JPS6232444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a tapered optical fiber bundle used, for example, as an optical distributor for optical fiber communications.

[Technical background of the invention and its problems]

FIG. 2 shows an optical distributor, which is one application example of a tapered optical fiber bundle. In the figure, 21 ₁ , 21 ₂ are tapered optical fiber bundles, and 22 is these optical fiber bundles 21 ₁ , 21
It is a mixer rod with a uniform refractive index that connects _{the two} . The optical operation of this optical distributor is as follows. Now, assuming that the optical fiber bundle ₂₁₁ on the left side is the input side, light incident on any optical fiber of this optical fiber bundle ₂₁₁ is converted from a waveguide mode to a cladding mode at its tapered portion and mixed. Further, the light is almost completely mixed by the mixer rod 22 and propagated to the optical fiber bundle ₂₁₂ on the right side, where the cladding mode is converted into a waveguide mode and the tapered optical fiber bundle ₂₁₂
is evenly distributed to each optical fiber that makes up the fiber. For example, if the optical fiber bundle 21 ₁ consists of n optical fibers and the optical fiber bundle 21 ₂ consists of m optical fibers, this optical splitter acts as an n×m optical splitter.

In addition to the above-mentioned applications, tapered optical fiber bundles can also be used for
It can also be used for 1×n optical splitters and various optical couplers.

FIG. 3 shows a conventional method of manufacturing a tapered optical fiber bundle constituting such a light distributor. As shown in FIG. 3a, a plurality of cleaned optical fibers 31 are bundled in a close-packed state, and a portion of the cleaned optical fibers 31 is heated using a heating means such as a burner 32 as shown in FIG. 3b. , this is stretched to form a tapered portion as shown in FIG. 3c. The tapered optical fiber bundle thus produced has an integrated structure in which the cladding layers of each optical fiber are fused to each other at the tapered portion.

By the way, in such a conventional method for manufacturing an optical fiber bundle, as the number of optical fibers to be bundled increases, the yield rate of completely fusing each optical fiber at the tapered portion tends to decrease. The number of optical fibers is usually 2 to 100, but if there are, for example, about 30 optical fibers, the yield of all the optical fibers being fused will be about 20%.

As a method to improve the manufacturing yield of tapered optical fiber bundles when the number of optical fibers increases,
A method is known in which an optical fiber bundle is pulled while being twisted. The manufacturing process is shown in FIG. Figure 4a
As shown in FIG. 4B, a plurality of optical fibers 31 are bundled in a close-packed state, and a part of the fibers is heated with a heating means such as a burner 32 to form a bundle of optical fibers 31 as shown in FIG. 4B. By pulling while applying twist, a tapered portion is formed as shown in FIG. 4c. In this case, to ensure high yield,
It is known from experience that the twist angle needs to be 180 degrees or more.

However, when a tapered optical fiber bundle obtained through processing with such twisting is used in an optical distributor as shown in Figure 2, the ability to evenly distribute light may deteriorate. Confirmed experimentally. The reason for this is that the optical fibers located near the center of the bundle are twisted differently than those located on the outer periphery.When twisting is applied, the alignment of the optical fibers is disturbed, and this disturbance in alignment causes each fiber to be twisted differently. It is possible that different bending stresses are applied to the optical fiber, and as a result, the guided mode and cladding mode are not converted and reconverted uniformly.

[Purpose of the invention]

SUMMARY OF THE INVENTION The present invention aims to improve the above-mentioned drawbacks, and aims to provide a method for manufacturing a tapered optical fiber bundle with high yield in which when applied to an optical distributor, the variation in light distributed to each output optical fiber is small. shall be.

[Summary of the invention]

The present invention involves bundling a plurality of optical fibers in a nearly dense state, wrapping optical fibers for alignment around this, and twisting the bundle of optical fibers as much as possible while heating a part of the plurality of optical fibers. It is characterized by stretching and processing it into a tapered shape without adding any.

〔Effect of the invention〕

According to the present invention, since the optical fibers for alignment keep the bundle of optical fibers more closely aligned, it is possible to increase the success rate of thermal fusion during taper processing, and therefore the tapered The manufacturing yield of optical fiber bundles can be increased. Furthermore, since the optical fiber bundle is tapered without twisting, when the tapered optical fiber bundle obtained by the method of the present invention is applied to an optical splitter, the light is evenly distributed to each output optical fiber. You can get the effect of becoming.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 1 shows the manufacturing process of one embodiment. First, as shown in FIG. 1a, a plurality of cleaned optical fibers 11 are bundled in a substantially close-packed state, and optical fibers 12 for alignment (hereinafter referred to as auxiliary fibers) are wound around this. optical fiber 1
In the case of a step-index fiber 1 made of multi-component glass, the auxiliary fiber 12 has a refractive index lower than the refractive index of the cladding layer of the optical fiber 11 and a softening point approximately equal to that of the optical fiber 11. A homogeneous glass fiber without a core is used. Both ends of the auxiliary fiber 12 are fixed to the bundle of optical fibers 11 mechanically or using adhesive, wax, or the like. After this, Figure 1b
As shown in FIG. 1C, a part of the bundled optical fibers 11 is heated by a heating means such as a burner 13, and the optical fibers 11 are stretched and tapered as shown in FIG. 1C while minimizing twisting.

According to this embodiment, the aligned state of the bundled optical fibers 11 is maintained by the auxiliary fibers 12, so that all the optical fibers are reliably fused even when there are a large number of optical fibers. Further, since no twist is applied during taper processing, when an optical distributor is constructed using the obtained tapered optical fiber bundle, light is evenly distributed to each output optical fiber. Furthermore, in this example,
Since a glass fiber having a refractive index lower than the refractive index of the cladding layer of the optical fiber 11 is used as the auxiliary fiber 12, the auxiliary fiber 12 acts as it is as the cladding layer of the optical fiber bundle after tapering. Therefore, there is almost no loss of light through this auxiliary fiber 12. By the way, strictly speaking, if the auxiliary optical fiber 12 is placed outside the cladding layer of the tapered portion of the bundled optical fibers 11 as in the present invention, a portion of the propagating light will pass through the cladding layer of the optical fiber 11 in the tapered portion. to auxiliary optical fiber 1
2, and a part of it leaks out from the end face of the auxiliary optical fiber 12, causing a kind of radiation loss. The magnitude of this radiation loss depends on the increase in the cross-sectional area of the cladding layer of the optical fiber bundle due to the auxiliary optical fiber 12, but since the increase in the cross-sectional area of the optical fiber bundle as a whole due to the auxiliary optical fiber is extremely small, This increase in radiation loss is suppressed to a negligible level.

It will be clarified based on data that the optical distributor constructed using the tapered optical fiber bundle according to this example has excellent characteristics. FIG. 5 is a histogram of excess loss for all input fiber and output fiber combinations of the optical splitter using the tapered optical fiber bundle obtained in this example. Here, the excess loss refers to the difference between the loss when ideal optical distribution is performed (for example, 3 dB in the case of two distribution) and the actual loss including loss due to other factors. FIG. 6 is a histogram of excess loss of an optical splitter using a tapered optical fiber bundle according to the conventional method described in FIG. As is clear from comparing the two, the uniformity of light distribution in the optical distributor using the tapered optical fiber bundle according to this embodiment is higher than that in the optical distributor using the tapered optical fiber bundle according to the conventional method. much better than.

The present invention is not limited to the above embodiments.
For example, the number of auxiliary fibers does not need to be one; two or three may be used depending on the number of optical fibers to be bundled. Further, in the present invention, the alignment member may be wrapped around not only the entire area of the heating section but also a part of the tapered section. Further, as the heating means, in addition to a burner, gas discharge, CO ₂ gas laser, etc. can be used.

[Brief explanation of the drawing]

1A to 1C are diagrams showing the manufacturing process of a tapered optical fiber bundle according to an embodiment of the present invention, FIG. 2 is a diagram showing an example of the configuration of an optical distributor using a tapered optical fiber bundle, and FIG. Figures a to c are diagrams showing an example of a conventional manufacturing process for a tapered optical fiber bundle, and Figures 4a to c are diagrams showing another example of a manufacturing process for a conventional tapered optical fiber bundle.
FIG. 5 is a diagram showing an excess loss histogram of an optical splitter constructed using the optical fiber bundle obtained in the example, and FIG. FIG. 6 is a diagram showing an excess loss histogram of the configured optical splitter. 11... Optical fiber, 12... Auxiliary fiber (alignment member), 13... Burner.

Claims (1)

[Claims] 1. In a method of manufacturing a tapered optical fiber bundle by bundling a plurality of optical fibers and heating and stretching a part of the fibers, a heating part of the bundled plurality of optical fibers is provided for alignment. A method for producing a tapered optical fiber bundle, which comprises winding optical fibers, heating and stretching them. 2. The tapered light beam according to claim 1, wherein the alignment optical fiber is made of a homogeneous material whose refractive index is less than or equal to the refractive index of the cladding layer of the plurality of optical fibers. Method for manufacturing fiber bundles.