JPS6163074A - Driving circuit for semiconductor laser diode - Google Patents

Abstract

PURPOSE:To prevent the deterioration and malfunction of a semiconductor laser diode from generating at the time of turning-ON of a power source by a method wherein the regulation for the maximum current value of current to impress on the laser diode is controlled interlocking with a detecting signal obtainable by the temperature detecting element of the LD. CONSTITUTION:A temperature detecting output obtainable by an ATC (automatic temperature control) circuit 16 is inputted in an APC (automatic photo output control) circuit 15. A circuit, which regulates the maximum current value of current to impress on the LD, is provided in the circuit 15 and this regulating circuit is controlled by the temperature detecting output obtainable by the circuit 16. As an example, if a power source is attempted to turn-ON on the circuit 15, which is provided so as to enable the temperature of the LD to make to a constant at 25 deg.C, and the LD driving circuit, which is provided so as to enable the maximum current value regulating circuit of the circuit 15 to regulate the maximum current value of current to impress on the LD on the abovementioned conditions that the circuit 15 is provided, at a temperature environment lower than 25 deg.C, the regulating value for the maximum current value of current to impress on the LD becomes smaller than the set value of 25 deg.C.

Description

Detailed Description of the Invention (Industrial Application Field) This invention relates to a semiconductor laser diode (hereinafter referred to as LD) used as a light source for optical communications or optical disk players.
LD to operate stably without deterioration.
Regarding drive circuits.

(Configuration of conventional example and its problems) Figure 1 is an I-I characteristic diagram showing the forward current current and optical output level L of an LD using temperature ("C") as a parameter. The maximum rated value of the output level is set for each, and if the LD is used beyond that value, it will cause damage or deterioration.As shown in the figure, the LD characteristics change greatly depending on the temperature ('C). It is driven at a constant temperature by performing automatic temperature control (ATC) using a Peltier element for temperature control, etc.Furthermore, a part of the output of the LD is guided to the light receiving element, and a bias current is adjusted according to the output level. The output of the LD is stabilized by performing automatic optical output control (referred to as APC) to apply this to the LD.

FIG. 2 shows a block diagram of an LD drive circuit using the above-mentioned ATC and APC. An input signal indicated by reference numeral 11 is input to the LD driver circuit 12 .

The configuration of the LD module 13 includes an LD 14, a Peltier element for temperature control, a temperature detection element, and a light receiving element.

Of these, the LD 14 is connected to the LD driver circuit 12, and the LD 14 is connected to the LD driver circuit 12.
An optical signal is output from.

On the other hand, a part of the optical output from the LD 14 is transmitted to the LD module 1.
The light output signal of the LD is stabilized by controlling the bias current applied to the LD 14 through the LD driver circuit after being guided to the light receiving element in 3, photoelectrically converted, detected and amplified by the APC circuit 15. ing. moreover,
By applying a detection signal that detects the temperature of the LD 14 using a thermistor element or a temperature detection element using a diode in the LD module 13 to the ATC circuit 16, the temperature of the LD 14 is kept constant by the Peltier element for temperature control. There is.

In devices using ATC or APC in the LD drive circuit, it takes time for the device to stabilize when the power is initially turned on. For example, if you set the ATC circuit to the operating temperature of the LD at room temperature 25.
If the setting temperature is set at , at the current value that allows the LD to operate normally at room temperature, the light output level increases when the temperature has not yet reached room temperature, and in some cases the light output level may exceed the maximum rated value. . To prevent this, the LD includes an APC circuit 15 that prevents a current exceeding a certain level from flowing. However, it can be seen from the IL characteristics in FIG. 1 that the current value at the maximum rated value of the optical output varies depending on the temperature of the LD. Therefore, 6APC generally has a very low maximum current so as not to exceed the maximum rating at room temperature.
Compared to ATC, the time it takes for the optical output level to stabilize after current is applied is shorter, but since APC is an automatic control circuit, it depends on the circuit design conditions such as the circuit's loop gain or frequency response. It has the transient response characteristics shown in Figure 3. In other words, the horizontal axis in Fig. 3 represents time t, and the vertical axis represents L.
17.18 represents the optical output level from D, and the control response speed is changed. As can be seen from this figure, the set optical output level may be exceeded from the time the power is turned on until the optical output level L is stabilized, and this cannot be avoided.

Therefore, the maximum current is regulated in the same manner as described for the ATC circuit.

From the above, it has been found that the LD drive circuit is in a very unstable state if the ambient temperature environment is low when the power is turned on, and this may lead to defective or destroyed LD in some cases. Note that due to this concern, the optical output level of the LD is often set to a low level.

(Object of the Invention) In view of the above, the present invention aims to eliminate the drawbacks of conventional LD drive circuits, and provides an LD drive that does not cause LD deterioration or failure when the power is turned on, regardless of the temperature environment. It is intended to provide a circuit.

(Structure of the Invention) In order to achieve the above-mentioned object, the present invention controls the maximum current value of the LD in conjunction with the detection signal obtained by the temperature detection element of the LD, thereby turning on the power of the LD drive circuit. In some cases, the maximum current value of the LD is configured to be smaller than that at normal temperature when starting at low temperature.Hereinafter, the present invention will be described in detail using one embodiment.

(Description of Embodiment) FIG. 4 is a block diagram showing an embodiment of the present invention, and since the operating principle is the same as that described in detail in FIG. 2, detailed explanation will be omitted. This invention is characterized in that the temperature detection output obtained by the ATC circuit is input to the APC circuit. AP
As described in the conventional example, the C circuit is provided with a circuit that regulates the maximum current value applied to the LD, and this regulating circuit is controlled by the temperature detection output of the ATC circuit. Figure 5 is a diagram showing the control characteristics, and the horizontal axis is the temperature of the LD ('C).
, the vertical axis is the regulation value of the maximum current flowing through the LD, 11x (
mA) is expressed as il.

- As an example, an APC circuit that is set so that the LD temperature is constant at 25℃, and an LD drive circuit that sets the maximum current value of the LD with the maximum current regulation circuit of the APC circuit under these conditions, If the power is turned on in a temperature environment, as shown in Figure 5, the maximum current limit for the LD is 1.
. will be less than the set value of 25°C.

The characteristics of this slope curve vary depending on the LD, but can be easily determined from the characteristics of the LD itself, that is, the temperature and IL characteristics shown in FIG. Also,
As can be seen from Figure 1, when the power is turned on to an LD drive circuit in an environment of 25°C or higher, the threshold current increases,
As a result, the maximum current value that regulates the optical power of the LD also increases. Therefore, as shown in Fig. 5, the maximum current value I□8 of the LD should have the characteristics shown by the solid line, and at a set temperature of 25°C or higher, the maximum current value I□8 as shown by the dotted line should be used. may be made constant.

This means that just as the optical output of the LD has its maximum rated value, the LD deteriorates as the forward current of the LD increases. Further, the characteristics shown in FIG. 5 are shown as an example, and the temperature at which the maximum current value of the LD is constant can be freely set.

The present invention has been described above, but in the present invention, the maximum current value is determined by the detection signal of the temperature detection element of the LD. Since this method is not a loop-like automatic control circuit like ATC or APC, it does not have temperature response characteristics, and therefore, when the power is turned on, the circuit will not operate at a current value that exceeds the maximum current value set by the temperature.

(Effects of the Invention) As is clear from the above detailed explanation, the present invention prevents the LD of the device from becoming defective or deteriorating even if the power is turned on in a low temperature environment, so that the device using the LD is reliable. can significantly improve the degree of Furthermore, since the optical output level of the LD can be safely set to a large value, there is also the effect that there is more leeway in the design of the device.

[Brief explanation of the drawing]

Fig. 1 is an I-L characteristic diagram of a semiconductor laser diode (LD), Fig. 2 is a block diagram of a conventional example of an LD drive circuit, and Fig. 3 is a transient diagram of an automatic optical output control circuit (APC). 4 is a block diagram of an LD drive circuit according to an embodiment of the present invention, and FIG. 5 is a block diagram of an LD drive circuit according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing temperature and maximum regulated current flowing through the LD. 11... Input signal, 12... LD driver circuit, 1
3...LD module, 14...LD, 15...
APC circuit, 16...ATC circuit, 17...APC
Response characteristics of the circuit, 18...Response characteristics when changing the response speed. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 Figure 1'':) lb Figure 3 Time (1) Figure 4 Figure 5 Temperature ('C)

Claims (2)

[Claims] (1) An automatic temperature control circuit that keeps the temperature of the semiconductor laser diode almost constant using a temperature detection element and a temperature control element driven by its detection output, and photoelectrically converts a part of the output of the semiconductor laser diode. A light receiving element,
In a semiconductor laser diode drive circuit having an automatic optical output control circuit that controls the forward current of the semiconductor laser diode by its output, a maximum current regulation circuit that regulates the maximum value of the forward current of the semiconductor laser diode is provided, A driving circuit for a semiconductor laser diode, characterized in that the maximum current of the maximum current regulating circuit is regulated by controlling this by the output of the temperature detecting element. (2) The semiconductor laser diode drive circuit according to claim (1), wherein the maximum current regulation value of the maximum current regulation circuit is regulated to be substantially constant above a certain set temperature.