JPS5931996B2 - Optical output stabilization method - Google Patents

Description

[Detailed Description of the Invention] (C) Field of Application of the Invention The present invention relates to an optical output stabilizing device when a semiconductor laser diode is used as a light source in an optical communication system, and particularly to a high-speed light source that superimposes a bias current on a signal current. The present invention provides a control method for semiconductor lasers that can

(2) Prior Art In optical communications, a semiconductor laser diode is used as a light source, but the optical output of this diode has the property of being extremely dependent on temperature and drive current.

For this reason, conventionally, a method has been adopted in which changes in the optical output monitoring light of the semiconductor laser are negatively fed back to the drive current, as shown in FIG. Briefly explaining the operation of this device, first, an electric signal inputted from a terminal 1 is converted into voltage and current by a drive circuit 2. In this case, in order to drive at high speed, it is desirable to superimpose a signal current on the bias current in order to reduce pattern effects of the semiconductor laser. Next, when the semiconductor laser 3 is driven by a current in which the bias current and the signal current are superimposed, an optical output proportional to the current is obtained at the terminal 6. On the other hand, the monitoring light of the semiconductor laser light output is converted into a current by the photoelectric conversion circuit 4. This current is used as a control signal, which is converted from AC to DC by peak value detection or average value detection in the control circuit 5, and then amplified to control the drive current. At this time, when the bias current is kept constant and the signal current is controlled, the temperature dependence of the threshold current is large, so that it cannot follow a wide range of temperature changes, and there is a drawback that waveform deterioration becomes large. Further, when controlling the bias current and the signal current simultaneously, it is difficult to determine the distribution ratio, and it is difficult to ensure control stability. For this reason,
Conventionally, a method of controlling bias current has been common. However, this method is not necessarily effective when there are manufacturing deviations or aging deterioration in the semiconductor laser characteristics. For example, consider the manufacturing deviation and aging deterioration of the differential quantum efficiency β. FIG. 2 shows the driving state of the semiconductor laser. In the figure, 1 is the light output Kerr current characteristic when the differential quantum efficiency is β in the standard state, and 2
is the light output Kerr current characteristic when the differential quantum efficiency β' is due to manufacturing deviation or aging deterioration. First, in the standard state, is the bias current Ib the signal current? A is superimposed and driven as shown in the figure. At this time, the optical output Po is Po−β(more than +IS
-Ith) ・・・・・・・・・・・・・・・・・・(
It becomes ha.

Here, Ith is a threshold current. Now, since the optical output decreases when the differential quantum efficiency becomes smaller than the value in the standard state, the bias current increases to compensate for this decrease.

However, when the bias current exceeds the threshold current as shown in Ib' in the figure, a DC component occurs in the optical output and the optical signal output remains constant below the specified value, resulting in significant S/N deterioration or an increase in the code error rate on the receiving side. occurs. Therefore, the permissible range is Ib<Ith, and the amount of deterioration Δβ of differential quantum efficiency is -1
a-υ J ~-Re11-υυ/' -4.

Here β. is the differential quantum efficiency which becomes b-1th, IbO is the initial bias current I, h-1b0 is at most 10 mA in the case of high-speed drive, and the signal current 18 is 30 to 40 mA.
mA, the deterioration in differential quantum efficiency is limited to 25 to 33%. This is an extremely severe condition for manufacturing deviations and aging deterioration of semiconductor lasers. (3) Object of the Invention In view of the problems of the prior art described above, the object of the present invention is to provide a semiconductor laser which can largely tolerate the limited range of manufacturing deviations and aging deterioration of semiconductor lasers, and which can monitor the DC component of optical output. To provide a light output stabilizing device having a leg type (4)
) General description of the invention In order to achieve the above object, the present invention provides the following control system.

That is, the first method is a method in which when a DC component occurs in the optical output, its average value increases rapidly, so this increase is detected and the signal current is controlled. The second method is to use the signal component of the optical output as the reference signal, separate the DC component and the signal component, control the signal current using the DC component, and control the bias current using the signal component. In this case, the bias current is controlled using the peak value detection signal. (5) Examples Hereinafter, the present invention will be explained in detail with reference to examples.

First, I will explain the principle. When the differential quantum efficiency deteriorates in FIG. 2, the DC component and signal component of the optical output become 0, where 1b' is a bias current determined by the amount of attenuation of the signal component of the optical output.

Using equations (1) to (3), this bias current is υ-RE51W0--υ.

Here, η is the coupling efficiency between the monitoring light and the photoreceiver, a is the photoelectric conversion coefficient, and G is the current amplification factor of the loop. β in equation (4).
When β5, Ib' is less than I,h, and becomes more than Ith only when βo>β50 Therefore, Ib'-1,
By controlling the signal current under the condition that h>0, the DC component of the optical output can be reduced. The control signal at this time is G77aI
8 (βo−β, and the control is β′18′−β.1
This is done to satisfy the condition 8.

When the above-mentioned logic is displayed using optical output, it looks like the following.
That is, from equations (3) and (4), the DC component of the optical output is.

Therefore, the total light output is .

Here, T indicates the period of the signal, and f(t) indicates the time change of the signal. In equation (6), the DC component becomes zero when βBf3O. That is, it is the average value of the optical output at this time.

Therefore, if we take equation (7) as the reference signal, then β5
Ku β. When , a DC component of optical output occurs. In this case, the reference signal does not have to be an average value, and if an AC signal component is used, it is possible to separate the DC component and the signal component. Therefore, the control signal at this time can be performed using the DC component of the optical output. FIG. 3 shows an embodiment of the present invention.

Here, 7 and 8 are signal and bias current drive circuits, 10 and 9 are signal and bias current control circuits, respectively, and 1
1 is a reference circuit, 20 is an integrating circuit, and 21 is a gating circuit. To explain the operation of this system in detail, first, the monitoring light is converted into a current by the photoelectric conversion circuit 4, and this current is a superimposition of a direct current component and an alternating current component. However, μ″〉PO
When , there is only the AC component, and β1 × β. It is only when this happens that a direct current component occurs, and the increase in 5 becomes extremely rapid. Therefore, if the integration circuit 20 integrates, a current corresponding to equation (6) can be obtained, so when this value exceeds a certain set value, the gate of the gating circuit 21 is opened and the output signal of the bias control circuit 9 is changed. The signal current control circuit 10 may be controlled as shown in O. The control signal at this time is β'18', and this and the signal β of the reference circuit 11. 18, and the signal current is controlled by the output signal.

In this case, the control signal and reference signal may be an integral signal or an alternating current signal. In this operation, when I>β, the optical output is controlled only by the bias current, and β5×β. 〇 Figure 4 shows another embodiment of the present invention 〇 Operation of this system The principle is to control the signal current using the DC component of the optical output, so it is necessary to separate the signal component and the DC component.

This is relatively simple, and it suffices to use the signal component of the optical output as the reference signal. Therefore, it is sufficient to detect the peak value in the bias control circuit 9, which has the advantage of being able to be used in common with the via input current control signal. Since the output of the photoelectric conversion circuit 4 includes a direct current component and an alternating current component, only the signal components can be canceled out by appropriately amplifying the output and comparing it with the reference signal obtained from the bias control circuit 9. That is, this operation is performed by the DC component detection circuit 12. Therefore, if the signal current support circuit 10 is controlled by the DC output signal of this circuit, the signal current will change accordingly. In this system, since the reference signal and the signal component are always equal, the DC component is zero when β7>βo, and the DC component is generated for the first time at β5-β', and a control signal is obtained. Therefore, by detecting this DC component, the DC component of the optical output can be monitored at the same time as control. Therefore, the restriction as shown in FIG. 3 is not necessary. In this case as well, it goes without saying that the reference signal and signal component may be integral or alternating current signals.Also, bias current control is always performed.As above, the feature of the present invention is that signal current and bias current control are separated. However, the purpose is to control the signal current only under the condition of β(βo).

As a result, it can be seen that the present invention has excellent advantages as shown below.It goes without saying that this method can also be applied to light emitting diodes. (6) Summary As explained above, according to the present invention, the control of bias current and signal current is separated in driving a semiconductor laser,
And the differential quantum efficiency of the semiconductor laser is β5.

Since the signal current is controlled only when the signal current is reached, the operation is stable, and the DC component of the optical output can be monitored and erased at the same time. In addition, since the DC component can be offset even in β2<βo, manufacturing deviations and aging deterioration of semiconductor lasers can be largely tolerated, so the manufacturing yield of semiconductor lasers can be greatly increased, leading to a significant reduction in manufacturing costs. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing a conventional embodiment, FIG. 2 is a diagram explaining the operating principle of the present invention, and FIGS. 3 and 4 are connection diagrams showing embodiments of the present invention.

Claims (1)

[Claims] 1. In an optical output stabilization method for a semiconductor laser driven by a superimposed current of a signal current and a bias current, the DC component and the signal component of the optical output of the stabilizing device are separately detected, and the DC component of the optical output is An optical output stabilization method characterized in that the signal current and the bias current are controlled by a signal component of the optical output.