JPS593409B2 - Method for manufacturing optical fiber with stepped refractive index distribution in circular core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Many optical integrated circuit devices operate with a single polarization.

Therefore, when using these Tepais as a transmission repeater or for reception, a single mode fiber with a fixed plane of polarization is desirable. Various structures have already been proposed as such optical fibers with a fixed (preserved) polarization plane. These include the following two types:

1: The cross section of the core 10 is circular. In addition, its cross section is divided into four sector shapes by two orthogonal diameters, one of which faces each other has a high refractive index part 20, and the other part has a high refractive index. It becomes a lower part 30. 40 is a cladding.

2: The cross section of the core 10 is circular.

The central band-shaped portion including one diameter is a high refractive index portion 20, and the arcuate portions on both sides thereof are low refractive index portions 30.
It is. As described above, the present invention includes: 1) a circular core 10; 2) a high refractive index portion 20 and a low refractive index portion 30 therein; 3) the refractive index of both parts 2
The present invention relates to a method of manufacturing an optical fiber having a structure in which the change occurs stepwise only at the boundary between 0 and 30, and remains constant within each portion 20 or 30.

Prior Art For example, when making the one shown in "Figure 1", the following procedure was used.

Both the high refractive index member 21, which is the source of the high refractive index portion 20 in the core, and the low refractive index member 31, which is the source of the low refractive index portion 30, have a cross section as shown in “Figure 3”. Prepare a fan-shaped column.

They are optically polished and put into a cladding tube 41 (FIG. 4), and fused under vacuum to form a base material, which is then spun. However, this method has the following problems: 1) Polishing is difficult.

2) When the surfaces of each column material are fused together, bubbles are likely to be trapped in between.

There are drawbacks such as.

The present invention eliminates the above drawbacks.

In the present invention, as a high refractive index member and a low refractive index member that become the source of the high refractive index portion 20 and the low refractive index portion 30,
Prepare a cylindrical object. Bundle them with their ends aligned and fuse the whole thing together to make it a single piece.

At that time, they are fused together while sequentially expelling the air from one end, and finally form a cylindrical core material. DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the invention will be mainly explained using an example in which the optical fiber shown in FIG. 1 is manufactured.

(1) As shown in "Fig. 5", the same material is used as the high refractive index member 22 that becomes the source of the high refractive index portion 20 in the core, and the low refractive index member 32 that becomes the source of the low refractive index portion 30. Prepare two cylindrical pieces each with the same diameter and length.

Arrange those four members in parallel with their edges aligned and put them together.

At that time, the pattern drawn by the high refractive index member 22 and the low refractive index member 32 on the end face becomes closest to the arrangement pattern of the high refractive index portion 20 and the low refractive index portion 30 in the core 10 in “Fig. 1”. Do it like this. That is, each member is arranged at the apex of a square (FIG. 5), and the high refractive index member 22 or the low refractive index member 32 is arranged to face each other diagonally. In this way, each member is in line contact (point contact in the cross section), and there is a gap 5 inside.
2 can be done. 3) As shown in FIG. 8, one end of the group of members is connected to a dummy rod 56, the other end is inserted into a dummy tube 58 and connected, and then attached to the glass lathe 54.

Note that the dummy tube 58 serves as an escape route for the air within the gap 52. Then, the group of members is heated by the oxyhydrogen flame 60 while being rotated.

The heating is gradually started from the end of the dummy rod 56 toward the dummy tube 58 as shown by the arrow 62 (for example, 8Tm1).
/Min). :4) When the surfaces of each member begin to melt, adjacent members first become linearly fused.

The fused portion 50 then gradually expands due to surface tension (FIG. 6). At this time, the air in the V-shaped grooves 53 between the members is forced out. Therefore, bubbles are not trapped in the fused portion 50. While trapping the oxyhydrogen flame 60 several times, the gap 52 gradually becomes smaller and finally collapses completely.

At this time, the gap 52 first collapses on the dummy rod 56 side, and then gradually collapses toward the dummy tube 58 (to trap the oxyhydrogen flame 60 in the direction of the arrow 62). Therefore, even at that time, the air within the gap 52 is gradually expelled and escapes through the dummy tube 58.
Therefore, no air remains inside. (5) Continue heating even after the whole becomes a solid solid body as described above.

Then, due to surface tension, a core material 64 having a circular cross section as shown in "Fig. 7" is formed. High refractive index member 2 inside it
2 and the low refractive index member 32 are arranged in the same pattern as in "FIG. 1". (6) Externally attaching clad soot (for example, SiO2-P2O5 composition) onto the core material 64.

Then, it is heated and dehydrated in chlorine gas, and then turned into transparent glass to form a base material. This is then spun using conventional techniques to create optical fibers. (7) High refractive index portion 20 within the core 10
Alternatively, the number of the high refractive index member 22 or the low refractive index member 32 that forms the basis of the low portion 30 is not limited to one each.

For example, as in the case of "Fig. 9" and "Fig. 2", one high refractive index portion 20 may be created from five high refractive index members 23 having different diameters. In this way, the circular members can be circumscribed with each other, and the arrangement pattern of the low refractive index members 33 and the high refractive index members 23 can easily approach the pattern shown in FIG. 2. First embodiment (Figs. 1, 5 to 8) The high refractive index member 22 is a circular rod (5th
! Figure) 2 pieces.

SiO2-GeO2 composition, △ (specific refractive index difference) is 2,0
%o The low refractive index member 32 is also 5rT1r] Two circular rods of 1φ.

SlO2-GeO2-P2O5 composition, △ is 1.5% o
They are put together as shown in Fig. 5 and set on the ganilla lathe 54 (Fig. 8). Rotate at 60 rpm, 0
240t. 8n1 while roasting with H260t oxyhydrogen flame
Trapase in the direction of arrow 62 with rn/Min.

After traparsing twice, the cross section looked like Figure 6.

J After one more trappering, the circular core material 64 of 10 Inn 1φ as shown in [Fig. 7] was obtained. A clad soot of SiO2-P2O5 composition was externally attached to it, and it was dehydrated and made into transparent vitrification to obtain a base material of 24.5 m [n1φ].
3 It was drawn, jacketed with a commercially available quartz tube, and spun into optical fiber in the usual manner. The outer diameter of the optical fiber is 125 μm1 The core diameter is 0.6 μm1 The cutoff wavelength is 0.5 μmMO loss is 0.633 μm at the wavelength
When measured using a He-Ne laser in
It was 3dB/Km.

On the other hand, the optical fiber manufactured by the conventional method (Figs. 3 and 4) has many bubbles, has an outer diameter variation of about ±15 μm around 125 μm, and has a loss of 25 dB/Km.
It was hot.

Second embodiment (Figures 2 and 8 to 12) The high refractive index member 23 is a circular rod 2 with a diameter of 6.51nrnφ.
It consists of four 3a pieces and one 23b piece of 7.5n1n1φ (Fig. 9).

The composition is SlO2-GeO2, Δ is 1.5%, and the low refractive index member 33 is 10 mIr [2 circular rods of 1φ]. SlO2
-GeO2 composition, △ is 1.2%o
Put it all together like this and set it on the glass lathe 54 (
Figure 8). H27Ot, 0235t oxyhydrogen flame 60,
Trapse in the direction of arrow 62 at a speed of 8wn/min to fuse each contact portion in the length direction. Next, another one under the same conditions
After traversing it once, it looked like ``Figure 10,'' and after one more traverse, it looked like ``Figure 11.''

Repeat flame polishing until it becomes a perfect circle, 20.6n
A core material 64 of In1φ was obtained (FIG. 12).

The width C of the high refractive index member 23 is 10.6n1rIb, and the height D of the low refractive index member 33 is 5, so it is extended to 10n1n1φ,
A SiO2-B2O3 glass was attached externally and sintered to obtain a rod with an outer diameter of 431 nn1, which was then jacketed with a commercially available quartz tube to form a fiber.

The outer diameter was 150 μm, the core diameter was 0.6 μM, the cutoff wavelength was 0.6 μM, and the loss was 25 dB/Km.

In contrast, optical fibers manufactured using conventional methods had a loss of 50 dB/Km.

Effects of the invention (1) Cylindrical materials are used as the high refractive index member and the low refractive index member which are the source of the high refractive index portion 20 and the low refractive index portion 30 in the core, and they are arranged in parallel and grouped together, and then fused. Because of the bonding process, as described above, the fused portion is initially linear and then gradually widens.

Therefore, no bubbles remain in the fused area. (2) When the gap 52 between each member is finally about to collapse, it is collapsed from one end to the other, so air is expelled and no bubbles remain in that area. .

(3) Even if it starts out as a bundle of multiple rods, once it begins to melt, surface tension will work and eventually it will naturally become a circular rod.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of different examples of optical fibers to be manufactured according to the present invention, and FIGS. 3 and 4 are sectional views of conventional manufacturing methods for the optical fiber of [Fig. 1]. 5, 6, and 7 are explanatory diagrams sequentially showing the manufacturing process of the core material 64 in the first embodiment of the present invention.
The figure is an explanatory view of the glass lathe 54, and FIGS. 9, 10, 11, and 12 are explanatory views sequentially showing the manufacturing process of the core material 64 in the second embodiment. 10... Core, 20... High refractive index portion, 30... Low refractive index portion, 21, 22
, 23... High refractive index member, 31, 32, 33...
...Low refractive index member, 50...Fusion part,
52...Gap.

Claims (1)

[Claims] 1. A circular core, which has a high refractive index portion and a low refractive index portion, and these portions are arranged in a predetermined pattern in a cross section perpendicular to the length direction. When manufacturing an optical fiber having a refractive index that changes in a stepwise manner only at the boundary, the source of the high and low refractive index portions in the core,
One or more cylindrical pieces of equal length are prepared as the high refractive index member and the low refractive index member, and these are
The end surfaces are aligned and brought together so that they are parallel to each other and the shape of the end surfaces approaches a circle as a whole, and therein, the arrangement of the high refractive index member and the low refractive index member is arranged on the end surface, A pattern is drawn that is closest to the arrangement of the high refractive index portions and low refractive index portions within the core, and then they are heat-fused and integrated. During this process, at least, in the end, When the gap between the members is about to collapse and become completely integrated, the heated portion of the group of members is sequentially moved from one end to the other end to close the gap between the parts. step-wise refractive index distribution in the circular core. A method for manufacturing an optical fiber having the following.