WO2020209049A1 - Optical device and method for producing same - Google Patents

Optical device and method for producing same Download PDF

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Publication number
WO2020209049A1
WO2020209049A1 PCT/JP2020/013065 JP2020013065W WO2020209049A1 WO 2020209049 A1 WO2020209049 A1 WO 2020209049A1 JP 2020013065 W JP2020013065 W JP 2020013065W WO 2020209049 A1 WO2020209049 A1 WO 2020209049A1
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optical
layer
electro
material layer
electrode
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PCT/JP2020/013065
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French (fr)
Japanese (ja)
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尚徳 増子
宏幸 高木
平澤　拓
寺部　一弥
敬志 土屋
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パナソニック株式会社
国立研究開発法人物質・材料研究機構
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Publication of WO2020209049A1 publication Critical patent/WO2020209049A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure

Definitions

  • This disclosure relates to an optical device and a method for manufacturing the same.
  • Patent Documents 1 and 2 and Non-Patent Documents 1 to 4 have been proposed (for example, Patent Documents 1 and 2 and Non-Patent Documents 1 to 4).
  • the index of refraction can be varied by various optical effects. For example, by changing the refractive index of the optical waveguide, the phase of the light propagating in the optical waveguide can be modulated.
  • the present disclosure provides an optical device capable of realizing a large refractive index modulation using an electro-optical effect.
  • FIG. 1A is a side view schematically showing the optical phase modulator in the exemplary embodiment of the present disclosure as viewed from the X direction.
  • FIG. 1B is a side view of the optical phase modulator in the exemplary embodiment of the present disclosure schematically shown from the Y direction.
  • FIG. 2A is a diagram schematically showing charge distribution in the pair of electrodes, the electro-optical material layer, and the electrolyte layer when a voltage is applied to the pair of electrodes.
  • FIG. 2B is a diagram schematically showing the relationship between the electric potential and the distance between the pair of electrodes along the Z direction from the upper surface of the first electrode.
  • FIG. 2C is a diagram schematically showing the relationship between the distance between the pair of electrodes from the upper surface of the first electrode along the Z direction and the strength of the electric field.
  • FIG. 4 is a flowchart showing a manufacturing process of the optical phase modulator.
  • FIG. 5 is a plan view schematically showing an example of a Mach-Zehnder type optical switching device.
  • FIG. 6A is a diagram schematically showing a first example of an optical phased array.
  • FIG. 6B is a diagram schematically showing a second example of an optical phased array.
  • Non-Patent Document 1 discloses an optical phase modulator using a stress-optic effect in which the refractive index changes with stress.
  • the piezoelectric body is deformed by applying a voltage to the piezoelectric body laminated on the optical waveguide. Due to the deformation of the piezoelectric body, stress is applied to the optical waveguide, and the refractive index of the optical waveguide changes. Due to the change in refractive index, the phase of light propagating in the optical waveguide is modulated.
  • the amount of change in the refractive index of the optical waveguide due to the piezoelectric material is small, for example, on the order of about 10-6 . Therefore, the phase of light cannot be significantly modulated unless the optical waveguide is lengthened. Lengthening the optical waveguide leads to an increase in the size of the optical phase modulator.
  • Non-Patent Documents 2 and 3 disclose an optical phase modulator using a thermo-optic effect in which the refractive index changes with heat.
  • the amount of change in refractive index due to thermo-optic effect is large, for example, 10 -2 order. Therefore, even when the optical phase modulator is small, the phase of light can be largely modulated.
  • the modulation speed of the refractive index due to the thermo-optical effect is low, and it is not possible to realize high-speed modulation exceeding, for example, several hundred kHz.
  • Non-Patent Document 4 discloses an optical phase modulator using an electro-optic effect in which the refractive index changes by applying an electric field.
  • electro-optical effects the Pockels effect and the Kerr effect are known. When no electric field is applied, the amount of change in the refractive index is zero.
  • the amount of change in the refractive index is determined by the product of the electro-optical constant inherent in the electro-optical material and the strength of the applied electric field.
  • the Kerr effect the amount of change in the refractive index is determined by the product of the electro-optic constant and the square of the strength of the applied electric field.
  • the change in the refractive index modulates the phase of the light propagating through the electro-optical material.
  • the modulation speed of the refractive index due to the electro-optical effect is high, and for example, modulation of several tens of MHz or more can be realized.
  • the stronger the applied electric field the greater the amount of change in the refractive index.
  • the strength of the applied electric field is limited to a strength lower than the dielectric breakdown electric field strength of the electro-optical material. Therefore, the amount of change in the refractive index is on the order of about 10-4 and does not become so large.
  • Patent Document 1 discloses an optical modulation device using an electro-optical effect.
  • the electro-optical material layer is in contact with the electrolyte layer.
  • an external voltage is applied to the electro-optical material layer and the electrolyte layer, a strong electric field is generated near the interface between the electro-optic material layer and the electrolyte layer.
  • the strength of the electric field exceeds the dielectric breakdown electric field strength of the electro-optical material layer.
  • the state in which light is transmitted through the electro-optical material layer and the state in which light is reflected by the electro-optical material layer are switched by changing the refractive index of the electro-optical material layer.
  • This optical modulation device is used as an optical switching element. It is not envisioned that the electro-optical material layer or electrolyte layer will be used as an optical waveguide. Furthermore, no specific material for the electrolyte layer is mentioned.
  • Patent Document 2 discloses an optical switch using an electrochromic effect.
  • the optical waveguide is surrounded by an electrochromic material layer.
  • the electrochromic material layer is in contact with the electrolyte layer.
  • a voltage is applied to the electrochromic material layer and the electrolyte layer.
  • a redox reaction occurs in the electrochromic material layer, and the electronic structure of the electrochromic material layer changes.
  • the refractive index of the electrochromic material layer changes due to the change in the electronic structure.
  • the oxidation reaction or reduction reaction occurs reversibly depending on the polarity of the voltage applied from the outside. The oxidized or reduced state is maintained even when no voltage is applied.
  • the amount of change in the refractive index is on the order of about 10-3 .
  • the modulation rate is very slow, at most a few Hz.
  • the electrolyte layer is provided to oxidize or reduce the electrochromic material layer.
  • the present inventor has come up with the optical device described in the following item, which can realize a large refractive index modulation using an electro-optical effect by using an electrolyte layer formed of a specific material.
  • the refractive index of the electro-optical material layer can be greatly modulated by a strong electric field generated near the interface between the electro-optical material layer and the electrolyte layer.
  • the optical device according to the second item further includes a control circuit for controlling the voltage in the optical device according to the first item.
  • the control circuit modulates the phase of light propagating through the electro-optical material layer by controlling the voltage to change the refractive index of the electro-optical material layer.
  • the phase of light propagating in the electro-optical material layer can be modulated by a control circuit.
  • the optical device according to the third item is 1 ⁇ x ⁇ 4 in the optical device according to the first or second item.
  • the electrolyte layer has Li ion conductivity effective for generating a strong electric field near the interface between the electro-optical material layer and the electrolyte layer.
  • the electrolyte layer has the above-mentioned effective Li-ion conductivity and has a flat surface.
  • the optical device according to the fifth item is the optical device according to any one of the first to fourth items, in which the electrolyte layer has an amorphous structure.
  • the flatness of the interface between the electro-optical material layer and the electrolyte layer can be improved.
  • the optical device according to the sixth item is the optical device according to any one of the first to fifth items, in which the electro-optical material layer is formed of potassium niobate tantalate.
  • the electro-optical material layer exhibits a high electro-optical effect near room temperature.
  • the method for manufacturing an optical device includes a step of forming a first electrode, a step of forming an electro-optical material layer on the first electrode, and Li x on the electro-optical material layer.
  • a step of forming an electrolyte layer formed from a substance represented by Zr z Si 1-z Oy (x> 0, y x / 2 + 2, 0 ⁇ z ⁇ 1) and a second step on the electrolyte layer. It includes a step of forming an electrode.
  • the step of forming the electrolyte layer is such that the electrolyte layer is charged with electricity at room temperature by a pulse laser deposition method. Includes the step of depositing on the optical material layer.
  • the electrolyte layer can be easily deposited on the electro-optical material layer. Further, the flatness of the interface between the electro-optical material layer and the electrolyte layer can be improved.
  • 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.
  • functional blocks other than the storage element may be integrated on one chip.
  • 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.
  • FPGA Field Programmable Gate Array
  • circuits, units, devices, members or parts can be performed by software processing.
  • 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.
  • light refers to electromagnetic waves including not only visible light (wavelength of about 400 nm to about 700 nm) but also ultraviolet rays (wavelength of about 10 nm to about 400 nm) and infrared rays (wavelength of about 700 nm to about 1 mm). means.
  • an optical phase modulator will be described as an example of an optical device capable of realizing a large refractive index modulation using an electro-optical effect.
  • FIGS. 1A and 1B are diagrams schematically showing the optical phase modulator 100 in the exemplary embodiment of the present disclosure.
  • the coordinate system including the X-axis, the Y-axis, and the Z-axis which are orthogonal to each other shown in FIGS. 1A and 1B is used.
  • the + Z direction is referred to as "upward”
  • the -Z direction is referred to as "downward”.
  • the dimension in the X direction is referred to as "length”
  • the dimension in the Y direction is referred to as "width”
  • the dimension in the Z direction is referred to as "thickness”.
  • FIG. 1A schematically shows the structure of the optical phase modulator 100 as viewed from the + X direction.
  • FIG. 1B schematically shows the structure of the optical phase modulator 100 as viewed from the ⁇ Y direction.
  • the optical phase modulator 100 includes a substrate 10, a first electrode 20a and a second electrode 20b, an electro-optical material layer 30, an electrolyte layer 40, and a control circuit 50.
  • the substrate 10 has a main surface 10s parallel to the XY plane.
  • the first electrode 20a is located on the main surface 10s of the substrate 10.
  • the electro-optical material layer 30 is located on the first electrode 20a.
  • the electrolyte layer 40 is located on the electro-optical material layer 30.
  • the second electrode 20b is located on the electrolyte layer 40. That is, the substrate 10, the first electrode 20a, the electro-optical material layer 30, the electrolyte layer 40, and the second electrode 20b are laminated in this order.
  • the first electrode 20a and the second electrode 20b may be referred to as a "pair of electrodes 20".
  • the substrate 10, the first electrode 20a and the second electrode 20b, the electro-optical material layer 30, and the electrolyte layer 40 have a structure extending at least in the X direction.
  • the substrate 10 supports a pair of electrodes 20, an electro-optical material layer 30, and an electrolyte layer 40.
  • the substrate 10 can be formed from, for example, at least one selected from the group consisting of magnesium oxide (MgO), spinel (MgAl 2 O 4 ), and ⁇ -alumina ( ⁇ -Al 2 O 3 ).
  • the substrate 10 may be omitted if it is unnecessary.
  • the pair of electrodes 20 directly or indirectly sandwich the electro-optical material layer 30 and the electrolyte layer 40 in the Z direction.
  • “Directly sandwiching” means that the first electrode 20a and the electro-optical material layer 30 are in contact with each other, and the second electrode 20b and the electrolyte layer 40 are in contact with each other.
  • “Indirectly sandwiching” means that another member is located between the first electrode 20a and the electro-optical material layer 30 and / or between the second electrode 20b and the electrolyte layer 40. To do.
  • the other member may be a dielectric member, a gas such as air, or a liquid such as water.
  • the X direction may be referred to as a "first direction”.
  • Each of the pair of electrodes 20 has a plane parallel to the XY plane.
  • a DC voltage is applied to the pair of electrodes 20.
  • the DC voltage may be a DC pulse voltage.
  • the time average of the voltage value of the DC pulse voltage may be treated as the value of the DC voltage. By changing the duty ratio of the DC pulse voltage, the time average value of the voltage can be adjusted.
  • Each of the pair of electrodes 20 may be a metal electrode or a transparent electrode.
  • the thickness of the first electrode 20a can be, for example, 100 nm or more and 200 nm or less.
  • the second electrode 20b was formed from, for example, at least one selected from the group consisting of SnO 2- doped In 2 O 3 (ITO), F-doped SnO 2 (FTO), and Sb-doped TiO 2 (ATO). It can be a transparent electrode.
  • the thickness of the second electrode 20b can be, for example, 100 nm or more and 200 nm or less.
  • the electro-optical material layer 30 functions as an optical waveguide layer that propagates light 32 along the X direction by total reflection.
  • the ellipse shown in FIG. 1A indicates that the intensity of the light 32 is high within the ellipse.
  • the refractive index of the electro-optical material layer 30 is higher than the refractive index of the medium around the optical phase modulator 100 and the refractive index of each of the substrate 10 and the electrolyte layer 40.
  • the first electrode 20a is a transparent electrode
  • the refractive index of the electro-optical material layer 30 is higher than the refractive index of the first electrode 20a.
  • the refractive index of the first electrode 20a is higher than that of the substrate 10.
  • the substrate 10 does not function as an optical waveguide layer.
  • the loss of light 32 can be ignored.
  • the refractive index of the electro-optical material layer 30 changes according to the strength of the applied electric field due to the Pockels effect or the Kerr effect. The stronger the applied electric field, the greater the amount of change in the refractive index of the electro-optical material layer 30. When no electric field is applied, the amount of change becomes zero.
  • the apparatus of this embodiment is different from the apparatus utilizing the electrochromic effect described above.
  • the refractive index changes from the initial value only when a voltage is applied, it is easy to turn on and off the optical phase modulator 100.
  • the phase of the light 32 propagating in the electro-optical material layer 30 can be modulated by the change in the refractive index of the electro-optical material layer 30 due to the application of an electric field. Due to the fast response of the electro-optic effect, the phase modulation rate can be high, for example, several tens of MHz or higher.
  • the wavelength of the light 32 in the air is ⁇
  • the refractive index of the electro-optical material layer 30 when no electric field is applied is n 0
  • the amount of change in the refractive index of the electro-optical material layer 30 due to the application of an electric field is ⁇ n
  • electricity is applied.
  • the length of the optical material layer 30 is L
  • each of the first electrode 20a and the second electrode 20b may be a transparent electrode or a metal electrode.
  • the loss of light 32 can be ignored. If the thickness of the electrolyte layer 40 is sufficiently large, the evanescent light of the light 32 does not reach the second electrode 20b. Therefore, when the thickness of the electrolyte layer 40 is sufficiently large, the loss of light 32 can be ignored even if the second electrode 20b is a metal electrode.
  • the electro-optical material layer 30 may be formed from a bulk or a thin film.
  • the thickness of the thin film can be, for example, 0.1 ⁇ m or more and 10 ⁇ m or less.
  • the cost of thin films is lower than the cost of bulk.
  • the electro-optical material layer 30 is composed of, for example, lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), potassium dihydrogen phosphate (KH 2 PO 4 ), and ammonium dihydrogen phosphate (KH 2 PO 4 ). It can be formed from at least one selected from the group consisting of NH 4 H 2 PO 4 ).
  • the electro-optical material layer 30 is, for example, for example, barium titanate (BaTiO 3), strontium titanate (SrTiO 3), potassium titanate (KTaO 3), zirconate lead lanthanum titanate ((Pb 1-x La x) (Zr y Ti 1-y) 1-x / 4 O 3: PLZT), and potassium tantalate niobate (KTa 1-x Nb x O 3: is selected from the group consisting of KTN) It can be formed from at least one. Among these, KTN exhibits a high electro-optical effect near room temperature by setting the composition ratio of Nb and Ta to an appropriate ratio.
  • KTN is transparent at a wavelength of 1550 nm for light used in optical communication. Therefore, application of KTN to optical devices is expected.
  • the electro-optical material layer 30 may be formed of a material exhibiting other electro-optical effects such as the electrochromic effect.
  • the electrolyte layer 40 is in contact with at least a part of the electro-optical material layer 30.
  • the electrolyte layer 40 has a structure extending at least in the X direction.
  • the electrolyte layer 40 is formed of an ionic conductor. In an ionic conductor, at least one of a positive ion and a negative ion moves by applying an electric field from the outside.
  • the electrolyte layer 40 is typically a solid electrolyte layer.
  • the solid electrolyte layer depending on its composition, may have a 10 -2 S / cm order of the order of the ion conductivity of 10 -8 S / cm. The material of the electrolyte layer 40 will be described later.
  • the control circuit 50 applies a DC voltage to the pair of electrodes 20.
  • the broken line with an arrow shown in FIG. 1A indicates that a signal is input from the control circuit 50 to the pair of electrodes 20.
  • the control circuit 50 modulates the phase of the light 32 propagating in the electro-optical material layer 30 by applying a voltage to the pair of electrodes 20 to change the refractive index of the electro-optical material layer 30.
  • the control circuit 50 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. In the following figure, the control circuit 50 may be omitted.
  • FIG. 2A is a diagram schematically showing the charge distribution in the pair of electrodes 20, the electro-optical material layer 30, and the electrolyte layer 40 when a voltage is applied to the pair of electrodes 20.
  • the upper part of FIG. 2A represents the optical phase modulator 100 shown in FIG.
  • the lower figure of FIG. 2A schematically shows an example of charge distribution in the region surrounded by the thick line shown in the upper figure.
  • the potential of the second electrode 20b is higher than the potential of the first electrode 20a, a downward electric field is generated between the pair of electrodes 20.
  • FIG. 2A shows the negative charge ( ⁇ ) in the first electrode 20a, the positive charge (+) in the second electrode 20b, and the polarization (+ ⁇ ) in the electro-optical material layer 30 at this time. ), And the distribution of positive ions (+) and negative ions ( ⁇ ) in the electrolyte layer 40 is schematically shown.
  • the negative charge contained in the first electrode 20a is distributed on the side of the electro-optical material layer 30.
  • the positive charge contained in the second electrode 20b is distributed on the side of the electrolyte layer 40. Due to the downward electric field generated between the pair of electrodes 20, positive ions among the ions contained in the electrolyte layer 40 move toward the electro-optical material layer 30, and negative ions move to the side of the second electrode 20b. Move to the side.
  • polarization of a pair of positive and negative charges occurs. Due to the movement of positive and negative ions in the electrolyte layer 40, an electric double layer surrounded by a broken line is formed at the interface 35 between the electro-optical material layer 30 and the electrolyte layer 40. Similarly, an electric double layer surrounded by a broken line is formed at the interface between the electrolyte layer 40 and the second electrode 20b.
  • the electric double layer functions as a capacitor.
  • the strengths of the electric potentials and electric fields generated in the electro-optical material layer 30 and the electrolyte layer 40 will be described. However, it is assumed that the electro-optical material layer 30 is formed from carrier-injected KTN.
  • FIG. 2B is a diagram schematically showing the relationship between the potential V and the distance Z along the Z direction from the upper surface of the first electrode 20a between the pair of electrodes 20.
  • V 1 represents the potential of the first electrode 20a, and V 2 represents the potential of the second electrode 20b.
  • the potential V sharply increases as the distance Z increases due to the formation of the electric double layer.
  • the potential V increases substantially parabolic with the increase in distance Z due to the carrier injection described above.
  • the potential V is substantially constant.
  • FIG. 2C is a diagram schematically showing the relationship between the distance Z between the pair of electrodes 20 along the Z direction from the upper surface of the first electrode 20a and the strength E of the electric field.
  • the electric field strength E shown in FIG. 2C corresponds to the absolute value of the gradient of the potential V shown in FIG. 2B.
  • the electric field strength E increases substantially linearly as the distance Z increases.
  • the electric field strength E sharply decreases as the distance Z increases.
  • the electro-optic material layer 30 in the portion near the interface 35, a strong electric field having an intensity of E m is generated. Even if the strength of the electric field locally exceeds the strength of the dielectric breakdown electric field, the electro-optical material layer 30 is not destroyed. Since there is no limitation on the dielectric breakdown electric field, the amount of change in the refractive index of the portion of the electro-optical material layer 30 near the interface 35 can be expected to be on the order of, for example, 10-2 or more. The amount of change in the refractive index is larger than that in the case without the electrolyte layer 40. On the other hand, the amount of change in the refractive index of the portion away from the interface 35 is on the order of about 10-3 on average.
  • the amount of change in the refractive index of the electro-optical material layer 30 varies depending on the location.
  • the average value of the change in the refractive index of the electro-optical material layer 30 in space may be the change ⁇ n in the refractive index of the electro-optical material layer 30.
  • the optical phase modulator 100 can modulate the phase of the light 32 propagating through the electro-optical material layer 30 at a large speed and at high speed by using a fast-responsive electro-optical effect.
  • the interface 35 between the electro-optical material layer 30 and the electrolyte layer 40 in this embodiment is flat.
  • the interface 35 does not necessarily have to be strictly flat and may have a portion having some inclination or recesses or protrusions.
  • the electric fields generated in the concave portion or the convex portion may weaken each other, and a strong electric field may not be concentrated in the vicinity of the interface 35. In that case, the amount of change in the refractive index of the portion of the electro-optical material layer 30 near the interface 35 may be small. Further, the light 32 may be lost due to the scattering of the light 32 by the concave or convex portion of the interface 35.
  • the interface 35 when the interface 35 is flat, a strong electric field is concentrated in the Z direction near the interface 35. As a result, the amount of change in the refractive index of the portion of the electro-optical material layer 30 near the interface 35 can be increased. Further, the flat interface 35 suppresses the loss of light 32.
  • the amount of change in the refractive index of the electro-optical material layer 30 is described by a tensor. Therefore, the refractive index of the electro-optical material layer 30 can change in a plurality of directions depending on the direction of the applied electric field. The amount of change in the refractive index of the electro-optical material layer 30 differs depending on the plurality of directions.
  • the refractive index of the electro-optical material layer 30 changes in the X direction and Y. It changes in the direction and the Z direction.
  • the amount of change in the refractive index of the electro-optical material layer 30 becomes maximum in the Z direction.
  • the phase of the light 32 in the TM (transverse magnetic) mode can be greatly modulated.
  • the light 32 in the TM mode has an electric field parallel to the Z direction.
  • a waveguide mode exists when the electro-optical material layer 30 has a width and thickness equal to or greater than a predetermined value. As a result, the electro-optical material layer 30 functions as an optical waveguide layer.
  • the width and thickness of the electro-optical material layer 30 are set to values that form an optical waveguide layer that propagates light 32 along the X direction.
  • LZSO Li x Zr z Si 1-z O y
  • z 0.5.
  • PLD Pulsed Laser Deposition
  • the surface of the LZSO layer becomes rough. This is because carbonates such as lithium carbonate are precipitated on the surface of the LZSO layer by the reaction between Li and CO 2 in the air. Therefore, if the amount of Li in the LZSO layer is small, the flatness of the surface of the LZSO layer can be improved. On the other hand, if the amount of Li in the LZSO layer is too small, the Li ion conductivity decreases. If the Li ion conductivity of the LZSO layer is on the order of about 10-8 S / cm or more, a strong electric field can be generated near the interface 35. From the above, when 1 ⁇ x ⁇ 4, at least the effectiveness of Li ion conductivity is satisfied.
  • the LZSO layer can be formed in an amorphous phase on both the Si substrate and the KTN layer.
  • the Li ion conductivity and surface roughness of the LZSO layer are determined by the amount of Li in the LZSO layer regardless of whether the base of the LZSO layer is a Si substrate or a KTN layer.
  • the LZSO layer has a crystal structure
  • temperature control is performed in order to deposit the LZSO layer having a crystal structure on the KTN layer. Due to the temperature control, the KTN layer and the LZSO layer may be thermally diffused. As a result, the interface 35 can be rough.
  • the LZSO layer has an amorphous structure
  • the LZSO layer can be deposited on the KTN layer at room temperature without controlling the temperature of heating or cooling. As a result, heat diffusion between the KTN layer and the LZSO layer is suppressed. As a result, the interface 35 becomes flat. Since no temperature control is required, the LZSO layer can be easily deposited on the KTN layer. As described above, when the interface 35 is flat, a strong electric field is likely to be generated in the vicinity of the interface 35. Further, the loss of light 32 due to scattering can be suppressed.
  • the thickness of the electrolyte layer 40 can be, for example, 500 nm or more and 2.5 ⁇ m or less. If the thickness of the electrolyte layer 40 is less than 500 nm, the evanescent light of the light 32 may reach the second electrode 20b. When the thickness of the electrolyte layer 40 is thicker than 2.5 ⁇ m, the strength of the electric field applied to the electro-optical material layer 30 and the electrolyte layer 40 may decrease due to the increase in the internal resistance of the electrolyte layer 40.
  • the LZSO layer has (1) a flat surface, (2) effective Li ion conductivity can be obtained, and (3) the LZSO layer can be easily deposited on the KTN layer. Has advantages.
  • FIG. 4 is a flowchart showing the manufacturing process of the optical phase modulator 100.
  • the method for manufacturing the optical phase modulator 100 includes the following steps S101 to S104.
  • step S101 an MgO substrate formed from an MgO (100) single crystal is prepared.
  • the MgO substrate corresponds to the substrate 10 shown in FIGS. 1A and 1B.
  • the LSSO layer and the KTN layer are formed on the main surface of the MgO substrate by epitaxial growth in this order.
  • the LSSO layer corresponds to the first electrode 20a shown in FIGS. 1A and 1B.
  • the LSSO layer exhibits electrical conductivity.
  • the LSSO layer is oriented in the [100] direction.
  • the thickness of the LSSO layer is 200 nm.
  • the KTN layer corresponds to the electro-optical material layer 30 shown in FIGS. 1A and 1B.
  • the thickness of the KTN layer is 500 nm.
  • the PLD method is used to form the LSSO layer and the KTN layer.
  • the MgO substrate and the target formed from LSSO are arranged to face each other.
  • the facing distance is 40 mm.
  • O 2 gas By injecting O 2 gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 10 Pa.
  • the MgO substrate is heated to 700 ° C.
  • the target formed from the LSSO is irradiated with an ArF excimer laser. As a result, the LSSO layer is deposited on the main surface 10s of the MgO substrate.
  • the MgO substrate on which the LSSO layer is formed on the main surface 10s is heated to 700 ° C., and the target formed from KTN is irradiated with an ArF excimer laser. As a result, the KTN layer is deposited on the LSSO layer. After cooling, the MgO substrate containing the LSSO layer and the KTN layer is removed from the vacuum chamber.
  • the amount of carbonate deposited on the surface of the LZSO layer is small.
  • the LZSO layer has an amorphous structure. Due to the small amount of Li and the amorphous structure, the surface of the LZSO layer is flat.
  • the LZSO layer corresponds to the electrolyte layer 40 shown in FIGS. 1A and 1B.
  • the thickness of the LZSO layer is 600 nm.
  • the PLD method is used to form the LZSO layer.
  • the MgO substrate containing the LSSO layer and the KTN layer and the target formed from LZSO are arranged to face each other.
  • the facing distance is 40 mm.
  • Targets formed from LZSO are irradiated with an ArF excimer laser at room temperature.
  • the LZSO layer is deposited on the KTN layer.
  • step S103 includes a step of depositing the electrolyte layer 40 on the electro-optical material layer 30 by the PLD method at room temperature.
  • an ITO layer formed of 10 wt% SnO 2- doped In 2 O 3 is formed on the LZSO layer at room temperature.
  • the ITO layer corresponds to the second electrode 20b shown in FIGS. 1A and 1B.
  • the thickness of the second electrode 20b is 100 nm.
  • a sputtering method is used to form the ITO layer.
  • an MgO substrate containing an LSSO layer, a KTN layer, and an LZSO layer and a target formed of ITO are arranged so as to face each other.
  • the facing distance is 45 mm.
  • Ar gas By injecting Ar gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 1.5 Pa.
  • the ITO layer is deposited on the LZSO layer by sputtering for 12 minutes at an RF power of 50 W.
  • the refractive indexes of the LSSO layer, the KTN layer, and the LZSO layer are about 2.0, 2.2, and 1.7, respectively. Therefore, the KTN layer having the highest refractive index functions as an optical waveguide layer.
  • the refractive index of the KTN layer can be changed in the range of about 2.0 to about 2.2. As a result, the phase of the light 32 propagating in the KTN layer can be modulated.
  • the following materials may be selected for the substrate 10, the pair of electrodes 20, and the electro-optical material layer 30.
  • step S101 instead of the MgO substrate may be prepared MgAl 2 O 4 substrate, or ⁇ -Al 2 O 3 ⁇ - Al 2 O 3 substrate formed from, formed from MgAl 2 O 4.
  • An LSSO layer can be formed as the first electrode 20a on the MgAl 2 O 4 substrate and the a—Al 2 O 3 substrate by epitaxial growth.
  • the MgAl 2 O 4 substrate and the a-Al 2 O 3 substrate are transparent at a wavelength of 1550 nm.
  • the refractive index of the MgAl 2 O 4 substrate and the a-Al 2 O 3 substrate is lower than that of the LSSO layer.
  • a KTN layer can be formed on the layer by epitaxial growth.
  • the layer is transparent at a wavelength of 1550 nm.
  • the refractive index of the layer is lower than that of the KTN layer.
  • the layer has electrical conductivity.
  • step S102 instead of the KTN layer, a layer formed from an electro-optical material exhibiting the Pockels effect or the Kerr effect described above may be formed.
  • a material capable of epitaxially growing the layer is selected for the first electrode 20a.
  • an FTO layer formed of F-doped SnO 2 (FTO) or an ATO layer formed of Sb-doped TiO 2 (ATO) may be formed.
  • the FTO layer and the ATO layer are transparent at a wavelength of 1550 nm.
  • the FTO and ATO layers can be deposited at room temperature.
  • the laminated structure produced by steps S101 to S104 can be patterned into an arbitrary shape by photolithography and dry etching.
  • the width of the laminated structure is designed to be, for example, 1 ⁇ m because there is a 0th-order TM mode in which the wavelength in air is 1550 nm.
  • the laminated structure may be patterned on a Mach-Zehnder type optical switching device or an optical phased array described later.
  • the control circuit 50 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 is modulated.
  • An application example using the phase modulation of the light 32 will be described below.
  • the optical phase modulator 100 in this embodiment can be applied to, for example, a Mach-Zehnder type optical switching device.
  • FIG. 5 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.
  • 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.
  • one of the optical waveguides includes the optical phase modulator 100 in this embodiment.
  • ⁇ 2 ⁇ / ⁇
  • ⁇ nL 2 ⁇ / ⁇
  • 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.
  • ⁇ ⁇ can be set by adjusting the value of the DC voltage applied to the pair of electrodes 20 in the optical phase modulator 100.
  • 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.
  • the intensity I out of the light output from the output waveguide 200c of the optical switching device 200 is changed from I in to 0. Can be adjusted continuously.
  • the optical phase modulator 100 capable of modulating the refractive index at a large speed and at a high speed enables the optical switching device 200 to be miniaturized and the intensity modulation of the light output from the optical switching device 200 to be accelerated.
  • optical phase modulator 100 in this embodiment can be applied to, for example, an optical phased array 300.
  • 6A and 6B 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 phase modulator 100 in this embodiment.
  • the plurality of lights output from the plurality of optical waveguides 300w interfere with each other.
  • the interference light output from the optical phased array 300 propagates in a specific direction.
  • 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.
  • the plurality of optical waveguides 300w are arranged at equal intervals, but may be arranged at different intervals.
  • 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.
  • the phase of the light output from the plurality of optical waveguides 300w is ⁇ along the Y direction. It increases little by little. 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.
  • 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 phase modulator 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. 6A and 6B, the optical phased array 300 can detect incident light from the direction opposite to the arrow.
  • the optical phase modulator 100 capable of modulating the refractive index at high speed makes it possible to reduce the size of the optical phased array 300 and to increase the speed and widening of the optical scan of the optical phased array 300.
  • 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.
  • an optical scanning system such as a LiDAR (Light Detection and Ranking) system and / or an optical detection system.
  • 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.
  • 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.
  • UAV Unmanned Aerial Vehicle, so-called drone
  • AGV Automatic Guided Vehicle
  • the optical phase modulator that modulates the phase of the light propagating in the optical waveguide has been described, but the present invention is not limited to this.
  • the present disclosure can be applied to any optical device that modulates the refractive index.
  • 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.
  • Substrate 10s Main surface 20: Electrode 20a: First electrode 20b: Second electrode 30: Electro-optical material layer 32: Light 35: Interface 40: Electrolyte layer 50: Control circuit 100: Optical phase modulator 200: Optical switching device 200a: Input waveguide 200b: Optical waveguide 200c: Output waveguide 300: Optical phased array 300w: Optical waveguide

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Abstract

An optical device (100) is provided with: an electro-optical material layer (30); an electrolyte layer (40) that is in contact with the electro-optical material layer (30) and that is formed from a material represented by LixZrzSi1 - zOy (wherein x > 0, y = x/2 + 2, and 0 ≤ z ≤ 1 ); and a first electrode (20a) and a second electrode (20b) for applying voltage to the electro-optical material layer (30) and the electrolyte layer (40).

Description

光デバイス、およびその製造方法Optical devices and their manufacturing methods
　本開示は、光デバイス、およびその製造方法に関する。 This disclosure relates to an optical device and a method for manufacturing the same.
　従来、屈折率を変化させる多くのデバイスが提案されている（例えば、特許文献１および２、ならびに非特許文献１から４）。屈折率は、様々な光学効果によって変化させることができる。例えば、光導波路の屈折率を変化させれば、光導波路を伝搬する光の位相を変調することができる。 Conventionally, many devices that change the refractive index have been proposed (for example, Patent Documents 1 and 2 and Non-Patent Documents 1 to 4). The index of refraction can be varied by various optical effects. For example, by changing the refractive index of the optical waveguide, the phase of the light propagating in the optical waveguide can be modulated.
特開２０１７－４４８５６号公報Japanese Unexamined Patent Publication No. 2017-44856 特開平７－１６８２１４号公報Japanese Patent Application Laid-Open No. 7-168214
　本開示は、電気光学効果を用いた大きい屈折率変調を実現することができる光デバイスを提供する。 The present disclosure provides an optical device capable of realizing a large refractive index modulation using an electro-optical effect.
　本開示の一態様に係る光デバイスは、電気光学材料層と、ＬｉｘＺｒｚＳｉ１－ｚＯｙ（ｘ＞０、ｙ＝ｘ／２＋２、０≦ｚ≦１）によって表される物質から形成され、前記電気光学材料層に接する電解質層と、前記電気光学材料層および前記電解質層に電圧を印加するための第１の電極および第２の電極と、を備える。 The optical device according to one aspect of the present disclosure is composed of an electro-optical material layer and a substance represented by Li x Zr z Si 1-z Oy (x> 0, y = x / 2 + 2, 0 ≦ z ≦ 1). It includes an electrolyte layer that is formed and is in contact with the electro-optical material layer, and a first electrode and a second electrode for applying a voltage to the electro-optical material layer and the electrolyte layer.
　本開示によれば、電気光学効果を用いた大きい屈折率変調を実現することができる。 According to the present disclosure, it is possible to realize a large refractive index modulation using an electro-optical effect.
図１Ａは、本開示の例示的な実施形態における光位相変調器を模式的に示すＸ方向から見た側面図である。FIG. 1A is a side view schematically showing the optical phase modulator in the exemplary embodiment of the present disclosure as viewed from the X direction. 図１Ｂは、本開示の例示的な実施形態における光位相変調器を模式的に示すＹ方向から見た側面図である。FIG. 1B is a side view of the optical phase modulator in the exemplary embodiment of the present disclosure schematically shown from the Y direction. 図２Ａは、一対の電極に電圧を印加した場合における、一対の電極、電気光学材料層、および電解質層内の電荷分布を模式的に示す図である。FIG. 2A is a diagram schematically showing charge distribution in the pair of electrodes, the electro-optical material layer, and the electrolyte layer when a voltage is applied to the pair of electrodes. 図２Ｂは、一対の電極間での、第１の電極の上面からＺ方向に沿った距離と、電位との関係を模式的に示す図である。FIG. 2B is a diagram schematically showing the relationship between the electric potential and the distance between the pair of electrodes along the Z direction from the upper surface of the first electrode. 図２Ｃは、一対の電極間での、第１の電極の上面からＺ方向に沿った距離と、電界の強度との関係を模式的に示す図である。FIG. 2C is a diagram schematically showing the relationship between the distance between the pair of electrodes from the upper surface of the first electrode along the Z direction and the strength of the electric field. 図３は、ｘ＝１、ｘ＝２、およびｘ＝４のＬＺＳＯ層のＬｉイオン伝導度および表面の粗さを示す図である。FIG. 3 is a diagram showing the Li ion conductivity and surface roughness of the LZSO layer of x = 1, x = 2, and x = 4. 図４は、光位相変調器の製造工程を示すフローチャートである。FIG. 4 is a flowchart showing a manufacturing process of the optical phase modulator. 図５は、マッハ・ツェンダー型の光スイッチングデバイスの例を模式的に示す平面図である。FIG. 5 is a plan view schematically showing an example of a Mach-Zehnder type optical switching device. 図６Ａは、光フェーズドアレイの第１の例を模式的に示す図である。FIG. 6A is a diagram schematically showing a first example of an optical phased array. 図６Ｂは、光フェーズドアレイの第２の例を模式的に示す図である。FIG. 6B is a diagram schematically showing a second example of an optical phased array.
　本開示の実施形態を説明する前に、本開示の基礎となった知見を説明する。 Before explaining the embodiments of the present disclosure, the findings underlying the present disclosure will be explained.
　非特許文献１は、応力によって屈折率が変化する応力光学効果（ｓｔｒｅｓｓ－ｏｐｔｉｃ　ｅｆｆｅｃｔ）を用いた光位相変調器を開示している。非特許文献１に開示されている光位相変調器では、光導波路上に積層された圧電体に電圧を印加することにより、圧電体が変形する。圧電体の変形に起因して、光導波路に応力がかかり、光導波路の屈折率が変化する。屈折率の変化に起因して、光導波路中を伝搬する光の位相が変調される。圧電体による光導波路の屈折率の変化量は小さく、例えば１０－６程度のオーダーである。このため、光導波路を長くしなければ、光の位相を大きく変調することができない。光導波路を長くすることは、光位相変調器の大型化を招く。 Non-Patent Document 1 discloses an optical phase modulator using a stress-optic effect in which the refractive index changes with stress. In the optical phase modulator disclosed in Non-Patent Document 1, the piezoelectric body is deformed by applying a voltage to the piezoelectric body laminated on the optical waveguide. Due to the deformation of the piezoelectric body, stress is applied to the optical waveguide, and the refractive index of the optical waveguide changes. Due to the change in refractive index, the phase of light propagating in the optical waveguide is modulated. The amount of change in the refractive index of the optical waveguide due to the piezoelectric material is small, for example, on the order of about 10-6 . Therefore, the phase of light cannot be significantly modulated unless the optical waveguide is lengthened. Lengthening the optical waveguide leads to an increase in the size of the optical phase modulator.
　非特許文献２および３は、熱によって屈折率が変化する熱光学効果（ｔｈｅｒｍｏ－ｏｐｔｉｃ　ｅｆｆｅｃｔ）を用いた光位相変調器を開示している。熱光学効果による屈折率の変化量は大きく、例えば１０－２程度のオーダーである。このため、光位相変調器が小さい場合でも、光の位相を大きく変調することができる。しかし、熱光学効果による屈折率の変調速度は低く、例えば数百ｋＨｚを超える高速の変調を実現することができない。 Non-Patent Documents 2 and 3 disclose an optical phase modulator using a thermo-optic effect in which the refractive index changes with heat. The amount of change in refractive index due to thermo-optic effect is large, for example, 10 -2 order. Therefore, even when the optical phase modulator is small, the phase of light can be largely modulated. However, the modulation speed of the refractive index due to the thermo-optical effect is low, and it is not possible to realize high-speed modulation exceeding, for example, several hundred kHz.
　非特許文献４は、電界を印加することによって屈折率が変化する電気光学効果（ｅｌｅｃｔｒｏ－ｏｐｔｉｃ　ｅｆｆｅｃｔ）を用いた光位相変調器を開示している。代表的な電気光学効果として、ポッケルス（Ｐｏｃｋｅｌｓ）効果、およびカー（Ｋｅｒｒ）効果が知られている。電界が印加されていないとき、屈折率の変化量はゼロである。ポッケルス効果では、屈折率の変化量は、電気光学材料固有の電気光学定数と、印加された電界の強度との積によって決定される。カー効果では、屈折率の変化量は、電気光学定数と、印加された電界の強度の２乗との積によって決定される。屈折率の変化により、電気光学材料を伝搬する光の位相が変調される。電気光学効果による屈折率の変調速度は高く、例えば数十ＭＨｚ以上の変調を実現することができる。 Non-Patent Document 4 discloses an optical phase modulator using an electro-optic effect in which the refractive index changes by applying an electric field. As typical electro-optical effects, the Pockels effect and the Kerr effect are known. When no electric field is applied, the amount of change in the refractive index is zero. In the Pockels effect, the amount of change in the refractive index is determined by the product of the electro-optical constant inherent in the electro-optical material and the strength of the applied electric field. In the Kerr effect, the amount of change in the refractive index is determined by the product of the electro-optic constant and the square of the strength of the applied electric field. The change in the refractive index modulates the phase of the light propagating through the electro-optical material. The modulation speed of the refractive index due to the electro-optical effect is high, and for example, modulation of several tens of MHz or more can be realized.
　電気光学効果を用いた光位相変調器では、印加された電界が強いほど、屈折率の変化量は大きい。しかし、印加される電界の強度は、電気光学材料の絶縁破壊電界強度よりも低い強度に制限される。このため、屈折率の変化量は１０－４程度のオーダーであり、それほど大きくならない。 In an optical phase modulator using an electro-optical effect, the stronger the applied electric field, the greater the amount of change in the refractive index. However, the strength of the applied electric field is limited to a strength lower than the dielectric breakdown electric field strength of the electro-optical material. Therefore, the amount of change in the refractive index is on the order of about 10-4 and does not become so large.
　特許文献１は、電気光学効果を用いた光変調装置を開示している。特許文献１に開示されている装置では、電気光学材料層が電解質層に接している。電気光学材料層および電解質層に外部から電圧を印加すると、電気光学材料層と電解質層との界面付近で、強い電界が発生する。当該電界の強度は、電気光学材料層の絶縁破壊電界強度を超える。そのような強い電界が印加されることにより、電気光学材料層の屈折率を大きく変化させることができる。特許文献１に開示されている装置では、電気光学材料層の屈折率を変化させることにより、電気光学材料層を光が透過する状態と、電気光学材料層で光が反射される状態とを切り替えることができる。この光変調装置は、光スイッチング素子として利用される。電気光学材料層または電解質層を光導波路として利用することは想定されていない。さらに、電解質層の具体的な材料については、言及されていない。 Patent Document 1 discloses an optical modulation device using an electro-optical effect. In the apparatus disclosed in Patent Document 1, the electro-optical material layer is in contact with the electrolyte layer. When an external voltage is applied to the electro-optical material layer and the electrolyte layer, a strong electric field is generated near the interface between the electro-optic material layer and the electrolyte layer. The strength of the electric field exceeds the dielectric breakdown electric field strength of the electro-optical material layer. By applying such a strong electric field, the refractive index of the electro-optical material layer can be significantly changed. In the apparatus disclosed in Patent Document 1, the state in which light is transmitted through the electro-optical material layer and the state in which light is reflected by the electro-optical material layer are switched by changing the refractive index of the electro-optical material layer. be able to. This optical modulation device is used as an optical switching element. It is not envisioned that the electro-optical material layer or electrolyte layer will be used as an optical waveguide. Furthermore, no specific material for the electrolyte layer is mentioned.
　特許文献２は、エレクトロクロミック効果（ｅｌｅｃｔｒｏｃｈｒｏｍｉｃ　ｅｆｆｅｃｔ）を用いた光スイッチを開示している。特許文献２に開示されている光スイッチでは、光導波路が、エレクトロクロミック材料層によって囲まれている。エレクトロクロミック材料層は電解質層に接している。エレクトロクロミック材料層および電解質層に電圧が印加される。これにより、当該エレクトロクロミック材料層内で、酸化還元反応が生じ、エレクトロクロミック材料層の電子構造が変化する。当該電子構造の変化により、エレクトロクロミック材料層の屈折率が変化する。酸化反応または還元反応は、外部から印加される電圧の極性に応じて可逆的に生じる。電圧を印加しなくても、酸化状態または還元状態が保持される。言い換えれば、一旦屈折率を変化させた後は、逆極性の電圧を印加しなければ、屈折率を戻すことはできない。この構造では、屈折率の変化量は１０－３程度のオーダーである。変調速度は非常に遅く、せいぜい数Ｈｚである。この光スイッチでは、電解質層は、エレクトロクロミック材料層を酸化または還元させるために設けられている。 Patent Document 2 discloses an optical switch using an electrochromic effect. In the optical switch disclosed in Patent Document 2, the optical waveguide is surrounded by an electrochromic material layer. The electrochromic material layer is in contact with the electrolyte layer. A voltage is applied to the electrochromic material layer and the electrolyte layer. As a result, a redox reaction occurs in the electrochromic material layer, and the electronic structure of the electrochromic material layer changes. The refractive index of the electrochromic material layer changes due to the change in the electronic structure. The oxidation reaction or reduction reaction occurs reversibly depending on the polarity of the voltage applied from the outside. The oxidized or reduced state is maintained even when no voltage is applied. In other words, once the refractive index is changed, the refractive index cannot be restored unless a voltage of opposite polarity is applied. In this structure, the amount of change in the refractive index is on the order of about 10-3 . The modulation rate is very slow, at most a few Hz. In this optical switch, the electrolyte layer is provided to oxidize or reduce the electrochromic material layer.
　本発明者は、以上の検討に基づき、特定の材料から形成された電解質層により、電気光学効果を用いた大きい屈折率変調を実現することができる以下の項目に記載の光デバイスに想到した。 Based on the above studies, the present inventor has come up with the optical device described in the following item, which can realize a large refractive index modulation using an electro-optical effect by using an electrolyte layer formed of a specific material.
　第１の項目に係る光デバイスは、電気光学材料層と、ＬｉｘＺｒｚＳｉ１－ｚＯｙ（ｘ＞０、ｙ＝ｘ／２＋２、０≦ｚ≦１）によって表される物質から形成され、前記電気光学材料層に接する電解質層と、前記電気光学材料層および前記電解質層に電圧を印加するための第１の電極および第２の電極と、を備える。 The optical device according to the first item is formed of an electro-optical material layer and a substance represented by Li x Zr z Si 1-z Oy (x> 0, y = x / 2 + 2, 0 ≦ z ≦ 1). It is provided with an electrolyte layer in contact with the electro-optical material layer, and a first electrode and a second electrode for applying a voltage to the electro-optical material layer and the electrolyte layer.
　この光デバイスでは、電気光学材料層と電解質層との界面付近で発生する強電界により、電気光学材料層の屈折率を大きく変調することができる。 In this optical device, the refractive index of the electro-optical material layer can be greatly modulated by a strong electric field generated near the interface between the electro-optical material layer and the electrolyte layer.
　第２の項目に係る光デバイスは、第１の項目に係る光デバイスにおいて、前記電圧を制御する制御回路をさらに備える。前記制御回路は、前記電圧を制御して前記電気光学材料層の屈折率を変化させることにより、前記電気光学材料層を伝搬する光の位相を変調する。 The optical device according to the second item further includes a control circuit for controlling the voltage in the optical device according to the first item. The control circuit modulates the phase of light propagating through the electro-optical material layer by controlling the voltage to change the refractive index of the electro-optical material layer.
　この光デバイスでは、制御回路により、電気光学材料層を伝搬する光の位相を変調することができる。 In this optical device, the phase of light propagating in the electro-optical material layer can be modulated by a control circuit.
　第３の項目に係る光デバイスは、第１または第２の項目に係る光デバイスにおいて、１≦ｘ≦４である。 The optical device according to the third item is 1 ≦ x ≦ 4 in the optical device according to the first or second item.
　この光デバイスでは、電解質層は、電気光学材料層と電解質層との界面付近に強電界を発生させるために有効なＬｉイオン伝導度を有する。 In this optical device, the electrolyte layer has Li ion conductivity effective for generating a strong electric field near the interface between the electro-optical material layer and the electrolyte layer.
　第４の項目に係る光デバイスは、第３の項目に係る光デバイスにおいて、ｘ＝１である。 The optical device according to the fourth item is x = 1 in the optical device according to the third item.
　この光デバイスでは、電解質層は、上記の有効なＬｉイオン伝導度を有し、かつ、平坦な表面を有する。 In this optical device, the electrolyte layer has the above-mentioned effective Li-ion conductivity and has a flat surface.
　第５の項目に係る光デバイスは、第１から第４の項目のいずれかに係る光デバイスにおいて、前記電解質層が、アモルファス構造を有する。 The optical device according to the fifth item is the optical device according to any one of the first to fourth items, in which the electrolyte layer has an amorphous structure.
　この光デバイスでは、電気光学材料層と電解質層との界面の平坦性を向上させることができる。 With this optical device, the flatness of the interface between the electro-optical material layer and the electrolyte layer can be improved.
　第６の項目に係る光デバイスは、第１から第５の項目のいずれかに係る光デバイスにおいて、前記電気光学材料層が、タンタル酸ニオブ酸カリウムから形成されている。 The optical device according to the sixth item is the optical device according to any one of the first to fifth items, in which the electro-optical material layer is formed of potassium niobate tantalate.
　この光デバイスでは、電気光学材料層は、常温付近で高い電気光学効果を示す。 In this optical device, the electro-optical material layer exhibits a high electro-optical effect near room temperature.
　第７の項目に係る光デバイスの製造方法は、第１の電極を形成する工程と、前記第１の電極上に電気光学材料層を形成する工程と、前記電気光学材料層上に、ＬｉｘＺｒｚＳｉ１－ｚＯｙ（ｘ＞０、ｙ＝ｘ／２＋２、０≦ｚ≦１）によって表される物質から形成された電解質層を形成する工程と、前記電解質層上に第２の電極を形成する工程とを含む。 The method for manufacturing an optical device according to the seventh item includes a step of forming a first electrode, a step of forming an electro-optical material layer on the first electrode, and Li x on the electro-optical material layer. A step of forming an electrolyte layer formed from a substance represented by Zr z Si 1-z Oy (x> 0, y = x / 2 + 2, 0 ≦ z ≦ 1) and a second step on the electrolyte layer. It includes a step of forming an electrode.
　この光デバイスの製造方法では、電気光学材料層と電解質層との界面付近で発生する強電界によって電気光学材料層の屈折率を大きく変調することができる光デバイスを製造することができる。 In this method of manufacturing an optical device, it is possible to manufacture an optical device capable of greatly modulating the refractive index of the electro-optical material layer by a strong electric field generated near the interface between the electro-optical material layer and the electrolyte layer.
　第８の項目に係る光デバイスの製造方法は、第７の項目に係る光デバイスの製造方法において、前記電解質層を形成する工程が、前記電解質層を、室温で、パルスレーザ堆積法によって前記電気光学材料層上に堆積する工程を含む。 In the method for manufacturing an optical device according to the eighth item, in the method for manufacturing an optical device according to the seventh item, the step of forming the electrolyte layer is such that the electrolyte layer is charged with electricity at room temperature by a pulse laser deposition method. Includes the step of depositing on the optical material layer.
　この光デバイスの製造方法では、電解質層を、電気光学材料層上に容易に堆積することができる。さらに、電気光学材料層と電解質層との界面の平坦性を向上させることができる。 In this method of manufacturing an optical device, the electrolyte layer can be easily deposited on the electro-optical material layer. Further, the flatness of the interface between the electro-optical material layer and the electrolyte layer can be improved.
　本開示において、回路、ユニット、装置、部材または部の全部または一部、またはブロック図における機能ブロックの全部または一部は、例えば、半導体装置、半導体集積回路（ＩＣ）、またはＬＳＩ（ｌａｒｇｅ　ｓｃａｌｅ　ｉｎｔｅｇｒａｔｉｏｎ）を含む１つまたは複数の電子回路によって実行され得る。ＬＳＩまたはＩＣは、１つのチップに集積されてもよいし、複数のチップを組み合わせて構成されてもよい。例えば、記憶素子以外の機能ブロックは、１つのチップに集積されてもよい。ここでは、ＬＳＩまたはＩＣと呼んでいるが、集積の度合いによって呼び方が変わり、システムＬＳＩ、ＶＬＳＩ（ｖｅｒｙ　ｌａｒｇｅ　ｓｃａｌｅ　ｉｎｔｅｇｒａｔｉｏｎ）、もしくはＵＬＳＩ（ｕｌｔｒａ　ｌａｒｇｅ　ｓｃａｌｅ　ｉｎｔｅｇｒａｔｉｏｎ）と呼ばれるものであってもよい。ＬＳＩの製造後にプログラムされる、Ｆｉｅｌｄ　Ｐｒｏｇｒａｍｍａｂｌｅ　Ｇａｔｅ　Ａｒｒａｙ（ＦＰＧＡ）、またはＬＳＩ内部の接合関係の再構成またはＬＳＩ内部の回路区画のセットアップができるｒｅｃｏｎｆｉｇｕｒａｂｌｅ　ｌｏｇｉｃ　ｄｅｖｉｃｅも同じ目的で使うことができる。 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.
　さらに、回路、ユニット、装置、部材または部の全部または一部の機能または動作は、ソフトウェア処理によって実行することが可能である。この場合、ソフトウェアは１つまたは複数のＲＯＭ、光学ディスク、ハードディスクドライブなどの非一時的記録媒体に記録され、ソフトウェアが処理装置（ｐｒｏｃｅｓｓｏｒ）によって実行されたときに、そのソフトウェアで特定された機能が処理装置（ｐｒｏｃｅｓｓｏｒ）および周辺装置によって実行される。システムまたは装置は、ソフトウェアが記録されている１つまたは複数の非一時的記録媒体、処理装置（ｐｒｏｃｅｓｓｏｒ）、および必要とされるハードウェアデバイス、例えばインターフェースを備えていてもよい。 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.
　本開示において、「光」とは、可視光（波長が約４００ｎｍ～約７００ｎｍ）だけでなく、紫外線（波長が約１０ｎｍ～約４００ｎｍ）および赤外線（波長が約７００ｎｍ～約１ｍｍ）を含む電磁波を意味する。 In the present disclosure, "light" refers to electromagnetic waves including not only visible light (wavelength of about 400 nm to about 700 nm) but also ultraviolet rays (wavelength of about 10 nm to about 400 nm) and infrared rays (wavelength of about 700 nm to about 1 mm). means.
　以下、図面を参照しながら、本開示のより具体的な実施形態を説明する。ただし、必要以上に詳細な説明は省略する場合がある。例えば、既によく知られた事項の詳細説明および実質的に同一の構成に対する重複する説明を省略することがある。これは、以下の説明が不必要に冗長になることを避け、当業者の理解を容易にするためである。なお、発明者らは、当業者が本開示を十分に理解するために添付図面および以下の説明を提供するのであって、これらによって特許請求の範囲に記載の主題を限定することを意図するものではない。以下の説明において、同一または類似する構成要素については、同じ参照符号を付している。 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.
　（実施形態）
　以下では、電気光学効果を用いた大きい屈折率変調を実現することができる光デバイスの一例として、光位相変調器を説明する。 (Embodiment)
In the following, an optical phase modulator will be described as an example of an optical device capable of realizing a large refractive index modulation using an electro-optical effect.
　図１Ａおよび図１Ｂは、本開示の例示的な実施形態における光位相変調器１００を模式的に示す図である。以下の説明において、図１Ａおよび図１Ｂに示す互いに直交するＸ軸、Ｙ軸、およびＺ軸からなる座標系を用いる。説明の便宜上、＋Ｚ方向を「上方向」と称し、－Ｚ方向を「下方向」と称する。これらの呼称は、便宜上のものにすぎず、現実に使用される光位相変調器１００の配置または姿勢を限定することを意図するものではない。以下の説明では、Ｘ方向における寸法を「長さ」と称し、Ｙ方向における寸法を「幅」と称し、Ｚ方向における寸法を「厚さ」と称する。 1A and 1B are diagrams schematically showing the optical phase modulator 100 in the exemplary embodiment of the present disclosure. In the following description, the coordinate system including the X-axis, the Y-axis, and the Z-axis which are 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 phase modulator 100 in practice. In the following description, the dimension in the X direction is referred to as "length", the dimension in the Y direction is referred to as "width", and the dimension in the Z direction is referred to as "thickness".
　図１Ａは、＋Ｘ方向から見た光位相変調器１００の構造を模式的に示している。図１Ｂは、－Ｙ方向から見た光位相変調器１００の構造を模式的に示している。 FIG. 1A schematically shows the structure of the optical phase modulator 100 as viewed from the + X direction. FIG. 1B schematically shows the structure of the optical phase modulator 100 as viewed from the −Y direction.
　光位相変調器１００は、基板１０と、第１の電極２０ａおよび第２の電極２０ｂと、電気光学材料層３０と、電解質層４０と、制御回路５０とを備える。 The optical phase modulator 100 includes a substrate 10, a first electrode 20a and a second electrode 20b, an electro-optical material layer 30, an electrolyte layer 40, and a control circuit 50.
　基板１０は、ＸＹ平面に平行な主面１０ｓを有する。第１の電極２０ａは、基板１０の主面１０ｓ上に位置する。電気光学材料層３０は、第１の電極２０ａ上に位置する。電解質層４０は、電気光学材料層３０上に位置する。第２の電極２０ｂは、電解質層４０上に位置する。すなわち、基板１０、第１の電極２０ａ、電気光学材料層３０、電解質層４０、および第２の電極２０ｂは、この順に積層されている。第１の電極２０ａおよび第２の電極２０ｂを、「一対の電極２０」と称することがある。基板１０と、第１の電極２０ａおよび第２の電極２０ｂと、電気光学材料層３０と、電解質層４０とは、少なくともＸ方向に延びた構造を有する。 The substrate 10 has a main surface 10s parallel to the XY plane. The first electrode 20a is located on the main surface 10s of the substrate 10. The electro-optical material layer 30 is located on the first electrode 20a. The electrolyte layer 40 is located on the electro-optical material layer 30. The second electrode 20b is located on the electrolyte layer 40. That is, the substrate 10, the first electrode 20a, the electro-optical material layer 30, the electrolyte layer 40, and the second electrode 20b are laminated in this order. The first electrode 20a and the second electrode 20b may be referred to as a "pair of electrodes 20". The substrate 10, the first electrode 20a and the second electrode 20b, the electro-optical material layer 30, and the electrolyte layer 40 have a structure extending at least in the X direction.
　以下に、各構成要素をより具体的に説明する。 Each component will be described in more detail below.
　基板１０は、一対の電極２０、電気光学材料層３０、および電解質層４０を支持する。基板１０は、例えば、酸化マグネシウム（ＭｇＯ）、スピネル（ＭｇＡｌ２Ｏ４）、およびα－アルミナ（α－Ａｌ２Ｏ３）からなる群から選択される少なくとも１つから形成され得る。基板１０は、不要であれば省略してもよい。 The substrate 10 supports a pair of electrodes 20, an electro-optical material layer 30, and an electrolyte layer 40. The substrate 10 can be formed from, for example, at least one selected from the group consisting of magnesium oxide (MgO), spinel (MgAl 2 O 4 ), and α-alumina (α-Al 2 O 3 ). The substrate 10 may be omitted if it is unnecessary.
　一対の電極２０は、Ｚ方向において、電気光学材料層３０および電解質層４０を直接的または間接的に挟む。「直接的に挟む」とは、第１の電極２０ａと電気光学材料層３０とが接し、第２の電極２０ｂと電解質層４０とが接することを意味する。「間接的に挟む」とは、第１の電極２０ａと電気光学材料層３０との間、および／または、第２の電極２０ｂと電解質層４０との間に他の部材が位置することを意味する。当該他の部材は、誘電体部材であってもよいし、空気などの気体であってもよし、水などの液体であってもよい。本明細書では、Ｘ方向を「第１の方向」と称することがある。 The pair of electrodes 20 directly or indirectly sandwich the electro-optical material layer 30 and the electrolyte layer 40 in the Z direction. “Directly sandwiching” means that the first electrode 20a and the electro-optical material layer 30 are in contact with each other, and the second electrode 20b and the electrolyte layer 40 are in contact with each other. "Indirectly sandwiching" means that another member is located between the first electrode 20a and the electro-optical material layer 30 and / or between the second electrode 20b and the electrolyte layer 40. To do. The other member may be a dielectric member, a gas such as air, or a liquid such as water. In the present specification, the X direction may be referred to as a "first direction".
　一対の電極２０の各々は、ＸＹ平面に平行な面を有する。一対の電極２０には、直流電圧が印加される。これにより、電気光学材料層３０および電解質層４０に、電界が印加される。直流電圧は、直流パルス電圧であってもよい。直流パルス電圧の電圧値の時間平均を直流電圧の値として扱ってもよい。直流パルス電圧のデューティ比を変えることにより、電圧の時間平均値を調整することができる。一対の電極２０の各々は、金属電極であってもよいし、透明電極であってもよい。第１の電極２０ａは、例えば、ＬａドープＳｒＳｎＯ３（ＬＳＳＯ）、およびＡドープＳｒｘＢａ１－ｘＳｎＯ３（Ａ＝Ｌａ、Ｔａ、またはＮｂ）からなる群から選択された少なくとも１つから形成された透明電極であり得る。第１の電極２０ａの厚さは、例えば１００ｎｍ以上２００ｎｍ以下であり得る。第２の電極２０ｂは、例えば、ＳｎＯ２ドープＩｎ２Ｏ３（ＩＴＯ）、ＦドープＳｎＯ２（ＦＴＯ）、およびＳｂドープＴｉＯ２（ＡＴＯ）からなる群から選択された少なくとも１つから形成された透明電極であり得る。第２の電極２０ｂの厚さは、例えば１００ｎｍ以上２００ｎｍ以下であり得る。 Each of the pair of electrodes 20 has a plane parallel to the XY plane. A DC voltage is applied to the pair of electrodes 20. As a result, an electric field is applied to the electro-optical material layer 30 and the electrolyte layer 40. The DC voltage may be a DC pulse voltage. The time average of the voltage value of the DC pulse voltage may be treated as the value of the DC voltage. By changing the duty ratio of the DC pulse voltage, the time average value of the voltage can be adjusted. Each of the pair of electrodes 20 may be a metal electrode or a transparent electrode. The first electrode 20a is formed from, for example, at least one selected from the group consisting of La-doped SrSnO 3 (LSSO) and A-doped Sr x Ba 1-x SnO 3 (A = La, Ta, or Nb). It can be a transparent electrode. The thickness of the first electrode 20a can be, for example, 100 nm or more and 200 nm or less. The second electrode 20b was formed from, for example, at least one selected from the group consisting of SnO 2- doped In 2 O 3 (ITO), F-doped SnO 2 (FTO), and Sb-doped TiO 2 (ATO). It can be a transparent electrode. The thickness of the second electrode 20b can be, for example, 100 nm or more and 200 nm or less.
　電気光学材料層３０は、図１Ｂに示すように、全反射によって光３２をＸ方向に沿って伝搬させる光導波層として機能する。図１Ａに示す楕円は、光３２の強度が当該楕円内で高いことを表している。電気光学材料層３０の屈折率は、光位相変調器１００の周辺の媒質の屈折率、ならびに基板１０および電解質層４０のそれぞれの屈折率よりも高い。第１の電極２０ａが透明電極である場合、電気光学材料層３０の屈折率は、第１の電極２０ａの屈折率よりも高い。第１の電極２０ａの屈折率は、基板１０の屈折率よりも高い。これにより、基板１０は光導波層として機能しない。第１の電極２０ａが透明電極である場合、光３２のロスは無視できる。 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 ellipse shown in FIG. 1A indicates that the intensity of the light 32 is high within the ellipse. The refractive index of the electro-optical material layer 30 is higher than the refractive index of the medium around the optical phase modulator 100 and the refractive index of each of the substrate 10 and the electrolyte layer 40. When the first electrode 20a is a transparent electrode, the refractive index of the electro-optical material layer 30 is higher than the refractive index of the first electrode 20a. The refractive index of the first electrode 20a is higher than that of the substrate 10. As a result, the substrate 10 does not function as an optical waveguide layer. When the first electrode 20a is a transparent electrode, the loss of light 32 can be ignored.
　電気光学材料層３０の屈折率は、ポッケルス効果またはカー効果により、印加された電界の強度に応じて変化する。印加された電界が強いほど、電気光学材料層３０の屈折率の変化量が大きくなる。電界を印加しないときは、当該変化量はゼロになる。この点で、本実施形態の装置は、前述のエレクトロクロミック効果を利用した装置とは異なる。本実施形態によれば、電圧が印加されているときだけ屈折率が初期値から変化するので、光位相変調器１００のオンおよびオフが容易である。電界の印加による電気光学材料層３０の屈折率の変化により、電気光学材料層３０内を伝搬する光３２の位相を変調することができる。電気光学効果の速い応答性により、位相の変調速度は高く、例えば数十ＭＨｚ以上にすることができる。 The refractive index of the electro-optical material layer 30 changes according to the strength of the applied electric field due to the Pockels effect or the Kerr effect. The stronger the applied electric field, the greater the amount of change in the refractive index of the electro-optical material layer 30. When no electric field is applied, the amount of change becomes zero. In this respect, the apparatus of this embodiment is different from the apparatus utilizing the electrochromic effect described above. According to this embodiment, since the refractive index changes from the initial value only when a voltage is applied, it is easy to turn on and off the optical phase modulator 100. The phase of the light 32 propagating in the electro-optical material layer 30 can be modulated by the change in the refractive index of the electro-optical material layer 30 due to the application of an electric field. Due to the fast response of the electro-optic effect, the phase modulation rate can be high, for example, several tens of MHz or higher.
　光３２の空気中での波長をλ、電界が印加されていないときの電気光学材料層３０の屈折率をｎ０、電界の印加による電気光学材料層３０の屈折率の変化量をΔｎ、電気光学材料層３０の長さをＬ、電気光学材料層３０を伝搬する前の光３２の位相をφ＝０とする。このとき、電気光学材料層３０を伝搬した後の光３２の位相は、φ＝（２π／λ）（ｎ０＋Δｎ）Ｌである。このうち、電界の印加による光３２の位相の変化量は、Δφ＝（２π／λ）ΔｎＬである。 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 amount of change in the refractive index of the electro-optical material layer 30 due to the application of an electric field is Δn, and electricity. The length of the optical material layer 30 is L, and the phase of the light 32 before propagating through the electro-optical material layer 30 is φ = 0. At this time, the phase of the light 32 after propagating through the electro-optical material layer 30 is φ = (2π / λ) (n 0 + Δn) L. Of these, the amount of change in the phase of the light 32 due to the application of an electric field is Δφ = (2π / λ) ΔnL.
　前述のように、第１の電極２０ａおよび第２の電極２０ｂの各々は、透明電極であってもよいし、金属電極であってもよい。第１の電極２０ａが透明電極である場合、光３２のロスは無視できる。電解質層４０の厚さが十分に大きい場合、光３２のエバネッセント光は、第２の電極２０ｂまで達しない。したがって、電解質層４０の厚さが十分に大きい場合は、第２の電極２０ｂが金属電極であっても、光３２のロスは無視できる。 As described above, each of the first electrode 20a and the second electrode 20b may be a transparent electrode or a metal electrode. When the first electrode 20a is a transparent electrode, the loss of light 32 can be ignored. If the thickness of the electrolyte layer 40 is sufficiently large, the evanescent light of the light 32 does not reach the second electrode 20b. Therefore, when the thickness of the electrolyte layer 40 is sufficiently large, the loss of light 32 can be ignored even if the second electrode 20b is a metal electrode.
　電気光学材料層３０は、バルクから形成されていてもよいし、薄膜から形成されていてもよい。薄膜の厚さは、例えば０．１μｍ以上１０μｍ以下であり得る。薄膜のコストは、バルクのコストよりも低い。ポッケルス効果を用いる場合、電気光学材料層３０は、例えば、ニオブ酸リチウム（ＬｉＮｂＯ３）、タンタル酸リチウム（ＬｉＴａＯ３）、リン酸二水素カリウム（ＫＨ２ＰＯ４）、およびリン酸二水素アンモニウム（ＮＨ４Ｈ２ＰＯ４）からなる群から選択される少なくとも１つから形成され得る。カー効果を用いる場合、電気光学材料層３０は、例えば、例えば、チタン酸バリウム（ＢａＴｉＯ３）、チタン酸ストロンチウム（ＳｒＴｉＯ３）、チタン酸カリウム（ＫＴａＯ３）、ジルコン酸チタン酸鉛ランタン（（Ｐｂ１－ｘＬａｘ）（ＺｒｙＴｉ１－ｙ）１－ｘ／４Ｏ３：ＰＬＺＴ）、およびタンタル酸ニオブ酸カリウム（ＫＴａ１－ｘＮｂｘＯ３：ＫＴＮ）からなる群から選択される少なくとも１つから形成され得る。この中でも、ＫＴＮは、ＮｂとＴａとの組成比を適切な比に設定することにより、常温付近で高い電気光学効果を示す。ＫＴＮは、光通信に用いられる光の波長１５５０ｎｍで透明である。したがって、ＫＴＮの光デバイスへの応用が期待されている。なお、電気光学材料層３０は、エレクトロクロミック効果などの他の電気光学効果を示す材料から形成されていてもよい。 The electro-optical material layer 30 may be formed from a bulk or a thin film. The thickness of the thin film can be, for example, 0.1 μm or more and 10 μm or less. The cost of thin films is lower than the cost of bulk. When the Pockels effect is used, the electro-optical material layer 30 is composed of, for example, lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), potassium dihydrogen phosphate (KH 2 PO 4 ), and ammonium dihydrogen phosphate (KH 2 PO 4 ). It can be formed from at least one selected from the group consisting of NH 4 H 2 PO 4 ). When using the Kerr effect, the electro-optical material layer 30 is, for example, for example, barium titanate (BaTiO 3), strontium titanate (SrTiO 3), potassium titanate (KTaO 3), zirconate lead lanthanum titanate ((Pb 1-x La x) (Zr y Ti 1-y) 1-x / 4 O 3: PLZT), and potassium tantalate niobate (KTa 1-x Nb x O 3: is selected from the group consisting of KTN) It can be formed from at least one. Among these, KTN exhibits a high electro-optical effect near room temperature by setting the composition ratio of Nb and Ta to an appropriate ratio. KTN is transparent at a wavelength of 1550 nm for light used in optical communication. Therefore, application of KTN to optical devices is expected. The electro-optical material layer 30 may be formed of a material exhibiting other electro-optical effects such as the electrochromic effect.
　電解質層４０は、電気光学材料層３０の少なくとも一部に接している。電解質層４０は、少なくともＸ方向に延びた構造を有する。電解質層４０は、イオン伝導体から形成されている。イオン伝導体では、正イオンおよび負イオンの少なくとも一方が、外部からの電界印加によって移動する。電解質層４０は、典型的には固体電解質層である。固体電解質層は、その組成に応じて、１０－８Ｓ／ｃｍから１０－２Ｓ／ｃｍ程度のオーダーのイオン伝導度を有し得る。電解質層４０の材料については、後述する。 The electrolyte layer 40 is in contact with at least a part of the electro-optical material layer 30. The electrolyte layer 40 has a structure extending at least in the X direction. The electrolyte layer 40 is formed of an ionic conductor. In an ionic conductor, at least one of a positive ion and a negative ion moves by applying an electric field from the outside. The electrolyte layer 40 is typically a solid electrolyte layer. The solid electrolyte layer, depending on its composition, may have a 10 -2 S / cm order of the order of the ion conductivity of 10 -8 S / cm. The material of the electrolyte layer 40 will be described later.
　制御回路５０は、一対の電極２０に直流電圧を印加する。図１Ａに示す矢印付きの破線は、制御回路５０から一対の電極２０に信号が入力されることを表している。制御回路５０は、一対の電極２０に電圧を印加して電気光学材料層３０の屈折率を変化させることにより、電気光学材料層３０を伝搬する光３２の位相を変調する。制御回路５０は、例えばデジタルシグナルプロセッサ（ＤＳＰ）、フィールドプログラマブルゲートアレイ（ＦＰＧＡ）などのプログラマブルロジックデバイス（ＰＬＤ）、または中央演算処理装置（ＣＰＵ）もしくは画像処理用演算プロセッサ（ＧＰＵ）とコンピュータプログラムとの組み合わせによって実現されてもよい。なお、以下の図では、制御回路５０を省略することがある。 The control circuit 50 applies a DC voltage to the pair of electrodes 20. The broken line with an arrow shown in FIG. 1A indicates that a signal is input from the control circuit 50 to the pair of electrodes 20. The control circuit 50 modulates the phase of the light 32 propagating in the electro-optical material layer 30 by applying a voltage to the pair of electrodes 20 to change the refractive index of the electro-optical material layer 30. The control circuit 50 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. In the following figure, the control circuit 50 may be omitted.
　図２Ａは、一対の電極２０に電圧を印加した場合における、一対の電極２０、電気光学材料層３０、および電解質層４０内の電荷分布を模式的に示す図である。図２Ａの上段は、図１に示す光位相変調器１００を表している。図２Ａの下の図は、上の図に示す太線によって囲まれた領域における電荷分布の例を模式的に表している。第２の電極２０ｂの電位が第１の電極２０ａの電位よりも高い場合、一対の電極２０間には、下向きの電界が発生する。図２Ａの下の図は、このときの第１の電極２０ａ内の負の電荷（－）、第２の電極２０ｂ内の正の電荷（＋）、電気光学材料層３０内の分極（＋－）、ならびに電解質層４０内の正イオン（＋）および負イオン（－）の分布を模式的に表している。 FIG. 2A is a diagram schematically showing the charge distribution in the pair of electrodes 20, the electro-optical material layer 30, and the electrolyte layer 40 when a voltage is applied to the pair of electrodes 20. The upper part of FIG. 2A represents the optical phase modulator 100 shown in FIG. The lower figure of FIG. 2A schematically shows an example of charge distribution in the region surrounded by the thick line shown in the upper figure. When the potential of the second electrode 20b is higher than the potential of the first electrode 20a, a downward electric field is generated between the pair of electrodes 20. The lower figure of FIG. 2A shows the negative charge (−) in the first electrode 20a, the positive charge (+) in the second electrode 20b, and the polarization (+ −) in the electro-optical material layer 30 at this time. ), And the distribution of positive ions (+) and negative ions (−) in the electrolyte layer 40 is schematically shown.
　第１の電極２０ａに含まれる負の電荷は、電気光学材料層３０の側に分布する。第２の電極２０ｂに含まれる正の電荷は、電解質層４０の側に分布する。一対の電極２０の間に発生する下方向の電界により、電解質層４０に含まれるイオンのうち、正イオンは、電気光学材料層３０の側に移動し、負イオンは、第２の電極２０ｂの側に移動する。電気光学材料層３０内では、正の電荷および負の電荷を一対とする分極が発生する。電解質層４０内の正イオンおよび負イオンの移動に起因して、電気光学材料層３０と電解質層４０との界面３５には、破線によって囲まれた電気二重層が形成される。同様に、電解質層４０と第２の電極２０ｂとの界面にも、破線によって囲まれた電気二重層が形成される。電気二重層は、キャパシタとして機能する。 The negative charge contained in the first electrode 20a is distributed on the side of the electro-optical material layer 30. The positive charge contained in the second electrode 20b is distributed on the side of the electrolyte layer 40. Due to the downward electric field generated between the pair of electrodes 20, positive ions among the ions contained in the electrolyte layer 40 move toward the electro-optical material layer 30, and negative ions move to the side of the second electrode 20b. Move to the side. Within the electro-optical material layer 30, polarization of a pair of positive and negative charges occurs. Due to the movement of positive and negative ions in the electrolyte layer 40, an electric double layer surrounded by a broken line is formed at the interface 35 between the electro-optical material layer 30 and the electrolyte layer 40. Similarly, an electric double layer surrounded by a broken line is formed at the interface between the electrolyte layer 40 and the second electrode 20b. The electric double layer functions as a capacitor.
　次に、図２Ｂおよび図２Ｃを参照して、電気光学材料層３０、および電解質層４０内に生じる電位および電界の強度を説明する。ただし、電気光学材料層３０は、キャリア注入されたＫＴＮから形成されているとする。 Next, with reference to FIGS. 2B and 2C, the strengths of the electric potentials and electric fields generated in the electro-optical material layer 30 and the electrolyte layer 40 will be described. However, it is assumed that the electro-optical material layer 30 is formed from carrier-injected KTN.
　図２Ｂは、一対の電極２０間での、第１の電極２０ａの上面からＺ方向に沿った距離Ｚと、電位Ｖとの関係を模式的に示す図である。Ｚ＝０は、第１の電極２０ａの上面の位置を表している。Ｚ＝Ｚ１は、電気光学材料層３０と電解質層４０との界面３５の位置を表している。Ｚ＝Ｚ２は、第２の電極２０ｂの下面の位置を表している。Ｖ１は、第１の電極２０ａの電位を表し、Ｖ２は、第２の電極２０ｂの電位を表している。Ｚ＝Ｚ１付近およびＺ＝Ｚ２付近では、電気二重層の形成により、電位Ｖが、距離Ｚの増加に伴い急峻に増加する。電気光学材料層３０のうち、Ｚ＝Ｚ１から離れた部分では、電位Ｖは、上記のキャリア注入に起因して、距離Ｚの増加に伴いほぼ放物線的に増加する。電解質層４０のうち、Ｚ＝Ｚ１およびＺ＝Ｚ２から離れた部分では、電位Ｖはほぼ一定である。 FIG. 2B is a diagram schematically showing the relationship between the potential V and the distance Z along the Z direction from the upper surface of the first electrode 20a between the pair of electrodes 20. Z = 0 represents the position of the upper surface of the first electrode 20a. Z = Z 1 represents the position of the interface 35 between the electro-optical material layer 30 and the electrolyte layer 40. Z = Z 2 represents the position of the lower surface of the second electrode 20b. V 1 represents the potential of the first electrode 20a, and V 2 represents the potential of the second electrode 20b. In the vicinity of Z = Z 1 and in the vicinity of Z = Z 2 , the potential V sharply increases as the distance Z increases due to the formation of the electric double layer. In the portion of the electro-optical material layer 30 away from Z = Z 1 , the potential V increases substantially parabolic with the increase in distance Z due to the carrier injection described above. In the portion of the electrolyte layer 40 away from Z = Z 1 and Z = Z 2 , the potential V is substantially constant.
　図２Ｃは、一対の電極２０間での、第１の電極２０ａの上面からＺ方向に沿った距離Ｚと、電界の強度Ｅとの関係を模式的に示す図である。図２Ｃに示す電界の強度Ｅは、図２Ｂに示す電位Ｖの勾配の絶対値に相当する。電気光学材料層３０のうち、Ｚ＝Ｚ１から離れた部分では、電界の強度Ｅは、距離Ｚの増加に伴い、ほぼ直線的に増加する。電気光学材料層３０のうち、Ｚ＝Ｚ１付近の部分では、電界の強度Ｅは、最大になる（Ｅ＝Ｅｍ）。電解質層４０のうち、Ｚ＝Ｚ１付近の部分では、電界の強度Ｅは、距離Ｚの増加に伴い急峻に減少する。電解質層４０のうち、Ｚ＝Ｚ１およびＺ＝Ｚ２から離れた部分では、電界の強度Ｅはほぼゼロである（Ｅ＝０）。電解質層４０のうち、Ｚ＝Ｚ２付近の部分では、電界の強度Ｅは、距離Ｚの増加に伴い急峻に増加する。 FIG. 2C is a diagram schematically showing the relationship between the distance Z between the pair of electrodes 20 along the Z direction from the upper surface of the first electrode 20a and the strength E of the electric field. The electric field strength E shown in FIG. 2C corresponds to the absolute value of the gradient of the potential V shown in FIG. 2B. In the portion of the electro-optical material layer 30 away from Z = Z 1 , the electric field strength E increases substantially linearly as the distance Z increases. In the portion of the electro-optical material layer 30 near Z = Z 1 , the electric field strength E becomes maximum (E = Em ). In the portion of the electrolyte layer 40 near Z = Z 1 , the electric field strength E sharply decreases as the distance Z increases. In the portion of the electrolyte layer 40 away from Z = Z 1 and Z = Z 2 , the electric field strength E is almost zero (E = 0). In the portion of the electrolyte layer 40 near Z = Z 2 , the strength E of the electric field sharply increases as the distance Z increases.
　図２Ｃに示すように、電気光学材料層３０のうち、界面３５付近の部分では、Ｅｍの強度を有する強い電界が発生する。当該電界の強度が局所的に絶縁破壊電界の強度を超えていても、電気光学材料層３０は破壊されない。絶縁破壊電界の制限がないことから、電気光学材料層３０のうち、界面３５付近の部分の屈折率の変化量は、例えば１０－２以上のオーダーになることが期待できる。当該屈折率の変化量は、電解質層４０がない場合と比較して大きい。一方、界面３５付近から離れた部分の屈折率の変化量は平均して１０－３程度のオーダーである。このように、電気光学材料層３０の屈折率の変化量は、場所によって異なる。簡単のために、電気光学材料層３０の屈折率の変化量の空間での平均値を、電気光学材料層３０の屈折率の変化量Δｎとしてもよい。 As shown in Figure 2C, of the electro-optic material layer 30, in the portion near the interface 35, a strong electric field having an intensity of E m is generated. Even if the strength of the electric field locally exceeds the strength of the dielectric breakdown electric field, the electro-optical material layer 30 is not destroyed. Since there is no limitation on the dielectric breakdown electric field, the amount of change in the refractive index of the portion of the electro-optical material layer 30 near the interface 35 can be expected to be on the order of, for example, 10-2 or more. The amount of change in the refractive index is larger than that in the case without the electrolyte layer 40. On the other hand, the amount of change in the refractive index of the portion away from the interface 35 is on the order of about 10-3 on average. As described above, the amount of change in the refractive index of the electro-optical material layer 30 varies depending on the location. For simplicity, the average value of the change in the refractive index of the electro-optical material layer 30 in space may be the change Δn in the refractive index of the electro-optical material layer 30.
　以上の構成により、光位相変調器１００では、速い応答性の電気光学効果を用いて、電気光学材料層３０を伝搬する光３２の位相を大きくかつ高速に変調することができる。 With the above configuration, the optical phase modulator 100 can modulate the phase of the light 32 propagating through the electro-optical material layer 30 at a large speed and at high speed by using a fast-responsive electro-optical effect.
　本実施形態における電気光学材料層３０と電解質層４０との界面３５は平坦である。界面３５は必ずしも厳密に平坦でなくてもよく、多少の傾斜または凹部もしくは凸部を有する部分が存在していてもよい。しかし、界面３５が全体にわたって凹部または凸部を有する場合、凹部または凸部で発生する電界が弱め合い、界面３５付近には、強い電界が集中しない可能性がある。その場合、電気光学材料層３０のうち、界面３５付近の部分の屈折率の変化量が小さくなる可能性がある。また、界面３５の凹部または凸部による光３２の散乱により、光３２のロスが生じ得る。これに対し、界面３５が平坦である場合、界面３５付近には、Ｚ方向に強い電界が集中する。これにより、電気光学材料層３０の界面３５付近の部分の屈折率の変化量を大きくできる。また、平坦な界面３５により、光３２のロスが抑制される。 The interface 35 between the electro-optical material layer 30 and the electrolyte layer 40 in this embodiment is flat. The interface 35 does not necessarily have to be strictly flat and may have a portion having some inclination or recesses or protrusions. However, when the interface 35 has a concave portion or a convex portion as a whole, the electric fields generated in the concave portion or the convex portion may weaken each other, and a strong electric field may not be concentrated in the vicinity of the interface 35. In that case, the amount of change in the refractive index of the portion of the electro-optical material layer 30 near the interface 35 may be small. Further, the light 32 may be lost due to the scattering of the light 32 by the concave or convex portion of the interface 35. On the other hand, when the interface 35 is flat, a strong electric field is concentrated in the Z direction near the interface 35. As a result, the amount of change in the refractive index of the portion of the electro-optical material layer 30 near the interface 35 can be increased. Further, the flat interface 35 suppresses the loss of light 32.
　電気光学材料層３０の屈折率の変化量は、テンソルによって記述される。したがって、印加された電界の方向に応じて、電気光学材料層３０の屈折率は、複数の方向において変化し得る。電気光学材料層３０の屈折率の変化量は、当該複数の方向に応じて異なる。図１Ａおよび図１Ｂに示す例において、Ｚ方向に沿って配向した結晶構造を有する電気光学材料層３０に、電界をＺ方向に印加すると、電気光学材料層３０の屈折率は、Ｘ方向、Ｙ方向、およびＺ方向において変化する。電気光学材料層３０の屈折率の変化量は、Ｚ方向において最大になる。これにより、ＴＭ（ｔｒａｎｓｖｅｒｓｅ　ｍａｇｎｅｔｉｃ）モードでの光３２の位相を大きく変調することができる。ＴＭモードでの光３２は、Ｚ方向に平行な電界を有する。 The amount of change in the refractive index of the electro-optical material layer 30 is described by a tensor. Therefore, the refractive index of the electro-optical material layer 30 can change in a plurality of directions depending on the direction of the applied electric field. The amount of change in the refractive index of the electro-optical material layer 30 differs depending on the plurality of directions. In the examples shown in FIGS. 1A and 1B, when an electric field is applied to the electro-optical material layer 30 having a crystal structure oriented along the Z direction, the refractive index of the electro-optical material layer 30 changes in the X direction and Y. It changes in the direction and the Z direction. The amount of change in the refractive index of the electro-optical material layer 30 becomes maximum in the Z direction. As a result, the phase of the light 32 in the TM (transverse magnetic) mode can be greatly modulated. The light 32 in the TM mode has an electric field parallel to the Z direction.
　電気光学材料層３０が、所定値以上の幅および厚さを有するとき、導波モードが存在する。これにより、電気光学材料層３０は、光導波層として機能する。電気光学材料層３０の幅および厚さは、Ｘ方向に沿って光３２を伝搬させる光導波層を形成する値に設定されている。 A waveguide mode exists when the electro-optical material layer 30 has a width and thickness equal to or greater than a predetermined value. As a result, the electro-optical material layer 30 functions as an optical waveguide layer. The width and thickness of the electro-optical material layer 30 are set to values that form an optical waveguide layer that propagates light 32 along the X direction.
　（電解質層４０の材料）
　次に、電解質層４０の材料を、詳細に説明する。本開示では、電解質層４０は、ＬｉｘＺｒｚＳｉ１－ｚＯｙ（ｘ＞０、ｙ＝ｘ／２＋２、０≦ｚ≦１）（ＬＺＳＯ）によって表される物質から形成されている。以下に、ＬＺＳＯ層のＬｉイオン伝導度および表面の粗さを説明する。 (Material of electrolyte layer 40)
Next, the material of the electrolyte layer 40 will be described in detail. In this disclosure, the electrolyte layer 40 is formed from Li x Zr z Si 1-z O y (x> 0, y = x / 2 + 2,0 ≦ z ≦ 1) material represented by (LZSO). The Li ion conductivity and surface roughness of the LZSO layer will be described below.
　図３は、代表的な値としてｘ＝１、ｘ＝２、およびｘ＝４のＬＺＳＯ層のＬｉイオン伝導度および表面の粗さを示す図である。これらの例では、ｚ＝０．５である。ｘ＝１のＬＺＳＯ層は、ＬｉＺｒ０．５Ｓｉ０．５Ｏ２．５から形成されている。ｘ＝２のＬＺＳＯ層は、Ｌｉ２Ｚｒ０．５Ｓｉ０．５Ｏ３から形成されている。ｘ＝４のＬＺＳＯ層は、Ｌｉ４Ｚｒ０．５Ｓｉ０．５Ｏ４から形成されている。左下、左上、および右上の挿入図は、それぞれ、Ｓｉ基板上に、後述するパルスレーザ堆積（Ｐｕｌｓｅｄ　Ｌａｓｅｒ　Ｄｅｐｏｓｉｔｉｏｎ：ＰＬＤ）法によって堆積されたｘ＝１、ｘ＝２、およびｘ＝４のＬＺＳＯ層の断面を示す走査電子顕微鏡図である。左下、および左上の挿入図に示す例では、ｘ＝１のＬＺＳＯ層とＳｉ基板との間、およびｘ＝２のＬＺＳＯ層とＳｉ基板との間に、それぞれ、非常に薄いＳｉＯｘ層が形成されている。右上の挿入図に示す例では、ｘ＝４のＬＺＳＯ層とＳｉ基板との間に、厚さ２５０ｎｍ程度のＳｉＯｘ層が形成されている。 FIG. 3 is a diagram showing the Li ion conductivity and surface roughness of the LZSO layer having x = 1, x = 2, and x = 4 as typical values. In these examples, z = 0.5. The LZSO layer with x = 1 is formed from LiZr 0.5 Si 0.5 O 2.5 . The LZSO layer with x = 2 is formed from Li 2 Zr 0.5 Si 0.5 O 3 . The LZSO layer with x = 4 is formed from Li 4 Zr 0.5 Si 0.5 O 4 . The lower left, upper left, and upper right insets show the x = 1, x = 2, and x = 4 LZSO layers deposited on a Si substrate by the Pulsed Laser Deposition (PLD) method described below, respectively. It is a scanning electron microscope view which shows the cross section of. In the examples shown in the lower left and upper left insets, very thin SiO x layers are formed between the LZSO layer with x = 1 and the Si substrate, and between the LZSO layer with x = 2 and the Si substrate, respectively. Has been done. In the example shown in the insertion view on the upper right, a SiO x layer having a thickness of about 250 nm is formed between the LZSO layer having x = 4 and the Si substrate.
　ｘ＝１のＬＺＳＯ層のＬｉイオン伝導度は、４．０×１０－８Ｓ／ｃｍである。左下の挿入図に示すように、ｘ＝１のＬＺＳＯ層の表面は、平坦である。ｘ＝２のＬＺＳＯ層のＬｉイオン伝導度は、４．０×１０－８Ｓ／ｃｍである。左上の挿入図に示すように、ｘ＝２のＬＺＳＯ層の表面は、ｘ＝１のＬＺＳＯ層の表面よりも粗くなる。ｘ＝４のＬＺＳＯ層のＬｉイオン伝導度は、２．０×１０－７Ｓ／ｃｍである。ｘ＝４のＬＺＳＯ層のＬｉイオン伝導度は、ｘ＝１およびｘ＝２のＬＺＳＯ層のＬｉイオン伝導度よりも高い。右上の挿入図に示すように、ｘ＝４のＬＺＳＯ層の表面は、ｘ＝２のＬＺＳＯ層の表面よりも粗くなる。 The Li ion conductivity of the LZSO layer with x = 1 is 4.0 × 10-8 S / cm. As shown in the lower left inset, the surface of the LZSO layer with x = 1 is flat. The Li ion conductivity of the LZSO layer with x = 2 is 4.0 × 10-8 S / cm. As shown in the upper left inset, the surface of the LZSO layer with x = 2 is rougher than the surface of the LZSO layer with x = 1. The Li ion conductivity of the LZSO layer with x = 4 is 2.0 × 10-7 S / cm. The Li-ion conductivity of the LZSO layer of x = 4 is higher than the Li-ion conductivity of the LZSO layer of x = 1 and x = 2. As shown in the upper right inset, the surface of the LZSO layer with x = 4 is rougher than the surface of the LZSO layer with x = 2.
　Ｌｉ量が増加すると、ＬＺＳＯ層の表面が粗くなる。これは、Ｌｉと空気中のＣＯ２との反応により、ＬＺＳＯ層の表面に炭酸リチウムなどの炭酸塩が析出するからである。したがって、ＬＺＳＯ層中のＬｉ量が少なければ、ＬＺＳＯ層の表面の平坦性を向上させることができる。一方、ＬＺＳＯ層中のＬｉ量が少なすぎると、Ｌｉイオン伝導度が減少する。ＬＺＳＯ層のＬｉイオン伝導度が１０－８Ｓ／ｃｍ程度のオーダー以上であれば、界面３５付近に強い電界を発生させることができる。以上から、１≦ｘ≦４のとき、少なくともＬｉイオン伝導度の有効性が満たされる。上限のｘ＝４は、化学量論組成に基づいている。さらに、ｘ＝１のとき、ＬＺＳＯ層の表面の平坦性、およびＬｉイオン伝導度の有効性の両方が満たされる。ｚ＞０のとき、ＬＺＳＯ層中のＬｉイオン伝導度は、ｚ＝０のときと比較して増加する。 As the amount of Li increases, the surface of the LZSO layer becomes rough. This is because carbonates such as lithium carbonate are precipitated on the surface of the LZSO layer by the reaction between Li and CO 2 in the air. Therefore, if the amount of Li in the LZSO layer is small, the flatness of the surface of the LZSO layer can be improved. On the other hand, if the amount of Li in the LZSO layer is too small, the Li ion conductivity decreases. If the Li ion conductivity of the LZSO layer is on the order of about 10-8 S / cm or more, a strong electric field can be generated near the interface 35. From the above, when 1 ≦ x ≦ 4, at least the effectiveness of Li ion conductivity is satisfied. The upper limit x = 4 is based on the stoichiometric composition. Furthermore, when x = 1, both the flatness of the surface of the LZSO layer and the effectiveness of the Li ion conductivity are satisfied. When z> 0, the Li ion conductivity in the LZSO layer increases as compared with the case of z = 0.
　上記の議論は、図３に示すＳｉ基板上に形成されたＬＺＳＯ層以外に、電気光学材料層３０であるＫＴＮ層上に形成されたＬＺＳＯ層についても成り立つ。ＬＺＳＯ層は、Ｓｉ基板およびＫＴＮ層のどちらの上にもアモルファス相で形成することができる。ＬＺＳＯ層のＬｉイオン伝導度および表面の粗さは、ＬＺＳＯ層の下地がＳｉ基板であるかＫＴＮ層であるかにかかわらず、ＬＺＳＯ層中のＬｉ量によって決定される。 The above discussion holds true for the LZSO layer formed on the KTN layer, which is the electro-optical material layer 30, in addition to the LZSO layer formed on the Si substrate shown in FIG. The LZSO layer can be formed in an amorphous phase on both the Si substrate and the KTN layer. The Li ion conductivity and surface roughness of the LZSO layer are determined by the amount of Li in the LZSO layer regardless of whether the base of the LZSO layer is a Si substrate or a KTN layer.
　ＬＺＳＯ層が結晶構造を有する場合、ＫＴＮ層上に、結晶構造を有するＬＺＳＯ層を堆積するために、温度制御が行われる。当該温度制御により、ＫＴＮ層とＬＺＳＯ層とが熱拡散する可能性がある。その結果、界面３５が粗くなり得る。これに対し、ＬＺＳＯ層がアモルファス構造を有する場合、加熱または冷却の温度制御をせずに、室温で、ＫＴＮ層上にＬＺＳＯ層を堆積することができる。これにより、ＫＴＮ層とＬＺＳＯ層との熱拡散が抑制される。その結果、界面３５は平坦になる。温度制御が不必要であることから、ＬＺＳＯ層のＫＴＮ層上への堆積が容易になる。前述したように、界面３５が平坦であると、界面３５付近に強い電界が発生しやすくなる。さらに、散乱による光３２のロスを抑制することができる。 When the LZSO layer has a crystal structure, temperature control is performed in order to deposit the LZSO layer having a crystal structure on the KTN layer. Due to the temperature control, the KTN layer and the LZSO layer may be thermally diffused. As a result, the interface 35 can be rough. On the other hand, when the LZSO layer has an amorphous structure, the LZSO layer can be deposited on the KTN layer at room temperature without controlling the temperature of heating or cooling. As a result, heat diffusion between the KTN layer and the LZSO layer is suppressed. As a result, the interface 35 becomes flat. Since no temperature control is required, the LZSO layer can be easily deposited on the KTN layer. As described above, when the interface 35 is flat, a strong electric field is likely to be generated in the vicinity of the interface 35. Further, the loss of light 32 due to scattering can be suppressed.
　電解質層４０の厚さは、例えば５００ｎｍ以上２．５μｍ以下であり得る。電解質層４０の厚さが５００ｎｍより薄いと、光３２のエバネッセント光が、第２の電極２０ｂに達する可能性がある。電解質層４０の厚さが２．５μｍよりも厚いと、電解質層４０の内部抵抗の増加により、電気光学材料層３０および電解質層４０に印加された電界の強度が減少する可能性がある。 The thickness of the electrolyte layer 40 can be, for example, 500 nm or more and 2.5 μm or less. If the thickness of the electrolyte layer 40 is less than 500 nm, the evanescent light of the light 32 may reach the second electrode 20b. When the thickness of the electrolyte layer 40 is thicker than 2.5 μm, the strength of the electric field applied to the electro-optical material layer 30 and the electrolyte layer 40 may decrease due to the increase in the internal resistance of the electrolyte layer 40.
　以上のように、ＬＺＳＯ層は、（１）表面が平坦であり、（２）有効なＬｉイオン伝導度が得られ、および、（３）ＬＺＳＯ層のＫＴＮ層上への堆積が容易であるという利点を有する。 As described above, the LZSO layer has (1) a flat surface, (2) effective Li ion conductivity can be obtained, and (3) the LZSO layer can be easily deposited on the KTN layer. Has advantages.
　（製造方法）
　以下に、光位相変調器１００の製造方法を説明する。 (Production method)
The manufacturing method of the optical phase modulator 100 will be described below.
　図４は、光位相変調器１００の製造工程を示すフローチャートである。光位相変調器１００の製造方法は、以下のステップＳ１０１からステップＳ１０４を含む。 FIG. 4 is a flowchart showing the manufacturing process of the optical phase modulator 100. The method for manufacturing the optical phase modulator 100 includes the following steps S101 to S104.
　ステップＳ１０１において、ＭｇＯ（１００）単結晶から形成されたＭｇＯ基板が用意される。ＭｇＯ基板は、図１Ａおよび図１Ｂに示す基板１０に相当する。 In step S101, an MgO substrate formed from an MgO (100) single crystal is prepared. The MgO substrate corresponds to the substrate 10 shown in FIGS. 1A and 1B.
　ステップＳ１０２において、ＭｇＯ基板の主面上に、ＬＳＳＯ層およびＫＴＮ層が、この順に、エピタキシャル成長によって形成される。ＬＳＳＯ層は、図１Ａおよび図１Ｂに示す第１の電極２０ａに相当する。ＬＳＳＯ層は、電気伝導性を示す。ＬＳＳＯ層は、［１００］方向に配向している。ＬＳＳＯ層の厚さは、２００ｎｍである。ＫＴＮ層は、図１Ａおよび図１Ｂに示す電気光学材料層３０に相当する。ＫＴＮ層の厚さは５００ｎｍである。 In step S102, the LSSO layer and the KTN layer are formed on the main surface of the MgO substrate by epitaxial growth in this order. The LSSO layer corresponds to the first electrode 20a shown in FIGS. 1A and 1B. The LSSO layer exhibits electrical conductivity. The LSSO layer is oriented in the [100] direction. The thickness of the LSSO layer is 200 nm. The KTN layer corresponds to the electro-optical material layer 30 shown in FIGS. 1A and 1B. The thickness of the KTN layer is 500 nm.
　ＬＳＳＯ層およびＫＴＮ層の形成には、ＰＬＤ法が用いられる。真空チャンバ内に、ＭｇＯ基板と、ＬＳＳＯから形成されたターゲットとが対向して配置される。対向距離は４０ｍｍである。真空チャンバ内を真空排気した後Ｏ２ガスを注入することにより、真空チャンバ内の圧力が１０Ｐａになる。ＭｇＯ基板は７００℃に加熱される。ＬＳＳＯから形成されたターゲットは、ＡｒＦエキシマレーザで照射される。これにより、ＭｇＯ基板の主面１０ｓ上に、ＬＳＳＯ層が堆積される。同様の手法により、ＬＳＳＯ層が主面１０ｓ上に形成されたＭｇＯ基板が７００℃に加熱され、ＫＴＮから形成されたターゲットがＡｒＦエキシマレーザで照射される。これにより、ＬＳＳＯ層上に、ＫＴＮ層が堆積される。冷却後、ＬＳＳＯ層およびＫＴＮ層を含むＭｇＯ基板が、真空チャンバから取り出される。 The PLD method is used to form the LSSO layer and the KTN layer. In the vacuum chamber, the MgO substrate and the target formed from LSSO are arranged to face each other. The facing distance is 40 mm. By injecting O 2 gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 10 Pa. The MgO substrate is heated to 700 ° C. The target formed from the LSSO is irradiated with an ArF excimer laser. As a result, the LSSO layer is deposited on the main surface 10s of the MgO substrate. By the same method, the MgO substrate on which the LSSO layer is formed on the main surface 10s is heated to 700 ° C., and the target formed from KTN is irradiated with an ArF excimer laser. As a result, the KTN layer is deposited on the LSSO layer. After cooling, the MgO substrate containing the LSSO layer and the KTN layer is removed from the vacuum chamber.
　ステップＳ１０３において、ＫＴＮ層上に、ｘ＝１のＬＺＳＯ層が形成される。当該ＬＺＳＯ層の表面に析出する炭酸塩は少ない。また、ＬＺＳＯ層は、アモルファス構造を有する。少ないＬｉ量およびアモルファス構造により、ＬＺＳＯ層の表面は平坦である。ＬＺＳＯ層は、図１Ａおよび図１Ｂに示す電解質層４０に相当する。ＬＺＳＯ層の厚さは、６００ｎｍである。 In step S103, an LZSO layer with x = 1 is formed on the KTN layer. The amount of carbonate deposited on the surface of the LZSO layer is small. Further, the LZSO layer has an amorphous structure. Due to the small amount of Li and the amorphous structure, the surface of the LZSO layer is flat. The LZSO layer corresponds to the electrolyte layer 40 shown in FIGS. 1A and 1B. The thickness of the LZSO layer is 600 nm.
　ＬＺＳＯ層の形成には、ＰＬＤ法が用いられる。真空チャンバ内に、ＬＳＳＯ層およびＫＴＮ層を含むＭｇＯ基板と、ＬＺＳＯから形成されたターゲットが対向して配置される。対向距離は４０ｍｍである。真空チャンバ内を真空排気した後Ｏ２ガスを注入することにより、真空チャンバ内の圧力が２Ｐａになる。ＬＺＳＯから形成されたターゲットは、室温で、ＡｒＦエキシマレーザで照射される。これにより、ＬＺＳＯ層が、ＫＴＮ層上に堆積される。このように、ステップＳ１０３は、電解質層４０を、室温で、ＰＬＤ法によって電気光学材料層３０上に堆積するステップを含む。 The PLD method is used to form the LZSO layer. In the vacuum chamber, the MgO substrate containing the LSSO layer and the KTN layer and the target formed from LZSO are arranged to face each other. The facing distance is 40 mm. By injecting O 2 gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 2 Pa. Targets formed from LZSO are irradiated with an ArF excimer laser at room temperature. As a result, the LZSO layer is deposited on the KTN layer. As described above, step S103 includes a step of depositing the electrolyte layer 40 on the electro-optical material layer 30 by the PLD method at room temperature.
　ステップＳ１０４において、ＬＺＳＯ層上に、室温で、１０ｗｔ％ＳｎＯ２ドープＩｎ２Ｏ３から形成されたＩＴＯ層が形成される。ＩＴＯ層は、図１Ａおよび図１Ｂに示す第２の電極２０ｂに相当する。第２の電極２０ｂの厚さは、１００ｎｍである。ＩＴＯ層の形成には、スパッタ法が用いられる。高周波スパッタ装置の真空チャンバ内に、ＬＳＳＯ層、ＫＴＮ層、およびＬＺＳＯ層を含むＭｇＯ基板と、ＩＴＯから形成されたターゲットが対向して配置される。対向距離は４５ｍｍである。真空チャンバ内を真空排気した後Ａｒガスを注入することにより、真空チャンバ内の圧力が１．５Ｐａになる。ＲＦパワー５０Ｗで１２分スパッタリングすることにより、ＩＴＯ層が、ＬＺＳＯ層上に堆積される。 In step S104, an ITO layer formed of 10 wt% SnO 2- doped In 2 O 3 is formed on the LZSO layer at room temperature. The ITO layer corresponds to the second electrode 20b shown in FIGS. 1A and 1B. The thickness of the second electrode 20b is 100 nm. A sputtering method is used to form the ITO layer. In the vacuum chamber of the high-frequency sputtering apparatus, an MgO substrate containing an LSSO layer, a KTN layer, and an LZSO layer and a target formed of ITO are arranged so as to face each other. The facing distance is 45 mm. By injecting Ar gas after evacuating the inside of the vacuum chamber, the pressure inside the vacuum chamber becomes 1.5 Pa. The ITO layer is deposited on the LZSO layer by sputtering for 12 minutes at an RF power of 50 W.
　ＬＳＳＯ層、ＫＴＮ層、およびＬＺＳＯ層の屈折率は、それぞれ、２．０、２．２および１．７程度である。したがって、一番高い屈折率のＫＴＮ層が、光導波層として機能する。一対の電極２０に電圧を印加することにより、ＫＴＮ層の屈折率を、約２．０から約２．２の範囲内で変化させることができる。これにより、ＫＴＮ層を伝搬する光３２の位相を変調することができる。 The refractive indexes of the LSSO layer, the KTN layer, and the LZSO layer are about 2.0, 2.2, and 1.7, respectively. Therefore, the KTN layer having the highest refractive index functions as an optical waveguide layer. By applying a voltage to the pair of electrodes 20, the refractive index of the KTN layer can be changed in the range of about 2.0 to about 2.2. As a result, the phase of the light 32 propagating in the KTN layer can be modulated.
　基板１０、一対の電極２０、および電気光学材料層３０には、以下の材料を選択してもよい。 The following materials may be selected for the substrate 10, the pair of electrodes 20, and the electro-optical material layer 30.
　ステップＳ１０１において、ＭｇＯ基板の代わりに、ＭｇＡｌ２Ｏ４から形成されたＭｇＡｌ２Ｏ４基板、またはα－Ａｌ２Ｏ３から形成されたα－Ａｌ２Ｏ３基板を準備してもよい。ＭｇＡｌ２Ｏ４基板、およびａ－Ａｌ２Ｏ３基板上には、第１の電極２０ａとしてＬＳＳＯ層をエピタキシャル成長によって形成することができる。ＭｇＡｌ２Ｏ４基板、およびａ－Ａｌ２Ｏ３基板は、波長１５５０ｎｍで透明である。ＭｇＡｌ２Ｏ４基板、およびａ－Ａｌ２Ｏ３基板の屈折率は、ＬＳＳＯ層の屈折率よりも低い。 In step S101, instead of the MgO substrate may be prepared MgAl 2 O 4 substrate, or α-Al 2 O 3 α- Al 2 O 3 substrate formed from, formed from MgAl 2 O 4. An LSSO layer can be formed as the first electrode 20a on the MgAl 2 O 4 substrate and the a—Al 2 O 3 substrate by epitaxial growth. The MgAl 2 O 4 substrate and the a-Al 2 O 3 substrate are transparent at a wavelength of 1550 nm. The refractive index of the MgAl 2 O 4 substrate and the a-Al 2 O 3 substrate is lower than that of the LSSO layer.
　ステップＳ１０２において、ＬＳＳＯ層の代わりに、ＡドープＳｒｘＢａ１－ｘＳｎＯ３（Ａ＝Ｌａ、Ｔａ、またはＮｂ）から形成された層を形成してもよい。当該層上には、ＫＴＮ層をエピタキシャル成長によって形成することができる。当該層は、波長１５５０ｎｍで透明である。当該層の屈折率は、ＫＴＮ層の屈折率よりも低い。当該層は、電気伝導性を有する。 In step S102, a layer formed from A-doped Sr x Ba 1-x SnO 3 (A = La, Ta, or Nb) may be formed instead of the LSSO layer. A KTN layer can be formed on the layer by epitaxial growth. The layer is transparent at a wavelength of 1550 nm. The refractive index of the layer is lower than that of the KTN layer. The layer has electrical conductivity.
　ステップＳ１０２において、ＫＴＮ層の代わりに、前述したポッケルス効果またはカー効果を示す電気光学材料から形成された層を形成してもよい。ただし、第１の電極２０ａには、当該層をエピタキシャル成長することができる材料が選択される。 In step S102, instead of the KTN layer, a layer formed from an electro-optical material exhibiting the Pockels effect or the Kerr effect described above may be formed. However, for the first electrode 20a, a material capable of epitaxially growing the layer is selected.
　ステップＳ１０４において、ＩＴＯ層の代わりに、ＦドープＳｎＯ２（ＦＴＯ）から形成されたＦＴＯ層、またはＳｂドープＴｉＯ２（ＡＴＯ）から形成されたＡＴＯ層を形成してもよい。ＦＴＯ層およびＡＴＯ層は、波長１５５０ｎｍで透明である。ＦＴＯ層およびＡＴＯ層は、室温で堆積することができる。 In step S104, instead of the ITO layer, an FTO layer formed of F-doped SnO 2 (FTO) or an ATO layer formed of Sb-doped TiO 2 (ATO) may be formed. The FTO layer and the ATO layer are transparent at a wavelength of 1550 nm. The FTO and ATO layers can be deposited at room temperature.
　ステップＳ１０１からステップＳ１０４によって製造された積層構造は、フォトリソグラフィおよびドライエッチングにより、任意の形状にパターニングすることができる。上記のＫＴＮ層において、空気中での波長が１５５０ｎｍである０次のＴＭモードが存在するために、当該積層構造の幅は、例えば１μｍに設計される。当該積層構造は、後述するマッハ・ツェンダー（Ｍａｃｈ－Ｚｅｈｎｄｅｒ）型の光スイッチングデバイス、または光フェーズドアレイにパターニングしてもよい。 The laminated structure produced by steps S101 to S104 can be patterned into an arbitrary shape by photolithography and dry etching. In the above KTN layer, the width of the laminated structure is designed to be, for example, 1 μm because there is a 0th-order TM mode in which the wavelength in air is 1550 nm. The laminated structure may be patterned on a Mach-Zehnder type optical switching device or an optical phased array described later.
　（応用例）
　本実施形態における光位相変調器１００では、制御回路５０は、一対の電極２０に印加される直流電圧の値を変化させることにより、電気光学材料層３０の屈折率を変化させる。これにより、電気光学材料層３０内を伝搬する光３２の位相が変調される。以下に、光３２の位相変調を利用した応用例を説明する。 (Application example)
In the optical phase modulator 100 of the present embodiment, the control circuit 50 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 is modulated. An application example using the phase modulation of the light 32 will be described below.
　本実施形態における光位相変調器１００は、例えば、マッハ・ツェンダー型の光スイッチングデバイスに適用することができる。図５は、マッハ・ツェンダー型の光スイッチングデバイス２００の例を模式的に示す平面図である。光スイッチングデバイス２００は、入力導波路２００ａ、分岐された２つの光導波路２００ｂ、および出力導波路２００ｃを備える。分岐された２つの光導波路２００ｂは、入力導波路２００ａと出力導波路２００ｃとの間に位置する。図５に示す例では、入力導波路２００ａ側の分岐点Ａ、および出力導波路２００ｃ側の分岐点Ｂでの光の反射は考慮されない。分岐された２つの光導波路２００ｂのうち、一方の光導波路は、本実施形態における光位相変調器１００を含む。 The optical phase modulator 100 in this embodiment can be applied to, for example, a Mach-Zehnder type optical switching device. FIG. 5 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. 5, 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 phase modulator 100 in this embodiment.
　当該一方の光導波路内を伝搬する光の位相は、他方の光導波路内を伝搬する光の位相と比較して、Δφ＝（２π／λ）ΔｎＬだけシフトする。光位相変調器１００における一対の電極２０に印加する直流電圧の値が０Ｖのとき、Δφ＝０である。このとき、分岐された２つの光導波路２００ｂからそれぞれ出力された光の位相は、同位相である。このため、同位相の２つの光が出力導波路２００ｃに入力すると、当該２つの光は重なり合う。したがって、出力導波路２００ｃから出力された光の強度Ｉｏｕｔは、入力導波路２００ａに入力された光の強度Ｉｉｎに等しい。 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 phase modulator 100 is 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.
　一方、光位相変調器１００における一対の電極２０に印加する直流電圧の値を調整することにより、Δφ＝πにすることができる。このとき、分岐された２つの光導波路２００ｂからそれぞれ出力された光の位相は、逆位相になる。このため、逆位相の２つの光が出力導波路２００ｃに入力すると、当該２つの光は打ち消しあう。したがって、出力導波路２００ｃから出力された光の強度Ｉｏｕｔは０になる。 On the other hand, Δφ = π can be set by adjusting the value of the DC voltage applied to the pair of electrodes 20 in the optical phase modulator 100. 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.
　以上のように、光位相変調器１００における一対の電極２０に印加する直流電圧を変化させることにより、光スイッチングデバイス２００の出力導波路２００ｃから出力された光の強度Ｉｏｕｔを、Ｉｉｎから０まで連続的に調整することができる。屈折率を大きくかつ高速に変調することができる光位相変調器１００により、光スイッチングデバイス２００の小型化、および光スイッチングデバイス２００から出力された光の強度変調の高速化が可能になる。 As described above, by changing the DC voltage applied to the pair of electrodes 20 in the optical phase modulator 100, the intensity I out of the light output from the output waveguide 200c of the optical switching device 200 is changed from I in to 0. Can be adjusted continuously. The optical phase modulator 100 capable of modulating the refractive index at a large speed and at a high speed enables the optical switching device 200 to be miniaturized and the intensity modulation of the light output from the optical switching device 200 to be accelerated.
　また、本実施形態における光位相変調器１００は、例えば、光フェーズドアレイ３００に適用することができる。図６Ａおよび図６Ｂは、光フェーズドアレイ３００の例を模式的に示す図である。光フェーズドアレイ３００は、Ｙ方向に配列された複数の光導波路３００ｗを備える。複数の光導波路３００ｗの各々は、本実施形態における光位相変調器１００を含む。複数の光導波路３００ｗからそれぞれ出力された複数の光は、互いに干渉する。これにより、光フェーズドアレイ３００から出力された干渉光は、特定の方向に伝搬する。図６Ａおよび図６Ｂに示す例において、破線は、複数の光導波路３００ｗからそれぞれ出力された複数の光の波面を表している。実線は、光フェーズドアレイ３００から出力された干渉光の波面を表している。図６Ａおよび図６Ｂに示す例において、複数の光導波路３００ｗは、等間隔で配列されているが、異なる間隔で配列されていてもよい。 Further, the optical phase modulator 100 in this embodiment can be applied to, for example, an optical phased array 300. 6A and 6B 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 phase modulator 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. 6A and 6B, 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. 6A and 6B, the plurality of optical waveguides 300w are arranged at equal intervals, but may be arranged at different intervals.
　図６Ａに示す例では、光位相変調器１００における一対の電極２０に印加する直流電圧の値が０Ｖのとき、複数の光導波路３００ｗから出力される光の位相は、同位相である。したがって、光フェーズドアレイ３００から出力された干渉光は、複数の光導波路３００ｗが延びるＸ方向と同じ方向に伝搬する。 In the example shown in FIG. 6A, when the value of the DC voltage applied to the pair of electrodes 20 in the optical phase modulator 100 is 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.
　図６Ｂに示す例では、光位相変調器１００における一対の電極２０に印加する直流電圧の値を調整することにより、複数の光導波路３００ｗから出力される光の位相は、Ｙ方向に沿ってΔφずつ増加する。したがって、光フェーズドアレイ３００から出力された干渉光は、複数の光導波路３００ｗが延びるＸ方向とは異なる方向に伝搬する。 In the example shown in FIG. 6B, by adjusting the value of the DC voltage applied to the pair of electrodes 20 in the optical phase modulator 100, the phase of the light output from the plurality of optical waveguides 300w is Δφ along the Y direction. It increases little by little. 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.
　以上のように、光位相変調器１００における一対の電極２０に印加する直流電圧を変化させることにより、光フェーズドアレイ３００から出力された干渉光の伝搬方向を調整することができる。すなわち、光ビームスキャンが可能になる。さらに、光フェーズドアレイ３００は、特定の方向から入射する光を検出することも可能である。図６Ａおよび図６Ｂに示す例では、光フェーズドアレイ３００は、矢印とは逆の方向から入射した光を検出することができる。屈折率を大きくかつ高速に変調することができる光位相変調器１００により、光フェーズドアレイ３００の小型化、ならびに、光フェーズドアレイ３００における光スキャンの高速化および広角度化が可能になる。 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 phase modulator 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. 6A and 6B, the optical phased array 300 can detect incident light from the direction opposite to the arrow. The optical phase modulator 100 capable of modulating the refractive index at high speed makes it possible to reduce the size of the optical phased array 300 and to increase the speed and widening of the optical scan of the optical phased array 300.
　光フェーズドアレイ３００は、例えば、ＬｉＤＡＲ（Ｌｉｇｈｔ　Ｄｅｔｅｃｔｉｏｎ　ａｎｄ　Ｒａｎｇｉｎｇ）システムなどの光スキャンシステムおよび／または光検出システムにおけるアンテナとして用いられ得る。ＬｉＤＡＲシステムでは、ミリ波などの電波を用いたレーダシステムと比較して、可視光、赤外線、または紫外線などの短波長の電磁波が用いられる。このため、物体の距離分布を高い分解能でスキャンおよび検出することができる。そのようなＬｉＤＡＲシステムは、例えば自動車、ＵＡＶ（Ｕｎｍａｎｎｅｄ　Ａｅｒｉａｌ　Ｖｅｈｉｃｌｅ、所謂ドローン）、またはＡＧＶ（Ａｕｔｏｍａｔｅｄ　Ｇｕｉｄｅｄ　Ｖｅｈｉｃｌｅ）などの移動体に搭載され、衝突回避技術の１つとして使用され得る。 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.
　上記では、光導波路を伝搬する光の位相を変調する光位相変調器を説明したが、これに限定されない。本開示は、屈折率を変調する任意の光デバイスに適用することができる。 In the above, the optical phase modulator that modulates the phase of the light propagating in the optical waveguide has been described, but the present invention is not limited to this. The present disclosure can be applied to any optical device that modulates the refractive index.
　本開示の実施形態における光デバイスは、例えば、マッハ・ツェンダー型の光スイッチングデバイス、または自動車、ＵＡＶ、もしくはＡＧＶなどの車両に搭載されるＬｉＤＡＲシステムの用途に利用できる。 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　　　：基板
　　１０ｓ　　：主面
　　２０　　：電極
　　２０ａ　　：第１の電極
　　２０ｂ　　：第２の電極
　　３０　　　：電気光学材料層
　　３２　　　：光
　　３５　　　：界面
　　４０　　　：電解質層
　　５０　　　：制御回路
　　１００　　：光位相変調器
　　２００　　：光スイッチングデバイス
　　２００ａ　：入力導波路
　　２００ｂ　：光導波路
　　２００ｃ　：出力導波路
　　３００　　：光フェーズドアレイ
　　３００ｗ　：光導波路 10: Substrate 10s: Main surface 20: Electrode 20a: First electrode 20b: Second electrode 30: Electro-optical material layer 32: Light 35: Interface 40: Electrolyte layer 50: Control circuit 100: Optical phase modulator 200: Optical switching device 200a: Input waveguide 200b: Optical waveguide 200c: Output waveguide 300: Optical phased array 300w: Optical waveguide

Claims (8)

  1. 　電気光学材料層と、
    　ＬｉｘＺｒｚＳｉ１－ｚＯｙ（ｘ＞０、ｙ＝ｘ／２＋２、０≦ｚ≦１）によって表される物質から形成され、前記電気光学材料層に接する電解質層と、
    　前記電気光学材料層および前記電解質層に電圧を印加するための第１の電極および第２の電極と、
    を備える、
    光デバイス。     Electro-optic material layer and
    An electrolyte layer formed from a substance represented by Li x Zr z Si 1-z Oy (x> 0, y = x / 2 + 2, 0 ≦ z ≦ 1) and in contact with the electro-optical material layer, and
    A first electrode and a second electrode for applying a voltage to the electro-optical material layer and the electrolyte layer,
    To prepare
    Optical device.
  2. 　前記電圧を制御する制御回路をさらに備え、
    　前記制御回路は、前記電圧を制御して前記電気光学材料層の屈折率を変化させることにより、前記電気光学材料層を伝搬する光の位相を変調する、
    請求項１に記載の光デバイス。     Further provided with a control circuit for controlling the voltage,
    The control circuit modulates the phase of light propagating through the electro-optical material layer by controlling the voltage and changing the refractive index of the electro-optical material layer.
    The optical device according to claim 1.
  3. 　１≦ｘ≦４である、
    請求項１または２に記載の光デバイス。     1 ≦ x ≦ 4,
    The optical device according to claim 1 or 2.
  4. 　ｘ＝１である、
    請求項３に記載の光デバイス。     x = 1,
    The optical device according to claim 3.
  5. 　前記電解質層は、アモルファス構造を有する、
    請求項１から４のいずれかに記載の光デバイス。     The electrolyte layer has an amorphous structure.
    The optical device according to any one of claims 1 to 4.
  6. 　前記電気光学材料層は、タンタル酸ニオブ酸カリウムから形成されている、
    請求項１から５のいずれかに記載の光デバイス。     The electro-optical material layer is made of potassium niobate tantalate.
    The optical device according to any one of claims 1 to 5.
  7. 　第１の電極を形成する工程と、
    　前記第１の電極上に電気光学材料層を形成する工程と、
    　前記電気光学材料層上に、ＬｉｘＺｒｚＳｉ１－ｚＯｙ（ｘ＞０、ｙ＝ｘ／２＋２、０≦ｚ≦１）によって表される物質から形成された電解質層を形成する工程と、
    　前記電解質層上に第２の電極を形成する工程と、
    を含む、
    光デバイスの製造方法。     The process of forming the first electrode and
    A step of forming an electro-optical material layer on the first electrode and
    A step of forming an electrolyte layer formed of a substance represented by Li x Zr z Si 1-z Oy (x> 0, y = x / 2 + 2, 0 ≦ z ≦ 1) on the electro-optical material layer. When,
    The step of forming the second electrode on the electrolyte layer and
    including,
    Manufacturing method of optical device.
  8. 　前記電解質層を形成する工程は、前記電解質層を、室温で、パルスレーザ堆積法によって前記電気光学材料層上に堆積する工程を含む、
    請求項７に記載の光デバイスの製造方法。     The step of forming the electrolyte layer includes a step of depositing the electrolyte layer on the electro-optical material layer by a pulse laser deposition method at room temperature.
    The method for manufacturing an optical device according to claim 7.
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JPS5960814A (en) * 1982-09-29 1984-04-06 株式会社日立製作所 Amorphous ion conductor for lithium oxide series
JPH10282044A (en) * 1997-04-04 1998-10-23 Tokuyama Corp Solid electrolyte type gas sensor element
US20080212914A1 (en) * 2004-09-13 2008-09-04 Marks Tobin J Transparent conducting components and related electro-optic modulator devices
JP2013238651A (en) * 2012-05-11 2013-11-28 Mitsubishi Electric Corp Manufacturing method of polarization reversal element, manufacturing method of waveguide type wavelength conversion element, and waveguide type wavelength conversion element
JP2017044856A (en) * 2015-08-26 2017-03-02 パナソニックＩｐマネジメント株式会社 Optical modulator

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Publication number Priority date Publication date Assignee Title
CN115274298A (en) * 2022-05-20 2022-11-01 沈阳工业大学 Lead zirconate nano composite dielectric film and preparation method thereof
CN115274298B (en) * 2022-05-20 2023-10-03 沈阳工业大学 Lead zirconate nano composite dielectric film and preparation method thereof

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