JP2012083688A - Control method of optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize appearance of optical element using electro-optical materials that makes a change in control output of light difficult regardless of changes of conditions including a repetition frequency of control signal supplied externally.SOLUTION: In a control method of optical element including optical components that are made of electro-optical materials having electro-optical effects, a control method of optical element in which the electro-optical materials are made to run within a temperature range showing paraelectricity including a ferroelectric phase transition temperature, and an optical element including temperature control means are provided.

Description

  The present invention relates to an optical element controlled by an electric signal supplied from the outside, and in particular, the control method of the optical element in which the control output of light is hardly changed even if conditions such as a repetition frequency of the electric signal change, The present invention relates to an optical element preferably used for a control method.

An optical modulator that can electrically control the intensity of light as an optical element using an optical component made of an electro-optic material whose optical physical properties such as refractive index change due to an externally applied electric field Has been known for a long time. For example, it is described in Non-Patent Document 1. An example of the electro-optic material is described in Non-Patent Document 2.
L. P. Kaminov and E.M. H. Turner, “Electrical Light Modulator”, Appl. Optics 5 [10] (1966) pp. 1612-1618 H. Jiang, et. al. "Transparent Electro-Optical ceramics and Devices", SPIE Photonics Asia, November 2004.

  The structure and operation of the optical modulator 1 will be described with reference to FIG. In FIG. 1, reference numerals 21 and 22 denote optical parts obtained by processing an electro-optic material, and the end faces in the longitudinal direction are optically polished so that light enters and exits. The optical component 21 has electrodes 211 and 212 formed on upper and lower surfaces parallel to the light propagation path, and an electric field is generated in the vertical direction inside the optical component 21 by applying a voltage to the electrodes from the external voltage source 4. To do. Similarly, electrodes 221 and 222 are formed on the left and right surfaces parallel to the light propagation path in the optical component 22, and an electric field is generated in the left and right direction inside the optical component 22. A polarizer 31 is installed on the incident side of the light 11 of the optical component 21 so that the polarization direction of the light is inclined by 45 degrees with respect to the direction of generation of the electric field. A polarizer 32 is installed so that the polarization direction is orthogonal to 31. The optical components 21 and 22 and the polarizers 31 and 32 are linearly arranged in the optical axis direction in which light propagates.

  In the state where no voltage is applied to the electro-optic material, the optical components 21 and 22 are isotropic with respect to the incident light 11, so that the light only causes a phase shift corresponding to the length of the optical components 21 and 22. Not affected. For this reason, the light emitted from the optical component cannot pass through the polarizer 32 orthogonal to the incident-side polarizer 31, and no light is output from the optical modulator.

  When a direct current voltage is applied to the electrodes of the optical components 21 and 22, the electro-optic material is distorted, and the optical component is anisotropic. , Abnormal light), the light transmission speed changes, and the polarization direction of the light emitted from the optical component rotates. This phenomenon is generally known as an electro-optic effect. When the length of the optical components 21 and 22 and the applied voltage are adjusted, the polarization direction of the outgoing light 12 can be rotated by 90 degrees with respect to the incident light 11, and the incident light 11 can pass without loss as the outgoing light 12. .

  In general, the temperature dependence of birefringence differs depending on the polarization component of light in an electro-optic material, but the influence can be compensated by arranging the electrode positions of the two optical components 21 and 22 in a cascade.

  Using this principle, the optical modulator 1 is used as a variable optical attenuator (VOA) that electrically changes the intensity of light or a Q switch that switches loss.

  Hereinafter, the problem of the conventional optical element will be described by taking the optical modulator 1 shown in FIG. 1 as an example. In an optical element typified by the optical modulator 1, by using a material having a large electro-optic constant in the optical components 21 and 22, the electro-optic material is shortened in the light propagation axis direction. Thus, the size of the optical element can be reduced, and at the same time, the voltage applied to the electro-optic material can be further reduced.

In recent years, xPb (Mg _1/3 Nb _2/3 ) O _3- (1-x) PbTiO ₃ (hereinafter abbreviated as PMN-PT) ceramics is an example of an optically transparent material having a large electro-optic constant. It is reported in Patent Document 2.

This material is known as relaxor-based ferrobskite-type ferroelectrics (Ferroelectrics). When the composition component of Pb (Mg _1/3 Nb _2/3 ) O ₃ is 10%, the ferroelectric phase transition temperature ( Ferroelectric phase transition temperature, phase transition temperature from paraelectric phase to ferroelectric phase (hereinafter abbreviated as Tc) is about 30 ° C. In general, a ferroelectric has a characteristic that the amount of physical properties affected by an electric field such as a dielectric constant increases in the vicinity of Tc. For this reason, the electro-optic constant has a large value in the vicinity of Tc, and it is considered that it is suitable for application to an optical element when the operating temperature region is close to Tc.

  FIG. 1 shows the temperature dependence of the relative dielectric constant of PMN-PT ceramics when x is approximately 10%. The peak of the dielectric constant is around 30 ° C., but the peak position varies greatly depending on the frequency to be measured. This phenomenon is related to the movement of the polarization domain in the ferroelectric phase, which will be described later, and is expressed as the frequency dispersion of the dielectric constant.

  In a ferroelectric material, at a temperature A sufficiently higher than Tc, the relationship between dielectric polarization P (Dielectric polarization) and electric field strength E is almost linear as shown by a curve A1 in FIG. The values of polarization are almost the same. On the other hand, at a temperature B sufficiently lower than Tc, the relationship between the dielectric polarization P and the electric field strength E becomes a curve shown by a curve B1 in FIG. 3, and the values of the electric polarization at the time of increasing and decreasing of the electric field do not coincide with each other. Indicates hysteresis. This phenomenon is also caused by the movement of the polarization domain.

ここで、ｎ_０は誘電分極がないときの等方的な光の屈折率を示し、Ｐは電気光学定数を示す。ｇはカー定数として知られている。The difference in refractive index Δn between ordinary light and extraordinary light that causes the electro-optic effect to appear is caused by the dielectric polarization P and can be expressed by the following equation.

Here, n ₀ represents the refractive index of isotropic light when there is no dielectric polarization, and P represents the electro-optic constant. g is known as the Kerr constant.

ここでε_０は真空中の誘電率、εは電気光学材料の比誘電率を示す。In the ferroelectric phase, the electric polarization P is represented by the sum of spontaneous polarization P _S (Spontaneous polarization) and induced polarization excited by the electric field E, and is represented by the following equation.

Here, ε ₀ represents the dielectric constant in vacuum, and ε represents the relative dielectric constant of the electro-optic material.

第１項は電気光学材料全体において平均的に存在する自発分極Ｐ_Ｓの総和によって変化する成分を示し、第３項は外部から印加する電界Ｅのみで変化する成分を示す。第２項は自発分極Ｐ_Ｓと電界Ｅの両方が寄与する項目を示す。Substituting Equation 2 into Equation 1 gives the following equation.

The first term represents a component that varies with the sum of the spontaneous polarization P _S present on average in the entire electro-optical material, the third term shows the component that changes only at an electric field E is applied from the outside. The second term indicates both contribute items of the spontaneous polarization P _S and the electric field E.

  In general, the contribution of the third term is sufficiently small to the electro-optic effect in the ferroelectric phase, and only the second term is focused and handled as the Pockels effect. In the case of a relaxor-based ferrobskite ferroelectric, the contribution of the third term cannot be ignored because the relative dielectric constant ε is very large in a very wide temperature range of the ferroelectric phase.

  In the optical modulator 1 of FIG. 1, due to the difference Δn between the ordinary light and the extraordinary light refractive index in Expression 3, no light is emitted from the optical modulator when no voltage is applied to the optical components 21 and 22, and the optical components 21 and 22. When an appropriate voltage Vπ is applied to the light, the phase difference between ordinary light and extraordinary light is shifted by 90 °, and light can be emitted without loss.

  Differences in operating characteristics of the optical modulator 1 when the electro-optic material is in the paraelectric phase and in the ferroelectric phase will be described with reference to the schematic diagram of FIG. In FIG. 4, the horizontal axis indicates the voltage applied to the optical components 21 and 22, and the vertical axis indicates the light intensity output from the optical modulator.

  Curve A2 shows the characteristics of the optical modulator when the electro-optic material is in the paraelectric phase, that is, when the temperature of FIG. 2A or the temperature at which the electric field-dielectric polarization characteristics such as A1 of FIG. 3 are obtained. Is. In the curve A2, the light emission intensity shows the maximum value at the voltage Vπ where the phase difference between the ordinary light and the extraordinary light is shifted by 90 °, and decreases again as the voltage further increases. As the voltage rises, the voltage at which the light emission intensity becomes maximum appears many times. Further, no hysteresis is observed in the curve A2 of the optical output corresponding to the fact that there is no hysteresis in the curve A1 when the voltage rises and falls. It is also symmetric with respect to the positive and negative voltages. FIG. 5A shows light output characteristics actually measured at a very slow repetition period of 1/300 Hz. Since the scale of the vertical axis is expressed in dB, it seems to have a slight hysteresis when the voltage rises and falls, but the hysteresis is generally small and symmetric with respect to the positive and negative of the voltage.

  On the other hand, the curve B2 indicates the operating characteristics of the optical modulator when the electro-optic material is in the ferroelectric phase, that is, the temperature at which the temperature of B in FIG. Is shown. When the voltage change is a slow change of 1 second or more, the voltage at which the light emission intensity reaches the maximum with the voltage change appears many times as in the paraelectric phase. However, the curve B1 in FIG. Hysteresis also appears in the light output curve B2 in the same way that hysteresis is seen when descending. FIG. 5B shows the light output characteristics actually measured at a repetition period of 1/300 Hz. It can be seen that there is a large hysteresis when the voltage rises and falls.

  Next, problems when a high-speed square wave signal in the ferroelectric phase is applied to the electro-optic element will be described with reference to FIG.

  FIG. 6A shows a square wave signal in which a voltage (VOA voltage) is switched at a high speed in 100 ns or less at the temperature of point B in FIG. The change of the optical output when a period is 10 kHz is shown. The optical output from the optical modulator 1 appears to switch at high speed substantially following the applied square wave signal. On the other hand, FIG. 6-2 shows a change in light output when a very slow voltage of 5 Hz is applied under the same voltage condition. As can be seen from the figure, the light output rapidly increases as soon as the voltage is switched, but thereafter the light output slowly decays.

In FIG. 4 showing the relationship between the external electric field and the optical output, this phenomenon shows a change without hysteresis as shown by the curve B3 in the 10 kHz square wave signal, but has a hysteresis as shown by the curve B4 in the 5 Hz square wave signal. It shows that there is a change. In other words, this phenomenon has a very response component that follows in the order of 100 ns and a very slow component that follows in the order of 10 ms, following the component that the optical output follows to the electrical signal applied to the optical components 21 and 22 from the outside. It shows that

  Next, this phenomenon will be described by paying attention to the ferroelectric behavior inside the electro-optic material. The relaxor-based ferrobskite ferroelectric has a total of eight spontaneous polarization orientations including positive and negative directions in the ferroelectric phase. When an electric field is not applied from the outside, there exists a domain having a spontaneous polarization (Domain, a region having a spontaneous polarization orientation), and the average polarization of the entire optical components 21 and 22 is zero. That is, the entire optical components 21 and 22 look optically isotropic.

  A phenomenon in which an extremely fast response component and a very slow response component exist when an electro-optic material is used as an optical modulator will be described with reference to FIG. Here, in order to simplify the explanation, it is assumed that there are six directions of spontaneous polarization in the vertical and horizontal directions in the paper, the left-right direction, and the direction perpendicular to the paper, including positive and negative directions. When the electro-optic material is ceramic, the inside is composed of a collection of ceramic particles of the order of 10 μm as indicated by 51 and 52. Individual particles are single crystals of electro-optic material. When the electro-optic material is in the ferroelectric phase, there are domains inside the particle. For example, inside the particle 51, there are a domain 61 having spontaneous polarization upward with respect to the paper surface and a domain 62 having spontaneous polarization rightward with respect to the paper surface. Similarly, inside the particle 52, there exist a domain 63 having a spontaneous polarization downward with respect to the paper surface and a domain 64 having a spontaneous polarization in a direction perpendicular to the paper surface. For the light 13 propagating from the left to the right of the page, the polarization of the component perpendicular to the propagation method of the light 13 is affected as in the domains 61, 63 and 64. In the entire optical component 23, the total sum of polarization components perpendicular to the light propagation direction affects the phase velocity of the light 13. When there is no external electric field E, it appears as the contribution of Δn in the first term of Equation 3. In general, in the case of a ceramic material, when there is no external electric field E, the total sum of the spontaneous polarization is almost zero.

Electrodes 231 and 232 are provided in the vertical direction of the optical component 23, and an electric field E is generated inside the optical component 23 by applying a voltage to the electrodes from the outside. At this time, the magnitude of the domain 61 having the polarization in the direction corresponding to the electric field E increases, and the magnitude of the polarization of the domain 63 having the polarization opposite to the electric field E is decreased. At the same time, the domain walls 71 and 72 separating the domains move in a direction to increase the amount of the domain 61 and to decrease the amount of the domain 63. As a result the entire optical component generates spontaneous polarization P _S of the direction of the electric field E will influence the light 13 as the contribution of Δn of the first and second terms of Equation 3. This contribution is known as the Pockels effect.

  Like 61 and 63, the change in the magnitude of the dielectric polarization inside one domain is an ionic polarization contribution that appears when the arrangement of atoms or ions inside the crystal of the electro-optic material changes. Follow quickly. The amount of each domain changes as one of the domain walls 71 and 72 moves. This movement is generally very slow, and changes appear with a delay of 10 ms or more with respect to changes in the external electric field E. The reason why there are a fast response component and a slow response component with respect to the change of the external electric field shown in FIGS. It can be understood by the existence of two.

  When the optical modulator 1 is actually applied to an optical communication system, the time width of the optical signal to be modulated always changes and is not fixedly repeated with a constant time width. When the electro-optic material is in the ferroelectric phase, the output waveform from the optical modulator can change from the response waveform as shown in FIG. 6A to the response waveform as shown in FIG. This means that the optical modulator showing the operations of FIGS. 6-1 and 6-2 is difficult to apply in an optical communication system.

  The present invention includes an extremely fast response component and a very slow response component in the component that the optical output follows for the electrical signal applied to the optical components 21 and 22 obtained by processing the electro-optic material. This solves the problem of not being able to follow any modulation signal when the optical element is applied to an optical communication system.

  The method for controlling an optical element according to the present invention is based on the operation of an electro-optic material in order to avoid a problem that a ferroelectric material used for an optical component includes a very fast response component and a very slow response component in the ferroelectric phase. Set temperature range to paraelectric phase as much as possible. However, since relaxor-based ferrobskite ferroelectrics have a large electro-optic constant in the vicinity of Tc, it is beneficial to include Tc in the operating temperature region of the optical element. The method for controlling an optical element of the present invention uses a lower limit temperature range in which frequency dispersion of the paraelectric phase and relative permittivity of the electro-optic material to be used does not occur. Alternatively, in the case where a rectangular signal having a repetition frequency of 10 kHz or more is applied and a square wave signal having a repetition frequency of about 5 Hz is applied, the vicinity of Tc of the electro-optic material in which the light output level of the optical element hardly changes is applied. The temperature range of the paraelectric phase is limited.

  The optical element control method of the present invention can utilize only the very fast response component that the optical output follows by using the vicinity of Tc and the paraelectric phase of the electro-optic material used in the optical component in a limited manner. An optical modulator using a material enables modulation of an optical signal at every time interval in an optical communication system.

It is a figure which shows the structure of an optical modulator, and its operation principle. It is a figure which shows the temperature change of the dielectric constant of ferroelectric PMN-PT. It is a figure which shows the relationship between the external electric field E and the dielectric polarization P of a ferroelectric substance. It is a figure which shows the relationship between the external electric field and optical output of an optical modulator. It is a figure which shows the optical output of the actual optical modulator shown when an electro-optic material is in a paraelectric phase. It is a figure which shows the optical output of the actual optical modulator shown when an electro-optical material exists in a ferroelectric phase. It is an output time response waveform of the optical modulator with respect to a 10 kHz square wave repetition signal shown when the electro-optic material is in the ferroelectric phase. It is an output time response waveform of the optical modulator with respect to a 5 Hz square wave repetition signal shown when the electro-optic material is in the ferroelectric phase. It is an output time response waveform of the optical modulator with respect to a 10 kHz square wave repetition signal shown when the electro-optic material is at Tc. It is an output time response waveform of the optical modulator with respect to a square wave repetition signal of 5 Hz shown when the electro-optic material is at Tc. It is a figure explaining the internal state and operation | movement when an electro-optic material is in a ferroelectric phase. It is a figure explaining the internal state and operation | movement when an electro-optic material is in a paraelectric phase. It is a figure which shows the relationship between the operating temperature of the electro-optic material used for the optical element of this invention, and its Tc. It is a figure which shows an example of the structure which temperature-controls the optical element of this invention. It is a figure which shows the other example of an optical element.

  For example, the optical modulator 1 shown in FIG. 1 is used in the method for controlling an optical element of the present invention.

  According to an embodiment of the present invention, in the method for controlling an optical element including an optical component made of an electro-optic material having an electro-optic effect as described in claim 1, the optical component includes a ferroelectric phase transition temperature. By controlling to operate in a temperature range that exhibits dielectric properties, it is possible to use only a very fast response component that the optical output of the optical element follows, and in a system such as optical communication, the optical signal at every time interval can be used. Modulation can be possible. Further, for example, as described in claim 2, it is possible to control the electro-optic material so that the electro-optic effect is operated in a temperature range in which frequency dispersion due to domain movement composed of a single spontaneous polarization does not appear. . For example, as described in claim 3, the electro-optic material can be controlled to operate in a temperature range where the relative permittivity of the electro-optic material does not exhibit frequency dispersion in a frequency range of 100 Hz to 100 kHz. Further, for example, when a square wave signal is applied to the electro-optic material as described in claim 4, the repetition frequency is 10 kHz and 5 Hz, and control is performed so as to operate in a temperature range in which the light output level from the optical element does not change. It is also possible to do.

Further, as an embodiment of the present invention, in the method for controlling an optical element including an optical component using a relaxor-type ferrobskite ferroelectric as the electro-optic material as described in claim 5, the electro-optic material is a ferroelectric material. By controlling to operate in a temperature range that exhibits paraelectricity including the target phase transition temperature, it is possible to use only a very fast response component that the optical output of the optical element follows, and in any system such as optical communication Modulation of optical signals at time intervals can be enabled. In addition, as described in claim 6, a ferroelectric material mainly composed of xPb (Mg _1/3 Nb _2/3 ) O _3- (1-x) PbTiO ₃ can be used for the electro-optic material. Further, as described in claim 7, ceramics can be used for the electro-optic material. Further, as described in claim 8, a single crystal can be used for the electro-optic material.

    Further, as an embodiment of the present invention, paraelectricity in which the temperature of the electro-optic material includes a ferroelectric phase transition temperature regardless of an external environmental temperature in which the optical element is used as described in claim 9. By controlling the temperature so that it falls within the indicated temperature range, only the very fast response component that the optical output of the optical element follows can be used, and modulation of optical signals at every time interval can be performed in systems such as optical communication. Can be possible. In addition, when the external environmental temperature at which the optical element is used is lower than the ferroelectric phase transition temperature of the electro-optic material as described in claim 10, the electro-optic material is made ferroelectric by heating the optical element. It is also possible to control the temperature within a temperature range showing a paraelectric phase including a phase transition temperature. Further, when the ferroelectric phase transition temperature of the electro-optic material is within the range of the external environmental temperature in which the optical element is used as described in claim 11, the optical element is cooled or heated by a Peltier element. The temperature can also be controlled in a temperature range in which the electro-optic material exhibits paraelectricity including a ferroelectric phase transition temperature.

  As an embodiment of the present invention, an optical element including an optical component made of an electro-optical material having an electro-optical effect as described in claim 12, wherein the optical component includes a ferroelectric phase transition temperature. By configuring the optical element to include temperature control means that controls to operate in a temperature range indicating, it is possible to use only a very fast response component that the optical output of the optical element follows, such as optical communication In this system, it is possible to modulate an optical signal at any time interval. A preferable example of the electro-optical material according to claim 12 is, for example, as described in any one of claims 13 to 16.

(First embodiment)
In the optical modulator 1 of FIG. 1, for example, PMN-PT ceramics having x of 10% is used for the optical components 21 and 22. FIGS. 6-3 and 6-4 show optical modulation outputs when the optical modulator 1 is operated at a temperature at which the relative permittivity of C in FIG. 2 has almost no frequency dispersion. FIG. 6-3 shows a change in optical output when a square wave signal whose voltage is switched at a high speed of 100 ns or less is applied to the optical components 21 and 22 of the optical modulator 1 and the repetition period is 10 kHz. . On the other hand, FIG. 6-2 shows the change in light output when a very slow voltage of 5 Hz is applied under the same voltage condition. In both FIGS. 6-3 and 6-4, there is almost no change in the optical output level of the response waveform.

  The results of FIGS. 6-3 and 6-4 correspond to the change in optical output without hysteresis with respect to the external signal as shown by the curve C1 in both the 10 kHz and 5 Hz square wave signals in FIG. . This means that a slow response component is not included in the optical output of the optical modulator 1 with respect to the application of the external electric field E. In the present invention, the light output from the light modulation element at the lower limit temperature at which the dielectric constant measured at a frequency of 100 Hz to 100 kHz has no dispersion or the repetition frequency of the square wave signal applied to the optical component from the outside is 10 kHz and 5 Hz. The lower limit temperature at which the level does not change is defined as the ferroelectric phase transition temperature Tc. The same results as in FIGS. 6-3 and 6-4 are obtained even at a temperature A where the electro-optic material of Tc or higher in FIG. 2 is a paraelectric phase.

  The optical element control method of the present invention can use only the very fast response component that the optical output follows by limiting the operating temperature range to only the paraelectric phase including Tc of the electro-optic material. In the optical modulator using the optical system, it is possible to modulate the optical signal at every time interval in the optical communication system.

Next, this phenomenon will be described by focusing on the dielectric behavior inside the electro-optic material. FIG. 7-2 shows the polarization state of the electro-optic material when in the paraelectric phase. When the electro-optic material is ceramic, the inside is composed of a collection of ceramic particles as indicated by 5 as in FIG. Unlike ferroelectric phase in Figure 6-1 when the inner external electric field E, is within the ceramic particles not present spontaneous polarization P _S, the domain wall is also absent. When an external electric field E is applied here, a polarization 63 is generated in the electric field direction corresponding to the relative dielectric constant of the electro-optic material, and a difference in refractive index between ordinary light and extraordinary light as shown in Equation 1 occurs. At this time, there is no movement of the domain wall as in the ferroelectric phase shown in FIG. For this reason, since a response component with a slow light output accompanying the movement of the domain wall is not included, only a fast response component due to the contribution of ion polarization that changes the arrangement of atoms or ions inside the crystal of the electro-optic material can be used.

  Next, the relationship between the Tc of the electro-optic material used in the present invention and the operating temperature region of the optical element 1 will be described with reference to FIG. The Tc of the electro-optic material used in the present invention is set to approximately the lower limit of the operating temperature range of the optical element.

  In general, an optical related device is required to have an operation guarantee of 0 ° C. to 70 ° C. The composition and manufacturing conditions of the electro-optic material used for the optical components 21 and 22 in the optical element 1 of the present invention are adjusted so that the phase transition temperature Tc is 0 ° C. For example, in the case of PMN-PT ceramics, the composition can be realized by setting x to 5%.

(Second Embodiment)
The optical element control method of the present invention can be used by limiting the paraelectric phase and the vicinity of Tc of the electro-optic material used in the optical component by operating the optical element itself by heating. For example, when the operating temperature of the light-related device incorporating the light modulator is 0 ° C. to 70 ° C., the Tc of the electro-optic material used for the light modulator 1 is set to 70 ° C. or more to control the heating of the light modulation element 1 by Tc. The vicinity and the paraelectric phase can be used in a limited manner.

  For example, in the case of PMN-PT ceramics, the composition can be realized by setting x to 13% or more.

  Next, a method for controlling the heating of the optical element will be described with reference to FIG. In FIG. 9, 8 is an electric circuit board on which the optical element 201 used in the present invention is mounted and used or controlled. 101 is a light input / output terminal of the optical modulator 201, and 102 is an electric signal input terminal. A heater 81 for heating the optical element and a sensor 82 for detecting the temperature are mounted in the vicinity of the optical element 201 in the electric circuit board 8, which is an embodiment of the temperature control means of the present invention. . The heater 81 is heated and controlled by a signal from the sensor 82 so that the electro-optic material of the optical element always has a temperature equal to or higher than Tc. The sensor 82 may be a thermistor or a thermocouple.

  In the above description, the operating temperature of the electro-optic material is controlled to be equal to or higher than Tc by heating. However, when the Tc of the electro-optic material is included in the external environmental temperature range of the optical element, the thermoelectric element can be heated or cooled. It is also possible to control the optical element so that the temperature of the electro-optic material is near or above Tc where the electro-optic effect is large.

  In the above description of the optical element control method of the present invention, the optical modulator 1 shown in FIG. 1 is shown as an example. However, the optical modulator is not limited to this, and for example, the light as shown in FIG. Applicable to modulators.

  The optical modulator 2 in FIG. 10 includes a polarizer 33, an optical component 24 obtained by processing an electro-optic material, and an optical reflecting film 9. Electrodes 241 and 242 for applying a voltage are formed on the optical component 24. In this optical modulator 2, the polarizer 33, the electro-optic material 24, and the optical reflection film 9 are linearly arranged, and the incident light 14 passes through the polarizer 33 and the electro-optic material 24 and is reflected by the optical reflection film 9. The light again passes through the electro-optical material 24 and the polarizer 33 and is output as the outgoing light 15. This optical modulator 2 operates in the same manner as the optical modulator 1 of FIG. 1 by applying a voltage to the electrodes 241 and 242, and has the merit that it can be made smaller than that of FIG. 1 and the structure can be simplified.

  In the above description, an example is shown in which a ferroelectric ceramic is used as the electro-optic material. However, a ferroelectric single crystal can also be used as the electro-optic material. Unlike ceramics, ferroelectric single crystals do not have boundaries like ceramic particles, so there is no restriction on the movement of the polarization domain that appears in the ferroelectric phase, and the frequency dispersion of the relative permittivity and the optical element with domain movement more than ceramics The effect of a very slow response component becomes remarkable. However, even in the ferroelectric single crystal, only the very fast response component that the optical output follows can be used by limited use of the vicinity of Tc and the paraelectric phase.

  In addition, by applying the present invention to other optical elements using an electro-optic material, it is possible to use only a very fast response component that the optical output follows, and in the optical communication system, modulation of an optical signal at every time interval. Can be made possible.

1, 2, 201 Light modulators 11, 14 Incident light 12, 15 Emitted light 13 Light traveling direction 21, 22, 23, 24 Optical components 211, 212, 221, 222, 231, 232, 241, 242 Electrode 31, 32, 33 Polarizer 4 Voltage source 5, 51, 52 Ceramic particles 61, 62, 63, 64 Spontaneous polarization 71, 72 Domain wall 8 Electric circuit board 81 Heater 82 Temperature sensor 9 Optical reflection film 101 Light input / output of light modulator Terminal 102 Optical signal input terminal of the optical modulator

Claims (16)

In a method for controlling an optical element including an optical component made of an electro-optic material having an electro-optic effect,
A method for controlling an optical element, wherein the optical component is operated in a temperature range exhibiting paraelectricity including a ferroelectric phase transition temperature.   2. The method of controlling an optical element according to claim 1, wherein the electro-optic material is operated in a temperature range in which frequency dispersion due to movement of a domain composed of a single spontaneous polarization does not appear in the electro-optic effect of the electro-optic material.   3. The method of controlling an optical element according to claim 1, wherein the electro-optic material is operated in a temperature range where the relative permittivity of the electro-optic material is in a frequency range of 100 Hz to 100 kHz and the relative permittivity does not exhibit frequency dispersion. .   4. The device according to claim 1, wherein when a square wave signal is applied to the electro-optic material, the repetition frequency is 10 kHz and 5 Hz, and the operation is performed in a temperature range in which the light output level from the optical element does not change. The control method of the optical element in any one.   5. The method for controlling an optical element according to claim 1, wherein the electro-optic material is a relaxor-based ferrobskite ferroelectric. The optical element according to claim 5, wherein the electro-optic material is a ferroelectric mainly composed of xPb (Mg _1/3 Nb _2/3 ) O _3- (1-x) PbTiO ₃ . Control method.   7. The method of controlling an optical element according to claim 5, wherein the electro-optic material is ceramic.   7. The method of controlling an optical element according to claim 5, wherein the electro-optic material is a single crystal.   The temperature is controlled so that the temperature of the electro-optic material is in a temperature range exhibiting paraelectricity including a ferroelectric phase transition temperature regardless of an external environmental temperature in which the optical element is used. The method for controlling an optical element according to claim 1.   When the ambient temperature outside the optical element is lower than the ferroelectric phase transition temperature of the electro-optic material, the electro-optic material includes the ferroelectric phase transition temperature by heating the optical element. 10. The method of controlling an optical element according to claim 8, wherein the temperature is controlled in a temperature range showing a paraelectric phase.   When the ferroelectric phase transition temperature of the electro-optic material is within the range of the external environmental temperature in which the optical element is used, the electro-optic material is cooled or heated by a Peltier element so that the electro-optic material becomes the ferroelectric material. 9. The method of controlling an optical element according to claim 8, wherein the temperature is controlled in a temperature range including the paraelectric property including a target phase transition temperature.   In an optical element including an optical component made of an electro-optic material having an electro-optic effect, temperature control means for controlling the optical component to operate in a temperature range exhibiting paraelectricity including a ferroelectric phase transition temperature is included. An optical element.   The optical element according to claim 12, wherein the electro-optic material is a relaxor-type ferrobskite ferroelectric. The optical element according to claim 13, wherein the electro-optic material is a ferroelectric mainly composed of xPb (Mg _1/3 Nb _2/3 ) O _3- (1-x) PbTiO ₃ .   15. The optical element according to claim 13, wherein the electro-optic material is ceramic.   15. The optical element according to claim 13, wherein the electro-optic material is a single crystal.

Images