JP2015099386A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator including a ridge type optical waveguide and an eaves-like signal electrode and capable of performing high speed operation.SOLUTION: An optical modulator 100 includes: a ridge type optical waveguide 5; and a modulation electrode 15. The modulation electrode 15 comprises: a signal electrode 7 to which a modulation signal is supplied; a first ground electrode 11; and a second ground electrode 12. The signal electrode 7 includes a wide width part 7W having width wider than the width W5 of an uppermost part of the ridge type optical waveguide 5, the first ground electrode 11 includes a center part ground electrode element 11C formed on a first surface 3A so as to be extended along a first direction and the second ground electrode 12 includes a center part ground electrode element 12C formed on a second surface 3B so as to be extended along the first direction. The center part ground electrode element 11C and the center part ground electrode element 12C respectively include first through holes 11B and second through holes 12B and are overlapped to the wide width part 7W of the signal electrode 7 in plane view.

Description

  The present invention relates to an optical modulator.

  The following Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 describe an optical modulator having a ridge-type optical waveguide. The optical modulators described in the following Patent Document 1 and Non-Patent Document 1 have eaves-like signal electrodes provided on a ridge-type optical waveguide, and are described in Patent Document 2 and Non-Patent Document 2 below. The optical modulator has a mushroom-shaped signal electrode.

Japanese Patent Application Laid-Open No. 11-101962 JP-A-8-122722

Makoto Minakata, “Recent Progress of 40 GHz high-speed LiNbO3optical modulator,” Proceedings of SPIE, Vol.4532, Active and Passive OpticalComponents for WDM Communication, 16 (July 30, 2001) p.16-27 R. Madabushi, “Microwave Attenuation Reduction Techniques for Wide-BandTi: LiNbO3 Optical Modulators” IEICE TRANS. ELECTRON., VOL. E81-C, NO. 8 AUGUST 1998

  In the optical modulator having a ridge-type optical waveguide described in Patent Document 1, an eaves shape (that is, the width of the optical waveguide) is formed on the optical waveguide as described in FIGS. Signal electrode having a wider width). In addition, a ground electrode that is thinly formed so as not to contact the signal electrode is provided on the side surface of the ridge-shaped portion of the optical waveguide so as to contact the ridge-shaped portion of the optical waveguide. According to the optical modulator having such a structure, a low driving voltage, speed matching between the light guided in the optical waveguide and the modulation signal applied to the signal electrode, and low electrode loss can be realized. Is described in the literature.

  However, the conventional optical modulator described in Patent Document 1 has a problem that high-speed modulation operation is difficult for the following reasons.

  That is, in order to achieve a high-speed modulation operation, impedance matching is performed. Specifically, the output impedance of an external element that supplies a modulation signal applied to the modulation electrode (signal electrode and ground electrode), and optical It is necessary to make the input impedance of the modulator close to the same value (for example, 50Ω).

  However, in the optical modulator as described in Patent Document 1, the distance between the eaves-shaped signal electrode and the ground electrode provided on the side surface of the ridge-shaped portion of the optical waveguide is reduced. The capacitance between the ground electrode and the ground electrode increases. This reduces the impedance between the signal electrode and the ground electrode. Patent Document 1 shows that in a design optimized in an optical modulator as described in the document, the characteristic impedance is 18.4Ω, and as a result, the optical modulator and the above-mentioned Since it becomes difficult to achieve impedance matching with an external element, it becomes difficult to achieve a high-speed modulation operation substantially.

  The same thing becomes a problem also in the optical modulator having a signal electrode protruding in a mushroom shape described in Patent Document 2. The configuration using the signal electrode protruding in a mushroom shape described in Patent Document 2 is one of the very effective configurations for realizing speed matching and low electrode loss. However, there is a problem that characteristic impedance is lowered. Non-Patent Document 2 describes that the problem with the configuration having a signal electrode protruding in a mushroom shape is that the characteristic impedance is deviated from 50Ω, and that the reflection characteristic S11 of the electrode is inferior to −10 dB. Has been.

  The adverse effect of the deterioration of the reflection characteristics due to the deviation of the characteristic impedance from 50Ω can be avoided by incorporating the impedance converter or the impedance conversion circuit into the modulator. However, an optical modulator having a low characteristic impedance even when the power of the drive signal is the same causes a problem that the voltage between the signal electrode and the ground electrode in the action electrode portion of the signal electrode is lowered. This decrease in voltage between the signal electrode and the ground electrode is particularly caused by an electro-optic effect (a phenomenon in which the refractive index changes according to the applied electric field, that is, the Pockels effect and the like, as in an optical modulator in which an optical waveguide is constituted by lithium niobate. The optical modulator based on the optical Kerr effect is extremely disadvantageous from the viewpoint of driving with high efficiency (low power consumption). Therefore, in order to drive with high efficiency (low power consumption), it is desirable to design while avoiding a decrease in characteristic impedance.

  The present invention has been made in view of such problems, and provides an optical modulator having a ridge-type optical waveguide and an eaves-shaped or mushroom-shaped signal electrode that can operate at high speed. With the goal.

  The present invention is based on the principle of reducing the interelectrode capacitance and increasing the characteristic impedance by cutting out a part of the ground electrode element that acts opposite to the signal electrode.

  That is, in order to solve the above-described problem, an optical modulator according to the present invention is provided on a main body portion having a main surface and a main surface of the main body portion, and extends along a first direction along the main surface. A ridge-type optical waveguide; and a modulation electrode for modulating light guided in the ridge-type optical waveguide. The main surface of the base portion is an installation surface provided with the ridge-type optical waveguide; The modulation electrode is supplied with a modulation signal. The modulation electrode has a first surface and a second surface that are positioned so as to sandwich the installation surface along a second direction along the main surface. The signal electrode comprises a signal electrode, a first ground electrode, and a second ground electrode. The signal electrode is a portion provided on the ridge-type optical waveguide so as to extend along the first direction, and is formed on the ridge-type optical waveguide. The uppermost portion has a wide portion having a width wider than the width in the second direction, and the first ground electrode extends along the first direction. The first ground electrode element is provided on the first surface so as to extend, and the second ground electrode has the second ground electrode element provided on the second surface so as to extend along the first direction. The first ground electrode element has at least one first through hole provided only in a part of the first ground electrode element in the first direction, and the second ground electrode element is the second ground electrode element. It has at least one second through hole provided only in a part in the first direction, and the at least one first through hole overlaps with the wide portion of the signal electrode in a plan view or the wide portion. And the at least one second through hole overlaps with the wide portion of the signal electrode in a plan view, or faces the wide portion in the second direction. The through hole is opposed to the wide part when the electric lines of force generated from the wide part reach around the opening of the through hole and are terminated, and the presence or absence of the through hole indicates the capacitance of the circuit of the modulation electrode. Alternatively, there is a significant influence on the characteristic impedance value (the relative difference in capacitance or characteristic impedance value depending on the presence or absence of the through-hole is 0.3 accuracy, which is the general accuracy of the impedance calibration circuit board of the high-frequency network analyzer. % Aspect). It should be noted that the opening of the through hole and the bottom of the through hole may not be directly seen from the wide part.

  In the optical modulator according to the present invention, each of the first ground electrode element and the second ground electrode element overlaps with the wide portion of the signal electrode in plan view or faces the wide portion in the second direction. A first through hole and a second through hole. Therefore, compared with the case where the first ground electrode element and the second ground electrode element do not have the first through hole and the second through hole, respectively, between the signal electrode, the first ground electrode, and the second ground electrode. Since the capacity can be reduced, the characteristic impedance of the modulation electrode can be increased. As a result, according to the optical modulator of the present invention, when the signal electrode functions as a lumped constant electrode, the capacitance between the signal electrode, the first ground electrode, and the second ground electrode, which hinders high frequency driving, is reduced. In addition, when the signal electrode functions as a traveling waveform electrode, it is possible to avoid a decrease in the characteristic impedance of the modulation electrode and to easily achieve impedance matching between the external element that supplies the modulation signal and the modulator. High-speed modulation operation and high-efficiency driving are possible.

  Furthermore, in the optical modulator according to the present invention, the at least one first through hole and the at least one second through hole have a circular shape, an elliptical shape, a racetrack shape, or a corner in plan view. It preferably has a round rectangular shape. Thereby, the interface (side surface of the first ground electrode element) adjacent to the first through hole of the first ground electrode element in plan view and the interface adjacent to the second through hole of the second recessed ground electrode element in plan view The (side surface of the second ground electrode element) has a curved shape having no corners or protrusions. As a result, when a modulation signal is applied to the modulation electrode, it is difficult for excessive electric field concentration to occur at the corners and protrusions at the adjacent interface, so that the modulation caused by the formation of the first and second through-holes Signal propagation loss can be suppressed.

  Furthermore, in the optical modulator according to the present invention, the first ground electrode element has a plurality of first through holes, and the plurality of first through holes are provided in order along the first direction, The second ground electrode element preferably has a plurality of second through holes, and the plurality of second through holes are preferably provided in order along the first direction.

  As a result, when the signal electrode functions as a lumped constant electrode, it is possible to reduce the capacitance between the electrodes that hinders high-frequency driving, and when the signal electrode functions as a traveling waveform electrode, the characteristics of the modulation electrode Since the impedance can be further increased, impedance matching between the external element that supplies the modulation signal and the modulator can be easily achieved with higher accuracy. As a result, according to the optical modulator of the present invention, it is possible to perform modulation operation at higher speed and efficient driving.

  Further, in the optical modulator according to the present invention, the at least one first through hole is spaced apart from a side surface of the first ground electrode element on the ridge-type optical waveguide side in a plan view, and the at least one first through hole is formed. The two through holes are preferably separated from the side surface of the second ground electrode element on the ridge-type optical waveguide side in plan view.

  As a result, the first ground electrode element and the second ground are disposed so that the through-holes are opened to the ridge-type optical waveguide side on the side surface of the first ground electrode element and the side surface of the second ground electrode element in plan view. It is possible to prevent the corner portion from being formed on the side surface of the electrode element on the ridge-type optical waveguide side. As a result, when the modulation signal is applied to the modulation electrode, the concentration of the electric field is less likely to occur on the side surface, so that the propagation loss of the modulation signal due to the formation of the through hole can be suppressed.

  Furthermore, in the optical modulator according to the present invention, the at least one first through hole is separated from the side surface of the first ground electrode element on the ridge-type optical waveguide side by 20 μm or more in plan view, and at least one first through-hole is provided. The two through holes are preferably 20 μm apart from the side surface of the second ground electrode element on the ridge-type optical waveguide side in plan view. As a result, the separation distance between the modulation electrode and the first and second through-holes also increases, so that when a modulation signal is applied to the modulation electrode, electric field concentration is less likely to occur on the side surface. Propagation loss can be further suppressed.

In the case of the configuration of Non-Patent Document 1, the propagation loss of the modulation signal in a mode in which no through hole is provided in the first ground electrode element and the second ground electrode element is about 0.2 dB / [cm (GHz) ^1/2 ]. In the case of the similar configuration of Patent Document 2, it is about 0.18 dB / [cm (GHz) ^1/2 ], and in the case of using the configuration of Patent Document 2 together with the ridge type optical waveguide, 0.15 dB / [cm (GHz) ^{1 / 2} ]. When the separation distance between the first through hole and the side surface on the ridge type optical waveguide side in plan view and the separation distance between the second through hole and the side surface on the ridge type optical waveguide side in plan view are about 20 μm, Modulation when a rounded rectangular through hole array having a width of 10 μm and a length of 50 μm is arranged as the first through hole and the second through hole in the first ground electrode element and the second ground electrode element along the first direction at an interval of 10 μm The deterioration width of the signal propagation loss is about 0.1 dB / [cm (GHz) ^1/2 ] in the case of the configuration of Non-Patent Document 1, and 0.02 dB / [cm (GHz) in the case of the similar configuration of Patent Document 2. ) ^1/2 ]. When the separation distance is about 30 μm, the propagation loss of the modulation signal due to the formation of the first through hole and the second through hole can be almost ignored.

  When the separation distance between the first through hole and the side surface of the ridge-type optical waveguide in plan view and the separation distance between the second through hole and the side surface on the ridge-type optical waveguide side in plan view are large, the first grounding is performed. The effect of reducing the capacitance between the signal electrode, the first ground electrode, and the second ground electrode by forming the first and second through holes in the electrode element and the second ground electrode element and the effect of increasing the characteristic impedance of the modulation electrode are as follows: Relatively low. However, even in such an embodiment, the present invention provides a case where an optical modulator having a configuration such as Non-Patent Document 1 or Non-Patent Document 2 is manufactured using an optical waveguide made of a high dielectric constant material such as lithium niobate. Provides a practically useful means for adjusting the capacitance between the signal electrode and the first ground electrode, the second ground electrode, and the characteristic impedance of the modulation electrode.

  When the first and second ground electrode elements are arranged in the first direction at intervals of 10 μm as rounded rectangular rows of round holes having a width of 10 μm and a length of 50 μm as the first and second through holes. In the case of the configuration of Non-Patent Document 1, the increase width of the characteristic impedance of the modulation signal greatly depends on the width of the ridge waveguide portion, and the optical waveguide width is a realistic value in this configuration. When it is set to ˜8 μm, the characteristic impedance of the modulation signal can be increased by about 5 to 10Ω. In the case of a configuration similar to Non-Patent Document 2, it is possible to increase the characteristic impedance of the modulation signal by about 2 to 5Ω, although it depends greatly on the shape of the signal electrode and the shape of the protruding signal side surface.

  When the separation distance between the first through hole and the side surface of the ridge type optical waveguide in plan view and the separation distance between the second through hole and the side surface on the ridge type optical waveguide side in plan view are about 30 μm, the signal electrode The effect of reducing the capacitance between the first and second ground electrodes and the second ground and the effect of increasing the characteristic impedance of the modulation electrode are further reduced, but the characteristic impedance of several Ω can be adjusted. Since the propagation loss of the modulation signal due to the formation of the first and second through holes can be almost ignored, the practical utility value is high.

  Furthermore, in the optical modulator according to the present invention, it is preferable that the first ground electrode element and the second ground electrode element are provided substantially in line symmetry with respect to the optical axis of the ridge-type optical waveguide in plan view. . As a result, it is possible to reduce the scale of the optical modulator characteristic analysis calculation, and to avoid the bias of stress and strain of the substrate when the temperature of the optical modulator changes, and to obtain the stability of the operation of the optical modulator. I can expect.

  Although the arrangement positions of the first and second through holes are asymmetrical, the effect of reducing the capacitance between the signal electrode, the first ground electrode and the second ground electrode and the effect of increasing the characteristic impedance of the modulation electrode can be obtained. For convenience, it is desirable to have a symmetrical arrangement so that the size of the characteristic analysis calculation is small. If the first and second through holes are arranged with the center portion of the signal electrode as a symmetric line, the calculation scale of the finite element analysis and the propagation analysis can be halved. Furthermore, with such a symmetrical arrangement, the asymmetrical deviation of the stress / strain of the substrate is dispersed, and it can be expected that the operation stability of the optical modulator is obtained. In addition, the symmetrical arrangement of the first and second through holes has an advantage that the scale of analysis calculation can be reduced even in the design and analysis of stress and strain.

  A plurality of rows of first and second through holes may be formed, which has a higher effect of reducing the capacitance between the signal electrode, the first ground electrode, and the second ground electrode and increasing the characteristic impedance of the modulation electrode. Needless to say. However, since the propagation loss of the control signal increases due to the formation of the first and second through holes, the first and second through holes that are the minimum necessary are formed in a range where the propagation loss characteristic of the control signal is allowed. It is desirable.

  In forming the first and second through holes, it is desirable to consider from the viewpoint of ensuring line width resolution in the photolithography process and reproduction in the plating process. First and second through holes are formed at positions spaced apart from the edge of the first ground electrode on the ridge waveguide side and the edge of the second ground electrode on the ridge waveguide side at the same degree as or more than the width of the ridge waveguide. It is desirable to do.

  According to the present invention, there is provided an optical modulator that includes a ridge-type optical waveguide and an eaves-like or mushroom-like signal electrode that can operate at high speed. In particular, it is effective in solving the problem of characteristic impedance reduction that has been manifested in an optical modulator using an optical waveguide made of lithium niobate described in Non-Patent Document 1 and Non-Patent Document 2.

It is a top view which shows the structure of the optical modulator which concerns on 1st Embodiment. It is sectional drawing of the optical modulator along the II-II line | wire of FIG. FIG. 3 is a perspective view of the optical modulator in the vicinity of the cross-sectional view of FIG. 2. It is a top view which shows the structure of the optical modulator which concerns on 2nd Embodiment. It is sectional drawing of the optical modulator along the VV line of FIG. It is a top view which shows the structure of the optical modulator which concerns on 3rd Embodiment. It is sectional drawing of the optical modulator along the VII-VII line of FIG. It is a top view which shows the structure of the optical modulator which concerns on 4th Embodiment. It is sectional drawing of the optical modulator along the IX-IX line of FIG. It is sectional drawing of the optical modulator which concerns on 5th Embodiment. It is a top view which shows the structure of the optical modulator which concerns on 6th Embodiment. It is sectional drawing of the optical modulator along the IX-IX line of FIG.

  Hereinafter, an optical modulator according to an embodiment will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used for the same elements when possible. In addition, the dimensional ratios in the components in the drawings and between the components are arbitrary for easy viewing of the drawings.

  The feature of the optical modulator of the present embodiment described below is that a part of the ground electrode element that acts opposite to the signal electrode is notched, thereby reducing the capacitance between these electrodes and increasing the characteristic impedance. An embodiment that is based on the principle and is particularly effective for improving the characteristics of an optical modulator having high practical value is described below. Furthermore, the optical modulator of the present embodiment also incorporates a technique for suppressing the propagation loss of the signal electrode, which is an adverse effect of the introduction of the principle, and is characterized by an industrially valuable technique. It is an optical modulator.

(First embodiment)
FIG. 1 is a plan view showing the configuration of the optical modulator according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the optical modulator along the line II-II in FIG. FIG. 3 is a perspective view of the optical modulator in the vicinity of the cross-sectional view of FIG. 2.

  As shown in FIGS. 1 to 3, the optical modulator 100 of the present embodiment is a device that modulates input light CL, which is continuous light introduced by an optical fiber or the like, and outputs modulated light ML to the outside. . The optical modulator 100 can include a base portion 3, a ridge-type optical waveguide 5, and a modulation electrode 15.

The base portion 3 is a plate-like member made of a dielectric material that exhibits an electro-optic effect such as lithium niobate (LiNbO ₃ ). The base 3 has a substantially flat main surface 3S. FIG. 1 shows an orthogonal coordinate system RC in which the X axis and the Y axis are set in a direction parallel to the main surface 3S, and the Z axis is set in a direction orthogonal to the main surface 3S. In each of the drawings subsequent to FIG. 2, the orthogonal coordinate system RC is shown so as to correspond to FIG. 1 as necessary.

  The base portion 3 has a longitudinal shape extending in the Y-axis direction (first direction). The main surface 3S of the base body portion 3 includes an installation surface 3E on which the ridge type optical waveguide 5 is provided, a first surface 3A, and a second surface 3B. The installation surface 3E, the first surface 3A, and the second surface 3B are surfaces that extend in the Y-axis direction, and extend from one end in the negative Y-axis direction to the other end in the positive Y-axis direction. The first surface 3A and the second surface 3B are positioned so as to sandwich the installation surface 3E along the X-axis direction (second direction).

  In the present embodiment, the ridge type optical waveguide 5 is provided on the entire installation surface 3E of the main surface 3S. The ridge-type optical waveguide 5 is an optical waveguide having a shape protruding in the Z-axis direction and extending along the Y-axis direction. The input light CL is introduced into the optical modulator 100 from the end surface in the negative Y-axis direction of the core portion 5A of the ridge-type optical waveguide 5, and is guided along the optical axis 5AX of the core portion 5A. The modulated light ML is output to the outside of the optical modulator 100 from the end surface of the core portion 5A in the positive Y-axis direction.

The ridge-type optical waveguide 5 includes a core portion 5A, a cladding portion 5B, and a buffer layer 5C that extend along the Y-axis direction. The core portion 5A is made of a material having a higher refractive index than the cladding portion 5B. The core portion 5A and the cladding portion 5B are each made of a dielectric material that exhibits an electro-optic effect. The core portion 5A is made of, for example, lithium niobate (LiNbO ₃ ) containing a metal such as titanium (Ti), and the cladding portion 5B is made of, for example, lithium niobate (LiNbO ₃ ). The buffer layer 5C is made of a material having a lower refractive index than that of the core portion 5A, and is made of a dielectric material such as silicon oxide (SiO ₂ ). The buffer layer 5 </ b> C is interposed between the core portion 5 </ b> A and the signal electrode 7, thereby reducing the propagation loss of light guided in the core portion 5 </ b> A due to the signal electrode 7. The ridge type optical waveguide 5 may not have the buffer layer 5C.

The structure including the base portion 3 and the ridge-type optical waveguide 5 provided on the base portion 3 as described above is a plate-shaped initial substrate made of a dielectric material such as lithium niobate (LiNbO ₃ ). A metal such as titanium (Ti) is diffused in a region to be the core portion 5A in the vicinity of the main surface of the initial substrate, and a dielectric made of a dielectric material constituting the buffer layer 5C is formed on the entire main surface. After the body film is formed, it can be obtained by etching the initial substrate and the dielectric film so as to leave the regions to be the ridge type optical waveguide 5 and the base portion 3. Alternatively, the structure can also be obtained by preparing the base portion 3 and forming the ridge type optical waveguide 5 on the installation surface 3E of the main surface 3S of the base portion 3.

The base portion 3 is made of an optical material such as SiO ₂ , Al ₂ O ₃ , optical glass, or optical resin, and the ridge-type optical waveguide 5 is made of a dielectric material having an electrooptic effect such as lithium niobate. The waveguide structure 3 and the first control signal electrode 5 can be made of different materials. This configuration should be the ridge type optical waveguide 5 and the base part 3 after the base part material and the material of the ridge type optical waveguide part are bonded together and the film of the ridge part waveguide material is formed on the base part material. It can be obtained by etching the initial substrate and the dielectric film so as to leave a region. In this case, the refractive index of the base material needs to be selected as a combination of materials smaller than the refractive index of the ridge type optical waveguide material in the wavelength and polarization conditions of the incident light used for the optical modulator. In this configuration, since the entire ridge-shaped portion 5 functions as the core portion of the optical waveguide, the portion 5A having a high refractive index may not be formed in the ridge-shaped portion 5.

  The modulation electrode 15 includes a signal electrode 7, a first ground electrode 11, and a second ground electrode 12. The modulation electrode 15 is an electrode having a shape extending along the XY plane, and is made of a material that is a good conductor at a high frequency, for example, a metal such as gold (Au), silver (Ag), copper (Cu), or a superconductive material. The The modulation electrode 15 is provided to modulate the input light CL guided in the ridge-type optical waveguide 5.

  In the present embodiment, the signal electrode 7 includes an input-side transmission unit 7T1, a wide portion 7W, and an output-side transmission unit 7T2. The input side transmission unit 7T1 includes an input pad 7P1 and a signal transmission unit 7E1. The input pad 7P1 is provided, for example, in the vicinity of the end on the positive side of the X axis in the main surface 3S of the base body portion 3, and functions as an input portion to which a modulation signal supplied from an external element is input. The modulation signal includes a high-frequency electric signal of, for example, 10 GHz or more. One end of the signal transmission unit 7E1 is electrically connected to the input pad 7P1, and the signal transmission unit 7E1 transmits the modulation signal input to the input pad 7P1 to the wide portion 7W. The portion in the vicinity of the wide portion 7W of the signal transmission portion 7E1 has a shape that gradually increases so that the width in plan view (when viewed from the Z-axis direction) approaches the width of the wide portion 7W as it approaches the wide portion 7W. The structure prevents reflection loss due to impedance mismatch.

  One end of the wide portion 7W is electrically connected to the other end of the signal transmission portion 7E1. The wide portion 7W is provided on the ridge type optical waveguide 5 so as to extend along the Y-axis direction. The width W7W in the X-axis direction of the wide portion 7W is larger than the width W5 in the X-axis direction at the top of the ridge-type optical waveguide 5. Therefore, in the cross section orthogonal to the Y-axis direction, the wide portion 7 </ b> W has an eaves shape or a mushroom shape as shown in FIGS. 1 to 3 with respect to the ridge type optical waveguide 5. Here, the wide portion 7 </ b> W has an eaves shape when the wide portion 7 </ b> W of the signal electrode 7 extends from the upper surface of the ridge optical waveguide 5 to the ridge optical waveguide 5 in the second direction. 5 means a cross-sectional structure in which a ridge is attached to the upper surface of the ridge-type optical waveguide 5. In addition, the wide portion 7W has a mushroom shape means that the wide portion 7W of the signal electrode 7 is a base portion in contact with the upper surface of the ridge-type optical waveguide 5 and a portion above the base portion and wider than the base portion. A wide upper portion, that is, the wide portion 7W of the signal electrode 7 has an overhang portion (above-mentioned upper portion) protruding in the second direction with respect to the ridge-type optical waveguide 5, and This means that the wide portion 7W is wider than the ridge-type optical waveguide 5w of the ridge-type optical waveguide 5, and the cross-sectional shape of the wide portion 7W is a mushroom shape provided on the upper surface of the ridge-type optical waveguide 5. Means.

  The wide part 7W functions as a modulation action part that gives a modulation action to light guided in the core part 5A. Specifically, an electric field can be applied to the core portion 5A of the ridge-type optical waveguide 5 by the wide portion 7W, the strength of the applied electric field, the type of material constituting the core portion 5A, and the core portion 5A The refractive index of the core portion 5A changes depending on the direction of dielectric polarization and the like. When the modulation signal is supplied to the signal electrode 7, the wide portion 7W applies an electric field corresponding to the modulation signal to the core portion 5A of the ridge-type optical waveguide 5 and changes the refractive index in the core portion 5A according to the modulation signal. Change. Thereby, the input light CL is modulated according to the modulation signal.

  The shape of the cross section perpendicular to the Y-axis of the wide portion 7W is not limited to the flat plate shape as one aspect of the eaves shape as shown in FIG. 2, for example, a rectangular shape, an elliptical shape, or an inverted trapezoidal shape that gradually protrudes It may be a shape that protrudes into a mushroom, may be a shape that protrudes into a mushroom shape, or may be an intermediate shape or a composite shape thereof.

  The output side transmission unit 7T2 includes an output pad 7P2 and a signal transmission unit 7E2. One end of the signal transmission unit 7E2 is electrically connected to the other end of the wide portion 7W, and the signal transmission unit 7E2 transmits the modulation signal transmitted through the wide portion 7W to the output pad 7P2. The portion in the vicinity of the wide portion 7W of the signal transmission portion 7E2 has a shape in which the width in plan view gradually decreases as it approaches the output pad 7P2, and has a structure that prevents the occurrence of reflection loss due to impedance mismatch. ing. The other end of the signal transmission unit 7E2 is electrically connected to the output pad 7P2. The output pad 7P2 is provided, for example, in the vicinity of the end on the positive side of the X axis in the main surface 3S of the base 3 and functions as an output unit that outputs a modulation signal. The output pad 7P2 may be electrically connected to a resistor included in a termination portion (not shown) that is an electrical termination of the modulation signal.

  The first ground electrode 11 and the second ground electrode 12 are electrodes connected to the ground potential. The first ground electrode 11 and the second ground electrode 12 are electrodes each having a shape extending along the XY plane, and are provided on the main surface 3 </ b> S of the base portion 3. The first ground electrode 11 and the second ground electrode 12 are each made of a metal such as gold (Au).

  The first ground electrode 11 includes one end ground electrode element 11E1, a center ground electrode element 11C as the first ground electrode element, and the other end ground electrode element 11E2. The one-end ground electrode element 11E1 is an electrode element on the Y-axis negative direction side of the first ground electrode 11, and the center-ground electrode element 11C is a central part of the first ground electrode 11 at the center in the Y-axis direction. The other end ground electrode element 11 </ b> E <b> 2 is an electrode element on the Y axis positive side direction side of the first ground electrode 11.

  Similarly, the second ground electrode 12 includes one end ground electrode element 12E1, a central ground electrode element 12C as the second ground electrode element, and the other end ground electrode element 12E2. The one end ground electrode element 12E1 is an electrode element in the Y-axis negative side direction of the second ground electrode 12, and the central ground electrode element 12C is an electrode in the Y-axis direction central part of the second ground electrode 12. The other end ground electrode element 12 </ b> E <b> 2 is an electrode element in the Y axis positive side direction of the second ground electrode 12.

  The one end ground electrode element 11E1 and the one end ground electrode element 12E1 extend from the vicinity of the input pad 7P1 to one end of the central ground electrode element 11C and the central ground electrode element 12C in the Y-axis negative side direction, respectively. Connected. The other end ground electrode element 11E2 and the other end ground electrode element 12E2 extend from the vicinity of the output pad 7P2 to the other end of the center ground electrode element 11C and the center ground electrode element 12C in the positive Y-axis direction, respectively. It is electrically connected to the other end. The first ground electrode 11 and the second ground electrode 12 are electrically connected to an element having an external ground potential in a region near the input pad 7P1 of the one end ground electrode element 11E1 and the one end ground electrode element 12E1. In addition, in the region near the output pad 7P2 of the other end ground electrode element 11E2 and the other end ground electrode element 12E2, it can be electrically connected to an element having an external ground potential.

  The central portion ground electrode element 11C is provided on the first surface 3A of the main surface 3S of the base portion 3 so as to extend along the Y-axis direction, that is, along the extending direction of the wide portion 7W. . In the present embodiment, the central ground electrode element 11 </ b> C is in contact with the ridge type optical waveguide 5 in the X-axis direction on the main surface 3 </ b> S of the base portion 3. Therefore, a part of the center part ground electrode element 11C overlaps with the wide part 7W in plan view. The thickness T11C of the central ground electrode element 11C in the Z-axis direction is lower than the height T5 of the ridge-type optical waveguide 5 in the Z-axis direction. Therefore, the central ground electrode element 11C is separated from the wide portion 7W in the Z-axis direction. The thickness T11C of the central ground electrode element 11C is, for example, 1 μm or more and 3 μm or less, and the height T5 of the ridge-type optical waveguide 5 can be, for example, 3 μm or more and 10 μm or less.

  The center part ground electrode element 11C has a plurality of first through holes 11B. The first through hole 11B is a hole that penetrates the central ground electrode element 11C along the Z-axis direction. Each first through hole 11B is provided in a region of the central ground electrode element 11C that overlaps with the wide portion 7W in plan view. Therefore, each 1st through-hole 11B overlaps with the wide part 7W by planar view. Each first through hole 11B is spaced apart from the side surface 11S of the central ground electrode element 11C on the ridge-type optical waveguide 5 side in the X-axis direction in plan view. Each first through-hole 11B has a shape that does not have a corner, for example, a circular shape, an elliptical shape, a race track shape, or a rounded rectangular shape in plan view. The racetrack shape has an outer edge having first and second arc portions and first and second straight portions, and an opening in the first arc portion and an opening in the second arc portion. The first and second arc portions are arranged so as to face each other, one end of the first arc portion and one end of the second arc portion on the one end side are connected by the first linear portion, The other end of a 1st circular arc part and the other end of a 2nd circular arc part say the shape connected by the 2nd linear part. The plurality of first through holes 11B may have the same planar view shape, or part or all of them may have different planar view shapes.

  The plurality of first through holes 11B are periodically provided with a period P11B in order along the Y-axis direction. From the viewpoint of realizing the effect of reducing the capacitance between the signal electrode 7 and the first ground electrode 11 and the second ground electrode 12 and the effect of increasing the characteristic impedance of the modulation electrode 15, the first through-hole 11 </ b> B having the same shape is formed in the first shape. For example, a plurality of types of first through-holes 11B having different shapes may be arranged, or a plurality of types of first through-holes 11B may be arranged discretely or You may arrange | position with a predetermined period along the extension direction of the signal electrode 7. FIG. Rather than disposing the first through-holes 11B discretely or disposing a plurality of types of first through-holes 11B having different shapes, it is preferable to periodically dispose a plurality of first through-holes 11B having the same shape. Since the size of the characteristic analysis calculation is small, it is advantageous in design, and the design analysis is facilitated. Therefore, it is easy to prevent the characteristic deterioration of the loss of the propagation signal due to unintended impedance mismatch.

  In the case of a structure in which the first through-holes 11B are periodically provided, the structure acts as a bandpass filter circuit corresponding to a specific frequency, so that a specific frequency signal is coupled to the bandpass filter circuit. However, the signal propagating through the signal electrode may be deteriorated. The deterioration of the modulation signal is avoided by setting the period in which the first through-hole 11B is provided to ¼ or less of the wavelength of the main frequency component of the modulation signal (the wavelength of the frequency component in the band-pass filter circuit). can do.

  Similarly, the central portion ground electrode element 12C is provided on the second surface 3B of the main surface 3S of the base portion 3 so as to extend along the Y-axis direction, that is, along the extending direction of the wide portion 7W. It has been. In the present embodiment, the central ground electrode element 12 </ b> C is in contact with the ridge type optical waveguide 5 in the X-axis direction on the main surface 3 </ b> S of the base portion 3. Therefore, a part of the central portion ground electrode element 12C overlaps with the wide portion 7W in plan view. The thickness T12C of the central ground electrode element 12C in the Z-axis direction is lower than the height T5 of the ridge-type optical waveguide 5 in the Z-axis direction. Therefore, the center part ground electrode element 12C is separated from the wide part 7W in the Z-axis direction. The thickness T12C of the central ground electrode element 12C is, for example, not less than 1 μm and not more than 3 μm.

  The center ground electrode element 12C has a plurality of second through holes 12B. The second through hole 12B is a hole that penetrates the central ground electrode element 12C along the Z-axis direction. Each 2nd through-hole 12B is provided in the area | region which overlaps with the wide part 7W by planar view among 12 C of center part ground electrode elements. Therefore, each 2nd through-hole 12B overlaps with the wide part 7W by planar view. Each of the second through holes 12B is spaced apart from the side surface 12S of the central ground electrode element 12C on the ridge-type optical waveguide 5 side in the X-axis direction in plan view. Each of the second through holes 12B has a shape that does not have a corner, for example, a circular shape, an elliptical shape, a race track shape, or a rounded rectangular shape in plan view.

  The plurality of second through holes 12B are periodically provided in a cycle P12B in order along the Y-axis direction. Points to note about the periodicity and shape of the arrangement of the second through holes are the same as in the case of the first through holes 11B described above. Furthermore, it is preferable that the first through hole 11B and the second through hole 12B have a line symmetry with respect to the optical axis 5AX of the core portion 5A in plan view, because the calculation scale in the design analysis is small.

  In the optical modulator 100 according to the present embodiment as described above, the central ground electrode element 11C and the central ground electrode element 12C each have a first through hole that overlaps the wide portion 7W of the signal electrode 7 in plan view. 11B and the 2nd through-hole 12B (refer FIG.1 and FIG.2). Therefore, compared with the case where the center part ground electrode element 11C and the center part ground electrode element 12C do not have the first through hole 11B and the second through hole 12B, respectively, the signal electrode 7 and the first ground electrode 11 and Since the capacitance between the second ground electrodes 12 can be reduced, the characteristic impedance of the modulation electrode 15 can be increased.

  As a result, according to the optical modulator 100 according to the present embodiment, when the signal electrode 7 functions as a lumped constant electrode, the signal electrode 7, the first ground electrode 11, and the second ground electrode hinder high frequency driving. 12 can be reduced, and when the signal electrode 7 functions as a traveling waveform electrode, a decrease in characteristic impedance of the modulation electrode 15 can be avoided, and an external element and a modulator for supplying a modulation signal Therefore, high-speed modulation operation and high-efficiency driving are possible.

  As described above, the technique employed in the present embodiment is designed to reduce the capacitance between the signal electrode 7, the first ground electrode 11, and the second ground electrode 12 when designing the characteristic impedance of the modulation electrode 15 to be high. This is an effective technology. Therefore, light modulation is performed using the base portion 3 made of a material having a high relative dielectric constant, such as lithium niobate (the relative dielectric constant of lithium niobate has anisotropy, and the relative dielectric constant is 28 and 45). This is particularly effective when the container 100 is manufactured. This is particularly effective when the optical modulator 100 that is driven by a high-frequency control signal or a broadband control signal including a component in the GHz band is manufactured.

  In particular, in the optical modulator 100 according to the present embodiment, the first through holes 11B and the second through holes 12B are provided so as to overlap the wide portion 7W in plan view (see FIG. 1). ), The entire capacitance between the signal electrode 7 and the first ground electrode 11 and the second ground electrode 12 is a parallel plate capacitor corresponding to the total area of the first through hole 11B, the second through hole 12B and the through hole. Therefore, the characteristic impedance of the modulation electrode 15 can be further increased.

  Furthermore, in the optical modulator 100 according to the present embodiment, each of the first through holes 11B and the second through holes 12B has a shape that does not have a corner such as a circular shape or an elliptical shape in plan view. (See FIG. 1 and FIG. 3). Thus, the interface adjacent to the first through hole 11B of the central ground electrode element 11C in plan view and the interface adjacent to the second through hole 12B of the central ground electrode element 12C in plan view have corners. It becomes a curve shape that does not. As a result, when a modulation signal is applied to the modulation electrode 15, electric field concentration is less likely to occur at the adjacent interface, so that propagation loss of the modulation signal can be suppressed.

  Furthermore, in the optical modulator 100 according to the present embodiment, the center ground electrode element 11C has a plurality of first through holes 11B, and the plurality of first through holes 11B are sequentially in the Y-axis direction. The central ground electrode element 12C has a plurality of second through holes 12B, and the plurality of second through holes 12B are sequentially provided along the Y-axis direction (FIGS. 1 and 3).

  Thereby, since the impedance of the modulation electrode 15 can be further increased, impedance matching between the external element that supplies the modulation signal and the optical modulator 100 can be easily achieved with higher accuracy. As a result, according to the optical modulator 100 according to the present embodiment, a higher-speed modulation operation can be performed.

  Furthermore, in the optical modulator 100 according to the present embodiment, the first through hole 11B is separated from the side surface 11S on the ridge-type optical waveguide 5 side of the central ground electrode element 11C in plan view, and the second through hole The hole 12B is separated from the side surface 12S on the ridge-type optical waveguide 5 side of the central ground electrode element 12C in plan view (see FIG. 1).

  Thereby, it can prevent that a corner | angular part is formed in the said side 11S of the center part ground electrode element 11C and the said side 12S of the center part ground electrode element 12C by planar view. As a result, when the modulation signal is applied to the modulation electrode 15, electric field concentration is less likely to occur on the side surfaces 11S and 12S, and thus propagation loss of the modulation signal can be suppressed.

  In the optical modulator 100 according to the present embodiment, the central ground electrode element 11C is in contact with the ridge-type optical waveguide 5 in the X-axis direction on the main surface 3S of the base body 3, and the central ground electrode element 12C is in contact with the ridge type optical waveguide 5 in the X-axis direction on the main surface 3S of the base portion 3 (see FIGS. 1 to 3). As a result, the area of the central portion ground electrode element 11C and the area of the central portion ground electrode element 12C that overlap with the wide portion 7W in plan view are increased, so that the region and the central portion of the wide portion 7W and the central portion ground electrode element 11C are increased. The ratio of the power of the control signal transmitted through the gap between the ground electrode element 12C and the area increases, and the speed of the modulation signal increases, and the light guided in the ridge-type optical waveguide 5 and the modulation applied to the signal electrode 7 are increased. Speed matching with the signal is possible, and the surface area of the central ground electrode element 11C and the central ground electrode element 12C is widened to avoid electric field concentration, so that low electrode loss can be more easily realized.

  As a result, in the optical modulator having the conventional configuration, the increase in interelectrode capacitance and the decrease in characteristic impedance, which are the disadvantages of the configuration using the signal electrodes that project in the form of eaves, are caused in the optical modulator 100 of the present embodiment. Can be improved by providing each of the first through holes 11B and the second through holes 12B in the central ground electrode element 11C and the central ground electrode element 12C.

  Further, in the optical modulator 100 according to the present embodiment, each first through hole 11B is separated from the side surface 11S of the central ground electrode element 11C on the ridge-type optical waveguide 5 side by 2 μm or more in the X-axis direction in plan view. Each of the second through holes 12B is preferably separated from the side surface 12S of the central ground electrode element 12C on the ridge-type optical waveguide 5 side by 2 μm or more in the X-axis direction in plan view. The skin depth due to the skin effect at a frequency of 10 GHz, which is a good conductor generally used as an electrode material of an optical modulator corresponding to a high frequency, is approximately 1 μm or less. In the preferred embodiment described above, each of the first through holes 11B and the second through holes 12B has a central ground electrode element 11C and a side surface 11S on the ridge-type optical waveguide 5 side of the central ground electrode element 12C in plan view. The distance from 12S is more than the surface layer depth. Thereby, even if an electric field concentrates in the vicinity of each 1st through-hole 11B and each 2nd through-hole 12B among center part ground electrode element 11C and center part ground electrode element 12C, it is enough for a high frequency current Since the skin depth is secured, it is possible to suppress the occurrence of modulation signal propagation loss.

  Further, the distance in the X-axis direction between each first through-hole 11B in plan view and the side surface 11S on the ridge-type optical waveguide 5 side of the central ground electrode element 11C is from the viewpoint of suppressing the generation of propagation loss. It is not particularly limited, and may be appropriately determined according to the design of the capacitance between the signal electrode 7 and the first ground electrode 11 and the second ground electrode 12 or the characteristic impedance of the modulation electrode 15. When the separation distance is large, the effect of lowering the capacitance between the signal electrode 7 and the first ground electrode 11 and the second ground electrode 12 and increasing the characteristic impedance of the modulation electrode 15 tends to be reduced. Since 11B and the 2nd through-hole 12B are provided so that it may overlap with the wide part 7W by planar view, the dependence to the said separation distance of the said effect is comparatively small. The same applies to the distance in the X-axis direction from the side surface 12S on the ridge-type optical waveguide 5 side of the central ground electrode element 12C. Therefore, the decrease in the capacitance between the signal electrode 7 and the first ground electrode 11 and the second ground electrode 12 and the increase in the characteristic impedance of the modulation electrode 15 are mainly the first through-hole 11B and the second through-hole, not the above-mentioned separation distance. The total area in a plan view of 12B can be adjusted.

  In the optical modulator 100 according to the present embodiment, the central ground electrode element 11C and the central ground electrode element 12C are substantially lined with respect to the optical axis of the core portion 5A of the ridge-type optical waveguide 5 in plan view. It is preferable that they are provided symmetrically (see FIG. 1). Thereby, the scale of the analytical calculation required for the characteristic design can be reduced. In addition, it is expected that the stress / strain of the substrate during the temperature change due to the uneven arrangement of the first through-hole 11B and the second through-hole 12B is avoided, and the stability of the operation of the optical modulator is obtained. it can.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In each of the embodiments after the second embodiment, differences from the other embodiments will be mainly described, and the same elements as those in the other embodiments will be denoted by the same reference numerals and detailed description thereof will be given. May be omitted.

  FIG. 4 is a plan view showing the configuration of the optical modulator according to the second embodiment, and FIG. 5 is a cross-sectional view of the optical modulator along the line VV in FIG. The optical modulator 200 of this embodiment differs from the optical modulator 100 of the first embodiment in the position where the first through hole is provided and the position where the second through hole is provided.

  That is, as shown in FIGS. 4 and 5, the modulation electrode 215 of this embodiment includes a first ground electrode 211, a signal electrode 7, and a second ground electrode 212. The central ground electrode element 211C included in the first ground electrode 211 is different from the central ground electrode element 11C of the first embodiment at a position where a plurality of first through holes are formed. Specifically, the plurality of first through holes 211B of the present embodiment are provided in a region of the central portion ground electrode element 211C that does not overlap with the wide portion 7W in plan view. Therefore, each first through hole 211B faces the wide portion 7W in the X-axis direction in plan view.

  Similarly, the central ground electrode element 212C of the second ground electrode 212 is different from the central ground electrode element 12C of the first embodiment at a position where a plurality of second through holes are formed. Specifically, the plurality of second through holes 212B of the present embodiment are provided in a region of the central portion ground electrode element 212C that does not overlap with the wide portion 7W in plan view. Therefore, each second through-hole 212B faces the wide portion 7W in the X-axis direction in plan view.

  The plurality of first through holes 211B are periodically provided at a period P211B in order along the Y-axis direction, like the first through holes 11B of the first embodiment. From the viewpoint of developing the effect of reducing the capacitance between the signal electrode 7 and the first ground electrode 11 and the second ground electrode 12 and the effect of increasing the characteristic impedance of the modulation electrode 215, the first through hole 11B having the same shape is directed to the direction. For example, a plurality of types of first through-holes 11B having different shapes may be arranged, or a plurality of types of first through-holes 11B may be discretely or signaled. You may arrange | position with a predetermined period along the extension direction of the electrode 7. FIG. Rather than disposing the first through-holes 11B discretely or disposing a plurality of types of first through-holes having different shapes, it is preferable to periodically dispose a plurality of first through-holes 11B having the same shape. Since the size of the characteristic analysis calculation is small, it is advantageous in design, and the design analysis becomes easy. Therefore, it is easy to prevent the characteristic deterioration of the loss of the propagation signal due to unintended impedance mismatch.

  In the case of a structure in which the first through-holes 11B are periodically provided, the structure acts as a bandpass filter circuit corresponding to a specific frequency, so that a specific frequency signal is coupled to the bandpass filter circuit. However, the signal propagating through the signal electrode may be deteriorated. The deterioration of the modulation signal is avoided by setting the period in which the first through-hole 11B is provided to ¼ or less of the wavelength of the main frequency component of the modulation signal (the wavelength of the frequency component in the band-pass filter circuit). can do. The same applies to the plurality of second through holes 12B.

  According to the optical modulator 200 according to the present embodiment, it is easy to achieve impedance matching between the optical modulator 200 and an external element that supplies a modulation signal based on the same reason as the optical modulator 100 of the first embodiment. Therefore, high-speed modulation operation is possible.

  Further, in the optical modulator 200 of the present embodiment, the plurality of first through holes 211B are provided in a region of the central portion ground electrode element 211C that does not overlap with the wide portion 7W in plan view. Since the 2 through hole 212B is provided in a region of the central ground electrode element 212C that does not overlap with the wide portion 7W in plan view (see FIGS. 4 and 5), the modulation electrode 215 and the first through hole 211B are provided. Because of the large separation, the edge effect is less likely to occur at the edge of the first through hole 211B, and the propagation loss of the modulation signal due to the presence of the first through hole 211B can be reduced.

  However, in the case where the modulation electrode 215 has a flat structure with a flat cross section, if the separation distance is large, the capacitance between the signal electrode 7 and the first ground electrode 211 and the second ground electrode 212 decreases and the characteristics of the modulation electrode 215. The effect of increasing impedance is reduced. In the embodiment in which the base portion and the ridge waveguide portion are composed of lithium niobate, the speed matching and the low loss propagation of the modulation signal can be realized in this embodiment. For example, the width W7W of the wide portion 7W of the signal electrode 7 is ridged. When the separation distance is about 8 times the width W5 of the ridge waveguide portion, the effect of lowering the interelectrode capacitance and raising the characteristic impedance is obtained. May be relatively low.

  On the other hand, when the cross-sectional shape of the modulation electrode 215 is a structure having a large area corresponding to the side surface, such as a rectangular shape, an elliptical shape, an inverted trapezoidal shape, or a mushroom shape, the situation is different. Since the region of the central ground electrode element 211C that does not overlap with the wide portion 7W in plan view corresponds to a region that acts substantially opposite to the side surface portion of the modulation electrode 15, the first through hole 211B is formed in this portion. This is an effective means for reducing the capacitance between the signal electrode 7 and the first ground electrode 211 and the second ground electrode 212 and increasing the characteristic impedance of the modulation electrode 215. In particular, the effect is great when the height T607W of the signal electrode (see FIG. 12) is larger than the width W7W of the wide portion 7W of the signal electrode 7. Even if the first through hole 211B is formed in a region overlapping with the wide portion 7W in plan view in the central portion ground electrode element 211C or in a region not overlapping, the signal electrode 7 and the first ground electrode 211, Although the effect of lowering the capacitance between the second ground electrodes 212 and raising the characteristic impedance of the modulation electrode 215 can be obtained, it is advantageous to form the non-overlapping regions in that the modulation signal loss is small.

(Third embodiment)
Next, a third embodiment of the present invention will be described. FIG. 6 is a plan view showing the configuration of the optical modulator according to the third embodiment, and FIG. 7 is a cross-sectional view of the optical modulator along the line VII-VII in FIG. The optical modulator 300 of the third embodiment is different from the optical modulator 200 of the second embodiment in the plan view shape of the first through hole and the second through hole.

  That is, as shown in FIGS. 6 and 7, the modulation electrode 315 of this embodiment includes a first ground electrode 311, a signal electrode 7, and a second ground electrode 312. And the planar view shape of several 1st through-hole 311B provided in the center part ground electrode element 311C which the 1st ground electrode 311 has is respectively the 1st through-hole 211B (refer FIG. 4) of 2nd Embodiment. Is different, and is a shape having corners such as a rectangular shape. Similarly, the planar view shapes of the plurality of second through holes 312B provided in the central ground electrode element 312C of the second ground electrode 312 are respectively the second through hole 212B (see FIG. 4) of the second embodiment. Is different, and is a shape having corners such as a rectangular shape.

  According to the optical modulator 200 according to the present embodiment, it is easy to achieve impedance matching between the optical modulator 200 and an external element that supplies a modulation signal based on the same reason as the optical modulator 100 of the first embodiment. Therefore, high-speed modulation operation is possible.

  Furthermore, in the optical modulator 300 of this embodiment, the planar view shape of the plurality of first through holes 311B is a shape having corners such as a rectangular shape, and the planar view shape of the plurality of second through holes 312B. Since each has a corner shape such as a rectangular shape (see FIG. 6), the calculation scale of the characteristic analysis necessary for the design can be greatly reduced. Since each first through-hole 311B and each second through-hole 312B have a simple structure that does not include a curved portion, it is necessary to subdivide the element size in the finite element analysis compared to the case where these include the curved portion. The calculation scale is greatly reduced. In addition, an effect of greatly saving labor in inputting a model for calculation is exhibited.

  When the first through hole 311B and the second through hole 312B having corners are formed in a region overlapping with the signal electrode wide portion 7W in a plan view of the central ground electrode element 311C and the central ground electrode element 312C, Since the distance between the first through-hole 311B and the second through-hole 312B and the signal electrode 7W is short, the influence of the edge effect may be relatively increased, and the loss of the signal electrode 7 may be relatively increased. However, as in the present embodiment, the first through-hole 311B and the second through-holes 312B are formed in a region that does not overlap with the signal electrode wide portion 7W in a plan view of the central ground electrode element 311C and the second through-holes 312B. Is formed, since the distance between the first through hole 311B and the second through hole 312B and the signal electrode 7W is large, the influence of the edge effect is slight, and the loss of the signal electrode is reduced.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. FIG. 8 is a plan view showing the configuration of the optical modulator according to the fourth embodiment, and FIG. 9 is a cross-sectional view of the optical modulator along the line IX-IX in FIG. The light modulator 400 of the fourth embodiment further includes a first terrace portion 3T1 and a second terrace portion 3T2, and a point that the first ground electrode 11 further includes an on-terrace ground electrode element 11D. The second ground electrode 12 is different from the optical modulator 100 of the first embodiment (see FIGS. 1 to 3) in that the second ground electrode 12 further includes a terrace ground electrode element 12D.

  The first terrace portion 3T1 is a terrace-shaped member provided on the first surface 3A of the main surface 3S, and the second terrace portion 3T2 is a terrace-shaped member provided on the second surface 3B of the main surface 3S. It is a member. The first terrace portion 3T1 and the second terrace portion 3T2 have substantially the same height as the ridge-type optical waveguide 5. A first recess 3C1 is defined on the first surface 3A and the installation surface 3E by the first terrace portion 3T1 and the ridge-type optical waveguide 5, and a second surface 3B is defined by the second terrace portion 3T2 and the ridge-type optical waveguide 5. And the 2nd recessed part 3C2 is prescribed | regulated on the installation surface 3E. The first recess 3C1 and the second recess 3C2 each have a shape extending along the Y-axis direction in plan view, and the shape of the ridge-type optical waveguide 5 of this embodiment is the first recess 3C1 and the second recess Defined by 3C2.

The first terrace portion 3T1 and the second terrace portion 3T2 are each made of a dielectric material that exhibits an electro-optic effect, such as lithium niobate (LiNbO ₃ ), and may be made of the same material as the base portion 3. Such a structure composed of the base portion 3, the ridge-type optical waveguide 5, the first terrace portion 3T1, and the second terrace portion 3T2 is a plate-like structure made of a dielectric material such as lithium niobate (LiNbO ₃ ). A dielectric material for preparing a buffer layer 5C on the entire main surface is prepared by diffusing a metal such as titanium (Ti) in a region to be the core portion 5A in the vicinity of the main surface of the initial substrate. And etching the initial substrate and the dielectric film so as to leave the regions to be the ridge-type optical waveguide 5, the base portion 3, the first terrace portion 3T1, and the second terrace portion 3T2. Can be obtained. Alternatively, in the structure, the base portion 3 is prepared, the ridge-type optical waveguide 5 on the installation surface 3E of the main surface 3S of the base portion 3, the first terrace portion 3T1 on the first surface 3A and the second surface 3B, and It can also be obtained by forming the second terrace portion 3T2.

  The on-terrace ground electrode element 11D of the first ground electrode 11 is made of, for example, the same metal material as the central ground electrode element 11C and is electrically connected to the central ground electrode element 11C. It is provided on the side and top surfaces of 3T1. Similarly, the terrace ground electrode element 12D of the second ground electrode 12 is made of, for example, the same metal material as the central ground electrode element 12C and is electrically connected to the central ground electrode element 12C. The two terrace portions 3T2 are provided on the side surface and the upper surface. The thickness of the on-terrace ground electrode element 11D on the upper surface of the first terrace portion 3T1 is preferably thicker than the thickness of the central ground electrode element 11C, and can be, for example, 10 μm or more and 80 μm or less. Similarly, the thickness of the on-terrace ground electrode element 12D on the upper surface of the second terrace portion 3T2 is preferably thicker than the thickness of the central ground electrode element 12C, and can be, for example, 10 μm or more and 80 μm or less.

  According to the optical modulator 400 according to the present embodiment, it is easy to achieve impedance matching between the optical modulator 400 and an external element that supplies a modulation signal based on the same reason as the optical modulator 100 according to the first embodiment. Therefore, high-speed modulation operation is possible.

  Furthermore, in the optical modulator 400 of this embodiment, the terrace ground electrode element 11D provided on the first terrace portion 3T1 is electrically connected to the center ground electrode element 11C, and the center ground electrode element 12C. The terrace ground electrode element 12D and the signal electrode 7 are formed at the same height or close to each other because the terrace ground electrode element 12D is provided on the second terrace portion 3T2. This makes it easy to perform characteristic inspection using a high-frequency probe of GSG (Ground-Signal-Ground) type and wire bonding, flip chip bonding when mounting the modulator chip on the case. is there. Also, when fabricating ridge-type optical waveguides using lithium niobate, reactive ion etching and mechanical processing are mainly used, but in either method, the area of the processed part should be smaller. It is convenient in terms of the process, and it is desirable to form the first surface 3A and the second surface 3B to the minimum necessary. The configuration in which the portions corresponding to the terrace portions 3T1 and 3T2 are left without being processed as in the present embodiment is a realistic configuration.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. FIG. 10 is a cross-sectional view of the optical modulator according to the fifth embodiment, corresponding to FIG. 9 of the fourth embodiment. The optical modulator 500 of the fifth embodiment is similar to the optical modulator 400 of the fourth embodiment (FIG. 8) in the aspect of the central ground electrode element of the first ground electrode and the central ground electrode element of the second ground electrode. And FIG. 9).

  That is, as shown in FIG. 10, in the optical modulator 500 of this embodiment, the central ground electrode element 511 </ b> C included in the first ground electrode 11 is connected to the ridge-type optical waveguide 5 on the main surface 3 </ b> S of the base portion 3. Separated in the X-axis direction. Similarly, the central ground electrode element 512 </ b> C included in the second ground electrode 12 of the present embodiment is separated from the ridge type optical waveguide 5 in the X-axis direction on the main surface 3 </ b> S of the base portion 3. The distance in the X-axis direction between the central ground electrode element 511C and the ridge-type optical waveguide 5 and the distance in the X-axis direction between the central ground electrode element 512C and the ridge-type optical waveguide 5 are, for example, 1 μm or more and 160 μm or less. Can do. The central portion ground electrode element 511C and the central portion ground electrode element 512C partially overlap the wide portion 7W in plan view.

  According to the optical modulator 500 according to the present embodiment, it is easy to achieve impedance matching between the optical modulator 500 and an external element that supplies a modulation signal based on the same reason as the optical modulator 100 of the first embodiment. Therefore, high-speed modulation operation is possible.

  Further, according to the optical modulator 500 according to the present embodiment, the central portion ground electrode element 511C and the central portion ground electrode element 512C are separated from the ridge type optical waveguide 5 in the X-axis direction on the main surface 3S of the base portion 3. Therefore, there is an advantage that it is easy to reduce the capacitance between the signal electrode 7 and the first ground electrode 511 and the second ground electrode 512 and increase the characteristic impedance of the modulation electrode. In this embodiment, the capacitor having the ridge type optical waveguide 5 and the base portion 3 sandwiched between the signal electrode 7 and the central portion ground electrode element 511C, and the ridge type optical waveguide portion 5 and the base portion 3 are connected to the signal electrode 7 and the central portion ground electrode element. It is equivalent to a parallel circuit of a capacitor sandwiched between 512C, a capacitor sandwiched between the signal electrode 7 and the central ground electrode element 511C, and a capacitor sandwiched between the signal electrode 7 and the central ground electrode element 512C. It can be considered as simplified.

  In this way, the increase in the separation distance between the central portion ground electrode element 511C and the central portion ground electrode element 512C and the ridge-type optical waveguide 5 on the main surface 3S of the base portion 3 results in an increase in the separation distance between the capacitors. Therefore, it directly contributes to a reduction in capacitance between the signal electrode 7 and the first ground electrode 511 and the second ground electrode 512 and an increase in the characteristic impedance of the modulation electrode. However, the separation distance between the central portion ground electrode element 511C and the central portion ground electrode element 512C and the ridge-type optical waveguide 5 on the main surface 3S of the base portion 3 directly affects the effective electric field in the optical waveguide portion 5, and the signal electrode When the same voltage is applied between 7 and the ground electrode element, the effective electric field in the optical waveguide portion 5 becomes smaller as the separation distance becomes larger, so that the driving efficiency as the optical modulator is lowered. Therefore, it is necessary to design the separation distance in consideration of the required drive efficiency and characteristic impedance.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described. FIG. 11 is a plan view showing the configuration of the optical modulator according to the sixth embodiment, and FIG. 12 is a cross-sectional view of the optical modulator along the line XII-XII in FIG. The optical modulator 600 of the sixth embodiment is different from the optical modulator 400 of the fourth embodiment in the aspect of the modulation electrode.

  Specifically, as shown in FIGS. 11 and 12, the modulation electrode 615 of this embodiment includes a first ground electrode 611, a second ground electrode 612, and a signal electrode 607. The central ground electrode element 611C included in the first ground electrode 611 and the central ground electrode element 612C included in the second ground electrode 612 are the central ground electrode elements 11C and 12C according to the fourth embodiment (see FIGS. 8 and 9). Unlike the case, the signal electrode 607 of the modulation electrode 615 does not overlap in plan view. Therefore, the first through hole 611B and the second through hole 612B provided in the central portion ground electrode element 611C and the central portion ground electrode element 612C also do not overlap with the wide portion 607W of the signal electrode 607 in plan view.

  The modulation electrode 615 includes a wide portion 607W as the wide portion of the present embodiment, and the first ground electrode 611 includes the terrace ground electrode element 611D as the terrace ground electrode element of the present embodiment and the center ground electrode element. 611C, and the second ground electrode 612 includes a terrace ground electrode element 612D as the terrace ground electrode element of the present embodiment, and a center ground electrode element 612C. The thickness along the Z-axis direction of the wide portion 607W, the terrace ground electrode element 611D, and the terrace ground electrode element 612D is the same as the wide portion 7W, terrace ground electrode element 11D, and It is thicker than the thickness along the Z-axis direction of the terraced ground electrode element 12D. In the present embodiment, the thickness of the central ground electrode element 611C in the Z-axis direction and the thickness of the central ground electrode element 612C in the Z-axis direction are the height T5 of the ridge-type optical waveguide 5, respectively. Bigger than.

  The wide part 607W of the signal electrode 607 does not have to be a rectangular shape constituting the eaves shape as shown in FIG. 12, but gradually becomes an elliptical shape or an inverted trapezoidal shape as shown in Non-Patent Document 2. The same effect can be obtained even if the shape is a protruding shape, a protruding shape in a mushroom shape, an intermediate shape thereof, or a combined shape thereof. Further, the portion installed on the main surface 3A of the ground electrode element 611D and the portion installed on the main surface 3B of the ground electrode element 612D are thinner than the portion installed on the terrace, but have a thick structure. May be. A thickness T611D along the Z-axis direction on the upper surface of the first terrace portion 3T1 of the on-terrace ground electrode element 611D and a thickness along the Z-axis direction on the upper surface of the second terrace portion 3T2 of the on-terrace ground electrode element 612D. The thickness may be substantially the same as T612D.

  When the wide portion 607W of the signal electrode 607 and the terrace ground electrode elements 611D and 612D are thick as in the sixth embodiment, the characteristic impedance values of the modulation electrodes are the first through hole 611B and the second through hole 612B. Rather than the shape, size, position and quantity, the distance between the central ground electrode elements 611C and 612C and the ridge-type optical waveguide 5, the shape of the wide portion 607W, particularly the side surface of the wide portion 607W protruding in the X-axis direction Depends greatly on the shape of the. The adjustment of the characteristic impedance by the shape, size, position, and quantity of the first through hole 611B and the second through hole 612B is effective, but is auxiliary.

  Therefore, in order to greatly increase the characteristic impedance of the modulation electrode, first, the distance between the central ground electrode elements 611C and 612C and the ridge type optical waveguide 5 may be increased. However, the separation distance between the central ground electrode elements 611C and 612C and the ridge-type optical waveguide 5 is in a trade-off relationship with the strength of the electric field in the ridge-type optical waveguide 5, and when the separation distance is increased, the ridge-type optical waveguide 5 is increased. As a result, the intensity of the electric field is lowered and efficient modulation cannot be realized. Accordingly, the distance between the central ground electrode elements 611C and 612C and the ridge-type optical waveguide 5 is designed with priority given to modulation efficiency over impedance, so that impedance characteristics that are too low can be obtained in the first through-hole 611B and the second through-hole 611B. By adjusting and correcting according to the shape, size, position, quantity, and the like of the through-hole 612B and designing so as to have a desired characteristic value, an optical modulator with good characteristics can be realized.

  In the case of the sixth embodiment, the separation distance between the central ground electrode elements 611C and 612C and the ridge type optical waveguide 5 is large, and the first through hole 611B and the second through hole 612B are formed in the central ground electrode elements 611C and 612C. However, since the loss of the high frequency control signal is small, there is almost no adverse effect on other characteristics due to the first through hole 611B and the second through hole 612B. Thus, the advantages in designing and manufacturing a high-frequency optical modulator and a broadband optical modulator are great.

  The thickness T607W along the Z-axis direction of the wide portion 607W can be, for example, 25 μm or more and 80 μm or less, and the thickness along the Z-axis direction on the upper surface of the first terrace portion 3T1 of the on-terrace ground electrode element 611D. The thickness T612D along the Z-axis direction on the upper surface of the second terrace portion 3T2 of the T611D and the terraced ground electrode element 612D can be, for example, 25 μm or more and 80 μm or less, respectively. As a result, the effective surface area in which the wide portion 607W and the central portion ground electrode elements 611C and 612C are opposed to each other is greatly increased, the concentration of the electric field at a specific location is avoided, and the propagation loss of the control signal is reduced. Reduce significantly.

  The thickness T607W can be, for example, not less than 4 times and not more than 10 times the width W5 of the ridge-type optical waveguide 5, or not less than 2 times and not more than 5 times the width W in the X-axis direction of the wide portion 607W. For example, the thickness T611D and the thickness T612D can be approximately the same as the thickness T607W, respectively.

  According to the optical modulator 600 according to the present embodiment, it is easy to achieve impedance matching between an external element that supplies a modulation signal and the optical modulator 600 based on the same reason as the optical modulator 100 according to the first embodiment. Therefore, high-speed modulation operation is possible. Although the method for adjusting the characteristic impedance is an auxiliary method, it is practically effective because it does not cause deterioration of other characteristics.

  Furthermore, according to the optical modulator 600 according to the present embodiment, the thickness of the wide portion 607W, the terrace ground electrode element 611D, and the terrace ground electrode element 612D is larger than the thickness of the corresponding element in the other embodiments. Since the effective surface area in which the thick portion 607W of the signal electrode 607 and the central portion ground electrode elements 611C and 612C act in opposition to each other is particularly large, the concentration of the electric field at a specific location is avoided, and the control signal The effect of significantly reducing the propagation loss of the. When gold, silver, or copper with low signal propagation loss is used as the material of the central ground electrode elements 611C and 612C, the skin depth at which current concentrates due to the skin effect is 1 μm or less at a frequency of 10 GHz or more, and the skin Loss becomes significant. In the case of driving with a control signal including such a high-frequency component, the optical modulator 600 of the sixth embodiment that can greatly increase the effective surface area has a great effect.

  In addition, the terrace ground electrode elements 611D and 612D and the wide portion 607W can be easily formed at the same height, and wire bonding, flip chip bonding, GSG (Ground-Signal) when mounting the modulator chip on the case, and the like. -Ground) -type high-frequency probe is easy to perform characteristic inspection.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in each of the above-described embodiments, the plurality of first through holes 11B, 211B, 311B, and 611B are side surfaces of the central ground electrode elements 11C, 211C, 311C, and 611C on the ridge-type optical waveguide 5 side in plan view. 11S is spaced apart in the X-axis direction (see FIGS. 1, 4, 6, 8, and 11), but in a plan view, the ridge-type optical waveguide of the central ground electrode elements 11C, 211C, 311C, and 611C You may contact 5 side surface 11S.

  Similarly, in each of the above-described embodiments, the second through holes 12B, 212B, 312B, 612B have the side surface 12S on the ridge-type optical waveguide 5 side of the central ground electrode elements 12C, 212C, 312C, 612C in plan view. Are spaced apart from each other in the X-axis direction (see FIGS. 1, 4, 6, 8, and 11), but in the plan view, the ridge-type optical waveguide 5 of the central ground electrode elements 12C, 212C, 312C, 6112C It may be in contact with the side surface 12S.

  In each of the above-described embodiments, the plurality of first through holes 11B, 211B, 311B, and 611B are periodically provided in order along the Y-axis direction (FIGS. 1, 4, 6, and 6). 8 and 11), they may be provided aperiodically. Similarly, in each of the above-described embodiments, the plurality of second through holes 12B, 212B, 312B, and 612B are periodically provided in order along the Y-axis direction (FIGS. 1 and 4). 6, 8, and 11), they may be provided aperiodically.

  In the above-described embodiments, the central ground electrode elements 11C, 211C, 311C, and 611C of the first ground electrodes 11, 211, 311, and 611 have a plurality of first through holes 11B, 211B, 311B, and 611B. Although it has (refer FIG.1, FIG.4, FIG.6, FIG.8 and FIG.11), you may have only one 1st through-hole. Similarly, in the above-described embodiments, the central ground electrode elements 12C, 212C, 312C, 612C of the second ground electrodes 12, 212, 312, 612 have a plurality of second through holes 12B, 212B, 312B, 612B. (See FIGS. 1, 4, 6, 8, and 11), it may have only one first through hole.

  Moreover, the aspect which combined the feature of 2 or 3 or more of each above-mentioned embodiment is also possible. For example, the shape of the first through hole 11B and the second through hole 12B in the optical modulator 100 of the first embodiment in plan view is the same as the first through hole 311B and the second through hole 312B in the optical modulator 300 of the third embodiment. It may be a shape having a corner such as a rectangular shape (see FIGS. 1, 4, 6, 8, and 11).

  In the optical modulators 100, 200, 300, and 400 according to the first to fourth embodiments, the central portion ground electrode elements 11C, 211C, and 311C and the central portion ground electrode elements 12C, 212C, and 312C are the same as those of the fifth embodiment. Like the central ground electrode element 511C and the central ground electrode element 512C in the optical modulator 500, they may be spaced apart from the ridge-type optical waveguide 5 in the X-axis direction on the main surface 3S of the base 3 (FIG. 2). , FIG. 5, FIG. 7 and FIG. 9).

  In the optical modulators 100, 200, 300, 400, and 500 according to the first to fifth embodiments, the central ground electrode elements 11C, 211C, 311C, and 511C and the central ground electrode elements 12C, 212C, 312C, and 512C are As in the central portion ground electrode element 611C and the central portion ground electrode element 612C of the sixth embodiment, whether to overlap with the wide portion 7W in plan view can be selected according to the required effect (FIG. 1). , FIG. 4, FIG. 6, FIG. 8 and FIG. 11).

  The optical modulators 100, 200, 300, 400, 500, and 600 according to the above-described embodiments include one ridge-type optical waveguide 5 and one eaves-like wide portion 7 </ b> W provided on the ridge-type optical waveguide 5. , 607W (see FIG. 1, FIG. 4, FIG. 6, FIG. 8 and FIG. 11), a plurality of such sets may be provided. In that case, the present invention can be applied to each of the plurality of sets. For example, in an optical modulator including a Mach-Zehnder type optical waveguide and an elongate signal electrode corresponding to the wide portion of the present application provided thereon, each of the two arm optical waveguides of the Mach-Zehnder type optical waveguide The present invention can be applied to.

  In the optical modulators of the above-described embodiments, the wide portion of the signal electrode has a flat or rectangular eaves shape protruding from the ridge-type optical waveguide in the X-axis direction. The wide portion 7W of the electrode is not limited to having such a shape. For example, the wide portion of the signal electrode may have a mushroom shape such as a shape that gradually protrudes and protrudes into an inverted trapezoidal shape, as shown in Non-Patent Document 2, These composite shapes may also be used. In the optical modulators of the above-described embodiments, in the cross section orthogonal to the Y-axis direction, the wide portion of the signal electrode has a symmetrical shape in the second direction (X-axis direction) with respect to the ridge-type optical waveguide. Although it has, the wide part of the signal electrode in the optical modulator of this invention is not restricted to what has such a shape. For example, in the cross section, the wide portion of the signal electrode is provided to be biased in any direction (+ X axis direction or −X axis direction) along the second direction with respect to the ridge type optical waveguide, or the ridge type For example, in any direction along the second direction (+ X axis direction or −X axis direction) with respect to the ridge type optical waveguide. It may have a mushroom shape in which the protruding shape along the second direction is asymmetric with respect to the biased eaves shape or the ridge type optical waveguide. Further, as shown in the pamphlet of International Publication No. 2005/089332, a signal electrode in a cross section orthogonal to the predetermined direction in an optical modulator having two ridge type optical waveguides extending along a predetermined direction. The wide portion may have a shape extending from one ridge type optical waveguide to the other ridge type optical waveguide. The signal electrode may be an optical modulator having a wide portion having a width larger than the width in the X-axis direction of the ridge-type optical waveguide, and the technology described with respect to each of the embodiments described above is such that the ground electrode is located at a position lower than the signal electrode. This is particularly effective in an optical modulator having an arranged configuration.

  In addition, the optical modulators of the above-described embodiments have been described on the assumption that they have a traveling wave type electrode configuration. In general, the length of the action portion of the traveling wave electrode of the optical modulator is long, and it is necessary to form a large number of through holes according to the length of the electrode and the size and density of the through holes. An important design index is the characteristic impedance when the signal electrode and the ground electrode are viewed as lines. On the other hand, in the case of an optical modulator driven as a lumped constant type electrode, the length of the electrode to be formed is generally short. Therefore, the through holes are formed by appropriately designing the size, shape, and quantity according to the interelectrode capacity corresponding to the drive frequency. When the electrode length and area are small, the number of through holes to be installed is small.

  The optical modulators of the above-described embodiments are phase modulators in which linear signal electrodes are arranged on the linear ridge-type optical waveguide 5, but the optical modulator of the present invention has such a configuration of light. Not limited to modulators. The optical modulator according to the present invention changes the refractive index of the material by the electro-optic effect (a phenomenon in which the refractive index changes according to the applied electric field, that is, the Pockels effect and the optical Kerr effect), and the phase and propagation mode of the propagating light. This includes devices that control the light intensity, phase, traveling direction, mode, optical pulse, etc. by combining the phase and mod control of the propagating light.

  3 ... Base part, 3S ... Main surface of base part, 3A ... First surface of main surface, 3B ... Second surface of main surface, 3E ... Installation surface of main surface, 5 ... Ridge type optical waveguide, 7 ... Signal electrode, 11 ... First ground electrode, 11C ... Central part ground electrode element (first ground electrode element), 12 ... Second ground electrode, 12C: Center part ground electrode element (second ground electrode element), 11B: First through hole, 12B: Second through hole, 15: Modulation electrode.

Claims (2)

A base portion having a main surface; a ridge-type optical waveguide provided on the main surface of the base portion and extending in a first direction along the main surface; and light guided in the ridge-type optical waveguide A modulation electrode, and a first terrace portion and a second terrace portion provided on the main surface of the base portion,
The main surface of the base portion sandwiches the installation surface along a second direction that is orthogonal to the first direction and along the main surface with the installation surface provided with the ridge-type optical waveguide. A first surface and a second surface located at
The first terrace portion is provided on the first surface so as to be spaced apart from the ridge-type optical waveguide in the second direction, and the first terrace portion and the ridge-type optical waveguide provide the first terrace portion. A first recess extending along the first direction is defined on the surface and the installation surface;
The second terrace portion is provided on the second surface so as to be separated from the ridge-type optical waveguide in the second direction, and the second terrace portion and the ridge-type optical waveguide provide the second terrace portion. A second recess extending along the first direction is defined on the surface and the installation surface;
The modulation electrode includes a signal electrode to which a modulation signal is supplied, a first ground electrode, and a second ground electrode,
The signal electrode is a portion provided on the ridge-type optical waveguide so as to extend along the first direction, and has a width wider than the width of the uppermost portion of the ridge-type optical waveguide in the second direction. Having a wide part,
The first ground electrode is electrically connected to the first ground electrode element, the first ground electrode element provided on the first surface so as to extend along the first direction, and the first direction. A first terrace ground electrode element provided from the side surface to the upper surface of the first terrace portion so as to extend along
The second ground electrode is electrically connected to the second ground electrode element, the second ground electrode element provided on the second surface so as to extend along the first direction, and the first direction. A second terrace ground electrode element provided from the side surface to the upper surface of the second terrace portion so as to extend along
The first ground electrode element has at least one first through hole provided only in a part of the first ground electrode element in the first direction, and in the plan view, in the wide portion and the second direction. Apart,
The second ground electrode element has at least one second through hole provided only in a part of the second ground electrode element in the first direction, and in the plan view, in the wide portion and the second direction. Apart,
The at least one first through hole is opposed to the wide portion of the signal electrode in the plan view in the second direction,
The at least one second through hole is an optical modulator facing the wide portion of the signal electrode in the second direction in plan view. The thickness of the wide part is 25 μm or more and 80 μm or less,
The thickness of the first terrace ground electrode element on the top surface of the first terrace portion is 25 μm or more and 80 μm or less, and the thickness of the second terrace ground electrode element on the top surface of the second terrace portion. The optical modulator according to claim 1, wherein is 25 μm or more and 80 μm or less.

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