JPH0142513B2 - - Google Patents
Info
- Publication number
- JPH0142513B2 JPH0142513B2 JP11424582A JP11424582A JPH0142513B2 JP H0142513 B2 JPH0142513 B2 JP H0142513B2 JP 11424582 A JP11424582 A JP 11424582A JP 11424582 A JP11424582 A JP 11424582A JP H0142513 B2 JPH0142513 B2 JP H0142513B2
- Authority
- JP
- Japan
- Prior art keywords
- current
- temperature
- thermistor
- optical output
- semiconductor laser
- 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
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/068—Stabilisation of laser output parameters
- H01S5/06804—Stabilisation of laser output parameters by monitoring an external parameter, e.g. temperature
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Description
【発明の詳細な説明】
発明の技術分野
本発明は半導体レーザの駆動回路に関し、高速
変調時の温度特性を改良しようとするものであ
る。DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a semiconductor laser drive circuit, and is intended to improve temperature characteristics during high-speed modulation.
技術の背景
半導体レーザを駆動するのに広く採用される方
法は、一定の信号電流と可変バイアス電流を重畳
するというものである。即ち、温度、レーザ素子
の劣化などによる閾値変化、光出力の変化などを
検出し、バイアス電流を変化させて光出力を一定
に保とうとするものである。Background of the Technology A widely adopted method for driving semiconductor lasers is to superimpose a constant signal current with a variable bias current. That is, it detects changes in the threshold value, changes in optical output, etc. due to temperature, deterioration of the laser element, etc., and attempts to keep the optical output constant by changing the bias current.
従来技術と問題点
しかしながらこの方法では信号電流は一定とし
ているので温度あるいはレーザ素子の劣化による
量子効率の変化を補償することができず、高速変
調時に光出力波形の変動、消光比の変動を引き起
す。第１図でこれを説明すると、Ｉはレーザ駆動
電流、Ｌは光出力、T1，T2，T3は該電流対光出
力の温度T1，T2，T3における特性を示す。温度
はT1＜T2＜T3である。T2が標準温度とし、L0が
所望（基準）光出力とすると、レーザ駆動電流は
パルス電流IP2に選ばれる。そして従来方式では
温度がT3の如く大になるとパルス電流IPはその
まゝにしてバイアス電流をIB2からIB4に変え、
光出力をL0に維持していた。しかしこのように
すると無信号でも電流IB4が流れ、発光が見られ
て消光比が悪くなる。なお光出力の制御は平均値
が一定になるようにするのが普通なので、常時発
光があればバイアス電流の変更はそれを含めたも
のになる（図示状態より若干小になる）。温度が
下つた場合も同様であり、この場合はバイアス電
流を小にして平均光出力が一定になるようにす
る。Conventional technology and problems However, in this method, since the signal current is kept constant, it is not possible to compensate for changes in quantum efficiency due to temperature or laser element deterioration, which causes fluctuations in the optical output waveform and extinction ratio during high-speed modulation. cause. To explain this with reference to FIG. 1, I represents the laser driving current, L represents the optical output, and T 1 , T 2 , and T 3 represent the characteristics of the current versus optical output at temperatures T 1 , T 2 , and T 3 . The temperature is T 1 <T 2 <T 3 . If T 2 is the standard temperature and L 0 is the desired (reference) light output, the laser drive current is chosen to be the pulsed current IP 2 . In the conventional method, when the temperature increases to T 3 , the pulse current IP remains the same and the bias current is changed from IB 2 to IB 4 .
The light output was maintained at L 0 . However, if this is done, the current IB 4 will flow even when there is no signal, light emission will be seen, and the extinction ratio will deteriorate. Note that it is normal to control the light output so that the average value remains constant, so if there is constant light emission, the change in bias current will include this (it will be slightly smaller than in the illustrated state). The same holds true when the temperature drops; in this case, the bias current is reduced to keep the average optical output constant.
またレーザには発振遅延時間があり、電流IP
が閾値（横軸Ｉと特性線T1，T2…の交点）から
立上る場合発振遅延時間がほゞ零であるが、閾値
以外の場合は遅延が生じる。これは特に高速変調
時に入力パルス波形と出力光出力波形との間の相
似性をくずし、光出力の検出には固定基準値以上
の検出出力を取出すという方式をとるのが普通な
ので、検出出力パルスのパルス幅変動を招く（高
温のときパルス幅が大に、低温のとき小になる）。
これは信号が000…のときと111…のとき等では受
信出力の変化態様が異なるというパターン効果を
生じ、好ましくない。 Lasers also have an oscillation delay time, and the current IP
The oscillation delay time is almost zero when it rises from the threshold value (the intersection of the horizontal axis I and the characteristic lines T 1 , T 2 . . . ), but when it is outside the threshold value, a delay occurs. This destroys the similarity between the input pulse waveform and the output optical output waveform, especially during high-speed modulation, and the detection output pulse (The pulse width becomes large when the temperature is high and becomes small when the temperature is low.)
This causes a pattern effect in which the received output changes in different ways when the signal is 000... and when the signal is 111..., which is undesirable.
発明の目的
本発明は温度変化による量子効率の変化を補償
し、使用温度範囲において常に一定の光出力およ
び消光比を確保でき、出力波形変動のないレーザ
駆動回路を提供しようとするものである。OBJECTS OF THE INVENTION The present invention aims to provide a laser drive circuit that compensates for changes in quantum efficiency due to temperature changes, can always maintain a constant optical output and extinction ratio in the operating temperature range, and has no output waveform fluctuations.
発明の構成
本発明は一対のトランジスタのエミツタを抵抗
に共通に接続し、一方のトランジスタのコレクタ
に半導体レーザを接続したレーザ駆動回路におい
て、前記抵抗の一部をサーミスタとし、該サーミ
スタにはコンデンサを並列に接続して、周囲温度
変化によるレーザ発光閾値の変動に一致して変る
バイアス電流を半導体レーザに流すようにし、ま
た前記トランジスタの一方に加える入力信号を半
導体レーザの平均光出力が一定になるように制御
するようにしてなることを特徴とするが、次に実
施例を参照しながらこれを説明する。Structure of the Invention The present invention provides a laser drive circuit in which the emitters of a pair of transistors are commonly connected to a resistor, and a semiconductor laser is connected to the collector of one of the transistors. connected in parallel to cause a bias current to flow through the semiconductor laser that varies in accordance with variations in the laser emission threshold due to changes in ambient temperature, and to apply an input signal to one of the transistors such that the average optical output of the semiconductor laser remains constant. The present invention is characterized in that it is controlled as follows, which will be explained next with reference to embodiments.
発明の実施例
第２図は本発明の実施例を示す。高速レーザ駆
動回路にはCML（カレントモードロジツク）回路
が用いられるが、本発明ではその共通エミツタ回
路にサーミスタを挿入する。図で１０，１２はト
ランジスタ、１４は抵抗で、これらはCMLを構
成する。１６，１８はCMLの負荷抵抗、２０は
半導体レーザ、２２はインダクタンスである。２
４はサーミスタで、CMLのエミツタ抵抗の一部
を置き換たものである（残部は固定抵抗１４が受
持つ）。２６は交流（信号）成分をバイパスする
コンデンサである。トランジスタの一方１０には
入力信号Sgが、他方１２には基準電圧Vrが付加
される。この回路はサーミスタ２４を除いて又は
固定抵抗として考えると通常と同じであり、入力
信号Sgはバイアス電流IBと信号パルスIPとの和
（但し電圧に換算したもの）であつて、標準温度
ではIB＝Vrである。従つて無信号時にはトラン
ジスタ１２がオン、１０はオフで電流はトランジ
スタ１２側に流れ、信号パルスが入るとトランジ
スタ１０がオン、１２はオフに切換わり、レーザ
２０はパルスIP2で駆動され、光出力L0を生じる。
温度が変ると閾値及び光出力が変るが、従来は平
均光出力を検出してそれが一定になるようにイン
ダクタンス２２を通してレーザ２０の直流電流
（バイアス電流）を調整していた。本回路ではサ
ーミスタ２４を設けるので動作は次の如くなる。Embodiment of the invention FIG. 2 shows an embodiment of the invention. A CML (current mode logic) circuit is used in the high-speed laser drive circuit, and in the present invention, a thermistor is inserted into the common emitter circuit. In the figure, 10 and 12 are transistors, and 14 is a resistor, which constitute a CML. 16 and 18 are CML load resistances, 20 is a semiconductor laser, and 22 is an inductance. 2
4 is a thermistor that replaces a part of the emitter resistance of the CML (the rest is handled by the fixed resistor 14). 26 is a capacitor that bypasses the alternating current (signal) component. An input signal Sg is applied to one transistor 10, and a reference voltage Vr is applied to the other transistor 12. This circuit is the same as usual if you remove the thermistor 24 or consider it as a fixed resistor, and the input signal Sg is the sum of the bias current IB and the signal pulse IP (converted to voltage), and at standard temperature IB = Vr. Therefore, when there is no signal, transistor 12 is on, transistor 10 is off, and current flows to the transistor 12 side. When a signal pulse is input, transistor 10 is turned on and transistor 12 is turned off, and the laser 20 is driven by the pulse IP 2 to emit light. produces an output L 0 .
When the temperature changes, the threshold value and optical output change, but conventionally, the average optical output was detected and the direct current (bias current) of the laser 20 was adjusted through the inductance 22 so that it remained constant. Since the thermistor 24 is provided in this circuit, the operation is as follows.
サーミスタは周知のように周囲温度が上ると抵
抗が小になり、周囲温度が下ると抵抗が大になる
負性抵抗素子であるから、第２図の回路で周囲温
度が上るとサーミスタ２４の抵抗は小となり、共
通エミツタ接続点Ｅの電位（これもＥで示す。他
もこれに準ずる）がＥ＝Vr−VBEになるまで抵抗
１４およびサーミスタ２４を流れる電流が増大す
る（こゝでVBEはトランジスタ１０のベース・エ
ミツタ間電圧）。温度が下つた場合はこの逆で、
サーミスタ２４の抵抗が増大し、このため電流は
減少する。固定抵抗２４およびサーミスタ２４の
抵抗を適当に選択すると、前述の閾値、第２図で
言えばSg＞Vrとなつて電流がトランジスタ１２
から１０へスイツチングする時の電流値が第１図
に示す如く温度による変化するように設定でき
る。またサーミスタ２４はコンデンサ２６により
バイパスされているので交流的にはないのと同様
で、そして図示しない回路によりレーザ２０の平
均光出力を検出し、それが一定になるように信号
Sgを調整し、第１図に示すように温度がT3の如
く高ければ駆動電流パルスIP3にまた温度がT1の
如く低ければ駆動電流パルスIP1にする。このよ
うにすると温度の高低に拘わらずバイアス電流
IBは閾値に、レーザ駆動電流パルスは平均光出
力が一定になるように調整できる。 As is well known, a thermistor is a negative resistance element whose resistance decreases when the ambient temperature rises and increases when the ambient temperature falls. Therefore, in the circuit shown in Figure 2, when the ambient temperature rises, the resistance of the thermistor 24 decreases. becomes small, and the current flowing through the resistor 14 and thermistor 24 increases until the potential at the common emitter connection point E (also denoted by E, and the same applies to others) becomes E = Vr - V BE (where V BE is the base-emitter voltage of transistor 10). The opposite is true when the temperature drops,
The resistance of thermistor 24 increases, so the current decreases. If the resistances of the fixed resistor 24 and thermistor 24 are appropriately selected, the threshold value mentioned above, or Sg>Vr in FIG.
The current value when switching from 1 to 10 can be set so that it changes depending on the temperature as shown in FIG. Also, since the thermistor 24 is bypassed by the capacitor 26, it is as if there is no alternating current, and a circuit (not shown) detects the average optical output of the laser 20 and sends a signal to keep it constant.
Sg is adjusted, and as shown in FIG. 1, if the temperature is high like T3 , the drive current pulse is set to IP3 , and if the temperature is low like T1 , the drive current pulse is set to IP1 . In this way, the bias current remains constant regardless of the temperature.
IB can be adjusted to a threshold value, and the laser drive current pulse can be adjusted to keep the average optical output constant.
発明の効果
以上説明したように、本発明では温度変化によ
る閾値変化に応じてバイアス電流を調整してバイ
アスが常に閾値にあるようにし、また温度変化に
よる光出力の変化に応じて信号振幅を変えて平均
光出力が一定になるように制御するので、消光
比、出力パルス幅などの悪化をもたらすことなく
光出力制御が可能になる。またバイアス制御はサ
ーミスタを用いたオープンループ制御で、光出力
制御のみ閉ループ制御なので両制御が干渉し合う
というようなことがなく、極めて円滑な制御を行
なうことができる。Effects of the Invention As explained above, in the present invention, the bias current is adjusted according to the threshold value change due to temperature change so that the bias is always at the threshold value, and the signal amplitude is adjusted according to the change in optical output due to temperature change. Since the average optical output is controlled to be constant, the optical output can be controlled without deteriorating the extinction ratio, output pulse width, etc. Also, bias control is open-loop control using a thermistor, and only optical output control is closed-loop control, so there is no interference between the two controls, and extremely smooth control can be performed.
第１図は光出力とバイアス及び駆動電流との関
係を示す特性図、第２図は本発明の実施例を示す
回路図である。
図面で１０，１２は一対のトランジスタ、２０
は半導体レーザ、２４はサーミスタ、２６はコン
デンサである。
FIG. 1 is a characteristic diagram showing the relationship between optical output, bias, and drive current, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the drawing, 10 and 12 are a pair of transistors, and 20
2 is a semiconductor laser, 24 is a thermistor, and 26 is a capacitor.
Claims (1)
に接続し、一方のトランジスタのコレクタに半導
体レーザを接続したレーザ駆動回路において、前
記抵抗の一部をサーミスタとし、該サーミスタに
はコンデンサを並列に接続して、周囲温度変化に
よるレーザ発光閾値の変動に一致して変るバイア
ス電流を半導体レーザに流すようにし、また前記
トランジスタの一方に加える入力信号を半導体レ
ーザの平均光出力が一定になるように制御するよ
うにしてなることを特徴とする半導体レーザの駆
動回路。1. In a laser drive circuit in which the emitters of a pair of transistors are commonly connected to a resistor and a semiconductor laser is connected to the collector of one transistor, a part of the resistor is a thermistor, and a capacitor is connected in parallel to the thermistor. , a bias current is caused to flow through the semiconductor laser that changes in accordance with fluctuations in the laser emission threshold due to changes in ambient temperature, and an input signal applied to one of the transistors is controlled so that the average optical output of the semiconductor laser is constant. A semiconductor laser drive circuit characterized by:
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11424582A JPS595685A (en) | 1982-07-01 | 1982-07-01 | Driving circuit for semiconductor laser |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11424582A JPS595685A (en) | 1982-07-01 | 1982-07-01 | Driving circuit for semiconductor laser |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS595685A JPS595685A (en) | 1984-01-12 |
| JPH0142513B2 true JPH0142513B2 (en) | 1989-09-13 |
Family
ID=14632917
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP11424582A Granted JPS595685A (en) | 1982-07-01 | 1982-07-01 | Driving circuit for semiconductor laser |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS595685A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0534124Y2 (en) * | 1984-10-09 | 1993-08-30 | ||
| US5974064A (en) * | 1998-04-14 | 1999-10-26 | Optobahn Corporation | Temperature compensation of laser diodes |
-
1982
- 1982-07-01 JP JP11424582A patent/JPS595685A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS595685A (en) | 1984-01-12 |
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