JPS63313105A - Image fiber - Google Patents

Abstract

PURPOSE:To obtain an image fiber having a low transmission loss by incorporating TiO2 as a dopant into glass to constitute cores and incorporating >=1,000ppm hydroxyl group therein. CONSTITUTION:A clad 1 consists of pure silica and the many cores 2... are dispersed in the clad 1. Each core is formed to about 2-4mum diameter. A jacket 3 consisting of the pure silica is provided around the clad 1 and further, a protective film 4 consisting of a modified silicone resin or the like is provided on the outside circumference thereof. The cores 2 consist of the silica glass which is added with at least TiO2 as the dopant and in which the OH group is incorporated at >=1,000ppm by weight, more preferably SiO2, TiO2, GeO2, and the melt viscosity thereof has the value of 80-120% of the melt viscosity of the pure silica. The silica glass in the range of TiO2:GeO2: SiO2=5-20:10-20:60-85 by molar ratio is thereby obtd. and the melt viscosity having the value of 80-120% of the melt viscosity of the silica is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a long image fiber mainly used for industrial purposes.

[Prior art and its problems]

Recently, there has been a demand for image fibers to be smaller in diameter and have more pixels. In order to meet these demands, the core is made of silica doped with a large amount of GeO2 to increase its refractive index, and the cladding is made of silica doped with a large amount of fluorine to lower its refractive index. Increase the relative refractive index difference to about 4%, and increase the core diameter (pixel diameter) to 3μ
It is known that the diameter is as thin as m1fj degrees.

However, in this image fiber AP1, air bubbles are inevitably generated during manufacturing, and these bubbles remain in the manufactured image fiber, resulting in a problem of low productivity.

This is because both the core glass and the cladding glass are doped with a large amount of GeO2 or fluorine, which lowers the melt viscosity of the silica dupe that becomes the jacket during melt spinning. This is because a large difference easily occurs between the melt viscosity and the melt viscosity.

As a solution to this inconvenience, TL is added to the core.
Image fibers using silica doped with O2 and GeO2 and pure silica for the cladding have been considered. This is because when TL O2 as a dopant increases the refractive index, it also increases Wj@viscosity, so it can compensate for the decrease in melt viscosity due to large A doping of GeO2, and the core This is because it can have a high refractive index.

However, with this image fiber, due to the addition of LO2, the TL' is extremely large (several hundred dB/8 JR).
There is a problem in that transmission loss inevitably occurs, making it unsuitable for long image fibers.

(Means for Solving the Problems) In the present invention, at least TLO
The solution was to contain Z and hydroxyl groups of 1000 ppa+ or more. By introducing this hydroxyl group, an increase in transmission loss due to the inclusion of TLO2 is suppressed, and a long image fiber can be obtained.

The drawing shows an example of the image fiber of the present invention, and reference numeral 1 in the drawing indicates a cladding. This cladding 1 is made of pure silica, and a large number of cores 2... are dispersed within this cladding 1. Core 2 constitutes the pixels of this image fiber, and its diameter is approximately 2 to 2.
The thickness is approximately 4 μm. Additionally, a jacket 3 made of pure silica is provided around the cladding 1.
A protective coating 4 made of modified silicone resin, ultraviolet curing resin, or the like is provided around the outer periphery of this jacket 3.

In the core 2, at least TL O2 is added as a dopant, and the water M group (011 group) has a weight ratio T: 1100.
Silica glass containing 0pp or more, preferably 5iOz
, TLOz and σGe0z, and its melt viscosity is 80 to 120% that of pure silica (0,8-1,2
It is made of silica glass containing 1000 ppH or more of hydroxyl X^. To make the core 2 have a melt viscosity of 80 to 120% of that of silica, the molar ratio is TL-02:GeO2:5L02-
This is achieved by setting the ratio to be in the range of 5 to 20:10 to 20:60 to 85. In addition, since the glass having such a composition also has a high refractive index because TL O2 increases the refractive index of Ge02b, the relative refractive index difference with respect to silica can be increased to about 5%. On the other hand, the cladding 1 is made of pure silica as described above, and the difference in the northern v1 ratio between the core and the cladding is about 415%, so the diameter of the core 2 can be made as thin as about 2 μm as described above. Furthermore, since ]72 contains a hydroxyl group in multiple hl, T
The transmission loss of TL''' due to the addition of L02 is suppressed, and the increase in transmission loss is reduced.If the content h1 of the water N! group is less than 11000 pp, the effect of suppressing the increase in transmission loss is insufficient, It becomes impossible to use it for a long image fiber.The upper limit of the content 1 of hydroxyl 1j is T
From the point of view of suppressing the increase in transmission loss due to L'', there are no particular restrictions, but the absorption peak of water M11 such as 1 and 24μ skin becomes significantly large, and the base of the absorption peak extends into the visible region. The upper limit is about 50001) DI.

Manufacturing of such an image fiber is performed as follows. First, a preform consisting of a core part and a cladding part is produced. The creation of this Brynoom is by M
CV l) method, VAD method, etc. MCVL
) method, attach the silica tube that will become the cladding part to the glass mW, and place 5
Introducing frit gas such as LCIa, GeCfa, TLC14, high purity water (steam) and oxygen gas,
Heated by a traversing external heating source. At this time, a shielding gas of oxygen gas is flowed in order to prevent a reaction between the a-pure water and the metal halide glass raw material gas. As a result, after depositing the glass that will become the core on the inner wall surface of the silica tube, it is ignited (making it solid).
and use it as a preform. In addition, in the method based on the V A l) method, a multi-tube burner is equipped with the glass raw material gas, Pa
Cold gas and hydrogen gas are supplied, glass soot is generated in the flame, and glass soot is deposited on the tip of the starting bar. Next, this was placed in a sintering furnace and heated in a helium-high-purity water gas atmosphere to make it transparent and vitrified, and water II was introduced. After stretching this, a silica tube that would become the cladding part was inked. Blinohm and Zuru.

Such a preform is melt-spun and has a diameter of 150 to 20 mm.
Spelled out as 0μm plain fiber. This raw fiber is cut to a fixed length, and the fixed length fiber is aligned and housed in a silica tube that serves as a jacket, and melt-spun from one end to form a target image fiber.

During this production, the viscosity of the glass forming the core of the bluff 4-me is 80-120% of that of silica, which is close to that of silica. During rudding, only the core part does not decrease in viscosity and become soft, and no foaming phenomenon occurs. Also, Ba1f? Similarly, when the base fiber is housed in a silica tube serving as a jacket and spun into an image fiber, foaming does not occur because the viscosity of the base fiber is close to that of silica. Further, the cladding portion of the preform can be formed using a silica tube, and a thick cladding portion can be easily formed. Therefore, this image fiber! lj″m has high productivity and product yield.

〔Example〕

A glass serving as a core portion was formed by MCVD on the inner surface of a silica tube having an inner diameter of 20 txs and an outer diameter of 25 aw+ and serving as a cladding portion. The types and flow rates of frit gases and the like for forming glass in the core portion are as follows.

SL C14 100 cc/min Gc (J 4 30 cc/molecule LCj 450 CC/min High purity steam 5 to 10 cc/min Acid 9 600 cc/min The rotation speed of the silica duplex is 20 ram, and the external il
The traverse speed of the heat burner was set to 50 IH for 7 minutes, and after 100 traverses, the silica tube was ignited to make it into a Kotsu Plus, outer diameter 21 m, core part 1 yen 7, length 500.
A transparent preform of M was obtained.

This puri-nome was melt-spun at 2100°C, and the diameter was 150.
A μm plain fiber was obtained. The relative refractive index of this elementary fiber was 5%.

Next, this raw fiber was cut into a length of 200rWR, and this was made into a jacket with an outer diameter of 30III and an inner diameter of 2.
Arranged and housed in a 7 m silica tube, this was placed in a 21
An image fiber having an outer diameter of 0.3 mm was obtained by spinning at 00°C.

At this time, by changing the amount of high-purity water vapor supplied and changing the content of hydroxyl groups in the core glass, an image fiber of several seconds was fabricated, and water Il! The IJ relationship between the group-containing suspension and the transmission loss at 0.63 μm was determined.

The results are shown below.

Suspension containing 1 lN of water (pp■) Transmission loss (dB/floor) 300 2 QO Also, the number of bubbles in this image fiber is 1!
When observed, there were 1 to 2 pieces per 100 m in length. Furthermore, the diameter of the image 1A could be reduced to 2 μm.

On the other hand, in a conventional image fiber in which the core is made of GeOz-doped silica (relative refractive index difference +2.5%) and the cladding is made of fluorine-doped silica (relative refractive index difference -1.5%),
The number of bubbles per 100 m of length was 10 to 12@l. Furthermore, since the core/cladding ratio was 171 and the difference in analysis rate was 4%, the pixel diameter was limited to 33 μm.

(Effects of the Invention) As explained above, the image fiber of the present invention has
In the multi-core image fiber, the glass that forms the C1 core contains at least TLO2 as a dopant, and contains hydroxyl groups of 1000 pppH or more. The increase in transmission loss caused by TL"° can be prevented by introducing 1B of water, and by adding TL O2, the molten viscosity can be reduced by 1B.
The incidental inconvenience caused by preventing the generation of bubbles during manufacturing is eliminated in the first step, resulting in an image fiber with low transmission loss. For this reason, a long image fiber of, for example, 20 to 30 m is put into practical use. In addition, since the core can have a refractive index of 1, it is possible to make the diameter smaller and make it rainier.

[Brief explanation of the drawing]

The drawing is a schematic cross-sectional view showing an example of the image fiber of the present invention. 1...Clad, 2...Core.

Claims (1)

[Claims] In a multi-core image fiber made up of a large number of cores, the glass forming the core contains at least T as a dopant.
An image fiber containing iO_2 and 1000 ppm or more of hydroxyl groups.