JPH0593935A - Polarization state control method - Google Patents
Polarization state control methodInfo
- Publication number
- JPH0593935A JPH0593935A JP25395291A JP25395291A JPH0593935A JP H0593935 A JPH0593935 A JP H0593935A JP 25395291 A JP25395291 A JP 25395291A JP 25395291 A JP25395291 A JP 25395291A JP H0593935 A JPH0593935 A JP H0593935A
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- wave plate
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、偏波多重光波通信にお
ける受信側での偏波状態制御方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization state control method on the receiving side in polarization multiplexed lightwave communication.
【０００２】[0002]
【従来の技術】光波通信の分野では、位相雑音による感
度劣化の低減を目的とし、光の偏波状態を用いてデータ
を伝送する通信方式の研究が盛んに行なわれており、最
近では２つの直交偏波を夫々変調するようにした通信方
法（信学技報，Vol.９１，No．６３，ＯＣＳ９１−１
０，ｐｐ．７〜１２）も提案されている。この通信方法
は位相雑音に原理的に不感応であり、信号帯域を従来の
半分にできるという利点を有している。しかし、受信さ
れる信号光の偏波状態を完全な円偏波として仮定してお
り、偏波制御回路を持たないことから、伝送路中での偏
波変動が考えられる光ファイバ通信等では該偏波変動の
影響により受信感度が著しく劣化すると考えられる。2. Description of the Related Art In the field of lightwave communication, research has been actively conducted on a communication system for transmitting data using the polarization state of light for the purpose of reducing sensitivity deterioration due to phase noise, and recently two types have been studied. Communication method for modulating each of the orthogonal polarizations (Technical Report, Vol. 91, No. 63, OCS 91-1
0, pp. 7-12) have also been proposed. This communication method is insensitive to phase noise in principle, and has an advantage that the signal band can be reduced to half that of the conventional method. However, the polarization state of the received signal light is assumed to be a perfect circular polarization, and since it does not have a polarization control circuit, it may be It is considered that the reception sensitivity is significantly degraded due to the influence of polarization fluctuation.
【０００３】一方、受信側での偏波状態制御方法に関す
る報告もいくつかあり、その一例（信学論，Vol.Ｊ６８
−Ｃ，No．２，ｐｐ．７７〜８６）を図１２に示す。On the other hand, there are some reports on the method of controlling the polarization state on the receiving side, one example of which is shown in (Theoretical theory, Vol. J68).
-C, No. 2, pp. 77-86) is shown in FIG.
【０００４】この制御系では、まず受信信号光Ｐを４５
°傾いた２つの移相器（電気光学位相変調器）１２１，
１２２に通過させ、該信号光をハーフミラー１２３で分
岐し、分岐した信号光を４５°傾いたロッションプリズ
ム１２４に通す。そして、この信号光から２つの光検出
器１２５，１２６でＸ軸から±４５°傾いた成分の電力
Ｓ1 ，Ｓ2 （図１３参照）を検出し、差動増幅器１２７
で差をとって誤差信号（Ｓ1 −Ｓ2 ）を得て、この誤差
信号で移相器１２１の電圧を制御する。また、ハーフミ
ラー１２３を通過した信号光をハーフミラー１２８で分
岐し、分岐した信号光を４５°傾けた１／４波長板１２
９とロッションプリズム１３０に通す。そして、この信
号光から２つの検出器１３１，１３２でＸ軸及びＹ軸方
向の電力Ｓ3 ，Ｓ4 （図１４参照）を検出し、差動増幅
器１３３で差をとって誤差信号（Ｓ3 −Ｓ4 ）を得て、
この誤差信号で移相器１２２の電力を制御する。以上の
動作によってＸ軸方向の直線偏波が作り出される。In this control system, first, the received signal light P is changed to 45
Two tilted phase shifters (electro-optical phase modulator) 121,
Then, the signal light is passed through the beam splitter 122, split by the half mirror 123, and the split signal light is passed through the Lotion prism 124 inclined at 45 °. Then, from the signal light, the two photodetectors 125 and 126 detect the electric powers S1 and S2 (see FIG. 13) of the components inclined by ± 45 ° from the X axis, and the differential amplifier 127
To obtain the error signal (S1-S2), and the voltage of the phase shifter 121 is controlled by this error signal. Further, the signal light that has passed through the half mirror 123 is branched by the half mirror 128, and the branched signal light is inclined by 45 °.
9 and the lotion prism 130. Then, the two detectors 131 and 132 detect the electric powers S3 and S4 (see FIG. 14) in the X-axis and Y-axis directions from this signal light, and the differential amplifier 133 takes the difference to obtain an error signal (S3-S4). Got
The power of the phase shifter 122 is controlled by this error signal. The above operation produces a linearly polarized wave in the X-axis direction.
【０００５】[0005]
【発明が解決しようとする課題】上述のような従来の偏
波状態制御方法は偏波状態が情報に依存しない場合には
有効であるが、偏波変調や偏波多重のように偏波状態が
情報に依存する場合を考えたときに、制御信号の極性の
反転などによって正確に動作しなくなる欠点がある。Although the conventional polarization state control method as described above is effective when the polarization state does not depend on information, the polarization state control such as polarization modulation or polarization multiplexing is effective. However, when considering the case where is dependent on information, there is a drawback that it does not operate correctly due to inversion of the polarity of the control signal.
【０００６】本発明は上記問題点に鑑みてなされたもの
で、その目的とするところは、２つの直交偏波を利用し
た偏波多重光波通信において、偏波状態が変動する受信
信号光を所定方向の直線偏波に安定させることができる
偏波状態制御方法を提供することにある。The present invention has been made in view of the above problems, and an object of the present invention is to provide a received signal light whose polarization state fluctuates in a polarization multiplexed lightwave communication using two orthogonal polarizations. It is an object of the present invention to provide a polarization state control method capable of stabilizing linearly polarized waves in any direction.
【０００７】[0007]
【課題を解決するための手段】上記目的を達成するため
請求項１記載の制御方法では、２つの直交した偏波状態
をもつ受信信号光を１／４波長板及び１／２波長板に通
過させ、該信号光の２つの直交偏波軸（Ｘ−Ｙ）成分を
夫々ヘテロダイン検波して２つの中間周波数帯信号を検
出し、このＸ成分と位相をπ／２遅らせたＹ成分との積
に、復調信号を乗算した信号で１／４波長板を制御する
と共に、Ｘ成分とＹ成分の和と差の積に、復調信号を乗
算した信号で１／２波長板を制御している。In order to achieve the above object, in the control method according to claim 1, the received signal light having two orthogonal polarization states is passed through a quarter wave plate and a half wave plate. Then, two orthogonal polarization axes (X-Y) components of the signal light are heterodyne-detected to detect two intermediate frequency band signals, and the product of this X component and the Y component whose phase is delayed by π / 2 is detected. In addition, the 1/4 wavelength plate is controlled by the signal multiplied by the demodulation signal, and the 1/2 wavelength plate is controlled by the signal obtained by multiplying the product of the sum and difference of the X component and the Y component by the demodulation signal.
【０００８】請求項２記載の制御方法では、２つの直交
した偏波状態をもつ受信信号光を１／４波長板及び１／
２波長板に通過させ、該信号光の２つの直交偏波軸（Ｘ
−Ｙ）成分を夫々ヘテロダイン検波して２つの中間周波
数帯信号を検出し、このＸ成分と位相をπ／２遅らせた
Ｙ成分との積に、復調信号を乗算した信号で１／４波長
板を制御すると共に、Ｘ成分の二乗とＹ成分の二乗との
差に、復調信号を乗算した信号で１／２波長板を制御し
ている。In the control method according to the second aspect of the present invention, the received signal light having two polarization states orthogonal to each other is converted into a 1/4 wavelength plate and a 1 / wave plate.
The two orthogonal polarization axes (X
-Y) component is heterodyne-detected to detect two intermediate frequency band signals, and the product of the X component and the Y component whose phase is delayed by π / 2 is multiplied by the demodulation signal to obtain a quarter wave plate. And the difference between the square of the X component and the square of the Y component is multiplied by the demodulation signal to control the ½ wavelength plate.
【０００９】請求項３記載の制御方法では、２つの直交
した偏波状態をもつ受信信号光を１／４波長板及び１／
２波長板に通過させ、該信号光と局部発振光夫々の２つ
の直交偏波軸（Ｘ−Ｙ）成分を夫々ホモダイン検波して
４つの中間周波数帯信号を検出し、このＸＩ成分とＹＱ
成分の積とＸＱ成分とＹＩ成分の積との差に、復調信号
を乗算した信号で１／４波長板を制御すると共に、ＸＩ
成分の二乗とＸＱ成分の二乗の和とＹＩ成分の二乗とＹ
Ｑ成分の二乗の和との差に、復調信号を乗算した信号で
１／２波長板を制御している。According to a third aspect of the control method, the received signal light having two orthogonal polarization states is converted into a quarter wave plate and a one / fourth wave plate.
The two orthogonal polarization axes (X-Y) components of the signal light and the local oscillation light are respectively homodyne-detected to detect four intermediate frequency band signals, and these XI component and YQ are passed.
The ¼ wavelength plate is controlled by a signal obtained by multiplying the difference between the product of the components and the product of the XQ component and the YI component by the demodulation signal, and
The sum of the square of the component and the square of the XQ component and the square of the YI component and Y
The 1/2 wavelength plate is controlled by a signal obtained by multiplying the demodulated signal by the difference between the sum of the squares of the Q components and the demodulated signal.
【００１０】請求項４記載の制御方法では、２つの直交
した偏波状態をもつ受信信号光を１／４波長板及び１／
２波長板に通過させ、該信号光と局部発振光夫々の２つ
の直交偏波軸（Ｘ−Ｙ）成分を夫々ホモダイン検波して
４つの中間周波数帯信号を検出し、このＸＩ成分とＹＱ
成分の積とＸＱ成分とＹＩ成分の積との差に、復調信号
を乗算した信号で１／４波長板を制御すると共に、ＸＩ
成分とＹＩ成分の和と差の積と、ＸＱ成分とＹＱ成分の
和と差の積との差に、復調信号を乗算した信号で１／２
波長板を制御している。According to a fourth aspect of the control method, the received signal light having two orthogonal polarization states is converted into a quarter wavelength plate and a one / fourth wavelength plate.
The two orthogonal polarization axes (X-Y) components of the signal light and the local oscillation light are respectively homodyne-detected to detect four intermediate frequency band signals, and these XI component and YQ are passed.
The ¼ wavelength plate is controlled by a signal obtained by multiplying the difference between the product of the components and the product of the XQ component and the YI component by the demodulation signal, and
The product of the sum and difference of the component and the YI component, and the product of the sum and the difference of the XQ component and the YQ component, multiplied by the demodulated signal
It controls the wave plate.
【００１１】[0011]
【作用】請求項１記載の制御方法によれば、ヘテロダイ
ン検波後の偏波のＸ成分と、位相をπ／２遅らせたＹ成
分との積は、復調された信号を乗算することによって該
信号に依存する成分がキャンセルされ、伝送路中に生じ
たｘ，ｙ成分間の位相差のみを含んだ信号となる。ま
た、Ｘ成分とＹ成分の和と差の積（電力の差）について
も、復調された信号を乗算することによって該信号に依
存する成分がキャンセルされ、受信信号光と受信側偏波
ビームスプリッタとの主軸の傾きに対応する信号とな
る。つまり、前者の信号で１／４波長板を制御すること
によって受信信号光を所定方向の直線偏波にすることが
でき、また後者の信号で１／２波長板を制御することに
よってその直線偏波を受信軸から４５°傾いた方向に合
わせることができる。According to the control method of the present invention, the product of the X component of the polarized wave after the heterodyne detection and the Y component of which the phase is delayed by π / 2 is multiplied by the demodulated signal to obtain the signal. The component dependent on is canceled and the signal becomes a signal containing only the phase difference between the x and y components generated in the transmission path. Regarding the product of the sum and difference (power difference) of the X component and the Y component, the component dependent on the signal is canceled by multiplying the demodulated signal, and the received signal light and the reception side polarization beam splitter The signal corresponds to the inclinations of the main axes of and. That is, by controlling the ¼ wavelength plate with the former signal, the received signal light can be linearly polarized in a predetermined direction, and by controlling the ½ wavelength plate with the latter signal, the linear polarization can be changed. The waves can be aligned in a direction inclined by 45 ° from the receiving axis.
【００１２】請求項２記載の制御方法によれば、ヘテロ
ダイン検波後の偏波のＸ成分の二乗とＹ成分の二乗との
差は、復調された信号を乗算することによって該信号に
依存する成分がキャンセルされ、受信信号光と受信側偏
波ビームスプリッタとの主軸の傾きに対応する信号とな
る。請求項１の制御方法とは１／２波長板に対する制御
信号の演算方法を異にするが、同様の作用が得られる。According to the control method of the second aspect, the difference between the square of the X component and the square of the Y component of the polarized wave after the heterodyne detection depends on the demodulated signal and is dependent on the signal. Is canceled and becomes a signal corresponding to the inclination of the principal axis of the reception signal light and the polarization beam splitter on the reception side. Although the method of calculating the control signal for the half-wave plate is different from that of the control method according to claim 1, the same operation can be obtained.
【００１３】請求項３記載の制御方法によれば、ホモダ
イン検波後の偏波のＸＩ成分とＹＱ成分の積とＸＱ成分
とＹＩ成分の積との差は、復調された信号を乗算するこ
とによって該信号に依存する成分がキャンセルされ、伝
送路中で生じたｘ，ｙ成分間の位相差のみを含んだ信号
となる。また、ＸＩ成分の二乗とＸＱ成分の二乗の和と
ＹＩ成分の二乗とＹＱ成分の二乗の和との差について
も、復調された信号を乗算することによって該信号に依
存する成分がキャンセルされ、受信信号光と受信側偏波
ビームスプリッタとの主軸の傾きに対応する信号とな
る。つまり、前者の信号で１／４波長板を制御すること
によって受信信号光を所定方向の直線偏波にすることが
でき、また後者の信号で１／２波長板を制御することに
よってその直線偏波を受信軸から４５°傾いた方向に合
わせることができる。According to the control method of the third aspect, the difference between the product of the XI component and the YQ component of the polarization after the homodyne detection and the product of the XQ component and the YI component is multiplied by the demodulated signal. The component dependent on the signal is canceled and the signal contains only the phase difference between the x and y components generated in the transmission path. Further, regarding the difference between the sum of the squares of the XI component and the square of the XQ component and the sum of the square of the YI component and the square of the YQ component, the component dependent on the signal is canceled by multiplying the demodulated signal, It becomes a signal corresponding to the inclination of the principal axes of the received signal light and the receiving side polarization beam splitter. That is, by controlling the ¼ wavelength plate with the former signal, the received signal light can be linearly polarized in a predetermined direction, and by controlling the ½ wavelength plate with the latter signal, the linear polarization can be changed. The waves can be aligned in a direction inclined by 45 ° from the receiving axis.
【００１４】請求項４記載の制御方法によれば、ホモダ
イン検波後の偏波のＸＩ成分とＹＩ成分の和と差の積
と、ＸＱ成分とＹＱ成分の和と差の積との差は、復調さ
れた信号を乗算することによって該信号に依存する成分
がキャンセルされ、受信信号光と受信側偏波ビームスプ
リッタとの主軸の傾きに対応する信号となる。請求項３
の制御方法とは１／２波長板に対する制御信号の演算方
法を異にするが、同様の作用が得られる。According to the control method of the fourth aspect, the difference between the product of the sum and difference of the XI component and the YI component of the polarized wave after homodyne detection and the product of the sum and the difference of the XQ component and the YQ component is By multiplying the demodulated signal, the component dependent on the signal is canceled and the signal becomes a signal corresponding to the inclination of the principal axes of the received signal light and the reception side polarization beam splitter. Claim 3
Although the method of calculating the control signal for the half-wave plate is different from the control method of, the same effect can be obtained.
【００１５】[0015]
【実施例】まず、請求項１に記載した発明の実施例を図
１示す光受信機の構成図を参照して説明する。同図にお
いて１は１／４波長板、２は１／２波長板、３は光カッ
プラ、４は局部発振用レ−ザ、５は偏波ビ−ムスプリッ
タ、６ａ，６ｂは光検出器、７はπ／２位相遅延器、８
ａ乃至８ｃは低域通過フィルタ、９は符号判定器、１
ａ，１０ｂは１ｂｉｔ遅延器、１１は加算器、１２は減
算器、１３ａ乃至１３ｅは乗算器である。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of the invention described in claim 1 will be described with reference to the block diagram of the optical receiver shown in FIG. In the figure, 1 is a quarter wavelength plate, 2 is a half wavelength plate, 3 is an optical coupler, 4 is a laser for local oscillation, 5 is a polarization beam splitter, 6a and 6b are photodetectors, 7 is a π / 2 phase delay device, 8
a to 8c are low-pass filters, 9 is a code determiner, 1
Reference numerals a and 10b are 1-bit delay devices, 11 is an adder, 12 is a subtractor, and 13a to 13e are multipliers.
【００１６】受信信号光Ｐは、まず１／４波長板１及び
１／２波長板２を順に通過し、局部発振用レ−ザ４の発
振光と共に光カップラ３に入る。光カップラ３で合波さ
れた信号光は偏波ビ−ムスプリッタ５に入り、２つの直
交偏波軸（Ｘ−Ｙ）成分に分離される。このＸ成分とＹ
成分は夫々光検出器６ａ，６ｂに入り、ＩX とＩY のＩ
Ｆ（中間周波数）帯電流に変換される。The received signal light P first passes through the quarter-wave plate 1 and the half-wave plate 2 in order, and enters the optical coupler 3 together with the oscillation light of the local oscillation laser 4. The signal light multiplexed by the optical coupler 3 enters the polarization beam splitter 5 and is separated into two orthogonal polarization axis (X-Y) components. This X component and Y
The components enter the photodetectors 6a and 6b, respectively, and the I of IX and IY
Converted to F (intermediate frequency) band current.
【００１７】ヘテロダイン検波後の電流ＩX ，ＩY は乗
算器１３ａで乗算された後、低域通過フィルタ８ａと符
号判定器９を通過して復調信号Ａとなる。The currents IX and IY after the heterodyne detection are multiplied by the multiplier 13a and then passed through the low-pass filter 8a and the sign determiner 9 to become the demodulated signal A.
【００１８】また、電流ＩX と、π／２位相遅延器７で
位相を遅らされた電流ＩY は乗算器１３ｂで乗算された
後、低域通過フィルタ８ｂと１ｂｉｔ遅延器１０ａを通
過し、さらに乗算器１３ｃで上記の復調信号Ａと乗算さ
れて信号Ｂとなる。この信号Ｂは制御信号として１／４
波長板１に帰還される。The current IX and the current IY whose phase has been delayed by the π / 2 phase delay unit 7 are multiplied by the multiplier 13b and then passed through the low pass filter 8b and the 1-bit delay unit 10a, and further, The demodulated signal A is multiplied by the multiplier 13c to obtain a signal B. This signal B is 1/4 as a control signal
It is returned to the wave plate 1.
【００１９】更に、電流ＩX ，ＩY は加算器１１と減算
器１２で夫々加・減算され、これら和と差が乗算器１３
ｄで乗算された後、低域通過フィルタ８ｃと１ｂｉｔ遅
延器１０ｂを通過し、さらに乗算器１３ｅで上記の復調
信号Ａと乗算されて信号Ｃとなる。この信号Ｃは制御信
号として１／２波長板２に帰還される。Further, the currents IX and IY are added and subtracted by an adder 11 and a subtractor 12, respectively, and the sum and difference thereof are multiplied by a multiplier 13.
After being multiplied by d, it passes through the low-pass filter 8c and the 1-bit delay device 10b, and is further multiplied by the demodulated signal A in the multiplier 13e to become a signal C. This signal C is fed back to the half-wave plate 2 as a control signal.
【００２０】図２は図１に示した光受信機に対応する光
送信機の変調部の構成図で、同図において２１は半導体
レ−ザ、２２ａ，２２ｂは偏波ビ−ムスプリッタ、２３
ａ，２３ｂは位相変調器である。FIG. 2 is a block diagram of a modulator of an optical transmitter corresponding to the optical receiver shown in FIG. 1, in which 21 is a semiconductor laser, 22a and 22b are polarization beam splitters, and 23 is a polarization beam splitter.
Reference numerals a and 23b are phase modulators.
【００２１】半導体レ−ザ１からの信号光は、まず偏波
ビ−ムスプリッタ２２ａに入り、２つの直交偏波軸（ｘ
−ｙ）成分に分離される。偏波のｘ軸成分とｙ軸成分は
夫々位相変調器２３ａ，２３ｂで変調され、偏波ビ−ム
スプリッタ２２ｂで合波される。変調された信号光は、
図３に示すように２つの直交した直線偏波状態を持つこ
とになる。The signal light from the semiconductor laser 1 first enters the polarization beam splitter 22a and two orthogonal polarization axes (x
-Y) separated into components. The x-axis component and the y-axis component of the polarized wave are modulated by the phase modulators 23a and 23b, respectively, and combined by the polarized beam splitter 22b. The modulated signal light is
As shown in FIG. 3, it has two orthogonal linear polarization states.
【００２２】ここで、上述の偏波状態制御について具体
式を挙げて詳しく説明する。Here, the above-mentioned polarization state control will be described in detail with reference to specific equations.
【００２３】図２に示した光送信機側の偏波ビームスプ
リッタ２２ａ，２２ｂの直交軸をｘ−ｙとすると、送信
電界のｘ，ｙ成分ＥTx、ＥTyは夫々、 ＥTx＝ＡTxｃｏｓ（ωs ｔ＋φs ＋πｄx ） ＥTy＝ＡTyｃｏｓ（ωs ｔ＋φs ＋πｄy ） となる。上式のＡTx，ＡTyは夫々送信電界のｘ，ｙ成分
の振幅、ωs は送信光の角周波数、φs は送信光の位相
雑音、ｄx ，ｄy は夫々ｘ，ｙ成分の電界を位相変調し
た２値データ信号（０または１）である。Assuming that the orthogonal axes of the polarization beam splitters 22a and 22b on the optical transmitter side shown in FIG. 2 are xy, the x and y components ETx and ETy of the transmission electric field are ETx = ATxcos (ωst + φs + πdx), respectively. ) ETy = ATycos (ωst + φs + πdy). Where ATx and ATy are the amplitudes of the x and y components of the transmission electric field, ωs is the angular frequency of the transmission light, φs is the phase noise of the transmission light, and dx and dy are the phase modulation of the electric fields of the x and y components, respectively. It is a value data signal (0 or 1).
【００２４】この信号光は伝送中、伝送路である光ファ
イバの複屈折の影響を受け、受信端では電界のｘ，ｙ成
分間に位相差が生じる。また、送信側偏波ビームスプリ
ッタ２２ａ，２２ｂと受信側偏波ビームスプリッタ５の
主軸の傾き、及び伝送路中での偏波方向の回転等によ
り、受信信号光Ｐと受信側偏波ビームスプリッタ５の間
には主軸に傾きが生じる。During transmission, this signal light is affected by the birefringence of the optical fiber that is the transmission line, and a phase difference occurs between the x and y components of the electric field at the receiving end. In addition, the received signal light P and the reception-side polarization beam splitter 5 are caused by the inclination of the main axes of the transmission-side polarization beam splitters 22a and 22b and the reception-side polarization beam splitter 5, rotation of the polarization direction in the transmission path, and the like. There is a tilt in the main axis.
【００２５】一方、光受信機の偏波ビームスプリッタ５
の直交軸をＸ−Ｙとすると、受信電界ＥRX，ＥRYは夫
々、 ＥRX＝ｃｏｓθＡTxｃｏｓ（ωs ｔ＋φs ＋πｄx ＋ψ） −ｓｉｎθＡTyｃｏｓ（ωs ｔ＋φs ＋πｄy ） ＥRY＝ｃｏｓθＡTyｃｏｓ（ωs ｔ＋φs ＋πｄy −ψ） ＋ｓｉｎθＡTxｃｏｓ（ωs ｔ＋φs ＋πｄx ） となる。上式のθは信号光からみた送信側偏波ビームス
プリッタ２２ａ，２２ｂの主軸と受信側偏波ビームスプ
リッタ５の主軸のずれ、ψは伝送路中に生じたｘ，ｙ成
分間の位相差である。On the other hand, the polarization beam splitter 5 of the optical receiver
Letting X-Y be the orthogonal axis of X, the received electric fields ERX and ERY are ERX = cos θATxcos (ωst + φs + πdx + ψ) -sinθATycos (ωst + φs + πdysω + x + s + t + cos + ATs + ωd + sθ + sd + φs + Δs + Δs + Δs + A). Becomes In the above equation, θ is the shift between the main axes of the transmission side polarization beam splitters 22a and 22b and the reception side polarization beam splitter 5 viewed from the signal light, and ψ is the phase difference between the x and y components generated in the transmission path. is there.
【００２６】この信号光は図１に示した光受信機におい
てＸ，Ｙ成分が夫々独立に局部発振光と合波されヘテロ
ダイン検波される。ここでは、 ＡTx＝ＡTy＝ＡT ＡLX＝ＡLY＝ＡL が成立する。上式のＡLX，ＡLYは夫々局部発振光の電界
のＸ，Ｙ成分の振幅である。In the optical receiver shown in FIG. 1, the signal light is heterodyne-detected by independently combining the X and Y components with the local oscillation light. In this case, ATx = ATy = AT ALX = ALY = AL. ALX and ALY in the above equation are the amplitudes of the X and Y components of the electric field of the local oscillation light, respectively.
【００２７】ヘテロダイン検波によって得られるＩＦ帯
電流ＩX ，ＩYは夫々、 ＩX ＝Ｋ［ｃｏｓθｃｏｓ（ωi ｔ＋φ＋πｄx ＋ψ） −ｓｉｎθｃｏｓ（ωi ｔ＋φ＋πｄy ）］ ＩY ＝Ｋ［ｃｏｓθｃｏｓ（ωi ｔ＋φ＋πｄy −ψ） ＋ｓｉｎθｃｏｓ（ωi ｔ＋φ＋πｄx ）］ 但し、Ｋ＝ηｅＡT ＡL ／ｈν となる。上式のωi はビート角周波数、φはビート位相
雑音、ηは光検出器の量子効率、ｅは電子の電荷、ｈは
プランク定数、νは局部発振光の周波数である。そし
て、各電流ＩX ，ＩY を用いて復調信号Ａと信号Ｂと信
号Ｃが夫々演算される。The IF band currents IX and IY obtained by the heterodyne detection are respectively IX = K [cos θcos (ωi t + φ + πdx + ψ) -sin θcos (ωit + φ + πdy)] IY = K [cos θcos (ωi t + φ + πsd co ((ωi t + φ + πdy-co) (ωi t + φ + πdy-ψ) However, K = ηeAT AL / hν. In the above equation, ω i is the beat angular frequency, φ is the beat phase noise, η is the quantum efficiency of the photodetector, e is the electron charge, h is the Planck's constant, and ν is the frequency of the locally oscillated light. Then, the demodulated signal A, the signal B, and the signal C are calculated using the respective currents IX and IY.
【００２８】即ち、電流ＩX ，ＩY の積は、低域通過フ
ィルタ（ＬＰＦ）８ａで高調波成分を取り除かれた後に
符号判定器（ＤＥＣ）９で判定され、θとψが小さいと
きに復調信号Ａとして、 ＤＥＣ｛ＬＰＦ［ＩX ×ＩY ］｝＝ｃｏｓπ（ｄx −ｄy ）＝±１ が得られる。That is, the product of the currents IX and IY is judged by the code judging device (DEC) 9 after the harmonic components are removed by the low pass filter (LPF) 8a, and the demodulated signal is obtained when θ and ψ are small. As A, DEC {LPF [IX × IY]} = cosπ (dx−dy) = ± 1 is obtained.
【００２９】また、電流ＩX と、位相をπ／２遅らせた
電流ＩY （｜ＩY ｜π／２）の積は、低域通過フィルタ
（ＬＰＦ）８ｂで高調波成分を取り除かれた後に上記の
復調信号Ａを乗算され、信号Ｂとして、 ＬＰＦ［ＩX ×｜ＩY ｜π／２］×ＤＥＣ｛ＬＰＦ［ＩX ×ＩY ］｝ ＝−１／２×Ｋ2 ｃｏｓ2 θｓｉｎ２ψ が得られる。この信号Ｂは１／４波長板１への制御信号
として帰還され、ψを０に制御する。つまり、任意の楕
円偏波を所定方向の直線偏波に変換するように働く。Further, the product of the current IX and the current IY whose phase is delayed by π / 2 (| IY | π / 2) is demodulated after the harmonic components are removed by the low pass filter (LPF) 8b. The signal A is multiplied to obtain the signal B as LPF [IX × | IY | π / 2] × DEC {LPF [IX × IY]} = − 1/2 × K 2 cos 2 θ sin2ψ. This signal B is fed back as a control signal to the quarter-wave plate 1 to control ψ to 0. That is, it works to convert an arbitrary elliptical polarization into a linear polarization in a predetermined direction.
【００３０】更に、電流ＩX ，ＩY の和と差の積（電力
の差）は、低域通過フィルタ（ＬＰＦ）８ｂで高調波成
分を取り除かれた後に上記の復調信号Ａを乗算され、信
号Ｃとして、 ＬＰＦ［（ＩX ＋ＩY ）×（ＩX −ＩY ）］×ＤＥＣ｛ＬＰＦ［ＩX ×ＩY ］｝ ＝−Ｋ2 ｃｏｓψｓｉｎ２θ が得られる。この信号Ｃはψ＝０のときに１／２波長板
２への制御信号として帰還され、θを０またはπに制御
する。つまり、受信信号光Ｐの主軸を受信側偏波ビーム
スプリッタ５の主軸に合わせるように働く。Further, the product (difference in power) of the sum and difference of the currents IX and IY is multiplied by the above demodulated signal A after the harmonic components are removed by the low pass filter (LPF) 8b, and the signal C is obtained. as, LPF [(IX + IY) × (IX -IY)] × DEC {LPF [IX × IY]} = -K 2 cosψsin2θ is obtained. This signal C is fed back as a control signal to the half-wave plate 2 when ψ = 0, and controls θ to 0 or π. That is, the main axis of the received signal light P works so as to be aligned with the main axis of the reception side polarization beam splitter 5.
【００３１】尚、図１に１４で示した破線枠部分の構成
は図４に示す構成で置き換えることが可能であり、同図
において３１ａ，３１ｂは偏波ビ−ムスプリッタ、３２
は局部発振用レ−ザ、３３ａ，３３ｂは光カップラであ
る。また、図１に１５で示した破線枠部分の構成は図５
に示す構成で置き換えることが可能であり、同図におい
て４１ａ，４１ｂは二乗器、４２は減算器で、この場合
には電流ＩX の二乗と電流ＩY の二乗との差に、復調信
号Ａが乗算されて信号Ｃが得られる。更に、１／４波長
板１と１／２波長板２はこれと同様の働きをする他の電
気光学素子であってもよい。The configuration of the broken line frame portion shown by 14 in FIG. 1 can be replaced by the configuration shown in FIG. 4, and 31a and 31b in the figure are polarization beam splitters and 32.
Is a laser for local oscillation, and 33a and 33b are optical couplers. Further, the structure of the broken line frame portion indicated by 15 in FIG.
In the same figure, 41a and 41b are squarers and 42 is a subtracter. In this case, the difference between the square of the current IX and the square of the current IY is multiplied by the demodulated signal A. Then, the signal C is obtained. Further, the quarter-wave plate 1 and the half-wave plate 2 may be other electro-optical elements having the same function.
【００３２】次に、請求項３に記載した発明の実施例を
図６示す光受信機の構成図を参照して説明する。同図に
おいて５１は１／４波長板、５２は１／２波長板、５３
ａ，５３ｂは偏波ビ−ムスプリッタ、５４は局部発振用
レ−ザ、５５ａ，５５ｂは光π／２ハイブリッド、５６
ａ乃至５６ｄは光検出器、５７は符号判定器、５８ａ，
５８ｂは１ｂｉｔ遅延器、５９ａ乃至５９ｆは乗算器、
６０ａ乃至６０ｃは加算器、６１ａ，６１ｂは減算器、
６２ａ乃至６２ｄは二乗器である。Next, an embodiment of the invention described in claim 3 will be described with reference to the configuration diagram of the optical receiver shown in FIG. In the figure, 51 is a quarter-wave plate, 52 is a half-wave plate, and 53.
a and 53b are polarization beam splitters, 54 is a laser for local oscillation, 55a and 55b are optical .pi. / 2 hybrids, 56
a to 56d are photodetectors, 57 is a code determiner, 58a,
58b is a 1-bit delay device, 59a to 59f are multipliers,
60a to 60c are adders, 61a and 61b are subtractors,
Reference numerals 62a to 62d are squarers.
【００３３】受信信号光Ｐは、まず１／４波長板６１及
び１／２波長板６２を順に通過し、偏波ビ−ムスプリッ
タ５３ａで２つの直交偏波軸（Ｘ−Ｙ）成分に分離さ
れ、光π／２ハイブリッド５８ａ，５８ｂに夫々入る。
また、局部発振用レ−ザ４の発振光が偏波ビ−ムスプリ
ッタ５３ｂで２つの直交偏波軸（Ｘ−Ｙ）成分に分離さ
れ、光π／２ハイブリッド５８ａ，５８ｂに夫々入る。
これらＸＩ成分とＸＱ成分とＹＩ成分とＹＱ成分（Ｉは
同相成分，Ｑは直交成分を表す）は夫々光検出器５６ａ
乃至５６ｄに入り、ＩXIとＩXQとＩYIとＩYQのＩＦ（中
間周波数）帯電流に変換される。The received signal light P first passes through the quarter-wave plate 61 and the half-wave plate 62 in order, and is separated into two orthogonal polarization axis (XY) components by the polarization beam splitter 53a. And enters the optical π / 2 hybrids 58a and 58b, respectively.
Further, the oscillation light of the local oscillation laser 4 is separated into two orthogonal polarization axis (X-Y) components by the polarization beam splitter 53b and enters the optical .pi. / 2 hybrids 58a and 58b, respectively.
These XI component, XQ component, YI component, and YQ component (I represents the in-phase component, Q represents the quadrature component) are respectively detected by the photodetector 56a.
56 to 56d and converted into IF (intermediate frequency) band currents of IXI, IXQ, IYI and IYQ.
【００３４】ホモダイン検波後の電流ＩXI，ＩYIは乗算
器５９ａで乗算され、また電流ＩXQ，ＩYQは乗算器５９
ｂで乗算され、夫々の積が加算器６０ａで加算された
後、符号判定器９を通過して復調信号Ａとなる。The currents IXI and IYI after the homodyne detection are multiplied by the multiplier 59a, and the currents IXQ and IYQ are multiplied by the multiplier 59a.
After being multiplied by b and the respective products are added by the adder 60a, they pass through the code determination unit 9 and become the demodulated signal A.
【００３５】また、電流ＩXI，ＩYQは乗算器５９ｃで乗
算され、また電流ＩXQ，ＩYIは乗算器５９ｂで乗算さ
れ、夫々の積が減算器６１ａで減算された後、１ｂｉｔ
遅延器５８ａを通過し、さらに乗算器５９ｅで上記の復
調信号Ａと乗算されて信号Ｂとなる。この信号Ｂは制御
信号として１／４波長板５１に帰還される。The currents IXI and IYQ are multiplied by the multiplier 59c, and the currents IXQ and IYI are multiplied by the multiplier 59b. The respective products are subtracted by the subtractor 61a and then 1 bit is added.
The signal passes through the delay device 58a and is further multiplied by the demodulated signal A in the multiplier 59e to become a signal B. This signal B is fed back to the quarter-wave plate 51 as a control signal.
【００３６】更に、電流ＩXIは二乗器６２ａで二乗さ
れ、また電流ＩXQは二乗器６２ｂで二乗され、夫々の二
乗値が加算器６０ｂで加算される。また、電流ＩYIは二
乗器６２ｃで二乗され、また電流ＩYQは二乗器６２ｄで
二乗され、夫々の二乗値が加算器６０ｃで加算される。
そして、両加算器６０ｂ，６０ｃにおける和が減算器６
１ｂで減算された後、１ｂｉｔ遅延器５８ｂを通過し、
さらに乗算器５９ｅで上記の復調信号Ａと乗算されて信
号Ｃとなる。この信号Ｃは制御信号として１／２波長板
５２に帰還される。Further, the current IXI is squared by the squarer 62a, the current IXQ is squared by the squarer 62b, and the respective squared values are added by the adder 60b. The current IYI is squared by the squarer 62c, the current IYQ is squared by the squarer 62d, and the respective squared values are added by the adder 60c.
Then, the sum in both adders 60b and 60c is the subtractor 6
After being subtracted by 1b, it passes through a 1-bit delay device 58b,
Further, the signal is multiplied by the demodulated signal A in the multiplier 59e and becomes a signal C. This signal C is fed back to the half-wave plate 52 as a control signal.
【００３７】ここで、上述の偏波状態制御について具体
式を挙げて詳しく説明する。Here, the above-mentioned polarization state control will be described in detail with reference to specific equations.
【００３８】図６に示した光受信機では、受信信号光Ｐ
および局部発振光は夫々偏波ビームスプリッタ５３ａ，
５３ｂで直交偏波成分（Ｘ成分、Ｙ成分）に分離され、
夫々光π／２ハイブリッド５５ａ，５５ｂでホモダイン
検波される。In the optical receiver shown in FIG. 6, the received signal light P
And the local oscillation light is polarized beam splitter 53a,
It is separated into orthogonal polarization components (X component, Y component) at 53b,
Homodyne detection is performed by the optical π / 2 hybrids 55a and 55b, respectively.
【００３９】ホモダイン検波によって得られるＩＦ帯電
流ＩXI，ＩXQ，ＩYI，ＩYQは、 ＩXI＝Ｋ［ｃｏｓθｃｏｓ（φ＋πｄx ＋ψ） −ｓｉｎθｃｏｓ（φ＋πｄy ）］ ＩXQ＝Ｋ［ｃｏｓθｓｉｎ（φ＋πｄx ＋ψ） −ｓｉｎθｓｉｎ（φ＋πｄy ）］ ＩYI＝Ｋ［ｓｉｎθｃｏｓ（φ＋πｄx ） ＋ｃｏｓθｃｏｓ（φ＋πｄy −ψ）］ ＩYQ＝Ｋ［ｓｉｎθｓｉｎ（φ＋πｄx ） ＋ｃｏｓθｓｉｎ（φ＋πｄy −ψ）］ 但し、Ｋ＝ηｅＡT ＡL ／ｈν となる。上式の各パラメータは先の実施例と同じであ
る。The IF band currents IXI, IXQ, IYI, and IYQ obtained by the homodyne detection are given by IXI = K [cos θcos (φ + πdx + ψ) -sin θcos (φ + πdy)] IXQ = K [cosθsin (φ + πdx + ψ) -sinθsin (φ) + sinθsin (φ) + sin). IYI = K [sin θcos (φ + πdx) + cos θcos (φ + πdy−φ)] IYQ = K [sin θsin (φ + πdx) + cos θsin (φ + πdy−φ)] However, K = ηeAT AL / hν. Each parameter in the above equation is the same as in the previous embodiment.
【００４０】そして、各電流ＩXI、ＩXQ、ＩYI、ＩYQを
用いて復調信号Ａと信号Ｂと信号Ｃが夫々演算される。Then, the demodulated signals A, B and C are calculated using the respective currents IXI, IXQ, IYI and IYQ.
【００４１】即ち、電流ＩXI，ＩYIと電流ＩXQ，ＩYQの
夫々の積の和は、 （ＩXI×ＩYI）＋（ＩXQ×ＩYQ） ＝Ｋ2 （ｃｏｓ2 θｃｏｓ２ψ−ｓｉｎ2 θ）ｃｏｓπ（ｄx −ｄy ） となり、この信号は符号判定器（ＤＥＣ）５７で判定さ
れ、θとψが小さいときに復調信号Ａとして、 ＤＥＣ［（ＩXI×ＩXQ）＋（ＩYI×ＩYQ）］＝ｃｏｓπ（ｄx −ｄy ）＝±１ が得られる。That is, the sum of the products of the currents IXI, IYI and the currents IXQ, IYQ is (IXI × IYI) + (IXQ × IYQ) = K 2 (cos 2 θcos 2 ψ-sin 2 θ) cosπ (dx −dy ), This signal is judged by the code judging device (DEC) 57, and when θ and ψ are small, the demodulation signal A is DEC [(IXI × IXQ) + (IYI × IYQ)] = cosπ (dx−dy) = ± 1 is obtained.
【００４２】また、電流ＩXI，ＩYIと電流ＩXQ，ＩYQの
夫々の積の差は、 （ＩXI×ＩYI）−（ＩXQ×ＩYQ） ＝−Ｋ2 ｃｏｓ2 θｓｉｎ２ψｃｏｓπ（ｄx −ｄy ） となり、これに上記の復調信号Ａを乗算され、信号Ｂと
して、 ｛（ＩXQ×ＩYI）−（ＩXI×ＩYQ）｝ ×ＤＥＣ［（ＩXI×ＩXQ）＋（ＩYI×ＩYQ）］ ＝−Ｋ2 ｃｏｓ2 θｓｉｎ２ψ が得られる。この信号Ｂは１／４波長板５１への制御信
号として帰還され、ψを０に制御する。つまり、任意の
楕円偏波を所定方向の直線偏波に変換するように働く。Further, current IXI, iyi current IXQ, the difference in the respective product of IYQ, (IXI × IYI) - (IXQ × IYQ) = -K 2 cos 2 θsin2ψcosπ (dx -dy) , and the above this Is multiplied by the demodulated signal A of {(IXQ × IYI) − (IXI × IYQ)} × DEC [(IXI × IXQ) + (IYI × IYQ)] = − K 2 cos 2 θsin2ψ .. This signal B is fed back as a control signal to the quarter-wave plate 51 and controls ψ to 0. That is, it works to convert an arbitrary elliptical polarization into a linear polarization in a predetermined direction.
【００４３】更に、電流ＩXI，ＩXQの夫々の二乗の和と
電流ＩYI，ＩYQの夫々の二乗の和との差は、 （ＩXI2 ＋ＩXQ2 ）−（ＩYI2 ＋ＩYQ2 ） ＝−２Ｋ2 ｓｉｎ２θｃｏｓψｃｏｓπ（ｄx −ｄy ） となり、これに上記のデ−タ符号判定出力Ａを乗算さ
れ、信号Ｃとして、 ｛（ＩXI2 ＋ＩXQ2 ）−（ＩYI2 ＋ＩYQ2 ）｝ ×ＤＥＣ［（ＩXI×ＩXQ）＋（ＩYI×ＩYQ）］ ＝−２Ｋ2 ｓｉｎ２θｃｏｓψ が得られる。この信号Ｃはψ＝０のときに１／２波長板
２への制御信号として帰還され、θを０またはπに制御
する。つまり、受信信号光Ｐの主軸を受信側偏波ビーム
スプリッタ５３ａの主軸に合わせるように働く。Further, the difference between the sum of the squares of the currents IXI and IXQ and the sum of the squares of the currents IYI and IYQ is (IXI 2 + IXQ 2 ) − (IYI 2 + IYQ 2 ) = − 2K 2 sin 2θcos ψcosπ ( dx-dy), which is multiplied by the above-mentioned data code determination output A, and as a signal C, {(IXI 2 + IXQ 2 ) − (IYI 2 + IYQ 2 )} × DEC [(IXI × IXQ) + ( IYI × IYQ)] = − 2K 2 sin2θ cos ψ is obtained. This signal C is fed back as a control signal to the half-wave plate 2 when ψ = 0, and controls θ to 0 or π. That is, the main axis of the received signal light P works so as to align with the main axis of the reception side polarization beam splitter 53a.
【００４４】尚、図６に６３で示した破線枠部分の構成
は図７に示す構成で置き換えることが可能であり、同図
において７１は光π／２ハイブリッド、７２は局部発振
用レ−ザ、７３ａ，７３ｂは偏波ビ−ムスプリッタであ
る。また、図６に６４で示した破線枠部分の構成は図８
に示す構成で置き換えることが可能であり、同図におい
て８１ａ乃至８１ｃは加算器、８２ａ，８２ｂは減算
器、８３ａ，８３ｂは乗算器で、この場合には電流ＩX
I，ＩYIの和と差の積と電流ＩXQ，ＩYQの和と差の積と
の差に、復調信号Ａが乗算されて信号Ｃが得られる。更
に、図６に６５で示した破線枠部分の構成は、図９に示
す構成で置き換えることが可能であり、同図において９
１ａ，９１ｂは符号判定器、９２は排他的論理和回路で
ある。更にまた、上記実施例の１／４波長板５１と１／
２波長板５２はこれと同様の働きをする他の電気光学素
子であってもよい。The configuration of the broken line frame portion shown by 63 in FIG. 6 can be replaced by the configuration shown in FIG. 7, in which 71 is an optical .pi. / 2 hybrid and 72 is a laser for local oscillation. , 73a, 73b are polarization beam splitters. In addition, the configuration of the broken line frame portion shown by 64 in FIG.
Can be replaced by the configuration shown in FIG. 11, in which 81a to 81c are adders, 82a and 82b are subtractors, and 83a and 83b are multipliers.
The difference between the product of the sum and difference of I and IYI and the product of the sum and difference of currents IXQ and IYQ is multiplied by demodulated signal A to obtain signal C. Further, the configuration of the broken line frame portion shown by 65 in FIG. 6 can be replaced by the configuration shown in FIG.
Reference numerals 1a and 91b are code determiners, and 92 is an exclusive OR circuit. Furthermore, the 1/4 wavelength plate 51 and 1 /
The two-wave plate 52 may be another electro-optical element having a similar function.
【００４５】以上の説明では、光源の位相雑音を考慮し
た場合について述べたが、光ＰＬＬを用いて信号光の位
相と局部発振光の位相が同期した場合、中間周波数帯に
おける位相雑音の項は無視でき、各電流ＩXI，ＩXQ，Ｉ
YI，ＩYQは次のように捕らえることができる。In the above description, the case where the phase noise of the light source is taken into consideration has been described. However, when the phase of the signal light and the phase of the local oscillation light are synchronized by using the optical PLL, the term of the phase noise in the intermediate frequency band becomes It can be ignored and each current IXI, IXQ, I
YI and IYQ can be captured as follows.
【００４６】ＩXI＝Ｋ［ｃｏｓθｃｏｓ（πｄx ＋ψ） −ｓｉｎθｃｏｓ（πｄy ）］ ＩXQ＝Ｋ［ｃｏｓθｓｉｎ（πｄx ＋ψ） −ｓｉｎθｓｉｎ（πｄy ）］ ＩYI＝Ｋ［ｓｉｎθｃｏｓ（πｄx ） ＋ｃｏｓθｃｏｓ（πｄy −ψ）］ ＩYQ＝Ｋ［ｓｉｎθｓｉｎ（πｄx ） ＋ｃｏｓθｓｉｎ（πｄy −ψ）］ 但し、Ｋ＝ηｅＡT ＡL ／ｈν となる。上式の各パラメータは先の実施例と同じであ
る。このとき、 ＩXI2 −ＩYI2 ＝−２Ｋ2 ｓｉｎ２θｃｏｓψ となり、図６に６４で示した破線枠部分の構成を図１０
または図１１に示す構成で置き換えることが可能とな
る。図１１において１０１は加算器、１０２は減算器、
１０３が乗算器であり、また図１２において１１１ａ，
１１１ｂは二乗器、１１２は乗算器である。IXI = K [cos θcos (πdx + ψ) -sinθcos (πdy)] IXQ = K [cosθsin (πdx + ψ) -sinθsin (πdy)] IYI = K [sinθcos (πdx) + cosθcos (πdy) −πdyψ (πdy) (πdy)) K [sin θsin (πdx) + cos θsin (πdy −ψ)] where K = ηeAT AL / hν. Each parameter in the above equation is the same as in the previous embodiment. At this time, IXI 2 −IYI 2 = −2K 2 sin2θ cos ψ, and the configuration of the broken line frame portion shown by 64 in FIG.
Alternatively, the configuration shown in FIG. 11 can be replaced. In FIG. 11, 101 is an adder, 102 is a subtractor,
103 is a multiplier, and 111a,
111b is a squarer, and 112 is a multiplier.
【００４７】[0047]
【発明の効果】以上説明したように、請求項１乃至４記
載の制御方法によれば、受信信号光が所定方向の直線偏
波になるように１／４波長板を制御し、しかも該直線偏
波を受信軸から４５°傾いた方向に合うように１／２波
長板を制御して受信信号光を所定方向の直線偏波に安定
させることができ、偏波多重光波通信において伝送路中
で生じる偏波変動を補償して、偏波変動による特性の劣
化を低減することができる。As described above, according to the control method of the first to fourth aspects, the quarter wave plate is controlled so that the received signal light becomes a linearly polarized wave in a predetermined direction, and the linear wave plate is controlled. By controlling the ½ wavelength plate so that the polarized wave is aligned with the direction inclined by 45 ° from the receiving axis, the received signal light can be stabilized to the linear polarized wave in the predetermined direction. It is possible to compensate the polarization fluctuation caused by the above and reduce the deterioration of the characteristics due to the polarization fluctuation.
【図１】 請求項１に記載した発明の実施例を示す光受
信機の構成図FIG. 1 is a configuration diagram of an optical receiver showing an embodiment of the invention described in claim 1.
【図２】 図１の光受信器に対応した光送信機の変調部
の構成図2 is a block diagram of a modulator of an optical transmitter corresponding to the optical receiver of FIG.
【図３】 変調された信号光の偏波状態図[Fig. 3] Polarization state diagram of modulated signal light
【図４】 図１に示した光受信機の部分代替構成を示す
図FIG. 4 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図５】 図１に示した光受信機の部分代替構成を示す
図5 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図６】 請求項３に記載した発明の実施例を示す光受
信機の構成図FIG. 6 is a block diagram of an optical receiver showing an embodiment of the invention described in claim 3;
【図７】 図６に示した光受信機の部分代替構成を示す
図7 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図８】 図６に示した光受信機の部分代替構成を示す
図8 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図９】 図６に示した光受信機の部分代替構成を示す
図9 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図１０】 図６に示した光受信機の部分代替構成を示
す図10 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図１１】 図６に示した光受信機の部分代替構成を示
す図11 is a diagram showing a partial alternative configuration of the optical receiver shown in FIG.
【図１２】 従来の偏波状態制御系の構成図FIG. 12 is a block diagram of a conventional polarization state control system.
【図１３】 偏波状態制御過程の偏波状態図FIG. 13: Polarization state diagram of polarization state control process
【図１４】 偏波状態制御過程の偏波状態図FIG. 14: Polarization state diagram of polarization state control process
Ｐ…受信信号光、１，５１…１／４波長板，２，５２…
１／２波長板、Ａ…復調信号、Ｂ，Ｃ…制御信号。P ... Received signal light, 1,51 ... 1/4 wavelength plate, 2, 52 ...
Half-wave plate, A ... Demodulation signal, B, C ... Control signal.
Claims (4)
光を１／４波長板及び１／２波長板に通過させ、 該信号光の２つの直交偏波軸（Ｘ−Ｙ）成分を夫々ヘテ
ロダイン検波して２つの中間周波数帯信号を検出し、 このＸ成分と位相をπ／２遅らせたＹ成分との積に、復
調信号を乗算した信号で１／４波長板を制御すると共
に、 Ｘ成分とＹ成分の和と差の積に、復調信号を乗算した信
号で１／２波長板を制御する、 ことを特徴とする偏波状態制御方法。1. A received signal light having two orthogonal polarization states is passed through a quarter-wave plate and a half-wave plate, and two orthogonal polarization axis (XY) components of the signal light are generated. Each is heterodyne-detected to detect two intermediate frequency band signals, and the product of this X component and the Y component whose phase is delayed by π / 2 is multiplied by the demodulation signal to control the ¼ wavelength plate, and A polarization state control method, characterized in that the half-wave plate is controlled by a signal obtained by multiplying a demodulated signal by a product of the sum and difference of the X component and the Y component.
光を１／４波長板及び１／２波長板に通過させ、 該信号光の２つの直交偏波軸（Ｘ−Ｙ）成分を夫々ヘテ
ロダイン検波して２つの中間周波数帯信号を検出し、 このＸ成分と位相をπ／２遅らせたＹ成分との積に、復
調信号を乗算した信号で１／４波長板を制御すると共
に、 Ｘ成分の二乗とＹ成分の二乗との差に、復調信号を乗算
した信号で１／２波長板を制御する、 ことを特徴とする偏波状態制御方法。2. A received signal light having two orthogonal polarization states is passed through a quarter wavelength plate and a half wavelength plate, and two orthogonal polarization axes (XY) components of the signal light are generated. Each is heterodyne-detected to detect two intermediate frequency band signals, and the product of this X component and the Y component whose phase is delayed by π / 2 is multiplied by the demodulation signal to control the ¼ wavelength plate, and A polarization state control method, characterized in that the half-wave plate is controlled by a signal obtained by multiplying a difference between the square of the X component and the square of the Y component by a demodulation signal.
光を１／４波長板及び１／２波長板に通過させ、 該信号光と局部発振光夫々の２つの直交偏波軸（Ｘ−
Ｙ）成分を夫々ホモダイン検波して４つの中間周波数帯
信号を検出し、 このＸＩ成分とＹＱ成分の積とＸＱ成分とＹＩ成分の積
との差に、復調信号を乗算した信号で１／４波長板を制
御すると共に、 ＸＩ成分の二乗とＸＱ成分の二乗の和とＹＩ成分の二乗
とＹＱ成分の二乗の和との差に、復調信号を乗算した信
号で１／２波長板を制御する、 ことを特徴とする偏波状態制御方法。3. A received signal light having two orthogonal polarization states is passed through a quarter-wave plate and a half-wave plate, and two orthogonal polarization axes of the signal light and the local oscillation light (X −
The Y) component is homodyne-detected to detect four intermediate frequency band signals, and the difference between the product of the XI component and the YQ component and the product of the XQ component and the YI component is multiplied by the demodulated signal to obtain 1/4. The wave plate is controlled, and the 1/2 wave plate is controlled by a signal obtained by multiplying the difference between the sum of the squares of the XI component and the square of the XQ component and the square of the YI component and the square of the YQ component by the demodulation signal. A polarization state control method characterized by the following.
光を１／４波長板及び１／２波長板に通過させ、 該信号光と局部発振光夫々の２つの直交偏波軸（Ｘ−
Ｙ）成分を夫々ホモダイン検波して４つの中間周波数帯
信号を検出し、 このＸＩ成分とＹＱ成分の積とＸＱ成分とＹＩ成分の積
との差に、復調信号を乗算した信号で１／４波長板を制
御すると共に、 ＸＩ成分とＹＩ成分の和と差の積と、ＸＱ成分とＹＱ成
分の和と差の積との差に、復調信号を乗算した信号で１
／２波長板を制御する、ことを特徴とする偏波状態制御
方法。4. A received signal light having two orthogonal polarization states is passed through a quarter-wave plate and a half-wave plate, and two orthogonal polarization axes of the signal light and the local oscillation light (X −
The Y) component is homodyne-detected to detect four intermediate frequency band signals, and the difference between the product of the XI component and the YQ component and the product of the XQ component and the YI component is multiplied by the demodulated signal to obtain 1/4. While controlling the wave plate, the difference between the product of the sum and the difference of the XI component and the YI component and the product of the sum and the difference of the XQ component and the YQ component is multiplied by the demodulated signal to obtain 1
A polarization state control method comprising: controlling a half-wave plate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25395291A JPH0593935A (en) | 1991-10-01 | 1991-10-01 | Polarization state control method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25395291A JPH0593935A (en) | 1991-10-01 | 1991-10-01 | Polarization state control method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH0593935A true JPH0593935A (en) | 1993-04-16 |
Family
ID=17258259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP25395291A Pending JPH0593935A (en) | 1991-10-01 | 1991-10-01 | Polarization state control method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0593935A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8244138B2 (en) | 2007-03-20 | 2012-08-14 | Fujitsu Limited | Polarization-multiplexing optical transmitter polarization-multiplexing optical receiver, polarization-multiplexing optical transceiving system, and controlling method thereof |
-
1991
- 1991-10-01 JP JP25395291A patent/JPH0593935A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8244138B2 (en) | 2007-03-20 | 2012-08-14 | Fujitsu Limited | Polarization-multiplexing optical transmitter polarization-multiplexing optical receiver, polarization-multiplexing optical transceiving system, and controlling method thereof |
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