JPH0616071B2 - Method of measuring thermal resistance of light emitting device - Google Patents

Description

The present invention relates to a method for measuring thermal resistance of a light emitting element such as a semiconductor laser, and more specifically, it will improve measurement accuracy and increase measurement speed by using an APC circuit. The proposed method is to measure the thermal resistance of a light-emitting device.

[Prior art]

In order to prolong the device life of a semiconductor laser, it is important to more efficiently dissipate the heat generated between the devices to the outside.Thermal resistance is used as an index, and this thermal resistance is used during the development process of the semiconductor laser. Accurate measurement of is required.

Thus, conventionally, as shown in FIG. 4, a pulse having a current value I ₁ and a time width t ₁ is supplied before and after a process of supplying a current having a current value I ₂ and a time width t _{2 to} a semiconductor laser to raise its temperature. The forward voltages VF ₁ and VF ₂ before and after the temperature rise are measured as shown in FIG. The time t ₁ is a short time such that the temperature rise due to the pulse current application can be sufficiently ignored.

The semiconductor laser has a linear relationship between the forward voltage VF and the temperature T as shown in FIG. 6, like a general diode. Therefore, the temperature rise ΔT from the measured values of VF ₁ and VF ₂
Can be asked. Therefore, the thermal resistance Rt is However, V · I can be calculated as the supplied power.

[Problems to be solved by the invention]

In the case of the conventional method as described above, the change in forward voltage VF ₂
-VF ₁ is small and there is a problem that a short pulse current desired accuracy for measuring at can not be obtained.

That is, as shown in Fig. 6, the change in forward voltage is -0.85mV /
This is as small as ℃, and a sufficient measurement resolution cannot be obtained for a voltage of 1.5 V during measurement.

Furthermore, the time t ₂ for raising the temperature is as long as several tens of seconds, and it takes a long time for one measurement.

[Means for solving problems]

The present invention has been made to solve the above problems, by measuring the change in the operating current of the light-emitting element using the APC circuit, it is possible to measure the thermal resistance with high accuracy in a short time. The purpose is to provide a method.

The method for measuring the thermal resistance of a light emitting device according to the present invention is to drive a light emitting device by supplying a pulse current to the light emitting device with an APC circuit that keeps the light output constant, and at two points during the pulse current supply. At, the operating current of the light emitting element is measured, and the temperature rise between the operating currents at the two time points is obtained based on the relationship between the operating current of the light emitting element and the temperature at the constant light output obtained in advance. It is characterized in that the thermal resistance is obtained based on the temperature rise.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof. FIG. 1 is a circuit diagram showing a state in which a semiconductor laser LD whose thermal resistance is to be measured is connected to an APC circuit known per se.

The semiconductor laser is driven by the current flowing through the transistor Tr to emit light, and the light emitted from this is received by the light receiving diode PIN. A voltage signal based on this amount of received light is given to the inverting input of the operational amplifier OP. On the other hand, a constant voltage generated by a constant voltage circuit including a constant voltage diode D, a capacitor C ₁ and a variable resistor VR is applied to the non-inverting input of the operational amplifier OP.

The output of the operational amplifier OP is given to the base of the transistor Tr. The capacitor C ₂ is for preventing oscillation.

When the APC circuit configured as above is used, when the output of the semiconductor laser LD increases (decreases), the inverting input potential of the operational amplifier OP increases (decreases), and the output of the operational amplifier OP decreases (rises). Along with this, the base current of the transistor Tr decreases (increases) and the operating current of the semiconductor laser LD is suppressed, whereby the output thereof is controlled to decrease (increase). As a result, the output of the semiconductor laser LD is kept constant.

Now, in the present invention, a pulse current is supplied to the semiconductor laser as shown in FIG. 2 by on / off control of a switch provided between the semiconductor laser and a power source not shown in FIG. Immediately after the start and immediately before the end of the supply, the operating currents I ₁ and I ₂ of the semiconductor laser are measured (second
See figure).

FIG. 3 shows the optical output-operating current characteristics of the semiconductor laser with temperature as a parameter, and it can be seen that the current value greatly changes with temperature if the optical output is controlled to be constant by the APC circuit.

The semiconductor laser LD emits Joule heat by the current supplied to the semiconductor laser LD to raise the temperature thereof, but since the optical output is kept constant, the operating current increases accordingly. The rate of increase of this operating current is approximately 0.4mA / ° C, and it is possible to perform measurement with sufficient accuracy for an operating current of approximately 40mA during measurement.

In addition, a sufficient current change (temperature change) can be obtained within a period of several msec to 1 sec for energizing the semiconductor laser LD, and measurement can be performed in a short time.

From the difference between the current values I ₂ and I ₁ measured as described above, the temperature rise value ΔT between the measurement time points can be obtained. This ΔT
The thermal resistance Rt is calculated by substituting in the equation (1).

The present invention is not limited to the semiconductor laser and can be applied to other light emitting elements.

〔effect〕

As described above, according to the present invention, it is possible to measure the thermal resistance with high accuracy in a short time, and it is possible to efficiently and accurately evaluate the life of a light emitting element such as a semiconductor laser during development.

[Brief description of drawings]

FIG. 1 is a circuit diagram for carrying out the method of the present invention, FIG. 2 is a graph showing changes in the operating current of a semiconductor laser, FIG. 3 is a light output-operating current characteristic diagram of the semiconductor laser, and FIGS. FIG. 6 is an explanatory diagram of a conventional method. LD: Semiconductor laser, PIN: Light receiving diode Tr: Transistor, OP: Operational amplifier D: Constant voltage diode

Front page continuation (72) Inventor Norio Tabuchi 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-59-145586 (JP, A) National Convention Lecture Collection [Volume 4] No. 61

Claims (1)

[Claims] 1. An APC in which a light emitting element has a constant light output.
The circuit is driven by supplying a pulse current to the light emitting element, the operating current of the light emitting element is measured at two points during the supply of the pulse current, and the light emitting element of the light emitting element at the constant light output obtained in advance is measured. A method for measuring thermal resistance of a light-emitting element, characterized in that a temperature rise during this period is obtained from the difference between the operating currents at the two points of time based on the relationship between operating current and temperature, and the thermal resistance is obtained based on the temperature rise.