JPH0810848B2 - Optical transmitter - Google Patents
Optical transmitterInfo
- Publication number
- JPH0810848B2 JPH0810848B2 JP61102417A JP10241786A JPH0810848B2 JP H0810848 B2 JPH0810848 B2 JP H0810848B2 JP 61102417 A JP61102417 A JP 61102417A JP 10241786 A JP10241786 A JP 10241786A JP H0810848 B2 JPH0810848 B2 JP H0810848B2
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- JP
- Japan
- Prior art keywords
- frequency
- optical
- output
- laser
- modulation
- 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.)
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Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は、光通信等で使用させる光送信器に関するも
のである。TECHNICAL FIELD The present invention relates to an optical transmitter used in optical communication or the like.
（従来の技術） 光通信システムにおいては、光送信器として半導体レ
ーザへの注入電流を変調して出力強度を変調する方式が
一般に用いられている。(Prior Art) In an optical communication system, a method of modulating an injection current to a semiconductor laser to modulate an output intensity is generally used as an optical transmitter.
特に、光ディジタル信号変調をする場合、予め、レー
ザの直流バイアス電流を発振しきい値に設定し、送信符
号に対応したパルス電流をこのバイアス電流に重畳する
ことによって強度変調された光パルス出力を得ている。
この場合、パルス符号のスペースに対応する光出力は、
マークに対応する光出力に比較し、充分小さくないと、
消光比劣化による通信品質の低下を引き起こす。従って
スペースに対応する注入電流は、しきい値電流よりわず
かに低い値に設定するのが一般である。しかし、このよ
うな変調方法で、1Gb/s以上の高ビットレートの変調を
行なうと、レーザへのバイアス電流をしきい値付近にま
で低下させると、レーザの応答が遅くなり、波形のすそ
引きが大きく、高速変調できなくなる欠点があった。ま
た1Gb/s以上の高ビットレート変調でバイアス電流をし
きい値付近に設定すると、直接変調に伴なう周波数揺ら
ぎ（チャーピング）が大きく、長距離伝送において、光
ファイバの分散による波形歪を生する問題点もあった。In particular, in the case of optical digital signal modulation, the direct current bias current of the laser is set to the oscillation threshold value in advance, and the pulse current corresponding to the transmission code is superimposed on this bias current to obtain the intensity-modulated optical pulse output. It has gained.
In this case, the optical output corresponding to the pulse code space is
Compared to the optical output corresponding to the mark, if it is not sufficiently small,
It causes deterioration of communication quality due to deterioration of extinction ratio. Therefore, the injection current corresponding to the space is generally set to a value slightly lower than the threshold current. However, when modulation at a high bit rate of 1 Gb / s or more is performed by such a modulation method, if the bias current to the laser is reduced to near the threshold value, the response of the laser becomes slow and the waveform tails. Is large, and there is a drawback that high speed modulation cannot be performed. Also, when the bias current is set near the threshold value in high bit rate modulation of 1 Gb / s or more, the frequency fluctuation (chirping) due to direct modulation is large, and the waveform distortion due to dispersion of the optical fiber is caused in long distance transmission. There were some problems that arose.
これに対し、半導体レーザへの注入電流を、送信符号
に対応したパルス電流により変調することでレーザ光を
周波数変調し、この周波数変調された信号光を周波数弁
別器を用いて強度変調に変換して送信する変調方法を用
いると、レーザへのバイアス電流をしきい値以上にして
も、周波数弁別器の弁別特性により消光比による劣化量
を抑圧した光強度変調波を得られるための、1Gb/s以上
の高ビットレートの変調を行なうことができる。On the other hand, the injection current to the semiconductor laser is modulated with a pulse current corresponding to the transmission code to frequency-modulate the laser light, and this frequency-modulated signal light is converted into intensity modulation using a frequency discriminator. When the modulation method for transmitting is used, even if the bias current to the laser is above the threshold value, it is possible to obtain a light intensity modulated wave that suppresses the deterioration amount due to the extinction ratio due to the discrimination characteristics of the frequency discriminator. High bit rate modulation of s or more can be performed.
（発明が解決しようとする問題点） しかし、この変調方法のままでは、半導体レーザの発
振波長、周波数弁別器の周波数弁別特性が、周囲の温度
変化、振動等の外乱により変化すると消光比が劣化した
り信号光の強度変調分が小さくなる欠点がある。本発明
の目的は、この欠点を解決することにある。(Problems to be solved by the invention) However, with this modulation method, the extinction ratio deteriorates when the oscillation wavelength of the semiconductor laser and the frequency discrimination characteristics of the frequency discriminator change due to ambient temperature changes, disturbances such as vibrations, etc. However, there is a drawback that the intensity modulation amount of the signal light becomes small. The object of the invention is to overcome this drawback.
（問題を解決するための手段） 本発明は、周波数変調成分を含む信号光を出力する光
源部と、前記信号光の周波数変調成分を強度変調成分に
変換して送信出力する光周波数弁別器と、前記周波数弁
別器の出力をモニタして送信信号の消光比を改善するよ
う前記光源部の発振周波数または光周波数弁別器の周波
数特性を制御する負帰還回路とを備えた構成となってい
る。(Means for Solving the Problem) The present invention provides a light source unit that outputs a signal light including a frequency modulation component, and an optical frequency discriminator that converts the frequency modulation component of the signal light into an intensity modulation component and outputs the signal. A negative feedback circuit that monitors the output of the frequency discriminator and controls the oscillation frequency of the light source unit or the frequency characteristic of the optical frequency discriminator so as to improve the extinction ratio of the transmission signal.
（作用） 以下、光源部として半導体レーザを用いた例で本発明
の原理について説明する。一般に半導体レーザの発振周
波数は注入電流量や半導体レーザの温度により変化す
る。（コバヤシ他、アイ・イー・イー・イーQE18巻、58
2ページ〜595ページ1982年刊）このためレーザへの注入
電流を発振しきい値以上としておくと、注入電流を変化
させることで強度変調をかけると同時に周波数変調をか
けることができる。このようにして直接注入電流変調し
て得られた周波数変調光を、光周波数弁別器に入力す
る。この時、信号がマークの時には、弁別器の透過率が
ｋ（ｋ＜１）、スペース時には透過率が０となるように
弁別器に弁別特性を持たせると、弁別器の透過出力とし
てマーク時には、強度はｋ倍にスペース時には強度は０
とすることができるので、消光比による劣化量を抑圧し
た光強度変調波を得ることができる。(Operation) Hereinafter, the principle of the present invention will be described with an example in which a semiconductor laser is used as a light source unit. Generally, the oscillation frequency of a semiconductor laser changes depending on the amount of injected current and the temperature of the semiconductor laser. (Kobayashi et al., I / E / E / QE18, 58
For this reason, if the injection current to the laser is set above the oscillation threshold value, it is possible to apply frequency modulation at the same time as intensity modulation by changing the injection current. The frequency-modulated light obtained by direct injection current modulation in this way is input to the optical frequency discriminator. At this time, if the discriminator has a discriminating characteristic such that the transmissivity of the discriminator is k (k <1) when the signal is a mark and the transmissivity is 0 when the signal is a space, the permeation output of the discriminator is marked at the time of the mark. , Strength is k times, and strength is 0 at space
Therefore, it is possible to obtain a light intensity modulated wave in which the deterioration amount due to the extinction ratio is suppressed.
以下、周波数弁別器としてマハツェンダ干渉計を考え
マーク率ｍのNRZ符号の場合を例にとって説明する。こ
の時、周波数弁別器への入力光パワーをマーク時には
PM、スペース時にはPSとすると、消光比が最良となるマ
ーク時の透過率ｋ、スペース時の透過率０の場合には、
出力Pmoniは、 Pmoni＝ｍ（１−ｋ）PM＋（１−ｍ）PS となる。さて、ここでレーザの発振周波数が温度等の外
乱により変化したことを考えると、マーク時の透過率は
ｋが１より小さいので、発振周波数ずれに比例して変化
するが、スペース時の透過率は、発振周波数ずれの方向
に依らず透過率は０より大きくなる。ここで、マーク時
の透過率は、外乱による一次の微小変化となるが、スペ
ース時の透過率は、外乱による２次の微小変化となるた
め外乱による透過率の微小変化量をΔｋとすると出力Pm
oniは１次近似で、 Pmoni≒ｍ（１−ｋ−Δｋ）PM＋（１−ｍ）PS となる。これと最良値との差をとり、これに比例してレ
ーザの温度、注入電流、あるいはマイケルソン干渉計の
光路差へ負帰還をかければ、消光比を最良に保つことが
できる。またｋを0.9程度に設定すれば送信信号光振幅
の減少も0.5dB以内となる。また、周波数弁別器の弁別
特性も同様な負帰還で制御できる。Considering a Maha-Zehnder interferometer as a frequency discriminator, a case of an NRZ code with a mark ratio m will be described below as an example. At this time, when marking the input optical power to the frequency discriminator
If P M and P S in space, the extinction ratio is best when the transmittance k at mark and the transmittance 0 at space are
Output Pmoni becomes Pmoni = m (1-k) P M + (1-m) P S. Now, considering that the oscillation frequency of the laser changes due to disturbance such as temperature, the transmittance at the time of mark is smaller than 1, so that it changes in proportion to the deviation of the oscillation frequency. Indicates that the transmittance is greater than 0 regardless of the direction of the oscillation frequency shift. Here, the transmittance at the time of the mark is a first minute change due to the disturbance, but the transmittance at the time of space is a second minute change due to the disturbance. Therefore, if the minute change amount of the transmittance due to the disturbance is Δk, it is output. Pm
oni is a first-order approximation, and Pmoni≈m (1-k-Δk) P M + (1-m) P S. By taking the difference between this value and the best value and applying negative feedback to the temperature of the laser, the injection current, or the optical path difference of the Michelson interferometer in proportion to this, the extinction ratio can be kept at the best. Further, if k is set to about 0.9, the decrease of the transmission signal light amplitude is within 0.5 dB. Further, the discrimination characteristic of the frequency discriminator can be controlled by the same negative feedback.
（実施例） 第１図は、本発明の典型的な実施例の構成図である。
第2,3図は各部の特性を示す図である。この実施例で
は、半導体レーザ１と周波数弁別器としてのマハツェン
ダ干渉計６およびレーザの温度コントローラ３への負帰
還回路21で構成される。(Embodiment) FIG. 1 is a configuration diagram of a typical embodiment of the present invention.
2 and 3 are diagrams showing the characteristics of each part. In this embodiment, the semiconductor laser 1, a Maha-Zehnder interferometer 6 as a frequency discriminator, and a negative feedback circuit 21 to the laser temperature controller 3 are used.
次に本実施例の動作と動作条件を第１〜３図を用いて
説明する。第１図において、1Gb/sの直接パルス電流変
調を受けた波長1.5μｍの半導体レーザ１の出力光20
は、ハーフミラー５およびミラー４からなるマハツェン
ダ干渉計６に入力される。マハツェンダ干渉計６は、周
波数弁別器として動作する。ここで用いた半導体レーザ
１は、発振電流しきい値20mAの単一軸モード発振するレ
ーザであり、信号がスペースの時の電流値I1は30mA、マ
ーク時の電流値I2を50mAとした。この時、マーク時とス
ペース時の発振周波数の差は第２図に示すように約20GH
zとなった。次にマハツェンダ干渉計の光路30,31の光路
差を25GHzの周波数が弁別可能な約6mmにし、さらに信号
がスペース時に出力光９が出ないように光路差を微調し
た（第３図）。また、光路差6mmによる時間遅れで生ず
る出力光９の立上り・立下りのジッタは25ps以下に抑え
られ、1Gb/sの伝送では問題を生じない。この時、出力
光９の消光比は、1:100となり強度変調成分もレーザ１
の出力光20に比らべ1.3倍となった。この時、光検出器
７の電圧出力と直流電源11の電圧を一致させ、差動増幅
器８の出力を零とする。この差動増幅器８の出力は、光
検出器７の電圧出力が直流電源11より大きくなった時に
はレーザ１の温度を下げ発振周波数を上げるように調節
し、また光検出器の電圧出力が直流電源11の電圧より下
がった時にはレーザ１の温度を上げるように調節した。Next, the operation and operating conditions of this embodiment will be described with reference to FIGS. In FIG. 1, the output light 20 of the semiconductor laser 1 with a wavelength of 1.5 μm subjected to the direct pulse current modulation of 1 Gb / s
Is input to a Maha-Zehnder interferometer 6 including a half mirror 5 and a mirror 4. The Mach-Zehnder interferometer 6 operates as a frequency discriminator. The semiconductor laser 1 used here is a laser that oscillates in a single axis mode with an oscillation current threshold value of 20 mA, the current value I 1 when the signal is a space is 30 mA, and the current value I 2 at the time of marking is 50 mA. At this time, the difference between the oscillation frequency at the time of marking and that at the time of space is about 20GH as shown in Fig.2.
became z. Next, the optical path difference between the optical paths 30 and 31 of the Maha-Zehnder interferometer was set to about 6 mm at which the frequency of 25 GHz can be discriminated, and the optical path difference was finely adjusted so that the output light 9 did not come out when the signal was in space (Fig. 3). Also, the rising / falling jitter of the output light 9 caused by the time delay due to the optical path difference of 6 mm is suppressed to 25 ps or less, and there is no problem in 1 Gb / s transmission. At this time, the extinction ratio of the output light 9 is 1: 100, and the intensity modulation component is also the laser 1
It was 1.3 times higher than the output light of 20. At this time, the voltage output of the photodetector 7 and the voltage of the DC power supply 11 are made to coincide with each other, and the output of the differential amplifier 8 is made zero. The output of the differential amplifier 8 is adjusted so that when the voltage output of the photodetector 7 becomes larger than the DC power supply 11, the temperature of the laser 1 is lowered and the oscillation frequency is raised, and the voltage output of the photodetector is the DC power supply. The temperature of the laser 1 was adjusted to rise when the voltage dropped below 11.
この結果出力光９の消光比が1:100のまま安定に得ら
れた。第２の実施例の構成を第４図に示した。この実施
例が第１の実施例と異なる点は、外乱の影響を打ち消す
ためにマハツェンダ干渉計６の光路差へ負帰還を行なっ
ていることである。本実施例では、レーザの温度制御は
行なっていない。この光路差を変化させるため、ここで
は、位相整合器10としてLiNbO3の結晶に電圧を印加する
ことで実効光学長を変化させる素子を用いた。本実施例
においても、半導体レーザ１、マハツェンダ干渉計６お
よび直流電源11は第１の実施例と同様に設定した。差動
増幅器８の出力電圧を位相整合器10に印加することで、
光検出器７の出力電圧が直流電源11の設定電圧値より大
きい時、位相整合器10の実効長を短かくして、マハツェ
ンダ干渉計６の透過特性を高周波側にシフトし、消光比
を保ち、逆の場合、位相整合器10の実効長を長くしてマ
ハツェンダ干渉計６の透過特性を低周波側にシフトして
消光比を保った。この結果、出力光９は消光比が1:100
のまま、安定な強度変調波となった。As a result, the extinction ratio of the output light 9 was stable at 1: 100. The structure of the second embodiment is shown in FIG. This embodiment differs from the first embodiment in that negative feedback is performed to the optical path difference of the Maha-Zehnder interferometer 6 in order to cancel the influence of disturbance. In this embodiment, laser temperature control is not performed. In order to change this optical path difference, here, an element that changes the effective optical length by applying a voltage to a crystal of LiNbO 3 is used as the phase matching device 10. Also in this embodiment, the semiconductor laser 1, the Maha-Zehnder interferometer 6 and the DC power supply 11 are set in the same manner as in the first embodiment. By applying the output voltage of the differential amplifier 8 to the phase matching device 10,
When the output voltage of the photodetector 7 is higher than the set voltage value of the DC power supply 11, the effective length of the phase matching device 10 is shortened and the transmission characteristic of the Maha-Zehnder interferometer 6 is shifted to the high frequency side to keep the extinction ratio and reverse. In this case, the effective length of the phase matching device 10 was increased to shift the transmission characteristic of the Maha-Zehnder interferometer 6 to the low frequency side to maintain the extinction ratio. As a result, the output light 9 has an extinction ratio of 1: 100.
As it was, it became a stable intensity modulated wave.
本発明においては、以上の実施例の他にも様々な変形
例がある。例えばマハツェンダ干渉計のかわりに回折格
子を用いることも可能であるし、位相整合器としては、
圧電素子で媒質を圧縮することで屈折率を変化させる方
式のものを使用することもできる。また、レーザの温度
や、干渉計の弁別特性に負帰還をかけるかわりにレーザ
への注入電流量へ負帰還をかけることもできる。In the present invention, there are various modified examples other than the above-described embodiment. For example, it is possible to use a diffraction grating instead of the Maha-Zehnder interferometer, and as a phase matching device,
It is also possible to use a method of changing the refractive index by compressing the medium with a piezoelectric element. Further, instead of applying negative feedback to the temperature of the laser or the discrimination characteristics of the interferometer, it is also possible to apply negative feedback to the amount of current injected into the laser.
（発明の効果） 以上のように本発明によれば、半導体レーザを直接変
調し得られた周波数変調成分を含む信号光を周波数弁別
器で弁別して前記周波数変調成分を強度変調に変換する
変調方式において、消光比を安定に保ち、光強度変調振
幅も安定に保つことができる。(Effect of the Invention) As described above, according to the present invention, a modulation method in which a signal light including a frequency modulation component obtained by directly modulating a semiconductor laser is discriminated by a frequency discriminator and the frequency modulation component is converted into intensity modulation. In, the extinction ratio can be kept stable and the light intensity modulation amplitude can be kept stable.
第１図は本発明の典型的な実施例の構成図、第２図は半
導体レーザの発振周波数と注入電流量の関係を表わした
図、第３図は光周波数弁別器の透過率と入力周波数の関
係を表わした図、第４図は第２の実施例の構成図であ
る。 図において 1:半導体レーザ、6:マハツェンダ干渉計 2:変調信号源、7:光検出器 3:温度コントローラ、8:差動増幅器 4:ミラー、10:位相整合器 5:ハーフミラー、11:直流電源 である。FIG. 1 is a configuration diagram of a typical embodiment of the present invention, FIG. 2 is a diagram showing a relationship between an oscillation frequency of a semiconductor laser and an injection current amount, and FIG. 3 is a transmittance and an input frequency of an optical frequency discriminator. FIG. 4 is a diagram showing the relationship of the above, and FIG. 4 is a configuration diagram of the second embodiment. In the figure, 1: Semiconductor laser, 6: Maha-Zehnder interferometer 2: Modulation signal source, 7: Photodetector 3: Temperature controller, 8: Differential amplifier 4: Mirror, 10: Phase matching device 5: Half mirror, 11: DC Power supply.
───────────────────────────────────────────────────── 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 10/142 10/152 ─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. 6 Identification code Office reference number FI technical display location H04B 10/142 10/152
Claims (1)
源部と、前記信号光の周波数変調成分を強度変調成分に
変換する光周波数弁別器と、前記周波数弁別器の出力を
モニタし、送信信号の消光比を改善するよう前記光源部
の発振周波数または光周波数弁別器の周波数特性を制御
する負帰還回路とを備えていることを特徴とする光送信
器。1. A light source section for outputting a signal light containing a frequency modulation component, an optical frequency discriminator for converting the frequency modulation component of the signal light into an intensity modulation component, and the output of the frequency discriminator is monitored and transmitted. An optical transmitter, comprising: a negative feedback circuit that controls an oscillation frequency of the light source unit or a frequency characteristic of an optical frequency discriminator so as to improve a signal extinction ratio.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61102417A JPH0810848B2 (en) | 1986-05-02 | 1986-05-02 | Optical transmitter |
| EP87102199A EP0235662B1 (en) | 1986-02-17 | 1987-02-17 | Optical transmitter comprising an optical frequency discriminator |
| DE87102199T DE3787902T2 (en) | 1986-02-17 | 1987-02-17 | Optical transmitter with an optical frequency discriminator. |
| US07/015,705 US4805235A (en) | 1986-02-17 | 1987-02-17 | Optical transmitter comprising an optical frequency discriminator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61102417A JPH0810848B2 (en) | 1986-05-02 | 1986-05-02 | Optical transmitter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS62258528A JPS62258528A (en) | 1987-11-11 |
| JPH0810848B2 true JPH0810848B2 (en) | 1996-01-31 |
Family
ID=14326870
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP61102417A Expired - Fee Related JPH0810848B2 (en) | 1986-02-17 | 1986-05-02 | Optical transmitter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0810848B2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8922681D0 (en) * | 1989-10-09 | 1989-11-22 | Secr Defence | Oscillator |
| EP0772313A3 (en) * | 1990-09-14 | 1997-09-03 | Fujitsu Ltd | SCM optical communication system |
| JP2970776B2 (en) * | 1990-12-17 | 1999-11-02 | 富士通株式会社 | Optical transmitter |
| JP2015102537A (en) * | 2013-11-28 | 2015-06-04 | キヤノン株式会社 | Optical interference tomograph meter |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2107147B (en) * | 1981-09-03 | 1985-07-10 | Standard Telephones Cables Ltd | Optical requency modulation system |
| JPS60145737A (en) * | 1984-01-09 | 1985-08-01 | Nec Corp | Optical signal transmitter |
-
1986
- 1986-05-02 JP JP61102417A patent/JPH0810848B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62258528A (en) | 1987-11-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| LAPS | Cancellation because of no payment of annual fees |