JP4735567B2 - Optical transmission apparatus and method - Google Patents

Optical transmission apparatus and method Download PDF

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JP4735567B2
JP4735567B2 JP2007042579A JP2007042579A JP4735567B2 JP 4735567 B2 JP4735567 B2 JP 4735567B2 JP 2007042579 A JP2007042579 A JP 2007042579A JP 2007042579 A JP2007042579 A JP 2007042579A JP 4735567 B2 JP4735567 B2 JP 4735567B2
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ラース ヤンセン サンダー
逸郎 森田
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本発明は、複数のサブキャリアを含む電気信号を、アナログ光変調により伝送する光伝送装置及び方法に関する。   The present invention relates to an optical transmission apparatus and method for transmitting an electrical signal including a plurality of subcarriers by analog optical modulation.

光信号を、無線周波数帯の電気信号の振幅に応じて、例えば、強度変調して伝送するシステムが提案されている（例えば、非特許文献１、参照。）。   A system that transmits an optical signal after, for example, intensity modulation according to the amplitude of an electric signal in a radio frequency band has been proposed (for example, see Non-Patent Document 1).

非特許文献１は、直交周波数分割多重（ＯＦＤＭ：Ｏｒｔｈｏｇｏｎａｌ Ｆｒｅｑｕｅｎｃｙ Ｄｉｖｉｓｉｏｎ Ｍｕｌｔｉｐｌｅｘｉｎｇ）技術を用いたものであり、光伝送装置は、まず、高速フーリエ逆変換処理及びデジタルアナログ変換処理により実数部及び虚数部のベースバンド信号を生成し、実数部及び虚数部のベースバンド信号、それぞれを、互いに直交する同一周波数の正弦波信号により周波数変換して加算することで、レーザダイオードからの連続光を変調するための、変調電気信号を生成している。   Non-Patent Document 1 uses Orthogonal Frequency Division Multiplexing (OFDM) technology, and an optical transmission apparatus first performs real and imaginary part processing by fast Fourier inverse transform processing and digital / analog conversion processing. The baseband signal is generated, and the baseband signal of the real part and the imaginary part are respectively frequency-converted by the same frequency sine wave signals orthogonal to each other and added to modulate the continuous light from the laser diode. Generating a modulated electrical signal.

変調電気信号により強度変調された光信号は、レーザダイオードの発光周波数である光キャリア信号を対称軸とし、情報を搬送する側波帯が高周波側と低周波側に配置された光スペクトラムを有するが、非特許文献１に記載の光伝送装置は、一方の側波帯をフィルタで除去、つまり、片側側波帯（ＳＳＢ：Ｓｉｎｇｌｅ Ｓｉｄｅ Ｂａｎｄ）方式にて光信号を送信している。   The optical signal whose intensity is modulated by the modulated electric signal has an optical spectrum in which the optical carrier signal, which is the emission frequency of the laser diode, is an axis of symmetry, and the sidebands carrying information are arranged on the high frequency side and the low frequency side. In the optical transmission device described in Non-Patent Document 1, one sideband is removed by a filter, that is, an optical signal is transmitted using a single sideband (SSB) system.

また、上記光信号を受信した光伝送装置は、まず、フォトダイオードにより、受信光信号を、変調電気信号に変換し、変調電気信号と同相及び直交する正弦波を、それぞれ、変調電気信号に乗じて、実数部及び虚数部のベースバンド信号に変換し、デジタルアナログ変換処理及び高速フーリエ変換処理により、実数部及び虚数部のベースバンド信号を、周波数領域の複素信号に変換している。   In addition, the optical transmission device that has received the optical signal first converts the received optical signal into a modulated electrical signal by a photodiode, and multiplies the modulated electrical signal by a sine wave that is in phase and orthogonal to the modulated electrical signal. Thus, the baseband signals of the real part and the imaginary part are converted into baseband signals of the real part and the imaginary part, and the baseband signals of the real part and the imaginary part are converted into complex signals in the frequency domain by digital analog conversion processing and fast Fourier transform processing.

Ｊａｍｅｓ Ｌｏｗｅｒｙ ｅｔ ａｌ、“Ｏｒｔｈｏｇｏｎａｌ−ｆｒｅｑｕｅｎｃｙ−ｄｉｖｉｓｉｏｎ ｍｕｌｔｉｐｌｅｘｉｎｇ ｆｏｒ ｄｉｓｐｅｒｓｉｏｎ ｃｏｍｐｅｎｓａｔｉｏｎ ｏｆ ｌｏｎｇ−ｈａｕｌ ｏｐｔｉｃａｌ ｓｙｓｔｅｍｓ”、Ｏｐｔｉｃｓ Ｅｘｐｒｅｓｓ， ｖｏｌ．１４、Ｎｏ．６、ｐｐ．２０７９−２０８４、２００６年３月James Lowery et al, "Orthogonal-frequency-division multiplexing for dispersal compensation of long-haul optical systems," Optics Express. 14, no. 6, pp. 2079-2084, March 2006

図６は、非特許文献１に記載の光伝送装置が送信する光信号の概略的な光スペクトラムを示す図である。なお、ベースバンド信号を周波数変換するための正弦波信号の周波数をｆＴＸ、変調電気信号に含まれる一番低いサブキャリアと、一番高いサブキャリアの周波数差、つまり、変調電気信号の帯域をｆＳＩＧとする。図６によると、複数のサブキャリアを含む上側側波帯３０の中心周波数は、光キャリア２０から、周波数変換に使用した正弦波信号の周波数ｆＴＸだけ離れている。ここで、光キャリア２０の周波数は、外部光変調器に入力されるレーザダイオードの発光周波数に等しい。 FIG. 6 is a diagram illustrating a schematic optical spectrum of an optical signal transmitted by the optical transmission device described in Non-Patent Document 1. Note that the frequency of the sine wave signal for frequency conversion of the baseband signal is f TX , and the frequency difference between the lowest subcarrier and the highest subcarrier included in the modulated electric signal, that is, the band of the modulated electric signal is f SIG . According to FIG. 6, the center frequency of the upper sideband 30 including a plurality of subcarriers is separated from the optical carrier 20 by the frequency f TX of the sine wave signal used for frequency conversion. Here, the frequency of the optical carrier 20 is equal to the emission frequency of the laser diode input to the external optical modulator.

非特許文献１にも記載されている様に、ＯＦＤＭといった、複数のサブキャリアを含む側波帯３０を有する光信号を、フォトダイードにより変調電気信号に変換した場合、相互変調（Ｉｎｔｅｒｍｏｄｕｌａｔｉｏｎ）とも呼ばれる、各サブキャリア間の相互混合（Ｉｎｔｅｒｍｉｘｉｎｇ）により相互混合ノイズが発生する。図７は、フォトダイードに対して、図６に示す光信号を入力した場合に出力される電気信号の概略的な周波数スペクトルを示す図である。図７によると、変調電気信号５０の中心周波数は、光キャリア２０と側波帯３０の中心との周波数差に等しくｆＴＸであり、相互混合ノイズ４０が、直流からほぼ周波数ｆＳＩＧまで発生している。なお、この相互混合ノイズ４０の外挿ノイズ（Ｅｘｔｒａｐｏｌａｔｉｏｎ）が、周波数ｆＳＩＧより高い周波数領域にまで漏れ込むため、周波数ｆＳＩＧより高い領域に存在する信号も、実際には影響を受けることになる。 As described in Non-Patent Document 1, when an optical signal having a sideband 30 including a plurality of subcarriers such as OFDM is converted into a modulated electric signal by photo diode, it is also called intermodulation (Intermodulation). Mutual mixing noise is generated by intermixing between subcarriers. FIG. 7 is a diagram showing a schematic frequency spectrum of an electric signal output when the optical signal shown in FIG. 6 is input to the photodiode. According to FIG. 7, the center frequency of the modulated electrical signal 50 is equal to the frequency difference between the optical carrier 20 and the center of the sideband 30 and is f TX , and the intermixing noise 40 is generated from the direct current to the frequency f SIG. ing. Note that extrapolation noise of this intermixing noise 40 (Extrapolation) is, because leaking to a higher frequency range than the frequency f SIG, signals present in higher areas than the frequency f SIG also will be affected in practice .

非特許文献１によると、相互混合ノイズ４０は、キャリア対信号比（ＣＳＲ：Ｃａｒｒｉｅｒ ｔｏ Ｓｉｇｎａｌ Ｒａｔｉｏ）が小さくなる程大きくなる。つまり、光伝送に使用できる光パワーの多くを光キャリア２０に割り振ることで、相互混合ノイズ４０を小さくできるが、これは、側波帯３０、つまり、伝送する情報を有している信号に割り振れる光パワーが小さくなることを意味し、信号対雑音比（ＳＮＲ：Ｓｉｇｎａｌ ｔｏ Ｎｏｉｓｅ Ｒａｔｉｏ）が劣化してしまう。このため、非特許文献１においては、光キャリア２０と側波帯３０には同一光パワーを配分し、相互混合ノイズ４０を避けるため、ｆＴＸをｆＳＩＧの１．５倍とし、光キャリア２０と側波帯３０との間に、周波数幅ｆＳＩＧのガード帯域を確保することとしている。 According to Non-Patent Document 1, the intermixed noise 40 increases as the carrier-to-signal ratio (CSR) decreases. In other words, the intermixing noise 40 can be reduced by allocating much of the optical power that can be used for optical transmission to the optical carrier 20, but this is allocated to the sideband 30, that is, a signal having information to be transmitted. This means that the optical power that can be swung is reduced, and the signal-to-noise ratio (SNR) is deteriorated. For this reason, in Non-Patent Document 1, in order to distribute the same optical power to the optical carrier 20 and the sideband 30 and avoid the mutual mixing noise 40, f TX is set to 1.5 times f SIG , and the optical carrier 20 A guard band having a frequency width f SIG is secured between the sideband 30 and the sideband 30.

相互混合ノイズ４０による信号への影響は低いことが好ましく、かつ、そのことは、確保すべきガード帯域を減少させ周波数帯域を有効に利用することにつながる。   It is preferable that the influence of the intermixing noise 40 on the signal is low, and this leads to the reduction of the guard band to be secured and the effective use of the frequency band.

したがって、本発明は、複数のサブキャリアを含む電気信号を、アナログ光変調により伝送する場合において、従来技術より確保すべきガード帯域を狭くすることができる、いいかえると、同一ガード帯域においては、相互混合ノイズの影響を抑えることができる光伝送装置及び方法を提供することを目的とする。   Therefore, according to the present invention, when an electric signal including a plurality of subcarriers is transmitted by analog optical modulation, the guard band to be secured can be made narrower than that in the prior art. In other words, in the same guard band, An object of the present invention is to provide an optical transmission apparatus and method capable of suppressing the influence of mixed noise.

本発明の光伝送装置によれば、
複数のサブキャリアに対応する側波帯を含む光信号を受信する光伝送装置であって、前記光信号に含まれる側波帯の波形整形を行う手段と、波形整形後の光信号を電気信号に変換する手段とを備えており、波形整形は、上側側波帯については周波数が高いほど光パワーを減少させ、下側側波帯については周波数が低いほど光パワーを減少させることを特徴とする。 According to the optical transmission device of the present invention,
An optical transmission apparatus for receiving an optical signal including sidebands corresponding to a plurality of subcarriers, the means for shaping the waveform of the sideband included in the optical signal, and the optical signal after waveform shaping The waveform shaping is characterized by decreasing the optical power as the frequency is higher for the upper sideband, and decreasing the optical power as the frequency is lower for the lower sideband. To do.

本発明の光伝送方法によれば、
送信側伝送装置において、光キャリア信号を、複数のサブキャリアを含む電気信号で変調し、複数のサブキャリアに対応する側波帯を含む光信号を生成するステップと、生成した光信号を送信するステップと、受信側光伝送装置において、前記光信号に含まれる側波帯の波形整形を行うステップと、波形整形後の光信号を電気信号に変換するステップとを備えており、波形整形は、上側側波帯については周波数が高いほど光パワーを減少させ、下側側波帯については周波数が低いほど光パワーを減少させることを特徴とする。 According to the optical transmission method of the present invention,
In the transmission-side transmission device, a step of modulating an optical carrier signal with an electric signal including a plurality of subcarriers to generate an optical signal including sidebands corresponding to the plurality of subcarriers, and transmitting the generated optical signal And a step of performing waveform shaping of a sideband included in the optical signal, and a step of converting the optical signal after waveform shaping into an electrical signal in the reception-side optical transmission device, For the upper sideband, the optical power is decreased as the frequency is higher, and for the lower sideband, the optical power is decreased as the frequency is lower.

また、複数のサブキャリアに対応する側波帯を含む光信号は、片側側波帯光信号であることも好ましく、更に、隣接するサブキャリアにおいて、周波数の高いサブキャリアの変調フォーマットの多値度は、周波数の低いサブキャリアの変調フォーマットの多値度以上であることも好ましい。   In addition, the optical signal including the sidebands corresponding to the plurality of subcarriers is preferably a single sideband optical signal. Further, in the adjacent subcarriers, the multilevel degree of the modulation format of the subcarrier having a high frequency is used. Is preferably more than the multi-level of the modulation format of the subcarrier having a low frequency.

相互混合ノイズは、各サブキャリアの周波数差をその周波数成分とするため、光電気変換後に、低周波側となるサブキャリアの光パワーは、あまり減少させず、相互混合ノイズの影響を受けない、高周波側となるサブキャリアの光パワーを減少させることで、相互混合ノイズを抑え信号対雑音比を改良することができ、よって、従来技術より、ガード帯域を減少させることが可能になる。更に、隣接するサブキャリアにおいて、周波数の高いサブキャリアの変調フォーマットの多値度を、周波数の低いサブキャリアの変調フォーマットの多値度以上とすることを波形整形と組み合わせることで、信号対雑音比を更に改良することができる。   Since the intermixing noise uses the frequency difference of each subcarrier as its frequency component, the optical power of the subcarrier on the low frequency side after photoelectric conversion does not decrease so much and is not affected by the intermixing noise. By reducing the optical power of the subcarrier on the high frequency side, it is possible to suppress the mutual mixing noise and improve the signal-to-noise ratio, and thus it is possible to reduce the guard band as compared with the prior art. Furthermore, in the adjacent subcarriers, the signal-to-noise ratio is obtained by combining the waveform shaping with the multilevel of the modulation format of the subcarrier having the higher frequency being equal to or greater than the multilevel of the modulation format of the subcarrier having the lower frequency. Can be further improved.

本発明を実施するための最良の実施形態について、以下では図面を用いて詳細に説明する。   The best mode for carrying out the present invention will be described in detail below with reference to the drawings.

図１は、本発明による光伝送装置の送信側のブロック図である。図１によると、光伝送装置は、変調部１と、周波数変換部２と、光信号生成部３と、光変調部４と、光フィルタ５とを備えている。   FIG. 1 is a block diagram of a transmission side of an optical transmission apparatus according to the present invention. According to FIG. 1, the optical transmission device includes a modulation unit 1, a frequency conversion unit 2, an optical signal generation unit 3, an optical modulation unit 4, and an optical filter 5.

変調部１は、複数のサブキャリアを含むベースバンド信号を周波数変換部２に入力し、周波数変換部２は、ベースバンド信号を無線周波数（ＲＦ：Ｒａｄｉｏ Ｆｒｅｑｕｅｎｃｙ）帯の電気信号に周波数変換し、複数のサブキャリアを含む変調電気信号５０を出力する。なお、複数のサブキャリアを含む変調電気信号５０の例としては、ＯＦＤＭ信号や、副搬送波多重（ＳＣＭ：Ｓｕｂ−Ｃａｒｒｉｅｒ Ｍｕｌｔｉｐｌｅｘｉｎｇ）方式で光信号により伝送される信号があるが、これらに限定されるものではない。また、以下の説明において、変調電気信号５０の帯域をｆＳＩＧ、その中心周波数をｆＴＸとする。 The modulation unit 1 inputs a baseband signal including a plurality of subcarriers to the frequency conversion unit 2, and the frequency conversion unit 2 performs frequency conversion of the baseband signal into an electric signal of a radio frequency (RF) band, A modulated electric signal 50 including a plurality of subcarriers is output. Note that examples of the modulated electric signal 50 including a plurality of subcarriers include an OFDM signal and a signal transmitted by an optical signal in a sub-carrier multiplexing (SCM) system, but are not limited thereto. It is not a thing. In the following description, the band of the modulated electric signal 50 is f SIG and the center frequency is f TX .

光信号生成部３は、例えば、分布帰還型レーザダイオードであり、連続光を光変調部４に出力する。光変調部４は、例えば、マッハツェンダ変調器といった連続光を変調する外部光変調器であり、変調電気信号５０で連続光を変調し、光フィルタ５は、光変調部４が出力する光信号の一方の側波帯、本実施形態においては、下側側波帯を抑圧して、図２に示す、光キャリア２０及び上側側波帯３０を含む光信号、つまり、光ＳＳＢ信号を、光伝送路に送信する。なお、以下、上側側波帯３０を利用する実施形態で説明を行うが、下側側波帯を利用することも可能であり、また、両側側波帯方式であっても良い。   The optical signal generation unit 3 is, for example, a distributed feedback laser diode, and outputs continuous light to the optical modulation unit 4. The optical modulation unit 4 is an external optical modulator that modulates continuous light, such as a Mach-Zehnder modulator, for example. The optical modulation unit 4 modulates the continuous light with the modulated electric signal 50, and the optical filter 5 outputs the optical signal output from the optical modulation unit 4. One sideband, in this embodiment, the lower sideband is suppressed, and the optical signal including the optical carrier 20 and the upper sideband 30 shown in FIG. 2, that is, the optical SSB signal, is optically transmitted. Send to the road. In the following description, the embodiment using the upper sideband 30 will be described. However, the lower sideband can also be used, and a double sideband system may be used.

図３は、本発明による光伝送装置の受信側のブロック図である。図３によると、光伝送装置は、光フィルタ６と、光電気変換部７と、周波数変換部８と、復調部９とを備えている。   FIG. 3 is a block diagram of the receiving side of the optical transmission apparatus according to the present invention. As shown in FIG. 3, the optical transmission device includes an optical filter 6, a photoelectric conversion unit 7, a frequency conversion unit 8, and a demodulation unit 9.

光フィルタ６は、光伝送路から受信する光ＳＳＢ信号の側波帯３０に対して、周波数軸上で、光キャリア２０から離れるに従いその光パワーが減少する様に波形整形を行う。具体的には、使用している側波帯３０が上側側波帯である場合には、周波数が高いほど減衰量を強くし、下側側波帯である場合には、周波数が低いほど減衰量を強くして波形整形を行う。図４に、光フィルタ６が出力する光ＳＳＢ信号の概略的なスペクトラムを示す。以後、側波帯の光キャリア２０に最も近いサブキャリアの光パワーと、最も遠いサブキャリアの光パワーとの差、つまり、図４でＸにて示す量を、チルト量と呼ぶ。   The optical filter 6 performs waveform shaping on the sideband 30 of the optical SSB signal received from the optical transmission line so that the optical power decreases as the distance from the optical carrier 20 increases on the frequency axis. Specifically, when the sideband 30 being used is the upper sideband, the higher the frequency, the stronger the attenuation amount. When the sideband 30 is the lower sideband, the lower the frequency, the lower the attenuation. Increase the amount to shape the waveform. FIG. 4 shows a schematic spectrum of the optical SSB signal output from the optical filter 6. Hereinafter, the difference between the optical power of the subcarrier closest to the sideband optical carrier 20 and the optical power of the farthest subcarrier, that is, the amount indicated by X in FIG. 4 is referred to as a tilt amount.

光電気変換部７は、例えば、フォトダイオードであり、光フィルタ６が出力する光信号を変調電気信号５０に変換し、周波数変換部８は、周波数ｆＴＸの正弦波信号により変調電気信号５０をベースバンド信号に変換し、復調部９は、ベースバンド信号の復調を行う。 The photoelectric conversion unit 7 is, for example, a photodiode, and converts an optical signal output from the optical filter 6 into a modulated electric signal 50. The frequency conversion unit 8 converts the modulated electric signal 50 by a sine wave signal having a frequency f TX. The baseband signal is converted into a baseband signal, and the demodulator 9 demodulates the baseband signal.

相互混合ノイズ４０は、各サブキャリアの周波数差をその周波数成分とするため、変調電気信号５０に近い位置に発生する相互混合ノイズ４０は、主に、両端のサブキャリアに基づき発生したものである。このため、相互混合ノイズ４０の発生位置近傍となる、光キャリア２０に近いサブキャリアの光パワーは、あまり減少させず、相互混合ノイズ４０の影響を受けない、光キャリア２０から遠い位置にあるサブキャリアの光パワーを減少させることで、相互混合ノイズ４０を抑え、変調電気信号５０の信号対雑音比を改良することができる。また、これにより、従来技術より、ガード帯域を減少させることが可能になる。   Since the mutual mixing noise 40 uses the frequency difference of each subcarrier as its frequency component, the mutual mixing noise 40 generated at a position close to the modulated electric signal 50 is mainly generated based on the subcarriers at both ends. . For this reason, the optical power of the subcarrier close to the optical carrier 20 near the generation position of the intermixing noise 40 does not decrease so much and is not affected by the intermixing noise 40 and is located at a position far from the optical carrier 20. By reducing the optical power of the carrier, the intermixing noise 40 can be suppressed and the signal-to-noise ratio of the modulated electrical signal 50 can be improved. This also makes it possible to reduce the guard band compared to the prior art.

図５は、光フィルタ６で波形整形して電気信号に変換した場合と、波形整形せずに電気信号に変換した場合、それぞれの、キャリア対信号比（ＣＳＲ）に対する誤り率（ＢＥＲ：Ｂｉｔ Ｅｒｒｏｒ Ｒａｔｉｏ）を示す図である。なお、シミュレーションの条件は変調電気信号５０としてＦＦＴサイズを５１２、帯域７ＧＨｚ、各サブキャリアの変調フォーマットがＱＰＳＫのＯＦＤＭ信号を使用し、自然放出光雑音（ＡＳＥ：Ａｍｐｌｉｆｉｅｄ Ｓｐｏｎｔａｎｅｏｕｓ Ｅｍｉｓｓｉｏｎ）を印加する場合には、信号対雑音比（ＳＮＲ）を１１ｄＢとした。   FIG. 5 shows an error rate (BER: Bit Error) with respect to the carrier-to-signal ratio (CSR) when the waveform is shaped by the optical filter 6 and converted into an electrical signal and when the waveform is not transformed into an electrical signal. It is a figure which shows (Ratio). The simulation condition is that an OFDM signal having an FFT size of 512, a bandwidth of 7 GHz, and a modulation format of each subcarrier of QPSK is used as the modulated electric signal 50, and spontaneous emission optical noise (ASE) is applied. Used a signal-to-noise ratio (SNR) of 11 dB.

ＣＳＲが大きい領域においては、相互混合ノイズ４０は小さく、ＡＳＥの影響が支配的となる。図６からも明らかなように、ＣＳＲが増大するに従い、信号のパワーも減少するため、誤り率が劣化し、波形整形による差は見られない。   In the region where the CSR is large, the mutual mixing noise 40 is small, and the influence of ASE becomes dominant. As apparent from FIG. 6, as the CSR increases, the signal power also decreases, so that the error rate deteriorates and there is no difference due to waveform shaping.

しかしながら、ＣＳＲが小さい領域においては、相互混合ノイズ４０が増大し、相互混合ノイズ４０の影響が支配的となる。図６から、ＡＳＥを印加した場合と印加しない場合の両方において、波形整形を行うことによりＢＥＲが改善することが分かる。また、チルト量によってもＢＥＲが変動することが分かる。   However, in a region where the CSR is small, the mutual mixing noise 40 increases, and the influence of the mutual mixing noise 40 becomes dominant. It can be seen from FIG. 6 that the BER is improved by performing waveform shaping both when the ASE is applied and when it is not applied. It can also be seen that the BER varies depending on the tilt amount.

なお、シミュレーション結果において、２０ｄＢのチルト量は、１０ｄＢのチルト量より低いＢＥＲを示しているが、チルト量を大きくすることは、光キャリア２０から遠い位置にあるサブキャリの光パワーを光フィルタ６において、強く減少させることを意味し、チルト量を大きくしすぎると、これら、光キャリア２０から遠い位置にあるサブキャリのＢＥＲが大きく劣化することになる。したがって、最適なチルト量は、相互混合ノイズ４０のパワー、光電気変換部７の感度、復調部９におけるアナログデジタル変換処理の分解能等に応じて決定することになる。   In the simulation results, the tilt amount of 20 dB indicates a BER lower than the tilt amount of 10 dB. However, increasing the tilt amount causes the optical power of the subcarrier at a position far from the optical carrier 20 to be increased in the optical filter 6. If the tilt amount is too large, the BER of the sub-carrier located far from the optical carrier 20 is greatly deteriorated. Therefore, the optimum tilt amount is determined according to the power of the intermixing noise 40, the sensitivity of the photoelectric conversion unit 7, the resolution of the analog-digital conversion processing in the demodulation unit 9, and the like.

また、チルト量を大きくしすぎることによる信号品質の劣化を避けるため、サブキャリアごとの変調フォーマットを異なるものとすることも好ましい。具体的には、隣接するサブキャリにおいて、周波数の高いサブキャリアの変調フォーマットの多値度を、周波数の低いサブキャリアの変調フォーマットの多値度以上とする。光キャリア２０から近い位置にあるサブキャリは、相互混合ノイズ４０及びその外挿ノイズにより影響を受ける為、光キャリア２０から近い位置にあるサブキャリ程、多値度の低い変調フォーマットを使用することで、更に、ＳＮＲが改善される。   In order to avoid deterioration of signal quality due to an excessively large tilt amount, it is also preferable that the modulation format for each subcarrier is different. Specifically, in the adjacent subcarriers, the multilevel degree of the modulation format of the subcarrier having the high frequency is set to be equal to or higher than the multilevel degree of the modulation format of the subcarrier having the low frequency. Since the sub-carrier located closer to the optical carrier 20 is affected by the mutual mixing noise 40 and its extrapolated noise, the sub-carrier located closer to the optical carrier 20 uses a modulation format with a lower multi-level, Furthermore, the SNR is improved.

本発明による光伝送装置の送信側のブロック図である。It is a block diagram of the transmission side of the optical transmission apparatus according to the present invention. 光伝送装置が送信する光信号の概略的な光スペクトルを示す図である。It is a figure which shows the schematic optical spectrum of the optical signal which an optical transmission apparatus transmits. 本発明による光伝送装置の受信のブロック図である。It is a block diagram of reception of the optical transmission apparatus by this invention. 受信側の光フィルタが出力する光信号の概略的なスペクトラムを示す図である。It is a figure which shows the schematic spectrum of the optical signal which the optical filter of the receiving side outputs. キャリア対信号比に対する誤り率を示す図である。It is a figure which shows the error rate with respect to a carrier to signal ratio. 光ＳＳＢ−ＯＦＤＭ信号の概略的なスペクトラム図である。It is a schematic spectrum figure of an optical SSB-OFDM signal. 図６に示す光信号を電気信号に変換した場合の概略的なスペクトラム図である。FIG. 7 is a schematic spectrum diagram when the optical signal shown in FIG. 6 is converted into an electrical signal.

符号の説明Explanation of symbols

１ 変調部
２、８ 周波数変換部
３ 光信号生成部
４ 光変調部
５、６ 光フィルタ
７ 光電気変換部
９ 復調部
２０ 光キャリア
３０ 側波帯
４０ 相互混合ノイズ
５０ 変調電気信号 DESCRIPTION OF SYMBOLS 1 Modulation part 2, 8 Frequency conversion part 3 Optical signal generation part 4 Optical modulation part 5, 6 Optical filter 7 Photoelectric conversion part 9 Demodulation part 20 Optical carrier 30 Sideband 40 Mutual mixing noise 50 Modulation electric signal

Claims (4)

複数のサブキャリアに対応する側波帯を含む光信号を受信する光伝送装置であって、
前記光信号に含まれる側波帯の波形整形を行う手段と、
波形整形後の光信号を電気信号に変換する手段と、
を備えており、
波形整形は、上側側波帯については周波数が高いほど光パワーを減少させ、下側側波帯については周波数が低いほど光パワーを減少させる、
光伝送装置。 An optical transmission device that receives an optical signal including sidebands corresponding to a plurality of subcarriers,
Means for shaping a waveform of a sideband included in the optical signal;
Means for converting the optical signal after waveform shaping into an electrical signal;
With
Waveform shaping reduces the optical power as the frequency is higher for the upper sideband, and decreases the optical power as the frequency is lower for the lower sideband.
Optical transmission device. 前記光信号は、片側側波帯光信号である、請求項１に記載の光伝送装置。   The optical transmission device according to claim 1, wherein the optical signal is a one-sideband optical signal. 送信側光伝送装置において、
光キャリア信号を、複数のサブキャリアを含む電気信号で変調し、複数のサブキャリアに対応する側波帯を含む光信号を生成するステップと、
生成した光信号を送信するステップと、
受信側光伝送装置において、
前記光信号に含まれる側波帯の波形整形を行うステップと、
波形整形後の光信号を電気信号に変換するステップと、
を備えており、
波形整形は、上側側波帯については周波数が高いほど光パワーを減少させ、下側側波帯については周波数が低いほど光パワーを減少させる、
光伝送方法。 In the transmission side optical transmission device,
Modulating an optical carrier signal with an electrical signal including a plurality of subcarriers to generate an optical signal including sidebands corresponding to the plurality of subcarriers;
Transmitting the generated optical signal; and
In the receiving side optical transmission device,
Performing waveform shaping of sidebands included in the optical signal;
Converting the optical signal after waveform shaping into an electrical signal;
With
Waveform shaping reduces the optical power as the frequency is higher for the upper sideband, and decreases the optical power as the frequency is lower for the lower sideband.
Optical transmission method. 隣接するサブキャリアにおいて、周波数の高いサブキャリアの変調フォーマットの多値度は、周波数の低いサブキャリアの変調フォーマットの多値度以上である、
請求項３に記載の方法。 In adjacent subcarriers, the multi-level of the modulation format of the high-frequency sub-carrier is greater than the multi-level of the modulation format of the low-frequency sub-carrier.
The method of claim 3.
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