on the binary data. In this way, optical modulation can be performed without supplying a DC voltage component to each KTP.

Further, as shown in FIG. 1, a specific example of the inside of the power supply unit 1 is a power supply 11 or 12 which is a DC power supply, a pair of first voltage terminals a, and a pair of second voltage terminals. b, the changeover switches 14 and 15 for switching between the first voltage and the second voltage, and the control unit 13 that controls the operation of these changeover switches 14 and 15.

The power supply section 1 is controlled by the control section 13 so that the change-over switches 14 and 15 are switched over in a predetermined time, thereby alternately switching between the first voltage and the second voltage. ing. Further, the first voltage and the second voltage can be switched by using a power supply that generates an AC voltage as the power supply.

Further, the power supply unit 1 outputs the binary data from the data supply unit to the control unit 13, so that the first voltage and the second voltage are supplied in accordance with the binary data. Is being switched.

According to the above optical modulator, the laser light incident from the incident light optical path Y has the first KTP2 and the second KTP3 to which the optical modulation drive voltage is applied from the power supply unit 1 to each electrode layer.
When passing through and, the DC component of the intensity is modulated and controlled by the electro-optical effect of these KTPs, and this modulated output laser light is emitted from the emission optical path Z. Further, since no DC voltage component is supplied to the KTP during the above-mentioned light modulation, deterioration of these KTPs due to damage to the gray track is avoided.

The power supply unit 1 is, for example, a DC power supply, which switches the direction of the light modulation drive voltage between one direction and the other direction, and outputs the light modulation drive voltage. A DC voltage component is supplied to each KTP. The above-mentioned KTP is prevented from being deteriorated due to damage to the gray track.

Here, the power supply unit 1 is a power supply device which generates an AC voltage, and prevents the DC voltage component from being supplied to the KTPs, thereby avoiding deterioration of the KTPs due to gray track damage.

Alternatively, the power supply unit 1 is provided with, for example, a control unit 13 which is connected to a data supply unit for outputting binary data, and the optical modulation drive is performed according to the binary data. The voltage direction is switched and output, and the DC voltage component is not supplied to each of the KTPs to prevent deterioration of each of the KTPs due to damage to the gray track.

In this embodiment, the power supply unit 1 is constituted by a power supply 1 which is a DC power supply as shown in FIG.
The first voltage and the second voltage are switched by switching the terminals having the power supply terminals 1 and 12 and connected to these power sources, but the present invention is not limited to this, and the output terminal is not limited to this. It does not matter as long as the polarities of the outputs from 7 and 8 are interchanged.

In this embodiment, two KTPs are used as the electro-optical modulator, but the present invention is not limited to this, and only one may be used. Also,
Although an example using KTP is given as the electro-optical modulation element, the present invention is not limited to this, and the present invention is not limited to this, and other electro-optical modulation elements such as barium borate (BBO) and lithium borate (LBO) can be used. The same effect as the invention can be obtained.

[0052]

As described above, according to the optical modulation method of the present invention, the direction of the optical modulation drive voltage as an electric signal applied to the electro-optical modulation element at the time of optical modulation is set to one direction and the other direction. Since they are alternately switched and applied to the electro-optical modulation element, the light modulation can be performed without applying a DC voltage component to the electro-optical modulation element, and the deterioration of the electro-optical modulation element is possible. Can be avoided.

Further, according to the present invention, when the light modulation driving voltage is applied to the electro-optical modulator, the application time in the one direction is equal to the application time in the reverse direction. Thus, the optical modulation can be performed without applying a DC voltage component to the electro-optical modulation element, and deterioration of the electro-optical modulation element can be avoided.

Further, according to the present invention, since the light modulation driving voltage is an AC voltage, a DC voltage component is not applied to the electro-optical modulation element, so that deterioration of the electro-optical modulation element can be avoided. In addition, it becomes possible to control the DC component of the intensity of the incident light without supplying the DC component. .

Further, according to the present invention, the light modulation driving voltage is switched between the one direction and the opposite direction according to one value of the binary data of the digital signal and is applied to the electro-optical modulation element. , Optical modulation based on the digital signal becomes possible without using a DC voltage component, and since a DC voltage component is not applied to the electro-optical modulator,
It is possible to avoid the deterioration of the electro-optical modulator.

Further, according to the present invention, in the above-described optical modulation method, by using the KTiOPO ₄ crystal element as the electro-optical modulation element, it is possible to efficiently perform optical modulation. Further, since the DC component in the KTiOPO ₄ crystal device is not applied, the KTiOPO ₄ crystal element graying damage, so-called gray track damage (gray track
There is no risk of damage).

Further, according to the optical modulator of the present invention, the direction of the optical modulation drive voltage applied to each electrode of the electro-optical modulator at the time of optical modulation is alternately switched between the one direction and the opposite direction to perform the electro-optical modulation. Since the voltage is applied to the element, the light modulation can be performed without supplying a DC voltage component to the electro-optical modulation element, and deterioration of the electro-optical modulation element can be avoided. .

Further, according to the present invention, the voltage supply means makes the time for outputting the light modulation drive voltage in one direction equal to the time for outputting the light modulation drive voltage in the opposite direction, so that the direct current voltage component is generated. It becomes possible to carry out the above-mentioned optical modulation even without supplying it to the device, and it is possible to avoid deterioration of the electro-optical modulator.

Further, according to the present invention, since the DC voltage component is not applied to the electro-optical modulation element by using the AC voltage as the light modulation driving voltage, deterioration of the electro-optical modulation element can be avoided. In addition, it is possible to control the DC component of the intensity of the incident light without supplying the DC component.

Further, according to the present invention, the data supply means is provided, and the light modulation drive voltage is switched between the one direction and the opposite direction according to the binary data of the digital signal from the data supply means. Since it is applied to the electro-optical modulator, optical modulation based on the digital signal is possible without using a DC voltage component, and since the DC voltage component is not applied to the electro-optical modulator, the electro-optical modulator is It is possible to avoid deterioration of the modulation element.

Further, according to the present invention, in the above-mentioned optical modulator, by using the KTiOPO ₄ crystal element as the electro-optical modulator, the optical modulation can be efficiently performed. Further, since the DC component in the KTiOPO ₄ crystal device is not applied, the KTiOPO ₄ crystal element graying damage, so-called gray track damage (gray track
There is no risk of damage).

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a main part of an optical modulation device to which an optical modulation method of the present invention is applied.

FIG. 2 is a diagram showing a relationship between a voltage output from a power source of the optical modulator and time, and a relationship between an intensity of the modulated output laser light and a voltage.

FIG. 3 is a diagram showing the relationship between the voltage output from the power supply and time and the relationship between the intensity and voltage of modulated output laser light when a data supply unit is provided in the power supply.

[Explanation of symbols]

 1 Power Supply Section 2 First KTP 3 Second KTP 4a, 4b, 4c, 4d Electrode Layer

Claims (10)

[Claims] 1. A light modulation method for applying a light modulation driving voltage to an electro-optical modulation element to modulate light incident on the electro-optical modulation element, wherein the direction of the light modulation driving voltage applied to the electro-optical modulation element is changed. An optical modulation method characterized by alternately switching between one direction and the other direction. 2. The light modulation method according to claim 1, wherein the light modulation drive voltage is a voltage whose application time in the one direction is equal to application time in the opposite direction. 3. The light modulation method according to claim 1, wherein the light modulation driving voltage is an AC voltage that switches between the one direction and the opposite direction at a constant cycle. 4. The light according to claim 1, wherein the light modulation driving voltage is a voltage that switches between the one direction and the opposite direction according to one value of binary data of a digital signal. Modulation method. 5. The electro-optic modulator is KTiOPO.
The optical modulation method according to claim 1, wherein the optical modulation method is a _four- crystal element. 6. An optical modulation device for applying a light modulation driving voltage to an electro-optical modulation element provided with an electrode to modulate light incident on the electro-optical modulation element, wherein the light modulation device is connected to each of the electrodes and An optical modulator comprising voltage supply means for alternately switching the direction of the optical modulation drive voltage applied between the electrodes between one direction and the other direction. 7. The voltage supply means generates and outputs an optical modulation drive voltage between the electrodes, the time applied in the one direction and the time applied in the opposite direction being equal to each other. 6. The light modulation device according to 6. 8. The optical modulator according to claim 6, wherein the voltage supply unit outputs an AC voltage that switches between the one direction and the opposite direction at a constant cycle. 9. A data supply means for supplying digital data is provided, and the voltage supply means outputs a voltage that switches between the one direction and the reverse direction according to one value of binary data of a digital signal. 7. The optical modulation method according to claim 6, wherein 10. The electro-optical modulator is KTiOP.
The optical modulator according to claim 6, which is an O ₄ crystal element.