JP2004023537A - Optical phase detection apparatus, optical phase control apparatus, and optical transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical phase detection apparatus capable of detecting an inter-bit phase state of a carrier of a modulation optical signal, an optical phase control apparatus for controlling a carrier phase on the basis of phase detection information of the carrier, and an optical transmission apparatus. <P>SOLUTION: The optical phase detection apparatus related to this invention in order to solve the tasks above and for detecting the inter-bit phase difference of the carrier of the modulation signal light is characterized in by including: a phase difference provisioning means that divides the modulation signal light into at least two, provides a prescribed phase difference to the first branched modulation signal light and the second modulation signal light and composes the results; and a phase difference detection means for detecting the inter-bit phase difference of the carrier of the modulation signal light on the basis of the luminous intensity of the output as a result of the composition by the phase difference provisioning means. <P>COPYRIGHT: (C)2004,JPO

Description

で与えられる。
【００８０】
図１２は、石英製のＰＬＣ部１０１０に対する温度コントローラ１０５０による温度制御と、ＰＬＣ部１０１０に入力した変調信号光の位相変化との関係を示した説明図である。
【００８１】
図１２では、ＰＬＣ部１０１０のアーム導波路１０１５とアーム導波路１０１６との導波路長差を、２５℃を基準として５．１７ｍｍと１５．５１ｍｍとに設定した場合のものである。
【００８２】
ＰＬＣ部１０１０は石英製であるため、１５５０ｎｍ帯の光が感ずる屈折率の温度係数は３×１０−６である。また、熱膨張係数が６．８×１０−７であるので、１℃の上昇に対し、例えば５．１７ｍｍの導波路長差は３５ｎｍ変化する。基準となる温度からの温度差に対する導波路長差を図１２に示す。
【００８３】
図１２に示すように、導波路長差１５．５１ｍｍのＰＬＣ部１０１０の温度を±２５℃制御することで、両アームで与えられる導波路長の差にキャリアの位相で２πに相当する変化を与えることができる。
【００８４】
（Ｃ−２）第３の実施形態の効果
本実施形態では、温度コントローラ１０５０が、ＰＬＣ部１０１０の温度を制御することにより、ＰＬＣ部１０１０を導波する信号光の位相を調整することができる。
【００８５】
例えば、基準点から２５℃ずらすことにより、ＰＬＣ部１０１０のアーム導波路長差にキャリアの位相で２πに相当する変化を与えることができるため、この範囲で温度を設定することにより所望の位相差を作り出すことができる。
【００８６】
このため、ＰＬＣ部１０１０を作成する上で、アーム導波路長差の精度によらず、第２の実施形態で説明したようにＰＬＣ部４１０内の位相差π／２の状態を簡易に作り出すことができ、キャリアのビット間位相差をモニタすることができる。
【００８７】
（Ｄ）第４の実施形態
以下、本発明に係る光位相モニタ装置の第４の実施形態について図面を参照して説明する。
【００８８】
上述した第３の実施形態では、位相検知部１０６０のＰＬＣ部１０１０を温度コントローラ１０５０で温度制御したのに対して、第４の実施形態は、ＰＬＣ部が有する２本のアーム導波路のうち、一本のアーム導波路周辺の温度のみを調整する場合について説明する。
【００８９】
（Ｄ−１）第４の実施形態の構成及び動作
図１３は、第４の実施形態に係るＰＬＣ部の構成を示したブロック図である。また、図１４は、第４の実施形態に係る位相検知部の構成を断面的に示した図である。
【００９０】
図１４に示すように、第４の実施形態に係る位相検知部は、ＰＬＣ部１３１０と、ペルチェ素子１３１７と、サーミスタ１３１８とを備えている。
【００９１】
また、図１３に示すように、第４の実施形態に係るＰＬＣ部１３１０は、入力導波路１３１１と、Ｙ分岐導波路１３１２と、アーム導波路１３１３と、アーム導波路１３１４と、反射面１３１５と、反射面１３１６と、ヒータ１３１９、電源１３２０とを有するものである。
【００９２】
ここで、これら構成要件は、第１〜第３の実施形態で説明した構成要件と全く同一のものではないが、それぞれ対応するものであり、これら構成要件に対応する符号を付す。またこれらの機能説明は省略する。
【００９３】
本実施形態に係るＰＬＣ部１３１０は、第３の実施形態と異なり、ヒータ１３１９及びそのヒータ１３１９に電源電圧を供給する電源１３２０を備えている。
【００９４】
このヒータ１３１９は、電源１３２０からの電源電圧の供給をうけて、ＰＬＣ部１３１０が有するアーム導波路１３１４の周辺のみの温度を変化させるものである。
【００９５】
アーム導波路１３１３とアーム導波路１３１４との導波路長差は、３ビット分の１５．５１ｍｍに設定されている。また、アーム導波路１３１４は、ヒータ１３１９により温度調整されるものであり、そのヒータ１３１９による温度可変部の長さは２０ｍｍに設定されている。
【００９６】
次に、第４の実施形態に係る位相検知部の動作を説明する。
【００９７】
ＰＬＣ部１３１０に入力する変調信号光は、Ｙ分岐導波路１３１２によって分岐されて、アーム導波路１３１４及び１３１３へ与えられる。
【００９８】
ヒータ１３１９は、アーム導波路１３１４周辺の温度調整をしており、アーム導波路１３１４は、温度の影響を受けて屈折率が変化する。
【００９９】
ＰＬＣ全体の温度はサーミスタ１３１８とペルチェ素子１３１７により、例えば２５℃に制御される。
【０１００】
例えば、アーム導波路１３１４の屈折率がΔｎだけ変化すると、アーム導波路１３１３とアーム導波路１３１４との間で生じる、温度１℃あたりの位相変化量は、温度可変部の長さをｄ２とすると
【数２】

で与えられる。
【０１０１】
このように、温度可変部の長さｄ２は、第３の実施形態における導波路長差ｄ１に比して比較的大きく設計できる。
【０１０２】
つまり、本実施形態では、例えば温度可変部の長さｄ２を基準となる２５℃で２０．００ｍｍとすると、合波する際の２波の変調信号光の位相差は４０ｍｍの差となる。このような結果から、本実施形態は、２πの位相変化を１９℃の温度上昇で可能とすることができる。
【０１０３】
（Ｄ−２）第４の実施形態の効果
以上、第４の実施形態によれば、ヒータ１３１９を一方のアーム導波路にのみ設置して、一方にのみ温度調整するようにして温度可変部を比較的長くすることができるので、より小さな温度変化によりキャリアの位相変化を与えることができる。
【０１０４】
第４の実施形態では、１９℃の温度上昇をさせることで、２πの位相変化が可能になる。
【０１０５】
（Ｅ）第５の実施形態
次に、本発明に係る光位相モニタ装置の第５の実施形態について図面を参照して説明する。
【０１０６】
第５の実施形態は、ＰＬＣ部が有する２分岐されたアーム導波路のそれぞれの下部に、それぞれ独立に温度制御することを特徴とする。
【０１０７】
（Ｅ−１）第５の実施形態の構成及び動作
図１５は、第５の実施形態に係るＰＬＣ部の構成を示したブロック図である。また、図１６は、第５の実施形態に係る位相検知部の構成を断面的に示した図である。
【０１０８】
図１６に示すように、第５の実施形態に係る位相検知部１５６０は、ＰＬＣ部１５１０と、ペルチェ素子１５１７及び１５１９と、サーミスタ１５１８及び１５２０とを備えている。
【０１０９】
また、ＰＬＣ部１５１０は図１５に示すように、第１〜第３の実施形態で説明したＰＬＣ部に対応する構成要件を備えるものである。ここでは、これら構成要件の機能説明は省略する。
【０１１０】
なお、本実施形態では、アーム導波路１５１３とアーム導波路１５１４との導波路長差は３ビット分の１５．５１ｍｍに設定されている。また、アーム導波路１５１３の温度可変部の長さは１０ｍｍであり、アーム導波路１５１４の温度可変部の長さは２０ｍｍとする。
【０１１１】
ＰＬＣ部１５１０は、上述してきたＰＬＣ部と同様に２分岐されたアーム導波路１５１３及び１５１４を備えている。
【０１１２】
図１６に示すように、位相検知部１５６０は、ＰＬＣ部１５１０が有する２つのアーム導波路１５１３及び１５１４のそれぞれの下部に独立したペルチェ素子１５１７及び１５１９と、サーミスタ１５１８及び１５２０とを設置している。
【０１１３】
すなわち、ペルチェ素子１５１７とサーミスタ１５１８は、アーム導波路１５１３のみの温度調整をするものであり、ペルチェ素子１５１９とサーミスタ１５２０は、アーム導波路１５１４のみの温度調整をするものである。
【０１１４】
このような構成を備えた第５の実施形態に係る位相検知部の動作について説明する。
【０１１５】
ＰＬＣ部１５１０のＹ分岐導波路１５１２により分岐された変調信号光は、アーム導波路１５１３及び１５１４をそれぞれ通過する。
【０１１６】
アーム導波路１５１３は、直下に設置されているペルチェ素子１５１７及びサーミスタ１５１８により、温度調整されて屈折率が変化する。
【０１１７】
同様に、アーム導波路１５１４も、直下に設置されているペルチェ素子１５１９及びサーミスタ１５２０により、温度調整されて屈折率が変化する。
【０１１８】
これらアーム導波路１５１３及び１５１４は、それぞれ独立に温度調整される。
【０１１９】
一般的に、アーム導波路１５１３の温度可変部長をｄ３、アーム導波路１５１４の温度可変部長をｄ４とした場合、アーム導波路１５１３及び１５１４間で温度が１℃の変化した場合の位相変化量Δφは、
【数３】

例えば、基準点２５℃として、アーム導波路１５１３の周辺温度を下げるようにペルチェ素子１５１７は下げる方向に変化させ、アーム導波路１５１４の周辺温度を上げるようにペルチェ素子１５１９を上げる方向に変化させる。
【０１２０】
また、アーム導波路１５１３の温度可変部長を基準点２５℃で１０ｍｍとし、アーム導波路１５１４の温度可変部長を基準点２５℃で２０ｍｍとすると、位相変化量Δφを決定付ける温度可変部長ｄは３０ｍｍとなり、しかも変調信号光が往復することから６０ｍｍとなり比較的大きく設計することができる。
【０１２１】
なお、本実施形態に係る位相検知部は、それぞれ１３℃の温度変化で、２πの位相変化が可能となる。
【０１２２】
（Ｅ−２）第５の実施形態の効果
以上、第５の実施形態によれば、ＰＬＣ部１５１０が有する２つのアーム導波路１５１３及び１５１４のそれぞれに独立した温度調整回路を備え、それぞれについて独立して温度調整することにより、より効率よく位相変化量を調整することができる。
【０１２３】
例えば、２５℃を基準とし、それぞれペルチェ素子を逆方向に１３℃の温度変化をさせることで、両アーム導波路による位相差で２πの変化が可能になるため、比較的小さな温度変化で、ＰＬＣ出力に対して、所望の位相状態を作り出すことができる。
【０１２４】
（Ｆ）第６の実施形態
以下、本発明に係る光位相モニタ装置の第６の実施形態について図面を参照して説明する。
【０１２５】
上述してきた第１〜第５の実施形態に係る光位相モニタ装置は、サーキュレータと反射型ＰＬＣ部とを備えてモニタ制御する方式について説明したが、第６の実施形態に係る光位相モニタ装置は、より構成を簡易にした光位相モニタ装置について説明する。
【０１２６】
（Ｆ−１）第６の実施形態の構成及び動作
図１７は、第６の実施形態に係る光位相モニタ装置の内部構成を示すブロック図である。図１７に示すように、光位相モニタ装置は、位相検知部１７１０と、温度コントローラ１７２０と、光／電気変換部１７３０と、入力部１７４０と、出力部１７５０とを備えるものである。
【０１２７】
位相検知部１７１０は、図１７に示すように、入力部１７４０から変調信号光を受け取り、その変調信号光を２分岐して、温度コントローラ１７２０による温度制御を受けて、それら変調信号光に対して位相差を与えるものである。また、位相検知部１７１０は、分岐された２つの変調信号光を合波して、光／電気変換部１７３０へ与えるものである。
【０１２８】
また、図１８は、本実施形態に係る位相検知部１７１０の構成を説明する図である。
【０１２９】
図１８に示すように、位相検知部１７１０は、ＰＬＣ部１７１１と、ペルチェ素子１７１６と、サーミスタ１７１７とを有している。ＰＬＣ部１７１１は、入力導波路１７１２と、Ｙ分岐導波路１７１３と、アーム導波路１７１３及び１７１４と、合波導波路１７１５と、出力導波路１７１６とを有している。
【０１３０】
アーム導波路１７１３とアーム導波路１７１４とは、分岐された変調信号光が通過する導波路であり、それぞれ異なる導波路長を備えている。
【０１３１】
出力導波路１７１６は、アーム導波路１７１３を通過してきた変調信号光と、アーム導波路１７１４を通過してきた変調信号光とが合波された合波出力信号光を、光／電気変換部１７３０へ与えるものである。
【０１３２】
すなわち、位相検知部１７１０は、分岐した変調信号光に位相差を与えた後、それら変調信号光を合波して、そのまま光／電気変換部１７３０へ与える。
【０１３３】
第６の実施形態に係る光位相モニタ装置の動作を説明する。
【０１３４】
変調光信号は、例えばカプラ（図示しない）等で分岐されて、その一部の変調信号光が、入力部１７４０へ与えられる。
【０１３５】
入力部１７４０に入力された変調光信号は、位相検知部１７１０に与えられる。
【０１３６】
位相検知部１７１０に入力された変調信号光は、ＰＬＣ部１７１１の入力導波路１７１２を通過し、Ｙ分岐導波路１７１２により分岐される。
【０１３７】
Ｙ分岐導波路１７１２により分岐された変調信号光の一方は、アーム導波路１７１３を通過し、他方はアーム導波路１７１４を通過する。
【０１３８】
これらアーム導波路１７１３及び１７１４は所定の導波路長差を備えている。
【０１３９】
アーム導波路１７１３を通過してきた変調信号光と、アーム導波路１７１４を通過してきた変調信号光とは、合波導波路１７１５により重ね合わされる。
【０１４０】
このとき、両アーム導波路１７１３及び１７１４間で与えられる位相差は、巨視的には１ビット（例えば４０Ｇｂｉｔ／ｓであれば２５ｐｓ）である。
【０１４１】
また、微視的にキャリアの位相に対し２πの整数倍から、πだけずれていれば、キャリアのビット間位相差によって、ＰＬＣ出力は図９（ａ）〜（ｅ）で示した波形となる。
【０１４２】
また、微視的にキャリアの位相に対し２πの整数倍から、π／２だけずれていれば、キャリアのビット間位相差は図９（ｆ）〜（ｊ）で示した波形となる。
【０１４３】
（Ｆ−２）第６の実施形態の効果
以上、本実施形態によれば、位相検知部１７１０からの出力を、そのまま光／電気変換部１７３０へ与えるようにしたので、光位相装置にサーキュレータを省くことができる。その結果として、装置構成をより簡便にすることができる。
【０１４４】
（Ｇ）第７の実施形態
以下では、本発明に係る光位相制御装置についての実施形態を説明する。
【０１４５】
第７の実施形態は、ＯＴＤＭ伝送方式を採用した高速光伝送システムにおいて、送信器から送信された変調信号光の一部をモニタする光位相モニタ装置を備え、その光位相モニタ装置からのモニタ信号を用いて、ビット間キャリア位相差を制御する装置に適用した場合について説明する。
【０１４６】
なお、変調信号光の伝送速度は４０Ｇｂｉｔ／ｓであるとする。
【０１４７】
（Ｇ−１）第７の実施形態の構成
図１９は、本実施形態に係る光位相制御装置の構成を示したブロック図である。
【０１４８】
図１９に示すように、光位相制御装置は、大別して、ＯＴＭＤモジュール６００と、光位相モニタ装置とを備えており、この光位相モニタ装置は位相検知部１０６０と、温度コントローラ１０５０と、光／電気制御部７００とを備えている。
【０１４９】
光位相モニタ装置は、上述してきた第１〜第６の実施形態に係る光位相モニタ装置に適用することができるものであるが、本実施形態では、第４の実施形態で説明した光位相モニタ装置を適用する。
【０１５０】
なお、光位相モニタ装置の各構成要件には、第４の実施形態で説明した構成要件に対応する符号を付した。
【０１５１】
ＯＴＭＤモジュール６００は、ハーフミラー６０３と、プリズム６０４と、ＥＡ変調器６０５と、プリズム６０６と、ＥＡ変調器６０７と、プリズム６０８と、ビット間キャリア位相差コントローラ８００と、ハーフミラー６１０と、プリズム６１１と、プリズムと６１２、プリズム６１３とを有するものである。
【０１５２】
ハーフミラー６０３は、ＯＴＤＭモジュール６００に入力してきた２０ＧＨｚの光短パルス列を受け、その光短パルス列を２分岐して、一方をプリズム６０４を通じてＥＡ変調器６０５へ与え、他方をプリズム６１２及び６１３を通じてＥＡ変調器６０７へ与える。
【０１５３】
ＥＡ変調器６０５及び６０７は、ハーフミラー６０３により分岐されたそれぞれの光短パルス列を受け取り、それぞれの光短パルス列を２０Ｇｂｉｔ／ｓ電気変調信号によりコーディングして、ＲＺ光データ信号列として出力するものである。
【０１５４】
また、ＥＡ変換器６０７は、コーディングしたＲＺ光データ信号列をビット間キャリア位相差コントローラ８００へ与えるものである。また、ＥＡ変換器６０５は、コーディングしたＲＺ光データ信号列をプリズム６０６及び６１１を介して、ハーフミラー６１０へ与えるものである。
【０１５５】
ビット間キャリア位相差コントローラ８００は、ＥＡ変調器６０７からＲＺ光データ信号列を受け取り、また、光／電気変換部７００からのモニタ信号を受け取り、そのモニタ信号に基づく温度調整によって、そのＲＺ光データ信号列の位相を調整するものである。ビット間キャリア位相差コントローラ８００は、光／電気変換部７００からのモニタ信号に基づいて温度調整を行ない、光路の屈折率の変化させ及び熱膨張を生じさせることにより、光路長を変化させるものである。
【０１５６】
ビット間キャリア位相差コントローラ８００は、ＲＺ光データ信号列の位相を調整してハーフミラー６１０に与えるものである。
【０１５７】
ハーフミラー６１０は、ＥＡ変換器６０５からＲＺ光データ信号列を受け取り、又、ビット間キャリア位相差コントローラ８００から位相調整されたＲＺ光データ信号列を受け取り、これらＲＺ光データ信号列を重ね合せて合波するものである。
【０１５８】
（Ｇ−２）第７の実施形態の動作
２０ＧＨｚの光短パルス列が、ＯＴＤＭモジュール６００へ入力する。
【０１５９】
入力した光短パルス列は、ハーフミラー６０３により２分岐され、一方の系統の光短パルス列（光短パルス列１）は、プリズム６０４で反射されてＥＡ変調器６０５に与えられ、また他方の系統の光短パルス列（光短パルス列２）は、プリズム６１２及び６１３で反射されてＥＡ変調器６０７へ与えられる。
【０１６０】
光短パルス列１は、ＥＡ変調器６０５により、２０Ｇｂｉｔ／ｓ電気変調信号によりコーディングされ、ＲＺ光データ信号列１となる。
【０１６１】
ＥＡ変調器６０５からのＲＺ光データ信号列１は、プリズム６０６及び６１１で反射され、ハーフミラー６１０に与えられる。
【０１６２】
また、光短パルス列２も、ＥＡ変調器６０７により、２０Ｇｂｉｔ／ｓ電気変調信号によりコーディングされ、ＲＺ光データ信号列２となる。
【０１６３】
ＥＡ変調器６０７からのＲＺ光データ信号列２は、プリズム６０８で反射され、ビット間キャリア位相差コントローラ８００に与えられる。
【０１６４】
ＥＡ変調器６０７からのＲＺ光データ信号列は、ビット間キャリア位相差コントローラ８００により位相変調を受け、位相変調を受けたＲＺ光データ信号列がハーフミラー６１０に与えられる。
【０１６５】
ハーフミラー６１０に与えられた２系統のＲＺ光データ信号列は、ハーフミラー６１０により合波され出力される。
【０１６６】
なお、２系統間の光路差は７．５ｍｍに設定されており、ビット間キャリア位相差コントローラ８００は波長以下の精度で微調することができる。すなわち、ビット間キャリア位相コントローラ８００は、光／電気変換部７００からのモニタ信号に基づいて温度を調整して、屈折率を変化させ又熱膨張を生じさせて、光路長を変化させる。
【０１６７】
このようにして、ＯＴＤＭモジュール６００から出力信号（変調信号光）が出力される。
【０１６８】
ＯＴＤＭモジュール６００から出力された信号（変調信号光）は、カプラ２００により、少量が位相検知部１０６０へ与えられる。
【０１６９】
例えば、ＯＴＤＭモジュール６００からの出力信号（変調信号光）のうち、１％だけ分岐され位相検知部１０６０に入力される。
【０１７０】
位相検知部１０６０に入力された変調信号光は、第４の実施形態で説明した動作により、光位相モニタされる。つまり、図示しない２本のアーム導波路間の導波路長差が変調信号光に対して、１／２πの位相差が生じるように設定してある。
【０１７１】
温度コントローラ１０５０は、位相検知部０１０６０のＰＬＣ部（図示しない）の温度が一定になるように制御する。
【０１７２】
位相検知部１０６０によって１／２の位相差が与えられた変調信号光は、光／電気変換部７００へ与えられる。
【０１７３】
また、カプラ２００により分岐された変調信号光は、カプラ９００により、さらに分岐されて、光／電気変換部７００へ与えられる。
【０１７４】
位相検知部１０６０からの変調信号光と、カプラ９００からの変調信号光とは、光／電気変換部７００において、それぞれの平均パワーが求められ、それらの平均パワー比がビット間キャリア位相差コントローラ８００へ与えられる。この平均パワー比がモニタ信号である。
【０１７５】
このように、光／電気変換部７００がそれぞれの変調信号光平均パワーを求めるのは、変調信号光が変動した場合の影響を抑えるようにするためである。
【０１７６】
また、平均パワー比をビット間キャリア位相差コントローラ８００にフィードバックすることで、ビット間キャリア位相差コントローラ８００が、温度調整をして、ＯＴＭＤモジュール６００から出力される信号のビット間のキャリア位相差をπずらした状態になるように制御できる。
【０１７７】
図２０は、温度調整によるビット間キャリア位相差の変化を示した図である。
【０１７８】
図２０に示すように、横軸は基準点からの温度差であり、縦軸はビット間キャリア位相差である。
【０１７９】
このように、キャリアのビット間位相差は、基準となる温度で１０ｍｍの長さであれば、±９℃で２πの変化が可能であることが分かる。また、基準となる温度で５ｍｍの長さであれば、±１８℃で２πの変化が可能であることが分かる。
【０１８０】
（Ｇ−３）第７の実施形態の効果
以上、本実施形態によれば、光位相モニタ装置によりモニタされた光信号の光平均パワーに対して、位相コントローラの温度を変化させるフィードハック制御系を構成するため、キャリアのビット間位相差がπであるＣＳ−ＲＺフォーマットを維持することができる。
【０１８１】
（Ｈ）第８の実施形態
次に、本発明に係る光位相制御装置の実施形態について図面を参照して説明する。
【０１８２】
第８の実施形態は、第７の実施形態と同様に、ＯＴＭＤモジュール６００が光／電気変換部７００からのモニタ信号（平均パワー比）に基づいてビット間キャリア位相差を制御する装置に適用したものである。
【０１８３】
第８の実施形態は、印加される電圧により屈折率が変化するＥＣＢ（Ｅｌｅｃｔｒｉｃａｌｌｙ　Ｃｏｎｔｒｏｌｌｅｄ　Ｂｉｒｅｆｒｅｇｅｎｃｅ）を備え、光／電気変換部からのモニタ信号（平均光パワー）に基づいて、ビット間のキャリア位相を変化させるものである。
【０１８４】
（Ｈ−１）第８の実施形態の構成及び動作
第８の実施形態に係る光位相制御装置の全体構成は、図１９に示す第７の実施形態に係る光位相制御装置の全体構成に対応するものであり、第８の実施形態は、ＯＴＭＤモジュール６００のビット間キャリア位相差コントローラが、第７の実施形態と異なる。
【０１８５】
従って、以下では、このビット間キャリア位相差コントローラのみについて詳細に説明して、これ例外の機能構成の説明は省略する。
【０１８６】
第８の実施形態に係るビット間キャリア位相差コントローラは、少なくともＥＣＢセルと、このＥＣＢセルに印加する電源とを有するものである。
【０１８７】
図２１は、ＥＣＢセルの簡単な構成を示した説明図である。
【０１８８】
図２１に示すように、ＥＣＢセルは、２個の電極２１０１及び２１０２と、２個の基板２１０４及び２１０５と、液晶層２１０３とを有している。
【０１８９】
電極２１０１及び２１０２は、電源（図示しない）から電圧を印加される電極である。この２電極間に印加される電圧に応じて、液晶層２１０３の屈折率が変化する。
【０１９０】
図２２は、電源２２００に接続する液晶層２１０３の配向方向変化を示した図である。
【０１９１】
この液晶層２１０３は、結晶軸に対して光学異方性と、誘電率異方性とを有するものである。液晶層２１０３は、入力する信号光に対して、結晶軸の水平方向と垂直方向とに対してそれぞれ異なる屈折率を有しているものである。通常、結晶軸の水平方向が遅い軸であり、垂直方向が早い軸である。また、液晶層２１０３は、誘電率異方性を有するので、２電極間２１０１及び２１０２に印加される電圧に応じて、液晶の配向方向が変化する。
【０１９２】
例えば、電源２２００から電圧Ｅが印加された場合、結晶軸の水平方向は、基板平面からθ（Ｅ）となり、ＯＴＤＭモジュール６００内を進行する信号光の感じる屈折率は、
【数４】

となる。
【０１９３】
このようなＥＣＢセル２１００は、ＯＴＤＭモジュール６００内において偏光方向が維持され、この偏光方向が結晶軸の方向と一致するように設置される。
【０１９４】
また、ＥＣＢセル２１００は、動作安定化のため、例えば２５℃等に温度コントロールされている。
【０１９５】
次に、第８の実施形態に係る光位相制御装置の動作について説明する。
【０１９６】
ＯＴＤＭモジュール６００からの出力信号が、位相検知部１０６０に入力して位相差が与えられ、モニタ処理されるまでは、第７の実施形態と同様である。
【０１９７】
光／電気変換部７００によって求められた平均光パワー比は、ビット間キャリア位相差コントローラ８００に与えられる。
【０１９８】
ビット間キャリア位相差コントローラ８００は、電源２２００と、ＥＣＢセル２１００とを有しており、電源２２００によって、光／電気変換部７００からの平均光パワー比に基づいた電圧が、ＥＣＢセル２１００に印加される。
【０１９９】
ＥＣＢセル２１００に電圧が印加されると、その印加電圧に基づいて液晶層２１０３の屈折率が変化するので、ＯＴＭＤモジュール６００内を通過するビット間のキャリア位相差が調整される。
【０２００】
この液晶の屈折率異方性は、例えば１．７に対し０．２と大きいため、ＥＣＢセル２１００は、数μｍの液晶層２１０３に若干の電界を印加することで大きな屈折率変化を得ることができる。このため、基板の厚さを考慮しても小型化を図ることができる。
【０２０１】
（Ｈ−２）第８の実施形態の効果
以上、本実施形態によれば、ＯＴＭＤモジュール内を通過する信号光の偏光状態を維持する液晶層を有するＥＣＢセルを備えることにより、その液晶層の屈折異方性を利用して、ビット間のキャリア位相を制御することができる。このため、装置の小型化と小消費電力化を図ることができる。
【０２０２】
（Ｉ）第９の実施形態
次に、本発明に係る光位相制御装置の実施形態について図面を参照して説明する。
【０２０３】
第９の実施形態は、マッハツェンダ型の変調器によって出力されるＲＺ信号光の位相制御に適用した装置について説明する。
【０２０４】
（Ｉ−１）第９の実施形態の構成及び動作
図２３は、第９の実施形態に係る光位相制御装置の構成を示した構成図である。
【０２０５】
図２３に示すように、第８の実施形態に係る光位相制御装置は、交番位相ＲＺ変換器２３００と、カプラ２００と、カプラ９００と、位相検知部１０６０と、温度コントローラ１０５０と、光／電気変換器及び制御信号発生器２３２０とを備えるものである。
【０２０６】
また、交番位相ＲＺ変換器２３００は、デュアルドライブ型マッハツェンダ変調器２３０１と、バイアス２３０２と、電気終端２３０３と、電気終端２３０４と、移相器２３０５と、パワーデバイダ２３０６と、増幅器２３０７と、光信号入力端２３０８と、電気信号入力端２３０９と、バイアス印加２３１０とを有する。
【０２０７】
以下、第９の実施形態に係る光位相制御装置の動作を説明する。
【０２０８】
デュアルドライブ型マッハツェンダ変調器２３０１の出力は、カプラ２００により一部分岐され、位相検知部１０６０へ与えられる。位相検知部１０６０のＰＬＣ部（図示しない）により位相差が与えられる。
【０２０９】
ここで、図２４は、位相検知部から出力される平均パワーを示した図である。
【０２１０】
位相検知部１０６０のＰＬＣ部からの出力は、両アーム導波路の導波路長差により図２４に示した平均パワーが得られる。
【０２１１】
ただし、ＰＬＣ部の入力パワーは両アーム導波路の導波路長差によって位相が合致するように合波された場合、最も傾きが大きく、感度が高い。このような平均パワーを十分帯域の狭いフォトダイオードで光−電気変換することで、図２４で示した平均パワーを電気信号に変えることができる。
【０２１２】
また、入力信号の強度変動による影響を除くために、ＰＬＣの入力信号の一部を分岐し、同様に帯域の狭いフォトダイオードで光−電気変換し、この値と前述のＰＬＣ出力から得られた電気信号の比をとることで、制御信号とする。
【０２１３】
（Ｉ−２）第９の実施形態の効果
以上、本実施形態によれば、制御信号を増幅器２３０７にフィードバックをかけることで出力光信号が安定する振幅をマッハツェンダ変調器に供給することができる。
【０２１４】
（Ｊ）他の実施形態
上述した第１〜第６の実施形態で説明したキャリア位相差検出装置は、上述した第７〜第９の実施形態で説明した光位相制御装置に採用することができる。
【０２１５】
また、上述した第１〜第６の実施形態で説明したＰＬＣ部は、１つの入力導波路と、１つのＹ分岐導波路と、２つのアーム導波路及びそれぞれのアーム導波路が有する全反射面を備える場合と、また、１つの入力導波路と、１つのＹ分岐導波路と、２つのアーム導波路と、１つのＹ合波導波路及び１つの出力導波路とを備える場合との２つの構成例について説明したが、これら構成に限られることなく、所望のキャリア位相差を得ることができれば、ＰＬＣ部の形態によらず、同様の効果を得ることができる。
【０２１６】
また、光学ブロックなどで所望の位相差を得ることができればＰＬＣに限らず、同様の効果を得ることができる。
【０２１７】
また、キャリアの位相を変調するコントローラの材質はＢＫ７に限らず、ＳＦ６など別の材料によっても同様の効果を得ることができる。また、位相をコントロールする手段によらず、同様の効果を得ることができる。
【０２１８】
さらに、上述した実施形態のＰＬＣ部が、入力される変調信号光を２分岐することとして説明したが、２分岐以上できるようにしてもよい。例えば、ＰＬＣ部が３分岐できるものとする場合、第１の変調信号光のキャリアと、第２の変調信号光のキャリアとの間で位相差を与えて、それらの合波出力の第１の光強度を求め、またさらに、第２の変調信号光のキャリアと、第３の変調信号光のキャリアとの間で別の位相差を与えて、それらの合波出力の第２の光強度を求めるようにしてもよい。
【０２１９】
【発明の効果】
以上、本発明によれば、変調信号光のキャリアのビット間位相差を検知する光位相検知装置において、変調信号光を少なくとも２分岐して、第１の分岐変調信号光と、第２の分岐変調信号光とに所定の位相差を与えた後に合波する位相差付与手段と、位相差付与手段により合波された合波出力の光強度に基づいて、変調信号光のキャリアのビット間位相差を検知する位相差検出手段とを備えることにより、簡単な構成で変調信号光のキャリアのビット間位相差を検知できる。
【図面の簡単な説明】
【図１】第１の実施形態の光位相検知装置を含む伝送システムの構成を示した図である。
【図２】第１の実施形態の光位相モニタ部の構成を示した図である。
【図３】第１の実施形態の平面導波路の構成を示した図である。
【図４】第１の実施形態のＰＬＣ部による合波された信号多重を説明する説明図である
【図５】第１の実施形態キャリア位相差と光強度との関係を説明する説明図である。
【図６】第２の実施形態の光位相モニタ部の構成を示した図である。
【図７】第２の実施形態の平面導波路の構成を示した図である。
【図８】第２の実施形態キャリア位相差と光強度との関係を説明する説明図である。
【図９】第２の実施形態に係るＰＬＣ部の出力信号波形を示した図である。
【図１０】第３の実施形態の光位相モニタ部の構成を示した図である。
【図１１】第３の実施形態の位相検知部と温度コントローラとの接続構成を示した図である。
【図１２】第３の実施形態の位相検知部により基準となる温度からの温度差に対する位相差を示した図である。
【図１３】第４の実施形態の位相検知部の構成を示した図である。
【図１４】第４の実施形態の位相検知部の構成を示した図である。
【図１５】第５の実施形態の位相検知部の構成を示した図である。
【図１６】第５の実施形態の位相検知部の構成を示した図である。
【図１７】第６の実施形態の光位相モニタ部の構成を示した図である。
【図１８】第６の実施形態の位相検知部を構成を示した図である。
【図１９】第７の実施形態の位相制御装置の構成を示した構成図である。
【図２０】第７の実施形態における基準点からの温度差と位相差との関係を説明する図である。
【図２１】第８の実施形態のＥＣＢセルの構成を示す図である。
【図２２】第８の実施形態のＥＣＢセルの動作を説明する説明図である。
【図２３】第９の実施形態の駆動電圧制御装置の構成を示す図である。
【図２４】第９の実施形態の駆動電圧制御装置の電圧と出力強度との関係を説明する図である。
【符号の説明】
３００、４００…モニタ部、
１０６０、１３６０、１５６０、１７１０位相検知部、
３１０、４１０、１０１０、１３１０、１５１０、１７１０…平面導波路、
３１１、４１１、１０１１、１３１１、１５１１、１７１１…入出力導波路、３１２、４１２、１０１２、１３１２、１５１２、１７１２…Ｙ分岐導波路、
３１３、３１４、４１３、４１４、１０１３、１０１４、
１３１３、１３１４、１５１３、１５１４、１７１３、１７１４…アーム導波路、
３１５、３１６、４１５、４１６、１０１５、１０１６、
１３１５、１３１６、１５１５、１５１６、１７１５、１７１６…反射面、
３３０、４３０、７００、１０３０、１７３０…光／電気変換部、
１０５０、１７２０…温度コントローラ、
６００…ＯＴＤＭモジュール、８００…ビット間キャリア位相差コントローラ、
６０５、６０７…ＥＡ変換器、２１００…ＥＣＢセル、
２１０１、２１０２…電極、２１０３…液晶層
２３００…交番位相ＲＺ変換器、２３０７…増幅器、２３０５…移相器、
２３２０…光／電気変換器及び制御信号発生器。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical phase detection device, an optical phase control device, and an optical transmission device, and can be applied to, for example, an optical phase control system using a planar lightwave circuit (PLC) in an optical transmission system.
[0002]
In addition, for example, an optical transmission including a drive voltage control device of an alternating phase RZ modulation system using a lithium niobate (LiNbO3) Mach-Zehnder optical modulator (hereinafter referred to as LN-MZM) widely used as a high-speed optical modulator. Applicable to the device.
[0003]
[Prior art]
For example, in a high-speed optical transmission system of 40 Gbit / s or more, in order to extend long-distance transmission, it is necessary to increase the input intensity of the signal light. As a result, waveform deterioration is caused, and transmission quality is also deteriorated.
[0004]
As a technique for preventing such waveform deterioration, generally, RZ (return-to-to-turn) is used to improve the limit of self-phase modulation effect (SPM), which is one of nonlinear optical effects in an optical fiber. -Zero) There is a modulation method.
[0005]
Further, as a modulation method for preventing waveform deterioration more than the RZ modulation method described above, there is a CS (Carrier-Suppressed) -RZ modulation method employing a Mach-Zehnder modulator described in the following document.
[0006]
Reference: Y. Miyamoto et. al. , OAA'99, PDA4, 1999
The transmission system based on the CS (Carrier-Suppressed) -RZ modulation system employing the Mach-Zehnder modulator described in this document is a system capable of suppressing waveform deterioration due to a more nonlinear effect and increasing input power. It is.
[0007]
[Problems to be solved by the invention]
However, since the transmission system based on the CS-RZ modulation system described in the above-mentioned literature uses a Mach-Zehnder modulator having two electrodes, the carrier phase difference between the bits of the carrier causes the fluctuation of the modulation amplitude. Caused by As a result, the waveform after transmission is deteriorated, and there is a problem that interference occurs between ON / OFF level codes of light.
[0008]
Further, in a transmission system employing the OTDM system as the multiplex transmission system, there is a possibility that a phase shift may occur due to a transmission environment.
[0009]
One method of monitoring such a phase shift is to use an optical spectrum analyzer. However, since the optical spectrum analyzer is expensive and large-scale, it is not practical to incorporate it as a part of the transmitter. Absent.
[0010]
Therefore, there is a need for an optical phase detector that can detect the inter-bit phase state of the carrier of a modulated optical signal used in the OTDM transmission system. There is also a need for an optical phase control device and an optical transmission device that control the carrier phase based on the carrier phase detection information from the optical phase detection device.
[0011]
[Means for Solving the Problems]
In order to solve such a problem, an optical phase detection device according to a first aspect of the present invention is an optical phase detection device that detects a phase difference between bits of a carrier of a modulation signal light, wherein the modulation signal light is split into at least two branches. Phase difference providing means for combining the first branched modulated signal light and the second branched modulated signal light after providing a predetermined phase difference, and the optical intensity of the combined output combined by the phase difference providing means And phase difference detection means for detecting a phase difference between bits of the carrier of the modulated signal light based on
[0012]
An optical phase control device according to a second aspect of the present invention is an optical phase control device for controlling a phase difference between bits of a carrier of a modulated signal light based on optical phase detection information fed back from the optical phase detection device. First modulation means for branching at least two optical pulse trains and modulating one of the branched optical pulse trains; and second modulation for modulating another one of the branched optical pulse trains Means for receiving optical phase detection information from the optical phase detection device, and adjusting the carrier phase of the modulated signal light modulated by the first modulation means based on the optical phase detection information; And a modulation signal light multiplexing means for multiplexing the modulation signal light from the means and the modulation signal light from the second modulation means.
[0013]
Further, the optical transmitting apparatus according to the third aspect of the present invention includes a carrier generation unit that generates carriers, and a data signal that is input using a refractive index change based on an electric field generated by an externally applied voltage. An optical transmission apparatus comprising: a modulation unit that modulates the intensity of the carrier generated by the carrier generation unit; and a phase control unit that controls the phase of the carrier so that the inter-bit phase difference of the carrier of the modulation signal light is inverted. And a drive voltage control means for controlling the voltage amplitude of the carrier controlled by the phase control means based on the optical phase detection information from the optical phase detection device for detecting the bit difference between the bits of the carrier.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(A) First embodiment
Hereinafter, a first embodiment of an optical phase detection device according to the present invention will be described in detail with reference to the drawings.
[0015]
In the first embodiment, in a high-speed optical transmission system employing CS-RZ modulation in the OTDM transmission method, a part of a modulated signal light transmitted from a transmitter is monitored, and a reflection type planar optical waveguide (PLC) is used. The case where the carrier phase of a part of the modulated signal is detected will be described.
[0016]
(A-1) Configuration of First Embodiment
FIG. 1 is an overall configuration diagram showing an overall configuration of a system having an optical phase detection device according to the present embodiment. The optical phase detection device will be described as an optical phase monitor.
[0017]
As shown in FIG. 1, the optical phase monitor 300 of the present embodiment receives a small amount of modulated signal light branched by the optical coupler 200 from the modulated signal light output from the transmitter 100, and modulates the small amount of modulated light. The monitoring is performed based on the signal light. Most of the remaining modulated signal light output from the transmitter 100 is output to the transmission path.
[0018]
FIG. 2 is a block diagram showing the internal configuration of the optical phase monitor 300. As shown in FIG. 2, the optical phase monitor 300 includes a planar optical waveguide (PLC) 310, a circulator 320, and an optical / electrical converter 330.
[0019]
The circulator 320 receives the modulated signal light provided from the input unit 340, outputs the modulated signal light from the PLC-side output port 321, and provides the modulated signal light to the PLC unit 310. The circulator 320 receives the output signal light from the PLC unit 310, outputs the output signal light from the optical / electrical converter side output port 322, and gives the output signal light to the optical / electrical conversion unit 330.
[0020]
The planar optical waveguide section (PLC section) 310 receives the modulated signal light from the circulator 320, demultiplexes the received modulated signal light, and gives a carrier phase difference between the bits of the two demultiplexed modulated signal lights. Things. Further, the planar optical waveguide section (PLC section) 310 further combines the two modulated signal lights having the phase differences and then supplies the combined signal light to the circulator 320. The detailed configuration of the planar optical waveguide (PLC) 310 will be described later.
[0021]
The optical / electrical conversion unit 330 receives the output signal light of the PLC unit 310 from the circulator 320, and converts the average power of the output signal light into a voltage.
[0022]
FIG. 3 is an internal configuration diagram showing the internal configuration of the planar optical waveguide section (PLC section) 310. The PLC section 310 has an input / output waveguide 311, a Y-branch waveguide 312, an arm waveguide 313, an arm waveguide 314, a reflection surface 315, and a reflection surface 316. The reflecting surfaces 315 and 316 can be obtained by depositing gold or the like after etching.
[0023]
The Y-branch waveguide 312 has two waveguides, an arm waveguide 313 and an arm waveguide 314. An end of the arm waveguide 313 has a reflection surface 315, and an end of the arm waveguide 314 is It has a reflective surface 316.
[0024]
There is a phase difference between the arm waveguides 313 and 314 so that the carrier phases can cancel each other between the branching and the re-combining.
[0025]
In the present embodiment, since the CS-RZ modulation method is adopted, the phase difference between the modulation signal light passing through the arm waveguide 313 and the modulation signal light passing through the arm waveguide 314 is delayed by one bit. So that only the amount equivalent to is given.
[0026]
(A-2) Operation of the first embodiment
Next, the operation of the optical phase detection device according to the first embodiment will be described.
[0027]
The modulated signal light from the transmitter 100 is split by the optical coupler 200, and a part of the modulated signal light is provided to the optical phase monitor 300.
[0028]
The modulated signal light provided to the optical phase monitor 300 is provided from the input unit 340 to the circulator 320, and is provided from the PLC side output port 321 of the circulator 320 to the PLC unit 310.
[0029]
The modulated signal light supplied to the PLC unit 310 is input from the input / output waveguide 311 and is branched into two by the Y branch waveguide 312.
[0030]
One of the branched modulated signal lights passes through the arm waveguide 313, is reflected by the reflection surface 1315, and passes through the arm waveguide 313 again.
[0031]
The other of the branched modulated signal lights passes through the arm waveguide 314, is reflected by the reflection surface 316, and passes through the arm waveguide 314 again.
[0032]
In this way, each modulated signal light returns to the Y branch circuit 312 again, is multiplexed by the Y branch circuit 312, and is output from the input / output waveguide 311.
For example, when the bit rate of the CS-RZ-modulated CS-RZ format signal (modulated signal light) is 40 Gbit / s, the PLC section 310 gives a phase difference between the branched modulated signal lights, thereby causing the carrier bit to be changed. The relationship between the phase difference and the light intensity will be described below.
[0033]
FIG. 4 is an explanatory diagram illustrating a signal multiplexing operation in which the PLC unit 310 gives a phase difference to two modulated signal lights and combines them. 4A shows a case where the carrier phase difference between adjacent bits is π, and FIG. 4B shows a case where the carrier phase difference between adjacent bits is 0. .
[0034]
In FIG. 4A, (1) to (3) show the other signal sequence of the modulated signal light (that is, the one that passes through the arm optical waveguide 314), and (4) to (6) show the modulated signal light. , Which is a delayed signal train (that is, one that passes through the arm optical waveguide 313).
[0035]
(1) and (4) show the logic of the input signal. (2) and (5) show the phase of the carrier for each bit of the CS-RZ format signal (modulated signal light). (3) and (6) show the intensity of the light pulse.
[0036]
Assuming that the phase difference given by the difference between the two arm waveguide lengths from the time when the modulated signal light is branched to the time when the modulated signal light is recombined is 25 ps (picoseconds), (4) and (4) in FIG. As shown in 5) and (6), the modulated signal light is delayed by exactly one bit, and is superimposed at exactly the same position as the previous signal. This phase difference of 25 ps (picosecond) corresponds to about 5.17 mm in the case of a quartz PLC.
[0037]
In this case, since the carrier phase of each bit of the OTDM signal is π, the output of the signal multiplexed by the Y branch circuit cancels out the bit whose carrier phase is inverted as shown in (11). .
[0038]
Also, in FIG. 4B, (7) and (8) show signals when the carrier phase of each bit is the same. In this case, the signals delayed by the PLC unit 310 are as shown in (9) and (10). When the signals are multiplexed by the Y-branch waveguide 312, “1” s are strengthened.
[0039]
As described above, when the phase difference between the bits of the carrier is π, the average optical output is minimized. When the phase difference between the bits of the carrier is 0, the average optical output becomes maximum.
[0040]
FIG. 5 is an explanatory diagram illustrating the relationship between the carrier phase difference every other bit and the average value of the output light intensity of the PLC unit 310. The result of FIG. 5 shows, as an example, a case where the modulated signal light to the PLC section 310 is 0 dBm (1 mW).
[0041]
Such output light of the PLC unit 310 is output from the optical / electrical converter side output port 322 without being returned to the main signal by the circulator 320, and is provided to the optical / electrical converter 330.
[0042]
The optical average power of the output light of the PLC section 310 is converted into a voltage by the optical / electrical conversion section 330.
[0043]
(A-3) Effects of the first embodiment
As described above, according to the first embodiment, since the phase state of light can be converted into a voltage, it is possible to monitor the phase state of light with a simple device by branching the monitor light from the main signal. become.
[0044]
The relationship between the phase state of light and the average power is as shown in FIG. When the phase difference between the carriers between the bits is π, the value of the monitor voltage is a minimum value, and when the phases of the carriers between the bits are aligned, the value of the monitor voltage is a maximum value. By converting this average power into an appropriate voltage, the carrier phase difference between bits can be grasped as a voltage.
[0045]
(B) Second embodiment
Hereinafter, a second embodiment of the optical phase detection device according to the present invention will be described in detail with reference to the drawings.
[0046]
In the second embodiment, the overall configuration of the system shown in FIG. 1 described in the first embodiment is the same as that of the first embodiment, and the configuration of the PLC unit of the optical phase monitor is the same as that of the first embodiment. And different.
[0047]
The PLC unit according to the second embodiment has a length of the arm waveguide so that the phase difference of the carrier of the optical signal becomes π / 2 when the two modulated modulation signal lights are multiplexed again. Is characterized in that it is finely adjusted.
[0048]
(B-1) Configuration of Second Embodiment
FIG. 6 is a block diagram showing the internal configuration of the optical phase monitor according to the second embodiment. FIG. 7 is a configuration diagram showing the configuration of the planar optical waveguide unit (PLC unit) 410.
[0049]
As shown in FIG. 7, the PLC section 410 according to the second embodiment includes an input / output waveguide 411, a Y-branch waveguide 412, an arm waveguide 413, an arm waveguide 414, a reflection surface 415, and a reflection surface 416. . The reflection surfaces 415 and 416 can be obtained by depositing and embedding gold or the like after etching.
[0050]
For example, when the bit rate of the modulated optical signal is 40 Gbit / s, the difference between the waveguide lengths of the reciprocating motion between the arm waveguides 413 and 414 is 5.17 mm macroscopically.
[0051]
However, when these are combined, the length between the arm waveguides 413 and 414 is adjusted so that the phase difference of the optical signal carrier becomes π / 2.
[0052]
Specifically, the length between the arm waveguides 413 and 414 is designed to be longer by an integral multiple (1.06 μm × n) of the wavelength in the PLC unit 410 by 0.27 μm (π / 2).
[0053]
The dimensions of such a configuration are manufactured by controlling the etching conditions when forming the reflection surface of the PLC.
[0054]
(B-2) Operation of the second embodiment
As in the first embodiment, a part of the modulated signal light from the transmitter 100 is supplied to the PLC component 410, and the modulated signal light supplied to the PLC unit 410 is branched by the Y-branch waveguide 412.
[0055]
One of the branched modulated signal lights passes through the arm waveguide 413, is reflected by the reflection surface 415, and passes through the arm waveguide 413 again.
[0056]
Another one of the branched modulated signal lights passes through the arm waveguide 414, is reflected by the reflection surface 416, and passes through the arm waveguide 414.
[0057]
These two modulated signal lights return to the Y branch circuit 412 again, and are combined by the Y branch circuit 412.
[0058]
The phase difference of the signal light carrier between the arm waveguides 413 and 414 is designed to be longer than an integral multiple (1.06 μm × n) to 0.27 μm (π / 2) of the wavelength in the PLC.
[0059]
For this reason, in the embodiment of the present invention, the phase difference between the two arm waveguides within the PLC section 410 is 25 ps (ie, 5.17 mm) macroscopically, but the carrier phase is shifted by π / 2 at the wavelength level. It is multiplexed in the state.
[0060]
In this case, the average power of the signal multiplexed by the PLC unit 410 has the maximum value when the carrier phase difference between the bits is shifted by π / 2, and the minimum value is obtained when the carrier position between the bits is low. This is the case where the phase difference is shifted by 3π / 2. When the carrier phase difference between bits is π, the sign of the slope does not change.
[0061]
FIG. 8 shows the average of the output of the PLC unit 410 when the light intensity of the modulated signal light input to the PLC unit 410 is 1 mW (0 dB), and when the phase difference between the arm waveguides is actually changed from half a bit. It shows the result of calculating the power.
[0062]
FIG. 8 also shows the results when the phase difference between the two arm waveguides 413 and 414 of the PLC section 410 is π / 2, when the phase difference is 0, when π, and when the phase difference is 3π / 2.
[0063]
FIG. 9 shows an example of the output signal waveform of the PLC unit 410. As shown in FIG. 9, (a) to (e) show the case where the phase difference between both arm waveguides is π, and (f) to (j) show the case where π / 2 in the present embodiment. From this calculation result, the average power with respect to the phase difference between the two signals generated by the two arm waveguides of the PLC can be obtained when the phase difference between the bits of the carrier is π by setting the phase difference by the PLC to π / 2. Is also no longer an extreme value.
[0064]
(B-3) Effects of the second embodiment
As described above, according to the second embodiment, the measurement sensitivity is improved as compared with the optical phase detection device according to the first embodiment, and it is possible to identify the change direction of the inter-bit phase difference of the carrier.
[0065]
That is, in the first embodiment, since the observation point is an extreme value, the inclination is 0, and thus the measurement sensitivity to a slight inter-bit phase difference of the carrier is low. However, in the second embodiment, by setting the carrier phase difference at the time of multiplexing to π / 2, the inclination can be increased and the measurement sensitivity can be increased even when the variation in the carrier bit-to-bit phase difference is small. .
[0066]
In the first embodiment, since the observation point is an extreme value, when the measured value changes, the direction of the change in the carrier phase difference based on the measured value (that is, whether the carrier phase difference increases or decreases) cannot be known. However, according to the second embodiment, by setting the carrier phase difference at the time of multiplexing to π / 2, it is possible to know the direction of the change in the inter-bit phase difference based on the measured value.
[0067]
(C) Third embodiment
Next, a third embodiment of the optical phase detecting device according to the present invention will be described with reference to the drawings.
[0068]
The optical phase detection device according to the third embodiment is characterized in that the temperature controller adjusts the temperature of the PLC unit to adjust the phase difference given to the modulated signal light input to the PLC unit.
[0069]
Therefore, the optical phase detection device according to the third embodiment can finely adjust the arm waveguide length difference by temperature control when creating the PLC section.
[0070]
(C-1) Configuration and Operation of Third Embodiment
FIG. 10 is a configuration diagram illustrating an internal configuration of the optical phase detection device according to the third embodiment. As shown in FIG. 10, the optical phase detection device has a phase detection unit 1060, a temperature controller 1050, a circulator 1020, and an optical / electrical conversion unit 1030. Note that components other than the temperature controller 1050 are connected by optical fibers.
[0071]
FIG. 11 is a diagram showing a connection between the optical phase detection unit 1060 and the temperature controller 1050 and an internal configuration.
[0072]
As shown in FIG. 11, the optical phase detection unit 1060 includes a PLC unit 1010, a Peltier device 1017, and a thermistor 1018.
[0073]
The PLC section 1010 has an input / output waveguide 1011, a Y-branch waveguide 1012, an arm waveguide 1013, an arm waveguide 1014, a reflection surface 1015, and a reflection surface 1016. The reflective surfaces 1015 and 1016 can be obtained by etching and then depositing and embedding gold or the like. In the present embodiment, the PLC unit 1010 is made of quartz. Therefore, the temperature coefficient of the refractive index felt by light of 1550 nm is 3 × 10 * −6. (Note that 10 * -6 means 10 to the sixth power.)
The waveguide length difference between the arm waveguide 1015 and the arm waveguide 1016 is set to, for example, 5.17 mm when shifted by 1 bit and 15.51 mm when shifted by 3 bits with reference to 25 ° C. Therefore, they are set to 2.59 nm and 7.75 nm.
[0074]
The temperature controller 1050 adjusts the temperature of the PLC unit 1010. The temperature controller 1050 changes the phase of the modulated signal light input to the PLC unit 1010 by shifting a predetermined temperature from the reference point.
[0075]
An operation of the optical phase monitoring device according to the third embodiment will be described.
[0076]
Similarly to the operations of the first and second embodiments described above, the modulation signal light input from the circulator 1020 is input to the PLC unit 1010 of the phase detection unit 1060, and the modulation signal light is split into two. Is given a phase difference. These two modulated signal lights are multiplexed by the PLC unit 1010 and provided to the circulator 1020.
[0077]
The temperature of the PLC section 1010 is adjusted by a temperature controller 1050 from a reference point (25 ° C. in the present embodiment), and the phase of the input modulated signal light is adjusted.
[0078]
Next, the results obtained by the present embodiment will be described with reference to the drawings.
[0079]
First, generally, the phase of light after propagating through a substance having a length d1 is given by 2πnd1 / λ, where n is the refractive index of the substance. Therefore, assuming that the thermal expansion coefficient ΔD and the temperature coefficient of the refractive index are Δn, the phase change Δφ when the temperature changes by 1 ° C. is
(Equation 1)

Given by
[0080]
FIG. 12 is an explanatory diagram showing the relationship between the temperature control of the quartz PLC unit 1010 by the temperature controller 1050 and the phase change of the modulated signal light input to the PLC unit 1010.
[0081]
FIG. 12 shows a case where the waveguide length difference between the arm waveguide 1015 and the arm waveguide 1016 of the PLC unit 1010 is set to 5.17 mm and 15.51 mm based on 25 ° C.
[0082]
Since the PLC section 1010 is made of quartz, the temperature coefficient of the refractive index at which light in the 1550 nm band is perceived is 3 × 10 −6. Further, since the coefficient of thermal expansion is 6.8 × 10 −7, for example, a waveguide length difference of 5.17 mm changes by 35 nm with a rise of 1 ° C. FIG. 12 shows a difference in waveguide length with respect to a temperature difference from a reference temperature.
[0083]
As shown in FIG. 12, by controlling the temperature of the PLC section 1010 having a waveguide length difference of 15.51 mm by ± 25 ° C., the change in the waveguide length given by both arms causes a change corresponding to 2π in carrier phase. Can be given.
[0084]
(C-2) Effects of the third embodiment
In the present embodiment, the temperature controller 1050 controls the temperature of the PLC unit 1010 so that the phase of the signal light guided through the PLC unit 1010 can be adjusted.
[0085]
For example, by shifting the arm waveguide length difference of the PLC unit 1010 by 25 ° C. from the reference point, a change corresponding to 2π in the phase of the carrier can be given. Therefore, by setting the temperature within this range, the desired phase difference can be obtained. Can be produced.
[0086]
For this reason, when creating the PLC unit 1010, regardless of the accuracy of the arm waveguide length difference, the state of the phase difference π / 2 in the PLC unit 410 can be easily created as described in the second embodiment. And the phase difference between the bits of the carrier can be monitored.
[0087]
(D) Fourth embodiment
Hereinafter, a fourth embodiment of the optical phase monitoring device according to the present invention will be described with reference to the drawings.
[0088]
In the above-described third embodiment, the temperature of the PLC section 1010 of the phase detection section 1060 is controlled by the temperature controller 1050. On the other hand, in the fourth embodiment, of the two arm waveguides of the PLC section, A case in which only the temperature around one arm waveguide is adjusted will be described.
[0089]
(D-1) Configuration and Operation of Fourth Embodiment
FIG. 13 is a block diagram illustrating a configuration of a PLC unit according to the fourth embodiment. FIG. 14 is a cross-sectional view illustrating a configuration of a phase detection unit according to the fourth embodiment.
[0090]
As shown in FIG. 14, the phase detection unit according to the fourth embodiment includes a PLC unit 1310, a Peltier element 1317, and a thermistor 1318.
[0091]
As shown in FIG. 13, the PLC unit 1310 according to the fourth embodiment includes an input waveguide 1311, a Y-branch waveguide 1312, an arm waveguide 1313, an arm waveguide 1314, and a reflection surface 1315. , A reflection surface 1316, a heater 1319, and a power supply 1320.
[0092]
Here, these components are not exactly the same as the components described in the first to third embodiments, but correspond to the respective components, and reference numerals corresponding to the components are given. Description of these functions is omitted.
[0093]
The PLC unit 1310 according to the present embodiment includes a heater 1319 and a power supply 1320 that supplies a power supply voltage to the heater 1319 unlike the third embodiment.
[0094]
The heater 1319 changes the temperature only around the arm waveguide 1314 of the PLC unit 1310 in response to the supply of the power supply voltage from the power supply 1320.
[0095]
The waveguide length difference between the arm waveguide 1313 and the arm waveguide 1314 is set to 15.1 mm for 3 bits. The temperature of the arm waveguide 1314 is adjusted by a heater 1319, and the length of the temperature variable portion by the heater 1319 is set to 20 mm.
[0096]
Next, the operation of the phase detector according to the fourth embodiment will be described.
[0097]
The modulated signal light input to the PLC unit 1310 is branched by the Y-branch waveguide 1312 and provided to the arm waveguides 1314 and 1313.
[0098]
The heater 1319 adjusts the temperature around the arm waveguide 1314, and the refractive index of the arm waveguide 1314 changes under the influence of the temperature.
[0099]
The temperature of the entire PLC is controlled to, for example, 25 ° C. by the thermistor 1318 and the Peltier element 1317.
[0100]
For example, when the refractive index of the arm waveguide 1314 changes by Δn, the amount of phase change generated between the arm waveguide 1313 and the arm waveguide 1314 per 1 ° C. is given assuming that the length of the temperature variable portion is d2.
(Equation 2)

Given by
[0101]
As described above, the length d2 of the temperature variable portion can be designed to be relatively large as compared with the waveguide length difference d1 in the third embodiment.
[0102]
That is, in the present embodiment, for example, if the length d2 of the temperature variable portion is 20.00 mm at 25 ° C. as a reference, the phase difference between the two modulated signal lights at the time of multiplexing is 40 mm. From such a result, in the present embodiment, a phase change of 2π can be made possible by a temperature rise of 19 ° C.
[0103]
(D-2) Effects of the fourth embodiment
As described above, according to the fourth embodiment, the heater 1319 is installed in only one arm waveguide, and the temperature can be adjusted only in one of the arm waveguides, so that the temperature variable section can be made relatively long. The change can give a phase change of the carrier.
[0104]
In the fourth embodiment, a 2π phase change is possible by increasing the temperature by 19 ° C.
[0105]
(E) Fifth Embodiment
Next, a fifth embodiment of the optical phase monitoring device according to the present invention will be described with reference to the drawings.
[0106]
The fifth embodiment is characterized in that the temperature is controlled independently below each of the two branched arm waveguides of the PLC section.
[0107]
(E-1) Configuration and Operation of Fifth Embodiment
FIG. 15 is a block diagram illustrating a configuration of a PLC unit according to the fifth embodiment. FIG. 16 is a cross-sectional view illustrating a configuration of a phase detection unit according to the fifth embodiment.
[0108]
As shown in FIG. 16, the phase detection unit 1560 according to the fifth embodiment includes a PLC unit 1510, Peltier elements 1517 and 1519, and thermistors 1518 and 1520.
[0109]
Further, as shown in FIG. 15, the PLC unit 1510 has components corresponding to the PLC units described in the first to third embodiments. Here, the description of the functions of these components is omitted.
[0110]
In the present embodiment, the difference between the waveguide lengths of the arm waveguides 1513 and 1514 is set to 15.51 mm for three bits. The length of the temperature variable portion of the arm waveguide 1513 is 10 mm, and the length of the temperature variable portion of the arm waveguide 1514 is 20 mm.
[0111]
The PLC unit 1510 includes arm waveguides 1513 and 1514 that are branched into two similarly to the PLC unit described above.
[0112]
As shown in FIG. 16, the phase detection unit 1560 is provided with independent Peltier elements 1517 and 1519 and thermistors 1518 and 1520 below the two arm waveguides 1513 and 1514 of the PLC unit 1510, respectively. .
[0113]
That is, the Peltier element 1517 and the thermistor 1518 adjust the temperature of only the arm waveguide 1513, and the Peltier element 1519 and the thermistor 1520 adjust the temperature of only the arm waveguide 1514.
[0114]
An operation of the phase detection unit according to the fifth embodiment having such a configuration will be described.
[0115]
The modulated signal light branched by the Y branch waveguide 1512 of the PLC unit 1510 passes through the arm waveguides 1513 and 1514, respectively.
[0116]
The temperature of the arm waveguide 1513 is adjusted by the Peltier element 1517 and the thermistor 1518 installed immediately below, and the refractive index changes.
[0117]
Similarly, the arm waveguide 1514 is temperature-adjusted by the Peltier element 1519 and the thermistor 1520 installed immediately below, and the refractive index changes.
[0118]
The temperature of these arm waveguides 1513 and 1514 is independently adjusted.
[0119]
Generally, when the temperature variable portion length of the arm waveguide 1513 is d3 and the temperature variable portion length of the arm waveguide 1514 is d4, the phase change amount Δφ when the temperature changes by 1 ° C. between the arm waveguides 1513 and 1514. Is
[Equation 3]

For example, assuming that the reference point is 25 ° C., the Peltier element 1517 is changed so as to lower the peripheral temperature of the arm waveguide 1513, and the Peltier element 1519 is changed so as to increase the peripheral temperature of the arm waveguide 1514.
[0120]
Further, if the length of the temperature variable portion of the arm waveguide 1513 is 10 mm at the reference point 25 ° C. and the length of the temperature variable portion of the arm waveguide 1514 is 20 mm at the reference point 25 ° C., the length d of the temperature variable portion that determines the phase change Δφ is 30 mm. In addition, since the modulated signal light reciprocates, the distance becomes 60 mm, which can be designed relatively large.
[0121]
The phase detector according to the present embodiment can change the phase by 2π at a temperature change of 13 ° C.
[0122]
(E-2) Effects of the fifth embodiment
As described above, according to the fifth embodiment, each of the two arm waveguides 1513 and 1514 of the PLC unit 1510 is provided with an independent temperature adjustment circuit, and the temperature is adjusted independently for each of the two arm waveguides. The amount of change can be adjusted.
[0123]
For example, by changing the temperature of the Peltier element by 13 ° C. in the opposite direction with respect to 25 ° C., it becomes possible to change 2π by the phase difference between the two arm waveguides. A desired phase state can be created for the output.
[0124]
(F) Sixth embodiment
Hereinafter, a sixth embodiment of the optical phase monitoring device according to the present invention will be described with reference to the drawings.
[0125]
Although the optical phase monitoring devices according to the first to fifth embodiments described above have been described with respect to a method of performing monitor control by including a circulator and a reflective PLC unit, the optical phase monitoring device according to the sixth embodiment An optical phase monitor device having a simpler configuration will be described.
[0126]
(F-1) Configuration and Operation of Sixth Embodiment
FIG. 17 is a block diagram illustrating an internal configuration of the optical phase monitor device according to the sixth embodiment. As shown in FIG. 17, the optical phase monitoring device includes a phase detection unit 1710, a temperature controller 1720, an optical / electrical conversion unit 1730, an input unit 1740, and an output unit 1750.
[0127]
As shown in FIG. 17, the phase detection unit 1710 receives the modulated signal light from the input unit 1740, splits the modulated signal light into two, receives the temperature control by the temperature controller 1720, and It gives a phase difference. Further, the phase detection unit 1710 combines the two branched modulated signal lights and supplies the combined signal light to the optical / electrical conversion unit 1730.
[0128]
FIG. 18 is a diagram illustrating the configuration of the phase detection unit 1710 according to the present embodiment.
[0129]
As shown in FIG. 18, the phase detection unit 1710 has a PLC unit 1711, a Peltier element 1716, and a thermistor 1717. The PLC section 1711 has an input waveguide 1712, a Y-branch waveguide 1713, arm waveguides 1713 and 1714, a multiplex waveguide 1715, and an output waveguide 1716.
[0130]
The arm waveguide 1713 and the arm waveguide 1714 are waveguides through which the branched modulated signal light passes, and have different waveguide lengths.
[0131]
The output waveguide 1716 outputs a multiplexed output signal light obtained by multiplexing the modulation signal light passing through the arm waveguide 1713 and the modulation signal light passing through the arm waveguide 1714 to the optical / electric conversion unit 1730. Is to give.
[0132]
That is, the phase detection unit 1710 gives a phase difference to the branched modulated signal lights, and then multiplexes the modulated signal lights and directly supplies the modulated signal light to the optical / electrical conversion unit 1730.
[0133]
The operation of the optical phase monitor according to the sixth embodiment will be described.
[0134]
The modulated optical signal is split by, for example, a coupler (not shown) or the like, and a part of the modulated optical signal is supplied to the input unit 1740.
[0135]
The modulated optical signal input to input unit 1740 is provided to phase detection unit 1710.
[0136]
The modulated signal light input to the phase detection unit 1710 passes through the input waveguide 1712 of the PLC unit 1711 and is branched by the Y branch waveguide 1712.
[0137]
One of the modulated signal lights branched by the Y branch waveguide 1712 passes through the arm waveguide 1713, and the other passes through the arm waveguide 1714.
[0138]
These arm waveguides 1713 and 1714 have a predetermined waveguide length difference.
[0139]
The modulated signal light that has passed through the arm waveguide 1713 and the modulated signal light that has passed through the arm waveguide 1714 are overlapped by the multiplex waveguide 1715.
[0140]
At this time, the phase difference given between both arm waveguides 1713 and 1714 is macroscopically 1 bit (for example, 25 ps if 40 Gbit / s).
[0141]
If the phase of the carrier is microscopically shifted by π from an integral multiple of 2π, the PLC output has the waveforms shown in FIGS. 9A to 9E due to the phase difference between the bits of the carrier. .
[0142]
If the phase of the carrier is microscopically shifted from the integral multiple of 2π by π / 2, the phase difference between the bits of the carrier becomes the waveforms shown in FIGS. 9F to 9J.
[0143]
(F-2) Effects of the sixth embodiment
As described above, according to the present embodiment, the output from the phase detection unit 1710 is directly supplied to the optical / electrical conversion unit 1730, so that the circulator can be omitted in the optical phase device. As a result, the device configuration can be simplified.
[0144]
(G) Seventh embodiment
Hereinafter, an embodiment of an optical phase control device according to the present invention will be described.
[0145]
According to a seventh embodiment, in a high-speed optical transmission system employing an OTDM transmission system, an optical phase monitor for monitoring a part of a modulated signal light transmitted from a transmitter is provided, and a monitor signal from the optical phase monitor is provided. A case where the present invention is applied to an apparatus for controlling the inter-bit carrier phase difference using the above will be described.
[0146]
It is assumed that the transmission speed of the modulated signal light is 40 Gbit / s.
[0147]
(G-1) Configuration of Seventh Embodiment
FIG. 19 is a block diagram illustrating a configuration of the optical phase control device according to the present embodiment.
[0148]
As shown in FIG. 19, the optical phase control device roughly includes an OTMD module 600 and an optical phase monitor device. The optical phase monitor device includes a phase detection unit 1060, a temperature controller 1050, and an optical / optical controller. And an electric control unit 700.
[0149]
The optical phase monitor device can be applied to the optical phase monitor devices according to the first to sixth embodiments described above. In this embodiment, the optical phase monitor device described in the fourth embodiment is used. Apply the device.
[0150]
It should be noted that the components corresponding to the components described in the fourth embodiment are denoted by the same reference numerals.
[0151]
The OTMD module 600 includes a half mirror 603, a prism 604, an EA modulator 605, a prism 606, an EA modulator 607, a prism 608, an inter-bit carrier phase difference controller 800, a half mirror 610, and a prism 611. , A prism 612, and a prism 613.
[0152]
The half mirror 603 receives the 20 GHz optical short pulse train input to the OTDM module 600, splits the short optical pulse train into two, gives one to the EA modulator 605 through the prism 604, and gives the other to the EA modulator 605 through the prisms 612 and 613. The signal is supplied to the modulator 607.
[0153]
The EA modulators 605 and 607 receive each optical short pulse train split by the half mirror 603, code each optical short pulse train with a 20 Gbit / s electric modulation signal, and output it as an RZ optical data signal train. is there.
[0154]
The EA converter 607 supplies the coded RZ optical data signal sequence to the inter-bit carrier phase difference controller 800. The EA converter 605 supplies the coded RZ optical data signal sequence to the half mirror 610 via the prisms 606 and 611.
[0155]
The inter-bit carrier phase difference controller 800 receives the RZ optical data signal sequence from the EA modulator 607, receives a monitor signal from the optical / electrical converter 700, and adjusts the RZ optical data by temperature adjustment based on the monitor signal. This is for adjusting the phase of the signal train. The inter-bit carrier phase difference controller 800 adjusts the temperature based on the monitor signal from the optical / electrical converter 700, and changes the refractive index of the optical path and causes thermal expansion to change the optical path length. is there.
[0156]
The inter-bit carrier phase difference controller 800 adjusts the phase of the RZ optical data signal sequence and supplies it to the half mirror 610.
[0157]
The half mirror 610 receives the RZ optical data signal sequence from the EA converter 605, receives the phase-adjusted RZ optical data signal sequence from the inter-bit carrier phase difference controller 800, and superimposes these RZ optical data signal sequences. They combine.
[0158]
(G-2) Operation of Seventh Embodiment
An optical short pulse train of 20 GHz is input to the OTDM module 600.
[0159]
The input short optical pulse train is split into two by the half mirror 603, and one short optical pulse train (short optical pulse train 1) is reflected by the prism 604 and given to the EA modulator 605, and the other short optical pulse train is used. The short pulse train (light short pulse train 2) is reflected by the prisms 612 and 613 and provided to the EA modulator 607.
[0160]
The optical short pulse train 1 is coded by the EA modulator 605 using a 20 Gbit / s electric modulation signal, and becomes an RZ optical data signal train 1.
[0161]
The RZ optical data signal sequence 1 from the EA modulator 605 is reflected by the prisms 606 and 611 and provided to the half mirror 610.
[0162]
The optical short pulse train 2 is also coded by the EA modulator 607 using a 20 Gbit / s electric modulation signal, and becomes an RZ optical data signal train 2.
[0163]
The RZ optical data signal sequence 2 from the EA modulator 607 is reflected by the prism 608 and provided to the inter-bit carrier phase difference controller 800.
[0164]
The RZ optical data signal sequence from the EA modulator 607 is subjected to phase modulation by the inter-bit carrier phase difference controller 800, and the phase-modulated RZ optical data signal sequence is provided to the half mirror 610.
[0165]
The two RZ optical data signal trains provided to the half mirror 610 are multiplexed by the half mirror 610 and output.
[0166]
The optical path difference between the two systems is set to 7.5 mm, and the inter-bit carrier phase difference controller 800 can perform fine adjustment with an accuracy equal to or less than the wavelength. That is, the inter-bit carrier phase controller 800 adjusts the temperature based on the monitor signal from the optical / electrical converter 700 to change the refractive index and cause thermal expansion, thereby changing the optical path length.
[0167]
Thus, the output signal (modulated signal light) is output from the OTDM module 600.
[0168]
A small amount of the signal (modulated signal light) output from the OTDM module 600 is provided to the phase detection unit 1060 by the coupler 200.
[0169]
For example, the output signal (modulated signal light) from the OTDM module 600 is branched by 1% and input to the phase detection unit 1060.
[0170]
The modulated signal light input to the phase detection unit 1060 is optically monitored by the operation described in the fourth embodiment. That is, the waveguide length difference between the two arm waveguides (not shown) is set so that a phase difference of 1 / 2π is generated with respect to the modulated signal light.
[0171]
The temperature controller 1050 controls the temperature of a PLC unit (not shown) of the phase detection unit 01060 so as to be constant.
[0172]
The modulated signal light provided with a phase difference of に よ っ て by the phase detection unit 1060 is supplied to the optical / electrical conversion unit 700.
[0173]
The modulated signal light branched by the coupler 200 is further branched by the coupler 900 and provided to the optical / electrical conversion unit 700.
[0174]
The modulated signal light from the phase detection unit 1060 and the modulated signal light from the coupler 900 are averaged in the optical / electrical conversion unit 700, and their average power ratio is determined by the inter-bit carrier phase difference controller 800. Given to. This average power ratio is the monitor signal.
[0175]
The reason why the optical / electrical converter 700 obtains the average power of each modulated signal light is to suppress the influence when the modulated signal light fluctuates.
[0176]
Also, by feeding back the average power ratio to the inter-bit carrier phase difference controller 800, the inter-bit carrier phase difference controller 800 adjusts the temperature and calculates the carrier phase difference between the bits of the signal output from the OTMD module 600. It can be controlled to be shifted by π.
[0177]
FIG. 20 is a diagram showing a change in a carrier phase difference between bits due to temperature adjustment.
[0178]
As shown in FIG. 20, the horizontal axis represents the temperature difference from the reference point, and the vertical axis represents the inter-bit carrier phase difference.
[0179]
Thus, it can be seen that the phase difference between the bits of the carrier can be changed by 2π at ± 9 ° C. if the length is 10 mm at the reference temperature. Further, it can be seen that a change of 2π at ± 18 ° C. is possible if the length is 5 mm at the reference temperature.
[0180]
(G-3) Effect of the seventh embodiment
As described above, according to the present embodiment, the feed hack control system that changes the temperature of the phase controller with respect to the optical average power of the optical signal monitored by the optical phase monitoring device is configured. The CS-RZ format of π can be maintained.
[0181]
(H) Eighth embodiment
Next, an embodiment of an optical phase control device according to the present invention will be described with reference to the drawings.
[0182]
The eighth embodiment is applied to an apparatus in which the OTMD module 600 controls the inter-bit carrier phase difference based on the monitor signal (average power ratio) from the optical / electrical conversion unit 700, as in the seventh embodiment. Things.
[0183]
The eighth embodiment includes an ECB (Electrically Controlled Birefence) in which a refractive index changes according to an applied voltage, and changes a carrier phase between bits based on a monitor signal (average optical power) from an optical / electrical conversion unit. To change it.
[0184]
(H-1) Configuration and Operation of Eighth Embodiment
The overall configuration of the optical phase control device according to the eighth embodiment corresponds to the overall configuration of the optical phase control device according to the seventh embodiment shown in FIG. 19, and the eighth embodiment includes an OTMD module. The 600 inter-bit carrier phase difference controllers are different from the seventh embodiment.
[0185]
Therefore, hereinafter, only the inter-bit carrier phase difference controller will be described in detail, and the description of the exceptional functional configuration will be omitted.
[0186]
The inter-bit carrier phase difference controller according to the eighth embodiment has at least an ECB cell and a power supply applied to the ECB cell.
[0187]
FIG. 21 is an explanatory diagram showing a simple configuration of the ECB cell.
[0188]
As shown in FIG. 21, the ECB cell has two electrodes 2101 and 2102, two substrates 2104 and 2105, and a liquid crystal layer 2103.
[0189]
The electrodes 2101 and 2102 are electrodes to which a voltage is applied from a power supply (not shown). The refractive index of the liquid crystal layer 2103 changes according to the voltage applied between the two electrodes.
[0190]
FIG. 22 is a diagram showing a change in the alignment direction of the liquid crystal layer 2103 connected to the power supply 2200.
[0191]
The liquid crystal layer 2103 has optical anisotropy and dielectric anisotropy with respect to the crystal axis. The liquid crystal layer 2103 has different refractive indexes for the input signal light in the horizontal direction and the vertical direction of the crystal axis. Usually, the horizontal direction of the crystal axis is the slow axis, and the vertical direction is the fast axis. In addition, since the liquid crystal layer 2103 has dielectric anisotropy, the alignment direction of the liquid crystal changes according to the voltage applied between the two electrodes 2101 and 2102.
[0192]
For example, when the voltage E is applied from the power supply 2200, the horizontal direction of the crystal axis becomes θ (E) from the plane of the substrate, and the refractive index felt by the signal light traveling in the OTDM module 600 is:
(Equation 4)

It becomes.
[0193]
Such an ECB cell 2100 is installed such that the polarization direction is maintained in the OTDM module 600 and the polarization direction matches the direction of the crystal axis.
[0194]
The temperature of the ECB cell 2100 is controlled, for example, to 25 ° C. to stabilize the operation.
[0195]
Next, the operation of the optical phase control device according to the eighth embodiment will be described.
[0196]
The process until the output signal from the OTDM module 600 is input to the phase detection unit 1060, a phase difference is given, and the monitor process is performed is the same as in the seventh embodiment.
[0197]
The average optical power ratio determined by the optical / electrical converter 700 is provided to the inter-bit carrier phase difference controller 800.
[0198]
The inter-bit carrier phase difference controller 800 has a power supply 2200 and an ECB cell 2100, and the power supply 2200 applies a voltage based on the average optical power ratio from the optical / electrical converter 700 to the ECB cell 2100. Is done.
[0199]
When a voltage is applied to the ECB cell 2100, the refractive index of the liquid crystal layer 2103 changes based on the applied voltage, so that the carrier phase difference between bits passing through the OTMD module 600 is adjusted.
[0200]
Since the refractive index anisotropy of this liquid crystal is as large as 1.7, for example, 1.7, the ECB cell 2100 can obtain a large refractive index change by applying a slight electric field to the liquid crystal layer 2103 of several μm. Can be. For this reason, downsizing can be achieved even in consideration of the thickness of the substrate.
[0201]
(H-2) Effects of the eighth embodiment
As described above, according to the present embodiment, the ECB cell having the liquid crystal layer that maintains the polarization state of the signal light passing through the OTMD module is provided. The carrier phase can be controlled. Therefore, the size and power consumption of the device can be reduced.
[0202]
(I) Ninth embodiment
Next, an embodiment of an optical phase control device according to the present invention will be described with reference to the drawings.
[0203]
The ninth embodiment describes an apparatus applied to phase control of RZ signal light output by a Mach-Zehnder modulator.
[0204]
(I-1) Configuration and Operation of Ninth Embodiment
FIG. 23 is a configuration diagram showing a configuration of the optical phase control device according to the ninth embodiment.
[0205]
As shown in FIG. 23, the optical phase control device according to the eighth embodiment includes an alternating phase RZ converter 2300, a coupler 200, a coupler 900, a phase detector 1060, a temperature controller 1050, an optical / electrical A converter and a control signal generator 2320 are provided.
[0206]
The alternating phase RZ converter 2300 includes a dual-drive Mach-Zehnder modulator 2301, a bias 2302, an electric termination 2303, an electric termination 2304, a phase shifter 2305, a power divider 2306, an amplifier 2307, and an optical signal. It has an input terminal 2308, an electric signal input terminal 2309, and a bias application 2310.
[0207]
Hereinafter, the operation of the optical phase control device according to the ninth embodiment will be described.
[0208]
The output of the dual-drive Mach-Zehnder modulator 2301 is partially branched by the coupler 200 and provided to the phase detection unit 1060. A phase difference is given by a PLC unit (not shown) of the phase detection unit 1060.
[0209]
Here, FIG. 24 is a diagram illustrating the average power output from the phase detection unit.
[0210]
The output from the PLC unit of the phase detection unit 1060 has the average power shown in FIG. 24 due to the waveguide length difference between the two arm waveguides.
[0211]
However, when the input power of the PLC unit is multiplexed so that the phases match according to the waveguide length difference between the two arm waveguides, the inclination is the largest and the sensitivity is high. The average power shown in FIG. 24 can be converted into an electric signal by performing the photoelectric conversion of the average power with a photodiode having a sufficiently narrow band.
[0212]
Further, in order to eliminate the influence of the intensity fluctuation of the input signal, a part of the input signal of the PLC is branched and similarly subjected to light-to-electric conversion by a photodiode having a narrow band, and obtained from this value and the aforementioned PLC output. The control signal is obtained by taking the ratio of the electric signal.
[0213]
(I-2) Effects of the ninth embodiment
As described above, according to the present embodiment, the amplitude at which the output optical signal is stabilized can be supplied to the Mach-Zehnder modulator by feeding back the control signal to the amplifier 2307.
[0214]
(J) Other embodiments
The carrier phase difference detection devices described in the first to sixth embodiments can be employed in the optical phase control device described in the seventh to ninth embodiments.
[0215]
The PLC section described in the first to sixth embodiments includes one input waveguide, one Y branch waveguide, two arm waveguides, and a total reflection surface of each arm waveguide. And one configuration including one input waveguide, one Y-branch waveguide, two arm waveguides, one Y-multiplexed waveguide and one output waveguide. Although an example has been described, the present invention is not limited to these configurations, and if a desired carrier phase difference can be obtained, a similar effect can be obtained regardless of the form of the PLC unit.
[0216]
In addition, if a desired phase difference can be obtained by an optical block or the like, the same effect can be obtained without being limited to the PLC.
[0219]
Further, the material of the controller for modulating the phase of the carrier is not limited to BK7, and the same effect can be obtained by using another material such as SF6. Further, a similar effect can be obtained irrespective of the means for controlling the phase.
[0218]
Furthermore, although the PLC unit of the above-described embodiment has been described as splitting the input modulated signal light into two, it may be configured to split the modulated signal light into two or more. For example, when the PLC unit is capable of branching into three, a phase difference is provided between the carrier of the first modulated signal light and the carrier of the second modulated signal light, and the first of the combined outputs thereof is given. The light intensity is obtained, and further another phase difference is given between the carrier of the second modulation signal light and the carrier of the third modulation signal light, and the second light intensity of the combined output thereof is calculated. You may ask for it.
[0219]
【The invention's effect】
As described above, according to the present invention, in the optical phase detection device that detects the inter-bit phase difference of the carrier of the modulated signal light, the modulated signal light is split into at least two, and the first split modulated signal light and the second split A phase difference providing means for multiplexing the modulated signal light after giving a predetermined phase difference to the modulated signal light; and a bit interval of a carrier of the modulated signal light based on the light intensity of the multiplexed output multiplexed by the phase difference providing means. By providing the phase difference detecting means for detecting the phase difference, the phase difference between the bits of the carrier of the modulated signal light can be detected with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a transmission system including an optical phase detection device according to a first embodiment.
FIG. 2 is a diagram illustrating a configuration of an optical phase monitor unit according to the first embodiment.
FIG. 3 is a diagram illustrating a configuration of a planar waveguide according to the first embodiment.
FIG. 4 is an explanatory diagram illustrating multiplexed signal multiplexing by the PLC unit according to the first embodiment;
FIG. 5 is an explanatory diagram illustrating a relationship between a carrier phase difference and light intensity according to the first embodiment.
FIG. 6 is a diagram illustrating a configuration of an optical phase monitor unit according to a second embodiment.
FIG. 7 is a diagram illustrating a configuration of a planar waveguide according to a second embodiment.
FIG. 8 is an explanatory diagram illustrating a relationship between a carrier phase difference and light intensity according to the second embodiment.
FIG. 9 is a diagram illustrating an output signal waveform of a PLC unit according to the second embodiment.
FIG. 10 is a diagram illustrating a configuration of an optical phase monitoring unit according to a third embodiment.
FIG. 11 is a diagram illustrating a connection configuration between a phase detection unit and a temperature controller according to a third embodiment.
FIG. 12 is a diagram illustrating a phase difference with respect to a temperature difference from a reference temperature by a phase detection unit according to the third embodiment.
FIG. 13 is a diagram illustrating a configuration of a phase detection unit according to a fourth embodiment.
FIG. 14 is a diagram illustrating a configuration of a phase detection unit according to a fourth embodiment.
FIG. 15 is a diagram illustrating a configuration of a phase detection unit according to a fifth embodiment.
FIG. 16 is a diagram illustrating a configuration of a phase detection unit according to a fifth embodiment.
FIG. 17 is a diagram illustrating a configuration of an optical phase monitoring unit according to a sixth embodiment.
FIG. 18 is a diagram illustrating a configuration of a phase detection unit according to a sixth embodiment.
FIG. 19 is a configuration diagram illustrating a configuration of a phase control device according to a seventh embodiment.
FIG. 20 is a diagram illustrating a relationship between a temperature difference from a reference point and a phase difference according to the seventh embodiment.
FIG. 21 is a diagram illustrating a configuration of an ECB cell according to an eighth embodiment.
FIG. 22 is an explanatory diagram illustrating an operation of an ECB cell according to the eighth embodiment.
FIG. 23 is a diagram illustrating a configuration of a drive voltage control device according to a ninth embodiment.
FIG. 24 is a diagram illustrating the relationship between the voltage and the output intensity of the drive voltage control device according to the ninth embodiment.
[Explanation of symbols]
300, 400 ... monitor part,
1060, 1360, 1560, 1710 phase detector,
310, 410, 1010, 1310, 1510, 1710 ... planar waveguide,
311, 411, 1011, 1311, 1511, 1711... Input / output waveguides, 312, 412, 1012, 1312, 1512, 1712.
313, 314, 413, 414, 1013, 1014,
1313, 1314, 1513, 1514, 1713, 1714 ... arm waveguide,
315, 316, 415, 416, 1015, 1016,
1315, 1316, 1515, 1516, 1715, 1716 ... reflection surface,
330, 430, 700, 1030, 1730 ... optical / electrical conversion unit,
1050, 1720 ... temperature controller,
600: OTDM module, 800: inter-bit carrier phase difference controller,
605, 607 ... EA converter, 2100 ... ECB cell,
2101, 2102: electrodes, 2103: liquid crystal layer
2300: Alternating phase RZ converter, 2307: Amplifier, 2305: Phase shifter,
2320 ... optical / electrical converter and control signal generator.

Claims (13)

In an optical phase detection device that detects a phase difference between bits of a carrier of a modulated signal light,
Phase difference applying means for splitting the modulated signal light into at least two, giving a predetermined phase difference between the first branched modulated signal light and the second branched modulated signal light, and multiplexing them;
An optical phase detection device comprising: a phase difference detection unit configured to detect a phase difference between bits of a carrier of the modulated signal light based on a light intensity of a multiplexed output multiplexed by the phase difference providing unit. . 2. The optical phase detection device according to claim 1, further comprising an optical / electrical conversion unit that converts the light intensity of the combined output detected by the phase difference detection unit into an electric intensity. The phase difference providing means,
Branching means for splitting the modulated signal light into at least two,
A first waveguide length of the first branched modulation signal light; and a second waveguide length of the second branch modulation signal light. Waveguide means different from the predetermined length,
3. The optical phase detection device according to claim 1, further comprising a multiplexing unit that multiplexes the branch modulation signal light from the waveguide unit. The optical phase detecting device according to claim 3, wherein the phase difference providing means is a planar waveguide. The said phase difference provision means gives the phase difference of 0 or (pi) to the branched 1st branched modulation signal light and the 2nd branched modulation signal light, The Claim 1 characterized by the above-mentioned. Optical phase detector. A temperature control means for controlling a temperature of the phase difference providing means so as to give a predetermined phase difference between the first branch modulation signal light and the second branch modulation signal light. 5. The optical phase detection device according to any one of 5. The optical phase detecting device according to claim 6, wherein the temperature control means is independent of each of the waveguides of the phase difference providing means. Based on the optical phase detection information fed back from the optical phase detection device, in the phase control device that controls the inter-bit phase difference of the carrier of the modulated signal light,
First modulating means for branching an input optical pulse train into at least two and modulating one input optical pulse among the branched optical pulse trains;
Second modulating means for modulating another input light pulse among the branched light pulses;
Phase adjustment means for receiving optical phase detection information from the optical phase detection device and adjusting the carrier phase of the modulated signal light modulated by the first modulation means based on the optical phase detection information;
A phase control device comprising: a modulation signal light multiplexing unit that multiplexes the modulation signal light from the phase adjustment unit and the modulation signal light from the second modulation unit. A phase control device, wherein the optical phase detection device is the optical phase detection device according to any one of claims 1 to 7. 10. The phase control device according to claim 8, wherein the phase adjustment means controls the temperature in accordance with the optical phase detection information fed back from the optical phase detection device to adjust the carrier phase. 10. The ECB cell having a liquid crystal layer whose refractive index is variable by a voltage controlled according to optical phase detection information fed back from the optical phase detection device, wherein the phase adjusting means is an ECB cell. 3. The phase control device according to claim 1. Carrier generation means for generating a carrier,
Using a refractive index change based on an electric field generated by an externally applied voltage, a modulation means for intensity-modulating an input data signal with a carrier generated by the carrier generation means,
An optical transmission device comprising:
A driving voltage control unit that controls a voltage amplitude of the carrier controlled by the phase control unit based on optical phase detection information from an optical phase detection device that detects a bit difference between bits of a carrier of the modulated signal light. Optical transmission device. An optical transmission device, wherein the optical phase detection device is the optical phase detection device according to any one of claims 1 to 7.

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