JPH07109994B2 - Polarization diversity type optical heterodyne receiver - Google Patents
Polarization diversity type optical heterodyne receiverInfo
- Publication number
- JPH07109994B2 JPH07109994B2 JP63191496A JP19149688A JPH07109994B2 JP H07109994 B2 JPH07109994 B2 JP H07109994B2 JP 63191496 A JP63191496 A JP 63191496A JP 19149688 A JP19149688 A JP 19149688A JP H07109994 B2 JPH07109994 B2 JP H07109994B2
- Authority
- JP
- Japan
- Prior art keywords
- polarization
- light
- signal
- local oscillation
- optical heterodyne
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- Optical Communication System (AREA)
- Radio Transmission System (AREA)
Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は、コヒーレント光通信方式に用いられる偏波ダ
イバーシチ型光ヘテロダイン受信装置に関するものであ
る。TECHNICAL FIELD The present invention relates to a polarization diversity type optical heterodyne receiver used in a coherent optical communication system.
（従来技術） 光ヘテロダイン検波通信（コヒーレント光通信）方法
は、光の強度を変調する直接検波通信方法と比べ大幅に
受信感度が高く、また周波数利用効率も高いため、長距
離高密度伝送が可能であるという利点を有する（斉藤、
山本、木村「コヒーレント光ファイバ伝送変復調技術−
FSKヘテロダイン検波−」電電公社研究実用化報告第31
巻第12号1982年）。(Prior Art) The optical heterodyne detection communication (coherent optical communication) method has a much higher reception sensitivity than the direct detection communication method that modulates the intensity of light, and also has a high frequency utilization efficiency, enabling long-distance high-density transmission. Has the advantage that (Saito,
Yamamoto, Kimura "Coherent optical fiber transmission modulation and demodulation technology-
FSK heterodyne detection- "
Volume No. 12, 1982).
このコヒーレント光通信では、光送信部から送られてき
た信号光と、光受信部に内蔵されている局部発振光源の
光を合波したものを光検出器で受光する。この場合、光
検出器の出力には信号光と局部発振光の周波数差に相当
するビートが中間周波数の電気信号として現れ、これを
復調することによってベースバンド信号を得ることがで
きる。In this coherent optical communication, the signal light sent from the optical transmitter and the light from the local oscillation light source built in the optical receiver are multiplexed by the photodetector. In this case, a beat corresponding to the frequency difference between the signal light and the local oscillation light appears as an electric signal of an intermediate frequency in the output of the photodetector, and a baseband signal can be obtained by demodulating the beat.
ところで、この方法では局部発振光と信号光の周波数差
の変動および偏波の不一致により中間周波数信号の周波
数と電力レベルにゆらぎが生じ、受信特性が劣化する。
このため、信号光と局部発振光の偏波不一致に対する補
償と中間周波数安定化のための制御系が不可欠となる。
ところで偏波の補償方法の主なものに、偏波制御方式と
偏波ダイバーシチ方式が有る。このうち偏波ダイバーシ
チ方式は、信号光の速い偏波変動に対する追従性が優れ
るという利点がある。従来この方式を実現する場合、信
号光を直交する２つの偏波に分離し、それらを２系統の
受信器で独立に光ヘテロダイン、ホモダイン検波復調し
た後、合成する方法が用いられてきた。また中間周波数
（IF）の安定化のための制御信号も２系統の受信器で独
立にIFの周波数弁別を行ない、得られた２つの弁別信号
を合成することによって作り出す方法が用いられてい
た。By the way, according to this method, fluctuations in the frequency difference between the local oscillation light and the signal light and inconsistencies in polarization cause fluctuations in the frequency and power level of the intermediate frequency signal, which deteriorates the reception characteristics.
Therefore, a control system for compensating for the polarization mismatch between the signal light and the local oscillation light and stabilizing the intermediate frequency is indispensable.
By the way, there are a polarization control method and a polarization diversity method as main polarization compensation methods. Among them, the polarization diversity method has an advantage that it has excellent followability to fast polarization fluctuation of signal light. Conventionally, in order to realize this system, a method has been used in which signal light is separated into two polarizations orthogonal to each other, and the signals are independently subjected to optical heterodyne and homodyne detection demodulation by two receivers and then combined. In addition, a method has also been used in which a control signal for stabilizing the intermediate frequency (IF) is generated by independently performing IF frequency discrimination by two receivers and synthesizing the obtained two discrimination signals.
すなわち、偏波ダイバーシチ方式では２系統のIF信号の
搬送波の相対位相が強い相関を持つ上、信号光偏波状態
に応じて同相から逆相の間で変動する。このため、通常
のシステムでは単純にIFを合成すると信号光の偏波状態
によってIF信号が消滅してしまう場合がでてくる。した
がってシステム規模が大きくなっても、２系統の受信器
で独立にIF信号の周波数弁別を行なう必要があった。That is, in the polarization diversity method, the relative phases of the carrier waves of the two IF signals have a strong correlation, and also vary between the in-phase and the anti-phase depending on the polarization state of the signal light. Therefore, in an ordinary system, if IF is simply combined, the IF signal may disappear depending on the polarization state of the signal light. Therefore, even if the system scale becomes large, it is necessary to independently perform frequency discrimination of the IF signal by the two receivers.
（発明か解決しようとする課題） このため、偏波ダイバーシチ方式は偏光制御方式よりも
システム規模が大きくなるという欠点を有している。(Problem to be solved by the invention) Therefore, the polarization diversity method has a drawback that the system scale becomes larger than that of the polarization control method.
本発明の目的は、２系統の受信器のうちIF制御回路部分
を簡略化することによって偏波ダイバーシチシステムの
規模を小さくした装置を提供することにある。An object of the present invention is to provide a device in which the scale of the polarization diversity system is reduced by simplifying the IF control circuit part of the two receivers.
（課題を解決するための手段） 本発明による偏波ダイバーシチ型ヘテロダイン受信装置
は、信号光を互いに直交する２偏光に分離するための偏
光分離素子と、局部発振光を偏光状態が互いに直交する
様に２分岐するための分岐器と、分岐された前記２系統
の局部発振光の片方を遅延させるための光ファイバ遅延
線と、これら２系統の局部発振光を偏光分離された前記
信号光とそれぞれ合波するための２台の合波器と、前記
２台の合波器から出射される合波光を光ヘテロダイン検
波するための２台の光受信器と、前記光受信器から出力
される２系統のIF信号を合成するための合成回路とこの
合成回路からの出力を周波数弁別し、前記局部発振光の
周波数制御信号を得るための周波数弁別回路とを有する
ことを特徴とする。(Means for Solving the Problem) A polarization diversity type heterodyne receiver according to the present invention is such that a polarization splitting element for splitting signal light into two polarizations orthogonal to each other and a polarization state of local oscillation light are orthogonal to each other. For branching into two, an optical fiber delay line for delaying one of the branched local oscillation lights of the two systems, and the signal light obtained by polarization-separating the local oscillation lights of these two systems, respectively. Two multiplexers for multiplexing, two optical receivers for optical heterodyne detection of the combined light emitted from the two multiplexers, and two optical receivers for outputting 2 It is characterized in that it has a combination circuit for combining the IF signals of the systems and a frequency discrimination circuit for frequency discriminating the output from this composing circuit and obtaining the frequency control signal of the local oscillation light.
（作用） 本発明では、２分岐した局部発振光の相対位相をずらす
ことによって、２つのIF信号の搬送波の位相の相関を低
減させる。これによってIF合成時の打ち消し合いを無く
すことができ、IF周波数安定化のための制御信号を信号
光偏波によらず定常的に取り出すことが可能となる。(Operation) In the present invention, the correlation between the phases of the carrier waves of the two IF signals is reduced by shifting the relative phases of the locally oscillated light beams that are branched. As a result, it is possible to eliminate the cancellation at the time of IF combination, and it is possible to steadily extract the control signal for stabilizing the IF frequency regardless of the polarization of the signal light.
（実施例） 第１図に本発明の第１の実施例の構成を示す。第１の実
施例は本発明を、バランスレシーバ型偏波ダイバーシチ
受信器に適用したものである。(Embodiment) FIG. 1 shows the configuration of a first embodiment of the present invention. The first embodiment is an application of the present invention to a balanced receiver type polarization diversity receiver.
光ファイバで伝送された400Mb/sのFSK信号光１は第１の
偏光ビームスプリッタ２で偏光分離された後、各々第１
の合波器６と第２の合波器７に入射される。局部発振光
源３より出射された局部発振光は分岐器４で1:1に２分
岐された後一方は長さ5mの遅延ファイバ５で遅延された
後第１の合波器６に入射され他方は直接第２の合波器７
に入射される。但し２分岐された局部発振光の相対偏波
は第１及び第２の合波器6,7に入射される前に直交状態
となる様に調整されている。第１及び第２の合波器6,7
で合波された光は、各々第１のバランスドレシーバ８と
第２のバランスドレシーバ９に入射され、局部発振光の
強度雑音の抑圧と同時に光ヘテロダイン検波が行なわれ
る。各バランスドレシーバ8,9から出力された第１のIF
信号10と第２のIF信号11は400Mb/sFSK単一フィルタ検波
方式の第１の復調回路14と第２の復調回路15及びIF合成
回路12に入力される。このIF合成回路12では、入力され
た２つのIF信号が振幅加算される。第２図（ａ）〜
（ｃ）に各々第１のIF信号、第２のIF信号、前記IF合成
回路12のIF信号スペクトルを示す。この図に示される様
に、信号光の偏波状態に依存せずに出力信号のレベルが
一定レベル以上に保たれることが分る。但し、第１のIF
信号10と第２のIF信号11との相対位相は、遅延ファイバ
５の長さに依存した相関がわずかに有るため、IF合成回
路12の出力スペクトルにはわずかな干渉縞が、現れる
が、IF安定化を行なう上で必要な制御信号は取り出すこ
とができる。IF合成回路12の出力は周波数弁別器13に入
力される。周波数弁別器13からは、IF安定化のための制
御信号が出力され、この制御信号は局部発振光源３に入
力される。以上により信号光１の偏波に依存せずにIFは
一定値に安定化される。また、第１及び第２の復調回路
14,15の出力は、加算器16で振幅加算され、一定レベル
の復調信号が取り出される。The 400 Mb / s FSK signal light 1 transmitted by the optical fiber is polarized and separated by the first polarization beam splitter 2, and then each of the first
It is incident on the multiplexer 6 and the second multiplexer 7. The local oscillation light emitted from the local oscillation light source 3 is branched into 1: 1 by the branching device 4, and one of them is delayed by the delay fiber 5 having a length of 5 m and then is incident on the first multiplexer 6 and the other. Is the second multiplexer 7 directly
Is incident on. However, the relative polarization of the locally oscillated light split into two is adjusted so as to be in an orthogonal state before being incident on the first and second multiplexers 6 and 7. First and second multiplexers 6,7
The lights multiplexed in (1) are incident on the first balanced receiver 8 and the second balanced receiver 9, respectively, and the optical heterodyne detection is performed simultaneously with the suppression of the intensity noise of the local oscillation light. First IF output from each balanced receiver 8 and 9
The signal 10 and the second IF signal 11 are input to the first demodulation circuit 14, the second demodulation circuit 15, and the IF synthesis circuit 12 of the 400 Mb / s FSK single filter detection method. In this IF synthesis circuit 12, the two input IF signals are amplitude-added. Fig. 2 (a) ~
(C) shows the first IF signal, the second IF signal, and the IF signal spectrum of the IF synthesis circuit 12, respectively. As shown in this figure, it can be seen that the level of the output signal is maintained above a certain level without depending on the polarization state of the signal light. However, the first IF
Since the relative phase between the signal 10 and the second IF signal 11 has a slight correlation depending on the length of the delay fiber 5, a slight interference fringe appears in the output spectrum of the IF synthesis circuit 12, The control signal necessary for stabilization can be taken out. The output of the IF synthesis circuit 12 is input to the frequency discriminator 13. The frequency discriminator 13 outputs a control signal for stabilizing the IF, and this control signal is input to the local oscillation light source 3. As described above, the IF is stabilized at a constant value without depending on the polarization of the signal light 1. Also, the first and second demodulation circuits
The outputs of 14 and 15 are amplitude-added by the adder 16 and a demodulated signal of a constant level is taken out.
第３図は本発明の第２の実施例の構成を示す図である。
第２の実施例はフロントエンドに構成の簡単なシングル
デイテクタ型レシーバを用いた点と、局部発振光の分岐
に偏光ビームスプリッタを用いた点が第１の実施例と異
なる所である。以上ではこの第１の実施例と異なる点に
ついて説明し、共通部分については説明を省略する。FIG. 3 is a diagram showing the configuration of the second embodiment of the present invention.
The second embodiment is different from the first embodiment in that a simple detector type receiver having a simple structure is used for the front end and a polarization beam splitter is used for branching the local oscillation light. The differences from the first embodiment will be described above, and the description of the common parts will be omitted.
局部発振光源３から出射された局部発振光は第２の偏光
ビームスプリッタ22で分岐された後２つの偏波保存ファ
イバに入射される。一方の偏波保存ファイバは、長さ5m
遅延ファイバ５が接続されており、ここで位相の遅延が
与えられる。The locally oscillated light emitted from the locally oscillated light source 3 is split by the second polarization beam splitter 22 and then enters the two polarization maintaining fibers. One polarization-maintaining fiber is 5 m long
A delay fiber 5 is connected, where a phase delay is provided.
また、２分岐された信号光１も偏波保存ファイバに入射
される。そして各信号光は、偏波保存ファイバ型光カプ
ラで構成される第１の合波器６と第２の合波器７で局部
発振光と合波される。第１、第２の合波器6,7から出射
された合波光は、各々第１及び第２のレシーバ20,21に
入射され、ここで光ヘテロダイン検波が行なわれる。そ
してIF合成回路12から出力されるIF信号の電力レベル
は、第１の実施例と同様に信号光１の偏波状態に依存せ
ずに一定値以上保たれる。The signal light 1 split into two is also incident on the polarization maintaining fiber. Then, each signal light is combined with the local oscillation light by the first multiplexer 6 and the second multiplexer 7 which are composed of polarization-maintaining fiber type optical couplers. The combined lights emitted from the first and second multiplexers 6 and 7 are incident on the first and second receivers 20 and 21, respectively, where optical heterodyne detection is performed. Then, the power level of the IF signal output from the IF synthesizing circuit 12 is maintained above a certain value without depending on the polarization state of the signal light 1 as in the first embodiment.
これにより、安定にIF制御信号を得ることができる。ま
た本発明はここで述べた例の他にも、ASKあるいはPSK変
調方式においても適用可能である。また、遅延ファイバ
の長さは、ここでは5mとしたが、光源のスペクトル幅が
狭い場合は更にファイバ長を長くすることによって位相
の相関を低くすることが可能である。Thereby, the IF control signal can be stably obtained. The present invention is also applicable to ASK or PSK modulation systems other than the examples described here. The length of the delay fiber is 5 m here, but when the spectral width of the light source is narrow, the phase correlation can be lowered by further increasing the fiber length.
（発明の効果） 以上詳しく述べた様に本発明を用いることによって構成
の簡単な偏波ダイバーシチ型光ヘテロダイン受信装置を
実現することが可能となる。(Effect of the Invention) As described in detail above, by using the present invention, it is possible to realize a polarization diversity type optical heterodyne receiver having a simple structure.
第１図は本発明第１の実施例を示す構成図、第２図
（ａ）〜（ｃ）はIF信号のスペクトルを示す図、第３図
は本発明第２の実施例を示す構成図である。 各図において、 1:信号光、2:第１の偏光ビームスプリッタ、3:局部発振
光源、4:分岐器、5:遅延ファイバ、6:第１の合波器、7:
第２の合波器、8:第１のバランスドレシーバ、9:第２の
バランスドレシーバ、10:第１のIF信号、11:第２のIF信
号、12:IF合成回路、13:周波数弁別器、14:第１の復調
回路、15:第２の復調回路、16:加算器、20:第１のレシ
ーバ、21:第２のレシーバ、22:第２の偏光ビームスプリ
ッタ である。FIG. 1 is a block diagram showing a first embodiment of the present invention, FIGS. 2 (a) to (c) are diagrams showing an IF signal spectrum, and FIG. 3 is a block diagram showing a second embodiment of the present invention. Is. In each figure, 1: signal light, 2: first polarization beam splitter, 3: local oscillation light source, 4: branching device, 5: delay fiber, 6: first multiplexer, 7:
2nd multiplexer, 8: 1st balanced receiver, 9: 2nd balanced receiver, 10: 1st IF signal, 11: 2nd IF signal, 12: IF synthesis circuit, 13: Frequency A discriminator, 14: first demodulation circuit, 15: second demodulation circuit, 16: adder, 20: first receiver, 21: second receiver, 22: second polarization beam splitter.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.6 識別記号 庁内整理番号 ＦＩ 技術表示箇所 Ｈ０４Ｂ 10/06 10/142 ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. 6 Identification code Office reference number FI technical display location H04B 10/06 10/142
Claims (1)
置において、信号光を互いに直交する２偏光に分離する
ための偏光分離素子と、局部発振光を偏光状態が互いに
直交する様に２分岐するための分岐器と、分岐された前
記２系統の局部発振光の片方に遅延させるための光ファ
イバ遅延線と、これら２系統の局部発振光を偏光分離さ
れた前記信号光とそれぞれ合波するための２台の合波器
と、前記２台の合波器から出射される合波光を光ヘテロ
ダイン検波するための２台の光受信器と、前記光受信器
から出力される２系統のIF信号を合成するための合成回
路とこの合成回路からの出力を周波数弁別し、前記局部
発振光の周波数制御信号を得るための周波数弁別回路と
を有することを特徴とする偏波ダイバーシチ型光ヘテロ
ダイン受信装置。1. A polarization diversity type optical heterodyne receiver, comprising: a polarization splitting element for splitting signal light into two polarizations orthogonal to each other; and a local oscillation light for splitting into two so that polarization states are orthogonal to each other. A branching device, an optical fiber delay line for delaying the branched local oscillation light of the two systems to one side, and 2 for multiplexing the local oscillation lights of these two systems with the polarization separated signal light, respectively. Two multiplexers, two optical receivers for optical heterodyne detection of the combined light emitted from the two multiplexers, and two systems of IF signals output from the optical receivers And a frequency discriminating circuit for discriminating the output from the synthesizing circuit to obtain a frequency control signal of the local oscillation light, and a polarization diversity type optical heterodyne receiver.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63191496A JPH07109994B2 (en) | 1988-07-29 | 1988-07-29 | Polarization diversity type optical heterodyne receiver |
| EP89113983A EP0352809B1 (en) | 1988-07-29 | 1989-07-28 | Polarization diversity optical heterodyne receiver with phase adjustment of two i.f. signals for control of a local optical source |
| DE68927969T DE68927969T2 (en) | 1988-07-29 | 1989-07-28 | Optical heterodyne polarization diversity receiver with phase adjustment of two intermediate frequency signals to control a local light source |
| US07/386,072 US5023946A (en) | 1988-07-29 | 1989-07-28 | Polarization diversity optical heterodyne receiver with phase adjustment of two I.F. signals for control of a local optical source |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63191496A JPH07109994B2 (en) | 1988-07-29 | 1988-07-29 | Polarization diversity type optical heterodyne receiver |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0239741A JPH0239741A (en) | 1990-02-08 |
| JPH07109994B2 true JPH07109994B2 (en) | 1995-11-22 |
Family
ID=16275612
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP63191496A Expired - Lifetime JPH07109994B2 (en) | 1988-07-29 | 1988-07-29 | Polarization diversity type optical heterodyne receiver |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH07109994B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04150628A (en) * | 1990-10-15 | 1992-05-25 | Nec Corp | Wavelength stabilizing method for optical communication system and its circuit |
| NL9200748A (en) * | 1992-04-23 | 1993-11-16 | Nederland Ptt | OPTICAL SIGNAL TRANSMISSION WITH POLARIZATION-SENSITIVE COHERENT DETECTION AND FREQUENCY STABILIZATION ON THE RECEPTION SIDE. |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2633593B2 (en) * | 1987-12-10 | 1997-07-23 | 富士通株式会社 | Polarization diversity optical receiver for coherent optical communication |
-
1988
- 1988-07-29 JP JP63191496A patent/JPH07109994B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0239741A (en) | 1990-02-08 |
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