JP2626470B2 - Optical output control device in digital optical communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical output control device in a digital optical communication system, and more particularly to an optical output control device for a light source that generates an optical signal corresponding to a digital data signal.

[0002]

2. Description of the Related Art In a digital optical communication system, in order to perform stable reception, it is necessary that a peak value of an optical transmission output, that is, an optical power of one pulse is constant. To stabilize the optical output, the transmitter usually includes a feedback control system that controls the drive current of the light emitting element for transmission by feeding back the average value of the optical output, and a mark ratio (digital signal) of the data signal to be transmitted. Of "1" in
A mark ratio correction system that changes the average light output in proportion to
Is provided.

FIG. 3 is a schematic circuit configuration diagram of a conventional light output control device.

In FIG. 1, a light emitting element 101 is driven to blink by a driving circuit 102 in accordance with a data signal, and a light output of the light emitting element 101 is detected by a monitor circuit 103. The monitor circuit 103 outputs a voltage Vi1 proportional to the average value of the optical output to the inverting input terminal of the differential amplifier 104.

On the other hand, a mark ratio detection circuit 105 receives a data signal, generates a mark ratio signal whose voltage changes with a positive slope to the mark ratio M of the digital signal, and generates a voltage Vi2.
To the non-inverting input terminal of the differential amplifier 104.

Therefore, the output voltage of the differential amplifier 104 is
It changes with a negative slope with respect to the monitor signal (voltage Vi1) of the light emitting element, and changes with a positive slope with respect to the mark rate signal (voltage Vi2).

The output voltage of the differential amplifier 104 is
02, the driving current level of the light emitting element 101 is changed. As a result, a negative feedback control system in which the drive current level of the light emitting element 101 decreases when the monitor signal increases with an increase in the optical output.

With only this feedback control system,
The average light output increases due to the increase in the mark ratio of the data signal, which increases the monitor signal voltage Vi1.
The peak value of the light output is reduced. That is, a change in the mark ratio causes a change in the light output. The mark ratio correction circuit corrects this variation.

Here, when the amplification factor of the differential amplifier 104 is sufficiently large, the voltage Vi1 is stabilized in a state substantially equal to the voltage Vi2. Therefore, by supplying a mark ratio signal (voltage Vi2) proportional to the mark ratio of the data signal to the non-inverting input terminal of the differential amplifier 104, the change in the mark ratio of the data signal is corrected, and the light peak from the light emitting element 101 is corrected. The output can be controlled to be constant.

Such an optical output control circuit is disclosed in
-20388 and JP-A-62-131635.

[0011]

However, in the above-described conventional light output control device, adjustment for changing the light output level of the light emitting element 101 is not easy.

In the conventional circuit, the monitor signal voltage Vi1
Alternatively, if the light output level is changed by changing only the output of the differential amplifier, the linear relationship with the mark ratio is lost. Therefore, in order to change the light output level while maintaining the mark ratio correction, it is necessary to adjust the amplitude of the mark ratio signal.

For example, when the set level of the optical output is 1 mW and the mark ratio M is 0.5 (50%), the mark ratio signal voltage V
If i2 = 0.5V (that is, Vi2 = M), the monitor signal voltage Vi1 also becomes 0.5V in a stable state.

In this state, in order to increase the set level of the optical output to 2 mW, it is necessary to stabilize the monitor signal voltage Vi1 at 1V which is twice as high. Therefore, when the mark ratio M = 0.5, the mark ratio signal voltage Vi2 is set to 1 V (that is, Vi2 = 2M).
Must be adjusted.

As described above, it is necessary to adjust the amplitude of the mark ratio signal, and it is not easy to change the light output level.

[0016]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical output control device which can easily set an arbitrary optical output without adjusting a mark ratio signal.

A light output control device according to the present invention includes a monitor circuit for detecting an average light output of the light source and outputting a first control signal that changes at a positive slope with respect to the change in the average light output; A mark ratio correction control circuit that adjusts Vr according to the mark ratio M of the data signal, and outputs a voltage proportional to a voltage (M × Vr) obtained by multiplying the reference voltage Vr and the mark ratio M as a second control signal; A differential amplifier that inputs the first control signal to an inverting input terminal and the second control signal to a non-inverting input terminal, and a driving circuit that determines an optical output of the light source according to an output of the differential amplifier. It is characterized by becoming.

[0018]

The voltage proportional to the voltage (M.times.Vr) is applied to the non-inverting input terminal of the differential amplifier as the second control signal. The first control signal voltage input to the terminal can be changed, and as a result, the light output of the light source can be set to an arbitrary level.

Even if the reference voltage Vr is changed, the mark rate M for the first control signal applied to the inverting input terminal of the differential amplifier is always constant. There is no need to readjust the rate signal amplitude.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic block diagram for explaining a control system in one embodiment of a light output control circuit according to the present invention.

In FIG. 1, a light emitting element 1 is driven by a drive circuit 2 and generates an optical signal corresponding to a data signal. The optical output is detected by the monitor circuit 3, and a monitor signal voltage Vi1 proportional to the average optical output is input to the inverting input terminal of the differential amplifier 4.

On the other hand, the pulse width modulator 5 inputs a mark rate signal proportional to the mark rate M of the data signal, and
A pulse signal having a duty ratio equal to

The analog switch 6 receives the reference voltage Vr, and further receives a pulse from the pulse width modulator 5 as a control signal. Since the analog switch 6 opens and closes according to the high level / low level of the pulse signal, the output of the analog switch 6 passes through the smoothing circuit 7 and becomes a voltage (M × Vr) mark ratio correction signal of the differential amplifier 4. Input to the non-inverting input terminal. That is, the input voltage Vi2 = M × Vr at the non-inverting input terminal.

The drive circuit 2 determines the light output level of the light emitting element 1 according to the output voltage of the differential amplifier 4.

As described above, when the amplification factor of the differential amplifier 4 is sufficiently large, the two input voltages of the differential amplifier 4 become Vi1 = V
It becomes i2 and becomes stable. Here, since Vi2 = M × Vr, it is understood that the monitor signal voltage Vi1 can be adjusted by adjusting the reference voltage Vr. That is, the reference voltage V
It is possible to stably set the light output of the light emitting element 1 to an arbitrary level simply by increasing or decreasing r.

At this time, since Vi1 = Vi2 = M × Vr, the inclination of the mark ratio M with respect to Vi1 is always constant regardless of Vr, and it is not necessary to readjust the mark ratio signal voltage.

FIG. 2 is a block diagram showing one embodiment of the light output control device according to the present invention.

In FIG. 1, a laser diode module (LD module) 10 has a built-in laser diode 11 as a light emitting element and a photodiode 12 as a light receiving element for monitoring. It is arranged to receive the emitted light.

The laser diode 11 is driven by a drive circuit 13 and transmits an optical signal composed of an optical pulse corresponding to a data signal.

The output current of the photodiode 12 is subjected to current-voltage conversion by the monitor circuit 14, and is input to the inverting input terminal of the differential amplifier 15 as a control signal proportional to the average light output. The drive circuit 13 sets a drive current to the laser diode 11 according to the output voltage of the differential amplifier 15 and determines an optical output.

The data signal is input to the drive circuit 13 and also to the mark ratio detection circuit 16 to generate a mark ratio signal having a voltage proportional to the mark ratio M.

The pulse width modulation circuit 17 receives the mark rate signal and outputs a pulse signal having a duty ratio equal to the mark rate M to the control terminal of the analog switch 18.

The analog switch 18 adjusts the reference voltage Vr by performing a switching operation in accordance with the pulse signal as described above, and the output thereof is smoothed by passing through the smoothing circuit 19 so that the mark ratio of the voltage M × Vr is obtained. A correction signal is generated and input to the non-inverting input terminal of the differential amplifier 15.

Next, the operation of this embodiment will be described.

When the control mark rate for stabilizing the optical output is constant, that is, when the voltage Vi2 at the non-inverting input terminal of the differential amplifier 15 is constant, the laser diode 11
Increases, the average optical output detected by the photodiode 12 and the monitor circuit 14 also increases, and the voltage Vi1 at the inverting input terminal of the differential amplifier 15 increases. As a result, the output voltage of the differential amplifier 15 drops,
The drive circuit 13 reduces the drive current to the laser diode 11 to suppress the light output. If the light output decreases,
Conversely, it operates to increase the drive current to the laser diode 11. The light output is kept constant by such negative feedback control.

Mark Rate Correction Control Assume that the mark rate M of the optical signal output from the laser diode 11 has changed from, for example, 50% to 75%. As a result, the voltage Vi1 input from the monitor circuit 14 to the inverting input terminal of the differential amplifier 15 also becomes 75/50 = 1.5 times.

On the other hand, the duty ratio of the pulse signal output from the pulse width modulation circuit 17 also becomes 1.5 times,
The conduction time of the analog switch 18 also becomes 1.5 times longer according to the duty ratio. As a result, the output voltage of the smoothing circuit 19, that is, the voltage Vi2 also becomes 1.5 times and is input to the non-inverting input terminal of the differential amplifier 15.

Accordingly, the system is stable with both the input voltages Vi1 and Vi2 of the differential amplifier 15 rising 1.5 times. That is, the change in the mark ratio M is corrected, and the light output does not change.

Setting of Light Output Level The light output level of the laser diode 11 is equal to the reference voltage Vr.
Can be set arbitrarily. When the reference voltage Vr is set high, the input voltage Vi2 of the differential amplifier 15 also increases, and as a result, the optical output increases as described above. However, since the change in the mark rate appears in the duty ratio of the pulse signal by the pulse width modulation circuit 17, the change in the mark rate is changed based on the set reference voltage Vr.
And appears as a fluctuation of the voltage Vi2 by the smoothing circuit 19.
That is, even if the setting of the reference voltage Vr is changed, the mark ratio correction control always functions correctly.

[0041]

As described above in detail, the light output control device according to the present invention can change the light output of the light source while making the light output stabilization control and the mark ratio correction control function normally only by changing the reference voltage Vr. The output can be set to any level.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram for explaining a control system in one embodiment of a light output control circuit according to the present invention.

FIG. 2 is a block diagram of an embodiment of a light output control device according to the present invention.

FIG. 3 is a schematic circuit configuration diagram of a conventional light output control device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light emitting element 2 light emitting element drive circuit 3 monitor circuit 4 differential amplifier 5 pulse width modulator 6 analog switch 7 smoothing circuit 10 LD module 11 laser diode 12 photodiode 13 LD module drive circuit 14 monitor circuit 15 differential amplifier 16 mark rate Detection circuit 17 Pulse width modulation circuit 18 Analog switch 19 Smoothing circuit

Claims (4)

(57) [Claims] 1. An apparatus for controlling an optical output of a light source that generates an optical signal corresponding to a data signal, wherein the average optical output of the light source is detected, and the average optical output changes with a positive slope with respect to the change of the average optical output. A monitor circuit for outputting the first control signal, and a product (M of the reference voltage Vr and the mark ratio M of the data signal)
× Vr) as a second control signal, a mark ratio correction control circuit that outputs a voltage proportional to the second control signal, and a differential amplifier that inputs the first control signal to an inverting input terminal and inputs the second control signal to a non-inverting input terminal. And a drive circuit for determining an optical output level of the light source according to an output of the differential amplifier. 2. The mark ratio correction circuit, comprising: a mark ratio detection circuit that receives the data signal and outputs a voltage proportional to the mark ratio M as a mark ratio signal; A pulse width modulation circuit that generates a pulse signal having a duty ratio equal to the mark rate M; a switch circuit that receives the reference voltage Vr and adjusts the reference voltage Vr by a switching operation according to the pulse signal; The output of the circuit is smoothed and the product (M × V
The light output control device according to claim 1 , further comprising: a smoothing circuit that outputs a voltage proportional to r) as the second control signal . 3. An apparatus for controlling an optical output of a light source that generates an optical signal corresponding to a data signal, comprising: a negative feedback using an average optical output of the light source.
Control means for controlling the light output of the light source by negative (negative feedback) control, and the product of the reference voltage Vr and the mark ratio M of the data signal (M
× Vr), a mark ratio correction signal generating unit that generates a voltage proportional to the mark ratio correction signal, and the mark ratio correction signal is used as a control signal, and the mark ratio correction signal is generated due to an operation of the control unit. An optical output control device for digital optical communication, comprising: mark ratio correction control means for correcting a variation in optical output. Wherein said mark ratio correcting signal generating means includes a pulse generating circuit for generating a pulse signal having a mark ratio M equal to the duty ratio, and inputs the reference voltage Vr, the switching operation in accordance with the pulse signal Switch means for adjusting the reference voltage Vr according to the following formula: and smoothing the output of the switch means to obtain the product (M × V
4. The light output control device according to claim 3 , further comprising: a smoothing unit that outputs a voltage proportional to r) as the mark ratio correction signal .