JPS6160596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a module device for optically coupling a semiconductor laser and a single mode optical fiber, and in particular to a semiconductor laser for a single mode optical fiber that achieves hermetic sealing and has high coupling efficiency. The aim is to obtain a modular device.

Conventionally, a semiconductor laser module device for coupling a semiconductor laser and a single mode optical fiber has been constructed as shown in FIGS. 1 to 4 in order to increase the coupling efficiency. That is, as shown in FIGS. 1 and 2, the light from the semiconductor laser 11 passes through the cylindrical lens 12.
The light is focused by the laser beam and is incident on the core 14 at the end face of the single mode optical fiber 13. Or Figures 3 and 4
As shown in the figure, one end of the single mode optical fiber 13 is a tapered part 15, and a hemispherical lens 16 is formed at the tip of the tapered part 15.
At 6, the light from the semiconductor laser 11 is focused and made to enter the core 14 through the tapered portion 15. Note that in FIGS. 2 and 4, 17 indicates a heat sink (radiator) for the semiconductor laser 11;
One end surface of the heat sink 17 and the semiconductor laser 1
Laser 1 is placed on the same plane as the light emitting surface of Laser 1.
1 is attached to a heat sink 17.

In order to efficiently couple the light from the semiconductor laser 11 to the single mode optical fiber 13, the outer diameter of the cylindrical lens 12 should be 10 to 20 μm, and the hemispherical lens 1 should have a tapered tip.
6 is required to have an extremely small diameter of 10 to 30 μm. Furthermore, the distance D ₁ between the single mode optical fiber 13 and the light emitting end face of the semiconductor laser 11 and
D ₂ is within 30 μm. Therefore, in order to ensure the reliability of the semiconductor laser, the semiconductor laser 1
If you try to insert an airtight window between 1 and optical fiber 13, the thickness of the window will be at least several 100 μm.
Since m is required, the coupling efficiency will be significantly reduced if this window is inserted, and the effect of using the lenses 12 and 16 will be lost.

Therefore, the structure shown in FIG. 5, which combines a cylindrical lens and a self-cleaning lens, was devised. That is, a semiconductor laser 17 mounted on a heat sink 17 is housed in a stem 18 as a laser package, and the stem 18 is hermetically sealed with an airtight window 19 made of sapphire or the like while also housing the cylindrical lens 12. The light emitting end face of the semiconductor laser 11 and one end face of a self-occurring lens (cylindrical focusing lens) 21 are made to face each other via the window 19, and the other end face of the self-occurring lens 21 and the end face of the optical fiber 13 are made to face each other. The lens 21 is held by a lens holder 22, and the optical fiber 13 is held by a fiber holder 23. The optical axis of the cylindrical lens 12 is aligned with that of the semiconductor laser 11 by a heat sink 17.

In order to improve the coupling efficiency in this configuration, the diameter of the cylindrical lens 12 must be selected to be 10 to 20 μm. The positional accuracy of the lens required when integrating such a microlens with the semiconductor laser 11 is proportional to the focal length of the lens, and as a guide, the permissible positional deviation is 1/20 of the focal length. Therefore, in the conventional windowed semiconductor laser module, the mounting accuracy for the cylindrical lens 12 is required to be 0.5 to 1 μm, which has been a major obstacle in manufacturing.

This invention aims to obtain a semiconductor laser module with guaranteed hermetic sealing for a single mode optical fiber.
A lens system with a relatively long focal length is used, and therefore the permissible displacement is relatively large, easy to manufacture, and high efficiency coupling between a semiconductor laser and a single mode optical fiber is realized. This will be explained in detail with reference to the drawings from FIG. 6 onwards.

FIG. 6 is a principle diagram illustrating the coupling principle of this invention. Here, W ₀ 〓 and W ₀ 〓 are the radii of the oscillation beam 24 of the semiconductor laser, and correspond to the beam radii in the direction perpendicular to and parallel to the junction surface, respectively. The beam diameter of the oscillated beam 24 is converted by a beam conversion lens 25 into a light beam 26, and this beam 26 is further converted in beam diameter by a beam conversion lens 27 to become a light beam 28. When the focal lengths of the beam conversion lenses 25 and 27 are f ₁ and f ₂ , W ₀ 〓 and W ₀ 〓 are converted and the radius of the light beam 26 is respectively W ₁ 〓=λf ₁ /πW ₀ 〓, W ₁ 〓=λ
This becomes f ₁ /πW ₀ 〓, which is further converted and the radius of the light beam 28 becomes W ₂ 〓=λf ₂ /πW ₁ 〓, W ₂ 〓=
λf ₂ /πW ₁ 〓. Therefore, the laser beam radii W ₀ 〓, W ₀ 〓 are W ₂ 〓= due to f ₁ and f ₂
It can be seen that it is converted to (f ₂ /f ₁ )W ₀ 〓, W ₂ 〓= _{( f} 2 /f 1 )W ₀ 〓. This shows that by selecting the ratio of the focal lengths of the first lens 25 and the second lens 27, the laser beam radius can be converted to an arbitrary magnification. The beam radius of a single mode optical fiber is W ₀
Then, since there is a relationship of W ₀ > W ₀ 〓 > W ₀ 〓,
W ₂ 〓＞W ₀ ＞W ₂ 〓, more precisely W ₀ =
Just choose f ₂ /f ₁ so that √ ₂ 〓 ₂ 〓. Normally W ₀ = 5 μm, W ₀ = 0.6 to 0.8 μm, W ₀
= 1 to 2 μm, so f ₂ /f ₁ = 3 to 7 times should be selected. From the above considerations, if the focal length of the second lens 27 is set to 1 to 3 mm, the focal length of the first lens 25 will be several 100 μm to 1 mm, which is a significantly longer focal length than the lens 12 in FIG. 5. be able to. In this way, you can change the focal length by
When it is 100 μm to 1 mm, it becomes neither too small nor too large, making it easy to handle.

FIG. 7 shows an embodiment of the invention. The semiconductor laser 11 is mounted on a heat sink 17 within a stem 18 and housed in a package hermetically sealed using a window 19 made of metalized sapphire or the like. As a lens for coupling with the single mode optical fiber 13, a lens made of sapphire, ruby, glass, etc. and having a large focal length with respect to its aperture;
For example, a spherical lens 29 and a lens with small convergence, such as a converging lens 31 as a gradient index lens, are used, and the focal length of each is determined by the semiconductor laser 1 used.
The beam radius of 1 is selected as described in connection with FIG. The first lens 29 is bonded to the window 19 via a lens holder 32, and is adjusted to substantially coincide with the optical axis of the laser 11. At this time, set the focal length of lens 29 to 500 μm.
With the above setting, the positional deviation from the optical axis is allowed to be about 1/20 of the focal length as mentioned earlier, so the positional deviation tolerance in this case is 25 μm,
The mounting precision of the cylindrical lens used for conventional single mode optical fibers is significantly reduced compared to tapered tip spherical fibers and the like.

The second lens 31 is attached to the lens holder 22 and fixed to the surface of the window 19 with one end face facing the first lens 29. The second lens 31 is fixed by adjusting it within a plane perpendicular to the optical axis so as to compensate for the axial deviation of the first lens 29. The positional shift required at this time is further alleviated because the focal length of the second lens 31 is large.

The single mode optical fiber 13 is usually covered with a coating 33 and is fixed to the fiber holder 23 via a fiber holder 34. At this time, adjust the holder 2 in the optical axis direction and in the plane perpendicular to the optical axis.
2 and 23 are fixed to each other using adhesive or the like.

In the above explanation, the distance between the laser 11 and the first lens 29, and the distance between the first lens 29 and the second lens 31 are the focal length of the first lens 29 and the distance between the first and second lenses, respectively, as shown in FIG. Although this was limited to the case where the focal lengths of the two lenses were the sum, even if these distances were slightly deviated, the size of the image formed would hardly change and the effect on efficiency would be small. Therefore, the first lens 2
Even if 9 and the second lens 31 are shifted in the optical axis direction, high coupling efficiency can be obtained by adjusting the position of the coupling single mode optical fiber 12 on the optical axis. Note that 35 is a spacer between the stem 18 and the window 19.

FIG. 8 shows another embodiment of the invention. In this example, the first lens 29 is mounted together with the laser 11 inside a window 19 made of metallized sapphire or the like for airtight sealing. The position of this lens 29 should be such that the light emitting end face of the laser is close to the object space focal plane of the first lens 29, as described above, and it is sufficient that its accuracy is within ±50 μm. Therefore, the distance between the surface of the spacer 35 on the holder 32 side and the light emitting end surface of the laser 11 is determined in advance, and the distance between the surface of the first lens on the laser side of the holder 32 and the surface of the lens 29 is selected. All you have to do is integrate. In the conventional single mode optical fiber module shown in FIG. Positioning within 1 μm of the heat sink 17 and stem 18 was required. In this invention, the light emitting end face of the laser 11 and the first
The space between the first lens 29 and the first lens 29 is wide.
In the case of a ruby ball with a diameter of 1 mm, the above spacing is
80μm±50μm. Therefore, since the distance between the laser 11 and the lens 29 is large and the precision is loose, the lens holder 32 and the window 19 are metalized without using the commonly used epoxy adhesive, and are fixed airtight with solder material. A seal can be achieved. Furthermore, in this invention, the laser 1
Because the accuracy of the surface alignment of the light emitting end face in 1 becomes loose,
Mass production is also improved and economicalization is achieved. In this example, a spacer 36 made of glass or the like is inserted between the second lens and the single mode optical fiber 13. The thickness of the spacer 36 is selected so that the light from the second lens 31 is focused on the incident surface of the fiber 13, and the adjustment by several tens of micrometers is performed using an optical adhesive or the like. Therefore, reflection from the input end of the optical fiber can be eliminated. Note that the first lens 29
It is possible to eliminate the air layer from the optical fiber input end to the optical fiber input end. Further, it is also possible to apply an antireflection film to the incident side of the first lens 29.

As explained above, since this invention combines a lens system with a relatively long focal length, it is possible to use metallization for airtight sealing between the semiconductor laser and the first lens, or between the first lens and the second lens. It becomes possible to provide a window, and the reliability of the laser can be ensured. In addition, since the mounting accuracy of the first lens is more than 10 times looser than that of conventional modules, the yield in mounting the lens system can be greatly improved, and there are great advantages in terms of manufacturability and economy. Furthermore, it can be applied to a wide range of applications even when used as a multimode fiber by simply replacing the fiber.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional semiconductor laser module device for single mode optical fiber, Fig. 2 is a front view thereof, and Fig. 3 is a configuration diagram of another conventional semiconductor laser module device for single mode optical fiber. 4 is a front view thereof, FIG. 5 is a sectional view showing still another example of the conventional device, FIG. 6 is a diagram showing the principle of the device of the present invention, and FIG. 7 is an embodiment of the device of the present invention. FIG. 8 is a sectional view showing the configuration of another embodiment of the device of the present invention. 11... Semiconductor laser, 13... Single mode optical fiber, 14... Fiber, 17... Laser chip heat sink, 18... Stem, 19...
Airtight window, 22... Focusing lens holder, 23
... Fiber holder, 29 ... Ball lens (first lens), 31 ... Focusing lens (second lens), 3
2... Ball lens holder, 33... Fiber coating,
34...Fiber wire holder, 35...Spacer.

Claims (1)

[Claims] 1 A semiconductor laser chip, a first lens, a second lens, and a single mode optical fiber are arranged in sequence, and are configured to couple the semiconductor laser and the single mode optical fiber, and the first lens has a focal length of A spherical lens with a diameter of several 100 μm to 1 mm is used, a gradient index lens with a longer focal length than the first lens is used as the second lens, and between the semiconductor laser chip and the first lens, Alternatively, a semiconductor laser module device for a single mode optical fiber, in which a hermetically sealed window is provided between the first lens and the second lens.