JPH0828551B2 - Array laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an array type semiconductor laser, and more particularly to an array laser in which a plurality of light emitting portions existing in the same chip do not interfere with each other.

[Conventional technology]

2A and 2B show the structure of a conventional array laser device and array laser. FIG. 2A shows a semiconductor laser which emits three laser beams in one package. In FIG. 2 (a), 1 is a stem,
2 is a cap for packaging the array laser, 3 is an optical window formed in the cap 2, 4 is a heat sink,
A laser chip 5 having a plurality of laser elements is fixed to this. Reference numeral 6 denotes a terminal of the stem 1. One of the four terminals 6 is connected to the heat sink 4 side of the laser chip 5, and the remaining three are connected to the surface electrodes of the laser chip 5.

FIG. 2B is a sectional view showing a structural example of the array laser.

In this figure, 7 is a light emitting portion of laser light, 8 is a substrate, and 9 is a separation groove, which is separated into the light emitting portions 7 of each laser element. 10,1
Reference numeral 1 is an electrode, and 12, 13 and 14 are laser elements.

FIG. 2B is a monolithic type and has three laser light emitting portions 7 in one chip. Each laser element 12,1
The light emitting portions 7 of 3, 14 are electrically separated by the separation groove 9 reaching the substrate 8, and independent drive currents can be supplied to the laser elements 12, 13, 14. Such an array laser is used for a laser beam printer, an optical disk, etc., and it is necessary to control the positioning of a plurality of light beams with high accuracy by one optical system. For this purpose, it is important that the positional accuracy of each light emitting section 7, the interval accuracy of each light emitting section 7, and the optical axis accuracy of each radiation beam are uniform. In the monolithic array of FIG. 2 (b), since the laser elements 12 to 14 are simultaneously processed in the step of processing the laser crystal into chips (wafer process), the positional intervals of the light emitting portions 7 and the optical axis of the radiation beam are also set. There are no problems in terms of assembly.

However, since the substrate 8 is common in the monolithic type, operating each light emitting section 7 independently affects the electrical and optical characteristics of other laser elements.

FIG. 3 shows an operation example of the monolithic array laser. Here, the laser elements 12, 13, and 14 are referred to as first, second, and third laser elements for convenience. This figure shows the first
The advance flowing driving current I ₁ of the constant laser element 12, ON driving current I ₂ of the second laser element 13 adjacent a light output P ₁ of the first laser element 12 in the case where the OFF time t It is a characteristic view which shows the relationship with. Due to the driving state of the second laser element 13, the optical output P _{1 of} the first laser element 12 is not constant but fluctuates. This is a result of the heat generated in the second laser element 13 spreading from the light emitting portion 7 to the periphery and affecting the adjacent first laser element 12 through the substrate 8.

When using such an array laser in a printer,
One laser beam corresponds to one dot row, and three rows are printed at the same time. However, if one laser element is operating while another laser element is operating, the optical output will decrease due to thermal interference, and the print density will decrease. Is reduced. Even if printing is performed at high speed with three beams, uneven density occurs in the print result, which is inconvenient.

Another conventional example is one in which separated laser chips are housed in one package. In this individual array laser, since each chip is independent, there is no mutual interference of heat, but since the individual chips are assembled separately, it is not possible to align the positions, intervals, optical axes, etc. of the light emitting parts to the required accuracy. There is inconvenience.

[Problems to be Solved by the Invention]

In the conventional array type semiconductor laser as described above, since the substrate 8 is common in the monolithic type, there is a problem that the laser elements 12 to 14 cannot be driven independently by mutual interference of heat. In the individual type, the required position, spacing,
There was a problem in that it was not possible to obtain a device with high optical axis accuracy.

The present invention has been made in order to solve the above problems, and an object thereof is to obtain an array laser in which the position / spacing / optical axis accuracy of the light emitting portion is high and the thermal mutual interference is small.

[Means for Solving the Problems] An array laser according to the present invention is such that a material having a thermal conductivity lower than that of the substrate is embedded in the substrate between the light emitting units of a plurality of light emitting units provided on the same substrate. A plurality of laser elements having separate substrates are configured.

[Action]

In the present invention, since each laser element is separated by the embedding material having a thermal conductivity smaller than that of the substrate, heat generated in each laser element is hard to be transmitted to the adjacent laser element.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing a manufacturing method for obtaining the array laser of the present invention. First, FIG. 1 (a) is a cross section of a chip before separating each laser element. The thickness of the chip is, for example, 350 μm, but the substrate 8 occupies the majority, and the portion directly related to the laser operation is about 20 μm at most. Next, as shown in FIG. 1B, the spaces between the light emitting portions 7 are removed by etching or the like to the required depths, and the separation grooves 9 are dug. In the conventional example, the depth is about 20 to 30 μm to reach the substrate 8 in order to electrically separate the laser elements.
Although the etching is performed up to this point, in the present invention, it is dug deeper to, for example, about 100 μm. Then, the separation groove 9 is filled with a material 15 having a lower thermal conductivity than the substrate 8. Next, as shown in FIG. 1 (c), the wafer is ground from the substrate 8 side by polishing / etching or the like until the material embedded in the separation groove 9 is reached. Wafer thickness after grinding is 100μ
It will be about m. After that, electrodes 10 and 11 are attached to both surfaces of the wafer and patterning is performed, and as shown in FIG.
The array laser of the present invention can be obtained.

 Next, the operation will be described.

In FIG. 1, as in the description of the conventional example, a constant current is made to flow through one laser element of the array laser of the present invention, and the drive currents of the adjacent laser elements are turned on and off while monitoring the optical output. I will try. Part of the electric power injected into the adjacent laser element contributes to light emission, and most of the remaining electric power mainly becomes heat in the light emitting unit 7. This heat is transmitted to the substrate 8 side while diffusing to the surroundings. In the conventional example, since the laser elements are connected by the substrate 8 having good thermal conductivity, heat is further conducted to the adjacent laser element through the substrate 8. However, in this embodiment, since the material having a low thermal conductivity is embedded between the adjacent laser element, the heat is transmitted in the package direction rather than in the lateral direction. Therefore, even if the drive current of the adjacent laser element is turned on and off, the influence of the heat generation is not transmitted to other laser elements. Further, since the laser elements are simultaneously formed in the wafer state in the buried layer of this embodiment, the position, spacing, and optical axis accuracy of each laser element are monolithic, and can be formed with extremely high accuracy.

Although the three-point array laser having the three light emitting portions 7 has been described in the above embodiment, the same effect can be obtained when the array laser has two or more points.

In addition, in the above-described embodiment, the case where the electrode 11 on the substrate 8 side is not separated but is common is described.
Even if 11 is separated, the same effect can be obtained.

〔The invention's effect〕

As described above, according to the present invention, a material having a lower thermal conductivity than that of the substrate is embedded in the substrate between the light emitting parts, and the plurality of laser devices are configured so that the substrates are separated from each other. Thermal interference can be reduced. Further, the array laser after being filled with a material having a thermal conductivity lower than that of the substrate is in a monolithic state, and it is possible to obtain an array laser having extremely high accuracy in position, spacing, and optical axis of the light emitting portion. Further, there is an effect that the assembly can be easily performed at either the junction up or down without the need for a special electrode patterned assembly mount.

[Brief description of drawings]

1 (a) to 1 (d) are cross-sectional views showing a manufacturing process of an array laser according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are outlines and chip cross sections of a conventional array laser. Figure,
FIG. 3 is a diagram showing light output characteristics when a conventional array laser is operated. In the figure, 7 is a light emitting part, 8 is a substrate, 9 is a separation groove, and 10 and 1
Reference numeral 1 is an electrode, and 12, 13, 14 are laser elements. The same reference numerals in each drawing indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A monolithic array laser having a plurality of light emitting portions on the same substrate, wherein a material having a lower thermal conductivity than that of the substrate is embedded in the substrate between the light emitting portions.
An array laser comprising a plurality of laser elements each having the substrate separated.