JP2007003949A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device having a uniform electrooptical effect even when an optical element wherein phase transition temperatures in a plurality of places in the one optical element are different from each other is used. <P>SOLUTION: The optical device having the optical element 1 formed by using a material having the electrooptical effect and inducing paraelectric/ferroelectric phase transition at a phase transition temperature is provided with a first temperature adjusting element 8-1 for adjusting the temperature at a first place of the optical element and a second temperature adjusting element 8-2 for adjusting the temperature at a second place of the optical element. The first and the second temperature adjusting elements hold temperature at the first and the second places to temperature at which a desired electrooptical coefficient is shown based on the temperature measured by a temperature detecting element 2 or the capacitance measured by a capacitance measuring circuit 12 and a characteristic of the electrooptical effect of the optical device can be made uniform. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical device using an electro-optic effect. More specifically, the present invention relates to temperature control of an optical element in an optical device that uses an electro-optic effect.

  Various terminals including computers and information appliances are connected to a network, and communication forms are diversified. Under such circumstances, a communication system capable of transmitting a large amount of information at high speed is desired, and a system using optical communication technology is promising as such a communication system. In recent years, with the development of such optical communication technology, demands for optical elements have been diversified and advanced.

Examples of optical devices that are expected to increase the capacity, speed, and functionality of optical communication systems include optical switches and optical modulators, and materials used for these optical devices have electro-optic effects ( Also called “electro-optic material”). Recently, a material called KTa _1-x Nb _x O ₃ (0 <x <1) (KTN) having a high electro-optic coefficient has attracted attention as an electro-optic material. Furthermore, since the large crystals of this material can be produced, its application is drawing attention.

  This material called KTN can change the ferroelectric-paraelectric transition temperature from −273 ° C. to + 470 ° C. by the Nb / (Nb + Ta) ratio (also simply referred to as “composition” in this specification).

FIG. 1 shows an example of the temperature dependence of the electro-optic coefficient of the electro-optic material. This material undergoes a phase transition at the paraelectric-ferroelectric phase transition temperature (T _c ) (also referred to herein simply as “phase transition temperature”), and has a large dielectric constant near this phase transition temperature, It is also known that the electro-optic effect is maximized by having a very large electro-optic coefficient in the vicinity of the phase transition temperature. In addition, it is known that the electro-optic effect of this material is very large when used near the paraelectric / ferroelectric phase transition temperature.

An optical switch using this material is known (see Non-Patent Document 1). FIG. 2 shows the configuration of the optical switch described in Non-Patent Document 1.
The optical switch shown in FIG. 2 includes a temperature detecting element 2 and a Peltier element 3 so as to sandwich an optical element 1 formed by forming a waveguide using a KTN material and thereby forming a Mach-Zehnder interferometer. And are provided. Further, the temperature detection element 2 and the Peltier element 3 are electrically connected to the temperature control circuit 4 via a conductive wire or the like (in this specification, simply referred to as “electrically connected”). In the configuration of FIG. 2, the temperature of the optical element 1 is controlled by using the Peltier element 3. That is, the temperature control circuit 4 controls the Peltier element 3 based on the electrical signal relating to the temperature of the optical element 1 detected by the temperature detection element 2.

  The temperature control circuit 4 controls the Peltier element 3 so as to keep the temperature of the optical element 1 constant at a temperature higher than the phase transition temperature. By controlling the temperature of the optical element 1 in this way, the characteristic of the electro-optic effect of the optical switch is prevented from shifting.

S. Toyoda et al, “LOW DRIVING VOLTAGE POLARIZATION-INDEPENDENT> 3 GHz-RESPONSE ELECTRO-OPTIC SWITCH USING KTN WAVEGUIDES” Proc. ECOC 2003

However, it is difficult to make the Nb / (Ta + Nb) ratio completely uniform in the manufacture of KTa _1-x Nb _x O ₃ . Accordingly, it is inevitable that the phase transition temperature (T _C ) at different locations of the same optical element varies due to the non-uniform composition.

FIG. 3 shows the result of measuring the electro-optic coefficient for two locations 1 and 2 of the same optical element. The phase transition temperatures T _C1 and T _{C2 at} locations 1 and 2 show different temperatures due to compositional inhomogeneities. As a result, at different locations 1 and 2 in the same optical element, even if the temperature is the same, the electro-optic coefficient is different and the properties of the electro-optic effect at locations 1 and 2 are also different.

Further, as shown in the figure, the electro-optic coefficient of the optical element changes greatly in the vicinity of the phase transition temperatures T _C1 and T _C2 . Therefore, when the temperature of the optical elements 1 and 2 is uniformly controlled to a temperature close to the phase transition temperature T _C1 or T _C2 , the electro-optic coefficient at the locations 1 and 2 is greatly different, and the electro-optic effect at the locations 1 and 2 is different. As a result, there is a problem that the characteristics of the entire optical device are deteriorated.

For example, assuming that the compositions at locations 1 and 2 at both ends of the optical element are x1 and x2, respectively, the phase transition temperatures corresponding to the compositions x1 and x2 are T _C1 and T _C2 (TC ₁ <TC ₂ ). To do. Then, assuming that the temperature of the optical element is set to uniformly T _C1, the location 2, will be the temperature at a point away from the phase transition temperature by T _C1 -T _C2 is set, the electro-optic coefficient Compared to the case where the phase transition temperature is set, the temperature is lowered.

  Assuming that the phase transition temperature has changed uniformly from place 1 to place 2, an approximation that the change in electro-optic coefficient with temperature change was also linear and changed from place 1 to place 2 uniformly. Further, assuming that the electro-optic coefficient at the location 2 is halved compared with the location 1, the effective electro-optic coefficient for the entire optical device from the location 1 to the location 2 is (1 + 0.5) / 2 = 0.75, which is about 25% lower than when the whole is set to the phase transition temperature.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical device having different phase transition temperatures at a plurality of locations in one optical device, or an electric device depending on the composition and temperature. An object of the present invention is to provide an optical device capable of making the characteristics of the electro-optic effect uniform even when an optical element formed of a material having an optical coefficient is used.

  In order to achieve the above object, the present invention provides an optical element formed of a material having an electro-optic effect and causing a paraelectric / ferroelectric phase transition at a phase transition temperature. An optical device comprising: first temperature adjusting means for adjusting the temperature of the first location of the optical element; and second temperature adjusting means for adjusting the temperature of the second location of the optical element. It is characterized by that.

  The invention according to claim 2 is the optical switch according to claim 1, wherein the first temperature measuring means for measuring the temperature of the first location of the optical element, and the second of the optical element. Second temperature measuring means for measuring the temperature of the first place and first temperature adjusting means for controlling the first temperature adjusting means so that the temperature of the first place to be measured is maintained at a predetermined first temperature. And a second temperature control means for controlling the second temperature adjusting means so that the temperature of the second place to be measured is maintained at a predetermined second temperature. It is characterized by that.

  A third aspect of the present invention is the optical switch according to the first aspect, wherein the first capacitance measuring means for measuring the capacitance of the first location of the optical element, and the first of the optical element. A second capacitance measuring means for measuring the electric capacity of the second place, and the temperature of the first place is set to a temperature at which the electric capacity of the first place to be measured becomes a predetermined first value. The first temperature control means for controlling the first temperature adjustment means to hold and the second capacitance measured at the second location is set to a temperature at which the second value is predetermined. And a second temperature control means for controlling the second temperature adjusting means so as to maintain the temperature of the place.

4. The optical device according to claim 1, wherein the material is KTa _1-x Nb _x O ₃ (0 <x <1) or K _1-y Li _y Ta _1-x Nb _x O. ₃ (0 <x <1, 0 <y <1).

  As described above, according to the present invention, the temperature at two locations in an optical element having different phase transition temperatures is controlled and held, whereby the phase transition temperatures at two locations in one optical device are controlled. An optical device that can make the characteristics of the electro-optic effect uniform can be provided even when an optical element having a different electromagnetism or an optical element made of a material having an electro-optic coefficient depending on the composition and temperature is used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same functions are denoted by the same reference numerals, and repeated description thereof is omitted.

  The optical device of the present invention has an optical element formed of a material that causes a paraelectric / ferroelectric phase transition at a phase transition temperature, and controls temperatures of a plurality of locations in the optical element having different phase transition temperatures. Hold. As a result, even if an optical element having different phase transition temperatures at a plurality of locations in one optical element or an optical element formed of a material having an electro-optic coefficient depending on the composition and temperature is used, uniform electrical An optical device having an optical effect can be provided.

  Further, the optical device of the present invention is configured to measure the capacitance of a plurality of locations in an optical element having different phase transition temperatures, and to control and hold the temperature of each location based on the measured capacitance. You can also

  Since the relationship between the electro-optic coefficient and the temperature of the material has a single peak as shown in FIG. 3, there are two temperatures at which the desired electro-optic coefficient can be obtained across the phase transition temperature. For this reason, when used in the paraelectric phase, the temperature of the optical element must always be higher than the phase transition temperature.

  For example, the temperature control circuit may be configured so that the phase transition temperature is examined in advance for each desired location of the optical element, and the temperature at each location is controlled to be higher than the phase transition temperature. it can. Alternatively, the temperature control circuit is configured to control the temperature to a desired electro-optic coefficient within a range where the temperature is gradually increased and the electro-optic coefficient is increased after the temperature is sufficiently raised. You may do it.

  The optical device according to the present invention may be an optical switch, an optical modulator, a Q switch, a deflector, or the like as long as it is a device using an optical element having an electro-optic effect.

As a material for forming an optical element, a material that causes a paraelectric / ferroelectric phase transition and has an electro-optic effect depending on the composition and temperature, KTN (KTa _1-x Nb _x O _{3) (0 <x <1} ), KLTN (K 1-y Li y Ta 1-x Nb x O 3) (0 <x <1,0 <y <1) may be any of, or PLZT (lanthanum-added Other materials such as lead zirconate titanate) may be used.

  The optical device according to the present invention is an optical device that utilizes the electro-optic effect of an optical element, such as an optical switch or an optical modulator. Therefore, the optical device includes an electrode that electrically drives the optical element, and a region that changes a state such as a phase of light that passes through the electro-optic effect (also simply referred to as an “operation region” in this specification). Have. For example, when the optical device of the present invention is implemented as an optical switch or an optical modulator, the operation region indicates a phase modulation unit.

  The optical device according to the present invention controls the temperatures of a plurality of regions (also simply referred to as “location” in the present specification) including the operation region in the optical element.

  The present invention relates to an optical device having an optical element formed of a material having an electro-optic effect and causing a paraelectric / ferroelectric phase transition at a phase transition temperature, and adjusting a temperature at a first location of the optical element First temperature adjusting means for adjusting, and second temperature adjusting means for adjusting the temperature of the second location of the optical element. As a result, even if a crystal optical element having a size different in phase transition temperature between the first place and the second place is used, the electro-optic coefficient of the first place and the second place is maximized and uniform. The characteristics of the electro-optic effect in the optical device can be made uniform.

<Embodiment 1>
FIG. 4 shows an embodiment of an optical device according to the present invention. In the optical device of the present embodiment, the temperature detection elements 2-1 and 2-2 and the temperature adjustment elements 8-1 and 8-2 are arranged so as to sandwich the optical element 1 in which the waveguide is formed using the KTN material. Is provided. The temperature detection element 2-1 and the temperature adjustment element 8-1 are electrically connected to the temperature control circuit 9-1 via a conducting wire or the like. In this way, the temperature detection element 2-2 and the temperature adjustment element 8-2 are electrically connected to the temperature control circuit 9-2 via a lead wire or the like.

  In the present embodiment, the temperature detection elements 2-1 and 2-2 measure the temperatures of the two places of the optical element 1, and the temperatures of the two places of the optical element 1 are adjusted based on the measured temperatures. The The temperature control circuits 9-1 and 9-2 are arranged so that the temperature of the Peltier element is constant so that the temperature measured by the temperature detection elements 2-1 and 2-2 is constant at a temperature indicating a predetermined electro-optic coefficient. The adjusting elements 8-1 and 8-2 are controlled to keep the temperatures of the two locations of the optical element 1 constant. This makes it possible to control the optical element 1 so as to obtain a certain electro-optic effect.

  In this embodiment, by examining the relationship between the electro-optic coefficient and the temperature in advance at two locations of the optical element, the temperature at which the electro-optic coefficient at the two locations is a similar value is obtained. The temperature control circuits 9-1 and 9-2 control the temperature adjustment elements 8-1 and 8-2 so that the temperatures at the respective locations are determined in advance.

As shown in FIG. 5, for the location A and location B examines the electro-optic coefficient and temperature relationships, the value of the electro-optic coefficient is previously obtained temperature T _A and T _B to be R at each location. Temperature control circuit 9-1 and 9-2, the temperature of the location A and B are respectively measured by the temperature detecting element 2-1 and 2-2, held constant at each pre-determined temperatures _{T A} and _{T B} As described above, the temperature adjusting elements 8-1 and 8-2 are respectively controlled. As a result, the value of the electro-optic coefficient at location A and location B becomes R, and a uniform electro-optic effect can be obtained.

  The temperature control circuit may be either an analog control circuit or a digital control circuit. In addition, the temperature information of the element 1 may be transmitted from the temperature detecting element 2 to the temperature control circuit 9 by analog signals such as voltage and current or digital signals.

  The temperature adjusting element 8 may be any element that can adjust the temperature of the optical element 1, such as a Peltier element, a thin film heater, or a combination thereof.

  In this embodiment, the temperature of two places in the optical element is controlled, but the temperature of three or more places may be controlled as necessary.

<Embodiment 2>
FIG. 6 shows another embodiment of the optical device according to the present invention. The optical device according to this embodiment includes an optical element 1 in which a waveguide is formed using a KTN material, and a capacitance measuring circuit 12-that measures the electric capacity between electrodes 5-1 and 6-1 provided in the optical element 1. 1 and a capacitance measuring circuit 12-2 that measures the electric capacitance between the electrodes 5-2 and 6-2 provided in the optical element 1, and the electricity measured by the capacitance measuring circuits (12-1 and 12-2). A temperature control circuit 9 that controls the temperature of the optical element 1 based on the capacitance, and temperature adjustment elements 8-1 and 8-2 that adjust the temperature of the optical element 1 according to instructions from the temperature control circuit are provided. . The temperature control circuit 9 is electrically connected to each of the capacitance measuring circuits (12-1 and 12-2) and the temperature adjusting elements (8-1 and 8-2).

  In this embodiment, instead of using the temperature detection element that detects the temperature of the optical element 1, the capacitance (that is, the dielectric constant) of the locations 1 and 2 of the optical element 1 is measured by the capacitance measurement circuit (12-1 and 12-2). And the temperatures of the locations 1 and 2 of the optical element 1 are adjusted based on the measured capacitance. The temperature control circuit 9 is configured so that the electric capacity of the places 1 and 2 measured by the capacitance measuring circuits (12-1 and 12-2) is constant at a predetermined electric capacity, respectively. 8-1 and 8-2) are controlled to keep the temperatures of the locations 1 and 2 of the optical element 1 constant. This makes it possible to control the optical element 1 so as to obtain a certain electro-optic effect.

  FIG. 7A shows the temperature dependence of the electro-optic coefficient of the KTN material, and FIG. 7B shows an example of the temperature dependence of the capacitance. Since the electro-optic coefficient depends on the dielectric constant, it has a temperature dependency similar to that of the electric capacity. The optical device of the present invention uses the temperature dependence of the capacitance instead of detecting the temperature of the optical device, that is, measures the capacitance of the optical device, and based on the measured capacitance, the temperature of the optical device. To control.

  That is, the temperature control circuit 9 controls the temperature of the optical element so that the electric capacitances of the locations 1 and 2 of the optical element 1 to be measured have a predetermined value, thereby reducing the electro-optic coefficient of the optical element. Can be constant. By doing in this way, the characteristic of the photoelectric effect of an optical device can be made uniform irrespective of the dispersion | variation in the composition of the material in an optical element.

  In the present embodiment, as described in the first embodiment, it is not necessary to investigate the relationship between the electro-optic coefficient and the temperature at a plurality of locations of the optical element in advance, and even temperature control that keeps the capacitance constant is performed. That's fine.

  Various methods such as a bridge measurement, an impedance method, and a network method are known as the capacitance measurement circuit, and any of these may be used.

  The temperature control circuit may be either an analog control circuit or a digital control circuit. In addition, the capacitance information may be transmitted from the capacitance measuring circuit to the temperature control circuit by analog signals such as voltage and current or digital signals.

  The temperature adjusting element may be any one that can adjust the temperature of the optical element 1, such as a Peltier element, a thin film heater, or a combination thereof.

  Further, since the capacitance measuring circuit can electrically measure the capacitance, it can obtain a faster response than a temperature sensing element such as a thermistor.

  In this embodiment, the temperature of two places in the optical element is controlled, but the temperature of three or more places may be controlled as necessary.

It is a figure which shows the relationship between an electro-optic coefficient and temperature. It is a block diagram of a prior art optical device. It is a figure which shows the dispersion | variation in the temperature dependence of an electro-optic coefficient. It is a figure which shows embodiment of the optical device which concerns on this invention. It is a figure which shows the relationship between the electro-optic coefficient and temperature in a different place. It is a figure which shows embodiment of the optical device which concerns on this invention. (A) is a figure which shows the relationship between an electro-optic coefficient and temperature, (b) is a figure which shows the relationship between an electrical capacitance and temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 2 Temperature detection element 3 Peltier element 4 Temperature control circuit 8 Temperature adjustment element 9 Temperature control circuit 5, 6 Electrode 12 Capacity measurement circuit

Claims (5)

An optical device having an optical element formed of a material having an electro-optic effect and causing a paraelectric / ferroelectric phase transition at a phase transition temperature,
First temperature adjusting means for adjusting the temperature of the first location of the optical element;
An optical device comprising: a second temperature adjusting means for adjusting a temperature at a second location of the optical element. First temperature measuring means for measuring the temperature of the first location of the optical element;
Second temperature measuring means for measuring the temperature of the second location of the optical element;
First temperature control means for controlling the first temperature adjusting means so that the temperature of the first place to be measured is maintained at a predetermined first temperature, and the second place to be measured. The optical device according to claim 1, further comprising: a second temperature control unit that controls the second temperature adjusting unit so that the temperature is maintained at a predetermined second temperature. First capacitance measuring means for measuring the capacitance of the first location of the optical element;
Second capacitance measuring means for measuring an electric capacitance at the second location of the optical element;
A first temperature control unit that controls the first temperature adjusting means to maintain the temperature of the first place at a temperature at which the electric capacity of the first place to be measured becomes a predetermined first value. The second temperature adjusting means is controlled so that the temperature of the second place is kept at a temperature at which the electric capacity of the second place to be measured and the second place is a predetermined second value. The optical device according to claim 1, further comprising: a second temperature control means. The optical device according to claim 1, wherein the material is KTa _1-x Nb _x O ₃ (0 <x <1). 4. The light according to claim 1, wherein the material is K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1). device.

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