JPS6035300B2 - Method for manufacturing single-polarization single-mode optical fiber - Google Patents

Description

Detailed Description of the Invention The present invention provides a single-polarization, single-mode optical fiber that can propagate polarized optical signals while maintaining the polarization direction, which has excellent symmetry, excellent polarization maintenance, and low loss. The present invention relates to a method for manufacturing a single-polarization single-mode optical fiber.

Single-polarized single-mode optical fibers consisting of a core and a cladding are HE, . It is possible to transmit light in only the fundamental mode called mode, but if an asymmetric birefringence is created in the core, HE, . The mode is divided into HE, HEr, and two modes in which the electric field vibration directions of light vibrate in directions perpendicular to each other, and if only one mode is excited, only one vibration mode will be transmitted through the optical fiber. .

As a method for producing such a single-polarized single-mode optical fiber, the jacket method as shown in Fig. 1 has been known. Fiber manufacturing method - JP-A-57-205333). In FIG. 1, 1 is a core portion, 2 is a cladding portion, 3 is a glass for applying stress, 4 is a spacer for filling a space, and 5 is a jacket tube.

It is known as an effective method to arrange a stress-applying base material 3 and a base material 4 around a base material consisting of a core 1 and a cladding 2, insert them into a jacket tube 5, and draw the wire. During actual manufacturing, it is impossible for the material placed inside the jacket tube 5 to be completely immovable, and some of the material may move during drawing. As a result, when looking at the end face of the obtained optical fiber, as shown in FIG. 1B, the stress-applying portion sometimes causes zero fluctuation in the direction viewed from the core central axis. In this case, it is usually about 2 to 5 degrees, but it is known that if this fluctuation occurs in the longitudinal direction of the optical fiber, it will seriously affect the polarization maintenance of a single-polarized single-mode optical fiber. There is. Therefore, in order to manufacture an optical fiber with excellent polarization maintaining properties using conventional methods, the dimensional accuracy of each constituent material is required to be extremely high, and this processing requires advanced technology. In addition, there are many gaps between the materials, which sometimes traps air bubbles, which can have a negative effect on the optical fiber. In order to solve these drawbacks of the prior art, the present invention was invented to improve polarization maintenance and reproducibility by processing the optical fiber base material itself. The means will be explained in detail with reference to the drawings.

Well-known methods for synthesizing optical fiber base materials include the vapor deposition method (VAD method [Figure 2A]) and the external attachment method [Figure 2B]. , 6 is a seed yarn, 7 is a deposited porous base material, 8 is a burner for core matrix synthesis, and 9 is a burner for cladding synthesis. SIC So4, G
A glass-forming raw material gas such as C so 4 or PC so 3 is ejected from a burner 8 or 9 along with oxyhydrogen gas, etc.
Produces a flame hydrolysis reaction within the flame. The glass particles produced by the reaction are deposited on the tip of the seed rod (FIG. 2A) or around it (FIG. 2B). In FIG. 2A (VAD method), the porous matrix 7 grows in the axial direction by rotating the seed rod 6 and pulling it upward as the porous matrix grows.

Burner 9 applies fine glass particles for cladding around the core base material.
If it is deposited by On the other hand, in FIG. 2B, the seed rod 6 is kept rotating, and the glass forming raw material is ejected from the burner 9 together with oxyhydrogen gas, reacts in the flame formed in front of the burner, and forms glass fine particles. At the same time, by reciprocating the burner 9 from side to side, a porous base material 7 is formed. Initially, the core composition (e.g. S
If the steam of iQ-Snake 02) is ejected and the desired thickness is deposited, then the vapor of the cladding composition (SiQ) is ejected.
A porous base material for optical fiber is obtained. The mother village produced through these steps may be processed according to the steps shown in FIG. That is, in FIG. 3, 10 is a core part, 11 is a cladding part, 12 is a hole created in the center of the base material produced by the external attachment method, 13 is a hole formed in a part of the cladding part,
13' is the hole.

In the process shown in Figure 2, the cladding part is filled with glass porous material, and as shown in Figure 3C, the area corresponding to 13 of this cladding part is exposed to a carbon dioxide laser (CQ laser).
The light from 14 is reflected by the reflecting mirror 15, and the light from the porous base material 11 is
The irradiated area is heated to a high temperature and a hole 13' is formed. By controlling the positions of the mirror 15 and the scissor 14 by the control system 16, a hole 13' of a desired shape can be formed in the portion 13. The apparent density of the porous mother village is 0.2 to 0.5 g.
/ is the degree, but when using laser light, it is desirable to have a low density. On the other hand, a drill may be used mechanically for this drilling process, and any means thereof is not limited. When the porous base material with holes drilled in the region 13 is heated at about 1500 o'clock in the electric furnace 17 shown in FIG. 3D, it becomes a transparent base material as shown in FIG. 3D.

If a dehydrating gas such as CZ2 or SOC2, which has a remarkable dehydrating effect, is flowed as an atmospheric gas during this transparentization process, the OH groups remaining in the transparent matrix can be easily reduced to 0.1
It is possible to lower it to about ppm. Transparent mother village 3rd
The sectional view taken along the plane a-a' shown in Figure D is Figure 3E.
As shown in FIG.
is formed. This base material may be stretched to have a desired outer diameter, if necessary.

A glass whose thermal expansion coefficient is larger than that of the cladding 11 (for example, Sj02
-B203-Snake 02) Insert the shank 18 and the whole into the jacket tube 19. If the combined matrix is heated to about 210,000 ℃ in a carbon furnace or the like and drawn, an optical fiber having a cross section almost similar to that of the matrix shown in FIG. 3 can be obtained. Needless to say, if the outer cover of the transparent base material 11 is sufficiently thick, there is no need to insert it into the jacket tube 19. The glass to be inserted into the working part 13 is Si, which has a coefficient of thermal expansion smaller than that of the cladding part.
02-Ti02 glass may also be used.

In addition, in FIG. 3, after drilling according to FIG.
A base material in which the cladding and the stress applying part are integrated is obtained.
FIG. 4 shows another embodiment of the present invention, in which the glass forming raw material is flowed together with oxygen gas through the hole 13' of the drilled hole 11, and heated from an external heating source 20'.
A glass film having a stress-imparting glass composition is formed within 3'.

This method differs from the method of inserting a stress-applying glass rod, and can provide a base material for optical fiber with lower loss.
FIG. 5 shows holes 13' and 21 in the cladding part 11 of the base material.
If a glass having a large coefficient of thermal expansion is inserted into the hole 13' and a glass having a small coefficient of thermal expansion is inserted into the hole 21, an even larger birefringence can be obtained. As a specific example, as shown in FIG.
%mol%Si02, 15mol%B.

3.5 mol% snake 02), after transparentization, core diameter 5 wind, cladding outer wall 50 side, pore diameter 1 x cape, distance between hole center and core center 1
There should be 5 ribs.

Furthermore, in order to use it as a base material for wire reference, the base material of the 5-diameter cladding was stretched so that the outer diameter of the cladding was 13.5 mm, and after inserting it into a jacket tube with an outer diameter of 26 mm and an inner diameter of 14 ribs, the optical fiber was If the fiber is drawn to a diameter of 150 μm, a single-polarization, single-mode optical fiber with a cutoff wavelength of 1.2 μm is obtained. The birefringence produced in the core is as large as about 1×10-4, and since the optical fiber is uniform in the longitudinal direction, it also has excellent polarization preservation properties. The loss at a wavelength of 1.3 m is also 0. Mother B/
Object, wavelength 1. The absorption loss of OH groups that occurs in Madarabutsu m is also 1 dose/
It was a small thing. In this embodiment, it is also possible to externally deposit glass on the area corresponding to the jacket tube by the method shown in FIG. 2B.

As explained above, according to the method for manufacturing a single-polarized single-mode optical fiber of the present invention, a hole into which a stress applying section is inserted is formed in a part of the cladding section in advance at the porous stage.
There is no difficulty in drilling holes in transparent glass sills, and the machining accuracy is sufficiently high.

Moreover, it has dimensional accuracy in the longitudinal direction and excellent polarization maintenance. The use of acid water treatment technology has advantages such as the ability to satisfy low loss characteristics at the same time. Brief explanation of the drawings Figure 1 is a cross-sectional view showing a method for manufacturing a single-polarization single-mode optical fiber, Figure 2 is a diagram showing a method for synthesizing a porous base material, and Figure 3 is a cross-sectional view showing a method for manufacturing a single-polarized single-mode optical fiber. FIG. 4 is a diagram showing another embodiment of the invention, and FIG. 5 is a diagram showing another embodiment.

1...Core, 2...Clad, 3...
Stress applying part, 4... Subasa, 5... Jacket pipe, 6
... Seed stick, 7 ... Porous mother village, 8 ...
... Torch for core, 9... Torch for cladding, 10...
Core, 11... Clad, 12... Hole corresponding to the seed rod part, 13... Hole corresponding to the stress applying part, 13'... Hole, 14... Laser, 15...Reflector, 16...Control device, 17...Electric furnace, 18...Glass rod (stress applying member), 19.
... Jacket tube, 20 ... Heat source, 2
1...hole.

Figure 1 Figure 2 Figure 3 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A glass comprising a core with a high refractive index and a cladding with a low refractive index surrounding it, which are arranged symmetrically with respect to the central axis of the core, and the glasses constituting the cladding have different coefficients of thermal expansion. A method for producing a single-polarized single-mode optical fiber that produces a birefringent index distribution in the core and the vicinity of the core by means of a stress-applying part, in which a glass-forming raw material that reacts to become glass is thermally oxidized and then flame-formed. The glass fine particles produced by reacting with means such as hydrolysis reaction are treated with quartz glass,
A part of the base material consisting of a porous core and cladding obtained by depositing on or around the tip of a seed rod made of materials such as ceramic carbon is removed by mechanical, optical or chemical methods, and as necessary. At the same time, the base material is heated and cleared using a heating means such as an electric furnace, and the transparent base material with holes in the desired areas is heated with heat that is larger or smaller than the coefficient of thermal expansion of the cladding part to apply stress. A method for manufacturing a single-polarized single-mode optical fiber, which comprises inserting a glass body having an expansion coefficient and drawing the fiber. 2. In the method for manufacturing a single-polarized, single-mode optical fiber according to claim 1, the coefficient of thermal expansion of the hole portion of the porous base material in which the hole is formed is greater than the coefficient of thermal expansion of the cladding portion. After inserting a stress-applying porous glass rod of large or small glass composition, dehydration treatment,
A method for manufacturing a single-polarization single-mode optical fiber, characterized by making it transparent. 3. In the perforated porous preform or transparent preform formed by the method for manufacturing a single-polarized single-mode optical fiber according to claim 1, a stress-applying glass layer is provided in the perforated portion, A method for producing a single-polarized, single-mode optical fiber, which is deposited by a thermal oxidation method, a flame hydrolysis reaction, or a liquid phase reaction method. 4. In the manufacturing method according to claim 1 or 2, two pairs of holes, that is, four in total, are formed with respect to the central axis of the core, and the lines connecting the central axes of each pair of holes are orthogonal to each other. . A method of manufacturing a single-polarization single-mode optical fiber, which comprises inserting or forming in each pair a glass whose thermal expansion coefficient is larger than that of the cladding portion, and a glass whose thermal expansion coefficient is smaller than that of the cladding portion.