JPS6050502A - Optical fiber - Google Patents

Abstract

PURPOSE:To prevent diffusion and attack of H2 and to obtain stable light transmission characteristics for a long term by providing the outside of light transmitting part of a core and a clad with an F-contg. quartz glass layer for preventing diffusion of H2 from outside and providing its inside with an F-not contg. quartz glass layer. CONSTITUTION:Quartz glass layers 4.4A.4B contg. F for preventing diffusion of H2 from the outside are provided on the outside of the part of a core 1 and a clad 2, etc. for transmitting light, and pure quartz glass layers 3.3A.3B not contg. F are formed on the inside of said layers 4.4A.4B. The use of said F- contg. layers prevents H2 generated by heat, UV rays, radiation, or the like and water vapor from diffusion to the light transmission part and attack and deterioration of it. The H2 diffusion prevention effect is made higher the thicker the layer 4.4A.4B becomes, and the layer 3.3A.3B made of pure quartz glass serves for enhancing said effect. As a result, the obtained optical fiber is not attacked by H2 and can maintain transmission characteristics stable for a long term.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical fiber with stable optical transmission characteristics over a long period of time.
There are many things related to optical fibers that are advantageous for use in optical communications in the long wavelength range around μm.

[Prior art]

Although there are various types of optical fibers, silica-based optical fibers are widely used as optical communication lines because of their low loss. The silica optical fiber has a wavelength of 0.
85/jm? is the loss power 2,4 dB/km.

0.6dB/km at 1.30/jm, 1.55μm
Since it has an extremely low loss of 0.4 dB/km, it is ideal as a communication channel. Another advantage of Shifuliang optical fiber is that it has high environmental resistance both mechanically and in terms of transmission characteristics, and is stable over a long period of time. For example, it is said that their properties G hardly deteriorate even when exposed to water or moist heat. This is because the surface of quartz glass has strong corrosion resistance against water and chemicals, and the diffusion of water within the quartz glass is extremely small.

As described above, quartz fiber optical fiber has been believed to have high environmental resistance, but according to the recent investigation by #DI customers, quartz fiber optical fiber has higher transmission characteristics than 142VC. It was found that it deteriorated. It has been speculated to some extent from the literature that H, diffuses quickly in silica glass and that the diffused H2 forms 〒OH groups in the silica glass. One point was that it was invaded. The water resistance of silica-based optical fibers has not been sufficiently studied, but H2
They were completely defenseless against it. The reason is,
This is probably because it was thought that although there is a lot of water around optical fibers, there is almost no water present.

However, it has become clear that the adherends of optical fibers may deteriorate due to heat, ultraviolet rays, radiation, water vapor, etc. and generate H2, and that H2 exists around optical fibers.

[Purpose of the invention]

Under these circumstances, it is important to create an environment that prevents the generation of H2, but the most important thing is to create a light source that will not invade H2 even if it exists. The present invention has been developed from the perspective of It is.

[Structure of the invention]

In order to achieve the above-mentioned object, the present invention provides an external T to the outside of the core, cladding, and other parts of the optical fiber through which light propagates.
The present invention is characterized in that a fluorine-containing quartz glass layer is provided to prevent the diffusion of -T, and the inside of this fluorine-containing quartz glass layer is constructed with a fluorine-free quartz glass layer.

An example of the configuration of an uninvented optical fiber (force) is shown in the first example.
As shown in Figures 4 to 4. The optical fiber shown in Fig. 1 has a
A fluorine-containing quartz glass layer 4 for preventing H2 diffusion is provided via an intermediate glass layer 3 that does not contain fluorine. The optical fiber shown in FIG. 2 has a corrosion-resistant glass layer 5 provided as the outermost layer on the outside of the optical fiber shown in FIG. 1 to increase water resistance. The optical fiber in FIG. 3 has a first fluorine-containing quartz glass layer 4 disposed outside the core 1 and the cladding 2 via a first intermediate glass layer 3AF that does not contain fluorine.
A, and a second intermediate glass layer 3B that does not contain glass on the outside thereof? i: A second fluorine-containing quartz glass layer 4B is provided through the optical fiber ◇The optical fiber shown in FIG. The provided core 1 and cladding 2 are the portions through which light propagates, and are the portions that have the greatest influence on the transmission characteristics VC.

As in the conventional case, this part may be made of doped quartz glass or pure silica glass, and the refractive index distribution may be SI type, GI type, or the like. The usual dopant can be used, but Ge
0z, A720s 72 are the best ↑, P, 0. When using Vc (or o, 7 to reduce the occurrence of defects)
It is preferable to set it to 4@z or less.

The fluorine-containing silica glass layers 4, 4A, and 4B prevent H existing outside the optical fiber from diffusing into the light propagation portion. Fluorine-doped silica glass has T-stone properties that trap H7 well diffused from the outside. This fluorine-containing quartz glass layer may be doped with only fluorine, or may be doped with fluorine and G
e, P, B.

Oxidized qyJ such as T1 with 1 or more yuzu! It is also possible to compose ↑ the one that has been expanded. In short, it is sufficient to contain 8n of fluorine as a dopant. The higher the fluorine content and the thicker the fluorine-containing quartz glass layer, the more
■1. Highly effective in preventing the spread of.

The intermediate glass layer 3 contains fluorine! l: No quartz glass, preferably pure quartz glass. This intermediate glass layer is effective for increasing the H2 diffusion prevention effect.

Optical fibers having fluorine-doped glass layers have been known for some time. For example, as shown in FIG. 5, there is an optical fiber consisting of a core 1 of pure silica glass and a cladding 2 of fluorine-doped silica glass, or as shown in FIG. There is an optical fiber having a cladding 2 of monolithic silica glass and an outermost layer 5 of pure silica glass.

However, as will be shown later as a comparative example, such optical fibers do not necessarily have good hydrogen resistance. Figure 1r (as shown in Figure 3, fluorine-containing quartz glass 4.4A, 4B)
Inside [7 Intermediate glass layer not containing element 3.3A, 3
B), or if the fluorine-containing quartz glass layer 4 has a Clara += 2 V immediately inside the fluorine-containing quartz glass layer 4 as shown in FIG. Effective in improving hydrogen resistance.

The corrosion-resistant glass layer 5 is provided in order to prevent the fluorine-containing quartz glass layer 4 from being corroded by water. Although pure silica glass is suitable for this nK, doped quartz glass having corrosion resistance can also be used. This corrosion-resistant glass layer has a sufficient thickness of 5 to 6 μm.

However, ↑, the layers other than the core, that is, the cladding layer 2, the intermediate glass layers 3.3A, 3B, and the silica glass containing 7 m4.
If there is a layer with a higher refractive index than other layers among the layers 4A, 4B and the corrosion-resistant glass layer 5, there is a possibility that light will propagate therein and generate an abnormal signal. For this reason, it is preferable that the layers other than the core have substantially the same refraction. For example, quartz glass I
Since doping with C7 glass lowers the refractive index, when pure silica glass is used as the intermediate glass layer, the refractive index of the intermediate glass layer becomes relatively high. In such a case, the fluorine-containing quartz glass layer should be co-doped with a dopant other than fluorine that increases the refractive index, such as Ge Ot, so that the refractive index of the fluorine-containing quartz glass layer is the same as that of the intermediate glass layer. . Furthermore, even if there is a layer other than the core and cladding that has a higher refractive index than the others, if the light transmittance of that layer is low (if the loss is large), there is no problem of abnormal signal generation.

In addition, it is preferable in terms of transmission characteristics that the quartz glass layer 4.4A containing 7 glass be provided too close to the core 2, that is, that the cladding 2 and the intermediate glass layer 3.3A be too thin. The appropriate position is approximately 6 times or more the diameter of the single mode optical fiber Teha core diameter, and for multimode PSI type optical fiber, the cladding thickness is 15μ.
In the case of a multimode GI type optical fiber, it is the outside of the diameter with a cladding thickness of 10 μm or more. Preferably, the anti-diffusion layer is a single mode optical fiber fiber r-r.
On the outside of the diameter of 6 times the diameter + 1oμm thickness, the diameter of 1,000 mm + 2
It is preferable that the outer diameter of 0 μm thick is about 1 M−r.

Note that the corrosion properties and stiffness properties of H and rtc are stronger in multimode optical fibers than in single mode optical fibers, and stronger in doped silica core optical fibers than in pure silica core optical fibers, so the effects of the present invention are is remarkable in a multimode optical fiber having a core made of doped silica glass.

〔Example〕

What is the hydrogen resistance test in the following examples and comparative examples? i: The specimen was held at 200° C. for 4 hours in a hydrogen atmosphere of 1 atm, and the loss increase 2 that occurred at this time was investigated.

It is assumed that hydrogen resistance is poor when the increase in loss is large.

Further, Δn is the refractive index difference ↑ with respect to pure silica glass.

Example 1 Inner surface of quartz tube 1cP205 F 5i02 (Δn=0
%, P2O, content 0.5%) and GeO2P 20B S i 02 (Δn=1%
A core glass film of GI (containing 20 g of P and 460.5 insects N%) was formed using the MCVD method, and this was flapped to obtain a glass pellet. 5iO2-GeOz soot is formed on this,
After heating at 1000°C for 16 hours in a 02 air stream, 145
The temperature was raised to 0° C., and transparent vitrification was performed in an air flow of SFa +5OC1z +He. The obtained glass layer is Ge0t
It was a F5ift (Δn = 0%, Ge0t content 2% by weight) glass. The glass base material obtained in this way is
Outer diameter 20mm5 Intermediate glass layer outer diameter L 501111,
The outer diameter of the cladding was 9.6mm5 and the core diameter was 8mm1n.

This was drawn into a fiber with an outer diameter of 125 μm and coated with ultraviolet curing acrylate resin. This fiber has a core diameter of 50 μm, a cladding outer diameter of 60 μm, and an intermediate glass layer outer diameter of 94 μm, and is of the first type. The transmission loss number of this optical fiber was 1.31 b km. The results of the hydrogen resistance test are shown in Table 1.
Yes, it was very good.

Example 2 Quartz tube inner surface 1cP20s F 5iO2 (Δn = Q
%, P, a glass film for diffusion prevention with a content of 1 h (%), S i 02 Bt Os Ge01 (Δn=o
%, G e 02 content 2 times 1%) glass film for intermediate layer, P2O5F-8in2 (Δn = 0%, P2O content 0.5% by weight) glass film for cladding, Geo,
A GI type cocoa glass film of pm 05S i 02 (Δn=1%, P, O content: 0.5% by weight) was formed, and the film was collapsed to obtain a glass rod. The outer periphery was polished to an outer diameter of 20 mm and a fluorine-doped glass layer with an outer diameter of 1
9mm5 Intermediate glass layer outer diameter 15mm5 Cladding outside d9.
A glass preform having a diameter of 6 mm and a core diameter of 81 ml was obtained. This fiber was drawn into a fiber with an outer diameter of 125 μm, and coated with ultraviolet curing acrylate resin. This fiber has a core diameter of 50 μm
It is of the type shown in FIG. 2, with one cladding diameter of 60 μm, one intermediate glass layer outer diameter of 94 μm, and one fluorine-doped quartz glass layer outer diameter of 119 μm. The transmission loss of this optical fiber is 1.3μm
at 0.6 dB/, , 1.55 pm -ts
The hydrogen resistance was good as shown in Table 1.

Example 3 A soot consisting of a core and a cladding was synthesized by the VAD method, heated to 900°C, dehydrated in a He 12 atmosphere, and then heated in a dish at 1100°C for 5 hours in an 02 stream.
The glass rod (core Gf Ge0t Stow TE Δn=
1%, GI type, cladding is 5in2)f, GeO on the inner surface
2P2O11-F 5j02 (Δn = Q%, 08
A glass film of m2@prevalence 1%, P2O, content 1%) was inserted into a quartz tube attached internally by the MCVD method, collapsed, and the outer surface was polished to obtain a glass base material. The outer diameter of this base material is 25 mm, and the outer diameter of the silica glass layer containing 2411
The cladding outer diameter of 1m% pure silica glass was 19mm, and the core diameter was 10111111. This was drawn into a fiber with an outer diameter of 12,577 m, and coated with an ultraviolet curing acrylate resin. This optical fiber has a core diameter of 50 μm, a cladding outer diameter of 95 μm (this cladding is thick 5ift, so there is no intermediate glass layer), and a fluorine-containing quartz glass layer outer diameter of 12 μm.
0pm, type shown in Figure 4 (with outermost layer)
. The transmission loss number of this optical fiber is 11.3 pmM O,
6dB/km, 0.5dB/km at 1.55 prn
As shown in Table 1, the hydrogen resistance was good.

Example 4 7-stone glass layer Gem2-P in Example 3
20a F-8iOz instead of B203 Ge02F
Sin, (Δn=o%, B2us content 0.5
(Ge 02 content: 1% by weight), the hydrogen resistance was 1 as shown in Table 1.

Example 5 Fluorine-containing quartz glass layer Ge02P2 in Example 3
Ti1t F 5i0 instead of 011 F 5ift
Example 6 Fluorine-containing quartz glass layer Ge02- in Example 3 P
, 0a-F-8102 instead of G e 02 F −
When S i 02 (Δn=0%, G e O2 content 1% by weight) was used, the hydrogen resistance was t as shown in Table 1.

Example 7 GeO2S i OH (Δn=1.0
%):17 and a SiO2 cladding was synthesized, heat treated at 900°C for 6 hours in a 02 air stream, and then transparently vitrified in an atmosphere of He+02+SFa at 1400°C. A fused silica tube was heat-noted on this, S 10
-T e SFa +Ot to make the glass transparent, and a rough fused silica tube was coated. This base material is outside (f
i 25 mms fluorine-containing quartz glass layer (Ge02F
5ift, Δn-〇%, Ge 02 content 2jusha%)
Outer diameter of 24mm5 Outer diameter of intermediate glass layer (5ift)2
0 mm% cladding (8402-F, Δn-%,
15%) outer diameter 14mmq F (core 0t F 5i
ft, Δn=0.85%) and had a diameter of iomm. This 7"L was drawn into a fiber with an outer diameter of 125 μm and coated with an ultraviolet curing acrylate resin. This optical fiber had a core diameter of 5θ, a cladding diameter of 70 μm, an intermediate glass layer outer diameter of 1
00 μm1 The outer diameter of the fluorine-containing quartz glass layer is 120 μm, and it is of the type shown in FIG. The transmission loss of this optical fiber is 0.5 dB/km at 1.3 μm.

1.55/7rr1 is 0-4dB/km, and the first
As shown in the table, hydrogen resistance was good.

The 02 gas used in the above example was heated to 900°C to remove hydrogen compound impurities in order to reduce the loss of the optical fiber.
After passing through a platinum catalyst, it was purified through a molecular sieve and a liquid nitrogen cold trap.

Comparative Example 1 :)y of 5ift (Δn = 0%, SI type) and F-8iO.

An optical fiber of the type shown in FIG. 5 (with ultraviolet curable acrylate resin Ml) having a cladding of (Δn − -o, s%) was prepared. The core diameter is 50 μm and the outer diameter of one cladding is 125/7 m. The hydrogen resistance of this optical fiber was not as good as shown in Table 1.

Comparative Example 2 SiOz (Δn = 01, SIm))7 and F-8
iO.

The optical fiber of the type shown in Fig. 6 (covered with UV-curable acrylate resin) consists of a cladding of (Δn - 0, 8%) and an outermost layer of Sin. i: Created. Core diameter 50 μm 1 Clad outer diameter 120 pm, Fiber outer diameter 1
There are 25 ρt. The hydrogen resistance of this optical fiber was not as good as shown in Table 1.

Table 1 [Effects of the Invention] From the above explanation, it is clear that according to the present invention, a fluorine-containing silica glass layer is provided outside the light propagation part of the optical fiber, By constructing the quartz glass layer that does not contain 2, the light propagating portion 1c H2 is prevented from being diffused, and an optical fiber with stable transmission characteristics over a long period of time can be obtained.

[Brief explanation of drawings]

Figures 1m to 4 are sectional views showing examples of the structure of the optical fiber of the present invention, and Figures 5 and 6 are T sectional views showing conventional optical fibers, respectively. I...Core, 2...Clad, 3...
...-intermediate glass layer, 4...fluorine-containing quartz glass layer. Figure 1 Figure 4 Figure 2 Figure 5 Figure 3 Figure 6

Claims (2)

[Claims] (1) A fluorine-containing quartz glass layer is provided outside the core, cladding, and other parts where light propagates to prevent H2 from diffusing from the outside, and a fluorine-free quartz glass layer is placed inside this fluorine-containing quartz glass layer. An optical fiber characterized by comprising: (2) An optical fiber as described in item 1 of @FIM as requested by special ifl:111111, which is made of pure silica glass with a fluorine-free silica glass layer.