JPS61251534A - Production of multi-core optical fiber - Google Patents

Abstract

PURPOSE:To obtain the titled fiber having extremely improved dimensional accuracy, being easily coincided with the axis, by inserting plural glass rods having high refractive indexes, respectively, into plural holes bored in a starting quartz glass rod, integrating them under heating and grinding specifically the starting quartz glass rod. CONSTITUTION:The plural holes 2 are bored in the quartz glass rod 1 which becomes a clad in such a way that the centers of the holes are arranged in the straight line A passing the center of the section in the diameter direction. Then, the glass rod 3 having higher refractive index than the glass 1 is inserted into each of the hole 2, integrated under heating under the heat source 5 to form the preform 4, which is drawn or drawn while being integrated under heating to give a fiber. Consequently, a multi-core fiber having extremely improved dimensional accuracy is obtained. Or, the rod 1 is cut in parallel with the straight line A. Consequently, since the arranged axis of the plural cores can be easily judged from the outside, complicated operations of axis coincidence are not required and the axis coincidence can be easily carried out only by confirmation of the external form.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a multi-core fiber with high dimensional accuracy. In recent years, copper cables have been replaced by original cables for transmitting information, and accordingly, the amount of information transmitted relative to the cross-sectional area of the cable has increased dramatically, and there is a demand for further increases in the amount of information. For this reason, punch fibers in which a plurality of cores are formed in one fiber are being developed.

(Conventional technology) Conventional methods for producing punched fibers include bundling multiple glass rods that serve as the core and cladding, inserting them into a quartz tube, heating them together, and then drawing them.

(Problems to be Solved by the Invention) However, the above-described method of bundling a plurality of sheets and heating them together has the disadvantage that the dimensional accuracy is completely poor, such as the position of the core being non-circular. The purpose of the present invention is to provide a novel method for manufacturing a multi-core fiber that eliminates the above-mentioned drawbacks. (Ninth means for solving the problem) Drill a plurality of holes so that their centers are lined up on a straight line passing through the center in the radial direction, insert all of the glass rods with a higher refractive index than the starting rod into the plurality of holes, and use this as a core. This is a heating and unifying method, and the method for producing a multi-core original fiber is characterized in that the quartz glass rod is ground so as to have a cross section that is V-shaped in a chord parallel to the straight line.

The method of the present invention will be explained below with reference to the drawings.

1 and 2 show one embodiment of the present invention, and FIGS. 1(a) and (1)) are the same cross-sections of the glass (quartz rod) 1 that becomes the n-cladding, respectively. Figure 2 is a front view in the axial direction, and 2 is the ninth axial direction in which the cores are inserted into the glass 1 serving as the cladding so that the centers of each core are lined up on a line A passing through the center of the same radial cross section. It is a hollow hole. A core glass rod 3t having a higher refractive index than the glass 1 serving as the cladding is inserted into the hole 2. Drilling is done using an ultrasonic hole drill.

Figure 2 shows 3t of core glass in hole 2 of cladding glass 1.
- Insert the preform 4 by heating it with the heat source 5 and integrating it into the preform 4.
The process of creating t- is schematically shown. In addition to the method of using flame or the like as a heat source as shown in Figure tIE2, a method of heating using an electric furnace as a total heat source may be used. A fiber is produced by drawing after heating and integrating in this manner, or by drawing while heating and integrating.

A method for drawing wire while heating and integrating is to insert the core glass rod 3 into the opened cladding glass rod 1, and then close one end of the hole in the cladding glass rod 1 by heating and fusing.
A method of drawing this preform while reducing pressure inside the hole,
Alternatively, after inserting the core glass rod 5r4 into the opened cladding glass rod 1, one end of the hole in the cladding glass is closed by heat fusion, and while the hole is filled with gold, the hole is not closed. There is a method in which the other end is similarly closed to obtain a preform in which the inside of the hole is in a vacuum state and a glass rod for a core is placed inside the hole, and the preform is drawn with gold wire.

As described above, according to the method of the present invention in which a plurality of holes are drilled on one plane passing through the axial center of the cladding, the core is inserted, and the core is heated and integrated to form a fiber, the positional accuracy of the fiber core is as follows. Since this depends only on the dimensional accuracy at the time of opening, it is possible to obtain a multi-core fiber with very high dimensional accuracy.

In addition, by making the diameter of the hole in the cladding and the inserted core almost the same, the gap between the core and the cladding can be minimized, so that the change in shape after heating and integration is small, and the non-circularity of the core can be minimized. It is possible.

Furthermore, in connecting multi-core fibers, alignment of core axes is very important and difficult. Unless the dimensional accuracy of the fiber itself is good, it is impossible to align the axis of multiple cores at the same time. However, according to the method of the present invention, a fiber with very good dimensional accuracy can be obtained. I can solve the points. By cutting parallel to the straight line connecting the centers of the two cores, you can easily determine the axis of alignment of multiple cores from the outside.

This eliminates the need for complicated axis alignment operations, and allows axis alignment to be performed easily by simply checking the outer shape.

Also, the cross section of the cladding has two parallel chords e!, as shown in Figure 5. It may be ground so that it does.

The quartz glass serving as the cladding in the method of the present invention may contain additives in addition to pure quartz, and any glass may be used for the core.

(Example) Example 1 Pure silica soot was synthesized by the WAD method, dehydrated in an electric furnace, and then made transparent in an 8F, gas, and He gas atmosphere to obtain fluorine-containing M quartz glass. Diameter 40
A hole with a diameter of 1211II is made using an ultrasonic hole drilling machine on a glass rod for a glass clamp of 1.5mm. [Two were installed at symmetrical positions with respect to the center of the best.

A portion of the outer periphery of this rod was then ground to give it a shape with chords parallel to the axis of the holes.

Then, in these two holes, 7n each with a diameter of 11 w, o ”I
An 8101-G90B glass rod manufactured by the AD method is inserted as a core glass rod, and the cladding glass and core glass are heated and fused at one end of the hole to close the hole, and then a Makabe pump is used to open the hole. Wire is drawn in an electric furnace while completely depressurizing the inside.
A fiber with an outer diameter of 125 μm was obtained.90 The two core diameters of the obtained fiber were 34.4 μm and 3
43 μm, and the ellipticity is less than 1%, making it possible to obtain a multi-core multi-mode fiber with extremely good dimensional f/ff.

Example 2 A SiO,-PIOI soot was synthesized by the VAD method, dehydrated in an electric furnace at 81 F gas, and then made transparent in a He gas atmosphere to form a SiO,-PIOI soot containing phosphorus and fluorine.
Obtained quartz rod gold for cladding. Five holes each having a diameter of 4 mm were drilled in the quartz rod, and then a portion of the outer periphery was ground to obtain a rod having a cross section in which the holes were lined up and a chord was parallel to the diameter. Next, a quartz bar with a diameter of 3 wm was inserted into the hole for a gold core, and then heated and integrated. The above quartz rod for core is VAD
Pure silica produced by the method)! After dehydration, it is made transparent and stretched. The heated and integrated preform was drawn in an electric furnace to obtain a fiber with an outer diameter of 125 μm.

The three core diameters of the obtained fibers are jL7.
5 pm, 7.5 μm, 16 μm, the ellipticity is n
is less than 1゜Ots, making it a multi-core with good dimensional accuracy.
Next a single mode fiber is obtained.

Example 3 Pure silica soot obtained by the VAD method was dehydrated with cctl IP= gas in an electric furnace and became transparent. Five holes with a diameter of 5 sm are drilled on the same diameter of the obtained glass for cladding with a diameter of 60 mm, and then a part of the outer periphery is ground to form a rod with an outer diameter that has a chord parallel to the diameter where the holes are lined up. Toshitsugi. Then, in each hole on the rondo,
Sing-GeO1 with a diameter of 4 cm manufactured by VAD method
Insert a glass rod into your friend. Furthermore, the cladding glass and the core glass are heat-sealed at one end of the hole to close the hole, and then a vacuum pump is used to keep the inside of the hole solid, and the other end of the hole is closed. The hole was closed by heat-sealing the tube glass and the core glass. The thus obtained preform, whose holes are in a vacuum state, is drawn using an electric furnace to form a wire having a cross-sectional shape consisting of an arc with an outer diameter of 150 μm and one chord.

Got ivar.

The core diameter of each n of the obtained A7t fiber is 9.8 pm.
, 1 (L Opm, 1 (L 1 pm, 1αOp
m, 9.9 pm, and the ellipticity is 1.0 T
A multi-core single mode fiber with extremely good dimensional accuracy was obtained, with a distance between each core of 16.7 μm, and crosstalk was below the measurement limit.

(Effects of the Invention) In the method for manufacturing a multi-core original fiber of the present invention, since the core position tn of the fiber depends only on the dimensional accuracy at the time of opening, it is possible to obtain a drawn product with very high dimensional accuracy, and also to form a heated and integrated fiber. Changes are small and the non-circularity of the core can be minimized. Furthermore, by grinding the cross section of the cladding so that it has a chord parallel to the diameter of the cores, the alignment axis of the cores can be determined from the outside, making it easier to align the axis of multi-core fibers, which was difficult with conventional methods. mouth that has the advantage of becoming

[Brief explanation of the drawing]

Figures 1(a) and 1(a) show an embodiment of the present invention.
FIG. 2 is a cross-sectional view and an axial front view of the glass serving as the cladding. FIG. 2 is a diagram illustrating a process of heating and integrating the cladding and the core in one embodiment of the present invention. FIG. 3 is a diagram illustrating another embodiment of the present invention.

Claims (1)

[Claims] (1) A plurality of holes are drilled in the starting quartz glass rod so that their centers are aligned on a straight line passing through the center in the radial direction of the starting rod, and the holes have a refractive index higher than that of the starting rod. A method for manufacturing a multi-core optical fiber, which is a method of inserting a glass rod to form a core and heating and integrating the core, the method comprising: grinding the quartz glass rod so that it has a cross section having a chord parallel to the straight line. .