JP2011250079A - Optical-code-division-multiplex transmitting circuit and optical-code-division-multiplex receiving circuit - Google Patents

Optical-code-division-multiplex transmitting circuit and optical-code-division-multiplex receiving circuit Download PDF

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JP2011250079A
JP2011250079A JP2010120480A JP2010120480A JP2011250079A JP 2011250079 A JP2011250079 A JP 2011250079A JP 2010120480 A JP2010120480 A JP 2010120480A JP 2010120480 A JP2010120480 A JP 2010120480A JP 2011250079 A JP2011250079 A JP 2011250079A
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Shin Kaneko
慎 金子
Junki Miki
準基 三鬼
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Nippon Telegraph and Telephone Corp
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Abstract

PROBLEM TO BE SOLVED: To provide an optical-code-division-multiplex transmitting circuit and an optical-code-division-multiplex receiving circuit that are capable of increasing the degree of encoding multiplexing without requiring an increase in the number of optical modulating means and optical detecting means and causing deterioration in wavelength dispersion.SOLUTION: The optical-code-division-multiplex transmitting circuit performs, for plural optical carriers having different optical frequencies, multi-valued modulation on each of two branched optical carriers with two of plural multi-valued electric signals to generate a multi-valued signal beam obtained such that phases of both are made orthogonal to each other for combination, and performs optical frequency multiplexing on the multi-valued signal beam before output.

Description

本発明は、光符号分割多重通信に用いられる光符号分割多重用送信回路及び光符号分割多重用受信回路に関する。   The present invention relates to an optical code division multiplexing transmission circuit and an optical code division multiplexing reception circuit used for optical code division multiplexing communication.

光符号分割多重(CDM:Code Division Multiplexing)方式は、固有符号に応じて符号拡散された光CDM信号を多重伝送する方式である。各々の光CDM送受信回路には、固有符号が割り当てられる。各送信回路は、割り当てられた固有符号に対応した符号化により拡散された光CDM信号を出力する。受信側では、多重された光CDM信号から、受信回路と同じ固有符号を割り当てられた送信回路が出力する光CDM信号のみを復号可能であり、所望の光CDM信号を選択的に受信する。   An optical code division multiplexing (CDM) system is a system that multiplex-transmits an optical CDM signal that has been code-spread according to a specific code. A unique code is assigned to each optical CDM transmission / reception circuit. Each transmission circuit outputs an optical CDM signal spread by encoding corresponding to the assigned unique code. On the receiving side, only the optical CDM signal output from the transmission circuit assigned the same unique code as that of the reception circuit can be decoded from the multiplexed optical CDM signal, and a desired optical CDM signal is selectively received.

これまでに、パルス信号光の各光周波数成分の光位相を、送信回路に割り当てられた固有符号に応じて変調することにより、パルス信号光を時間軸上に拡散する方式が提案されている(例えば、非特許文献1及び2を参照。)。また、SSFBG(Superstructured Fiber Bragg Grating)などを用いて、パルス信号光を直接的に時間軸上に拡散する方式も提案されている(例えば、非特許文献3を参照。)。   So far, there has been proposed a method of spreading the pulse signal light on the time axis by modulating the optical phase of each optical frequency component of the pulse signal light in accordance with the unique code assigned to the transmission circuit ( For example, see Non-Patent Documents 1 and 2.) In addition, a method of directly diffusing pulse signal light on the time axis using SSFBG (Superstructured Fiber Bragg Grating) or the like has been proposed (for example, see Non-Patent Document 3).

しかしながら、これらの方式では、光位相の厳密な制御やチップ時間(=ビット時間/符号長)オーダの時間制御を行う光符復号デバイスが必要となる。また、多元接続干渉(MAI:Multiple Access Interference)や、複数の光CDM信号が同時に受信回路へ入力された際に検波時に生じるビート雑音により、符号多重数が制限される。そのため、信号光間での時間同期に基づく時間ゲートや、光媒質の非線形特性を用いた光閾値デバイス、前方誤り訂正(FEC: Forward Error Correction)の適用により、MAIやビート雑音の影響を低減することが必要となり、送受信回路構成の複雑化を招く。   However, these systems require an optical codec device that performs strict control of the optical phase and time control of the chip time (= bit time / code length) order. In addition, the number of code multiplexing is limited by multiple access interference (MAI) and beat noise generated at the time of detection when a plurality of optical CDM signals are simultaneously input to the receiving circuit. Therefore, the influence of MAI and beat noise is reduced by applying a time gate based on time synchronization between signal lights, an optical threshold device using nonlinear characteristics of an optical medium, and forward error correction (FEC). This requires a complicated transmission / reception circuit configuration.

これに対し、図1のように、送信回路内の2値/多値変換手段における電気段符号拡散に基づいて生成された多値電気信号で、各光周波数成分を多値振幅変調(ASK: Amplitude Shift Keying)した多値ASK信号光を光周波数多重した多波長信号光を送受信する方式が提案されている(例えば、非特許文献4を参照。)。   On the other hand, as shown in FIG. 1, each optical frequency component is multi-valued amplitude modulated (ASK: ASK) with a multi-valued electrical signal generated based on electrical stage code diffusion in the binary / multi-value converting means in the transmission circuit. There has been proposed a method for transmitting / receiving multi-wavelength signal light obtained by optical frequency multiplexing of multi-level ASK signal light (Amplitude Shift Keying) (see, for example, Non-Patent Document 4).

多値ASK信号光の光強度レベルは、変調器に印加される多値電気信号のシンボル値に応じて変動し、とりうる光強度レベルは等間隔である。受信側では、光周波数ごとに分波した各光周波数成分をそれぞれ直接検波して生成した多値電気信号を、電気復号化手段において、受信回路に割り当てられた固有符号に応じて加減算を行う。ここで、生成される多値電気信号は、各シンボル値に対応する電圧レベルが等間隔であり、電圧レベル間隔は異なる光検波器が生成する多値電気信号同士で一致する。よって、アダマール符号やビットシフトしたM系列符号などの直交符号を固有符号として用いる場合、加減算によりMAIを除去することができる。また、光領域で信号光の多重を行わないため、検波時にビート雑音が生じない。つまり、この方式では、電気段で符復号化を行うために光符復号デバイスが不要である上、MAIやビート雑音低減のために参考文献1〜3で必要であった時間ゲートや光閾値デバイスが不要である。そのため、送受信回路内の光デバイス構成の大幅なシンプル化が図れる。   The light intensity level of the multilevel ASK signal light varies according to the symbol value of the multilevel electrical signal applied to the modulator, and the possible light intensity levels are equally spaced. On the receiving side, the multi-value electric signal generated by directly detecting each optical frequency component demultiplexed for each optical frequency is added / subtracted in the electric decoding means in accordance with the unique code assigned to the receiving circuit. Here, in the generated multilevel electric signal, the voltage levels corresponding to the respective symbol values are equally spaced, and the voltage level intervals coincide with each other between the multilevel electric signals generated by the different optical detectors. Therefore, when an orthogonal code such as a Hadamard code or a bit-shifted M-sequence code is used as a unique code, MAI can be removed by addition / subtraction. In addition, since signal light is not multiplexed in the optical region, no beat noise occurs during detection. That is, in this system, an optical codec device is not required for performing code decoding at the electric stage, and a time gate and an optical threshold device required in References 1 to 3 for MAI and beat noise reduction are provided. Is unnecessary. Therefore, the optical device configuration in the transmission / reception circuit can be greatly simplified.

更には、電気段での符号拡散を空間的に行うため、時間拡散において要求されるチップレート(=ビットレート´符号長)での動作(例えば、非特許文献5を参照。)が不要であり、ビットレートと同等の動作速度を有する電気回路で構成可能である。   Furthermore, since code spreading at the electrical stage is performed spatially, an operation at a chip rate (= bit rate ′ code length) required in time spreading (see, for example, Non-Patent Document 5) is unnecessary. It can be configured by an electric circuit having an operation speed equivalent to the bit rate.

V. J. Hernandez, et al., “A 320−Gb/s capacity (32−user ´ 10Gb/s) SPECTS O−CDMA network testbed with enhanced spectral efficiency through forward error correction,” J. Lightwave Technol., pp. 79−86, Jan. 2007V. J. et al. Hernandez, et al. , “A 320-Gb / s capacity (32-user′10 Gb / s) SPECTS O-CDMA network testbed with enhanced spectral efficiency through error correction,”. Lightwave Technol. , Pp. 79-86, Jan. 2007 P. Toliver, et al., “Demonstration of high spectral efficiency coherent OCDM using DQPSK, FEC, and integrated ring resonator−based spectral phase encoder/decoders,” OFC2007, PDP7, 2007P. Toliver, et al. , “Demonstration of high spectral efficiency coherent OCDM using DQPSK, FEC, and integrated ring resonator-based spectral phase encoder / decoders 7 T. Hamanaka, et al., “Compound data rate and data−rate−flexible 622 Mb/s−10 Gb/s OCDMA experiments using 511−chip SSFBG and cascaded SHG−DFG−based PPLN waveguide optical thresholder,” IEEE J. Selected Topics in Quantum Electron., pp. 1516−1521, Sep./Oct. 2007)T.A. Hamanaka, et al. , “Compound data rate and data-rate-flexible 622 Mb / s-10 Gb / s OCDMA experiments using 511-chip Selected Topics in Quantum Electron. , Pp. 1516-1521, Sep. / Oct. 2007) S. Kaneko, et al., “Beat−noise−free OCDM technique employing spectral M−ary ASK based on electrical−domain spatial code spreading,” OFC2009, OThI5, 2009S. Kaneko, et al. , “Beat-noise-free OCDM technical encoding spectral M-ary ASK based on electrical-domain spatial code spreading,” OFC2009, OThI5, 2009 G. C. Gupta, et al., “A simple one−system solution COF−PON for metro/access networks,” J. Lightwave Technol., pp. 193−200, Jan. 2007G. C. Gupta, et al. "A simple one-system solution COF-PON for metro / access networks," J. et al. Lightwave Technol. , Pp. 193-200, Jan. 2007

所定の符号長からとりうる符号多重数は有限であり、符号多重数をそれ以上に拡大するためには、符号長を拡張する必要がある。参考文献4の方式では、送受信される多波長信号光を構成する光周波数成分の数は、固有符号のうち符号長が最長である固有符号の符号長と等しい。よって、符号多重数の拡大にあたり、符号長の拡張にともなう光周波数成分数の増加により、必要となる光強度変調器や光検波器の数を増加する必要があるという課題がある。更に、隣接する光周波数成分の間隔を一定とすると、符号多重数の拡大で多波長信号光の光周波数帯域が広くなるため、波長分散の影響が大きくなるという課題もある。   The number of code multiplexes that can be taken from a predetermined code length is finite, and in order to expand the code multiplex number beyond that, it is necessary to extend the code length. In the method of Reference 4, the number of optical frequency components constituting the transmitted / received multi-wavelength signal light is equal to the code length of the unique code having the longest code length among the unique codes. Therefore, when the number of code multiplexes is increased, there is a problem that it is necessary to increase the number of required optical intensity modulators and optical detectors due to an increase in the number of optical frequency components accompanying the extension of the code length. Furthermore, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light is widened by increasing the number of code multiplexes, and there is another problem that the influence of chromatic dispersion becomes large.

そこで、本発明は、光強度変調器や光検波器の数の増加を必要とせず、波長分散耐性を劣化させずに、従来方式と比べて符号多重数を拡大できる光符号分割多重用送信回路及び光符号分割多重用受信回路を提供することを目的とする。   Therefore, the present invention does not require an increase in the number of optical intensity modulators or optical detectors, and does not deteriorate the chromatic dispersion tolerance, and can increase the number of code multiplexes compared with the conventional method. It is another object of the present invention to provide a receiving circuit for optical code division multiplexing.

上記目的を達成するために、本発明に係る光符号分割多重用送信回路は、光周波数が異なる複数の光搬送波のそれぞれについて、分岐した2つの光搬送波を複数の多値電気信号のうちの2つでそれぞれ多値変調し、互いに位相を直交させて合波した多値信号光を生成し、その多値信号光をさらに光周波数多重して出力することとした。なお、以下の説明で、光符号分割多重用送信回路及び光符号分割多重用受信回路をそれぞれ光CDM送信回路及び光CDM受信回路と記載する。   In order to achieve the above object, an optical code division multiplexing transmission circuit according to the present invention splits two optical carriers into two of a plurality of multilevel electric signals for each of a plurality of optical carriers having different optical frequencies. Then, multi-level modulation is performed, and multi-level signal light is generated by combining the phases so that the phases are orthogonal to each other. The multi-level signal light is further optical frequency multiplexed and output. In the following description, the optical code division multiplexing transmission circuit and the optical code division multiplexing reception circuit are referred to as an optical CDM transmission circuit and an optical CDM reception circuit, respectively.

具体的には、本発明に係る光CDM送信回路は、N個(Nは2以上の整数)の2値信号から、2種の符号要素で構成された符号長がK以下(Kは2以上の整数)であるN個の固有符号に基づき、K個の多値信号を生成する2値/多値変換手段と、互いに異なる光周波数の連続光である光搬送波が入力され、前記光搬送波を2分岐し、前記2値/多値変換手段からの前記多値信号のうちの2個を用いてそれぞれの前記光搬送波を変調するとともに前記光搬送波の光位相を互いに直交させ、2つの前記光搬送波を合流した多値信号光を出力する複数の光変調手段と、各々の前記光変調手段が出力する前記多値信号光を合波した多波長信号光を出力する光合波手段と、を備える。なお、ここで「前記光搬送波を2分岐し、前記2値/多値変換手段からの前記多値信号のうちの2個を用いてそれぞれの前記光搬送波を変調する」とは、「光搬送波1を多値信号1、光搬送波2を多値信号2で変調する」という意味である。   Specifically, the optical CDM transmission circuit according to the present invention has a code length composed of two types of code elements from N (N is an integer of 2 or more) binary signals, where K is 2 or less (K is 2 or more). Binary / multilevel conversion means for generating K multilevel signals based on N unique codes, and an optical carrier wave that is continuous light of different optical frequencies, and the optical carrier wave is The two optical signals are branched into two to modulate each of the optical carriers using two of the multilevel signals from the binary / multilevel conversion means, and to make the optical phases of the optical carriers orthogonal to each other. A plurality of optical modulation means for outputting multi-level signal light combined with a carrier wave; and an optical multiplexing means for outputting multi-wavelength signal light obtained by multiplexing the multi-level signal light output from each of the optical modulation means. . Here, “the optical carrier is branched into two and each of the optical carriers is modulated using two of the multilevel signals from the binary / multilevel converter” means “optical carrier” 1 is modulated by the multilevel signal 1 and the optical carrier wave 2 is modulated by the multilevel signal 2.

また、本発明に係る光CDM受信回路は、前記光CDM送信回路が出力する前記多波長信号光を光ファイバ伝送路を介して入力され、前記多波長信号光を光周波数成分ごとに分波して出力する光周波数分波手段と、前記光周波数分波手段から入力された前記光周波数成分を検波し、光位相が互いに直交する2つの光搬送波が搬送するそれぞれの多値信号を出力する2個の出力端を有する光検波手段と、1番目からN番目の前記固有符号のうちの1つが割り当てられ、前記光検波手段の各出力端が接続されており、割り当てられた前記固有符号を構成する前記符号要素を前記光検波手段の前記出力端へ順に対応させた際に、前記固有符号を構成する2種の前記符号要素のうちの一方に対応する前記出力端からの入力を正、他方の前記符号要素に対応する前記出力端からの入力を負として加える加減算を行うことにより、前記2値/多値変換手段に入力された前記2値信号のうちの1つを選択的に取り出す電気復号化手段と、を備える。なお、ここで「光位相が互いに直交する2つの光搬送波が搬送するそれぞれの多値信号を出力する」とは、「出力端1から多値信号1を、出力端2から多値信号2を出力する」という意味である。   The optical CDM receiving circuit according to the present invention receives the multi-wavelength signal light output from the optical CDM transmission circuit via an optical fiber transmission line, and demultiplexes the multi-wavelength signal light into optical frequency components. Output optical frequency demultiplexing means, and the optical frequency components input from the optical frequency demultiplexing means are detected, and respective multilevel signals carried by two optical carriers whose optical phases are orthogonal to each other are output 2 An optical detection means having a number of output ends and one of the 1st to Nth unique codes are assigned, and each output end of the optical detection means is connected to form the assigned unique code When the code elements corresponding to the output terminal of the optical detection means are sequentially associated, the input from the output terminal corresponding to one of the two kinds of code elements constituting the unique code is positive, the other To the sign element of Electro-decoding means for selectively extracting one of the binary signals input to the binary / multi-value conversion means by performing addition / subtraction to add the input from the corresponding output terminal as negative; Is provided. Here, “outputting each multilevel signal carried by two optical carriers whose optical phases are orthogonal to each other” means “outputting the multilevel signal 1 from the output end 1 and the multilevel signal 2 from the output end 2”. It means “output”.

本発明に係る光CDM送信回路及び光CDM受信回路は、光位相を互いに直行した光搬送波を変復調することで、非特許文献4の光CDM伝送システムと同数の光変調手段および光検波手段の数で符号長を2倍に拡張することができる。この周波数利用効率の向上により、本発明に係る光CDM送信回路及び光CDM受信回路は、符号長を拡大しても多波長信号光の光周波数帯域が変わらず、波長分散耐性が劣化しない。   The optical CDM transmission circuit and the optical CDM reception circuit according to the present invention modulate and demodulate optical carriers whose optical phases are orthogonal to each other, thereby providing the same number of optical modulation means and optical detection means as the optical CDM transmission system of Non-Patent Document 4. The code length can be doubled. By improving the frequency utilization efficiency, the optical CDM transmission circuit and the optical CDM reception circuit according to the present invention do not change the optical frequency band of the multi-wavelength signal light even when the code length is increased, and the chromatic dispersion tolerance does not deteriorate.

従って、本発明は、光変調手段や光検波手段の数の増加を必要とせず、波長分散耐性の劣化も発生させずに、符号多重数を拡大できる光CDM送信回路及び光CDM受信回路を提供することができる。   Accordingly, the present invention provides an optical CDM transmission circuit and an optical CDM reception circuit that can increase the number of code multiplexes without requiring an increase in the number of optical modulation means and optical detection means, and without causing deterioration of chromatic dispersion tolerance. can do.

本発明に係る光CDM送信回路の前記2値/多値変換手段は、N個の前記2値信号と1対1に対応するN個の拡散符号器及びK個の加算器を有しており、各々の前記拡散符号器は、前記固有符号が割り当てられ、割り当てられた前記固有符号の符号長以上の個数の出力端を有し、前記固有符号を構成する各符号要素を前記出力端へ順に対応させた際に、前記2種の符号要素のうちの一方の符号要素に対応する前記出力端からは前記拡散符号器へ入力された2値信号とシンボル値が一致する信号を出力し、他の前記出力端からは0を出力し、k番目(k=1,2,・・・,K)の前記加算器は、k番目の前記多値信号のシンボル値が、各々の前記拡散符号器のk番目の前記出力端からの出力信号のシンボル値の和となるように、各々の前記拡散符号器のk番目の前記出力端からの出力信号のシンボル値を加算することを特徴とする。   The binary / multilevel conversion means of the optical CDM transmission circuit according to the present invention has N spreading codes and K adders corresponding to the N binary signals on a one-to-one basis. Each of the spreading encoders is assigned with the unique code, has a number of output ends equal to or greater than the code length of the assigned unique code, and sequentially transmits each code element constituting the unique code to the output end. When it is made to correspond, a signal whose symbol value matches the binary signal input to the spreading encoder is output from the output end corresponding to one of the two types of code elements, 0 is output from the output terminal, and the k-th (k = 1, 2,..., K) adder indicates that the symbol value of the k-th multilevel signal is equal to each spread encoder. Each of the spreads to be the sum of the symbol values of the output signals from the kth output terminal Characterized by adding the symbol value of the output signal from the k th said output end of issue unit.

本発明に係る光CDM送信回路の前記光変調手段が出力する前記多値信号光は、光位相が互いに直交する2つの前記光搬送波それぞれのとりうる光電界振幅レベルが等間隔であり、且つ、前記光変調手段へ入力された2個の前記多値信号の一方のシンボル値に応じて変動することを特徴とする。   The multilevel signal light output from the optical modulation means of the optical CDM transmission circuit according to the present invention has optical field amplitude levels that can be taken by each of the two optical carriers whose optical phases are orthogonal to each other, and It fluctuates according to the symbol value of one of the two multi-level signals input to the light modulation means.

本発明に係る光CDM送信回路の前記光変調手段が出力する前記多値信号光は、光位相が互いに直交する2つの光搬送波それぞれのとりうる光電界振幅レベルが、等間隔であり、且つ、前記光変調手段へ入力された2個の前記多値信号の一方のシンボル値に応じて変動し、前記光変調手段内での前記光搬送波それぞれの光位相シフト量が、前記光変調手段へ入力された2個の前記多値信号のうち一方のシンボル値に応じて、差がπである2値のいずれかとなることを特徴とする。   The multi-level signal light output from the optical modulation means of the optical CDM transmission circuit according to the present invention has optical field amplitude levels that can be taken by each of two optical carriers whose optical phases are orthogonal to each other, and It fluctuates in accordance with one symbol value of the two multi-level signals input to the optical modulation means, and the optical phase shift amount of each of the optical carriers in the optical modulation means is input to the optical modulation means. According to the symbol value of one of the two multi-level signals, the difference is one of the binary values of π.

また、本発明に係る光CDM受信回路の前記光検波手段は、出力光の光周波数が、前記光周波数分波手段からの入力光と所定の周波数差となるように調整された局発光源と、前記局発光源からの出力光と、前記光周波数分波手段からの入力光との混合光を2乗検波する光検波器と、前記光検波器の出力から、周波数が前記所定の周波数差と一致し、位相が互いに直交する2つの搬送波それぞれが搬送する信号成分を透過するバンドパスフィルタと、VCO、ミキサー及びループフィルタを含み、前記2値信号の信号帯域より十分に狭い電気帯域の電気位相同期ループを有し、前記2つの搬送波それぞれが搬送する多値信号を復調して別々に出力する位相同期検波回路と、を備え、前記VCOの出力の周波数および位相は、前記2個の搬送波のうちの一方と同期するように前記ループフィルタで調整され、前記ミキサーは、前記バンドパスフィルタからの入力を前記VCOの出力により検波して、前記2つの搬送波のうちの一方が搬送する多値信号を復調することを特徴とする。   The optical detection means of the optical CDM receiving circuit according to the present invention includes a local light source adjusted so that the optical frequency of the output light is a predetermined frequency difference from the input light from the optical frequency demultiplexing means, An optical detector that squarely detects mixed light of the output light from the local light source and the input light from the optical frequency demultiplexing means; and the frequency from the output of the optical detector is the predetermined frequency difference Including a band-pass filter that transmits a signal component carried by each of two carriers whose phases are orthogonal to each other, a VCO, a mixer, and a loop filter. A phase-locked loop having a phase-locked loop and demodulating a multilevel signal carried by each of the two carriers and outputting them separately, and the frequency and phase of the output of the VCO are the two carriers of The mixer is adjusted by the loop filter so as to be synchronized with one of the two, and the mixer detects the input from the bandpass filter by the output of the VCO, and outputs a multilevel signal carried by one of the two carriers. It is characterized by demodulating.

また、本発明に係る光CDM受信回路の前記光検波手段は、局発光源、光検波器及びループフィルタを含み、前記2値信号の信号帯域より十分に狭い電気帯域の光位相同期ループを備え、光位相が互いに直交する2つの光搬送波それぞれが搬送する多値信号を復調して別々に出力し、前記局発光源の出力光の光周波数および光位相は、前記2個の光搬送波のうちの一方と同期するように前記ループフィルタで調整され、前記光検波器は、前記局発光源からの出力光と、前記光周波数分波手段からの入力光との混合光を2乗検波することを特徴とする。   The optical detection means of the optical CDM receiving circuit according to the present invention includes a local light source, an optical detector, and a loop filter, and includes an optical phase-locked loop having an electrical band sufficiently narrower than the signal band of the binary signal. The multi-level signal carried by each of the two optical carriers whose optical phases are orthogonal to each other is demodulated and output separately, and the optical frequency and optical phase of the output light of the local light source are the two of the two optical carriers. Adjusted by the loop filter so as to synchronize with one of the light, and the optical detector squarely detects mixed light of the output light from the local light source and the input light from the optical frequency demultiplexing means. It is characterized by.

本発明は、光強度変調器や光検波器の数の増加を必要とせず、波長分散耐性を劣化させずに、従来方式と比べて符号多重数を拡大できる光CDM送信回路及び光CDM受信回路を提供することができる。   The present invention does not require an increase in the number of optical intensity modulators or optical detectors, and does not deteriorate the chromatic dispersion tolerance, and can increase the number of code multiplexes as compared with the conventional system, and an optical CDM transmission circuit and an optical CDM reception circuit Can be provided.

電気段符号拡散と多値振幅変調を用いた従来の光CDM伝送システム構成例を説明する図である。It is a figure explaining the example of a structure of the conventional optical CDM transmission system using electrical stage code | symbol spreading | diffusion and multi-value amplitude modulation. 本発明に係る光CDM送信回路及び光CDM受信回路を説明する図である。It is a figure explaining the optical CDM transmission circuit and optical CDM receiving circuit which concern on this invention. 本発明に係る光CDM送信回路の2値/多値変換手段を説明する図である。It is a figure explaining the binary / multi-value conversion means of the optical CDM transmission circuit according to the present invention. 本発明に係る光CDM送信回路の2値/多値変換手段が有するプリバイアス回路を説明する図である。It is a figure explaining the pre-bias circuit which the binary / multi-value conversion means of the optical CDM transmission circuit concerning this invention has. 本発明に係る光CDM送信回路の2値/多値変換手段が有するプリバイアス回路を説明する図である。It is a figure explaining the pre-bias circuit which the binary / multi-value conversion means of the optical CDM transmission circuit concerning this invention has. 本発明に係る光CDM送信回路が出力する多値信号光の光電界を説明する図である。It is a figure explaining the optical electric field of the multilevel signal light which the optical CDM transmission circuit which concerns on this invention outputs. 本発明に係る光CDM送信回路の光変調手段を説明する図である。It is a figure explaining the optical modulation means of the optical CDM transmission circuit based on this invention. 本発明に係る光CDM受信回路の光検波手段を説明する図である。It is a figure explaining the optical detection means of the optical CDM receiving circuit which concerns on this invention. 本発明に係る光CDM受信回路を説明する図である。It is a figure explaining the optical CDM receiving circuit based on this invention. 本発明に係る光CDM受信回路の光検波手段を説明する図である。It is a figure explaining the optical detection means of the optical CDM receiving circuit which concerns on this invention. 本発明に係る光CDM送信回路が出力する多値信号光の光電界を説明する図である。It is a figure explaining the optical electric field of the multilevel signal light which the optical CDM transmission circuit which concerns on this invention outputs.

添付の図面を参照して本発明の実施形態を説明する。以下に説明する実施形態は本発明の実施例であり、本発明は、以下の実施形態に制限されるものではない。なお、本明細書及び図面において符号が同じ構成要素は、相互に同一のものを示すものとする。また、枝番号を付さずに説明する場合は、その構成要素全てに共通する説明である。   Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components. Moreover, when it demonstrates without attaching a branch number, it is description common to all the components.

(実施形態1)
図2は、本実施形態の光CDM伝送システム301を説明する図である。光CDM伝送システム301は、光CDM送信回路201と、複数の光CDM受信回路(202−1、202−2、・・・202−N)とを、光ファイバ伝送路203が接続する構造である。
(Embodiment 1)
FIG. 2 is a diagram illustrating the optical CDM transmission system 301 according to the present embodiment. The optical CDM transmission system 301 has a structure in which an optical fiber transmission line 203 connects an optical CDM transmission circuit 201 and a plurality of optical CDM reception circuits (202-1, 202-2,... 202-N). .

[光CDM送信回路]
光CDM送信回路201は、2値/多値変換手段11、複数の光変調手段12、及び光合波手段13を備える。各々の光変調手段12は、それぞれ光周波数fが異なる連続光である光搬送波が光源14から入力され、入力された光搬送波を2値/多値変換手段11にて生成された多値信号のうちの2個を用いて変調した多値信号光を出力する。光周波数合波手段13は、各光変調手段12が出力する多値信号光を合波して多波長信号光を出力する。光周波数合波手段13は、例えば、アレイ導波路回折格子(AWG:Arrayed Waveguide Grating)、多層膜フィルタである。光周波数合波手段13の代わりに、光ファイバやPLC(Planar Lightwave Circuit)で作成された光カプラを用いることも可能である。多波長信号光は、光ファイバ伝送路203を介して、各光CDM受信回路202へ伝送される。
[Optical CDM transmission circuit]
The optical CDM transmission circuit 201 includes a binary / multilevel conversion unit 11, a plurality of optical modulation units 12, and an optical multiplexing unit 13. Each optical modulation means 12 receives an optical carrier wave, which is continuous light having a different optical frequency f, from the light source 14, and converts the input optical carrier wave into a multilevel signal generated by the binary / multilevel conversion means 11. Multi-level signal light modulated using two of them is output. The optical frequency multiplexing unit 13 combines the multi-level signal light output from each optical modulation unit 12 and outputs multi-wavelength signal light. The optical frequency multiplexing means 13 is, for example, an arrayed waveguide grating (AWG) or a multilayer filter. Instead of the optical frequency multiplexing means 13, it is also possible to use an optical coupler made of an optical fiber or PLC (Planar Lightwave Circuit). The multiwavelength signal light is transmitted to each optical CDM receiving circuit 202 via the optical fiber transmission line 203.

ここで、多波長信号光の各光周波数成分の光強度は等しい。図2中の光CDM送信回路201のように出力光の光周波数が異なる各光源14と各光変調手段12を1対1に接続する構成の他、多波長光源の出力を光周波数成分ごとに分離して各光変調手段12へ入力する構成も可能である。単一モード光の出力を高周波正弦波で変調して多波長化する構成、モード同期レーザ等を多波長光源として用いることが可能である。   Here, the light intensity of each optical frequency component of the multi-wavelength signal light is equal. In addition to the configuration in which each light source 14 and each light modulation means 12 having different optical frequencies of output light are connected one-to-one like the optical CDM transmission circuit 201 in FIG. 2, the output of the multi-wavelength light source is output for each optical frequency component. A configuration in which the signals are separated and input to each light modulation means 12 is also possible. A configuration in which the output of single-mode light is modulated with a high-frequency sine wave to obtain multiple wavelengths, a mode-locked laser, or the like can be used as the multi-wavelength light source.

2値/多値変換手段11は、N個の固有符号に基づき、シンボル値がそれぞれD(t)〜D(t)であるN個の2値信号から、符号長が最長である固有符号の符号長Kの個数の多値信号を生成する。k番目(k=1,2,・・・,K)の多値信号のシンボル値D (t)は、

Figure 2011250079
と表せる。cn,kは固有符号n(n=1,2,・・・,N)のk番目(k=1,2,・・・,K)の符号要素である。固有符号としては、光周波数領域において符号化を行う光CDM方式において用いられるアダマール符号やビットシフトしたM系列符号などを用いる。ここで、各シンボル値D (t)〜D (t)に対応する電圧レベルは、2値/多値変換手段11内にて、所望の間隔となるように調整されている。 The binary / multi-level conversion means 11 is based on N unique codes, and has a longest code length from N binary signals having symbol values D 1 (t) to D N (t), respectively. The number of multilevel signals corresponding to the code length K of the code is generated. The symbol value D # k (t) of the k-th (k = 1, 2,..., K) multilevel signal is
Figure 2011250079
It can be expressed. cn , k are k-th (k = 1, 2,..., K) code elements of the unique code n (n = 1, 2,..., N). As the inherent code, Hadamard code used in the optical CDM system that performs encoding in the optical frequency domain, bit-shifted M-sequence code, or the like is used. Here, the voltage levels corresponding to the symbol values D # 1 (t) to D # K (t) are adjusted in the binary / multilevel conversion means 11 so as to have a desired interval.

図3は、2値/多値変換手段11の構成例である。2値/多値変換手段11は、N個の拡散符号器21、K個の加算器22及びプリバイアス回路24を含む。   FIG. 3 is a configuration example of the binary / multi-value conversion means 11. The binary / multilevel conversion means 11 includes N spreading coders 21, K adders 22, and a pre-bias circuit 24.

拡散符号器21は、割り当てられた固有符号の符号長以上の個数の出力端23を有し、固有符号を構成する各符号要素{1},{0}を各出力端23へ順に対応させた際に、符号要素{1}に対応する各出力端23から、シンボル値が拡散符号器21への入力2値信号のシンボル値と一致する信号を出力する。それ以外の出力端21からは0を出力する。つまり、固有符号n(n=1,2,・・・,N)のk番目(k=1,2,・・・,K)の符号要素cn,kが割り当てられた拡散符号器nのk番目の出力端の出力信号のシンボル値は、符号要素cn,kの値と拡散符号器nへの入力2値信号のシンボル値D(t)との積cn,k×D(t)で表せる。 The spread encoder 21 has a number of output ends 23 equal to or greater than the code length of the assigned unique code, and sequentially associates each code element {1}, {0} constituting the unique code with each output end 23. At this time, a signal whose symbol value matches the symbol value of the binary signal input to the spread encoder 21 is output from each output terminal 23 corresponding to the code element {1}. The other output terminals 21 output 0. That is, the spread encoder n to which the k-th (k = 1, 2,..., K) code element cn , k of the unique code n (n = 1, 2,..., N) is assigned. The symbol value of the output signal at the k-th output terminal is the product c n, k × D n of the value of the code element c n, k and the symbol value D n (t) of the binary signal input to the spread encoder n. It can be expressed by (t).

拡散符号器21は、K個のスイッチ(SW)を備える。入力された2値信号は分岐され、各SWを介して出力端23より出力される。符号要素{1}に対応する出力端23に接続するSWのみをONとすることにより、各符号要素の値と拡散符号器21への入力信号のシンボル値との積を出力端23より出力することが可能となる。例えば、固有符号1{1,1,0,・・・,0}が割り当てられた拡散符号器21−1の各出力端23の出力信号のシンボル値は、D(t)=1の場合、順に“1”,“1”,“0”,・・・,“0”となり、D(t)=0の場合はすべて“0”となる。 The spread encoder 21 includes K switches (SW). The input binary signal is branched and output from the output terminal 23 via each SW. By turning on only the SW connected to the output terminal 23 corresponding to the code element {1}, the product of the value of each code element and the symbol value of the input signal to the spread encoder 21 is output from the output terminal 23. It becomes possible. For example, the symbol value of the output signal of each output terminal 23 of the spreading encoder 21-1 to which the unique code 1 {1, 1, 0,..., 0} is assigned is D 1 (t) = 1. In this order, “1”, “1”, “0”,..., “0”, and when D 1 (t) = 0, all become “0”.

プリバイアス回路24は、加算器22の出力信号の各シンボル値に対応する電圧レベルの間隔を調整する。図4は、プリバイアス回路24の構成例である。プリバイアス回路24は、多値信号の多値数をMとすると、M−1個以上の重み付け回路31を有する。入力された多値信号は分岐され、各重み付け回路31へ入力される。重み付け回路31は、入力信号の電圧レベルが閾値電圧以上の場合に1を、閾値電圧以下の場合に0を出力する識別器32と、識別器32の出力に所定の重み付け係数(X,X,・・・)を乗じて出力する乗算器33を含む。各重み付け回路31の出力は加算され、光変調手段12へ入力される。 The pre-bias circuit 24 adjusts the voltage level interval corresponding to each symbol value of the output signal of the adder 22. FIG. 4 is a configuration example of the pre-bias circuit 24. The pre-bias circuit 24 includes M−1 or more weighting circuits 31 where M is the number of multi-level signals. The input multilevel signal is branched and input to each weighting circuit 31. The weighting circuit 31 outputs a 1 when the voltage level of the input signal is equal to or higher than the threshold voltage, a 0 when the voltage level is lower than the threshold voltage, and a predetermined weighting coefficient (X 1 , X 2 ,...) And a multiplier 33 that outputs the result. The outputs of the weighting circuits 31 are added and input to the light modulation means 12.

m番目(m=1,2,・・・,M−1)の重み付け回路31における識別器32の閾値電圧VTh_mは、入力多値信号のシンボル値“m−1”に対応する電圧レベルと、シンボル値“m”に対応する電圧レベルとの間に設定される。ある時刻における入力多値信号がシンボル値“i”に対応する場合、重み付け回路(31−1〜31−i)内の識別回路32が1を出力し、他の識別回路32が0を出力するため、各重み付け回路31の出力を加算したプリバイアス回路24の出力は、X+X+・・・+Xとなる。同様に、入力多値信号がシンボル値“i+1”に対応する場合、プリバイアス回路24の出力は、X+X+・・・+X+Xi+1となる。よって、プリバイアス回路24が出力する多値信号の各シンボル値に対応する電圧レベルの間隔は、順に、X,X,・・・,XM−1となる。つまり、重み付け係数X〜XM−1を変化させることにより、各シンボル値に対応する電圧レベルの間隔が所望の比である多値信号を、柔軟に生成することが可能である。 The threshold voltage V Th_m of the discriminator 32 in the m-th (m = 1, 2,..., M−1) weighting circuit 31 is a voltage level corresponding to the symbol value “m−1” of the input multilevel signal. , And a voltage level corresponding to the symbol value “m”. When the input multilevel signal at a certain time corresponds to the symbol value “i”, the identification circuit 32 in the weighting circuit (31-1 to 31-i) outputs 1 and the other identification circuit 32 outputs 0. Therefore, the output of the pre-bias circuit 24 obtained by adding the outputs of the weighting circuits 31 is X 1 + X 2 +... + X i . Similarly, when the input multilevel signal corresponds to the symbol value “i + 1”, the output of the pre-bias circuit 24 is X 1 + X 2 +... + X i + X i + 1 . Therefore, the voltage level intervals corresponding to the respective symbol values of the multilevel signal output from the pre-bias circuit 24 are X 1 , X 2 ,..., X M−1 in order. That is, by changing the weighting coefficients X 1 to X M−1 , it is possible to flexibly generate a multilevel signal in which the voltage level interval corresponding to each symbol value is a desired ratio.

2値/多値変換手段11に入力されるN個の2値信号は、必ずしも信号間でビット同期していなくてもよく、信号速度が異なっていてもよい。また、拡散符号器21、加算器22およびプリバイアス回路24での演算を予め記憶させたメモリとD/Aコンバータを組み合わせて2値/多値変換手段11を構成してもよい。更には、シンボル値D (t)に応じてSW〜SWM−1のいずれかがONとなる図5のような回路をプリバイアス回路24として用いることも可能である。 The N binary signals input to the binary / multilevel conversion means 11 do not necessarily have to be bit-synchronized between the signals, and may have different signal speeds. Further, the binary / multilevel conversion means 11 may be configured by combining a memory in which the computations of the spread encoder 21, adder 22, and pre-bias circuit 24 are stored in advance and a D / A converter. Furthermore, a circuit as shown in FIG. 5 in which any one of SW 0 to SW M−1 is turned on according to the symbol value D # k (t) can be used as the pre-bias circuit 24.

光変調手段12は、光位相が互いに直交する2個の光搬送波それぞれがとりうる光電界振幅レベルが等間隔である多値信号光を出力する。光電界振幅レベルは、2値/多値変換手段11から入力された2個の多値信号のうち対応する一方の信号のシンボル値に応じて変動する。多値信号光の光電界状態E(t)は、振幅レベル間隔をΔEとすると、

Figure 2011250079
と表せる。D (t),D h+1(t) (h=1,3,・・・,K−1)は光変調手段12へ入力された2個の多値信号のシンボル値、f,φ(t)は、それぞれ多値信号光の光周波数、位相雑音である。多値信号光の光電界状態をプロットすると、D (t),D h+1(t)の組み合わせに応じて、図6のように格子点を遷移する。図6中のM,Mh+1は、光変調手段12へ入力される各多値信号の多値度である。 The optical modulation means 12 outputs multilevel signal light in which the optical electric field amplitude levels that can be taken by two optical carriers whose optical phases are orthogonal to each other are equally spaced. The optical electric field amplitude level varies according to the symbol value of one of the two multilevel signals input from the binary / multilevel converter 11. The optical electric field state E S (t) of the multilevel signal light has an amplitude level interval of ΔE.
Figure 2011250079
It can be expressed. D # h (t), D # h + 1 (t) (h = 1, 3,..., K−1) are symbol values of two multilevel signals input to the optical modulation means 12, f k , φ S (t) is the optical frequency and phase noise of the multilevel signal light, respectively. When the optical electric field state of the multi-level signal light is plotted, the lattice point transitions as shown in FIG. 6 according to the combination of D # h (t) and D # h + 1 (t). M h and M h + 1 in FIG. 6 are the multilevel values of the multilevel signals input to the optical modulation means 12.

図7は、光変調手段12の構成例である。アーム長が等しいMach−Zehnder干渉計の各アームに、強度変調にともなう位相チャープがないゼロチャープ型の光強度変調手段81を組み込み、分岐した入力光それぞれを強度変調した多値ASK信号光を合波する構成である。また、少なくとも一方のアーム内に光位相シフタ82を配置する。光位相シフタ82は、多値ASK信号光を合波した際に、それぞれの光搬送波の光位相が互いに直交するように、光搬送波の光位相を調整する。図7の光変調手段12は、一方のアームを経由した光搬送波の光位相を、他方のアームを経由した光搬送波の光位相と比較して、p/2だけシフトさせるとした。   FIG. 7 is a configuration example of the light modulation means 12. A zero-chirp type light intensity modulation means 81 having no phase chirp due to intensity modulation is incorporated in each arm of a Mach-Zehnder interferometer having the same arm length, and multi-level ASK signal light obtained by intensity-modulating each branched input light is multiplexed. It is the structure to do. An optical phase shifter 82 is disposed in at least one arm. The optical phase shifter 82 adjusts the optical phase of the optical carrier so that the optical phases of the optical carriers are orthogonal to each other when the multi-level ASK signal light is multiplexed. The optical modulation unit 12 in FIG. 7 shifts the optical phase of the optical carrier wave that passes through one arm by p / 2 compared with the optical phase of the optical carrier wave that passes through the other arm.

光強度変調手段81へ入力される多値信号は、2値/多値変換手段11において各シンボル値に対応する電圧レベルが調整されている。光強度変調の非線形性を補償するように、電圧レベル間隔を調整することにより、各シンボル値に対応する光電界振幅レベルが等間隔である多値ASK信号光が生成される。   The multilevel signal input to the light intensity modulation means 81 is adjusted in voltage level corresponding to each symbol value in the binary / multilevel conversion means 11. By adjusting the voltage level interval so as to compensate for the non-linearity of the light intensity modulation, multilevel ASK signal light having optical field amplitude levels corresponding to each symbol value at equal intervals is generated.

ゼロチャープ型の光強度変調手段81は、例えば、図7のように、差動信号生成手段83が2値/多値変換手段11からの多値信号から生成した極性が反転関係にある2信号を、LN強度変調器などのDual−Drive Mach−Zehnder干渉計型の光強度変調器84の各電極に印加する構成により実現できる。差動信号生成手段83として、ディバイダとインバータを組み合わせた構成の他、差動アンプを用いることができる。   For example, as shown in FIG. 7, the zero chirp type light intensity modulation unit 81 generates two signals whose polarity is inverted from the multilevel signal from the binary / multilevel conversion unit 11 by the differential signal generation unit 83. It can be realized by a configuration in which each electrode of a dual-drive Mach-Zehnder interferometer type light intensity modulator 84 such as an LN intensity modulator is applied. As the differential signal generation means 83, a differential amplifier can be used in addition to a configuration in which a divider and an inverter are combined.

[光CDM受信回路]
光CDM受信回路202は、光周波数分波手段16、複数の光検波手段43、及び電気復号化手段45を備える。光CDM受信回路202へ入力された多波長信号光は、光周波数分波手段16により光周波数成分ごとに分離される。各光周波数成分は、光周波数分波手段16の各々の出力端と1対1に接続された光検波手段43に入力される。k番目の光検波手段43−kに入力される光周波数成分は、光電界状態が式(2)で表される光周波数がfである多値信号光である。ここで、各光周波数成分間では、光強度が等しい。光検波手段43は、入力された多値信号光をヘテロダイン同期検波して、光位相が互いに直交する2個の光搬送波それぞれが搬送する多値信号を復調して、別々の出力端から出力する。
[Optical CDM receiver circuit]
The optical CDM receiving circuit 202 includes an optical frequency demultiplexing unit 16, a plurality of optical detection units 43, and an electrical decoding unit 45. The multi-wavelength signal light input to the optical CDM receiving circuit 202 is separated for each optical frequency component by the optical frequency demultiplexing means 16. Each optical frequency component is input to the optical detection means 43 connected one-to-one with each output terminal of the optical frequency demultiplexing means 16. The optical frequency component input to the k-th optical detection means 43-k is multilevel signal light whose optical frequency is represented by equation (2) as fk . Here, the light intensity is equal between the optical frequency components. The optical detection means 43 performs heterodyne synchronous detection on the input multilevel signal light, demodulates the multilevel signal carried by each of the two optical carriers whose optical phases are orthogonal to each other, and outputs them from separate output ends. .

図8は、ヘテロダイン同期検波を用いた光検波手段43の構成例である。光検波手段43は、局発光源51、光検波器53、バンドパスフィルタ(BPF:Bandpass Filter)54、位相同期検波回路55を備える。局発光の光周波数は、光検波手段43へ入力される多値信号光とfIFだけ異なるように調整される。つまり、光周波数がfである多値信号光が入力されるk番目の光検波手段43内で、局発光の光周波数はf−fIFとなるように調整され、その光電界E(t)は、

Figure 2011250079
と表せる。ここで、E,φ(t)は、それぞれ、局発光の光電界振幅および位相雑音である。 FIG. 8 is a configuration example of the optical detection means 43 using heterodyne synchronous detection. The optical detection unit 43 includes a local light source 51, an optical detector 53, a band pass filter (BPF) 54, and a phase-locked detection circuit 55. Bureau optical frequency of the emitted light is adjusted by different multilevel signal light and f IF input to the optical detecting means 43. That is, the optical frequency of the local light is adjusted to be f k −f IF in the k-th optical detection means 43 to which the multilevel signal light having the optical frequency f k is input, and the optical electric field E L (T)
Figure 2011250079
It can be expressed. Here, E L and φ L (t) are the local electric field amplitude and phase noise, respectively.

光検波器53は、多値信号光と局発光との混合光を2乗検波し、その出力Q(t)は、

Figure 2011250079
と表せる。但し、[ ]msは時間に関する二乗平均を表す。ここで、
Figure 2011250079
であり、φ(t),φ(t)の時間変動は、送信回路にて2値/多値変換手段11へ入力される2値信号の信号速度と比べて、十分に緩やかである。 The optical detector 53 square-detects the mixed light of the multilevel signal light and the local light, and its output Q (t) is
Figure 2011250079
It can be expressed. However, [] ms represents the root mean square regarding time. here,
Figure 2011250079
The time fluctuations of φ S (t) and φ L (t) are sufficiently gradual as compared with the signal speed of the binary signal input to the binary / multilevel conversion means 11 in the transmission circuit. .

光検波手段43は、偏波調整手段52で局発光と多値信号光の少なくとも一方の偏波状態を調整することにより、局発光と多値信号光の偏波状態が一致するように調整する。光CDM送信回路201において信号光の偏波状態を時間ごとに変化させる偏波スクランブルの構成や、直交する偏波状態を足し合わせた信号光を送信する構成や、光検波手段43における偏波ダイバーシティの構成などにより、光CDM受信回路202における偏波調整を省くことも可能である。   The optical detection means 43 adjusts the polarization state of the local light and the multilevel signal light so that the polarization states of the local light and the multilevel signal light coincide with each other by adjusting the polarization state of at least one of the local light and the multilevel signal light. . In the optical CDM transmission circuit 201, a configuration of polarization scrambling for changing the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and polarization diversity in the optical detection means 43 The polarization adjustment in the optical CDM receiving circuit 202 can be omitted by the above configuration.

BPF54は、fIF近傍に透過帯域を有し、式(4)中の右辺第1〜3項にあたる直接検波成分を除去し、fIFを中心周波数とする中間周波信号R(t)を出力する。中間周波信号R(t)は、式(6)で表されるように、搬送波の位相が互いに直交する2信号の和である。

Figure 2011250079
The BPF 54 has a transmission band in the vicinity of f IF , removes direct detection components corresponding to the first to third terms on the right side in the equation (4), and outputs an intermediate frequency signal R (t) having f IF as the center frequency. . The intermediate frequency signal R (t) is the sum of two signals whose carrier phases are orthogonal to each other, as represented by Expression (6).
Figure 2011250079

位相同期検波回路55は、VCO61、ミキサー62、及びループフィルタ63を含む電気位相同期ループ57を備え、中間周波信号R(t)を同期検波して、シンボル値がD (t),D h+1(t)である多値ベースバンド信号を別々に出力する。図8は、一方の搬送波と位相同期したVCO61の出力の位相を位相シフタ64がπ/2だけシフトし、電気位相同期ループ57外のミキサー58に入力することにより、他方の搬送波に搬送される信号成分を復調する構成である。電気位相同期ループ57では、VCO61の発振周波数および位相が、中間周波信号R(t)を構成する2信号のどちらか一方の搬送波と同期するように、ループフィルタ63により調整される。 The phase-locked detection circuit 55 includes an electric phase-locked loop 57 including a VCO 61, a mixer 62, and a loop filter 63. The phase-locked detection circuit 55 detects the intermediate frequency signal R (t) synchronously, and the symbol value is D # h (t), D A multi-value baseband signal of # h + 1 (t) is output separately. In FIG. 8, the phase shifter 64 shifts the phase of the output of the VCO 61 that is phase-synchronized with one carrier wave by π / 2, and is input to the mixer 58 outside the electric phase-locked loop 57 so that it is conveyed to the other carrier wave. The signal component is demodulated. In the electric phase locked loop 57, the oscillation frequency and phase of the VCO 61 are adjusted by the loop filter 63 so as to synchronize with one of the two carriers constituting the intermediate frequency signal R (t).

電気位相同期ループ57で、VCO61の位相が、式(6)の右辺第1項の搬送波の位相Δφ(t)と同期するとすると、ミキサー62からの検波出力S(t)は、

Figure 2011250079
と表せる。ミキサー62の出力は、LPF56Aにて低域濾波され、式(7)の右辺第3項で表される多値ベースバンド信号が出力される。多値ベースバンド信号は、シンボル値D (t)に対応する各電圧レベルが等間隔である。 When the phase of the VCO 61 is synchronized with the carrier phase Δφ (t) of the first term on the right side of Equation (6) in the electrical phase locked loop 57, the detection output S 1 (t) from the mixer 62 is
Figure 2011250079
It can be expressed. The output of the mixer 62 is low-pass filtered by the LPF 56A, and a multi-value baseband signal expressed by the third term on the right side of Expression (7) is output. In the multi-level baseband signal, each voltage level corresponding to the symbol value D # h (t) is equally spaced.

ミキサー58は、位相がΔφ(t)に同期したVCO61の出力が、位相がπ/2だけシフトさせて入力される。ミキサー58からの検波出力S(t)は、

Figure 2011250079
と表せる。ミキサー58の出力は、LPF56Bにて低域濾波され、シンボル値D h+1(t)に対応する各電圧レベルが等間隔である多値ベースバンド信号が生成される。 The mixer 58 receives the output of the VCO 61 whose phase is synchronized with Δφ (t) with the phase shifted by π / 2. The detection output S 2 (t) from the mixer 58 is
Figure 2011250079
It can be expressed. The output of the mixer 58 is low-pass filtered by the LPF 56B, and a multi-value baseband signal in which each voltage level corresponding to the symbol value D # h + 1 (t) is equally spaced is generated.

電気復号化手段45へは、光検波手段43の各出力端からの多値ベースバンド信号が入力され、割り当てられた固有符号を構成する各符号要素{1},{0}を各光検波手段43の出力端71へ順に対応させた際に、{1}に対応する出力端からの入力を正、{0}に対応する出力端からの入力を負として加える加減算を行う。ここで、上述のように、光検波手段の出力する多値ベースバンド信号において、各シンボル値に対応する電圧レベルは等間隔である。また、各光検波手段43に入力される多値信号光の光強度は一致しているため、異なる光検波手段43の出力する多値ベースバンド信号同士で電圧レベル間隔が一致する。よって、アダマール符号やビットシフトしたM系列符号などを固有符号として用いる場合、符号の直交性によりMAIを除去することができる。よって、光CDM送信回路201において2値/多値変換手段11へ入力されたN個の2値信号のうちの所望信号を選択的に受信することが可能である。   A multi-value baseband signal from each output terminal of the optical detection means 43 is input to the electrical decoding means 45, and each code element {1}, {0} constituting the assigned inherent code is assigned to each optical detection means. When the output terminals 71 of 43 are sequentially associated, addition / subtraction is performed by adding the input from the output terminal corresponding to {1} as positive and the input from the output terminal corresponding to {0} as negative. Here, as described above, in the multi-level baseband signal output from the optical detection means, the voltage levels corresponding to the respective symbol values are equally spaced. In addition, since the light intensities of the multilevel signal lights input to the respective optical detection means 43 match, the voltage level intervals of the multilevel baseband signals output from the different optical detection means 43 match. Therefore, when a Hadamard code, a bit-shifted M-sequence code, or the like is used as a unique code, MAI can be removed due to code orthogonality. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 201.

図2中の各光CDM受信回路202は1個の電気復号化手段45を備える構成であるが、図9のように、それぞれ異なる固有符号を割り当てられた複数の電気復号化手段45’を備えることも可能である。光検波手段43の出力は分岐され、各電気復号化手段45’へ入力される。固有符号を割り当てられた各電気復号化手段45’は、光CDM送信回路201内の2値/多値変換手段11にて同じ符号に基づいて符号拡散される2値信号を出力する。一方、符号を割り当てられない電気符号化手段45’が0を出力するとすると、各光CDM受信回路202’が所望する情報量の大小に応じて、各光CDM受信回路202’内の電気復号化手段45’への固有符号の割り当てを動的に変化させることにより、伝送効率を向上させることが可能となる。つまり、大きな情報量を所望する光CDM受信回路202’内の複数の電気復号化手段45’へ固有符号を割り当てることにより、複数の信号を同時に受信し、一定時間に受信できる情報量を増大することが可能となる。   Each optical CDM receiving circuit 202 in FIG. 2 is configured to include one electrical decoding unit 45, but includes a plurality of electrical decoding units 45 ′ to which different unique codes are assigned as shown in FIG. It is also possible. The output of the optical detection means 43 is branched and input to each electric decoding means 45 '. Each electric decoding unit 45 ′ assigned with a unique code outputs a binary signal that is code-spread based on the same code by the binary / multilevel conversion unit 11 in the optical CDM transmission circuit 201. On the other hand, if the electrical encoding means 45 ′ to which no code is assigned outputs 0, the electrical decoding in each optical CDM reception circuit 202 ′ is performed according to the amount of information desired by each optical CDM reception circuit 202 ′. Transmission efficiency can be improved by dynamically changing the assignment of the unique code to the means 45 ′. That is, by assigning a unique code to a plurality of electro-decoding means 45 ′ in the optical CDM receiving circuit 202 ′ for which a large amount of information is desired, a plurality of signals are received at the same time, and the amount of information that can be received in a fixed time is increased. It becomes possible.

実施形態1においては、光CDM送信回路201内の各光変調手段12に、2値/多値変換手段11にて生成された多値信号を2個ずつ入力するため、従来の光CDM伝送システム(図1)と同数の光変調手段12および光検波手段43の数を用いて、符号長を2倍に拡張し、とりうる最大符号多重数を拡大できる。その際、隣接する光周波数成分の間隔を一定とすると、多波長信号光の光周波数帯域が変わらないため、波長分散耐性が劣化しない。   In the first embodiment, two multi-level signals generated by the binary / multi-level conversion unit 11 are input to each optical modulation unit 12 in the optical CDM transmission circuit 201, so that a conventional optical CDM transmission system is used. By using the same number of optical modulation means 12 and optical detection means 43 as in FIG. 1, the code length can be doubled to increase the maximum possible code multiplexing number. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

(実施形態2)
実施形態2は、実施形態1における光CDM受信回路202内において、ヘテロダイン同期検波の光検波手段43の代わりに、ホモダイン検波を行う光検波手段43’を配置した光CDM伝送システムである。
(Embodiment 2)
Embodiment 2 is an optical CDM transmission system in which optical detection means 43 ′ for performing homodyne detection is arranged in the optical CDM receiving circuit 202 in Embodiment 1 instead of the optical detection means 43 for heterodyne synchronous detection.

光検波手段43’の構成例を図10に示す。光検波手段43’は、局発光源51、光検波器53、及びループフィルタ63を含む光位相同期ループ91を備え、光位相が互いに直交する2個の光搬送波それぞれが搬送する多値信号を光位相同期ホモダイン検波により復調して、別々に出力する。光検波器53は、局発光と多値信号光との混合光を2乗検波する。光検波手段43’は、局発光と多値信号光の少なくとも一方の偏波状態を偏波調整手段52で調整することにより、局発光と多値信号光の偏波状態が一致するように調整する。光CDM送信回路201において信号光の偏波状態を時間ごとに変化させる偏波スクランブルの構成や、直交する偏波状態を足し合わせた信号光を送信する構成や、光検波手段43’における偏波ダイバーシティの構成などにより、光CDM受信回路202における偏波調整を省くことも可能である。   A configuration example of the optical detection means 43 'is shown in FIG. The optical detection means 43 ′ includes an optical phase locked loop 91 including a local light source 51, an optical detector 53, and a loop filter 63, and receives a multilevel signal carried by each of two optical carriers whose optical phases are orthogonal to each other. Demodulated by optical phase-locked homodyne detection and output separately. The optical detector 53 squarely detects mixed light of local light and multilevel signal light. The optical detection means 43 ′ adjusts the polarization state of at least one of the local light and the multilevel signal light by the polarization adjustment means 52 so that the local light and the multilevel signal light have the same polarization state. To do. In the optical CDM transmission circuit 201, a configuration of polarization scrambling for changing the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and polarization in the optical detection means 43 ′ The polarization adjustment in the optical CDM receiving circuit 202 can be omitted depending on the diversity configuration or the like.

ループフィルタ63は、局発光の光周波数および光位相を、多値信号光の光位相が互いに直交する2個の光搬送波のうちの一方と同期するように調整を行う。ここで、多値信号光の光電界状態は、実施形態1中の式(2)で表せる。   The loop filter 63 adjusts the optical frequency and optical phase of the local light so as to synchronize with one of the two optical carriers whose optical phases of the multilevel signal light are orthogonal to each other. Here, the optical electric field state of the multilevel signal light can be expressed by Expression (2) in the first embodiment.

光位相同期ループ91で、局発光の光位相が、式(2)の右辺第1項の光搬送波の光位相φ(t)と同期するとすると、光検波器の出力Q (t)は、

Figure 2011250079
と表せる。局発光の光電界振幅Eを、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅D (t)・ΔE,D h+1(t)・ΔEよりも十分に大きくすると、多値信号光の直接検波成分である式(9)の右辺第1、2項は、局発光とのビート成分である右辺第4項と比べて無視できる。よって、位相同期ループ1の出力は、シンボル値D (t)に対応する各電圧レベルが等間隔である多値ベースバンド信号と見なせる。 When the optical phase of the local light is synchronized with the optical phase φ S (t) of the optical carrier of the first term on the right side of Expression (2) in the optical phase locked loop 91, the output Q 1 * (t) of the optical detector. Is
Figure 2011250079
It can be expressed. The optical field amplitude E L of the local light, optical field amplitude of the multilevel signal to be input to the optical phase synchronous homodyne detection circuit D # h (t) · ΔE , when sufficiently larger than D # h + 1 (t) · ΔE The first and second terms on the right side of Equation (9), which are direct detection components of multilevel signal light, can be ignored compared to the fourth term on the right side, which is a beat component with local light. Therefore, the output of the phase locked loop 1 can be regarded as a multi-value baseband signal in which each voltage level corresponding to the symbol value D # h (t) is equally spaced.

光位相同期ループ外の光検波器53’には、光位相がφ(t)に同期した局発光が、光位相シフタ65で位相がp/2だけシフトさせて入力される。光検波器53’の出力Q (t)は、

Figure 2011250079
と表せる。ここで、局発光の光電界振幅Eは、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅D (t)・ΔE, D h+1(t)・ΔEよりも十分に大きいため、光位相同期ループ内の光検波手段と同様に多値信号光の直接検波成分が無視でき、光検波器の出力は、シンボル値D h+1(t)に対応する各電圧レベルが等間隔である多値ベースバンド信号と見なせる。 The local light whose optical phase is synchronized with φ S (t) is input to the optical detector 53 ′ outside the optical phase locked loop with the phase shifted by p / 2 by the optical phase shifter 65. The output Q 2 * (t) of the optical detector 53 ′ is
Figure 2011250079
It can be expressed. Here, the optical field amplitude E L of the local light, optical field of the multi-level signal input to the optical phase-locked homodyne detection circuit amplitude D # h (t) · ΔE , than D # h + 1 (t) · ΔE sufficient Therefore, the direct detection component of the multilevel signal light can be ignored similarly to the optical detection means in the optical phase locked loop, and the output of the optical detector has each voltage level corresponding to the symbol value D # h + 1 (t). It can be regarded as a multi-value baseband signal that is equally spaced.

光CDM送信回路201内の2値/多値変換手段11へ入力される各2値信号がビット同期している際には、局発光源、90°光ハイブリッド、差動光検波器、ディジタル信号処理(DSP:Digital Signal Processing)回路を備えるディジタルコヒーレント受信器を光検波手段43’として用いることが可能である。DSP回路において多値信号光と局発光の光位相差の推定が可能であるため、光位相同期ホモダイン検波において必要である多値信号光と局発光との光位相同期が不要である。この光検波手段を用いる場合、光変調手段12へ入力される多値信号は差動符号化(Differential Encoding)される。   When each binary signal input to the binary / multilevel conversion means 11 in the optical CDM transmission circuit 201 is bit-synchronized, a local light source, a 90 ° optical hybrid, a differential optical detector, a digital signal A digital coherent receiver provided with a processing (DSP: Digital Signal Processing) circuit can be used as the optical detection means 43 ′. Since the DSP circuit can estimate the optical phase difference between the multilevel signal light and the local light, the optical phase synchronization between the multilevel signal light and the local light, which is necessary in the optical phase-locked homodyne detection, is unnecessary. When this optical detection means is used, the multilevel signal input to the optical modulation means 12 is differentially encoded (Differential Encoding).

電気復号化手段45に、光検波手段43’の各出力端からの多値ベースバンド信号が実施形態1で説明したように入力される。よって、光CDM送信回路202において2値/多値変換手段11へ入力されたN個の2値信号のうちの所望信号を選択的に受信することが可能である。   As described in the first embodiment, the multi-value baseband signal from each output terminal of the optical detection unit 43 ′ is input to the electric decoding unit 45. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 202.

このように、実施形態2でも、従来の光CDM伝送システム(図1)と同数の光変調手段12および光検波手段43’の数を用いて、符号長を2倍に拡張し、とりうる最大符号多重数を拡大できる。その際、隣接する光周波数成分の間隔を一定とすると、多波長信号光の光周波数帯域が変わらないため、波長分散耐性が劣化しない。   As described above, even in the second embodiment, the code length is doubled by using the same number of optical modulation means 12 and optical detection means 43 ′ as the conventional optical CDM transmission system (FIG. 1), and the maximum possible The number of code multiplexes can be expanded. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

(実施形態3)
実施形態3における光CDM伝送システムは、実施形態1における光CDM送信回路201内の光変調手段12が、光位相が互いに直交する2個の光搬送波それぞれの光電界振幅および光位相を変調した多値信号光を出力する。各光搬送波がとりうる光振幅レベルは等間隔であり、光変調手段12内での光位相シフト量は差がπである2値のいずれかである。光電界振幅および光位相シフト量は、2値/多値変換手段11から入力された2個の多値信号のうち対応する一方の信号のシンボル値に応じて変動する。多値信号光の光電界状態E’(t)は、振幅レベル間隔をΔEとすると、

Figure 2011250079
と表せる。また、θ(t),θh+1(t) (h=1,3,・・・,K−1)は、それぞれD (t),D h+1(t)に応じて、差がπである2値のいずれかをとる。θ(t),θh+1(t)が、0またはπのいずれかをとるとすると、多値信号光の光電界状態は、D (t),D h+1(t)の組み合わせに応じて、図11のように格子点を遷移する。図11中のM,Mh+1は、光変調手段12へ入力される各多値信号の多値度である。 (Embodiment 3)
In the optical CDM transmission system according to the third embodiment, the optical modulation means 12 in the optical CDM transmission circuit 201 according to the first embodiment modulates the optical electric field amplitude and optical phase of two optical carriers whose optical phases are orthogonal to each other. Outputs value signal light. The optical amplitude levels that can be taken by each optical carrier are equally spaced, and the optical phase shift amount in the optical modulation means 12 is one of binary values having a difference of π. The optical electric field amplitude and the optical phase shift amount vary according to the symbol value of the corresponding one of the two multilevel signals input from the binary / multilevel converter 11. The optical electric field state E ′ S (t) of the multilevel signal light has an amplitude level interval of ΔE.
Figure 2011250079
It can be expressed. Further, θ h (t), θ h + 1 (t) (h = 1, 3,..., K−1) have a difference according to D # h (t) and D # h + 1 (t), respectively. It takes one of two values that are π. Assuming that θ h (t) and θ h + 1 (t) are either 0 or π, the optical electric field state of the multi-level signal light is a combination of D # h (t) and D # h + 1 (t). In response, the grid points are changed as shown in FIG. M h and M h + 1 in FIG. 11 are the multilevel values of the multilevel signals input to the light modulation means 12.

光変調手段12として、例えば、図7の光変調手段12を用い、各アームに組み込んだDual−Drive Mach−Zehnder干渉計型の光強度変調器84を、差動信号生成手段83の出力信号がとりうる最大電圧と最小電圧の中間電圧が印加された時に透過率が最小となるようにバイアスすることにより、所望の多値信号光が生成される。   For example, the optical modulation unit 12 of FIG. 7 is used as the optical modulation unit 12, and a dual-drive Mach-Zehnder interferometer type optical intensity modulator 84 incorporated in each arm is used. A desired multilevel signal light is generated by biasing so that the transmittance is minimized when an intermediate voltage between the maximum voltage and the minimum voltage that can be taken is applied.

光CDM受信回路202は、実施形態1と同様の構成であり、光CDM受信回路202へ入力された多波長信号光の各光周波数成分を、光周波数分波手段16の各々の出力端と1対1に接続された光検波手段43において、それぞれヘテロダイン同期検波する。k番目の光検波手段43に入力される光周波数成分は、光電界状態が式(11)で表される光周波数がfである多値信号光である。 The optical CDM receiving circuit 202 has the same configuration as that of the first embodiment, and each optical frequency component of the multi-wavelength signal light input to the optical CDM receiving circuit 202 is connected to each output terminal of the optical frequency demultiplexing means 16 and 1. The optical detection means 43 connected to the pair 1 performs heterodyne synchronous detection. The optical frequency component input to the k-th optical detection means 43 is multilevel signal light whose optical frequency is represented by the equation (11) and whose optical frequency is f k .

図8の光検波手段43を用いる場合、BPF54が出力する中間周波信号R**(t)は、式(12)のように、2信号の和で表される。

Figure 2011250079
電気位相同期ループ57は、VCO61の発振周波数および位相が、中間周波信号R**(t)を構成する2信号のどちらか一方の搬送波と同期するように、ループフィルタ63により調整される。ここで、電気位相同期ループ57の電気帯域は、光CDM送信回路201にて2値/多値変換手段11へ入力される2値信号の信号帯域よりも十分に狭い。 When the optical detection means 43 of FIG. 8 is used, the intermediate frequency signal R ** (t) output from the BPF 54 is represented by the sum of two signals as shown in Expression (12).
Figure 2011250079
The electric phase locked loop 57 is adjusted by the loop filter 63 so that the oscillation frequency and phase of the VCO 61 are synchronized with either one of the two carriers constituting the intermediate frequency signal R ** (t). Here, the electric band of the electric phase-locked loop 57 is sufficiently narrower than the signal band of the binary signal input to the binary / multilevel converter 11 in the optical CDM transmission circuit 201.

電気位相同期ループ57で、VCO61の位相が式(12)の右辺第1項の搬送波の位相と同期するとすると、電気帯域が光CDM送信回路201にて2値/多値変換手段11へ入力される2値信号の信号帯域よりも十分に狭いループフィルタ63はθ(t)による電圧変動を感じないため、VCO61の位相はΔφ(t)と同期し、ミキサー62からの検波出力S **(t)は、

Figure 2011250079
と表せる。ミキサー62の出力は、LPF56Aにて低域濾波され、式(13)の右辺第3項で表される多値ベースバンド信号が出力される。θ(t)は差がπである2値のいずれかをとるため、多値ベースバンド信号は、シンボル値D (t)に対応してとりうる各電圧レベルが、
Figure 2011250079
に対応する電圧レベルを中心として対称で、等間隔となる。 If the phase of the VCO 61 is synchronized with the phase of the carrier wave of the first term on the right side of the equation (12) in the electrical phase locked loop 57, the electrical band is input to the binary / multilevel converter 11 by the optical CDM transmission circuit 201. Since the loop filter 63 that is sufficiently narrower than the signal band of the binary signal does not feel voltage fluctuation due to θ h (t), the phase of the VCO 61 is synchronized with Δφ (t) and the detection output S 1 * from the mixer 62 is detected . * (T) is
Figure 2011250079
It can be expressed. The output of the mixer 62 is low-pass filtered by the LPF 56A, and a multi-value baseband signal expressed by the third term on the right side of Expression (13) is output. Since θ h (t) takes one of two values with a difference of π, the multilevel baseband signal has each voltage level that can be taken corresponding to the symbol value D # h (t),
Figure 2011250079
Symmetrically and equally spaced around the voltage level corresponding to.

電気位相同期ループ外のミキサー58には、位相がΔφ(t)に同期したVCO61の出力が、位相がπ/2だけシフトさせて入力される。ミキサー58からの検波出力S **(t)は、

Figure 2011250079
と表せる。ミキサー58の出力は、LPF56Bにて低域濾波され、シンボル値D h+1(t)に対応してとりうる各電圧レベルが、
Figure 2011250079
に対応する電圧レベルを中心として対称で、等間隔である多値ベースバンド信号が生成される。 The output of the VCO 61 whose phase is synchronized with Δφ (t) is input to the mixer 58 outside the electrical phase locked loop with the phase shifted by π / 2. The detection output S 2 ** (t) from the mixer 58 is
Figure 2011250079
It can be expressed. The output of the mixer 58 is low-pass filtered by the LPF 56B, and each voltage level that can be taken corresponding to the symbol value D # h + 1 (t)
Figure 2011250079
A multi-value baseband signal that is symmetric with respect to the voltage level corresponding to is equally spaced.

電気復号化手段45に、光検波手段43の各出力端からの多値ベースバンド信号が実施形態1で説明したように入力される。よって、光CDM送信回路202において2値/多値変換手段11へ入力されたN個の2値信号のうちの所望信号を選択的に受信することが可能である。   The multi-value baseband signal from each output terminal of the optical detection means 43 is input to the electric decoding means 45 as described in the first embodiment. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 202.

このように、実施形態3でも、従来の光CDM伝送システム(図1)と同数の光変調手段12および光検波手段43の数を用いて、符号長を2倍に拡張し、とりうる最大符号多重数を拡大できる。その際、隣接する光周波数成分の間隔を一定とすると、多波長信号光の光周波数帯域が変わらないため、波長分散耐性が劣化しない。   As described above, also in the third embodiment, the code length is doubled by using the same number of optical modulation means 12 and optical detection means 43 as the conventional optical CDM transmission system (FIG. 1), and the maximum code that can be taken Multiplex number can be expanded. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

(実施形態4)
実施形態4は、実施形態3における光CDM受信回路202内において、ヘテロダイン同期検波の光検波手段43の代わりに、ホモダイン検波を行う光検波手段43’を配置した光CDM伝送システムである。
(Embodiment 4)
Embodiment 4 is an optical CDM transmission system in which optical detection means 43 ′ for performing homodyne detection is arranged in the optical CDM reception circuit 202 in Embodiment 3 instead of the optical detection means 43 for heterodyne synchronous detection.

光CDM受信回路202は、実施形態2と同様の構成であり、光CDM受信回路202へ入力された多波長信号光の各光周波数成分を、光周波数分波手段16の各々の出力端と1対1に接続された光検波手段43’において、それぞれホモダイン検波する。k番目の光検波手段43’−kに入力される光周波数成分は、光電界状態が式(11)で表される光周波数がfである多値信号光である。 The optical CDM receiving circuit 202 has the same configuration as that of the second embodiment, and each optical frequency component of the multi-wavelength signal light input to the optical CDM receiving circuit 202 is connected to each output terminal of the optical frequency demultiplexing means 16 and 1. The optical detection means 43 'connected to the pair 1 performs homodyne detection. The optical frequency component input to the k-th optical detection means 43′-k is multilevel signal light whose optical frequency is represented by the equation (11) as fk .

光位相同期ループ91内は、電気帯域が光CDM受信回路201にて2値/多値変換手段11へ入力される2値信号の信号帯域よりも十分に狭い。光位相同期ループ91で、局発光の光位相が式(11)の右辺第1項の光搬送波の光位相と同期する場合、ループフィルタ63はθ(t)による電圧変動を感じないため、局発光の光位相はφ(t)と同期し、光検波器の出力Q ***(t)を、

Figure 2011250079
と表せる。局発光の光電界振幅Eを、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅
Figure 2011250079
よりも十分に大きくすると、多値信号光の直接検波成分である式(15)の右辺第1,2項は、局発光とのビート成分である右辺第4項と比べて無視できる。よって、光位相同期ループの出力は、シンボル値D (t)に対応する各電圧レベルが、
Figure 2011250079
に対応する電圧レベルを中心として対称で、等間隔である多値ベースバンド信号と見なせる。 In the optical phase-locked loop 91, the electrical band is sufficiently narrower than the signal band of the binary signal input to the binary / multilevel converter 11 in the optical CDM receiving circuit 201. In the optical phase locked loop 91, when the optical phase of the local light is synchronized with the optical phase of the optical carrier of the first term on the right side of the equation (11), the loop filter 63 does not feel voltage fluctuation due to θ h (t). The optical phase of local light is synchronized with φ S (t), and the output Q 1 *** (t) of the optical detector is
Figure 2011250079
It can be expressed. The optical field amplitude E L of the local light, optical field amplitude of the multilevel signal to be input to the optical phase synchronous homodyne detection circuit
Figure 2011250079
If it is made sufficiently larger, the first and second terms on the right side of Equation (15), which are direct detection components of multilevel signal light, can be ignored compared to the fourth term on the right side, which is a beat component with local light. Therefore, the output of the optical phase-locked loop has each voltage level corresponding to the symbol value D # h (t) as
Figure 2011250079
It can be regarded as a multi-value baseband signal that is symmetric with respect to the voltage level corresponding to 1 and is equally spaced.

光位相同期ループ91外の光検波器53’は、位相がφ(t)に同期した局発光が、光位相が光位相シフタ65でπ/2だけシフトさせて入力される。光検波器の出力Q ***(t)は、

Figure 2011250079
と表せる。ここで、局発光の光電界振幅Eは、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅
Figure 2011250079
よりも十分に大きいため、光検波器の出力は、シンボル値D h+1(t)に対応する各電圧レベルが、
Figure 2011250079
に対応する電圧レベルを中心として対称で、等間隔である多値ベースバンド信号と見なせる。 The optical detector 53 ′ outside the optical phase locked loop 91 receives the local light whose phase is synchronized with φ S (t) with the optical phase shifted by π / 2 by the optical phase shifter 65. The output Q 2 *** (t) of the optical detector is
Figure 2011250079
It can be expressed. Here, local light optical field amplitude E L is the optical field amplitude of the multilevel signal to be input to the optical phase synchronous homodyne detection circuit
Figure 2011250079
Is sufficiently larger than the output of the optical detector so that each voltage level corresponding to the symbol value D # h + 1 (t)
Figure 2011250079
It can be regarded as a multi-value baseband signal that is symmetric with respect to the voltage level corresponding to 1 and is equally spaced.

なお、送信回路内の2値/多値変換手段へ入力される各2値信号がビット同期している場合、実施形態2で説明したようにディジタルコヒーレント受信器を光検波手段として用いることが可能である。DSP回路において多値信号光と局発光の光位相差の推定が可能であるため、光位相同期ホモダイン検波において必要である多値信号光と局発光との光位相同期が不要である。この光検波手段を用いる場合、光変調手段へ入力される多値信号は差動符号化(Differential Encoding)される。   When each binary signal input to the binary / multilevel conversion means in the transmission circuit is bit-synchronized, a digital coherent receiver can be used as the optical detection means as described in the second embodiment. It is. Since the DSP circuit can estimate the optical phase difference between the multilevel signal light and the local light, the optical phase synchronization between the multilevel signal light and the local light, which is necessary in the optical phase-locked homodyne detection, is unnecessary. When this optical detection means is used, the multilevel signal input to the optical modulation means is differentially encoded (Differential Encoding).

電気復号化手段45に、光検波手段43’の各出力端からの多値ベースバンド信号が実施形態1で説明したように入力される。よって、光CDM送信回路202において2値/多値変換手段11へ入力されたN個の2値信号のうちの所望信号を選択的に受信することが可能である。   As described in the first embodiment, the multi-value baseband signal from each output terminal of the optical detection unit 43 ′ is input to the electric decoding unit 45. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 202.

このように、実施形態2でも、従来の光CDM伝送システム(図1)と同数の光変調手段12および光検波手段43’の数を用いて、符号長を2倍に拡張し、とりうる最大符号多重数を拡大できる。その際、隣接する光周波数成分の間隔を一定とすると、多波長信号光の光周波数帯域が変わらないため、波長分散耐性が劣化しない。   As described above, even in the second embodiment, the code length is doubled by using the same number of optical modulation means 12 and optical detection means 43 ′ as the conventional optical CDM transmission system (FIG. 1), and the maximum possible The number of code multiplexes can be expanded. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

11:2値/多値変換手段
12、12−1、12−2、・・・、12−K’:光変調手段
13:光周波数合波手段
14、14−1、14−2、・・・、14−K’:光源
16:光周波数分波手段
21、21−1、21−2、・・・、21−N:拡散符号器
22、22−1、22−2、・・・、22−K:加算器
23、23−11、23−12、・・・:出力端
24、24−1、24−2、・・・、24−K:プリバイアス回路
31、31−1、31−2、・・・、31−M−1:重み付け回路
32:識別器
33:乗算器
42:光周波数分波手段
43、43−1、43−2、・・・、43−K’:光検波手段
43’、43’−1、43’−2、・・・、43’−K’:光検波手段
45、45−1、45−2、・・・、45−N:電気復号化手段
45’、45’−1、45’−2、・・・、45’−N:電気復号化手段
51:局発光源
52、52’:偏波調整手段
53、53’:光検波器
54:BPF
55:電気位相同期ループ回路
56A、56B:LPF
57:電気位相同期ループ
58:ミキサー
61:VCO
62:ミキサー
63:ループフィルタ
64:位相シフタ
65:光位相シフタ
71:入力端
81:光強度変調手段
82:光位相シフタ
83:差動信号生成手段
84:光強度変調器
91:光位相同期ループ
201:光CDM送信回路
202、202−1、202−2、・・・、202−N:光CDM受信回路
202’:光CDM受信回路
203:光ファイバ伝送路
301:光CDM伝送システム
11: Binary / multilevel conversion means 12, 12-1, 12-2,..., 12-K ′: Optical modulation means 13: Optical frequency multiplexing means 14, 14-1, 14-2,. 14-K ′: light source 16: optical frequency demultiplexing means 21, 21-1, 21-2,..., 21-N: spreading encoders 22, 22-1, 22-2,. 22-K: adders 23, 23-11, 23-12,...: Output terminals 24, 24-1, 24-2,..., 24-K: pre-bias circuits 31, 31-1, 31 -2, ..., 31-M-1: Weighting circuit 32: Discriminator 33: Multiplier 42: Optical frequency demultiplexing means 43, 43-1, 43-2, ..., 43-K ': Light Detection means 43 ', 43'-1, 43'-2, ..., 43'-K': Optical detection means 45, 45-1, 45-2, ..., 45-N: Electric decoding means 45 ', 45' -1, 45′-2,..., 45′-N: Electrical decoding means 51: Local light source 52, 52 ′: Polarization adjusting means 53, 53 ′: Optical detector 54: BPF
55: Electric phase-locked loop circuit 56A, 56B: LPF
57: Electric phase locked loop 58: Mixer 61: VCO
62: Mixer 63: Loop filter 64: Phase shifter 65: Optical phase shifter 71: Input end 81: Light intensity modulation means 82: Optical phase shifter 83: Differential signal generation means 84: Light intensity modulator 91: Optical phase locked loop 201: Optical CDM transmission circuit 202, 202-1, 202-2, ..., 202-N: Optical CDM reception circuit 202 ': Optical CDM reception circuit 203: Optical fiber transmission line 301: Optical CDM transmission system

Claims (7)

N個(Nは2以上の整数)の2値信号から、2種の符号要素で構成された符号長がK以下(Kは2以上の整数)であるN個の固有符号に基づき、K個の多値信号を生成する2値/多値変換手段と、
互いに異なる光周波数の連続光である光搬送波が入力され、前記光搬送波を2分岐し、前記2値/多値変換手段からの前記多値信号のうちの2個を用いてそれぞれの前記光搬送波を変調するとともに前記光搬送波の光位相を互いに直交させ、2つの前記光搬送波を合流した多値信号光を出力する複数の光変調手段と、
各々の前記光変調手段が出力する前記多値信号光を合波した多波長信号光を出力する光合波手段と、
を備える光CDM送信回路。
Based on N (N is an integer greater than or equal to 2) binary signals and K unique codes whose code length is composed of two types of code elements and whose code length is less than or equal to K (K is an integer greater than or equal to 2). Binary / multi-value conversion means for generating a multi-value signal of
An optical carrier wave that is continuous light having different optical frequencies is input, the optical carrier wave is branched into two, and each of the optical carrier waves is obtained by using two of the multilevel signals from the binary / multilevel converter. And a plurality of optical modulation means for outputting multi-level signal light obtained by joining the two optical carriers, with the optical phases of the optical carriers orthogonal to each other, and
Optical multiplexing means for outputting multi-wavelength signal light obtained by multiplexing the multi-level signal light output by each of the light modulation means;
An optical CDM transmission circuit.
前記2値/多値変換手段は、
N個の前記2値信号と1対1に対応するN個の拡散符号器及びK個の加算器を有しており、
各々の前記拡散符号器は、前記固有符号が割り当てられ、割り当てられた前記固有符号の符号長以上の個数の出力端を有し、前記固有符号を構成する各符号要素を前記出力端へ順に対応させた際に、前記2種の符号要素のうちの一方の符号要素に対応する前記出力端からは前記拡散符号器へ入力された2値信号とシンボル値が一致する信号を出力し、他の前記出力端からは0を出力し、
k番目(k=1,2,・・・,K)の前記加算器は、k番目の前記多値信号のシンボル値が、各々の前記拡散符号器のk番目の前記出力端からの出力信号のシンボル値の和となるように、各々の前記拡散符号器のk番目の前記出力端からの出力信号のシンボル値を加算することを特徴とする請求項1に記載の光CDM送信回路。
The binary / multivalue conversion means includes:
N number of the binary signals and N number of spreading coders and K number of adders corresponding to each other,
Each of the spreading encoders is assigned with the unique code, has a number of output ends equal to or greater than the code length of the assigned unique code, and sequentially corresponds each code element constituting the unique code to the output end. A signal whose symbol value matches the binary signal input to the spreading encoder is output from the output end corresponding to one of the two types of code elements. 0 is output from the output end,
The k-th (k = 1, 2,..., K) adder is such that the symbol value of the k-th multilevel signal is an output signal from the k-th output terminal of each spreading encoder. 2. The optical CDM transmission circuit according to claim 1, wherein the symbol values of the output signals from the k-th output terminal of each of the spreading encoders are added so as to be a sum of the symbol values.
前記光変調手段が出力する前記多値信号光は、
光位相が互いに直交する2つの前記光搬送波それぞれのとりうる光電界振幅レベルが等間隔であり、且つ、前記光変調手段へ入力された2個の前記多値信号の一方のシンボル値に応じて変動することを特徴とする請求項1または2に記載の光CDM送信回路。
The multi-level signal light output from the light modulation means is
The optical electric field amplitude levels that can be taken by each of the two optical carriers whose optical phases are orthogonal to each other are equally spaced, and according to one symbol value of the two multilevel signals input to the optical modulation means The optical CDM transmission circuit according to claim 1, wherein the optical CDM transmission circuit varies.
前記光変調手段が出力する前記多値信号光は、
光位相が互いに直交する2つの光搬送波それぞれのとりうる光電界振幅レベルが、等間隔であり、且つ、前記光変調手段へ入力された2個の前記多値信号の一方のシンボル値に応じて変動し、
前記光変調手段内での前記光搬送波それぞれの光位相シフト量が、前記光変調手段へ入力された2個の前記多値信号のうち一方のシンボル値に応じて、差がπである2値のいずれかとなることを特徴とする請求項1または2に記載の光CDM送信回路。
The multi-level signal light output from the light modulation means is
The optical field amplitude levels that can be taken by each of the two optical carriers whose optical phases are orthogonal to each other are equally spaced, and according to one symbol value of the two multilevel signals input to the optical modulation means Fluctuate,
A binary value in which the optical phase shift amount of each of the optical carrier waves in the optical modulation means is a difference of π according to one symbol value of the two multilevel signals input to the optical modulation means The optical CDM transmission circuit according to claim 1, wherein the optical CDM transmission circuit is any one of the following.
請求項1から4のいずれかに記載の光CDM送信回路が出力する前記多波長信号光が光ファイバ伝送路を介して入力され、前記多波長信号光を光周波数成分ごとに分波して出力する光周波数分波手段と、
前記光周波数分波手段から入力された前記光周波数成分を検波し、光位相が互いに直交する2つの光搬送波が搬送するそれぞれの多値信号を出力する2個の出力端を有する光検波手段と、
1番目からN番目の前記固有符号のうちの1つが割り当てられ、前記光検波手段の各出力端が接続されており、割り当てられた前記固有符号を構成する前記符号要素を前記光検波手段の前記出力端へ順に対応させた際に、前記固有符号を構成する2種の前記符号要素のうちの一方に対応する前記出力端からの入力を正、他方の前記符号要素に対応する前記出力端からの入力を負として加える加減算を行うことにより、前記2値/多値変換手段に入力された前記2値信号のうちの1つを選択的に取り出す電気復号化手段と、
を備える光CDM受信回路。
5. The multi-wavelength signal light output from the optical CDM transmission circuit according to claim 1 is input via an optical fiber transmission line, and the multi-wavelength signal light is demultiplexed and output for each optical frequency component. Optical frequency demultiplexing means to perform,
Optical detection means having two output terminals for detecting the optical frequency components input from the optical frequency demultiplexing means and outputting respective multilevel signals carried by two optical carriers whose optical phases are orthogonal to each other; ,
One of the first to Nth unique codes is assigned, and each output terminal of the optical detection means is connected, and the code elements constituting the assigned unique code are assigned to the optical detection means When corresponding to the output terminal in order, the input from the output terminal corresponding to one of the two types of code elements constituting the unique code is positive, and the output terminal corresponding to the other code element is Electrodecoding means for selectively extracting one of the binary signals input to the binary / multilevel conversion means by performing addition / subtraction to add the input of
An optical CDM receiving circuit.
前記光検波手段は、
出力光の光周波数が、前記光周波数分波手段からの入力光と所定の周波数差となるように調整された局発光源と、
前記局発光源からの出力光と、前記光周波数分波手段からの入力光との混合光を2乗検波する光検波器と、
前記光検波器の出力から、周波数が前記所定の周波数差と一致し、位相が互いに直交する2つの搬送波それぞれが搬送する信号成分を透過するバンドパスフィルタと、
VCO、ミキサー及びループフィルタを含み、前記2値信号の信号帯域より狭い電気帯域の電気位相同期ループを有し、前記2つの搬送波それぞれが搬送する多値信号を復調して別々に出力する位相同期検波回路と、
を備え、
前記VCOの出力の周波数および位相は、前記2個の搬送波のうちの一方と同期するように前記ループフィルタで調整され、
前記ミキサーは、前記バンドパスフィルタからの入力を前記VCOの出力により検波して、前記2つの搬送波のうちの一方が搬送する多値信号を復調することを特徴とする請求項5に記載の光CDM受信回路。
The optical detection means includes
A local light source adjusted so that an optical frequency of output light has a predetermined frequency difference from input light from the optical frequency demultiplexing means;
An optical detector that squarely detects mixed light of output light from the local light source and input light from the optical frequency demultiplexing means;
A band pass filter that transmits a signal component carried by each of two carrier waves having a frequency that matches the predetermined frequency difference and whose phases are orthogonal to each other, from the output of the optical detector;
A phase lock circuit that includes a VCO, a mixer, and a loop filter, has an electrical phase locked loop having an electrical band narrower than the signal band of the binary signal, and demodulates and outputs separately the multilevel signal carried by each of the two carrier waves A detection circuit;
With
The frequency and phase of the output of the VCO are adjusted by the loop filter so as to be synchronized with one of the two carriers.
6. The light according to claim 5, wherein the mixer detects an input from the band-pass filter based on an output of the VCO, and demodulates a multilevel signal carried by one of the two carrier waves. CDM receiving circuit.
前記光検波手段は、
局発光源、光検波器及びループフィルタを含み、前記2値信号の信号帯域より狭い電気帯域の光位相同期ループを備え、光位相が互いに直交する2つの光搬送波それぞれが搬送する多値信号を復調して別々に出力し、
前記局発光源の出力光の光周波数および光位相は、前記2個の光搬送波のうちの一方と同期するように前記ループフィルタで調整され、
前記光検波器は、前記局発光源からの出力光と、前記光周波数分波手段からの入力光との混合光を2乗検波することを特徴とする請求項5に記載の光CDM受信回路。
The optical detection means includes
Including a local light source, an optical detector and a loop filter, comprising an optical phase-locked loop having an electrical band narrower than the signal band of the binary signal, and carrying a multilevel signal carried by each of two optical carriers whose optical phases are orthogonal to each other Demodulate and output separately,
The optical frequency and optical phase of the output light of the local light source are adjusted by the loop filter so as to be synchronized with one of the two optical carriers,
6. The optical CDM receiving circuit according to claim 5, wherein the optical detector square-detects a mixed light of the output light from the local light source and the input light from the optical frequency demultiplexing means. .
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