JPS6251514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser light source that combines a semiconductor laser and an optical fiber so that the laser light obtained from the light emitting end face of the semiconductor laser enters the optical fiber from the light input end face. This invention relates to improvements in fiber coupling devices.

Conventionally, such a semiconductor laser-optical fiber coupling device has a semiconductor laser 1 and an optical fiber 2, as shown in FIG. A non-reciprocal circuit 6 having a configuration (not shown) in which a Faraday effect element made of a YIG crystal plate is inserted between two polarizing plates is inserted between the light incident end face 5 which is an end face, On the other hand, the laser light obtained by spreading from the light emitting end face 3 of the semiconductor laser 1 is placed between the light emitting end face 3 of the semiconductor laser 1 and the non-reciprocal circuit 6 so as to be parallel to the optical axis of its optical path. A lens 7 is inserted so that the laser beam enters the circuit 6 perpendicularly, and between the non-reciprocal circuit 6 and the light incident end face 5 of the optical fiber 2, the laser beam obtained in parallel from the non-reciprocal circuit 6 is directed into the optical fiber 2. A configuration has been proposed in which another lens 8 is inserted in order to make the light incident from the light incident end face 5 in a focused manner.

However, in the case of such a conventional device, the semiconductor laser 1
Since a non-reciprocal circuit 6 is inserted between the light output end face 3 of the optical fiber 2 and the light input end face 5 of the optical fiber 2, a part of the laser light that is about to enter the optical fiber 2 is redirected to the light of the optical fiber 2. Even if the reflected light is reflected at the incident end surface 5, the reflected light does not enter the semiconductor laser 1 unnecessarily from the light incident end surface 3, thereby stably maintaining the semiconductor laser 1 with the desired characteristics. It has the feature that it can be operated by

However, in the case of the conventional device shown in FIG. Two lenses 7 and 8 are required between the two lenses, which requires a large number of parts as a whole, complicates the entire device, and furthermore reduces the light output end face of the semiconductor laser 1. 3 and the entrance end surface 5 of the optical fiber 2 becomes long, resulting in an increase in the size of the entire device.

Furthermore, in the case of the conventional device shown in FIG.
It is undeniable that the laser beam is reflected by the lens 8, even if an anti-reflection film is attached to them. In particular, in the non-reciprocal circuit 6, since the laser beam is incident on the non-reciprocal circuit 6 parallel to the optical axis of its optical path, the laser beam is reflected by the lens 8. with a reflection,
The reflectance of the light enters the semiconductor laser 1 as a non-negligible factor. For this reason, in the above description, it was stated that the conventional device shown in FIG. However, it has the disadvantage that the stability of operation is not fully satisfactory.

The present invention therefore proposes a novel semiconductor laser-optical fiber coupling device free from the above-mentioned drawbacks, which will become clear from the detailed description below.

FIG. 2 shows a theoretical first embodiment of a semiconductor laser-optical fiber coupling device according to the present invention, and parts corresponding to those in FIG. 1 are denoted by the same reference numerals.
It has a semiconductor laser 1 and an optical fiber 2, and a YIG
A crystal sphere 11 is inserted as a Faraday effect element 12 having a shape that provides a convex lens function, and is placed between the Faraday effect element 12 and the light entrance end surface 5 of the optical fiber 2 on the light entrance end surface 5. A birefringent crystal plate 13 is inserted in this manner.

In this case, the distance L between the light output end face 3 of the semiconductor laser 1 and the light input end face 5 of the optical fiber 2 is expanded from the light output end face 3 of the semiconductor laser 1, and the laser light obtained is transmitted to the Faraday effect element 12. as
The distance a (fifth (see figure), and the distance b between the center of the YIG crystal sphere 11 and the point where the laser beam is focused.
(See Figure 5). or,
YIG crystal sphere 11 as Faraday effect element 12
In this example, if the laser light emitted from the light emitting end face 3 of the semiconductor laser 1 is obtained as linearly polarized light in the horizontal direction as shown in FIG. Light is the third
As shown in FIG. B, a magnetic field is applied from the magnetic field generating means 14 so as to obtain linearly polarized light in a direction inclined at 45 degrees with respect to the horizontal direction. Further, the birefringent crystal plate 13 is arranged so that the laser beam obtained from the YIG crystal sphere 11 passes through the birefringent crystal 13 as it is and reaches the optical fiber 2 side without being refracted. is inserted between the YIG crystal sphere 11 and the optical fiber 2 with the angle θ (see FIG. 4) formed between the optical axis of the laser beam and the optical axis of the optical path of the laser beam being selected.

The above is the basic configuration of the first embodiment of the semiconductor laser-optical fiber coupling device according to the present invention. It is clear that the light enters the optical fiber 2 from its light incident end face 5 via the YIG crystal sphere 11 as the Faraday effect element 12 and the birefringent crystal plate 13. In this case, the YIG crystal sphere 11 and a birefringent crystal plate 13, even if part of the laser light that is intended to enter the optical fiber 2 from the light incident end face 5 is reflected, the semiconductor laser 1 is stabilized by the reflected light. operation with the intended characteristics is not impaired in any way. The reason is as follows.

That is, when the laser light obtained from the light emitting end face 3 of the semiconductor laser 1 is horizontally linearly polarized light as shown in FIG. 3A, the laser light entering the optical fiber 2 is polarized as shown in FIG. 3B. As shown, the light is linearly polarized in a direction inclined at 45 degrees with respect to the horizontal direction, but in this case, the above-mentioned reflected light between the YIG crystal sphere 11 and the optical fiber 2 is as shown by the solid line in FIG. As shown in Fig. 4, if the laser beam is linearly polarized in the same direction as the laser beam entering the optical fiber 2 (a direction inclined at 45 degrees from the horizontal direction), the reflected light will be reflected by a birefringent crystal, as shown in Fig. 4. Since the normal light is obtained through the plate 13, the reflected light is obtained as light on the optical axis of the optical path of the laser beam. Therefore, the reflected light enters the semiconductor laser 1 via the YIG crystal sphere 11. However, as shown by the solid line in FIG. 3D, the reflected light is inclined at 45 degrees between the semiconductor laser 1 and the YIG crystal sphere 11 with respect to the horizontal direction between the YIG crystal sphere and the optical fiber 2. from the direction
The light is linearly polarized in the direction in which it can be rotated by 45 degrees, that is, in the vertical direction, and therefore the reflected light is reflected by the semiconductor laser 1.
Even if the reflected light enters the semiconductor laser 1
This is because it does not substantially have an adverse effect on the stable operation with desired characteristics. or,
The reflected light between the YIG crystal sphere 11 and the optical fiber 2 is reflected by the optical fiber 2 as shown by the dotted line in FIG. 3C.
The reflected light is linearly polarized in a direction that can be rotated by 90 degrees with respect to the laser beam that enters the interior, and the reflected light is reflected between the semiconductor laser 1 and the YIG crystal sphere 11 as shown in Fig. 3D.
Even if the reflected light is obtained as linearly polarized light in the same horizontal direction as the laser light on the light emitting end surface 3 of the semiconductor laser 1 as shown by the dotted line, the reflected light is polarized by the fourth polarized light due to the presence of the birefringent crystal plate 13. As shown in the figure, it is obtained as extraordinary light that is distant from the optical axis of the optical path of the laser beam. This is because the reflected light does not substantially enter the semiconductor laser 1.

In addition, in the case of the device according to the present invention described above in FIG. 2, although the YIG crystal sphere 11 is inserted between the semiconductor laser 1 and the optical fiber 2,
Since 1 is literally a sphere, even if the laser light from the semiconductor laser 1 is reflected by the YIG crystal sphere 11, the reflected light diverges from the optical axis of the optical path of the laser light, and therefore the reflected light is undesirable. The light does not necessarily enter the semiconductor laser 1.

Therefore, according to the apparatus according to the present invention shown in FIG. 2, the semiconductor laser 1 can be operated more stably and with desired characteristics than in the case of the conventional apparatus described above in FIG. It has characteristics.

Furthermore, in the case of the device according to the invention, the features just mentioned are:
Between the semiconductor laser 1 and the optical fiber 2, one
This can be achieved by simply arranging a YIG crystal sphere 11 and one birefringent crystal plate 13. Therefore, as a whole, the number of parts is smaller than in the case of the conventional device shown in FIG. is simplified, and furthermore, the optical path length between the semiconductor laser 1 and the optical fiber 2 is
It has great features such as being shorter than the case shown in the figure, making the overall device more compact.

Further, in the case of the device of the present invention shown in FIG. 2, when the light emitting end face 3 of the semiconductor laser 1 is about 1 to 3 μm and the diameter of the core 4 of the optical fiber 2 is about 10 to 50 μm,
Light emitting end face 3 of semiconductor laser 1 and YIG crystal sphere 11
The distance (a-R) (where R is the radius of the YIG crystal sphere 11) from the end face of the YIG crystal sphere 11 is approximately 125 μm.
By setting the angle θ _c at which the laser beam from the semiconductor laser 1 can be captured to 65°, the laser beam from the semiconductor laser 1 can be made to enter the optical fiber 2 efficiently.

Next, a second embodiment of the principle of the device according to the present invention will be described with reference to FIG. 6. Parts corresponding to those in FIG. 2 will be given the same reference numerals, and detailed explanation thereof will be omitted. Also, in the configuration described above in Figure 2, the
The structure is the same as that shown in FIG. 2, except that a magnification conversion lens 15 is inserted between the YIG crystal sphere 11 and the birefringent crystal plate 13.

The above is the configuration of the second embodiment of the device according to the present invention. According to this configuration, it is possible to
Except for the above-mentioned matters, it has the same configuration as the case in FIG. 2, so a detailed explanation thereof will be omitted. Because of the existence of It has the characteristic that it can be easily made incident on the light source.

The principle of the first and second embodiments of the device according to the present invention has been clarified above. Although omitted, as shown in FIG. 7, a mounting plate 21 on which the semiconductor laser 1 is mounted and placed on a heat sink 27; a spacer plate 22; laser light transmitting plates 23 and 24; an optical fiber 2, and a YIG crystal sphere 11. and a holder 25 for holding the magnetic field generating means 14; a holder 26 for holding the core 4 of the optical fiber 2 and the birefringent crystal plate 13; The specific configuration is as follows.
Similarly, a detailed explanation will be omitted, but as shown in FIG. 8 in accordance with the case of FIG.
1; Spacer plate 22; Laser light transmitting plates 23 and 24; Holder 25a that holds the YIG crystal sphere 11 and magnetic field generating means 14; Holder 25b that holds the magnification conversion lens 15; Holder 25c that holds the optical fiber 2; It can be easily constructed using the holder 26 that holds the core 4 of the optical fiber 2 and the birefringent crystal plate 13, and the like. In FIGS. 7 and 8, reference numeral 28 denotes a laser beam monitoring guide.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional semiconductor laser-optical fiber coupling device, FIG. 2 is a schematic diagram showing a first embodiment of the principle of the semiconductor laser-optical fiber coupling device according to the present invention, and FIG. 4 and 5 are diagrams for explaining the same, FIG. 6 is a schematic diagram showing a second embodiment of the principle of the semiconductor laser-optical fiber coupling device according to the present invention, and FIGS. 7 and 5 are diagrams for explaining the same. FIG. 8 is a schematic diagram showing a specific example of the apparatus according to the invention shown in FIGS. 2 and 6, respectively. In the figure, 1 is a semiconductor laser, 2 is an optical fiber, and 3 is a semiconductor laser.
is a light output end face, 4 is a core, 5 is a light input end face, 11
is a YIG crystal ball, 12 is a Faraday effect element, 13
14 represents a birefringent crystal plate, 14 represents a magnetic field generating means, and 15 represents a magnification conversion lens.

Claims (1)

[Scope of Claims] 1. A semiconductor laser-optical fiber coupling device for coupling a semiconductor laser and an optical fiber so that the laser light obtained from the light-emitting end face of the semiconductor laser enters the optical fiber from its light-input end face. A Faraday effect element having a shape that provides a convex lens function is inserted between the light output end face of the semiconductor laser and the light input end face of the optical fiber, and a Faraday effect element having a shape that provides a convex lens function is inserted between the light output end face of the semiconductor laser and the light input face of the optical fiber. A semiconductor laser-optical fiber coupling device characterized in that a birefringent crystal plate is inserted in the semiconductor laser. 2. Semiconductor laser recited in claim 1
1. A semiconductor laser-optical fiber coupling device, wherein the Faraday effect element is a YIG crystal sphere.