JPH01148722A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To obtain the title preform capable of providing an optical fiber having excellent resistance to hydrogen and radiation, stability, and reliability by inserting a core rod into a clad pipe, fusing and integrating both materials while allowing a reducing gas to flow in the gap between them so as to eliminate a peroxy bonding at the interface. CONSTITUTION:The core rod 1 consisting of pure quartz glass, etc., is inserted into the clad pipe 2 consisting of F-added quartz glass, etc., 0.5-50vol.% reducing gas such as D2 and CO, based on the total gas amt., an inert gas such as N2, Ar, and He, and a dehydrating agent such as Cl2 and SOCl2, if necessary, are supplied in the gap between both materials at a rate of 10-500cc/min (however the content of D2 is controlled to 0.5-4.0vol.% to prevent explosion when Cl2 is added as the dehydrating agent), the periphery of the pipe 2 is simultaneously heated by an H2/O2 burner 3, and both materials 1 and 2 are fused together at 1300-1800 deg.C collapsing temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an original fiber base material by a rod-in-tube method, and particularly to
Non-bridging oxygen defects due to Si-0.
ingOxygen associatedHo1e
The present invention relates to a method of manufacturing a base material of an original fiber without any Center-NBOHC.

[Conventional technology]

For example, the original fiber is made by inserting a core rod into a cladding pipe and heating and melting them to vitrify them (
A base material is manufactured by the so-called rod-in-tube method (hereinafter referred to as "collapse"), and this is drawn into a wire.

The above-mentioned pipe for glue 2 is produced by, for example, supplying gas phase glass raw materials, oxygen, hydrogen, and other gas phase components onto a hollow mandrel using a flame hydrolysis burner such as a multi-tube burner, and then P is manufactured by depositing porous glass using a deposition method, dehydrating it, and vitrifying it by bath melting.

Next, the above-mentioned core rod is also made by supplying the above-mentioned vapor phase glass raw material etc. with the above-mentioned flame caloric water decomposition burner, and PJr.
Create porous glass using the so-called VAD method, dehydrate it,
It is manufactured by melting it in a heating bath, vitrifying it, and stretching it to a desired diameter.

[Problem that the invention seeks to solve]

In the cladding pipes and core rods manufactured in the above manner, during the porous glass backing or vitrification, Sl takes in excess oxygen, which is called peroxy bonding. o-o-st @ bonds may be included.

In addition, there are Si-, 5i-0, 5i-0-0-, and other defects on the inner surface of the cladding pipe and the surface of the core opening, and when collapsing these defects, it is necessary to , Si・+5i-0--+5i-0-8i There is no problem if only the bond is generated, but 51-0・+51-0
-+ 5i-0-0-8i bond, or 5i-0-0-+ Si・-+ 5i-0-0-8i
It also creates a bond.

This peroxy bond is broken during the above-mentioned wire drawing or in a radiation environment, resulting in so-called non-bri”dgingOx defects in U51-0.
ygen associatedHo1e Cent
er -N B OHC) is said to be produced.

The presence or absence of this NBOHC is determined by the large absorption at the wavelength α63 μm.

In addition, in the original fiber in which NBOHC exists, during long-term use, Sl-〇 reacts with H, O in the usage environment and H of other H sources to generate Mi-S1-○H bonds. High absorption near wavelength 1.39 μm, 1.5 μm band, 1.
This results in an increase in transmission loss in the 5 μm band.

Therefore, peroxy bonding, as a precursor of NBOHC, worsens the radiation resistance and hydrogen resistance of the original fiber, reducing long-term stability and reliability.

By the way, peroxy bonding is scattered in the radial direction of the cladding pipe and the core rod. On the other hand, since strain exists at the core-clad interface due to the difference in physical properties between the two, the bonding is likely to be broken at the interface. Therefore, the above-mentioned NBOHC is likely to be generated at the core-cladding interface.

Therefore, in the present invention, we propose a method for manufacturing a base material for the original fiber without NBOHC caused by the bonding by eliminating the peroxy bonding near the core-cladding interface. Means for Solving] The present invention solves the above problem by inserting a D2. This problem can be solved by flowing a reducing gas such as Co. 〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〇〔Operation〕] In the present invention, when collagen is formed by flowing a reducing gas into the gap between the core rod and the cladding pipe, the problem will be solved by flowing a reducing gas such as Co into the gap between the core rod and the cladding pipe. Then, the above-mentioned defects (Si・, S10・, Si-〇-〇・, etc.) existing near the inner surface of the cladding pipe are reduced by the above-mentioned reducing gas, and the defects at the core-cladding interface are reduced. The amount of rope separation decreases, and as a result, 5i-
The probability of creating a 0-0-3i combination is reduced.

In addition, the peroxy bond that has already been generated is first cut off, and then:
It is reduced with a reducing gas, for example, as follows.

A5i-0・+D2-+ 7Si・+D, 05S1-o
・+ co −→ ”; Si−+ co.

When N2 is used as this reducing gas,
, increases transmission loss in the 3μm band and 1.5μm band:
There is a possibility that a 3Si-OH bond will be generated.

On the other hand, the Mi5i that may be generated by using D2
It has been confirmed that -OD coupling does not cause an increase in transmission loss at least in the above wavelength band.

The above reducing gases are N2 and Ar for dilution.

With inert gas such as Ho or ct2.5oc
Supplied together with a dehydrating agent such as z2.

The mixing ratio of reducing gas in these supplied gases is such that if the reducing gas is too small, the above-mentioned reducing effect will not occur, and if it is too large, the reducing effect will be saturated, which is not economical. The amount Q is preferably 5 to 50 vol%.0 Note that D2 is used as the reducing gas and C as the dehydrating agent.
When using 2z, D2 should be 0.5 to prevent explosion.
It is desirable to set it to 4.0701%.

The amount of reducing gas supplied varies depending on the mixing ratio of the above-mentioned reducing gases, but if it is too small, the above-mentioned reducing effect will not occur, and if it is too large, the core-li-2-rad interface will be damaged. 10 to 500 c.
c/min is preferable, and in order to obtain a stable reducing effect, it is suitable to set the rate to 50 to 500 cc/min. Furthermore, the reducing gas is allowed to flow into the gap in advance before collapse,
It is most preferable to replace the gap with a reducing atmosphere and continue to flow the atmosphere during the collapse, but good results may be obtained even if the atmosphere is flowed only during the collagen. However, if the reducing gas is flowed only before collagen formation, good results cannot be obtained.

In addition, collagenase@degree in the present invention is a normal temperature of 13
00 to 1800°C can be adopted. Within this temperature range, the above-mentioned reduction effect also occurs satisfactorily.

〔Example〕

Example 1 A core rod made of pure silica glass and a cladding pipe made of F-doped silica glass were used, in which the core and cladding had a refractive index Δn of -α7%.

The above core rod was inserted into the above cladding pipe, and N2 was supplied to the gap between the two at a rate of 950 cc/min and D2 at a rate of 50 cc/min to replace the atmosphere in the gap.

After that, as shown in Fig. 1, one end of the core rod 1 and cladding pipe 2 is sealed, and from the opposite end N and D
2 at the above ratio, heat it from the outer periphery of the cladding pipe 2 with the N2102 burner 6, and heat it to +700c @
The original fiber matrix was produced by collapsing the fiber at a certain temperature.

The transmission loss of the original fiber obtained by drawing this base material is λ=
α at 66 μm & OdB/km% at λ=1.38 μm (L 8 clB/km bλ= 1.55 Jim at [119 dEl/km).

This original fiber was placed in a H, 1 atm atmosphere at 200°C for 20 minutes.
When we investigated the transmission loss after the time change, we found no change from the above value.

For comparison, collapse was carried out under exactly the same conditions as in Example 1, except that only SiN2 was flowed at 1000 cc/minute, and an original fiber preform was produced.

The transmission loss of the original fiber obtained by drawing this base material is λ=
20 dB/km at 163 μm, [
LB aB/km, λ = 1.55 Am [L20d
6D at B/km; the presence of NBOHC due to 5t-O- is evident.

In addition, the transmission loss after penetration of this original fiber into H under the same conditions as in Example 1 is λ = (7aB/km at L63μm,
7.6dB/kmb at λ=1.58μmλ=1.55
cL62dB/km''''ch at #m: t, 5si-
It is clear that o- has become 3s1-oH.

Example 2 An original fiber preform was produced by collapsing under the same conditions as in Example 1, except that N2 was supplied at a rate of 500 cc/min and Co at a rate of 500 cc/min.

The transmission loss of the original fiber obtained by drawing this base material is λ=
5.9 dB/km at 0.65 μm, λ=1.38 μm
119 dB/km at 1119 d at λ=1.55 μm
It was B/km.

The transmission loss after this original fiber was impregnated with Ht under the same conditions as in Example 1 showed no change from the above value.

Example 3 N2 at 500 cc/min and Co at 50 cc/min only during collapse.
A raw fiber was manufactured under the same conditions as in Example 1 except that the supply was performed at a rate of 0 cc/min.

The transmission loss of this original fiber is λ=[1L63μm and 6-
α9 dB/km at 2aB/km%λ=1.38μm.

When λ=1.55 μm, α+ was 94 B/km, and after N2 penetration under the same conditions as in Example 1, there was no change from the above initial value.

Example 4 N2 at 500 cc/min and CO at 5 cc/min just before collapse.
A raw fiber was manufactured under the same conditions as in Example 1 except that the fiber was supplied at a rate of 0.00 cc/min.

The transmission loss of this original fiber has an initial value of λ=α63μm
At a 2 dB/kmb λ= 1.58 Am at 1.
0a13/km % λ = 1.55 μm (L
l) at 20 dB/krn, H under the same conditions as Example 1, and after penetration, λ = (-1.2 dB/km at L63 μm,
At λ=1.55 μm, it was +11 dB/km.

Example 5 Ct: 500 cc/min, N: 300 cc/min,
A raw fiber was manufactured under exactly the same conditions as in Example 1, except that C0 was supplied at a rate of 200 cc/min.

The transmission loss of this original fiber has an initial value of λ=16511
6.2 aB/km % λ = 1.58 Am
[1L7aB/km % λ = 1.55 μm [119dB/km 1], H under the conditions consistent with Example 1
After the second infiltration, there was no change from the above value.

Example 6 Original fiber 'ft1K was manufactured under exactly the same conditions as in Example fl11, except that He was supplied at a rate of 500 cc/min and CO at a rate of 500 cc/min.

The transmission loss of this original fiber is λ = (5.9 at L63μm)
dB/km, λ: t [19 dB/fa at 38 μm
n.

CL at λ = 1.55μm, 19 dB/km,
After H2 infiltration under the same conditions as in Example 1, no change was observed from the above values.

〔Effect of the invention〕

According to the present invention, peroxy bonding 95t-o-o-st-E- at the core-cladding interface is performed in D2. The bonding is cut at the core-cladding interface to eliminate it by reducing it with a reducing gas such as CO9 51-
It is possible to produce an original fiber base material free of NBOHC due to o.

The original fiber obtained by drawing this original fiber base material has excellent long-term stability and reliability without deteriorating in its hydrogen-resistant or radiation-resistant properties.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment N of the method of the present invention.

Claims (2)

[Claims] (1) In a method of manufacturing an optical fiber preform by inserting a core rod into a cladding pipe and melting and integrating the two, flowing a reducing gas between the core rod and the cladding pipe, A method for manufacturing an optical fiber preform, which comprises melting and integrating the core rod and cladding pipe. (2) The method according to claim (1), in which deuterium or carbon monoxide is used as the reduction gas.