JPH11183858A - Traveling-wave type optical modulator and optical modulation method - Google Patents
Traveling-wave type optical modulator and optical modulation methodInfo
- Publication number
- JPH11183858A JPH11183858A JP35483697A JP35483697A JPH11183858A JP H11183858 A JPH11183858 A JP H11183858A JP 35483697 A JP35483697 A JP 35483697A JP 35483697 A JP35483697 A JP 35483697A JP H11183858 A JPH11183858 A JP H11183858A
- Authority
- JP
- Japan
- Prior art keywords
- electric signal
- electrode
- traveling
- optical
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- 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
- G02F1/0356—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 controlled by a high-frequency electromagnetic wave component in an electric waveguide structure
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、進行波型光変調器
及び進行波型光変調方法に関し、さらに詳しくは、高速
光通信やケーブルテレビ（ＣＡＴＶ）などに有効に使用
することのできる、進行波型光変調器及び進行波型光変
調方法に関する。The present invention relates to a traveling-wave optical modulator and a traveling-wave optical modulation method, and more particularly, to a traveling-wave optical modulator and a traveling-wave optical modulator that can be effectively used for high-speed optical communication and cable television (CATV). The present invention relates to a wave type optical modulator and a traveling wave type optical modulation method.
【０００２】[0002]
【従来の技術】近年の光通信分野においては、半導体ダ
イオードレーザの直接変調に代わって、ニオブ酸リチウ
ム（ＬｉＮｂＯ3 ：以下、ＬＮと略す場合がある）など
の電気光学効果を有する基板に光導波路を形成し、さら
に、この光導波路の直上又は近傍に電極を形成した、い
わゆる進行波型の高速外部光変調器が用いられるように
なってきた。In Recently field of optical communication, in place of direct modulation of the semiconductor diode laser, lithium niobate (LiNbO 3: hereinafter sometimes abbreviated as LN) waveguide on a substrate having an electro-optical effect, such as And a so-called traveling wave type high-speed external optical modulator in which an electrode is formed immediately above or in the vicinity of the optical waveguide.
【０００３】図１は、このような進行波型光変調器の概
略を示した図である。基板９は、電気光学効果を有する
材料、例えば、ＬＮから構成される。光導波路３は、い
わゆるマッハツエンダー型光導波路であり、基板９上
に、例えばチタン（Ｔｉ）などを堆積させた後、熱拡散
させて形成する。また、図１には示していないが、光導
波路３中を伝搬する光の電極層への吸収を少なくするた
め、酸化シリコン（ＳｉＯ2 ）などからなるバッファ層
を、基板９上に形成することもできる。FIG. 1 is a diagram schematically showing such a traveling-wave optical modulator. The substrate 9 is made of a material having an electro-optic effect, for example, LN. The optical waveguide 3 is a so-called Mach-Zehnder type optical waveguide, and is formed by depositing, for example, titanium (Ti) on the substrate 9 and then thermally diffusing the same. Although not shown in FIG. 1, a buffer layer made of silicon oxide (SiO 2 ) is formed on the substrate 9 to reduce absorption of light propagating in the optical waveguide 3 into the electrode layer. Can also.
【０００４】接地電極４及び信号電極５は、金（Ａｕ）
などの金属から形成する。また、図１では、入射光の余
分な成分を除去して偏光を揃えるために、ラミポール偏
光子２を設けている。図１に示す進行波型光変調器を用
いた高速光変調は、以下のようにして行う。入射光は、
入射側光ファイバ１から入射させ、ラミポール偏光子２
を通過させた後、光導波路３中を２分割して進行させ
る。The ground electrode 4 and the signal electrode 5 are made of gold (Au)
Formed from such a metal. In FIG. 1, a Ramipole polarizer 2 is provided in order to remove unnecessary components of the incident light to make the polarization uniform. High-speed optical modulation using the traveling wave optical modulator shown in FIG. 1 is performed as follows. The incident light is
The incident light from the incident side optical fiber 1 and the Ramipole polarizer 2
After passing through, the optical waveguide 3 is advanced by being divided into two.
【０００５】一方、信号電極５には、駆動ドライバ７か
ら給電ケーブル６を通して、マイクロ波帯域の高周波交
流電圧を印加する。この電圧は、信号電極５からの電気
信号として、光導波路３に印加される。On the other hand, a high frequency AC voltage in a microwave band is applied to the signal electrode 5 from a driving driver 7 through a power supply cable 6. This voltage is applied to the optical waveguide 3 as an electric signal from the signal electrode 5.
【０００６】電気信号の印加により光導波路の屈折率が
変化するため、導波路中を進行する光の位相もこの屈折
率変化に起因して変化する。したがって、分岐した各光
導波路３中を進行してきた光は、互いの位相が異なるた
めに、光導波路３の終端において再び結合すると、その
合成された光は互いに干渉し合って、互いの光強度成分
を打ち消し合う。Since the refractive index of the optical waveguide changes due to the application of an electric signal, the phase of light traveling in the waveguide also changes due to the change in the refractive index. Therefore, since the light traveling in each of the branched optical waveguides 3 has a different phase from each other, when the light is coupled again at the end of the optical waveguide 3, the combined light interferes with each other and the light intensity of each other is increased. Cancel each other out.
【０００７】これにより、出射側光ファイバ１０を通っ
て得られる出射光の光強度は、入射光の光強度よりも小
さくなり、光変調がなされる。このようにマイクロ波を
用いた高速光変調の場合においては、駆動ドライバ７か
ら信号電極５に伝送される高周波交流電圧が最大となる
ように、接地電極４及び信号電極５のインピーダンス
（特性インピーダンス）を、駆動ドライバ７のインピー
ダンスに整合するように設定する。また、信号電極５中
を伝送する前記高周波交流電圧が最大となるように、図
１に示す進行波型光変調器の出力側には、前記特性イン
ピーダンスと同じ値の抵抗値を有する終端抵抗８を設置
し、インピーダンス整合を取る。As a result, the light intensity of the output light obtained through the output side optical fiber 10 becomes smaller than the light intensity of the incident light, and the light is modulated. As described above, in the case of high-speed optical modulation using microwaves, the impedance (characteristic impedance) of the ground electrode 4 and the signal electrode 5 is set so that the high-frequency AC voltage transmitted from the drive driver 7 to the signal electrode 5 is maximized. Is set to match the impedance of the drive driver 7. Also, a terminating resistor 8 having the same value as the characteristic impedance is provided on the output side of the traveling wave type optical modulator shown in FIG. 1 so that the high-frequency AC voltage transmitted through the signal electrode 5 is maximized. And take impedance matching.
【０００８】したがって、駆動ドライバ７として、従来
から高速光変調に使用されている汎用の駆動ドライバを
用いた場合においては、そのインピーダンスが５０Ωで
あるため、前記電極の特性インピーダンス及び終端抵抗
８の抵抗値も５０Ωに設定する必要があった。また、進
行波型光変調器の駆動電圧を下げるなどの目的で、前記
特性インピーダンスを２５Ωに設定した場合は、駆動ド
ライバ７のインピーダンス及び終端抵抗８の抵抗値も２
５Ωに設定する必要があった。Therefore, when a general-purpose drive driver conventionally used for high-speed light modulation is used as the drive driver 7, the impedance is 50Ω, so that the characteristic impedance of the electrode and the resistance of the terminating resistor 8 are reduced. The value also had to be set to 50Ω. When the characteristic impedance is set to 25Ω for the purpose of lowering the driving voltage of the traveling wave optical modulator, the impedance of the driving driver 7 and the resistance value of the terminating resistor 8 are also 2.
It was necessary to set to 5Ω.
【０００９】[0009]
【発明が解決しようとする課題】図２は、進行波型光変
調器における従来の光変調特性を示す図である。図２か
ら明らかなように、信号電極５に印加される高周波交流
電圧の周波数が高くなるにつれて、光導波路３中を伝搬
する光強度変調成分が減少する。すなわち、進行波型光
変調器における従来の光変調方法では、変調周波数が高
くなる程、光変調特性が劣化していた。FIG. 2 is a diagram showing a conventional optical modulation characteristic of a traveling wave type optical modulator. As is clear from FIG. 2, as the frequency of the high-frequency AC voltage applied to the signal electrode 5 increases, the light intensity modulation component propagating in the optical waveguide 3 decreases. That is, in the conventional light modulation method in the traveling wave type light modulator, the light modulation characteristic deteriorates as the modulation frequency increases.
【００１０】したがって、高速光通信やケーブルテレビ
などにおいて、高速でパルスパターンを伝送する場合、
周波数の高いパルスパターン成分の角の部分が丸くなっ
て劣化し、パルス形状が矩形な状態からずれてしまって
いた。このため、特に、高速デジタル通信などの伝送特
性上好ましくない問題を生じていた。Therefore, when transmitting a pulse pattern at high speed in high-speed optical communication or cable television, etc.
The corners of the high-frequency pulse pattern component were rounded and deteriorated, and the pulse shape was shifted from a rectangular state. For this reason, there has been a problem that transmission characteristics such as high-speed digital communication are not preferable.
【００１１】本発明の目的は、上記問題に鑑み、高速で
光変調を行った場合においても、光変調特性の劣化の少
ない進行波型光変調器及び光変調方法を提供することで
ある。SUMMARY OF THE INVENTION An object of the present invention is to provide a traveling wave optical modulator and an optical modulation method in which the optical modulation characteristics are not deteriorated even when the optical modulation is performed at a high speed in view of the above problem.
【００１２】[0012]
【課題を解決するための手段】本発明者らは、上記問題
に鑑みて鋭意検討した結果、駆動ドライバからの進行波
型電極に入力される高周波交流電圧の電気信号と逆向き
に伝搬する電気信号を生じさせ、この電気信号と駆動ド
ライバからの電気信号を合成し、この合成した電気信号
を用いて光変調を行うことにより上記問題を解決できる
ことを見い出し本発明をするに至った。すなわち、本発
明は、少なくとも電気光学効果を有する基板に形成され
た光導波路と、この光導波路の直上又は近傍に形成さ
れ、前記光導波路中を進行する光に電気信号を印加し
て、前記光を変調するための電極とを具える進行波型光
変調器において、前記電気信号と前記電気信号と逆向き
の電気信号とを合成し、この合成された電気信号により
前記光導波路中を進行する光の変調を行うことを特徴と
する進行波型光変調器である。また、本発明は、少なく
とも電気光学効果を有する基板に形成された光導波路中
を進行する光に対して、前記光導波路の直上又は近傍に
形成された電極から電気信号を印加して、前記光導波路
中を進行する光を変調する進行波型光変調方法におい
て、前記電気信号と前記電気信号と逆向きの電気信号と
を合成し、この合成された電気信号により前記光導波路
中を進行する光の変調を行うことを特徴とする進行波型
光変調方法である。Means for Solving the Problems The inventors of the present invention have made intensive studies in view of the above-mentioned problems, and as a result, have found that an electric signal propagating in the opposite direction to an electric signal of a high-frequency AC voltage input to a traveling-wave-type electrode from a driving driver. The present invention has been found that the above problem can be solved by generating a signal, synthesizing the electric signal and the electric signal from the drive driver, and performing optical modulation using the synthesized electric signal. That is, the present invention provides an optical waveguide formed on a substrate having at least an electro-optic effect, and an optical signal formed immediately above or near this optical waveguide and applying an electric signal to light traveling in the optical waveguide. A traveling wave optical modulator comprising an electrode for modulating the electric signal, the electric signal and an electric signal in a direction opposite to the electric signal are combined, and the electric signal travels in the optical waveguide by the combined electric signal. This is a traveling wave optical modulator that performs light modulation. In addition, the present invention provides an optical waveguide that applies an electric signal to light traveling at least through an optical waveguide formed on a substrate having an electro-optical effect from an electrode formed immediately above or near the optical waveguide. In a traveling wave optical modulation method for modulating light traveling in a wave path, a light traveling in the optical waveguide is synthesized by combining the electric signal and an electric signal in a direction opposite to the electric signal. This is a traveling-wave-type optical modulation method characterized by performing the following modulation.
【００１３】以下、図面を参照しながら本発明について
説明する。図３は、光導波中を進行する光と逆向きの電
気信号のみを用いた場合における、進行波型光変調器の
光変調特性を示したものである。尚、理解を容易にすべ
く、光強度変調成分は誇張して表している。図３から明
らかなように、このような逆向きの電気信号によっても
光強度変調成分を有し、入射光信号を変調できることが
分かる。Hereinafter, the present invention will be described with reference to the drawings. FIG. 3 shows the optical modulation characteristics of the traveling wave optical modulator when only the electric signal in the opposite direction to the light traveling in the optical waveguide is used. Note that the light intensity modulation component is exaggerated for easy understanding. As is clear from FIG. 3, it can be seen that such an electric signal in the opposite direction also has a light intensity modulation component and can modulate an incident light signal.
【００１４】図４は、駆動ドライバからの高周波交流電
圧の電気信号と、この電気信号と逆向きの電気信号とを
合成してなる電気信号を用いた場合における、進行波型
光変調器の光変調特性を示したものである。FIG. 4 shows the light of a traveling-wave optical modulator when an electric signal obtained by synthesizing an electric signal of a high-frequency AC voltage from a driving driver and an electric signal in a direction opposite to this electric signal is used. It shows a modulation characteristic.
【００１５】図４（ａ）は、図３に示した逆向きの電気
信号による光強度変調成分を反転させて、いわゆる差分
を取った場合の光変調特性を示したものであり、図４
（ｂ）は、図３に示した逆向きの電気信号による光強度
変調成分をそのまま重畳させた場合の光変調特性を示し
たものである。FIG. 4A shows a light modulation characteristic obtained when a so-called difference is obtained by inverting the light intensity modulation component by the electric signal in the opposite direction shown in FIG.
(B) shows the light modulation characteristic when the light intensity modulation component by the electric signal in the opposite direction shown in FIG. 3 is superimposed as it is.
【００１６】図４（ａ）では、高周波交流電圧（電気信
号）の周波数に対して、光強度変調成分はフラットな状
態を呈する。したがって、周波数の高い電気信号を用い
て高速の光変調を実施した場合においても、光変調を有
効に行うことができる。In FIG. 4A, the light intensity modulation component exhibits a flat state with respect to the frequency of the high-frequency AC voltage (electric signal). Therefore, even when high-speed optical modulation is performed using an electric signal having a high frequency, the optical modulation can be effectively performed.
【００１７】一方、図４（ｂ）では、光強度変調成分が
全体的に増加する。したがって、電気信号の使用周波数
領域が、前記光強度変調成分よりも全体的に増加した領
域において使用する場合、有効に光変調を行うことがで
きる。On the other hand, in FIG. 4B, the light intensity modulation component increases as a whole. Therefore, in the case where the electric signal is used in a region where the used frequency region is larger than the light intensity modulation component as a whole, light modulation can be performed effectively.
【００１８】以上、本発明にしたがって、駆動ドライバ
からの高周波交流電圧の電気信号と逆向きの電気信号を
使用して光変調を実施することにより、高速光変調を実
施することができる。As described above, according to the present invention, high-speed light modulation can be performed by performing light modulation using an electric signal having a direction opposite to the high-frequency AC voltage electric signal from the driving driver.
【００１９】[0019]
【発明の実施の形態】以下、本発明を、図面を参照しな
がら、発明の実施の形態に則して詳細に説明する。本発
明においては、図１と同様の進行波型光変調器を使用す
ることができる。駆動ドライバ７からの高周波交流電圧
の電気信号と逆向きの電気信号は、前記駆動ドライバ７
とは別の独立した駆動ドライバを使用する方法及び進行
波型光変調器内にインピーダンス不整合を生じさせる方
法によって発生させることができるが、前記逆向きの電
気信号を簡易に発生させることができるという理由か
ら、後者のインピーダンス不整合を生じさせる方法を用
いることが好ましい。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings according to embodiments of the present invention. In the present invention, a traveling wave optical modulator similar to that shown in FIG. 1 can be used. The electric signal of the opposite direction to the electric signal of the high-frequency AC voltage from the driving driver 7 is
Although it can be generated by a method using an independent drive driver and a method of causing an impedance mismatch in the traveling wave optical modulator, the reverse electric signal can be easily generated. For this reason, it is preferable to use the latter method of causing impedance mismatch.
【００２０】インピーダンス不整合による前記逆向きの
電気信号の発生は具体的には以下のようにして行う。す
なわち、接地電極４及び信号電極５の特性インピーダン
スと、これらの接地電極４及び信号電極５の終端部にお
けるインピーダンスとを異なる値に設定することによ
り、この終端部において駆動ドライバ７からの電気信号
が反射し、前記電気信号と逆向きの電気信号を得ること
ができるものである。The generation of the electric signal in the opposite direction due to the impedance mismatch is specifically performed as follows. That is, by setting the characteristic impedance of the ground electrode 4 and the signal electrode 5 to a different value from the impedance at the terminal portions of the ground electrode 4 and the signal electrode 5, an electric signal from the drive driver 7 is generated at the terminal portion. It is possible to obtain an electric signal which is reflected and has a direction opposite to the electric signal.
【００２１】例えば、図１における信号電極５の終端部
分に相当する電極パッド１１のインピーダンス、あるい
は図１における終端抵抗８の抵抗値を、接地電極４及び
信号電極５の特性インピーダンスと異なる値に設定する
方法、及び図１の終端抵抗８の代わりに、駆動ドライバ
７と独立した駆動ドライバを設置し、印加電気信号のタ
イミングを調整する方法により実施することができる。
前記逆向きの電気信号を簡易に発生させることができ、
また装置の複雑化を防止するという観点からは、前者の
方法を用いることが好ましい。For example, the impedance of the electrode pad 11 corresponding to the terminal portion of the signal electrode 5 in FIG. 1 or the resistance value of the terminal resistor 8 in FIG. 1 is set to a value different from the characteristic impedance of the ground electrode 4 and the signal electrode 5. 1 and a method of installing a drive driver independent of the drive driver 7 in place of the terminating resistor 8 in FIG. 1 and adjusting the timing of the applied electric signal.
The electric signal in the opposite direction can be easily generated,
From the viewpoint of preventing the device from becoming complicated, it is preferable to use the former method.
【００２２】接地電極４及び信号電極５の終端部におけ
る電気信号の反射の度合いは、下記（１）式に示すよう
な反射係数Γを用いて評価することができる。 Γ＝（ＺR −ＺO ）／（ＺR ＋ＺO ） （１） ここで、ＺO は接地電極４及び信号電極５の特性インピ
ーダンスを、ＺR は接地電極４及び信号電極５の終端部
におけるインピーダンスあるいは抵抗値を表す。The degree of reflection of the electric signal at the terminal portions of the ground electrode 4 and the signal electrode 5 can be evaluated using a reflection coefficient よ う な as shown in the following equation (1). Γ = (Z R −Z O ) / (Z R + Z O ) (1) Here, Z O is the characteristic impedance of the ground electrode 4 and the signal electrode 5, and Z R is the terminal end of the ground electrode 4 and the signal electrode 5. Represents the impedance or resistance value at.
【００２３】（１）式において、ＺR ＞ＺO の場合、す
なわち、前記終端部のインピーダンスあるいは抵抗値が
前記特性インピーダンスよりも大きい場合、反射係数は
正の値をとる。このように反射係数が正の値を示すと、
逆向きの電気信号は、駆動ドライバ７からの電気信号で
ある高周波交流電圧と同じ符号の高周波交流電圧を有す
る。In the equation (1), when Z R > Z O , that is, when the impedance or the resistance value of the terminal portion is larger than the characteristic impedance, the reflection coefficient takes a positive value. Thus, when the reflection coefficient shows a positive value,
The electric signal in the opposite direction has a high-frequency AC voltage having the same sign as the high-frequency AC voltage that is the electric signal from the drive driver 7.
【００２４】例えば、駆動ドライバ７から＋ＶO の値の
高周波交流電圧の電気信号が接地電極４及び信号電極５
に印加された場合、前記終端部で反射して得られる逆向
きの電気信号は、その絶対値こそ異なるものの、前記電
気信号と同じプラスの値を有する高周波交流電圧として
作用する。For example, an electric signal of a high-frequency AC voltage having a value of + V O is supplied from the driving driver 7 to the ground electrode 4 and the signal electrode 5.
When applied to the terminal, the electric signal in the opposite direction, which is obtained by reflection at the end portion, acts as a high-frequency AC voltage having the same positive value as the electric signal, although the absolute value is different.
【００２５】同様に、ＺR ＜ＺO の場合、すなわち、前
記終端部のインピーダンスあるいは抵抗値が前記特性イ
ンピーダンスよりも小さい場合、反射係数は負の値を取
る。したがって、例えば、駆動ドライバ７から＋ＶO の
値の高周波交流電圧の電気信号が接地電極４及び信号電
極５に印加された場合、前記終端部で得られる逆向きの
電気信号は、前記電気信号の高周波交流電圧と異なっ
て、マイナスの値を有する高周波交流電圧として作用す
る。Similarly, when Z R <Z O , that is, when the impedance or the resistance value of the terminal portion is smaller than the characteristic impedance, the reflection coefficient takes a negative value. Therefore, for example, when an electric signal of a high-frequency AC voltage having a value of + V O is applied from the drive driver 7 to the ground electrode 4 and the signal electrode 5, the electric signal in the opposite direction obtained at the terminal portion is the electric signal of the electric signal. Unlike the high-frequency AC voltage, it acts as a high-frequency AC voltage having a negative value.
【００２６】ＺR ＞ＺO の場合は、上述したように、駆
動ドライバ７からの電気信号と逆向きの電気信号とが同
じ符号を有するため、図２に示す前記電気信号による光
強度変調成分と、図３に示す前記逆向きの光強度変調成
分とが重畳して、図４（ｂ）に示すような光変調特性を
示す。When Z R > Z O , as described above, since the electric signal from the drive driver 7 and the electric signal in the opposite direction have the same sign, the light intensity modulation component by the electric signal shown in FIG. 4 and the light intensity modulation component in the opposite direction shown in FIG. 3 are superimposed to show a light modulation characteristic as shown in FIG.
【００２７】一方、ＺR ＜ＺO の場合は、駆動ドライバ
７からの電気信号と逆向きの電気信号とが異なる符号を
有するため、図２に示す前記電気信号による光強度変調
成分と、図３に示す前記逆向きの光強度変調成分とが互
いに打ち消し合って、いわゆる差分を取った形を呈する
ので、図４（ａ）に示すような光変調特性を示す。On the other hand, when Z R <Z O , since the electric signal from the driving driver 7 and the electric signal in the opposite direction have different signs, the light intensity modulation component by the electric signal shown in FIG. The light intensity modulation components in the opposite direction shown in FIG. 3 cancel each other out, so that they take a so-called difference form, so that the light modulation characteristics as shown in FIG.
【００２８】図４（ａ）では、光強度変調成分の絶対値
的な大きさは減少しているものの、この大きさは、入力
光量を大きくすることによって、自在に大きくすること
ができる。したがって、図４（ｂ）に比較して図４
（ａ）の方が電気信号の周波数依存性が小さいため、よ
り周波数の高い電気信号で光変調を実施した場合におい
ても、光強度変調成分の劣化が少ない。In FIG. 4A, although the magnitude of the absolute value of the light intensity modulation component is reduced, this magnitude can be freely increased by increasing the input light amount. Therefore, as compared with FIG.
Since the frequency dependency of the electric signal is smaller in (a), even when the light modulation is performed with the electric signal having a higher frequency, the deterioration of the light intensity modulation component is small.
【００２９】すなわち、ＺR ＜ＺO の場合に相当する、
前記終端部のインピーダンスあるいは抵抗値が、前記特
性インピーダンスよりも小さい場合の方が好ましい。ま
た、上記（１）式で示される反射係数の絶対値が大きい
ほど、前記逆向きの電気信号の信号レベルが大きくな
り、図３に示される光強度変調成分の強度が増す。した
がって、図４に示す進行波型光変調器の光強度変調成分
に対する前記逆向きの電気信号の影響が大きくなる。し
かしながら、逆向きの電気信号の影響が大きすぎると、
光変調特性が大きく変化してしまうため、かえってパル
ス伝送特性が劣化してしまう。That is, it corresponds to the case where Z R <Z O.
It is preferable that the impedance or the resistance value of the terminating portion is smaller than the characteristic impedance. Further, as the absolute value of the reflection coefficient represented by the above equation (1) increases, the signal level of the electric signal in the opposite direction increases, and the intensity of the light intensity modulation component illustrated in FIG. 3 increases. Therefore, the influence of the electric signal in the opposite direction on the light intensity modulation component of the traveling wave optical modulator shown in FIG. 4 increases. However, if the effect of the opposite electrical signal is too great,
Since the optical modulation characteristics change significantly, the pulse transmission characteristics deteriorate rather.
【００３０】本発明者らは、おおむね｜Γ｜＜０．５
（｜Γ｜≠０）であれば変調特性は良好であることを見
出した。さらには、｜Γ｜≦０．３の場合、より好まし
い光変調特性となる。しかし、｜Γ｜が小さすぎるとク
ラットな光変調特性が得られなくなり、本発明の効果は
期待できない。実験によれば、０．０５≦｜Γ｜であれ
ば本発明の効果が期待できる。The present inventors have generally found that | Γ | <0.5
It was found that if (| Γ | ≠ 0), the modulation characteristics were good. Further, when | Γ | ≦ 0.3, more preferable light modulation characteristics are obtained. However, if | Γ | is too small, it will not be possible to obtain a good light modulation characteristic, and the effects of the present invention cannot be expected. According to experiments, the effects of the present invention can be expected if 0.05 ≦ | Γ |.
【００３１】以上の理由から、前記反射係数の大きさ｜
Γ｜は、｜Γ｜＜０．５（｜Γ｜≠０）であることが好
ましく、さらには、０．０５≦｜Γ｜≦０．３であるこ
とが好ましい。For the above reason, the magnitude of the reflection coefficient |
Γ | is preferably | Γ | <0.5 (| Γ | ≠ 0), and more preferably 0.05 ≦ | Γ | ≦ 0.3.
【００３２】[0032]
【実施例】以下、本発明を実施例に則してさらに詳述す
る。 実施例１ 本実施例では、上記（１）式において、ＺR ＞ＺO の場
合、すなわち、接地電極４及び信号電極５の終端部にお
けるインピーダンスが、接地電極４及び信号電極５の特
性インピーダンスよりも大きい場合について説明する。
基板として、ニオブ酸リチウム基板（ＬＮ基板）を用
い、この基板のＺ面上にフォトリソグラフィー技術を用
いて導波路パターンを形成した後、真空蒸着法により金
属チタンを８００Åに堆積させ、１０００℃で１０時間
加熱して、この金属チタンを基板中に拡散させ、図１に
示すような幅７μm のマッハツエンダー型の光導波路３
を形成した。続いて、図１には示していないが、真空蒸
着法を用いることにより、この基板上に、バッファ層と
しての酸化シリコン（ＳｉＯ2 ）を０．４μｍの厚さに
形成した。次に、前記ＬＮ基板上にチタンと金（Ａｕ）
からなる合金層を、真空蒸着法により下地層として約２
０００Åの厚さに形成した後、さらに電気メッキ法を用
いて８μｍの厚さに形成する。その後、ケミカルエッチ
ング法によって余分な合金層を除去し、図１に示すよう
な幅３０μｍ、長さ２ｃｍの信号電極５を形成し、さら
に、間隔１０μｍで接地電極４を形成した。その後、光
ファイバを入射側及び出射側に設け、接地電極４及び信
号電極５に給電ケーブル６及び駆動ドライバ７を接続し
た後、接地電極４をグランドに落とし、さらにラミポー
ル偏光子２及び抵抗値５１Ωの終端抵抗８を接続して、
図１に示すような進行波型光変調器を製造した。この進
行波型光変調器の接地電極４及び信号電極５の特性イン
ピーダンスを、いわゆるＴＤＲ法によって測定したとこ
ろ、２５Ωのインピーダンス値を示した。さらに、この
進行波型光変調器の光変調特性を光コンポチネントアナ
ライザにより測定したところ、図５（ａ）に示すような
光変調特性を示した。The present invention will be described below in more detail with reference to Examples. Embodiment 1 In the present embodiment, in the above equation (1), when Z R > Z O , that is, the impedance at the terminal portions of the ground electrode 4 and the signal electrode 5 is smaller than the characteristic impedance of the ground electrode 4 and the signal electrode 5. Is also described.
As a substrate, a lithium niobate substrate (LN substrate) is used. A waveguide pattern is formed on the Z surface of the substrate by using a photolithography technique, and then metal titanium is deposited at 800 ° by a vacuum deposition method. This metal titanium is diffused into the substrate by heating for 10 hours, and a Mach-Zehnder type optical waveguide 3 having a width of 7 μm as shown in FIG.
Was formed. Subsequently, although not shown in FIG. 1, silicon oxide (SiO 2 ) as a buffer layer was formed to a thickness of 0.4 μm on this substrate by using a vacuum evaporation method. Next, titanium and gold (Au) are formed on the LN substrate.
Alloy layer consisting of about 2
After being formed to a thickness of 000 mm, it is further formed to a thickness of 8 μm by electroplating. Thereafter, an excess alloy layer was removed by a chemical etching method, a signal electrode 5 having a width of 30 μm and a length of 2 cm as shown in FIG. 1 was formed, and further, a ground electrode 4 was formed at an interval of 10 μm. Thereafter, optical fibers are provided on the incident side and the output side, and after the power supply cable 6 and the drive driver 7 are connected to the ground electrode 4 and the signal electrode 5, the ground electrode 4 is dropped to the ground, and the Ramipole polarizer 2 and the resistance value 51Ω are connected. Connect the terminating resistor 8 of
A traveling wave optical modulator as shown in FIG. 1 was manufactured. When the characteristic impedance of the ground electrode 4 and the signal electrode 5 of this traveling wave optical modulator was measured by the so-called TDR method, an impedance value of 25Ω was shown. Further, when the optical modulation characteristics of the traveling wave optical modulator were measured by an optical component analyzer, the optical modulation characteristics as shown in FIG.
【００３３】実施例２ 本実施例では、上記（１）式において、ＺR ＜ＺO の場
合、すなわち、接地電極４及び信号電極５の終端部にお
けるインピーダンスが、接地電極４及び信号電極５の特
性インピーダンスよりも小さい場合について説明する。
進行波型光変調器は、抵抗値１７Ωの終端抵抗８を用い
た以外、上記実施例１と同様にして製造した。この進行
波型光変調器の光変調特性を上記実施例１と同様にして
測定したところ、図５（ｂ）に示すような光変調特性を
示した。Embodiment 2 In this embodiment, in the above equation (1), when Z R <Z O , that is, when the impedance at the terminal portions of the ground electrode 4 and the signal electrode 5 is larger than that of the ground electrode 4 and the signal electrode 5, The case where the impedance is smaller than the characteristic impedance will be described.
The traveling wave optical modulator was manufactured in the same manner as in Example 1 except that the terminating resistor 8 having a resistance value of 17Ω was used. When the light modulation characteristics of the traveling wave type optical modulator were measured in the same manner as in Example 1, the light modulation characteristics as shown in FIG. 5B were exhibited.
【００３４】比較例 本比較例では、ＺR ＝ＺO の場合、すなわち、進行波型
光変調器の従来の光変調方法である、接地電極４及び信
号電極５の終端部におけるインピーダンスと、接地電極
４及び信号電極５の特性インピーダンスとが等しい場合
について説明する。接地電極４及び信号電極５の特性イ
ンピーダンスと同じ抵抗値である、２５Ωの終端抵抗８
を用いた以外は、上記実施例１と同様にして進行波型光
変調器を製造した。この進行波型光変調器の光変調特性
を上記実施例１と同様にして測定したところ、図５
（ｃ）に示すような光変調特性を示した。図５（ａ）及
び（ｃ）に示すように、実施例１のＺR ＞ＺO の場合に
おいては、駆動ドライバ７からの電気信号による光強度
変調成分と、逆向きの電気信号による光強度変調成分と
が重畳しているため、比較例に示すＺR ＝ＺO の従来の
光変調方法に比較して、光強度変調成分が全体として増
加していることが分かる。特に、１．２ＧＨｚ以下の周
波数の比較的低い部分で増加している。一方、図５
（ｂ）及び（ｃ）に示すように、実施例２のＺR ＜ＺO
の場合においては、駆動ドライバ７からの電気信号によ
る光強度変調成分と、逆向きの電気信号による光強度変
調成分とが打ち消し合って、いわゆる差分を取った状態
を呈するため、従来の光変調方法である比較例の場合に
比較して、光強度変調成分としては全体的に減少する。
しかしながら、光強度変調強度成分の電気信号の周波数
依存性は小さくなり、光強度変調成分は、電気信号の広
い周波数帯域においてフラットな状態を呈することが分
かる。Comparative Example In this comparative example, when Z R = Z O , that is, the impedance at the terminal end of the ground electrode 4 and the signal electrode 5, which is the conventional optical modulation method of the traveling wave optical modulator, and the ground The case where the characteristic impedances of the electrode 4 and the signal electrode 5 are equal will be described. 25 Ω terminating resistor 8 having the same resistance value as the characteristic impedance of ground electrode 4 and signal electrode 5
A traveling-wave optical modulator was manufactured in the same manner as in Example 1 except that was used. The light modulation characteristics of this traveling wave optical modulator were measured in the same manner as in Example 1 above.
Light modulation characteristics as shown in (c) were exhibited. As shown in FIGS. 5A and 5C, when Z R > Z O in the first embodiment, the light intensity modulation component due to the electric signal from the driving driver 7 and the light intensity due to the electric signal in the opposite direction. Since the modulation component is superimposed, it can be seen that the light intensity modulation component is increased as a whole as compared with the conventional light modulation method of Z R = Z O shown in the comparative example. In particular, it increases at relatively low frequencies below 1.2 GHz. On the other hand, FIG.
As shown in (b) and (c), Z R <Z O of Example 2
In the case of (1), the light intensity modulation component due to the electric signal from the drive driver 7 and the light intensity modulation component due to the opposite electric signal cancel each other out, so that a so-called difference state is obtained. As compared with the case of the comparative example, the light intensity modulation component decreases as a whole.
However, it can be seen that the frequency dependence of the electric signal of the light intensity modulation intensity component is reduced, and the light intensity modulation component exhibits a flat state in a wide frequency band of the electric signal.
【００３５】したがって、本発明の進行波型光変調器及
び光変調方法を用いることにより、光変調特性を大きく
劣化させることなく、高速光変調を行うことができる。
上記実施例では、いずれも終端抵抗８の抵抗値を変化さ
せることによって、逆向きの電気信号を生ぜしめる場合
について示したが、上述したように、信号電極５の終端
部に相当する電極パッド１１のインピーダンスを変化さ
せることによっても実施することができる。この場合
は、例えば、上記実施例で示した信号電極５の電極パッ
ド１１に相当する部分の幅を１３００μｍとし、かつ電
極パッド１１の部分における接地電極４との間隔を７０
０μｍとすることによって、インピーダンスが約４０Ω
の電極パッドを形成することができる。Therefore, by using the traveling-wave optical modulator and the optical modulation method of the present invention, high-speed optical modulation can be performed without greatly deteriorating the optical modulation characteristics.
In the above embodiment, the case where the resistance value of the terminating resistor 8 is changed to generate an electric signal in the opposite direction has been described. However, as described above, the electrode pad 11 corresponding to the terminating end of the signal electrode 5 is used. Can also be implemented by changing the impedance of. In this case, for example, the width of the portion corresponding to the electrode pad 11 of the signal electrode 5 shown in the above embodiment is set to 1300 μm, and the interval between the electrode pad 11 and the ground electrode 4 is set to 70 μm.
By setting it to 0 μm, the impedance becomes about 40Ω
Electrode pads can be formed.
【００３６】[0036]
【発明の効果】以上説明したように、本発明の進行波型
光変調器及び光変調方法を用いることにより、電気信号
の変調周波数を高くした場合においても、光強度変調成
分の劣化が少ない光変調特性を特性を得ることができ
る。したがって、高速光通信やケーブルテレビなどの高
速光変調が必要とされる分野において、極めて有効な進
行波型光変調器及び光変調方法を提供することができ
る。As described above, by using the traveling wave type optical modulator and the optical modulation method of the present invention, even when the modulation frequency of the electric signal is increased, the optical intensity modulation component is less deteriorated. Modulation characteristics can be obtained. Therefore, it is possible to provide a traveling wave optical modulator and an optical modulation method that are extremely effective in a field requiring high-speed optical modulation such as high-speed optical communication and cable television.
【図１】進行波型光変調器の概略を示した図である。FIG. 1 is a diagram schematically showing a traveling wave optical modulator.
【図２】進行波型光変調器の従来の光変調特性を示した
図である。FIG. 2 is a diagram showing a conventional optical modulation characteristic of a traveling wave optical modulator.
【図３】逆向きの電気信号を用いた場合における、進行
波型光変調器の光変調特性を示した図である。FIG. 3 is a diagram showing optical modulation characteristics of a traveling wave optical modulator when an electric signal in a reverse direction is used.
【図４】合成された電気信号を用いた場合における、進
行波型光変調器の光変調特性を示す図である。FIG. 4 is a diagram illustrating light modulation characteristics of a traveling-wave optical modulator when a combined electric signal is used.
【図５】本発明の実施例における進行波型光変調器の光
変調特性を示す図である。FIG. 5 is a diagram showing an optical modulation characteristic of the traveling wave optical modulator according to the embodiment of the present invention.
１ 入射側光ファイバ ２ ラミポール偏光子 ３ 光導波路 ４ 接地電極 ５ 信号電極 ６ 給電ケーブル ７ 駆動ドライバ ８ 終端抵抗 ９ 基板 １０ 出射側光ファイバ １１ 電極パッド DESCRIPTION OF SYMBOLS 1 Incident-side optical fiber 2 Ramipole polarizer 3 Optical waveguide 4 Ground electrode 5 Signal electrode 6 Feeding cable 7 Drive driver 8 Terminating resistor 9 Substrate 10 Outgoing-side optical fiber 11 Electrode pad
Claims (9)
形成された光導波路と、この光導波路の直上又は近傍に
形成され、前記光導波路中を進行する光に電気信号を印
加して、前記光を変調するための電極とを具える進行波
型光変調器において、 前記電気信号と前記電気信号と逆向きの電気信号とを合
成し、この合成された電気信号により前記光導波路中を
進行する光の変調を行うことを特徴とする進行波型光変
調器。1. An optical waveguide formed on a substrate having at least an electro-optic effect, and an electric signal applied to light formed immediately above or in the vicinity of the optical waveguide and traveling in the optical waveguide, thereby converting the light. A traveling wave type optical modulator comprising an electrode for modulating, wherein the electric signal and an electric signal in a direction opposite to the electric signal are combined, and the light traveling in the optical waveguide by the combined electric signal. A traveling-wave optical modulator characterized by performing modulation.
記電極の特性インピーダンスと異なる値の抵抗を前記電
極の終端部に設置することにより発生させることを特徴
する、請求項１に記載の進行波型光変調器。2. The electric signal according to claim 1, wherein the electric signal in the opposite direction to the electric signal is generated by installing a resistor having a value different from a characteristic impedance of the electrode at a terminal end of the electrode. Traveling wave optical modulator.
は、前記電極の特性インピーダンスよりも小さいことを
特徴とする請求項２に記載の進行波型光変調器。3. The traveling wave optical modulator according to claim 2, wherein a value of a resistor installed at a terminal portion of the electrode is smaller than a characteristic impedance of the electrode.
記電極を構成する信号電極の終端部のインピーダンス
を、前記電極の特性インピーダンスと異なる値に設定す
ることにより発生させることを特徴とする、請求項１に
記載の進行波型光変調器。4. An electric signal in a direction opposite to the electric signal is generated by setting an impedance of a terminal portion of a signal electrode constituting the electrode to a value different from a characteristic impedance of the electrode. The traveling wave optical modulator according to claim 1.
は、前記電極の特性インピーダンスよりも小さいことを
特徴とする請求項４に記載の進行波型光変調器。5. The traveling wave optical modulator according to claim 4, wherein the impedance at the end of the signal electrode is smaller than the characteristic impedance of the electrode.
板は、ニオブ酸リチウムであることを特徴とする請求項
１〜５にいずれか一に記載の進行波型光変調器。6. The traveling wave optical modulator according to claim 1, wherein the substrate having at least the electro-optical effect is lithium niobate.
形成された光導波路中を進行する光に対して、前記光導
波路の直上又は近傍に形成された電極から電気信号を印
加して、前記光導波路中を進行する光を変調する進行波
型光変調方法において、 前記電気信号と前記電気信号と逆向きの電気信号とを合
成し、この合成された電気信号により前記光導波路中を
進行する光の変調を行うことを特徴とする進行波型光変
調方法。7. An optical waveguide, wherein an electric signal is applied to light traveling in an optical waveguide formed on a substrate having at least an electro-optical effect from an electrode formed immediately above or in the vicinity of the optical waveguide. In the traveling wave type light modulation method of modulating light traveling in the light, the electric signal and the electric signal in the opposite direction to the electric signal are combined, and the combined electric signal is used for light traveling in the optical waveguide. A traveling-wave-type light modulation method, comprising performing modulation.
記電極の特性インピーダンスと異なる値の抵抗を前記進
行波型光変調器の終端部に設置することにより発生させ
ることを特徴する、請求項７に記載の進行波型光変調方
法。8. The electric signal in a direction opposite to the electric signal is generated by installing a resistor having a value different from a characteristic impedance of the electrode at a terminal end of the traveling wave optical modulator. Item 10. A traveling wave optical modulation method according to Item 7.
記電極を構成する信号電極の終端部のインピーダンス
を、前記電極の特性インピーダンスと異なる値に設定す
ることにより発生させることを特徴とする、請求項７に
記載の進行波型光変調器。9. An electric signal in a direction opposite to the electric signal is generated by setting an impedance of a terminal portion of a signal electrode constituting the electrode to a value different from a characteristic impedance of the electrode. The traveling wave optical modulator according to claim 7.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP09354836A JP3088988B2 (en) | 1997-12-24 | 1997-12-24 | Traveling wave optical modulator and optical modulation method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP09354836A JP3088988B2 (en) | 1997-12-24 | 1997-12-24 | Traveling wave optical modulator and optical modulation method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11183858A true JPH11183858A (en) | 1999-07-09 |
| JP3088988B2 JP3088988B2 (en) | 2000-09-18 |
Family
ID=18440238
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP09354836A Expired - Lifetime JP3088988B2 (en) | 1997-12-24 | 1997-12-24 | Traveling wave optical modulator and optical modulation method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3088988B2 (en) |
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