JPH0244789A - Laser diode drive control method - Google Patents

Abstract

PURPOSE:To make it possible to control the optical output level of an optical relay on a light transmitting path by setting the magnitude of a pulse current base on the magnitude of a supplied current, setting the level of the light signal outputted from a laser diode, changing the supplied current, and adaptively changing the level of the light output from the laser diode. CONSTITUTION:The magnitude of a supplied current Ia flowing through a feeder line is detected with a current detector 1. A laser-diode driving circuit 3 is controlled with a detected voltage value Vb. Therefore, when an input signal (s) is inputted into the laser-diode driving circuit 3, the magnitude of a pulse current Ic is adjusted, and a light signal at a light output level corresponding to the magnitude of the supplied current Ia flowing through the feeder line is outputted. At this time, the pulse current Ic is further applied into a laser diode 5 in which a bias current Ib indicating a threshold current value has been already supplied. Thus the light signal at the light output level corresponding to the magnitude of the pulse current is outputted. In this way, the level of the light output from a terminal through an optical relay can be adjusted to the optimum level without newly providing a control line.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a laser diode drive control system, and aims to make it possible to control the optical output level of an optical repeater on an optical transmission path without installing a new control line. In an optical repeater that is supplied with power from a feed line and drives a laser diode by superimposing a pulse current on a bias current according to an input signal, a current detector detects the magnitude of the feed current flowing through the feed line. By setting the magnitude of the pulse current based on the magnitude of the power supply current detected by the current detector, the level of the optical signal output by the laser diode is set, and the laser diode driving device drives the laser diode. A circuit was provided so that the optical output level of the laser diode could be adaptively changed by changing the feeding current.

[Industrial application field]

The present invention relates to a laser diode drive control system, and more particularly to a laser diode drive control system for an optical repeater to which power is supplied from a feed line.

In the optical submarine cable transmission system, when operating optical repeaters that each do not have their own power supply, a power supply line is provided from a terminal station on land to supply power to the optical repeaters. In a system that employs such a power supply method, optical repeaters are installed in locations where it is difficult to easily repair or replace a failed part in the event of a failure.

Additionally, the lifetime of a laser diode generally decreases as the optical output level increases.

Therefore, it is desired that an optical repeater using a laser diode having such characteristics can operate stably for a long period of time.

[Conventional technology]

FIG. 4 shows a transmitting section of a conventional optical repeater.

In FIG. 4, one of the two optical signals from the laser diode 10 is output to an optical transmission line, and the other is output to a monitoring light receiver 11.

The photoreceiver 11 generates a voltage a corresponding to the optical output level of the input optical signal and outputs it to the bias circuit 12 .

The bias circuit 12 adjusts the bias current supplied to the laser diode 10 to match the threshold current of the laser diode by comparing the output voltage a from the light receiver with a set voltage. The threshold current of this laser diode is a current value at the boundary between whether the laser diode emits light or not. By constantly applying this threshold current to the laser diode 10, the drive current C
When C is input, an optical output level corresponding to the magnitude of the drive current C can be obtained. Therefore, the optical output level can be easily controlled.

Further, the input signal S is converted by the drive circuit 13 into a drive current C such that an optical signal having a level set at a desired constant value is obtained from the laser diode 10, and is supplied to the laser diode 10.

[Problem to be solved by the invention]

As described above, the transmitting section of a conventional optical repeater can only output at a light output level set to a certain value. In addition, if an optical signal is sent at the minimum required optical output level for a long period of time, the error rate will increase due to deterioration of the optical transmission line, so this optical output level should be set slightly higher than the minimum required level. is set to .

Therefore, since the optical output level of the laser diode is higher than the minimum required optical output level, the life of the laser diode is shorter than when the optical signal is transmitted at the minimum required optical output level. There is a problem with putting it away.

The lifespan of a laser diode can be extended by reducing its optical output level to the minimum necessary.
Because of the above-mentioned problem of the increase in error occurrence rate over time, it is not preferable to set the optical output level of the laser diode to the minimum necessary value.

On the other hand, it is possible to detect the repeater's error rate inside the repeater and adjust the optical output level appropriately to the minimum necessary value, but this would complicate the configuration of the optical repeater and cause failures. increases.

It is also possible to detect the error rate at the terminal station and adjust the pre-output level of the repeater, but this would require a new control line to the repeater.

Therefore, an object of the present invention is to enable the terminal station to adjust the optical output level of the optical repeater to the optimum value without providing a new control line.

[Means to solve the problem]

A diagram of the principle of the present invention is shown in FIG.

In FIG. 1, first, a current detector I detects a voltage value Va corresponding to the magnitude of a power supply current 1a flowing through a power supply line, and supplies it to a bias circuit 2 and a laser diode drive circuit 3. The laser diode drive circuit 3 sets an optical output level corresponding to the input voltage value VaO value, and supplies a pulse current 1c with an amplitude corresponding to the set optical output level to the laser diode 5 in accordance with the input signal S. It is outputting.

The optical receiver 4 receives the monitoring optical signal output from the laser diode 5, generates a voltage corresponding to the magnitude of the optical signal, and outputs it to the bias circuit 2 as an optical output voltage vb.

The laser diode 5 generates and outputs an optical signal using the pulse current Ic superimposed on the bias current Ib from the bias circuit 2.

The bias circuit 2 sets the magnitude of the bias current Ib of the laser diode by comparing the voltage value Va from the current detector 1 with the optical output voltage b indicating the magnitude of the optical output level. It is set to the threshold value of the laser diode and output to the laser diode 5.

[Effect]

The current detector 1 measures the magnitude of the feed current 1a flowing through the feed line.
The laser diode drive circuit 3 is controlled by the detected voltage value vb. Therefore, when the input signal S is input to the laser diode drive circuit 3, the magnitude of the pulse current 1c is adjusted to generate an optical signal with an optical output level corresponding to the magnitude of the power supply current 1a flowing through the power supply line. It is outputting. At this time, by further applying a pulse current Ic to the laser diode that has already been supplied with a bias current Ib indicating a threshold current, an optical signal with an optical output level corresponding to the magnitude of the pulse current is output. There is.

Therefore, by changing the magnitude of the feed current Ia flowing through the feed line, it is possible to freely set the magnitude of the pulse current 1c that determines the optical output level of the optical signal.

In addition, as mentioned above, in the section composed of the bias circuit 2, the photodetector 4, and the laser diode 5, the bias current I
The value of b is always set (auto power control) to the threshold current of the laser diode. This auto power control operation detects the optical output level of the laser diode 5 and sets the voltage vb corresponding to the optical output level.
is generated, the difference between the voltage vb corresponding to the optical output level and a constant voltage is detected, and the bias current 1b is set. Therefore, when the optical output level is changed as described above, the voltage vb corresponding to the optical output level changes, so that the value of the bias current 1b deviates from the threshold current of the laser diode.

Therefore, when the optical output level is changed due to a change in the feeding current Ia, the bias circuit 2 similarly to the laser diode drive circuit 3 creates a voltage value according to the change in the feeding current Ia, and this voltage value and the optical output level are By detecting the difference between the bias current Ib and the voltage vb corresponding to the voltage vb in the bias circuit 2, it becomes possible to always set the bias current Ib to the threshold current of the laser diode, regardless of changes in the drive pulse Ic.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to FIGS. 2 and 3. The current detector 1 in FIG. 1 corresponds to the part consisting of the resistors R1, R2, R3 and the operational amplifier 0PAI in FIG. 2, and the bias circuit 2 in FIG. 1 corresponds to the operational amplifier 0PA2. Corresponding to the part consisting of transistor Trl + coil, the laser diode driving means 3 in FIG. 1 is the optical output level setting circuit 3 consisting of resistors R5, R6, R7, R8 and operational amplifier 0PA3 in FIG. 2.
1, resistor R9, RIO, R11,) transistor Tr4
．． A constant current circuit 32 consisting of Tr5 and a transistor T
Corresponding to the part constituted by the pulse drive circuit 33 consisting of r2+ Tr3, the light receiver 4 in FIG. 1 is connected to the resistor R in FIG.
4. The laser diode 5 in FIG. 1 corresponds to the laser diode LD in FIG. 2.

In FIG. 2, first, the power supply current Ia supplied from the terminal station to the power supply line for driving the optical interruption layer is connected to the resistor R in the current detector 1.
1, a voltage Vp is generated and input to one terminal of the operational amplifier 0PAL.

On the other hand, a constant reference potential Vc is also input to the other terminal of the operational amplifier 0PAL. At this time, the resistance R1 for detecting the voltage Vp from the feed current Ia flowing through the feed line is preferably set to a value as small as possible in consideration of loss in the feed line.

In the operational amplifier 0PAL, the difference voltage between the input constant voltage Vc and the voltage value VpO is calculated by the ratio (R3/R
2), and outputs it to the operational amplifier 0PA2 of the bias circuit 2 and the operational amplifier 0PA3 of the optical output level setting circuit 3 as a set voltage Va.

In the optical output level setting circuit 31 in the laser diode driving means 3, a set voltage Va is inputted to the operational amplifier 0PA3 via a resistor R5, and a constant voltage Vg supplied from the outside is inputted via a resistor R8. At this time,
For example, when R6/R5=R8/R7 is set, the output voltage Vq of the operational amplifier 0PA3 has such a value.

This output voltage Vq is set as the optical output level setting voltage Vq.
It is supplied to the constant current circuit 32 together with the constant voltage vh.

In the constant current circuit 32, first, the optical output level setting voltage νq is connected to the collector and base of the transistor Tr4 via the resistor R9, and the constant voltage vh is connected to the emitter of the transistor Tr4 via the resistor 10. Here, if the voltage between the base and emitter when the transistor is in a conductive state is Vbe, the current rd flowing through the transistor Tr4 becomes R9+R10.

At this time, the voltages between the base and emitter of transistor Tr4 and transistor Tr5 are equal, so RIO and R
The voltages applied to 11 will be equal. Therefore, T d R1
0=I c R11, and the current flowing through the transistor Tr5 (hereinafter referred to as pulse current Ic) is expressed by the following equation.

At this time, R9, RIO, R11, Vh, and Vbe are constant values, and the only element that changes the value of the pulse current Ic is the value of Vq.

On the other hand, in the pulse drive circuit 33, the collector of the transistor Tr5 is connected to the emitters of the transistors Tr2 and Tr3 whose emitters are connected to each other, and the human input signal S of O or 1 is input to the base of the transistor Tr2. A laser diode 5 is connected to the collector. Further, a constant voltage Vf is applied to the base of the transistor Tr3.
is input and the collector is grounded. At this time, by setting the constant voltage Vf to a level smaller than the 1 level of the input signal and larger than the 0 level, when the input signal S is 1, the pulse current 1c set by the constant current circuit 41 is set.
flows through the transistor Tr2, and when the input signal is 0, a pulse current Ic set by the constant current circuit 41 flows through the transistor Tr3.

A bias current 1b is constantly flowing through the laser diode LD by a bias circuit as shown in FIG. 3, and the bias current rb is a threshold current at which the laser diode LD emits light. Therefore, with only the threshold current 1b,
The laser diode LD does not emit light. bias current r
When pulse current 1c is superimposed on b, pulse current Ic
An optical signal with an optical output level corresponding to the magnitude of is sent from the laser diode LD to the optical transmission path and output to the monitoring light receiver 4.

At this time, as the value of the power supply current Ia changes, the voltage VpO value corresponding to the value of the power supply current 1a changes, and the set voltage Va, which is the voltage Vp amplified at the ratio of (R3/R2), also changes. . And as shown in the first equation, Va
The value of the optical output level setting voltage VqO changes according to the value of the optical output level setting voltage Vq, and further, the value of the pulse current IcO changes according to the value of the optical output level setting voltage Vq, as shown in the second equation. In addition, the light output level changes as the pulse current changes. Therefore, by changing the power supply current Ia, the optical output level can be changed.

On the other hand, in the photoreceiver 5, an optical signal from a laser diode is input, and a photodiode FD whose one end is connected to a constant voltage vb generates an optical output current corresponding to the optical output level of the optical signal. This optical output current is converted into a voltage according to the optical output level by a resistor R4 whose one end is grounded, and is outputted to the operational amplifier 0PA2 of the bias circuit 2 as an optical output voltage vb.

The operational amplifier PA2 is the set voltage V from the current detector 1.
A differential voltage Vs between a and the optical output voltage vb is created and output to the base of the transistor Tri.

In the transistor Tri, the differential voltage Vs is used as a base voltage, and the constant voltage Ve supplied from the outside is used as an emitter voltage. At this time, the value of the bias current Ib of the laser diode LD that constantly flows through the transistor Tri is determined by the potential difference between the base voltage Vs and the emitter voltage Ve. This value is set to the threshold current value of the laser diode LD as shown in FIG. In addition, by increasing the output impedance of the bias circuit at high frequencies, the coil L is designed to avoid being adversely affected by other circuits.
This is to isolate it from other circuits in terms of high frequency.

Therefore, by detecting the difference value between the optical output voltage vb and the set voltage Va, it is possible to monitor whether the bias current has reached the threshold current and check (auto power control), so that the surrounding temperature etc. Even when the threshold value of the laser diode changes somewhat due to changes, the bias current Ib flowing through the bias circuit will accurately indicate the threshold value of the laser diode.

At this time, when the optical output level of the optical signal input to the optical receiver 4 increases due to a change in the magnitude of the pulse current Ic, the optical output voltage vbO value output from the optical receiver 4 to the operational amplifier 0PA2 increases. . This optical output voltage vbO
When the value increases, if the voltage compared with the optical output voltage vb does not change, the potential difference between the two voltages will increase,
The base voltage Vs of the transistor Tri also increases. Therefore, by setting the input of the operational amplifier to the optical output voltage vb and the set voltage Va, when changing the magnitude of the optical output level, the set voltage Va changes according to the amount of change.
By using this, the potential difference between the optical output voltage vb and the set voltage Va is made to be the same as before the optical output level changes.

In addition, the constant voltages Vc, Vd, Ve, Vf,
Vg.

vh is a voltage that is a constant voltage generated by a Zener diode ZD in the power supply line and is set to a constant value in each converter.

[Effects of the present invention]

As described above, according to the present invention, it is possible to change the optical output level of an optical signal by changing the magnitude of the feeding current flowing through the feeding line. Therefore, by detecting the error occurrence rate at the terminal station and controlling the optical output level accordingly, it is possible to minimize the optical output level signal output from the laser diode. Therefore, it has become possible to use the laser diode efficiently, and the life of the laser diode can now be used without extending it.

Furthermore, since the lifespan of a laser diode is shorter than that of other parts such as ICs and LSIs, by extending the lifespan of the laser diode, it becomes possible to substantially extend the lifespan of the optical repeater.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is an embodiment of the present invention, Fig. 3 is a diagram of the relationship between the current value of each part and the optical output level, and Fig. 4 is a transmitting section of a conventional optical repeater. In the figure, 1... Current detector 2... Bias circuit 3.
...Laser diode drive circuit 4...Receiver 5...Laser diode 10...Laser diode 11...Receiver 12...Bias circuit 13...Drive circuit Principle mouth half 1 closed

Claims (1)

[Claims] 1. In an optical repeater that is supplied with power from a power supply line and drives a laser diode by superimposing a pulse current (Ic) on a bias current (Ib) according to an input signal (S). , a current detector (1) that detects the magnitude of the power supply current (Ia) flowing through the power supply line; and a current detector (1) that detects the magnitude of the power supply current (Ia) flowing through the power supply line; ) by setting the level of the optical signal output by the laser diode (5), a laser diode drive circuit (3) is provided to drive the laser diode (5), and the power supply current (
The laser diode (5
) A laser diode drive control method characterized by being able to adaptively change the optical output level of the laser diode. 2. By receiving the optical signal output from the laser diode and detecting the optical output level of the optical signal,
A light receiver (4) that generates a voltage (Vb) corresponding to the optical output level of the optical signal compares the voltage corresponding to the optical output level with a set voltage, and based on the comparison result, a bias current is supplied to the laser diode. (Ib), and when changing the optical output level of the laser diode (5) according to a change in the feeding current (Ia), the current detector By changing the set voltage of the bias circuit (2) according to the magnitude of the feed current (Ia) detected in (1), the value of the bias current (Ib) is adjusted to the optical output level of the laser diode (5). 2. The laser diode drive control method according to claim 1, wherein the laser diode drive control method is controlled to maintain the laser diode at a threshold value despite a change in the laser diode.