JPH0459799B2 - - 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, an emitted beam from a semiconductor laser 1 having a double heterojunction 21 is converted into a parallel light beam 11 by a first lens 2, and then passes through an optical component 3 such as a semiconductor laser package window to a second lens 4.
The light is focused and coupled to the optical fiber 5. Semiconductor laser 1, first lens 2, second lens 4
are arranged with all optical axes aligned to maximize 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 a conventional semiconductor laser coupler as shown in FIG.
The reflected light beam 12 due to Fresnel reflection etc. generated from the optical component 3 inserted between the lenses 2 of
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 the same elements and optical parts are on the optical axis.

In order to eliminate this drawback, the present invention tilts the end face of the optical component inserted between the first lens and the second lens in a specific direction with respect to the optical axis of the semiconductor laser beam. The purpose is to effectively suppress the influence of reflected light on the semiconductor laser while suppressing a decrease in coupling efficiency by minimizing the inclination of the end face.

FIG. 2 shows an embodiment of the present invention, which includes a semiconductor laser 1 having a double heterojunction 12, a first lens 2, a second lens 4, and a semiconductor laser 1 inserted between the first lens 2 and the second lens 4. Laser package window 3
and an optical fiber 5, and the normal AA' of the laser package window 3 is relative to the common optical axis 00' of the semiconductor laser output beam, the first lens 2, the second lens 4, and the fiber 5. The laser package window 3 is installed so as to form an angle of Δθ in the xz plane. Here, the x-z plane is perpendicular to the double heterojunction plane (y-z plane) and the optical axis is 0.
This is within the plane including 0'.

Now, the beam emitted from the semiconductor laser 1 is
The light is converted into a parallel beam 11 by the lens 2, passes through the laser package window 3, is focused by the second lens 4, and is transmitted to the optical fiber 5. Incidentally, reflection occurs at the entrance/exit end face of the laser package window 3 due to discontinuity in the refractive index. This reflected light flux 12 is
Since the laser package window 3 is installed with an angle of Δθ in the above-mentioned direction, the light enters the first lens 2 again at an angle of 2Δθ with respect to its optical axis 00'.

As a result, the reflected light beam 12 is again focused by the first lens 2, but the focused position is a distance Δx from the semiconductor laser active layer.
Δx is given by Δx=f·tan 2Δθ (1) where f is the focal length of the first lens. Now, the reflected light flux 1 to the semiconductor laser
In order to minimize the influence of 2 on the semiconductor laser characteristics, it is not necessary to let the reflected light beam 12 escape to the outside of the laser chip, but rather to increase the distance Δx between the above-mentioned condensing position of the reflected light beam 12 and the semiconductor laser active layer to a certain extent. The experimental results described later clarified what was achieved by this method. This can be achieved by increasing the inclination △θ of the laser package window 3 according to equation (1), but on the other hand, making △θ too large increases the reflectance of the laser package window and lowers the transmittance. Moreover, it is not preferable because it increases sorption and deteriorates the coupling efficiency, and it becomes necessary to increase the distance between the first lens and the second lens, resulting in an increase in size. Therefore, it is essential to maximize the effect of suppressing the influence of reflected light with the minimum tilt angle Δθ in order to manufacture a highly efficient, compact and stable semiconductor laser coupler.

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 on the size of the tilt angle varies greatly depending on the direction in which the laser package window is tilted. We will discuss the results.

FIG. 3 shows a block diagram of the experimental measurement system, in which an incident beam 11 from a semiconductor laser 1 is converted into a parallel beam by a first 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 inclination angle Δθ of the reflecting surface 3 is measured. If the characteristics of the semiconductor laser 1 change due to the reflected light, the rear output of the laser will also change, so by this measurement it is possible to confirm whether there is an influence of the reflected light.

FIG. 4 shows an example of measurement results obtained by this measurement system, in which the horizontal axis shows the inclination angle Δθ of the reflecting surface 3, 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.

In addition, here, the diameter of the first lens 2 is
An 800μm ball lens is used.

The solid line in FIG. 4 is the optical axis 00' normal to the reflecting surface 3.
The dashed line in Figure 4 shows the case where the tilt △θ is taken in a plane parallel to the double heterojunction surface of the semiconductor laser (hereinafter referred to as parallel plane). The case is shown in which the beam is directed in a plane (hereinafter referred to as vertical plane) that is perpendicular to the double heterojunction plane and includes the optical axis 00' of the semiconductor laser beam.
In both cases, the rear output of the laser increases abnormally in the range where the inclination △θ is minute compared to the case without the reflective surface 3. This shows that in this range, the influence of the reflected light by the reflective surface 3 on the semiconductor laser increases. It can be seen that this is remarkable. Now, from this measurement result, in order to suppress the influence of reflection by taking the inclination Δθ of the reflecting surface in a parallel plane, it is necessary to tilt the reflecting surface by 8 to 9 degrees or more. Inclination of reflective surface in vertical plane △
When θ is used, it is found that the influence of reflection can be sufficiently suppressed by tilting the reflecting surface by 3 to 4 degrees or more. That is, by tilting the reflecting surface within the vertical plane, the maximum effect can be obtained with the minimum angle of inclination.
In addition, Δx is calculated from equation (1) when the inclination Δθ is 4° and 9°. In the single mode optical fiber semiconductor laser coupler taken as an example here, the focal length of the first lens is 444 μm, so Δx is 62 μm and 144 μm, respectively. The reason why the effect of suppressing the influence of reflection differs depending on the direction of inclination of the reflecting surface is that the height of the active region of a double heterojunction semiconductor laser is at most 0.2 to 0.3 μm in the vertical plane, whereas it is It is estimated that this is due to the fact that the diameter is usually 2 to 3 μm. Therefore, the results of this measurement are considered not to be merely an example, but to represent general characteristics when using a semiconductor laser having a double heterojunction. Therefore, the present invention is effective for general semiconductor laser couplers using double heterojunction semiconductor lasers.

In addition, although the case where the laser package window 3 is considered as the cause of reflected light and the window is tilted has been described above, the present invention is not limited to this, and can also be applied to other optical components whose input or output end faces are flat. It can also be applied to the case where the lens is inserted between the first lens and the second lens.

In addition, in the above-mentioned embodiment, the normal line A-A' of the end surface of the optical component 3 is the x-z plane in FIG. 2, that is,
Although we have explained the case where there is no component in the y-axis direction because the plane is perpendicular to the double heterojunction plane and includes the optical axis of the output beam, the above normal A-
A′ is not necessarily limited to a configuration that does not have a component in the y-axis direction, but may have a configuration that has a slight component in the y-axis direction, and the size of the component depends on the geometric dimensions of the entire device or the fiber 5. It may be selected as appropriate, taking into account the bonding efficiency, etc.

In other words, the projection line obtained by projecting the normal line A-A' onto a plane perpendicular to the double heterojunction surface and including the optical axis of the emitted beam and the optical axis of the emitted beam from the semiconductor laser 1. It is sufficient if the angle formed is an acute angle.

As described above, in the semiconductor laser coupler according to the present invention, the entrance/exit plane of the optical component inserted between the first lens and the second lens is set such that the normal line thereof coincides with the optical axis of the output beam from the semiconductor laser. The first lens is located on a surface that intersects the double heterojunction surface of the semiconductor laser, and is formed so as to intersect with the optical axis of the output beam of the semiconductor laser, and is reflected by the incident or output end face of the optical component. Since the condensing position of the reflected light returned to the semiconductor laser is shifted in the direction perpendicular to the double heterojunction surface of the semiconductor laser, the light is reflected by the incident or output end face of the optical component and reaches the first lens. Therefore, compared to the case where the condensing position of the reflected light that is returned to the semiconductor laser is displaced in a direction parallel to the double heterojunction surface of the semiconductor laser, the light can be By minimizing the reduction in coupling efficiency to the fiber and eliminating the influence of reflected light such as Fresnel reflection from this end face on the semiconductor laser characteristics, we have created a compact semiconductor laser with stable characteristics and high coupling efficiency. This has the effect of providing a coupler.

[Brief explanation of drawings]

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 measurement, and 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. Note 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 a normal line to the incident or output end face of the optical component exists on a plane that intersects the double heterojunction surface of the semiconductor laser, and the normal line is the optical axis of the output beam of the semiconductor laser. The input or output end face of the optical component is formed so as to intersect with the optical axis of the output beam of the optical component, and the reflection is reflected by the input or output end face of the optical component and returned to the semiconductor laser side by the first lens. A semiconductor laser coupler characterized in that the light condensing position is displaced from the active layer of the semiconductor laser by displacing the light condensing position in a direction perpendicular to the double heterojunction surface of the semiconductor laser. .