JPS6344689B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a base material for a single-polarization, single-mode optical fiber, and more specifically, to a method for manufacturing a base material for a single-polarization single-mode optical fiber, and more specifically, a method for manufacturing a clad portion and a core portion of the base material using a vapor phase axis mounting method. The present invention relates to a manufacturing method using a round bar-shaped porous glass base material having the following properties.

It is known that in the structure of an optical fiber, if the refractive index of regions in two orthogonal axial directions in a cross section perpendicular to the longitudinal direction (hereinafter simply referred to as cross section) is different from each other, it has single polarization characteristics. (For example, see Takataka Ohkoshi, "Study of the possibilities and problems of optical heterodyne or optical homodyne type frequency division multiplexing optical fiber communication," Institute of Electronics and Communication Engineers, Photon Quantum Electronics Study Group OQE78-139, p. 61). As a method for manufacturing a base material for a single-polarized single-mode optical fiber, the following method is known, which uses a base material for an optical fiber produced by the chemical vapor deposition method (internal attachment method) shown in Figure 1. ing. In FIG. 1a, reference numeral 1 indicates an optical fiber base material manufactured by the internal attachment method, and as shown in FIG. Polished to base metal 2
Create. Next, the base material 2 is a glass tube (hereinafter referred to as a jacket tube) whose refractive index is different from that of the base material 2.
After forming a base material by covering the base material, an optical fiber is produced by drawing with a heating device such as a carbon resistance heating furnace.

In the above method, a long optical fiber cannot be manufactured because a base material for optical fiber manufactured by an internal attachment method is used and polishing is required, and since the base material that has already been made into transparent glass is polished, a processed layer is required. This method has disadvantages in that bubbles are generated on the surface of the base material, and air bubbles are introduced at the boundary between the base material and the jacket tube due to irregular polishing, resulting in an increase in the transmission loss of the manufactured optical fiber.

By the way, a vapor phase axial mounting method is known as a method for manufacturing optical fibers. This method generally uses SiCl ₄ as a glass raw material and GeCl ₄ as a dopant,
BCl ₄ , POCl ₃ , etc. are transformed into glass particles such as SiO ₂ , GeO ₂ , B ₂ O ₃ , P ₂ O ₅ by hydrolysis reaction using an oxyhydrogen flame or oxidation reaction using a high-temperature heat source under the starting rod. and deposited on the starting rod, at this time, a high refractive index material containing, for example, GeO ₂ is deposited in the center of the deposit.
SiO ₂ glass particles are deposited (formation of the core part), and SiO ₂ glass particles with a low refractive index containing, for example, B ₂ O ₃ are deposited on the outer periphery (formation of the cladding part), and the deposition rate is In this method, a starting rod is rotated and pulled up to produce a round rod of glass fine particles, that is, a porous glass base material, which is then heated to become transparent vitrified and drawn to produce an optical fiber.

In order to solve the above-mentioned drawbacks, the present inventors came up with the idea of using the above-mentioned optical fiber base material produced by the vapor phase axis attachment method instead of the optical fiber base material produced by the internal attachment method, and conducted a multifaceted study. As a result, we have arrived at the present invention.

That is, an object of the present invention is to provide a method for manufacturing a preform for a single-polarized single-mode optical fiber that is long and has low transmission loss.

A method for producing a preform for a single-polarized, single-mode optical fiber that achieves the above-mentioned purpose involves forming a longitudinal phase of a round rod-shaped porous glass preform having a cladding portion and a core portion produced by a vapor phase axial mounting method. Liquid boron alkoxide is applied or sprayed in a straight line on both opposing parallel sides to infiltrate the porous glass matrix, and then the porous glass matrix is heated in steam. It is characterized by hydrolyzing boron alkoxide in the material to form a porous glass region containing B ₂ O ₃ , and then converting it into transparent glass.

In the method of the present invention, a round bar-shaped porous glass base material having a cladding part and a core part made by a vapor phase axial mounting method is used as a raw material, and liquid boron alkoxide is applied or sprayed onto the surface of the base material. When sprayed, boron alkoxide penetrates into the base material,
This was done based on the knowledge that when this is hydrolyzed, a porous glass region containing the generated B ₂ O ₃ is formed.

The method of the present invention will be explained with reference to the drawings.
Figures a to d are schematic diagrams showing the steps of the present invention, and a
11 is a round bar-shaped porous glass base material, 12
For example, 13 is a core made of SiO ₂ / GeO ₂ ,
This is a cladding part made of SiO ₂ . Liquid boron alkoxide is applied or sprayed onto the base material 11 as shown in FIG. b to form a region 14 in which boron alkoxide has penetrated into the base material 11.
Next, this base material 11 is exposed to water vapor to form a region 14' in which the boron alkoxide in _the region ₁₄ in FIG. Next, the base material 11 shown in FIG. 13' is a core portion made of transparent vitrified SiO ₂ .GeO ₂ , 13 ′ is a cladding portion also made of SiO ₂ , and 14 ″ is a cladding portion also made of SiO ₂ .B ₂ O ₃ .

FIG. 3a is an enlarged sectional view of the base material 15 of FIG. 2d,
b is a model diagram three-dimensionally representing the refractive index distribution within the cross section. FIG. 4a is an enlarged cross-sectional view of the base material 15 in which boron alkoxide is infiltrated so that the distribution of B ₂ O ₃ reaches the core, and FIG. It is a model diagram expressed dimensionally. As shown in FIGS. 3 and 4, when regions with different refractive indexes exist along two orthogonal directions in the cross section, the base material has single polarization characteristics.

Examples of boron alkoxides used in the present invention include B(OCH ₃ ) ₃ , B(OC ₂ H ₅ ) ₃ , B
(OC ₃ H ₇ ) ₃ , B(OC ₄ H ₉ ) ₂ and the like, and when boron alkoxide is exposed to water vapor, it is converted into B ₂ O ₃ through the following reaction.

2B(OR) ₃ +3H ₂ O→B ₂ O ₃ +6ROH Formula R is -CH ₃ , -C ₂ H ₅ , -C ₃ H ₇ , -
Indicates an alkyl group such as C ₄ H ₉ .

When infiltrating the base material 11 shown in FIG. 2b with boron alkoxide, the tip of the glass tube is brought as close to the base material 11 as possible and the boron alkoxide is extruded from the tip of the glass tube. Alternatively, a metal mask having a slit is brought close to the base material 11 and boron alkoxide is sprayed through the slit.

Next, the present invention will be explained with reference to examples, but the present invention is not limited thereto.

Example 1 A cladding radius of 15 mm (cladding part is SiO ₂ ) and a core radius of 5 mm, manufactured by the conventional vapor phase axial mounting method.
A glass tube with a _diameter of 2 mm is brought close to a porous glass base material (core part is 96 mol% SiO ₂ / 4 mol% GeO ₂ ) at room temperature to extrude liquid B(OCH ₃ ) ₃ . ₃
B(OCH ₃ ) ₃ C so that only B(OCH 3 ) 3 C
permeates and diffuses into the base material. At this time, the base material is supported vertically and the glass tube is moved downward at a speed of Vmm/min to carry out linear coating.
At this time, the descending speed of the glass tube is Vmm/min and B
The relationship between (OCH ₃ ) ₃ and the diffusion distance Lmm is shown in FIG. When V=3.5 to 4 mm/min, the base material shown in FIG. 3 is obtained, and when V=3 to 2.8 mm/min, the base material shown in FIG. 4 is obtained.

B ₂ O ₃ was generated by maintaining the base material in which B(OCH ₃ ) ₃ was permeated and diffused in a steam atmosphere at 200° C. for 30 minutes. This base material is prepared in advance in a chlorine gas atmosphere.
It was heated to around 800°C to remove attached moisture and hydroxyl groups bonded to the glass base material, and then heated at 1300°C for 100 minutes to form transparent glass. The size of this transparent vitrified base material was approximately 1/2 that of the porous glass base material. Also, the composition of the region where B ₂ O ₃ diffused is
It contained 96 mol% of SiO ₂ and 4 mol% of B ₂ O ₃ .

When the obtained base material was drawn by a conventional method, a single-polarization single-mode optical fiber was obtained, and this fiber had a transmission loss of less than 0.2 dB/Km at a wavelength of 1.5 μm.

Example 2 A metal plate mask having a slit with a width of 2 mm was brought close to the porous glass base material so that the slit was parallel to the longitudinal direction, and B(OCH ₃ ) ₃ was sprayed with a sprayer using N ₂ gas as a carrier gas. As a result of carrying out the same experiment as in Example 1 except that the base material was infiltrated into the base material, a similar base material was obtained.

As is clear from the above description, according to the present invention, it is possible to omit the polishing step of the transparent base material that was required in the conventional technology, and the problem of increasing the length of the optical fiber can be solved. is easily obtained,
In addition, since the porous glass base material is processed, it is possible to treat it with chlorine, etc. after processing, resulting in an optical fiber with low OH group content, and the advantage of being able to achieve a transmission loss of 0.2 dB/Km or less at a wavelength of 1.5 μm. There is.

The single-polarized single-mode optical fiber produced in this way is difficult to use in systems using semiconductor lasers, optical switches, optical modulators, directional couplers, etc., since these devices have polarization dependence. It has the advantage of increasing bond stability and simplifying the system configuration.

Furthermore, it has the advantage that it can be easily configured in future communication systems that utilize the phase of light waves, that is, coherent optical transmission systems.

[Brief explanation of drawings]

Figure 1 a is a drawing showing the base material obtained by the internal attachment method, b is a drawing showing the shape of the base material after cutting and polishing, Figures 2 a to d are schematic diagrams of the steps of implementing the present invention, and Figures 3 and 4.
In the figure, a is an enlarged view showing the shapes of regions with different refractive indexes in the cross section of the optical fiber base material of the present invention, b is a model diagram three-dimensionally expressing the refractive index distribution of the cross section, and FIG. 2 is a graph showing the relationship between the moving speed of the application port and the diffusion distance of boron alkoxide during application of boron alkoxide in an example of the present invention. 1... Optical fiber base material produced by internal attachment method,
2... Cut (or polished) base material, 3, 4... Cut surface of base material 2, 11... Rod-shaped porous glass base material produced by vapor phase axial mounting method, 12... Core part, 13...
Cladding part, 14...A region where boron alkoxide has permeated and diffused, 14'...A region where B ₂ O ₃ is distributed, 12', 13', 14''...Transparent glass portion corresponding to 12, 13, 14', 15... Transparent vitrified base material.

Claims (1)

[Claims] 1. Liquid boron alkoxide is applied in a straight line on both parallel longitudinal sides of a round rod-shaped porous glass base material having a cladding part and a core part made by the vapor phase axial mounting method. Boron alkoxide is infiltrated into the porous glass base material by spraying or spraying, and then the boron alkoxide in the porous glass base material is hydrolyzed in steam.
1. A method for producing a preform for a single-polarized, single-mode optical fiber, which comprises forming a porous glass region containing B ₂ O ₃ and then converting it into transparent glass.