JPH09166722A - Connection structure for optical guide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection structure capable of enlarging a projecting part and a recessed part formed on the connection part of an optical guide as large as possible. SOLUTION: In a connection part 12 for mutually connecting an optical fiber 10 having a 1st core 15 and a clad 16 and an optical waveguide 11 having a 2nd core 30 and a clad 31, enlarged parts 20, 35 are respectively formed on the end parts of the cores 15, 30. A projection 25 projected in the axial line direction of the fiber 10 is formed on one enlarged part 20 and a recessed part 40 to be engaged with the projection 25 is formed on the other enlarged part 35. Thus the fiber 10 and the waveguide 11 are mutually fixed in the mutually engaged state of the projection 25 and the recessed part 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection structure for a light guide such as an optical fiber used for transmitting signal light in optical communication.

[0002]

2. Description of the Related Art An optical fiber such as an optical fiber or a flat plate optical waveguide used for optical communication is composed of a core located at the center of the optical guide and a clad surrounding the core. By making the refractive index larger than the refractive index, light rays are guided inside the core. Various methods have heretofore been considered for connecting a plurality of light guides to each other.

For example, one light guide (optical fiber, etc.)
Of the cores of both light guides by forming a protrusion on the end face of the core and forming a recess in the core of the other light guide having a shape that can be fitted to the above protrusion, and fitting the protrusion into the recess. Attempts have been proposed for positioning and for fixing the ends of both light guides to each other by suitable fixing means. According to such a concavo-convex connection structure, it is possible to prevent the center lines of both cores from being displaced in the radial direction as long as the positions of the protrusion and the recess are accurate.

[0004]

However, the above-mentioned concavo-convex connection structure has difficulty in forming the projection and the recess. For example, in the case of a single-mode silica optical fiber, the mode field system is as small as about 9.5 μm, so the core diameter becomes smaller. Therefore, the protrusions and recesses formed on the core are considerably small. It is difficult to form such small protrusions or recesses on the end face of the core, and the strength of the protrusions or recesses is weakened, so that they are easily damaged. Moreover, the smaller the protrusions and recesses, the more
When they are fitted to each other, it is difficult to guide the ends of both light guides to a position where the projection and the recess can be fitted with each other with high precision, and there is also a problem that connection work becomes difficult.

Therefore, an object of the present invention is to provide a connection structure for a light guide in which the projections and recesses formed in the connection portion can be made as large as possible even in a light guide having a small core diameter, and the above problems can be solved. To provide.

[0006]

The present invention, which has been developed to achieve the above object, provides an enlarged portion having a core diameter larger than that of other portions at the end portion of the core of the first light guide. A protrusion protruding in the axial direction of the light guide is formed on the end face side of the enlarged portion, an enlarged portion is also provided on the end portion of the core of the second light guide, and the protrusion can be fitted to the end face side of the enlarged portion. It is characterized in that a concave portion having a shape is formed, and the end portion of the first light guide and the end portion of the second light guide are fixed to each other in a state where the projection and the recess are fitted to each other. To form the enlarged portion in the core of the optical fiber, the end portion of the optical fiber is heated by a burner or the like to thermally diffuse the dopant at the end portion of the core, thereby substantially changing the core diameter without changing the fiber diameter. Can be expanded.

As described above, since the enlarged portions are provided at the end portions of the cores of both light guides and the protrusions and the concave portions are provided in the enlarged portions, even the light guides having a small core diameter have relatively large protrusions and concave portions. Can be formed. Therefore, it is easy to form the protrusion and the recess, and the strength of the protrusion and the recess is increased. It is also easy to fit the projection and the recess when connecting both light guides.

When the projection is formed in a conical shape, and the top of the projection is located substantially on the center line of the core, and when the recess is formed in the shape of a skirt, the projection is fitted into the recess to allow self-alignment. Aligning is done by lining (self-guided), and axial misalignment of the end faces of both cores is prevented.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, an optical fiber 10 functioning as a first light guide and an optical waveguide 11 functioning as a second light guide are optically and mechanically connected to each other at a connecting portion 12.

The optical fiber 10 has a first core 15 through which light rays pass, and a clad 16 covering the outer periphery of the core 15. The core 15 has a refractive index higher than that of the cladding 16 by adding a dopant such as germanium, phosphorus, aluminum or titanium to quartz glass.

An enlarged portion 20 is provided at the end of the core 15. The enlarged portion 20 has the end face 21 side via the portion 23 in which the core diameter is tapered so that the core diameter on the end face 21 side of the fiber 10 is larger than the core diameter of the core main portion 22 other than the end portion. Has a larger core diameter.

To form the enlarged portion 20, the end portion 10a of the optical fiber 10 having the straight core 15 is locally heated by an electric furnace or a burner as shown in FIG. By thermally diffusing the dopant, the core diameter is increased without changing the outer diameter of the cladding 16 as shown in FIG.

As shown in FIG. 4 and the like, the enlarged portion 20 is provided with a conical projection 25 on the end face 21 side of the fiber 10. The protrusion 25 is formed by etching or machining so that the protrusion 25 projects in the axial direction of the fiber 10 and the top portion 25 a of the protrusion 25 is located on the center line of the core 15. In this case, since the enlarged portion 20 having a large core diameter is provided at the end of the core 15,
A relatively large protrusion 25 can be formed, and the protrusion 25
And the protrusion 25 can be easily formed.

Optical waveguide 1 functioning as a second light guide
1 is a high refractive index second core 30 located at the center,
It is composed of a clad 31 having a low refractive index and covering the core 30. The optical waveguide 11 in the illustrated example is a flat waveguide used in a planar lightwave circuit such as a branch coupler, and the core 30 is doped with the above-mentioned dopant. This core 3
The enlarged portion 35 is also provided at the end portion of 0.

As shown in FIG. 5 and the like, the enlarged portion 35 has a tapered core width so that the core width on the end face 36 side of the optical waveguide 11 is larger than the core width of the core main portion 37. The core width on the side of the end face 36 is increased via the portion 38. The enlarged portion 35 is formed by the well-known CVD (Chemical Vap
or Deposition) or FHD (Flame HydrolysisDe
When forming a step index type waveguide by the position) method or a graded index type waveguide by the ion exchange method, the core 30 is enlarged and the core 30 and the clad 31 are formed at the end of the waveguide by using, for example, a masking method. It is manufactured so that the difference in refractive index is small. Further, as in the case of the optical fiber 10, the enlarged portion 35 may be formed by locally heating with an electric furnace, a burner or the like.

It is preferable that the number of guided modes in the expanded portions 20 and 35 be equal to the number of guided modes in the cores 15 and 30. For example, when the system of the optical fiber and the optical waveguide to be connected is a single mode system, the expansion unit 2
The enlarged portions 20 and 35 should be formed so that the 0 and 35 are also in the single mode. Similarly, in a multimode system in which three modes up to the 0th order, the 1st order, and the 2nd order are guided modes, the expanded sections 20 and 35 are also configured so that the three modes become guided modes. 20, 35 should be formed.

In the case of an optical fiber, if the method of diffusing the dopant of the core in the process of forming the enlarged portion is adopted, the difference in the refractive index between the core and the clad becomes small on the contrary even if the core becomes large. If heat diffusion is performed below, the number of guided modes is maintained. In addition, when the expanding portions 20 and 35 spread rapidly, the cores 15 and 3 in the expanding portions 20 and 35 are increased.
Radiation modes are generated in the part where 0 spreads and the part where 0 narrows, leading to loss. Therefore, the cores 15 and 30 should spread as gently as possible.

As shown in FIG. 6, a recess 40 in the shape of a pleat is formed on the end face 36 side of the enlarged portion 35 of the optical waveguide 11. The recess 40 has a size and shape that can be fitted exactly to the protrusion 25, and the core 1 is
In order to avoid radial displacement between 5 and 30,
The center of the recess 40 is formed so as to be located on the center line of the core 30. The recess 40 is formed by a chemical method such as machining or etching. Since the recess 40 is provided in the enlarged portion 35, the recess 4 is relatively large.
0 can be formed, and thus it is relatively easy to form the recess 40.

The projections 25 of the optical fiber 10 and the recesses 40 of the optical waveguide 11 are fitted to each other in the axial direction so that the cores 15 and 30 are aligned with each other in a self-aligning manner. As a result, the end faces 21, 36 of the two cores 15, 30 are accurately and easily aligned with each other, and the connection loss of the cores 15, 30 can be minimized. In the case of this embodiment, the large protrusion 25 is larger than that in the case of fitting the small protrusion and the recess in the related art.
Since the recesses 40 are fitted together, the strength of the projections 25 and the recesses 40 is high, and the optical fiber 10 and the optical waveguide 11 can be easily guided to a position where the projections 25 and the recesses 40 are fitted together.

With the projection 25 and the recess 40 fitted together as described above, the ends of the optical fiber 10 and the optical waveguide 11 are fixed to each other by appropriate fixing means. For example, core 1
The optical fiber 10 may be fixed to the optical waveguide 11 by an adhesive having a refractive index close to that of 5, 30 or by the connection reinforcing material 45. Alternatively, the connecting portion 12 may be embedded and fixed in a fixing synthetic resin. When the connecting portion 12 is fixed by using a connector or the like, the refractive index matching liquid is used.
May be satisfied.

The protrusion 25 is formed on the core 3 on the optical waveguide 11 side.
0 and the recess 40 may be provided in the core 15 on the optical fiber 10 side. Further, when connecting the optical fibers to each other, the projection 25 similar to that in the above embodiment is provided on the end surface of one optical fiber, and the recess 40 similar to that in the above embodiment is provided to the end surface of the other optical fiber. Good.

[0022]

According to the present invention, the core of an optical guide such as an optical fiber or an optical waveguide is enlarged, and a projection is provided on the end face of one enlarged portion and a concave portion is provided on the end face of the other enlarged portion. Since the projections and recesses are fitted together,
The protrusion and the recess can be made larger than before. As a result, the mode field diameter increases as the expanded portion of the core expands, and the allowable range of axial misalignment between the cores increases, so that the allowable range of shape accuracy after machining can be increased. Then, the strength of the projection and the recess is increased, the processing of the projection and the recess is facilitated, and the projection and the recess can be easily fitted together.

[Brief description of the drawings]

FIG. 1 is a sectional view of a connecting portion of a light guide showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state before an enlarged portion is formed on the first light guide.

FIG. 3 is a cross-sectional view showing a state in which an enlarged portion is formed on the first light guide.

FIG. 4 is a cross-sectional view showing a state in which a protrusion is formed on the first light guide.

FIG. 5 is a cross-sectional view showing a state before a recess is formed in the end portion of the second light guide.

FIG. 6 is a cross-sectional view showing a state in which a recess is formed at the end of the second light guide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Optical fiber 11 ... Optical waveguide 12 ... Connection part 15 ... 1st core 16 ... Cladding 20 ... Expansion part 25 ... Protrusion 30 ... Second core 31 ... Clad 35 ... Expansion part 40 ... Recessed part

Claims (4)

[Claims] 1. A connection structure of a light guide for connecting a first light guide having a first core and a cladding and a second light guide having a second core and a cladding to each other, wherein An enlarged portion having a core diameter larger than that of the other portion is provided at the end of the first core, and a projection protruding in the axial direction of the light guide is formed on the end face side of the enlarged portion, and the end of the second core is formed. Is also provided with an enlarged portion, and a concave portion having a shape that can be fitted to the protrusion is formed on the end face side of the enlarged portion, and the protrusion and the concave portion are fitted to each other.
The light guide connection structure, wherein the end portion of the light guide and the end portion of the second light guide are fixed to each other. 2. The projection is formed in a conical shape, the top of the projection is located substantially on the center line of the core, and the recess is formed in a serpentine shape and located substantially in the center of the core. The light guide connection structure according to claim 1. 3. The optical guide connection structure according to claim 1, wherein the first light guide is an optical fiber and the second light guide is a flat optical waveguide. 4. The optical guide connection structure according to claim 1, wherein both the first light guide and the second light guide are optical fibers.