WO2017145998A1 - Light ssb modulator - Google Patents
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- WO2017145998A1 WO2017145998A1 PCT/JP2017/006195 JP2017006195W WO2017145998A1 WO 2017145998 A1 WO2017145998 A1 WO 2017145998A1 JP 2017006195 W JP2017006195 W JP 2017006195W WO 2017145998 A1 WO2017145998 A1 WO 2017145998A1
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
Abstract
A light SSB modulator (10) is provided with: an electro-optical crystal substrate (12) comprising a dielectric material; a Mach-Zehnder optical waveguide (30) that is formed on the electro-optical crystal substrate (12)and has a first optical waveguide (31) and a second optical wave guide (32); an antenna (21) that receives a wireless signal (5); and a first resonance-type electrode (22a) and a second resonance-type electrode (22b) that are connected to the antenna (21) and are arranged along the first optical waveguide (31) and the second optical waveguide (32) respectively. In the electro-optical crystal substrate (12), a polarization inversion structure (23) is formed such that a light wave traveling through the first optical waveguide (31) is cosine-modulated, and a light wave traveling through the second optical waveguide (32) is sine-modulated, the optical path of the first optical waveguide (31) being longer than the length of the optical path of the second optical waveguide (32) by a length corresponding to a phase difference of π/2.
Description
本発明は、光波を無線信号で変調することによりＳＳＢ（Ｓｉｎｇｌｅ Ｓｉｄｅ Ｂａｎｄ）変調された光信号を出力する光ＳＳＢ変調器に関する。
The present invention relates to an optical SSB modulator that outputs an optical signal that is SSB (Single Side Band) modulated by modulating a light wave with a radio signal.
ミリ波は、次世代無線の有力候補である。特に、６０ＧＨｚ帯は、各種規格も定めらており、Ｇｂｐｓ伝送（つまり、大容量通信）が容易である。ミリ波無線では、セルサイズが小さくなるために、無線信号を光信号に変換して光ファイバーで伝送するＲａｄｉｏ－ｏｖｅｒ－Ｆｉｂｅｒ（ＲｏＦ）方式が有効である。ＲｏＦミリ波無線システムを構築するためには、ミリ波無線信号を光信号に変換する光強度変調器が重要である。
Millimeter wave is a promising candidate for next-generation radio. In particular, in the 60 GHz band, various standards are defined, and Gbps transmission (that is, large-capacity communication) is easy. In the millimeter wave radio, since the cell size is small, a radio-over-fiber (RoF) system in which a radio signal is converted into an optical signal and transmitted through an optical fiber is effective. In order to construct a RoF millimeter-wave radio system, an optical intensity modulator that converts a millimeter-wave radio signal into an optical signal is important.
光強度変調器は、両側波帯（Ｄｏｕｂｌｅ Ｓｉｄｅ Ｂａｎｄ；ＤＳＢ）変調器であるが、光ＤＳＢ変調器で変調された信号を光ファイバーで伝送すると、光ファイバーの波長分散により強度変調信号が位相変調信号に変換される状況が生じ得る。それゆえ、信号をフォトダイオード等で検波・復調することが困難になる。また、ＤＳＢ信号には冗長性があり、情報伝送のためには、ＳＳＢ信号で十分である。光ＳＳＢ信号では波長分散による問題も生じない。
The optical intensity modulator is a double side band (DSB) modulator. When a signal modulated by the optical DSB modulator is transmitted through an optical fiber, the intensity modulated signal is converted into a phase modulation signal by the wavelength dispersion of the optical fiber. A situation can occur that is transformed. Therefore, it becomes difficult to detect and demodulate the signal with a photodiode or the like. Further, the DSB signal has redundancy, and the SSB signal is sufficient for information transmission. The optical SSB signal does not cause a problem due to chromatic dispersion.
そこで、従来、ミリ波帯無線信号から光ＳＳＢ変調信号を生成する光ＳＳＢ変調器が提案されている（例えば、特許文献１参照）。特許文献１の技術によれば、マッハツェンダー型光導波路が形成された電気光学結晶基板に分極反転構造を設けることで、低電力で駆動可能であり、小型の構成であっても、１０ＧＨｚ以上の高周波域で高効率に動作する光ＳＳＢ変調器が実現される。
Therefore, conventionally, an optical SSB modulator that generates an optical SSB modulation signal from a millimeter-wave band radio signal has been proposed (see, for example, Patent Document 1). According to the technique of Patent Document 1, by providing a polarization inversion structure on an electro-optic crystal substrate on which a Mach-Zehnder type optical waveguide is formed, it can be driven with low power, and even with a small configuration, 10 GHz or more. An optical SSB modulator that operates with high efficiency in a high frequency range is realized.
しかしながら、特許文献１の技術では、低電力ではあるものの、駆動のために最低限の電力が必要とされ、電源を必要とするという問題がある。さらに、特許文献１の技術では、光ＳＳＢ変調信号が出力されるものの、その光ＳＳＢ変調信号には不要な側波帯が残留している（つまり、不要な側波帯の抑圧度が十分ではない）という問題もある。
However, although the technique of Patent Document 1 has low power, there is a problem that a minimum power is required for driving and a power source is required. Furthermore, in the technique of Patent Document 1, an optical SSB modulation signal is output, but unnecessary sidebands remain in the optical SSB modulation signal (that is, the degree of suppression of unnecessary sidebands is not sufficient). There is also a problem of not.
そこで、本発明は、上記問題に鑑みてなされたものであり、電源を必要とすることなく、かつ、不要な側波帯が従来よりも抑圧された光ＳＳＢ変調信号を生成する光ＳＳＢ変調器を提供することを目的とする。
Therefore, the present invention has been made in view of the above problems, and an optical SSB modulator that generates an optical SSB modulation signal that does not require a power source and that suppresses unnecessary sidebands as compared with the prior art. The purpose is to provide.
上記目的を達成するために、本発明の一形態に係る光ＳＳＢ変調器は、光波を無線信号で変調することによりＳＳＢ（Ｓｉｎｇｌｅ Ｓｉｄｅ Ｂａｎｄ）変調された光信号を出力する光ＳＳＢ変調器であって、誘電性材料からなる電気光学結晶基板と、前記電気光学結晶基板に形成され、第１光導波路及び第２光導波路を有するマッハツェンダー型光導波路と、前記無線信号を受信するアンテナと、前記アンテナに接続され、前記第１光導波路及び前記第２光導波路のそれぞれに沿って設けられた第１共振型電極及び第２共振型電極とを備え、前記電気光学結晶基板には、前記第１光導波路を進行する光波に対してｃｏｓ変調を与えるように前記第１共振型電極に対向する領域の一部に分極反転構造が形成され、かつ、前記第２光導波路を進行する光波に対してｓｉｎ変調を与えるように前記第２共振型電極に対向する領域の一部に分極反転構造が形成され、前記第１光導波路及び前記第２光導波路の一方の光路は、他方の光路よりも、前記光波におけるπ／２の位相差に相当する長さだけ長い。
In order to achieve the above object, an optical SSB modulator according to an embodiment of the present invention is an optical SSB modulator that outputs an optical signal that is SSB (Single Side Band) modulated by modulating a light wave with a radio signal. An electro-optic crystal substrate made of a dielectric material; a Mach-Zehnder type optical waveguide formed on the electro-optic crystal substrate and having a first optical waveguide and a second optical waveguide; an antenna for receiving the radio signal; A first resonance type electrode and a second resonance type electrode connected to an antenna and provided along each of the first optical waveguide and the second optical waveguide; A domain-inverted structure is formed in a part of a region facing the first resonant electrode so as to apply cos modulation to the light wave traveling through the optical waveguide, and the second optical waveguide A domain-inverted structure is formed in a part of the region facing the second resonant electrode so as to apply sin modulation to the traveling light wave, and one optical path of the first optical waveguide and the second optical waveguide is: It is longer than the other optical path by a length corresponding to a phase difference of π / 2 in the light wave.
これにより、第１共振型電極及び第２共振型電極には、アンテナで受信された無線信号が供給されるので、特許文献１の技術で必要とされた、第１共振型電極及び第２共振型電極に無線信号を供給するための変調信号源及び可変直流電圧源等の電源が不要となる。さらに、本発明の光ＳＳＢ変調器では、第１光導波路及び第２光導波路にπ／２の位相差に相当する光路差（光バイアス）を与えるために、これらの光路長に差を設けているので、光波にバイアス電圧を印加する方法と異なり、電源を必要としない。よって、本発明の光ＳＳＢ変調器は、電源を必要とすることなく、無線信号から光ＳＳＢ変調信号が生成される。
Thereby, since the radio signal received by the antenna is supplied to the first resonance type electrode and the second resonance type electrode, the first resonance type electrode and the second resonance type required in the technique of Patent Document 1 are used. A power source such as a modulation signal source and a variable DC voltage source for supplying a radio signal to the mold electrode becomes unnecessary. Further, in the optical SSB modulator of the present invention, in order to give an optical path difference (optical bias) corresponding to a phase difference of π / 2 to the first optical waveguide and the second optical waveguide, a difference is provided in these optical path lengths. Therefore, unlike the method of applying a bias voltage to the light wave, no power source is required. Therefore, the optical SSB modulator of the present invention generates an optical SSB modulated signal from a radio signal without requiring a power source.
さらに、本発明の光ＳＳＢ変調器によれば、アンテナによって受信された無線信号が第１共振型電極及び第２共振型電極に供給される。より具体的には、前記第１光導波路及び前記第２光導波路は、互いに並行して延在するように前記電気光学結晶基板上に形成され、前記第１共振型電極及び前記第２共振型電極は、それぞれ前記第１光導波路及び前記第２光導波路に沿って、互いに並行して延在するように前記電気光学結晶基板上に設けられ、前記アンテナは、前記電気光学結晶基板上に設けられ、前記第１共振型電極に直交するように接続される第１アンテナ素子、及び、前記第２共振型電極に直交するように接続される第２アンテナ素子を有し、前記第１アンテナ素子と前記第２アンテナ素子とは、前記電気光学結晶基板上において、前記第１共振型電極及び前記第２共振型電極に対して、対称の位置に設けられてもよい。
Furthermore, according to the optical SSB modulator of the present invention, the radio signal received by the antenna is supplied to the first resonance type electrode and the second resonance type electrode. More specifically, the first optical waveguide and the second optical waveguide are formed on the electro-optic crystal substrate so as to extend in parallel with each other, and the first resonant electrode and the second resonant type are formed. The electrodes are provided on the electro-optic crystal substrate so as to extend in parallel with each other along the first optical waveguide and the second optical waveguide, respectively, and the antenna is provided on the electro-optic crystal substrate. A first antenna element connected to be orthogonal to the first resonance type electrode, and a second antenna element connected to be orthogonal to the second resonance type electrode, the first antenna element And the second antenna element may be provided on the electro-optic crystal substrate at positions symmetrical with respect to the first resonance electrode and the second resonance electrode.
これにより、第１共振型電極及び第２共振型電極の一方だけに対して変調信号を供給する特許文献１の技術と異なり、第１共振型電極及び第２共振型電極の両方に対して変調信号が供給されて第１共振型電極及び第２共振型電極において強くて歪の少ない変調電界が発生するので、第１光導波路及び第２光導波路を進行する光波に対して歪の少ないｃｏｓ変調及びｓｉｎ変調が施され、特許文献１の技術よりも不要な側波帯が抑圧された光ＳＳＢ変調信号が生成される。
Thus, unlike the technique of Patent Document 1 in which the modulation signal is supplied to only one of the first resonance electrode and the second resonance electrode, the modulation is performed on both the first resonance electrode and the second resonance electrode. Since a strong electric field with little distortion is generated at the first resonance type electrode and the second resonance type electrode when a signal is supplied, cos modulation with little distortion is applied to the light wave traveling through the first optical waveguide and the second optical waveguide. And an optical SSB modulation signal in which sidebands unnecessary for the technique of Patent Document 1 are suppressed are generated.
また、前記第１アンテナ素子が前記第１共振型電極と接続される接続点は、前記第１共振型電極における、前記第１アンテナ素子と前記第１共振型電極とがインピーダンス整合する複数の接続点のうち、前記第１共振型電極の端部に最も近い接続点であり、前記第２アンテナ素子が前記第２共振型電極と接続される接続点は、前記第２共振型電極における、前記第２アンテナ素子と前記第２共振型電極とがインピーダンス整合する複数の接続点のうち、前記第２共振型電極の端部に最も近い接続点であってもよい。
The connection point at which the first antenna element is connected to the first resonance electrode is a plurality of connections in the first resonance electrode where the first antenna element and the first resonance electrode are impedance matched. Among the points, the connection point that is closest to the end of the first resonance type electrode, and the connection point where the second antenna element is connected to the second resonance type electrode is the connection point in the second resonance type electrode, Of a plurality of connection points at which the second antenna element and the second resonance type electrode are impedance matched, the connection point closest to the end of the second resonance type electrode may be used.
これにより、第１アンテナ素子及び第２アンテナ素子はそれぞれ第１共振型電極及び第２共振型電極とインピーダンス整合する複数の接続点のうち第１共振型電極及び第２共振型電極の端部に最も近い接続点で接続されて整合されるので、第１共振型電極及び第２共振型電極で不要な共振が生じることが抑制されるともに第１共振型電極及び第２共振型電極で強い変調電界が生じ、出力される光ＳＳＢ変調信号に不要な側波帯が残留してしまうことが抑制される。
As a result, the first antenna element and the second antenna element are respectively connected to the ends of the first resonance type electrode and the second resonance type electrode among a plurality of connection points impedance-matched with the first resonance type electrode and the second resonance type electrode. Since it is connected and matched at the nearest connection point, unnecessary resonance is suppressed from occurring in the first resonance electrode and the second resonance electrode, and strong modulation is performed in the first resonance electrode and the second resonance electrode. An electric field is generated, and unnecessary sidebands are prevented from remaining in the output optical SSB modulation signal.
また、前記アンテナ、前記第１共振型電極、前記第２共振型電極及び前記分極反転構造を一組の変調部とした場合に、前記第１光導波路及び前記第２光導波路に沿う複数の箇所のそれぞれに、前記変調部が設けられてもよい。より具体的には、前記変調部は、前記光波が進行する方向に沿って並ぶ第１変調部、第２変調部、第３変調部及び第４変調部を、この並び順で、含み、前記第１変調部及び前記第３変調部を構成する前記分極反転構造は、同一の第１分極反転構造を有し、前記第２変調部及び前記第４変調部を構成する前記分極反転構造は、前記第１分極反転構造とは異なる、同一の第２分極反転構造を有してもよい。
Further, when the antenna, the first resonance electrode, the second resonance electrode, and the polarization inversion structure are used as a pair of modulation units, a plurality of locations along the first optical waveguide and the second optical waveguide. Each of the above may be provided with the modulation section. More specifically, the modulation unit includes a first modulation unit, a second modulation unit, a third modulation unit, and a fourth modulation unit arranged in the arrangement order along the direction in which the light wave travels, The polarization inversion structures constituting the first modulation unit and the third modulation unit have the same first polarization inversion structure, and the polarization inversion structures constituting the second modulation unit and the fourth modulation unit are: You may have the same 2nd polarization inversion structure different from the said 1st polarization inversion structure.
これにより、第１光導波路及び第２光導波路を進行する光波は、複数の箇所に設けられた変調部によって変調を受けるので、一つの変調部によって変調を受ける場合に比べ、それぞれ、より歪みの少ないｃｏｓ変調及びｓｉｎ変調を受けて合波され、不要な側波帯がより抑圧された光ＳＳＢ変調信号が生成される。また、複数の変調部において同一の方向から入射する無線信号に対して最も強い光ＳＳＢ変調信号が生成されるので、無線信号の入射方向についての指向性が強くなる。
As a result, since the light waves traveling in the first optical waveguide and the second optical waveguide are modulated by the modulation units provided at a plurality of locations, each of them is more distorted than when modulated by one modulation unit. An optical SSB modulation signal in which unnecessary sidebands are further suppressed is generated by being combined by receiving a small amount of cos modulation and sin modulation. In addition, since the strongest optical SSB modulation signal is generated for a radio signal incident from the same direction in the plurality of modulation units, the directivity in the incident direction of the radio signal is increased.
本発明により、電源を必要とすることなく、かつ、不要な側波帯が従来よりも抑圧された光ＳＳＢ変調信号を生成する光ＳＳＢ変調器が提供される。
According to the present invention, there is provided an optical SSB modulator that generates an optical SSB modulation signal that does not require a power source and that suppresses unnecessary sidebands as compared with the prior art.
よって、本発明に係る光ＳＳＢ変調器は、小型で、かつ、無給電で動作する無線－光信号変換デバイスであり、ミリ波帯による次世代無線通信システムの構築が期待される今日において、実用的価値は極めて高い。
Therefore, the optical SSB modulator according to the present invention is a small-sized wireless-to-optical signal conversion device that operates without power supply, and is expected to be constructed in the next generation wireless communication system using the millimeter wave band. Value is extremely high.
以下、本発明の実施の形態について、図面を用いて詳細に説明する。なお、以下で説明する実施の形態は、いずれも本発明の一具体例を示すものである。以下の実施の形態で示される数値、形状、材料、構成要素、構成要素の配置位置及び接続形態、工程、工程の順序等は、一例であり、本発明を限定する主旨ではない。また、以下の実施の形態における構成要素のうち、本発明の最上位概念を示す独立請求項に記載されていない構成要素については、任意の構成要素として説明される。
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that each of the embodiments described below shows a specific example of the present invention. Numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of constituent elements, processes, order of processes, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept of the present invention are described as optional constituent elements.
図１は、実施の形態における光ＳＳＢ変調器１０の構成を示す外観図である。ここでは、光ＳＳＢ変調器１０の上方斜めから見た透視的な外観図（図１の（ａ））と、図１の（ａ）における破線枠で囲まれた面で切断して得られる断面図（図１の（ｂ）とが図示されている。また、本図には、説明の便宜のために、互いに直交するｘ軸、ｙ軸及びｚ軸も示されている。
FIG. 1 is an external view showing a configuration of an optical SSB modulator 10 according to the embodiment. Here, a perspective view (FIG. 1 (a)) seen obliquely from the upper side of the optical SSB modulator 10, and a cross section obtained by cutting along a plane surrounded by a broken line frame in FIG. 1 (a). The figure ((b) of FIG. 1 is shown. In addition, for convenience of explanation, the x axis, the y axis, and the z axis that are orthogonal to each other are also shown in the figure.
光ＳＳＢ変調器１０は、光波をミリ波等の無線信号５で変調することによりＳＳＢ変調された光信号（光ＳＳＢ変調信号）を出力する電気光学変調器であり、図１の（ａ）に示されるように、主要な構成要素として、誘電性材料からなる電気光学結晶基板１２と、電気光学結晶基板１２に形成され第１光導波路３１及び第２光導波路３２を有するマッハツェンダー型光導波路３０と、無線信号５を受信するアンテナ２１と、アンテナ２１に接続され第１光導波路３１及び第２光導波路３２のそれぞれに沿って設けられた第１共振型電極２２ａ及び第２共振型電極２２ｂとを備える。なお、第１共振型電極２２ａと第２共振型電極２２ｂとを合わせて、共振型電極２２と呼ぶ。
The optical SSB modulator 10 is an electro-optic modulator that outputs an SSB-modulated optical signal (optical SSB modulated signal) by modulating a light wave with a radio signal 5 such as a millimeter wave. FIG. As shown, a Mach-Zehnder type optical waveguide 30 having an electro-optic crystal substrate 12 made of a dielectric material and a first optical waveguide 31 and a second optical waveguide 32 formed on the electro-optic crystal substrate 12 as main components. An antenna 21 that receives the radio signal 5, and a first resonance type electrode 22a and a second resonance type electrode 22b that are connected to the antenna 21 and provided along the first optical waveguide 31 and the second optical waveguide 32, respectively. Is provided. The first resonance type electrode 22a and the second resonance type electrode 22b are collectively referred to as the resonance type electrode 22.
電気光学結晶基板１２には、第１光導波路３１を進行する光波に対してｃｏｓ変調を与えるように第１共振型電極２２ａに対向する領域の一部に分極反転構造２３が形成され、かつ、第２光導波路３２を進行する光波に対してｓｉｎ変調を与えるように第２共振型電極２２ｂに対向する領域の一部にも分極反転構造２３が形成されている。なお、「分極反転構造」とは、自発分極の向きが周りと異なる（例えば、分極反転構造が施された箇所の自発分極の向きがｚ軸の正方向で、周りがｚ軸の負方向となる）構造をいう。また、「第１光導波路３１を進行する光波に対してｃｏｓ変調を与え、かつ、第２光導波路３２を進行する光波に対してｓｉｎ変調を与える」とは、第１光導波路３１を進行する光波と第２光導波路３２を進行する光波とに対して、位相がπ／２（つまりＴ／４）ずれたタイミングで位相変化量が最大となるように変調を施すことをいう。Ｔは、無線信号５の周波数（対象周波数）に対応する周期である。
The electro-optic crystal substrate 12 has a domain-inverted structure 23 formed in a part of a region facing the first resonance type electrode 22a so as to apply cos modulation to the light wave traveling through the first optical waveguide 31, and The domain-inverted structure 23 is also formed in a part of the region facing the second resonance electrode 22b so as to apply sin modulation to the light wave traveling through the second optical waveguide 32. Note that the “polarization inversion structure” is different from the direction of spontaneous polarization from the surroundings (for example, the direction of spontaneous polarization of the portion where the polarization inversion structure is applied is the positive direction of the z axis and the surrounding is the negative direction of the z axis. Is the structure. In addition, “cos modulation is applied to the light wave traveling through the first optical waveguide 31 and sin modulation is applied to the light wave traveling through the second optical waveguide 32” means that the light wave traveling through the first optical waveguide 31 travels through the first optical waveguide 31. This refers to modulating the light wave and the light wave traveling through the second optical waveguide 32 so that the phase change amount is maximized at the timing when the phase is shifted by π / 2 (that is, T / 4). T is a period corresponding to the frequency (target frequency) of the radio signal 5.
また、光ＳＳＢ変調信号を生成するために、第１光導波路３１及び第２光導波路３２には、光波におけるπ／２の位相差（１／４波長分の長さ）に相当する光路差（光バイアス）が与えられている。つまり、第１光導波路３１及び第２光導波路３２の一方（本実施の形態では、第１光導波路３１）の光路が、他方（本実施の形態では、第２光導波路３２）の光路よりも、光波におけるπ／２の位相差に相当する長さだけ長くなるように、第１光導波路３１の一部に湾曲部３１ａが形成されている。
Further, in order to generate an optical SSB modulation signal, the first optical waveguide 31 and the second optical waveguide 32 are provided with an optical path difference corresponding to a phase difference of π / 2 (length corresponding to ¼ wavelength) in the light wave ( Light bias). That is, the optical path of one of the first optical waveguide 31 and the second optical waveguide 32 (the first optical waveguide 31 in the present embodiment) is more than the optical path of the other (the second optical waveguide 32 in the present embodiment). A curved portion 31 a is formed in a part of the first optical waveguide 31 so as to be longer by a length corresponding to a phase difference of π / 2 in the light wave.
なお、マッハツェンダー型光導波路３０は、図面に向かって左端部（ｙ軸の負方向の端部）に光波が入力又は出力される第１ポート３０ａを有し、右端部（ｙ軸の正方向の端部）に光ＳＳＢ変調信号が出力又は入力される第２ポート３０ｂを有する（本実施の形態では、第１ポート３０ａを入力ポートとし、第２ポート３０ｂを出力ポートとして使用している）。また、第１共振型電極２２ａ及び第２共振型電極２２ｂは、定在波共振型電極であり、分極反転構造２３によって変調位相を制御しやすいように、対象周波数における２波長分の長さを有し、互いに両端が短絡されている。
The Mach-Zehnder type optical waveguide 30 has a first port 30a through which light waves are input or output at the left end (end in the negative direction of the y-axis) toward the drawing, and the right end (positive direction of the y-axis). (In the present embodiment, the first port 30a is used as an input port and the second port 30b is used as an output port). . The first resonance type electrode 22a and the second resonance type electrode 22b are standing wave resonance type electrodes, and have a length corresponding to two wavelengths at the target frequency so that the modulation phase can be easily controlled by the polarization inversion structure 23. And both ends are short-circuited.
ここで、第１光導波路３１及び第２光導波路３２は、互いに並行（ここでは、ｙ軸方向に並行）して延在するように電気光学結晶基板１２に形成されている。また、第１共振型電極２２ａ及び第２共振型電極２２ｂは、それぞれ第１光導波路３１及び第２光導波路３２に沿って、互いに並行して（ここでは、ｙ軸方向に並行して）電気光学結晶基板１２上（ここでは、下面）に延在するように設けられている。そして、アンテナ２１は、電気光学結晶基板１２上（ここでは、下面）に設けられ、平面視において、第１共振型電極２２ａに直交する（ここでは、ｙ軸方向に延びる）ように接続される第１アンテナ素子２１ａ、及び、第２共振型電極２２ｂに直交するように接続される第２アンテナ素子２１ｂを有する。第１アンテナ素子２１ａと第２アンテナ素子２１ｂとは、電気光学結晶基板１２上（ここでは、下面）において、第１共振型電極２２ａ及び第２共振型電極２２ｂに対して、対称（線対称）の位置に設けられている。
Here, the first optical waveguide 31 and the second optical waveguide 32 are formed on the electro-optic crystal substrate 12 so as to extend in parallel to each other (here, parallel to the y-axis direction). The first resonance type electrode 22a and the second resonance type electrode 22b are electrically connected in parallel to each other along the first optical waveguide 31 and the second optical waveguide 32, respectively (in this case, in parallel to the y-axis direction). It is provided so as to extend on the optical crystal substrate 12 (here, the lower surface). The antenna 21 is provided on the electro-optic crystal substrate 12 (here, the lower surface) and connected so as to be orthogonal to the first resonance electrode 22a (here, extending in the y-axis direction) in plan view. It has the 1st antenna element 21a and the 2nd antenna element 21b connected so as to be orthogonal to the 2nd resonance type electrode 22b. The first antenna element 21a and the second antenna element 21b are symmetrical (line symmetric) with respect to the first resonant electrode 22a and the second resonant electrode 22b on the electro-optic crystal substrate 12 (here, the lower surface). It is provided in the position.
より具体的には、第１アンテナ素子２１ａが第１共振型電極２２ａと接続される接続点は、第１共振型電極２２ａにおける、第１アンテナ素子２１ａと第１共振型電極２２ａとがインピーダンス整合する複数の接続点のうち、第１共振型電極２２ａの端部（ここでは、第１ポート３０ａに近い端部）に最も近い接続点である。同様に、第２アンテナ素子２１ｂが第２共振型電極２２ｂと接続される接続点は、第２共振型電極２２ｂにおける、第２アンテナ素子２１ｂと第２共振型電極２２ｂとがインピーダンス整合する複数の接続点のうち、第２共振型電極２２ｂの端部（ここでは、第１ポート３０ａに近い端部）に最も近い接続点である。
More specifically, the connection point where the first antenna element 21a is connected to the first resonance electrode 22a is impedance matching between the first antenna element 21a and the first resonance electrode 22a in the first resonance electrode 22a. Among the plurality of connection points, the connection point closest to the end portion of the first resonance electrode 22a (here, the end portion close to the first port 30a). Similarly, the connection point at which the second antenna element 21b is connected to the second resonance electrode 22b is a plurality of points where the impedance of the second antenna element 21b and the second resonance electrode 22b in the second resonance electrode 22b is impedance-matched. Among the connection points, the connection point is closest to the end of the second resonance electrode 22b (here, the end close to the first port 30a).
なお、本実施の形態では、アンテナ２１、第１共振型電極２２ａ、第２共振型電極２２ｂ及び分極反転構造２３を一組の変調部とした場合に、第１光導波路３１及び第２光導波路３２に沿う複数の箇所のそれぞれに、４つの変調部（第１変調部２０ａ、第２変調部２０ｂ、第３変調部２０ｃ及び第４変調部２０ｄ）が、この並び順で、設けられている。ここで、第１変調部２０ａ及び第３変調部２０ｃを構成する分極反転構造２３は、同一の第１分極反転構造を有し、一方、第２変調部２０ｂ及び第４変調部２０ｄを構成する分極反転構造２３は、第１分極反転構造とは異なる、同一の第２分極反転構造を有する。
In the present embodiment, when the antenna 21, the first resonance electrode 22a, the second resonance electrode 22b, and the polarization inversion structure 23 are used as a pair of modulation units, the first optical waveguide 31 and the second optical waveguide are used. Each of a plurality of locations along 32 includes four modulation units (a first modulation unit 20a, a second modulation unit 20b, a third modulation unit 20c, and a fourth modulation unit 20d) in this arrangement order. . Here, the polarization inversion structures 23 constituting the first modulation unit 20a and the third modulation unit 20c have the same first polarization inversion structure, while constituting the second modulation unit 20b and the fourth modulation unit 20d. The domain-inverted structure 23 has the same second domain-inverted structure that is different from the first domain-inverted structure.
このような複数の変調部（アレイアンテナ電極と分極反転構造）により、第１光導波路３１及び第２光導波路３２を進行する光波は、複数の箇所に設けられた変調部によって変調を受けるので、一つの変調部によって変調を受ける場合に比べ、それぞれ、より歪みの少ないｃｏｓ変調及びｓｉｎ変調を受けて合波され、不要な側波帯がより抑圧された光ＳＳＢ変調信号が生成される。また、複数の変調部において同一の方向から入射する無線信号５に対して最も強い光ＳＳＢ変調信号が生成されるので、無線信号５の入射方向についての指向性が強くなる。
By such a plurality of modulation units (array antenna electrode and polarization inversion structure), the light waves traveling through the first optical waveguide 31 and the second optical waveguide 32 are modulated by the modulation units provided at a plurality of locations. Compared with the case where the modulation is performed by one modulation unit, the optical SSB modulation signal is generated by being subjected to cos modulation and sin modulation with less distortion, and by suppressing unnecessary sidebands. In addition, since the strongest optical SSB modulation signal is generated for the radio signal 5 incident from the same direction in the plurality of modulation units, the directivity in the incident direction of the radio signal 5 is increased.
また、光ＳＳＢ変調器１０は、図１の（ｂ）に示されるように、最上層から、電気光学結晶基板１２、バッファ層１４、接着剤１６及びベース基板１８で構成される積層構造を有する。
Further, as shown in FIG. 1B, the optical SSB modulator 10 has a laminated structure including an electro-optic crystal substrate 12, a buffer layer 14, an adhesive 16, and a base substrate 18 from the uppermost layer. .
電気光学結晶基板１２は、強誘電性の材料（例えば、ｚ－ｃｕｔ ＬｉＮｂＯ３又はｚ－ｃｕｔ ＬｉＴａＯ３）からなる厚さ約５０μｍの平板状の基板である。電気光学結晶基板１２の下面に、第１光導波路３１及び第２光導波路３２を有するマッハツェンダー型光導波路３０が形成されている。また、電気光学結晶基板１２には、第１共振型電極２２ａに対向する領域の一部に分極反転構造２３が形成され、第２共振型電極２２ｂに対向する領域の一部にも分極反転構造２３が形成されている。
The electro-optic crystal substrate 12 is a flat substrate having a thickness of about 50 μm made of a ferroelectric material (for example, z-cut LiNbO 3 or z-cut LiTaO 3 ). A Mach-Zehnder type optical waveguide 30 having a first optical waveguide 31 and a second optical waveguide 32 is formed on the lower surface of the electro-optic crystal substrate 12. In addition, the electro-optic crystal substrate 12 has a domain-inverted structure 23 formed in a part of the region facing the first resonant electrode 22a, and the domain-inverted structure is also formed in a part of the region opposed to the second resonant electrode 22b. 23 is formed.
バッファ層１４は、電気光学結晶基板１２の下面を覆う絶縁層であり、例えば、厚さ０．２μｍのＳｉＯ２からなる薄膜である。バッファ層１４の下面には、アンテナ２１、第１共振型電極２２ａ及び第２共振型電極２２ｂが設けられている。第１共振型電極２２ａ及び第２共振型電極２２ｂは、それぞれ、第１光導波路３１及び第２光導波路３２の直下に設けられる。本実施の形態では、第１共振型電極２２ａ及び第２共振型電極２２ｂは、それぞれ、断面視における端部の直上に第１光導波路３１及び第２光導波路３２が位置するように、バッファ層１４の下面に設けられている。
The buffer layer 14 is an insulating layer that covers the lower surface of the electro-optic crystal substrate 12 and is, for example, a thin film made of SiO 2 having a thickness of 0.2 μm. On the lower surface of the buffer layer 14, an antenna 21, a first resonance electrode 22a, and a second resonance electrode 22b are provided. The first resonance type electrode 22a and the second resonance type electrode 22b are provided directly below the first optical waveguide 31 and the second optical waveguide 32, respectively. In the present embodiment, the first resonance type electrode 22a and the second resonance type electrode 22b are respectively formed in the buffer layer so that the first optical waveguide 31 and the second optical waveguide 32 are located immediately above the end portions in a cross-sectional view. 14 is provided on the lower surface.
接着剤１６は、アンテナ２１、第１共振型電極２２ａ及び第２共振型電極２２ｂが設けられたバッファ層１４とベース基板１８とを接着する部材であり、例えば、紫外線硬化型樹脂からなる接着剤である。
The adhesive 16 is a member that bonds the buffer layer 14 provided with the antenna 21, the first resonance electrode 22a, and the second resonance electrode 22b to the base substrate 18, and is made of, for example, an ultraviolet curable resin. It is.
ベース基板１８は、光ＳＳＢ変調器１０の実効誘電率を減少させてアンテナ２１及び共振型電極２２の性能を向上させるため、並びに、アンテナ２１、第１共振型電極２２ａ及び第２共振型電極２２ｂが設けられたバッファ層１４が形成された電気光学結晶基板１２に外力が加わったときに割れてしまうことを防止するために補強する基板であり、例えば、底面にグランドパターンが施された、厚さ約２５０μｍのＳｉＯ２からなる基板である。
The base substrate 18 reduces the effective dielectric constant of the optical SSB modulator 10 to improve the performance of the antenna 21 and the resonant electrode 22, and the antenna 21, the first resonant electrode 22a, and the second resonant electrode 22b. Is a substrate that is reinforced to prevent cracking when an external force is applied to the electro-optic crystal substrate 12 on which the buffer layer 14 provided with is formed. For example, a thickness having a ground pattern on the bottom surface This is a substrate made of SiO 2 having a thickness of about 250 μm.
以上のように構成された本実施の形態における光ＳＳＢ変調器１０は、次の工程で、製造される。つまり、図１の（ｂ）に示される断面図を上下反転した状態で、下層（つまり、電気光学結晶基板１２）から上層に向けて、製造していく。
The optical SSB modulator 10 according to the present embodiment configured as described above is manufactured in the following steps. That is, manufacturing is performed from the lower layer (that is, the electro-optic crystal substrate 12) toward the upper layer in a state where the cross-sectional view shown in FIG.
まず、電気光学結晶基板１２を準備し、電気光学結晶基板１２上の所望の部分にパルス電圧を選択的に印加することにより、分極反転構造２３を形成する。次に、分極反転構造２３を施した電気光学結晶基板１２の表面に、安息香酸プロトン交換法によりマッハツェンダー型光導波路３０を形成する。第１光導波路３１及び第２光導波路３２は、例えば、幅約４μｍ、深さ約１．５μｍである。
First, the electro-optic crystal substrate 12 is prepared, and the polarization inversion structure 23 is formed by selectively applying a pulse voltage to a desired portion on the electro-optic crystal substrate 12. Next, the Mach-Zehnder type optical waveguide 30 is formed on the surface of the electro-optic crystal substrate 12 to which the domain-inverted structure 23 has been applied, by a benzoic acid proton exchange method. For example, the first optical waveguide 31 and the second optical waveguide 32 have a width of about 4 μm and a depth of about 1.5 μm.
次に、電気光学結晶基板１２の表面全域にＳｉＯ２からなるバッファ層１４を形成し、バッファ層１４の上に、フォトリソグラフィ技術によって、第１光導波路３１及び第２光導波路３２の直上の位置にそれぞれアルミニウム製の第１共振型電極２２ａ及び第２共振型電極２２ｂを作製するとともに、アルミニウム製のアンテナ２１を作成する。アンテナ２１及び共振型電極２２の大きさ及びレイアウト例は、図２に示される通りであり、本実施の形態では、５９ＧＨｚ（ミリ波）の無線信号５を対象周波数として共振する値に設計されている。つまり、第１共振型電極２２ａ及び第２共振型電極２２ｂは、内側間の距離が３０μｍ、外側間の距離が９０μｍとなるように、間隔をおいて互いに並行して延在する長さが２．４６０ｍｍ（電気長が２波長分）の直線部で構成される。第１アンテナ素子２１ａ及び第２アンテナ素子２１ｂは、長さが５４６μｍ（電気長が半波長）の辺で囲まれた正方形の放射板と、幅が５０μｍの配線パターンとで構成されるパッチアンテナとして形成され、それぞれ、第１共振型電極２２ａ及び第２共振型電極２２ｂの長手方向（ｙ軸方向）の中心から１．１０ｍｍずれた位置で第１共振型電極２２ａ及び第２共振型電極２２ｂに接続される。また、４つの変調部（第１変調部２０ａ、第２変調部２０ｂ、第３変調部２０ｃ及び第４変調部２０ｄ）は、３．５０ｍｍ間隔で配置される。なお、これらのアンテナ２１及び共振型電極２２の大きさ及びレイアウト、並びに、４つの変調部の間隔は、下層（バッファ層１４、電気光学結晶基板１２及びベース基板１８）の誘電率等から定まる実効誘電率を考慮し、５９ＧＨｚの無線信号５に共振する値になっている。共振の詳細は、図５Ａ～図８を用いて後述する。
Next, a buffer layer 14 made of SiO 2 is formed over the entire surface of the electro-optic crystal substrate 12, and a position immediately above the first optical waveguide 31 and the second optical waveguide 32 by photolithography technology on the buffer layer 14. First, the first resonance electrode 22a and the second resonance electrode 22b made of aluminum are prepared, and the antenna 21 made of aluminum is made. The sizes and layout examples of the antenna 21 and the resonant electrode 22 are as shown in FIG. 2, and in this embodiment, the antenna 21 and the resonant electrode 22 are designed to resonate with a radio signal 5 of 59 GHz (millimeter wave) as a target frequency. Yes. That is, the first resonance type electrode 22a and the second resonance type electrode 22b have a length of 2 extending in parallel with each other so that the distance between the inner sides is 30 μm and the distance between the outer sides is 90 μm. 460 mm (electric length is 2 wavelengths). The first antenna element 21a and the second antenna element 21b are patch antennas composed of a square radiating plate surrounded by a side having a length of 546 μm (electrical length is a half wavelength) and a wiring pattern having a width of 50 μm. Formed on the first resonance electrode 22a and the second resonance electrode 22b at positions shifted by 1.10 mm from the center in the longitudinal direction (y-axis direction) of the first resonance electrode 22a and the second resonance electrode 22b, respectively. Connected. The four modulation units (first modulation unit 20a, second modulation unit 20b, third modulation unit 20c, and fourth modulation unit 20d) are arranged at an interval of 3.50 mm. The size and layout of the antenna 21 and the resonant electrode 22 and the spacing between the four modulation units are determined by the dielectric constants of the lower layers (buffer layer 14, electro-optic crystal substrate 12 and base substrate 18). In consideration of the dielectric constant, the value resonates with the 59 GHz radio signal 5. Details of the resonance will be described later with reference to FIGS. 5A to 8.
最後に、アンテナ２１、第１共振型電極２２ａ及び第２共振型電極２２ｂが形成されたバッファ層の表面に接着剤１６を塗布し、そこに、底面にグランドパターンが施されたベース基板１８を、グランドパターンが施されていない面が接着されるように、貼り合わせる。
Finally, the adhesive 16 is applied to the surface of the buffer layer on which the antenna 21, the first resonance type electrode 22a, and the second resonance type electrode 22b are formed, and the base substrate 18 having a ground pattern on the bottom surface is applied thereto. Then, bonding is performed so that the surface on which the ground pattern is not applied is adhered.
このようにして、本実施の形態における光ＳＳＢ変調器１０が製造される。
In this way, the optical SSB modulator 10 according to the present embodiment is manufactured.
次に、以上のようにして製造された本実施の形態における光ＳＳＢ変調器１０の動作原理及び特徴的な構成について説明する。
Next, the operation principle and characteristic configuration of the optical SSB modulator 10 according to the present embodiment manufactured as described above will be described.
図３は、本実施の形態における光ＳＳＢ変調器１０の動作原理を説明する図である。本図には、マッハツェンダー型光導波路３０を進行する光波のスペクトル４１～４４も併せて図示されている。なお、スペクトル４１～４４を表す軸において、Ｒｅが付された軸は実数成分を示し、Ｉｍが付された軸は虚数成分を示し、ｆが付された軸は周波数を示す。
FIG. 3 is a diagram for explaining the operation principle of the optical SSB modulator 10 in the present embodiment. In this figure, spectra 41 to 44 of light waves traveling through the Mach-Zehnder type optical waveguide 30 are also shown. Of the axes representing the spectra 41 to 44, the axis with Re indicates a real component, the axis with Im indicates an imaginary component, and the axis with f indicates a frequency.
マッハツェンダー型光導波路３０の第１ポート３０ａから入射された光波は、分波されて第１光導波路３１及び第２光導波路３２のそれぞれを進行する。
The light wave incident from the first port 30a of the Mach-Zehnder type optical waveguide 30 is demultiplexed and travels through the first optical waveguide 31 and the second optical waveguide 32, respectively.
第１光導波路３１及び第２光導波路３２のそれぞれを進行する光波は、第１変調部２０ａ～第４変調部２０ｄにおいて、互いに位相がπ／２ずれたタイミングで位相変化量が最大となるように変調を受ける。つまり、第１光導波路３１を進行する光波は、第１変調部２０ａ～第４変調部２０ｄにおいて、上方から入射した無線信号５がアンテナ２１で受信されて第１共振型電極２２ａで生じた定在波による変調電界及び第１共振型電極２２ａに対向して設けられた分極反転構造２３により、ｃｏｓ変調を受け、スペクトル４１で示される信号成分をもつ光波となった後、湾曲部３１ａでπ／２の位相分だけ遅延され、その結果、スペクトル４２で示される信号成分をもつ光波となる。一方、第２光導波路３２を進行する光波は、第１変調部２０ａ～第４変調部２０ｄにおいて、上方から入射した無線信号５がアンテナ２１で受信されて第２共振型電極２２ｂで生じた定在波による変調電界及び第２共振型電極２２ｂに対向して設けられた分極反転構造２３により、ｓｉｎ変調を受け、スペクトル４３で示される信号成分をもつ光波となる。
The light wave traveling through each of the first optical waveguide 31 and the second optical waveguide 32 has the maximum amount of phase change at the timing when the phases are shifted by π / 2 in the first modulation unit 20a to the fourth modulation unit 20d. Received modulation. That is, the light wave traveling through the first optical waveguide 31 is a constant wave generated by the first resonance type electrode 22a when the first modulation unit 20a to the fourth modulation unit 20d receive the radio signal 5 incident from above by the antenna 21. The modulated electric field due to the standing wave and the polarization reversal structure 23 provided opposite to the first resonance type electrode 22a are subjected to cos modulation to become a light wave having a signal component indicated by the spectrum 41, and then π at the bending portion 31a. Is delayed by a phase of / 2, resulting in a light wave having a signal component indicated by spectrum 42. On the other hand, the light wave traveling through the second optical waveguide 32 is generated by the first resonance unit 20a to the fourth modulation unit 20d when the radio signal 5 incident from above is received by the antenna 21 and generated by the second resonance electrode 22b. The modulated electric field due to the standing wave and the polarization inversion structure 23 provided facing the second resonance electrode 22 b are subjected to sin modulation and become a light wave having a signal component indicated by the spectrum 43.
その後、第１光導波路３１を進行してきた、スペクトル４２で示される信号成分をもつ光波と、第２光導波路３２を進行してきた、スペクトル４３で示される信号成分をもつ光波とは、第１光導波路３１及び第２光導波路３２の合流箇所で合成され、その結果、片側の側波帯がキャンセルされ、スペクトル４４で示される信号成分をもつ光ＳＳＢ変調信号となって、第２ポート３０ｂから出力される。
Thereafter, the light wave having the signal component indicated by the spectrum 42 traveling through the first optical waveguide 31 and the light wave having the signal component represented by the spectrum 43 traveling through the second optical waveguide 32 are the first light guide. As a result, the sideband on one side is canceled and an optical SSB modulation signal having a signal component indicated by the spectrum 44 is output from the second port 30b. Is done.
図４は、本実施の形態における光ＳＳＢ変調器１０の第１変調部２０ａ～第４変調部２０ｄのそれぞれを構成するアンテナ電極（アンテナ２１と共振型電極２２とを合わせたもの）の動作を示す図である。ここでは、４つの変調部（第１変調部２０ａ～第４変調部２０ｄ）のうちの一つの変調部を構成するアンテナ電極の動作が示されている。また、無線信号５は、上方から（Ｚ軸の負方向に進行して）光ＳＳＢ変調器１０に入射している。
FIG. 4 shows the operation of the antenna electrodes (a combination of the antenna 21 and the resonant electrode 22) constituting each of the first modulation unit 20a to the fourth modulation unit 20d of the optical SSB modulator 10 in the present embodiment. FIG. Here, the operation of the antenna electrode constituting one of the four modulation units (the first modulation unit 20a to the fourth modulation unit 20d) is shown. The radio signal 5 is incident on the optical SSB modulator 10 from above (traveling in the negative direction of the Z axis).
この場合、第１アンテナ素子２１ａ及び第２アンテナ素子２１ｂには、図４において、横軸をｘ軸、縦軸を電圧（Ｖ）とするグラフに示されるように、同相の電圧が誘起され、その結果、第１アンテナ素子２１ａから第２アンテナ素子２１ｂに向かう矢印で示されるように、同一方向（ｘ軸方向）に電流が流れる。これにより、第１共振型電極２２ａ及び第２共振型電極２２ｂに対して、奇対称に給電が行われ、奇モードで選択的に励起される。
In this case, an in-phase voltage is induced in the first antenna element 21a and the second antenna element 21b as shown in the graph in FIG. 4 where the horizontal axis is the x-axis and the vertical axis is the voltage (V), As a result, current flows in the same direction (x-axis direction) as indicated by an arrow from the first antenna element 21a to the second antenna element 21b. As a result, the first resonance type electrode 22a and the second resonance type electrode 22b are fed with odd symmetry and selectively excited in the odd mode.
図５Ａ～図５Ｄは、本実施の形態における光ＳＳＢ変調器１０の変調部（第１変調部２０ａ～第４変調部２０ｄ）を構成する分極反転構造２３によるｃｏｓ変調及びｓｉｎ変調の原理を説明するための図である。
5A to 5D illustrate the principles of cos modulation and sin modulation by the polarization inversion structure 23 that constitutes the modulation units (first modulation unit 20a to fourth modulation unit 20d) of the optical SSB modulator 10 according to the present embodiment. It is a figure for doing.
図５Ａは、時刻ｔ＝ｔ０において、第１変調部２０ａの第１共振型電極２２ａの中心（ｙ軸方向の中心）に位置する光波が第１共振型電極２２ａ上に立つ２波長分の定在波による変調電界を見る電界分布を説明する図である。図５Ａの（ａ）は、電気光学結晶基板１２に分極反転構造２３が設けられていない場合に、時刻ｔ＝ｔ０において第１変調部２０ａの第１共振型電極２２ａの中心に位置する光波が見る変調電界の分布を示す。本実施の形態では、図５Ａの（ｂ）に示されるように、第１変調部２０ａの第１共振型電極２２ａ上に立つ２波長分の定在波のうちの先の一波長分（ｙ軸上の負の領域）に対向する電気光学結晶基板１２中の領域に分極反転構造２３が設けられている。よって、第１共振型電極２２ａ上に立つ２波長分の定在波のうちの先の一波長分の位相が反転され、時刻ｔ＝ｔ０において第１変調部２０ａの第１共振型電極２２ａの中心に位置する光波が見る変調電界は、図５Ａの（ｃ）に示されるように、変調の極性が揃った分布となる。これによって、第１光導波路３１を進行する光波が進行する際に逆の符号をもつ変調電界中を進行することによって累積的な変調成分がキャンセルされてしまう走行時間効果が補償され、第１光導波路３１を進行する光波は、累積的な変調作用を受ける。
FIG. 5A shows the determination of two wavelengths at which the light wave positioned at the center (center in the y-axis direction) of the first resonance electrode 22a of the first modulator 20a stands on the first resonance electrode 22a at time t = t0. It is a figure explaining the electric field distribution which sees the modulation electric field by a standing wave. FIG. 5A shows that when the electro-optic crystal substrate 12 is not provided with the domain-inverted structure 23, the light wave positioned at the center of the first resonance electrode 22a of the first modulation unit 20a at time t = t0. The distribution of the modulation electric field to be seen is shown. In the present embodiment, as shown in FIG. 5A (b), one wavelength (y) of the standing wave of two wavelengths standing on the first resonance type electrode 22a of the first modulation unit 20a. A domain-inverted structure 23 is provided in a region in the electro-optic crystal substrate 12 opposite to the negative region on the axis. Therefore, the phase of the previous one of the standing waves of two wavelengths standing on the first resonance type electrode 22a is inverted, and at time t = t0, the first resonance type electrode 22a of the first modulation unit 20a The modulation electric field seen by the light wave located at the center has a distribution in which the polarity of the modulation is uniform, as shown in FIG. 5A (c). As a result, the traveling time effect that the cumulative modulation component is canceled by traveling in the modulation electric field having the opposite sign when the light wave traveling in the first optical waveguide 31 travels is compensated, and the first light The light wave traveling through the waveguide 31 undergoes a cumulative modulation action.
図５Ｂは、時刻ｔ＝ｔ０＋Ｔ／４において、第１変調部２０ａの第２共振型電極２２ｂの中心（ｙ軸方向の中心）に位置する光波が第２共振型電極２２ｂ上に立つ２波長分の定在波による変調電界を見る電界分布を説明する図である。図５Ｂの（ａ）は、電気光学結晶基板１２に分極反転構造２３が設けられていない場合に、時刻ｔ＝ｔ０＋Ｔ／４において第１変調部２０ａの第２共振型電極２２ｂの中心に位置する光波が見る変調電界の分布を示す。本実施の形態では、図５Ｂの（ｂ）に示されるように、第１変調部２０ａの第２共振型電極２２ｂ上に立つ２波長分の定在波のうちの最初の１／４波長及び最後の１／４波長に対向する電気光学結晶基板１２中の領域に分極反転構造２３が設けられている。よって、第２共振型電極２２ｂ上に立つ２波長分の定在波のうちの最初の１／４波長及び最後の１／４波長の位相が反転され、時刻ｔ０＋Ｔ／４において第１変調部２０ａの第２共振型電極２２ｂの中心に位置する光波が見る変調電界は、図５Ｂの（ｃ）に示されるように、変調の極性が揃った分布となる。これによって、第２光導波路３２を進行する光波は、走行時間効果が補償され、累積的な変調作用を受ける。
FIG. 5B shows two wavelengths corresponding to the light wave positioned at the center (center in the y-axis direction) of the second resonance electrode 22b of the first modulator 20a on the second resonance electrode 22b at time t = t0 + T / 4. It is a figure explaining the electric field distribution which sees the modulation electric field by standing wave of. FIG. 5B (a) is located at the center of the second resonance type electrode 22b of the first modulation unit 20a at time t = t0 + T / 4 when the domain-inverted structure 23 is not provided on the electro-optic crystal substrate 12. The distribution of the modulated electric field seen by the light wave is shown. In the present embodiment, as shown in FIG. 5B (b), the first quarter wavelength of the standing waves for two wavelengths standing on the second resonance electrode 22b of the first modulation section 20a and A domain-inverted structure 23 is provided in a region in the electro-optic crystal substrate 12 facing the last quarter wavelength. Therefore, the phases of the first quarter wavelength and the last quarter wavelength of the standing waves for two wavelengths standing on the second resonance electrode 22b are inverted, and the first modulation unit 20a is performed at time t0 + T / 4. The modulation electric field seen by the light wave located at the center of the second resonance electrode 22b has a distribution in which the polarity of the modulation is uniform, as shown in FIG. 5B (c). Thereby, the light wave traveling in the second optical waveguide 32 is compensated for the travel time effect and is subjected to a cumulative modulation action.
図５Ｃは、時刻ｔ＝ｔ０において、第２変調部２０ｂの第１共振型電極２２ａの中心（ｙ軸方向の中心）に位置する光波が第１共振型電極２２ａ上に立つ２波長分の定在波による変調電界を見る電界分布を説明する図である。図５Ｃの（ａ）は、電気光学結晶基板１２に分極反転構造２３が設けられていない場合に、時刻ｔ＝ｔ０において第２変調部２０ｂの第１共振型電極２２ａの中心に位置する光波が見る変調電界の分布を示す。本実施の形態では、図５Ｃの（ｂ）に示されるように、第２変調部２０ｂの第１共振型電極２２ａ上に立つ２波長分の定在波のうちの後の一波長分（ｙ軸上の正の領域）に対向する電気光学結晶基板１２中の領域に分極反転構造２３が設けられている。よって、第１共振型電極２２ａ上に立つ２波長分の定在波のうちの後の一波長分の位相が反転され、時刻ｔ＝ｔ０において第２変調部２０ｂの第１共振型電極２２ａの中心に位置する光波が見る変調電界は、図５Ｃの（ｃ）に示されるように、変調の極性が揃った分布となる。これによって、第１光導波路３１を進行する光波は、走行時間効果が補償され、累積的な変調作用を受ける。
In FIG. 5C, at time t = t0, the light wave positioned at the center of the first resonance type electrode 22a (the center in the y-axis direction) of the second modulation unit 20b is determined for two wavelengths on the first resonance type electrode 22a. It is a figure explaining the electric field distribution which sees the modulation electric field by a standing wave. FIG. 5C shows a case where a light wave located at the center of the first resonance type electrode 22a of the second modulation unit 20b at time t = t0 when the polarization inverting structure 23 is not provided on the electro-optic crystal substrate 12. The distribution of the modulation electric field to be seen is shown. In the present embodiment, as shown in (b) of FIG. 5C, one wavelength (y) after the standing wave of two wavelengths standing on the first resonance type electrode 22a of the second modulation unit 20b. A domain-inverted structure 23 is provided in a region in the electro-optic crystal substrate 12 facing the positive region on the axis. Therefore, the phase of the subsequent one of the two standing waves standing on the first resonance electrode 22a is inverted, and the time of the first resonance electrode 22a of the second modulation unit 20b at the time t = t0 is reversed. The modulation electric field seen by the light wave located at the center has a distribution in which the polarity of the modulation is uniform, as shown in FIG. 5C (c). Thus, the light wave traveling through the first optical waveguide 31 is compensated for the travel time effect and is subjected to a cumulative modulation action.
図５Ｄは、時刻ｔ＝ｔ０＋Ｔ／４において、第２変調部２０ｂの第２共振型電極２２ｂの中心（ｙ軸方向の中心）に位置する光波が第２共振型電極２２ｂ上に立つ２波長分の定在波による変調電界を見る電界分布を説明する図である。図５Ｄの（ａ）は、電気光学結晶基板１２に分極反転構造２３が設けられていない場合に、時刻ｔ＝ｔ０＋Ｔ／４において第２変調部２０ｂの第２共振型電極２２ｂの中心に位置する光波が見る変調電界の分布を示す。本実施の形態では、図５Ｄの（ｂ）に示されるように、第２変調部２０ｂの第２共振型電極２２ｂ上に立つ２波長分の定在波のうちの２つ目の１／４波長及び３つ目の１／４波長に対向する電気光学結晶基板１２中の領域に分極反転構造２３が設けられている。よって、第２共振型電極２２ｂ上に立つ２波長分の定在波のうちの２つ目の１／４波長及び３つ目の１／４波長の位相が反転され、時刻ｔ０＋Ｔ／４において第２変調部２０ｂの第２共振型電極２２ｂの中心に位置する光波が見る変調電界は、図５Ｄの（ｃ）に示されるように、変調の極性が揃った分布となる。これによって、第２光導波路３２を進行する光波は、走行時間効果が補償され、累積的な変調作用を受ける。
FIG. 5D shows two wavelengths for a light wave positioned at the center (the center in the y-axis direction) of the second resonance electrode 22b of the second modulator 20b on the second resonance electrode 22b at time t = t0 + T / 4. It is a figure explaining the electric field distribution which sees the modulation electric field by standing wave of. FIG. 5D shows a case where the electro-optic crystal substrate 12 is not provided with the domain-inverted structure 23 and is located at the center of the second resonance type electrode 22b of the second modulation unit 20b at time t = t0 + T / 4. The distribution of the modulated electric field seen by the light wave is shown. In the present embodiment, as shown in FIG. 5D (b), the second quarter of the standing wave for two wavelengths standing on the second resonance electrode 22b of the second modulation unit 20b. A domain-inverted structure 23 is provided in a region in the electro-optic crystal substrate 12 facing the wavelength and the third quarter wavelength. Therefore, the phase of the second quarter wavelength and the third quarter wavelength of the standing wave for two wavelengths standing on the second resonance electrode 22b is inverted, and the second quarter wavelength and the third quarter wavelength are inverted at time t0 + T / 4. The modulation electric field seen by the light wave located at the center of the second resonance electrode 22b of the two modulation section 20b has a distribution in which the polarity of the modulation is uniform, as shown in FIG. 5D (c). Thereby, the light wave traveling in the second optical waveguide 32 is compensated for the travel time effect and is subjected to a cumulative modulation action.
なお、第３変調部２０ｃの分極反転構造２３は、第１変調部２０ａの分極反転構造２３と同じ構造であり、第４変調部２０ｄの分極反転構造２３は、第２変調部２０ｂの分極反転構造２３と同じ構造である。
The polarization inversion structure 23 of the third modulation unit 20c is the same structure as the polarization inversion structure 23 of the first modulation unit 20a, and the polarization inversion structure 23 of the fourth modulation unit 20d is the polarization inversion of the second modulation unit 20b. The structure is the same as the structure 23.
このように、本実施の形態における光ＳＳＢ変調器１０の４つの変調部（第１変調部２０ａ～第４変調部２０ｄ）では、１／４周期ずれたタイミングで位相変化量が最大となるように、第１光導波路３１及び第２光導波路３２に対して分極反転が施されているので、第１光導波路３１及び第２光導波路３２を進行する光波に対して、それぞれ、ｃｏｓ変調及びｓｉｎ変調が等価的に与えられる。
As described above, in the four modulation units (first modulation unit 20a to fourth modulation unit 20d) of the optical SSB modulator 10 according to the present embodiment, the phase change amount is maximized at a timing shifted by a quarter cycle. In addition, since polarization inversion is applied to the first optical waveguide 31 and the second optical waveguide 32, cos modulation and sin are applied to the light waves traveling through the first optical waveguide 31 and the second optical waveguide 32, respectively. Modulation is given equivalently.
図６は、本実施の形態における光ＳＳＢ変調器１０のアンテナ２１の共振特性を示す図である。ここでは、電磁界シミュレータ（ＨＦＳＳ（Ansoft Corporationの登録商標））を用いて、上述したサイズのアンテナ２１の片側の素子（第１アンテナ素子２１ａ又は第２アンテナ素子２１ｂ）を対象とした共振特性（反射係数）を解析した結果が示されている。横軸は周波数であり、縦軸は解析で得られた反射係数Ｓ１１である。本図から分かるように、上述したサイズのアンテナ２１は、５９ＧＨｚで共振する。
FIG. 6 is a diagram illustrating the resonance characteristics of the antenna 21 of the optical SSB modulator 10 according to the present embodiment. Here, using an electromagnetic field simulator (HFSS (registered trademark of Ansoft Corporation)), resonance characteristics (first antenna element 21a or second antenna element 21b) on one side of the antenna 21 having the above-described size ( The result of analyzing the reflection coefficient) is shown. The horizontal axis is frequency and the vertical axis represents the reflection coefficient S 11 obtained by the analysis. As can be seen from the figure, the antenna 21 having the above-described size resonates at 59 GHz.
図７は、本実施の形態における光ＳＳＢ変調器１０の共振型電極２２の給電位置を変化させたときの給電点での反射係数を説明する図である。図７の（ａ）は、給電位置を説明する図である。図７の（ｂ）は、上記電磁界シミュレータを用いて、給電位置を変えたときの給電点における反射係数を解析した結果を示す図である。横軸は周波数であり、縦軸は解析で得られた反射係数Ｓ１１である。
FIG. 7 is a diagram for explaining the reflection coefficient at the feeding point when the feeding position of the resonant electrode 22 of the optical SSB modulator 10 in the present embodiment is changed. (A) of FIG. 7 is a figure explaining an electric power feeding position. (B) of FIG. 7 is a figure which shows the result of having analyzed the reflection coefficient in the feeding point when changing a feeding position using the said electromagnetic field simulator. The horizontal axis is frequency and the vertical axis represents the reflection coefficient S 11 obtained by the analysis.
本解析では、図７の（ａ）に示されるように、第１共振型電極２２ａ及び第２共振型電極２２ｂの給電位置として、長手方向（ｙ軸方向）の中心から左側（ｙ軸の負方向）にずれた距離Δｙを変えている。図７の（ｂ）に示されるように、Δｙ＝１．１０ｍｍのときに、反射係数Ｓ１１が最小となった。このΔｙ＝１．１０ｍｍで示される給電点は、アンテナ２１と共振型電極２２とがインピーダンス整合する（本実施の形態では、共振型電極２２の入力インピーダンスが５０Ωとなる）複数の接続点のうち、共振型電極２２の左側の端部（第１ポート３０ａに近い端部）に最も近い接続点である。なお、第１共振型電極２２ａ及び第２共振型電極２２ｂの給電位置として、長手方向の中心から右側（ｙ軸の正方向）にずれた距離（－Δｙ）を変えた場合についても、同様の結果が得られる。つまり、上記複数の接続点のうち、共振型電極２２の右側の端部（第２ポート３０ｂに近い端部）に最も近い接続点を給電位置とした場合にも、反射係数Ｓ１１が最小となる。
In this analysis, as shown in FIG. 7A, the feeding position of the first resonance type electrode 22a and the second resonance type electrode 22b is set to the left side (y axis negative) from the center in the longitudinal direction (y axis direction). The distance Δy shifted in the direction) is changed. As shown in FIG. 7 (b), when [Delta] y = 1.10 mm, the reflection coefficient S 11 is minimized. The feeding point indicated by Δy = 1.10 mm is the impedance matching between the antenna 21 and the resonant electrode 22 (in this embodiment, the input impedance of the resonant electrode 22 is 50Ω). The connection point closest to the left end of the resonance electrode 22 (the end close to the first port 30a). The same applies to the case where the distance (−Δy) shifted from the center in the longitudinal direction to the right side (positive direction of the y-axis) is changed as the feeding position of the first resonance type electrode 22a and the second resonance type electrode 22b. Results are obtained. That is, the one of the plurality of connection points, right end portion even when the nearest connection point (end closer to the second port 30b) and the feeding position, the reflection coefficient S 11 of the resonant electrode 22 is minimized Become.
この解析結果から、第１アンテナ素子２１ａ及び第２アンテナ素子２１ｂはそれぞれ第１共振型電極２２ａ及び第２共振型電極２２ｂとインピーダンス整合する複数の接続点のうち第１共振型電極２２ａ及び第２共振型電極２２ｂの端部に最も近い接続点で接続されて整合されるので、第１共振型電極２２ａ及び第２共振型電極２２ｂで不要な共振が生じることが抑制されるともに第１共振型電極２２ａ及び第２共振型電極２２ｂで強い変調電界が生じ、出力される光ＳＳＢ変調信号に不要な側波帯が残留してしまうことが抑制される。
From the analysis results, the first antenna element 21a and the second antenna element 21b are connected to the first resonance electrode 22a and the second resonance element 22b, respectively, out of a plurality of connection points that are impedance matched with the first resonance electrode 22a and the second resonance electrode 22b. Since it is connected and matched at the connection point closest to the end of the resonance type electrode 22b, unnecessary resonance is suppressed from occurring in the first resonance type electrode 22a and the second resonance type electrode 22b, and the first resonance type is obtained. A strong modulation electric field is generated in the electrode 22a and the second resonance electrode 22b, and unnecessary sidebands are prevented from remaining in the output optical SSB modulation signal.
図８は、本実施の形態における光ＳＳＢ変調器１０のアンテナ電極（アンテナ２１と共振型電極２２とを合わせたもの）の電界についての解析結果を示す図である。横軸は共振型電極２２における位置を示し、縦軸は、その位置における共振型電極２２での電界の増倍率、つまり、アンテナ２１に誘起されたｘ軸方向における入射電界Ｅ０に対する共振型電極２２で生じた定在波によるｚ軸方向の電界Ｅｚの比（Ｅｚ／Ｅ０）を示している。
FIG. 8 is a diagram illustrating an analysis result of the electric field of the antenna electrode (a combination of the antenna 21 and the resonance electrode 22) of the optical SSB modulator 10 in the present embodiment. The horizontal axis indicates the position at the resonant electrode 22, and the vertical axis indicates the multiplication factor of the electric field at the resonant electrode 22 at that position, that is, the resonant electrode with respect to the incident electric field E 0 in the x-axis direction induced by the antenna 21. 22 shows the ratio (E z / E 0 ) of the electric field E z in the z-axis direction due to the standing wave generated at 22.
本図から分かるように、入射電界の約１３０倍もの極めて強い電界で、かつ、ｃｏｓ波形及びｓｉｎ波形に近い歪の少ない電界が共振型電極２２で生じている。このように、本実施の形態における光ＳＳＢ変調器１０のアンテナ電極の構造により、第１共振型電極及び第２共振型電極の一方だけに対して変調信号を供給する従来技術と異なり、第１共振型電極２２ａ及び第２共振型電極２２ｂの両方に対して変調信号が供給されて第１共振型電極２２ａ及び第２共振型電極２２ｂにおいて定在波共振が生じ、極めて強くて、かつ、歪の少ない変調電界が発生するので、第１光導波路３１及び第２光導波路３２を進行する光波に対して歪の少ないｃｏｓ変調及びｓｉｎ変調が施され、従来技術よりも不要な側波帯が抑圧された光ＳＳＢ変調信号が生成される。
As can be seen from the figure, an electric field having an extremely strong electric field of about 130 times the incident electric field and a small distortion close to the cos waveform and the sin waveform is generated in the resonant electrode 22. As described above, the structure of the antenna electrode of the optical SSB modulator 10 in the present embodiment differs from the prior art in which the modulation signal is supplied to only one of the first resonance type electrode and the second resonance type electrode. A modulation signal is supplied to both the resonance type electrode 22a and the second resonance type electrode 22b, and standing wave resonance occurs in the first resonance type electrode 22a and the second resonance type electrode 22b. Therefore, cos modulation and sin modulation with less distortion are applied to the light waves traveling through the first optical waveguide 31 and the second optical waveguide 32, and unnecessary sidebands are suppressed compared to the prior art. An optical SSB modulated signal is generated.
図９は、本実施の形態における光ＳＳＢ変調器１０の動作を確認するための実験装置の構成を示すブロック図である。
FIG. 9 is a block diagram showing a configuration of an experimental apparatus for confirming the operation of the optical SSB modulator 10 in the present embodiment.
光ＳＳＢ変調器１０の第１ポート３０ａには、搬送波として、レーザー素子５０から出射された１．５～１．６μｍの波長のレーザーが、レンズ５１で集光された後に、入射される。
A laser having a wavelength of 1.5 to 1.6 μm emitted from the laser element 50 as a carrier wave is incident on the first port 30a of the optical SSB modulator 10 after being condensed by the lens 51.
また、光ＳＳＢ変調器１０のアンテナに向けて、変調信号として、発振器６０から出力された約６０ＧＨｚの無線信号が増幅器６１で増幅された後に、ホーンアンテナ６２を介して、供給される。
Further, a radio signal of about 60 GHz output from the oscillator 60 is amplified by the amplifier 61 as a modulation signal toward the antenna of the optical SSB modulator 10 and then supplied through the horn antenna 62.
光ＳＳＢ変調器１０の第２ポート３０ｂから出力される光波（光ＳＳＢ変調信号）は、レンズ５２で集光された後に、光ファイバー５３を介して光スペクトラムアナライザ５５に入力され、周波数分析される。
The light wave (optical SSB modulation signal) output from the second port 30 b of the optical SSB modulator 10 is collected by the lens 52 and then input to the optical spectrum analyzer 55 via the optical fiber 53 and subjected to frequency analysis.
図１０は、図９に示される実験装置による実験結果を示す図である。ここでは、図９における光スペクトラムアナライザ５５で得られたスペクトラムの例を示す図である。
FIG. 10 is a diagram showing an experimental result by the experimental apparatus shown in FIG. Here, it is a figure which shows the example of the spectrum obtained with the optical spectrum analyzer 55 in FIG.
図１０の（ａ）は、光波（つまり、搬送波）として１５３４ｎｍの波長のレーザーを用いてＬＳＢ（下側側波帯）を抑圧した光ＳＳＢ変調信号を生成した場合におけるスペクトルが示されている。ＵＳＢ（上側側波帯）については、搬送波のピークよりも４９．２８ｄＢ低い値でピークが観測され、一方、ＬＳＢ（下側側波帯）については、ほとんど観測されておらず、強く抑圧されていることが分かる。
(A) of FIG. 10 shows a spectrum when an optical SSB modulation signal in which LSB (lower sideband) is suppressed is generated using a laser having a wavelength of 1534 nm as a light wave (that is, a carrier wave). For USB (upper sideband), a peak is observed at a value 49.28 dB lower than the peak of the carrier wave, while LSB (lower sideband) is hardly observed and strongly suppressed. I understand that.
図１０の（ｂ）は、光波（つまり、搬送波）として１５６５．５ｎｍの波長のレーザーが用いてＵＳＢ（上側側波帯）を抑圧した光ＳＳＢ変調信号を生成した場合におけるスペクトルが示されている。ＬＳＢ（下側側波帯）については、搬送波のピークよりも４９．５０ｄＢ低い値でピークが観測され、一方、ＵＳＢ（上側側波帯）については、ほとんど観測されておらず、強く抑圧されていることが分かる。
FIG. 10B shows a spectrum when an optical SSB modulation signal in which USB (upper sideband) is suppressed is generated by using a laser having a wavelength of 1565.5 nm as a light wave (that is, a carrier wave). . As for the LSB (lower sideband), a peak is observed at a value 49.50 dB lower than the peak of the carrier wave, while the USB (upper sideband) is hardly observed and strongly suppressed. I understand that.
図１１は、図１０におけるＵＳＢ（上側側波帯）を復調して得られた実験結果としての無線信号の周波数依存性（丸印のプロット）を示す図である。
FIG. 11 is a diagram showing the frequency dependence (circled plot) of the radio signal as an experimental result obtained by demodulating the USB (upper sideband) in FIG.
以上の実験結果から分かるように、本実施の形態における光ＳＳＢ変調器１０によれば、無線信号によって光波が変調され、不要な側波帯が抑圧された光ＳＳＢ変調信号が生成される。
As can be seen from the above experimental results, according to the optical SSB modulator 10 in the present embodiment, the optical wave is modulated by the radio signal, and an optical SSB modulated signal in which unnecessary sidebands are suppressed is generated.
以上、本発明の光ＳＳＢ変調器について、実施の形態に基づいて説明したが、本発明は、この実施の形態に限定されるものではない。本発明の主旨を逸脱しない限り、当業者が思いつく各種変形を本実施の形態に施したものや、実施の形態における一部の構成要素を組み合わせて構築される別の形態も、本発明の範囲内に含まれる。
The optical SSB modulator of the present invention has been described based on the embodiment, but the present invention is not limited to this embodiment. Without departing from the gist of the present invention, various modifications conceived by those skilled in the art have been made in the present embodiment, and other forms constructed by combining some components in the embodiment are also within the scope of the present invention. Contained within.
例えば、上記実施の形態では、光ＳＳＢ変調器１０に、４つの変調部（第１変調部２０ａ、第２変調部２０ｂ、第３変調部２０ｃ及び第４変調部２０ｄ）が設けられたが、１つの変調部だけが設けられてもよい。１つの変調部だけが設けられる場合であっても、上述した特徴的な構造を有するアンテナ電極によって、第１共振型電極２２ａ及び第２共振型電極２２ｂの両方に対して変調信号が供給されて第１共振型電極２２ａ及び第２共振型電極２２ｂにおいて定在波共振が生じ、極めて強くて、かつ、歪の少ない変調電界が発生するので、第１光導波路３１及び第２光導波路３２を進行する光波に対して歪の少ないｃｏｓ変調及びｓｉｎ変調が施され、従来技術よりも不要な側波帯が抑圧された光ＳＳＢ変調信号が生成される。そして、１つの変調部だけが設けられた光ＳＳＢ変調器は、複数の変調部が設けられた光ＳＳＢ変調器に比べ、無線信号の入射方向についての指向性が緩和される。
For example, in the above embodiment, the optical SSB modulator 10 is provided with four modulation units (the first modulation unit 20a, the second modulation unit 20b, the third modulation unit 20c, and the fourth modulation unit 20d). Only one modulation unit may be provided. Even when only one modulation unit is provided, the modulation signal is supplied to both the first resonance type electrode 22a and the second resonance type electrode 22b by the antenna electrode having the characteristic structure described above. Standing wave resonance occurs in the first resonance type electrode 22a and the second resonance type electrode 22b, and a very strong and less distorted modulation electric field is generated, so that the first and second optical waveguides 31 and 32 travel. Cos modulation and sin modulation with less distortion are applied to the light wave to be generated, and an optical SSB modulation signal in which unnecessary sidebands are suppressed as compared with the prior art is generated. In addition, the optical SSB modulator provided with only one modulation unit has less directivity in the incident direction of the radio signal than the optical SSB modulator provided with a plurality of modulation units.
また、上記実施の形態では、光ＳＳＢ変調器１０のアンテナ２１は、パッチアンテナであったが、これに限られず、他のタイプの平面アンテナ、例えば、ダイポールアンテナ等であってもよい。
In the above embodiment, the antenna 21 of the optical SSB modulator 10 is a patch antenna, but is not limited thereto, and may be another type of planar antenna such as a dipole antenna.
また、上記実施の形態では、光ＳＳＢ変調器１０のアンテナ２１及び共振型電極２２は、５９ＧＨｚの無線信号５を対象とするサイズ及びレイアウト例が示されたが、本形態における光ＳＳＢ変調器１０は、少なくとも１０ＧＨｚ～６０ＧＨｚで動作することが確認されている。原理的には、上記実施の形態における光ＳＳＢ変調器１０は、３００ＭＨｚ～３００ＧＨｚの無線信号を対象とした場合であっても動作し、上記実施の形態と同様の効果を発揮し得る。
In the above embodiment, the antenna 21 and the resonant electrode 22 of the optical SSB modulator 10 are shown in the size and layout examples for the 59 GHz radio signal 5, but the optical SSB modulator 10 in the present embodiment. Has been confirmed to operate at least from 10 GHz to 60 GHz. In principle, the optical SSB modulator 10 in the above embodiment operates even when a wireless signal of 300 MHz to 300 GHz is targeted, and can exhibit the same effects as in the above embodiment.
また、上記実施の形態では、第１光導波路３１及び第２光導波路３２にπ／２の位相差に相当する光路差（光バイアス）を与えるために、第１光導波路３１に湾曲部３１ａが設けられたが、これに代えて、第２光導波路３２に同様の湾曲部が設けられてもよい。
In the above embodiment, the first optical waveguide 31 has the curved portion 31a in order to give the first optical waveguide 31 and the second optical waveguide 32 an optical path difference (optical bias) corresponding to a phase difference of π / 2. However, instead of this, the second optical waveguide 32 may be provided with a similar curved portion.
本発明に係る光ＳＳＢ変調器は、小型で、かつ、無給電で動作する無線－光信号変換デバイスとして、例えば、ミリ波無線を光信号に変換して伝送するＲｏＦ方式の伝送システムにおける変調器として、利用できる。
An optical SSB modulator according to the present invention is a modulator in a RoF transmission system that converts a millimeter-wave radio into an optical signal and transmits the optical signal as a small-sized wireless-to-optical signal conversion device that operates without power supply. As available.
５ 無線信号
１０ 光ＳＳＢ変調器
１２ 電気光学結晶基板
１４ バッファ層
１６ 接着剤
１８ ベース基板
２０ａ～２０ｄ 変調部
２１ アンテナ
２１ａ 第１アンテナ素子
２１ｂ 第２アンテナ素子
２２ 共振型電極
２２ａ 第１共振型電極
２２ｂ 第２共振型電極
２３ 分極反転構造
３０ マッハツェンダー型光導波路
３０ａ 第１ポート
３０ｂ 第２ポート
３１ 第１光導波路
３１ａ 湾曲部
３２ 第２光導波路
５０ レーザー素子
５１、５２ レンズ
５３ 光ファイバー
５５ 光スペクトラムアナライザ
６０ 発振器
６１ 増幅器
６２ ホーンアンテナ 5Radio signal 10 Optical SSB modulator 12 Electro-optic crystal substrate 14 Buffer layer 16 Adhesive 18 Base substrate 20a to 20d Modulator 21 Antenna 21a First antenna element 21b Second antenna element 22 Resonance type electrode 22a First resonance type electrode 22b 2nd resonance type electrode 23 Polarization inversion structure 30 Mach-Zehnder type optical waveguide 30a 1st port 30b 2nd port 31 1st optical waveguide 31a Bending part 32 2nd optical waveguide 50 Laser element 51, 52 Lens 53 Optical fiber 55 Optical spectrum analyzer 60 Oscillator 61 Amplifier 62 Horn antenna
１０ 光ＳＳＢ変調器
１２ 電気光学結晶基板
１４ バッファ層
１６ 接着剤
１８ ベース基板
２０ａ～２０ｄ 変調部
２１ アンテナ
２１ａ 第１アンテナ素子
２１ｂ 第２アンテナ素子
２２ 共振型電極
２２ａ 第１共振型電極
２２ｂ 第２共振型電極
２３ 分極反転構造
３０ マッハツェンダー型光導波路
３０ａ 第１ポート
３０ｂ 第２ポート
３１ 第１光導波路
３１ａ 湾曲部
３２ 第２光導波路
５０ レーザー素子
５１、５２ レンズ
５３ 光ファイバー
５５ 光スペクトラムアナライザ
６０ 発振器
６１ 増幅器
６２ ホーンアンテナ 5
Claims (5)
- 光波を無線信号で変調することによりＳＳＢ（Ｓｉｎｇｌｅ Ｓｉｄｅ Ｂａｎｄ）変調された光信号を出力する光ＳＳＢ変調器であって、
誘電性材料からなる電気光学結晶基板と、
前記電気光学結晶基板に形成され、第１光導波路及び第２光導波路を有するマッハツェンダー型光導波路と、
前記無線信号を受信するアンテナと、
前記アンテナに接続され、前記第１光導波路及び前記第２光導波路のそれぞれに沿って設けられた第１共振型電極及び第２共振型電極とを備え、
前記電気光学結晶基板には、前記第１光導波路を進行する光波に対してｃｏｓ変調を与えるように前記第１共振型電極に対向する領域の一部に分極反転構造が形成され、かつ、前記第２光導波路を進行する光波に対してｓｉｎ変調を与えるように前記第２共振型電極に対向する領域の一部に分極反転構造が形成され、
前記第１光導波路及び前記第２光導波路の一方の光路は、他方の光路よりも、前記光波におけるπ／２の位相差に相当する長さだけ長い
光ＳＳＢ変調器。 An optical SSB modulator that outputs an optical signal that is SSB (Single Side Band) modulated by modulating an optical wave with a radio signal,
An electro-optic crystal substrate made of a dielectric material;
A Mach-Zehnder type optical waveguide formed on the electro-optic crystal substrate and having a first optical waveguide and a second optical waveguide;
An antenna for receiving the radio signal;
A first resonant electrode and a second resonant electrode connected to the antenna and provided along each of the first optical waveguide and the second optical waveguide;
In the electro-optic crystal substrate, a polarization inversion structure is formed in a part of a region facing the first resonance type electrode so as to give cos modulation to the light wave traveling in the first optical waveguide, and A domain-inverted structure is formed in a part of the region facing the second resonant electrode so as to apply sin modulation to the light wave traveling through the second optical waveguide,
An optical SSB modulator in which one optical path of the first optical waveguide and the second optical waveguide is longer than the other optical path by a length corresponding to a phase difference of π / 2 in the light wave. - 前記第１光導波路及び前記第２光導波路は、互いに並行して延在するように前記電気光学結晶基板上に形成され、
前記第１共振型電極及び前記第２共振型電極は、それぞれ前記第１光導波路及び前記第２光導波路に沿って、互いに並行して延在するように前記電気光学結晶基板上に設けられ、
前記アンテナは、前記電気光学結晶基板上に設けられ、前記第１共振型電極に直交するように接続される第１アンテナ素子、及び、前記第２共振型電極に直交するように接続される第２アンテナ素子を有し、
前記第１アンテナ素子と前記第２アンテナ素子とは、前記電気光学結晶基板上において、前記第１共振型電極及び前記第２共振型電極に対して、対称の位置に設けられている
請求項１記載の光ＳＳＢ変調器。 The first optical waveguide and the second optical waveguide are formed on the electro-optic crystal substrate so as to extend in parallel with each other,
The first resonant electrode and the second resonant electrode are provided on the electro-optic crystal substrate so as to extend in parallel with each other along the first optical waveguide and the second optical waveguide, respectively.
A first antenna element provided on the electro-optic crystal substrate and connected to be orthogonal to the first resonant electrode; and a first antenna element connected to be orthogonal to the second resonant electrode. Having two antenna elements,
2. The first antenna element and the second antenna element are provided on the electro-optic crystal substrate at positions symmetrical with respect to the first resonance electrode and the second resonance electrode. The optical SSB modulator described. - 前記第１アンテナ素子が前記第１共振型電極と接続される接続点は、前記第１共振型電極における、前記第１アンテナ素子と前記第１共振型電極とがインピーダンス整合する複数の接続点のうち、前記第１共振型電極の端部に最も近い接続点であり、
前記第２アンテナ素子が前記第２共振型電極と接続される接続点は、前記第２共振型電極における、前記第２アンテナ素子と前記第２共振型電極とがインピーダンス整合する複数の接続点のうち、前記第２共振型電極の端部に最も近い接続点である
請求項２記載の光ＳＳＢ変調器。 The connection point at which the first antenna element is connected to the first resonance type electrode is a plurality of connection points of the first resonance type electrode at which the first antenna element and the first resonance type electrode are impedance matched. Of these, the connection point closest to the end of the first resonant electrode,
The connection point at which the second antenna element is connected to the second resonance electrode is a plurality of connection points in the second resonance electrode at which the second antenna element and the second resonance electrode are impedance matched. 3. The optical SSB modulator according to claim 2, wherein the connection point is closest to an end of the second resonant electrode. - 前記アンテナ、前記第１共振型電極、前記第２共振型電極及び前記分極反転構造を一組の変調部とした場合に、前記第１光導波路及び前記第２光導波路に沿う複数の箇所のそれぞれに、前記変調部が設けられている
請求項１～３のいずれか１項に記載の光ＳＳＢ変調器。 When the antenna, the first resonance electrode, the second resonance electrode, and the domain-inverted structure are used as a pair of modulators, each of a plurality of locations along the first optical waveguide and the second optical waveguide The optical SSB modulator according to any one of claims 1 to 3, wherein the modulator is provided. - 前記変調部は、前記光波が進行する方向に沿って並ぶ第１変調部、第２変調部、第３変調部及び第４変調部を、この並び順で、含み、
前記第１変調部及び前記第３変調部を構成する前記分極反転構造は、同一の第１分極反転構造を有し、
前記第２変調部及び前記第４変調部を構成する前記分極反転構造は、前記第１分極反転構造とは異なる、同一の第２分極反転構造を有する
請求項１～４のいずれか１項に記載の光ＳＳＢ変調器。 The modulation unit includes a first modulation unit, a second modulation unit, a third modulation unit, and a fourth modulation unit arranged in the arrangement order along the direction in which the light wave travels,
The polarization inversion structures constituting the first modulation unit and the third modulation unit have the same first polarization inversion structure,
The polarization inversion structure constituting the second modulation unit and the fourth modulation unit has the same second polarization inversion structure different from the first polarization inversion structure. The optical SSB modulator described.
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