JPH03187285A - Multibeam semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent the optical inference between each laser diode chip so that each laser diode chip may be driven independently by widening the luminous stripe width near the end face on, at least, the photodiode side of a laser diode chip than the luminous stripe width on the other end face side. CONSTITUTION:The widths of the luminous stripes 10a-10c on, at least, the rear of each laser diode chip 1a-1c, that is, on the photodiode 2a-2c sides for monitors are made wider than the luminous stripe widths on the light emission side at the front. This way, by the luminous stripes 10a-10c whose widths are wide only on the rear sides, the laser beams on the rear sides are made narrow beams, and the rear beams enter favorably the photodiodes 2a-2c for monitors on the rear sides. Accordingly, trouble disappears such as that one part each of the rear beams reach adjacent photodiodes for monitors, so the optical interference of each laser beam lessens. Hereby, the optical interference between each laser diode chip can be prevented, and each laser can independently be driven.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-beam semiconductor laser in which a plurality of laser diodes are monolithically integrated.

[Prior art] Fig. 2 shows, for example, the Journal of Electro
nic Engineer Vol-24, No.
, 248 August 1987 (DempaPu
FIG. 2 is a partially exploded perspective view showing the overall configuration of the conventional multi-beam semiconductor laser shown in P 54 to P 5B.

In the figure, (la) to (1c) are three multi-beam laser diode chips, (la), (lc
) is the outer laser diode chip, and (lb) is the center laser diode chip. (2a) to (2c) are three photodiodes that monitor the respective rear lights from three laser diode chips (1a) to (lc) (2a to (2c) are laser diode chips (Ia) The laser beams of each of (1c) to (1c) are independently monitored.

(3a) to (3c) are each laser diode chip (1a
) to (laser electrodes for driving each lcJ independently, (4a) to (4c) are monitor photodiodes (
electrodes for detecting each output of 2a) to (2C), (5
) is a common electrode of laser diode chips (1a) to (1c) and photodiodes (2a) to (2c), (6
) is a stem, (7) is a cap for filling each element with nitrogen, (8) is a glass window for taking out the front light of each laser to the outside, and (11) is a laser emitted light.

Figure 3 shows a series of laser diode chips (1a) to (IC) and photodiodes (2a) to (2) shown in Figure 2.
It is a schematic diagram showing an enlarged positional relationship of (9a).
) to (9c) are laser diode chips (la) to (I
c) is a light emitting stripe for controlling the spread angle and transverse mode of the laser beam. Figure 4 shows the positional relationship between the laser diode chips (la) to (lc) and photodiodes (2a) to (2C) when the widths of the light emitting stripes (9a) to (9C) in Figure 3 are widened. It is a schematic diagram.

Next, the operation will be explained. In general, a laser diode is an optical element that can directly convert a current signal into an optical signal, and is capable of so-called direct modulation. Furthermore, since the ratio of the optical outputs emitted from both end faces of the laser diode chip is always constant, the optical output to the front side can be feedback-controlled by monitoring the optical output at the rear side. Therefore, a combination of a laser diode chip and a photodiode is generally used.

Figure 2 shows three combinations of laser diode chips (1a) to (1C) and photodiodes (2a) to (2C).
The two sets are assembled in the same package. Therefore, each laser diode chip (1a) to (lc) and each photodiode (2a) to (2C) are electrically independent from each other, and for example, the current injected from the laser electrode (3a) flows through the laser diode chip. Only the laser beam (1a) is emitted, and only the photodiode (2a) detects the laser beam. Laser diode chip (lb), (
lc), photodiode (2b), (2c)
The same principle applies to the laser electrodes (3b) and (3c), but the common electrode (5) is commonly used by all elements.

Based on the above principle, each laser diode chip (LA)
Since the ICs can be driven simultaneously and independently, it is possible to speed up the information processing speed of the system by, for example, parallelizing the exchange of information on optical discs, etc., and performing reading and writing simultaneously.

Although each element of a conventional multi-beam semiconductor laser is electrically independent as described above, optically they are not necessarily completely independent.

The spread angle of the laser beam in the horizontal direction with respect to the junction surface is determined by the lateral diameter of the light emitting spot at the end face of the laser diode chips (la) to (lc), and the smaller the diameter, the wider the spread angle. And the spot diameter is the third
It is determined by the width W of the light emitting stripes (9a) to (9C) shown in the figure. Normal laser diode chip (1a) ~
In the case of (lc), this luminescent stripe (9a) to (9C
) is approximately 2 to 4 μm, and fundamental mode operation is realized within this W range. Furthermore, in a multi-beam semiconductor laser, the emission interval of each laser beam is a very important parameter, and the emission stripe (9a) to
(9C) is generally set close to about 100 μm, but if the distance is larger than this, matching with the optical system in the optical system may be impaired.

When the light-emitting stripes (9a) to (9C) having a certain degree of beam spread are placed close to each other in this way, each of the photodiodes (2a) to (2C) on the rear surface may receive another adjacent laser beam. Vine.

FIG. 4 shows that the beam spread angle is made relatively narrow by widening the width W of the light emitting stripes (9a) to (9C), and each laser beam is connected to each photodiode (2a) to (2c).
Another photodiode (2a) that has good celestial measurements and is adjacent to
~(2C) is designed to prevent laser light from entering. However, as the width W of the light-emitting stripe (9) increases, it becomes difficult to obtain a fundamental mode, and higher-order modes tend to exist.

In addition, not only the rear light but also the front light becomes a narrow beam, which improves the optical coupling with the system's optical system, making it more susceptible to the effects of return light, etc., and reducing problems such as noise. It becomes more likely to occur.

[Problems to be Solved by the Invention] Since the conventional multi-beam semiconductor laser is configured as described above, when designing and driving each laser diode chip in a state in which it can emit good output light,
There is a problem in that optical interference between the laser diode chips is large, making it difficult to drive each laser diode chip completely independently.

This invention was made in order to solve the above-mentioned problems. Each laser beam to be emitted has good optical characteristics on the front surface, and each laser diode chip has good independent drive. The purpose is to obtain a multi-beam semiconductor laser that can be used.

[Means for Solving the Problems] The multi-beam semiconductor laser according to the present invention widens only the width of the light emitting stripe on the rear surface side of light emission, so that the laser light emitted from the rear surface and incident on the monitoring photodiode is It has a narrower beam.

[Function] In the multi-beam semiconductor laser according to the present invention, the laser light on the rear side is made into a narrow beam by the wide light emitting stripe only on the rear side, and the rear light is incident on the monitor photodiode on the rear side in a good manner. Therefore, a portion of the rear light does not reach the adjacent monitor photodiode, so optical interference between the respective laser beams in the multi-beam semiconductor laser is reduced.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a schematic diagram showing the relative positions of a laser diode chip and a photodiode of a multi-beam semiconductor laser.

In the figure (Ia) to (lc).

(2a) to (2c) are the same as those shown in the conventional example of FIG. 2, so their explanation will be omitted. (10a) to (10c)
is a light-emitting stripe in which only the width of the stripe on the rear side is widened.

Next, the operation will be explained.

The width of the light emitting stripes (10a) to (10c) in FIG. 1 is about 2 to 4 .mu.m at the front surface, which is the same as the conventional one, and is widened to about 7 to 10 .mu.m or more at the rear surface. Therefore, the front light emission spot and the horizontal spread angle of the beam exhibit almost the same characteristics as the conventional example, but the rear light emission spot diameter becomes larger in the horizontal direction, and the horizontal spread angle of the beam becomes larger than that of the front light. It gets narrower. Therefore,
For example, the rear light emitted from the light emitting stripe (10b) enters only the photodiode (2b) for monitoring the light emitting stripe (Job), and the rear light emitted from the light emitting stripe (10b) enters only the photodiode (2b) for monitoring the light emitting stripe (Job), and enters the adjacent photodiode (2b).
2a).

It is no longer incident on (2C).

That is, laser diode chips (la) to (1c)
The monitor photodiodes (2a) to (2C) for controlling their optical outputs are independent from each other and do not interfere electrically or optically. The oscillation mode of each laser can also be changed from the front side to the laser diode chip (
la) to (1c) The width of the narrow light emitting stripes (IOa) to (loc) reaching the center of each makes the fundamental mode, so the characteristics of the laser beam emitted from the front are also different from those of the conventional example. , it's no different.

In the above embodiment, the case of three multi-beam semiconductor lasers has been described, but it may be two, four or more multi-beam lasers.

Further, in the above embodiment, the laser diode chips (1a) to
(lc) and photodiodes (2a) to (2c) are combined on a stem to form a monolith. However, this is a case in which a laser diode and a photodiode are monolithically integrated on the same wafer. This embodiment also produces the same effects as the above embodiment.

[Effects of the Invention] As described above, according to the present invention, in a so-called multi-beam semiconductor laser in which a plurality of sets of a laser diode chip and a monitoring photodiode are integrated into the same element, each laser At least the width of the light emitting stripe on the rear side of the diode chip, that is, on the monitor photodiode side, is made wider than the width of the light emitting stripe on the light output side of the front surface, thereby preventing optical interference in controlling the light output between each laser diode chip. This has the effect that each laser can convert a current signal into an optical signal completely independently.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the positional relationship between a laser diode chip and a photodiode of a multi-beam semiconductor laser according to an embodiment of the present invention, FIG. 2 is a partially exploded perspective view of a conventional multi-beam semiconductor laser, and FIG. 3 and Figure 4 is the second
FIG. 3 is a schematic diagram showing the positional relationship between a laser diode chip and a photodiode of the multi-beam semiconductor laser shown in the figure. In the figure, (la) to (IC) are laser diode chips, (2) to (2C) are 7t diodes, (lOa
) to (IOc) are luminescent stripes. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] A set of a laser diode chip and a photodiode for controlling the optical output of the laser diode chip,
In a so-called multi-beam semiconductor laser in which multiple sets of laser diode chips are integrated in parallel and in the same device, the width of the light emitting stripe near the end face of the laser diode chip at least on the photodiode side is equal to the width of the light emitting stripe on the other end face side. A multi-beam semiconductor laser characterized by being wider than its width.