WO2023176054A1 - 光変調器 - Google Patents

光変調器 Download PDF

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Publication number
WO2023176054A1
WO2023176054A1 PCT/JP2022/043689 JP2022043689W WO2023176054A1 WO 2023176054 A1 WO2023176054 A1 WO 2023176054A1 JP 2022043689 W JP2022043689 W JP 2022043689W WO 2023176054 A1 WO2023176054 A1 WO 2023176054A1
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WO
WIPO (PCT)
Prior art keywords
electrode
optical waveguide
optical modulator
optical
dielectric constant
Prior art date
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Ceased
Application number
PCT/JP2022/043689
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English (en)
French (fr)
Japanese (ja)
Inventor
聡希 ▲浜▼村
康弘 會田
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Murata Manufacturing Co Ltd
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Murata Manufacturing Co Ltd
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Application filed by Murata Manufacturing Co Ltd filed Critical Murata Manufacturing Co Ltd
Priority to JP2024507507A priority Critical patent/JP7729468B2/ja
Priority to CN202280089433.1A priority patent/CN118591759A/zh
Publication of WO2023176054A1 publication Critical patent/WO2023176054A1/ja
Priority to US18/765,418 priority patent/US20240361622A1/en
Anticipated expiration legal-status Critical
Priority to JP2025134601A priority patent/JP2025166141A/ja
Ceased legal-status Critical Current

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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
    • 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
    • G02F1/0305—Constructional arrangements
    • G02F1/0316—Electrodes
    • 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 
    • G02F1/21—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  by interference
    • G02F1/212—Mach-Zehnder type
    • 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
    • G02F2202/00—Materials and properties
    • G02F2202/20—LiNbO3, LiTaO3

Definitions

  • the present disclosure relates to an optical modulator.
  • An optical transceiver includes an optical modulator as a main component.
  • An optical modulator is responsible for converting electrical signals into optical signals.
  • Patent Document 1 A conventional optical modulator is disclosed in, for example, Japanese Patent Laid-Open No. 2008-250080 (Patent Document 1).
  • the optical modulator of Patent Document 1 includes a thin plate having an electro-optic effect, an optical waveguide formed in the thin plate, and a control electrode for controlling light passing through the optical waveguide.
  • the control electrode includes a first electrode and a second electrode, and the first electrode and the second electrode are arranged to sandwich a thin plate.
  • the first electrode has a coplanar electrode including at least a signal electrode and a ground electrode.
  • the second electrode has at least a ground electrode.
  • a low refractive index layer having a width larger than at least the width of the signal electrode of the first electrode is formed below the thin plate. Further, a buffer layer may be formed at least between the thin plate and the first electrode.
  • the signal electrode of the first electrode has a rectangular shape in a cross section perpendicular to the extending direction of the optical waveguide, and the signal electrode is aligned with the optical waveguide in the thickness direction of the optical waveguide. There is. In this case, since the entire bottom surface of the signal electrode faces the optical waveguide, light leaking from the optical waveguide is likely to be absorbed by the signal electrode, resulting in optical loss. Further, in the optical modulator of Patent Document 1, a buffer layer is formed between the first electrode including the signal electrode and the thin plate. The buffer layer contributes to adjusting the effective refractive index. If the buffer layer does not exist, the difference between the effective refractive index perceived by the electrical signal and the effective refractive index perceived by the light wave will not become small, making it impossible to increase the modulation frequency.
  • An object of the present disclosure is to provide an optical modulator that can suppress optical loss and increase modulation frequency.
  • An optical modulator includes an optical waveguide made of a material having an electro-optic effect, a control electrode for controlling light passing through the optical waveguide, and a low dielectric constant layer having a dielectric constant lower than that of the optical waveguide. Equipped with The control electrode includes a first electrode and a second electrode that form a potential difference with each other.
  • the first electrode is provided on one side in the width direction of the optical waveguide and on one side in the thickness direction of the optical waveguide
  • the second electrode is provided on one side in the width direction of the optical waveguide. It is provided on the other side and on the other side in the thickness direction of the optical waveguide.
  • a low dielectric constant layer is interposed between the first electrode and the optical waveguide, and a portion of the first electrode close to the optical waveguide is embedded in the low dielectric constant layer.
  • optical modulator According to the optical modulator according to the present disclosure, it is possible to suppress optical loss and increase the modulation frequency.
  • FIG. 1 is a schematic diagram showing a cross section of an optical modulator according to a first embodiment.
  • FIG. 2 is a schematic diagram for explaining the properties of the substrate in the optical modulator according to the first embodiment.
  • FIG. 3 is a schematic diagram showing a cross section of an optical modulator according to a second embodiment.
  • FIG. 4 is a schematic diagram showing a cross section of an optical modulator according to a third embodiment.
  • FIG. 5 is a schematic diagram showing a cross section of an optical modulator according to a fourth embodiment.
  • FIG. 6 is a schematic diagram showing a cross section of an optical modulator according to a fifth embodiment.
  • FIG. 7 is a schematic diagram showing a cross section of an optical modulator according to a sixth embodiment.
  • FIG. 1 is a schematic diagram showing a cross section of an optical modulator according to a first embodiment.
  • FIG. 2 is a schematic diagram for explaining the properties of the substrate in the optical modulator according to the first embodiment.
  • FIG. 3 is a schematic diagram showing
  • FIG. 8 is a schematic diagram showing a cross section of an optical modulator according to a seventh embodiment.
  • FIG. 9 is a schematic diagram showing a cross section of an optical modulator according to the eighth embodiment.
  • FIG. 10 is a schematic diagram showing a cross section of an optical modulator according to a ninth embodiment.
  • FIG. 11 is a schematic diagram showing a cross section of an optical modulator according to a tenth embodiment.
  • FIG. 12 is a schematic diagram showing a cross section of an optical modulator according to the eleventh embodiment.
  • FIG. 13A is a schematic diagram showing the strength of the electric field when the first electrode and the second electrode are not stretched.
  • FIG. 13B is a schematic diagram showing the strength of the electric field when only the first electrode is stretched.
  • FIG. 13C is a schematic diagram showing the strength of the electric field when both the first electrode and the second electrode are stretched.
  • the optical modulator includes an optical waveguide made of a material having an electro-optic effect, a control electrode for controlling light passing through the optical waveguide, and a low dielectric constant layer having a dielectric constant lower than that of the optical waveguide. , is provided.
  • the control electrode includes a first electrode and a second electrode that form a potential difference with each other.
  • the first electrode is provided on one side in the width direction of the optical waveguide and on one side in the thickness direction of the optical waveguide
  • the second electrode is provided on one side in the width direction of the optical waveguide. It is provided on the other side and on the other side in the thickness direction of the optical waveguide.
  • a low dielectric constant layer is interposed between the first electrode and the optical waveguide, and a portion of the first electrode close to the optical waveguide is embedded in the low dielectric constant layer (first configuration). .
  • the first electrode is shifted to one of the widthwise sides of the optical waveguide with respect to the optical waveguide, and the second electrode is shifted to one of the widthwise sides of the optical waveguide. Offset to the other of the sides. Further, with respect to the optical waveguide, the first electrode is shifted to one side of both sides in the thickness direction of the optical waveguide, and the second electrode is shifted to the other side of both sides of the optical waveguide in the thickness direction. It's off. That is, the first electrode, the optical waveguide, and the second electrode are arranged obliquely in this order with respect to the width direction and thickness direction of the optical waveguide. Further, a low dielectric constant layer is interposed between the first electrode and the optical waveguide, and a portion of the first electrode close to the optical waveguide is buried in this low dielectric constant layer. The first electrode is not in contact with the optical waveguide.
  • the rectangular electrode is aligned with the optical waveguide in the thickness direction or width direction of the optical waveguide, and the rectangular electrode is aligned with the optical waveguide in the thickness direction or width direction of the optical waveguide.
  • the area in which the first electrode and the second electrode face the optical waveguide becomes smaller. This makes it difficult for light leaking from the optical waveguide to be absorbed by the first electrode and the second electrode. Therefore, optical loss can be suppressed.
  • the electric field directed from the first electrode toward the optical waveguide passes through the low dielectric constant layer. This reduces the effective refractive index felt by the electrical signal.
  • the effective refractive index felt by the electric signal can be made smaller than usual.
  • the effective refractive index felt by electrical signals is larger than the effective refractive index felt by light waves. This reduces the difference between the effective refractive index felt by the electrical signal and the effective refractive index felt by the light wave. Therefore, the modulation frequency can be increased.
  • the first electrode may include a corner. This corner is placed on the optical waveguide side and buried in the low dielectric constant layer (second configuration).
  • the electric field is concentrated at the corner of the first electrode, the intensity of the electric field directed from the first electrode toward the optical waveguide can be increased. Therefore, a decrease in the electric field applied to the optical waveguide between the first electrode and the second electrode can be suppressed.
  • the optical modulator of the first configuration or the second configuration includes, for example, the following configuration.
  • the optical waveguide In a cross-sectional view perpendicular to the direction in which the optical waveguide extends, the optical waveguide includes a first side extending in the width direction and a second side disposed parallel to the first side and extending in the width direction.
  • the first electrode is provided on the first side (third configuration).
  • the optical modulator of the first configuration or the second configuration may have the following configuration.
  • the optical waveguide In a cross-sectional view perpendicular to the direction in which the optical waveguide extends, the optical waveguide has a semi-elliptical shape including a base as a long axis extending in the width direction.
  • the first electrode is provided on the bottom side (fourth configuration).
  • the above optical modulator may further include the following configuration.
  • the first electrode In a cross-sectional view perpendicular to the direction in which the optical waveguide extends, the first electrode has a rectangular shape, and the first electrode is embedded in the surface of the low dielectric constant layer opposite to the optical waveguide. 5 configuration).
  • the above optical modulator may further include the following configuration.
  • the first electrode is provided only on one side above the center in the thickness direction of the optical waveguide, and the second electrode is provided on one side above the center in the thickness direction of the optical waveguide. (sixth configuration).
  • the optical modulator described above preferably has the following configuration.
  • An auxiliary low dielectric constant layer is provided between the second electrode and the optical waveguide.
  • the auxiliary low dielectric constant layer has a dielectric constant lower than that of the optical waveguide (seventh configuration).
  • the modulation frequency can be further increased.
  • the above optical modulator preferably has the following configuration.
  • the material of the optical waveguide is LiNbO 3 (eighth configuration). LiNbO 3 (lithium niobate) has a particularly high electro-optic effect. In this specification, LiNbO 3 may be referred to as LN.
  • the material of the optical waveguide is not particularly limited as long as it has an electro-optic effect.
  • the material of the optical waveguide may be LiTaO 3 (lithium tantalate), PLZT (lead lanthanum zirconate titanate), KTN (potassium tantalate niobate), BaTiO 3 (barium titanate), etc. It may be.
  • the above optical modulator preferably has the following configuration.
  • One of the first electrode and the second electrode extends from the optical waveguide in the thickness direction, and the other extends from the optical waveguide in the width direction (ninth configuration). In this case, the electric field becomes stronger with respect to the optical waveguide.
  • the above optical modulator may further include a substrate provided with an optical waveguide (tenth configuration).
  • the optical modulator with the tenth configuration may include the following configuration.
  • the substrate is made of the same material as the optical waveguide, and the optical waveguide is ridge-shaped (eleventh configuration). In this case, it becomes possible to cover the periphery of the optical waveguide except for the boundary with the substrate with a low dielectric constant layer. Therefore, adjustment of the effective refractive index is easy. Furthermore, light can be further confined within the optical waveguide.
  • an optical waveguide can also be formed by diffusing titanium (Ti) into the substrate.
  • Optical waveguides can also be formed by proton exchange methods.
  • the optical modulator in any one of the first to ninth configurations may include two optical modulator units arranged in parallel.
  • the two optical modulator units each include an optical waveguide, a control electrode, and a low dielectric constant layer (twelfth configuration).
  • the optical modulator of the twelfth configuration constitutes a Mach-Zehnder type optical modulator.
  • intensity modulation is also possible in addition to phase modulation. This allows multilevel modulation to be performed and increases transmission capacity.
  • the optical modulator of the twelfth configuration provides the same effects as the first to ninth configurations.
  • the optical modulator with the twelfth configuration may include the following configuration.
  • the first electrode of one optical modulator unit is formed integrally with the first electrode of the other optical modulator unit (13th configuration).
  • the first electrode of one optical modulator unit can be shared with the first electrode of the other optical modulator unit.
  • the optical modulator with the twelfth configuration or the thirteenth configuration may have the following configuration.
  • Each of the optical modulator units further includes a substrate provided with an optical waveguide.
  • the substrate of one of the two optical modulator units is arranged in parallel with the substrate of the other optical modulator unit (fourteenth configuration).
  • the fourteenth configuration of the optical modulator may include the following configuration.
  • the substrate is made of the same material as the optical waveguide, and the optical waveguide is ridge-shaped (fifteenth configuration).
  • the optical modulator with the fifteenth configuration corresponds to the eleventh configuration. Therefore, similarly to the eleventh configuration, the effective refractive index can be easily adjusted, and furthermore, light can be further confined within the optical waveguide.
  • the optical modulator of the fourteenth configuration or the fifteenth configuration may have the following configuration.
  • the substrate of one optical modulator unit is integrated with the substrate of the other optical modulator unit, and the optical waveguide of one optical modulator unit and the optical waveguide of the other optical modulator unit are connected to each other.
  • the direction of spontaneous polarization is opposite to that of the optical waveguide.
  • Voltages having the same phase are applied to the first electrode of one optical modulator unit and the first electrode of the other optical modulator unit (sixteenth configuration).
  • the substrate of one optical modulator unit can be shared with the substrate of the other optical modulator unit.
  • the optical waveguide of one optical modulator unit and the optical waveguide of the other optical modulator unit are provided on a shared substrate. Therefore, the distance between the optical waveguide of one optical modulator unit and the optical waveguide of the other optical modulator unit can be reduced. In this case, the width of the entire optical modulator can be reduced.
  • FIG. 1 is a schematic diagram showing a cross section of an optical modulator 100 according to the first embodiment.
  • FIG. 1 shows a cross section perpendicular to the direction in which the optical waveguide 2 extends.
  • the direction in which the optical waveguide 2 extends can also be said to be a direction along the optical waveguide 2.
  • a cross section means a cross section perpendicular to the direction in which the optical waveguide 2 or optical waveguides 2A and 2B described below extend.
  • the support plate 7 that supports the whole is located at the bottom, the thickness direction of the optical modulator 100 corresponds to the up-down direction, and the width direction of the optical modulator 100 corresponds to the left-right direction.
  • upper, lower, left, and right are defined for convenience of explanation, and do not limit the actual posture of the optical modulator 100.
  • an optical modulator 100 includes a substrate 1, an optical waveguide 2, a first electrode 3, a second electrode 4, and a low dielectric constant layer 5.
  • the first electrode 3 and the second electrode 4 are included in a control electrode for controlling light passing through the optical waveguide 2.
  • the first electrode 3 and the second electrode 4 form a potential difference with each other.
  • the first electrode 3 is, for example, a signal electrode.
  • the second electrode 4 is not particularly limited as long as it forms a potential difference with the first electrode 3.
  • the second electrode 4 is, for example, a ground electrode.
  • the second electrode 4 may be a reverse signal electrode that applies a voltage with a phase opposite to the potential of the first electrode 3.
  • the second electrode 4 is arranged at a position below the first electrode 3.
  • the substrate 1, the optical waveguide 2, the low dielectric constant layer 5, the first electrode 3, and the second electrode 4 are supported by a support plate 7.
  • the support plate 7 is arranged at the bottom.
  • the optical waveguide 2 is made of a material that has an electro-optic effect.
  • the material of the optical waveguide 2 is, for example, LN.
  • the optical waveguide 2 is formed on the substrate 1. Specifically, an optical waveguide 2 is formed on the top of the substrate 1. This optical waveguide 2 is formed by diffusing Ti into the substrate 1. The portion of the substrate 1 where Ti is diffused has a high refractive index and can confine light, so it can be used as the optical waveguide 2.
  • the optical waveguide 2 can have a cross-sectional shape in which the width (the horizontal dimension) is larger than the thickness (the vertical dimension).
  • the cross-sectional shape of the optical waveguide 2 is substantially wide and generally rectangular.
  • the cross-sectional shape of the optical waveguide 2 includes a first side extending in the width direction and a second side arranged parallel to the first side and extending in the width direction.
  • the cross-sectional shape of the optical waveguide 2 further includes a third side and a fourth side, each extending in the thickness direction.
  • the first side and the second side are a pair of long sides
  • the third side and the fourth side are a pair of short sides.
  • the cross-sectional shape of the optical waveguide 2 is a wide rectangle, one of the pair of long sides (the upper first side) is on the surface of the substrate 1, and the other long side (the lower first side) is on the surface of the substrate 1. 2 sides) are inside the substrate 1.
  • the first and second long sides are connected by the third and fourth short sides.
  • the third side and the fourth side of the optical waveguide 2 are linear in a cross-sectional view of the optical modulator 100, and are parallel to the thickness direction of the optical waveguide 2.
  • the third side and the fourth side may be inclined with respect to the thickness direction of the optical waveguide 2, and do not necessarily need to be linear.
  • the third side and the fourth side of the optical waveguide 2 may have a curved shape, or may have a shape that is a combination of a straight line and a curved line.
  • the length of the third side may be the same as the length of the fourth side, or may be different.
  • the length of the first side may be the same as the length of the second side, or may be different.
  • the cross-sectional shape of the optical waveguide 2 may be a wide semi-ellipse.
  • the cross-sectional shape of the optical waveguide 2 includes a base serving as a long axis extending in the width direction, and an elliptical arc-shaped side extending in the width direction.
  • the base is on the surface of the substrate 1 and the elliptical arc-shaped sides are inside the substrate 1.
  • a low dielectric constant layer 5 is laminated on the substrate 1 .
  • a low dielectric constant layer 5 is laminated on the optical waveguide 2.
  • the low dielectric constant layer 5 directly covers the upper surface of the optical waveguide 2 and the upper surface of the substrate 1 around it.
  • the cross-sectional shape of the optical waveguide 2 is a wide rectangle, in the cross-section of the optical modulator 100, the low dielectric constant layer 5 is mainly formed on one long side (the upper long side) of the optical waveguide 2.
  • the low dielectric constant layer 5 is mainly provided along the above-mentioned bottom side of the optical waveguide 2 in the cross section of the optical modulator 100.
  • the dielectric constant of the low dielectric constant layer 5 is lower than that of the optical waveguide 2.
  • the material of the low dielectric constant layer 5 is not particularly limited as long as the dielectric constant is lower than the dielectric constant of the optical waveguide 2.
  • an oxide eg, Al 2 O 3 , SiO 2 , LaAlO 3 , LaYO 3 , ZnO, HfO 2 , MgO, Y 2 O 3
  • a polymer eg, BCB (benzocyclobutene), PI (polyimide)
  • BCB benzocyclobutene
  • PI polyimide
  • the first electrode 3 is arranged above the substrate 1.
  • the second electrode 4 is arranged at the bottom of the substrate 1. From another point of view, the second electrode 4 is buried in the lower part of the substrate 1.
  • the first electrode 3 and the second electrode 4 are made of a metal material, and each has a rectangular cross-sectional shape. For example, when the cross-sectional shape of the optical waveguide 2 is a wide rectangle, the first electrode 3 is parallel to one long side (upper first side) of the optical waveguide 2 in the cross-section of the optical modulator 100. It has a pair of sides.
  • the first electrode 3 When the cross-sectional shape of the optical waveguide 2 is a wide semi-ellipse, the first electrode 3 has a pair of sides parallel to the above-mentioned bottom side of the optical waveguide 2 in the cross-section of the optical modulator 100 .
  • a first electrode 3 is embedded in a surface of the low dielectric constant layer 5 that is opposite to the optical waveguide 2 .
  • the thickness (vertical dimension) of the low dielectric constant layer 5 at the portion where the first electrode 3 is located is significantly smaller than the thickness of the low dielectric constant layer 5 in other parts.
  • the first electrode 3 can be buried in the low dielectric constant layer 5, for example, as follows. That is, first, the low dielectric constant layer 5 is formed on the surface of the substrate 1 on which the optical waveguide 2 is formed. Subsequently, a groove is formed in the low dielectric constant layer 5 by photolithography and etching. Thereafter, the first electrode 3 is formed by performing vapor deposition and lift-off on the groove. Thereby, the first electrode 3 embedded in the low dielectric constant layer 5 can be formed.
  • the first electrode 3 and the second electrode 4 are arranged to sandwich the optical waveguide 2 in a direction oblique to the thickness direction of the optical waveguide 2.
  • the first electrode 3 is provided on one side of the optical waveguide 2 in the width direction and on one side of the optical waveguide 2 in the thickness direction.
  • the second electrode 4 is provided on the other side of the optical waveguide 2 in the width direction and on the other side of the optical waveguide 2 in the thickness direction. That is, with respect to the optical waveguide 2, the first electrode 3 is shifted to one side (to the right in FIG. 1) of both sides of the optical waveguide 2 in the width direction, and the second electrode 4 is It is shifted to the other side (to the left in FIG. 1) of both sides in the width direction.
  • the first electrode 3 is shifted to one side (upward in FIG. 1) of both sides of the optical waveguide 2 in the thickness direction
  • the second electrode 4 is It is shifted to the other side (downward in FIG. 1) of both sides in the thickness direction.
  • a low dielectric constant layer 5 is interposed between the first electrode 3 and the optical waveguide 2.
  • the lower part of the first electrode 3 is buried in the low dielectric constant layer 5. That is, a portion of the first electrode 3 close to the optical waveguide 2 is buried in the low dielectric constant layer 5.
  • a corner portion of the first electrode 3 located on the optical waveguide 2 side is embedded in the low dielectric constant layer 5 . In this case, the corner of the first electrode 3 exists near the optical waveguide 2. The first electrode 3 is not in contact with the optical waveguide 2.
  • the first electrode 3 is provided only on one side of the optical waveguide 2 from the center in the thickness direction, and the second electrode 4 is provided in the thickness direction of the optical waveguide 2. It is provided only on the other side of the center.
  • the first electrode 3 is provided entirely on the one long side (upper long side) side of the center of the optical waveguide 2 in the thickness direction.
  • the entire second electrode 4 is provided closer to the other long side (lower long side) than the center of the optical waveguide 2 in the thickness direction.
  • the first electrode 3 is provided entirely on the bottom side of the center of the optical waveguide 2 in the thickness direction
  • the second electrode 4 is provided entirely on the bottom side of the optical waveguide 2 in the thickness direction. It is provided closer to the side of the elliptical arc shape than the center of the wave path 2 in the thickness direction.
  • the first electrode 3 does not overlap with the optical waveguide 2 when viewed along the left-right direction. Similarly, when the second electrode 4 is viewed along the left-right direction, there is no part that overlaps with the optical waveguide 2. Further, the first electrode 3 has no portion overlapping with the optical waveguide 2 when viewed in the vertical direction. Similarly, when the second electrode 4 is viewed in the vertical direction, there is no part that overlaps with the optical waveguide 2.
  • a support plate 7 is laminated under the substrate 1.
  • the optical modulator 100 of this embodiment when the optical modulator 100 is operated, an electric field acts from the first electrode 3 toward the second electrode 4, and the electric field is applied to the optical waveguide 2.
  • the first electrode 3 and the second electrode 4 are arranged to sandwich the optical waveguide 2 in a direction oblique to the thickness direction of the optical waveguide 2, and the first A portion of the electrode 3 that is close to the optical waveguide 2 is buried in a low dielectric constant layer 5. Therefore, the following effects can be obtained.
  • the signal electrode is not buried in the low dielectric constant layer and is simply in contact with the surface of the low dielectric constant layer having a certain thickness.
  • a portion of the electrode near the optical waveguide 2 more specifically, a corner of the first electrode 3 is buried in the low dielectric constant layer 5 and exists near the optical waveguide 2 . Since the electric field is concentrated at the corner of the first electrode 3, the intensity of the electric field from the first electrode 3 toward the optical waveguide 2 increases. Therefore, the electric field applied to the optical waveguide 2 does not decrease. Therefore, a decrease in the electric field applied to the optical waveguide 2 can be suppressed.
  • the low dielectric constant layer 5 is interposed between the first electrode 3 and the optical waveguide 2, the first electrode 3 is not in contact with the optical waveguide 2, and a part (corner) thereof is It only exists near wave path 2. Therefore, the shortest separation distance between the optical waveguide 2 and the first electrode 3 is the same compared to the case where the upper surface of the optical waveguide with a rectangular cross section is placed opposite the lower surface of the signal electrode with a rectangular cross section.
  • the area of the first electrode 3 that faces the optical waveguide 2 is small. Therefore, absorption of light leaking from the optical waveguide 2 into the first electrode 3 is suppressed. Therefore, optical loss can be suppressed.
  • the electric field directed from the first electrode 3 to the optical waveguide 2 passes through the low dielectric constant layer 5. This reduces the effective refractive index felt by the electrical signal.
  • the part of the first electrode 3 close to the optical waveguide 2, more specifically the corner of the first electrode 3, is buried in the low dielectric constant layer 5, so that the electrode is placed on the low dielectric constant layer.
  • the contact area between the first electrode 3 and the low dielectric constant layer 5 becomes larger, and the electric field passing through the low dielectric constant layer 5 increases. Therefore, the effective refractive index felt by the electric signal can be made smaller than usual.
  • the optical response includes ionic polarization, so the effective refractive index perceived by electrical signals (GHz) is larger than the effective refractive index perceived by light waves (THz). This reduces the difference between the effective refractive index felt by the electrical signal and the effective refractive index felt by the light wave. Therefore, the modulation frequency can be increased.
  • FIG. 2 is a schematic diagram for explaining the properties of the optical waveguide 2 in the optical modulator 100 according to the first embodiment.
  • FIG. 2 shows a cross section of the optical modulator 100.
  • the first electrode 3 and the second electrode 4 are arranged to sandwich the optical waveguide 2 in a direction oblique to the thickness direction of the optical waveguide 2.
  • the refractive index changes due to the electro-optic effect.
  • the direction of the electric field can be considered to be parallel to the straight line L (see thick line in FIG. 2) connecting the corners of the first electrode 3 and the second electrode 4 that are closest to each other. If the inclination of the crystal axis (eg, c-axis in the case of LN) of the optical waveguide 2 is parallel to the direction of the electric field, the refractive index can be effectively changed.
  • the inclination of the electric field that is, the inclination ⁇ of the electrode arrangement, is based on the following formula (1), and the widthwise (left-right direction) component w of the shortest distance between the first electrode 3 and the second electrode 4, and the thickness direction It can be calculated using the component t in the vertical direction.
  • ⁇ arctan(t/w) ⁇ 180/ ⁇ .
  • a wafer generally called an X-cut may be used as the material for the optical waveguide 2 (substrate 1). If the inclination ⁇ of the electrode arrangement is 85 to 90 degrees, a wafer generally called Z-cut may be used as the material (substrate 1) for the optical waveguide 2.
  • FIG. 3 is a schematic diagram showing a cross section of the optical modulator 100 according to the second embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the first embodiment.
  • the optical modulator 100 further includes an auxiliary low dielectric constant layer 6.
  • an auxiliary low dielectric constant layer 6 is laminated under the substrate 1.
  • the dielectric constant of the auxiliary low dielectric constant layer 6 is lower than that of the optical waveguide 2, similarly to the low dielectric constant layer 5.
  • the material of the auxiliary low dielectric constant layer 6 is not particularly limited as long as the dielectric constant is lower than the dielectric constant of the optical waveguide 2.
  • the material of the auxiliary low dielectric constant layer 6 may be the same as the material of the low dielectric constant layer 5, or may be different.
  • the support plate 7 is laminated under the auxiliary low dielectric constant layer 6. Furthermore, the second electrode 4 is arranged inside the auxiliary low dielectric constant layer 6. That is, the auxiliary low dielectric constant layer 6 is provided between the second electrode 4 and the optical waveguide 2. In this case, the auxiliary low dielectric constant layer 6 directly covers the lower surface of the substrate 1 and covers the lower surface of the optical waveguide 2 .
  • the auxiliary low dielectric constant layer 6 is provided between the second electrode 4 and the optical waveguide 2, the electric field also passes through the auxiliary low dielectric constant layer 6. This further reduces the effective refractive index felt by the electrical signal. Therefore, the difference between the effective refractive index felt by the electric signal and the effective refractive index felt by the light wave becomes smaller. Therefore, the modulation frequency can be further increased.
  • FIG. 4 is a schematic diagram showing a cross section of the optical modulator 100 according to the third embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the first embodiment.
  • the substrate 1 has a ridge-shaped optical waveguide 2. That is, the substrate 1 has a protrusion on its upper part, and this protrusion functions as the optical waveguide 2. Protrusions are formed on the substrate 1 by processing a wafer as a raw material. The protrusions can confine light in the thickness direction and width direction.
  • the cross-sectional shape of the ridge-type optical waveguide 2 is approximately rectangular. Strictly speaking, the cross-sectional shape of the ridge-type optical waveguide 2 is often trapezoidal.
  • the first electrode 3 has a portion that very slightly overlaps with the optical waveguide 2 when viewed in the vertical direction.
  • the second electrode 4 also has a portion that very slightly overlaps with the optical waveguide 2 when viewed in the vertical direction.
  • the substrate 1 is made of the same material as the optical waveguide 2. However, the material of the substrate 1 may be different from the material of the optical waveguide 2. In this case, the material of the substrate 1 is, for example, Si.
  • the optical modulator 100 of this embodiment has the same effects as the first embodiment.
  • the optical waveguide 2 is of a ridge type, it is possible to cover the periphery of the optical waveguide 2 except for the boundary with the substrate 1 with the low dielectric constant layer 5.
  • the low dielectric constant layer 5 covers a wide area around the optical waveguide 2. Therefore, adjustment of the effective refractive index is easy. Furthermore, light can be further confined within the optical waveguide 2.
  • the configuration of this embodiment may be applied to the optical modulator 100 of the second embodiment.
  • FIG. 5 is a schematic diagram showing a cross section of the optical modulator 100 according to the fourth embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the third embodiment.
  • the optical waveguide 2 is of a ridge type.
  • the first electrode 3 has a portion that overlaps with the optical waveguide 2 when viewed in the vertical direction.
  • the first electrodes 3 may overlap within 10% of the total width W from the widthwise end of the widthwise region of the optical waveguide 2 .
  • the second electrode 4 also has a portion that overlaps with the optical waveguide 2 when viewed along the vertical direction.
  • the second electrode 4 may overlap within 10% of the total width W from the widthwise end of the widthwise region of the optical waveguide 2 .
  • the optical modulator 100 of this embodiment has the same effects as the first embodiment.
  • the configuration of this embodiment may be applied to an optical waveguide 2 formed on the substrate 1 by Ti diffusion.
  • FIG. 6 is a schematic diagram showing a cross section of the optical modulator 100 according to the fifth embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the third embodiment.
  • the optical waveguide 2 is of a ridge type.
  • the first electrode 3 does not have a portion that overlaps with the optical waveguide 2 when viewed in the vertical direction. However, the first electrode 3 has a portion that overlaps with the optical waveguide 2 when viewed along the left-right direction.
  • the first electrodes 3 may overlap within 10% of the total thickness T from the upper end of the region in the thickness direction of the optical waveguide 2 .
  • the second electrode 4 also has no overlapping portion with the optical waveguide 2 when viewed in the vertical direction. However, the second electrode 4 has a portion that overlaps with the optical waveguide 2 when viewed along the left-right direction.
  • the second electrode 4 may overlap within 10% of the total thickness T from the lower end of the region in the thickness direction of the optical waveguide 2 .
  • the optical modulator 100 of this embodiment has the same effects as the first embodiment.
  • the configuration of this embodiment may be applied to an optical waveguide 2 formed on the substrate 1 by Ti diffusion.
  • FIG. 7 is a schematic diagram showing a cross section of an optical modulator 100 according to a sixth embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the third embodiment.
  • the optical waveguide 2 is of a ridge type.
  • the first electrode 3 has a portion that overlaps with the optical waveguide 2 when viewed in the vertical direction. Furthermore, the first electrode 3 has a portion that overlaps with the optical waveguide 2 when viewed along the left-right direction.
  • the first electrodes 3 may overlap within 10% of the total width W from the widthwise end of the widthwise region of the optical waveguide 2 .
  • the first electrodes 3 may overlap within 10% of the total thickness T from the upper end of the region in the thickness direction of the optical waveguide 2 .
  • the second electrode 4 has a portion that very slightly overlaps with the optical waveguide 2 when viewed in the vertical direction. Furthermore, the second electrode 4 has a portion that overlaps with the optical waveguide 2 when viewed along the left-right direction.
  • the optical modulator 100 of this embodiment has the same effects as the first embodiment.
  • FIG. 8 is a schematic diagram showing a cross section of the optical modulator 100 according to the seventh embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the third embodiment.
  • the low dielectric constant layer 5 and the auxiliary low dielectric constant layer 6 are integrated. That is, in a cross-sectional view of the optical modulator 100, the entire circumference of the optical waveguide 2 is covered by the low dielectric constant layer 5 and the auxiliary low dielectric constant layer 6, which are integrated. Therefore, more electric fields pass through the low dielectric constant layer 5, making it easier to adjust the effective refractive index.
  • the first electrode 3 is entirely buried in the low dielectric constant layer 5. A portion of the first electrode 3 may be buried in the low dielectric constant layer 5.
  • FIG. 9 is a schematic diagram showing a cross section of the optical modulator 101 according to the eighth embodiment.
  • the optical modulator 101 of this embodiment constitutes a Mach-Zehnder type optical modulator.
  • the optical modulator 101 of this embodiment is a modification of the optical modulator 100 of the third embodiment to which the configuration of the second embodiment is applied, and each element of the optical modulator 100 of the third embodiment is They are arranged in parallel.
  • the optical modulator 101 of this embodiment includes two optical modulator units 100A and 100B.
  • One optical modulator unit 100A includes a substrate 1A, an optical waveguide 2A, a first electrode 3A, a second electrode 4A, a low dielectric constant layer 5A, and an auxiliary low dielectric constant layer 6A.
  • the other optical modulator unit 100B includes a substrate 1B, an optical waveguide 2B, a first electrode 3B, a second electrode 4B, a low dielectric constant layer 5B, and an auxiliary low dielectric constant layer 6B.
  • the optical modulator unit 100A and the optical modulator unit 100B are supported by a support plate 7.
  • the substrates 1A and 1B correspond to the substrate 1 described above.
  • the optical waveguides 2A and 2B correspond to the optical waveguide 2 described above.
  • the low dielectric constant layers 5A and 5B correspond to the low dielectric constant layer 5 described above.
  • the first electrodes 3A and 3B correspond to the first electrode 3 described above.
  • the second electrodes 4A and 4B correspond to the second electrode 4 described above.
  • the auxiliary low dielectric constant layers 6A and 6B correspond to the auxiliary low dielectric constant layer 6 described above.
  • the substrate 1A provided with the optical waveguide 2A is arranged in parallel with the substrate 1B provided with the optical waveguide 2B.
  • the optical waveguides 2A and 2B in which the optical waveguide 2A and the optical waveguide 2B are arranged side by side, are each ridge-shaped.
  • one input optical waveguide branches into the optical waveguide 2A and the optical waveguide 2B.
  • the optical waveguide 2A and the optical waveguide 2B merge into one output optical waveguide.
  • the optical modulator unit 100A is laterally symmetrical with the optical modulator unit 100B. That is, the optical modulator unit 100A is symmetrical with the optical modulator unit 100B in its width direction. Specifically, in the optical modulator unit 100A, the first electrode 3A is shifted toward the optical modulator unit 100B in the width direction with respect to the optical waveguide 2A, and the second electrode 4A is shifted toward the optical waveguide 2A. On the other hand, it is shifted toward the opposite side of the optical modulator unit 100B in the width direction.
  • the first electrode 3B is shifted toward the optical modulator unit 100A in the width direction with respect to the optical waveguide 2B, and the second electrode 4B is shifted in the width direction with respect to the optical waveguide 2B.
  • the direction is shifted to the opposite side of the optical modulator unit 100A.
  • the first electrodes 3A, 3B are located closer to each other in the width direction of the optical waveguides 2A, 2B than the second electrodes 4A, 4B.
  • the optical modulator unit 100A may be asymmetrical with respect to the optical modulator unit 100B.
  • optical modulator 101 of this embodiment Even with the optical modulator 101 of this embodiment, effects similar to those of the first embodiment described above can be obtained. Furthermore, since the optical modulator 101 of this embodiment constitutes a Mach-Zehnder type optical modulator, intensity modulation is also possible in addition to phase modulation. This allows multilevel modulation to be performed and increases transmission capacity.
  • the auxiliary low dielectric constant layer 6A and the auxiliary low dielectric constant layer 6B may not be provided as in the first embodiment. Further, in the optical modulator 101 of this embodiment, the substrates 1A and 1B may not be provided as in the seventh embodiment.
  • the optical waveguides 2A and 2B are ridge-type. Therefore, the same effects as in the third embodiment can be obtained.
  • the optical waveguides 2A and 2B may be formed by Ti diffusion.
  • FIG. 10 is a schematic diagram showing a cross section of an optical modulator 101 according to the ninth embodiment.
  • the optical modulator 101 of this embodiment is a modification of the optical modulator 101 of the eighth embodiment.
  • the first electrode 3A of the optical modulator unit 100A is formed integrally with the first electrode 3B of the optical modulator unit 100B. That is, the first electrode 3B is electrically integrated with the first electrode 3A. In this case, the first electrode 3B can be shared with the first electrode 3A.
  • FIG. 11 is a schematic diagram showing a cross section of an optical modulator 101 according to the tenth embodiment.
  • the optical modulator 101 of this embodiment is a modification of the optical modulator 101 of the ninth embodiment.
  • substrate 1A of optical modulator unit 100A is integrated with substrate 1B of optical modulator unit 100B.
  • the optical waveguide 2A and the optical waveguide 2B have opposite directions of spontaneous polarization.
  • the material of the substrate 1A and the substrate 1B is a ferroelectric crystal such as LN or LiTaO3
  • the direction of spontaneous polarization cannot be reversed by applying a high voltage to the ferroelectric crystal material. be.
  • the location where the polarization is reversed can be recognized by observation using an atomic force microscope or an electron microscope.
  • the first electrode 3B can be used in common with the first electrode 3A, and voltages having the same phase are applied to the first electrode 3A and the first electrode 3B.
  • the distance between the optical waveguide 2A and the optical waveguide 2B can be reduced.
  • the width of the entire optical modulator 101 can be reduced, and the optical modulator 101 can be made smaller.
  • FIG. 12 is a schematic diagram showing a cross section of the optical modulator 100 according to the eleventh embodiment.
  • the optical modulator 100 of this embodiment is a modification of the optical modulator 100 of the third embodiment.
  • the first electrode 3 is stretched upward. That is, the first electrode 3 extends from the optical waveguide 2 in the thickness direction.
  • the second electrode 4 is extended laterally. That is, the second electrode 4 extends from the optical waveguide 2 in the width direction. In this case, an electric field can be applied to the low dielectric constant layer 5 without changing the strength of the electric field.
  • the first electrode 3 may be stretched laterally. That is, the first electrode 3 may extend from the optical waveguide 2 in the width direction.
  • the second electrode 4 may be extended downward. That is, the second electrode 4 may extend from the optical waveguide 2 in the thickness direction.
  • FIGS. 13A to 13C are schematic diagrams showing the correlation between the length of the electrode and the strength of the electric field.
  • a cross section of the optical modulator 100 is shown in FIGS. 13A to 13C.
  • FIG. 13A shows the situation when the first electrode 3 and the second electrode 4 are not stretched.
  • FIG. 13B shows the situation when only the first electrode 3 is stretched.
  • FIG. 13C shows the situation when both the first electrode 3 and the second electrode 4 are stretched.
  • electrical potential (V) is drawn with contour lines. The narrower the interval between contour lines, the stronger the electric field (V/m). Outside the optical waveguide 2, the intervals between the contour lines become narrower in the order of FIGS. 13A, 13B, and 13C.
  • the first electrode 3 and the second electrode 4 are arranged to diagonally sandwich the optical waveguide 2, the first electrode 3 is stretched upward and the second electrode 4 is stretched upward, as shown in FIG. 13C. If it is stretched laterally, the electric field against the optical waveguide 2 becomes stronger.
  • Optical modulator 1 Substrate 2: Optical waveguide 3: First electrode 4: Second electrode 5: Low dielectric constant layer 6: Auxiliary low dielectric constant layer 7: Support plate

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
PCT/JP2022/043689 2022-03-17 2022-11-28 光変調器 Ceased WO2023176054A1 (ja)

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CN202280089433.1A CN118591759A (zh) 2022-03-17 2022-11-28 光调制器
US18/765,418 US20240361622A1 (en) 2022-03-17 2024-07-08 Optical modulator
JP2025134601A JP2025166141A (ja) 2022-03-17 2025-08-13 光変調器

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008250081A (ja) * 2007-03-30 2008-10-16 Sumitomo Osaka Cement Co Ltd 光制御素子
US20160139486A1 (en) * 2013-06-13 2016-05-19 The Regents Of The University Of California Sub-volt drive 100 ghz bandwidth electro-optic modulator
JP2017111238A (ja) * 2015-12-15 2017-06-22 日本電信電話株式会社 半導体マッハツェンダ光変調器及びそれを用いたｉｑ変調器
JP2020034610A (ja) * 2018-08-27 2020-03-05 日本ルメンタム株式会社 電気光学導波路素子及び光モジュール

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008250081A (ja) * 2007-03-30 2008-10-16 Sumitomo Osaka Cement Co Ltd 光制御素子
US20160139486A1 (en) * 2013-06-13 2016-05-19 The Regents Of The University Of California Sub-volt drive 100 ghz bandwidth electro-optic modulator
JP2017111238A (ja) * 2015-12-15 2017-06-22 日本電信電話株式会社 半導体マッハツェンダ光変調器及びそれを用いたｉｑ変調器
JP2020034610A (ja) * 2018-08-27 2020-03-05 日本ルメンタム株式会社 電気光学導波路素子及び光モジュール

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JP2025166141A (ja) 2025-11-05

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