JP7371522B2 - semiconductor laser equipment - Google Patents

Description

The present invention relates to a semiconductor laser device.

In recent years, semiconductor laser devices with a longer life span have been used as light sources for displays such as projectors, compared to conventional lamps. However, since laser light is coherent light, a speckled noise called speckle occurs on the screen. Semiconductor laser devices for display applications are required to reduce this speckle.

There are several measures to reduce speckle, one of which is to use a plurality of semiconductor laser elements with different oscillation wavelengths of several nanometers to several tens of nanometers. In order to reduce speckle by this measure, there is a demand for a device equipped with a plurality of semiconductor laser elements that are included in the same wavelength band but have different oscillation wavelengths. For example, in the red wavelength band, there is a demand for a device having not only a semiconductor laser element with an oscillation wavelength of 638 nm but also a semiconductor laser element with an oscillation wavelength of 640 nm, 642 nm, . . . , 660 nm, etc.

Although this speckle reduction can be achieved by preparing a semiconductor laser device in which semiconductor laser elements with different oscillation wavelengths are mounted in separate packages, it is necessary to have multiple semiconductor laser elements with different oscillation wavelengths in order to miniaturize the device. It is preferable that both are included in one package. Furthermore, mounting a plurality of semiconductor laser elements with different oscillation wavelengths in one package leads to lower costs than mounting semiconductor laser elements with different oscillation wavelengths in separate packages.

For example, Patent Document 1 discloses a device in which a plurality of semiconductor laser elements are arranged on one submount, and it is stated that the plurality of semiconductor laser elements may be in the same wavelength band or in different wavelength bands. ing. Further, Patent Document 1 describes that when a plurality of semiconductor laser elements are arranged, they may be connected in series.

Furthermore, for example, Patent Document 2 discloses a structure in which a plurality of heat sinks (submounts) are arranged in the longitudinal direction of a support block, and a laser chip is arranged on each heat sink, and the plurality of laser chips are electrically connected in series. It is also disclosed that they are connected.

Patent No. 6361293 Special Publication No. 2016-518726

When a plurality of semiconductor laser elements with different oscillation wavelengths are mounted in one package, it is desirable to mount them in series connection due to mounting space, wiring structure, etc. The same current flows through the plurality of semiconductor laser elements connected in series.

However, for example, in the case of a GaAs-based red laser, the oscillation wavelength is adjusted by the amount of strain in the active layer, so due to the ease of obtaining gain for the LH/HH of the strained quantum well, the oscillation threshold current will vary depending on the oscillation wavelength. Ith etc. change. As a result, when looking at a constant drive current in a package in which a plurality of semiconductor laser elements are mounted, the optical outputs of the semiconductor laser elements differ. Furthermore, as the oscillation wavelength becomes longer, the heterobarrier between the active layer and the p-cladding layer becomes higher, and electron overflow becomes less likely to occur, resulting in better temperature characteristics. As a result, as the operating conditions of the semiconductor laser device become higher temperature and larger current, the difference in optical output due to the difference in oscillation wavelength among the plurality of semiconductor laser elements becomes larger.

For this reason, when semiconductor laser devices with different oscillation wavelengths are driven with the same current, differences in optical output tend to occur, and generally speaking, the higher the optical output, the more the end face deterioration progresses. This causes variations in the lifespan, leading to a decrease in the reliability of the semiconductor laser device.
Therefore, an object of the present invention is to provide a highly reliable multi-wavelength semiconductor laser device.

In order to solve the above problems, one embodiment of a semiconductor laser device according to the present invention is a semiconductor laser device in which a plurality of semiconductor laser elements having different oscillation wavelengths within the wavelength band of the same color are electrically connected in series. Therefore, the reflectances at the emission end faces of the plurality of semiconductor laser elements are different from each other.

According to such a semiconductor laser device, the optical output characteristics of the semiconductor laser element can be adjusted by adjusting the reflectance. This allows for close proximity. Therefore, variations in the lifetime of a plurality of semiconductor laser elements are suppressed, and a highly reliable multi-wavelength semiconductor laser device can be obtained.

Further, in the semiconductor laser device, the plurality of semiconductor laser elements have different reflectances at their emission end faces, so that the difference in their oscillation thresholds is wider than when the reflectances are the same. is preferred.

According to such a preferable semiconductor laser device, the difference in the oscillation threshold values of the plurality of semiconductor laser elements is widened, so that it is easy to bring the optical outputs close to each other with the same drive current.

According to the present invention, a highly reliable multi-wavelength semiconductor laser device can be obtained.

1 is a diagram showing an embodiment of a semiconductor laser device of the present invention. FIG. 3 is a diagram showing a laser chip on a submount. It is a graph showing the input/output characteristics of a laser chip in a comparative example. It is a figure showing the structure of the end face in a laser chip. It is a table showing the reflectance of a laser chip. It is a graph showing the input/output characteristics of the laser chip in this embodiment.

Embodiments of the present invention will be described below based on the drawings.
FIG. 1 is a diagram showing an embodiment of a semiconductor laser device of the present invention.

The semiconductor laser device 100 includes a stem base 101, a stem block 102, and a plurality of (two in the example shown here) laser chips 103_1 and 103_2. The semiconductor laser device 100 may be of an open type, but in the example shown in FIG. 1, it is a closed type equipped with a stem cap 110.

The stem block 102 protrudes from the stem base 101, and the stem cap 110 is fixed to the stem base 101 and covers the stem block 102. The stem base 101, the stem block 102, and the stem cap 110 are all made of metal, and constitute a can package. The stem block 102 and the stem base 101 do not need to be made of the same material, and may be made of different materials, or a part of the stem base may be made of the material of the stem block, The opposite may be used, and there is no particular limitation.

In the stem block 102, a submount 104 on which laser chips 103_1 and 103_2 are mounted is fixed by solder to a part of the side surface rising from the stem base 101. The laser beams emitted from the laser chips 103_1 and 103_2 travel upward in FIG. 1, pass through the glass window 111 fitted in the stem cap 110, and are emitted from the semiconductor laser device 100.

Heat generated by the laser chips 103_1 and 103_2 when emitting light is transmitted to the stem block 102 via the submount 104, and further transmitted from the stem block 102 to the stem base 101.

The laser chips 103_1 and 103_2 may be of a multi-emitter type that emits laser beams of multiple spots, or may be of a single-emitter type that emits a laser beam of a single spot. The laser chips 103_1 and 103_2 correspond to an example of a semiconductor laser element according to the present invention. Although the laser chips 103_1 and 103_2 in this embodiment are laser chips using, for example, an AlGaInP-based semiconductor, the semiconductor laser element referred to in the present invention may be a laser chip using a semiconductor other than AlGaInP-based semiconductor. .

In order to supply power to the laser chips 103_1 and 103_2, the semiconductor laser device 100 is provided with power supply lead pins 105. The power supply lead pin 105 passes through the stem base 101 and has one end protruding into the stem cap 110.
A wire 106 is connected to the laser chips 103_1 and 103_2 from one end of the power supply lead pin 105 protruding into the stem cap 110.
FIG. 2 is a diagram showing a laser chip on a submount.
Here, for convenience of explanation, the upper part of the diagram is referred to as "upper" and the lower part of the diagram is referred to as "lower", regardless of the direction of gravity.

Two laser chips 103_1 and 103_2 are mounted on the upper surface of the submount 104. Specifically, the laser chips 103_1 and 103_2 are fixed with solder. Each laser chip 103_1, 103_2 has a front end 103a shown on the front left side of the figure and a rear end 103b hidden on the back right side of the figure, and emits a laser beam from the front end 103a.

Of the two laser chips 103_1 and 103_2, the first laser chip 103_1 has an oscillation wavelength of, for example, 643 nm, and the second laser chip 103_2 has an oscillation wavelength of, for example, 638 nm. All oscillation wavelengths are included in the red wavelength band of 615 nm or more and 700 nm or less. That is, these two laser chips 103_1 and 103_2 are included in the wavelength band of the same color (red in the example shown here) and have different oscillation wavelengths. Since the oscillation wavelengths of the two laser chips 103_1 and 103_2 are different in this way, speckles are reduced in the laser beam emitted from the semiconductor laser device 100 shown in FIG. 1.

Each of the laser chips 103_1 and 103_2 has electrodes on an upper surface and a lower surface, and emits a laser beam when a voltage is applied between the upper and lower electrodes. Further, the operating voltage of each laser chip 103_1 and 103_2 is 2V or more and 4V or less.

The two laser chips 103_1 and 103_2 are electrically connected in series by a wire 106 on the submount 104. Therefore, the driving voltage of the semiconductor laser device 100 is approximately 5V. For such electrical series connection, a plurality of (two in the example shown here) electrically partitioned electrode patterns 104a are formed on the upper surface of the submount 104, and each electrode pattern 104a is formed on each electrode pattern 104a. Laser chips 103_1 and 103_2 are mounted.
Here, input/output characteristics will be shown for a comparative example in which the reflectances of the front ends 103a of the two laser chips 103_1 and 103_2 are equal.
FIG. 3 is a graph showing the input/output characteristics of a laser chip in a comparative example.

The horizontal axis in FIG. 3 represents the input current value, and the vertical axis represents the optical output value. Further, a graph representing the input/output characteristics of the first laser chip 103_1 is shown by a dotted line, and a graph representing the input/output characteristics of the second laser chip 103_2 is shown by a solid line.

Even if the first laser chip 103_1 and the second laser chip 103_2 having different oscillation wavelengths have the same reflectance at the front end 103a, the laser oscillation threshold ( That is, the starting positions of the graphs are different from each other, and the slopes of the graphs are also different. On the other hand, the two laser chips 103_1 and 103_2 electrically connected in series are driven with the same drive current value D. Further, the drive current value D for a light source for display use is generally a constant value set in advance.

Therefore, as shown in FIG. 3, there is a possibility that an output difference ΔL will occur between the optical output values of the respective laser chips 103_1 and 103_2 at the same drive current value D. In the comparative example in which the reflectance of the front end 103a is equal, such an output difference ΔL is large, so the life of the laser chip with the larger output (the second laser chip 103_2 in the example of FIG. 3) is shortened, and the semiconductor laser The reliability of the device 100 decreases.

In contrast to such a comparative example, in the semiconductor laser device 100 of the present embodiment, the reflectances of the front ends 103a of the two laser chips 103_1 and 103_2 are different from each other. The difference in optical output between is suppressed.
FIG. 4 is a diagram showing the structure of the end face of the laser chip.

The laser chips 103_1 and 103_2 each have a semiconductor cleavage plane 121 on the front end 103a side and the rear end 103b side. The reflectance at the cleavage plane 121 itself is about 30%, but by overlaying the dielectric film 122 on the cleavage plane 121, the reflectance at the front end 103a side and the rear end 103b side is adjusted. An optical resonator is formed.

On the rear end 103b side, a large number of dielectric films 122 are stacked on the cleavage plane 121 of both the first laser chip 103_1 and the second laser chip 103_2, and have a high reflectance of, for example, 90% or more. It has become. Therefore, most of the light L1 that has traveled toward the rear end 103b returns into the optical resonator.

On the other hand, on the front end 103a side, there are fewer dielectric films 122 than on the rear end 103b side, and the reflectance is lower than on the rear end 103b side. Therefore, on the front end 103a side, part of the light L1 returns into the optical resonator, and another part of the light L2 is emitted as a laser beam from the laser chips 103_1 and 103_2.

Comparing the first laser chip 103_1 and the second laser chip 103_2 with respect to the dielectric film 122 on the front end 103a side, the first laser chip 103_1 has less dielectric film 122 and has a lower reflectance, while the second laser chip 103_1 has less dielectric film 122 and has a lower reflectance. The laser chip 103_2 has a large amount of dielectric film 122 and has a high reflectance.
In addition to changing the number of dielectric films, the reflectance may be changed by changing the film thickness or the material of the film.
FIG. 5 is a table showing the reflectance of the laser chip.

The upper part of FIG. 5 shows the reflectance of the first laser chip 103_1 and the second laser chip 103_2, and the lower part shows the reflectance of the second laser chip 103_1 based on the reflectance of the first laser chip 103_1. The reflectance of 103_2 is shown.

The reflectance of the first laser chip 103_1 (i.e., a laser chip with an oscillation wavelength of 643 nm) is 7%, while that of the second laser chip 103_2 (i.e., a laser chip with an oscillation wavelength of 638 nm) is 12%. There is. Based on the reflectance of the first laser chip 103_1, the reflectance of the second laser chip 103_2 is 5% higher.

In the second laser chip 103_2, since the reflectance of the front end 103a is large as described above, light confinement inside the resonator becomes stronger compared to the above comparative example having the same reflectance as the first laser chip 103_1. Therefore, sufficient gain can be obtained even with a low input current value, facilitating oscillation and lowering the oscillation threshold. On the other hand, the large reflectance of the front end 103a makes it difficult for light to be emitted, so the slope of the graph of the input/output characteristics decreases.
FIG. 6 is a graph showing the input/output characteristics of the laser chip in this embodiment.

The horizontal axis in FIG. 6 represents the input current value, and the vertical axis represents the optical output value. Further, a graph representing the input/output characteristics of the first laser chip 103_1 is shown by a dotted line, and a graph representing the input/output characteristics of the second laser chip 103_2 is shown by a solid line.

In this embodiment, the difference in the laser oscillation threshold (that is, the rising position of the graph) between the first laser chip 103_1 and the second laser chip 103_2 is wider than that in the comparative example shown in FIG. 3. Furthermore, as described above, the slope of the graph of the input/output characteristics of the second laser chip 103_2 is lower than that of the comparative example shown in FIG. 3. As a result, the optical output values at the set drive current value D are approximately equal for the first laser chip 103_1 and the second laser chip 103_2. Therefore, the semiconductor laser device 100 of this embodiment is a highly reliable device.

100... Semiconductor laser device, 101... Stem base, 102... Stem block,
103_1...first laser chip, 103_2...second laser chip,
103a...front end, 103b...rear end, 104...submount, 104a...electrode pattern,
105... Lead pin for power supply, 106... Wire, 110... Stem cap

Claims (2)

A semiconductor laser device in which a plurality of semiconductor laser elements included in wavelength bands of the same color and having different oscillation wavelengths are electrically connected in series,
A semiconductor laser device characterized in that the reflectances at the emission end faces of the plurality of semiconductor laser elements are different from each other such that the longer the oscillation wavelength is, the lower the reflectance is, and the shorter the oscillation wavelength is, the greater the reflectance is . 2. The semiconductor laser elements according to claim 1, wherein the plurality of semiconductor laser elements have different reflectances at their emission end faces, so that the difference in the oscillation thresholds is wider than when the reflectances are the same. The semiconductor laser device described.

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