JP6179532B2 - Light modulator - Google Patents

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JP6179532B2
JP6179532B2 JP2015017566A JP2015017566A JP6179532B2 JP 6179532 B2 JP6179532 B2 JP 6179532B2 JP 2015017566 A JP2015017566 A JP 2015017566A JP 2015017566 A JP2015017566 A JP 2015017566A JP 6179532 B2 JP6179532 B2 JP 6179532B2
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ground electrode
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terrace
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市川　潤一郎
潤一郎 市川
利夫 片岡
利夫 片岡
勝利 近藤
勝利 近藤
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Sumitomo Osaka Cement Co Ltd
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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Description

本発明は、光変調器に関する。   The present invention relates to an optical modulator.

下記の特許文献１、２及び非特許文献１、２には、リッジ型の光導波路を有する光変調器が記載されている。下記特許文献１及び非特許文献１に記載の光変調器は、リッジ型の光導波路上に設けられた、ひさし状の信号電極を有しており、下記特許文献２および非特許文献２に記載の光変調器は、キノコ状の信号電極を有している。   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.

特開平１１−１０１９６２号公報Japanese Patent Application Laid-Open No. 11-101962 特開平８−１２２７２２号公報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.16-27Makoto 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 1998R. Madabushi, “Microwave Attenuation Reduction Techniques for Wide-BandTi: LiNbO3 Optical Modulators” IEICE TRANS. ELECTRON., VOL. E81-C, NO. 8 AUGUST 1998

特許文献１に記載のリッジ型の光導波路を有する光変調器においては、当該文献の図７、図１１に記載されているように、光導波路上に、ひさし形状（即ち、当該光導波路の幅よりも広い幅を有する形状）の信号電極が設けられている。また、光導波路のリッジ形状部の側面には、信号電極に接しないように薄く形成された接地電極が、当該光導波路のリッジ形状部に接するように設けられている。このような構造を有する光変調器によれば、低駆動電圧、光導波路内を導波する光と信号電極に印加される変調信号との速度整合、及び、低電極損失が実現可能であることが当該文献に記載されている。   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.

しかしながら、特許文献１に記載されているような従来の光変調器においては、以下のような理由により、高速変調動作が難しいという問題があった。   However, the conventional optical modulator described in Patent Document 1 has a problem that high-speed modulation operation is difficult for the following reasons.

即ち、高速変調動作を達成するためには、インピーダンス整合を図ること、具体的には、変調電極（信号電極及び接地電極）に印加される変調信号を供給する外部の素子の出力インピーダンスと、光変調器の入力インピーダンスとを、同じ値（例えば５０Ω）に近づけることが必要である。   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).

しかしながら、特許文献１に記載されているような光変調器においては、ひさし形状の信号電極と、光導波路のリッジ形状部の側面に設けられた接地電極との距離が近くなるため、信号電極と接地電極との間の静電容量が大きくなる。これにより、信号電極と接地電極との間のインピーダンスが小さくなってしまう。特許文献１には、当該文献に記載されているような光変調器において最適化された設計では、特性インピーダンスが１８．４Ωであることが示されており、その結果、光変調器と、上記外部の素子との間のインピーダンス整合を図ることが難しくなってしまうため、実質的に高速変調動作を達成することが困難となってしまう。   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.

同様のことは、特許文献２に記載されているキノコ状にせり出した信号電極を有する光変調器おいても問題となる。特許文献２に記載されているキノコ状にせり出した信号電極を用いた構成は、速度整合や低電極損失の実現に非常に有効な構成の一つである。しかしながら、特性インピーダンスが低下する問題がある。非特許文献２には、キノコ状にせり出した信号電極を有する構成における問題が、特性インピーダンスの５０Ωからの乖離であること、及び、電極の反射特性Ｓ１１が−１０ｄＢと劣ることであることが記載されている。   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.

特性インピーダンスの５０Ωからの乖離に起因する反射特性の劣化の悪影響は、インピーダンス変換器やインピーダンス変換回路の変調器への組み込みにより、回避は可能である。しかしながら、駆動信号の電力が同じであっても特性インピーダンスの低い光変調器では、信号電極の作用部電極部における信号電極−接地電極間電圧が低くなってしまうという問題がある。この信号電極−接地電極間の電圧の低下は、特に、ニオブ酸リチウムによって光導波路を構成した光変調器のように電気光学効果（印加電界に応じて屈折率が変化する現象、つまりポッケルス効果および光カー効果）に基づく光変調器の場合、高効率（低消費電力）での駆動の観点からは、極めて不利である。そのため、高効率（低消費電力）での駆動のためには、特性インピーダンスの低下を避けて設計することが望ましい。   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.

本発明はこのような課題に鑑みてなされたものであり、リッジ型光導波路と、ひさし形状又はキノコ形状の信号電極を有する光変調器であって、高速動作可能な光変調器を提供することを目的とする。   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.

本発明は、信号電極と対向して作用する接地電極要素の一部を切り欠くことにより、電極間容量を下げ、特性インピーダンスを上昇させるという原理に基づくものである。   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.

即ち、上述の課題を解決するため、本発明に係る光変調器は、主面を有する基体部と、基体部の主面上に設けられ、当該主面に沿った第１方向に沿って延びるリッジ型光導波路と、当該リッジ型光導波路内を導波する光を変調するための変調電極と、を備え、基体部の主面は、リッジ型光導波路が設けられた設置面と、第１方向と直交し、かつ、主面に沿った第２方向に沿って上記設置面を挟むように位置する第１面及び第２面と、を有し、変調電極は、変調信号が供給される信号電極と、第１接地電極と、第２接地電極とからなり、信号電極は、リッジ型光導波路上に第１方向に沿って延びるように設けられた部分であって、リッジ型光導波路の最上部の第２方向の幅よりも広い幅を有する幅広部を有し、第１接地電極は、第１方向に沿って延びるように第１面上に設けられた第１接地電極要素を有し、第２接地電極は、第１方向に沿って延びるように第２面上に設けられた第２接地電極要素を有し、第１接地電極要素は、第１接地電極要素の第１方向の一部のみに設けられた少なくとも１つの第１貫通孔を有し、第２接地電極要素は、第２接地電極要素の第１方向の一部のみに設けられた少なくとも１つの第２貫通孔を有し、上記少なくとも１つの第１貫通孔は、平面視で信号電極の上記幅広部と重複する、又は、当該幅広部と第２方向に向かって対向し、上記少なくとも１つの第２貫通孔は、平面視で信号電極の上記幅広部と重複する、又は、当該幅広部と第２方向に向かって対向する。貫通孔が幅広部と対向するとは、幅広部から発する電気力線が、貫通孔の開口の周りに達して終端されている状態であって、貫通孔の有無が変調電極の回路の静電容量あるいは特性インピーダンスの値に有意な影響がある様態(貫通孔の有無により静電容量あるいは特性インピーダンスの値の相対的差が、高周波ネットワークアナライザのインピーダンス校正回路基板の一般的な精度である０．３％より大きい様態)であることを意味する。なお、幅広部から、貫通孔の開口部や貫通孔の底が直接見通せる様態で無くとも良い。   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.

本発明に係る光変調器においては、第１接地電極要素及び第２接地電極要素は、それぞれ、平面視で信号電極の幅広部と重複する、又は、当該幅広部と第２方向に向かって対向する第１貫通孔及び第２貫通孔を有する。そのため、第１接地電極要素及び第２接地電極要素が、それぞれ第１貫通孔及び第２貫通孔を有していない場合と比較して、信号電極と第１接地電極、第２接地電極間の容量を低下させることができるため、変調電極の特性インピーダンスを高くすることができる。その結果、本発明に係る光変調器によれば、信号電極が集中定数形電極として機能する場合には高周波駆動の妨げとなる信号電極と第１接地電極、第２接地電極間の容量を小さくすることができ、また、信号電極が進行波形電極として機能する場合は変調電極の特性インピーダンスの低下を避けることができ変調信号を供給する外部の素子と変調器とのインピーダンス整合を図り易くなるため、高速変調動作及び高効率駆動が可能となる。   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.

さらに、本発明に係る光変調器においては、上記少なくとも１つの第１貫通孔、及び、上記少なくとも１つの第２貫通孔は、平面視で、円形形状、楕円形状、レーストラック形状、又は、角丸矩形形状を有することが好ましい。これにより、平面視で第１接地電極要素の第１貫通孔と隣接する界面（第１接地電極要素の側面）、及び、平面視で第２凹部接地電極要素の第２貫通孔と隣接する界面（第２接地電極要素の側面）は、角部や突起部を有さない曲線形状となる。その結果、変調信号が変調電極に印加された際に当該隣接する界面において角部や突起部への過度の電界の集中が起きにくくなるため、第１及び第２貫通孔の形成に起因する変調信号の伝搬損失を抑制することができる。   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.

さらに、本発明に係る光変調器においては、第１接地電極要素は、複数の第１貫通孔を有し、当該複数の第１貫通孔は、第１方向に沿って順に設けられており、第２接地電極要素は、複数の第２貫通孔を有し、当該複数の第２貫通孔は、第１方向に沿って順に設けられていることが好ましい。   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.

これにより、信号電極が集中定数形電極として機能する場合には高周波駆動の妨げとなる電極間の容量を小さくすることができ、また、信号電極が進行波形電極として機能する場合は変調電極の特性インピーダンスをさらに高くすることができるため、変調信号を供給する外部の素子と変調器とのインピーダンス整合を、より高精度に図り易くなる。その結果、本発明に係る光変調器によれば、より高速での変調動作と効率の良い駆動が可能となる。   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.

さらに、本発明に係る光変調器においては、上記少なくとも１つの第１貫通孔は、平面視で、第１接地電極要素のリッジ型光導波路側の側面と離間しており、上記少なくとも１つの第２貫通孔は、平面視で、第２接地電極要素のリッジ型光導波路側の側面と離間していることが好ましい。   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.

これにより、平面視で第１接地電極要素の上記側面と第２接地電極要素の上記側面において、貫通孔がリッジ型光導波路側に開口するように配置されて第１接地電極要素や第２接地電極要素のリッジ型光導波路側の側面側に角部が形成されることを防止することができる。その結果、変調信号が変調電極に印加された際に当該側面において電界の集中が起きにくくなるため、貫通孔の形成に起因する変調信号の伝搬損失を抑制することができる。   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.

さらに、本発明に係る光変調器においては、少なくとも１つの第１貫通孔は、平面視で、第１接地電極要素のリッジ型光導波路側の側面と２０μｍ以上離間しており、少なくとも１つの第２貫通孔は、平面視で、第２接地電極要素のリッジ型光導波路側の側面と２０μｍ離間していることが好ましい。これにより、変調電極と第１、第２貫通孔との離間距離も大きくなるため、変調電極に変調信号が印加された際に、当該側面において電界の集中がさらに起きにくくなるため、変調信号の伝搬損失を一層抑制することができる。   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.

第１接地電極要素及び第２接地電極要素に貫通孔を設けない態様における変調信号の伝搬損失は、非特許文献１の構成の場合は、０．２ｄＢ／［ｃｍ（ＧＨｚ）１／２］程度、特許文献２の類似構成の場合０．１８ｄＢ／［ｃｍ（ＧＨｚ）１／２］程度、特許文献２の構成をリッジ型光導波路と併用した場合は、０．１５ｄＢ／［ｃｍ（ＧＨｚ）１／２］程度である。平面視での第１貫通孔とリッジ型光導波路側の側面との離間距離、及び、平面視での第２貫通孔とリッジ型光導波路側の側面との離間距離が２０μｍ程度の場合、第１貫通孔及び第２貫通孔として幅１０μｍ、長さ５０μｍの角丸長方形の貫通孔列を間隔１０μｍで第１方向に沿って第１接地電極要素及び第２接地電極要素に配置したときの変調信号の伝搬損失の悪化幅は、非特許文献１の構成の場合は、０．１ｄＢ／［ｃｍ（ＧＨｚ）１／２］程度、特許文献２の類似構成の場合０．０２ｄＢ／［ｃｍ（ＧＨｚ）１／２］程度である。上記離間距離を３０μｍ程度にすると、第１貫通孔及び第２貫通孔の形成による変調信号の伝搬損失はほとんど無視できるようになる。 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.

平面視での第１貫通孔とリッジ型光導波路の側面との離間距離、及び、平面視での第２貫通孔とリッジ型光導波路側の側面との離間距離が大きい場合は、第１接地電極要素及び第２接地電極要素への第１及び第２貫通孔の形成による信号電極と第１接地電極、第２接地電極間の容量を小さくする効果や変調電極の特性インピーダンスを上昇させる効果は相対的には低くなる。しかしながら、そのような態様においてさえも本発明は、非特許文献１や非特許文献２などの構成の光変調器をニオブ酸リチウムのような高い誘電率材料からなる光導波路を用いて作製する場合において、信号電極と第１接地電極、第２接地電極間容量や変調電極の特性インピーダンス調整するための実用上利用価値の高い手段を提供する。   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.

第１接地電極要素及び第２接地電極要素に、第１貫通孔及び第２貫通孔として幅１０μｍ、長さ５０μｍの角丸長方形の貫通孔列を間隔１０μｍで第１方向に沿って配置した場合における変調信号の特性インピーダンスの上昇幅は、非特許文献１の構成の場合は、リッジ導波路部の幅に依存性大きく依存し、光導波路幅を、この構成での現実的な値である６〜８μｍとした場合、変調信号の特性インピーダンスを約５〜１０Ω程度上昇させることが可能である。非特許文献２に類似する構成の場合には、信号電極の形状、張出した信号側面の形状大きく依存するが、変調信号の特性インピーダンスを２〜５Ω程度上昇させることが可能である。   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.

平面視での第１貫通孔とリッジ型光導波路の側面との離間距離、及び、平面視での第２貫通孔とリッジ型光導波路側の側面との離間距離を３０μｍ程度にすると、信号電極と第１接地電極、第２接地間の容量を小さくする効果や変調電極の特性インピーダンスを上昇させる効果は相対的にさらに低くなるが、当該特性インピーダンスの数Ωの調整は可能である一方、第１、第２貫通孔の形成による変調信号の伝搬損失がほとんど無視できるようになることから、実用上の利用価値は高い。   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.

さらに、本発明に係る光変調器においては、第１接地電極要素及び第２接地電極要素は、平面視で、リッジ型光導波路の光軸に対して略線対称に設けられていることが好ましい。これにより、光変調器の特性の解析計算の規模が小さくて済む、さらには、光変調器の温度変化の際の基板の応力・歪みの偏りを回避され光変調器の動作の安定性獲得が期待できる。   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.

第１、第２貫通孔の配置位置は非対称としても信号電極と第１接地電極、第２接地電極間の容量を小さくする効果や変調電極の特性インピーダンスを上昇させる効果は得られるが、設計の都合上、特性の解析計算の規模が小さくて済むよう対称的な配置とするほうが望ましい。第１、第２貫通孔を信号電極の中心部を対称線として配置すれば、有限要素解析や伝搬解析の計算規模は半分で済ませることができる。さらに、そのような対称的な配置により、基板の応力・歪みの非対称な偏りを分散され、光変調器の動作の安定性獲得が期待できる。また、第１、第２貫通孔の対称的な配置には、応力・歪みの設計・解析においても、解析計算の規模が小さくて済むという利点もある。   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.

複数列の第１、第２貫通孔を形成しても良く、その方が信号電極と第１接地電極、第２接地電極間の容量低減や変調電極の特性インピーダンスの上昇効果がより高いことは言うまでもない。ただし、第１、第２貫通孔の形成により、制御信号の伝搬損失が上昇するため、制御信号の伝搬損失特性が許容される範囲で、必要最小限の第１、第２貫通孔を形成することが望ましい。   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.

第１、第２貫通孔を形成するにあたっては、フォトリソ工程における線幅解像度やメッキ工程における再現製の確保の観点からも配慮をすることが望ましい。第１接地電極のリッジ導波路側の縁や第２接地電極のリッジ導波路側の縁から、リッジ導波路の幅程度と同程度かそれ以上離間した位置に第１、第２貫通孔を形成するのが望ましい。   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.

本発明によれば、リッジ型光導波路と、ひさし状あるいはキノコ状の信号電極を備える変調器であって、高速動作可能な光変調器が提供される。特に、非特許文献１や非特許文献２に記載されているニオブ酸リチウムからなる光導波路を用いた光変調器で顕在していた特性インピーダンス低下の問題の解決に有効である。   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.

第１実施形態に係る光変調器の構成を示す平面図である。It is a top view which shows the structure of the optical modulator which concerns on 1st Embodiment. 図１のＩＩ−ＩＩ線に沿った光変調器の断面図である。It is sectional drawing of the optical modulator along the II-II line | wire of FIG. 図２の断面図近傍における光変調器の斜視図である。FIG. 3 is a perspective view of the optical modulator in the vicinity of the cross-sectional view of FIG. 2. 第２実施形態に係る光変調器の構成を示す平面図である。It is a top view which shows the structure of the optical modulator which concerns on 2nd Embodiment. 図４のＶ−Ｖ線に沿った光変調器の断面図である。It is sectional drawing of the optical modulator along the VV line of FIG. 第３実施形態に係る光変調器の構成を示す平面図である。It is a top view which shows the structure of the optical modulator which concerns on 3rd Embodiment. 図６のＶＩＩ−ＶＩＩ線に沿った光変調器の断面図である。It is sectional drawing of the optical modulator along the VII-VII line of FIG. 第４実施形態に係る光変調器の構成を示す平面図である。It is a top view which shows the structure of the optical modulator which concerns on 4th Embodiment. 図８のＩＸ−ＩＸ線に沿った光変調器の断面図である。It is sectional drawing of the optical modulator along the IX-IX line of FIG. 第５実施形態に係る光変調器の断面図である。It is sectional drawing of the optical modulator which concerns on 5th Embodiment. 第６実施形態に係る光変調器の構成を示す平面図である。It is a top view which shows the structure of the optical modulator which concerns on 6th Embodiment. 図１１のＩＸ−ＩＸ線に沿った光変調器の断面図である。It is sectional drawing of the optical modulator along the IX-IX line of FIG.

以下、実施の形態に係る光変調器について、添付図面を参照しながら詳細に説明する。なお、各図面において、可能な場合には同一要素には同一符号を用いる。また、図面中の構成要素内及び構成要素間の寸法比は、図面の見易さのため、それぞれ任意となっている。   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.

以下に説明する本実施形態の光変調器の特徴は、信号電極と対向して作用する接地電極要素の一部を切り欠くことにより、これらの電極間の容量を下げ、特性インピーダンスを上昇させるという原理に基づくものであり、実用価値が高い光変調器の特性改善のために特に有効な実施形態が以下で説明されている。さらに、本実施形態の光変調器には、当該原理の導入の弊害である信号電極の伝搬損失を抑えるための技術も合わせて取り入れられており、産業的に価値の高い技術によって特徴付けられた光変調器となっている。   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.

（第１実施形態）
図１は、本発明の第１実施形態に係る光変調器の構成を示す平面図であり、図２は、図１のＩＩ−ＩＩ線に沿った光変調器の断面図であり、図３は、図２の断面図近傍における光変調器の斜視図である。 (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.

図１〜図３に示すように、本実施形態の光変調器１００は、光ファイバ等によって導入される連続光である入力光ＣＬを変調して、外部に変調光ＭＬを出力する装置である。光変調器１００は、基体部３と、リッジ型光導波路５と、変調電極１５と、を備え得る。   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.

基体部３は、例えばニオブ酸リチウム（ＬｉＮｂＯ３）などの電気光学効果を奏する誘電体材料から構成される板状の部材である。基体部３は、略平坦な主面３Ｓを有する。図１には、直交座標系ＲＣを示しており、主面３Ｓと平行な方向にＸ軸及びＹ軸を設定し、主面３Ｓと直交する方向にＺ軸を設定している。図２以降の各図面においても、必要に応じて図１と対応するように直交座標系ＲＣを示している。 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.

基体部３は、Ｙ軸方向（第１方向）に延びる長手形状を有している。基体部３の主面３Ｓは、リッジ型光導波路５が設けられた設置面３Ｅと、第１面３Ａと、第２面３Ｂと、からなる。設置面３Ｅ、第１面３Ａ、及び、第２面３Ｂは、それぞれＹ軸方向に延びる面であり、基体部３のＹ軸負方向の一端からＹ軸正方向の他端まで延びている。第１面３Ａ及び第２面３Ｂは、Ｘ軸方向（第２方向）に沿って設置面３Ｅを挟むように位置している。   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).

リッジ型光導波路５は、本実施形態では、主面３Ｓの設置面３Ｅの全体上に設けられている。リッジ型光導波路５は、Ｚ軸方向に突出し、Ｙ軸方向に沿って延びる形状の光導波路である。入力光ＣＬは、リッジ型光導波路５のコア部５ＡのＹ軸負方向の端面から光変調器１００内に導入され、コア部５Ａ内を当該コア部５Ａの光軸５ＡＸに沿って導波し、コア部５ＡのＹ軸正方向の端面から変調光ＭＬとして光変調器１００の外部に出力される。   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.

リッジ型光導波路５は、それぞれＹ軸方向に沿って延びるコア部５Ａと、クラッド部５Ｂと、バッファ層５Ｃとからなる。コア部５Ａは、クラッド部５Ｂよりも屈折率の高い材料からなる。コア部５Ａ及びクラッド部５Ｂは、それぞれ電気光学効果を奏する誘電体材料から構成される。コア部５Ａは、例えばチタン（Ｔｉ）等の金属を含有するニオブ酸リチウム（ＬｉＮｂＯ３）から構成され、クラッド部５Ｂは、例えばニオブ酸リチウム（ＬｉＮｂＯ３）から構成される。バッファ層５Ｃは、コア部５Ａよりも屈折率の低い材料からなり、例えば酸化シリコン（ＳｉＯ２）等の誘電体材料からなる。バッファ層５Ｃは、コア部５Ａと信号電極７との間に介在することにより、信号電極７に起因したコア部５Ａ内を導波する光の伝搬損失を低減させる。リッジ型光導波路５は、バッファ層５Ｃを有していなくてもよい。 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.

上述のような基体部３と基体部３上に設けられたリッジ型光導波路５とからなる構造体は、例えばニオブ酸リチウム（ＬｉＮｂＯ３）等の誘電体材料から構成される板状の初期基板を準備し、当該初期基板の主面近傍のコア部５Ａとなるべき領域にチタン（Ｔｉ）等の金属を拡散させ、当該主面の全体上にバッファ層５Ｃを構成する誘電体材料からなる誘電体膜を形成した後に、リッジ型光導波路５及び基体部３となるべき領域を残すように当該初期基板及び当該誘電体膜をエッチングすることにより、得ることできる。或いは、当該構造体は、基体部３を準備し、基体部３の主面３Ｓの設置面３Ｅ上にリッジ型光導波路５を形成することによっても、得ることができる。 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.

基体部３をＳｉＯ２、Ａｌ２Ｏ３や光学ガラス、光学樹脂などの光学材料で構成し、リッジ型光導波路５をニオブ酸リチウムなどの電気光学効果を奏する誘電体材料で構成するなど、光導波路構造３と第１制御用信号電極５を、互いに異なった材料で構成することも可能である。この構成は、基体部材料とリッジ型光導波路部の材料の貼り合わせや基体部材料上へのリッジ部導波路材料の膜形成を行った後に、リッジ型光導波路５及び基体部３となるべき領域を残すように当該初期基板及び当該誘電体膜をエッチングすることにより、得ることが出来る。この場合、光変調器に使用する入射光の波長や偏波条件において、基体部材料の屈折率は、リッジ型光導波路部材料の屈折率より小さい材料の組合せと選ぶ必要がある。また、この構成の場合、リッジ形状部５全体が光導波路のコア部として機能するため、リッジ形状部５に屈折率が高い部分５Ａを形成しなくてもよい。 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.

変調電極１５は、信号電極７と、第１接地電極１１と、第２接地電極１２と、を有する。変調電極１５は、ＸＹ平面に沿って延びる形状を有する電極であり、高周波において良導体である材料、例えば金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）等の金属や超伝導材料から構成される。変調電極１５は、リッジ型光導波路５内を導波する入力光ＣＬを変調するために設けられている。   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.

信号電極７は、本実施形態では、入力側伝達部７Ｔ１と、幅広部７Ｗと、出力側伝達部７Ｔ２と、を有する。入力側伝達部７Ｔ１は、入力パッド７Ｐ１と、信号伝達部７Ｅ１と、からなる。入力パッド７Ｐ１は、例えば、基体部３の主面３Ｓのうち、Ｘ軸正側の端部近傍に設けられており、外部の素子から供給される変調信号が入力される入力部として機能する。当該変調信号には、例えば１０ＧＨｚ以上の高周波電気信号が含まれている。信号伝達部７Ｅ１の一端は、入力パッド７Ｐ１と電気的に接続されており、信号伝達部７Ｅ１は、入力パッド７Ｐ１に入力された変調信号を幅広部７Ｗまで伝達する。信号伝達部７Ｅ１の幅広部７Ｗ近傍の部分は、幅広部７Ｗに近づくにつれて、平面視（Ｚ軸方向から見た場合）の幅が幅広部７Ｗの幅に近づくように漸次増加する形状を有しており、インピーダンスの不整合による反射損失の発生を防ぐ構造となっている。   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.

幅広部７Ｗの一端は、信号伝達部７Ｅ１の他端に電気的に接続されている。幅広部７Ｗは、リッジ型光導波路５上にＹ軸方向に沿って延びるように設けられている。幅広部７ＷのＸ軸方向の幅Ｗ７Ｗは、リッジ型光導波路５の最上部のＸ軸方向の幅Ｗ５よりも大きい。そのため、Ｙ軸方向と直交する断面において、幅広部７Ｗは、リッジ型光導波路５に対して、図１〜図３に示すような、ひさし形状、又は、キノコ形状を有する。ここで、幅広部７Ｗが、ひさし形状を有するとは、信号電極７の幅広部７Ｗが、リッジ型光導波路５の上面から当該リッジ型光導波路５に対して第２方向に当該リッジ型光導波路５の幅Ｗ５よりも広くなるように張り出しており、リッジ型光導波路５の上面にひさしを取り付けたような断面構造であることを意味する。また、幅広部７Ｗが、キノコ形状を有するとは、信号電極７の幅広部７Ｗが、リッジ型光導波路５の上面に接する基部と、当該基部より上方の部分であって上記基部よりも幅の広い上方部分と、を有する状態、即ち、信号電極７の幅広部７Ｗが、リッジ型光導波路５に対して第２方向にせり出したオーバーハング部（上記の上方部分）を有しており、かつ、幅広部７Ｗがリッジ型光導波路５のリッジ型光導波路５ｗよりも広くなっている状態を意味し、幅広部７Ｗの断面形状がリッジ型光導波路５の上面に設けられたキノコ形状であることを意味する。   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.

幅広部７Ｗは、コア部５Ａ内を導波する光に変調作用を与える変調作用部として機能する。具体的には、幅広部７Ｗによってリッジ型光導波路５のコア部５Ａに電界を印加可能であり、印加される電界の強さ、コア部５Ａを構成する材料の種類、及び、コア部５Ａの誘電分極の方向等に応じてコア部５Ａの屈折率は変化する。信号電極７に変調信号が供給されると、幅広部７Ｗは当該変調信号に応じた電界をリッジ型光導波路５のコア部５Ａに印加し、コア部５Ａ内の屈折率を当該変調信号に応じて変化させる。これにより、入力光ＣＬは変調信号に応じて変調される。   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.

幅広部７ＷのＹ軸と直交する断面における形状は、図２に示すような、ひさし形状の一態様としての平板状に限られず、例えば、矩形状、楕円形状、又は、徐々にせり出す逆台形状に張り出す形状であっても良いし、キノコ状に張り出す形状であってもよいし、これらの中間的な形状やこれらの複合した形状等であってもよい。   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.

出力側伝達部７Ｔ２は、出力パッド７Ｐ２と、信号伝達部７Ｅ２と、からなる。信号伝達部７Ｅ２の一端は、幅広部７Ｗの他端に電気的に接続されており、信号伝達部７Ｅ２は、幅広部７Ｗ内を伝達した変調信号を、出力パッド７Ｐ２まで伝達する。信号伝達部７Ｅ２の幅広部７Ｗ近傍の部分は、出力パッド７Ｐ２に近づくにつれて、平面視での幅が漸次減少する形状を有しており、インピーダンスの不整合による反射損失の発生を防ぐ構造となっている。信号伝達部７Ｅ２の他端は、出力パッド７Ｐ２に電気的に接続されている。出力パッド７Ｐ２は、例えば、基体部３の主面３Ｓのうち、Ｘ軸正側の端部近傍に設けられており、変調信号が出力される出力部として機能する。出力パッド７Ｐ２は、変調信号の電気的終端である終端部（図示せず）が有する抵抗器に電気的に接続されていてもよい。   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.

第１接地電極１１及び第２接地電極１２は、接地電位に接続される電極である。第１接地電極１１及び第２接地電極１２は、それぞれＸＹ平面に沿って延びる形状を有する電極であり、基体部３の主面３Ｓ上に設けられている。第１接地電極１１及び第２接地電極１２は、それぞれ例えば金（Ａｕ）等の金属から構成される。   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).

第１接地電極１１は、一端部接地電極要素１１Ｅ１と、第１接地電極要素としての中央部接地電極要素１１Ｃと、他端部接地電極要素１１Ｅ２と、からなる。一端部接地電極要素１１Ｅ１は、第１接地電極１１のうち、Ｙ軸負側方向側の電極要素であり、中央部接地電極要素１１Ｃは、第１接地電極１１のうち、Ｙ軸方向中央部の電極要素であり、他端部接地電極要素１１Ｅ２は、第１接地電極１１のうち、Ｙ軸正側方向側の電極要素である。   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.

同様に、第２接地電極１２は、一端部接地電極要素１２Ｅ１と、第２接地電極要素としての中央部接地電極要素１２Ｃと、及び、他端部接地電極要素１２Ｅ２と、からなる。一端部接地電極要素１２Ｅ１は、第２接地電極１２のうち、Ｙ軸負側方向の電極要素であり、中央部接地電極要素１２Ｃは、第２接地電極１２のうち、Ｙ軸方向中央部の電極要素であり、他端部接地電極要素１２Ｅ２は、第２接地電極１２のうち、Ｙ軸正側方向の電極要素である。   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.

一端部接地電極要素１１Ｅ１及び一端部接地電極要素１２Ｅ１は、それぞれ入力パッド７Ｐ１の近傍から中央部接地電極要素１１Ｃ及び中央部接地電極要素１２ＣのＹ軸負側方向の一端まで延びて当該一端と電気的に接続されている。他端部接地電極要素１１Ｅ２及び他端部接地電極要素１２Ｅ２は、それぞれ出力パッド７Ｐ２の近傍から中央部接地電極要素１１Ｃ及び中央部接地電極要素１２ＣのＹ軸正側方向の他端まで延びて当該他端と電気的に接続されている。第１接地電極１１及び第２接地電極１２は、一端部接地電極要素１１Ｅ１及び一端部接地電極要素１２Ｅ１の入力パッド７Ｐ１近傍の領域において、外部の接地電位を有する要素に電気的に接続されることができ、また、他端部接地電極要素１１Ｅ２及び他端部接地電極要素１２Ｅ２の出力パッド７Ｐ２近傍の領域において、外部の接地電位を有する要素に電気的に接続されることができる。   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.

中央部接地電極要素１１Ｃは、Ｙ軸方向に沿って延びるように、即ち、幅広部７Ｗの延び方向に沿って延びるように基体部３の主面３Ｓの第１面３Ａ上に設けられている。本実施形態では、中央部接地電極要素１１Ｃは、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に接している。そのため、平面視で中央部接地電極要素１１Ｃの一部は幅広部７Ｗと重複する。中央部接地電極要素１１ＣのＺ軸方向の厚さＴ１１Ｃは、リッジ型光導波路５のＺ軸方向の高さＴ５よりも低い。そのため、中央部接地電極要素１１Ｃは、幅広部７ＷとＺ軸方向に離間している。中央部接地電極要素１１Ｃの厚さＴ１１Ｃは、例えば１μｍ以上３μｍ以下であり、リッジ型光導波路５の高さＴ５は、例えば３μｍ以上１０μｍ以下とすることができる。   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.

中央部接地電極要素１１Ｃは、複数の第１貫通孔１１Ｂを有している。第１貫通孔１１Ｂは、中央部接地電極要素１１ＣをＺ軸方向に沿って貫通する孔である。各第１貫通孔１１Ｂは、中央部接地電極要素１１Ｃのうち、平面視で幅広部７Ｗと重複する領域に設けられている。そのため、各第１貫通孔１１Ｂは、平面視で、幅広部７Ｗと重複する。また、各第１貫通孔１１Ｂは、平面視で、中央部接地電極要素１１Ｃのリッジ型光導波路５側の側面１１ＳとＸ軸方向に離間している。また、各第１貫通孔１１Ｂは、平面視で、角部を有しない形状、例えば、円形形状、楕円形状、レーストラック形状、又は、角丸矩形形状を有する。なお、レーストラック形状とは、その外縁が、第１及び第２の円弧部と、第１及び第２の直線部とを有し、第１の円弧部の開口と第２の円弧部の開口とが向かい合うように第１及び第２の円弧部が配されており、第１の円弧部の一端と当該一端側にある第２の円弧部の一端とが第１の直線部によって接続され、第１の円弧部の他端と第２の円弧部の他端とが第２の直線部によって接続された形状をいう。複数の第１貫通孔１１Ｂは、同一の平面視形状を有していてもよいし、一部又は全部が互いに異なる平面視形状を有していてもよい。   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.

複数の第１貫通孔１１Ｂは、Ｙ軸方向に沿って順に周期Ｐ１１Ｂで周期的に設けられている。信号電極７と第１接地電極１１、第２接地電極１２間の容量を小さくする効果や変調電極１５の特性インピーダンスを上昇させる効果を発現させる視点からは、同じ形状の第１貫通孔１１Ｂを第一方向に沿って周期的に配置しなくともよく、例えば形状が異なる複数種類の第１貫通孔１１Ｂを配置してもよいし、複数種類の第１貫通孔１１Ｂを、離散的に、又は、信号電極７の延び方向に沿って所定の周期で配置してもよい。第１貫通孔１１Ｂを離散的に配置したり、形状の異なる複数種類の第１貫通孔１１Ｂを配置したりするよりも、同じ形状の複数の第１貫通孔１１Ｂを周期的に配置した方が、特性の解析計算の規模が小さくて済むため設計上有利であり、設計解析が容易になることから、意図しないインピーダンスの不整合による伝搬信号の損失の特性劣化を防ぎやすい。   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 11B having the same shape is formed in the first 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.

なお、第１貫通孔１１Ｂが周期的に設けられた構造の場合には、その構造が特定の周波数に対応したバンドパスフィルター回路として作用するため、特定の周波数信号がそのバンドパスフィルター回路に結合し、信号電極を伝搬する信号が劣化するおそれがある。その変調信号の劣化は、第１貫通孔１１Ｂが設けられた周期を変調信号の主要周波数成分の波長（バンドバスフィルター回路における、その周波数成分の波長）の１／４以下にすることで、回避することができる。   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.

同様に、中央部接地電極要素１２Ｃは、Ｙ軸方向に沿って延びるように、即ち、幅広部７Ｗの延び方向に沿って延びるように基体部３の主面３Ｓの第２面３Ｂ上に設けられている。本実施形態では、中央部接地電極要素１２Ｃは、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に接している。そのため、平面視で中央部接地電極要素１２Ｃの一部は幅広部７Ｗと重複する。中央部接地電極要素１２ＣのＺ軸方向の厚さＴ１２Ｃは、リッジ型光導波路５のＺ軸方向の高さＴ５よりも低い。そのため、中央部接地電極要素１２Ｃは、幅広部７ＷとＺ軸方向に離間している。中央部接地電極要素１２Ｃの厚さＴ１２Ｃは、例えば１μｍ以上３μｍ以下である。   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.

中央部接地電極要素１２Ｃは、複数の第２貫通孔１２Ｂを有している。第２貫通孔１２Ｂは、中央部接地電極要素１２ＣをＺ軸方向に沿って貫通する孔である。各第２貫通孔１２Ｂは、中央部接地電極要素１２Ｃのうち、平面視で幅広部７Ｗと重複する領域に設けられている。そのため、各第２貫通孔１２Ｂは、平面視で、幅広部７Ｗと重複する。また、各第２貫通孔１２Ｂは、平面視で、中央部接地電極要素１２Ｃのリッジ型光導波路５側の側面１２ＳとＸ軸方向に離間している。各第２貫通孔１２Ｂは、平面視で、角部を有しない形状、例えば、円形形状、楕円形状、レーストラック形状、又は、角丸矩形形状を有する。   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.

複数の第２貫通孔１２Ｂは、Ｙ軸方向に沿って順に周期Ｐ１２Ｂで周期的に設けられている。第２貫通孔の配置の周期性、形状についての留意点は上記で説明した第１貫通孔１１Ｂの場合と同様である。さらに、第１貫通孔１１Ｂと第２貫通孔１２Ｂは、平面視で、コア部５Ａの光軸５ＡＸに対して線対称となる態様である場合、設計解析における計算規模が小さくて済むため好ましい。   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.

上述のような本実施形態に係る光変調器１００においては、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃは、それぞれ、平面視で信号電極７の幅広部７Ｗと重複する第１貫通孔１１Ｂ及び第２貫通孔１２Ｂを有する（図１及び図２参照）。そのため、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃが、それぞれ第１貫通孔１１Ｂ及び第２貫通孔１２Ｂを有していない場合と比較して、信号電極７と第１接地電極１１及び第２接地電極１２間の静電容量を低下させることができるため、変調電極１５の特性インピーダンスを高くすることができる。   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.

その結果、本実施形態に係る光変調器１００によれば、信号電極７が集中定数形電極として機能する場合には高周波駆動の妨げとなる信号電極７と第１接地電極１１、第２接地電極１２間の容量を小さくすることができ、また、信号電極７が進行波形電極として機能する場合は変調電極１５の特性インピーダンスの低下を避けることができ変調信号を供給する外部の素子と変調器とのインピーダンス整合を図り易くなるため、高速変調動作及び高効率駆動が可能となる。   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.

このように本実施形態において採用している技術は、変調電極１５の特性インピーダンスを高く設計する際や、信号電極７と第１接地電極１１、第２接地電極１２間の容量を下げる設計を行う際に有効な技術である。したがって、ニオブ酸リチウムのように比誘電率が高い材料（ニオブ酸リチウムの比誘電率には、異方性があり、当該比誘電率は２８と４５）からなる基体部３を用いて光変調器１００を作製する際に特に有効である。またＧＨｚ帯の成分をふくむような高周波制御信号、広帯域制御信号で駆動させる光変調器１００を作製する際に特に有効である。   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.

また、特に本実施形態に係る光変調器１００においては、各第１貫通孔１１Ｂ及び第２貫通孔１２Ｂは、平面視で、幅広部７Ｗと重複するように設けられているため（図１参照）、信号電極７と第１接地電極１１及び第２接地電極１２間の全体の静電容量は、第１貫通孔１１Ｂ及び第２貫通孔１２Ｂと貫通孔の合計面積に対応する平行平板状コンデンサの容量に相当する分低下するため、変調電極１５の特性インピーダンスをより高くすることができる。   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.

さらに、本実施形態に係る光変調器１００においては、各第１貫通孔１１Ｂ、及び、第２貫通孔１２Ｂは、平面視で、円形形状又は楕円形状等の角部を有しない形状を有している（図１及び図３参照）。これにより、平面視で中央部接地電極要素１１Ｃの第１貫通孔１１Ｂと隣接する界面、及び、平面視で中央部接地電極要素１２Ｃの第２貫通孔１２Ｂと隣接する界面は、角部を有さない曲線形状となる。その結果、変調信号が変調電極１５に印加された際に当該隣接する界面において電界の集中が起きにくくなるため、変調信号の伝搬損失を抑制することができる。   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.

さらに、本実施形態に係る光変調器１００においては、中央部接地電極要素１１Ｃは、複数の第１貫通孔１１Ｂを有し、当該複数の第１貫通孔１１Ｂは、Ｙ軸方向に沿って順に設けられており、中央部接地電極要素１２Ｃは、複数の第２貫通孔１２Ｂを有し、当該複数の第２貫通孔１２Ｂは、Ｙ軸方向に沿って順に設けられている（図１及び図３参照）。   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).

これにより、変調電極１５のインピーダンスをさらに高くすることができるため、変調信号を供給する外部の素子と光変調器１００とのインピーダンス整合を、より高精度に図り易くなる。その結果、本実施形態に係る光変調器１００によれば、より高速での変調動作が可能となる。   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.

さらに、本実施形態に係る光変調器１００においては、第１貫通孔１１Ｂは、平面視で、中央部接地電極要素１１Ｃのリッジ型光導波路５側の側面１１Ｓと離間しており、第２貫通孔１２Ｂは、平面視で、中央部接地電極要素１２Ｃのリッジ型光導波路５側の側面１２Ｓと離間している（図１参照）。   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).

これにより、平面視で中央部接地電極要素１１Ｃの上記側面１１Ｓと中央部接地電極要素１２Ｃの上記側面１２Ｓに角部が形成されることを防止することができる。その結果、変調信号が変調電極１５に印加された際に当該側面１１Ｓ、１２Ｓにおいて電界の集中が起きにくくなるため、変調信号の伝搬損失を抑制することができる。   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.

また、本実施形態に係る光変調器１００においては、中央部接地電極要素１１Ｃは、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に接しており、中央部接地電極要素１２Ｃは、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に接している（図１〜図３参照）。これにより、平面視での幅広部７Ｗと重複する中央部接地電極要素１１Ｃの領域及び中央部接地電極要素１２Ｃの領域が大きくなるため、幅広部７Ｗと中央部接地電極要素１１Ｃの領域及び中央部接地電極要素１２Ｃの領域との間の空隙を伝わる制御信号のパワーの割合が大きくなり変調信号の速度が上昇し、リッジ型光導波路５内を導波する光と信号電極７に印加される変調信号との速度整合が可能になると共に、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃの表面積が広くなり電界の集中が避けられることから低電極損失がより容易に実現可能となる。   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, and therefore, the region and the central portion of the wide portion 7W and the central portion ground electrode element 11C. 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.

これにより、従来の構成の光変調器において、ひさし状に張り出した信号電極を用いた構成の欠点であった、電極間容量の増大と特性インピーダンスの低下は、本実施形態の光変調器１００においては、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃに各第１貫通孔１１Ｂ及び第２貫通孔１２Ｂを設けることで改善できる。   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.

また、本実施形態に係る光変調器１００においては、各第１貫通孔１１Ｂは、平面視で、中央部接地電極要素１１Ｃのリッジ型光導波路５側の側面１１ＳとＸ軸方向に２μｍ以上離間しており、各第２貫通孔１２Ｂは、平面視で、中央部接地電極要素１２Ｃのリッジ型光導波路５側の側面１２ＳとＸ軸方向に２μｍ以上離間していることが好ましい。高周波に対応する光変調器の電極材料として一般的に用いられる良導体である、金、銀や銅の、周波数１０ＧＨｚにおける表皮効果による表皮深さは、おおよそ１μｍ弱である。上述の好ましい態様においては、各第１貫通孔１１Ｂおよび各第２貫通孔１２Ｂは、平面視で、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃのリッジ型光導波路５側の側面１１Ｓ及び１２Ｓから、上記表層深さ以上離間することになる。これにより、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃのうち、各第１貫通孔１１Ｂおよび各第２貫通孔１２Ｂの近傍にエッジ効果によって電界が集中しても、高周波電流にとって十分な表皮深さが確保されているため、変調信号の伝搬損失の発生を抑制することができる。   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.

また、平面視での各第１貫通孔１１Ｂと、中央部接地電極要素１１Ｃのリッジ型光導波路５側の側面１１ＳとのＸ軸方向の離間距離は、伝搬損失の発生を抑制する観点からは特に制限されず、信号電極７と第１接地電極１１、第２接地電極１２間の容量又は変調電極１５の特性インピーダンスの設計に応じて適宜決定すればよい。当該離間距離が大きいと信号電極７と第１接地電極１１、第２接地電極１２間の容量の低下と変調電極１５の特性インピーダンスの増大の効果は小さくなる傾向にあるが、各第１貫通孔１１Ｂ及び第２貫通孔１２Ｂは、平面視で、幅広部７Ｗと重複するように設けられているため、当該効果の当該離間距離への依存性は比較的小さい。中央部接地電極要素１２Ｃのリッジ型光導波路５側の側面１２ＳとのＸ軸方向の離間距離についても同様である。したがって、信号電極７と第１接地電極１１、第２接地電極１２間の容量の低下と変調電極１５の特性インピーダンスの増大は、上記離間距離でなく主に第１貫通孔１１Ｂと第２貫通孔１２Ｂの平面視での総面積で調整することができる。   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.

また、本実施形態に係る光変調器１００においては、中央部接地電極要素１１Ｃ及び中央部接地電極要素１２Ｃは、平面視で、リッジ型光導波路５のコア部５Ａの光軸に対して略線対称に設けられていることが好ましい（図１参照）。これにより、特性の設計に必要な解析計算の規模が小さくて済む。さらには、第１貫通孔１１Ｂと第２貫通孔１２Ｂの不均等な配置に起因する、温度変化の際の基板の応力・歪みの偏りが回避され、光変調器の動作の安定性獲得が期待できる。   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.

（第２実施形態）
次に、本発明の第２実施形態について説明する。第２実施形態以降の各実施形態については、他の実施形態との相違点について主として説明し、他の実施形態の要素と同一の要素については、同一の符号を付すことにより、その詳細な説明を省略する場合がある。 (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.

図４は、第２実施形態に係る光変調器の構成を示す平面図であり、図５は、図４のＶ−Ｖ線に沿った光変調器の断面図である。本実施形態の光変調器２００は、第１貫通孔が設けられた位置、及び、第２貫通孔が設けられた位置において、第１実施形態の光変調器１００と相違する。   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.

即ち、図４及び図５に示すように、本実施形態の変調電極２１５は、第１接地電極２１１、信号電極７、及び、第２接地電極２１２を有する。そして、第１接地電極２１１が有する中央部接地電極要素２１１Ｃは、複数の第１貫通孔が形成された位置において、第１実施形態の中央部接地電極要素１１Ｃと相違する。具体的には、本実施形態の複数の第１貫通孔２１１Ｂは、中央部接地電極要素２１１Ｃのうち、平面視で幅広部７Ｗと重複しない領域に設けられている。そのため、各第１貫通孔２１１Ｂは、平面視で幅広部７ＷとＸ軸方向に対向する。   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.

同様に、第２接地電極２１２が有する中央部接地電極要素２１２Ｃは、複数の第２貫通孔が形成された位置において、第１実施形態の中央部接地電極要素１２Ｃと相違する。具体的には、本実施形態の複数の第２貫通孔２１２Ｂは、中央部接地電極要素２１２Ｃのうち、平面視で幅広部７Ｗと重複しない領域に設けられている。そのため、各第２貫通孔２１２Ｂは、平面視で幅広部７ＷとＸ軸方向に対向する。   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.

複数の第１貫通孔２１１Ｂは、第１実施形態の第１貫通孔１１Ｂと同様に、Ｙ軸方向に沿って順に周期Ｐ２１１Ｂで周期的に設けられている。信号電極７と第１接地電極１１、第２接地電極１２間の容量を小さくする効果や変調電極２１５の特性インピーダンスを上昇させる効果を発現させる視点からは、同じ形状の第１貫通孔１１Ｂを方向１に沿って周期的に配置しなくともよく、例えば形状が異なる複数種類の第１貫通孔１１Ｂを配置してもよいし、複数種類の第１貫通孔１１Ｂを、離散的に、又は、信号電極７の延び方向に沿って所定の周期で配置してもよい。第１貫通孔１１Ｂを離散的に配置したり、形状の異なる複数種類の第１貫通孔を配置したりするよりも、同じ形状の複数の第１貫通孔１１Ｂを周期的に配置した方が、特性の解析計算の規模が小さくて済むため設計上有利であり、設計解析が容易になることから、意図しないインピーダンスの不整合による伝搬信号の損失の特性劣化を防ぎやすい。   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.

なお、第１貫通孔１１Ｂが周期的に設けられた構造の場合には、その構造が特定の周波数に対応したバンドパスフィルター回路として作用するため、特定の周波数信号がそのバンドパスフィルター回路に結合し、信号電極を伝搬する信号が劣化するおそれがある。その変調信号の劣化は、第１貫通孔１１Ｂが設けられた周期を変調信号の主要周波数成分の波長（バンドバスフィルター回路における、その周波数成分の波長）の１／４以下にすることで、回避することができる。複数の第２貫通孔１２Ｂについても、同様である。   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.

本実施形態に係る光変調器２００によれば、第１実施形態の光変調器１００と同様の理由に基づき、変調信号を供給する外部の素子と光変調器２００とのインピーダンス整合を図り易くなるため、高速変調動作が可能となる。   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.

さらに、本実施形態の光変調器２００においては、複数の第１貫通孔２１１Ｂは、中央部接地電極要素２１１Ｃのうち、平面視で幅広部７Ｗと重複しない領域に設けられており、複数の第２貫通孔２１２Ｂは、中央部接地電極要素２１２Ｃのうち、平面視で幅広部７Ｗと重複しない領域に設けられているため（図４及び図５参照）、変調電極２１５と第１貫通孔２１１Ｂが大きく離間しているため、第１貫通孔２１１Ｂの縁においてエッジ効果が起こりにくくなっており、第１貫通孔２１１Ｂの存在に伴う変調信号の伝搬損失を低減することができる。   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.

ただし、変調電極２１５の断面形状が平板の、ひさし状の構造の場合、上記離間距離が大きいと信号電極７と第１接地電極２１１、第２接地電極２１２間容量の低下と変調電極２１５の特性インピーダンスの増大の効果は小さくなる。ニオブ酸リチウムで基体部及びリッジ導波路部を構成した態様において、本実施形態において速度整合と変調信号の低損失な伝搬が実現できるのは、例えば信号電極７の幅広部７Ｗの幅Ｗ７Ｗをリッジ型光導波路５の幅Ｗ５の３〜５倍程度とした際であるが、上記離間距離をリッジ導波路部の幅Ｗ５の８倍程度離すと、電極間容量の低下と特性インピーダンスの上昇の効果は、相対的に低くなる場合がある。   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.

一方、変調電極２１５の断面形状が、矩形状、楕円形状、逆台形状やキノコ状など、側面に相当する部分の面積が大きい構造の場合には、状況が異なる。中央部接地電極要素２１１Ｃのうち平面視で幅広部７Ｗと重複しない領域は、変調電極１５の側面部分と実質的に対向して作用する領域にあたるため、この部分に第１貫通孔２１１Ｂを形成することは、信号電極７と第１接地電極２１１、第２接地電極２１２間の容量の低減や変調電極２１５の特性インピーダンスの上昇に有効な手段である。特に、信号電極７の幅広部７Ｗの幅Ｗ７Ｗより信号電極の高さＴ６０７Ｗ（図１２参照）の方が大きい場合に効果が大きい。第１貫通孔２１１Ｂを、中央部接地電極要素２１１Ｃのうち平面視で幅広部７Ｗと重複する領域に形成しても、重複しない領域に形成しても、信号電極７と第１接地電極２１１、第２接地電極２１２間の容量の低下と変調電極２１５の特性インピーダンスの上昇の効果は得られるが、重複しない領域に形成するほうが、変調信号損失が小さい点で有利である。   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.

（第３実施形態）
次に、本発明の第３実施形態について説明する。図６は、第３実施形態に係る光変調器の構成を示す平面図であり、図７は、図６のＶＩＩ−ＶＩＩ線に沿った光変調器の断面図である。第３実施形態の光変調器３００は、第１貫通孔及び第２貫通孔の平面視形状において、第２実施形態の光変調器２００と相違する。 (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.

即ち、図６及び図７に示すように、本実施形態の変調電極３１５は、第１接地電極３１１、信号電極７、及び、第２接地電極３１２を有する。そして、第１接地電極３１１が有する中央部接地電極要素３１１Ｃに設けられた複数の第１貫通孔３１１Ｂの平面視形状は、それぞれ、第２実施形態の第１貫通孔２１１Ｂ（図４参照）とは異なり、矩形形状等の角部を有する形状である。同様に、第２接地電極３１２が有する中央部接地電極要素３１２Ｃに設けられた複数の第２貫通孔３１２Ｂの平面視形状は、それぞれ第２実施形態の第２貫通孔２１２Ｂ（図４参照）とは異なり、矩形形状等の角部を有する形状である。   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.

本実施形態に係る光変調器２００によれば、第１実施形態の光変調器１００と同様の理由に基づき、変調信号を供給する外部の素子と光変調器２００とのインピーダンス整合を図り易くなるため、高速変調動作が可能となる。   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.

さらに、本実施形態の光変調器３００においては、複数の第１貫通孔３１１Ｂの平面視形状は、それぞれ矩形形状等の角部を有する形状であり、複数の第２貫通孔３１２Ｂの平面視形状は、それぞれ矩形形状等の角部を有する形状であるため（図６参照）、設計に必要な特性解析の計算規模の大幅な縮小が可能である。各第１貫通孔３１１Ｂ及び各第２貫通孔３１２Ｂが曲線部を含まない単純な構造であるため、これらが曲線部を含む場合に比べて、有限要素解析においては要素のサイズを細分化する必要がなく計算規模が大幅に軽減される。また、計算のモデル入力の大幅に省力化されるという効果を発揮する。   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.

角部を有する第１貫通孔３１１Ｂ及び第２貫通孔３１２Ｂを、中央部接地電極要素３１１Ｃ及び中央部接地電極要素３１２Ｃのうち平面視で信号電極幅広部７Ｗと重複する領域に形成する場合、第１貫通孔３１１Ｂ及び第２貫通孔３１２Ｂと信号電極７Ｗとの距離が近いため、エッジ効果の影響が相対的に増加する場合があり、信号電極７の損失が相対的に増大する可能性があるが、本実施形態のように、中央部接地電極要素３１１Ｃ及び各第２貫通孔３１２Ｂのうち平面視で信号電極幅広部７Ｗと重複しない領域に第１貫通孔３１１Ｂ及び各第２貫通孔３１２Ｂがを形成する場合は、第１貫通孔３１１Ｂ及び第２貫通孔３１２Ｂと信号電極７Ｗとの距離が大きいため、エッジ効果の影響は軽微であり、信号電極の損失は低減される。   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.

（第４実施形態）
次に、本発明の第４実施形態について説明する。図８は、第４実施形態に係る光変調器の構成を示す平面図であり、図９は、図８のＩＸ−ＩＸ線に沿った光変調器の断面図である。第４実施形態の光変調器４００は、第１テラス部３Ｔ１と、第２テラス部３Ｔ２とをさらに備える点、及び、第１接地電極１１がテラス上接地電極要素１１Ｄをさらに有する点、及び、第２接地電極１２がテラス上接地電極要素１２Ｄをさらに有する点、において、第１実施形態の光変調器１００（図１〜図３参照）と異なる。 (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.

第１テラス部３Ｔ１は、主面３Ｓの第１面３Ａ上に設けられたテラス状の部材であり、第２テラス部３Ｔ２は、主面３Ｓの第２面３Ｂ上に設けられたテラス状の部材である。第１テラス部３Ｔ１及び第２テラス部３Ｔ２は、リッジ型光導波路５と略同じ高さを有する。第１テラス部３Ｔ１とリッジ型光導波路５とによって、第１面３Ａ及び設置面３Ｅ上に第１凹部３Ｃ１が規定され、第２テラス部３Ｔ２とリッジ型光導波路５とによって、第２面３Ｂ及び設置面３Ｅ上に第２凹部３Ｃ２が規定される。第１凹部３Ｃ１及び第２凹部３Ｃ２は、それぞれ平面視でＹ軸方向に沿って延びる形状を有しており、本実施形態のリッジ型光導波路５の形状は、第１凹部３Ｃ１及び第２凹部３Ｃ２によって規定される。   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.

第１テラス部３Ｔ１及び第２テラス部３Ｔ２は、それぞれニオブ酸リチウム（ＬｉＮｂＯ３）などの電気光学効果を奏する誘電体材料から構成され、基体部３と同一の材料から構成されてもよい。このような基体部３とリッジ型光導波路５と第１テラス部３Ｔ１と第２テラス部３Ｔ２とからなる構造体は、例えばニオブ酸リチウム（ＬｉＮｂＯ３）等の誘電体材料から構成される板状の初期基板を準備し、当該初期基板の主面近傍のコア部５Ａとなるべき領域にチタン（Ｔｉ）等の金属を拡散させ、当該主面の全体上にバッファ層５Ｃを構成する誘電体材料からなる誘電体膜を形成した後に、リッジ型光導波路５、基体部３、第１テラス部３Ｔ１及び第２テラス部３Ｔ２なるべき領域を残すように当該初期基板及び当該誘電体膜をエッチングすることにより、得ることできる。或いは、当該構造体は、基体部３を準備し、基体部３の主面３Ｓの設置面３Ｅ上にリッジ型光導波路５、第１面３Ａ及び第２面３Ｂ上に第１テラス部３Ｔ１及び第２テラス部３Ｔ２を形成することによっても、得ることができる。 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.

第１接地電極１１のテラス上接地電極要素１１Ｄは、例えば中央部接地電極要素１１Ｃと同様の金属材料からなり、当該中央部接地電極要素１１Ｃと電気的に接続されるように、第１テラス部３Ｔ１の側面及び上面に設けられている。同様に、第２接地電極１２のテラス上接地電極要素１２Ｄは、例えば中央部接地電極要素１２Ｃと同様の金属材料からなり、当該中央部接地電極要素１２Ｃと電気的に接続されるように、第２テラス部３Ｔ２の側面及び上面に設けられている。第１テラス部３Ｔ１の上面上のテラス上接地電極要素１１Ｄの厚さは、中央部接地電極要素１１Ｃの厚さよりも厚いことが好ましく、例えば１０μｍ以上、８０μｍ以下とすることができる。同様に、第２テラス部３Ｔ２の上面上のテラス上接地電極要素１２Ｄの厚さは、中央部接地電極要素１２Ｃの厚さよりも厚いことが好ましく、例えば１０μｍ以上、８０μｍ以下とすることができる。   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.

本実施形態に係る光変調器４００によれば、第１実施形態の光変調器１００と同様の理由に基づき、変調信号を供給する外部の素子と光変調器４００とのインピーダンス整合を図り易くなるため、高速変調動作が可能となる。   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.

さらに、本実施形態の光変調器４００においては、中央部接地電極要素１１Ｃと電気的に接続され、第１テラス部３Ｔ１上に設けられたテラス上接地電極要素１１Ｄと、中央部接地電極要素１２Ｃと電気的に接続され、第２テラス部３Ｔ２上に設けられたテラス上接地電極要素１２Ｄとを有するため、テラス上接地電極要素１２Ｄと信号電極７とを同じ高さ又は近接した高さに形成することが容易になるため、変調器チップをケースに実装する際のワイヤーボンディング、フリップチップボンディングや、ＧＳＧ(Ground-Signal-Ground)タイプの高周波プローブを用いた特性検査が行いやすいといったという利点がある。また、ニオブ酸リチウムを用いてリッジ型光導波路を作製する場合には、反応性イオンエッチングや機械的加工が主に使われているが、いずれの手法においても、加工部分の面積が小さい方が工程上の都合が良く、第１面３Ａおよび第２面３Ｂの形成は必要最小限にとどめるほうが望ましい。本実施形態のようにテラス部３Ｔ１や３Ｔ２に相当する部分を加工せずに残す構成は、現実的な構成である。   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.

（第５実施形態）
次に、本発明の第５実施形態について説明する。図１０は、第５実施形態に係る光変調器の断面図であり、第４実施形態の図９に対応する図である。第５実施形態の光変調器５００は、第１接地電極の中央部接地電極要素及び第２接地電極の中央部接地電極要素の態様の点において、第４実施形態の光変調器４００（図８及び図９参照）と異なる。 (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).

即ち、図１０に示すように、本実施形態の光変調器５００においては、第１接地電極１１が有する中央部接地電極要素５１１Ｃは、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に離間している。同様に、本実施形態の第２接地電極１２が有する中央部接地電極要素５１２Ｃは、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に離間している。中央部接地電極要素５１１Ｃとリッジ型光導波路５のＸ軸方向の離間距離及び中央部接地電極要素５１２Ｃとリッジ型光導波路５のＸ軸方向の離間距離は、例えば１μｍ以上、１６０μｍ以下とすることができる。中央部接地電極要素５１１Ｃ及び中央部接地電極要素５１２Ｃの一部は、平面視で幅広部７Ｗと重複している。   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.

本実施形態に係る光変調器５００によれば、第１実施形態の光変調器１００と同様の理由に基づき、変調信号を供給する外部の素子と光変調器５００とのインピーダンス整合を図り易くなるため、高速変調動作が可能となる。   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.

また、本実施形態に係る光変調器５００によれば、中央部接地電極要素５１１Ｃ及び中央部接地電極要素５１２Ｃが基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に離間しているため、信号電極７と第１接地電極５１１、第２接地電極５１２間の容量の低減させること、及び変調電極の特性インピーダンスの上昇させることが容易となるという利点がある。本実施構成は、リッジ型光導波路５及び基体部３を信号電極７と中央部接地電極要素５１１Ｃで挟んだコンデンサ、リッジ型光導波路部５及び基体部３を信号電極７と中央部接地電極要素５１２Ｃで挟んだコンデンサ、空気層を信号電極７と中央部接地電極要素５１１Ｃで挟んだコンデンサ、及び、空気層を信号電極７と中央部接地電極要素５１２Ｃで挟んだコンデンサの並列回路と等価であると簡略化して考えることができる。   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.

このように考えると、中央部接地電極要素５１１Ｃ及び中央部接地電極要素５１２Ｃと基体部３の主面３Ｓ上においてリッジ型光導波路５との離間距離の増加は、コンデンサ間の離間距離の増加に相当するため、信号電極７と第１接地電極５１１、第２接地電極５１２間の容量の低減及び変調電極の特性インピーダンスの上昇に直接寄与する。ただし、中央部接地電極要素５１１Ｃ及び中央部接地電極要素５１２Ｃと基体部３の主面３Ｓ上においてリッジ型光導波路５との離間距離は、光導波路部５における実効電界に直接影響し、信号電極７と接地電極要素の間に同じ電圧をかけた場合、離間距離が大きくなるほど光導波路部５における実効電界は小さくなるため、光変調器としての駆動効率が低下する。そのため、必要な駆動効率と特性インピーダンスの大きさを勘案しつつ、当該離間距離を設計する必要がある。   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.

（第６実施形態）
次に、本発明の第６実施形態について説明する。図１１は、第６実施形態に係る光変調器の構成を示す平面図であり、図１２は、図１１のＸＩＩ−ＸＩＩ線に沿った光変調器の断面図である。第６実施形態の光変調器６００は、変調電極の態様の点において、第４実施形態の光変調器４００と相違する。 (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.

具体的には、図１１及び図１２に示すように、本実施形態の変調電極６１５は、第１接地電極６１１、第２接地電極６１２、及び、信号電極６０７を有する。第１接地電極６１１が有する中央部接地電極要素６１１Ｃ及び第２接地電極６１２が有する中央部接地電極要素６１２Ｃは、第４実施形態の中央部接地電極要素１１Ｃ、１２Ｃ（図８及び図９参照）と異なり、平面視で変調電極６１５の信号電極６０７と重複していない。そのため、中央部接地電極要素６１１Ｃ及び中央部接地電極要素６１２Ｃに設けられた第１貫通孔６１１Ｂ及び第２貫通孔６１２Ｂも、平面視で信号電極６０７の幅広部６０７Ｗと重複していない。   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.

変調電極６１５は、本実施形態の幅広部として幅広部６０７Ｗを有し、第１接地電極６１１は、本実施形態のテラス上接地電極要素としてのテラス上接地電極要素６１１Ｄと、中央部接地電極要素６１１Ｃと、を有し、第２接地電極６１２は、本実施形態のテラス上接地電極要素としてのテラス上接地電極要素６１２Ｄと、中央部接地電極要素６１２Ｃと、を有する。そして、幅広部６０７Ｗ、テラス上接地電極要素６１１Ｄ、及び、テラス上接地電極要素６１２ＤのＺ軸方向の沿った厚さは、第４実施形態の幅広部７Ｗ、テラス上接地電極要素１１Ｄ、及び、テラス上接地電極要素１２ＤのＺ軸方向の沿った厚さよりも厚い。また、本実施形態においては、中央部接地電極要素６１１ＣのＺ軸方向の厚さ、及び、中央部接地電極要素６１２ＣのＺ軸方向の厚さは、それぞれ、リッジ型光導波路５の高さＴ５よりも大きい。   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.

信号電極６０７の幅広部６０７Ｗは、図１２に示されるような、ひさし形状を構成する矩形状でなくても良く、楕円形状や非特許文献２に示されるような、徐々にせり出し逆台形状に張り出す形状、キノコ状に張り出す形状、あるいは、これらの中間的な形状又はこれらの複合した形状であっても同様の効果が得られる。また、接地電極要素６１１Ｄの主面３Ａに設置された部分および接地電極要素６１２Ｄの主面３Ｂに設置された部分は、テラス上に設置された部分より薄くなっているが、厚い構成になっていても良い。テラス上接地電極要素６１１Ｄの第１テラス部３Ｔ１の上面におけるＺ軸方向に沿った厚さＴ６１１Ｄ、及び、テラス上接地電極要素６１２Ｄの第２テラス部３Ｔ２の上面におけるＺ軸方向に沿った厚さＴ６１２Ｄとほぼ同じ厚さとすることもできる。   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.

第６実施形態のように信号電極６０７の幅広部６０７Ｗ及びテラス上接地電極要素６１１Ｄ、６１２Ｄの厚さが厚い場合、変調電極の特性インピーダンスの値は、第１貫通孔６１１Ｂ及び第２貫通孔６１２Ｂの形状、サイズ、位置や数量よりも、むしろ中央部接地電極要素６１１Ｃ、６１２Ｃとリッジ型光導波路５との離間距離や、幅広部６０７Ｗの形状、特に幅広部６０７ＷのＸ軸方向に張出した側面の形状に大きく依存する。第１貫通孔６１１Ｂ及び第２貫通孔６１２Ｂの形状、サイズ、位置や数量による特性インピーダンスの調整は有効であるが、補助的なものになる。   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.

したがって変調電極の特性インピーダンスを大きく上昇させるには、まず、中央部接地電極要素６１１Ｃ、６１２Ｃとリッジ型光導波路５との離間距離を大きくすれば良い。しかしながら、中央部接地電極要素６１１Ｃ、６１２Ｃとリッジ型光導波路５との離間距離は、リッジ型光導波路５における電界の強度とトレードオフの関係にあり、その離間距離を大きくするとリッジ型光導波路５における電界の強度が低下してしまい、効率的な変調が実現できなくなる。そこで、中央部接地電極要素６１１Ｃ、６１２Ｃのリッジ型光導波路５との離間距離は、インピーダンスよりも変調効率を優先して設計することにより、低すぎるインピーダンス特性を、第１貫通孔６１１Ｂ及び第２貫通孔６１２Ｂの形状、サイズ、位置や数量などによって、調整補正し、所望の特性値となるように設計することにより、特性が良好な光変調器を実現できる。   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.

また、第６実施形態の場合、中央部接地電極要素６１１Ｃ、６１２Ｃとリッジ型光導波路５との離間距離は大きく、中央部接地電極要素６１１Ｃ、６１２Ｃに第１貫通孔６１１Ｂ及び第２貫通孔６１２Ｂを設けても、高周波制御信号の損失は小さいため、第１貫通孔６１１Ｂ及び第２貫通孔６１２Ｂに起因する他の特性への悪影響はほとんど無い。このように、高周波光変調器、広帯域光変調器の設計、作製における利点は大きい。   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.

幅広部６０７ＷのＺ軸方向に沿った厚さＴ６０７Ｗは、例えば２５μｍ以上、８０μｍ以下とすることができ、テラス上接地電極要素６１１Ｄの第１テラス部３Ｔ１の上面におけるＺ軸方向に沿った厚さＴ６１１Ｄ、及び、テラス上接地電極要素６１２Ｄの第２テラス部３Ｔ２の上面におけるＺ軸方向に沿った厚さＴ６１２Ｄは、例えばそれぞれ２５μｍ以上、８０μｍ以下とすることができる。これにより、幅広部６０７Ｗと中央部接地電極要素６１１Ｃ、６１２Ｃが互い対向して作用する実効的な表面積が大幅に増大されて、特定箇所への電界の集中が回避され、制御信号の伝搬損失は大幅に低減する。   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.

厚さＴ６０７Ｗは、例えばリッジ型光導波路５の幅Ｗ５の４倍以上、１０倍以下、又は、幅広部６０７ＷのＸ軸方向の幅Ｗの２倍以上、５倍以下とすることができ、厚さＴ６１１Ｄ及び厚さＴ６１２Ｄは、例えばそれぞれ厚さＴ６０７Ｗと同程度とすることができる。   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.

本実施形態に係る光変調器６００によれば、第１実施形態の光変調器１００と同様の理由に基づき、変調信号を供給する外部の素子と光変調器６００とのインピーダンス整合を図り易くなるため、高速変調動作が可能となる。特性インピーダンスの調整方法としては、補助的なものになるが、他の特性の悪化を伴わないために、実用上有効である。   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.

さらに、本実施形態に係る光変調器６００によれば、幅広部６０７Ｗ、テラス上接地電極要素６１１Ｄ、及び、テラス上接地電極要素６１２Ｄの厚さが他の実施形態における対応する要素の厚さよりも厚く、信号電極６０７の幅広部６０７Ｗと中央部接地電極要素６１１Ｃ、６１２Ｃが互い対向して作用する実効的な表面積が特に大きくなっているため、特定箇所への電界の集中が回避され、制御信号の伝搬損失を大幅に低減するという効果を発揮する。中央部接地電極要素６１１Ｃ、６１２Ｃの材料として信号伝搬損失の少ない金、銀、又は、銅を用いた場合、１０ＧＨｚ以上周波数においては、表皮効果により電流が集中する表皮深さが１μｍ以下となり、表皮損失が顕著となる。そのような高周波成分を含む制御信号で駆動する場合において、実効的な表面積を大きく増やすことのできる第６実施形態の光変調器６００が発揮する効果は大きい。   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.

また、テラス上接地電極要素６１１Ｄ、６１２Ｄと幅広部６０７Ｗとを同じ高さ形成することも容易になり、変調器チップをケースに実装する際のワイヤーボンディング、フリップチップボンディングや、ＧＳＧ(Ground-Signal-Ground)タイプの高周波プローブを用いた特性検査が行いやすい。   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.

本発明は上述の実施形態に限定されず、様々な変形態様が可能である。例えば、上述の各実施形態においては、複数の第１貫通孔１１Ｂ、２１１Ｂ、３１１Ｂ、６１１Ｂは、平面視で、中央部接地電極要素１１Ｃ、２１１Ｃ、３１１Ｃ、６１１Ｃのリッジ型光導波路５側の側面１１ＳとＸ軸方向に離間しているが（図１、図４、図６、図８及び図１１参照）、平面視で、中央部接地電極要素１１Ｃ、２１１Ｃ、３１１Ｃ、６１１Ｃのリッジ型光導波路５側の側面１１Ｓと接していてもよい。   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.

同様に、上述の各実施形態においては、第２貫通孔１２Ｂ、２１２Ｂ、３１２Ｂ、６１２Ｂは、平面視で、中央部接地電極要素１２Ｃ、２１２Ｃ、３１２Ｃ、６１２Ｃのリッジ型光導波路５側の側面１２ＳとＸ軸方向に離間しているが（図１、図４、図６、図８及び図１１参照）、平面視で、中央部接地電極要素１２Ｃ、２１２Ｃ、３１２Ｃ、６１１２Ｃのリッジ型光導波路５側の側面１２Ｓと接していてもよい。   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.

また、上述の各実施形態においては、複数の第１貫通孔１１Ｂ、２１１Ｂ、３１１Ｂ、６１１Ｂは、Ｙ軸方向に沿って順に周期的に設けられているが（図１、図４、図６、図８及び図１１参照）、非周期的に設けられていてもよい。同様に、また、上述の各実施形態においては、複数の第２貫通孔１２Ｂ、２１２Ｂ、３１２Ｂ、６１２Ｂは、Ｙ軸方向に沿って順に周期的に設けられているが（図１、図４、図６、図８及び図１１参照）、非周期的に設けられていてもよい。   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.

また、上述の各実施形態においては、第１接地電極１１、２１１、３１１、６１１の中央部接地電極要素１１Ｃ、２１１Ｃ、３１１Ｃ、６１１Ｃは、複数の第１貫通孔１１Ｂ、２１１Ｂ、３１１Ｂ、６１１Ｂを有しているが（図１、図４、図６、図８及び図１１参照）、１つの第１貫通孔のみを有していてもよい。同様に、上述の各実施形態においては、第２接地電極１２、２１２、３１２、６１２の中央部接地電極要素１２Ｃ、２１２Ｃ、３１２Ｃ、６１２Ｃは、複数の第２貫通孔１２Ｂ、２１２Ｂ、３１２Ｂ、６１２Ｂを有しているが（図１、図４、図６、図８及び図１１参照）、１つの第１貫通孔のみを有していてもよい。   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.

また、上述の各実施形態のうちの２つ又は３つ以上の特徴を組み合わせた態様も可能である。例えば、第１実施形態の光変調器１００における第１貫通孔１１Ｂ及び第２貫通孔１２Ｂの平面視形状は、第３実施形態の光変調器３００における第１貫通孔３１１Ｂ及び第２貫通孔３１２Ｂのように矩形形状等の角部を有する形状であってもよい（図１、図４、図６、図８及び図１１参照）。   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).

また、第１〜第４実施形態の光変調器１００、２００、３００、４００において、中央部接地電極要素１１Ｃ、２１１Ｃ、３１１Ｃ及び中央部接地電極要素１２Ｃ、２１２Ｃ、３１２Ｃは、第５実施形態の光変調器５００における中央部接地電極要素５１１Ｃ及び中央部接地電極要素５１２Ｃのように、基体部３の主面３Ｓ上においてリッジ型光導波路５とＸ軸方向に離間していてもよい（図２、図５、図７及び図９参照）。   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).

また、第１〜第５実施形態の光変調器１００、２００、３００、４００、５００において、中央部接地電極要素１１Ｃ、２１１Ｃ、３１１Ｃ、５１１Ｃ及び中央部接地電極要素１２Ｃ、２１２Ｃ、３１２Ｃ、５１２Ｃは、第６実施形態の中央部接地電極要素６１１Ｃ及び中央部接地電極要素６１２Ｃのように、必要とされる効果に応じて、平面視で幅広部７Ｗと重複することの有無を選択できる（図１、図４、図６、図８及び図１１参照）。   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).

また、上述の各実施形態の光変調器１００、２００、３００、４００、５００、６００は、１つのリッジ型光導波路５及びリッジ型光導波路５上に設けられた１つのひさし状の幅広部７Ｗ、６０７Ｗからなる１つの組を備えているが（図１、図４、図６、図８及び図１１参照）、当該組を複数有していてもよい。その場合、当該複数の組のそれぞれについて、本発明を適用することができる。例えば、マッハツェンダー型光導波路、及び、その上に設けられた本願の幅広部に対応する、ひさし状の信号電極を備える光変調器において、当該マッハツェンダー型光導波路の２つのアーム光導波路のそれぞれについて、本発明を適用することができる。   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.

上述の各実施形態の光変調器においては、信号電極の幅広部は、リッジ型光導波路からＸ軸方向に張り出した平板状又は矩形状の、ひさし形状を有しているが、本発明の信号電極の幅広部７Ｗは、このような形状を有するものに限られない。例えば、信号電極の幅広部は、非特許文献２に示されるような、徐々にせり出し逆台形状に張り出す形状等のキノコ形状を有するものであっても良いし、これらの中間的な形状やこれらの複合した形状であっても良い。また、上述の各実施形態の光変調器では、Ｙ軸方向と直交する断面において、信号電極の幅広部は、リッジ型光導波路に対して第２方向（Ｘ軸方向）に対称的な形状を有しているが、本発明の光変調器における信号電極の幅広部は、このような形状を有するものに限られない。例えば、当該断面において、信号電極の幅広部は、リッジ型光導波路に対して第２方向に沿ったいずれかの方向（＋Ｘ軸方向又は−Ｘ軸方向）に偏って設けられていたり、リッジ型光導波路に対して当該いずれかの方向のみに張出していたりしてもよく、例えば、リッジ型光導波路に対して第２方向に沿ったいずれかの方向（＋Ｘ軸方向又は−Ｘ軸方向）に偏ったひさし形状やリッジ型光導波路に対して第２方向に沿った張出し方が非対称なキノコ形状を有していてもよい。また、国際公開第２００５／０８９３３２号パンフレットに示されているように、所定の方向に沿って延びる２つのリッジ型光導波路を有する光変調器において、当該所定の方向に直交する断面において、信号電極の幅広部は、一方のリッジ型光導波路上から、他方のリッジ型光導波路上に亘って延びる形状を有していてもよい。信号電極がリッジ型光導波路のＸ軸方向の幅より大きな幅の幅広部を有した光変調器であればよく、上述の各実施形態に関して説明した技術は、信号電極より低い位置に接地電極が配されている構成を有する光変調器において、特に有効である。   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.

また、上述の各実施形態の光変調器については、進行波型の電極構成であることを前提として説明をしてきた。一般に光変調器の進行波電極の作用部の長さは長く、その電極の長さと貫通孔の大きさ・密度に応じて多数の貫通孔を形成する必要がある。重要な設計指標は、信号電極と接地電極を線路と見たときの特性インピーダンスである。一方、集中定数型の電極として駆動する光変調器の場合、形成する電極の長さは一般に短い。そのため、貫通孔の形成は、駆動周波数に対応した電極間容量に応じて、大きさ、形状、数量を適宜設計し、設置する。電極長さおよび面積が小さい場合は、設置する貫通孔の数量は少なくて済む。   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.

上述の各実施形態の光変調器は、直線状のリッジ型光導波路５上に直線状の信号電極を配した位相変調器であるが、本発明の光変調器は、このような構成の光変調器に限らない。本発明の光変調器は、電気光学効果（印加電界に応じて屈折率が変化する現象、つまりポッケルス効果および光カー効果）によって、材料の屈折率が変化させ、伝搬する光の位相や伝搬モードを制御するデバイスのことを差しており、伝搬光の位相やモッドの制御を組み合わせて、光の強度、位相、進行方向、モード、光パルスの制御・整形などを行うデバイスを含む。   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・・・基体部、３Ｓ・・・基体部の主面、３Ａ・・・主面の第１面、３Ｂ・・・主面の第２面、３Ｅ・・・主面の設置面、５・・・リッジ型光導波路、７・・・信号電極、１１・・・第１接地電極、１１Ｃ・・・中央部接地電極要素（第１接地電極要素）、１２・・・第２接地電極、１２Ｃ・・・中央部接地電極要素（第２接地電極要素）、１１Ｂ・・・第１貫通孔、１２Ｂ・・・第２貫通孔、１５・・・変調電極。   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 (4)

主面を有する基体部と、前記基体部の前記主面上に設けられ、当該主面に沿った第１方向に沿って延びるリッジ型光導波路と、当該リッジ型光導波路内を導波する光を変調するための変調電極と、前記基体部の前記主面上に設けられた第１テラス部及び第２テラス部と、を備え、
前記基体部の前記主面は、前記リッジ型光導波路が設けられた設置面と、前記第１方向と直交し、かつ、前記主面に沿った第２方向に沿って前記設置面を挟むように位置する第１面及び第２面と、を有し、
前記第１テラス部は、前記リッジ型光導波路と前記第２方向に離間するように前記第１面上に設けられており、前記第１テラス部と前記リッジ型光導波路とによって、前記第１面及び前記設置面上に、前記第１方向に沿って延びる第１凹部が規定され、
前記第２テラス部は、前記リッジ型光導波路と前記第２方向に離間するように前記第２面上に設けられており、前記第２テラス部と前記リッジ型光導波路とによって、前記第２面及び前記設置面上に、前記第１方向に沿って延びる第２凹部が規定され、
前記変調電極は、変調信号が供給される信号電極と、第１接地電極と、第２接地電極とからなり、
前記信号電極は、前記リッジ型光導波路上に前記第１方向に沿って延びるように設けられた部分であって、当該リッジ型光導波路の最上部の前記第２方向の幅よりも広い幅を有する幅広部を有し、
前記第１接地電極は、前記第１方向に沿って延びるように前記第１面上に設けられた第１接地電極要素と、前記第１接地電極要素と電気的に接続され、前記第１方向に沿って延びるように前記第１テラス部の側面から上面に亘って設けられた第１テラス上接地電極要素と、を有し、
前記第２接地電極は、前記第１方向に沿って延びるように前記第２面上に設けられた第２接地電極要素と、前記第２接地電極要素と電気的に接続され、前記第１方向に沿って延びるように前記第２テラス部の側面から上面に亘って設けられた第２テラス上接地電極要素と、を有し、
前記第１接地電極要素は、当該第１接地電極要素の前記第１方向の一部のみに設けられた少なくとも１つの第１貫通孔を有し、
前記第２接地電極要素は、当該第２接地電極要素の前記第１方向の一部のみに設けられた少なくとも１つの第２貫通孔を有し、
前記少なくとも１つの第１貫通孔は、平面視で前記信号電極の前記幅広部と重複する、又は、当該幅広部と前記第２方向に向かって対向し、
前記少なくとも１つの第２貫通孔は、平面視で前記信号電極の前記幅広部と重複する、又は、当該幅広部と前記第２方向に向かって対向し、
前記第１接地電極要素の上面は、前記幅広部の上面よりも前記基体部側にあり、前記第２接地電極要素の上面は、前記幅広部の上面よりも前記基体部側にある光変調器。 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;
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,
The at least one first through hole overlaps with the wide portion of the signal electrode in plan view, or faces the wide portion toward the second direction,
The at least one second through hole overlaps with the wide portion of the signal electrode in plan view, or faces the wide portion toward the second direction ,
An optical modulator in which an upper surface of the first ground electrode element is closer to the base portion than an upper surface of the wide portion, and an upper surface of the second ground electrode element is closer to the base portion than the upper surface of the wide portion . 前記第１テラス部及び前記第２テラス部は、前記リッジ型光導波路と略同じ高さを有する請求項１に記載の光変調器。   2. The optical modulator according to claim 1, wherein the first terrace portion and the second terrace portion have substantially the same height as the ridge-type optical waveguide. 前記第１テラス部の上面上の前記第１テラス上接地電極要素の厚さは、前記第１接地電極要素の厚さよりも厚く、前記第２テラス部の上面上の前記第２テラス上接地電極要素の厚さは、前記第２接地電極要素の厚さよりも厚い請求項１又は２に記載の光変調器。   The thickness of the first terrace ground electrode element on the upper surface of the first terrace portion is greater than the thickness of the first ground electrode element, and the second terrace ground electrode on the upper surface of the second terrace portion. The optical modulator according to claim 1, wherein the thickness of the element is larger than the thickness of the second ground electrode element. 前記第１テラス部の上面上の前記第１テラス上接地電極要素の厚さは、１０μｍ以上、８０μｍ以下であり、前記第２テラス部の上面上の前記第２テラス上接地電極要素の厚さは、１０μｍ以上、８０μｍ以下である請求項１〜３のいずれか一項に記載の光変調器。   The thickness of the first terrace ground electrode element on the upper surface of the first terrace portion is 10 μm or more and 80 μm or less, and the thickness of the second terrace ground electrode element on the upper surface of the second terrace portion. The optical modulator according to claim 1, wherein the optical modulator is 10 μm or more and 80 μm or less.
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