JPH04287386A - Semiconductor light emitting device - Google Patents
Semiconductor light emitting deviceInfo
- Publication number
- JPH04287386A JPH04287386A JP5193391A JP5193391A JPH04287386A JP H04287386 A JPH04287386 A JP H04287386A JP 5193391 A JP5193391 A JP 5193391A JP 5193391 A JP5193391 A JP 5193391A JP H04287386 A JPH04287386 A JP H04287386A
- Authority
- JP
- Japan
- Prior art keywords
- light emitting
- emitting device
- semiconductor light
- optical communication
- chirping
- 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.)
- Withdrawn
Links
- 239000004065 semiconductor Substances 0.000 title claims abstract description 37
- 230000003287 optical effect Effects 0.000 claims abstract description 26
- 238000004891 communication Methods 0.000 claims abstract description 17
- 230000010355 oscillation Effects 0.000 claims abstract description 9
- 230000005540 biological transmission Effects 0.000 abstract description 8
- 238000010586 diagram Methods 0.000 description 6
- 238000007796 conventional method Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000000295 emission spectrum Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000003321 amplification Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 239000013307 optical fiber Substances 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
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- Semiconductor Lasers (AREA)
Abstract
Description
【0001】0001
【産業上の利用分野】本発明は,CATV等のアナログ
光通信システムにおける半導体発光装置に関する。CA
TV等のアナログ光通信システムにおいては,40チャ
ネルのTV信号を15km程度,画質を劣化させること
なく伝送する必要がある。そのため,光伝送のための光
源としてDFB半導体レーザ等の半導体発光装置が用い
られている。しかし,従来におけるそのような光通信シ
ステムにおいては,光信号を伝送する光ファイバ内部に
おいて送信光がレイリー散乱し,送信光とレイリー散乱
光との間でホモダイン検波を生じるため,雑音が多いも
のであった。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device in an analog optical communication system such as CATV. CA
In analog optical communication systems such as TVs, it is necessary to transmit 40 channels of TV signals over a distance of approximately 15 km without deteriorating image quality. Therefore, a semiconductor light emitting device such as a DFB semiconductor laser is used as a light source for optical transmission. However, in such conventional optical communication systems, the transmitted light undergoes Rayleigh scattering inside the optical fiber that transmits the optical signal, and homodyne detection occurs between the transmitted light and the Rayleigh scattered light, resulting in a lot of noise. there were.
【0002】本発明は,CATV等の光通信においてノ
イズの少ない光伝送を可能とする半導体発光装置を提供
することを目的とする。SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor light emitting device that enables optical transmission with less noise in optical communications such as CATV.
【0003】0003
【従来の技術】図4により従来の技術を説明する。図に
おいて,(a) は光通信システムを示し,図(b)
は半導体レーザにおける変調方法を示す。図(a) に
おいて,30は半導体レーザ,31は光伝送路,33は
受光ダイオード,34はチャネル側と光源側の結合用の
コンデンサ,35は高周波電流遮断用のコイル,36は
抵抗である。2. Description of the Related Art A conventional technique will be explained with reference to FIG. In the figure, (a) shows an optical communication system, and figure (b)
shows a modulation method in a semiconductor laser. In Figure (a), 30 is a semiconductor laser, 31 is an optical transmission line, 33 is a light receiving diode, 34 is a capacitor for coupling between the channel side and the light source side, 35 is a coil for cutting off high frequency current, and 36 is a resistor.
【0004】図の動作は,次の通りである。半導体レー
ザ30にバイアス電流Ibが流れることにより,半導体
レーザ30はレーザ光を出力する。チャネル信号(Ch
信号)により光変調された半導体レーザ30の出力は,
光伝送路31を介して受信側に送信される。そして,受
信側において,受光ダイオード33で受光され,電気信
号に変換される。変換された電気信号は,増幅されて復
調される(増幅回路,復調回路は図示せず)。The operation shown in the figure is as follows. When the bias current Ib flows through the semiconductor laser 30, the semiconductor laser 30 outputs laser light. Channel signal (Ch
The output of the semiconductor laser 30 optically modulated by the signal) is
It is transmitted to the receiving side via the optical transmission line 31. Then, on the receiving side, the light is received by a light receiving diode 33 and converted into an electrical signal. The converted electrical signal is amplified and demodulated (the amplification circuit and demodulation circuit are not shown).
【0005】図(b) は,半導体レーザにおける変調
方法の例で,アナログ信号形式で直接変調する場合を示
す。
図(b) において,縦軸は光強度,横軸は半導体レー
ザに流れる電流を示す。電流・光出力特性40の半導体
レーザに,チャネル信号41によりバイアス電流(Ib
)を中心にした変動電流が流れる。その結果,チャネル
信号41により強度変調された光出力42が得られる。[0005] Figure (b) shows an example of a modulation method in a semiconductor laser, in which direct modulation is performed in an analog signal format. In figure (b), the vertical axis shows the light intensity and the horizontal axis shows the current flowing through the semiconductor laser. A bias current (Ib
) A fluctuating current flows around the center. As a result, an optical output 42 whose intensity is modulated by the channel signal 41 is obtained.
【0006】図5は,半導体レーザにおけるチャーピン
グの説明図である。図において横軸は変動周波数fであ
り,縦軸はレーザ光のスペクトル強度を示す。半導体レ
ーザは,高速に変調を行うと波長が過渡的に変動するチ
ャーピングを起こすことが知られている。FIG. 5 is an explanatory diagram of chirping in a semiconductor laser. In the figure, the horizontal axis represents the fluctuation frequency f, and the vertical axis represents the spectral intensity of the laser beam. Semiconductor lasers are known to cause chirping, which is a transient fluctuation in wavelength, when modulated at high speed.
【0007】図において,41は中心波であって,半導
体レーザにより定まるものである。42,42’は,変
動波であって,動的に波長がシフトしたものである。4
3は出力波であって,中心波41を中心に変動した変動
波42,42’により実際に観測されるものを示す。図
示のように,変調したとき実際に観測される半導体レー
ザの出力波は,チャーピングによる変動波42,42’
が時間平均された図示のように幅Δfを持ったものであ
る。In the figure, numeral 41 is a center wave, which is determined by the semiconductor laser. 42 and 42' are fluctuating waves whose wavelengths have been dynamically shifted. 4
3 is an output wave, which is actually observed by fluctuating waves 42, 42' that fluctuate around the center wave 41. As shown in the figure, the output waves of the semiconductor laser that are actually observed when modulated are fluctuating waves 42, 42' due to chirping.
is time-averaged and has a width Δf as shown in the figure.
【0008】[0008]
【発明が解決しようとする課題】半導体レーザ光を変調
して信号伝送する場合,変調を加える信号周波数が高い
場合には,上述のΔfは狭い方が信号対雑音指数(CN
R)はよいのであるが,信号周波数が低い場合には,Δ
fが大きい方がCNRは良くなることが知られている。[Problem to be Solved by the Invention] When transmitting signals by modulating semiconductor laser light, if the signal frequency to be modulated is high, the narrower the above Δf, the better the signal-to-noise figure (CN).
R) is good, but when the signal frequency is low, Δ
It is known that the larger f is, the better the CNR is.
【0009】CATV等の光通信において使用される周
波数(50MHz〜300MHz)の範囲では,Δfは
大きい方がよくなるが,従来は,レーザ出力光のΔfが
小さく,CNRが悪いため良好な通信を行うことができ
なかった。本発明は,CATV等の光通信に使用した場
合,良好なCNRが得られる半導体発光装置を得ること
を目的とする。[0009] In the frequency range (50 MHz to 300 MHz) used in optical communications such as CATV, the larger Δf is, the better; however, conventionally, the Δf of the laser output light was small and the CNR was poor, so good communication was not achieved. I couldn't. An object of the present invention is to obtain a semiconductor light emitting device that can obtain good CNR when used in optical communications such as CATV.
【0010】0010
【課題を解決するための手段】本発明は,半導体レーザ
におけるチャーピングを利用することにより,チャネル
の信号周波数において良好なCNRが得られるようなΔ
fを半導体発光装置に持たせるようにした。そのために
,最大利得波長λgの半導体レーザにおいて,発振波長
λpに対して,Δλp=λp−λgが十分大きくなるよ
うな構造とした。具体的には,CATV等においては,
チャーピングによる周波数の変動が,変調電流1mAに
対して400MHz/mA(FM変調度)であればよい
ことが実験的に求められているので,Δλを400MH
z/mAのFM変調度が得られる程度にした。[Means for Solving the Problems] The present invention utilizes chirping in a semiconductor laser to achieve a Δ
The semiconductor light emitting device is made to have f. For this purpose, in a semiconductor laser having a maximum gain wavelength λg, a structure is adopted such that Δλp=λp−λg is sufficiently large with respect to the oscillation wavelength λp. Specifically, in CATV etc.
It has been experimentally determined that the frequency fluctuation due to chirping should be 400 MHz/mA (FM modulation degree) for 1 mA of modulation current, so Δλ is set to 400 MHz.
It was set to such an extent that an FM modulation degree of z/mA could be obtained.
【0011】図1により本発明の原理を説明する。図は
,ホモダイン検波における周波数と雑音強度の関係を示
す。Δλをパラメータとして,縦軸は雑音強度,横軸は
信号周波数(チャネル周波数)である。曲線1はΔλが
小の場合を示し,曲線2はΔλが中の場合,曲線3はΔ
λが大の場合を示す。faは実際の光通信に使用される
チャネル周波数である。本発明においては,半導体発光
装置におけるλgとλpをΔλが大となるようにし,4
00MHz/mA程度のFM変調度が得られるようにし
た。The principle of the present invention will be explained with reference to FIG. The figure shows the relationship between frequency and noise intensity in homodyne detection. With Δλ as a parameter, the vertical axis is the noise intensity, and the horizontal axis is the signal frequency (channel frequency). Curve 1 shows when Δλ is small, curve 2 shows when Δλ is medium, and curve 3 shows when Δλ is small.
The case where λ is large is shown. fa is a channel frequency used in actual optical communication. In the present invention, λg and λp in the semiconductor light emitting device are set such that Δλ is large, and 4
An FM modulation degree of approximately 00 MHz/mA was obtained.
【0012】0012
【作用】図の雑音強度対信号周波数の関係から示される
ように,Δλが十分小さく,出力光のスペクトルの幅が
狭ければ,周波数faにおいて,雑音強度は小さくなり
,CNRは良好になる。しかし,実際の出力光はチャー
ピングのためスペクトルに幅を持ち,曲線2に示すよう
な雑音強度と信号周波数の関係となり,実際に通信で使
われる周波数faの付近で,CNRが悪かった。[Operation] As shown from the relationship between the noise intensity and the signal frequency in the figure, if Δλ is sufficiently small and the spectral width of the output light is narrow, the noise intensity will be small at the frequency fa and the CNR will be good. However, the actual output light has a spectrum width due to chirping, resulting in a relationship between noise intensity and signal frequency as shown in curve 2, and the CNR was poor near the frequency fa actually used in communication.
【0013】一方,Δλを大きくすると,曲線3に示さ
れるように,周波数faにおいて,雑音強度が小さくな
り良好な光通信が可能となる。光通信においては,通常
はチャーピングを抑えることにより,できるだけ狭い発
光スペクトルを持つレーザ光が得られるようにしていた
が,本発明においては,逆に,発光スペクトルの幅を広
くするようことにより,雑音強度を小さくするようにし
た。On the other hand, when Δλ is increased, as shown by curve 3, the noise intensity becomes smaller at the frequency fa, making it possible to perform good optical communication. In optical communication, normally, by suppressing chirping, a laser beam with an emission spectrum as narrow as possible is obtained, but in the present invention, on the contrary, by widening the width of the emission spectrum, I tried to reduce the noise intensity.
【0014】[0014]
【実施例】図2は,DFB半導体レーザにおける場合の
本発明の実施例を示す。図(a)はDFB半導体レーザ
を示し,図(b) は半導体レーザにおける波長と利得
の関係を示す。図(a) において,20はP型層(P
−InP),21は活性層(InGaAsP),22は
ガイド層(InGaAsP),23は回折格子,24は
n型層(n−InP)である。Embodiment FIG. 2 shows an embodiment of the invention in a DFB semiconductor laser. Figure (a) shows a DFB semiconductor laser, and Figure (b) shows the relationship between wavelength and gain in the semiconductor laser. In figure (a), 20 is a P-type layer (P
-InP), 21 is an active layer (InGaAsP), 22 is a guide layer (InGaAsP), 23 is a diffraction grating, and 24 is an n-type layer (n-InP).
【0015】図の構成の動作において,P型層20から
n型層24に向かって電流が流れると,活性層21にお
いて励起された光が反射鏡25,25’の間を往復する
ことにより活性層の電子を励起し,電子密度の反転状態
が形成され,レーザ発振される。その発振スペクトルの
うち,回折格子23で決められる発振波長λpの光がレ
ーザ光として出力される。In the operation of the configuration shown in the figure, when a current flows from the P-type layer 20 to the N-type layer 24, the light excited in the active layer 21 is activated by reciprocating between the reflecting mirrors 25 and 25'. Electrons in the layer are excited, an inverted state of electron density is formed, and laser oscillation occurs. Of the oscillation spectrum, light having an oscillation wavelength λp determined by the diffraction grating 23 is output as a laser beam.
【0016】図(b) は発振波長と利得の関係を示し
,最大利得波長λgにおいて,出力光の最大利得が得ら
れることを示す。一般的には,図(a) における回折
格子23による発振波長が最大利得波長になるように選
択するのがレーザ発振効率の点からは有利である。しか
し,本発明では,λpとλgに対してΔλ=λp−λg
が大きくなるように回折格子22の格子間隔を定める(
Δλ≧15nm,この範囲に定める理由は後述)。具体
的には,CATV等の光通信において必要とされる40
0MHz/mA以上のFM変調度を得るためにはΔλ≧
15nmとする。Figure (b) shows the relationship between the oscillation wavelength and the gain, and shows that the maximum gain of the output light is obtained at the maximum gain wavelength λg. In general, it is advantageous from the point of view of laser oscillation efficiency to select the oscillation wavelength by the diffraction grating 23 in FIG. 2A to be the maximum gain wavelength. However, in the present invention, for λp and λg, Δλ=λp−λg
The grating spacing of the diffraction grating 22 is determined so that (
Δλ≧15 nm, the reason for setting this range will be described later). Specifically, the 40
In order to obtain an FM modulation degree of 0MHz/mA or more, Δλ≧
It is set to 15 nm.
【0017】図3によりその理由を説明する。図3にD
FB半導体レーザにおけるチャーピング幅とΔλの関係
を示す実験データである。図において,縦軸は変調電流
1mA当たりのチャーピング幅(MHz/mA),横軸
はΔλ(nm)である。図示の実験データから示される
ように,Δλが15nm以上あれば,約380MHz以
上のチャーピング幅が得られ,CATVにおいて必要と
される400MHz/mAをほぼ満たすことができる。The reason for this will be explained with reference to FIG. D in Figure 3
This is experimental data showing the relationship between chirping width and Δλ in an FB semiconductor laser. In the figure, the vertical axis is the chirping width (MHz/mA) per 1 mA of modulation current, and the horizontal axis is Δλ (nm). As shown from the experimental data shown, if Δλ is 15 nm or more, a chirping width of about 380 MHz or more can be obtained, which can almost satisfy the 400 MHz/mA required for CATV.
【0018】図2(a) におけるDFB半導体レーザ
において,上記の条件を満たす一例は次の通りである。
回折格子23のピッチを2045nm,ガイド層22の
層厚0.15nm,活性層21の層厚0.1nm,活性
層の材料で決められる固有波長を1295nmとしたと
き,λp=1320nm,λg=1300nmとなりΔ
λ=20nmが得られる。上記のように,本実施例によ
れば,従来から知られているDFB半導体レーザにおけ
る格子間隔をΔλが上記の条件を満たすようにするだけ
の簡単な構成で,40チャネル,15kmの伝送時にお
いて,低ノイズ(CNR56dB),低歪みの光伝送シ
ステムを実現できる。An example of the DFB semiconductor laser shown in FIG. 2A that satisfies the above conditions is as follows. When the pitch of the diffraction grating 23 is 2045 nm, the thickness of the guide layer 22 is 0.15 nm, the thickness of the active layer 21 is 0.1 nm, and the characteristic wavelength determined by the material of the active layer is 1295 nm, λp = 1320 nm, λg = 1300 nm. Next Δ
λ=20 nm is obtained. As described above, according to this embodiment, a conventional DFB semiconductor laser has a simple configuration in which the grating spacing is set so that Δλ satisfies the above conditions, and 40 channels and 15 km transmission can be achieved. , a low-noise (CNR56dB), low-distortion optical transmission system can be realized.
【0019】[0019]
【発明の効果】本発明によれば,光伝送路における信号
対雑音比を確実に向上させることができ,低雑音,低歪
みのCATV等の光通信を可能にする。According to the present invention, it is possible to reliably improve the signal-to-noise ratio in an optical transmission line, and to enable low-noise, low-distortion optical communication such as CATV.
【図1】本発明の原理説明図でる。FIG. 1 is a diagram explaining the principle of the present invention.
【図2】本発明の実施例を示す図である。FIG. 2 is a diagram showing an embodiment of the present invention.
【図3】チャーピング幅とΔλの関係を示す図である。FIG. 3 is a diagram showing the relationship between chirping width and Δλ.
【図4】従来の技術の説明図である。FIG. 4 is an explanatory diagram of a conventional technique.
【図5】半導体レーザにおけるチャーピングの説明図で
ある。FIG. 5 is an explanatory diagram of chirping in a semiconductor laser.
1 :Δλ小の特性曲線 2 :Δλ中の特性曲線 3 :Δλ大の特性曲線 1: Characteristic curve of small Δλ 2: Characteristic curve during Δλ 3: Characteristic curve with large Δλ
Claims (2)
置において,該半導体発光装置から出力される発振波長
をλpとし,該半導体発光装置の最大利得波長をλgと
したとき,Δλ=λp−λgとして,Δλを15nm以
上とし,光変調するための信号周波数における雑音強度
が小さくなる程度に出力波のチャーピング幅を大きくす
るようにしたことを特徴とする半導体発光装置。Claim 1: In a semiconductor light emitting device in an optical communication system, where λp is the oscillation wavelength output from the semiconductor light emitting device, and λg is the maximum gain wavelength of the semiconductor light emitting device, Δλ=λp−λg, Δλ 15 nm or more, and the chirping width of the output wave is made large enough to reduce noise intensity at a signal frequency for optical modulation.
単一モードレーザであり,回折格子の格子間隔によりλ
pを定めたことを特徴とする半導体発光装置。[Claim 2] In Claim 1, the semiconductor light emitting device is a single mode laser, and the λ
A semiconductor light emitting device characterized in that p is determined.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP5193391A JPH04287386A (en) | 1991-03-18 | 1991-03-18 | Semiconductor light emitting device |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP5193391A JPH04287386A (en) | 1991-03-18 | 1991-03-18 | Semiconductor light emitting device |
Publications (1)
Publication Number | Publication Date |
---|---|
JPH04287386A true JPH04287386A (en) | 1992-10-12 |
Family
ID=12900674
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP5193391A Withdrawn JPH04287386A (en) | 1991-03-18 | 1991-03-18 | Semiconductor light emitting device |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPH04287386A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2003069144A (en) * | 2001-08-28 | 2003-03-07 | Furukawa Electric Co Ltd:The | Distributed feedback semiconductor laser element |
-
1991
- 1991-03-18 JP JP5193391A patent/JPH04287386A/en not_active Withdrawn
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2003069144A (en) * | 2001-08-28 | 2003-03-07 | Furukawa Electric Co Ltd:The | Distributed feedback semiconductor laser element |
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