JPH03223131A - Production of elliptical core-type polarization plane-maintaining optical - Google Patents

Abstract

PURPOSE:To obtain low-loss elliptical core-type polarization plane-maintaining optical fiber by grinding both sides of a core rod, having a specific composition and composed of a core and a clad in the axial direction, depositing fine glass particles on the outer peripheral part, sintering the particles, forming a preform and hot drawing a wire. CONSTITUTION:A core rod 10 having a structure composed of three layers of a core glass layer 6 containing GeO2 from the center, the first clad glass layer 7 containing F and the second clad glass layer 9 of pure SiO2 is produced by a VAD method. Both sides 11 of the aforementioned core rod 10 are then ground in the axial direction and fine glass particles (soot) 13 for forming a support 16 are subsequently deposited on the outer periphery of the resultant ground core rod 12 by the VAD method and sintered to form a preform 17, which is then hot drawn into a wire to produce elliptical core-type polarization plane-maintaining optical fiber. Thereby, since the SiO2 glass layer 9 is formed on the outermost layer of the core rod 10, mixing of H2O and H2 from an oxyhydrogen flame into the ground core rod 12 can be suppressed to reduce OH loss of the elliptical core fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a polarization maintaining optical fiber (hereinafter referred to as elliptical core fiber) whose core has an elliptical cross section.

[Prior art] One of the methods for manufacturing an elliptical core fiber is disclosed in Japanese Patent Application No. 1986-3.
There are methods described in Japanese Patent Application No. 07735 and Japanese Patent Application No. 128498/1982.

In this method, both sides of a core rod consisting of a core glass layer containing GeO Next, 5if2 glass soot is externally attached to the outer periphery of this ground core rod and sintered to form a support glass layer, and this glass base material is used as an optical fiber base material and is drawn into an ellipse. Manufactures core fiber.

[Problems to be Solved by the Invention] Using this manufacturing method, an elliptical core fiber was prototyped and its loss characteristics were evaluated, and the absorption loss due to OH groups at a wavelength of 1.39 μm (hereinafter referred to as OH loss) was 15 dB/■ This is large, and due to the effect of this OH loss, 1.3
The loss in the ~1.5 μm band increased, and the loss at 1.54 μm was 0.4 dB/Km.

In order to obtain an elliptical core fiber with even lower loss, it is necessary to reduce the OH loss.

We investigated the cause of this increase in OH loss through repeated trial production and evaluation, and found that 820% of the OH loss was caused by an oxyhydrogen fire in the process of externally attaching soot to the ground core rod using the VAD method. It was found that OH loss increases due to the incorporation of H2.

The present invention aims to eliminate the drawbacks of the prior art described above and provide a low-loss elliptical core fiber.

[Means for Solving the Problems] The present invention involves grinding both side surfaces of a core rod consisting of a core and a cladding in the axial direction, depositing glass particles (soot) on the outer periphery of the ground core rod, and baking the soot. In the method for manufacturing a polarization maintaining optical fiber, the structure of the ground core rod is G130 from the center.
2 (germanium oxide), a core glass layer containing F(
a first clad glass layer containing fluorine), and a pure 5
in2 (gay metal oxide) second cladding glass layer, 3
It consists of layers.

[Function] The gist of the present invention is that the conventional GeOz-containing core glass layer, F
The reason is that a 5i02+02 glass girder core rod is used on the outer periphery of the cladding glass layer, which suppresses the mixing of H2O and H2 into the core rod from oxyhydrogen fires that occur during the process, and reduces OH loss. This is what I did.

The reason for providing the SiO2 glass layer is based on the experimental result that SiO2 glass has a slower diffusion rate of H20 and H2 than F-containing glass. It is presumed that the difference in diffusion rate is due to the difference in the bonding state of the glass atoms.

It is desirable that the outer periphery of the first cladding of the core rod after grinding be completely surrounded by the second cladding (S+02 glass layer) in order to reduce OH loss.If the grinding extends to the first cladding, a 5in2 glass layer The effect of suppressing H, O, and H2 becomes smaller and OH loss increases.

[Example] Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a process diagram showing the manufacturing process of an elliptical core fiber according to an embodiment of the present invention.

Example 1 Gf30* and 5ift are supplied from the core burner 1, and 5iOz is supplied from the clad burner 2, and soot is deposited by the VAD method to form the porous base material 5 consisting of the core part 3 and the clad part 4 (first Figure (a)), GeO2 in the core part 3 is 1 with a non-refractive index difference (Δ) based on the cladding.
．． A 2% amount was added.

This porous base material 5 was sintered and vitrified in a fluorine-containing helium atmosphere to form a core rod 8 consisting of a core 6 and a first cladding 7 (FIG. 1b)).

At this time, the flow rate of fluorine is the relative refractive index difference (Δ−
) was set to a value such that it decreased by 0.3% relative to silica. Further, the first clad diameter/core diameter ratio was set to 2.5.

After this vitrified core rod 8 was stretched to a diameter of 2011 m, soot was again deposited on the stretched rod by the VAD method, and the core rod was sintered and vitrified in a helium atmosphere to form a 5 in 2 glass layer 9 serving as a second cladding. Furthermore, stretching, external attachment, and sintering were performed to form a SiO2 glass layer, thereby producing a core rod 10 having a second cladding diameter/core diameter ratio of 11 (FIG. 1(C)).

After this core cladding 10 was stretched to a diameter of 30ai, both sides 11 of the second cladding 9 were mechanically ground in the axial direction. The grinding ratio (minor axis/long axis ratio) was set to 0.3 (Fig. 1(d)
)).

Thereafter, a 5iOi glass soot 13 for support is externally attached to the outer periphery of this three-layered ground core rod 12 (FIG. 1(e)), and this is sintered into glass. This process was repeated three times to finish the outer diameter to 30 nn.

In this way, the elliptical core 14 as shown in FIG.
．． A preform 17 consisting of an elliptical cladding 15 and a support 16 was formed. Here, SiO2 glass soot 1
During the sintering of Sample No. 3, a contraction force was applied to the core 6 and the cladding 7, causing them to become ovalized in the same direction.

Furthermore, this Glyform was heated and drawn to have an outer diameter of 125μ.
An elliptical core fiber of m was prepared. When this fiber was sampled over a length of 1000 m and its loss wavelength characteristics were measured, the results shown in FIG. 2 were obtained. The cutoff wavelength was 1.35 μm, the OH loss at a wavelength of 1.39 μm was 1.3 dB/1, the OH loss at a wavelength of 1.54 μm was 0.25 dB/K+e, and the extinction ratio was −31 dB.

Example 2 Core 6, first clad 7, second clad 9 (Δ-1.2
%, Δ-=0.3%), and the core rod 10 has a structure in which the first cladding diameter/core diameter ratio = 2.5 and the second cladding diameter/core diameter ratio = 7 (see Fig. 1 (C)). This was ground using the same machine as in Example 1 at a grinding ratio of 0.3. The grinding surface extended to the first cladding 7.

FIG. 3 shows the structure of this ground core rod 12, which consists of a core 6, a first clad 7, and a second clad 9.

Using this three-layered grinding rod 12, the same steps as in Example 1 were carried out to fabricate an elliptical core fiber. wavelength 1
．． The OH loss at 39 μm was 5 dB/1, which was larger than that in Example 1. OH loss at wavelength 1.54μm is 0.3
0dB/Akebono, extinction ratio -30dB (fiber length IKm)
Met.

[Effects of the Invention] As described above, according to the present invention, the grinding core rod has a three-layer structure and the outermost layer is provided with a 5in2 glass layer, thereby suppressing the incorporation of H20 and H2 from the oxyhydrogen flame into the grinding core rod. As a result, an elliptical core fiber with low loss in the 1.3 to 1.5 μm band can be obtained.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing the method for manufacturing an elliptical core fiber according to an embodiment of the present invention, FIG. 2 is a loss wavelength characteristic diagram of the elliptical core fiber produced in Example 1, and FIG. FIG. 3 is a cross-sectional view of the ground core rod used. In the figure, 1 is a core burner, 2 is a clad burner, 3 is a core part, 4 is a clad part, 5 is a porous base material, 6 is a core, 7 is a first clad, 8 is a core rod, and 9 is a second clad. A SiO2 glass layer, 10 a core rod, 11 a ground portion, 12 a ground core rod, 13 a SiO2 glass soot, 14 an elliptical core, 15 an elliptical cladding, 16 a support, and 17 a preform.

Claims (1)

[Claims] 1. After grinding both sides of the core rod consisting of the core and cladding in the axial direction, fine glass particles are deposited on the outer periphery of the ground core rod, and this is sintered to form a preform. In the method for manufacturing a polarization maintaining optical fiber by heating drawing, the structure of the ground core rod includes, from the center, a core glass layer containing GeO_2, a first cladding glass layer containing F, and a second cladding glass layer of pure SiO_2. A method for manufacturing an elliptical core polarization maintaining optical fiber characterized by comprising three layers.