JPS6296338A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To form an integrated dry gel free from delamination at the interface between a clad and a core, by gelatinizing a raw material sol for clad and pouring a raw material sol for core into the hollow part of the clad material within a specific period. CONSTITUTION:A raw material sol for clad composed mainly of silicone alkoxide is gelatinized under rotation in a rotary vessel and a raw material sol for clad is poured into the hollow part of the gelatinized clad material and left at rest. As an alternative method, the poured sol for core is gelatinized under rotation to obtain an integrated gel of clad and core. The above process is carried out in a manner to satisfy the formula Tint<5Tg wherein Tint is period from the gelatinization of the raw material sol for clad to the pouring of the raw material sol for core and Tg is time required for the gelatinization of the raw material sol for clad. An integrated dry gel free from delamination at the interface between a clad and a core can be produced in high yield and a high-quality optical fiber can be produced from the dry gel at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an optical fiber preform by a sol-gel method.

[Summary of the invention]

The present invention is a method for manufacturing an optical fiber base material using a sol-gel method using silicon alkoxide as the main raw material, in which the raw material sol for the cladding is gelled while rotating in a rotating container, and then the raw material sol for the core is poured into the hollow part. In the process of making a cladding-core integrated gel by allowing it to gel while standing still or rotating it, the time from when the raw material sol for the cladding gels until the raw material sol for the core is poured is the time required for the raw material sol for the cladding to gel. This is a method for producing an optical fiber base material, in which a gel is prepared in a time less than five times the time required for the process, and the gel is dried and sintered to form a transparent glass body.

[Conventional technology]

Several methods for producing optical fiber preforms using the sol-gel method have been reported. The sol-gel method has the advantages of easy purification of raw materials, wide selection of materials, and low manufacturing costs because transparent glass bodies can be obtained below the transition point. This method is attracting attention as a method that can provide Hikari 7 Eyeper base material in large quantities at low cost.

For example (Unexamined Japanese Patent Publication No. 57-22137) Pulling St-
After the hydrolysis of the alkyl silicate, which is the raw material for the cladding, was poured into a tubular container equipped with the gel,
Pull out the pulled woman, add hydrolyzed water s/#at of alkyl silicate containing dopant into the hollow part, and gel it.
There is a method of producing, drying, and sintering a core-clad integrated gel to use as a base material for optical fibers. Furthermore, a method for producing an optical fiber preform has been reported in which the raw material is placed in a cylindrical container and gelated while being rotated (Japanese Patent Laid-Open No. 58-99134). Recently, an epoch-making method for producing a fairly large optical fiber base material using the sol-gel method has been reported (our patent arrangement A20671).

To briefly explain this method, a raw material sol is a mixture of a hydrolysis solution of an alkyl silicate using an acid catalyst and fine particle silica obtained by hydrolysis of an alkyl silicate using an ammonia catalyst. After pouring into the container and gelling it while rotating, pour the sol containing a dopant for adjusting the refractive index into the hollow part and gelling it while rotating in the same way. - A core-integrated gel is produced, dried and sintered to form an optical fiber base material. In such a method, it is possible to create a dry gel with strong interparticle bonding even though it has relatively large pores inside, and therefore it is possible to manufacture a Mars optical fiber base material.

[Problems and Objects to be Solved by the Invention] In the above invention, a peeling phenomenon between the clad gel and the core gel is recognized as a phenomenon that significantly reduces the yield of dry gel. A possible cause of this is that after the cladding sol gels, the surface activity decreases while the core sol is poured. The raw material sol in the present invention gels while causing a dehydration combination reaction between or within the silica particles, and even after gelation, the condensation reaction gradually progresses. Immediately after gelation, at least on the surface, there are many active species that have not yet undergone a condensation reaction, that is, free water groups.
As time passes, the condensation reaction progresses and the number gradually decreases. Accordingly, it is thought that the activity of the gel surface to bond with other gels is gradually lost.

The present invention solves the above-mentioned problems of the conventional sol-gel method for manufacturing optical fiber preforms. The purpose of the present invention is to provide a method for producing an integrated dry gel with a high yield without peeling between the cladding and the core.

[Means for solving problems]

In the method of manufacturing an optical fiber base material by the sol-gel method of the present invention, the sol for the cladding is rotated in the same container to form a gel, and then, while the inner surface of the cladding gel is in a sufficiently active state, the sol for the core is It is characterized by creating an integrated dry gel with strong bonding force at the cladding-core interface by gelling it while pouring it or rotating it.

The activity of the gel surface depends on the dehydration condensation reaction rate, and it is thought that the slower the reaction rate, the longer the gel surface activity will be preserved. Furthermore, since the condensation reaction rate determines the gelation time of the sol, the gelation time of the cladding sol can serve as a guideline for determining the surface activation time after gelation, that is, the effective time until the core sol is poured. Time from gelation of sol for cladding to penetration of core sol t-g (Ti
nt) is the time required for the cladding sol to gel (Tg
), the clad gel and core gel will not bond. That is, the conditions under which the clad gel and core gel do not separate are Tint (5Tg, but preferably Tint
(37g 1 More preferably Tint (Tg).

A long Tg is advantageous in that the surface activity is preserved for a long time, but the strength of the gel itself does not improve for a long time and the gel collapses under its own weight when the rotation reactor is completely stopped, resulting in poor production efficiency. It is necessary to select the highest value f, taking into account the operability during preparation, etc.

[Example 1] ■ Preparation of ammonia synthetic silica (Ammosil) Purified commercially available ethyl silica) 10509, ethanol 4500/ammonia water (29%) 3582, water 3
After adding 632 and stirring for 2 hours, the mixture was stirred. As a result, fine silica particles having an average area α of 15 μm were formed. Rotary evaporator and 112! The above synthetic solution was concentrated under reduced pressure until the total silica concentration became (L4(1/(:IC!). 2N hydrochloric acid was added dropwise to this, and the PH'f
: Adjusted to 4.50 (volume 860 rat) ■Preparation of sol for cladding 687f of purified commercially available ethyl silicate was mixed with 268v of [L02 normal salting], stirred, and hydrolyzed pf! I went to Said Ammodyl'WL688. In addition, it was used as a sol for cladding.

(commercially available ethyl silica prepared and purified with sol for recore), 160F (102
Specified distance d21's: 55 f of alcohol was added and stirred to perform partial hydrolysis of ethyl silicate. To this, 10.8 f of tetraethyl silicate was added.
Add a wet mixture of ethanol and 9.5 f of ethanol dropwise for about 50 minutes.
After stirring for 1 minute, (LO2 normal salt [4αor) was added and stirred to complete hydrolysis. To this was added 172-? of ammodyl solution according to F\ri to obtain a core sol.

■ Preliminary experiment Taking advantage of the fact that gelation time differs depending on the pH value, put the sol for cladding into a 14t FL polyethylene beaker at a pH of 1.2 normal ammonia water.
After each sol was gelled at its own gelation time, the core sol t-g was placed on top of the gel to form a gel.

At this time, the time from when the sol for the crat was gelled to when the sol for the core was completely poured was varied. Each lid was covered with aluminum foil, a pinhole was drilled, and the mixture was dried in a thermostatic chamber at 60°C. Make sure that all drying conditions, such as the number of pinholes, are the same. The state of peeling at the interface for each gel until completion of drying is summarized below.

◎・・・・・・Completely integrated after drying ○・・・・・・Partially peeled off after drying Δ・・・・・・Peeled during drying×・・・・・・2 days after gel death Peeling within ■ Cladding
Preparation of core integrated gel P115. Adjusted to OO and added water to a final volume of 2000 ml. Internal diameter 5 as a rotating container
．． The above Krat sol 1 is placed in a cylindrical container with a length of 102 am.
886mtkMtL included and a silicone rubber cap as shown in Figure 1. ! I attached it to the 1st transfer device.

This was rotated at a rotational speed of 1500φm, and after confirming that the monitor sample had gelled after being separated from the SO, an additional 5
Rotate for a minute, and when the strength of the gel has increased to a certain extent, remove the rotating device and set the pH of the hollow part to 4.80.
The prepared core sol was poured into the final product fRt-saa- and gelled. At this time, the time from when the cladding sol gelled to when the core sol was poured was 20 minutes.

■Drying The gel prepared by the above method was transferred to an acrylic box-shaped container (vertical f2GcNX horizontal x 10 cm x height 25 cWt), covered with a lid with an opening of 541%, and dried in a thermostatic chamber maintained at 60°C. .

After 20 days, the gel was completely dried without peeling at the cladding-core interface.

The above-mentioned sintered dry gel (outer diameter: 5250×length: 65G) was sintered in a gas atmosphere furnace according to the following program.

Raise the temperature from room temperature to 200°C at a rate of 30°C/hr, hold at that temperature for 10 hours, then increase the temperature to 300°C at a rate of 50'C/hr.
The temperature was raised at 100° C. and maintained at that temperature for 10 hours.

The temperature was further increased to 900°C at a rate of 60°C/hr and held for 5 hours. All of the above sintering was performed in a mixed atmosphere of nitrogen and oxygen (N
t:O! ==4:1). Next, 900
A mixed atmosphere of helium and chlorine (ae: cz,
= 1o:1) and held for 1 hour, the temperature was raised to 1000°C at 60°C/hr and held there for 2 hours. Next, the temperature was raised to 1,100°C at a rate of 60°C/hr while only oxygen was flowing, and the temperature was increased to 1100°C for 20
Holds time. Next, flow only helium at 30℃/h.
When the temperature was raised to 1250 °C with R and held for 5 hours, the sample was taken out from the gas atmosphere furnace and transferred to a box-shaped electric furnace.
When the temperature was raised to 1400°C at 60'C/hr and held for 1 hour, an optical fiber base material of transparent glass body with Talarado core structure (outer diameter 2.35. )was gotten.

Furthermore, when the refractive index distribution was measured using a pre-7 ohm analyzer, it was found that it had a step-type distribution with Δn; α5X.

(2) Drawing and Loss After polishing the outer periphery of the optical fiber base material, a commercially available quartz glass tube was jacketed and drawn to obtain a single mode fiber with a cladding diameter of 125 μm and a core diameter of 10 μm. At the same time, the fibers were reinforced by coating them with silicone resin.

When we investigated the optical loss wavelength characteristics using the cutback method, we found that
It was 2.54 B/Km at 185 μm and 14 dB/Km at t 56 μm.

〔Effect of the invention〕

As explained above, in the method for manufacturing an optical fiber base material by the sol-gel method, the core sol is poured into the hollow part of the cladding gel in a time less than five times the time required for the cladding sol to gel. By drying and drying, an integrated dry glue without peeling at the cladding-core interface can be obtained.

In addition, the characteristics of the original fiber obtained by this are V,
This method is comparable to the AD method, etc., and will be a method that can provide inexpensive, high-quality optical fibers for optical communications, for which demand is expected to be large in the future.

Furthermore, such bonding of different types of gels can be applied to the production of optical waveguides and the like, for example, by the sol-gel method.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a rotating device used to create a tubular gel. 1...Cylindrical container 2...Motor 5...Bearing 4...Fixing jig 5...Guide rail 6... ...Support stand. Above 1... Circular power capacity 2... L-tar 3... Axis conflict is raw 11. Gunji tool number...-tr'i-Ikashi-1 Shira 10. This is the 1st page of the series.1: Schematic diagram of the 73 rotating device used Figure 1

Claims (1)

[Claims] (1) In a method for manufacturing an optical fiber base material using a sol-gel method using silicon alkoxide as the main raw material, the raw material sol for the cladding is gelled while rotating in a rotating container, and then the raw material sol for the core is poured into the hollow part. After the raw material sol for the cladding is gelled in the process of making a cladding-core integrated gel by allowing it to gel while standing still or rotating,
A method for producing an optical fiber base material, characterized in that the time required to pour the core raw material sol is five times or less the time required for the cladding raw material sol to gel.