JPS6147403B2 - - Google Patents

Info

Publication number
JPS6147403B2
JPS6147403B2 JP55052994A JP5299480A JPS6147403B2 JP S6147403 B2 JPS6147403 B2 JP S6147403B2 JP 55052994 A JP55052994 A JP 55052994A JP 5299480 A JP5299480 A JP 5299480A JP S6147403 B2 JPS6147403 B2 JP S6147403B2
Authority
JP
Japan
Prior art keywords
light
signal light
signal
local light
local
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.)
Expired
Application number
JP55052994A
Other languages
Japanese (ja)
Other versions
JPS56150731A (en
Inventor
Nobuyuki Imoto
Yoshihisa Yamamoto
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
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Nippon Telegraph and Telephone Corp filed Critical Nippon Telegraph and Telephone Corp
Priority to JP5299480A priority Critical patent/JPS56150731A/en
Publication of JPS56150731A publication Critical patent/JPS56150731A/en
Publication of JPS6147403B2 publication Critical patent/JPS6147403B2/ja
Granted legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2/00—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light
    • G02F2/002—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light using optical mixing

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • General Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Optics & Photonics (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)
  • Optical Communication System (AREA)

Description

【発明の詳細な説明】[Detailed description of the invention]

本発明は光ヘテロダイン又は光ホモダイン検波
方式を用いた光フアイバ伝送において、信号光と
局発光を等しい偏光状態で合波し、検波効率を最
大にするための光合波装置に関するものである。 光フアイバ伝送においてヘテロダイン又はホモ
ダイン検波方式を用いた場合、一般的に用いられ
ている強度変調二乗検波方式に較べ最小受信レベ
ルが下がるため、より長距離の伝送が可能となる
（山本：「各種光デイジタル変復調方式の基礎検
討」電子通信学会通信方式研究会資料、CS79―
144，1979）。この方式では信号光と局発光を合波
した後受信器に入射し、干渉成分を検出する方法
をとつている。従つて干渉の効率を最大とするた
め信号光と局発光の偏光状態を一致させておく必
要がある。しかし、フアイバを長距離伝搬して来
た信号光の偏光状態は不安定であり、時間と共に
変化する。このため受信部で信号光と局発光の偏
光状態を常に一致させるべき機構が必要となる
が、従来このような機構の構成例はまだ知られて
いない。 本発明は従来の技術の上記欠点を改善すること
を目的とし、その特徴は信号光と局発光の偏光状
態又はその差を検出し、両者が一致した状態で合
波するべく信号光又は局発光の路上に挿入された
電気光学結晶又は位相板を制御するようにしたも
ので、以下詳細に説明する。 信号光Ｅsは一般にだ円偏光である。このだ円
の長軸と45゜の角をなす方向をｘ軸とし、ｘ軸と
直交する方向をｙ軸に選べば、Ｅsのｘ成分Ｅsx
とｙ成分Ｅsyは位相は異なるが振幅は等しくな
り、解析が簡単となる。ＥsxとＥsyは次式で表わ
される。 ここでωsは信号光角周波数、φは位相差であ
る。これに対し局発光ＥLを次式で表わす。 ここでωLは局発光角周波数、φx，φyはｘ成
分、ｙ成分の位相差である。信号光と局発光を合
波し、ヘテロダイン検波し、得られるIF信号を
検波したDC出力をＩとすれば、 ここで、 The present invention relates to an optical multiplexing device for multiplexing signal light and local light in an equal polarization state to maximize detection efficiency in optical fiber transmission using optical heterodyne or optical homodyne detection methods. When a heterodyne or homodyne detection method is used in optical fiber transmission, the minimum reception level is lower than that of the commonly used intensity modulation square law detection method, making it possible to transmit over longer distances (Yamamoto: ``Various types of optical “Basic Study of Digital Modulation and Demodulation Systems” IEICE Communication Systems Study Group Materials, CS79.
144, 1979). This method uses a method in which signal light and local light are combined and then input to a receiver, and interference components are detected. Therefore, in order to maximize the efficiency of interference, it is necessary to match the polarization states of the signal light and the local light. However, the polarization state of the signal light propagated over long distances through the fiber is unstable and changes over time. For this reason, a mechanism is required to always match the polarization states of the signal light and the local light in the receiving section, but a configuration example of such a mechanism has not yet been known. The present invention aims to improve the above-mentioned drawbacks of the conventional technology, and its feature is to detect the polarization state of the signal light and the local light or the difference thereof, and to combine the signal light or the local light in a state where both are in agreement. This device controls an electro-optic crystal or a phase plate inserted into the path of the motor, and will be explained in detail below. The signal light E s is generally elliptical polarized light. If we choose the direction that makes a 45° angle with the long axis of this ellipse as the x-axis and the direction perpendicular to the x-axis as the y-axis, then the x component of E s is E sx
and the y component E sy have different phases but the same amplitude, making analysis easy. E sx and E sy are expressed by the following equations. Here, ω s is the signal light angular frequency, and φ is the phase difference. On the other hand, the local light E L is expressed by the following equation. Here, ω L is the local light angular frequency, and φ x and φ y are the phase differences between the x component and the y component. If the signal light and local light are combined, heterodyne detection is performed, and the DC output obtained by detecting the obtained IF signal is I, here,

【式】である。信号光及び局 発光強度が一定の場合、(3)式は、[Formula]. signal light and station When the emission intensity is constant, equation (3) becomes

【式】か つφy−φx＝φの場合に最大値Maximum value if [Formula] and φ y −φ x = φ

【式】とな る。即ち局発光の偏光状態を信号光に一致させた
場合に検波出力が最大になる。 このように、偏光状態を合わせるには一般に２
つの自由度を一致させる必要がある。逆に信号光
を局発光に合わせても良いが、普通信号光は弱く
局部光は強いので、局発光の偏光状態を変化させ
ることが望ましい。 第１図に本発明の１実施例を示す。この例では
局部光を信号光に合わせるため、まず信号光の偏
光を表わすだ円の長軸を検出し、局発光側に挿入
された１／４波長板の軸を一致させる。次に検波後の DC出力が最大となるように１／２波長板により局発光 の直線偏光方向を回転させる。以上により局発光
の偏光状態は信号光に一致する。各部品の働きは
次の通りである。信号光ＥSは10dB半透鏡１によ
り一部を偏光方向検出のため取り出され、検光子
２を通過後受光器３により強度を測定される。強
度出力はサーボモータ４を制御し、強度出力最大
となる方向に検光子を回転させる。検光子２と局
発光側の１／４波長板５は連動しており、信号光の軸 と１／４波長板５の軸は一致する。局発光は１／２波長
板６ により偏光方向を自由に回転させられ、半透鏡７
により信号光と合波する。受光器８によるヘテロ
ダイン検波出力は１／２波長板６と連結したサーボモ ータ９を制御する。本実施例の特徴は、１／４波長板 ５の制御が１／２波長板６の制御と独立に行えること である。これにより、２つの自由度を交互に制御
し収束させることなく制御可能である。従つて２
つの制御系の応答時間の和だけで偏光状態変化に
追随する。 上記実施例では信号光の偏光方向及び検波出力
の双方をフイードバツク信号として用い、１／４波長 板及び１／２波長板の軸の方向で示される２つの自由 度を制御したが、１／４波長板を省略することも考え られる。即ち、第１図において１〜５を省略する
と、局発光の偏向方向のみを制御する系となる。
この場合(3)式においてφx＝φyとなり、最悪の整
合状態（φ＝π／２）でも完全な整合状態（φ＝
０）に較べ光強度で3dBの損失にしかならないこ
とがわかる。 第２図に本発明の他の実施例を示す。半透鏡
１、検光子２、受光器３及びサーボモータ４を用
いて前実施例と同様、信号光ＥSのだ円偏光の軸
を検出する。本実施例では検光子２の回転軸と位
相板１０の回転軸が連動しており、検光子２の主
軸と位相板１０の主軸は45゜傾けておく。また、
局発光ＥLは直線偏光にしておき、偏光方向は入
射光のだ円偏光の主軸と一致させておく。１／２波長 板６はＥLの偏光方向を一致させるために用いる
が、偏光方向の角度変化は１／２波長板の角度変化の ２倍であることに注意し、歯車等を用いて上記目
的を実現する。１／２波長板の代わりに偏光白色光源 と偏光子を用いる場合回転角変化と偏光方向変化
は１：１なので、位相板１０と主軸を合わせ、回
転軸を共通にすればよい。次に受光器８によるヘ
テロダイン検波出力が最大となるように位相板１
０の位相補償量を変化させる。これを自動的に行
うためには、ラツク、ピニオン等の歯車又はねじ
を用いてサーボモータ９の回転運動を位相板のく
さび出し入れ運動に変換し、サーボモータ制御を
ヘテロダイン検波出力を用いて行う。 第１図の１／４波長板５及び第２図の位相板１０で はモーターにより位相板の主軸の回転や位相補償
量の制御を行つたが、これを電気的に行うことも
できる。 第３図は電気的に主軸の方向や位相補償量変化
を行う位相板の構成を示す。１１は電気光学結晶
でｚ方向に３回対称軸を有するものである。１２
はｘ方向及びｙ方向に電界Ｅx及びＥyを加えるた
めの電極である。今ＥxとＥyを次のように表わ
す。[Formula] becomes. That is, the detection output is maximized when the polarization state of the local light is matched with the signal light. In this way, in order to match the polarization state, generally 2
It is necessary to match the two degrees of freedom. Conversely, the signal light may be matched to the local light, but since the signal light is normally weak and the local light is strong, it is desirable to change the polarization state of the local light. FIG. 1 shows one embodiment of the present invention. In this example, in order to match the local light with the signal light, first the long axis of the ellipse representing the polarization of the signal light is detected, and the axes of the quarter-wave plate inserted on the local light side are matched. Next, the linear polarization direction of the local light is rotated using a 1/2 wavelength plate so that the DC output after detection is maximized. As described above, the polarization state of the local light matches the signal light. The function of each part is as follows. A portion of the signal light E S is taken out by a 10 dB semi-transparent mirror 1 for polarization direction detection, and after passing through an analyzer 2, its intensity is measured by a light receiver 3. The intensity output controls the servo motor 4 to rotate the analyzer in the direction where the intensity output is maximized. The analyzer 2 and the quarter-wave plate 5 on the local light side are interlocked, and the axis of the signal light and the axis of the quarter-wave plate 5 coincide. The polarization direction of the local light can be freely rotated by a 1/2 wavelength plate 6, and a semi-transparent mirror 7
is combined with the signal light. The heterodyne detection output from the light receiver 8 controls a servo motor 9 connected to a 1/2 wavelength plate 6. A feature of this embodiment is that the quarter-wave plate 5 can be controlled independently of the half-wave plate 6. This makes it possible to alternately control the two degrees of freedom without causing convergence. Therefore 2
Changes in the polarization state can be followed simply by the sum of the response times of the two control systems. In the above embodiment, both the polarization direction of the signal light and the detection output are used as feedback signals to control the two degrees of freedom indicated by the axis directions of the quarter-wave plate and the half-wave plate. It is also possible to omit the wave plate. That is, if 1 to 5 are omitted in FIG. 1, the system becomes a system that controls only the deflection direction of the local light.
In this case, φ x = φ y in equation (3), and even the worst matching state (φ = π/2) is a perfect matching state (φ =
It can be seen that the loss in optical intensity is only 3 dB compared to 0). FIG. 2 shows another embodiment of the invention. Using a semi-transparent mirror 1, an analyzer 2, a light receiver 3, and a servo motor 4, the axis of elliptical polarization of the signal light E S is detected as in the previous embodiment. In this embodiment, the rotation axis of the analyzer 2 and the rotation axis of the phase plate 10 are interlocked, and the main axis of the analyzer 2 and the main axis of the phase plate 10 are tilted at an angle of 45 degrees. Also,
The local light E L is linearly polarized, and the polarization direction is made to match the principal axis of the elliptical polarization of the incident light. The 1/2 wavelength plate 6 is used to match the polarization direction of E L , but please note that the angular change in the polarization direction is twice the angular change of the 1/2 wavelength plate, and use gears etc. to Realize your purpose. When using a polarized white light source and a polarizer instead of a 1/2 wavelength plate, the change in rotation angle and the change in polarization direction are 1:1, so the main axis may be aligned with the phase plate 10 and the rotation axis may be common. Next, set the phase plate 1 so that the heterodyne detection output by the optical receiver 8 is maximized.
Change the phase compensation amount of 0. To do this automatically, gears such as racks and pinions or screws are used to convert the rotational motion of the servo motor 9 into a wedge-in/out motion of the phase plate, and the servo motor is controlled using the heterodyne detection output. In the quarter-wave plate 5 of FIG. 1 and the phase plate 10 of FIG. 2, the rotation of the main axis of the phase plate and the amount of phase compensation are controlled by a motor, but this can also be done electrically. FIG. 3 shows the configuration of a phase plate that electrically changes the direction of the principal axis and the amount of phase compensation. Reference numeral 11 denotes an electro-optic crystal having a three-fold symmetry axis in the z direction. 12
are electrodes for applying electric fields E x and E y in the x and y directions. Now, E x and E y are expressed as follows.

【表】 このとき、（ｘ，ｙ）軸を次の(5)式で定義され
るθだけ回転し、（x′，y′）軸とすると、（x′，
y′）軸を主軸とし、(6)式で表わされるΓだけ位相
差を生ずる位相板として働く。 θ＝−１／２［＋sin-1（ｒ２２／ｒ）］ ……(5) Γ＝２πdn３ ０／rE0／λ ……(6) ここで、ｒ＝√〓＋〓，r11，r22：電気光
学テンソル成分、ｄ：結晶長、n0：結晶の屈
折率、λ：波長 である。(5)式及び(6)式から、位相板の主軸はに
より、位相補償量はE0により制御されることが
分る。この電圧制御位相板を第１図の実施例の１／４ 波長板５の代わりに用いる場合、信号光のだ円偏
光の軸の向きθを検出し、θから(4)式のＥx，Ｅy
の電圧をつくる必要がある。E0は１／４波長板である ことから(6)式よりΓ＝π／２とおいて定まる。従つて θからcos，sinの信号を得る必要があるが、
これを実現する機構の１例を第４図に示す。１〜
４で信号光の軸の向きθを検出する。検光子２と
検光子１４は歯車等の連結機構により、２の軸角
度θと１４の軸角度が(5)式を満足するように連
動している。１３はｘ偏光又はｙ偏光を発する光
源であり、ｘ偏光光源の場合検光子１４を通過後
受光器１５によりcosの出力を生ずる。さらに
増幅器１６によりE0cosの信号となる。同様に
１３としてｙ偏光光源を用いれば１６の出力は
E0sinとなる。以上により信号光の偏光方向θ
から電圧制御位相板に必要なＥx，Ｅyを得ること
ができる。また、第２図の実施例の位相板１０の
代わりに用いる場合は、ヘテロダイン検波出力が
最大となるようにE0をも制御する必要がある
が、これは検波出力を用いて増幅器１６の増幅率
を制御することにより実現される。 本実施例ではヘテロダイン検波の場合を説明し
たが、ホモダイン検波でも全く同様であり本発明
をそのまま適用することができる。 以上説明したように、信号光の偏光状態又はヘ
テロダイン検波出力を用いて機械的又は電気的に
位相板の軸方向及び位相補償量を変化させること
により局発光の偏光状態を信号光と一致させ合波
するので、常に最大の効率でヘテロダイン検波を
実現することができる。また、偏光状態の制御に
必要な２つの自由度を独立に制御するので、応答
速度も速く、信号光の偏光状態の変化に要易に追
随する。[Table] At this time, if the (x, y) axis is rotated by θ defined by the following equation (5) and set as the (x', y') axis, then (x',
The main axis is the y′) axis, and it acts as a phase plate that generates a phase difference by Γ expressed by equation (6). θ=-1/2 [+sin -1 (r 22 /r)] ...(5) Γ=2πdn 3 0 /rE 0 /λ ...(6) Here, r=√〓+〓, r 11 , r 22 : electro-optic tensor component, d: crystal length, n 0 : refractive index of crystal, λ: wavelength. From equations (5) and (6), it can be seen that the main axis of the phase plate is controlled by , and the amount of phase compensation is controlled by E 0 . When this voltage-controlled phase plate is used in place of the 1/4 wavelength plate 5 in the embodiment shown in FIG. 1, the direction θ of the axis of elliptical polarization of the signal light is detected, and from θ E E y
It is necessary to create a voltage of Since E 0 is a quarter-wave plate, it is determined from equation (6) that Γ=π/2. Therefore, it is necessary to obtain cos and sin signals from θ, but
An example of a mechanism for realizing this is shown in FIG. 1~
4, the direction θ of the axis of the signal light is detected. The analyzer 2 and the analyzer 14 are interlocked by a coupling mechanism such as a gear so that the axial angle θ of 2 and the axial angle of 14 satisfy equation (5). Reference numeral 13 denotes a light source that emits x-polarized light or y-polarized light. In the case of an x-polarized light source, after passing through an analyzer 14, a cosine output is produced by a light receiver 15. Further, the amplifier 16 converts the signal into an E 0 cos signal. Similarly, if a y-polarized light source is used as 13, the output of 16 will be
E 0 sin. As a result of the above, the polarization direction θ of the signal light
E x and E y required for the voltage controlled phase plate can be obtained from . Furthermore, when used in place of the phase plate 10 in the embodiment shown in FIG. 2, it is necessary to also control E 0 so that the heterodyne detection output is maximized. This is achieved by controlling the rate. In this embodiment, the case of heterodyne detection has been described, but the present invention can be applied as is since the same is true for homodyne detection. As explained above, by mechanically or electrically changing the axial direction and phase compensation amount of the phase plate using the polarization state of the signal light or the heterodyne detection output, the polarization state of the local light can be made to match that of the signal light. wave, so heterodyne detection can always be achieved with maximum efficiency. Furthermore, since the two degrees of freedom necessary for controlling the polarization state are independently controlled, the response speed is fast and the change in the polarization state of the signal light can be easily followed.

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

第１図は本発明の一実施例、第２図は本発明の
他の実施例、第３図はモータ制御の位相板を電気
的に制御する構成に置換するための説明図、第４
図は本発明の他の実施例である。 １…10dB半透鏡、２…検光子、３…受光器、
４…サーボモータ、５…１／４波長板、６…１／２波長
板 （又は偏光子）、７…半透鏡、８…受光器、９…サ
ーボモータ、１０…位相板、１１…電気光学結
晶、１２…電極、１３…光源、１４…検光子、１
５…受光器、１６…増幅器。 FIG. 1 is an embodiment of the present invention, FIG. 2 is another embodiment of the present invention, FIG. 3 is an explanatory diagram for replacing the phase plate of motor control with an electrically controlled configuration, and FIG.
The figure shows another embodiment of the invention. 1...10dB semi-transparent mirror, 2...analyzer, 3...light receiver,
4... Servo motor, 5... 1/4 wavelength plate, 6... 1/2 wavelength plate (or polarizer), 7... Semi-transparent mirror, 8... Light receiver, 9... Servo motor, 10... Phase plate, 11... Electro-optics Crystal, 12... Electrode, 13... Light source, 14... Analyzer, 1
5... Light receiver, 16... Amplifier.

Claims (1)

【特許請求の範囲】[Claims] １ 半透鏡又は光カツプラーにより信号光と局発
光を合波する光ヘテロダイン検波用合波装置にお
いて、信号光及び局発光の少なくとも一方に偏光
状態を制御する位相板または電気光学結晶を介し
て、信号光及び局発光を半透鏡又は光カツプラー
により合波し、前記位相板の位相補償量または電
気光学結晶の主軸の方向の制御が、信号光又は局
発光の検光子を介した検光出力、又はヘテロダイ
ン検波出力、又はそれら両者のフイードバツク信
号により、信号光と局発光を等しい偏光状態で合
波するごとく行なわれることを特徴とする光偏光
整合合波装置。1. In an optical heterodyne detection multiplexing device that combines signal light and local light using a semi-transparent mirror or optical coupler, the signal is transmitted through a phase plate or an electro-optic crystal that controls the polarization state of at least one of the signal light and the local light. The light and the local light are combined by a semi-transparent mirror or an optical coupler, and the phase compensation amount of the phase plate or the direction of the main axis of the electro-optic crystal is controlled by the analysis output of the signal light or the local light via an analyzer, or An optical polarization matching multiplexing device characterized in that signal light and local light are multiplexed in an equal polarization state using a heterodyne detection output or a feedback signal of both.
JP5299480A 1980-04-23 1980-04-23 Optical polarization matching and combining device Granted JPS56150731A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP5299480A JPS56150731A (en) 1980-04-23 1980-04-23 Optical polarization matching and combining device

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP5299480A JPS56150731A (en) 1980-04-23 1980-04-23 Optical polarization matching and combining device

Publications (2)

Publication Number Publication Date
JPS56150731A JPS56150731A (en) 1981-11-21
JPS6147403B2 true JPS6147403B2 (en) 1986-10-18

Family

ID=12930471

Family Applications (1)

Application Number Title Priority Date Filing Date
JP5299480A Granted JPS56150731A (en) 1980-04-23 1980-04-23 Optical polarization matching and combining device

Country Status (1)

Country Link
JP (1) JPS56150731A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62237117A (en) * 1986-04-07 1987-10-17 Ngk Spark Plug Co Ltd Rotary power transmitting mechanism

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5736367Y2 (en) * 1980-09-26 1982-08-11
JPS5913434A (en) * 1982-07-14 1984-01-24 Nec Corp Method of optical heterodyne detection
JPS60121424A (en) * 1983-12-05 1985-06-28 Nippon Telegr & Teleph Corp <Ntt> Optical receiver
JPS61153616A (en) * 1984-12-27 1986-07-12 Kokusai Denshin Denwa Co Ltd <Kdd> Polarization matching device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
APPLIEO OPTICS=1975 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62237117A (en) * 1986-04-07 1987-10-17 Ngk Spark Plug Co Ltd Rotary power transmitting mechanism

Also Published As

Publication number Publication date
JPS56150731A (en) 1981-11-21

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