JPS5858293B2 - Manufacturing method of optical fiber base material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A method of depositing a glass film on the inside of a quartz tube using a vapor phase chemical reaction method is well known as a method that can produce a uniform optical fiber with low loss.

In addition, as a method for producing a single mode fiber with low loss in the optical wavelength region of 1.1 μm or more using this method, pure SiO2 is deposited as a cladding layer on the inside of a quartz tube, and then a high refractive index material as a core layer is deposited on the inside of a quartz tube. Methods of forming SiO2 containing Ge, PI dopant agents are well known.

However, this method uses pure SiO as the cladding layer.
Since 2 is used, the glass synthesis temperature is as high as 1600° C., and the OH groups contained in the quartz tube thermally diffuse and mix into the synthetic glass, resulting in an increase in transmission loss.

In addition, due to the high synthesis temperature, it is difficult to deposit a large amount of glass film in a short time due to the generation of bubbles, etc., and it takes a long time to form a sufficiently thick cladding layer to prevent the diffusion and incorporation of OH groups. It has the disadvantage of lacking productivity.

The present invention eliminates such drawbacks and provides a method for manufacturing fibers particularly suitable for low-loss single-mode transmission with high productivity.

In the method of the present invention, first, an S t 02 glass film containing P2O5, which can be synthesized at a lower temperature than pure Si 02, is deposited inside the quartz tube in order to prevent the diffusion of OH groups from the quartz tube.

In a glass film with this composition, pure SiO2 can be formed without generating bubbles.
It is possible to synthesize a film 3 to 4 times thicker than a glass film.

Furthermore, inside it, the optical absorption is 5in2 containing P2O5.
After depositing a smaller pure SiO2 film as a cladding layer, a high refractive index SiO2 containing GeO2 etc. becomes the core layer.
Forms a film.

FIG. 1 shows a cross section of an optical fiber obtained by the method of the present invention.

14 is a jacket layer from a quartz tube which is the starting base material; 11
and 12 indicate the core and pure SiO2 cladding, and 13 is an OH group diffusion prevention layer from the quartz tube.

When this barrier layer 13 contains only P2O as a dopant, the refractive index is higher than that of the jacket layer 14 and the cladding layer 12, so light propagating through the barrier layer 13 and optical power leak from the core. In order to prevent this from occurring, it is desirable that the difference in refractive index between the 14th layer and the 13th layer be small.

We have experimentally found that by setting this refractive index difference to 1.5.times.10@-' or less, the above-mentioned disadvantages in transmission characteristics can be eliminated.

In addition, as the barrier layer 13, P2O3 and F (or B2
03), consider the bending characteristics of the optical fiber and
It is desirable to control the respective dopant concentrations so that the two layers have the same refractive index.

In a single mode fiber, the propagating optical power is in the core region 1
However, in the method of the present invention, a layer that prevents thermal diffusion of impurities (OH groups) from the quartz tube and a layer near the core where the optical power propagates are distributed. SiO containing P2O, which can separate the cladding layer and deposit a large amount of OH group diffusion barrier layer at low temperature in a short time.
The cladding region through which light propagates is a pure 5i02 layer with low intrinsic absorption of light.

As a result, the method of the present invention is similar to the conventional gas phase chemical reaction method (
It is possible to overcome the low productivity disadvantage of single mode fibers fabricated by internal soot coating.

Examples are shown below.

S on a commercially available quartz tube with an outer diameter of 20 mm and a length of 1200 mm.
1c14180CC/min +P QC132CC
/min.

02 gas was fed at 11/min and heated to 1500°C with an oxyhydrogen burner moving at 12 ClrL/min installed outside the quartz tube. Glass films were deposited 30 times.

Gas composition not containing POCl3 (SiC14180cc
An attempt was made to deposit a pure Si02 glass film using a similar method using 02 gas (11/min, 02 gas 11/m1n), but the heating temperature with the oxyhydrogen burner rose to 1600°C, and the thermal shrinkage deformation of the quartz tube was significant. As the deposition progressed and the number of depositions exceeded 10, minute bubbles remained in the deposited glass layer, making it impossible to continue the deposition.

Although it is possible to increase the number of times of deposition by reducing the amount of 5 IC 14 supplied to 600 C/min or less, the deposition time increases by more than three times.

After depositing 30 layers of 5iO2-P206 composition glass film according to the method of the present invention, an additional 5iC1440cC
/min.

A cladding layer (15 layers) having a pure SiO2 composition was formed by feeding 0.611/min of 0.02 gas and heating it to 1600°C.

After that, the raw material gas is S 1c1440 QC/mi
n *GeCl46CC/min, 0 gas 0.611
/min, and a high refractive index glass film having a composition of 5i02 GeO2 was deposited five times.

The composite tube of synthetic glass membrane and quartz tube is made solid by raising the heating temperature of the oxyhydrogen burner to 1900℃.
A rod having an outer diameter of about 11 mmψ was obtained.

Furthermore, the time required to produce the above-mentioned preform by the method of the present invention, even including the solidifying step, is reduced to about 1/3 compared to the time required to produce the preform by the conventional method.

In the preform of the present invention, a part of the cladding layer contains P2O.
Because of the glass layer containing 5, the glass viscosity of the entire preform is reduced, and the time required for solidification, which is viscosity-dependent, is reduced to approximately 1/2. In order to obtain the ratio, another quartz tube (OD 201
n11Lψ, jacketed with wall thickness 4 doors 0, finally 1
Finished as a 9mmψ preformed rod.

The refractive index difference between the core layer and the cladding layer was measured using an interference microscope and was found to be 3.6XIO-3.

By heating this preform in a resistance furnace, the outer diameter of
Spun into 25 μm fiber.

When the loss of this fiber was measured at an optical wavelength of 1.1 to 1.6 μm, a low loss value of 1.0 dB/Ax or less was obtained near 1.55 μm.

Light absorption due to OH groups is observed at a wavelength of 1.38 μm, but in the fiber produced by the method of the present invention, the absorption is 1.5 dB.
/Iar1 and about 11 compared to a conventional fiber whose cladding layer is made of only a pure SiO2 layer that does not contain P2O5.
It has decreased to 5 or less.

By the method of the present invention, a layer that prevents thermal diffusion of impurities (OH groups) from the quartz tube and a cladding layer near the core through which optical power propagates are separated, and a large amount of impurities (OH groups) can be produced in a short time at low temperature as an OH group diffusion barrier layer. This is the result of depositing a SiO2 glass film containing P2O, which can be deposited.

The reduction in optical absorption by the O group is useful for stably obtaining fiber loss with good repeatability at optical wavelengths of 1:3 μm and 1°55 μm used in optical fiber communications.

Fifteen single mode fibers were fabricated using the method of the present invention and the conventional method, and the loss value at a wavelength of 1.3 μm was measured. 2n in dB/, average value 0 in conventional method
．． It was 72 dB/f, with a standard deviation of about 0.48 dB/l.

On the other hand, when we fabricated a single-mode fiber in which the pure SiO2 layer also contained P2O, and compared it with the fiber fabricated using the method of the present invention, we found that the influence of the infrared absorption edge of P-0 coupling at a wavelength of 1.55 μm It was seen.

The fiber produced by the method of the present invention has an average loss of 0.29 dB at a wavelength of 1.55 μm, and a standard deviation of 0.29 dB.
09 dB/1cIn, compared to a single mode fiber containing P2O5 throughout the cladding layer with an average value of 0.38 dB/1a11 standard deviation of 0.14 dB.
/lan, and the transmission loss value increased.

As described above, a low loss single mode fiber can be manufactured with high productivity by the method disclosed in the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a fiber obtained by the method of the present invention. 11...Core layer, 12...Pure SiO2
Cladding layer, 13... Barrier layer, 14...
...(quartz tube) jacket layer.

Claims (1)

[Claims] 1 A silica glass layer containing P2O5 is deposited on the inside of a quartz tube using a vapor phase chemical reaction method, and a pure silica glass film is deposited on the inside as a cladding layer, which then becomes a core layer with a higher refractive index than the cladding layer. A method for producing an optical fiber base material, comprising depositing a glass film.