JP2005277713A - Optical transmission system and optical receiver for the same - Google Patents

Optical transmission system and optical receiver for the same Download PDF

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JP2005277713A
JP2005277713A JP2004087167A JP2004087167A JP2005277713A JP 2005277713 A JP2005277713 A JP 2005277713A JP 2004087167 A JP2004087167 A JP 2004087167A JP 2004087167 A JP2004087167 A JP 2004087167A JP 2005277713 A JP2005277713 A JP 2005277713A
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Mitsuru Otani
満 大谷
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Toshiba Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/40—Transceivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
    • H04B10/25752—Optical arrangements for wireless networks
    • H04B10/25758—Optical arrangements for wireless networks between a central unit and a single remote unit by means of an optical fibre
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
    • H04B10/25752—Optical arrangements for wireless networks
    • H04B10/25753—Distribution optical network, e.g. between a base station and a plurality of remote units

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Communication System (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission system capable of simply and effectively suppressing deterioration in signal quality due to multiple reflection, and to provide an optical transmission apparatus for the system. <P>SOLUTION: An optical transmitter OT down-converts a main signal 1 to generate a low frequency signal and composes the low frequency signal with the main signal 1 to suppress a beat noise component. When the main signal 1 is e.g., a wireless frequency signal modulated by the CDM system, since the main signal 1 substantially has a random waveform, the waveform of the low frequency signal is inevitably irregular. Thus, it is possible to effectively suppress a spurious wave component caused by multiple reflection even on the occurrence of the multiple reflection. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、無線信号などのアナログ信号で変調した光信号を光ファイバを介して伝送する光伝送システムと、この光伝送システムに用いられる光送信装置に関する。特に本発明は、ＩＭＴ−２０００などの移動通信システムの無線区間に使用される無線周波数信号により光信号を強度変調して伝送する光伝送システムに関する。   The present invention relates to an optical transmission system that transmits an optical signal modulated with an analog signal such as a radio signal via an optical fiber, and an optical transmitter used in the optical transmission system. In particular, the present invention relates to an optical transmission system in which an optical signal is intensity-modulated and transmitted by a radio frequency signal used in a radio section of a mobile communication system such as IMT-2000.

近年、アナログの信号をアナログのまま伝送する通信システムが見直されている。なかでも光ファイバを用いた光アナログ伝送システムが注目されている。光ファイバを用いることで、広帯域伝送を効率良く実現することができる。この種のシステムは、例えば携帯電話網における中継システムとして、あるいはＣＡＴＶ（Cable Television）ネットワークなどに適用される。   In recent years, communication systems that transmit analog signals as analog have been reviewed. In particular, an optical analog transmission system using an optical fiber is attracting attention. By using an optical fiber, broadband transmission can be realized efficiently. This type of system is applied, for example, as a relay system in a mobile telephone network or in a CATV (Cable Television) network.

この種の光伝送システムにおいては、いわゆるダークファイバと称される既設の光ファイバ伝送路が利用されることが多い。ダークファイバは、ネットワークベンダ（システム提供者など）からユーザ（通信事業者など）に規定の料金で貸し出される。ユーザはダークファイバに支線ファイバを接続して独自のネットワークを構築する。光ファイバは、融着、あるいはコネクタなどの光部品による接合により互いに接続される。   In this type of optical transmission system, an existing optical fiber transmission line called a so-called dark fiber is often used. The dark fiber is rented from a network vendor (such as a system provider) to a user (such as a telecommunications carrier) at a specified fee. The user connects the branch fiber to the dark fiber and constructs a unique network. The optical fibers are connected to each other by fusion bonding or joining by optical parts such as connectors.

ところで、光ファイバの接合部分では光信号が反射しやすい。反射成分がごく僅かであっても反射が繰り返されることにより、いわゆる多重反射が生じる。この現象を生じると伝送光にノイズ成分が混入して伝送品質が劣化するため、何らかの対策を要する。   By the way, an optical signal is likely to be reflected at the joint of the optical fiber. Even if the reflection component is very small, so-called multiple reflection occurs due to repeated reflection. When this phenomenon occurs, noise components are mixed into the transmitted light and transmission quality deteriorates, so some countermeasure is required.

特許文献１には、レーザ出力光の周波数を低周波により変調（チャーピング）してレーザ出力光のスペクトルを拡大し、無線周波数出力内に含まれる雑音および歪みが情報帯域の外側に押し出されるようにして信号品質の劣化を抑制できるようにした雑音および歪み抑制装置が開示される。
特開平６−１０４８４３号公報 In Patent Document 1, the frequency of laser output light is modulated (chirped) with a low frequency to expand the spectrum of laser output light, and noise and distortion included in the radio frequency output are pushed out of the information band. Thus, a noise and distortion suppression apparatus capable of suppressing deterioration of signal quality is disclosed.
JP-A-6-104843

以上述べたように、伝送主信号に低周波信号を重畳することにより伝送品質の劣化を防止する技術が提供されているが、信号発生器が必要となるなど、さらに改良の余地がある。特に上記特許文献１には単純な正弦波を用いるよりもランダムな波形を持つ信号を使用するほうがより効果的であることが説明されているが、その具体的な実現手法は述べられていない。
本発明は上記事情によりなされたもので、その目的は、多重反射による信号品質の劣化を簡易かつ効果的に抑制できるようにした光伝送システムとその光送信装置を提供することにある。 As described above, there is provided a technique for preventing deterioration in transmission quality by superimposing a low-frequency signal on a transmission main signal, but there is room for further improvement such as the need for a signal generator. In particular, Patent Document 1 describes that it is more effective to use a signal having a random waveform than to use a simple sine wave, but a specific method for realizing it is not described.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical transmission system and an optical transmission device thereof that can easily and effectively suppress deterioration of signal quality due to multiple reflection.

上記目的を達成するために本発明の一態様によれば、光信号を光ファイバに送出する光送信装置と、前記光ファイバを介して伝送される光信号を受信する光受信装置とを具備する光伝送システムにおいて、前記光送信装置は、不規則な波形パターンを有する無線周波数帯域の主信号を２つに分配する分配手段と、前記分配された一方の主信号を前記無線周波数帯域よりも帯域の低い低帯域信号にダウンコンバートする周波数変換手段と、前記分配された他方の主信号に前記低帯域信号を合成する合成手段と、この合成手段により前記低帯域信号の合成された主信号を電気／光変換して前記光ファイバに送出する電気／光変換手段とを備え、前記光受信装置は、前記光ファイバを介して到来する光信号を電気信号に変換する光／電気変換手段と、この変換された電気信号から前記低帯域信号を除去するハイパスフィルタとを備えることを特徴とする光伝送システムが提供される。   In order to achieve the above object, according to one aspect of the present invention, an optical transmission device that transmits an optical signal to an optical fiber and an optical reception device that receives an optical signal transmitted through the optical fiber are provided. In the optical transmission system, the optical transmission device includes a distribution unit that distributes a main signal in a radio frequency band having an irregular waveform pattern to two, and the one main signal that has been distributed in a band more than the radio frequency band. Frequency converting means for down-converting to a low-band signal having a low frequency, synthesizing means for synthesizing the low-band signal with the other distributed main signal, and the synthesized main signal of the low-band signal by the synthesizing means. An optical / electrical conversion means for converting the optical signal and sending it to the optical fiber, wherein the optical receiver is an optical / electrical conversion means for converting an optical signal arriving via the optical fiber into an electrical signal; Optical transmission system characterized by comprising a high pass filter for removing the low-band signal from the converted electric signal.

このような手段を講じることにより、伝送すべき主信号にはランダム波形を持つ低帯域信号が重畳される。これにより、多重反射による不要波成分をより効果的に抑圧することが可能となる。しかも低帯域信号は、ランダム波形を持つ主信号それ自体をダウンコンバートすることにより生成される。主信号をダウンコンバートするには例えば低周波の正弦波信号を主信号の分岐信号に乗算するだけで良く、ランダム波形発生器などのような複雑な機構を必要としない。   By taking such means, a low-band signal having a random waveform is superimposed on the main signal to be transmitted. This makes it possible to more effectively suppress unnecessary wave components due to multiple reflection. Moreover, the low-band signal is generated by down-converting the main signal itself having a random waveform. In order to down-convert the main signal, for example, a low-frequency sine wave signal only needs to be multiplied by the branch signal of the main signal, and a complicated mechanism such as a random waveform generator is not required.

すなわち近年の無線通信では、主信号の変調方式として、ＣＤＭに代表されるスペクトラム拡散方式が採用される。本発明ではこの方式に基づく主信号がランダム性を持つことに着目し、主信号を低帯域信号に周波数変換して主信号と重畳するようにしている。これにより主信号をランダム波形で変調することができ、多重反射による信号品質の劣化を簡易かつ効果的に抑制することが可能になる。   That is, in recent wireless communication, a spread spectrum system represented by CDM is adopted as a main signal modulation system. In the present invention, focusing on the fact that the main signal based on this method has randomness, the main signal is frequency-converted into a low-band signal and superimposed on the main signal. As a result, the main signal can be modulated with a random waveform, and deterioration of signal quality due to multiple reflection can be easily and effectively suppressed.

本発明によれば、多重反射による信号品質の劣化を簡易かつ効果的に抑制できるようにした光伝送システムとその光送信装置を提供することができる。   ADVANTAGE OF THE INVENTION According to this invention, the optical transmission system which enabled it to suppress the signal quality degradation by multiple reflection easily and effectively, and its optical transmitter can be provided.

図１は、本発明に係わる光伝送システムの実施の形態を示すシステム図である。図１のシステムは、例えば携帯電話網などの移動通信システムを補助するために設けられ、基地局４０の展開するサービスエリアを光ファイバ３を用いて拡大するものである。この種のシステムはＲＯＦ（Radio Over Fiber）システムと称して知られている。この種の光アナログ伝送システムにおいては、光ファイバは、ネットワークベンダ（システム提供者など）からユーザ（通信事業者など）に規定の料金で貸し出される。ユーザは光ファイバに支線ファイバを接続して独自のネットワークを構築する。光ファイバは、融着、あるいはコネクタなどの光部品による接合により互いに接続される。   FIG. 1 is a system diagram showing an embodiment of an optical transmission system according to the present invention. The system of FIG. 1 is provided to assist a mobile communication system such as a cellular phone network, and expands the service area developed by the base station 40 using the optical fiber 3. This type of system is known as a ROF (Radio Over Fiber) system. In this type of optical analog transmission system, an optical fiber is rented from a network vendor (system provider or the like) to a user (communication company or the like) at a specified fee. The user connects the branch line fiber to the optical fiber and constructs a unique network. The optical fibers are connected to each other by fusion bonding or joining by optical parts such as connectors.

図１において、基地局４０は同軸ケーブルＣを介して親局装置２０に接続される。親局装置２０は、基地局４０から送信される無線周波数信号の一部を同軸ケーブルＣを介して取得する。親局装置２０は光ファイバ３を介して子局装置３０に接続される。なお親局装置２０と子局装置３０との間に光中継装置５０を設けても良い。無線周波数信号は、移動通信システムの無線区間通信に使用される帯域を有し、例えばスペクトラム拡散変調方式の一つであるＣＤＭ（Code Division Multiplex）などの方式に基づいて変調される。その波形パターンは時間とともに不規則に変化する。   In FIG. 1, a base station 40 is connected to the master station device 20 via a coaxial cable C. The master station device 20 acquires a part of the radio frequency signal transmitted from the base station 40 via the coaxial cable C. The master station device 20 is connected to the slave station device 30 via the optical fiber 3. An optical repeater 50 may be provided between the master station device 20 and the slave station device 30. The radio frequency signal has a band used for radio section communication of the mobile communication system, and is modulated based on a scheme such as CDM (Code Division Multiplex) which is one of spread spectrum modulation schemes. The waveform pattern changes irregularly with time.

基地局４０および移動局Ｔ１，Ｔ２は、例えばＩＭＴ−２０００に基づく移動通信システムに属する。基地局４０は例えば見晴らしの良いビル（ビル１００）の屋上などに設置されて無線ゾーンを展開する。無線ゾーン内に在圏する移動局Ｔ１は、このシステムに割り当てられたキャリア帯域の無線チャネルを介して基地局４０に接続される。   The base station 40 and the mobile stations T1, T2 belong to a mobile communication system based on, for example, IMT-2000. The base station 40 is installed on the rooftop of a building (building 100) with a good view, for example, and develops a wireless zone. The mobile station T1 located in the radio zone is connected to the base station 40 via a radio channel of a carrier band assigned to this system.

ビル１００の傍に高層ビル（ビル２００）が建設されたとすると、その直下などにおいては基地局４０からの無線周波数信号が届かず、不感地帯が形成されることがある。そこで子局装置３０を設け、光ファイバ３を介して基地局４０と子局装置３０との間に情報通信路を開設することにより不感地帯を解消することができる。このほか子局装置３０は、ビルの中などにも設置され、不感地帯の解消に役立てられる。   If a high-rise building (building 200) is constructed near the building 100, a radio frequency signal from the base station 40 does not reach immediately below the building 100, and a dead zone may be formed. Therefore, the dead zone can be eliminated by providing the slave station device 30 and opening an information communication path between the base station 40 and the slave station device 30 via the optical fiber 3. In addition, the slave station device 30 is installed in a building or the like, and is used to eliminate the dead zone.

図２は、本発明に係わる光送信装置および光受信装置の実施の形態を示す機能ブロック図である。図２の光送信機ＯＴは図１の親局装置２０に備えられ、光受信機ＯＲは子局装置３０に備えられるとする。すなわち図２はダウンリンクにおける構成を示す。アップリンクにおいては光送信機ＯＴは子局装置３０に備えられ、光受信機ＯＲは親局装置２０に備えられることになる。通常のシステムではアップリンクおよびダウンリンクの双方向通信を実現するため、親局装置２０および子局装置３０のいずれも光送信機ＯＴおよび光受信機ＯＲを備える。   FIG. 2 is a functional block diagram showing an embodiment of an optical transmitter and an optical receiver according to the present invention. The optical transmitter OT in FIG. 2 is provided in the master station device 20 in FIG. 1, and the optical receiver OR is provided in the slave station device 30. That is, FIG. 2 shows a configuration in the downlink. In the uplink, the optical transmitter OT is provided in the slave station device 30, and the optical receiver OR is provided in the master station device 20. In a normal system, both the master station device 20 and the slave station device 30 include an optical transmitter OT and an optical receiver OR in order to realize uplink and downlink bidirectional communication.

図２において、スペクトラム拡散変調された無線周波数信号は基地局４０（図１）から光送信機ＯＴに導入される。以下、この無線周波数信号に符号１を付し、主信号１と称する。主信号１は分配器２５により２系統に分配される。分配された一方の主信号１ａは乗算器２７により、正弦波発振器２８で発生されたローカル周波数信号と乗算される。これにより主信号１ａはダウンコンバートされ、主信号１の波形を反映するランダムパターンを持つ低周波信号が生成される。なお主信号の帯域が数ギガヘルツ帯域である場合、低周波信号の帯域は数〜数１０メガヘルツ帯域とするのが好ましい。   In FIG. 2, the spread spectrum modulated radio frequency signal is introduced from the base station 40 (FIG. 1) to the optical transmitter OT. Hereinafter, the radio frequency signal is denoted by reference numeral 1 and is referred to as a main signal 1. The main signal 1 is distributed to two systems by the distributor 25. One of the distributed main signals 1 a is multiplied by a local frequency signal generated by a sine wave oscillator 28 by a multiplier 27. As a result, the main signal 1a is down-converted, and a low-frequency signal having a random pattern that reflects the waveform of the main signal 1 is generated. When the main signal band is several gigahertz, the low frequency signal band is preferably several to several tens of megahertz.

この低周波信号は合成器２６により、分配された他方の主信号１ｂと周波数合成される。これにより主信号１は、ランダムな波形を持つ低周波信号により強度変調されることになる。変調された主信号１はＬＤモジュール２の発光素子３１により光信号に変換されて光ファイバ３に送出される。すなわち光ファイバ３には、主信号１により強度変調（Amplitude Modulation：ＡＭ）された光信号が送出される。   This low frequency signal is frequency synthesized with the other distributed main signal 1b by a synthesizer 26. As a result, the main signal 1 is intensity-modulated by a low-frequency signal having a random waveform. The modulated main signal 1 is converted into an optical signal by the light emitting element 31 of the LD module 2 and transmitted to the optical fiber 3. That is, an optical signal that has been subjected to intensity modulation (AM) by the main signal 1 is transmitted to the optical fiber 3.

この光信号は光ファイバ３を介して光受信機ＯＲに達し、光／電気変換部（Ｏ／Ｅ）４に入力され、光／電気変換部４の受光素子３２により電気信号に変換される。この電気信号はハイパスフィルタ２４に入力される。ハイパスフィルタ２４は電気信号に含まれる、低周波信号成分を除去する。これにより無線周波数帯域の主信号６が再生される。次に、上記構成における作用を説明する。   This optical signal reaches the optical receiver OR through the optical fiber 3, is input to the optical / electrical converter (O / E) 4, and is converted into an electrical signal by the light receiving element 32 of the optical / electrical converter 4. This electrical signal is input to the high pass filter 24. The high pass filter 24 removes a low frequency signal component contained in the electric signal. As a result, the main signal 6 in the radio frequency band is reproduced. Next, the operation of the above configuration will be described.

図３は、図２の光送信機ＯＴにおいて使用すべき低周波信号を示す模式図である。図２（ａ）に示されるように、主信号１の周波数をｆ２とすると、既存の技術では周波数ｆ１の低周波信号が用いられる。これに対し本実施形態では、図２（ｂ）に示すように、ランダム波形を持つ信号により低周波信号を変調することにより、低周波信号にある程度の帯域幅を持たせるようにする。   FIG. 3 is a schematic diagram showing a low-frequency signal to be used in the optical transmitter OT of FIG. As shown in FIG. 2A, when the frequency of the main signal 1 is f2, in the existing technology, a low frequency signal having the frequency f1 is used. On the other hand, in the present embodiment, as shown in FIG. 2B, the low frequency signal is modulated with a signal having a random waveform so that the low frequency signal has a certain bandwidth.

図４は低周波信号により変調された主信号１を示す模式図である。図示されるように本実施形態では低周波信号がある程度の幅を持つため、低周波信号により変調された主信号１の帯域も広がることになる。   FIG. 4 is a schematic diagram showing the main signal 1 modulated by the low frequency signal. As shown in the figure, since the low frequency signal has a certain width in this embodiment, the band of the main signal 1 modulated by the low frequency signal is also widened.

図５は、既存の技術において光ファイバ３に多重反射が生じた場合のスペクトラムの実験結果を示す図である。図５においては単純な正弦波波形を持つ低周波信号を用いており、このような信号においては主信号１と反射光との相関の度合いが比較的高い。このことからビート雑音のスペクトラムが大きくなり、これはそのまま伝送雑音として作用する。   FIG. 5 is a diagram illustrating a spectrum experiment result when multiple reflection occurs in the optical fiber 3 in the existing technology. In FIG. 5, a low frequency signal having a simple sine wave waveform is used, and in such a signal, the degree of correlation between the main signal 1 and the reflected light is relatively high. This increases the spectrum of beat noise, which acts as transmission noise as it is.

図６は、本実施形態において光ファイバ３に多重反射が生じた場合のスペクトラムの実験結果を示す図である。図６においてはランダム波形から生成した低周波信号を用いている。この低周波信号は図５に比べて広い帯域幅を持ち、これにより主信号１と反射光との相関度が低い。このことから、図示されるように、ビート雑音成分が平均化され、結果として不要波成分が抑圧される。   FIG. 6 is a diagram showing an experimental result of spectrum when multiple reflection occurs in the optical fiber 3 in the present embodiment. In FIG. 6, a low frequency signal generated from a random waveform is used. This low-frequency signal has a wider bandwidth than that in FIG. 5, and thus the degree of correlation between the main signal 1 and the reflected light is low. From this, as shown in the figure, beat noise components are averaged, and as a result, unnecessary wave components are suppressed.

図７は、比較のため既存の技術における光伝送システムを示すシステム図である。このシステムは、光送信機ＯＴに信号発生器２９を備え、この信号発生器２９により生成した信号を合成器２２により主信号１に直接合成するようになっている。信号発生器２９によりランダム波形を持つ信号を生成するには複雑な変調回路などが必要になり、回路規模の拡大や高コスト化などの弊害を生じる。逆に、シンプルな構成の信号発生器２９を用いた場合にはランダム波形を生成することが困難であり、主信号１と反射光との相関度の高い低周波信号を用いざるを得ないので不要波成分を充分に抑圧することが難しい。   FIG. 7 is a system diagram showing an optical transmission system in the existing technology for comparison. In this system, a signal generator 29 is provided in an optical transmitter OT, and a signal generated by the signal generator 29 is directly combined with a main signal 1 by a combiner 22. In order to generate a signal having a random waveform by the signal generator 29, a complicated modulation circuit or the like is required, which causes problems such as an increase in circuit scale and cost. Conversely, when the signal generator 29 having a simple configuration is used, it is difficult to generate a random waveform, and a low-frequency signal having a high degree of correlation between the main signal 1 and the reflected light must be used. It is difficult to sufficiently suppress unnecessary wave components.

これに対し本実施形態では、光送信機ＯＴにおいて主信号１をダウンコンバートすることにより低周波信号を生成し、この低周波信号を主信号１に合成することによりビート雑音成分を抑圧するようにしている。主信号１が例えばＣＤＭ方式により変調された無線周波数信号であれば、主信号１は本来、ランダムな波形を持つため、低周波信号の波形も必然的に不規則になる。従って、多重反射が生じてもこれにより生じる不要波成分を効果的に抑圧することが可能になる。   On the other hand, in the present embodiment, a low frequency signal is generated by down-converting the main signal 1 in the optical transmitter OT, and the beat noise component is suppressed by synthesizing this low frequency signal with the main signal 1. ing. If the main signal 1 is a radio frequency signal modulated by, for example, the CDM method, the main signal 1 originally has a random waveform, so that the waveform of the low frequency signal is inevitably irregular. Therefore, even if multiple reflection occurs, it is possible to effectively suppress unnecessary wave components caused by this.

しかも本実施形態によれば、主信号１をダウンコンバートすることによってランダムな波形を得ることができる。このための回路は正弦波発振器２８、乗算器２７、および合成器２６など、いずれも単純な手段により実現され、変調器などのような複雑な構成を必要としない。これらのことから、多重反射による信号品質の劣化を簡易かつ効果的に抑制できるようにした光伝送システムとその光送信装置を提供することが可能となる。   Moreover, according to the present embodiment, a random waveform can be obtained by down-converting the main signal 1. The circuit for this purpose is realized by simple means such as the sine wave oscillator 28, the multiplier 27, and the synthesizer 26, and does not require a complicated configuration such as a modulator. From these facts, it becomes possible to provide an optical transmission system and its optical transmission device that can easily and effectively suppress deterioration of signal quality due to multiple reflection.

なお、本発明は上記実施の形態に限定されるものではない。本実施形態においてはダウンリンクで送信する主信号を周波数変換してランダム波形を得るようにした。これに代えて、アップリンクで受信した無線周波数信号を用い、これをダウンコンバートすることによってもランダムな波形の低周波信号を得ることができる。   The present invention is not limited to the above embodiment. In this embodiment, the main signal transmitted on the downlink is frequency-converted to obtain a random waveform. Instead, a low-frequency signal having a random waveform can be obtained by using a radio frequency signal received on the uplink and down-converting it.

さらに、本発明は上記実施形態そのままに限定されるものではなく、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合わせにより、種々の発明を形成できる。例えば、実施形態に示される全構成要素から幾つかの構成要素を削除してもよい。   Furthermore, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

本発明に係わる光伝送システムの実施の形態を示すシステム図。1 is a system diagram showing an embodiment of an optical transmission system according to the present invention. 本発明に係わる光送信装置および光受信装置の実施の形態を示す機能ブロック図。1 is a functional block diagram showing an embodiment of an optical transmitter and an optical receiver according to the present invention. 図２の光送信機ＯＴにおいて使用すべき低周波信号を示す模式図。FIG. 3 is a schematic diagram showing a low frequency signal to be used in the optical transmitter OT of FIG. 2. 低周波信号により変調された主信号１を示す模式図。The schematic diagram which shows the main signal 1 modulated by the low frequency signal. 既存の技術において光ファイバ３に多重反射が生じた場合のスペクトラムの実験結果を示す図。The figure which shows the experimental result of the spectrum when multiple reflection arises in the optical fiber 3 in the existing technique. 本発明の実施の形態において光ファイバ３に多重反射が生じた場合のスペクトラムの実験結果を示す図。The figure which shows the experimental result of the spectrum when multiple reflection arises in the optical fiber 3 in embodiment of this invention. 比較のため既存の技術における光伝送システムを示すシステム図。The system figure which shows the optical transmission system in the existing technique for a comparison.

符号の説明Explanation of symbols

Ｃ…同軸ケーブル、Ｔ１，Ｔ２…移動局、ＯＴ…光送信機、ＯＲ…光受信機、２…ＬＤモジュール、３…光ファイバ、４…光／電気変換部、２０…親局装置、２２…合成器、２４…ハイパスフィルタ、２５…分配器、２６…合成器、２７…乗算器、２８…正弦波発振器、２９…信号発生器、３０…子局装置、３１…発光素子、３２…受光素子、４０…基地局、５０…光中継装置、１００…ビル   C ... Coaxial cable, T1, T2 ... Mobile station, OT ... Optical transmitter, OR ... Optical receiver, 2 ... LD module, 3 ... Optical fiber, 4 ... Optical / electrical converter, 20 ... Master station device, 22 ... Synthesizer, 24 ... high-pass filter, 25 ... distributor, 26 ... synthesizer, 27 ... multiplier, 28 ... sine wave oscillator, 29 ... signal generator, 30 ... slave station device, 31 ... light emitting element, 32 ... light receiving element , 40 ... base station, 50 ... optical repeater, 100 ... building

Claims (4)

光信号を光ファイバに送出する光送信装置と、前記光ファイバを介して伝送される光信号を受信する光受信装置とを具備する光伝送システムにおいて、
前記光送信装置は、
不規則な波形パターンを有する無線周波数帯域の主信号を２つに分配する分配手段と、
前記分配された一方の主信号を前記無線周波数帯域よりも帯域の低い低帯域信号にダウンコンバートする周波数変換手段と、
前記分配された他方の主信号に前記低帯域信号を合成する合成手段と、
この合成手段により前記低帯域信号の合成された主信号を電気／光変換して前記光ファイバに送出する電気／光変換手段とを備え、
前記光受信装置は、
前記光ファイバを介して到来する光信号を電気信号に変換する光／電気変換手段と、
この変換された電気信号から前記低帯域信号を除去するハイパスフィルタとを備えることを特徴とする光伝送システム。 In an optical transmission system comprising: an optical transmitter that transmits an optical signal to an optical fiber; and an optical receiver that receives an optical signal transmitted through the optical fiber.
The optical transmitter is
Distributing means for distributing the main signal of the radio frequency band having an irregular waveform pattern into two;
Frequency converting means for down-converting the distributed one main signal into a low-band signal having a band lower than the radio frequency band;
Combining means for combining the low-band signal with the other distributed main signal;
An electrical / optical converting means for electrically / optically converting the synthesized main signal of the low-band signal by this combining means and sending it to the optical fiber;
The optical receiver is
An optical / electrical conversion means for converting an optical signal arriving through the optical fiber into an electrical signal;
An optical transmission system comprising: a high-pass filter that removes the low-band signal from the converted electrical signal. 前記主信号は、スペクトラム拡散変調方式を用いる移動通信システムの無線区間通信に使用される信号であることを特徴とする請求項１に記載の光伝送システム。 The optical transmission system according to claim 1, wherein the main signal is a signal used for radio section communication of a mobile communication system using a spread spectrum modulation system. 不規則な波形パターンを有する無線周波数帯域の主信号によりアナログ変調された光信号を光伝送路を介して伝送する光伝送システムに使用される光送信装置であって、
前記主信号を２つに分配する分配手段と、
前記分配された一方の主信号を前記無線周波数帯域よりも帯域の低い低帯域信号にダウンコンバートする周波数変換手段と、
前記分配された他方の主信号に前記低帯域信号を合成する合成手段と、
この合成手段により前記低帯域信号の合成された主信号を電気／光変換して前記光ファイバに送出する電気／光変換手段とを具備することを特徴とする光送信装置。 An optical transmitter used in an optical transmission system for transmitting an optical signal analog-modulated by a main signal in a radio frequency band having an irregular waveform pattern through an optical transmission line,
Distributing means for distributing the main signal into two;
Frequency converting means for down-converting the distributed one main signal into a low-band signal having a band lower than the radio frequency band;
Combining means for combining the low-band signal with the other distributed main signal;
An optical transmission apparatus comprising: an electrical / optical conversion unit configured to perform electrical / optical conversion of the main signal synthesized from the low-band signal by the synthesis unit and send the converted signal to the optical fiber. 前記主信号は、スペクトラム拡散変調方式を用いる移動通信システムの無線区間通信に使用される信号であることを特徴とする請求項３に記載の光送信装置。 4. The optical transmission apparatus according to claim 3, wherein the main signal is a signal used for radio section communication in a mobile communication system using a spread spectrum modulation system.
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