JPH03123828A - Instrument and method for measuring characteristic of optical phase modulator - Google Patents

Instrument and method for measuring characteristic of optical phase modulator

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Publication number
JPH03123828A
JPH03123828A JP26162689A JP26162689A JPH03123828A JP H03123828 A JPH03123828 A JP H03123828A JP 26162689 A JP26162689 A JP 26162689A JP 26162689 A JP26162689 A JP 26162689A JP H03123828 A JPH03123828 A JP H03123828A
Authority
JP
Japan
Prior art keywords
optical
phase modulator
voltage
optical phase
bias
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
Application number
JP26162689A
Other languages
Japanese (ja)
Other versions
JP2939482B2 (en
Inventor
Hiromichi Jumonji
十文字 弘通
Hiroshi Miyazawa
弘 宮沢
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Telegraph and Telephone Corp
Original Assignee
Nippon Telegraph and Telephone Corp
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Filing date
Publication date
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Priority to JP26162689A priority Critical patent/JP2939482B2/en
Publication of JPH03123828A publication Critical patent/JPH03123828A/en
Application granted granted Critical
Publication of JP2939482B2 publication Critical patent/JP2939482B2/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Abstract

PURPOSE:To complete the measurement of the half-wavelength voltage of the optical phase modulator in a short time by applying the optical phase modulator with a bias modulating signal which has a shorter period than the time variation of an output voltage due to an equivalent phase shift of each element of an optical branch interference system. CONSTITUTION:The characteristic measuring instrument of the optical phase modulator 30 is used to apply the modulator 30 with the bias modulating signal which as the much shorter period than the time variation of the output voltage generated owing to the equivalent phase shift of each element of the optical branch interference system 31. Then variation of the output voltages of photodetector 32 and 33 and the variation of a bias voltage are recorded and measured by a voltage recording device 35 to measure the half-wavelength voltage of the modulator 30. Then the modulator 30 is applied with a low-frequency bias modulating signal which has a proper amplitude and a high-frequency modulating signal one over the other and the reception band width of an optical spectrum analyzer 36 is set larger than a bias modulation frequency to measure the modulation sensitivity of the modulator 30 to the high-frequency modulating signal.

Description

【発明の詳細な説明】 「産業上の利用分野」 この発明は、光位相変調器の特性測定装置および特性測
定方法に係り、詳しくは外部光位相変調器の特性パラメ
ータである半波長電圧や変調感度の周波数応答の測定に
適用して好適な光位相変調器の特性測定装置および特性
測定方法に関する。
DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a characteristic measuring device and a characteristic measuring method of an optical phase modulator. The present invention relates to a characteristic measuring device and a characteristic measuring method of an optical phase modulator suitable for measuring frequency response of sensitivity.

「従来の技術」 光のコヒーレンシーを利用する光波通信システム、光応
用計測機器の実現にあたっては、キーデバイスの一つと
して外部光変調器の利用が考えられ、Ti(チタン)拡
散導波路によるLiNb0(ニオブ酸リチウム)位相変
調器が注目されている。
``Prior art'' In realizing light wave communication systems and optical applied measurement equipment that utilize optical coherency, the use of external optical modulators can be considered as one of the key devices. Lithium niobate) phase modulators are attracting attention.

上記外部光変調器は、前咎、すなわち光波通信システム
においては、送信系におけるPCK(位相側移変R)あ
るいはFSK(周波数偏移変調)用の素子として、後者
、すなわち光応用計測機器°りにおいては、制御系、周
波数合成系における位相あるいは周波数変調用の素子と
して利用される。
The above external optical modulator is used as an element for PCK (phase shift R) or FSK (frequency shift keying) in a transmission system in a light wave communication system. It is used as a phase or frequency modulation element in control systems and frequency synthesis systems.

一方、Ti拡散導波路によるL i N b O3位相
変調器は、通常、導波路端部に偏波保持ファイバを接合
して、モジュール化する形態がとられる。従来の空間ビ
ーム形の光入出力構成をとる光位相変調器の評価に際し
ては、周知のように位相変調器の両側に直交する偏向子
、検光子を設け、位相変調器の光軸に対して45度傾く
偏波面をもつ直線偏光を入力して、位相変化を強度変化
信号として検出する方法が適用できる。しかし、ピグテ
イル化された位相変調器に対しては、入出力用のファイ
バを介しての偏波面の設定となるため、上記の様な方法
で強度変化信号を得ることは困難である。
On the other hand, an L i N b O3 phase modulator using a Ti diffusion waveguide is usually modularized by joining a polarization maintaining fiber to the end of the waveguide. When evaluating an optical phase modulator that has a conventional spatial beam type optical input/output configuration, as is well known, a polarizer and an analyzer are installed orthogonally on both sides of the phase modulator, and the optical axis of the phase modulator is An applicable method is to input linearly polarized light with a polarization plane tilted at 45 degrees and detect a phase change as an intensity change signal. However, for a pigtailed phase modulator, the plane of polarization is set via an input/output fiber, so it is difficult to obtain an intensity change signal using the method described above.

一方、モジュール化された位相変調器に関する特性(半
波長電圧や周波数特性等)評価法としては、ファブリペ
ロ共振器を利用して周波数変調された光信号をスペクト
ル分析する方法、自己へテロダイン系を構成して光信号
のスペクトル分析結果から半波長電圧を評価する方法等
が報告されている。
On the other hand, methods for evaluating the characteristics (half-wave voltage, frequency characteristics, etc.) of modularized phase modulators include a method of spectrum analysis of a frequency-modulated optical signal using a Fabry-Perot cavity, and a method of configuring a self-heterodyne system. A method for evaluating half-wavelength voltage from the spectrum analysis results of optical signals has been reported.

第7図は、前者の場合の測定系の構成を示すが、レーザ
光源Iからの出力を光学アイソレータ2を介して、測定
対象である光位相変調器3に接続し、その出力を走査形
ファブリペロ干渉計4に導き、さらにその透過光出力を
受光素子5で検出した後、スペクトル分析器6で分析す
る構成になっている。
FIG. 7 shows the configuration of the measurement system in the former case, in which the output from the laser light source I is connected via the optical isolator 2 to the optical phase modulator 3 to be measured, and the output is connected to the scanning Fabry-Perot. The light is guided to an interferometer 4, and its transmitted light output is detected by a light receiving element 5, and then analyzed by a spectrum analyzer 6.

この構成で、後述の半波長電圧を測定するには、光位相
変調器3の駆動電源7の周波数成分をもつスペクトルと
直流成分のスペクトルを同時にモニタする必要がある。
With this configuration, in order to measure a half-wave voltage, which will be described later, it is necessary to simultaneously monitor the spectrum having the frequency component of the drive power source 7 of the optical phase modulator 3 and the spectrum of the DC component.

第8図は、レーザ光源8と光位相変調器9との間に、音
響光学変調器10を挿入して、その非回折光を光位相変
調器9に導き、−次回折光と光位相変調器9の透過光を
合波して受光素子11で検出する自己ヘテロゲイン系の
構成である。この場合も、スペクトル分析器12で観測
される、光位相変調器9の駆動電源13の周波数成分を
もつスペクトルと直流成分のスペクトルを同時にモニタ
する必要がある。
In FIG. 8, an acousto-optic modulator 10 is inserted between a laser light source 8 and an optical phase modulator 9, the undiffracted light is guided to the optical phase modulator 9, and the -order diffracted light and the optical phase modulator are combined. This configuration is a self-hetero gain system in which the transmitted light of 9 is multiplexed and detected by the light receiving element 11. In this case as well, it is necessary to simultaneously monitor the spectrum having the frequency component of the drive power source 13 of the optical phase modulator 9 and the spectrum of the DC component observed by the spectrum analyzer 12.

これらの方法は、スペクトル分析結果をもとに評価する
、いわば間接法であり、精度、測定効率の点で問題があ
る。
These methods are so-called indirect methods that evaluate based on spectrum analysis results, and have problems in terms of accuracy and measurement efficiency.

これに対して、最近、偏波保持ファイバによる光学的分
岐干渉系と位相変調器を利用して、強度変調器を構成す
る方法が提案されている( Jour。
On the other hand, a method has recently been proposed in which an intensity modulator is constructed using an optical branching interference system using a polarization-maintaining fiber and a phase modulator (Jour.

or Opt、Comn、、Vol、7.pp、H−9
1(1986−03)) 、第9図は、この場合の測定
系の構成を示すが、レーザ光源14の出力を、2個の偏
波保持カブラ(結合器)15.16と偏波保持ファイバ
17および測定対象である光位相変調器I8とから構成
される光学的分岐干渉系に導き、第二の偏波保持カブラ
16の一方の出力を受光素子19に接続し、他方の出力
を受光素子20に接続する構成である。この場合、測定
系の安定化を図るために、レーザ光源14のバイアス電
流を低周波発振器21で変調すると同時に、受光素子2
0によって検出される電気信号をロックイン増幅器22
に印加し、その誤差信号をもとに、電流制御部23を介
してレーザ光源14に対する直流バイアスを制御する構
成がとられている。第9図の測定系においで1.光位相
変調器18の半波長電圧の測定は、その駆動電源24の
電圧と受光素子19で検出される光出力変化から求めら
れる。見方をかえれば、第9図の測定系の構成は、先位
相変調器18における位相変化を光の強度変化に変換す
る構成であり、光位相変調器18の特性評価法として利
用できる構成である。
or Opt,Comn,, Vol, 7. pp, H-9
1 (1986-03)), Fig. 9 shows the configuration of the measurement system in this case. 17 and an optical phase modulator I8 to be measured, one output of the second polarization maintaining coupler 16 is connected to the light receiving element 19, and the other output is connected to the light receiving element 19. 20. In this case, in order to stabilize the measurement system, the bias current of the laser light source 14 is modulated by the low frequency oscillator 21, and at the same time the light receiving element 2
The electrical signal detected by the lock-in amplifier 22
The DC bias applied to the laser light source 14 is controlled via the current control unit 23 based on the error signal. In the measurement system shown in Figure 9, 1. The half-wave voltage of the optical phase modulator 18 is determined from the voltage of its drive power source 24 and the change in optical output detected by the light receiving element 19. From another perspective, the configuration of the measurement system shown in FIG. 9 is a configuration that converts the phase change in the preceding phase modulator 18 into a change in the intensity of light, and is a configuration that can be used as a method for evaluating the characteristics of the optical phase modulator 18. .

「発明が解決しようとする課題」 しかしながら、上記第9図の測定系においては、振動、
温度変化等による光学的分岐干渉系内の位相変化も強度
変化信号に変換されるため、位相変化の雑音成分を補償
する制御回路を付加する必要があり、これに伴い、光学
系の構成も複雑になるという問題があった。
"Problem to be Solved by the Invention" However, in the measurement system shown in FIG.
Since phase changes within the optical branching interference system due to temperature changes, etc. are also converted into intensity change signals, it is necessary to add a control circuit to compensate for the noise component of the phase changes, and the configuration of the optical system is also complicated. There was a problem with becoming.

この発明は、上記事情に鑑みてなされたもので、モジュ
ール化された光位相変調器の簡便な測定法として、ファ
イバによる光学的分岐干渉系を構成し、何等の制御回路
を付加せずに、半波長電圧、周波数特性を測定する光位
相変調器の特性測定装置および特性測定方法を提供する
ことを目的としている。
This invention was made in view of the above circumstances, and as a simple measurement method for a modularized optical phase modulator, an optical branching interference system using fibers is configured, and without adding any control circuit, It is an object of the present invention to provide a characteristic measuring device and a characteristic measuring method of an optical phase modulator that measure half-wavelength voltage and frequency characteristics.

「課題を解決するための手段」 上記課題を解決するために、請求項1記載の発明は、第
1の光結合器の2個の出力ポートと第2の光結合器の2
@の人力ポートとを対向させ、当該一組の人出力ポート
間にファイバを接続し、当該他の組の入出力ポート間に
、光位相変調器を接続して光学的分岐干渉系を構成し、
前記光学的分岐干渉系の一方に単一モード光源からの光
を入射させ、他方に受光素子を接続し、その出力電圧を
記録できる電圧記録装置、および前記光学的分岐干渉系
の光出力をスペクトル分析できる先スペクトラム分析器
を併置する共に、前記光位相変調器の電気端子に、低周
波のバイアス変調信号と高周波信号を重畳して印加でき
るように構成したことを特徴としている。
"Means for Solving the Problem" In order to solve the above problem, the invention according to claim 1 provides two output ports of a first optical coupler and two output ports of a second optical coupler.
@Manual power ports are faced to each other, a fiber is connected between the human output ports of one set, and an optical phase modulator is connected between the input and output ports of the other set to configure an optical branching interference system. ,
A voltage recording device capable of inputting light from a single mode light source into one side of the optical branching interference system and connecting a light receiving element to the other side and recording the output voltage; and a voltage recording device capable of recording the output voltage of the optical branching interference system; It is characterized in that a spectrum analyzer capable of analysis is arranged in parallel, and a low frequency bias modulation signal and a high frequency signal can be applied in a superimposed manner to the electric terminal of the optical phase modulator.

請求項2記載の発明は、請求項!記載の光位相変調器の
特性測定装置を用いて、前記光位相変調器に、前記光学
的分岐干渉系の各要素の等価的位相変化に起因して発生
する出力電圧の時間的変動に較べて充分早い周期をもつ
バイアス変調信号を印加して、前記受光素子の出力電圧
の変化とバイアス電圧の変化を前記電圧記録装置により
記録測定して、前記光位相変調器の半波長電圧を測定す
ることを特徴としている。
The invention according to claim 2 is a claim! Using the optical phase modulator characteristic measuring device described above, it is possible to compare the temporal fluctuations in the output voltage generated in the optical phase modulator due to equivalent phase changes of each element of the optical branching interference system. Applying a bias modulation signal with a sufficiently fast cycle, recording and measuring changes in the output voltage of the light receiving element and changes in the bias voltage using the voltage recording device, and measuring the half-wave voltage of the optical phase modulator. It is characterized by

請求項3記載の発明は、請求項1記載の光位相変調器の
特性測定装置を用いて、前記光位相変調器に、適正な振
幅をもつ低周波バイアス変調信号を印加すると同時に、
高周波変調信号を重畳して印加する状態とし、萌記光ス
ペクトラム分析器の受信帯域幅をバイアス変調周波数に
較べて、十分大きな値に設定して、高周波変調信号に対
する前記光位相変調器の変調感度を測定することを特徴
としている。
The invention according to claim 3 is a method of applying a low frequency bias modulation signal having an appropriate amplitude to the optical phase modulator using the optical phase modulator characteristic measuring device according to claim 1;
A high frequency modulation signal is applied in a superimposed manner, and the reception bandwidth of the Moeki optical spectrum analyzer is set to a sufficiently large value compared to the bias modulation frequency, so that the modulation sensitivity of the optical phase modulator to the high frequency modulation signal is set. It is characterized by measuring.

「作用」 この発明によれば、光学的分岐干渉系内のランダムな位
相変化の性質が考慮されて、光位相変調器の半波長電圧
の測定を短時間に、すなわち、位相変化の無視できる時
間内に完了することができる。
"Operation" According to the present invention, the nature of random phase changes in the optical branching interference system is taken into account, and the half-wave voltage of the optical phase modulator can be measured in a short time, that is, in a time period in which the phase changes can be ignored. It can be completed within.

また、光位相変調器周波数特性の測定に際しては、位相
変調器に対して適正な振幅の低周波バイアス信号を重畳
することにより、測定周波数成分に対する雑音の影響を
低減することができる。
Furthermore, when measuring the frequency characteristics of the optical phase modulator, the influence of noise on the measurement frequency component can be reduced by superimposing a low frequency bias signal with an appropriate amplitude on the phase modulator.

「実施例」 以下、図面を参照してこの発明の実施例について説明す
る。
"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(i)測定系の構成 第1図は、この発明の一実施例である光位相変調器の特
性測定装置の構成を示すブロック図である。
(i) Structure of measurement system FIG. 1 is a block diagram showing the structure of an apparatus for measuring characteristics of an optical phase modulator, which is an embodiment of the present invention.

この図において、符号25はレーザ光源25.26はレ
ーザ光源25を制御する制御器、27゜28は前段およ
び後段の偏波保持カプラ、29は偏波保持ファイバ、3
0は測定対象である光位相変調器である。偏波保持ファ
イバ29および光位相変調器30は、2個の偏波保持カ
プラ27,28の間に並列接続されている。そして、ブ
ランチ11およびブランチ2が構成されている。ブラン
チ11およびブランチ2においては、偏光軸が−致する
ように接続されている。そして、これらの要素25〜3
0によって、光学的分岐干渉系31が構成されている。
In this figure, reference numeral 25 is a laser light source 25, 26 is a controller that controls the laser light source 25, 27° and 28 are front and rear polarization maintaining couplers, 29 is a polarization maintaining fiber, 3
0 is the optical phase modulator to be measured. A polarization maintaining fiber 29 and an optical phase modulator 30 are connected in parallel between two polarization maintaining couplers 27 and 28. A branch 11 and a branch 2 are configured. Branch 11 and branch 2 are connected so that their polarization axes coincide. And these elements 25-3
0 constitutes an optical branching interference system 31.

また、32.33は後段の偏波保持カプラ28の出力ポ
ートP 5 、P 6にそれぞれ接続された受光素子で
ある。レーザ光源25と前段の偏波保持カプラ27との
間には、偏波面調整のため偏波制御器34が接続されて
いる。受光素子32の出力は電圧記録装置35、受光素
子33の出力は光スペクトラム分析器36に接続されて
いる。電圧記録装置35としては、受光素子32の出力
電圧と後述のバイアス変調信号電圧を同時に測定記録で
きるメモリ機能付オツシロスコープなどが利用できる。
Moreover, 32 and 33 are light receiving elements respectively connected to output ports P 5 and P 6 of the polarization maintaining coupler 28 in the subsequent stage. A polarization controller 34 is connected between the laser light source 25 and the preceding polarization maintaining coupler 27 for polarization plane adjustment. The output of the light receiving element 32 is connected to a voltage recording device 35, and the output of the light receiving element 33 is connected to an optical spectrum analyzer 36. As the voltage recording device 35, an oscilloscope with a memory function or the like that can simultaneously measure and record the output voltage of the light receiving element 32 and the voltage of a bias modulation signal to be described later can be used.

一方、光位相変調器30に電気信号を印加する手段とし
て、低周波のバイアス変調を行なうための信号源37、
および高周波の変調を行なうための信号源38が、バイ
アス39を介して、光位相変調器30の入力端子に接続
されている。上記信号源37としては、通常、ファンク
ションジェネレータを、信号源38としてはシンセサイ
ザが使用される。また信号源37の出力端子は、電圧記
録装置35の端子にも分岐接続され、半波長電圧の測定
に供されるようになっている。
On the other hand, as means for applying an electrical signal to the optical phase modulator 30, a signal source 37 for performing low frequency bias modulation;
A signal source 38 for performing high frequency modulation is connected to the input terminal of the optical phase modulator 30 via a bias 39. Usually, a function generator is used as the signal source 37, and a synthesizer is used as the signal source 38. Further, the output terminal of the signal source 37 is branch-connected to a terminal of the voltage recording device 35 so as to be used for measuring the half-wavelength voltage.

(ii )半波長電圧の測定 次に、第1図の特性測定装置の適用による半波長電圧の
測定方法について説明する。
(ii) Measurement of half-wave voltage Next, a method for measuring half-wave voltage by applying the characteristic measuring device shown in FIG. 1 will be explained.

(ii −1)測定原理 まず、測定原理について述べる。(ii-1) Measurement principle First, the measurement principle will be described.

第1図の測定系で各受光素子32.33で検出される電
流と光学的分岐干渉系における光路差(DL=D、 −
D、 ’) 、光位相変調器30による位相変化(Φ(
1)) 、光源25の発振周波数(ν。:ω。/2π)
等との関係を、以下に示す。なお、位相変調器30への
入射光は直線偏光であり、かつ最大位相変化を与える光
位相変調器30の光軸に一致しているものとする。また
偏波保持カップラ27の出力、位相とも同一であり、光
学的分岐干渉系31内では偏波が保持されているものと
仮定する。
In the measurement system shown in Fig. 1, the current detected by each light receiving element 32, 33 and the optical path difference (DL=D, -
D, '), phase change by the optical phase modulator 30 (Φ(
1)), oscillation frequency of the light source 25 (ν.:ω./2π)
The relationship between the two is shown below. It is assumed that the light incident on the phase modulator 30 is linearly polarized light and coincides with the optical axis of the optical phase modulator 30 that provides the maximum phase change. It is also assumed that the output and phase of the polarization maintaining coupler 27 are the same, and that the polarization is maintained within the optical branching interference system 31.

偏波保持カップラ27の出力端での電界ベクトルをE、
、E、とおくと、 E+=Et=Eoexp(j (doj )     
    (1)で表され、ブランチl(長さ:L1)を
通過後の電界ベクトルE3.ブランチ2(長さ:L、)
を通過後の電界ベクトルE4とおくと、次式の様になる
The electric field vector at the output end of the polarization maintaining coupler 27 is E,
, E, then E+=Et=Eoexp(j (doj)
(1), the electric field vector E3 after passing through branch l (length: L1). Branch 2 (length: L,)
Letting the electric field vector E4 after passing through, the following equation is obtained.

E s= E +eXp(−jk  L+)E 4= 
E teXP (−j (k Lx+Φ(t>)   
   (2)ただし、k= 2 π/ n oλ=2π
νo/noc。
E s= E +eXp (-jk L+) E 4=
E teXP (-j (k Lx+Φ(t>)
(2) However, k= 2 π/noλ=2π
νo/noc.

no;ブランチ1.ブランチ2の屈折率。no; branch 1. Refractive index of branch 2.

co;光速、ν0=光波周波数 結合係数に、長さ2を有する偏波保持カプラ28の出力
ポートP5.P6の電界ベクトルE 、、E 。
co; speed of light, ν0=lightwave frequency coupling coefficient; output port P5 of polarization maintaining coupler 28 having length 2; The electric field vector E , , E of P6.

は、次式で表される。is expressed by the following formula.

E s= costc z E z −jsinにz 
E aEs=jsinにz E3+cosにz Ea 
    (3)に:結合係数。
E s= costc z E z −jsin z
E aEs=jsin z E3+cos z Ea
(3): Coupling coefficient.

2:結合部の長さ 変換効率η1.η2の受光素子32および33の出力電
流+1+lfは、 i+=  ηIEs・E、* iz=   ηtEe・E8*           
(4)ただし、Ei*とEiは複素共役の関係にある。
2: Length conversion efficiency of the joint portion η1. The output current +1+lf of the light receiving elements 32 and 33 of η2 is: i+= ηIEs・E, * iz= ηtEe・E8*
(4) However, Ei* and Ei are in a complex conjugate relationship.

ここで、(り〜(3)を(4)に代入すると、次式%式
% (1))) (5) ここで、DL(〜L2−Ll) :等価光路差偏波保持
カプラ28が3dB結合器の場合、5in2にZlであ
るから、 i +−77+(Eo)C1−5in(k DL+Φ(
1)))i を−n 2(EO)’ (1+5in(k
 DL+Φ(t)))       (6’)となる。
Here, by substituting (ri ~ (3) into (4), the following formula % formula % (1))) (5) Here, DL (~L2 - Ll): Equivalent optical path difference polarization maintaining coupler 28 In the case of a 3dB coupler, since there is Zl in 5in2, i +-77+(Eo)C1-5in(k DL+Φ(
1)))i −n 2(EO)' (1+5in(k
DL+Φ(t))) (6').

通常、各辺のファイバ長の差DLは数cm程度と考える
と、KDLは10’のオーダーとなる。
Considering that the difference DL between the fiber lengths on each side is usually on the order of several cm, KDL is on the order of 10'.

上式から明かなように、光位相変調器30に電圧を印加
しない場合(Φ(t )= 0 )でも、(kDL)が
変動すれば、各受光素子32.33の電流が正弦的に変
化することがわかる。
As is clear from the above equation, even when no voltage is applied to the optical phase modulator 30 (Φ(t) = 0), if (kDL) changes, the current of each light receiving element 32, 33 changes sinusoidally. I understand that.

一方、(6)式から、k−DLが一定をとなせる時間内
では、あたかも一定の位相オフセットが生じた状態と考
えることができ、Φ(t)−iの関係を求めることによ
り、光位相変調器30の半波長電圧が評価できる。すな
わち、Φ(1)と印加電圧V、との関係は、正弦波変調
した場合、 Φ、、(1)=Φ、。・5in(ω、を十〇)    
 (8)ここで、Φ、。oc(1o)’γV。
On the other hand, from equation (6), it can be considered as if a constant phase offset has occurred within the time when k-DL is constant, and by finding the relationship of Φ(t)-i, it is possible to The half-wave voltage of the phase modulator 30 can be evaluated. That is, the relationship between Φ(1) and the applied voltage V, when modulated by a sine wave, is Φ, (1)=Φ.・5in (ω, 10)
(8) Here, Φ. oc(1o)'γV.

no:変調器を伝播する光が感じる等価屈折率γ :電
気光学定数 ω、;変調角周波数、 で表現できる。
no: equivalent refractive index perceived by light propagating through the modulator; γ: electro-optic constant ω; modulation angular frequency.

Φ、0を駆動電圧V、のpeak−to−peak値(
Vpp=振幅の2倍の値)と位相角がπラジアン変化す
る時の電圧すなわち半波長電圧Vπで表現すると、 Φ+m0−(π/2)・(Vpp/Vπ)      
(8’)と表現できる。
Φ, 0 is the peak-to-peak value of the drive voltage V (
Vpp = twice the amplitude) and the voltage when the phase angle changes by π radians, that is, the half-wave voltage Vπ, is Φ + m0-(π/2)・(Vpp/Vπ)
It can be expressed as (8').

したがって、式(6)、(8)、(8’)より、1t(
i=1.2)はVl)l)の関数であり、vppを変化
させた場合、隣接する( f ILaM+ (it)m
tnを与える電圧値から、半波長電圧Vπが求められる
ことかわかる。
Therefore, from equations (6), (8), and (8'), 1t(
i=1.2) is a function of Vl)l), and when vpp is changed, the adjacent (f ILaM+ (it)m
It can be seen that the half-wavelength voltage Vπ can be found from the voltage value giving tn.

(ii −2)測定の具体例 次に、測定例について述べる。(ii-2) Specific example of measurement Next, a measurement example will be described.

具体的には、電極損失や位相速度の不整合が無視できる
低周波においてV、、とi□の関係を測定すれば良いこ
とになる。すなわち、光源25および受信系b(電圧記
録装置35を含む測定系)を動作状態とした後、信号源
37を動作させ、その周波数(100Hz〜10KHz
)、電圧(三角波、半波長電圧※(2〜5))を設定す
る。信号137の出力および受光素子32の出力を、そ
れぞれ電圧記録装置35のX軸およびY軸に接続して、
X(電圧)−Y(光強度信号)表示状態に設定し、偏波
制御器34を調整して、波形の対称性を確認しながら、
偏光軸の調整を行う。X軸に関して、対称な波形が得ら
れた時点で電圧記録装置35の掃引を停止し、その状態
を記録紙に出力する。この際、光強度信号の極太、極小
を与える電圧値を測定すれば、その電圧差から光位相変
調器30の半波長電圧を求めることができる。
Specifically, it is sufficient to measure the relationship between V and i□ at low frequencies where electrode loss and phase velocity mismatch can be ignored. That is, after the light source 25 and the receiving system b (the measuring system including the voltage recording device 35) are brought into operation, the signal source 37 is operated and its frequency (100 Hz to 10 KHz
), voltage (triangular wave, half-wavelength voltage *(2 to 5)). The output of the signal 137 and the output of the light receiving element 32 are connected to the X axis and Y axis of the voltage recording device 35, respectively.
Set to the X (voltage) - Y (light intensity signal) display state, adjust the polarization controller 34, and check the symmetry of the waveform.
Adjust the polarization axis. When a symmetrical waveform is obtained with respect to the X-axis, the voltage recording device 35 stops sweeping, and the state is output on recording paper. At this time, by measuring the voltage values that give the highest and lowest optical intensity signals, the half-wave voltage of the optical phase modulator 30 can be determined from the voltage difference.

第2図(a)は、光位相変調器30に電圧を印加しない
状態で、受光素子32 (Ge−APD/IMΩ負荷)
の出力電圧(Vld)を測定した結果である。
FIG. 2(a) shows the light receiving element 32 (Ge-APD/IMΩ load) with no voltage applied to the optical phase modulator 30.
This is the result of measuring the output voltage (Vld) of.

約20sec間の測定結果であるが、比較的緩やかで、
かつランダムな変化をすることがわかる。この変化は、
式・(6)の関係から、(k DL)の変化に帰着でき
る。なお、光学的分岐干渉系31を構成するファイバに
振動等が加わるとこの変化に重畳して急激な光出力変化
が現れることから、静置するように配慮する必要がある
This is a measurement result for about 20 seconds, but it is relatively slow.
And it can be seen that it changes randomly. This change is
From the relationship in equation (6), it can be concluded that (k DL) changes. Note that if vibration or the like is applied to the fiber constituting the optical branching interference system 31, a sudden change in optical output will appear superimposed on this change, so care must be taken to leave it stationary.

第2図(b)は、上記と同一のサンプルに対して、振幅
:約+ 15v (V L)9周波数:tkll、のバ
イアス変R(三角波)を変調を行い、約IO週期(10
+ms)にわたるVt、とVdの関係を測定した結果で
ある。このように、短時間に測定を行なう限り、系の位
相雑音(△(k−DL))の影響は無視でき、再現性ら
全く問題ないことが分かる。同図から、サンプルの半波
長電圧Vπは、光信号の極小または極大を与える電圧か
ら、5.8 (・11.6/2) Vと評価できる。
Fig. 2(b) shows that the same sample as above is modulated with a bias variable R (triangular wave) of amplitude: approximately +15V (V L), 9 frequency: tkll, and approximately IO week period (10
This is the result of measuring the relationship between Vt and Vd over a period of +ms). In this way, it can be seen that as long as the measurement is carried out in a short period of time, the influence of the phase noise (Δ(k-DL)) of the system can be ignored and there is no problem with reproducibility. From the figure, the half-wavelength voltage Vπ of the sample can be estimated to be 5.8 (·11.6/2) V from the voltage that gives the minimum or maximum of the optical signal.

なお、この測定では、受光素子32により合波後の光強
度に比例する出力電圧(Vd cx: i’ ))を測
定しているため、光学的分岐干渉系31を構成する各ブ
ランチを通過した光の強度、位相、偏波面が合波部であ
る偏波体技カプラ28で等しければ、大きな消光比が得
られることになる。このデータでは、消光比は高々4 
dB (= 201og (160/100))である
が、この原因は、主に各辺の損失を補償していないため
と考えられる。ブランチl側に光減衰器を挿入して、消
光比の改善は可能であるが、半波長電圧の測定、周波数
特性の測定には、支障がないことは言うまでもない。
In addition, in this measurement, since the output voltage (Vdcx: i')) which is proportional to the light intensity after multiplexing is measured by the light receiving element 32, the If the intensity, phase, and plane of polarization of the light are equal at the polarization coupler 28, which is a multiplexing section, a large extinction ratio can be obtained. In this data, the extinction ratio is at most 4
dB (=201og (160/100)), but this is thought to be mainly due to not compensating for losses on each side. Although it is possible to improve the extinction ratio by inserting an optical attenuator on the branch l side, it goes without saying that this does not impede measurement of half-wave voltage and frequency characteristics.

(iii )周波数特性の測定 次に、第1図の特性測定装置の適用による光位相変調器
の周波数特性の測定方法について説明する。
(iii) Measuring Frequency Characteristics Next, a method for measuring frequency characteristics of an optical phase modulator by applying the characteristic measuring device shown in FIG. 1 will be explained.

(iii −1)測定原理 まず、測定原理について述べる。(iii-1) Measurement principle First, the measurement principle will be described.

光位相変調器30には、(k−DL)の時間的変動に較
べて、十分大きな振幅の低周波のバイアス変調信号と測
定変調周波数成分の信号を重畳するものとする。
The optical phase modulator 30 is assumed to be superimposed with a low frequency bias modulation signal having a sufficiently large amplitude compared to the temporal fluctuation of (k-DL) and a signal of the measurement modulation frequency component.

Φ(t)=Φ、(t)+ΦL(t)         
(9)この式(9)を式(6)に代入して考えると、i
 l=η+(E o)”[1−sin(Φ、(1)+Φ
バt)+に−DL)] (to)ここで、Φt、(D=
ΦLo’5ln((t) tt)      (11)
Φbo4 (no)37 (tt/λ)(V、/GP)
式(8)1式(11)を式(10)に代入して、+1=
77 +(E o)” [1−sin(Φ+no”5l
n(ωsL十〇)+Φt、o”5in(ω己)+に−D
L)]        (12)ここで、高周波数成分
に着目すると、 i +(Jm)=[(sin(Φao”5Ln((t)
+at+θ))cos(Φto・5in((cl tt
))+cos(Φwan ’ 5in((tJ、を十〇
))sin(Φto・5in(ωtt)))cos(k
・DL) +(cos(Φ+so”S!n (ω、t+
θ))cos(Φ、。・5in(ω己))−sin(Φ
+++g’S!n(ωsL+θ))sin(Φto−s
in(ωtt)))sin(k−DL)]×η1(Eo
戸              (13)ここで、 5in(Φ、。・5in(ωゆt十〇))・2ΣJ□、
、(Φno)・5in((2i+1)(ω、1十〇))
cos (Φmo’51n(ω、t+θ))=JO(Φ
−0)”2ΣJtt(ΦlII。)−cos((2i(
ω叩十〇))sin(Φto−8in(ωtt))=2
Σ、Lt*+(Φ+、o)sin((2i+lXω1.
1))cos(ΦLo−sin(ωtt))Jo(Φt
、o)+2ΣJt+(Φ、o)cos((2i(ωtt
))f、の近傍周波数では、低周波変調信号のFMスペ
クトルが重畳して観測されることになる。
Φ(t)=Φ,(t)+ΦL(t)
(9) Substituting this equation (9) into equation (6), we get i
l=η+(E o)" [1-sin(Φ, (1)+Φ
(to) Here, Φt, (D=
ΦLo'5ln((t) tt) (11)
Φbo4 (no) 37 (tt/λ) (V, /GP)
Substituting equation (8)1 equation (11) into equation (10), +1=
77 + (E o)” [1-sin (Φ+no”5l
n(ωsL〇)+Φt, o”5in(ωself)+−D
L)] (12) Now, focusing on the high frequency component, i + (Jm) = [(sin(Φao”5Ln((t)
+at+θ))cos(Φto・5in((cl tt
))+cos(Φwan' 5in((tJ, 10))sin(Φto・5in(ωtt)))cos(k
・DL) +(cos(Φ+so”S!n (ω, t+
θ)) cos(Φ,.・5in(ωself))−sin(Φ
+++g'S! n(ωsL+θ)) sin(Φto−s
in(ωtt)) sin(k-DL)]×η1(Eo
Door (13) Here, 5in(Φ,.・5in(ωyut10))・2ΣJ□,
, (Φno)・5in ((2i+1)(ω, 100))
cos (Φmo'51n(ω, t+θ))=JO(Φ
−0)”2ΣJtt(ΦlII.)−cos((2i(
ω 10)) sin(Φto-8in(ωtt))=2
Σ, Lt*+(Φ+, o) sin((2i+lXω1.
1)) cos(ΦLo-sin(ωtt))Jo(Φt
,o)+2ΣJt+(Φ,o)cos((2i(ωtt
)) f, the FM spectrum of the low frequency modulation signal is observed to be superimposed.

11fJ−)cl:[(Jo(ΦLo)+2ΣJt+(
Φt、o)cos((2i(cc+ Lt)))cos
(lrDL)−(2ΣJti*+(Φt、o)sin(
2i+IXωt、t)))sin(?DL))・2J、
(Φso)”S!n(ωst十〇”)        
      (14)しかし、通常は、有限の帯域幅で
、複数の側帯波の電力相を測定することになる。光スペ
クラム分析器36の帯域幅をBとして時間平均をとれば
、となる。式(15)は、f=f、のスペクトルはJ、
(Φ。
11fJ-)cl: [(Jo(ΦLo)+2ΣJt+(
Φt, o) cos((2i(cc+Lt))) cos
(lrDL)−(2ΣJti*+(Φt, o)sin(
2i+IXωt, t))) sin(?DL))・2J,
(Φso)”S!n(ωst 10”)
(14) However, typically the power phases of multiple sidebands will be measured with a finite bandwidth. If the bandwidth of the optical spectrum analyzer 36 is taken as B and the time average is taken, the following is obtained. Equation (15) shows that the spectrum of f=f is J,
(Φ.

。))!〜(Φ、。)″に比例した電カスベクトルとな
ることを意味するが、その大きさはバイアス変調振幅(
Φ、。)に依存することと、系の位相雑音(k・DL)
の影響を受けることを意味している。
. ))! This means that the electric flux vector is proportional to ~(Φ,.)″, and its size is determined by the bias modulation amplitude (
Φ,. ) and the phase noise of the system (k・DL)
It means being influenced by.

第3図は、f=f、に於けるスペクトル強度に対する系
雑音(△(k−DL) )の影響を、バイアス変調振幅
(Φ、。)をパラメータにして評価した結果(第3図(
a))とスペクトル変動の最大値とバイアス変n振幅と
の関係を算出した結果(第3図(b))とを示すもので
ある。
Figure 3 shows the results of evaluating the influence of system noise (△(k-DL)) on the spectral intensity at f=f using the bias modulation amplitude (Φ, .) as a parameter (Figure 3 (
a)) and the result of calculating the relationship between the maximum value of the spectrum variation and the bias variation n amplitude (FIG. 3(b)).

第3図(λ)では、スペクトル強度として式(15)の
係数部分(【]の部分)をとることとし、系の位相雑音
としては(k−DL)の周期関数であることを考慮して
、0からπまでの範囲で解析した。
In Figure 3 (λ), the coefficient part ([] part) of equation (15) is taken as the spectral intensity, and considering that the phase noise of the system is a periodic function of (k-DL). , analyzed in the range from 0 to π.

また、測定される側帯波の数を10(πB/ωL=10
)としたが、5以上であれば、はぼ同様の結果かえられ
ることも、別途確認されている。この第3図(a)から
、スペクトル強度に与える系の位相雑音の影響は、ΦL
Oが大きい程、小さくなることがわかる。また第3図(
b)から、スペクトル強度の変動を完全に抑圧できるΦ
、。が存在すること、Φ、。がπ以上であれば変動幅は
3dB以下となること等が明らかであり、バイアス変調
の効果が明らかである。
Also, the number of sideband waves to be measured is set to 10 (πB/ωL=10
), but it has been separately confirmed that if the value is 5 or more, the same result can be obtained. From this Figure 3(a), the influence of the phase noise of the system on the spectral intensity is ΦL
It can be seen that the larger O is, the smaller it becomes. Also, Figure 3 (
From b), Φ can completely suppress the fluctuations in the spectral intensity.
,. The existence of Φ. It is clear that the fluctuation range is 3 dB or less when is greater than or equal to π, and the effect of bias modulation is clear.

なお、低周波変調を重畳しない場合(ΦLo=Q)には
、式(15)から [i 、(f、)] ”oe (cos (k−DL)
)”(J、(Φ5o))”−(cos(k−DL))”
(Φ、。)″     (16)となり、 図中に示すように、系の位相雑音(△(k−DL) )
の値によって、大幅な強度変化を伴うため、測定の効率
が低下することになる。
Note that when low frequency modulation is not superimposed (ΦLo=Q), from equation (15), [i, (f,)] ”oe (cos (k-DL)
)"(J, (Φ5o))"-(cos(k-DL))"
(Φ,.)'' (16), and as shown in the figure, the phase noise of the system (△(k-DL))
Depending on the value of , the efficiency of the measurement will be reduced due to large intensity changes.

以上の結果から、光周波数応答の測定にあたっては、適
当な振幅のバイアス変調信号を重畳し、受信帯域幅を充
分法<(〉バイアス変調周波数の10倍以上)とれば、
入力マイクロ波変調成分の光強度スペクトルの測定を効
率良く行なうことができることが明らかになった。
From the above results, when measuring the optical frequency response, if a bias modulation signal of an appropriate amplitude is superimposed and the reception bandwidth is set to a sufficient modulus <(>10 times or more of the bias modulation frequency), then
It has become clear that the optical intensity spectrum of input microwave modulation components can be measured efficiently.

(iii −2)光マイクロ波応答特性測定の具体例次
に、この例の特性測定装置の適用による光マイクロ波応
答特性の測定例について記述する。
(iii-2) Specific example of measuring optical microwave response characteristics Next, an example of measuring optical microwave response characteristics by applying the characteristic measuring device of this example will be described.

(a)測定系の調整とバイアス変調条件の選定測定系の
調整は、(ii −2)に述べた方法と同様であるので
、省略する。
(a) Adjustment of the measurement system and selection of bias modulation conditions The adjustment of the measurement system is the same as the method described in (ii-2), so it will be omitted.

第4図、第5図には、バイアス変調の有効性を確認する
ために、変調を行わなかった場合と、バイアス周波数を
約200Hz、変調振幅2XVπとした場合について、
高周波変”A (IGHz、 + 10dBm)周波数
における光出力信号のスペクトラムを測定した結果およ
びスペクトル強度の時間的変化の測定結果をそれぞれを
示す。測定試料は、1.5μm帯の光位相変調器で、そ
の半波長電圧■πは5.95Vのらのである。
In order to confirm the effectiveness of bias modulation, Figs. 4 and 5 show cases in which no modulation was performed and cases in which the bias frequency was approximately 200 Hz and the modulation amplitude was 2XVπ.
The results of measuring the spectrum of the optical output signal at the high frequency "A" (IGHz, +10 dBm) frequency and the measurement results of the temporal change in spectral intensity are shown respectively.The measurement sample was a 1.5 μm band optical phase modulator. , its half-wave voltage ■π is 5.95V.

バイアス変調を行わない場合には、単一スペクトルが観
測される第4図(a)が、そのピークレベルの変動が大
きく、時間的に光学的分岐干渉系の消光比程度(偏波結
合器の分岐比、各ブランチの損失に依存=lO〜25d
B)の変動が避けられない(第5図(a))。
When bias modulation is not performed, a single spectrum is observed in Figure 4(a), but the peak level fluctuates greatly, and the extinction ratio of the optical branching interference system (of the polarization coupler) changes over time. Branching ratio, depends on loss of each branch = lO~25d
B) fluctuations are unavoidable (Figure 5(a)).

一方、バイアス変調により、低周波のFM変調スペクト
ルが重畳することになり、この図の例では変調度が大き
いため、零次光が抑圧され、高次光が観測される(第4
図(b))。(iii −1)で考察したように、偶数
次スペクトルと奇数次スペクトルとが、光学的分岐干渉
系の位相条件(△(k・DL) )によって大小するが
、光スペクトラム分析器36の受信帯域幅を充分大きく
とることによって、測定されるピークレベル変動が大幅
に低減される。この場合、受信帯域幅を3 MHzとす
るとレベル変動は約±1dB程度になり(第5図(b)
)、周波数応答を評価するには十分な精度と言える。
On the other hand, due to bias modulation, the low-frequency FM modulation spectrum is superimposed, and in the example shown in this figure, the degree of modulation is large, so the zero-order light is suppressed and the high-order light is observed (the fourth
Figure (b)). As discussed in (iii-1), even-order spectra and odd-order spectra vary depending on the phase condition (△(k・DL)) of the optical branching interference system, but the reception band of the optical spectrum analyzer 36 By making the width sufficiently large, the measured peak level fluctuations are significantly reduced. In this case, if the reception bandwidth is 3 MHz, the level fluctuation will be approximately ±1 dB (Figure 5 (b)).
), it can be said that the accuracy is sufficient to evaluate the frequency response.

なお、前節の考察では、正弦波バイアス変調により、光
強度変化を低減できることを述べたが、この実験例のよ
うな三角波変調の場合でも、三角波のフーリエ成分に着
目して考察すれば、同様の効果が得られることは、容易
に推察できる。
In the discussion in the previous section, it was stated that changes in light intensity can be reduced by sinusoidal bias modulation, but even in the case of triangular wave modulation as in this experimental example, if we focus on the Fourier component of the triangular wave, we can achieve the same result. It can be easily inferred that an effect can be obtained.

この状態で、高周波変調の変調周波数を変化させ、受光
素子33で検出される信号出力を光スペクトラム分析器
36で測定することにより、先位相変n器30の周波数
応答が評価できる。ただし、あらかじめ受光素子33の
感度補正、RFケーブルの損失補正を要することは言う
までもない。
In this state, the frequency response of the first phase converter 30 can be evaluated by changing the modulation frequency of the high-frequency modulation and measuring the signal output detected by the light receiving element 33 with the optical spectrum analyzer 36. However, it goes without saying that it is necessary to correct the sensitivity of the light receiving element 33 and the loss of the RF cable in advance.

(b)測定例 第6図は、上記の光位相変調器の光周波数応答を測定し
た結果である。なお、バイアス変調信号は、周波数: 
200Hz、振幅=2×Vπとし、光スペクトラム分析
器36の受信帯域幅をSN比(>15dbat 20G
Hz)を考慮して、3MHzとした。また、光スペクト
ラム分析器36の最大レベル保持機能(M^X−Hol
d機能)を活用して、測定を行なった後、あらかじめ測
定しである光位相変調器のマイクロ波入力端子までのR
Fケーブルの損失を差し引いて、第6図のデータを得て
いる。
(b) Measurement Example FIG. 6 shows the results of measuring the optical frequency response of the optical phase modulator described above. Note that the frequency of the bias modulation signal is:
200Hz, amplitude = 2 x Vπ, and the reception bandwidth of the optical spectrum analyzer 36 is
Hz), the frequency was set at 3 MHz. In addition, the maximum level holding function (M^X-Hol) of the optical spectrum analyzer 36
d function) to measure the R to the microwave input terminal of the optical phase modulator that was previously measured.
The data shown in Figure 6 is obtained by subtracting the loss of the F cable.

第6図から明らかなように、測定レベルの平均化のため
所要時間の若干の増大は避けられないものの、バイアス
変調が適正であれば、通常の強度変調器の測定の場合と
同等の精度が得られる。
As is clear from Figure 6, although a slight increase in the required time due to the averaging of the measurement level is unavoidable, if the bias modulation is appropriate, the accuracy is equivalent to that of normal intensity modulator measurement. can get.

(iv )実施例の効果 以上、モジュール化した位相変調器(偏波保持ファイバ
ピグティル付)の簡易測定法として、偏波保持ファイバ
による分岐干渉系を構成し、何等の制御回路を付加せず
に、半波長電圧、周波数特性を測定する方法の開示を行
なうと共に、その原理、測定法の評価を実測例をまじえ
て説明した。
(iv) As a simple measurement method for a modularized phase modulator (with polarization-maintaining fiber pigtail), we constructed a branching interference system using polarization-maintaining fibers without adding any control circuit. In this paper, a method for measuring half-wavelength voltage and frequency characteristics was disclosed, and the principle and evaluation of the measurement method were explained using actual measurement examples.

この例の効果を要約すると以下の通りである。The effects of this example are summarized as follows.

(1)半波長電圧の測定は、測定系の変動が無視できる
程度の短時間(実測例く約20m5 )に行なうことに
より、再現性も問題がない。
(1) The measurement of half-wave voltage is carried out in a short period of time (about 20 m5 in actual measurement) such that fluctuations in the measurement system can be ignored, so there is no problem with reproducibility.

(2)光周波数応答の測定にあたっては、低周波バイア
ス変調によるスペクトル拡散を行って、測定系変動の影
響を低減することができる。低周波バイアス変調条件、
スペクトル分析器の受信帯域幅の選定を適切に行えば、
通常の強度変調器の評価と同等の精度が得られる事が明
らかになった。
(2) When measuring the optical frequency response, spectrum spreading by low frequency bias modulation can be performed to reduce the influence of measurement system fluctuations. Low frequency bias modulation conditions,
If the receiving bandwidth of the spectrum analyzer is selected appropriately,
It has become clear that the same accuracy as the evaluation of ordinary intensity modulators can be obtained.

(3)この例の測定方法は、従来のファブリペロ共振器
を利用して周波数変調された光信号のスペクトル分析す
る方法、自己ヘテロゲイン系を構成して光信号のスペク
トル分析結果から評価する方法と比較して、直接的に半
波長電圧が評価できるだけでなく、光周波数の応答の評
価にも有効である。
(3) The measurement method in this example is compared with a conventional method that uses a Fabry-Perot resonator to analyze the spectrum of a frequency-modulated optical signal, and a method that constructs a self-hetero gain system and evaluates it from the spectrum analysis results of the optical signal. This method is effective not only for directly evaluating half-wavelength voltage, but also for evaluating optical frequency response.

なお、上述したように、この発明においては、光学的分
岐干渉系の光路−差を小さくとり、分岐干渉系の特性変
動の影響が無視できる短い時間に半波長電圧の測定を行
うこと、また位相変調器にバイアス変凋信号を重畳して
、等価的に系の安定化を行なって周波数応答を測定する
方法について述べたか、周波数応答を測定するにあたっ
て有効なバイアス変調の効果は、上述の解析から明らか
なように、■分岐干渉系のいずれかのブランチに位相変
化を与えるか、■光源の波長を変化させても同様な効果
か得られるものである。
As mentioned above, in the present invention, the optical path difference of the optical branching interference system is kept small, and the half-wave voltage is measured in a short time when the influence of characteristic fluctuations of the branching interference system can be ignored. We have described a method of superimposing a bias variation signal on the modulator to equivalently stabilize the system and measure the frequency response.The above analysis shows that the effect of bias modulation is effective in measuring the frequency response. As is clear, the same effect can be obtained by (1) imparting a phase change to any branch of the branching interference system, or (2) changing the wavelength of the light source.

■の方法としては、この実施例で説明したように、測定
対象である光位相変調器にバイアス変調信号を重畳する
方法のほかに、光位相変調器を接続しであるブランチに
直列、あるいは他のブランチに、位相を変化できる素子
を接続して、同様にその素子に対してバイアス変調を行
う方法も有効である。
As method (2), in addition to the method of superimposing a bias modulation signal on the optical phase modulator to be measured, as explained in this example, the method of connecting the optical phase modulator to a branch in series or It is also effective to connect an element that can change the phase to the branch of the signal and perform bias modulation on that element.

また、■光源の波長を変化させて同様な効果を得る際に
は、式(lO)の(k −D L )に対するバイアス
変調に相当すると考えれば良い。したがって、光源とし
て半導体レーザを用いる場合、注入電流による光強度の
変化の小さい範囲で、注入電流によってkを変調する必
要があるので、分岐干渉系の光路差D Lを十分大きく
設定する必要がある。
Furthermore, when obtaining a similar effect by changing the wavelength of the light source (2), it is sufficient to consider that it corresponds to bias modulation for (k - D L ) in equation (lO). Therefore, when using a semiconductor laser as a light source, it is necessary to modulate k by the injection current within a range where the change in light intensity due to the injection current is small, so it is necessary to set the optical path difference D L of the branching interference system sufficiently large. .

また、上述の実施例においては、偏波保持カプラ、偏波
保持ファイバ、入出力ポート間の偏光軸を一致させる場
合について述べたが、通常の光カブラ、ファイバなどに
より構成することもできる。
Further, in the above-described embodiments, a case has been described in which the polarization axes between a polarization maintaining coupler, a polarization maintaining fiber, and an input/output port are made to coincide with each other, but it may also be constructed using a normal optical coupler, fiber, or the like.

「発明の効果」 以上説明したように、この発明の光位相変調器の特性測
定装置および特性測定法によれば、構成が簡単になる。
"Effects of the Invention" As explained above, according to the optical phase modulator characteristic measuring device and characteristic measuring method of the present invention, the configuration is simplified.

また、光位相変調器の半波長電圧の測定を、位相変化の
無視できる短時間内に行うことができる。
Furthermore, the half-wavelength voltage of the optical phase modulator can be measured within a short time when phase changes can be ignored.

また、光位相変調器周波数特性の測定に際しては、位相
変調器に対して適正な振幅の低周波バイアス信号を重畳
することにより、測定周波数成分に対する雑音の影響を
低減することができる。
Furthermore, when measuring the frequency characteristics of the optical phase modulator, the influence of noise on the measurement frequency component can be reduced by superimposing a low frequency bias signal with an appropriate amplitude on the phase modulator.

【図面の簡単な説明】[Brief explanation of drawings]

第1図は、この発明の一実施例である光位相変調器の特
性測定装置の構成を示すブロック図、第2図は、同特性
測定装置を適用して得られた測定データを示す特性曲線
図であり、第2図(a)は、系雑音による出力電圧時間
応答特性を示す図、第2図(b)は、バイアス変調時の
出力電圧とバイアス電圧との関係を示す関係図、 第3図は、バイアス変調による光スペクトル強度変化の
低減効果を説明するための図、第4図は、光出力信号の
高周波変調周波数におけるスペクトルに及ぼすバイアス
変調効果を説明するための図、 第5図は、光出力信号の高周波変調周波数におけるスペ
クトル細塵の時間的変化に及ぼすバイアス変調の効果を
説明するための図、 第6図は、光位相変調器の光周波数応答の測定結果を示
す図、 第7図ないし第9図は、従来の光位相変調器の特性測定
装置の構成を示すブロック図である。 25・・・・・・レーザ光源、27・・・・・・偏波保
持カプラ(第1の光結合器)、28・・・・・・偏波保
持カプラ(第2の光結合器)、29・・・・・・偏波保
持ファイバ、30・・・・・・光位相変調器、31・・
・・・光学的分岐干渉系、32.33・・・・・・受光
素子、35・・・・・・電圧記録装置、36・・・・・
・光スペクトラム分析器、37.38・・・・・・信号
源、P1〜P6・・・・・・偏波保持カプラの入出力ポ
ート。
FIG. 1 is a block diagram showing the configuration of a characteristic measuring device for an optical phase modulator which is an embodiment of the present invention, and FIG. 2 is a characteristic curve showing measurement data obtained by applying the same characteristic measuring device. 2(a) is a diagram showing the output voltage time response characteristic due to system noise, FIG. 2(b) is a relational diagram showing the relationship between the output voltage and the bias voltage during bias modulation, and FIG. 3 is a diagram for explaining the effect of reducing the optical spectrum intensity change due to bias modulation, FIG. 4 is a diagram for explaining the bias modulation effect on the spectrum at the high frequency modulation frequency of the optical output signal, and FIG. is a diagram for explaining the effect of bias modulation on the temporal change in spectral fines at the high-frequency modulation frequency of the optical output signal; FIG. 6 is a diagram showing the measurement results of the optical frequency response of the optical phase modulator; FIGS. 7 to 9 are block diagrams showing the configuration of a conventional optical phase modulator characteristic measuring device. 25... Laser light source, 27... Polarization maintaining coupler (first optical coupler), 28... Polarization maintaining coupler (second optical coupler), 29...Polarization maintaining fiber, 30...Optical phase modulator, 31...
...Optical branching interference system, 32.33... Light receiving element, 35... Voltage recording device, 36...
- Optical spectrum analyzer, 37.38... Signal source, P1 to P6... Input/output port of polarization maintaining coupler.

Claims (3)

【特許請求の範囲】[Claims] (1)第1の光結合器の2個の出力ポートと第2の光結
合器の2個の入力ポートとを対向させ、当該一組の入出
力ポート間にファイバを接続し、当該他の組の入出力ポ
ート間に、光位相変調器を接続して光学的分岐干渉系を
構成し、 前記光学的分岐干渉系の一方に単一モード光源からの光
を入射させ、他方に受光素子を接続し、その出力電圧を
記録できる電圧記録装置、および前記光学的分岐干渉系
の光出力をスペクトル分析できる光スペクトラム分析器
を併置する共に、前記光位相変調器の電気端子に、低周
波のバイアス変調信号と高周波信号を重畳して印加でき
るように構成したことを特徴とする光位相変調器の特性
測定装置。
(1) Two output ports of the first optical coupler and two input ports of the second optical coupler are made to face each other, and a fiber is connected between the pair of input and output ports, and the other An optical phase modulator is connected between the input and output ports of the pair to form an optical branching interference system, and the light from the single mode light source is input to one side of the optical branching interference system, and the light receiving element is connected to the other side. A voltage recording device that can be connected and record the output voltage, and an optical spectrum analyzer that can perform spectrum analysis of the optical output of the optical branching interference system are installed together, and a low frequency bias is applied to the electrical terminal of the optical phase modulator. A characteristic measuring device for an optical phase modulator, characterized in that it is configured to be able to apply a modulation signal and a high frequency signal in a superimposed manner.
(2)請求項1記載の光位相変調器の特性測定装置を用
いて、 前記光位相変調器に、前記光学的分岐干渉系の各要素の
等価的位相変化に起因して発生する出力電圧の時間的変
動に較べて充分早い周期をもつバイアス変調信号を印加
して、 前記受光素子の出力電圧の変化とバイアス電圧の変化を
前記電圧記録装置により記録測定して、前記光位相変調
器の半波長電圧を測定することを特徴とする光位相変調
器の特性測定法。
(2) Using the optical phase modulator characteristic measuring device according to claim 1, the output voltage generated in the optical phase modulator due to the equivalent phase change of each element of the optical branching interference system is measured. A bias modulation signal having a sufficiently fast period compared to temporal fluctuations is applied, and changes in the output voltage of the light receiving element and changes in the bias voltage are recorded and measured by the voltage recording device, and the half of the optical phase modulator is measured. A method for measuring characteristics of an optical phase modulator characterized by measuring wavelength voltage.
(3)請求項1記載の光位相変調器の特性測定装置を用
いて、 前記光位相変調器に、適正な振幅をもつ低周波バイアス
変調信号を印加すると同時に、高周波変調信号を重畳し
て印加する状態とし、 前記光スペクトラム分析器の受信帯域幅をバイアス変調
周波数に較べて、十分大きな値に設定して、 高周波変調信号に対する前記光位相変調器の変調感度を
測定することを特徴とする光位相変調器の特性測走法。
(3) Using the optical phase modulator characteristic measuring device according to claim 1, applying a low frequency bias modulation signal having an appropriate amplitude to the optical phase modulator and simultaneously applying a high frequency modulation signal in a superimposed manner. the reception bandwidth of the optical spectrum analyzer is set to a sufficiently large value compared to the bias modulation frequency, and the modulation sensitivity of the optical phase modulator to the high frequency modulation signal is measured. A method for measuring the characteristics of phase modulators.
JP26162689A 1989-10-06 1989-10-06 Apparatus and method for measuring characteristics of optical phase modulator Expired - Lifetime JP2939482B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP26162689A JP2939482B2 (en) 1989-10-06 1989-10-06 Apparatus and method for measuring characteristics of optical phase modulator

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Application Number Priority Date Filing Date Title
JP26162689A JP2939482B2 (en) 1989-10-06 1989-10-06 Apparatus and method for measuring characteristics of optical phase modulator

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Publication Number Publication Date
JPH03123828A true JPH03123828A (en) 1991-05-27
JP2939482B2 JP2939482B2 (en) 1999-08-25

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