JP3523975B2 - Optical control signal transmission device and optical control signal receiving device - Google Patents
Optical control signal transmission device and optical control signal receiving deviceInfo
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- JP3523975B2 JP3523975B2 JP00094597A JP94597A JP3523975B2 JP 3523975 B2 JP3523975 B2 JP 3523975B2 JP 00094597 A JP00094597 A JP 00094597A JP 94597 A JP94597 A JP 94597A JP 3523975 B2 JP3523975 B2 JP 3523975B2
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- signal
- light
- control signal
- optical
- light intensity
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Description
【０００１】[0001]
【発明の属する技術分野】本発明は、伝送するデータ信
号（本願明細書では「主信号」という。）とともに、伝
送系を監視または制御するための制御信号を伝送する光
制御信号伝送装置に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control signal transmission device that transmits a control signal for monitoring or controlling a transmission system together with a data signal to be transmitted (hereinafter referred to as "main signal").
【０００２】[0002]
【従来の技術】光伝送システムでは、主信号とともに、
例えば主信号の行き先に関する情報や、各伝送装置の動
作状態を監視するためのモニタ信号などが制御信号とし
て伝送される。ただし、制御信号として伝送される情報
量は主信号に比べて十分に少ないので、その伝送速度は
主信号に比べて十分に低くてよい。2. Description of the Related Art In an optical transmission system, along with a main signal,
For example, information about the destination of the main signal and a monitor signal for monitoring the operating state of each transmission device are transmitted as control signals. However, since the amount of information transmitted as the control signal is sufficiently smaller than that of the main signal, its transmission speed may be sufficiently lower than that of the main signal.
【０００３】制御信号を伝送する第１の方法は、時間多
重により主信号列の中に制御信号列を折り込む方法であ
る。しかし、この方法は、伝送系の途中のノードで制御
信号だけを読み出したいときでも、主信号とともにすべ
ての信号を復調してその中から制御信号列を取り出す必
要があり、効率的ではない。制御信号を伝送する第２の
方法は、サブキャリア多重を用いる方法である。主信号
は所定のスペクトル拡がりをもっている。このスペクト
ル帯域外の周波数をキャリア周波数とし、そのキャリア
周波数成分を制御信号により変調すると、受信側でフィ
ルタを用いて制御信号のキャリア周波数成分だけを抽出
すれば、制御信号のみを取り出すことができる。このと
き、主信号成分については復調する必要がないので、時
間多重による方法に比べて簡単な構成で制御信号を得る
ことができる。The first method of transmitting the control signal is to fold the control signal sequence into the main signal sequence by time division multiplexing. However, this method is not efficient because it is necessary to demodulate all the signals together with the main signal and take out the control signal sequence from them even when it is desired to read only the control signals at a node in the middle of the transmission system. The second method for transmitting the control signal is a method using subcarrier multiplexing. The main signal has a predetermined spectral spread. When a frequency outside the spectrum band is used as a carrier frequency and the carrier frequency component is modulated by the control signal, only the control signal can be extracted by extracting only the carrier frequency component of the control signal using a filter on the receiving side. At this time, since it is not necessary to demodulate the main signal component, it is possible to obtain the control signal with a simpler structure than the method of time multiplexing.
【０００４】[0004]
【発明が解決しようとする課題】ところで、主信号は一
般に、低周波数から高周波数まで（例えば、ビットレー
ト周波数の 1／10000 からビットレート周波数まで）の
広い帯域を占有している。したがって、サブキャリア多
重を用いる方法において、制御信号を伝送するキャリア
周波数は、主信号スペクトルの帯域よりも高周波数また
は低周波数とする必要がある。ここで、高周波数側に設
定する場合には、高速で応答する受信装置が不可欠とな
る。一方、低周波数側に設定すると、波長多重伝送の場
合に光ファイバ増幅器の混変調の影響が出てくる。By the way, the main signal generally occupies a wide band from a low frequency to a high frequency (for example, 1/10000 of the bit rate frequency to the bit rate frequency). Therefore, in the method using subcarrier multiplexing, the carrier frequency for transmitting the control signal needs to be higher or lower than the band of the main signal spectrum. Here, when setting to the high frequency side, a receiving device that responds at high speed is indispensable. On the other hand, if it is set to the low frequency side, the influence of the intermodulation of the optical fiber amplifier comes out in the case of wavelength division multiplexing transmission.
【０００５】本発明は、制御信号の周波数帯と主信号の
周波数帯を分離することなく、１つの信号光に制御信号
と主信号を多重して伝送することができる光制御信号伝
送装置および光制御信号受信装置を提供することを目的
とする。The present invention provides an optical control signal transmission device and an optical control signal transmission device capable of multiplexing and transmitting a control signal and a main signal in one signal light without separating the frequency band of the control signal and the frequency band of the main signal. An object is to provide a control signal receiving device .
【０００６】[0006]
【課題を解決するための手段】本発明の光制御信号伝送
装置は、主信号によって光強度を変調し、かつ制御信号
によって光周波数を変調した信号光を送信する送信手段
と、信号光の周波数偏移を検出して制御信号を取り出す
受信手段とにより構成される。この受信手段（本発明の
光制御信号受信装置）は、信号光を２分岐する分岐手段
と、分岐手段で分岐された一方の信号光を入力し、信号
光の周波数偏移を光強度に変換する透過帯域特性を有す
る光フィルタと、光フィルタの出力光を入力し、その光
強度を検出する第１の光検出器と、分岐手段で分岐され
た他方の信号光を入力し、その光強度を検出する第２の
光検出器と、第１の光検出器の検出信号を前記第２の光
検出器の検出信号で割算して信号光に重畳された制御信
号を出力する割算回路とを備える。これにより、制御信
号は、信号光の周波数変調成分を光強度に変換して受信
することができる。すなわち、主信号と制御信号は信号
光の強度変調成分と周波数変調成分にそれぞれ変換して
伝送することができる。An optical control signal transmission device of the present invention is a transmission means for transmitting a signal light whose optical intensity is modulated by a main signal and whose optical frequency is modulated by a control signal, and a frequency of the signal light. And a receiving means for detecting the deviation and extracting the control signal. This receiving means (of the present invention
The optical control signal receiving device) is a branching unit that splits the signal light into two.
And input one of the signal lights branched by the branching means,
Has a transmission band characteristic that converts the frequency shift of light into light intensity
Optical filter and the output light of the optical filter
The first photodetector for detecting the intensity is branched by the branching means.
The other signal light is input and the light intensity is detected.
The detection signal of the photodetector and the first photodetector is used as the second light.
The control signal superimposed on the signal light after being divided by the detection signal of the detector.
And a division circuit for outputting a signal. This allows the control signal
The signal is received by converting the frequency modulation component of the signal light into light intensity.
can do. That is, the main signal and the control signal can be converted into the intensity modulation component and the frequency modulation component of the signal light and transmitted.
【０００７】[0007]
【発明の実施の形態】図１は、本発明の光制御信号伝送
装置の送信手段の実施形態を示す。図において、送信手
段は、半導体レーザ１１と光強度変調器１２を接続して
構成される。半導体レーザ１１には、発振閾値以上の一
定バイアス電流および制御信号に応じた微小変調電流が
印加される。光強度変調器１２には、主信号が印加され
る。1 shows an embodiment of transmitting means of an optical control signal transmitting apparatus according to the present invention. In the figure, the transmitting means is constituted by connecting a semiconductor laser 11 and a light intensity modulator 12. A constant bias current equal to or higher than the oscillation threshold and a minute modulation current according to the control signal are applied to the semiconductor laser 11. A main signal is applied to the light intensity modulator 12.
【０００８】半導体レーザ１１は、印加電流が変調され
ていると、それに応じて発振周波数および光強度が変調
される性質があるが、変調電流幅が小さいときには周波
数変調が主となる。この性質を利用し、半導体レーザ１
１から制御信号により周波数変調された信号光（ＦＭ）
を出力する。光強度変調器１２はこの周波数変調光ＦＭ
を入力し、その光強度を主信号により変調して出力す
る。これにより、光強度変調器１２からは、主信号によ
り光強度が変調され、制御信号により光周波数が変調さ
れた信号光（ＦＭ＋ＩＭ）が出力される。When the applied current is modulated, the semiconductor laser 11 has a property that the oscillation frequency and the light intensity are modulated accordingly, but when the modulation current width is small, frequency modulation is the main. Utilizing this property, the semiconductor laser 1
Signal light (FM) frequency-modulated by control signal from 1
Is output. The light intensity modulator 12 uses this frequency modulated light FM.
Is input, and the light intensity is modulated by the main signal and output. As a result, the light intensity modulator 12 outputs signal light (FM + IM) whose light intensity is modulated by the main signal and whose optical frequency is modulated by the control signal.
【０００９】図２は、本発明の光制御信号伝送装置の受
信手段（本発明の光制御信号受信装置）の実施形態を示
す。なお、受信手段は、光伝送システムの中継ノードま
たは受信装置に設けられるが、ここでは制御信号の抽出
にかかわる部分のみについて示す。図において、受信手
段は、光分岐器２１，２２と、光フィルタ２３と、光検
出器２４，２５と、割算回路２６とにより構成される。
光分岐器２１は、伝送されてきた信号光の一部を分岐す
る。光分岐器２２は、光分岐器２１で分岐された信号光
をさらに２分岐し、その一方を光フィルタ２３に送出
し、他方を光検出器２５に送出する。光フィルタ２３
は、信号光の周波数偏移を検出する透過帯域特性を有
し、透過光を光検出器２４に送出する。光検出器２４，
２５は、それぞれ入力光の光強度を検出する。割算回路
２６は、光検出器２４の検出信号を光検出器２５の検出
信号で割算して出力する。FIG. 2 shows an embodiment of the receiving means (optical control signal receiving apparatus of the present invention) of the optical control signal transmitting apparatus of the present invention . Although the receiving means is provided in the relay node or the receiving device of the optical transmission system, only the part related to the extraction of the control signal is shown here. In the figure, the receiving means is composed of optical branchers 21 and 22, an optical filter 23, photodetectors 24 and 25, and a division circuit 26.
The optical branching device 21 branches a part of the transmitted signal light. The optical splitter 22 further splits the signal light split by the optical splitter 21 into two, one of which is sent to the optical filter 23 and the other of which is sent to the photodetector 25. Optical filter 23
Has a transmission band characteristic for detecting the frequency shift of the signal light, and sends the transmitted light to the photodetector 24. Photodetector 24,
25 detects the light intensity of the input light. The division circuit 26 divides the detection signal of the photodetector 24 by the detection signal of the photodetector 25 and outputs it.
【００１０】光フィルタ２３の出力光強度は、光フィル
タ２３への入力光強度Ｐinおよび光周波数ｆに依存し、
Ｐin・Ｔ(f) と表すことができる。ここで、Ｔ(f) は光
フィルタ２３の透過率である。また、Ｔ(f) は、信号光
の周波数偏移を光強度に変換できるような特性に設定す
る。この表記を用いると、光検出器２４の検出信号は、
ｋ1 ・Ｐin・Ｔ(f) と表すことができる（ｋ1 は比例定
数）。一方、光検出器２５の検出信号は、光フィルタ２
３への入力光強度Ｐinに比例しており、ｋ2 ・Ｐinと表
すことができる（ｋ2 は比例定数）。The output light intensity of the optical filter 23 depends on the input light intensity Pin to the optical filter 23 and the optical frequency f,
It can be expressed as Pin · T (f). Here, T (f) is the transmittance of the optical filter 23. Further, T (f) is set to a characteristic that can convert the frequency shift of the signal light into the light intensity. Using this notation, the detection signal of the photodetector 24 is
It can be expressed as k 1 · Pin · T (f) (k 1 is a proportional constant). On the other hand, the detection signal of the photodetector 25 is the optical filter 2
It is proportional to the input light intensity Pin to 3 and can be expressed as k 2 · Pin (k 2 is a proportional constant).
【００１１】割算回路２６では、光検出器２４の検出信
号(ｋ1・Ｐin・Ｔ(f) ）を光検出器２５の検出信号(ｋ2
・Ｐin）で割算する。したがって、その出力は、
(ｋ1・Ｐin・Ｔ(f))／(ｋ2・Ｐin) ＝(ｋ1／ｋ2)・Ｔ
(f)
となる。これは、入力光強度Ｐinに依存せず、入力光周
波数のみに依存する値である。ここでは、光周波数は制
御信号に応じて変調されており、割算回路２６は制御信
号に対応する信号を出力することになる。In the division circuit 26, the detection signal (k 1 · Pin · T (f)) of the photodetector 24 is converted to the detection signal (k 2 ) of the photodetector 25.
・ Pin) Therefore, the output is (k 1 · Pin · T (f)) / (k 2 · Pin) = (k 1 / k 2 ) · T
It becomes (f). This is a value that does not depend on the input light intensity Pin but only on the input light frequency. Here, the optical frequency is modulated according to the control signal, and the division circuit 26 outputs a signal corresponding to the control signal.
【００１２】このように、制御信号の抽出は、主信号と
はまったく独立に行うことができる。すなわち、時間多
重の場合と違って信号光から制御信号のみを簡単に取り
出すことができる。また、主信号と制御信号は１つの信
号光に多重されているが、サブキャリア多重の場合と違
って制御信号の周波数帯を主信号の周波数帯域外に設定
する必要はない。As described above, the control signal can be extracted completely independently of the main signal. That is, unlike the case of time multiplexing, only the control signal can be easily extracted from the signal light. Further, although the main signal and the control signal are multiplexed in one signal light, it is not necessary to set the frequency band of the control signal outside the frequency band of the main signal, unlike the case of subcarrier multiplexing.
【００１３】以上、１つの信号光を伝送する光伝送シス
テムについて説明したが、本発明は波長多重伝送システ
ムにも同様に適用することができる。以下、波長多重伝
送システムに適用した光制御信号伝送装置の送信手段お
よび受信手段の実施形態について説明する。半導体レー
ザおよび光強度変調器により構成される送信手段は、図
３に示すように各波長対応に複数組設けられる。各送信
手段の半導体レーザ１１−１〜１１−ｎは、互いに異な
る発振波長λ1 〜λn が設定され、それぞれ対応する制
御信号によりその光周波数が変調される。光強度変調器
１２−１〜１２−ｎは、各周波数変調光を入力し、その
光強度をそれぞれ対応する主信号により変調して出力す
る。主信号により光強度が変調され、制御信号により光
周波数が変調された各信号光は、合波器１３で合波され
て送信される。なお、全チャネルに共通する制御信号
は、いずれか１つの信号光に多重して伝送するようにし
てもよい。Although the optical transmission system for transmitting one signal light has been described above, the present invention can be similarly applied to a wavelength division multiplexing transmission system. Hereinafter, an embodiment of the transmitting means and the receiving means of the optical control signal transmission device applied to the wavelength division multiplexing transmission system will be described. As shown in FIG. 3, a plurality of sets of transmitting means each including a semiconductor laser and a light intensity modulator are provided for each wavelength. Oscillation wavelengths [lambda] 1 to [lambda] n different from each other are set in the semiconductor lasers 11-1 to 11-n of each transmitting means, and the optical frequencies thereof are modulated by the corresponding control signals. The light intensity modulators 12-1 to 12-n input each frequency-modulated light, modulate the light intensity by the corresponding main signal, and output it. Each signal light whose optical intensity is modulated by the main signal and whose optical frequency is modulated by the control signal is multiplexed by the multiplexer 13 and transmitted. The control signal common to all the channels may be multiplexed with any one of the signal lights and transmitted.
【００１４】図４に示す受信手段は、波長λ1 の信号光
に多重された制御信号を抽出するものである。伝送され
てきた波長多重信号光（λ1 〜λn ）の一部は光分岐器
２１で分岐され、光フィルタ２７で波長λ1 の信号光が
選択されて光分岐器２２に送出される。光分岐器２２以
下の構成は図２に示すものと同様である。なお、光フィ
ルタ２７の透過帯域特性は、光フィルタ２３の透過帯域
特性に対して十分に広帯域なものとする。The receiving means shown in FIG. 4 extracts the control signal multiplexed in the signal light of wavelength λ 1 . A part of the transmitted wavelength-multiplexed signal light (λ 1 to λ n ) is branched by the optical branching device 21, and the signal light of wavelength λ 1 is selected by the optical filter 27 and sent to the optical branching device 22. The configuration from the optical branching device 22 onward is the same as that shown in FIG. The transmission band characteristic of the optical filter 27 is sufficiently wider than the transmission band characteristic of the optical filter 23.
【００１５】また、光フィルタ２７に代えて、波長多重
信号光を各波長ごとに分波する波長分波器（例えばアレ
イ導波路回折格子型光分波器）を用い、光分岐器２２以
下の構成を各波長の信号光対応に設けることにより、複
数の制御信号を同時に抽出することができる。Further, instead of the optical filter 27, a wavelength demultiplexer (for example, an arrayed waveguide diffraction grating type optical demultiplexer) that demultiplexes the wavelength-division multiplexed signal light for each wavelength is used. By providing the configuration for the signal light of each wavelength, it is possible to simultaneously extract a plurality of control signals.
【００１６】[0016]
【発明の効果】以上説明したように、本発明の光制御信
号伝送装置および光制御信号受信装置を用いることによ
り、制御信号の周波数帯を主信号周波数の帯域外にする
必要なく、主信号および制御信号を多重して伝送するこ
とができる。As described above, by using the optical control signal transmitting device and the optical control signal receiving device of the present invention .
Ri, the frequency band of the control signals without the need to band of the main signal frequency, can be transmitted by multiplexing a main signal and control signal.
【図１】本発明の光制御信号伝送装置の送信手段の実施
形態を示すブロック図。FIG. 1 is a block diagram showing an embodiment of transmission means of an optical control signal transmission device of the present invention.
【図２】本発明の光制御信号伝送装置の受信手段の実施
形態を示すブロック図。FIG. 2 is a block diagram showing an embodiment of receiving means of the optical control signal transmission device of the present invention.
【図３】波長多重伝送システムに適用した光制御信号伝
送装置の送信手段の実施形態を示すブロック図。FIG. 3 is a block diagram showing an embodiment of transmission means of an optical control signal transmission device applied to a wavelength division multiplexing transmission system.
【図４】波長多重伝送システムに適用した光制御信号伝
送装置の受信手段の実施形態を示すブロック図。FIG. 4 is a block diagram showing an embodiment of receiving means of an optical control signal transmission device applied to a wavelength division multiplexing transmission system.
１１ 半導体レーザ １２ 光強度変調器 １３ 合波器 ２１，２２ 光分岐器 ２３，２７ 光フィルタ ２４，２５ 光検出器 ２６ 割算器 11 Semiconductor laser 12 Light intensity modulator 13 multiplexer 21,22 Optical splitter 23,27 Optical filter 24,25 photo detector 26 divider
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ Ｈ０４Ｊ 14/00 14/04 14/06 // Ｇ０２Ｆ 1/01 (58)調査した分野(Int.Cl.7，ＤＢ名) H04B 10/04 H04B 10/06 H04B 10/08 H04B 10/142 H04B 10/152 H04J 14/04 H04J 14/00 ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. 7 identification code FI H04J 14/00 14/04 14/06 // G02F 1/01 (58) Fields investigated (Int.Cl. 7 , DB name) H04B 10/04 H04B 10/06 H04B 10/08 H04B 10/142 H04B 10/152 H04J 14/04 H04J 14/00
Claims (3)
御信号によって光周波数を変調した信号光を送信する送
信手段と、 前記信号光の周波数偏移を検出して前記制御信号を取り
出す受信手段とを備え、 前記受信手段は、 信号光を２分岐する分岐手段と、 前記分岐手段で分岐された一方の信号光を入力し、信号
光の周波数偏移を光強度に変換する透過帯域特性を有す
る光フィルタと、 前記光フィルタの出力光を入力し、その光強度を検出す
る第１の光検出器と、 前記分岐手段で分岐された他方の信号光を入力し、その
光強度を検出する第２の光検出器と、 前記第１の光検出器の検出信号を前記第２の光検出器の
検出信号で割算して前記信号光に重畳された制御信号を
出力する割算回路とを備えた構成である ことを特徴とす
る光制御信号伝送装置。1. A transmitting means for transmitting a signal light whose optical intensity is modulated by a main signal and whose optical frequency is modulated by a control signal, and receiving means for detecting the frequency deviation of the signal light and extracting the control signal. with the door, the receiving means receives a branch unit that is branched into two signal lights, one of the signal light branched by said branching means, signal
Has a transmission band characteristic that converts the frequency shift of light into light intensity
Optical filter and the output light of the optical filter are input, and the light intensity is detected.
A first photodetector and the other signal light branched by the branching means,
A second photodetector for detecting the light intensity and a detection signal of the first photodetector for the second photodetector.
Divide the detection signal by the control signal superimposed on the signal light
An optical control signal transmission device having a configuration including an output division circuit .
た微小変調電流が印加され、発振光の光周波数を変調し
て出力する半導体レーザと、 前記半導体レーザの出力光を入力し、その光強度を主信
号により変調して出力する光強度変調器とを備えたこと
を特徴とする請求項１に記載の光制御信号伝送装置。2. A semiconductor laser for applying a constant bias current equal to or more than an oscillation threshold and a minute modulation current according to a control signal to the transmission means to modulate and output an optical frequency of oscillation light, and output light of the semiconductor laser. 2. The optical control signal transmission device according to claim 1, further comprising: a light intensity modulator that inputs the light intensity, modulates the light intensity with a main signal, and outputs the light intensity modulated light.
御信号によって光周波数を変調した信号光を受信し、そ
の信号光の周波数偏移を検出して前記制御信号を取り出
す光制御信号受信装置において、 前記信号光を２分岐する分岐手段と、 前記分岐手段で分岐された一方の信号光を入力し、信号
光の周波数偏移を光強度に変換する透過帯域特性を有す
る光フィルタと、 前記光フィルタの出力光を入力し、その光強度を検出す
る第１の光検出器と、 前記分岐手段で分岐された他方の信号光を入力し、その
光強度を検出する第２の光検出器と、 前記第１の光検出器の検出信号を前記第２の光検出器の
検出信号で割算して前記信号光に重畳された制御信号を
出力する割算回路とを備えたことを特徴とする光制御信
号受信装置。 3. The light intensity is modulated and controlled by a main signal.
Receives the signal light whose optical frequency is modulated by the
Of the control signal by detecting the frequency deviation of the signal light of
In the optical control signal receiving device, a branching unit for branching the signal light into two and one of the signal lights branched by the branching unit are input,
Has a transmission band characteristic that converts the frequency shift of light into light intensity
Optical filter and the output light of the optical filter are input, and the light intensity is detected.
A first photodetector and the other signal light branched by the branching means,
A second photodetector for detecting the light intensity and a detection signal of the first photodetector for the second photodetector.
Divide the detection signal by the control signal superimposed on the signal light
Optical control signal characterized by having a dividing circuit for outputting
No. receiver.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00094597A JP3523975B2 (en) | 1997-01-07 | 1997-01-07 | Optical control signal transmission device and optical control signal receiving device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00094597A JP3523975B2 (en) | 1997-01-07 | 1997-01-07 | Optical control signal transmission device and optical control signal receiving device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10200482A JPH10200482A (en) | 1998-07-31 |
| JP3523975B2 true JP3523975B2 (en) | 2004-04-26 |
Family
ID=11487823
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP00094597A Expired - Fee Related JP3523975B2 (en) | 1997-01-07 | 1997-01-07 | Optical control signal transmission device and optical control signal receiving device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3523975B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5962455B2 (en) | 2012-11-21 | 2016-08-03 | 富士通株式会社 | Optical transmission device, node device, optical transmission method, and optical transmission system |
| JP5937982B2 (en) * | 2013-03-05 | 2016-06-22 | 日本電信電話株式会社 | Optical transmission system using tunable light source |
| WO2023119391A1 (en) * | 2021-12-21 | 2023-06-29 | 日本電信電話株式会社 | Transmission device, reception device, and control method |
-
1997
- 1997-01-07 JP JP00094597A patent/JP3523975B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10200482A (en) | 1998-07-31 |
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