JP5665173B2 - Waveguide type optical modulator - Google Patents
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- JP5665173B2 JP5665173B2 JP2010153566A JP2010153566A JP5665173B2 JP 5665173 B2 JP5665173 B2 JP 5665173B2 JP 2010153566 A JP2010153566 A JP 2010153566A JP 2010153566 A JP2010153566 A JP 2010153566A JP 5665173 B2 JP5665173 B2 JP 5665173B2
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Description
本発明は、光変調や光のスイッチングを行う光変調器に関し、特に光導波路を用いた導波路型光変調器に関する。 The present invention relates to an optical modulator that performs optical modulation and optical switching, and more particularly to a waveguide type optical modulator that uses an optical waveguide.
近年、放送の再送信やネットワークの柔軟性を高める目的で、無線信号をそのまま光伝送する用途が広がっている。この場合、電源設備の不要化や、雷害、ノイズ対策などの理由で、無線電波の受信点から無給電で信号を受信伝送することが望まれることがある。このためには、受信電波のエネルギーだけで光変調を行うために、高速、高効率の光変調器が要求される。 In recent years, the use of optical transmission of radio signals as they are for the purpose of increasing broadcast resend and network flexibility has been expanding. In this case, there is a case where it is desired to receive and transmit a signal without power supply from a wireless radio wave reception point for reasons such as unnecessary power supply facilities, lightning damage, and noise countermeasures. For this purpose, a high-speed and high-efficiency optical modulator is required in order to perform optical modulation only with the energy of the received radio wave.
従来、マイクロ波帯などの超高周波域での高効率の光変調器は、導波路型光変調器で実現されている。このような導波路型光変調器としては、（１）通常の光通信システムで用いられている進行波型光変調器、（２）外付けの共振回路と組み合わせた分割型電極による光変調器（例えば、非特許文献１参照）、（３）共振型電極による光変調器（例えば、特許文献１参照）、などが知られている。 Conventionally, a high-efficiency optical modulator in an ultra-high frequency region such as a microwave band is realized by a waveguide type optical modulator. As such a waveguide type optical modulator, (1) a traveling wave type optical modulator used in a normal optical communication system, and (2) an optical modulator using a split type electrode combined with an external resonance circuit. (For example, refer nonpatent literature 1), (3) The optical modulator by a resonance type electrode (for example, refer patent document 1), etc. are known.
上記（１）の進行波型光変調器は、変調波と光波との速度整合を取ることにより広帯域特性を有し、電極長を大きくして低電圧動作可能な光変調器が実現され、光通信用として実用化されている。しかし、上述したような無給電で光変調する用途には十分でなく、また、電極間容量が大きいため、外付けの共振回路を付加することができない。 The traveling wave type optical modulator of (1) has a broadband characteristic by matching the speed of the modulated wave and the light wave, and an optical modulator capable of operating at a low voltage by increasing the electrode length is realized. It has been put to practical use for communications. However, it is not sufficient for the purpose of optical modulation without power supply as described above, and since the interelectrode capacitance is large, an external resonance circuit cannot be added.
上記（２）の光変調器方式では、光の通過時間の制限により電極長を短くする必要があるが、分割電極構造により電極間容量を小さくして共振回路の付加を可能とすることにより、印加電圧を大きくして高効率化している。また、上記（３）の共振電極型では、電極を変調波に対して共振器構造とすることにより、光導波路に印加される電圧を増大させ高効率化している。（２），（３）の方式とも帯域は狭いが、無線電波信号の伝送では狭帯域でも使用できる。 In the optical modulator method of (2) above, it is necessary to shorten the electrode length due to the limitation of the light passage time, but by making the interelectrode capacitance small by the divided electrode structure and adding a resonance circuit, The applied voltage is increased to increase efficiency. Further, in the resonant electrode type (3), the electrode has a resonator structure with respect to the modulated wave, thereby increasing the voltage applied to the optical waveguide and increasing the efficiency. The bandwidths of (2) and (3) are both narrow, but can be used even in a narrow bandwidth for radio wave signal transmission.
しかし、（２），（３）の方式でも、マイクロ波帯のように数ＧＨｚ以上の高周波域では、光波の通過時間による制限のため、有効な電極長がさらに小さくなり、変調効率が低下していた。 However, even in the methods (2) and (3), the effective electrode length is further reduced and the modulation efficiency is lowered in a high frequency range of several GHz or more such as a microwave band due to a limitation due to a light wave transit time. It was.
そこで、光導波路中の変調された光波の速度に整合させて複数の共振電極を周期的に配置する方法が提案されている（例えば、非特許文献２参照）。この方法では、共振電極の数だけ変調効率を増大させることができる。 Therefore, a method has been proposed in which a plurality of resonant electrodes are periodically arranged so as to match the speed of the modulated light wave in the optical waveguide (see, for example, Non-Patent Document 2). In this method, the modulation efficiency can be increased by the number of resonance electrodes.
しかしながら、上記の非特許文献２の方式では、独立に一定の周期で配置された複数の共振電極に印加するマイクロ波の位相を同相となるよう調整する必要があり、共振電極の外部における位相調整のための手段が必要となること、また、共振電極単体の長さに対して共振電極が配置される周期が大きいため、光導波路中の光波に対するマイクロ波の作用長を大きくできなく、変調効率が十分でないことなどの問題がある。 However, in the above-described method of Non-Patent Document 2, it is necessary to adjust the phase of microwaves applied to a plurality of resonant electrodes arranged independently at a constant period so that they are in phase, and phase adjustment outside the resonant electrode In addition, because the period of the resonant electrode is larger than the length of the resonant electrode alone, the microwave action length for the light wave in the optical waveguide cannot be increased, and the modulation efficiency There are problems such as not enough.
この場合、変調効率改善のため多くの共振電極を配置しようとすると、それらの間の位相調整の手段がさらに複雑化することになる。 In this case, if a large number of resonance electrodes are arranged for improving the modulation efficiency, the means for adjusting the phase between them becomes more complicated.
本発明は上記に鑑みてなされたものであり、簡単な構成でマイクロ波帯などの超高周波域で高い変調効率を実現することが可能な導波路型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 the above, and an object of the present invention is to provide a waveguide type optical modulator capable of realizing high modulation efficiency in an ultrahigh frequency region such as a microwave band with a simple configuration. .
本発明によれば、電気光学効果を有する材料からなる基板と、該基板上に形成された入力光導波路、該入力光導波路より分岐した２本の位相シフト光導波路、および該２本の位相シフト光導波路が合流した出力光導波路を有する光導波路と、前記基板上に配置された前記位相シフト光導波路に電界を印加するための変調電極と、該変調電極に変調信号を印加する変調信号印加手段とを備え、前記変調電極は、前記変調信号印加手段に接続される給電部と共振電極部とからなり、前記給電部は前記共振電極部に前記変調信号の電力を供給するための給電結合線路を有し、前記共振電極部はその両端に設けた共振結合線路と該共振結合線路の間に設けた前記位相シフト光導波路の延伸方向に平行で前記位相シフト光導波路に近接して配置されたスロット線路またはコプレーナ線路からなる電界印加線路とを有し、前記給電結合線路と前記共振結合線路とが近接して並置され互いに結合することにより、前記給電部より前記共振電極部に前記変調信号の電力の供給がなされ、前記共振電極部は前記共振結合線路と前記電界印加線路とが全体として共振するように構成される導波路型光変調器が提供される。 According to the present invention, a substrate made of a material having an electro-optic effect, an input optical waveguide formed on the substrate, two phase shift optical waveguides branched from the input optical waveguide, and the two phase shifts An optical waveguide having an output optical waveguide combined with the optical waveguide, a modulation electrode for applying an electric field to the phase shift optical waveguide disposed on the substrate, and a modulation signal applying means for applying a modulation signal to the modulation electrode And the modulation electrode includes a power supply unit connected to the modulation signal applying means and a resonance electrode unit, and the power supply unit supplies power of the modulation signal to the resonance electrode unit. And the resonant electrode section is disposed in parallel to the extending direction of the phase shift optical waveguide provided between the resonant coupling lines provided at both ends thereof and in proximity to the phase shift optical waveguide. The Electric field application line consisting of a transmission line or a coplanar line, and the modulation coupling signal from the power supply unit to the resonance electrode unit when the power supply coupling line and the resonance coupling line are juxtaposed in close proximity and coupled to each other A waveguide type optical modulator is provided in which the resonant electrode section is configured such that the resonant coupling line and the electric field applying line resonate as a whole.
ここで、前記変調電極は前記共振電極部を複数個有し、該共振電極部の少なくとも一方の共振結合線路は、前記給電結合線路または隣接する共振電極部の共振結合線路と近接して並置され互いに結合していてもよい。 Here, the modulation electrode has a plurality of the resonance electrode portions, and at least one resonance coupling line of the resonance electrode portions is juxtaposed in proximity to the feed coupling line or a resonance coupling line of an adjacent resonance electrode portion. They may be bonded to each other.
この場合、前記位相シフト光導波路の延伸方向に互いに隣接する前記共振電極部の前記電界印加線路により前記各位相シフト光導波路に印加される電界の方向が互いに反転するように形成されていてもよい。 In this case, the direction of the electric field applied to each of the phase shift optical waveguides may be reversed by the electric field application lines of the resonance electrode portions adjacent to each other in the extending direction of the phase shift optical waveguide. .
この場合、複数の前記電界印加線路は、前記位相シフト光導波路の等価屈折率をｎ、前記変調信号の周波数をｆ0、真空中での光速をｃとすると、前記位相シフト光導波路の延伸方向における複数の前記電界印加線路の中心間距離Ｐは、Ｐ＝ｃ／２ｎｆ（但し、ｆ＝0.4ｆ0〜１.3ｆ0）となるように配置されていることが望ましい。 In this case, the plurality of electric field application lines have a stretching direction of the phase shift optical waveguide, where n is the equivalent refractive index of the phase shift optical waveguide, f 0 is the frequency of the modulation signal, and c is the speed of light in vacuum. It is desirable that the center-to-center distance P of the plurality of electric field applying lines is set to be P = c / 2nf (where f = 0.4f 0 to 1.3f 0 ).
また、前記変調電極は、前記位相シフト光導波路の延伸方向に互いに隣接する前記共振電極部の前記電界印加線路により前記各位相シフト光導波路に印加される電界の方向が互いに同相となるように形成されていてもよい。 The modulation electrodes are formed such that the directions of the electric fields applied to the phase shift optical waveguides are in phase with each other by the electric field application lines of the resonance electrode portions adjacent to each other in the extending direction of the phase shift optical waveguide. May be.
この場合、複数の前記電界印加線路は、前記位相シフト光導波路の等価屈折率をｎ、前記変調信号の周波数をｆ0、真空中での光速をｃとすると、前記位相シフト光導波路の延伸方向における複数の前記電界印加線路の中心間距離Ｐは、Ｐ＝ｃ／ｎｆ（但し、ｆ＝0.4ｆ0〜１.3ｆ0）となるように配置されていることが望ましい。 In this case, the plurality of electric field application lines have a stretching direction of the phase shift optical waveguide, where n is the equivalent refractive index of the phase shift optical waveguide, f 0 is the frequency of the modulation signal, and c is the speed of light in vacuum. It is desirable that the center-to-center distance P of the plurality of electric field applying lines is set to be P = c / nf (where f = 0.4f 0 to 1.3f 0 ).
本発明の導波路型光変調器では、上記のように、電界印加線路と共振結合線路とが一体となって共振電極部を構成し、かつ、その共振電極部が変調周波数において全体として共振し、さらに、互いに隣接する電界印加線路により各位相シフト光導波路に印加される電界の方向が互いに反転するか、または互いに同相となるような共振モードを使用することにより、変調電極の外部における位相調整のための手段が不要となる。 In the waveguide type optical modulator of the present invention, as described above, the electric field application line and the resonant coupling line are integrated to form a resonant electrode portion, and the resonant electrode portion resonates as a whole at the modulation frequency. In addition, the phase adjustment outside the modulation electrode can be performed by using resonance modes in which the directions of the electric fields applied to the respective phase shift optical waveguides by the electric field application lines adjacent to each other are reversed or in phase with each other. The means for this becomes unnecessary.
また、互いに隣接する電界印加線路により各位相シフト光導波路に印加される電界の方向が互いに反転するように構成した場合、位相シフト光導波路近傍に位相シフト光導波路の延伸方向に互いに離間して配置される電界印加線路の周期は上記非特許文献２に記載の導波路型光変調器に比べて半分とできるため、光導波路中の光波に対するマイクロ波の作用長を従来に比べて２倍とすることができ、より高い変調効率が得られる。 Also, when the direction of the electric field applied to each phase shift optical waveguide is reversed by the electric field application lines adjacent to each other, they are arranged apart from each other in the extending direction of the phase shift optical waveguide in the vicinity of the phase shift optical waveguide The period of the applied electric field line can be halved compared to the waveguide type optical modulator described in Non-Patent Document 2 above, so that the action length of the microwave with respect to the light wave in the optical waveguide is doubled compared to the conventional one. And higher modulation efficiency can be obtained.
さらに、本発明においては、１つの共振電極部において位相シフト光導波路に印加される電界が打ち消されないように、共振状態において光変調に有効な電界が電界印加線路で発生し、その電界が反転する領域が位相シフト光導波路から離れた共振結合線路となるようにして不要な電界が位相シフト光導波路に印加されないようにすることで高い変調効率が得られる。これにより、単一の共振電極部であっても従来よりも高い変調効率が得られる。さらに、複数の共振電極部を設けた場合、共振結合線路中の変調信号の伝搬方向を位相シフト光導波路から離れるようにして位相シフト光導波路中の光波に作用させないようにすることで、互いに隣接する電界印加線路間の光波に対して作用しない部分の間隔を狭くできるので、長いマイクロ波の作用長が得られ、さらに高い変調効率が得られる。 Further, in the present invention, an electric field effective for light modulation is generated in the electric field application line in the resonance state so that the electric field applied to the phase shift optical waveguide is not canceled in one resonance electrode part, and the electric field is inverted. High modulation efficiency can be obtained by preventing the unnecessary electric field from being applied to the phase shift optical waveguide by making the region to be a resonant coupling line away from the phase shift optical waveguide. Thereby, even if it is a single resonance electrode part, modulation efficiency higher than before is obtained. Further, when a plurality of resonance electrode portions are provided, the propagation direction of the modulation signal in the resonance coupling line is separated from the phase shift optical waveguide so as not to act on the light wave in the phase shift optical waveguide, thereby adjacent to each other. Since the interval between the portions that do not act on the light wave between the applied electric field lines can be narrowed, a long microwave action length can be obtained, and higher modulation efficiency can be obtained.
以上のように、本発明の導波路型光変調器によれば、簡単な構成でマイクロ波帯などの超高周波域で高い変調効率を実現することができる。
As described above, according to the waveguide type optical modulator of the present invention, high modulation efficiency can be realized in a super-high frequency region such as a microwave band with a simple configuration.
次に、図面を参照して、本発明の実施の形態を説明する。 Next, embodiments of the present invention will be described with reference to the drawings.
以下の図面の記載において、同一または類似の部分には同一または類似の符号を付している。ただし、図面は模式的なものであり、現実のものとは異なることに留意すべきである。また、図面相互間においても互いの寸法の関係や比率が異なる部分が含まれていることはもちろんである。 In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.
また、以下に示す実施の形態は、この発明の技術的思想を具体化するための構造や方法を例示するものであって、この発明の技術的思想は、各構成部品の配置等を下記のものに特定するものでない。この発明の技術的思想は、特許請求の範囲において、種々の変更を加えることができる。 Further, the following embodiments exemplify structures and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the arrangement of each component as described below. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.
［第１の実施の形態］
図１（ａ）は本発明の第１の実施の形態に係る導波路型光変調器を示す平面図、図１（ｂ）は図１（ａ）に示す導波路型光変調器の位相シフト導波路中を伝搬する光の位相シフト量を示す図、図２は図１（ａ）におけるＡ−Ａ断面図である。
[First Embodiment]
FIG. 1A is a plan view showing a waveguide type optical modulator according to the first embodiment of the present invention, and FIG. 1B is a phase shift of the waveguide type optical modulator shown in FIG. The figure which shows the phase shift amount of the light which propagates in a waveguide, FIG. 2 is AA sectional drawing in Fig.1 (a).
図１、図２に示すように第１の実施の形態に係る導波路型光変調器１は、基板２と、マッハツェンダー型光導波路３（以下、単に光導波路３ということもある）と、バッファ層１１と、給電部６および４つの共振電極部９からなる変調電極と、変調信号入力端子１０とを備える。 As shown in FIGS. 1 and 2, the waveguide type optical modulator 1 according to the first embodiment includes a substrate 2, a Mach-Zehnder type optical waveguide 3 (hereinafter sometimes simply referred to as an optical waveguide 3), A buffer layer 11, a modulation electrode including a power feeding unit 6 and four resonance electrode units 9, and a modulation signal input terminal 10 are provided.
基板２は、電気光学効果を有するニオブ酸リチウム（ＬｉＮｂＯ３）からなる。第１の実施の形態では、ＬｉＮｂＯ３のＸカット基板を用いる。 The substrate 2 is made of lithium niobate (LiNbO 3 ) having an electro-optic effect. In the first embodiment, an LiNbO 3 X-cut substrate is used.
光導波路３は、基板２の上面側にＴｉ拡散により形成され、入力光導波路３ａと、この入力光導波路３ａから分岐した２本の位相シフト光導波路３ｂ，３ｃと、位相シフト光導波路３ｂ，３ｃが合流した出力光導波路３ｄとを有する。位相シフト光導波路３ｂ，３ｃの延伸方向の中央部分は互いに平行であり、この中央部分の間隔は２０〜５０μｍ程度である。 The optical waveguide 3 is formed by Ti diffusion on the upper surface side of the substrate 2, and includes an input optical waveguide 3a, two phase shift optical waveguides 3b and 3c branched from the input optical waveguide 3a, and phase shift optical waveguides 3b and 3c. And the output optical waveguide 3d. The central portions in the extending direction of the phase shift optical waveguides 3b and 3c are parallel to each other, and the interval between the central portions is about 20 to 50 μm.
バッファ層１１は、基板２上に形成されるＳｉＯ２からなる厚さ１００〜３０００ｎｍ程度の層であり、光導波路３を伝搬する光の一部が、変調電極によって吸収されることを防止する等の目的で設けられるものである。 The buffer layer 11 is a layer made of SiO 2 and having a thickness of about 100 to 3000 nm formed on the substrate 2, and prevents a part of light propagating through the optical waveguide 3 from being absorbed by the modulation electrode. It is provided for the purpose.
変調電極の給電部６は２つのスロット線路７ａ、８ａとそれらに接続し共振電極部９に変調信号の電力を供給するための給電結合線路７ｂ、８ｂとを有する。共振電極部９は、それぞれその両端部に設けたスロット線路からなる共振結合線路４ｂ、５ｂと、これらにそれぞれ接続され、これらの間の位相シフト光導波路３ｃ、３ｂ上にそれぞれ配置されたスロット線路からなる電界印加線路４ａ、５ａとを有する。給電結合線路７ｂ、８ｂと初段の共振電極部９の共振結合線路４ｂ、５ｂとがそれぞれ近接して並置され互いに結合することにより、給電部６より初段の共振電極部９に変調信号の電力の供給がなされ、２段目以降も各段の共振電極部９の共振結合線路４ｂ、５ｂが隣接する共振電極部９の共振結合線路４ｂ、５ｂとそれぞれ近接して並置され互いに結合している。さらに、各共振電極部９はそれぞれ共振結合線路４ｂ、５ｂと電界印加線路４ａ、５ａとがそれぞれ全体として共振するように構成されている。 The feeding portion 6 of the modulation electrode has two slot lines 7a and 8a and feed coupling lines 7b and 8b that are connected to them and supply the power of the modulation signal to the resonance electrode portion 9. The resonant electrode section 9 is connected to the resonant coupling lines 4b and 5b made of slot lines provided at both ends of the resonant electrode section 9 and the slot lines respectively disposed on the phase shift optical waveguides 3c and 3b therebetween. Electric field application lines 4a and 5a. The feed coupling lines 7b and 8b and the resonance coupling lines 4b and 5b of the first-stage resonance electrode section 9 are juxtaposed in close proximity and coupled to each other, so that the power of the modulation signal is fed from the feed section 6 to the first-stage resonance electrode section 9. In the second and subsequent stages, the resonance coupling lines 4b and 5b of the resonance electrode portions 9 in the second and subsequent stages are juxtaposed with and connected to the resonance coupling lines 4b and 5b of the adjacent resonance electrode section 9, respectively. Further, each resonance electrode portion 9 is configured such that the resonance coupling lines 4b and 5b and the electric field application lines 4a and 5a respectively resonate as a whole.
電界印加線路４ａにおいてはそのスロットの中央に位相シフト光導波路３ｃが位置し、電界印加線路５ａにおいてはそのスロットの中央に位相シフト光導波路３ｂが位置するように配置される。 In the electric field application line 4a, the phase shift optical waveguide 3c is positioned in the center of the slot, and in the electric field application line 5a, the phase shift optical waveguide 3b is positioned in the center of the slot.
この電界印加線路４ａ、５ａは、図２に示すように、それぞれ位相シフト光導波路３ｃ，３ｂにＺ軸方向の互いに逆向きの電界Ｅｚを印加するためのものである。 As shown in FIG. 2, the electric field applying lines 4a and 5a are for applying electric fields Ez in the Z-axis direction opposite to each other to the phase shift optical waveguides 3c and 3b, respectively.
すなわち、電界印加線路４ａを構成する第１のスロット線路と電界印加線路５ａを構成する第２のスロット線路の位相シフト光導波路３ｂ，３ｃに挟まれる部分の電極を変調信号を印加する共通電極とし、それらの対向側を接地電極とすることにより、位相シフト光導波路３ｃに印加される電界の方向と、位相シフト光導波路３ｂに印加される電界の方向とが反対方向になる。 That is, the electrode sandwiched between the phase shift optical waveguides 3b and 3c of the first slot line constituting the electric field applying line 4a and the second slot line constituting the electric field applying line 5a is used as a common electrode for applying the modulation signal. By using the opposite side as a ground electrode, the direction of the electric field applied to the phase shift optical waveguide 3c is opposite to the direction of the electric field applied to the phase shift optical waveguide 3b.
スロット線路は金（Ａｕ）等の導電性材料からなり、バッファ層１１を介して基板２上に設けられている。 The slot line is made of a conductive material such as gold (Au) and is provided on the substrate 2 via the buffer layer 11.
図１に示すように、４段の電界印加線路４ａ、５ａが位相シフト光導波路３ｂ，３ｃの延伸方向に周期的に互いに離間して配置されている。 As shown in FIG. 1, four stages of electric field application lines 4a and 5a are periodically spaced from each other in the extending direction of the phase shift optical waveguides 3b and 3c.
本実施の形態においては、各共振電極部９の共振結合線路４ｂ、５ｂの先端が短絡されていることにより変調信号の反射が生じ、変調信号の周波数において、各段の共振電極部が単体としても共振器として働くと同時に、４段の共振電極部全体としても共振器となるように構成されている。ここで、図１では４段目の共振電極部９の終端は給電部６と同様な線路に結合しているが、この終端は短絡端または開放端であってもよい。 In the present embodiment, the resonance signal lines are reflected by the short ends of the resonance coupling lines 4b and 5b of each resonance electrode section 9, and the resonance electrode sections at each stage are united at the frequency of the modulation signal. Is also configured to function as a resonator as well as the entire four-stage resonance electrode portion. Here, in FIG. 1, the termination of the fourth-stage resonance electrode unit 9 is coupled to the same line as the power feeding unit 6, but this termination may be a short-circuited end or an open end.
この場合の共振モードは、１段目と３段目の電界印加線路で同相の電界となり、２段目と４段目の電界印加線路でそれらの逆相の反転電界となるように、電界印加線路と共振結合線路を合わせたスロット線路長、およびそれらの各スロット線路長の比率が調整されている。 In this case, the electric field is applied so that the first and third electric field application lines have the same phase of the electric field, and the second and fourth electric field application lines have the reversed electric fields. The slot line length combining the line and the resonant coupling line, and the ratio of the respective slot line lengths are adjusted.
また、位相シフト光導波路３ｂ，３ｃの延伸方向における電界印加線路４ａ、５ａの配置の周期Ｐは、位相シフト光導波路３ｂ、３ｃの等価屈折率をｎ、変調信号の周波数をｆ、真空中での光速をｃとすると、Ｐ＝ｃ／２ｎｆとなるように配置されている。 The period P of the arrangement of the electric field application lines 4a and 5a in the extending direction of the phase shift optical waveguides 3b and 3c is n, the equivalent refractive index of the phase shift optical waveguides 3b and 3c is n, the frequency of the modulation signal is f, and in vacuum If the speed of light is c, then they are arranged so that P = c / 2nf.
上記のように構成された導波路型光変調器１において、導波路型光変調器１の入力光導波路３ａの入射口から、図示しない光源からの光を光導波路３に導入し、変調信号入力端子１０により変調電極に変調信号を印加すると、上述のように電界印加線路４ａ、５ａにより、２本の位相シフト光導波路３ｂ，３ｃに、Ｚ軸方向に互いに逆向きの電界が印加される。 In the waveguide type optical modulator 1 configured as described above, light from a light source (not shown) is introduced into the optical waveguide 3 from the entrance of the input optical waveguide 3a of the waveguide type optical modulator 1, and the modulation signal is input. When a modulation signal is applied to the modulation electrode by the terminal 10, electric fields opposite to each other in the Z-axis direction are applied to the two phase shift optical waveguides 3b and 3c by the electric field application lines 4a and 5a as described above.
これにより、位相シフト光導波路３ｂ，３ｃにおける電気光学効果による屈折率変化の方向が互いに逆向きとなり、位相シフト光導波路３ｂ，３ｃの伝搬光に互いに逆向きの位相シフトが生じ、この伝搬光が出力光導波路３ｄへの合流時に干渉して光強度が変調される。 As a result, the directions of refractive index change due to the electro-optic effect in the phase shift optical waveguides 3b and 3c are opposite to each other, and phase shifts in the opposite directions occur in the propagation light in the phase shift optical waveguides 3b and 3c. The light intensity is modulated by interference when merging with the output optical waveguide 3d.
ここで、位相シフト光導波路３ｂ，３ｃの等価屈折率をｎ、真空中での光速をｃとすると、変調された光は位相シフト光導波路３ｂ，３ｃ中をｃ／ｎの速度で進行する。したがって、ある時点でみると、変調信号の周波数ｆで変調された光は、図１（ｂ）に示すように、位相シフト光導波路３ｂ，３ｃ中では光伝搬方向にΛ＝ｃ／ｎｆの周期で位相シフト量が変化しており、Λ／２＝ｃ／２ｎｆの周期で位相シフト量が反転していることになる。具体的な数値例としては、等価屈折率ｎ＝２．１５、変調信号の周波数ｆ＝１０ＧＨｚとしたとき、Λ＝１４ｍｍとなる。 Here, if the equivalent refractive index of the phase shift optical waveguides 3b and 3c is n and the speed of light in vacuum is c, the modulated light travels through the phase shift optical waveguides 3b and 3c at a speed of c / n. Therefore, at a certain point in time, the light modulated at the frequency f of the modulation signal has a period of Λ = c / nf in the light propagation direction in the phase shift optical waveguides 3b and 3c, as shown in FIG. Therefore, the phase shift amount is changed, and the phase shift amount is inverted at a period of Λ / 2 = c / 2nf. As a specific numerical example, when the equivalent refractive index n = 2.15 and the modulation signal frequency f = 10 GHz, Λ = 14 mm.
第１の実施の形態に係る導波路型光変調器１では、互いに離間した電界印加線路の中心間距離Ｐを、Ｐ＝Λ／２＝ｃ／２ｎｆとなるように配置している。これにより、位相シフト光導波路３ｂ，３ｃを伝搬する光に対して、変調電極への印加電界により加算的に位相シフトを与えることができるので、実効的な変調電極長が長くなり、マイクロ波帯などの超高周波域でも高い変調効率を得ることができる。 In the waveguide type optical modulator 1 according to the first embodiment, the center-to-center distance P between the electric field application lines separated from each other is arranged such that P = Λ / 2 = c / 2nf. This makes it possible to add a phase shift to the light propagating through the phase shift optical waveguides 3b and 3c by the electric field applied to the modulation electrode, so that the effective modulation electrode length is increased and the microwave band is increased. High modulation efficiency can be obtained even in the ultra-high frequency range such as.
この場合、変調効率の周波数特性はＰ＝Λ／２＝ｃ／２ｎｆを満たす周波数ｆの付近を中心におおよそガウス分布に近い特性となっており、電界印加線路の段数が増加するに従って変調効率のピークはｆより小さい値からｆに近づいて行き、変調可能な周波数帯域幅は電界印加線路の段数が増加するに従って狭くなる。 In this case, the frequency characteristics of the modulation efficiency are characteristics close to a Gaussian distribution centered around the frequency f satisfying P = Λ / 2 = c / 2nf, and the modulation efficiency increases as the number of stages of the electric field application line increases. The peak approaches from f smaller than f, and the frequency bandwidth that can be modulated becomes narrower as the number of stages of the electric field application line increases.
また、位相シフト光導波路上に占める電界印加線路の割合にも依存する。すなわち、電界印加線路の段数が２段のとき、変調効率がピークとなる周波数および変調可能周波数が上記ｆの値に対して最も低周波側となり、例えば、電界印加線路に対する電界印加線路間の間隔の比率を０．２〜１としたとき、０．４ｆ〜１．３ｆ程度の周波数であれば電界印加線路が１段の場合よりも高い変調効率が得られる。 It also depends on the proportion of the electric field application line on the phase shift optical waveguide. That is, when the number of stages of the electric field application line is two, the frequency at which the modulation efficiency peaks and the frequency that can be modulated are on the lowest frequency side with respect to the value f. When the ratio is 0.2 to 1, if the frequency is about 0.4 f to 1.3 f, a higher modulation efficiency can be obtained than when the electric field application line has one stage.
同様に、電界印加線路の段数を５段以上としたときは、段数の増加に従って変調効率のピーク値は大きくなるが、１段の場合より高い効率が得られる変調可能帯域は０．７〜１．２５ｆ程度となる。 Similarly, when the number of stages of the electric field application line is 5 or more, the peak value of the modulation efficiency increases as the number of stages increases, but the modulation possible band for obtaining higher efficiency than the case of one stage is 0.7 to 1. About 25f.
［第２の実施の形態］
図３（ａ）は本発明の第２の実施の形態に係る導波路型光変調器を示す平面図、図３（ｂ）は図３（ａ）に示す導波路型光変調器の位相シフト導波路中を伝搬する光の位相シフト量を示す図である。
[Second Embodiment]
3A is a plan view showing a waveguide type optical modulator according to the second embodiment of the present invention, and FIG. 3B is a phase shift of the waveguide type optical modulator shown in FIG. It is a figure which shows the phase shift amount of the light which propagates the inside of a waveguide.
図３に示す第２の実施の形態の導波路型光変調器２０は、基本的な構成は第１の実施の形態と同じであるが、変調電極を第１の実施の形態の変調信号の周波数に対して２倍の周波数で共振するように構成している。すなわち、図２（ｂ）に示すようにこの場合の位相シフト導波路中を伝搬する光の位相シフト量の空間的な周期Ｐは図１の半分となる。 The waveguide type optical modulator 20 of the second embodiment shown in FIG. 3 has the same basic configuration as that of the first embodiment, but the modulation electrode of the modulation signal of the first embodiment is used. It is configured to resonate at twice the frequency. That is, as shown in FIG. 2B, the spatial period P of the phase shift amount of the light propagating in the phase shift waveguide in this case is half that of FIG.
ＸカットＬｉＮｂＯ３基板を基板２として用いること、変調電極の給電部１６は共振電極部１９に変調信号の電力を供給するための給電結合線路１７ｂ、１８ｂを有すること、共振電極部１９は、それぞれその両端部に設けたスロット線路からなる共振結合線路１４ｂ、１５ｂと、これらにそれぞれ接続され、これらの間の位相シフト光導波路３ｃ、３ｂ上にそれぞれ配置されたスロット線路からなる電界印加線路１４ａ、１５ａを有すること、各段の共振電極部１９の共振結合線路１４ｂ、１５ｂが隣接する共振電極部１９の共振結合線路とそれぞれ近接して並置され互いに結合していること、さらに、各共振電極部１９はそれぞれ共振結合線路１４ｂ、１５ｂと電界印加線路１４ａ、１５ａとが全体として共振するように構成されていること、電界印加線路４ａにおいてはそのスロットの中央に位相シフト光導波路３ｃが位置し、電界印加線路５ａにおいてはそのスロットの中央に位相シフト光導波路３ｂが位置するように配置されることなどは導波路型光変調器１と同様である。 Using an X-cut LiNbO 3 substrate as the substrate 2, the power supply portion 16 of the modulation electrode has power supply coupling lines 17 b and 18 b for supplying power of the modulation signal to the resonance electrode portion 19, and the resonance electrode portion 19 is respectively Resonant coupling lines 14b and 15b made of slot lines provided at both ends thereof, and electric field application lines 14a made of slot lines respectively connected to and disposed on the phase shift optical waveguides 3c and 3b between them, 15a, the resonance coupling lines 14b and 15b of the resonance electrode portion 19 of each stage are juxtaposed in close proximity to and coupled to the resonance coupling lines of the adjacent resonance electrode portion 19, and each resonance electrode portion 19 is configured such that the resonance coupling lines 14b and 15b and the electric field application lines 14a and 15a resonate as a whole. In other words, the phase shift optical waveguide 3c is positioned at the center of the slot in the electric field application line 4a, and the phase shift optical waveguide 3b is positioned at the center of the slot in the electric field application line 5a. This is the same as the waveguide type optical modulator 1.
但し、位相シフト光導波路３ｂ，３ｃの延伸方向における電界印加線路４ａ、５ａの配置の周期Ｐは、位相シフト光導波路３ｂ，３ｃの等価屈折率をｎ、変調信号の周波数をｆ、真空中での光速をｃとすると、Ｐ＝ｃ／ｎｆとなるように配置されている。 However, the period P of the arrangement of the electric field application lines 4a, 5a in the extending direction of the phase shift optical waveguides 3b, 3c is n, the equivalent refractive index of the phase shift optical waveguides 3b, 3c is n, the frequency of the modulation signal is f, and in vacuum If the speed of light is c, then they are arranged so that P = c / nf.
また、導波路型光変調器１と同様に、４段の共振電極部が全体として変調信号の周波数において共振器となるように構成されているが、導波路型光変調器１と異なり、この場合の共振モードは、１段目から４段目のすべての電界印加線路で同相の電界となるように、電界印加線路と共振結合線路を合わせたスロット線路長、およびそれらの各スロット線路長の比率が調整されている。 Further, like the waveguide type optical modulator 1, the four-stage resonant electrode portion is configured to be a resonator at the frequency of the modulation signal as a whole. In this case, the resonance mode is a slot line length including the electric field application line and the resonance coupling line so that all the electric field application lines from the first stage to the fourth stage have the same electric field, and The ratio has been adjusted.
このようにしても、導波路型光変調器１と同様に、位相シフト光導波路３ｂ，３ｃを伝搬する光に対して加算的に位相シフトを与えることができ、マイクロ波帯などの超高周波域でも高い変調効率を得ることができる。 Even in this case, similarly to the waveguide type optical modulator 1, it is possible to add a phase shift to the light propagating through the phase shift optical waveguides 3b and 3c, and to achieve an ultrahigh frequency region such as a microwave band. However, high modulation efficiency can be obtained.
導波路型光変調器２０は、同じ変調信号の周波数に対しては電界印加線路が配置される周期Ｐが導波路型光変調器１に比べ大きいため、光導波路中の光波に対するマイクロ波の作用長は導波路型光変調器１に比べ小さく、変調効率も小さいが、共振器長が小さいさらに高い周波数で変調を行う場合には適しており、従来の光変調器に比べて構成が簡単で位相調整の手段が不要になるという利点がある。 The waveguide-type optical modulator 20 has a larger period P in which the electric field application line is disposed for the same modulation signal frequency than the waveguide-type optical modulator 1, so that the action of the microwave on the light wave in the optical waveguide is increased. Although the length is smaller than that of the waveguide type optical modulator 1 and the modulation efficiency is small, it is suitable for modulation at a higher frequency where the resonator length is small and the structure is simpler than that of the conventional optical modulator. There is an advantage that means for adjusting the phase becomes unnecessary.
［第３の実施の形態］
図４（ａ）は本発明の第３の実施の形態に係る導波路型光変調器を示す平面図、図４（ｂ）は図４（ａ）に示す導波路型光変調器の位相シフト導波路中を伝搬する光の位相シフト量を示す図である。
[Third Embodiment]
4A is a plan view showing a waveguide type optical modulator according to the third embodiment of the present invention, and FIG. 4B is a phase shift of the waveguide type optical modulator shown in FIG. It is a figure which shows the phase shift amount of the light which propagates the inside of a waveguide.
図４に示す第３の実施の形態の導波路型光変調器３０は、共振電極部２９の段数が３段であること、給電部２６の給電結合線路２７ｂ、２８ｂ、および共振電極部の共振結合線路２４ｂ、２５ｂの構造が異なること以外の基本的な構成は第１の実施の形態と同じである。 In the waveguide type optical modulator 30 of the third embodiment shown in FIG. 4, the number of stages of the resonance electrode section 29 is three, the feed coupling lines 27b and 28b of the feed section 26, and the resonance of the resonance electrode section. The basic configuration is the same as that of the first embodiment except that the structures of the coupled lines 24b and 25b are different.
すなわち、ＸカットＬｉＮｂＯ３基板を基板２として用いること、変調電極の給電部２６は共振電極部２９に変調信号の電力を供給するための給電結合線路２７ｂ、２８ｂとを有すること、共振電極部２９は、それぞれその両端部に設けた共振結合線路２４ｂ、２５ｂと、これらにそれぞれ接続され、これらの間の位相シフト光導波路３ｃ、３ｂ上にそれぞれ配置されたスロット線路からなる電界印加線路２４ａ、２５ａとを有すること、各段の共振電極部２９の共振結合線路２４ｂ、２５ｂが隣接する共振電極部２９の共振結合線路とそれぞれ近接して並置され互いに結合していること、さらに、各共振電極部２９はそれぞれ共振結合線路２４ｂ、２５ｂと電界印加線路２４ａ、２５ａとが全体として共振するように構成されていること、電界印加線路２４ａにおいてはそのスロットの中央に位相シフト光導波路３ｃが位置し、電界印加線路２５ａにおいてはそのスロットの中央に位相シフト光導波路３ｂが位置するように配置されることなどは導波路型光変調器１と同様である。 That is, the X-cut LiNbO 3 substrate is used as the substrate 2, the modulation electrode power supply section 26 has power supply coupling lines 27 b and 28 b for supplying the modulation signal power to the resonance electrode section 29, and the resonance electrode section 29. Are respectively connected to the resonance coupling lines 24b and 25b provided at both ends thereof, and electric field application lines 24a and 25a composed of slot lines respectively connected to the phase shift optical waveguides 3c and 3b between them. The resonance coupling lines 24b and 25b of the resonance electrode portions 29 of each stage are juxtaposed in close proximity to the resonance coupling lines of the adjacent resonance electrode portions 29 and coupled to each other, and each resonance electrode portion 29 is configured such that the resonance coupling lines 24b and 25b and the electric field application lines 24a and 25a resonate as a whole, In the electric field application line 24a, the phase shift optical waveguide 3c is positioned in the center of the slot, and in the electric field application line 25a, the phase shift optical waveguide 3b is positioned in the center of the slot. This is the same as the optical modulator 1.
但し、本実施の形態においては、給電部２６の給電結合線路２７ｂ、２８ｂ、および共振電極部の共振結合線路２４ｂ、２５ｂは、それぞれコプレーナ線路と類似の線路として動作する。すなわち、互いに近接して並置され結合する給電結合線路と共振結合線路、または２つの共振結合線路は、２つの信号電極を持つコプレーナ線路とみることもできる。 However, in the present embodiment, the power supply coupling lines 27b and 28b of the power supply unit 26 and the resonance coupling lines 24b and 25b of the resonance electrode unit operate as lines similar to the coplanar lines. That is, the feed coupling line and the resonant coupling line, or the two resonant coupling lines, which are juxtaposed in close proximity to each other, or the two resonant coupling lines can be regarded as a coplanar line having two signal electrodes.
また、本実施の形態においては、電界印加線路２４ａ、２５ａを上記のようにそれぞれ独立な２つのスロット線路としてみるではなく、電界印加線路２４ａ、２５ａのスロットに挟まれた部分を信号電極とする１つのコプレーナ線路とみることができ、共振結合線路２４ｂ、２５ｂと電界印加線路２４ａ、２５ａとが全体として共振する場合にも、それらが一体化したコプレーナ線路の共振器としてみることができる。 In the present embodiment, the electric field application lines 24a and 25a are not regarded as two independent slot lines as described above, but a portion sandwiched between the slots of the electric field application lines 24a and 25a is used as a signal electrode. Even when the resonance coupling lines 24b and 25b and the electric field application lines 24a and 25a resonate as a whole, they can be regarded as a coplanar line resonator in which they are integrated.
また、この場合、第１および第２の実施の形態では給電結合線路と共振結合線路の先端は短絡端となっており、共振モードはその先端での電界強度が０となる共振モードとなるが、本実施の形態では、給電結合線路と共振結合線路の先端は開放端となるので、その先端で電界強度が最大となる共振モードである。光変調器として変調効率を大きくするためには位相シフト光導波路３ｂ，３ｃの延伸方向における電界印加線路の中央部分で電界強度が最大となるような共振モードを生じさせることが重要であり、目的とする変調信号周波数によって、このような共振モードを生じさせやすい実施の形態を選択することができる。 In this case, in the first and second embodiments, the tips of the feed coupling line and the resonance coupling line are short-circuited ends, and the resonance mode is a resonance mode in which the electric field strength at the tip is zero. In this embodiment, since the tips of the feed coupling line and the resonance coupling line are open ends, this is a resonance mode in which the electric field strength is maximum at the tips. In order to increase the modulation efficiency as an optical modulator, it is important to generate a resonance mode that maximizes the electric field strength at the center of the electric field application line in the extending direction of the phase shift optical waveguides 3b and 3c. According to the modulation signal frequency, an embodiment that easily generates such a resonance mode can be selected.
第１の実施の形態と同様に、変調信号の周波数において各段の共振電極部単体での共振と同時に３段の共振電極部が全体としても共振器となるように構成されている。ここで、３段目の共振電極部２９の終端は短絡または開放端であってもよい。 Similar to the first embodiment, at the same time as the resonance of each resonance electrode unit alone at the frequency of the modulation signal, the three-stage resonance electrode unit is configured as a resonator as a whole. Here, the termination of the third-stage resonance electrode portion 29 may be a short circuit or an open end.
共振モードは、１段目と３段目の電界印加線路で同相の電界となり、２段目の電界印加線路でそれらの逆相の反転電界となるように、電界印加線路と共振結合線路を合わせた線路長、およびそれらの各線路長の比率が調整されている。また、位相シフト光導波路３ｂ，３ｃの延伸方向における電界印加線路２４ａ、２５ａの配置の周期Ｐは、位相シフト光導波路３ｂ、３ｃの等価屈折率をｎ、変調信号の周波数をｆ、真空中での光速をｃとすると、Ｐ＝ｃ／２ｎｆとなるように配置されており、これにより、位相シフト光導波路３ｂ，３ｃを伝搬する光に対して、変調電極への印加電界により加算的に位相シフトを与えることができるので、実効的な変調電極長が長くなり、マイクロ波帯などの超高周波域でも高い変調効率を得ることができる。 In the resonance mode, the electric field application line and the resonant coupling line are combined so that the electric field in the same phase is in the first and third electric field application lines and the inverted electric field is in the opposite phase in the second electric field application line. The line lengths and the ratios of the respective line lengths are adjusted. The period P of the arrangement of the electric field application lines 24a and 25a in the extending direction of the phase shift optical waveguides 3b and 3c is n, the equivalent refractive index of the phase shift optical waveguides 3b and 3c is n, the frequency of the modulation signal is f, and in vacuum , Where c = n / 2nf, the phase of the light propagating through the phase shift optical waveguides 3b and 3c is added by the electric field applied to the modulation electrode. Since a shift can be given, the effective modulation electrode length becomes long, and high modulation efficiency can be obtained even in an ultrahigh frequency region such as a microwave band.
［第４の実施の形態］
図５（ａ）は本発明の第４の実施の形態に係る導波路型光変調器を示す平面図、図５（ｂ）は図４（ａ）に示す導波路型光変調器の位相シフト導波路中を伝搬する光の位相シフト量を示す図、図６は図５（ａ）におけるＡ−Ａ断面図である。
[Fourth Embodiment]
FIG. 5A is a plan view showing a waveguide type optical modulator according to the fourth embodiment of the present invention, and FIG. 5B is a phase shift of the waveguide type optical modulator shown in FIG. The figure which shows the phase shift amount of the light which propagates in a waveguide, FIG. 6 is AA sectional drawing in Fig.5 (a).
図５、図６に示す第４の実施の形態に係る導波路型光変調器４０は、図４に示す導波路型光変調器３０に対し、基板をＬｉＮｂＯ３のＺカット基板である基板３２に置き換え、変調電極を構成する電界印加線路は信号電極３５ａを位相シフト光導波路３ｂ上に配置したコプレーナ線路とした構成である。給電部３６の給電結合線路３７ｂ、３８ｂと共振電極部３９の共振結合線路３４ｂ、３５ｂは第３の実施の形態と同様な構成である。 The waveguide type optical modulator 40 according to the fourth embodiment shown in FIGS. 5 and 6 is different from the waveguide type optical modulator 30 shown in FIG. 4 in that the substrate is a substrate 32 that is a Z-cut substrate of LiNbO 3. The electric field application line constituting the modulation electrode is a coplanar line in which the signal electrode 35a is disposed on the phase shift optical waveguide 3b. The power supply coupling lines 37b and 38b of the power supply unit 36 and the resonance coupling lines 34b and 35b of the resonance electrode unit 39 have the same configuration as that of the third embodiment.
導波路型光変調器４０では、基板３２がＺカット基板であるため、電界印加線路において印加電界がＺ軸方向に印加されるように、コプレーナ線路の信号電極３５ａは位相シフト光導波路３ｂ上に配置され、その両側の接地電極の一方の端部３４ａが位相シフト光導波路３ｃ上に配置される。 In the waveguide type optical modulator 40, since the substrate 32 is a Z-cut substrate, the signal electrode 35a of the coplanar line is placed on the phase shift optical waveguide 3b so that the applied electric field is applied in the Z-axis direction in the electric field application line. One end 34a of the ground electrode on both sides thereof is disposed on the phase shift optical waveguide 3c.
これにより、位相シフト光導波路３ｃに印加される電界の方向と、位相シフト光導波路３ｂに印加される電界の方向とが反対方向になる。 Thereby, the direction of the electric field applied to the phase shift optical waveguide 3c is opposite to the direction of the electric field applied to the phase shift optical waveguide 3b.
導波路型光変調器４０においても３段の電界印加線路３４が位相シフト光導波路３ｂ，３ｃの延伸方向に周期的に互いに離間して配置されている。 Also in the waveguide type optical modulator 40, the three-stage electric field application lines 34 are periodically spaced apart from each other in the extending direction of the phase shift optical waveguides 3b and 3c.
第１の実施の形態と同様に、変調信号の周波数において各段の共振電極部単体での共振と同時に３段の共振電極部が全体としても共振器となるように構成されている。ここで、３段目の共振電極部３９の終端は短絡または開放端であってもよい。 Similar to the first embodiment, at the same time as the resonance of each resonance electrode unit alone at the frequency of the modulation signal, the three-stage resonance electrode unit is configured as a resonator as a whole. Here, the termination of the third-stage resonance electrode portion 39 may be a short circuit or an open end.
この場合の共振モードは、１段目と３段目の電界印加線路で同相の電界となり、２段目の電界印加線路でそれらの逆相の反転電界となるように、電界印加線路と共振結合線路を合わせた線路長、およびそれらの各線路長の比率が調整されている。 In this case, the resonance mode is resonantly coupled to the electric field application line so that the electric field in the same phase is in the first and third electric field application lines, and the reversed electric field is in the opposite phase in the second electric field application line. The line length of the combined lines and the ratio of each line length are adjusted.
また、導波路型光変調器１と同様に位相シフト光導波路３ｂ，３ｃの延伸方向における電界印加線路１４ａの配置の周期Ｐは、位相シフト光導波路３ｂ，３ｃの等価屈折率をｎ、変調信号の周波数をｆ、真空中での光速をｃとすると、Ｐ＝ｃ／２ｎｆとなるように配置されており、これにより、位相シフト光導波路３ｂ，３ｃを伝搬する光に対して、変調電極への印加電界により加算的に位相シフトを与えることができるので、実効的な変調電極長が長くなり、マイクロ波帯などの超高周波域でも高い変調効率を得ることができる。 Similarly to the waveguide type optical modulator 1, the period P of the arrangement of the electric field application line 14a in the extending direction of the phase shift optical waveguides 3b and 3c is n, and the equivalent refractive index of the phase shift optical waveguides 3b and 3c is n. , Where f is the frequency of light and c is the speed of light in a vacuum, P = c / 2nf. Thus, the light propagating through the phase shift optical waveguides 3b and 3c is transferred to the modulation electrode. Therefore, the effective modulation electrode length becomes long, and high modulation efficiency can be obtained even in an ultrahigh frequency region such as a microwave band.
［その他の実施の形態］
上記のように、本発明は第１、第２および第３の実施の形態によって記載したが、この開示の一部をなす論述および図面はこの発明を限定するものであると理解すべきではない。
[Other embodiments]
As described above, the present invention has been described according to the first, second, and third embodiments. However, it should not be understood that the description and drawings that constitute a part of this disclosure limit the present invention. .
この開示から当業者には様々な代替実施の形態、実施例および運用技術が明らかとなろう。 From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.
例えば、上記第１、第２、第３および第４の実施の形態においては、共振電極部の段数が３段および４段の例について説明したが、電界印加線路の段数は１段、２段および５段以上であってもよい。共振電極部の段数の増加に伴って変調効率は高くなる。 For example, in the first, second, third, and fourth embodiments, the example in which the number of resonant electrode portions is three and four has been described, but the number of electric field application lines is one and two. And 5 or more stages. The modulation efficiency increases with an increase in the number of resonant electrode sections.
また、上記の実施の形態においては、電界印加線路、共振結合線路、給電結合線路や給電部の線路をスロット線路やコプレーナ線路で構成した例について説明したが、他のマイクロ波線路を用いることができる。 In the above-described embodiment, the example in which the electric field application line, the resonance coupling line, the feed coupling line, and the feed line are configured by the slot line and the coplanar line has been described. However, other microwave lines may be used. it can.
電界印加線路、共振結合線路、給電結合線路や給電部の線路で互いに異なるマイクロ波線路を用いることも可能である。共振電極部を共振器として機能させる手段についても、上記の実施の形態以外のインピーダンスの不連続構造を線路中に反射点として設けることも可能である。 It is also possible to use different microwave lines for the electric field application line, the resonance coupling line, the feed coupling line, and the feed line. As for the means for causing the resonant electrode section to function as a resonator, it is also possible to provide a discontinuous structure of impedance other than the above embodiment as a reflection point in the line.
給電部への変調信号の給電方法なども公知のマイクロ波の結合方法を利用した手段が可能である。 As a method for supplying a modulation signal to the power supply unit, means using a known microwave coupling method can be used.
このように、本発明はここでは記載していない様々な実施の形態等を含むことは勿論である。したがって、本発明の技術的範囲は上記の説明から妥当な特許請求の範囲に係る発明特定事項によってのみ定められるものである。
As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.
１、２０、３０、４０ 導波路型光変調器
２、３２ 基板
３ マッハツェンダー型光導波路（光導波路）
３ａ 入力光導波路
３ｂ，３ｃ 位相シフト光導波路
３ｄ 出力光導波路
４ａ、５ａ、１４ａ、１５ａ、２４ａ、２５ａ 電界印加線路
４ｂ、５ｂ、１４ｂ、１５ｂ、２４ｂ、２５ｂ、３４ｂ、３５ｂ 共振結合線路
６、１６、２６、３６ 給電部
７ａ、８ａ スロット線路
７ｂ、８ｂ、１７ｂ、１８ｂ、２７ｂ、２８ｂ、３７ｂ、３８ｂ 給電結合線路
９、１９、２９、３９ 共振電極部
１０ 信号入力端子
１１ バッファ層
３４ａ 接地電極の一方の端部
３５ａ 信号電極
1, 20, 30, 40 Waveguide type optical modulator 2, 32 Substrate 3 Mach-Zehnder type optical waveguide (optical waveguide)
3a Input optical waveguide 3b, 3c Phase shift optical waveguide 3d Output optical waveguide 4a, 5a, 14a, 15a, 24a, 25a Electric field application lines 4b, 5b, 14b, 15b, 24b, 25b, 34b, 35b Resonant coupling lines 6, 16 , 26, 36 Feed section 7a, 8a Slot line 7b, 8b, 17b, 18b, 27b, 28b, 37b, 38b Feed coupling line 9, 19, 29, 39 Resonant electrode section 10 Signal input terminal 11 Buffer layer 34a Ground electrode One end 35a Signal electrode
Claims (6)
前記変調電極は、前記変調信号印加手段に接続される給電部と少なくとも１つの共振電極部とからなり、
前記給電部は前記共振電極部に前記変調信号の電力を供給するための給電結合線路を有し、
前記共振電極部はその両端部に設けた共振結合線路と該共振結合線路の間に設けた前記位相シフト光導波路の延伸方向に平行で前記位相シフト光導波路に近接して配置されたスロット線路またはコプレーナ線路からなる電界印加線路とを有し、
前記給電結合線路と前記共振結合線路とが近接して並置され互いに結合することにより、前記給電部より前記共振電極部に前記変調信号の電力の供給がなされ、
前記共振電極部は前記共振結合線路の前記電界印加線路より遠い側の端部を開放端または短絡端とすることにより前記共振結合線路と前記電界印加線路とが全体として共振するように構成されていることを特徴とする導波路型光変調器。 A substrate made of a material having an electro-optic effect, an input optical waveguide formed on the substrate, two phase shift optical waveguides branched from the input optical waveguide, and an output obtained by joining the two phase shift optical waveguides An optical waveguide having an optical waveguide, a modulation electrode for applying an electric field to the phase shift optical waveguide disposed on the substrate, and a modulation signal applying means for applying a modulation signal to the modulation electrode,
The modulation electrode includes a power feeding unit connected to the modulation signal applying unit and at least one resonance electrode unit,
The power supply unit has a power supply coupling line for supplying power of the modulation signal to the resonance electrode unit,
The resonant electrode section includes a resonant coupling line provided at both ends thereof and a slot line disposed in parallel to the extending direction of the phase shift optical waveguide provided between the resonant coupling lines and in proximity to the phase shift optical waveguide, or An electric field application line made of a coplanar line,
By supplying the power supply coupling line and the resonance coupling line in close proximity to each other and coupling each other, the power of the modulation signal is supplied from the power supply unit to the resonance electrode unit,
The resonance electrode section is configured such that the resonance coupling line and the electric field application line resonate as a whole by setting an end of the resonance coupling line far from the electric field application line as an open end or a short-circuit end. A waveguide type optical modulator characterized by comprising:
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