JP5189528B2 - Optical transmitter and optical communication system - Google Patents

Optical transmitter and optical communication system Download PDF

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JP5189528B2
JP5189528B2 JP2009054567A JP2009054567A JP5189528B2 JP 5189528 B2 JP5189528 B2 JP 5189528B2 JP 2009054567 A JP2009054567 A JP 2009054567A JP 2009054567 A JP2009054567 A JP 2009054567A JP 5189528 B2 JP5189528 B2 JP 5189528B2
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アブドゥッラー アルアミン
逸郎 森田
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本発明は、直接受信を行う光受信装置を使用する光通信システムの周波数利用効率を改善するための技術に関する。特に、直交周波数分割多重変調を使用する光通信システムの様に、光搬送波と側波帯との間に未使用帯域を設ける必要がある光通信システムの周波数利用効率を改善する技術に関する。   The present invention relates to a technique for improving the frequency utilization efficiency of an optical communication system using an optical receiver that performs direct reception. In particular, the present invention relates to a technique for improving the frequency utilization efficiency of an optical communication system that needs to provide an unused band between an optical carrier wave and a sideband, such as an optical communication system using orthogonal frequency division multiplexing modulation.

直交周波数分割多重（ＯＦＤＭ）変調は、送信データを複数のサブキャリアを用いて並列に伝送する方式であり、各サブキャリアのシンボルレートが比較的低くなるためシンボル間干渉に強く、デジタル地上波放送や、無線ＬＡＮ（Ｌｏｃａｌ Ａｅｒａ Ｎｅｔｗｏｒｋ）システムで既に使用されており、光通信システムへの適用についても検討されている（例えば、非特許文献１、参照。）。   Orthogonal frequency division multiplexing (OFDM) modulation is a method of transmitting transmission data in parallel using a plurality of subcarriers. Since the symbol rate of each subcarrier is relatively low, it is resistant to intersymbol interference, and digital terrestrial broadcasting In addition, it is already used in a wireless local area network (LAN) system, and its application to an optical communication system is also being studied (for example, see Non-Patent Document 1).

Ａｒｔｈｕｒ Ｊａｍｅｓ Ｌｏｗｅｒｙ、ｅｔ ａｌ．、“Ｏｒｔｈｏｇｏｎａｌ−ｆｒｅｑｕｅｎｃｙ−ｄｉｖｉｓｉｏｎ ｍｕｌｔｉｐｌｅｘｉｎｇ ｆｏｒ ｄｉｓｐｅｒｓｉｏｎ ｃｏｍｐｅｎｓａｔｉｏｎ ｏｆ ｌｏｎｇ−ｈａｕｌ ｏｐｔｉｃａｌ ｓｙｓｔｅｍｓ”、２００６ Ｏｐｔｉｃａｌ Ｓｏｃｉｅｔｙ ｏｆ Ａｍｅｒｉｃａ、ＯＰＴＩＣＳ ＥＸＰＲＥＳＳ ２０７９、Ｖｏｌ．１４ Ｎｏ．６、２００６年３月Arthur James Lowry, et al. , “Orthogonal-frequency-division multiplexing for dispersal compensation of long-haul optical systems”, 2006 Optical Society of America ETS E No. 14 6, March 2006

光ＯＦＤＭ通信は、光受信装置における処理によりコヒーレント方式と直接受信方式に分類することができる。コヒーレント方式とは、光受信装置に局発光源を設け、局発光と受信光信号を干渉させた信号をフォトダイードで電気信号に変換する方式であり、直接受信方式とは、光受信装置のフォトダイオードが受信光信号を電気信号に直接変換する、より詳しくは、受信光信号中の光搬送波と情報に対応する側波帯信号の干渉信号を電気信号に変換する方式である。   Optical OFDM communication can be classified into a coherent system and a direct reception system by processing in the optical receiver. The coherent method is a method in which a local light source is provided in the optical receiving device, and a signal obtained by interfering the local light and the received optical signal is converted into an electric signal by a photo diode. The direct receiving method is a photodiode of the optical receiving device. In this method, the received optical signal is directly converted into an electrical signal. More specifically, the interference signal of the sideband signal corresponding to the optical carrier and information in the received optical signal is converted into an electrical signal.

コヒーレント方式は、直接受信方式に比べ、信号対雑音比等の信号特性の点で優れているが、局発光と受信光信号を干渉させるための部品に加え、光受信装置における偏波制御が必要となるため装置コストは高くなる。このため、長距離伝送を必要としない光通信システムにおいては、装置コストの低い直接受信方式が有利となる。   The coherent method is superior to the direct reception method in terms of signal characteristics such as signal-to-noise ratio, but it requires polarization control in the optical receiver in addition to components that cause interference between the local light and the received optical signal. Therefore, the device cost is increased. For this reason, in an optical communication system that does not require long-distance transmission, a direct reception method with low apparatus cost is advantageous.

上述した様に、直接受信方式は、光搬送波と情報に対応する側波帯信号の干渉信号を電気信号に変換するものであるが、光ＯＦＤＭ通信において、側波帯信号は多数のサブキャリアを含むため、このサブキャリア同士の干渉信号も電気信号に変換されることになる。つまり、図３（ａ）に示す様に、光搬送波８０と、帯域Ｂ１（Ｈｚ）の光側波帯信号８１を含む光信号を電気信号に変換すると、図３（ｂ）に示す様に、光側波帯信号８１に対応する電気のＯＦＤＭ信号８２に加え、サブキャリア同士の干渉によるノイズ成分８３がＢ１（Ｈｚ）まで生じることになる。このノイズ成分を避ける最も簡易な方法は、図３（ｃ）に示す様に、光搬送波８０と光側波帯信号８１の間に、少なくとも光側波帯信号８１の帯域と同じ帯域の未使用帯域を設けることであるが、未使用帯域を設けることで周波数利用効率が低下する。なお、この未使用帯域を小さくする方法も提案されてはいるが、所定の未使用帯域を設ける必要があることには変わりなく周波数利用効率が低下する。 As described above, the direct reception method converts an interference signal of a sideband signal corresponding to an optical carrier wave and information into an electrical signal. In optical OFDM communication, a sideband signal includes a number of subcarriers. Therefore, the interference signal between the subcarriers is also converted into an electric signal. That is, as shown in FIG. 3A, when an optical signal including the optical carrier wave 80 and the optical sideband signal 81 in the band B 1 (Hz) is converted into an electrical signal, as shown in FIG. In addition to the electrical OFDM signal 82 corresponding to the optical sideband signal 81, a noise component 83 due to interference between subcarriers is generated up to B 1 (Hz). As shown in FIG. 3C, the simplest method for avoiding this noise component is that an unused band of at least the same band as that of the optical sideband signal 81 is used between the optical carrier 80 and the optical sideband signal 81. Although providing the band, the frequency utilization efficiency is reduced by providing the unused band. Although a method for reducing the unused band has been proposed, it is necessary to provide a predetermined unused band, and the frequency utilization efficiency is lowered.

また、周波数利用効率を改善するため、コヒーレント方式においては偏波多重の使用が提案されている。これに対して、直接受信方式において、同一周波数の光搬送波及び同一周波数の光側波帯信号を含む２つの光信号を偏波多重した場合、受信側においては、偏波の方向に関する情報が得られないため、偏波分離ができないという問題がある。つまり、たとえ、必要な未使用帯域を限りなく零に近づけたとしても、コヒーレント方式の様に偏波多重を利用して、さらに、周波数利用効率を高めることができないという問題がある。   In order to improve frequency utilization efficiency, the use of polarization multiplexing has been proposed in the coherent scheme. In contrast, in the direct reception method, when two optical signals including an optical carrier wave of the same frequency and an optical sideband signal of the same frequency are polarization multiplexed, information on the polarization direction is obtained on the reception side. Therefore, there is a problem that polarization separation cannot be performed. That is, there is a problem that even if the necessary unused band is made as close to zero as possible, the frequency utilization efficiency cannot be further increased by using polarization multiplexing as in the coherent method.

したがって、本発明は、従来技術より周波数利用効率の高い直接受信を行う光通信システムと、この光通信システムのための光送信装置を提供することを目的とする。   Accordingly, an object of the present invention is to provide an optical communication system that performs direct reception with higher frequency utilization efficiency than the prior art, and an optical transmitter for the optical communication system.

本発明による光通信システムは、
第１の側波帯、第２の側波帯、第１の光搬送波及び第２の光搬送波を含む光信号を生成して光伝送路に送信する光送信装置と、前記光伝送路から前記光信号を受信する光受信装置とを含む光通信システムであって、第１の側波帯及び第１の光搬送波の偏波面は同一であり、第２の側波帯及び第２の光搬送波とは直交し、第１の光搬送波の周波数は、第１の側波帯の最低周波数より低く、第２の光搬送波の周波数は、第２の側波帯の最高周波数より高く、第１の光搬送波の周波数は、第２の光搬送波の周波数より低く、第１の側波帯の最高周波数は、第２の側波帯の最低周波数より高く、第１の光搬送波は、第２の側波帯の帯域外であり、第２の光搬送波は、第１の側波帯の帯域外であり、光受信装置は、前記光信号の第１の光搬送波をフィルタリングして電気信号に変化する手段と、前記光信号の第２の光搬送波をフィルタリングして電気信号に変化する手段とを備えていることを特徴とする。 An optical communication system according to the present invention includes:
An optical transmitter that generates and transmits an optical signal including a first sideband, a second sideband, a first optical carrier, and a second optical carrier to an optical transmission line; and An optical communication system including an optical receiver for receiving an optical signal, wherein the first sideband and the first optical carrier have the same polarization plane, the second sideband and the second optical carrier , And the frequency of the first optical carrier is lower than the lowest frequency of the first sideband, the frequency of the second optical carrier is higher than the highest frequency of the second sideband, The frequency of the optical carrier is lower than the frequency of the second optical carrier, the highest frequency of the first sideband is higher than the lowest frequency of the second sideband, and the first optical carrier is on the second side Outside the waveband, the second optical carrier is outside the first sideband, and the optical receiver filters the first optical carrier of the optical signal. Characterized in that it comprises means for changing the electrical signal ring, and means for changing the electrical signal by filtering the second optical carrier of the optical signal.

本発明による光通信システムによると、
第１の側波帯の最高周波数が、第２の側波帯の最高周波数以上であること、さらに、第１の側波帯の最低周波数が、第２に側波帯の最高周波数以上であることも好ましい。 According to the optical communication system according to the present invention,
The highest frequency of the first sideband is equal to or higher than the highest frequency of the second sideband, and the lowest frequency of the first sideband is secondly equal to or higher than the highest frequency of the sideband. It is also preferable.

本発明による光通信システムの他の実施形態によると、
第１の側波帯、第２の側波帯、第１の光搬送波及び第２の光搬送波を含む光信号を生成して光伝送路に送信する光送信装置と、前記光伝送路から前記光信号を受信する光受信装置とを含む光通信システムであって、第１の側波帯及び第１の光搬送波の偏波面は同一であり、第２の側波帯及び第２の光搬送波とは直交し、第１の光搬送波の周波数が第１の側波帯の最低周波数より低い場合には、第２の光搬送波の周波数も第２の側波帯の最低周波数より低く、第１の光搬送波の周波数が第１の側波帯の最高周波数より高い場合には、第２の光搬送波の周波数も第２の側波帯の最高周波数より高く、第１の光搬送波の周波数は、第２の光搬送波の周波数より高く、かつ、第２の側波帯の最低周波数より低く、光受信装置は、前記光信号の第１の光搬送波をフィルタリングして電気信号に変化する手段と、前記光信号の第２の光搬送波をフィルタリングして電気信号に変化する手段とを備えていることを特徴とする。 According to another embodiment of the optical communication system according to the present invention,
An optical transmitter that generates and transmits an optical signal including a first sideband, a second sideband, a first optical carrier, and a second optical carrier to an optical transmission line; and An optical communication system including an optical receiver for receiving an optical signal, wherein the first sideband and the first optical carrier have the same polarization plane, the second sideband and the second optical carrier And the frequency of the first optical carrier is lower than the lowest frequency of the first sideband, the frequency of the second optical carrier is also lower than the lowest frequency of the second sideband, Is higher than the highest frequency of the first sideband, the frequency of the second optical carrier is also higher than the highest frequency of the second sideband, and the frequency of the first optical carrier is: The optical receiver is higher than the frequency of the second optical carrier wave and lower than the lowest frequency of the second sideband. Characterized in that it comprises means for changing the electrical signal by filtering transmitting and means for changing the electrical signal by filtering the second optical carrier of the optical signal.

本発明による光送信装置は、
上記光通信システムで使用されるものであり、第１の連続光を変調して第１の光搬送波及び第１の側波帯を含む光信号を出力する第１の変調手段と、第２の連続光を変調して第２の光搬送波及び第２の側波帯を含む光信号を出力する第２の変調手段と、第１の変調手段の出力光信号と、第２の変調手段の出力光信号を互いに直交する偏波の光信号として多重する手段とを備えていることを特徴とする。 An optical transmission device according to the present invention includes:
A first modulation means for use in the optical communication system, which modulates the first continuous light and outputs an optical signal including the first optical carrier wave and the first sideband; Second modulation means for modulating the continuous light and outputting an optical signal including the second optical carrier wave and the second sideband; an output optical signal of the first modulation means; and an output of the second modulation means And means for multiplexing the optical signals as optical signals having polarizations orthogonal to each other.

簡易な構成で周波数利用効率を改善することができる。   Frequency utilization efficiency can be improved with a simple configuration.

本発明による光通信システムのシステム構成図である。1 is a system configuration diagram of an optical communication system according to the present invention. 図１の各部における光スペクトラムの概略を示す図である。It is a figure which shows the outline of the optical spectrum in each part of FIG. 従来技術を説明する図である。It is a figure explaining a prior art. 本発明の他の形態を説明する図である。It is a figure explaining the other form of this invention. 本発明のさらに他の形態を説明する図である。It is a figure explaining the further another form of this invention. 本発明のさらに他の形態を説明する図である。It is a figure explaining the further another form of this invention. 本発明のさらに他の形態を説明する図である。It is a figure explaining the further another form of this invention.

本発明を実施するための形態について、以下では図面を用いて詳細に説明する。   EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated in detail below using drawing.

図１は、本発明による光通信システムのシステム構成図である。図１によると、光通信システムは、光送信装置１及び光受信装置２を含み、光送信装置１及び光受信装置２は、光ファイバで構成される光伝送路により接続されている。なお、光伝送路は１つ以上の光増幅器を含むものであっても良い。   FIG. 1 is a system configuration diagram of an optical communication system according to the present invention. According to FIG. 1, the optical communication system includes an optical transmission device 1 and an optical reception device 2, and the optical transmission device 1 and the optical reception device 2 are connected by an optical transmission line formed of an optical fiber. The optical transmission line may include one or more optical amplifiers.

また、光送信装置１は、光源１１と、光位相変調器１２と、波長分離器１３と、光変調器１４及び１５と、偏波合成器１６と、光フィルタ１７と、発振器１８とを備えており、光受信装置２は、分波器２１と、光フィルタ２２及び２３と、光受信機２４及び２５とを備えている。   The optical transmission device 1 includes a light source 11, an optical phase modulator 12, a wavelength separator 13, optical modulators 14 and 15, a polarization beam combiner 16, an optical filter 17, and an oscillator 18. The optical receiver 2 includes a duplexer 21, optical filters 22 and 23, and optical receivers 24 and 25.

以下に、本発明による光通信システムでの信号処理について説明する。光源１１は周波数ｆ０の連続光を生成して出力し、発振器１８は周波数（ｆ２−ｆ１）／２の正弦波電気信号を生成して出力し、光位相変調器１２は、光源１１からの連続光を、発振器１８からの電気信号で位相変調する。なお、ここではｆ２＞ｆ１とする。したがって、光位相変調器１２は、図２（ａ）に示す様に、周波数ｆ１、ｆ２に線スペクトラムを有する光信号を出力することになる。 The signal processing in the optical communication system according to the present invention will be described below. The light source 11 generates and outputs continuous light having a frequency f 0 , the oscillator 18 generates and outputs a sinusoidal electric signal having a frequency (f 2 −f 1 ) / 2, and the optical phase modulator 12 includes the light source 11. Is modulated with an electric signal from the oscillator 18. Here, it is assumed that f 2 > f 1 . Therefore, as shown in FIG. 2A, the optical phase modulator 12 outputs an optical signal having a line spectrum at frequencies f 1 and f 2 .

波長分離器１３は、図２（ａ）に示す光信号を波長分離して、周波数ｆ１の連続光を光変調器１４に、周波数ｆ２の連続光を光変調器１５に、それぞれ、出力する。光変調器１４及び１５は、入力される連続光を、ＯＦＤＭ変調された電気信号で変調を行う変調器である。したがって、光変調器１４の出力光信号の概略的な光スペクトラムは、図２（ｂ）に示す様に、光搬送波５１、下側側波帯６１及び上側側波帯６２を含むものになり、光変調器１５の出力光信号の概略的な光スペクトラムは、図２（ｃ）に示す様に、光搬送波５２、下側側波帯７１及び上側側波帯７２を含むものになる。なお、本実施形態においては、光搬送波５１／５２と側波帯の間には未使用帯域ＢＵ＝（ｆ２−ｆ１）／２（Ｈｚ）を設け、側波帯の帯域、つまり、ＯＦＤＭ信号の帯域は、未使用帯域ＢＵからガード帯域ＢＧを引いた値とする。 Wavelength demultiplexer 13, and wavelength separation of the optical signal shown in FIG. 2 (a), the optical modulator 14 to continuously light the frequency f 1, a continuous light of a frequency f 2 to the optical modulator 15, respectively, the output To do. Optical modulators 14 and 15 are modulators that modulate input continuous light with an electrical signal that has been subjected to OFDM modulation. Therefore, the schematic optical spectrum of the output optical signal of the optical modulator 14 includes the optical carrier 51, the lower sideband 61, and the upper sideband 62, as shown in FIG. A schematic optical spectrum of the optical signal output from the optical modulator 15 includes an optical carrier 52, a lower sideband 71, and an upper sideband 72, as shown in FIG. In this embodiment, an unused band B U = (f 2 −f 1 ) / 2 (Hz) is provided between the optical carrier 51/52 and the sideband, and the sideband band, that is, band of the OFDM signal, a value obtained by subtracting a guard band B G from unused bandwidth B U.

偏波合成器１６は、一方の入力端子に入力される光信号の偏波面を９０度だけ回転させて、偏波面を回転させない他方の入力端子に入力される光信号と合波して出力するものであり、光フィルタ１７は、光搬送波５１から光搬送波５２までの周波数帯域の信号を通過させ、下側側波帯６１と、上側側波帯７２を除去する光フィルタである。よって、光フィルタ１７の出力光信号は、図２（ｄ）に示す様に、偏波面が同一である光搬送波５１及び情報に対応する上側側波帯６２と、光搬送波５１及び上側側波帯６２とは直交する偏波面の光搬送波５２及び情報に対応する下側側波帯７１とを含むものとなる。   The polarization beam combiner 16 rotates the polarization plane of the optical signal input to one input terminal by 90 degrees, and combines and outputs the optical signal input to the other input terminal that does not rotate the polarization plane. The optical filter 17 is an optical filter that passes signals in the frequency band from the optical carrier 51 to the optical carrier 52 and removes the lower sideband 61 and the upper sideband 72. Therefore, as shown in FIG. 2 (d), the output optical signal of the optical filter 17 includes the optical carrier 51 having the same plane of polarization and the upper sideband 62 corresponding to the information, and the optical carrier 51 and the upper sideband. 62 includes an optical carrier wave 52 having an orthogonal polarization plane and a lower sideband 71 corresponding to information.

光受信装置２の分波器２１は、図２（ｄ）の光スペクトラムを有する光信号を２分岐して出力する。また、光フィルタ２２は、図２（ｄ）の光スペクトラムを有する光信号の光搬送波５２を除去するフィルタであり、光フィルタ２３は、図２（ｄ）の光スペクトラムを有する光信号の光搬送波５１を除去するフィルタである。したがって、光フィルタ２２の出力光信号の光スペクトラムは、図３（ｅ）に示すものとなり、光フィルタ２３の出力光信号の光スペクトラムは、図３（ｆ）に示すものとなる。なお、ガード帯域ＢＧは、光搬送波５１又は５２を除去する際の、側波帯６２及び７１への影響を抑えるためのものであるが、例えば、ノッチフィルタを使用することで、ガード帯域ＢＧについては、ほぼ零とすることができる。 The duplexer 21 of the optical receiver 2 divides the optical signal having the optical spectrum of FIG. The optical filter 22 is a filter for removing the optical carrier 52 of the optical signal having the optical spectrum of FIG. 2D, and the optical filter 23 is the optical carrier of the optical signal having the optical spectrum of FIG. 51 is a filter for removing 51. Therefore, the optical spectrum of the output optical signal from the optical filter 22 is as shown in FIG. 3E, and the optical spectrum of the output optical signal from the optical filter 23 is as shown in FIG. The guard band B G is for suppressing the influence on the sidebands 62 and 71 when the optical carrier 51 or 52 is removed. For example, the guard band B G can be obtained by using a notch filter. G can be set to almost zero.

光受信機２４及び２５は、直接受信方式、つまり、フォトダイオード等の光電気変換部を備えており、受信光信号を電気信号に変換して復調を行う。ここで、電気信号に変換されるのは、光搬送波及び側波帯の同一偏波方向の干渉信号のみであるが、光搬送波５１と下側側波帯７１は直交し、光搬送波５２と上側側波帯６２は直交しているため、光受信機２４内の光電気変換部は、上側側波帯６２のみを電気信号に変換し、光受信機２５内の光電気変換部は、下側側波帯７１のみを電気信号に変換することになる。よって、各光受信機は、一方の偏波の信号のみを取り出して復調することになる。   The optical receivers 24 and 25 are provided with a direct reception system, that is, an opto-electric converter such as a photodiode, and perform demodulation by converting the received optical signal into an electric signal. Here, only the interference signal in the same polarization direction of the optical carrier and the sideband is converted into the electric signal, but the optical carrier 51 and the lower sideband 71 are orthogonal, and the optical carrier 52 and the upper side Since the sidebands 62 are orthogonal, the photoelectric conversion unit in the optical receiver 24 converts only the upper sideband 62 into an electrical signal, and the photoelectric conversion unit in the optical receiver 25 is on the lower side. Only the sideband 71 is converted into an electric signal. Therefore, each optical receiver takes out only one polarization signal and demodulates it.

なお、光受信機２４内の光電気変換部は、上側側波帯６２の各サブキャリア間の干渉によるノイズ成分も出力するが、本実施形態においては、光搬送波５１と上側側波帯６２の間には上側側波帯の帯域以上の未使用帯域ＢＵを設けているため、ノイズ成分が復調に影響することはない。光受信機２５についても同様である。 Note that the photoelectric conversion unit in the optical receiver 24 also outputs a noise component due to interference between subcarriers in the upper sideband 62, but in this embodiment, the optical carrier 51 and the upper sideband 62 Since an unused band BU equal to or higher than the upper sideband is provided between them, noise components do not affect demodulation. The same applies to the optical receiver 25.

以上、光送信装置において、第１の偏波の第１の光搬送波及び該第１の光搬送波の上側側波帯を含む第１の光信号と、第１の偏波とは直交する第２の偏波の第２の光搬送波及び該第２の光搬送波の下側側波帯を含む光信号であって、周波数軸上において、前記下側側波帯が第１の光搬送波と前記上側側波帯の間に位置し、前記上側側波帯が第２の光搬送波と前記下側側波帯の間に配置された光信号を生成して送信する。この構成により、光受信装置においては、復調する偏波とは直交する偏波の光搬送波を除去するのみで、偏波分離を行うことなく各偏波で送信された信号の復調を行うことが可能となる。   As described above, in the optical transmission device, the first optical signal including the first optical carrier wave having the first polarization and the upper sideband of the first optical carrier wave and the first polarization are orthogonal to each other. And a lower sideband of the second optical carrier, the lower sideband being the first optical carrier and the upper side on the frequency axis. An optical signal located between the sidebands and having the upper sideband disposed between the second optical carrier and the lower sideband is generated and transmitted. With this configuration, the optical receiver can demodulate the signal transmitted with each polarization without performing polarization separation by simply removing the optical carrier wave having a polarization orthogonal to the polarization to be demodulated. It becomes possible.

従来技術においては、図３（ｃ）に示す様に、２Ｂ１（Ｈｚ）の帯域当たり、Ｂ１（Ｈｚ）のみを情報伝送に利用可能であったが、本願発明による光通信システムにおいては、図２（ｄ）から明らかな様に、２Ｂ１（Ｈｚ）の帯域の殆どを情報伝送に利用することができ、周波数利用効率が約２倍に改善される。 In the prior art, as shown in FIG. 3 (c), only B 1 (Hz) per band of 2B 1 (Hz) can be used for information transmission. However, in the optical communication system according to the present invention, As is apparent from FIG. 2 (d), most of the 2B 1 (Hz) band can be used for information transmission, and the frequency utilization efficiency is improved about twice.

なお、図４に示す様に、上側側波帯６２の最高周波数と下側側波帯７１の最低周波数が一致する状態においては２Ｂ１（Ｈｚ）の帯域当たり、Ｂ１（Ｈｚ）の帯域を情報伝送に使用することになり、周波数利用効率は従来技術と同じになる。よって、上側側波帯６２の最高周波数を、下側側波帯７１の最低周波数より高くすることで、従来技術より周波数利用効率が改善される。例えば、図５に示す様に、上側側波帯６２の最高周波数と下側側波帯７１の最高周波数が一致する状態においては、３Ｂ１（Ｈｚ）の帯域当たり、２Ｂ１（Ｈｚ）の帯域を情報伝送に使用することになる。さらに、図６に示す様に、光搬送波５２が、光搬送波５１と上側側波帯６２の間であり、光搬送波５１が、光搬送波５２と下側側波帯７１の間である様に配置する形態であっても従来技術よりは周波数利用効率は改善される。 As shown in FIG. 4, in a state where the highest frequency of the upper sideband 62 and the lowest frequency of the lower sideband 71 coincide with each other, the band of B 1 (Hz) is set to 2B 1 (Hz). It will be used for information transmission, and the frequency utilization efficiency will be the same as in the prior art. Therefore, by making the highest frequency of the upper sideband 62 higher than the lowest frequency of the lower sideband 71, the frequency utilization efficiency is improved over the prior art. For example, as shown in FIG. 5, in a state where the highest frequency of the upper sideband 62 and the highest frequency of the lower sideband 71 coincide with each other, a band of 2B 1 (Hz) per band of 3B 1 (Hz) Will be used for information transmission. Further, as shown in FIG. 6, the optical carrier 52 is arranged between the optical carrier 51 and the upper sideband 62, and the optical carrier 51 is arranged between the optical carrier 52 and the lower sideband 71. Even in this form, the frequency utilization efficiency is improved as compared with the prior art.

つまり、上側側波帯６２の最高周波数が、下側側波帯７１の最低周波数より高く、光搬送波５２の周波数が、光搬送波５１の周波数より高い状態において従来技術より周波数利用効率が改善されることになる。ただし、光搬送波５１及び上側側波帯６２に影響を与えず光搬送波５２を除去する必要があり、光搬送波５２及び下側波帯７１に影響を与えず光搬送波５１を除去する必要があるため、光搬送波５２が上側側波帯６２の帯域内にある状態と、光搬送波５１が下側側波帯７１の帯域内にある状態は除くものとする。   That is, the frequency utilization efficiency is improved over the prior art in a state where the highest frequency of the upper sideband 62 is higher than the lowest frequency of the lower sideband 71 and the frequency of the optical carrier 52 is higher than the frequency of the optical carrier 51. It will be. However, it is necessary to remove the optical carrier 52 without affecting the optical carrier 51 and the upper sideband 62, and it is necessary to remove the optical carrier 51 without affecting the optical carrier 52 and the lower sideband 71. The state where the optical carrier 52 is in the upper sideband 62 and the state where the optical carrier 51 is in the lower sideband 71 are excluded.

なお、上述した実施形態においては、側波帯の帯域以上の未使用帯域ＢＵを設けているが、必須ではなく、他の方法を併用して、側波帯の帯域未満の未使用帯域とする構成であっても良い。本発明は、直接受信方式で異なる偏波の利用を可能にするものであるため、この場合であっても、従来技術より周波数利用効率は改善される。 In the above-described embodiment, the unused band BU equal to or higher than the sideband band is provided. However, this is not indispensable, and an unused band less than the sideband band may be used in combination with other methods. It may be configured to do so. Since the present invention makes it possible to use different polarizations in the direct reception system, even in this case, the frequency utilization efficiency is improved over the prior art.

また、上述した実施形態においては、一方の偏波については光搬送波とその上側側波帯の片側側波帯信号とし、他方の偏波については、光搬送波とその下側側波帯の片側側波帯信号としているが、共に同じ側の片側側波帯信号としても良い。例えば、図７に示す様に、一方の光搬送波を、他方の光搬送波と他方の側波帯信号の間に配置することで周波数利用効率が改善される。   In the above-described embodiment, one polarization is an optical carrier and one sideband signal of its upper sideband, and the other polarization is one side of the optical carrier and its lower sideband. Although a waveband signal is used, both may be a single sideband signal on the same side. For example, as shown in FIG. 7, the frequency utilization efficiency is improved by arranging one optical carrier wave between the other optical carrier wave and the other sideband signal.

さらに、上述した実施形態においては、光源１１からの連続光を位相変調することにより２つの搬送波を生成しているが、偏波面及び周波数を制御できる光源を２つ用いる形態であっても良い。また、この場合、各光源の出力光の偏波面を互いに直交状態とし、偏波合成器１６を使用しない形態とすることもできる。また、偏波合成後に光フィルタ１７により不要な側波帯を除去しているが、偏波合成前に除去する構成であっても良い。   Furthermore, in the above-described embodiment, two carrier waves are generated by phase-modulating continuous light from the light source 11, but two light sources capable of controlling the polarization plane and frequency may be used. In this case, the polarization planes of the output lights of the light sources may be orthogonal to each other, and the polarization beam combiner 16 may not be used. Further, although unnecessary sidebands are removed by the optical filter 17 after the polarization synthesis, a configuration of removing before the polarization synthesis may be used.

１ 光送信装置
１１ 光源
１２ 位相変調器
１３ 波長分離器
１４、１５ 光変調器
１６ 偏波合成器
１７、２２、２３ 光フィルタ
１８ 発振器
２ 光受信装置
２１ 分波器
２４、２５ 光受信機
５１、５２、８０ 光搬送波
６１、６２、７１、７２、８１ 光側波帯信号
８２ 電気ＯＦＤＭ信号
８３ ノイズ成分 DESCRIPTION OF SYMBOLS 1 Optical transmitter 11 Light source 12 Phase modulator 13 Wavelength separator 14, 15 Optical modulator 16 Polarization combiner 17, 22, 23 Optical filter 18 Oscillator 2 Optical receiver 21 Demultiplexer 24, 25 Optical receiver 51, 52, 80 Optical carrier wave 61, 62, 71, 72, 81 Optical sideband signal 82 Electric OFDM signal 83 Noise component

Claims (7)

第１の側波帯、第２の側波帯、第１の光搬送波及び第２の光搬送波を含む光信号を生成して光伝送路に送信する光送信装置と、
前記光伝送路から前記光信号を受信する光受信装置と、
を含む光通信システムであって、
第１の側波帯及び第１の光搬送波の偏波面は同一であり、第２の側波帯及び第２の光搬送波とは直交し、
第１の光搬送波の周波数は、第１の側波帯の最低周波数より低く、第２の光搬送波の周波数は、第２の側波帯の最高周波数より高く、
第１の光搬送波の周波数は、第２の光搬送波の周波数より低く、
第１の側波帯の最高周波数は、第２の側波帯の最低周波数より高く、
第１の光搬送波は、第２の側波帯の帯域外であり、
第２の光搬送波は、第１の側波帯の帯域外であり、
光受信装置は、
前記光信号の第１の光搬送波をフィルタリングして第２の側波帯のみ電気信号に変化する手段と、
前記光信号の第２の光搬送波をフィルタリングして第１の側波帯のみ電気信号に変化する手段と、
を備えている光通信システム。 An optical transmitter that generates an optical signal including the first sideband, the second sideband, the first optical carrier, and the second optical carrier and transmits the optical signal to the optical transmission line;
An optical receiver for receiving the optical signal from the optical transmission path;
An optical communication system comprising:
The planes of polarization of the first sideband and the first optical carrier are the same, and are orthogonal to the second sideband and the second optical carrier,
The frequency of the first optical carrier is lower than the lowest frequency of the first sideband, the frequency of the second optical carrier is higher than the highest frequency of the second sideband,
The frequency of the first optical carrier is lower than the frequency of the second optical carrier,
The highest frequency of the first sideband is higher than the lowest frequency of the second sideband;
The first optical carrier is outside the band of the second sideband;
The second optical carrier is outside the band of the first sideband;
The optical receiver
Means for filtering the first optical carrier of the optical signal to change only the second sideband into an electrical signal;
Means for filtering the second optical carrier of the optical signal to change only the first sideband into an electrical signal;
An optical communication system. 第１の側波帯の最高周波数が、第２の側波帯の最高周波数以上である、
請求項１に記載の光通信システム。 The highest frequency of the first sideband is greater than or equal to the highest frequency of the second sideband;
The optical communication system according to claim 1. 第１の側波帯の最低周波数が、第２に側波帯の最高周波数以上である、
請求項２に記載の光通信システム。 The lowest frequency of the first sideband is second or higher than the highest frequency of the sideband;
The optical communication system according to claim 2. 第１の側波帯、第２の側波帯、第１の光搬送波及び第２の光搬送波を含む光信号を生成して光伝送路に送信する光送信装置と、
前記光伝送路から前記光信号を受信する光受信装置と、
を含む光通信システムであって、
第１の側波帯及び第１の光搬送波の偏波面は同一であり、第２の側波帯及び第２の光搬送波とは直交し、
第１の光搬送波の周波数が第１の側波帯の最低周波数より低い場合には、第２の光搬送波の周波数も第２の側波帯の最低周波数より低く、第１の光搬送波の周波数が第１の側波帯の最高周波数より高い場合には、第２の光搬送波の周波数も第２の側波帯の最高周波数より高く、
第１の光搬送波の周波数は、第２の光搬送波の周波数より高く、かつ、第２の側波帯の最低周波数より低く、
光受信装置は、
前記光信号の第１の光搬送波をフィルタリングして第２の側波帯のみ電気信号に変化する手段と、
前記光信号の第２の光搬送波をフィルタリングして第１の側波帯のみ電気信号に変化する手段と、
を備えている光通信システム。 An optical transmitter that generates an optical signal including the first sideband, the second sideband, the first optical carrier, and the second optical carrier and transmits the optical signal to the optical transmission line;
An optical receiver for receiving the optical signal from the optical transmission path;
An optical communication system comprising:
The planes of polarization of the first sideband and the first optical carrier are the same, and are orthogonal to the second sideband and the second optical carrier,
When the frequency of the first optical carrier is lower than the lowest frequency of the first sideband, the frequency of the second optical carrier is also lower than the lowest frequency of the second sideband, and the frequency of the first optical carrier Is higher than the highest frequency of the first sideband, the frequency of the second optical carrier is also higher than the highest frequency of the second sideband,
The frequency of the first optical carrier is higher than the frequency of the second optical carrier and lower than the lowest frequency of the second sideband;
The optical receiver
Means for filtering the first optical carrier of the optical signal to change only the second sideband into an electrical signal;
Means for filtering the second optical carrier of the optical signal to change only the first sideband into an electrical signal;
An optical communication system. 光送信装置は、
第１の連続光を変調して第１の光搬送波及び第１の側波帯を含む光信号を出力する第１の変調手段と、
第２の連続光を変調して第２の光搬送波及び第２の側波帯を含む光信号を出力する第２の変調手段と、
第１の変調手段の出力光信号と、第２の変調手段の出力光信号を互いに直交する偏波の光信号として多重する手段と、
を備えている、
請求項１から４のいずれか１項に記載の光通信システム。 The optical transmitter
First modulation means for modulating the first continuous light and outputting an optical signal including the first optical carrier wave and the first sideband;
Second modulation means for modulating the second continuous light and outputting an optical signal including the second optical carrier wave and the second sideband;
Means for multiplexing the output optical signal of the first modulation means and the output optical signal of the second modulation means as optical signals of polarization orthogonal to each other;
With
The optical communication system according to any one of claims 1 to 4. 第１の連続光を変調して第１の光搬送波及び第１の側波帯を含む光信号を出力する第１の変調手段と、
第２の連続光を変調して第２の光搬送波及び第２の側波帯を含む光信号を出力する第２の変調手段と、
第１の変調手段の出力光信号と、第２の変調手段の出力光信号を互いに直交する偏波の光信号として多重する手段と、
を備えている光送信装置であって、
第１の光搬送波の周波数は、第１の側波帯の最低周波数より低く、第２の光搬送波の周波数は、第２の側波帯の最高周波数より高く、第１の光搬送波の周波数は、第２の光搬送波の周波数より低く、第１の側波帯の最高周波数は、第２の側波帯の最低周波数より高く、第１の光搬送波は、第２の側波帯の帯域外であり、第２の光搬送波は、第１の側波帯の帯域外である、
光送信装置。 First modulation means for modulating the first continuous light and outputting an optical signal including the first optical carrier wave and the first sideband;
Second modulation means for modulating the second continuous light and outputting an optical signal including the second optical carrier wave and the second sideband;
Means for multiplexing the output optical signal of the first modulation means and the output optical signal of the second modulation means as optical signals of polarization orthogonal to each other;
An optical transmission device comprising:
The frequency of the first optical carrier is lower than the lowest frequency of the first sideband, the frequency of the second optical carrier is higher than the highest frequency of the second sideband, and the frequency of the first optical carrier is Lower than the frequency of the second optical carrier, the highest frequency of the first sideband is higher than the lowest frequency of the second sideband, and the first optical carrier is out of band of the second sideband. And the second optical carrier is outside the first sideband,
Optical transmitter. 第１の連続光を変調して第１の光搬送波及び第１の側波帯を含む光信号を出力する第１の変調手段と、
第２の連続光を変調して第２の光搬送波及び第２の側波帯を含む光信号を出力する第２の変調手段と、
第１の変調手段の出力光信号と、第２の変調手段の出力光信号を互いに直交する偏波の光信号として多重する手段と、
を備えている光送信装置であって、
第１の光搬送波の周波数が第１の側波帯の最低周波数より低い場合には、第２の光搬送波の周波数も第２の側波帯の最低周波数より低く、第１の光搬送波の周波数が第１の側波帯の最高周波数より高い場合には、第２の光搬送波の周波数も第２の側波帯の最高周波数より高く、第１の光搬送波の周波数は、第２の光搬送波の周波数より高く、かつ、第２の側波帯の最低周波数より低い、
光送信装置。 First modulation means for modulating the first continuous light and outputting an optical signal including the first optical carrier wave and the first sideband;
Second modulation means for modulating the second continuous light and outputting an optical signal including the second optical carrier wave and the second sideband;
Means for multiplexing the output optical signal of the first modulation means and the output optical signal of the second modulation means as optical signals of polarization orthogonal to each other;
An optical transmission device comprising:
When the frequency of the first optical carrier is lower than the lowest frequency of the first sideband, the frequency of the second optical carrier is also lower than the lowest frequency of the second sideband, and the frequency of the first optical carrier Is higher than the highest frequency of the first sideband, the frequency of the second optical carrier is also higher than the highest frequency of the second sideband, and the frequency of the first optical carrier is the second optical carrier And lower than the lowest frequency of the second sideband,
Optical transmitter.
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