JP4053266B2

JP4053266B2 - Optical fiber core wire contrast method and apparatus

Info

Publication number: JP4053266B2
Application number: JP2001257899A
Authority: JP
Inventors: 智渡辺; 文彦山本; 孝二荒川
Original assignee: Nippon Telegraph and Telephone East Corp
Current assignee: Nippon Telegraph and Telephone East Corp
Priority date: 2001-08-28
Filing date: 2001-08-28
Publication date: 2008-02-27
Anticipated expiration: 2021-08-28
Also published as: JP2003065894A

Description

【０００１】
【発明の属する技術分野】
本発明は、光ファイバ心線対照方法及び装置に関する。
【０００２】
【従来の技術】
近年、シングルモード光ファイバを用い、波長1.31μｍ帯及び1.55μｍ帯の通信光による波長多重方式を用いたサービスの導入が拡大されている。そのサービスを提供するために使用している光ファイバに故障修理や回線切替が発生した場合、即応性を確保する上で、運用中の回線についてサービスに影響を与えず、光回線の心線対照が行える方法が必要となる。
【０００３】
図３は、運用中回線として使用している光ファイバ３，３，３，…（ただし図示は対照試験対象の１本のみ）の心線対照を実施するための光線路構成の概略図である。運用中回線として使用している光ファイバ３の心線対照を実施しようとした場合、対照すべき光ファイバ３に、局内装置１を有する通信設備ビル側から、心線対照器光源部９によって発生した、通信光１３と異なった波長1.615μｍ〜1.675μｍの範囲の心線対照光１４を光カプラ２を介して入射する。一方、作業現場においては、心線対照器曲げ部１０により、光ファイバ３に曲げ半径12.5〜13.0ｍｍの曲げ３ａを加える。そして、その曲げ３ａによる心線対照光の放射光１１を心線対照器曲げ部１０に付属する所定の受光素子からなる受信機１２で検知する。これらの構成によって心線対照が行われている。
【０００４】
上記曲げ半径は、曲げによる伝送品質の劣化を最小にし、且つ心線対照装置が心線対照光を検知可能とする条件を同時に満足するために定められている。この方法は、山本他、特開平06-221958号公報「光ファイバ心線対照装置」で既知である。該方法では、前述のとおり心線対照光波長が通信光波長と異なるように波長配置されている。
【０００５】
更に、加入者端末７の入力部に透過特性に関し、波長依存性を有する心線対照光遮断型光フィルタ８を挿入することにより、たとえ運用中回線に心線対照光を入射してもサービス品質を劣化させることなく運用中回線の心線対照が実現されている。この場合、加入者端末７は、光ファイバ３を介して光信号を受信して電気信号に変換する光受信機４と、通信光１３の変調周波数に対応する帯域透過特性を有する帯域フィルタ５と、帯域フィルタ５から出力された電気信号を受信して復調する受信機６とから構成されている。
【０００６】
【発明が解決しようとする課題】
現在の心線対照方法においては、心線対照光遮断型光フィルタ８が対照すべき光ファイバ３に設置されていない場合、心線対照光１４と通信光１３は同時に加入者端末７に内蔵された光受信機４で受光される。心線対照光１４は通信光１３と共に電気信号に変換される。図４に変換後の受信信号スペクトルの模式図を示す。本図が示すように、たとえ心線対照光１４が通信光１３とは異なる波長を有していても通信信号と心線対照信号の重畳が生じ、この重畳周波数成分が雑音となり通信に影響を与えてしまう。このことを詳細に説明すると次のようになる。
【０００７】
心線対照光１４が通信光１３と比較して十分に低速で、且つパルス変調されていると仮定する。この時、心線対照光１４が加入者端末７に入射された場合の符号誤り率（BER）は以下の式で与えられる。
【数１】

ここで、S_Dは通信光１３の等価入力信号電流、σ₀ ²は通信光１３のみが加入者端末７に入射されているときの加入者端末７での等価入力雑音電流の全分散、S_IDは心線対照光１４の等価入カピーク電流、σ₁ ²は通信光１３と心線対照光１４が同時に加入者端末７に入射されている時の加入者端末７での等価入力雑音電流、erfc（x）は補誤差関数であり、
【数２】

で定義される。
【０００８】
また、通信光１３の受光平均パワをP_S、心線対照光１４の平均受光パワをP_ID、加入者端末７までの通信光１３の変換効率をρ_S、心線対照光１４の変換効率をρ_IDとすると、通信光１３と心線対照光１４の等価入力電流はそれぞれ、
【数３】

で与えられる。
【０００９】
式（１）を用いて、心線対照光１４の受光パワに依存したBER劣化を見積った結果を図５において点線で示す。ここでは、等価入力雑音電流の全分散に関し、心線対照光による増加分をショット雑音のみと仮定した。参考文献（ITU-T. Recommendation G.983.1,“Broadband optical access systems based on Passive Optical Networks（PON）,”1988）に従い、S_D ²/σ₀ ²＝22dB、P_S＝−33dBmとした。BER＜10^-9を満足しようとした場合、心線対照光１４の平均受光パワP_IDは−51dBm以下とする必要があることが分かる。例えば加入者端末７の入力部において心線対照光平均受光パワが−35dBmの場合、運用中回線の心線対照を実現するため、１６ｄＢ以上の遮断量を有する心線対照光遮断型光フィルタ８を挿入する必要がある。
【００１０】
しかし、心線対照光遮断型光フィルタ８の挿入は、光フィルタ固有の損失により、光線路全体の線路損失が増加し、光通信方式の適用距離を制限してしまうという欠点を有している。また、光フィルタの設置により、光通信システムで使用する光線路全体の高コスト化に繋がるという問題があった。
【００１１】
そこで本発明には、上記の事情を考慮し、従来に比べ低コストで、また光通信方式の適用距離の制限を改善することができる光ファイバ心線対照方法及び装置を提供することを目的とする。
【００１２】
【課題を解決するための手段】
上記課題を解決するため、請求項１記載の発明は、局内装置と加入者端末との間に設けられた光ファイバの心線対照を行うための心線対照方法において、前記局内装置側から被試験対象となる前記加入者端末への光ファイバに対して心線対照光を入力する際に、前記入力する心線対照光の変調周波数を、前記局内装置と前記加入者端末間の通信信号の変調周波数に対して、該通信信号の変調周波数の周波数帯域外で、かつ前記通信信号の変調周波数の周波数帯域と前記心線対照光の変調周波数の周波数帯域とに重畳が生じないように、かつ前記加入者端末に予め内蔵されている前記通信信号を抽出するための帯域フィルタによって、前記通信信号の変調周波数と前記心線対照光の変調周波数とのうち、前記心線対照光の変調周波数のみが遮断されるように周波数配置することを特徴とする。請求項２記載の発明は、前記局内装置と加入者端末との間に設けられた光ファイバを複数の光ファイバの中から選別する心線対照光受信装置が、前記心線対照光を受信する際に、前記心線対照光の変調周波数成分のみを透過する所定の帯域フィルタを用いて前記心線対照光に対応する信号を復調することを特徴とする。
【００１３】
請求項３記載の発明は、局内装置と加入者端末との間に設けられた光ファイバの心線対照を行うための心線対照装置において、前記局内装置と前記加入者端末間の通信信号の変調周波数の周波数帯域外であって、かつ前記通信信号の周波数帯域と重畳が生じない周波数帯域を有し、かつ前記加入者端末に内蔵された前記通信信号を抽出するための帯域フィルタによって遮断される周波数帯域内に、変調周波数を有する心線対照光を発生する心線対照光発生手段と、前記心線対照光発生手段によって発生された心線対照光を被試験対象となる前記加入者端末への光ファイバに入射する光カプラと、前記光ファイバを介して送られてくる心線対照光を受信して、前記局内装置と加入者端末との間に設けられた光ファイバを複数の光ファイバの中から選別する心線対照光受信手段とを備えることを特徴とする。請求項４記載の発明は、前記心線対照光受信手段が、前記心線対照光の変調周波数成分のみを透過する所定の帯域フィルタを有していることを特徴とする。
【００１４】
【発明の実施の形態】
以下、図面を参照して本発明の実施の形態について説明する。図１は、本発明による心線対照を実施するための光線路構成の概略図である。図２は、図１に示す帯域フィルタ１９の透過帯域と、心線対照光源部１７の変調周波数との配置を示す図である。なお、図１では、図３に示すものと同一の構成には同一の符号を付けている。
【００１５】
図１において、信号発生器１６により通信信号対域外の周波数ｆｃに周波数変調された心線対照光１５が、心線対照器光源部１７より光カプラ２を介して対照すべき光ファイバ３に入射される。作業現場で心線対照器曲げ部２１により光ファイバ３に曲げ３ａを加えることにより、光ファイバ３中の光が放射される。放射光１１は心線対照器曲げ部２に付属する受光部１８にて受信され、電気信号に変換される。本実施形態では、心線対照器曲げ部２１に心線対照光１５の変調周波数成分（周波数ｆｃ）を透過帯域とする帯域フィルタ１９を具備することにより、たとえ心線対照光１５と通信光１３が同時に放射されても、心線対照光１５の変調周波数成分のみが、心線対照器曲げ部２１の受信機２０で受信可能となる。これにより、作業現場にて光ファイバケーブル２２に収容されている多くの運用中の光ファイバ３，３，３，…から、対照すべき光ファイバ３の心線対照が可能となる。
【００１６】
一方、心線対照器光源部１７の変調周波数ｆｃは、図２に示すように、通信信号帯域外に周波数配置されているため、たとえ図３に示すような心線対照光遮断型光フィルタ８が未設置で、その心線対照光１５が加入者端末７の光受信機４に入射されても、加入者端末に予め内蔵された帯域フィルタ５によって、変調周波数成分ｆcは遮断されるためサービス品質は劣化せず、運用中回線の心線対照が可能となる。
【００１７】
上述したように、本実施形態では、光ファイバケーブルの心線対照を行うための光源部（信号発生器１６、心線対照器光源部１７、光カプラ２）と曲げ部（心線対照器曲げ部２１）で構成される光ファイバ心線対照器において、心線対照光１５の変調周波数ｆｃを通信信号帯域外に周波数配置する（図１参照）。また、光ファイバ３からの放射光１１を受信する心線対照器曲げ部２１に付属する受光部１８に心線対照光１５の有する変調周波数成分のみ透過する帯域フィルタ１９を具備する。これら２つの手段を光ファイバ心線対照器に施すことにより、心線対照光遮断型光フィルタ８を必要としない運用中回線の心線対照が実現可能となる。
【００１８】
すなわち、上記の構成によれば、心線対照光１５の変調周波数が、局内装置１と加入者端末７間の通信光１３（通信信号）の変調周波数帯域外であって、加入者端末７に内蔵された帯域フィルタ５によって遮断される周波数帯域内に設定される。つまり、心線対照器光源部１７を使用し、図２に示すように通信信号と心線対照信号とを周波数多重することにより、たとえ心線対照信号光１５が通信光１３と同時に加入者端末７へ入射しても、心線対照信号光１５の変調周波数に対応する周波数成分が、通信光１３の変調周波数に対応する帯域透過特性を有する帯域フィルタ５によって減衰（遮断）されるので、サービスの品質劣化を防ぐことが可能となる。このことを詳細に説明すると次のようになる。
【００１９】
心線対照光１５が通信光１３と比較して十分高速で変調されていると仮定する。この時、心線対照光１５が加入者端末７に入射された場合の符号誤り率BERは以下の式で与えられる。
【数４】

【００２０】
ここで、σ₂ ²は通信光１３と心線対照光１５とが同時に加入者端末７に入射されたときの等価雑音電流の全分散であり、心線対照光１５が正弦波変調されていると仮定するとσ₂ ²は以下の式で与えられる。
【数５】

【００２１】
ここで、σ² _Shotは心線対照光によるショット雑音電流、Ｋは加入者端末７に内蔵されている帯域フィルタ５の心線対照光変調周波数における透過率、ＯＭＩは心線対照光１５の光変調度を示す。図５において示された実線は式（５）を用い、K＝10^-3、ＯＭＩ＝35％のときのBER特性を示す。本図が示すように、心線対照光１５の変調周波数を通信信号帯域外に周波数配置することにより、許容受光パワが17dB増加することが分かる。この許容受光パワの増加により、心線対照光遮断型光フィルタ８を必要としない、運用中回線の心線対照が実現可能となる。
【００２２】
なお、本発明の実施の形態は、上記の形態に限定されることなく、例えば、帯域フィルタ１９に代えて変調周波数ｆｃより低い周波数帯域の成分を減衰させる高域フィルタを用いるようにすることなどの変更を適宜行うことができる。
【００２３】
【発明の効果】
本発明によれば、運用中回線の光線路において、通常、加入者端末近傍に設置される心線対照光遮断型光フィルタが未設置の場合でも、サービス品質を劣化させることなく心線対照を行うことを可能にすることから、光通信方式に使用される光線路の低損失化、光線路設備構築のためのコストの削減が図られる。
【図面の簡単な説明】
【図１】本発明による心線対照を実施するための光線路構成の概略図。
【図２】図１に示す帯域フィルタ１９の透過帯域と、心線対照光源部１７の変調周波数との配置を示す図。
【図３】従来の心線対照を実施するための光線路構成の概略図。
【図４】図３の構成における受信信号スペクトルを示す模式図。
【図５】本発明および従来例における心線対照光の加入者端末における平均受光パワと符号誤り率BER特性との関係を示す図。
【符号の説明】
１：局内装置
２：光カプラ
３：光ファイバ（被試験光ファイバ）
４：光受信機
５：帯域フィルタ
６：受信機
７：加入者端末
８：心線対照光遮断型光フィルタ
９，１７：心線対照器光源部
１０，２１：心線対照器曲げ部
１１：放射光（心線対照光あるいは通信光）
１２，２０：受光部
１３：通信光
１４，１５：心線対照光
１６：信号発生器
１８：受光部
１９：帯域フィルタ
２２：光ファイバケーブル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber core wire comparison method and apparatus.
[0002]
[Prior art]
In recent years, the introduction of services using a wavelength multiplexing method using communication light in the 1.31 μm band and 1.55 μm band using a single mode optical fiber has been expanded. If optical fiber used to provide the service is repaired or line switching occurs, the service will not be affected for the line in operation to ensure quick response, and the optical fiber core is controlled. A method that can do this is required.
[0003]
FIG. 3 is a schematic diagram of an optical line configuration for carrying out optical fiber contrasting of optical fibers 3, 3, 3,... (Used only as a control test target) used as a working line. . When the optical fiber 3 used as a working line is to be subjected to optical fiber contrast, the optical fiber 3 to be controlled is generated by the optical fiber light source unit 9 from the communication equipment building side having the in-station device 1. Then, the core wire contrast light 14 having a wavelength different from that of the communication light 13 in the range of 1.615 μm to 1.675 μm is incident through the optical coupler 2. On the other hand, at the work site, a bend 3a having a bend radius of 12.5 to 13.0 mm is added to the optical fiber 3 by the bending portion 10 of the core wire contrast device. Then, the radiated light 11 of the core wire contrast light due to the bend 3a is detected by the receiver 12 including a predetermined light receiving element attached to the core wire contrast device bending portion 10. The cords are controlled by these configurations.
[0004]
The bending radius is determined in order to minimize deterioration of transmission quality due to bending and simultaneously satisfy the condition that the core line contrast device can detect the core line contrast light. This method is known from Yamamoto et al., Japanese Patent Laid-Open No. 06-221958, “Optical Fiber Core Contrast Device”. In this method, as described above, the wavelengths are arranged so that the core-line contrast light wavelength is different from the communication light wavelength.
[0005]
Further, by inserting a core-line-contrast-light-blocking optical filter 8 having a wavelength dependency with respect to the transmission characteristics at the input part of the subscriber terminal 7, even if the core-line contrast light is incident on the operating line, the service quality The core contrast of the line in operation is realized without degrading the network. In this case, the subscriber terminal 7 receives an optical signal via the optical fiber 3 and converts it into an electrical signal, and a band filter 5 having a band transmission characteristic corresponding to the modulation frequency of the communication light 13. The receiver 6 receives and demodulates the electrical signal output from the band filter 5.
[0006]
[Problems to be solved by the invention]
In the current core line contrast method, when the core line contrast light blocking optical filter 8 is not installed in the optical fiber 3 to be contrasted, the core line contrast light 14 and the communication light 13 are simultaneously incorporated in the subscriber terminal 7. The light is received by the optical receiver 4. The cord control light 14 is converted into an electrical signal together with the communication light 13. FIG. 4 shows a schematic diagram of the received signal spectrum after conversion. As shown in this figure, even if the optical fiber reference light 14 has a wavelength different from that of the communication light 13, the communication signal and the optical fiber reference signal are superimposed, and this superimposed frequency component becomes noise and affects the communication. I will give it. This will be described in detail as follows.
[0007]
It is assumed that the core-line control light 14 is sufficiently slow compared with the communication light 13 and is pulse-modulated. At this time, the code error rate (BER) when the core-line contrast light 14 is incident on the subscriber terminal 7 is given by the following equation.
[Expression 1]

Here, _SD is the equivalent input signal current of the communication light 13, σ ₀ ² is the total variance of the equivalent input noise current at the subscriber terminal 7 when only the communication light 13 is incident on the subscriber terminal 7, and S _ID is an equivalent input peak current of the core wire reference light 14, σ ₁ ² is an equivalent input noise current at the subscriber terminal 7 when the communication light 13 and the core wire reference light 14 are simultaneously incident on the subscriber terminal 7, erfc (x) is the complementary error function,
[Expression 2]

Defined by
[0008]
Further, the average received light power of the communication light 13 is P _S , the average received power of the core line control light 14 is P _ID , the conversion efficiency of the communication light 13 up to the subscriber terminal 7 is ρ _S , and the conversion efficiency of the core line control light 14 Is ρ _ID , the equivalent input currents of the communication light 13 and the core-line contrast light 14 are respectively
[Equation 3]

Given in.
[0009]
The result of estimating the BER deterioration depending on the light receiving power of the core reference light 14 using the formula (1) is shown by a dotted line in FIG. Here, with respect to the total dispersion of the equivalent input noise current, it is assumed that the increase due to the contrast control light is only shot noise. According to a reference (ITU-T. Recommendation G.983.1, “Broadband optical access systems based on Passive Optical Networks (PON),” 1988), S _D ² / σ ₀ ² = 22 dB and P _S = −33 dBm. When trying to satisfy BER <10 ⁻⁹ , it can be seen that the average light receiving power P _ID of the core control light 14 needs to be −51 dBm or less. For example, when the core-line contrast light average light receiving power is −35 dBm at the input unit of the subscriber terminal 7, the core-line contrast light-blocking optical filter 8 having a cutoff amount of 16 dB or more in order to realize the core-line contrast of the active line. Need to be inserted.
[0010]
However, the insertion of the core line contrast light blocking type optical filter 8 has a drawback that the line loss of the entire optical line increases due to the inherent loss of the optical filter and limits the application distance of the optical communication system. . In addition, there is a problem that the installation of the optical filter leads to an increase in the cost of the entire optical line used in the optical communication system.
[0011]
In view of the above circumstances, an object of the present invention is to provide an optical fiber core wire comparison method and apparatus that can be manufactured at a lower cost than the prior art and that can improve the limitation of the application distance of the optical communication method. To do.
[0012]
[Means for Solving the Problems]
To solve the above problems, an invention according to claim 1, in core control method for performing core control of the optical fiber that is provided between the subscriber terminal and station apparatus, from the station apparatus side to be when entering the core control light to the optical fiber to the subscriber terminal to be tested, the modulation frequency of the core control light the input, the station apparatus and communication signals between the subscriber terminal The modulation frequency is out of the frequency band of the communication signal and so as not to overlap with the frequency band of the communication signal and the modulation frequency of the cord reference light, and Of the modulation frequency of the communication signal and the modulation frequency of the core contrast light, only the modulation frequency of the core contrast light is selected from the modulation frequency of the communication signal and the modulation frequency of the core contrast light by the band filter for extracting the communication signal built in the subscriber terminal in advance. Shut off Characterized by the frequency arrangement as. According to a second aspect of the present invention, the optical fiber reference light receiving device for selecting an optical fiber provided between the intra-station device and the subscriber terminal from a plurality of optical fibers receives the optical fiber reference light. when, wherein demodulating the signal corresponding to the core wire control light using a predetermined band filter that transmits only the modulation frequency component of the core wire control light.
[0013]
According to a third aspect of the invention, the core wire control device for performing core control of the optical fiber that is provided between the subscriber terminal and station apparatus, the station apparatus and communication signals between the subscriber terminal a frequency band of the modulation frequency, and is blocked by the communication has a frequency band that overlaps with the frequency band does not occur in the signal and band pass filter for extracting the communication signal incorporated in the subscriber terminal within a frequency band that the subscriber terminal and the core control light generating means for generating a core control light having a modulation frequency, the core control light generated by the core control light generating means becomes under test an optical coupler which enters the optical fiber to, and receives the cord control light transmitted through the optical fiber, a plurality of light optical fiber provided between the subscriber terminal and the station device In the fiber Characterized in that it comprises a core control light receiving means for sorting. Fourth aspect of the present invention, the core wire control light receiving means, characterized in that it has a predetermined band filter that transmits only the modulation frequency component of the core wire control light.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a configuration of an optical line for carrying out the contrast control according to the present invention. FIG. 2 is a diagram showing the arrangement of the transmission band of the band-pass filter 19 shown in FIG. 1 and the modulation frequency of the cord reference light source unit 17. In FIG. 1, the same components as those shown in FIG.
[0015]
In FIG. 1, the core line contrast light 15 frequency-modulated to a frequency fc outside the communication signal range by the signal generator 16 is incident on the optical fiber 3 to be contrasted from the core line contrast light source unit 17 via the optical coupler 2. Is done. By adding a bend 3a to the optical fiber 3 by the core wire contrast unit bending section 21 at the work site, the light in the optical fiber 3 is emitted. The radiated light 11 is received by the light receiving unit 18 attached to the cord contrast bending unit 2 and converted into an electrical signal. In the present embodiment, the cord contrast light 15 and the communication light 13 are provided by providing the band contrast filter bending portion 21 with the bandpass filter 19 having the modulation frequency component (frequency fc) of the cord contrast light 15 as a transmission band. Are simultaneously radiated, only the modulation frequency component of the core contrast light 15 can be received by the receiver 20 of the core contrast bending section 21. Thereby, the optical fiber 3 to be contrasted can be compared from the many optical fibers 3, 3, 3,... In operation accommodated in the optical fiber cable 22 at the work site.
[0016]
On the other hand, as shown in FIG. 2, the modulation frequency fc of the core line contrast light source unit 17 is arranged outside the communication signal band, and therefore, the core line contrast light blocking optical filter 8 as shown in FIG. Is not installed, and even if the optical fiber 15 is incident on the optical receiver 4 of the subscriber terminal 7, the modulation frequency component fc is cut off by the band filter 5 built in the subscriber terminal in advance. The quality is not degraded, and the cores of the operating line can be compared.
[0017]
As described above, in the present embodiment, a light source unit (signal generator 16, core wire contrast light source unit 17, optical coupler 2) and a bending portion (core wire contrast device bending) for optical fiber cable core contrast. In the optical fiber core line contrast device constituted by the unit 21), the modulation frequency fc of the core line control light 15 is arranged outside the communication signal band (see FIG. 1). In addition, a band filter 19 that transmits only the modulation frequency component of the core wire reference light 15 is provided in the light receiving portion 18 attached to the core wire contrast device bending portion 21 that receives the emitted light 11 from the optical fiber 3. By applying these two means to the optical fiber core contrast device, it is possible to realize the core control of the operating line that does not require the core wire control light blocking optical filter 8.
[0018]
That is, according to the above configuration, the modulation frequency of the core line reference light 15 is outside the modulation frequency band of the communication light 13 (communication signal) between the intra-station device 1 and the subscriber terminal 7, and the subscriber terminal 7 It is set within the frequency band cut off by the built-in band filter 5. That is, by using the core line contrast light source unit 17 and frequency-multiplexing the communication signal and the core line reference signal as shown in FIG. 7, the frequency component corresponding to the modulation frequency of the core-line contrast signal light 15 is attenuated (blocked) by the band filter 5 having the band transmission characteristic corresponding to the modulation frequency of the communication light 13. It is possible to prevent quality degradation of the product. This will be described in detail as follows.
[0019]
It is assumed that the core line control light 15 is modulated at a sufficiently high speed as compared with the communication light 13. At this time, the code error rate BER when the core-line contrast light 15 is incident on the subscriber terminal 7 is given by the following equation.
[Expression 4]

[0020]
Here, σ ₂ ² is the total dispersion of equivalent noise current when the communication light 13 and the core wire reference light 15 are simultaneously incident on the subscriber terminal 7, and the core wire reference light 15 is sinusoidally modulated. Assuming that σ ₂ ² is given by:
[Equation 5]

[0021]
Here, σ ² _Shot is the shot noise current caused by the core line contrast light, K is the transmittance at the core line contrast light modulation frequency of the bandpass filter 5 built in the subscriber terminal 7, and OMI is the light of the core line contrast light 15. Indicates the modulation degree. The solid line shown in FIG. 5 represents the BER characteristic when K = 10 ⁻³ and OMI = 35% using the equation (5). As shown in the figure, it is understood that the allowable light receiving power is increased by 17 dB by arranging the modulation frequency of the core-line contrast light 15 outside the communication signal band. Due to the increase in the permissible light receiving power, it is possible to realize the core-line contrast of the operating line that does not require the core-line contrast light blocking optical filter 8.
[0022]
The embodiment of the present invention is not limited to the above-described embodiment. For example, a high-pass filter that attenuates a component in a frequency band lower than the modulation frequency fc is used instead of the band filter 19. These changes can be made as appropriate.
[0023]
【The invention's effect】
According to the present invention, in the optical line of the working line, even if the core line contrast light blocking type optical filter usually installed near the subscriber terminal is not installed, the core line control is performed without degrading the service quality. Since it can be performed, the loss of the optical line used for the optical communication system can be reduced, and the cost for constructing the optical line facility can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an optical line configuration for carrying out a core contrast according to the present invention.
2 is a diagram showing an arrangement of a transmission band of a band filter 19 shown in FIG. 1 and a modulation frequency of a cord reference light source unit 17. FIG.
FIG. 3 is a schematic diagram of a configuration of an optical line for carrying out conventional core wire contrast.
4 is a schematic diagram showing a received signal spectrum in the configuration of FIG. 3;
FIG. 5 is a diagram showing the relationship between the average light receiving power and the code error rate BER characteristic at the subscriber terminal of the core line contrast light in the present invention and the conventional example.
[Explanation of symbols]
1: In-station device 2: Optical coupler 3: Optical fiber (optical fiber under test)
4: Optical receiver 5: Bandpass filter 6: Receiver 7: Subscriber terminal 8: Core wire contrast light blocking optical filter 9, 17: Core wire contrast light source unit 10, 21: Core wire contrast bending unit 11: Synchrotron radiation (cardiac contrast light or communication light)
12, 20: Light receiving unit 13: Communication light 14, 15: Core wire control light 16: Signal generator 18: Light receiving unit 19: Band filter 22: Optical fiber cable

Claims

In a method of contrasting an optical fiber provided between an in-station device and a subscriber terminal,
When entering the core control light to the optical fiber to the subscriber terminal as the object to be tested from the station apparatus side,
The modulation frequency of the core control light the input, the modulated frequency of the communication signals between the subscriber terminal and the station device, a frequency band of the modulation frequency of the communication signal, and the modulation frequency of the communication signal of as superimposed on the frequency band of the modulation frequency of the frequency band and the core wire control light does not occur, and the band-pass filter for extracting the communication signal being previously built in the subscriber terminal, the communication signal An optical fiber core-line contrast method, wherein the frequency arrangement is such that only the modulation frequency of the core-line contrast light is cut off between the modulation frequency of the core-line contrast light and the modulation frequency of the core-line contrast light.

An optical fiber contrast optical receiver for selecting an optical fiber provided between the intra-station device and a subscriber terminal from a plurality of optical fibers,
When receiving the core contrast light,
2. The optical fiber core contrast method according to claim 1, wherein a signal corresponding to the core contrast light is demodulated using a predetermined bandpass filter that transmits only the modulation frequency component of the core contrast light.

An optical fiber contrast device for optical fiber optical fiber contrast provided between an in-station device and a subscriber terminal,
A frequency band of the modulation frequency of the communication signals between the subscriber terminal and the station apparatus, and overlapped with the frequency band of the communication signal has a frequency band which does not occur, and is incorporated in the subscriber terminal A core contrast light generating means for generating a core contrast light having a modulation frequency in a frequency band cut off by a band filter for extracting the communication signal ;
An optical coupler for incident core control light generated by the core control light generating means to the optical fiber to the subscriber terminal as the object to be tested,
Receiving a cord control light transmitted through the optical fiber, core control optical receiver for selecting an optical fiber that is provided between the subscriber terminal and the station device from among a plurality of optical fibers And an optical fiber core wire contrast device.

The core control light receiving means, optical fiber control device according to claim 3, characterized in that it has a predetermined band filter that transmits only the modulation frequency component of the core wire control light.