WO2020208929A1

WO2020208929A1 - Optical device

Info

Publication number: WO2020208929A1
Application number: PCT/JP2020/005166
Authority: WO
Inventors: 山岡　義和; 平澤　拓
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2019-04-09
Filing date: 2020-02-10
Publication date: 2020-10-15
Also published as: JP2022084969A

Abstract

This optical device is provided with: a pair of electrodes to which DC voltage is applied; an electrooptical material layer located between the pair of electrodes; an ammeter that measures current flowing in the electrooptical material layer; a heating/cooling element that heats and/or cools the electrooptical material layer; and a control circuit that causes heating or cooling of the electrooptical material layer on the basis of a value of the DC voltage and a value of the current measured by the ammeter.

Description

Optical device

This disclosure relates to optical devices.

Conventionally, it has been proposed to use an electro-optical material exhibiting an electro-optical effect in which the refractive index changes by applying an electric field for an optical device (for example, Patent Documents 1 and 2). Among the electro-optical materials, potassium niobate tantalate (KTa _1-x Nb _x O ₃ : KTN) exhibits a high electro-optical effect near room temperature, for example, when x = 0.3.

JP-A-2007-3947 JP-A-2007-3949

The present disclosure provides an optical device that can easily maintain a high electro-optical effect of an electro-optical material.

The optical device according to one aspect of the present disclosure is an ammeter that measures a pair of electrodes to which a DC voltage is applied, an electro-optical material layer located between the pair of electrodes, and a current flowing through the electro-optical material layer. The heating / cooling element is controlled based on the heating / cooling element that heats and cools the electro-optical material layer, the value of the DC voltage, and the value of the current measured by the ammeter. It includes a control circuit.

According to the present disclosure, it becomes easy to maintain a high electro-optical effect of the electro-optical material.

FIG. 1A is a side view of the optical device in the exemplary embodiment of the present disclosure schematically shown in the X direction. FIG. 1B is a side view of the optical device in the exemplary embodiment of the present disclosure schematically shown from the Y direction. FIG. 2A is a diagram showing the relationship between the bulk temperature and the resistance value of the KTN single crystal. FIG. 2B is a diagram showing the relationship between the temperature and the resistance value of the KTN thin film. FIG. 3A is a flowchart of the operation of the control circuit for determining the Curie temperature of the electro-optical material layer. FIG. 3B is a flowchart of the operation of the control circuit for adjusting the electro-optical effect of the electro-optical material layer. FIG. 3C is a flowchart of the operation of the control circuit for adjusting the electro-optical effect of the electro-optical material layer. FIG. 4 is a diagram schematically showing an example in which an optical device further includes a heat insulating material. FIG. 5 is a diagram schematically showing an example in which an optical device further includes an electromagnetic shield. FIG. 6 is a diagram schematically showing an optical device in a modified example. FIG. 7 is a flowchart showing a manufacturing process of the optical device. FIG. 8 is a plan view schematically showing an example of a Mach-Zehnder type optical switching device. FIG. 9A is a diagram schematically showing a first example of an optical phased array. FIG. 9B is a diagram schematically showing a second example of an optical phased array. FIG. 10 is a diagram schematically showing the relationship between the temperature of KTN and the dielectric constant.

Before explaining the embodiments of the present disclosure, the findings underlying the present disclosure will be explained.

As typical electro-optical effects, the Pockels effect and the Kerr effect are known. In the Pockels effect, the amount of change in the refractive index of the electro-optical material is proportional to the magnitude of the applied electric field. In the Kerr effect, the amount of change in the refractive index of the electro-optical material is proportional to the square of the magnitude of the applied electric field. Electro-optics materials that exhibit the Pockels effect include, for example, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), potassium dihydrogen phosphate (KH ₂ PO ₄ ), and ammonium dihydrogen phosphate (NH ₄ H). There are ₂ PO ₄ ). The electro-optical material exhibiting the Kerr effect, for example, barium titanate (BaTiO _3), strontium titanate (SrTiO _3), potassium titanate (KTaO _3), and there is a KTN.

Let the refractive index of the electro-optical material exhibiting the Kerr effect be n ₀ , the vacuum permittivity be ε ₀ , the relative permittivity be ε _r , the Kerr coefficient be g, and the magnitude of the applied electric field be E. Then, the amount of change in the refractive index due to the application of the electric field is expressed as Δn = − (g / 2) n ₀ ³ ε ² E ² . When the car coefficient g and the relative permittivity ε _r are large, the amount of change Δn in the refractive index due to the application of an electric field also becomes large. Among the electro-optical materials exhibiting the Kerr effect described above, KTN has a large Kerr coefficient g and a large relative permittivity ε _r at room temperature. For example, Kerr coefficient g is of the order of about 0.1 m ⁴ C ^-2, maximum value of the relative dielectric constant is ε _r = 1.0 × 10 ⁴ about the order.

FIG. 10 is a diagram schematically showing the relationship between the temperature T of KTN and the relative permittivity ε _r . KTN is a ferroelectric substance. When the temperature T is increased, the ferroelectric substance exhibits a phase transition from the ferroelectric phase to the normal dielectric phase at the Curie temperature T _c . When the temperature T is increased, the relative permittivity ε _r of the ferroelectric substance increases sharply in the ferroelectric phase as it approaches the Curie temperature T _c, and gradually decreases in the normal dielectric phase. As shown in FIG. 10, the relative permittivity ε _r is maximized at the Curie temperature T _c . Therefore, in order to obtain a high electro-optical effect, the temperature T of KTN is adjusted to be around the Curie temperature T _c . In the ferroelectric phase in which the relative permittivity ε _r changes sharply, the electro-optical effect sharply decreases when the temperature T of KTN deviates from the Curie temperature Tc. On the other hand, in the normal dielectric phase in which the relative permittivity ε _r changes slowly, the electro-optical effect does not sharply decrease even if the temperature T of KTN deviates from the Curie temperature Tc. Therefore, in the normal dielectric phase, the relative permittivity ε _r can be easily maintained in a high state by adjusting the temperature T of KTN to the vicinity of the Curie temperature T _c . The Curie temperature T _{c of} KTN can be set to around room temperature by setting the composition ratio of Nb and Ta to an appropriate ratio. For the above reasons, application of KTN, which exhibits a high electro-optical effect near room temperature, to optical devices is expected.

The relative permittivity ε _r is reflected in the electric capacity. Patent Document 1 and Patent Document 2 disclose a technique for adjusting the temperature T of KTN based on the measured electric capacity of an electro-optical material in order to obtain a high electro-optical effect. An AC voltage is applied to the pair of electrodes for measuring the electric capacity. An LCR meter or an electrochemical measurement system is used to measure the electric capacity. Therefore, the structure of the optical device becomes complicated.

Based on the above studies, the present inventor has come up with the optical device described in the following items.

The optical device according to the first item includes a pair of electrodes to which a DC voltage is applied, an electro-optical material layer located between the pair of electrodes, and an ammeter that measures a current flowing through the electro-optical material layer. Control to control the heating / cooling element based on the heating / cooling element that heats and cools the electro-optical material layer, the value of the DC voltage, and the value of the current measured by the ammeter. It is equipped with a circuit.

In this optical device, the electro-optical material layer is heated or cooled by a heating / cooling element based on the value of the voltage applied to the pair of electrodes and the value of the current measured by the ammeter. This makes it easy to maintain a high electro-optical effect of the electro-optical material.

The optical device according to the second item is the optical device according to the first item, in which the control circuit changes the value of the DC voltage to change the refractive index of the electro-optical material layer.

In this optical device, a pair of electrodes is used not only to measure the resistance value of the electro-optical material layer but also to change the refractive index of the electro-optical material layer. This makes it possible to simplify the structure of the optical device.

The optical device according to the third item controls the phase of light guided through the electro-optical material layer by the change in the refractive index in the optical device according to the second item.

With this optical device, it is possible to control the phase of light guided through the electro-optical material layer.

The optical device according to the fourth item is the optical device according to any one of the first to third items, and the DC voltage is a DC pulse voltage.

In this optical device, by changing the duty ratio of the DC pulse voltage, the averaged value of the DC pulse voltage can be adjusted as the value of the DC voltage.

The optical device according to the fifth item is the resistance of the electro-optical material layer from the DC voltage value and the current value in the optical device according to any one of the first to fourth items. The value is calculated, and the heating / cooling element is controlled based on the change in the resistance value due to at least one of heating and cooling by the heating / cooling element.

With this optical device, the heating / cooling device can be controlled based on the DC voltage value and the current value.

The optical device according to the sixth item is the optical device according to any one of the first to fifth items, and the optical device further includes a thermometer. At the start of operation, when the temperature measured by the thermometer is lower than the reference temperature, the control circuit causes the heating / cooling element to heat the electro-optical material layer, and the temperature measured by the thermometer is the reference temperature. When it is higher than, the heating / cooling element causes the electro-optical material layer to cool.

In this optical device, the temperature of the electro-optical material layer at the start of operation can be known by a thermometer. Based on the temperature, the electro-optical material layer can be heated or cooled.

The optical device according to the seventh item is the optical device according to the sixth item, in which the electro-optical material layer is made of a ferroelectric substance. The reference temperature is the Curie temperature of the ferroelectric substance.

In this optical device, a high electro-optical effect can be obtained by the electro-optical material layer composed of a ferroelectric substance.

The optical device according to the eighth item is the optical device according to the sixth or seventh item, wherein the control circuit applies a DC voltage to the pair of electrodes, and the electro-optical material layer is applied to the heating / cooling element. The reference temperature is determined based on the change in the value of the current due to heating or cooling the electro-optical material layer and the value of the DC voltage.

In this optical device, the reference temperature is determined based on the temperature dependence of the electro-optical material layer.

The optical device according to the ninth item is the optical device according to any one of the first to eighth items, wherein the heating / cooling element includes a Peltier element.

In this optical device, the electro-optical material layer is heated or cooled by a heating / cooling element including a Peltier element.

The optical device according to the tenth item further includes a heat insulating material that covers at least a part of the electro-optical material layer in the optical device according to any one of the first to ninth items.

In this optical device, the heat insulating material can suppress the temperature change of the electro-optical material layer due to the temperature change of the outside air.

The optical device according to the eleventh item further includes an electromagnetic shield that covers at least a part of the electro-optical material layer in the optical device according to any one of the first to tenth items.

In this optical device, the electromagnetic shield can shield electromagnetic noise from the outside of the optical device and / or from the heating / cooling element.

The optical device according to the twelfth item is the optical device according to any one of the first to eleventh items, wherein the electro-optical material layer contains potassium niobate tantalate.

In this optical device, a high electro-optical effect can be obtained near room temperature due to the electro-optical material layer containing potassium niobate tantalate.

The optical device according to the thirteenth item is the optical device according to any one of the first to twelfth items, in which the thickness of the electro-optical material layer is 0.1 μm or more and 10 μm or less.

The cost of the electro-optical material layer can be reduced by the electro-optical material layer having a thickness of 0.1 μm or more and 10 μm or less.

The optical device according to the fourteenth item is a dielectric breakdown of the electro-optical material layer between the ammeter and one of the pair of electrodes in the optical device according to any one of the first to thirteenth items. Further equipped with a resistor for prevention.

In this optical device, the above-mentioned resistor can prevent dielectric breakdown of the electro-optical material layer even if a high voltage is applied to the pair of electrodes.

The optical device according to the fifteenth item includes a plurality of electrode pairs to which a DC voltage is applied, an electro-optical material layer located between each of the plurality of electrode pairs, and each of the plurality of electrode pairs. A plurality of current meters measuring the current flowing through the portion of the electro-optical material layer sandwiched by the corresponding one electrode pair of the above, and each sandwiched by the corresponding one electrode pair of the plurality of electrode pairs. By a plurality of heating and cooling elements that perform at least one of heating and cooling of the portion of the electro-optical material layer, the value of the DC voltage applied to each of the plurality of electrode pairs, and each of the plurality of current meters. A control circuit for controlling each of the plurality of heating / cooling elements based on the measured current value is provided.

In this optical device, the corresponding one electrode pair of the plurality of electrode pairs is based on the value of the voltage applied to each of the plurality of electrode pairs and the value of the current measured by each of the plurality of ammeters. The electro-optical material layer sandwiched between the electrodes is heated or cooled by the heating / cooling element. This makes it easy to maintain a high electro-optical effect of the electro-optical material.

In the present disclosure, all or part of a circuit, unit, device, member or part, or all or part of a functional block in a block diagram, is, for example, a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (range scale integration). ) Can be performed by one or more electronic circuits. The LSI or IC may be integrated on one chip, or may be configured by combining a plurality of chips. For example, functional blocks other than the storage element may be integrated on one chip. Here, it is called an LSI or an IC, but the name changes depending on the degree of integration, and it may be called a system LSI, a VLSI (very large scale integration), or a ULSI (ultra large scale integration). A Field Programmable Gate Array (FPGA) programmed after the LSI is manufactured, or a reconfigurable logistic device capable of reconfiguring the junction relationship inside the LSI or setting up the circuit partition inside the LSI can also be used for the same purpose.

Furthermore, all or part of the functions or operations of circuits, units, devices, members or parts can be performed by software processing. In this case, the software is recorded on a non-temporary recording medium such as one or more ROMs, optical discs, hard disk drives, etc., and when the software is executed by a processor, the functions identified by the software It is executed by a processor and peripheral devices. The system or device may include one or more non-temporary recording media on which the software is recorded, a processor, and the required hardware devices, such as an interface.

Hereinafter, a more specific embodiment of the present disclosure will be described with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed descriptions of already well-known matters and duplicate explanations for substantially the same configuration may be omitted. This is to avoid unnecessary redundancy of the following description and to facilitate the understanding of those skilled in the art. It should be noted that the inventors are intended to limit the subject matter described in the claims by those skilled in the art by providing the accompanying drawings and the following description in order to fully understand the present disclosure. is not. In the following description, the same or similar components are designated by the same reference numerals.

(Embodiment)
1A and 1B are diagrams schematically showing an optical device 100 according to an exemplary embodiment of the present disclosure. In the following description, the coordinate system consisting of the X, Y, and Z axes orthogonal to each other shown in FIGS. 1A and 1B is used. For convenience of explanation, the + Z direction is referred to as "upward" and the -Z direction is referred to as "downward". These designations are for convenience only and are not intended to limit the arrangement or orientation of the optical device 100 actually used.

FIG. 1A schematically shows the structure of the optical device 100 as viewed from the + X direction. FIG. 1B schematically shows the structure of the optical device 100 as viewed from the −Y direction. FIG. 1B shows only some of the components shown in FIG. 1A.

The optical device 100 includes a substrate 10, a first electrode 20a and a second electrode 20b, an electro-optical material layer 30, an ammeter 40, a resistor 42, a heating / cooling element 50, a thermometer 60, and the like. It includes a control circuit 70. The substrate 10, the first electrode 20a, the electro-optical material layer 30, and the second electrode 20b are laminated in this order.

The substrate 10 has a first surface 10s1 and a second surface 10s2 parallel to the XY plane. The first electrode 20a is located on the first surface 10s1 of the substrate 10. The electro-optical material layer 30 is located on the first electrode 20a. The second electrode 20b is located on the electro-optical material layer 30. The first electrode 20a and the second electrode 20b may be referred to as a "pair of electrodes 20". The electro-optical material layer 30 is located between the pair of electrodes 20. The ammeter 40 is connected to the second electrode 20b. A resistor 42 is connected between the ammeter 40 and the second electrode 20b. The resistor 42 is provided to prevent an excessively high voltage from being applied to the electro-optical material layer 30. In other words, the resistor 42 is provided to prevent dielectric breakdown of the electro-optical material layer 30. The resistor 42 is provided as needed. The heating / cooling element 50 is in contact with the second surface 10s2 of the substrate 10. The substrate 10 and the heating / cooling element 50 each have a warp. Therefore, the substrate 10 and the heating / cooling element 50 may be fixed by using a heat conductive adhesive. The thermometer 60 is located, for example, in the vicinity of the electro-optical material layer 30. The substrate 10, the first electrode 20a and the second electrode 20b, the electro-optical material layer 30, and the heating / cooling element 50 have a structure extending in the X direction.

Each component will be described in more detail below.

The substrate 10 supports a pair of electrodes 20 and an electro-optical material layer 30. The substrate 10 can be formed, for example, from at least one selected from the group consisting of strontium titanate (SrTIO ₃ : STO), magnesium oxide (MgO), tantalum pentoxide (Ta ₂ O ₅ ). The substrate 10 may be omitted if it is unnecessary.

A DC voltage is applied to the pair of electrodes 20. The first electrode 20a is grounded, and a DC voltage having a voltage value of _VDC is applied to the second electrode 20b. As a result, an electric field is generated downward between the pair of electrodes 20. The electric field changes the refractive index of the electro-optical material layer 30. The potential applied to the second electrode 20b may be positive or negative. The DC voltage may be a DC pulse voltage. By changing the duty ratio of the DC pulse voltage, the value obtained by averaging the DC pulse voltage can be adjusted as the value of the DC voltage. As will be described later, the pair of electrodes 20 is also used for measuring the resistance value R of the electro-optical material layer 30. At least one of the pair of electrodes 20 may be a metal electrode or a transparent electrode. The first electrode 20a can be, for example, a transparent electrode formed of strontium ruthenate (SrRuO ₃ : SRO). The second electrode 20b can be, for example, a transparent electrode formed of tin-doped indium oxide (ITO).

As shown in FIG. 1B, the electro-optical material layer 30 functions as an optical waveguide layer that propagates light 32 along the X direction by total reflection. The phase of the light 32 propagating in the electro-optical material layer 30 can be changed by the amount of change Δn in the refractive index of the electro-optical material layer 30 due to the application of an electric field. The wavelength of the light 32 in the air is λ, the refractive index of the electro-optical material layer 30 when no electric field is applied is n ₀ , the length of the electro-optic material layer 30 in the X direction is L, and the electro-optical material layer is The phase of the light 32 before propagating in 30 is set to φ = 0. At this time, the phase of the light 32 after propagating in the electro-optical material layer 30 is φ = (2π / λ) (n ₀ + Δn) L. Of these, the change in the phase of the light 32 due to the application of an electric field is Δφ = (2π / λ) ΔnL. When the pair of electrodes 20 are formed of transparent electrodes, the loss of light 32 can be ignored. The electro-optical material layer 30 may be formed from a bulk or a thin film, as will be described later. The thickness of the thin film can be, for example, 0.1 um or more and 10 um or less. The cost of thin films is lower than the cost of bulk. The electro-optical material layer 30 contains a ferroelectric substance having a Curie temperature T _c . The electro-optical material layer 30 is formed of, for example, KTN.

The ammeter 40 measures the current flowing through the electro-optical material layer 30 by applying a DC voltage to the pair of electrodes 20. The resistance value R of the electro-optical material layer 30 is calculated from the ratio of the DC voltage value and the current value. The electro-optical material layer 30 generally has a high resistance. Therefore, it is not necessary to use the four-terminal method for measuring the resistance of the electro-optical material layer 30. As shown in FIG. 1A, a two-terminal method using terminals connected to the first electrode 20a and the second electrode 20b, respectively, is sufficient. The resistance value of the resistor 42 between the ammeter 40 and the second electrode 20b is, for example, 500 kΩ or more. As a result, even if a DC voltage having a voltage value of _VDC = 300V is applied, dielectric breakdown of the electro-optical material layer 30 can be prevented. The resistor 42 is not always necessary for the optical device 100.

The heating / cooling element 50 performs at least one of heating and cooling of the electro-optical material layer 30. The heating / cooling element 50 is, for example, a Peltier element. When an electric current is passed through the Peltier element of the flat plate, heat is generated on one surface of the flat plate and heat is absorbed on the other surface. When the direction of current flow is reversed, endothermic reaction occurs on one surface and heat generation occurs on the other surface. In the example shown in FIGS. 1A and 1B, the heating / cooling element 50 heats or cools the electro-optical material layer 30 via the substrate 10 and the first electrode 20a. At this time, it is considered that the substrate 10, the first electrode 20a, and the electro-optical material layer 30 have substantially the same temperature.

In the examples shown in FIGS. 1A and 1B, the heating / cooling element 50 is in contact with the entire second surface 10s2 of the substrate 10. As a result, not only the portion of the electro-optical material layer 30 whose refractive index changes due to the application of an electric field, but also other portions are heated or cooled. The arrangement of the heating / cooling element 50 is not limited to the examples shown in FIGS. 1A and 1B. The heating / cooling element 50 may be provided so as to heat or cool only the portion of the electro-optical material layer 30 whose refractive index changes due to the application of an electric field. Alternatively, the heating / cooling element 50 may be in direct contact with a plane parallel to the XZ plane of the electro-optical material layer 30.

Thermometer 60 measures the ambient temperature _{T a} of the electro-optical material layer 30. Before operation for starting heating or cooling of the electro-optical material layer 30 by heating the cooling element 50, the temperature T of the electro-optical material layer 30 is believed to ambient temperature T _a to be approximately the same. Therefore, it is possible to know from the ambient temperature T _a which is measured by the thermometer 60, the temperature T of the electro-optical material layer 30 before the operation of the heating and cooling elements 50. The thermometer 60 may be an analog thermometer or a digital thermometer. The thermometer 60 is not always necessary for the optical device 100.

The control circuit 70 applies a DC voltage to the pair of electrodes 20. The control circuit 70 measures the current with an ammeter 40. The control circuit 70 inputs a signal for heating or cooling the electro-optical material layer 30 to the heating / cooling element 50 based on the value of the DC voltage and the value of the current measured by the ammeter 40. The control circuit 70 measures the ambient temperature Ta with _a thermometer 60. The dashed line with the arrow shown in FIG. 1A represents the input and output of signals between the control circuit 70 and other components. Due to the operation of the control circuit 70, the temperature T of the electro-optical material layer 30 approaches the Curie temperature T _c . Thereby, the electro-optical effect of the electro-optical material layer 30 can be enhanced. Details of the operation of the control circuit 70 will be described later. The control circuit 70 includes a programmable logic device (PLD) such as a digital signal processor (DSP) or a field programmable gate array (FPGA), or a central processing unit (CPU) or an image processing arithmetic processor (GPU) and a computer program. It may be realized by the combination of.

Next, the relationship between the temperature T of the electro-optical material layer 30 and the resistance value R will be described.

2A and 2B are diagrams showing the relationship between the temperature T and the resistance value R of the bulk of the KTN single crystal and the KTN thin film, respectively. A pair of electrodes were formed on each surface of the bulk of the KTN single crystal and the surface of the KTN thin film. The voltage and current applied to the pair of electrodes were measured. Each of the pair of electrodes is a comb-shaped electrode with an interelectrode gap of 200 μm. A parallel plate electrode may be used instead of the comb-shaped electrode. The vertical dashed line represents the Curie temperature T _c of the electro-optical material layer 30. The resistance value R of the electro-optical material layer 30 is obtained from the ratio of the value of the DC voltage and the value of the current measured by the ammeter 40. In the example shown in FIG. 2A, the bulk thickness of the KTN single crystal in the Z direction is 500 μm. A DC voltage having a voltage value of _VDC = 100V was applied to the pair of electrodes. In the example shown in FIG. 2B, the thickness of the KTN thin film in the Z direction is 1 μm. A DC voltage having a voltage value of _VDC = 220V was applied to the pair of electrodes.

In the example shown in FIG. 2A, the Curie temperature of the bulk of the KTN single crystal is estimated to be T _c ≈ 30 ° C. The bulk resistance value R of the KTN single crystal increases almost monotonically with increasing temperature from T = 25 ° C. to T = T _c . The rate of increase of the resistance value R increases as the temperature rises. The resistance value is substantially constant from T = T _c to T = 35 ° C. That is, when the bulk temperature T of the KTN single crystal is increased, the resistance value R does not increase with the Curie temperature T _c as the boundary. This makes it possible to estimate the Curie temperature T _c of the bulk of the KTN single crystal.

In the example shown in FIG. 2B, the Curie temperature of the KTN thin film is estimated to be T _c ≈ 28 ° C. The resistance value R of the KTN thin film increases almost monotonously with increasing temperature between T = 20 ° C. and T = Tc. The rate of increase of the resistance value R decreases as the temperature rises. The temperature characteristics of the thin film are considered to be similar to the temperature characteristics of the crystal. However, in this thin film, the rate of increase in resistance value slowed down in the ferroelectric phase, and the resistance value increased or decreased slightly in the ferroelectric phase. It is considered that the temperature dependence of such resistance value in this thin film is due to the film quality of the thin film. As described above, when the temperature T of the KTN thin film is increased, the resistance value R changes from an increase to a decrease with the Curie temperature T _c as a boundary. This makes it possible to know the Curie temperature T _c of the KTN thin film.

As shown in FIGS. 2A and 2B, the resistance value R of KTN has a significantly different temperature dependence near the Curie temperature T _c . Conventionally, as disclosed in Patent Document 1 and Patent Document 2, it has been known that the electric capacity of KTN has a significantly different temperature dependence near the Curie temperature T _c . This is because the electric capacity depends on the relative permittivity ε _r shown in FIG. However, it was not assumed that the resistance value R of KTN had the above temperature dependence. The present inventor has found that the electro-optical effect of KTN can be easily maintained high based on the relationship between the temperature T and the resistance value R of the electro-optical material layer 30.

The details of the operation of the control circuit 70 will be described below.

First, the Curie temperature T _c of the electro-optical material layer 30 is estimated before the operation of maintaining the electro-optical effect of the electro-optical material layer 30 high.

FIG. 3A is a flowchart of the operation of the control circuit 70 that determines the Curie temperature T _c of the electro-optical material layer 30.

In step S101, the control circuit 70 applies a DC voltage to the pair of electrodes 20. In step S102, the control circuit 70 measures the current flowing through the electro-optical material layer 30 with the ammeter 40. In step S103, the control circuit 70 causes the heating / cooling element 50 to heat or cool the electro-optical material layer 30. By heating or cooling the electro-optical material layer 30, the current flowing through the electro-optical material layer 30 changes. The change in the resistance value R of the electro-optical material layer 30 is monitored from the change in the current value measured by the ammeter 40 and the value of the DC voltage. From the change in the resistance value R, the temperature dependence of the resistance value R can be known. In step S104, the control circuit 70 based on the change in the resistance value R of the electro-optical material layer 30, estimates the Curie temperature _{T C.} The Curie temperature T _c can be estimated based on the relationship between the temperature T of the electro-optical material layer 30 and the resistance value R, as described with reference to FIGS. 2A and 2B. From the temperature dependence of the resistance value R, the phase transition point of the crystal phase in the electro-optical material layer 30 can be estimated, and the temperature corresponding to the phase transition point can be estimated to be the Curie temperature T _c .

The control circuit 70 may record the determined Curie temperature T _c of the electro-optical material layer 30 on a storage medium (not shown) such as a memory. As a result, it is not necessary to obtain the Curie temperature T _c of the electro-optical material layer 30 immediately before each operation. The control circuit 70 may record the relationship between the temperature T and the resistance value R of the electro-optical material layer 30 shown in FIGS. 2A and 2B in a storage medium. As a result, the Curie temperature T _c of the electro-optical material layer 30 can be estimated from the temperature dependence of the resistance value R of the electro-optical material layer 30. The storage medium may be built in the control circuit 70 or may be provided externally.

Next, assuming that the Curie temperature T _c of the electro-optical material layer 30 is known, an example of an operation of adjusting the temperature T of the electro-optical material layer 30 will be described.

FIG. 3B is a flowchart showing an example of the operation of the control circuit 70 that maintains a high electro-optical effect of the electro-optical material layer 30.

In step S201, the control circuit 70, at the start of operation, the ambient temperature _{T a} of the electro-optical material layer 30 is measured by the thermometer 60. When the thermometer 60 is arranged in the vicinity of the electro-optical material layer 30, the ambient temperature _Ta of the electro-optical material layer 30 corresponds to the temperature T of the electro-optical material layer 30.

In step S202, the control circuit 70, the ambient temperature _{T a} of the electro-optical material layer 30 determines whether lower or not than the Curie temperature _{T c.} If the determination in step S202 is Yes ( _Ta <T _c ), the control circuit 70 executes the next step S203.

In step S203, the control circuit 70 causes the heating / cooling element 50 to heat the electro-optical material layer 30.

In step S204, the control circuit 70 measures the resistance value R of the electro-optical material layer 30, the estimated temperature T _e of the electro-optical material layer 30 is determined from the resistance value R of the electro-optical material layer 30 is, the Curie temperature T _It is determined whether or not it is higher than _c . If the determination in step S204 is No ( _Te <T _c or _Te = T _c ), the control circuit 70 executes the next step S205.

In step S205, the control circuit 70 determines the estimated temperature _{T e} of the electro-optical material layer 30, or lower or not than the Curie temperature _{T c.} If the determination in step S205 is _{_{Yes (T e <T c)}} , the control circuit 70 again executes step S203 and step S204. If the determination in step S205 is _{_{No (T e = T c)}} , the control circuit 70 executes S204 again.

If the determination in step S204 is Yes, the control circuit 70 executes the next step S206.

In step S206, the control circuit 70 causes the heating / cooling element 50 to cool the electro-optical material layer 30, or stops the operation of the heating / cooling element 50. If the cooling rate of the electro-optical material layer 30 is not taken into consideration, the operation of the heating / cooling element 50 may be stopped to allow the electro-optical material layer 30 to cool naturally. After that, the control circuit 70 executes step S204 again.

On the other hand, when the determination in step S202 is No (T _a > T _c or T _a = T _c ), the control circuit 70 executes the next step S207.

In step S207, the control circuit 70, the ambient temperature _{T a} of the electro-optical material layer 30 is equal to or is higher than the Curie temperature _{T c.} If the determination in step S202 is No ( _Ta = T _c ), the control circuit 70 executes step S202 again. If the determination in step S207 is Yes ( _Ta > T _c ), the control circuit 70 executes the next step S208.

In step S208, the control circuit 70 causes the heating / cooling element 50 to cool the electro-optical material layer 30.

In step S209, the control circuit 70 measures the resistance value R of the electro-optical material layer 30, the estimated temperature T _e of the electro-optical material layer 30 is determined from the resistance value R of the electro-optical material layer 30 is, the Curie temperature T _It is determined whether or not it is lower than _c . If the determination in step S209 is No ( _Te > T _c or _Te = T _c ), the control circuit 70 executes the next step S210.

In step S210, the control circuit 70 determines the estimated temperature _{T e} of the electro-optical material layer 30, whether higher than the Curie temperature _{T c.} If the determination in step S210 is _{_{Yes (T e> T c)}} , the control circuit 70 again executes S208 and S209. If the determination in step S210 is _{_{No (T e = T c)}} , the control circuit 70 executes S209 again.

If the determination in step S209 is _{_{Yes (T e <T c)}} , the control circuit 70 executes the next step S211.

In step S211 of the control circuit 70, the heating / cooling element 50 heats the electro-optical material layer 30 or stops the operation of the heating / cooling element 50. If the heating rate of the electro-optical material layer 30 is not taken into consideration, the operation of the heating / cooling element 50 may be stopped to naturally warm the electro-optical material layer 30. After that, the control circuit 70 executes step S209 again.

The control circuit 70 repeatedly executes step S204 or step S209, for example, every second during operation. The control circuit 70 may stop operating after any step from step S201 to step S211.

Step S204 calculates, in step S205, step S209, and step S210, the control circuit 70, the estimated temperature _{T e} of the electro-optical material layer 30 is determined from the resistance value R, by a predetermined arithmetic expression based on the resistance value R You may. Alternatively, the control circuit 70, the estimated temperature T _e, may be determined by referring to the data table shown and the resistance value R of the relationship between the estimated temperature T _e. The data table is recorded on a storage medium (not shown).

Further, step S204, step S205, step S209, and in step S210, it is not necessary to calculate or reference to the estimated temperature _{T e.} By comparing the resistance value R itself or the rate of change of the resistance value R with respect to a predetermined heating / cooling energy with a threshold value stored in advance, it is determined whether the electro-optical material layer 30 should be heated or cooled. May be good. The control circuit 70 heats the electro-optical material layer 30 when the resistance value R of the electro-optical material layer 30 is lower than the threshold value. The control circuit 70 cools the electro-optical material layer 30 when the resistance value R of the electro-optical material layer 30 is higher than the threshold value. Alternatively, the control circuit 70 heats the electro-optical material layer 30 when the rate of change of the resistance value R of the electro-optical material layer 30 is higher than the threshold value. The control circuit 70 cools the electro-optical material layer 30 when the rate of change of the resistance value R of the electro-optical material layer 30 is lower than the threshold value.

By the operation shown in FIG. 3B, the control circuit 70 can adjust the temperature T of the electro-optical material layer 30 to the vicinity of the Curie temperature T _c . As a result, the electro-optical effect of the electro-optical material layer 30 can be maintained high. Further, instead of the Curie temperature T _c, the temperature above the Curie temperature T _c as the reference temperature T _s, may adjust the temperature T of the electro-optical material layer 30. As a result, even if the temperature T of the electro-optical material layer 30 becomes equal to or less than the reference temperature T _s , the electricity of the electro-optical material layer 30 is generated in the normal dielectric phase in which the relative permittivity ε _r gradually changes as shown in FIG. The optical effect does not drop sharply. Assuming that the reference temperature at which the Curie temperature is T _c or higher is T _s = T _c + ΔT, ΔT can be set to, for example, 5 ° C. or lower.

FIG. 3C is a flowchart showing the operation of the control circuit 70 when the heating / cooling control is directly performed by the resistance value R without obtaining the estimated temperature of the electro-optical material layer. In this case, it is not always necessary to use a thermometer.

In step S301, the control circuit 70 applies a DC voltage to the pair of electrodes 20 and measures the current flowing through the electro-optical material layer 30 with an ammeter 40. In step S302, the control circuit 70 causes the heating / cooling element 50 to heat or cool the electro-optical material layer 30. In step S303, the control circuit 70 monitors the rate of change of the resistance value of the electro-optical material layer 30 with respect to the temperature change based on the change of the current value due to heating or cooling. In step S304, the control circuit 70 determines whether or not the rate of change of the resistance value is larger than a predetermined threshold value. If the determination in step S304 is Yes, the control circuit 70 executes step S305. In step S305, the control circuit 70 causes the heating / cooling element 50 to heat the electro-optical material layer 30. If the determination in step S304 is No, the control circuit 70 executes step S306. In step S306, the control circuit 70 causes the heating / cooling element 50 to cool the electro-optical material layer 30. After step S305 and step S306, the control circuit 70 executes step S303 again.

According to the example shown in FIG. 3C, the value of the Curie temperature T _c of the electro-optical material layer 30 and the temperature of the electro-optical material layer 30 are adjusted to be near the Curie temperature T _c even if the current temperature is unknown. Can be done. As a result, the electro-optical effect can be maintained high.

Even in the example shown in FIG. 3C, the ambient temperature _Ta may be measured by a thermometer, and whether the temperature should be heated or cooled in step S302 may be determined depending on whether the temperature is higher or lower than the reference temperature stored in the memory. Good.

In the optical device 100 of the present embodiment, the pair of electrodes 20 can be used not only for applying an electric field to change the refractive index, but also for measuring the resistance value R of the electro-optical material layer 30. Thereby, the structure of the optical device 100 can be simplified. Further, since the position where the electric field is applied and the position where the resistance value R is measured are the same, the electro-optical material layer 30 has a variation in crystallinity and / or a variation in the composition ratio in the electro-optical material layer 30. It is not necessary to consider the difference in Curie temperature T _c at each position. Further, a DC voltage is applied instead of an AC voltage to measure the resistance value R. This facilitates the measurement of the resistance value R, which is the ratio of the DC voltage to the DC current.

The optical device 100 may further include the following components.

FIG. 4 is a diagram schematically showing an example in which the optical device 100 further includes the heat insulating material 80. In FIG. 4, some components are not shown. The heat insulating material 80 covers at least a part of the electro-optical material layer 30. In the example shown in FIG. 4, the portion of the electro-optical material layer 30 shown in FIG. 1A that comes into contact with the outside air is covered with the heat insulating material 80. Thereby, the temperature change of the electro-optical material layer 30 due to the temperature change of the outside air can be suppressed. The heat insulating material 80 does not need to be in direct contact with the above portion of the electro-optical material layer 30. Further, as shown in FIG. 4, the portion of the substrate 10, the first electrode 20a, and the second electrode 20b shown in FIG. 1A that comes into contact with the outside air may be covered with a heat insulating material. As a result, it is possible to suppress the temperature change of the substrate 10, the first electrode 20a, and the second electrode 20b due to the temperature change of the outside air. As a result, the temperature change of the electro-optical material layer 30 due to the temperature change of the outside air can be further suppressed. The heat insulating material 80 does not need to be in direct contact with the substrate 10, the first electrode 20a, and the above portion of the second electrode 20b. The insulation 80 can be formed from, for example, an epoxy resin.

FIG. 5 is a diagram schematically showing an example in which the optical device 100 further includes an electromagnetic shield 90. In FIG. 5, some components are not shown. The electromagnetic shield 90 covers at least a part of the electro-optical material layer 30. In the example shown in FIG. 5, the substrate 10, the first electrode 20a, the electro-optical material layer 30, and the second electrode 20b are covered with the electromagnetic shield 90. As a result, electromagnetic noise from the outside of the optical device 100 and / or from the heating / cooling element 50 can be shielded. As a result, the influence of electromagnetic noise when measuring the resistance of the electro-optical material layer 30 can be suppressed. The electromagnetic shield 90 does not need to be in direct contact with the electro-optical material layer 30. The electromagnetic shield 90 is formed from at least one selected from the group consisting of silver, copper, gold, aluminum, nickel, and iron. The heat insulating material 80 shown in FIG. 4 may be provided inside the electromagnetic shield 90 shown in FIG.

In addition to the above example, as a modification of the optical device 100, a DC voltage may be applied to the electro-optical material layer 30 by a plurality of electrode pairs.

FIG. 6 is a diagram schematically showing the optical device 110 in the modified example. In FIG. 6, some components are not shown. In the example shown in FIG. 6, the third electrode 20ba, the fourth electrode 20bb, and the fifth electrode 20bc are located in place of the second electrode 20b shown in FIG. 1A. The third electrode 20ba, the fourth electrode 20bb, and the fifth electrode 20bc have a DC voltage _having a first voltage value V _DCa , a second voltage value V _DCb , and a third voltage value V _DCc , respectively. Is applied. Each of the third electrode 20ba, the fourth electrode 20bb, and the fifth electrode 20bc and a part of the first electrode 20a facing each other can be considered as a pair of electrodes. In the example shown in FIG. 6, instead of the ammeter 40 shown in FIG. 1A, a first ammeter 40a, a second ammeter 40b, and a third ammeter 40c are provided. In the example shown in FIG. 6, instead of the heating / cooling element 50 shown in FIG. 1A, the first heating / cooling element 50a, the second heating / cooling element 50b, and the third heating / cooling element 50c are located.

In the example shown in FIG. 6, the refractive index of the three portions of the electro-optical material layer 30 can be changed separately by the third electrode 20ba, the fourth electrode 20bb, and the fifth electrode 20bc. Thereby, the phase of the light propagating in each of the above three portions of the electro-optical material layer 30 can be adjusted separately. When the first voltage value V _DCa , the second voltage value V _DCb , and the third voltage value V _DCc are all equal, the amount of change in the refractive index of the above three parts of the electro-optical material layer 30 is equal. When at least a part of the first voltage value V _DCa , the second voltage value V _DCb , and the third voltage value V _DCc is different, the amount of change in the refractive index of the above three parts of the electro-optical material layer 30 At least some of them are different. When the first voltage value V _DCa , the second voltage value V _DCb , and the third voltage value V _DCc are all different, the amount of change in the refractive index of the above three parts of the electro-optical material layer 30 is all different.

In the example shown in FIG. 6, the first ammeter 40a, the second ammeter 40b, and the third ammeter 40c, and the first heating / cooling element 50a, the second heating / cooling element 50b, and the third The temperature of the above three parts of the electro-optical material layer 30 can be adjusted separately by the heating / cooling element 50c of the above.

In the optical device 110 shown in FIG. 6, when the crystallinity and / or the composition ratio of the three parts of the electro-optical material layer 30 are different, the Curie temperature T _c at the three parts may be different. Even in this case, a high electro-optical effect can be obtained by adjusting the temperatures of the above three portions to the vicinity of the respective Curie temperatures T _c . The above three parts of the electro-optical material layer 30 may be separated.

As described above, the optical device 110 in this modification includes a plurality of electrode pairs, an electro-optical material layer 30, a plurality of heating / cooling elements, and a control circuit 70. A DC voltage is applied to each of the plurality of electrode pairs. The electro-optical material layer 30 is located between each of the plurality of electrode pairs. Each of the plurality of heating and cooling elements performs at least one of heating and cooling of a portion of the electro-optical material layer 30 sandwiched by one corresponding electrode pair among the plurality of electrode pairs. The control circuit 70 inputs a signal for heating or cooling the portion of the electro-optical material layer 30 to each of the plurality of heating / cooling elements based on the resistance value of the portion of the electro-optical material layer 30. The resistance value of the portion of the electro-optical material layer 30 is determined by the ratio of the value of the DC voltage applied to each of the plurality of electrode pairs to the value of the current measured by each of the plurality of ammeters. The operation of the control circuit 70 for heating or cooling the portion of the electro-optical material layer 30 is as shown in FIGS. 3A and 3B.

(Production method)
The manufacturing method of the optical device 100 will be described below.

FIG. 7 is a flowchart showing the manufacturing process of the optical device 100. The method for manufacturing the optical device 100 includes the following steps S401 to S405.

In step S401, the STO substrate is prepared. The STO substrate corresponds to the substrate 10 shown in FIG. 1A. In step S402, an SRO thin film and a KTN thin film are formed by epitaxial growth on the first surface of the STO substrate. The SRO thin film corresponds to the first electrode 20a shown in FIG. 1A. The KTN thin film corresponds to the electro-optical material layer 30 shown in FIG. 1A. A PLD (Pulsed Laser Deposition) apparatus is used for film formation. In the vacuum chamber of the PLD device, the STO substrate and the target formed from the SRO are arranged to face each other. The facing distance is 25 mm. By injecting O ₂ gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 1 Pa. The STO substrate is heated to 650 ° C. The target formed from the SRO is irradiated with an excimer laser. As a result, an SRO thin film is formed by epitaxial growth on the first surface 10s1 of the STO substrate. By the same method, the STO substrate on which the SRO thin film is formed on the first surface 10s1 is heated to 800 ° C., and the target formed from KTN is irradiated with an excimer laser. As a result, a KTN thin film is formed on the SRO thin film by epitaxial growth. After cooling, the STO substrate on which the SRO thin film and the KTN thin film are formed above the first surface 10s1 is taken out of the vacuum chamber.

In step S403, an ITO thin film is formed on the KTN thin film by using a high frequency sputtering apparatus. The ITO thin film corresponds to the second electrode 20b shown in FIG. 1A. In the vacuum chamber of the high frequency sputtering apparatus, the STO substrate and the target formed of ITO are arranged so as to face each other. The facing distance is 70 mm. The STO substrate includes an SRO thin film and a KTN thin film to which a metal mask for sputtering is attached. The ITO thin film is not formed at the place where the metal mask is attached. As a result, an ITO thin film is formed. A metal mask is not always necessary. By injecting O ₂ gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 1 Pa. By sputtering at RF power 137 W for 170 seconds, an ITO thin film having a film thickness of 100 nm is formed on the KTN thin film.

In step S404, the heating / cooling element 50 is attached to the second surface 10s2 of the STO substrate. In step S405, the ammeter 40 shown in FIG. 1A is attached to the ITO thin film.

(Application example)
In the optical device 100 of the present embodiment, the control circuit 70 changes the refractive index of the electro-optical material layer 30 by changing the value of the DC voltage applied to the pair of electrodes 20. As a result, the phase of the light 32 propagating in the electro-optical material layer 30 changes. By appropriately adjusting the temperature T of the electro-optical material layer 30 as described above, the electro-optical effect of the electro-optical material layer 30 can be maintained high. As a result, the phase of the light 32 can be significantly changed. An application example using the change in the phase of the light 32 will be described below.

The optical device 100 in this embodiment can be applied to, for example, a Mach-Zehnder type optical switching device. FIG. 8 is a plan view schematically showing an example of a Mach-Zehnder type optical switching device 200. The optical switching device 200 includes an input waveguide 200a, two branched optical waveguides 200b, and an output waveguide 200c. The two branched optical waveguides 200b are located between the input waveguide 200a and the output waveguide 200c. In the example shown in FIG. 8, the reflection of light at the branch point A on the input waveguide 200a side and the branch point B on the output waveguide 200c side is not considered. Of the two branched optical waveguides 200b, one of the optical waveguides includes the optical device 100 in this embodiment.

The phase of the light propagating in the one optical waveguide is shifted by Δφ = (2π / λ) ΔnL as compared with the phase of the light propagating in the other optical waveguide. When the value of the DC voltage applied to the pair of electrodes 20 in the optical device 100 is _VDC = 0V, Δφ = 0. At this time, the phases of the light output from the two branched optical waveguides 200b are in phase with each other. Therefore, when two lights having the same phase are input to the output waveguide 200c, the two lights overlap each other. Therefore, the intensity I _{out of} the light output from the output waveguide 200c is equal to the intensity I _in of the light input to the input waveguide 200a.

On the other hand, when the value of the DC voltage applied to the pair of electrodes 20 in the optical device 100 is _VDC ≠ 0V, Δφ = π can be set. At this time, the phases of the light output from the two branched optical waveguides 200b are opposite to each other. Therefore, when two lights having opposite phases are input to the output waveguide 200c, the two lights cancel each other out. Therefore, the intensity I _{out of} the light output from the output waveguide 200c becomes 0.

As described above, by changing the DC voltage applied to the pair of electrodes 20 in the optical device 100, the intensity I _{out of} the light output from the output waveguide 200c of the optical switching device 200 is continuously increased from I _in to 0. Can be adjusted.

Further, the optical device 100 in this embodiment can be applied to, for example, an optical phased array 300. 9A and 9B are diagrams schematically showing an example of an optical phased array 300. The optical phased array 300 includes a plurality of optical waveguides 300w arranged in the Y direction. Each of the plurality of optical waveguides 300w includes the optical device 100 in this embodiment. The plurality of lights output from the plurality of optical waveguides 300w interfere with each other. As a result, the interference light output from the optical phased array 300 propagates in a specific direction. In the examples shown in FIGS. 9A and 9B, the broken lines represent the wave planes of the plurality of lights output from the plurality of optical waveguides 300w, respectively. The solid line represents the wave surface of the interference light output from the optical phased array 300. In the examples shown in FIGS. 9A and 9B, the plurality of optical waveguides 300w are arranged at equal intervals, but may be arranged at different intervals.

In the example shown in FIG. 9A, when the value of the DC voltage applied to the pair of electrodes 20 in the optical device 100 is _VDC = 0V, the phases of the light output from the plurality of optical waveguides 300w are in phase. Therefore, the interference light output from the optical phased array 300 propagates in the same direction as the X direction in which the plurality of optical waveguides 300w extend.

In the example shown in FIG. 9B, the phase of the light output from the plurality of optical waveguides 300w increases by Δφ in the Y direction by adjusting the value of the DC voltage applied to the pair of electrodes 20 in the optical device 100. To do. Therefore, the interference light output from the optical phased array 300 propagates in a direction different from the X direction in which the plurality of optical waveguides 300w extend.

As described above, the propagation direction of the interference light output from the optical phased array 300 can be adjusted by changing the DC voltage applied to the pair of electrodes 20 in the optical device 100. That is, light beam scanning becomes possible. Further, the optical phased array 300 can also detect light incident from a specific direction. In the example shown in FIGS. 9A and 9B, the optical phased array 300 can detect incident light from the direction opposite to the arrow.

The optical phased array 300 can be used, for example, as an antenna in an optical scanning system such as a LiDAR (Light Detection and Ranking) system and / or an optical detection system. In the LiDAR system, electromagnetic waves having a short wavelength such as visible light, infrared rays, or ultraviolet rays are used as compared with a radar system using radio waves such as millimeter waves. Therefore, the distance distribution of the object can be scanned and detected with high resolution. Such a LiDAR system can be mounted on a moving body such as an automobile, a UAV (Unmanned Aerial Vehicle, so-called drone), or an AGV (Automated Guided Vehicle), and can be used as one of collision avoidance technologies.

The optical device according to the embodiment of the present disclosure can be used, for example, as a Mach-Zehnder type optical switching device or a LiDAR system mounted on a vehicle such as an automobile, UAV, or AGV.

10: Substrate 10s1: First surface 10s2: Second surface 20: Electrode 20a: First electrode 20b: Second electrode 20ba: Third electrode 20bb: Fourth electrode 20bc: Fifth electrode 30: Electro-optical material layer 32: Optical 40: Current meter 40a: First current meter 40b: Second current meter 40c: Third current meter 42: Resistor 50: Heating and cooling element 50a: First heating and cooling element 50b : Second heating / cooling element 50c: Third heating / cooling element 60: Thermometer 70: Control circuit 80: Insulation material 90: Electromagnetic shield 100, 110: Optical device 200: Optical switching device 200a: Input waveguide 200b: Branch Two optical waveguides 200c: Output waveguide 300: Optical phased array 300w: Multiple optical waveguides

Claims

A pair of electrodes to which a DC voltage is applied and
An electro-optical material layer located between the pair of electrodes,
An ammeter that measures the current flowing through the electro-optical material layer,
A heating / cooling element that heats and cools the electro-optical material layer,
A control circuit that controls the heating / cooling element based on the value of the DC voltage and the value of the current measured by the ammeter.
Optical device with.
The optical device according to claim 1, wherein the control circuit changes the refractive index of the electro-optical material layer by changing the value of the DC voltage.
The phase of the light guided through the electro-optical material layer is controlled by the change in the refractive index.
The optical device according to claim 2.
The DC voltage is a DC pulse voltage.
The optical device according to any one of claims 1 to 3.
The control circuit calculates the resistance value of the electro-optical material layer from the value of the DC voltage and the value of the current, and based on the change in the resistance value due to at least one of heating and cooling by the heating / cooling element, the said Control the heating and cooling elements,
The optical device according to any one of claims 1 to 4.
The optical device further comprises a thermometer.
At the start of operation, the control circuit
When the temperature measured by the thermometer is lower than the reference temperature, the heating / cooling element is used to heat the electro-optical material layer.
When the temperature measured by the thermometer is higher than the reference temperature, the heating / cooling element cools the electro-optical material layer.
The optical device according to any one of claims 1 to 5.
The electro-optical material layer is composed of a ferroelectric substance.
The reference temperature is the Curie temperature of the ferroelectric substance.
The optical device according to claim 6.
The control circuit
A DC voltage is applied to the pair of electrodes to
The heating / cooling element is allowed to heat or cool the electro-optical material layer.
The reference temperature is determined based on the change in the value of the current due to heating or cooling the electro-optical material layer and the value of the DC voltage.
The optical device according to claim 6 or 7.
The heating / cooling element includes a Peltier element.
The optical device according to any one of claims 1 to 8.
Further comprising a heat insulating material covering at least a part of the electro-optical material layer.
The optical device according to any one of claims 1 to 9.
The optical device according to any one of claims 1 to 10, further comprising an electromagnetic shield that covers at least a part of the electro-optical material layer.
The electro-optical material layer contains potassium niobate tantalate.
The optical device according to any one of claims 1 to 11.
The thickness of the electro-optical material layer is 0.1 μm or more and 10 μm or less.
The optical device according to any one of claims 1 to 12.
A resistor for preventing dielectric breakdown of the electro-optical material layer is further provided between the ammeter and one of the pair of electrodes.
The optical device according to any one of claims 1 to 13.
With multiple electrode pairs to which DC voltage is applied,
An electro-optic material layer located between each of the plurality of electrode pairs,
A plurality of ammeters, each of which measures a current flowing through a portion of the electro-optical material layer sandwiched by one corresponding electrode pair of the plurality of electrode pairs,
A plurality of heating and cooling elements, each of which performs at least one of heating and cooling of a portion of the electro-optical material layer sandwiched by one corresponding electrode pair of the plurality of electrode pairs.
A control circuit that controls each of the plurality of heating / cooling elements based on the value of the DC voltage applied to each of the plurality of electrode pairs and the value of the current measured by each of the plurality of ammeters. When,
Optical device with.