JPH0459800B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser coupler that optically couples a semiconductor laser and an optical fiber.

A conventional device of this type was constructed as shown in FIG. That is, the beam emitted from the semiconductor laser 1 having the double heterojunction 21 passes through the first lens 2.
The light is converted into a parallel light beam 11, passed through an optical component 3 such as a semiconductor laser package window, condensed by a second lens 4, and coupled to an optical fiber 5. The semiconductor laser 1, the first lens 2, and the second lens 4 are arranged so that their optical axes are all aligned in order to maintain maximum coupling efficiency.

Now, it is well known that the characteristics of a semiconductor laser having a double heterojunction change extremely sensitively to the injection of external light into the vicinity of the semiconductor laser active layer. In the conventional semiconductor laser coupler as shown in FIG. Since the light enters the lens and is focused on the active layer of the semiconductor laser 1, there is a drawback that the characteristics of the semiconductor laser 1 change unstablely. In Fig. 1, the parallel light beam 1
1 is shown by a solid line with an arrow, and the reflected light beam 12 is shown by a broken line with an arrow.

In addition, a common optical axis 00' is indicated by a dashed dotted line to indicate that all elements and optical components are on the same optical axis.

In order to eliminate this drawback, the present invention offsets the optical axis of the first lens in a specific direction with respect to the optical axis of the semiconductor laser beam.The purpose of this invention is to offset the optical axis of the first lens. The objective is to effectively suppress the influence of reflected light on the semiconductor laser while minimizing the deterioration of the coupling efficiency.

FIG. 2 shows an embodiment of the present invention, which includes a semiconductor laser 1 having a double heterojunction 21, a first lens 2, a second lens 4, and a laser diode inserted between the first lens 2 and the second lens 4. Laser package window 3
and an optical fiber 5, and the optical axis AA' of the first lens 2 is perpendicular to the double heterojunction surface of the semiconductor laser 1 and within a plane (x-z plane) that includes the optical axis 00' of the semiconductor laser output beam. It is offset by Δx with respect to the optical axis of the semiconductor laser emitted beam. The beam emitted from the semiconductor laser 1 is converted into a parallel beam 11 by a first lens 2 installed in an offset manner, passes through a laser package window 3, is focused by a second lens 4, and is transmitted to an optical fiber 5. . Now, since the first lens 2 is offset by Δx from the laser beam optical axis,
Parallel light beam 11 acute angle θ with respect to the optical axis of the first lens 2
to do. As a result, the parallel light beam is incident on the laser package window 3 having a plane perpendicular to the optical axis of the first lens 2 at an acute angle θ. Therefore, the light beam 12 reflected by the laser package window 3 is smaller than the incident light beam.
The reflected light beam 12 enters the first lens 2 again and is condensed, but the position of the convergence is at twice the offset amount of the first lens 2 from the semiconductor laser active layer, that is, 2 The position is △x away. In order to suppress the influence of the reflected light on the semiconductor laser, it is not necessarily necessary to deflect the reflected light to the outside of the laser chip, but rather to increase the distance between the above-mentioned condensing position of the reflected light beam 12 and the semiconductor laser active layer to a certain extent. It was clarified by the experimental results described later that this was achieved by this method. This can be achieved by increasing the offset amount △x of the first lens 2. On the other hand, if the offset amount △x of the first lens 2 is increased, the output beam from the semiconductor laser will be directed to the first lens. Pass through the edge of 2. In general, lenses have an aberration in which light rays that should be focused at one point on an image are scattered, so the farther the axis of the light flux is from the optical axis of the lens, the more the aberration of the lens is affected, leading to a reduction in coupling efficiency. In particular, in the case of single mode optical fiber, the decrease is significant. Furthermore, since the beam emitted from the semiconductor laser is a diverging light beam, the amount of spillover of the first lens 2 increases as the axis of the light beam moves away from the lens optical axis. Therefore, increasing the offset amount Δx of the first lens 2 leads to a decrease in coupling efficiency. Therefore, it is essential to produce a highly efficient and stable coupler to maximize the effect of suppressing the influence of reflected light with the minimum amount of offset Δx.

This invention is a double hetero semiconductor laser.
This was done based on the experimental knowledge that the effect of suppressing the influence of reflected light due to the offset varies widely depending on the direction of the offset of the first lens 2. Next, the results of this experiment will be described.

Figure 3 shows a block diagram of the measurement system for the experiment, in which the emitted beam 11 from the semiconductor laser 1 is
It is converted into a parallel light beam by a lens 2, and reflected by a reflection surface 3 installed in advance. On the other hand, the rear emitted beam 13 from the semiconductor laser 1 is detected by the photodetector 7, and the change in the laser rear output due to the offset Δx of the first lens 2 is measured by the XY recorder 8. If the characteristics of the semiconductor laser 1 change due to the reflected light, the rear output of the laser will also change, so the influence of the reflected light can be confirmed by this measurement. FIG. 4 shows an example of measurement results obtained by this measurement system, in which the horizontal axis shows the offset amount of the first lens 2, and the vertical axis shows the rear output of the laser. Note that the rear side output of the laser is shown normalized by the same output when the reflective surface 3 is not provided. Here, as the first lens 2, a spherical lens with a diameter of 800 μm, which is commonly used in semiconductor laser couplers for single mode optical fibers, is used. The solid line in Fig. 4 indicates the case where the direction of the offset of the first lens is taken in a plane parallel to the double heterojunction surface of the semiconductor laser (hereinafter referred to as "in the parallel plane"), and the broken line in Fig. 4 indicates the direction of the offset. The case is shown in which the beam is perpendicular to the double heterojunction surface of the semiconductor laser and within a plane (hereinafter referred to as the vertical plane) that includes the optical axis of the semiconductor laser output beam. In all cases, the offset amount is zero or in a very small range, and it is abnormally increased compared to the case where there is no laser rear output, which shows that the influence of reflected light is significant in this range.

Now, from this measurement result, an offset of 50 μm or more is required to suppress the influence of reflection due to the offset in the parallel plane of the first lens, whereas an offset in the vertical plane is required. It turns out that an offset of 10 μm or more is sufficient to suppress the influence of reflection. That is, the first
By offsetting the lens, the maximum effect can be obtained with the minimum amount of offset. The reason why the effect of suppressing the influence of reflection differs depending on whether the offset direction is in the vertical plane or in the parallel plane is that the active region of a double heterojunction semiconductor laser is at most 0.2 to 0.3 μm in the vertical plane. This is presumed to be due to the fact that it is usually 2 to 3 μm in parallel planes. Therefore, this measurement result is considered not to be just an example, but to represent general characteristics when a semiconductor laser having a double heterojunction is used. From this, this invention
This is effective for general semiconductor laser couplers using double hetero semiconductor lasers.

Although the laser package window 3 is assumed to be the cause of reflected light in the above description, the present invention is not limited to this, and other chemical parts may be caused by the first lens 2 and the second lens.
This can also be applied to cases in which the reflected light is present between the lenses 4, or the first lens exit end or the second lens entrance end itself is the cause of reflected light.

As described above, in the semiconductor laser coupler according to the present invention, the first lens is located on a plane whose optical axis intersects the double heterojunction surface of the semiconductor laser, which plane has the optical axis of the output beam from the semiconductor laser. The laser beam is arranged so as to be parallel to the optical axis of the output beam of the semiconductor laser, and the condensing position of the reflected light that is reflected by the input or output end face of the optical component and returned to the semiconductor laser by the first lens is set. Since the semiconductor laser is displaced in a direction perpendicular to the double heterojunction surface, the convergence position of the reflected light reflected from the input or output end face of the optical component and returned to the semiconductor laser by the first lens can be adjusted to Compared to the case where the first lens is displaced in a direction parallel to the double heterojunction surface of the laser, the decrease in the coupling efficiency to the optical fiber can be suppressed to the minimum with the minimum offset amount (displacement amount) of the first lens. It is possible to eliminate the influence of reflected light caused by incidence of optical components or Freranel reflection from the output end face on the characteristics of the semiconductor laser, and it is possible to realize a semiconductor laser coupler with stable characteristics and high coupling efficiency with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the arrangement of a conventional semiconductor laser coupler, FIG. 2 is a perspective view showing the arrangement of a semiconductor laser coupler according to the present invention, and FIG. 3 is a perspective view showing the arrangement of a semiconductor laser coupler according to the present invention. FIG. 4 is a block diagram showing the measurement system for the Natsu measurement, and FIG. 4 is a diagram showing the measurement results. In the figure, 1 is a semiconductor laser having a double heterojunction, 2 is a first lens, 3 is an optical component that causes reflection, 4 is a second lens, and 5 is an optical fiber. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1. A beam emitted from a semiconductor laser having a double heterojunction is converted into a substantially parallel beam by a first lens, which is then condensed again by a second lens and enters an optical fiber. In the semiconductor laser coupler, the semiconductor laser coupler has a coupling lens system that allows the laser beam to pass through the semiconductor laser, and an optical component having a flat light input or output end face is inserted between the first lens and the second lens. has the optical axis of the emitted beam on its surface, and the optical axis of the first lens exists on a plane intersecting the double heterojunction surface of the semiconductor laser, and the optical axis of the first lens The first lens is arranged so as to be parallel to the optical axis of the output beam of the semiconductor laser, and the reflection is reflected at the incident or output end face of the optical component and returned to the semiconductor laser by the first lens. A semiconductor laser coupling characterized in that the light condensing position is moved to a position away from the active layer of the semiconductor laser by displacing the light condensing position in a direction perpendicular to the double heterojunction surface on the semiconductor laser side. vessel.