JPH05281443A - Optical coupling method - Google Patents

Abstract

PURPOSE:To provide an optical coupling method which provides higher constant coupling efficiency than the prescribed efficiency even if a deviation between the propagation axis of light and the transmission axis of an optical transmission line is present thereon. CONSTITUTION:When single-mode laser beam 6 is coupled with a single-mode optical fiber 4, an optical waveguide part 5 where the waveguide becomes narrower in the transmission direction of the laser beam 6 is provided on the input part of the optical fiber 4 and then the single-mode laser beam 6 which is made incident on the optical waveguide 5 is optically coupled with the optical waveguide 4 temporarily in a multi-mode state and while being converted into the single-mode laser beam 6 the multi-mode laser beam 6 is guided to the optical fiber 4, so that the single-mode laser beam 6 is coupled with the optical fiber 4.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical coupling method,
In particular, it relates to an optical coupling method for coupling single mode light to a single mode optical transmission line.

[0002]

2. Description of the Related Art Conventionally, research and development of optical communication technology have been actively conducted. This is because optical signal transmission is superior to electrical signal transmission in terms of transmission speed and interference between signals.

In optical signal transmission, it is often necessary to couple single mode light emitted from a light emitting element such as a semiconductor laser into a single mode optical fiber. In this case, as shown in FIG. 14, the emission surface of the light emitting element 91 and the end surface (light input surface) of the optical fiber 92 come close to each other via an intermediate medium (not shown). The intermediate medium is
Generally, it is air or the like. In the figure, 94 represents the core of the optical fiber 92.

Light emitted from light emitting element 91 95 (single mode)
In order to increase the degree of coupling between the optical fiber 92 and the optical fiber 92, the so-called coupling efficiency,
It is necessary to adjust the positional relationship between the light emitting element 91 and the optical fiber 94 so that the transmission axis of the optical axis coincides.

However, the single mode optical fiber 9
In the case of coupling the single-mode emitted light 95 to 2, the coupling efficiency becomes extremely small if the propagation axis of the emitted light 95 and the transmission axis of the optical fiber 92 deviate from each other even a little. There is a problem in that it is difficult to realize mass production and cost reduction because it is necessary to make adjustments.

Even if the axes are aligned accurately, the optical parameters of the optical fiber 92 and the emitted light 95 are different from each other due to system restrictions, and only a part of the emitted light 95 is coupled to the optical fiber 94. There was a problem. For example, it is desirable that the emitted light 95 be incident on the optical fiber 94 in the form of a plane wave, but if this is to be realized, a light emitting element having a large beam waist is required and the device becomes large, so that the device is made compact. Is required, the emitted light 95 cannot be incident on the optical fiber 94 in the form of a plane wave, and the emitted light of the semiconductor laser is incident on the optical fiber 94 in a waveform such as a spherical wave as is the case. There is a problem of reduced efficiency.

[0007]

As described above, in order to couple the single-mode output light to the single-mode optical fiber with high coupling efficiency, it is necessary to perform accurate axis alignment. For this reason, the manual work of a skilled worker is required, and there is a problem in terms of productivity and economy. Further, even if the axes are correctly aligned, there is a problem that the coupling efficiency is lowered because the optical parameters may differ before and after the coupling to the optical fiber due to the system restrictions.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical coupling method which can surely obtain a coupling efficiency higher than a certain level.

[0009]

In order to achieve the above object, the optical coupling method of the present invention provides an input of the optical transmission line when the single mode light is coupled to the single mode optical transmission line. By providing an optical waveguide in which the waveguide becomes narrower toward the transmission direction of the light, the single mode light incident on the optical waveguide is once optically coupled to the optical waveguide in a multimode state. It is characterized in that the mode light is guided to the optical transmission line while being converted into the single mode light, and the single mode light is coupled to the optical transmission line.

Further, according to another optical coupling method of the present invention, when the single mode light is coupled to the single mode optical transmission line, it is guided to the input portion of the optical transmission line in the light transmission direction. By providing an optical waveguide having a narrow waveguide, light is coupled to the optical transmission line while changing the beam shape of the single mode light incident on the optical waveguide.

[0011]

In the present invention, an optical waveguide is provided between the optical transmission line and the light, the optical waveguide narrowing toward the optical transmission direction.

When a multimode optical waveguide is used, even if the propagation axis of light and the transmission axis of the optical waveguide are deviated,
The probability that light is coupled to the optical waveguide is much higher than that when a single mode optical waveguide is used. This is because, in the case of a multimode optical waveguide, there are many modes, and therefore light is coupled to any mode of the optical waveguide even if the propagation axis of light and the transmission axis of the optical waveguide are deviated. ..

When such coupling occurs, light is transmitted through the optical waveguide while repeating mode conversion and dispersion. That is, single mode light is converted into multimode light. Further, since the waveguide is narrowed toward the light transmission direction, the higher-order modes gradually disappear with the light transmission, and only one mode remains at the end. That is, multimode light is converted into single mode light and coupled to the optical transmission line. At this time, since the higher-order mode is converted to a single mode, loss due to mode conversion occurs, but by optimizing the mode conversion mechanism (waveguide shape, refractive index difference, etc.), simple direct coupling can be achieved. It is possible to increase the coupling efficiency.

Therefore, even if the light propagation axis and the transmission axis of the optical transmission line are deviated from each other and the light cannot be coupled to the optical transmission line, the light is incident on the optical waveguide and the light is transmitted to the optical waveguide. The coupling efficiency is not abruptly reduced due to the axis deviation. Similarly, even if there is a difference in the optical parameter before and after coupling to the optical transmission line due to system restrictions, if the above-mentioned optical waveguide is used, the optical parameter before coupling matches any parameter of the optical waveguide. The coupling efficiency does not become extremely small with respect to the axis deviation.

The light coupled to the input part of the optical waveguide is
It has a beam shape (light intensity distribution) corresponding to the shape and size of the input section. This beam shape changes as the light is transmitted because the waveguide is narrowed toward the light transmission direction. For this reason, when the input section is enlarged in the direction in which axis alignment is difficult and light can be reliably incident on the optical waveguide, even if the beam shape at the input section is poorly compatible with the optical transmission line, While the light is being transmitted through the optical waveguide, it can be changed into a beam shape having good compatibility with the optical transmission path.

Therefore, according to another optical coupling method of the present invention, by enlarging the input portion in a direction in which axis alignment is difficult, even if the light propagation axis and the optical waveguide transmission axis are deviated,
Increasing the tolerance of optical axis deviation for coupling, without significantly reducing coupling efficiency with respect to axis deviation, as in the case of directly coupling single mode light to a single mode optical transmission line. You can also

[0017]

Embodiments will be described below with reference to the drawings.

FIG. 1 is a perspective view of an optical fiber provided with an optical waveguide according to a first embodiment of the present invention and a semiconductor laser.

A single mode optical fiber 4 composed of a core 2 and a clad 3 concentrically covering the core 2 is
It is arranged in the vicinity of the semiconductor laser 1 via a medium such as air. The input part of the optical fiber 4 has a refractive index substantially equal to that of the core 2, and is covered with a conical optical waveguide 5. The outer diameter of the optical waveguide 5 is gradually reduced toward the transmission direction of the single mode laser light 6 of the semiconductor laser 1 until it becomes the same as the outer diameter of the optical fiber 4.
That is, the dimension in the longitudinal direction is a multi-mode optical transmission line on the side where the laser light 6 is input, and gradually approaches the single mode toward the coupling portion with the optical fiber 4.
The optical waveguide 5 should have a single mode at the coupling part with
It is chosen to be sufficiently large for the wavelength of the light inside. Specifically, it is preferably 10 times or more the wavelength of the light in the optical waveguide 5. Such an optical waveguide 5 may be produced, for example, by coating the light receiving side of the optical fiber 4 with a hardening material such as polymer or plastic, and then polishing or hardening this hardening material into an optical waveguide shape. Here, the refractive index of the optical waveguide 5 is made substantially equal to that of the core, but the point is that the refractive index of the optical waveguide 5 is larger than that of the cladding 3.

When the optical fiber 4 provided with such an optical waveguide 5 is used, the propagation axis of the laser light 6 and the optical fiber 4 are
The laser beam 6 transmitted to the optical fiber 4 does not extremely decrease even if the transmission axis is deviated from the transmission axis. This is explained as follows.

That is, when the multimode optical waveguide 5 is used, even if the propagation axis of the laser beam 6 and the transmission axis of the optical fiber 4 are deviated, the probability that light is coupled to the optical waveguide is a single mode. It is much higher than when an optical waveguide is used. This is because the optical waveguide 5 has multiple modes in the input section as described above, and therefore many modes exist, and the laser 6 light is transmitted by the optical waveguide 5.
This is because it is combined with any of the modes. The laser light 6 coupled to the optical waveguide 5 is transmitted through the optical waveguide 5 while repeating mode conversion and dispersion. That is, the single mode ray
The light 6 is converted into multimode laser light 6 and transmitted through the optical fiber 4. Moreover, since the waveguide of the optical waveguide 5 is narrowed toward the transmission direction of the laser light 6, the higher-order modes gradually disappear with the transmission of the laser light 6, and only one mode remains at the end. Therefore, the multimode laser light 6 is changed to the single mode laser light 6 and coupled to the optical fiber 4.

Therefore, even when the laser beam 6 cannot enter the optical fiber 4 due to the deviation between the propagation axis of the laser beam 6 and the transmission axis of the optical fiber 4, the optical waveguide 5 is often used.
Is incident on and coupled to a single-mode optical fiber, abruptly due to the deviation between the propagation axis of the laser light 6 and the transmission axis of the optical fiber 4, as in the case of directly coupling the single-mode laser light. The binding efficiency does not decrease, and the binding efficiency above a certain level can be reliably obtained.

Further, even if the propagation axis of the laser beam 6 and the transmission axis of the optical fiber 4 are aligned due to system restrictions,
Laser light 6 before and after the laser light 6 is coupled to the optical fiber 4
Even if there is a difference in the optical parameters, the optical parameters of the laser light 6 match any one of the parameters of the optical waveguide 5, so that the coupling efficiency does not become extremely small, and a certain coupling efficiency or more is surely obtained. Be done.

Thus, according to the present embodiment, even if the propagation axis of the laser beam 6 and the transmission axis of the optical fiber 4 are deviated, the coupling efficiency does not become extremely small. This eliminates the need for alignment and improves productivity and economic efficiency. Further, even if there is a difference in the optical parameter before and after the laser light 6 is coupled to the optical fiber 4, there is no problem that the coupling efficiency is extremely reduced.

FIG. 2 is a perspective view of an optical fiber provided with an optical waveguide according to the second embodiment of the present invention.

The outer diameter of the cladding 13a at the input part of the single-mode optical fiber 14 composed of the core 12 and the cladding 13 concentrically covering the core 12 is small, and the cladding 13a is refracted. It is covered with a conical optical waveguide 15 whose ratio is substantially equal to that of the core 12.
The outer diameter of the optical waveguide 15 gradually decreases in the laser light transmission direction, as in the previous embodiment. This optical waveguide 15 can be produced, for example, by forming the clad 13a by etching, coating the clad 13a with a hardening material such as polymer or plastic, and polishing or hardening this hardening material into an optical waveguide shape. good. The optical waveguide 15 is covered with a protective film 16 having a refractive index smaller than that of the optical waveguide 15, and the protective film 16 makes the outer diameter of the portion of the optical waveguide 15 substantially equal to that of the cladding layer 13. The protective film 16 may be formed, for example, by coating the optical waveguide 15 with a hardening material such as polymer or plastic, and then polishing or hardening the hardening material into a cylindrical shape.

Even with such a structure, the same effects as in the previous embodiment can be obtained, and the protection film 16 can improve the durability of the optical waveguide 15.

FIG. 3 is a perspective view of an optical fiber provided with an optical waveguide according to the third embodiment of the present invention.

The input part of the single mode optical fiber 24 composed of the core 22 and the clad 23 is covered with a conical optical waveguide 25 similar to that of the first embodiment. The optical waveguide 25 is protected by a supporting member 26 having a refractive index smaller than that of the optical waveguide 25. In order to provide such a supporting member 26 in the optical waveguide 25, for example, a supporting member 26 having a conical cavity is prepared, the optical fiber 24 is inserted into the supporting member 26, and then the optical fiber 2 is inserted.
The optical waveguide 25 may be formed by filling the gap between the support 4 and the support member 26 with a filler having a refractive index substantially equal to that of the core 22. Although a filler having a refractive index equal to that of the core 22 is used here, the point is that the refractive index of the filler is the cladding 23.
No more than that. With such a structure, the same effect as that of the second embodiment can be obtained.

FIG. 4 is a perspective view of an optical fiber provided with an optical waveguide according to the fourth embodiment of the present invention. This is a combination of the second and third embodiments.

That is, the cladding 3 of the input portion of the single mode optical fiber 34 composed of the core 32 and the cladding 33.
The outer diameter of 3a is small as in the second embodiment, the cladding 33a is covered with a conical optical waveguide 35 having a refractive index substantially equal to that of the core 32, and the optical waveguide 35 is supported. It is protected by the member 36.

Even with such a structure, the same effects as those of the third embodiment can be obtained, and the optical fiber 34 and the optical waveguide 35 can be more firmly fixed to each other.

FIG. 5 is a sectional view of an optical fiber provided with an optical waveguide according to the fifth embodiment of the present invention.

Explaining this in accordance with the forming process, first,
A coaxial single-mode optical fiber 44 is prepared, and one end of the optical fiber 44 is etched to form a clad 43a having a thickness B substantially equal to the diameter A of the core 2. Next, the clad 43a is covered with an optical waveguide material such as a polymer or plastic to be the optical waveguide 45, and then the optical waveguide material is polished or machined so as to have the same outer diameter as the clad 43. Next, an etching mask 46 having an annular groove is provided on the surface of this optical waveguide material, and then a tapered optical waveguide 45 is formed by wet etching or the like. Finally, a filling material 47 such as polymer or plastic having a refractive index substantially equal to that of the clad 43 is injected from the groove of the etching mask 46 so that the portion of the optical waveguide 45 is concentric with the clad 45. Even if the optical waveguide 45 formed in this way is used, the same effect as that of the previous embodiment can be obtained.

FIG. 6 is a perspective view of an optical fiber provided with an optical waveguide according to a sixth embodiment of the present invention and a semiconductor laser, and FIG. 7 is a view of FIG. 6 viewed from the A direction.

The shape of the input portion of the single-mode optical fiber 54, which is composed of the core 52 and the clad 53 that concentrically covers the core 52, is the cross-sectional shape when the optical fiber 54 is cut diagonally, that is, , And has an ellipse, and an optical waveguide 55 is provided at this input portion. This optical waveguide 5
The input part 5 is parallel to the emission surface of the semiconductor laser 51, and the shape of the input part is rectangular, and the long side direction is parallel to the surface on which the semiconductor laser 51 is mounted. Further, the dimensions of the input portion and the like of the optical waveguide 55 are selected so that the optical waveguide 55 has a single mode.

The semiconductor laser 51 and the optical fiber 54 are usually mounted on some kind of substrate.
The position adjustment between the optical fiber 54 and the optical fiber 54 is generally more difficult in the lateral direction (direction parallel to the substrate surface) with respect to the substrate to be mounted than in the vertical direction (direction perpendicular to the substrate surface). Therefore, there is a problem that the coupling efficiency between the laser light 56 and the optical fiber 54 becomes extremely small due to the deviation of the propagation axis of the laser light 56 and the transmission axis of the optical fiber 54 in the lateral direction.

However, in the present embodiment, since the optical waveguide 55 having the input portion having a large lateral dimension is used, even if the lateral positional adjustment is somewhat inaccurate, the laser beam 56 is used.
Can be coupled to the optical waveguide 55. Laser light 56 at this time
The beam shape (shape of the light intensity distribution) is an ellipse elongated in the direction parallel to the input part of the optical waveguide 55. Since the beam shape of the laser light 56 at the time of being coupled to the input portion of the optical waveguide 55 is not the same circle as the core 52, the compatibility with the core 52 is not good. However, since the waveguide of the optical waveguide 55 is narrowed in the horizontal axis direction in the propagation direction of the laser light 56, it changes from an ellipse to a circle with the transmission of the laser light 56 and approaches the cutoff condition of the light propagation. , The laser light 56 is coupled to the optical fiber 54 by gradually joining to the core 52.

Thus, according to the present embodiment, even if it is difficult to align the axis in a specific direction due to a process or a system, the tapered optical waveguide 55 having an input portion having a large dimension in that direction is used. By coupling the laser beam 56 and changing the beam shape to couple the laser beam 56 to the optical fiber 54, a coupling efficiency higher than a certain level can be reliably obtained, and the laser beam 56 can be directly fed to the optical fiber 54. As in the case of coupling with each other, there is no problem that the coupling efficiency is extremely lowered with respect to the axis shift. Although the input portion of the optical waveguide 55 and the emission surface of the semiconductor laser 51 are parallel to each other in the present embodiment, the input surface of the optical waveguide 55 is inclined by a minute angle Δθ as shown in FIGS. 8 and 9. May be. This is effective in preventing reflected light from the incident surface of the optical waveguide from being returned to a light source such as a semiconductor laser.

FIG. 10 is a perspective view of an optical fiber provided with an optical waveguide and a semiconductor laser according to the seventh embodiment of the present invention.

This is an example of arraying the optical fibers 54 provided with the optical waveguides 55 of FIG. 6, and by supporting the optical fibers 54 provided with the optical waveguides 55 in the grooves formed in the support base 56. Realization of array.

FIG. 11 is a side view of an optical fiber provided with an optical waveguide and a semiconductor laser according to the eighth embodiment of the present invention.

The optical waveguide of this embodiment is different from that of the sixth embodiment in that a non-reflection coating film 57 is provided on the input surface of the optical waveguide 55.

With such a structure, the same effect as in the previous embodiment can be obtained, and the laser beam 56 can be prevented from being reflected on the input surface of the optical waveguide 55 and being coupled to the semiconductor laser 51. There are advantages.

FIG. 12 is a view showing a modification of the eighth embodiment, in which the optical waveguide 55 is embedded in the optical fiber 54 and the exposed portion of the optical waveguide 55 is covered by the antireflection coating film 5.
7a to reduce the adverse effect of reflected light.

FIG. 13 is a perspective view of an optical fiber provided with an optical waveguide and a semiconductor laser according to the ninth embodiment of the present invention.

This is an example using a rectangular parallelepiped optical transmission path 62, and tapered optical waveguides 63 are provided on both side surfaces of the input portion of the optical transmission path 62. The input part of these two optical waveguides 63 and the input part of the optical transmission line 62 are in the same plane and are in parallel with the emitting surface of the semiconductor laser 61. By using such an optical waveguide 63, the same effect as when using a coaxial optical fiber is obtained.

The present invention is not limited to the above embodiment. For example, in the eighth and ninth embodiments, the optical waveguide in which the antireflection coating film is provided on the optical waveguide of the sixth embodiment has been described, but the optical waveguides of other embodiments are nonreflective. The same effect can be obtained by providing a coating film. Further, in the above embodiment, the case where the semiconductor laser is used as the light emitting element has been described, but the same effect can be obtained even in the case of another light emitting element, for example, a light emitting diode. Furthermore, the present invention can be applied to both step-type and graded-type optical fibers, and the shape of the optical waveguide is not limited to the above. In addition, various modifications can be made without departing from the scope of the present invention.

[0049]

As described above in detail, according to the present invention, even if there is a deviation between the optical axis of the light and the optical axis of the optical transmission line, or there is a difference in the optical parameters before and after coupling to the optical transmission line, It is possible to obtain a certain degree of coupling efficiency or more.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical fiber provided with an optical waveguide according to a first embodiment of the present invention and a semiconductor laser.

FIG. 2 is a perspective view of an optical fiber provided with an optical waveguide according to a second embodiment of the present invention.

FIG. 3 is a perspective view of an optical fiber provided with an optical waveguide according to a third embodiment of the present invention.

FIG. 4 is a perspective view of an optical fiber provided with an optical waveguide according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of an optical fiber provided with an optical waveguide according to a fifth embodiment of the present invention.

FIG. 6 is a perspective view of an optical fiber provided with an optical waveguide and a semiconductor laser according to a sixth embodiment of the present invention.

FIG. 7 is a view of an optical fiber provided with the optical waveguide shown in FIG. 6 and a semiconductor laser viewed from the direction A.

8 is a diagram showing a modification of the optical waveguide shown in FIG.

9 is a diagram showing another modification of the optical waveguide shown in FIG.

FIG. 10 is a perspective view of an optical fiber provided with an optical waveguide and a semiconductor laser according to a seventh embodiment of the present invention.

FIG. 11 is a side view of an optical fiber provided with an optical waveguide and a semiconductor laser according to an eighth embodiment of the present invention.

FIG. 12 is a diagram showing a modification of the eighth embodiment.

FIG. 13 is a perspective view of an optical transmission line provided with an optical waveguide according to a ninth embodiment of the present invention and a semiconductor laser.

FIG. 14 is a diagram for explaining a conventional optical coupling method.

[Explanation of reference numerals] 1,51,61 ... Semiconductor lasers, 2, 12, 22, 3
2, 42, 52 ... Core, 3, 13, 13a, 23, 3
3, 33a, 43, 53 ... Clad, 4, 14, 24,
34, 44, 54 ... Optical fiber, 5, 15, 25, 3
5,45,55,55a, 55b ... Optical waveguide, 6,56
... laser light, 16 ... protective film, 26, 36 ... support member, 4
6 ... Etching mask, 47 ... Filling material, 57, 57a
... non-reflective coating film, 62 ... optical transmission line.

Claims (2)

[Claims] 1. When coupling a single-mode light to a single-mode optical transmission line, an optical waveguide is provided at an input portion of the optical transmission line, the optical waveguide being narrowed toward the transmission direction of the light. , The single-mode light incident on the optical waveguide is optically coupled to the optical waveguide in a multimode state, and the multimode light is guided to the optical transmission line while being converted into the single-mode light. An optical coupling method comprising coupling single mode light to an optical transmission line. 2. When coupling a single-mode light to a single-mode optical transmission line, an optical waveguide is provided at an input portion of the optical transmission line, the optical waveguide narrowing toward the light transmission direction. An optical coupling method, wherein light is coupled to the optical transmission line while changing a beam shape of the single mode light incident on the optical waveguide.