JPS5934684A - Stabilization circuit for characteristic of semiconductor laser diode - Google Patents

Abstract

PURPOSE:To form a stabilization circuit for characteristics of a semiconductor laser diode with a simple structure by a method wherein the difference between the voltage which is proportional to a photo-current converted by a photo diode and the reference voltage is amplified, and the conduction current to an electron cooler which cools a laser vessel, and the laser bias current of the laser diode are controlled. CONSTITUTION:In a stabilization circuit for characteristic of a semiconductor laser diode, a conventional thermo-sensitive element is omitted so that an output of an error amplifier 7 is applied to a temperature controller 13 as the temperature measurements of a laser vessel 3. Since the bias current values I1, I2, and I3 for holding a light output at a constant value Lout correspond respectively to temperature T1, T2, and T3, the bias current values correspond to the laser diode 1, that is, the temperature measurements of the laser vessel 3. Meanwhile, since these bias current values are determined with the output of the error amplifier 7, as shown in the figure, inputting of the output of the error amplifier 7 to the temperature controller 3 is equivalent to applying the output of the conventional thermo-sensitive element.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a characteristic stabilizing circuit for a semiconductor laser diode, and particularly to a characteristic stabilizing circuit suitable for a simple configuration.

FIG. 1 is a diagram showing the relationship between the driving current of a semiconductor laser diode (hereinafter simply referred to as a laser diode) and the light emission output Lout. As shown in Figure 1, ■-Lo
The ut characteristic is that the ambient temperature is T□.

When the temperature rises from T2+T8, it moves greatly to the right side of the diagram as shown by curves a, b, and c. That is, as the ambient temperature rises, in order to keep the light emitting output Lout at a constant value in response to the increase, the drive current must be adjusted as follows: (1) + (2). ■We have to increase it to 3.

Another method for stabilizing the light output is to stabilize the temperature of the laser diode itself.
It is also being considered to use these methods in combination.

FIG. 2 is a circuit diagram of the conventional circuit.

Next, the operation of the circuit shown in FIG. 2 will be explained.

1 is a laser diode, and the laser diode 1 is housed together with a photodiode 2 in a small metal laser container 3, and the front light of its light output is transmitted through an optical fiber 4.
The rear light is directly incident on the photodiode 2, and the photodiode 2 converts it into a current proportional to the average light emission output, and the voltage generated across the resistor 4 and capacitor 5 and the reference voltage 6 are The difference is compared by the error amplifier 7, and the difference is further amplified by the error amplifier 7. In addition,
The resistor 4 is for converting the photocurrent of the photodiode 2 into a voltage, and the Q1 capacitor 5 is for detecting the average value. The output of the error amplifier 7 drives the laser diode 1 via a current amplifier 8 and a laser drive resistor 9. In this manner, the error amplifier 7 adjusts its output voltage to reduce the laser bias current when the optical output is too thick than the set value, and to increase the laser bias current when it is too small. In addition, laser diode 1
A coupling circuit 10 consisting of an ordinary resistor and a capacitor for
A signal 11 is applied through the oscillator, and the average optical output when this signal 11 has no DC component is equal to the optical output when the signal 11 is not applied.

A temperature sensing element (for example, a thermistor) 12 for detecting the temperature is attached to the laser container B that houses the laser diode 1 and the phototransistor 2, and the output thereof is received by a temperature regulator 16. Accordingly, the temperature regulator 16 adjusts the current flowing through the electronic cooling device (for example, a Peltier element) 14 to maintain the temperature of the laser container B at a predetermined temperature, thereby stabilizing the temperature.

In the manner described above, the temperature of the laser diode is stabilized and the optical output is stabilized, thereby ensuring stable and highly reliable laser operation.

However, according to FIG. 1, two sensors for optical output and temperature (two photodiodes and two
and temperature sensing element 12) are required, and the laser container 6
are generally small in size, and it is troublesome to attach the temperature sensing element 12 thereto. Furthermore, as the temperature sensing element 12, one must be used that has sufficiently stable temperature characteristics and is highly reliable.
In reality, there are problems such as the difficulty of doing so.

The present invention has been made in view of the above, and an object of the present invention is to provide a characteristic stabilization circuit for a semiconductor laser diode that can have a simple configuration.

The present invention is characterized by a photodiode that receives backward light of the light output from a semiconductor laser diode and converts it into a photocurrent proportional to the average value of the optical output, and a difference between a voltage proportional to the photocurrent and a reference voltage. an error amplifier that amplifies the output of the laser diode, and a temperature regulator that inputs the output of the error amplifier as a temperature measurement value of the laser container housing the laser diode and controls the current flowing to the electronic cooling device that cools the laser container. , and a current amplifier that amplifies the output of the error amplifier to control the laser bias current of the laser diode.

The present invention will be explained in detail below using the embodiment shown in FIG.

FIG. 6 is a circuit diagram showing an embodiment of the characteristic stabilizing circuit for a laser diode according to the present invention. The same parts as in FIG. 2 are denoted by the same reference numerals, and the explanation thereof will be omitted here.

The difference between FIG. 6 and FIG. 2 is that the output of the error amplifier 7 is given to the temperature regulator 16 as the temperature measurement value of the laser container B, and the temperature sensing element 12 in FIG. 2 is omitted. .

Other details are the same as in FIG. 2.

As can be seen from Fig. 1, the bias current value for maintaining the optical output at a constant value Lout □* ■'2* TB corresponds to the temperature T□ + T2+ TB, so the bias current value is 1, that is, corresponds to the temperature measurement value of laser container B. By the way, this bias current value is determined by the output of the error amplifier 7, so if the output of the error amplifier 7 is inputted to the temperature regulator 16 as shown in FIG. Temperature sensing element 1 in the figure
This is equivalent to giving an output of 2.

Therefore, according to the embodiment shown in FIG.
Even if 2 is not provided, the operation can be performed in the same manner as in FIG. 2, and the configuration can be simplified. Moreover, since the temperature is detected from the optical output of the laser diode 1, the temperature stabilization accuracy of the laser diode 1 can be improved.

As explained above, according to the present invention, it is possible to have a simple structure, and the temperature stabilization of the semiconductor laser diode can be further improved.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between laser diode drive current and light emitting output, Figure 2 is a circuit diagram of a conventional laser diode characteristic stabilization circuit, and Figure 6 is a diagram of the laser diode characteristic stabilization circuit of the present invention. FIG. 2 is a circuit diagram showing an example. 1: Laser diode, 2: Photodiode, 6: Laser container, 4: Resistor, 5: Capacitor, 6: Reference voltage,
7: error amplifier, 8: current amplifier, 13 two temperature regulators,
14:Electronic cooling de-(chair. Sai II2)

Claims (1)

[Claims] 1. In a characteristic stabilization circuit that maintains the temperature inside a laser container housing a semiconductor laser diode at a predetermined temperature and stabilizes the optical output of the laser diode, the backward light of the light output from the semiconductor laser diode is an error amplifier that amplifies the difference between a voltage proportional to the photocurrent and a reference voltage; A temperature regulator that uses a measured value to manually control the current flowing to the electronic cooling device that cools the laser container, and a current amplifier that amplifies the output of the error amplifier to control the laser bias current of the laser diode. A circuit for stabilizing the characteristics of a semiconductor laser diode.