JP6116001B2 - Optical transmitter and optical receiver - Google Patents
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本発明は、光ファイバの非線形効果の影響を抑える光通信システムの光送信装置及び光受信装置に関する。 The present invention relates to an optical transmission device and an optical reception device of an optical communication system that suppresses the influence of nonlinear effects of an optical fiber.
光通信システムにおいて生じる光ファイバの非線形効果は、シンプルな線形等化器では補償できない。このため、非特許文献１は、光ファイバの非線形効果による信号劣化を補償するための構成を開示している。 The nonlinear effect of the optical fiber generated in the optical communication system cannot be compensated by a simple linear equalizer. For this reason, Non-Patent Document 1 discloses a configuration for compensating for signal degradation due to a nonlinear effect of an optical fiber.
特許文献１に記載の方法は、二位相偏移変調（ＢＰＳＫ）にのみ適用でき、直交位相振幅変調（ＱＡＭ）には適用できない。 The method described in Patent Document 1 is applicable only to binary phase shift keying (BPSK), and not applicable to quadrature phase amplitude modulation (QAM).
本発明は、変調形式としてＱＡＭを使用でき、光ファイバの非線形効果による信号劣化を補償する光通信システムの光送信装置及び光受信装置を提供するものである。 The present invention provides an optical transmission device and an optical reception device of an optical communication system that can use QAM as a modulation format and compensate for signal degradation due to a nonlinear effect of an optical fiber.
本発明の一側面によると、光伝送路を介して光受信装置にデータを送信する光送信装置は、使用する変調形式に基づき、送信すべきデータを、当該データに対応する複素平面上の座標を示す第１の複素信号に変換する変換手段と、前記第１の複素信号の共役複素値と、前記光伝送路の色分散のインパルス応答を示す第１の値の共役複素値とを畳み込み演算することで第２の複素信号を生成し、前記第１の複素信号と前記第２の複素信号を多重して光信号として出力する出力手段と、を備えていることを特徴とする。
According to one aspect of the present invention, an optical transmission apparatus for transmitting data to the optical receiver via an optical transmission path, based on the type of modulation to use, the data to be transmitted, in the complex plane corresponding to the data Convolution of conversion means for converting into a first complex signal indicating coordinates, a conjugate complex value of the first complex signal, and a conjugate complex value of a first value indicating an impulse response of chromatic dispersion of the optical transmission line Output means for generating a second complex signal by calculation , multiplexing the first complex signal and the second complex signal, and outputting the multiplexed signal as an optical signal is provided.
本発明の一側面によると、光受信装置は、光送信装置から光伝送路を介してデータに対応する信号と、前記データに対応する信号の補償のための補償信号を含む光信号を受信して、前記データに対応する電気信号の同相成分を実数とし直交成分を虚数とする第１の複素信号と、前記補償信号に対応する電気信号の同相成分を実数とし直交成分を虚数とする第２の複素信号を出力する出力手段と、前記第１の複素信号と、前記光伝送路の色分散のインパルス応答を示す第１の値の共役複素値とを畳み込み演算することで第３の複素信号を生成する生成手段と、前記第２の複素信号と前記第３の複素信号を加算する加算手段と、を備えていることを特徴とする。 According to one aspect of the present invention, an optical receiver receives an optical signal including a signal corresponding to data and a compensation signal for compensating the signal corresponding to the data from the optical transmitter via an optical transmission line. A first complex signal in which the in-phase component of the electrical signal corresponding to the data is a real number and the quadrature component is an imaginary number, and a second complex signal in which the in-phase component of the electrical signal corresponding to the compensation signal is a real number and the quadrature component is an imaginary number . The third complex signal is obtained by performing a convolution operation on the output means for outputting the complex signal, the first complex signal, and the first complex conjugate value indicating the chromatic dispersion impulse response of the optical transmission line. And generating means for adding the second complex signal and the third complex signal, and adding means for adding the second complex signal and the third complex signal.
光ファイバの非線形効果による信号劣化を補償可能な光通信が可能になる。 Optical communication capable of compensating for signal deterioration due to the nonlinear effect of the optical fiber becomes possible.
以下、本発明の例示的な実施形態について図面を参照して説明する。なお、以下の各図においては、実施形態の説明に必要ではない構成要素については図から省略する。 Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.
図１は、本実施形態による光送信装置の概略的な構成図である。変換部１０は、まず、データを、使用する変調形式に合わせた複素信号に変換する。複素信号とは、光変調部１２において同相成分（Ｉ）を変調するための信号と、直交成分（Ｑ）を変調するための信号の２つの信号からなり、同相成分が実数に、直交成分が虚数に対応する。例えば、ＱＡＭを使用し、ビット（０、０）が複素平面における１＋ｊに対応するものとする。この場合、変換部１０は、データが（０、０）であると、このデータを１＋ｊを示す複素信号、つまり、１を示す実数成分の信号と、１を示す虚数成分の信号に変換して補償信号生成多重部１１に出力する。 FIG. 1 is a schematic configuration diagram of an optical transmission apparatus according to the present embodiment. The conversion unit 10 first converts data into a complex signal that matches the modulation format to be used. The complex signal is composed of two signals, a signal for modulating the in-phase component (I) and a signal for modulating the quadrature component (Q) in the optical modulation unit 12, and the in-phase component is a real number and the quadrature component is Corresponds to an imaginary number. For example, suppose QAM is used and bits (0, 0) correspond to 1 + j in the complex plane. In this case, when the data is (0, 0), the conversion unit 10 converts the data into a complex signal indicating 1 + j, that is, a real component signal indicating 1 and an imaginary component signal indicating 1. It outputs to the compensation signal generation multiplexing part 11.
補償信号生成多重部１１の補償信号生成部１１１は、受信する複素信号から、光受信装置において非線形効果による影響を抑圧するための補償信号を生成して多重部１１２に出力する。なお、補償信号も複素信号である。多重部１１２は、変換部１０から受信するデータに対応する複素信号と、補償信号生成部１１１から受信する補償信号を時分割多重した複素信号を出力する。図２に補償信号生成多重部１１が出力する複素信号を示す。図２において、データと表記された区間は、変換部１１から受信した複素信号そのままの区間、つまり、データに対応する複素信号の区間である。一方、ダミーと表記された区間は、補償信号生成部１１１が生成した複素信号、つまり、補償信号の区間である。なお、補償信号は、本実施形態では、その直前にあるデータと表記された区間の複素信号の補償を行うものとする。言い換えると、ある補償信号は、その直前のデータと表記された区間の複素信号から生成される。なお、補償信号は、その直後にあるデータと表記された区間の複素信号の補償を行うものであっても良い。さらには、補償信号は、その前後のデータと表記された区間以外の区間の補償を行うものであっても良い。また、データと表記された区間に含まれるシンボル数は、１つ以上の任意の値とすることができる。つまり、１シンボル毎に補償信号を挿入することも、連続した複数のシンボル毎に補償信号を挿入することもできる。なお、いずれにしても、補償信号の期間（ダミーと表記された区間）は、データと表記された区間のシンボル数に等しい。 The compensation signal generation unit 111 of the compensation signal generation multiplexing unit 11 generates a compensation signal for suppressing the influence of the nonlinear effect in the optical reception device from the received complex signal, and outputs the compensation signal to the multiplexing unit 112. The compensation signal is also a complex signal. The multiplexing unit 112 outputs a complex signal obtained by time-division multiplexing the complex signal corresponding to the data received from the conversion unit 10 and the compensation signal received from the compensation signal generation unit 111. FIG. 2 shows a complex signal output from the compensation signal generation multiplexing unit 11. In FIG. 2, a section represented as data is a section of the complex signal received from the conversion unit 11 as it is, that is, a section of the complex signal corresponding to the data. On the other hand, a section indicated as a dummy is a complex signal generated by the compensation signal generation unit 111, that is, a section of the compensation signal. In the present embodiment, it is assumed that the compensation signal compensates for a complex signal in a section indicated as data immediately before the compensation signal. In other words, a certain compensation signal is generated from a complex signal in a section expressed as the immediately preceding data. Note that the compensation signal may be a signal that compensates for a complex signal in a section indicated as data immediately after the compensation signal. Furthermore, the compensation signal may be one that compensates for a section other than the section indicated as the data before and after the compensation signal. Further, the number of symbols included in the section represented as data can be one or more arbitrary values. That is, it is possible to insert a compensation signal for each symbol or insert a compensation signal for each of a plurality of consecutive symbols. In any case, the period of the compensation signal (interval indicated as a dummy) is equal to the number of symbols in the interval indicated as data.
図１に戻り光変調部１２は入力される複素信号により連続光を例えばＱＡＭ変調し、その後、変調された光信号を増幅して光伝送路へと送信する。 Returning to FIG. 1, the optical modulator 12 QAM-modulates continuous light, for example, with the input complex signal, and then amplifies the modulated optical signal and transmits it to the optical transmission line.
続いて、補償信号生成部１１１における補償信号の生成方法と、この補償信号により光受信装置が非線形効果による信号の劣化を補償できることを説明する。まず、図３において、各三角形は光アンプを表しており、その番号を各光アンプの上段に示している。なお、番号０の光アンプは、光送信装置が有する光アンプであり、光受信装置は、番号Ｎの光アンプの出力信号を受信して復調するものとする。また、以下の説明において、非線形効果は、光パワーが強い光アンプの出力端でのみ生じ、光アンプで区切られた各光リンクの色分散のインパルス応答がｈ１であるものとする。また、番号ｋの光アンプが出力する光信号のうち、データに対応する区間、つまり、図２のデータと表記する区間に対応する電界成分をＥｋで表すものとする。 Next, a method for generating a compensation signal in the compensation signal generation unit 111 and that the optical receiver can compensate for signal degradation due to a nonlinear effect by using the compensation signal will be described. First, in FIG. 3, each triangle represents an optical amplifier, and its number is shown in the upper part of each optical amplifier. It is assumed that the optical amplifier of number 0 is an optical amplifier included in the optical transmission device, and the optical reception device receives and demodulates the output signal of the optical amplifier of number N. In the following description, it is assumed that the non-linear effect occurs only at the output end of an optical amplifier having high optical power, and the chromatic dispersion impulse response of each optical link partitioned by the optical amplifier is h1. In addition, in the optical signal output by the optical amplifier of number k, an electric field component corresponding to a section corresponding to data, that is, a section expressed as data in FIG.
まず、上記前提から、各光アンプが出力するデータに対応する光信号は以下の式で表される。 First, from the above assumption, the optical signal corresponding to the data output from each optical amplifier is expressed by the following equation.
なお、上記式において、 In the above formula,
ここで、ｅｊｘ＝１＋ｊｘとの近似を使用し、上記式（１）〜（３）により式（３）を変形すると、以下の式（４）が得られる。 Here, by using the approximation of ejx = 1 + jx and transforming the expression (3) by the above expressions (1) to (3), the following expression (4) is obtained.
光受信装置が受信する式（４）で表されるデータに対応する光信号の電界成分の複素値と、光伝送路の色分散のインパルス応答ｈＮの共役複素値との畳み込み演算を行うと以下の式（５）が得られる。 The complex value of the electric field component of the optical signal corresponding to data represented by the formula (4) where the light receiving device receives, when the convolution operation of the complex conjugate values of the impulse response h N of chromatic dispersion of the optical transmission line The following equation (5) is obtained.
ここで、式（５）の右辺の第１項は、光送信装置が送信した光信号の電界成分である。なお、この電界成分は、変調部１２に入力される複素信号の内の、データに対応する区間の複素信号に相当する。また、式（５）の右辺の第２項は非線形効果によるノイズを示している。 Here, the first term on the right side of Equation (5) is the electric field component of the optical signal transmitted by the optical transmitter. This electric field component corresponds to a complex signal in a section corresponding to data in the complex signal input to the modulation unit 12. Further, the second term on the right side of Equation (5) indicates noise due to a nonlinear effect.
続いて、本実施形態の光送信装置の補償信号生成部１１１における処理を説明する。補償信号生成部１１１は、変換部１０からのデータに対応する複素信号が示す複素値の共役複素値と、光伝送路の色分散のインパルス応答の共役複素値との畳み込み演算により補償信号を生成する。したがって、光変調部１２が出力する光信号のうち、補償信号に対応する区間の電界成分Ｄ０は、以下の式（６）で表される。 Subsequently, processing in the compensation signal generation unit 111 of the optical transmission apparatus of the present embodiment will be described. The compensation signal generation unit 111 generates a compensation signal by convolution of the complex complex value indicated by the complex signal corresponding to the data from the conversion unit 10 and the conjugate complex value of the impulse response of the chromatic dispersion of the optical transmission line. To do. Therefore, the electric field component D 0 in the section corresponding to the compensation signal in the optical signal output from the optical modulation unit 12 is expressed by the following equation (6).
上記式（１）〜（４）と同様に、上記式（６）で表される光信号は、光受信装置においては以下の式（７）で表される電界成分を持つ光信号として受信される。 Similarly to the above formulas (1) to (4), the optical signal represented by the above formula (6) is received as an optical signal having an electric field component represented by the following formula (7) in the optical receiver. The
式（５）で示す信号と式（７）で示す信号ＤＮを加算すると、以下の式（８）が得られる。 When the signal represented by Expression (5) and the signal DN represented by Expression (7) are added, the following Expression (8) is obtained.
式（８）の右辺の第１項は、データに対応する複素信号であり、第２項は非線形効果によるノイズである。しかしながら、式（５）と比較し、式（８）では、最初と最後の光リンクで生じる非線形効果によるノイズが残留するのみであり、非線形効果による影響が抑えられていることが分かる。 The first term on the right side of Equation (8) is a complex signal corresponding to data, and the second term is noise due to nonlinear effects. However, compared with Equation (5), it can be seen that in Equation (8), only noise due to the nonlinear effect generated in the first and last optical links remains, and the influence due to the nonlinear effect is suppressed.
図４は、本実施形態による光受信装置の概略的な構成図である。光電気変換部２０は、受信する光信号を電気信号に変換して複素信号を補償部２１に出力する。補償部２１の分離部２１１は、入力される複素信号の内、図２ではデータと表記する区間に対応する複素信号を畳み込み部２１２に出力し、図２ではダミーと表記する区間に対応する複素信号、つまり、補償信号に対応する部分を加算部２１３に出力する。畳み込み部２１２は、上記式（５）で示す様に、光伝送路の色分散のインパルス応答ｈＮの共役複素値と、入力される複素信号が示す複素値との畳み込み演算を行って、結果を加算部２１３に出力する。加算部２１３は、上記式（８）で示す様に、分離部２１１からの補償信号と、畳み込み部２１２からの畳み込み後の複素信号を加算して、結果を復調部２２に出力し、復調部２２は、復調を行う。なお、光受信装置にて行うその他の線形等化処理等は、簡単のため図４から省略している。 FIG. 4 is a schematic configuration diagram of the optical receiver according to the present embodiment. The photoelectric conversion unit 20 converts the received optical signal into an electrical signal and outputs a complex signal to the compensation unit 21. The separation unit 211 of the compensation unit 21 outputs a complex signal corresponding to a section expressed as data in FIG. 2 to the convolution unit 212 among the input complex signals, and a complex signal corresponding to a section expressed as a dummy in FIG. The signal, that is, the portion corresponding to the compensation signal is output to the adder 213. Convolution unit 212, as shown by the formula (5), by performing the conjugate complex value of the impulse response h N of chromatic dispersion of the optical transmission line, a convolution operation between the complex values indicating a complex signal to be inputted, the result Is output to the adder 213. The adder 213 adds the compensation signal from the separator 211 and the complex signal after convolution from the convolution unit 212, and outputs the result to the demodulator 22 as shown in the above equation (8). 22 performs demodulation. Note that other linear equalization processing performed by the optical receiver is omitted from FIG. 4 for simplicity.
以上の構成により、光ファイバの非線形効果による信号劣化を補償可能な光通信が可能になる。 With the above configuration, optical communication capable of compensating for signal degradation due to the nonlinear effect of the optical fiber becomes possible.
なお、上記実施形態において多重部１１２は、変換部１０から受信するデータに対応する複素信号と、補償信号生成部１１１から受信する補償信号を時分割多重した複素信号を出力していた。しかしながら、データに対応する複素信号と、補償信号の各々が伝送される光リンクの色分散のインパルス応答が略同じであれば、データに対応する複素信号と、補償信号の多重方式としては、空間多重、周波数多重、偏波多重等を使用することができる。なお、本実施形態では、時分割多重を使用しているため電気段で多重を行ったが、多重方式によっては光段で多重が行われる。つまり、図１の補償信号生成多重部１１と、光変調部１２の構成は、多重方式により異なるが、いずれにしても、データに対応する複素信号と、補償信号は、それぞれ、光信号として出力部から出力される。また、図４の光受信装置についても、同様であり、分離は、多重化方式によっては光段にて行われる。しかしながら、いずれにしても、光信号は、データに対応する信号と、データに対応する信号の補償信号を含み、この光信号から、最終的にデータに対応する電気信号である複素信号と、補償信号に対応する電気信号である複素信号が出力部において取り出される。 In the above embodiment, the multiplexing unit 112 outputs a complex signal obtained by time-division multiplexing the complex signal corresponding to the data received from the conversion unit 10 and the compensation signal received from the compensation signal generation unit 111. However, if the impulse response of the chromatic dispersion of the optical link through which each of the complex signal corresponding to the data and the compensation signal is transmitted is substantially the same, the multiplexing method of the complex signal corresponding to the data and the compensation signal may be spatial. Multiplexing, frequency multiplexing, polarization multiplexing, etc. can be used. In this embodiment, since time division multiplexing is used, multiplexing is performed at the electrical stage, but depending on the multiplexing method, multiplexing is performed at the optical stage. That is, the configurations of the compensation signal generation multiplexing unit 11 and the optical modulation unit 12 in FIG. 1 differ depending on the multiplexing method, but in any case, the complex signal corresponding to the data and the compensation signal are output as optical signals, respectively. Output from the section. The same applies to the optical receiver in FIG. 4, and the separation is performed at the optical stage depending on the multiplexing method. However, in any case, the optical signal includes a signal corresponding to the data and a compensation signal of the signal corresponding to the data. From this optical signal, a complex signal which is an electrical signal corresponding to the data and a compensation signal are finally obtained. A complex signal, which is an electrical signal corresponding to the signal, is extracted at the output unit.
Claims (2)
使用する変調形式に基づき、送信すべきデータを、当該データに対応する複素平面上の座標を示す第１の複素信号に変換する変換手段と、
前記第１の複素信号の共役複素値と、前記光伝送路の色分散のインパルス応答を示す第１の値の共役複素値とを畳み込み演算することで第２の複素信号を生成し、前記第１の複素信号と前記第２の複素信号を多重して光信号として出力する出力手段と、
を備えていることを特徴とする光送信装置。 An optical transmitter that transmits data to an optical receiver via an optical transmission line,
Conversion means for converting on the basis of the type of modulation to use, the data to be transmitted, the first complex signal indicating the coordinates on the complex plane corresponding to the data,
A second complex signal is generated by performing a convolution operation on a conjugate complex value of the first complex signal and a conjugate complex value of a first value indicating an impulse response of chromatic dispersion of the optical transmission line, Output means for multiplexing one complex signal and the second complex signal and outputting the multiplexed signal as an optical signal;
An optical transmission device comprising:
前記第１の複素信号と、前記光伝送路の色分散のインパルス応答を示す第１の値の共役複素値とを畳み込み演算することで第３の複素信号を生成する生成手段と、
前記第２の複素信号と前記第３の複素信号を加算する加算手段と、
を備えていることを特徴とする光受信装置。 An optical signal including a signal corresponding to data and a compensation signal for compensating the signal corresponding to the data is received from an optical transmission device via an optical transmission line, and an in-phase component of the electrical signal corresponding to the data is received. a first complex signal to the imaginary orthogonal component and real, and output means for outputting a second complex signal and imaginary quadrature component and real in-phase component of the electric signal corresponding to the compensation signal,
Generating means for generating a third complex signal by performing a convolution operation on the first complex signal and a conjugate complex value of a first value indicating an impulse response of chromatic dispersion of the optical transmission line ;
Adding means for adding the second complex signal and the third complex signal;
An optical receiver characterized by comprising:
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