JPH03268374A - Temperature regulation of semiconductor laser - Google Patents

Abstract

PURPOSE:To keep the temperature of a semiconductor laser constant in arbitrary operating currents, and to remove the thermal saturation of an optical output with the temperature rise of the semiconductor laser by controlling a temperature control means on the basis of the detecting value of voltage in the forward direction of the semiconductor laser. CONSTITUTION:A Peltier element 5 is used as a temperature control means for cooling or heating a laser chip 4, the voltage of the laser chip 4 is measured by a voltage measuring circuit 6, the measured value is output to a voltage- difference measuring circuit 8 as a voltage signal Vm, voltage Vin applied to a resistor 9 is measured by a reference-voltage signal generating circuit 7, and a reference voltage signal Vout based on the measured value is output to the voltage-difference measuring circuit 8. The difference DELTAV of both signals is measured by the voltage-difference measuring circuit 8 and output to a Peltier element controller 3, and the Peltier element 5 is controlled so that the DELTAV is brought to 0. Accordingly, the temperature of a semiconductor laser can be kept constant, thus completely removing the thermal saturation of an optical output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser used in optical information processing, optical communication, laser processing, etc., and particularly relates to a method for adjusting the temperature of a semiconductor laser.

[Conventional technology]

With the expansion of the range of applications of semiconductor lasers, the demand for higher output semiconductor lasers is increasing. At present, semiconductor laser arrays, broad area lasers, and the like are known as semiconductor lasers that can obtain a high optical output on the order of W units. Since these semiconductor lasers generate heat of several watts or more during subsequent operation, there is a problem that a high optical output cannot be stably obtained unless the generated heat is released to the outside. Therefore, in the case of these semiconductor lasers, contrivances for dissipating heat have been conventionally considered.

FIGS. 3 and 4 are schematic diagrams showing examples of packages for semiconductor laser arrays or broad area lasers that have been designed in this way. First, the example shown in FIG. 3 will be explained. In the figure, 11 is a large package such as To-3, and a metal block 13 to which a laser chip 12 is attached is fixed to the pan cage 11. Further, the package 11 is screwed to the radiation fins 14.

In this example, in such a configuration, the laser chip 12
The heat generated in the heat dissipation fins 14 is dissipated to the outside.

Next, the example shown in FIG. 4 will be explained. In the figure 1
1 is a package screwed to a heat radiation fin 14. A Peltier element 15 for cooling and a metal block 13 to which a laser chip 12 is attached are provided in this order in the package 11, and a thermistor 16 is provided within the block 13. In this example, in such a configuration, the temperature inside the package 11 is detected by the thermistor 16, and the temperature inside the package 11 is kept constant by the Peltier element 15 according to this detected value.

[Problem to be solved by the invention]

Even in the method described above, since the thermal resistance from the mounting part of the heat dissipation fin or thermistor to the active layer of the laser chip is not O, the temperature of the pn junction of the laser chip will not rise due to the heat generated during C-operation. It cannot be avoided. Therefore, C-current-light output characteristics during operation (I
-L characteristic), the optical output does not increase linearly as in the case of pulse operation, and the slope efficiency decreases due to an increase in the temperature of the active layer.

Figure 5 shows a stripe width of 150μm and a resonator length of 500μm.
Fig. 2 shows IL characteristics in a broad area laser with m. In the figure, (a) shows the characteristics when there is no temperature rise of the laser chip, and (b) shows the characteristics when there is a temperature rise of the laser chip. If there is a temperature rise in the laser chip, there is a problem that the slope efficiency decreases as the operating current increases, and as the temperature rise becomes large, the optical output becomes thermally saturated.

There is also the problem that an increase in the temperature of the laser chip leads to a decrease in the reliability of the semiconductor laser.

The present invention has been made in view of the above circumstances, and maintains the temperature of the semiconductor laser constant at any operating current by controlling the temperature adjustment means based on the detected value of the forward voltage of the semiconductor laser. This completely eliminates the thermal saturation of the optical output caused by the rise in temperature of the semiconductor laser.
The object of the present invention is to provide a method for adjusting the temperature of a semiconductor laser, which enables stable high output.

[Means to solve the problem]

A semiconductor laser temperature adjustment method according to the present invention is a method for adjusting the temperature of a semiconductor laser using a temperature adjustment means, in which a forward voltage of the semiconductor laser is detected, and the temperature adjustment means It is characterized by controlling.

[Effect]

In the semiconductor laser temperature adjustment method of the present invention, the forward voltage of the semiconductor laser is measured, and the temperature adjustment means is controlled based on the measured voltage value.

In this case, since the influence of the series resistance is taken into account in temperature adjustment, the temperature of the semiconductor laser can be kept constant.

〔principle〕

Next, the principle of the semiconductor laser temperature adjustment method according to the present invention (hereinafter referred to as the method of the present invention) will be explained.

Figure 6 shows the current-voltage characteristics (r-V characteristics) of a semiconductor laser.
shows. In the figure, (a) represents the characteristics when the temperature of the laser chip is constant, and (a) represents the characteristics when the temperature of the laser chip increases as the operating current increases (during CW operation). . Since the semiconductor laser is a diode, it exhibits characteristics according to the following equation (11) at low current.

Current flowing through the semiconductor laser Io: Current coefficient indicating the characteristics of the semiconductor laser q: Electron charge V: Voltage nun value of the semiconductor laser (=2) k
:Bormann constant T2 Temperature of the semiconductor laser However, as the operating current increases, the influence of the series resistance increases, and the above equation (11) is no longer followed.

As shown in FIG. 6 (bl), it is known that the voltage becomes smaller than when the temperature is constant (FIG. 6(a)).

In the method of the present invention, the r-v characteristics as shown in FIG. 6(al) at a certain set temperature are determined in advance, and the order of the semiconductor laser as shown in FIG. 6(b) during actual commercial operation of the semiconductor laser is determined in advance. Measure the voltage in the direction (a
The voltage difference between 1 and 1) is detected, and temperature adjustment means such as a Peltier element is controlled so that this voltage difference becomes 0. In addition, the temperature of the semiconductor laser can be maintained constant even when the operating current is arbitrary.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a diagram showing the configuration of an apparatus for carrying out the method of the present invention. In the figure, 4 is a laser chip of a semiconductor laser;
Reference numeral 5 indicates a Vertier element which is a temperature adjusting means for cooling or heating the laser chip 4. This laser chip 4
and the Bertier element 5 is a TO-3 type package 1
It is fixedly installed.

Further, this package 1 is screwed to a heat radiation fin (not shown). Laser chip 4 is connected to voltage detection device 2 .

The voltage detection device 2 measures the forward voltage of the semiconductor laser (laser chip 4) during operation with a resistor 9 of 0 or 1 Ω provided in series with the laser chip 4, and outputs it as a voltage signal V#. and a reference voltage signal V indicating the forward voltage that should be applied to the laser chip 4 for an arbitrary operating current at a set temperature in the laser chip 4. ut
a reference voltage signal generation circuit 7 that outputs the voltage, and a voltage measurement circuit 6
and the reference voltage signal V from the reference voltage signal generation circuit 7. Find the utO difference and calculate the difference signal ΔV (=
It has a voltage difference measuring circuit 8 that outputs vout (v-). The reference voltage signal generation circuit 7 stores the current-voltage characteristics of the laser chip 4.

Such characteristics, for example, reduce the pulse width to 10 μsec (
These characteristics were obtained using a method in which the temperature of the laser chip 4 does not rise when the duty is 0.1%).

The reference voltage signal generation circuit 7 then outputs the actual operating current I.

, (=ViI, 10.1), the reference voltage signal ■ matches the characteristics of the stored reference. ut is output to the voltage difference measuring circuit 8. FIG. 2 shows the characteristics stored in advance in the reference voltage signal generation circuit 7, and in this embodiment, the voltage V r n applied to the resistor 9 and the output reference voltage signal ■. Characteristics indicating the relationship with ut are stored in advance in the reference voltage signal generation circuit 7. If the resistance value of the resistor 9 is made too large, a large load will be placed on the power supply for driving the laser chip 4, and the laser chip 4 will
Since the current that can be passed through the resistor 9 becomes smaller, the resistance value of the resistor 9 is set to a value as in this embodiment.

The voltage difference measuring circuit 8 converts the difference signal ΔV into a normal PID!
IJ? Output to type II Peltier element controller 3.

The Peltier element controller 3 controls the ΔV so that it becomes O.
Controls the Bertier element 5.

Next, the operation will be explained.

For example, when the laser chip 4 is a broad area laser having a GaAlAs-based DH structure, a stripe groove of 150 pm, and a cavity length of 500 μm, the operating current I is. .

When is 1.6A, the fluctuating voltage (ΔV) is approximately 2.8m
V/'C. In the method of the present invention, attention is paid to the fact that voltage fluctuation occurs as the temperature rises, and the Vertier element 5 is controlled so that the actual measured value of the voltage matches the voltage value of the characteristic determined in advance.

The voltage of the laser chip 4 is measured by the voltage measuring circuit 6, and the measured value is outputted to the voltage difference measuring circuit 8 as a voltage signal 1. On the other hand, the voltage applied to the resistor 9■8. ．． is measured by the reference voltage signal generation circuit 7, and the reference voltage signal (■) is based on the measured value according to the characteristics shown in FIG. ,
is output to the voltage difference measuring circuit 8. The voltage difference measuring circuit 8 measures the difference ΔV (=V, uL−V, “) between the two signals, and outputs the difference signal ΔV to the Peltier element controller 3.

Then, the Peltier element controller 3 controls the Vertier element 5 so that Δ■ becomes O.

In the method of the present invention, as described above, the Vertier element 5 is controlled based on the measured voltage of the semiconductor laser, so the thermal resistance in the semiconductor laser can be made substantially zero, and the temperature of the semiconductor laser can be kept constant. can be kept.

Therefore, even during C-operation, the same IL characteristics can be obtained during pulse operation.

In the above-described embodiment, an example in which the Bertier element 5 is controlled in order to keep the temperature of the semiconductor laser constant for any operating current has been described in detail, but this is not limited to this. It is also possible to keep the oscillation wavelength constant. The characteristics of the temperature of the laser chip 4 and the voltage of the laser chip 4 are determined at a certain set wavelength, and these characteristics are stored in the reference voltage signal generation circuit 7 in advance. And a reference voltage signal ■ to realize the set oscillation wavelength for any operating current. , is the reference voltage signal generation circuit 7
output to the voltage difference measuring circuit 8. Then, the actual voltage value ■1 of the laser chip 4 and this reference voltage signal ■. The Peltier element controller 3
By controlling the Vertier element 5 according to the following, it is possible to realize a semiconductor laser whose oscillation wavelength is always constant for any operating current. Such an embodiment is effective when used in a solid-state laser excitation light source such as Nd:YAG or Nd;YLF.

It goes without saying that the method of the present invention can be applied to all semiconductor lasers using semiconductor materials, such as GaAlAs-based semiconductor lasers or InGaAIP-based semiconductor lasers.

〔Effect of the invention〕

As described above, in the method of the present invention, the thermal resistance of the semiconductor laser can be made substantially zero, so that the thermal saturation of the optical output, which could not be avoided with the conventional method, can be completely eliminated. In addition, even during C-operation of a semiconductor laser array or broad area laser where the operating current is large (and the heat generation amount is several W or more), it is possible to obtain the same I-L characteristics as during pulse operation. The present invention has excellent effects such as being able to significantly increase output.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of an apparatus for implementing the semiconductor laser temperature adjustment method according to the present invention, and FIG. 2 is a graph showing characteristics stored in advance in the reference voltage signal generation circuit.
Figures 3 and 4 are schematic diagrams showing puff cage examples of high-power semiconductor lasers, Figure 5 is a graph showing the current-optical output characteristics of the semiconductor laser, and Figure 6 is a graph showing the current-voltage characteristics of the semiconductor laser. It is.

Claims (1)

[Claims] 1. A method for adjusting the temperature of a semiconductor laser using a temperature adjustment means, comprising: detecting a forward voltage of the semiconductor laser, and controlling the temperature adjustment means based on the detected value. A method for adjusting the temperature of a semiconductor laser, characterized by: