JPS605040A - Polarization keeping optical fiber - Google Patents

Abstract

PURPOSE:To improve the radiation resistance, production efficiency, etc. of a polarization keeping optical fiber composed of a core, a clad, an inner jacket and an outer jacket, by specifying the composition and refractive index of each layer to respective specific levels. CONSTITUTION:The core 41 is composed of a high-purity SiO2 containing <=5 mol% B2O3, and the clad 42 surrounding the core 41 is made of a glass composed mainly of SiO2 and containing fluorine. The refractive index of the clad 42 is made lower than that of the inner jacket 43. The inner jacket 43 surrounding the clad 42 and having elliptic cross-section is made of a glass composed mainly of SiO2 and containing total 5-20mol% of P2O5 and B2O3 wherein the molar ratio (B2O3/P2O5) is 1-2. The refractive index of the inner jacket 43 is made lower than that of the core 41. The inner jacket is further covered with an outer jacket to obtain the titled optical fiber.

Description

[Detailed description of the invention] [Background and purpose of the invention] The present invention relates to polarization maintaining optical fibers.

Various structures have already been proposed for polarization-maintaining optical fibers, but the structure shown in FIG. 1 is currently receiving the most praise.

This is an optical fiber with a four-layer structure: core 11° cladding 12, inner jacket 17°, outer jacket 14.
It has the following.

The core 11 is made of 5i02 glass containing GeO2;
The cladding 12 is made of high-purity SiO2, the inner jacket 1 is made of 8102 glass containing P20S and 8203, and the outer jacket 1 is made of 5102 glass.

Although this polarization-maintaining optical fiber has extremely excellent properties, it has some drawbacks in terms of radiation resistance.

Since J, which is included in the core, is greatly affected by radiation, it was considered that transmission loss would increase in an environment where there is a possibility of exposure to radiation.

Similar to Qe, P is a well-known dopant.
However, even when P20S is contained in place of Qe 02, transmission loss still increases due to radiation.

As a result of investigation conducted by the present inventors, it became clear that high-purity SiO2 or high-purity Si02 containing B203 exists as a material with excellent radiation resistance.

However, when such a material is used as the core, its refractive index distribution tends to be as shown in Fig. 3, and the optical
There was a drawback that the outer diameter of the ribs was small.

This is due to the fact that quartz glass is used for the outermost layer in practice, but there is a problem in that it is difficult to form a circular layer with a large thickness (11) in terms of manufacturing.

The present invention addresses this situation by providing a specific configuration of a polarization-maintaining optical fiber that has excellent radiation resistance and is easy to manufacture by keeping the thickness of the elliptical layer below a certain level while using silica glass as the outermost layer. The purpose is to provide.

[Summary of the Invention] The present invention comprises a core having a circular or elliptical cross section, a circular or elliptical cladding provided around the outer periphery, and an inner jacket having an elliptical cross section provided around the outer periphery. In this polarization maintaining optical fiber, the material and refractive index of each layer are finely defined.

The core is made of high-purity silica containing B2O3, the maximum amount of B203 contained in the core is 5 mol% or less, the cladding is made of high-purity silica containing fluorine, and the inner jacket is made of high-purity silica containing P20s. and B203, the total amount of P20s and B203 is 5 to 20 mol%, and the ratio of 8203 to P205 is 1.0 to 2.0 times in mol%, and the outer jacket 1- is made of high-purity silica or non-high-purity quartz glass.

Regarding the refractive index relationship, the refractive index of the core is 111,
Assuming that the refractive index of the cladding is n2, the refractive index of the inner jacket is n3, and the refractive index of the outer jacket is 114, the relationship is as follows: 04≧nl>n3>n2.

Note that the high-purity silica here does not substantially contain transition metals such as Fe, which have a negative effect on light transmission, and may contain a small amount of other impurities.

[Embodiments of the Invention] Specific aspects of the present invention (1'6) will be explained in detail based on Examples.

(Example 1) As shown in FIG. The outer shells 1 to 43 were made of high-purity silica containing 10 mol% of B203 and 8 mol% of P20S, and the outer shells 1 to 44 were composed of quartz glass that was not of high purity.

The production was carried out by the internal CVD method accompanied by reduced pressure as disclosed in the well-known Japanese Patent Application Laid-Open No. 56-125233.

As a result, the core/41 and cladding 42 maintained a circular cross section because of their high viscosity, and the inner jacket 43 had an elliptical cross section because of its low viscosity.

Moreover, the refractive index distribution became as shown in FIG.

This is due to the fact that fluorine has the property of being able to significantly lower the refractive index with a small amount.

Inner jacket 43 is B203 and 1〕20s is 18
Since it also contained mol%, the viscosity was low and it easily took on an elliptical shape, but the refractive index was between that of the core 41 and the cladding 42.

The cladding 42 in contact with the core 41 has an inner surface 11 on its outer periphery.
If the refractive index is lower than that of the jacket 43, the total thickness of the cladding 42 and the inner jackets 1 to 43 can be made thinner, and manufacturing is easy.

In other words, with the refractive index distribution as shown in Figure 3, equivalent characteristics
J If there is only one J, the cladding and inner jacket 1
It is extremely difficult in manufacturing to create a thin elliptical layer because the thickness of the metal layer must be increased.
It is 1.

<Example 2> As shown in FIG. 6, the core 61 was made of high purity silica containing 4 mol% of 8203, and the cladding 62 was made of high purity silica containing 3 mol% of fluorine and 5 mol% of B2O3. , inner jacks 1 to 63 contain 10 mol% of 8203, 1]2
The outer jacket 64 was made of high-purity silica containing 5 mol% of 05, and the outer jacket 64 was made of quartz glass (14) which was not high purity.

The production is carried out by a thickening CVD method and a rod-in y with reduced pressure as shown in the well-known Japanese Patent Application Laid-Open No. 57-196728.
- As a result of IC performed in combination with the Cope method, the viscosity was low as in Inner Jackera 1-631J Example 1, so the shape of the fai surface was elliptical. The cross-sectional shape of the shape
is.

The refractive index distribution of 7j1 was as shown in FIG.

In contrast to Example 1, since the core 61 contains 4 mol% of B203 and -C, the refractive index of the outer shell 1 is 1.
It is lower than the refractive index of ~64.

In the case of Example 2, the transmission loss increased slightly compared to the case of Example 1, but the inner digital
In addition to 63, since the core 61 is oval,
Superior polarization preservation of light.

The present invention is not limited to the above embodiments, and the amount of fluorine contained in the cladding may be such that the refractive index of the cladding is clearly lower than that of the inner jacket 1.
About 2 to 5 mol% is practical.

B2O3 and P20S contained in the inner jet 17 are added for the purpose of imparting strain (d), adjusting viscosity, and controlling the refractive index, and the total amount of 820s and P20S is 5 to 20 mol%. required.

This range is mainly limited from a manufacturing perspective, and B2
When the ratio of Oa and P20s is less than 5 mol %, the viscosity is relatively low and it is difficult to form the inner jacket into an elliptical shape.

The inner jacket 1 ~ plays an important role in preserving the polarization plane of light, and J3 is sufficiently (necessary to have a 6-circular ratio, so at least one of B203 and one 205 is used)
is required to be at least 5 mol%, preferably at least 10 mol%.

Also, the combination of B203 and P20s ii'l' Q or 20
If the mol% exceeds the
When manufacturing by a method such as that described in Japanese Patent No. 125233, there is a fundamental problem that the inner layer cannot be vapor-deposited due to low efficiency, and it is also difficult to control the refractive index.

Even when manufactured by other methods, cracks are likely to occur as a result of a large content of 8203, resulting in low reliability.

In addition, J3 [Puru B203
It is desirable that the ratio is in the range of 1.0 to 2.0 times that of P20S. i.e. 1.0 for P20S
If it is less than 1.0 times, it will not be possible to keep the refractive index clearly lower than that of the core and outer jacket.
It needs to be at least twice as large.

If the ratio of B203 is much higher than P2O5 and is 2.0 times or more, the difference in coefficient of thermal expansion will be large compared to the outer jacket, etc., and the viscosity will not be low enough to cause cracks to occur. Undesirable.

For the outer jacket, commercially available industrial silica glass tubes can be used, but high-purity fXS is made of synthetic quartz.
Of course, iO2 may also be used.

Furthermore, the IC polarization-maintaining optical fiber obtained in this way is of course used for practical use by being concentrated with a predetermined resin composition, and the coating layer of the resin composition may be one layer or multiple layers. .

FIG. 8 shows a structure in which silicone resin 85 is coated and baked on the outer periphery of the polarization preserving optical fiber 8, and nylon 86 is extruded and deposited on the outside thereof.

[Effects of the Invention] If the polarization plane maintaining optical fiber as described above is used, the following significant effects can be achieved.

(1) Since the core is made of high-purity silica containing [3203] and substantially free of P20S and Qe 02, it has good radiation resistance.

(2) Since the cladding is made of high-purity silica containing F, it is easy to create a structure in which the inner jacket has a high viscosity and a low refractive index.

(3) The refractive index of the cladding is lower than that of the inner diagonal! Kome, Kurat and Inner Jackera 1~
The total thickness can be reduced, manufacturing is easy, and reproducibility is high.

(4,) 8203 and P2O contained in the inner jitoketsu 1
Since the opening of No. 5 is appropriately selected, it is easy to manufacture, including ensuring the ellipticity of the inside jacket No. 1 to 1, regardless of whether it is made using the internal angle method, outside angle method, or any other method. etc., and has high reliability and reproducibility.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional polarization-maintaining optical fiber, Figure 2 is a diagram showing the refractive index distribution of a conventional polarization-maintaining optical fiber, and Figure 3 is a comparative example for comparison with the present invention. FIGS. 4 and 6 are cross-sectional views showing two embodiments of the present invention, and FIGS. 5 and 7 are diagrams showing two embodiments of the present invention, respectively. FIG. 8 is a J-diagram showing the refractive index distribution in the example, and FIG.
It is an i-side view. 41.61: Core, 42,62: Clad, 43:. 63: Inner Ji 1? K1~. 44, 64: Outer jacket 1~. 1st Row 2nd Illustration 3 Illustration 4 Illustration M 5 Illustration 6 Illustration 7

Claims (1)

[Claims] A polarization preserving device comprising a core, a cladding provided on the outer periphery of the core, an inner jacket 1 with an elliptical cross section provided on the outer periphery, and an outer jacket 1 provided on the outer periphery. In the optical fiber, the core is B203
The core is made of high-purity SiO2 containing 1]
The mother of 203 is 5 mol% or less, and the cladding is 3i
The inner jacket is made of glass containing SiO2 as a main component and 4OJ containing fluorine, and the refractive index of the crat is -C lower than that of the inner jacket. Consisting of
The inner side 7 butt 20s and B203
The total amount of P2 OS is 5 to 20 mol%, and
The polarization preserving optical fiber 7I is characterized in that the ratio of B203 to the inner jacket is 1.0 to 2.0 times in mol%, and the refractive index of the inner jacket is lower than that of the core. .