JPS61265885A - Semiconductor laser and drive thereof - Google Patents

Abstract

PURPOSE:To stabilize the oscillation wavelength of a semiconductor laser and to miniaturize the light source thereof by a method wherein the semiconductor laser is provided with a first electrode, which feeds driving current to the light-emitting part, a second electrode, which is adjacent to the light-emitting part independent of the first electrode and feeds current to enable heat to generate in the P-N junction part, and a third electrode, which leads out the junction voltage of the P-N junction part. CONSTITUTION:An exothermic part electrode 10 and a derecting part electrode 11 are both coupled thermally with a light-emitting part 9. When the exothermic part electrode 10 is conducted, heat is generated in the P-N junction (constituted of a clad layer 5 and an active layer 4) under the electrodes and the exothermic part electrode 10 acts as a heater for the light-emitting part 9, while the detecting part electrode 11 acts as a temperature sensor, which catches a temperature change in the P-N junction under the electrodes as a change in the terminal voltage, by passing low current of several mA or thereabouts thereto. As the width of a chip for a normal semiconductor laser is 100-300mum, the exothermic part electrode 10 and the detecting part electrode 11 can be made adjacent to the light-emitting part 9 50-100mum away. As a result, the thermal coupling thereof with the light-emitting part 9 is also good and the thermal time constants thereof can be also lessened.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a semiconductor laser and a method of driving the semiconductor laser, and is particularly suitable for use as a light source for optical information equipment such as a laser beam printer, a laser facsimile, and an optical disk. The present invention relates to a semiconductor laser and its driving method.

(Prior Art) Compared to conventional refractive and reflective optical elements, diffractive optical elements are starting to be used industrially because they are easier to replicate and can be mass-produced at low cost. Examples include holographic laser scanners used in supermarket barcode readers and laser beam printers. As an example of a laser scanner used in a laser beam printer, Hideto Iwaoka and Takahiro Shiozawa, IEICE Technical Study Group Report Vol. 84, No. 193 (1), published by IEICE,
Published on November 19, 1984), pages 25-32 of the paper ``Linear, aberration-free hologram scanner'' (paper number 0Q)
E84-86). Using a diffractive optical element,
When the wavelength of the laser that is the light source changes, the direction of the output light from the optical element changes. In the example of a laser scanner in a laser beam printer given above, variations in the position of the scan line occur. The oscillation wavelength of a semiconductor laser is caused by a temperature change in the refractive index of the active layer and a temperature change in the band gap of the active layer. The former is a gradual change of 0.5 to 0.8 people/person, but the latter is large, 2 to 5 people/person, and also causes a jump of 3 to 8 people/person in the vertical mode. Therefore, in the above-mentioned paper, the temperature of the semiconductor laser is stabilized by controlling the bias current of the semiconductor laser and the duty ratio of the pulse to keep the power consumption constant regardless of whether it is emitting light or not. A method for stabilizing the oscillation wavelength is described. Another conventional method is to mount a semiconductor laser on a Vertier element and control the temperature.

(Problems to be Solved by the Invention) The above-mentioned conventional techniques have the following problems. The constant power drive disclosed in the above-mentioned papers cannot cope with changes in the ambient temperature of the semiconductor laser, and as a result, it becomes necessary to control the temperature of the semiconductor laser using a Vertier element. The heat capacity of the Vertier element is much larger than that of a semiconductor laser, so the thermal time constant is large, the time constant for temperature control is also large, and the response is slow. Also, a temperature detection element such as a thermocouple is used to control the Vertier element. However, its heat capacity is large, and there is a problem that depending on the mounting position, a time delay may occur due to heat conduction. Furthermore, the biggest problem is that when mounted on a Bertier element, the original compactness and lightness of the semiconductor laser light source is lost, and the semiconductor laser becomes extremely large in volume.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a semiconductor laser and a method for driving the same, which can solve the problems of the prior art, stabilize the oscillation wavelength, and downsize the light source.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the semiconductor laser provided by the first invention of the present application has a first semiconductor laser that supplies a driving current to a light emitting part.
a second electrode adjacent to the light emitting portion independently of the electrode of the p-n junction and supplying a current that causes the p-n junction to generate heat;
It is characterized in that it is provided with a third electrode for taking out the junction voltage of the junction part.

In addition, in order to solve the above-mentioned problems, the second invention of the present application provides a method for driving a semiconductor laser, in which a first DC current is supplied from a first electrode to a light emitting part, supplying a second direct current that causes the pn junction to generate heat from a second electrode provided adjacent to the light emitting part independently of the electrode;
The p-n junction is connected via a third electrode provided adjacent to the light emitting section independently of the first and second electrodes.
FE is taken out, and the second current is controlled based on the junction voltage to make the junction voltage constant.

Furthermore, in order to solve the above-mentioned problems, a method for driving a semiconductor laser provided by the third invention of the present application supplies a first pulse current from a first electrode to a light emitting part, and A current that causes the p-n junction to generate heat is supplied from a second electrode provided adjacent to the light emitting section independently of the electrode, and this heating current is generated by superimposing a direct current bias current on the second pulse current. The power waveforms of the first and second pulse currents are in opposite phases to each other, and the bias current is controlled based on the junction voltage to keep the junction voltage constant.

(Operation) The operation and principle of the present invention are as follows. In the present invention, first, instead of using a volumetrically large Vertier element, heat generated at the pn junction of a semiconductor laser is utilized. For this reason, an electrode is provided adjacent to the light emitting part to allow current to flow through the pn junction independently of the light emitting part, and this part is used as a heater. Further, as a temperature detection element in place of a thermocouple, temperature changes in the junction voltage of a pn junction are utilized. Therefore, an electrode for independently detecting the junction voltage is provided adjacent to the light emitting part, and this part is used as a temperature sensor. The basic function of the present invention is to control the heat generation of the heater using the output of the temperature sensor, to keep the temperature of the semiconductor laser constant, and to stabilize the oscillation wavelength. It is a well-known phenomenon that the oscillation wavelength of a semiconductor laser changes due to heat generated by driving power. An example of such data is 1 of 1 Optics, Vol. 13, No. 2 (published April 1984), published by the Society of Applied Physics Optics Conference, written by Takao Furuse.
This is explained in the article 1 "Electrical Use of Semiconductor Lasers" published on pages 18 to 124. It is known that wavelength fluctuations occur even with a drive pulse of one unit or less. This means that by providing an electrode independent of the light emitting part at the p-n junction of a semiconductor laser and injecting current, it is possible to provide a fast-response heater function that can change the temperature of the light emitting part. ing. Furthermore, when an AlGaAs semiconductor laser is driven with a low current below the oscillation threshold, the temperature change in the terminal voltage is about -1 mV/''C. By providing an electrode independent of the light emitting part and passing a low current through it, a compact and high-speed response temperature sensor function can be provided.In addition, the light emitting part of the semiconductor laser and the electrically independent heat generating part can be complementary to each other. If the semiconductor laser chip is driven by a pulse with a power waveform, the power consumption will be constant, and the temperature will be easily kept constant.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the first invention of the present application.Other than the heat generating part electrode 10 and the detecting part electrode 11, the basic structure is the same as that of a normal semiconductor laser. A GaAlAs visible semiconductor laser is basically an n-
It consists of a cladding layer 3, an active layer 4, a cladding layer 5, a cap layer 6, an insulating layer 7, a light emitting part electrode 8, and a substrate electrode 1 on a GaAs substrate 2. The light emitting section 9 has various types of gain waveguide structures and optical waveguide structures for stabilizing the oscillation transverse mode. FIG. 1 shows an example having a refractive index waveguide structure. This embodiment is characterized by a structure in which a total heat section electrode 10 and a detection section electrode 11 are added adjacent to the light emitting section 9 on the same chip of a semiconductor laser having such a basic structure. The total heat part electrode 10 and the detection part electrode 11 are thermally coupled to the light emitting part 9. When electricity is applied to the entire heating section electrode 10, heat is generated at the pn junction (composed of the cladding layer 5 and the active layer 4) under the electrode, which acts as a heater for the light emitting section 9. On the other hand, by flowing a low current of about several mA through the detection part electrode 11, it is possible to
- It acts as a temperature sensor that detects the temperature change of the n junction as a change in terminal voltage. Since the chip width of a typical semiconductor laser (width in the cross-sectional view shown in FIG. 1) is 100 to 3037 mm, the total heat section electrode 10 and the detection section electrode 11 are adjacent to the light emitting section 9 by 50 to 100 mm. It can be fabricated by using the same method, has good thermal coupling, and can have a small thermal time constant. If the embodiment shown in FIG. 1 is used, a Peltier element is not required in the light source, and the light source can be made smaller and lighter. In the embodiment shown in FIG. 1, the entire hot section electrode 10,
Although an example has been shown in which both the detection part electrode 11 and the current confinement structure are formed by the absolute RM 17, the first invention of the present application can also be realized by using a sticky electrode on the cannob layer 6.

FIG. 2 is a diagram showing an example of a drive circuit used to drive the semiconductor laser of the embodiment of FIG. 1, which can be driven with direct current, according to the second invention of the present application. code 12
The part shown by is the semiconductor laser chip of the embodiment in FIG. 1, in which three diodes, a light emitting section 13, a heat generating section 14, and a detecting section 15 are arranged on one chip. The terminal 16 is a drive terminal for the light emitting diode 13, and is driven by a nearly direct current that changes only relatively slowly.

A low current of about several mA is always passed through the detection unit 15,
The detection unit terminal voltage is compared with the reference voltage, and if the terminal voltage is higher than the reference voltage (corresponding to the case where the detection unit temperature is lower than the reference temperature), heat is generated so that the detection unit terminal voltage becomes the reference voltage. The current flowing to the heat generating section 14 is increased via the section control circuit 17. Conversely, if the terminal voltage is much lower than the reference voltage, the current flowing to the heat generating part 14 is reduced via the heat generating part control circuit 17 so that the detecting part terminal voltage becomes the reference voltage. With this driving method, the temperature of the light emitting section can be kept constant and the oscillation wavelength can be stabilized. Therefore, if the embodiment of the second invention of the present application explained in FIG. 2 is used, a Vertier element or the like is not required, so that the light source can be made smaller and lighter.

FIG. 3 is a block diagram showing an example of a drive circuit used to drive the semiconductor laser of the embodiment of FIG. 1, which is driven by a pulse current, according to the third invention of the present application. code 1
The part surrounded by 2 is the semiconductor laser chip of the embodiment in FIG. 1, in which three diodes, a light emitting part 13, a heat generating part 14, and a detecting part 15, are arranged on one chip. The terminal 16 is a drive terminal for the light emitting diode 13 and is driven by a pulse current. The inverting circuit 19 includes a light emitting section guiode 13
as well as a drive circuit for the heat generating part control circuit 17.
This is a circuit that supplies an inverted pulse of the driving pulse for the light emitting diode 13. The heat generating section control circuit 17 drives the heat generating section diode 14 using the supplied inversion pulse. The pulse drive power of the heat generating diode 14 is set to be complementary to the pulse drive power of the light emitting diode 13, and the sum of the pulse drive power of the heat generating diode 14 and the light emitting diode 13 is always constant. . As a result,
The inside of the semiconductor laser chip 12 has constant power consumption, and the temperature of the light emitting section 13 is kept constant. However, with constant power consumption, the chip temperature changes due to changes in ambient temperature, etc., so in this driving method, feedback is applied using the detection section 15. A low current of about several mA is always passed through the detection section 15, and the terminal of the detection section is compared with a reference voltage.If the terminal voltage is higher than the reference voltage (corresponding to the case where the temperature of the detection section is lower than the reference temperature) ) increases the bias current superimposed on the drive pulse of the heat generating unit 14 via the heat generating unit control circuit 17 so that the detection unit terminal voltage becomes the reference voltage. Conversely, when the terminal voltage is lower than the reference voltage, the bias current superimposed on the drive pulse to the heat generating part 14 is reduced via the heat generating part control circuit 17 so that the detecting part terminal voltage becomes the reference voltage. With this driving method, the temperature of the light emitting section is made constant and the oscillation wavelength is stabilized. Therefore, if the embodiment of the third invention of the present application described with reference to FIG. 3 is used, a Vertier element is not required in the light source, and the light source can be made smaller and lighter.

(Effects of the Invention) As described above, according to the invention of the present application, it is possible to provide a semiconductor laser whose oscillation wavelength can be stabilized and whose light source can be made compact, and a method for driving the semiconductor laser.

Therefore, by using the semiconductor laser and its driving method of the present invention, the internal temperature of the semiconductor laser chip can be made constant regardless of DC drive or pulse drive, and a stable oscillation wavelength that can be used as a light source for a diffractive optical element can be achieved. Laser light is obtained. Furthermore, compared to the conventional method using a Vertier element, the device can be significantly downsized and power consumption can be reduced.

[Brief explanation of drawings]

Figure 1 is a sectional view showing an embodiment of the first invention of the present application, and Figure 2 is a drive circuit used to drive the embodiment of Figure 1 driven by direct current according to the second invention of the present application. FIG. 3 is a block diagram showing an example of a drive circuit used to drive the embodiment of FIG. 1, which is driven by a pulse current, according to the third invention of the present application.・ 1... Substrate electrode, 2... n-GaAs substrate, 3...
- cladding layer, 4... active layer, 5... cladding layer,
6... Cap layer, 7... Insulating layer, 8... Light emitting part electrode, 9... Light emitting part, 10... Heat generating part electrode, 11.
...Detection part electrode, 12...Semiconductor laser chip, 13
... Light emitting part, 14... Heat generating part, 15... Detection part,
16... Drive terminal, 17... Heat generating part control circuit, 18
... Voltage detection circuit, 19... Inversion circuit. Representative Patent Attorney Shinsuke Honjo Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) A second electrode that supplies a current that causes the p-n junction to generate heat, which is adjacent to the light-emitting section independently of the first electrode that supplies a drive current to the light-emitting section; and a second electrode that supplies a current that causes the p-n junction to generate heat; 1. A semiconductor laser characterized in that a third electrode is provided for extracting a junction voltage of the semiconductor laser. (2) A first direct current is supplied from a first electrode to a light emitting section, and a p-n junction is connected from a second electrode provided adjacent to the light emitting section independently of the first electrode. A second DC current that generates heat is supplied, and a junction voltage of the p-n junction is supplied through a third electrode provided adjacent to the light emitting section independently of the first and second electrodes. 1. A method of driving a semiconductor laser, comprising: extracting a semiconductor laser, and controlling the second current based on the junction voltage to keep the junction voltage constant. (3) A first pulse current is supplied from the first electrode to the light emitting section, and the p-n junction generates heat from a second electrode provided adjacent to the light emitting section independently of the first electrode. The heating current is generated by superimposing a direct current bias current on the second pulse current, the power waveforms of the first and second pulse currents are in opposite phase to each other, and the heating current is generated based on the junction voltage. A method for driving a semiconductor laser, comprising controlling the bias current to make the junction voltage constant.