JPS59112675A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To maintain the temperature of a heat sink constant and to control the input current of a semiconductor laser element in response to the variation in the laser light by providing a thermoelectric cooling element of a temperature control element under the sink when mounting the laser element for emitting lights in bidirections and a detector for detecting one light on the sink of a support. CONSTITUTION:When a photodetector 5 and a semiconductor laser element 1 are placed on a heat sink fin 13, a thermoelectric cooling element 12 of a temperature control element is interposed therebetween. Then, a copper heat sink 8 having uneven surface is mounted on the element 12 through an insulating layer 11 and a metal plate 10, the photodetector 5 having an insulating layer is mounted on the bottom of the recess and at the side of the element 1, and the element for emitting lights 3, 4 in bidirections is provided. In this structure, a power source 7 for the thermoelectric cooling element having an amplifier 6 and a control circuit is connected between the photodetector 5 and the element 12, thereby maintaining the temperature of the element 12 constant and simultaneously correcting the variation in the laser lights.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an injection type semi-integrated laser, in particular a continuous or nearly continuous duty ratio (1) at room temperature or near room temperature.
) Uty 1latio).

In a semiconductor laser, the "threshold current" of the laser beam increases by half as the temperature of the device increases. For example, Ai Hayashi (Engineering)
) (aya3hi) and several others have published an academic journal in the United States [
Journal of Agelide Physics (Jo
Paper submitted to Urnal of Apuiecl Physics, Volume 42, Page 1929 (1971)
As reported in ``GaAs-AtxGa+-xAs Double Heterojunction Grooving Press-In Laser'', when a semiconductor laser is driven with a constant direct current, the laser output changes as the ambient temperature liquefies.

In other words, the temperature change of “threshold DC” Jth is J
th = Jo x p(T/To) −
-(1) (However, Jo l 'I'O is a parameter that determines the change in the "small flow" with respect to temperature,
Motokoyo #) Add Maru. ). Let us consider the case where a double hetero-quaternary structure GaAs-AtGaAs laser is operated. The temperature T of the semiconductor laser element changes by ΔT. If the operating flow of the semiconductor laser device is J, then the change ΔP in the laser output P due to the temperature change of the device is ΔP ΔJtb P J Jth .

If J-(1+ε) Jch (where ε is a parameter that determines the operating point of the semiconductor laser element).

When ε = 0.1 and To = 120', then if the temperature of the element rises by 6C from the operating point, then ~
The output will be halved. Of course, if the device is used with a large ε, the rate of change in laser output with respect to temperature changes will decrease, but on the other hand, the rate of deterioration of the semiconductor laser device will begin to rise as the operating current increases, so it is best to reduce the threshold current as much as possible. ``It is desirable to operate it nearby.

As mentioned above, the optical output of a semiconductor laser is easily influenced by the humidity of the device, so under normal conditions where no means are taken to maintain the temperature, other methods are required to maintain the laser output at a constant level. A means is required.

Conventionally, there are no half-barrel laser devices on the market that are equipped with such a means, but in the field of gas lasers, a portion of the laser beam is
5plitter), etc., to take out the
The extracted laser light is detected by an appropriate photodetector, and if the laser output changes, the detected output is fed back to the all-gas laser excitation acid source, and the O supply input to the gas laser is controlled. There is a push to adopt a means to maintain a constant output. The same method can be used in the case of semiconductor lasers, but introducing an optical system such as a beam splinter into a compact semiconductor laser device that relies on Ig:t would lead to an increase in the size of the device. Become. Moreover, large light losses occur in the beam splinter.

Since semiconductor lasers have a lower optical output than gas lasers, such light loss is a serious problem.

Enough light output? To achieve this, it is possible to increase the operating current, but since increasing the operating current causes a new temperature rise, this is not desirable from the point of view of stabilizing the laser output. increases as the operating current increases, which accelerates the deterioration of the semiconductor laser device.

[Purpose of the invention]

In view of these points, the present invention has been developed to emit *V output detection light without impairing the features of the semiconductor laser device such as small size and light weight, and without causing any loss to the output light extracted from the semiconductor laser device, and to stably output the light for output detection. An object of the present invention is to provide a semiconductor laser device that can extract a high optical output.

[Summary of the invention]

In order to achieve the object, the present invention provides a support means for arranging a semiconductor laser element and a light receiving element in a positional relationship such that they enter the optical path of the laser light from the semiconductor laser element, and One of the emitted laser beams is emitted as output light, the light is received by the light receiving element, and the input direct current of the semiconductor laser element is controlled according to the fluctuation thereof, and the semiconductor laser element is connected to the supporting means. The present invention is characterized in that a temperature control element is provided, and the temperature of the support means is maintained constant by the temperature control element.

Example The present invention will be explained below with reference to Examples.

FIG. 1 is a diagram schematically showing the configuration of an embodiment of a semiconductor laser device according to the present invention. This semiconductor laser device ut consists of a semiconductor laser cable 1, a copper heat link 8, a heat-transmitting cooling cable 12, a heating fin 13, and a photodetector 5. 6 is an amplifier for the output of the photodetector, and 7 is an optical detector. It is the power source for the thermoelectric cooling element, which refers to the variable constant voltage generator and control circuit. The semiconductor laser element 1 is a GaAs AZGaAs double hetero 14 laser, through which a power supply 14 and a load resistance of 15 gold are passed.
When a current higher than the "threshold current" is passed, a laser beam is generated, and the two cleavage planes (i.e., reflective planes) at both ends of the active layer 2
Laser beams 3 and 4 are emitted from the respective laser beams 3 and 4.

The laser beam 3 can be used as a light source for optical communication, optical information processing, chromameter, etc., and the laser beam 4 emitted from another reflective surface is detected by a photodetector 5 placed close to the semiconductor laser element 1. The light is irradiated onto the light receiving surface of this photodetector 5.
For example, for Q A S semiconductor lasers (oscillation wavelength within the range of about 7,500 to 9,000), solar ridges made of Si, PIN photodetectors, etc. are better in terms of sensitivity, temperature characteristics, etc. . In this embodiment, the photodetector 5 is used in short-circuit current mode, which is relatively stable with respect to temperature. The optical detector 5 is electrically insulated from the heat sink 8 by a thin insulating layer 9. The temperature T of the active layer 2 of the semiconductor laser device 1 is determined by the air input supplied to the laser device 1, the ambient temperature T, and the current flowing through the thermoelectric cooling element 12. Voltage supplied to the laser element.

The current is V and h, and the temperature of the heat sink 8 is Th.
Then, T1=Th+θVI ・・・・・・(5
) and Ith=Io eXp(T+/To)”・
There is the relationship (6). Here, θ is the thermal resistance of the laser element 1 and the heat sink 8, and Ith is the threshold current of the laser element 1. The optical output P of the laser is P=η−1,h
) ...... is given by (7). Here η is a proportionality constant. Laser output can be determined as a function of current and heat sink temperature from Kamiko's three equations. Figure 2 is a characteristic diagram that schematically shows the calculation results, where the vertical axis represents the laser output P, the horizontal axis represents the flow rate, and the nodal parameter is the temperature Th of the heat sink, and Tb3>Th.
+>Tb2. It can be seen from FIG. 2 that there are many combinations of leading and heat sink temperatures required to obtain the laser output P+. When the heat sink temperature is fixed, there are two types of current values necessary to improve the laser output PI, and of course a lower current value is preferable. When the heat sink is equipped with the thermoelectric cooling element 12 as in the embodiment shown in FIG. 1, the temperature of the heat sink can be selected within a certain range. Now the heat sink, l
li! If the degree is '1'b4, the required current will be ■Iris. From the point of view of obtaining the necessary laser output with as small a current as possible, it is desirable to select the heat sink temperature Th+ to be much lower than the ambient temperature T. That is, Th=T, -ΔT (
8). Here, ΔT is the temperature difference maintained by the thermoelectric cooling element 12, and is determined by the current supplied to the thermoelectric element. Now, the ambient temperature T, changes by aT for some reason, and the heat sink temperature Th3 (=Th++θ
T), and assuming that the current supplied to the thermoelectric cooling element does not change, the laser output decreases from the predetermined laser output 1-direction PI to P3.

1, the signal proportional to the laser output 4 monitored by the photodetector 5 is amplified by the amplifier 6 and then converted to a reference value (i.e., in this implementation, a predetermined laser output value PI). The current supplied to the thermoelectric cooling element 12 from #7 is changed so that the variation from the reference value approaches zero. In the above case, the temperature difference ΔT maintained by the thermoelectric cooling element is set to ΔTl? so as to cancel out the variation θT in the ambient temperature. It will be changed to T. Temperature determination using thermoelectric cooling elements has the advantage of fast response (less than 1 second) and the ability to raise or lower the ambient temperature by 1 degree depending on the polarity of the current, so it is possible to avoid large fluctuations in the ambient temperature. The advantage is that the laser output can be kept constant even in harsh environments. −
For example, when the ambient temperature is between 110G and 45C, output fluctuations can be suppressed to 5 degrees or less. Furthermore, another advantage of this embodiment is that the laser beam 4 for monitoring is used independently of the laser beam 3 to be used. That is, since the laser beams 3 and 4 are emitted from the same optical cavity, their outputs are proportional to each other, so by controlling the laser output 4 to be constant, the laser beam 3 to be used can be output can be kept constant.

This is convenient when an optical fiber or the like is brought close to the laser element 1 and the laser beam 3 is directly introduced into the fiber, since a monitoring optical system is not required. If the reflectances of the two reflective surfaces are equal, the magnitudes of laser outputs 3 and 4 are equal, but output 4 for monitoring may be small, so the reflective surface from which output 4 is taken out is coated with an insulating film and metal. It is preferable to use a film coating to increase the reflectance. This is because by increasing the reflectance of one reflecting surface, the threshold current value for oscillation can be reduced. Furthermore, in this embodiment, since the photodetector 5 is installed on the same heat sink 8 as the semiconductor laser element 1,
The temperature of the photodetector 5 is also kept almost constant, and therefore the sensitivity of the photodetector has the advantage of being less affected by the ambient temperature. Note that if the output of the semiconductor laser element is subjected to IK modulation, it is necessary to incorporate a low-pass filter into the amplifier 6. At this time, the time average value of the laser output is kept constant. Furthermore, in the embodiment shown in FIG. 1, since the photodetector is also kept at a substantially constant temperature, there is an advantage that the sensitivity of the photodetector is also kept substantially constant.

FIG. 3 shows a schematic configuration diagram of another embodiment of the semiconductor laser device according to the present invention. In FIG. 3, of the laser beams emitted from two reflective surfaces of the semiconductor laser device 1, four laser beams are irradiated onto a photodetector 5 mounted on a heat sink.

The output obtained by the photodetector 5 is amplified by an amplifier 6 and compared with the output corresponding to a predetermined laser output P1, and the input source 14 is applied to the laser element so as to cancel out the corresponding variation.
' rl groan. The non-embodiment differs from the configuration of the embodiment shown in FIG. 1 in that the change in laser output is canceled out by adjusting the power supplied to the laser element. As can be seen from the characteristic diagram in Figure 2, the maximum value of the laser output that can be obtained in continuous operation or operating conditions with a nearly continuous duty ratio is determined by the ambient temperature. Non-implemented examples are difficult to use. Also, as is clear from Figure 2, when the current is increased, the optical output decreases by 1 degree.
ll: Although there are conditions, it is not possible to use the output under such conditions (
It is undesirable to do so (goods) and should be operated under conditions such that the light output increases with the current. therefore,
In this embodiment, the optical output can be adjusted precisely between 1 and 20 kHz when the ambient temperature of the semiconductor laser element is kept almost constant, or when the heat sink temperature is kept almost constant by a thermoelectric cooling element. It can be used freely. - As an example, when there is a temperature change of ±3C around a room temperature of 25C, the output stability was ±2 degrees. When the laser beam is modulated, the provision of a low-pass filter in the amplifier 6 is the same as in the embodiment of FIG.

The current flow to the laser element is still too strong,
It is desirable to provide a current limiting device in the power supply 14' to prevent the laser from entering an unstable region where the laser output decreases as the current increases.

In addition, in the case of the embodiment shown in FIG. 3, the cavity of the semiconductor laser is formed by two opposing reflecting surfaces, but the reflecting surfaces are processed by cleaving, polishing, etching, ion milling, etc. In addition to the method that utilizes the entire plane surface obtained by using this method, the present invention can also be applied to devices that utilize the Bragg reflection obtained by the periodic structure provided in the active layer of the laser or the propagation path of the laser beam. can. This is because even in the latter case, it can be considered that there are two reflective surfaces isographically.

〔Effect of the invention〕

As explained above, according to the present invention, various effects as described below can be achieved. That is, ■ Of the laser beams sent out in both directions from the two reflective surfaces of the semiconductor laser element, one is extracted as the outgoing light and the other is monitored by a photodetector, so all the light from the two directions of the semiconductor laser element is detected. Can be used effectively. If you monitor only with light coming from one direction, the amount of light will decrease by that amount, resulting in a loss of light amount? I will invite you.

■ Moreover, since the light from the monitor is extracted without any special configuration, there is no need for a monitor optical system υ, and its position A
It does not have the complexity of a preparatory tank, and is known for its stability as a device. This makes it possible to reduce the cost per unit of the device and is excellent in mass production.

■ The semiconductor laser element and the light-receiving element can be housed in one package, and only one laser beam is needed to be taken out as the output light, so there is no problem between the reflective surface and the light exit window. It's easy.

■ After keeping the temperature of the support body on which the semiconductor laser is installed constant by the temperature control element, this temperature 11f11
Fluctuations in the output light that cannot be compensated for by the f output element are compensated for by the input current of the semiconductor laser, making it possible to stabilize the stack even more.

(2) Furthermore, since the temperature increase of -7'f due to an increase in input current can be suppressed by the pixel control element, deterioration of the semiconductor laser element due to an increase in input current can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of a semiconductor laser device according to the present invention, and FIG. 2 is a diagram showing the relationship between laser output, current, and heat sink temperature of a semiconductor laser that operates continuously or with a near-continuous tutee ratio. FIG. 3 is a sectional view of a second embodiment of a semiconductor laser device according to the present invention and a block diagram of a control circuit. 1 to 3, 1... semiconductor laser element, 2... active layer of semiconductor laser, 3, 4... laser light, 5... photodetector, 6... amplifier, 7... City 1j-circuit and thermoelectric cooling element power supply, 8... Heat sink, 9... Insulating layer, 10... Metal plate, 11... Insulating layer, 12... Thermoelectric cooling element, 13... Heat dissipation fin, 14... Semiconductor laser soldering source, 14'... Control circuit No. 2 Figure I'I

Claims (1)

[Claims] 1. A half-four laser element that extracts one of the laser beams emitted in both directions as output light, a light receiving element, and the above-mentioned in a positional relationship such that it enters the optical path of the other laser beam from the semiconductor laser element. It consists of a support means for arranging the pixel element, and a temperature control element connected to the support means. A semiconductor laser device characterized in that input direct current to the semiconductor laser element is controlled in accordance with fluctuations in received laser light.