JPS6131328A - Optical fiber - Google Patents

Abstract

PURPOSE:To provide an optical fiber with which an increase in the loss of a long wavelength is small at a low cost by using a core consisting of SiO2-GeO2-F and a clad whose inside layer part consists of SiO2-F and whose outside layer part consists of SiO2-B2O3 to constitute the optical fiber. CONSTITUTION:The clad 3 consisting of the inside layer part 3a which consists of SiO2-F contg. F at 0.05-1mol% concn. and is in proximity to the core 2 consisting of SiO2-GeO2-F contg. GeO2 at 3-20mol% concn. and F at 0.05-1mol% and the outside layer part 3b which contains B2O3 at 0.05-6mol% concn. is provided to the outside periphery of the core 2. The effect of preventing the formation of an OH group near the core owing to the hydrogen diffusion from the outside of the optical fiber is thus made large and the optical fiber which is free from the influence of the formation of the OH group by hydrogen for a long period of time is obtd. without the influence of the IR absorption loss at >=1.3mum wavelength and with the small transmission loss.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates primarily to optical fibers used for communication transmission.

(Prior Art) Gl-type optical fibers produced by the VAD method generally have a core made of silica-based porous glass and a cladding made of a natural quartz tube (jacket pipe).

The optical fiber was heated at 200°C in a 10oz hydrogen stream.
When heated for 4 hours, an increase in loss occurs at a wavelength of 1.4μ, and from this result, it is predicted that a non-negligible increase in long wavelength loss will occur when the optical fiber is put into practical use.

To improve this, it has already been proposed to dope the core with fluorine or to use a synthetic quartz tube instead of the natural quartz tube for the cladding.

Although the method of doping the core with fluorine does not pose a problem in terms of cost, it cannot significantly improve the increase in long wavelength loss.
On the other hand, the method of using synthetic quartz tubes improves the transmission characteristics sufficiently, but the material cost is as high as 300 yen/g, and this increased cost is actually a bottleneck in terms of availability.

(Problems to be Solved by the Invention) The present invention not only dopes the core of the optical fiber with fluorine, but also has a great effect of inhibiting the formation of OH group shadows near the core due to hydrogen diffusion from outside the optical fiber. Wavelength 1.3
As a glass for cladding, SiO2- We discovered that 8203 glass was effective, and by using this glass as part of the cladding and appropriately setting each part of the optical fiber, we attempted to provide a low-cost optical fiber with little increase in long-wavelength loss. It is something to do.

(Means for solving the problem) The optical fiber of the present invention has a core composition of S+02-GeO2-
F, and the composition of the cladding inner layer near the core is S.
+02-F, the cladding outer layer is made of SiO2-B203.

(Function) In the case of the optical fiber of the present invention, the following can be estimated.

Generally, the increase in long wavelength loss in optical fibers is caused by the glass portion (
This occurs when hydrogen molecules generated around the optical core diffuse into the cladding and core, which dissolve or react with structural defects in the glass to generate 5i-OH and Ge-OH.

It is said that 5i-OH in the above has an absorption peak of 1.39 μm, and Ge-OH has an absorption peak of 1.411 L fat.

In the case of the optical fiber according to the present invention, since both the core and the inner layer of the cladding contain fluorine, the concentration of structural defects that cause an increase in long wavelength loss is reduced by the following reaction.

(In the above formula, ○ indicates a structural defect.) Next, regarding the cladding made of natural quartz, it has a high concentration of structural defects as described above, and active species when hydrogen molecules pass through the natural quartz, such as H + or ) I - Since there are many occurrences of
Decomposition energy is given to hydrogen molecules to diffuse them into the core, easily producing 5i-OH and Ge-OH.

In the case of the optical fiber according to the present invention, since the inner layer of the cladding surrounding the outer periphery of the core is made of synthetic quartz, the above-mentioned active species are hardly generated, and therefore the increase in long wavelength loss is reduced.

Furthermore, since the outer layer of the cladding is not made of natural quartz but made of Vycor glass (S102-B203), this can also contribute to suppressing the increase in long wavelength loss.

Regarding cost reduction, although the present invention uses expensive synthetic quartz (approximately 300 yen/g) for the cladding, this is limited to the inner layer only, and the outer layer of the cladding is made of inexpensive equal glass (approximately 42 yen/g). g), the cost of the optical fiber can be reduced compared to the case where the entire cladding is made of synthetic quartz.

(Example) Examples of the optical fiber according to the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of an optical fiber 1 according to the present invention, and FIG. 2 shows a refractive index distribution (Gl type) of the optical fiber 1, which is composed of a core 2 and a cladding 3.
The cladding 3 is composed of an inner layer portion 3a and an outer layer portion 3b.

The composition of the core 2 is 5iO2-GeO2-F, the composition of the inner cladding layer 3a is S+02-F, and the composition of the outer cladding layer 3b is SiO2-8203. Furthermore core 2
The G e 02 concentration in the intestine oH is 3 to 20 oH, and the B2 o3 concentration in the cladding outer layer 3b is 0.05 to e peng o1
%, the F concentration in the inner layer 3a of the rad is 0.0
5 to 1 mol$, and these respective compositional concentrations were set in order to obtain the refractive index distribution illustrated in FIG.

In this case, the F concentration is 0.0 to improve the increase in long wavelength loss.
5 mol $ or more is required, but F exceeding 1 mol $
Doping F1a does not increase its effect, therefore F1a
The degree is (7) m'J O,05mol$"ls
It is reasonable to set it within the range of +oH(7).

In the case of the core 2, it contains F which has the effect of lowering the refractive index, but since this core contains GeO2 within the above range, a predetermined high refractive index for the cladding 3 can be obtained.

Even in the inner layer part 3a of the cladding 3, the refractive index decreases by that amount due to the inclusion of F, but the B in the outer layer part 3b decreases by that amount.
2O3 also has a refractive index lowering effect, and since it is contained within the above range, the refractive indexes of the inner layer portion 3a and the outer layer portion 3b almost match.

In Fig. 2, the dotted line is the refractive index of quartz, Δ is the relative refractive index difference of the optical fiber 1, Δ+ is the relative refractive index of the core 2, and Δ- is the relative refractive index of the inner layer 3a and outer layer 3b in the cladding 3. To give an example of these specific values, Δ is 1.8
．． Δ+ is 1.53$, and core- is 0.07%.

Note that it is more desirable that the Δ− of the inner layer portion 3a and the outer layer portion 3b match each other;
b does not exceed the refractive index of the outermost periphery of the core, and the difference is -0,0
If it is within 4%, you will be satisfied.

Next, a specific example of the optical fiber 1 of the present invention will be explained together with its manufacturing method.

When creating a porous base material with a Gl-type profile by the VAD method, a quadruple tube burner in which the first flow path (center flow path) to the fourth flow path (outermost circumferential flow path) are formed concentrically is used. , 02 of 7.5 AC l/inch is placed in the fourth wave path, Ar of S l/■in is placed in the third flow path, and 0.2 of 5ICI4 of 40°C is placed in the second flow path. Frit gas supported by At at IL/min and H2 in one layer of 3IL, and GeCl4 at 35° C. in the first flow path. l l
/sin of the doped raw material gas supported by At and 0.5
A predetermined porous base material was produced by a flame hydrolysis reaction of each of these gases by supplying Il/in H2.

When this porous base material is placed in an electric furnace at 1450°C and heat treated to make it transparent vitrified, there is a
5fL/riinノHe, IJIノminノ)le
Thionyl chloride supported by bubbling with 0.44
1/in of SF6 was supplied, and the porous base material inserted into the furnace tube was pulled up at a pulling speed of 180 m layers/Hr, and the extracted base material was turned into transparent vitrification to form a preform rod.

The preform rod obtained in this way has a core uniformly doped with fluorine, and a 125 gm layer on the outer periphery that will become the inner cladding layer. It is doped with fluorine so that Δ- matches that of the Vycor glass tube.

Thereafter, a Vycor glass tube, which will become the outer layer of the cladding, is jacketed around the outer periphery of the preform rod, and this is spun using a known spinning means to create a material with a core diameter/cladding diameter.
An 80/125 (lumen) optical fiber was prepared, and a silicone resin coating layer with an outer diameter (diameter > 380 g) was formed on the outer periphery of the optical fiber.

This optical fiber had a Gl type refractive index distribution shown in FIG. 2 above.

Next, a nylon coating was applied to the outer periphery of the above-mentioned coated optical fiber, and the results of a heating test will be described.

In an optical fiber l having a Gl type refractive index distribution, when the core 2 is doped with fluorine, the long wavelength loss increases (absorption peak 1.
4 JL tumor) was able to be reduced from 33 dB/k11 to 11 dB/, approximately 173 as shown in ■.

By forming the Crasito inner layer portion 3a around the outer periphery of the core 2, the increase in long wavelength loss (absorption peak: 1.41 Lm2) in the above heating test could be reduced to about 176.

Furthermore, since the cladding outer layer 3b was formed from a Vycor glass tube instead of natural quartz, the increase in long wavelength loss (absorption peak 1.4p) in the heating test was reduced to about 1/2.

As described above, the nylon-coated optical fiber according to the specific example of the present invention has taken various measures against long wavelengths, so that the long wavelength loss is extremely small as shown in Fig. 883.

In addition, in Comparative Example 1 in FIG. 3, the core is made of synthetic quartz (Gl type) made by VAD method, the cladding is made of natural quartz, the coating layer is made of silicone resin, and the covering layer is made of nylon. The same procedure as Comparative Example 1 was carried out except that the glass was made of Vycor glass.

These Comparative Examples 1 and 2 have extremely large increases in long wavelength loss in the heating test as compared to the specific examples of the present invention.

(Effects of the Invention) As explained above, in the optical fiber according to the present invention, the core composition may be S+02-GeO2-F, the composition of the inner cladding layer near the core may be 5102-F, and the composition of the outer cladding layer may be SiO2-8203. Therefore, it is possible to provide an optical fiber with a small increase in long-wavelength loss and at a low cost.

[Brief explanation of drawings]

1 and 2 are cross-sectional views and refractive index distribution diagrams of the optical fiber according to the present invention, and FIG. 3 is a diagram showing the long wavelength characteristics of the optical fiber of the present invention together with comparative examples thereof. l ・Optical fiber 2...Core 3...-Clad 3a...Inner layer of cladding 3be1111 Outer layer of cladding Patent attorney Yoshio Saito No. f Figure t12 Figure 3r:l
:I

Claims (5)

[Claims] (1) The composition of the core is SiO_2-GeO_2-F, and the composition of the inner layer of the cladding close to the core is SiO_2
-F, an optical fiber characterized in that the outer cladding layer portion is made of SiO_2-B_2O_3. (2) The optical fiber according to claim 1, wherein the core has a GeO_2 concentration of 3 to 20 mol%. (3) F concentration in core and cladding inner layer part is 0.05 to 1m
The optical fiber according to any one of claims 1 and 2, which is ol%. (4) B_2O_3 concentration in the outer cladding layer is 0.05~
6 mol% of the optical fiber according to claim 1. (5) The relative refractive index of the inner layer and outer layer in the cladding is
The optical fiber according to claim 1, wherein the relative refractive index does not exceed the relative refractive index of the outermost peripheral portion of the core and matches each other within a difference of -0.04%.