JPH1117625A - Light-emitting element drive circuit and optical transmitter using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration in an optical output waveform and skew in the high-speed synchronous parallel optical transmitter. SOLUTION: A light-emitting element drive circuit 1 is provided with a delay circuit 14, a modulation current generating circuit 11 that genertes a 1st drive current, a pulse width adjustment circuit 13, and a pulse current generating circuit 12 that generates a 2nd drive current. The pulse current, generated to be a same pattern as that of the modulation current, is in a current-on state in precedence by a time ton from the modulation current and reaches a current- off state substantially simultaneously as when an optical output turns into an on-state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element driving circuit and an optical transmitter using the same, and more particularly, to a light emitting element driving circuit for improving an optical transmission waveform for high-speed transmission and an optical transmitter using the same. .

[0002]

2. Description of the Related Art To construct a future information infrastructure, a large-capacity asynchronous transfer mode (Asynchronous Transfer Mode) is required.
Advanced information processing devices such as a non-transfer mode (ATM) switch, an ultra-high-speed transmission device, and a massively parallel computer are indispensable. Recent large-scale integrated circuits (V
With the development of LSIs, high-speed and high-density signal processing circuits of such advanced information processing apparatuses are becoming possible, and accordingly, high-speed and high-density signal wiring between and within the apparatuses is required.

Under such circumstances, research and development of optical wiring technology has been activated as a technology for realizing high-speed and high-density signal wiring which is difficult to realize with conventional electric cables. In particular, since the optical wiring of the optical parallel transmission device capable of synchronous parallel transmission can directly transmit the data signal to be processed in parallel, the multiplexing and clock extraction are compared with the optical wiring of the serial optical transmission device that multiplexes data. This eliminates the need for circuits necessary for frame synchronization and the like, and is a technique suitable for inter-device and intra-device wiring. In synchronous parallel transmission, in order to maintain synchronization between data, the transmitted parallel data is synchronized by a clock on the receiving side. Therefore, it is necessary to secure a phase margin between the clock and the data in the synchronous circuit. Therefore, the relative propagation delay time difference of the signal is reduced (low skew) and the duty of the optical signal is deteriorated (pulse width fluctuation).
Control is an important issue.

In an optical transmitter used in an optical parallel transmission device, in order to obtain a stable extinction level of an optical signal, a light emitting element is biased below an oscillation threshold current value to suppress the influence of electrical crosstalk. . As a result, oscillation delay occurs in the light emitting element, and even if the duty of the input signal is 50%, the duty of the optical signal is less than 50%. The oscillation delay time Td is a delay time from when a modulation current is applied to a light emitting element to when the injected carrier density of the light emitting element reaches an oscillation threshold and oscillates. The carrier life, threshold current and bias current of the light emitting element And a drive current such as a modulation current. In addition, the temperature dependency of the light emitting element characteristics, the manufacturing variation between the channels, and the manufacturing variation of the driving circuit are:
A skew occurs due to a variation in the oscillation delay time and a variation between channels.

Therefore, in order to maintain good transmission characteristics in parallel transmission, duty deterioration of an optical signal due to oscillation delay of a light emitting element is suppressed, and skew due to manufacturing variations and temperature dependence of the light emitting element characteristics. It is important to reduce

FIG. 12 shows a conventional light emitting element driving circuit used in an optical parallel transmission device. In this conventional example, the light-emitting element driving circuit includes an input terminal, a modulation current generation circuit, a bias current generation circuit, a temperature detection circuit, and a temperature characteristic control circuit. The modulation current generation circuit outputs a modulation current having a current amplitude Im, and the bias current generation circuit outputs a DC bias current equal to or smaller than a threshold current. The modulation current and the bias current are controlled by a temperature characteristic control circuit so as to suppress the fluctuation of the optical output power and the oscillation delay time with respect to the temperature. When the light emitting element is driven by the light emitting element driving circuit of the conventional example, the oscillation delay time td (T) and the light output power P
out (T) is approximately given by the following equation.

[0007]

(Equation 1)

[0008]

(Equation 2)

Here, τn (T) is the carrier lifetime of the light emitting element, Ith (T) is the threshold current, η (T) is the slope efficiency, Im (T) is the modulation current, Ib (T) is the bias current, T is the temperature. The modulation and bias currents are
For example, the oscillation delay time td (T) and the optical output power Po
In order that ut (T) is constant with respect to temperature,
It is determined by solving as a simultaneous equation of m (T) and Ib (T).

According to this conventional example, fluctuations in the optical output power and fluctuations in the oscillation delay time with respect to fluctuations in the temperature of the light emitting element are suppressed, so that skew due to the temperature dependence of the characteristics of the light emitting element can be suppressed. . As such a conventional light emitting element driving circuit and an optical parallel transmitter, those described in, for example, Lecture Paper 2, SC-5-4, pp. 224 to 225 of the 1996 IEICE Electronics Society Conference are known. I have.

FIG. 13 shows another conventional example of a light emitting element driving circuit which is not premised on application to an optical parallel transmission apparatus but can suppress the deterioration of the duty of an optical signal due to the oscillation delay of the light emitting element. Here, the light-emitting element driving circuit includes a signal input terminal, a delay circuit, an OR circuit, a modulation current amplifier circuit, and an output terminal. After the input signal is split into two,
One of the signals is delayed by the time d by the delay circuit, and is input to the OR circuit together with the other signal which is branched into two. The output of the OR circuit whose pulse width has been expanded by d is converted into a current amplitude Im by the modulation current generation circuit, and then output. Therefore, by setting the delay time d so as to offset the oscillation delay of the light emitting element, the duty deterioration due to the oscillation delay can be suppressed. An example of such a conventional light emitting element driving circuit is disclosed in Japanese Patent Application Laid-Open No. 2-60331.

Japanese Patent Application Laid-Open No. 55-133588 discloses a configuration in which a pre-pulse width generated by a pattern detection delay circuit is controlled by a detection circuit, but using a detector and a phase shifter. Therefore, the circuit is not suitable for a multi-channel transmission device. JP-A-4-2839
No. 78 describes a laser diode driving circuit provided with a pulse bias generating means. Japanese Patent Application Laid-Open No. 7-38184 describes a method of driving a laser diode in which a preceding pulse bias current smaller than a laser threshold value is applied. Further, Japanese Patent Application Laid-Open No. 8-64890 describes a method of configuring a semiconductor laser having a configuration in which a superimposed pulse is added to a DC bias.

[0013]

In order to improve the performance of the above-mentioned advanced information processing apparatus, it is necessary to increase the throughput of the optical parallel transmission apparatus. To this end, the transmission speed per channel is increased. It is effective. In order to realize good synchronous parallel transmission even when the transmission speed is increased, it is necessary to further reduce the oscillation delay and the skew according to the decrease of the time slot. However, in the above-described conventional example, the following problem occurs.

In the light emitting element driving circuit of the first conventional example, it is necessary to reduce the difference between the threshold current and the bias current in order to reduce the oscillation delay time. However, the injected carrier density of the active layer of the light emitting element, which has become lower than the oscillation threshold value as the modulation current is turned off, decreases exponentially with a time constant (carrier lifetime) of several nanoseconds. As a result, the injected carrier density may reach the threshold value again due to the fluctuation of the bias current level, and light may be emitted in a portion where the optical output should be at the extinction level. Such waveform deterioration causes an identification error of transmitted data, and deteriorates transmission characteristics. As the signal speed increases, it is more difficult to suppress ringing and crosstalk occurring at the falling portion of the drive current waveform, and a light emitting element drive circuit capable of suppressing waveform deterioration due to the ringing and crosstalk is required. Was.

A light-emitting element driving circuit according to a second conventional example includes:
When applied to an optical parallel transmitter, a deviation of the delay time from the design value due to a manufacturing variation of the delay circuit directly causes a rise time of the optical output signal, and causes a loss of synchronization of the transmitted parallel data. Therefore, in high-speed synchronous parallel transmission in which the oscillation delay time reaches several tens of percent of the pulse width of one bit of a signal, it is necessary to reduce skew due to manufacturing variations of the delay circuit.

The carrier density of the light emitting element decreases exponentially after the drive current is turned off. Therefore, in high-speed transmission in which the carrier life is almost equal to the signal period, the residual carrier has an equivalent bias. It becomes a current. As a result, in the optical transmitter, the waveform is deteriorated due to the fluctuation of the oscillation delay time depending on the bit pattern of each channel, which causes the deterioration of the transmission characteristics. For this reason, when high-speed transmission is performed by using a driving method that does not use a bias current or applies a bias current equal to or less than the threshold current of the light-emitting element, a light-emitting element drive circuit that reduces waveform deterioration due to residual carriers is required. .

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to suppress the waveform deterioration due to ringing and crosstalk, and reduce the waveform deterioration and skew due to manufacturing variations and residual carriers, even for a high-speed signal. An object of the present invention is to provide an element driving circuit and an optical transmitter having good transmission characteristics even when a transmission signal is speeded up.

[0018]

SUMMARY OF THE INVENTION According to the present invention, there is provided a first driving current set so that a light output power of a light emitting element becomes a predetermined value, and the current is turned on at a timing different from the first driving current. A light emitting element driving circuit that outputs a second driving current such that an overlap time with the first driving current is equal to or less than an allowable pulse width reduction amount of an optical signal, wherein a bit pattern of an input signal is It is a light emitting element drive circuit provided with a detecting means.

According to the light emitting element driving circuit of the present invention,
Since the drive current that has been turned on first becomes an equivalent bias current that exists only at the rising portion of the drive current that is applied to the light emitting element later, a DC bias current is unnecessary,
Alternatively, the DC bias current can be set sufficiently smaller than the threshold current. Accordingly, the oscillation delay time is reduced, and when the first drive signal changes from the current on to the current off, the light output waveform deterioration due to ringing and crosstalk occurring at the falling portion of the first drive current waveform and the second A light emitting element drive circuit in which optical output waveform deterioration due to application of a drive current is suppressed is realized.

Further, the current is turned on with a delay with respect to the first drive current having the expanded pulse width, and the second drive current having a pulse width of about the pulse width reduction amount of the optical output is applied, Since the variation in the pulse width of the first drive current is converted into the variation in the bias current of the second drive current, the influence of manufacturing variation on the pulse width of the light output of the light emitting element can be reduced.

The second drive current is turned on simultaneously with the first drive current having the expanded pulse width, and the second drive current having a pulse width of about the pulse width reduction amount of the optical output is applied, thereby providing the second drive current. Compared with the case without the current, the pulse extension width of the first drive current can be reduced, and the current value contributing to the oscillation of the light emitting element can be increased without substantially increasing the optical output power. The output pulse width deterioration can be reduced.

Further, according to the present invention, by adjusting the output of the driving current for suppressing the waveform deterioration due to the oscillation delay in accordance with the output of the bit pattern detection means, the skew due to the influence of the residual carrier is reduced. An element driving circuit is realized.

According to the optical transmitter of the present invention, the provision of the light emitting element driving circuit of the present invention reduces the oscillation delay, suppresses the deterioration of the optical output waveform due to ringing and crosstalk, and reduces the manufacturing variation of the delay circuit. Since an optical transmitter with reduced skew is provided, an optical transmitter having good transmission characteristics even when a signal is speeded up is realized.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of a light emitting element driving circuit according to the present invention. In FIG. 1, the light emitting element driving circuit 1 includes an input terminal 16, a delay circuit 14, a modulation current generating circuit 11 as a first driving current and its output terminal 17, a pulse width adjusting circuit 13, and a second driving current (here, A pulse current) and an output terminal 18 thereof.

The electric signal input from the input terminal 16 is 2
One of the branched signals is delayed by the time ton by the delay circuit 14, then converted into a signal having a current amplitude Im by the modulation current generation circuit 11, and output as a first drive signal. The other branched signal is converted to a pulse width tw by the pulse width adjustment circuit 13 and then output as a second drive signal having a current amplitude Ibp by the pulse current generation circuit.

FIG. 2 shows an example of an output waveform of the light emitting element drive circuit according to the present invention and an optical output waveform when the light emitting element is driven by the present drive circuit. FIG. 2A shows the case where the pulse current Ibp is turned on in advance of the modulation current Im by the time ton in addition to the modulation current Im to the light emitting element and the pulse current is turned off at the same time as the modulation current is turned on. (B)
This is a case where the pulse current is turned off after a fixed time after the modulation current is turned on.

The light output when the light emitting element is driven only by the modulation current has a large pulse width deterioration at the rising portion due to the oscillation delay as shown by the broken line waveform in FIG.
On the other hand, when the light emitting element is driven by adding a pulse current that is turned on prior to the modulation current, the increase in the injected carrier density due to the pulse current equivalently serves as a bias current. As shown by the solid line, a decrease in the pulse width due to the oscillation delay can be suppressed. Therefore, a DC bias current is not required, or a DC bias current that is sufficiently smaller than the threshold current of the light emitting element is sufficient, so that deterioration of the optical output waveform due to ringing or crosstalk when the modulation current is off can be suppressed.

When an overlap is provided between the modulation current and the pulse current as shown in FIG.
Since the driving current contributing to the oscillation can be increased as compared with the case of the above, the deterioration of the pulse width can be further reduced. For a plurality of light emitting elements having characteristic variations, by setting Ibp and ton such that the pulse width deterioration amount of the light output of the light emitting element having the maximum threshold current is equal to or less than a predetermined value, the driving for each channel is performed. No current adjustment is required. Also, the pulse width of the pulse current is set so that the overlap time with the modulation current is about the above-described pulse width deterioration amount,
Light output waveform deterioration due to pulse current application can be suppressed.

FIG. 3 shows a circuit configuration example of the light emitting element circuit according to the embodiment shown in FIGS. 1 and 2 and a schematic diagram of a circuit internal waveform. In FIG. 3A, the light emitting element driving circuit 1
Represents an input terminal 16, delay circuits 14-1 and 14-2,
AND circuit 20, current switch circuit 11 for generating a modulation current and its output terminal 17, current switch circuit 12 for generating a pulse current, and its output terminal 1
8. According to the present embodiment, as shown in FIG. 3B, in addition to the modulation current, the current is turned on prior to the current-on of the modulation current by the time ton = d1, and the pulse current having the pulse width tw = d1 + d2 is generated. The generated light emitting element driving circuit can be realized.

FIG. 4 shows a second embodiment of the light emitting element drive circuit according to the present invention. In FIG. 4, the light emitting element driving circuit includes:
It comprises an input terminal 16, a pulse width adjustment circuit 13-1, a modulation current generation circuit 11 and its output terminal 17, a delay circuit 14, a pulse width adjustment circuit 13-2, a pulse current generation circuit 12, and an output terminal 18 thereof. The signal from the input terminal 16 is branched into two signals, one of which is a pulse width extension circuit 1
After the pulse width is extended by the time ton in 3-1, the modulated current is converted into a modulated current having a current amplitude Im by the modulation current generation circuit 11 and output from the output terminal 17. The other of the two branched signals is delayed by a delay circuit 14 such that the pulse current is turned on with a delay of time ton from the current on of the modulation current, and then pulsed by a pulse width adjustment circuit 13-2. The width is adjusted and output from the output terminal 18 as a pulse current having a current amplitude Ibp.

FIG. 5 shows an example of a circuit configuration of the light emitting device circuit according to the present invention shown in FIG. 4 and a schematic diagram of a waveform inside the circuit.
In FIG. 5A, the light emitting element driving circuit includes an input terminal 1
6, delay circuits 14-1 and 14-2, OR circuit 30,
AND circuit 20, current switch circuit 11 for generating a modulation current and its output terminal 17, current switch circuit 12 for generating a pulse current, and its output terminal 1
8. After the signal from the input terminal 16 is branched into two, one of the signals is delayed by the time d1 in the delay circuit 14-1. The output of the delay circuit 14-1 is branched into three,
One of the signals is input to the OR circuit 30 together with the other of the two branched signals. The output of the OR circuit 30, which is a signal whose pulse width is expanded by d1, is input to the current switch circuit 11, converted into a modulation current having a current amplitude Im, and output from the output terminal 17. Another one of the three-branched signals is delayed by d2 in the delay circuit 14-2, and its inverted signal is the remaining one of the three-branched signals.
Are input to the AND circuit 20 together with the data. AND circuit 2
The output of 0 is converted into a pulse current having a current amplitude Ibp by the current switch circuit 12 and output from the output terminal 18. According to this embodiment, as shown in FIG. 5B, the pulse current is turned on with a delay of time ton = d1 from the current on of the modulation current, and the light emitting element driving circuit has a pulse width of tw = d2. Is realized.

FIG. 6 shows a third embodiment of the light emitting element driving circuit according to the present invention. In FIG. 6A, the light emitting element driving circuit includes an input terminal 16, delay circuits 14-1 and 14-.
2. OR circuit 30, AND circuit 20, current switch circuit 11 for generating a modulation current, and its output terminal 1.
7. Current switch circuit 12 for generating pulse current
And its output terminal 18. Input terminal 16
Is divided into three, and the first signal is a delay circuit 14
−1, the second signal is input to the OR circuit 30,
The third signal is input to the AND circuit 20. Delay circuit 14
The output of -1 is divided into two, and the first signal is OR circuit 30
, And the second signal is input to the delay circuit 14-2. The output of the OR circuit 30 is converted into a current amplitude Im by the modulation current generation circuit 11 and output from the output terminal 17.
The output of the delay circuit 14-2 is inverted and input to the AND circuit 20. The output of the AND circuit 20 is the current switch circuit 1
2, the current amplitude is converted to the current amplitude Ibp and output from the output terminal 18. According to the present embodiment, as shown in FIG. 6B, the modulation current has a pulse width expanded by d1, and the pulse current is turned on simultaneously with the modulation current, and the pulse width becomes tw = d1 + d2. A light emitting element drive circuit is realized.

Next, the fourth embodiment of the light emitting device driving circuit according to the present invention will be described.
The embodiment will be described with reference to FIG. FIG. 7 is a diagram in which a bit pattern detection circuit is added to the light emitting element drive circuit according to the present invention. FIG. 7A shows a light emitting element drive circuit capable of controlling the output ON / OFF of a pulse current as a second drive current by a control signal from a bit pattern detection circuit, and FIG.
FIG. 3 is a block diagram of a light emitting element drive circuit capable of controlling a pulse width of a modulation current as a first drive current by a control signal from a bit pattern detection circuit.

In order to explain the effect of the addition of the bit pattern detection circuit, as an example, a circuit configuration example and an internal waveform when a 3-bit bit pattern detection circuit is added to the light emitting element driving circuit shown in FIG. 8 is shown in FIG.
In FIG. 8A, the light emitting element driving circuit includes a data input terminal 16-1, a clock input terminal 16-2, a flip-flop circuit 70-1, a first delay circuit 14-1, and a first generating a modulation current. A current switch circuit 11 and its output terminal 17, a second delay circuit 14-2, a first AND circuit 20-1, a bit pattern detection circuit 40, a second AND circuit 20-2, a second circuit for generating a pulse current; , And an output terminal 18 thereof. The bit pattern detection circuit 40 includes three flip-prop circuits 70-2 to 70-4 and two AND circuits 20-3 and 20-4. In this embodiment, the bit pattern detection circuit 40
Only when the "001" pattern is input, a control signal of logic "1" is output from the AND circuit 20-4. Since the AND circuit 20-2 outputs the logical product of the output of the AND circuit 20-1 and the output of the AND circuit 20-4, the second current switch circuit 12, which receives the output of the AND circuit 20-2, 001 "
A pulse current having a pulse amplitude Ibp is output only when a pattern is input. Therefore, in the “101” pattern in which the influence of the residual carriers of the light emitting element is large, the light emitting element can be driven without adding a pulse current, so that the skew due to the residual carrier and the pulse current can be suppressed.

As a driving waveform example, as shown in FIG. 9A, a pulse current which is turned on prior to a rising portion of the modulation current is compared with a modulation current having a pulse current added to the rising portion as a bit pattern. And the pulse width of the modulation current may be controlled by a bit pattern as shown in FIG. 9B, but the effect of the present invention is limited to the driving current waveform shown here. It is not something to be done.

FIG. 10 shows an embodiment of an optical transmitter using the light emitting element drive circuit shown in FIG. In FIG. 10, the optical transmitter 90 includes a data input terminal 16-1, a clock input terminal 16-2, a waveform shaping circuit 71, a light emitting element driving circuit 1 according to the present invention, and a light emitting element 81. According to the present invention, since the drive current is controlled by the bit pattern, it is possible to realize an optical transmitter in which the influence of the residual carrier on the optical output waveform is reduced.

In the above embodiment, an example of the bit pattern detection circuit for detecting the "001" pattern has been described. However, the pattern to be detected is to be determined in consideration of the signal period and the carrier life. However, the present invention is not limited to the patterns shown in FIG.

Next, as another embodiment of the optical transmitter according to the present invention, the configuration of an optical parallel transmitter is shown in FIG. 11, an optical parallel transmitter includes an n-channel parallel data input terminal 16-1, a clock input terminal 16-2, a waveform shaping circuit 71, a flip-flop circuit 70-5, a light emitting element driving circuit array 10, a light emitting element array. 80, temperature detection circuit 5
0, a temperature characteristic control circuit 60. The light emitting element drive circuit array 10 includes a light emitting element drive circuit according to the present invention shown in FIG. 6, a bit pattern detection circuit, and a bias current generation circuit 15-1 for outputting a bias current sufficiently smaller than a threshold current of the light emitting element. And a bias current generating circuit for clock 15-
2, a clock drive circuit composed of a clock modulation current generation circuit 11-2 and a delay circuit 14-3.

The input data signal is subjected to waveform shaping by the waveform shaping circuit 71, the phases of the data channels are aligned by the flip-flop 70-5, and are input to each light emitting element driving circuit for each channel. The modulation current Im, the bias current Ib, and the pulse current Ibp are controlled by a temperature characteristic control circuit such that the light output fluctuation and the oscillation delay fluctuation of the light emitting element array 80 due to the temperature fall within a predetermined range. The clock bias current is set to a value larger than the threshold current of the light emitting element in order to eliminate the duty deterioration due to the oscillation delay of the clock optical signal. According to this embodiment, by using the light emitting element array and the light emitting element driving circuit array in which the light emitting element driving circuit according to the present invention is integrated, the optical parallelism in which the waveform deterioration and the skew of the optical output of each channel are sufficiently reduced. A transmitter is implemented.

Although the embodiments of the light emitting element driving circuit and the optical transmitter according to the present invention have been described above, the effectiveness of the present invention is not limited to the light emitting element driving circuit and the optical transmitter having the above-described configuration.

Next, the effects of the present invention will be described quantitatively.
A case where a light-emitting element is driven by the light-emitting element driving circuit illustrated in FIG. 3 or 5 is specifically described. As a light emitting element, at normal temperature, carrier lifetime τn = 2.5 ns, threshold current Ith = 2.0 mA, slope efficiency η = 0.4 W / A
The driving current value is set so that the optical output power of each channel can obtain Po = 2 mW. Here, since synchronous transmission is performed at 1 Gbit / s per channel, the light output pulse width degradation amount of the light emitting element is reduced to 100 ps.
Hereinafter, it is assumed that the skew due to manufacturing variations is suppressed to ± 100 ps or less.

According to the optical parallel transmitter according to the first conventional example, from the equations (1) and (2), the modulation current Im = 5.
By setting 2 mA and the bias current Ib = 1.8 mA, it is possible to set Po = 2 mW and reduce the optical output pulse width reduction due to oscillation delay to 100 ps or less. However, in the conventional example, in order to reduce the oscillation delay time, the noise margin given by Ith-Ib is 2.0-
1.8 = 0.2 mA only, and there is a high possibility that waveform deterioration due to ringing or crosstalk will occur. When the light emitting element driving circuit according to the present invention shown in FIG. 3 is used, the amount of light output pulse width deterioration is approximately given by the following equation.

[0043]

(Equation 3)

Here, since the pulse current hardly contributes to the light output power, the light output power is given by equation (1). The bias current is set to Ib = 0.2 mA, which is about the minimum current that makes the electric resistance of the light emitting element substantially constant with respect to the injection current and is advantageous for high-speed modulation. At this time, the modulation current becomes Im = 6.8 mA so that Po = 2 mW. According to the light emitting element drive circuit of the present invention, for example, the pulse current is set to 0.84 times the modulation current, Ibp = 5.44 mA, and the pulse current is turned on 730 ps ahead of the modulation current. The pulse width degradation can be reduced to 100 ps or less. The noise margin at this time is a sufficiently large value 2.0-0.2 = 1.8 m as compared with the conventional method.
A can be secured. When the threshold current variation is ± 10%, the skew at the time of the drive current is ± 50 ps.
By setting it to about 0 ps, even for a light-emitting element array having a variation in threshold current, the amount of pulse width deterioration of all channels can be made 100 ps or less, and excessive optical power output and waveform deterioration due to pulse current application are suppressed. it can.

Further, in the second conventional example in which the pulse width of the drive current is expanded to compensate for the deterioration of the optical output pulse width due to the oscillation delay, Im = 6.8 mA, Ib = 0.2 mA, FIG.
By setting the delay amount d in the middle delay circuit to d = 670 ps and extending the pulse width of the modulation current by 670 ps, the pulse width deterioration amount of the optical output can be reduced to 100 ps or less. However, when the manufacturing variation of the delay circuit is about ± 20%, the skew due to the delay time variation of the delay circuit reaches about ± 130 ps or more, and it is difficult to maintain good synchronous parallel transmission. According to the light emitting element driving circuit of the present invention shown in FIG. 5, the light output pulse width deterioration amount is approximately given by the following equation.

[0046]

(Equation 4)

When the modulation current is set equal to the conventional example,
A pulse current having a current amplitude of 3.5 mA, which is 0.5 times the modulation current, is applied as the second drive current, and the pulse extension width of the modulation current is set to 600 ps, thereby reducing the amount of degradation of the optical output pulse width to 100 ps or less. In addition, the skew caused by the delay time variation of the delay circuit can be reduced to ± 70 ps, which is about 50% of the related art.

[0048]

As described above, according to the present invention, in a light emitting element driving circuit, deterioration of an optical output waveform due to ringing or crosstalk of a driving current is suppressed, and a pulse width is reduced or skew is caused by an oscillation delay of the light emitting element. Therefore, a high-throughput optical transmitter can be achieved, which can contribute to the economical construction of an advanced information processing system such as an optical long-distance ultra-high-speed transmission device, a large-capacity exchange, and a massively parallel computer.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a light emitting element drive circuit according to the present invention.

FIG. 2 is a diagram showing a relationship between a drive current and a light output power in the first embodiment of the light emitting element drive circuit of the present invention.

FIG. 3 is a diagram illustrating a configuration diagram and a waveform of a first embodiment of a light emitting element drive circuit according to the present invention.

FIG. 4 is a block diagram showing a second embodiment of the light emitting element drive circuit according to the present invention.

FIG. 5 is a diagram illustrating a configuration diagram and waveforms of a second embodiment of the light emitting element drive circuit of the present invention.

FIG. 6 is a diagram illustrating a configuration diagram and a waveform of a third embodiment of the light emitting element drive circuit according to the present invention.

FIG. 7 is a block diagram of a light emitting element driving circuit according to a fourth embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration diagram and waveforms of a light emitting element drive circuit according to a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating an output waveform of a light emitting element drive circuit according to a fourth embodiment of the present invention.

FIG. 10 is a configuration diagram illustrating an embodiment of an optical transmitter according to the present invention.

FIG. 11 is a configuration diagram showing another embodiment of the optical transmitter of the present invention.

FIG. 12 is a configuration diagram of Conventional Example 1.

FIG. 13 is a block diagram of Conventional Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light emitting element drive circuit, 11 ... Modulation current generation circuit, 12
... Pulse current generation circuit, 13 ... Pulse width adjustment circuit, 14
... delay circuit, 15 ... bias current generation circuit, 20 ... AN
D circuit, 30 OR circuit, 40 bit pattern detection circuit, 50 temperature detection circuit, 60 temperature characteristic control circuit, 7
0: flip-flop circuit, 71: waveform shaping circuit, 80
... Light-emitting element array, 81 ... Light-emitting element, 90 ... Optical transmitter.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H01S 3/096 (72) Inventor Koji Nakahara 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo In the Central Research Laboratory of Hitachi, Ltd.

Claims (17)

[Claims] 1. A light emitting element drive circuit for controlling an optical output of a light emitting element according to an input signal, wherein a first current is output to set a predetermined optical output power in the light emitting element. A drive current generation circuit; and a second drive current generation circuit that outputs a current that is turned on prior to the current on of the output of the first drive current generation circuit; Is not more than the amplitude of the first drive current and not less than the threshold current value of the light emitting element, and the pulse width of the second drive current is smaller than the pulse width of the first drive current. Light emitting element driving circuit. 2. A light emitting element drive circuit for controlling light output of a light emitting element according to an input signal, wherein a pulse width of the input signal is extended by a time ton, and a predetermined light output is output by the light emitting element. A first drive current generation circuit that outputs a current set to obtain power, and a current that is turned on with a delay of time ton from a time when the output of the first drive current generation circuit is turned on. A second drive current generating circuit that outputs the second drive current, wherein the amplitude of the second drive current is equal to or less than the amplitude of the first drive current and equal to or greater than the threshold current value of the light emitting element; A light emitting element driving circuit, wherein a pulse width of a current is smaller than a pulse width of the input signal. 3. A light emitting element drive circuit for controlling light output of a light emitting element in accordance with an input signal, wherein a pulse width is extended with respect to the input signal, and a predetermined light output power is obtained by the light emitting element. A first drive current generation circuit that outputs a current set to be applied to the first drive current generation circuit; and a second drive circuit that outputs a current that turns on the current at the same time that the output of the first drive current generation circuit changes from the current off to the current on.
Wherein the amplitude of the second drive current is equal to or less than the amplitude of the first drive current and equal to or greater than the threshold current value of the light emitting element, and the pulse width of the second drive current is A light-emitting element drive circuit, wherein the pulse width is smaller than the pulse width of the input signal. 4. The light emitting element drive circuit according to claim 1, wherein the amplitude of the second drive current and the preceding time of the second drive current are determined by the amount of decrease in the pulse width of the optical output signal from the light emitting element. The pulse width of the second drive current is adjusted so that the time during which the first drive current and the second drive current overlap with each other is equal to or less than Δt. A light-emitting element driving circuit, comprising: 5. The light emitting element drive circuit according to claim 2, wherein the amplitude of the second drive current and the pulse extension width of the first drive current are such that the amount of decrease in the pulse width of the light output signal from the light emitting element is smaller. The pulse width of the second drive current is adjusted so that the time during which the first drive current and the second drive current overlap with each other is equal to or less than Δt. A light-emitting element driving circuit, comprising: 6. The light emitting element drive circuit according to claim 3, wherein a pulse width of the second drive current is equal to or less than a pulse width variation Δt allowed for an optical output signal from the light emitting element. 2. The light-emitting element drive circuit according to claim 2, wherein the amplitude of the drive current is adjusted so that the pulse width variation of the optical output signal from the light-emitting element is equal to or less than Δt. 7. The light emitting device driving circuit according to claim 3, wherein a pulse width of the second driving current is equal to or smaller than a pulse width variation Δt allowed for an optical output signal from the light emitting device. The pulse expansion width of the drive current is not more than the pulse width increase Δtp allowed for the light output from the light emitting element, and the amplitude of the second drive current is the pulse of the light output signal from the light emitting element. A light emitting element drive circuit, wherein the width variation is adjusted to be equal to or less than Δt. 8. The light emitting element driving circuit according to claim 1, wherein a third driving current generating circuit that outputs a current that is constant in time and equal to or less than an oscillation threshold current value of the light emitting element is provided. The light-emitting element driving circuit, wherein the third driving current has a current value at which an inter-terminal resistance of the light-emitting element is substantially constant in an injection current-to-terminal resistance characteristic of the light-emitting element. 9. The light emitting element driving circuit according to claim 1, further comprising a temperature detecting means, an output from said temperature detecting means being an input, and a first driving current and a second driving current. And a temperature characteristic control circuit capable of controlling at least one of the third drive current and the timing at which the output current is turned on in accordance with the temperature characteristic of the light emitting element driven by the light emitting element drive circuit. Characteristic light-emitting element driving circuit. 10. A light emitting element drive circuit for controlling the light output of a light emitting element according to an input signal, comprising: a bit pattern detecting means for the input signal; and a current of an output current according to an output of the bit pattern detecting means. A light emitting element drive circuit, comprising: at least one drive current generation circuit whose amplitude or pulse width is adjusted to a preset value. 11. The light emitting device drive circuit according to claim 10, wherein the drive current generation circuit capable of adjusting the output current according to the output of the bit pattern detection means outputs the light output from the light emitting device for every bit pattern. A light emitting element drive circuit, wherein an output current is adjusted to a preset value so that a pulse width of a signal becomes a predetermined value. 12. The light emitting element driving circuit according to claim 10, further comprising a temperature detecting means, receiving an output from said temperature detecting means as an input, and turning on a current amplitude of a driving current or an output current. A light-emitting element driving circuit comprising: a temperature characteristic control circuit capable of controlling timing according to a temperature characteristic of a light-emitting element driven by the light-emitting element driving circuit. 13. The light-emitting element drive circuit according to claim 1, further comprising: a bit pattern detection unit, wherein the first drive current is supplied in response to an output of the bit pattern detection unit. A light emitting element drive circuit, comprising: means for adjusting at least one of a pulse extension width or a leading time or a current amplitude of a second drive current to a preset value. 14. An optical transmitter comprising a light emitting element and a light emitting element driving circuit, wherein the light emitting element driving circuit is the light emitting element driving circuit according to any one of claims 1 to 13. And an optical transmitter. 15. An optical transmitter comprising a plurality of light emitting elements and a plurality of light emitting element driving circuits, wherein at least one of the plurality of light emitting element driving circuits is according to any one of claims 1 to 13. An optical transmitter characterized in that it is a light emitting element drive circuit of (1). 16. The optical transmitter according to claim 15, wherein the drive current amplitudes of the plurality of light emitting element driving circuits are adjusted with respect to the characteristics of the light emitting elements respectively driven by the plurality of light emitting element driving circuits. An optical transmitter, comprising: 17. The optical transmitter according to claim 15, wherein the timing at which the plurality of light emitting element driving circuits are turned on is adjusted with respect to characteristics of the light emitting elements respectively driven by the plurality of light emitting element driving circuits. An optical transmitter.