JPS6054891B2 - Preform manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a preform that is the basis for manufacturing a rod-shaped glass having a lens-like function or an optical transmission line used in optical communication.

These preforms have a predetermined refractive index distribution in the radial direction (for example, a step-shaped or parabolic refractive index distribution) and are uniform in the longitudinal direction (in the case of rod-shaped glass, depending on the purpose, the refractive index distribution may be uniform). The refractive index is adjusted to achieve a refractive index of come. How to make a preform with a predetermined refractive index distribution is as follows:
In addition to SELFOC (product name), which uses ion exchange,
JP 50-28339, 51-135915, 51-
126207, 53-102324. In this method, a phase splitting glass (for example, Na2O-1) is used.

O-B. O. -SiO. B) for heat treatment, elution, and washing after pulling up the rod. First, a porous glass rod made of SiO2 glass containing a small amount of
℃'s saturation W■, sNO.

A porous glass rod is placed in an aqueous solution of CsN in the micropores.
After filling with O, aqueous solution, put it in 0℃ water for 311r to precipitate, remove CSNO3 in the micropores from the outside, further precipitate in 30% H2O-70% CH3OH, and remove the CSNO3 in the outer micropores. After removing CSNO3, it is dried and then heated, and CSNO3 becomes CS2O.
As a result, CS2O is precipitated on the inner surface of the micropores in a predetermined concentration distribution), and then heated to a high temperature and thermally solidified to form a transparent glass rod. However, in this method, the pulling rod is subjected to phase separation heat treatment and acid elution is performed to create a porous glass rod.
While stress occurs during acid elution (when the eluted part is formed, the two phases (Na2O-K2O-B, O3 soft phase and B2O
Since the soft phase portion of the hard phase of 3-SjO2 is replaced with acid, the strain balance is lost and residual strain occurs.

The strain in these areas is applied to the undissolved glass area. ), the surface of acid elution progresses from the rod surface toward the center, but there is a singular point at the center where the progress stops at the destination.
The reason is not clearly known, but in any case, near the singular point at the center of the rod, the size of the micropores after acid elution becomes larger toward the center than at the periphery (or This was confirmed by electron microscopy. The results are shown in Figure 1a.
become that way.

That is, at the center of the porous glass rod 11, the size distribution of micropores is as shown by 12. When such a porous glass rod is used as a starting member, when making a preform, for example a step type, a hole is formed in the center of the core 13 as shown in FIG. 1b. Since more dopants are precipitated, the preform has a refractive index profile 15 that rises at the center. For example, in the case of a parabolic index profile, more dopants are deposited at the center 16 as shown in FIG. 1C. is precipitated, so that a pre-j form with a refractive index distribution 17 with an upward slope at the center is obtained. Optical transmission lines or rod lenses made from preforms with irregular points in the center have the disadvantage of increased signal distortion or disordered energy distribution, resulting in increased coupling loss, making them impractical for practical use. It has become a major problem. In order to solve these drawbacks, the present invention provides a method for preparing a porous glass rod without irregular micropores in the center, thereby producing a preform without irregularities in the center. It provides: In the present invention, based on the discovery that the part where these abnormal micropores are formed only occurs in the part corresponding to the end of acid elution and that cutting of porous glass is easy, we have developed a porous glass with the abnormal part removed. The present invention is characterized by a method of manufacturing a preform without irregularities by effectively utilizing the glass portion.

The present invention will be described in detail below.

As the phase splitting glass, for example, Na2O-B2O3-
SlO2, Na2O-K2O-SlO2Na2O-K2
Glasses of the O--B2O3-SiO2 system with defined compositions (these are found in the aforementioned patents and the VycOr patent) are used to make rods or tubes or plates as starting parts.

(It is made by a general method without using any special method.) Next, it is subjected to a phase separation heat treatment (this temperature and time conditions vary depending on the composition), and then a high temperature acid (for example, 100℃ 3NHC1
), the soft phase begins to dissolve. A prism is made by cutting this along the end of the elution. This cutting may be performed after washing with water after elution or after drying. For example, in the case of a plate 21 as shown in FIG. 2a, it is cut with a hacksaw along the end 22 of the elution, and then cut into thin pieces, such as a prism 23. The cross section of the prism 23 is, for example, a square like 23'' in FIG. 2b.

In the case of a rod, it is necessary to divide it into four equal parts along the central axis, and in the case of a tube, it is necessary to cut it out along the plane of the thickness.

The bar 23'' cut out in this way is then polished in the usual way to get the corners like 24 and 25, and finally becomes 26.
Make it into a round bar like this.

Next, by pickling and washing with water to remove cutting debris and dirt, a porous glass rod having uniform micropores throughout can be produced.

When a preform is made by the filling method using the porous glass rod thus made as a starting material, for example, in the case of a step type, there are irregularities in the refractive index distribution 32 at the center of the core 31 in FIG. 3a. For example, in the case of a parabolic refractive index distribution type preform, a preform with no irregularities in the refractive index distribution 34 with no abnormality at the center 33 in FIG. 3b is obtained.

An embodiment of the present invention will be described below.

However, the invention is not limited to these examples. 4%
Na2O-3%K2O-36%B2O3-57%SiO
The glass consisting of
It was poured into a f&×25TI0nt concave).

A 5h x 5 - x 25 t portion with no cracks was cut out. Next, this board was heat treated at 550°C x 6F1r, and then immersed in 3NHC1 at 100°C to give 9ea! When the solution was allowed to stand for a period of f, the elution was completely completed. After washing this with water, it was then prepared as shown in Fig. 2. 8.5T! n×4
Cut out a 5Tfr1nI square prism with a thin-blade hacksaw, then use a #400 sharpening machine to cut the corners, and then attach it to a rotary motor and rotate it using #600, 800, and #100.
0, I polished it with #1500 Serox powder and made it into a round bar.

Next, this was thoroughly washed with 3NHN03 water, and then washed with pure water to obtain a porous glass rod of 8TWLφ×40wrmI.

(This is referred to as sample A). On the other hand, a glass rod of 8 dia.
F[NO3 water washing and pure water washing were performed to prepare a porous glass rod. (This will be referred to as sample B) Next, heat these to 105°C.
After being immersed in an aqueous solution of CSNO3 for 4 hours, cooled to 20°C and washed at 311r (at this time, precipitation begins, and then the outer part gradually dissolves and becomes transparent).
After that, the dissolved CSNO3 in the outer part was allowed to precipitate by leaving it for 1 hour in 100% ethyl alcohol, and then the precipitated CSNO3 in the outer part was further dissolved in 80% ethyl alcohol.
Washed with 20% water for 48 hours to reduce the concentration of CSNO3 on the outside. Next, these were soaked in C3H7OH and heated to 850℃ while slowly vacuum drying.
Tnm1). When we investigated these refractive index distributions, we found that there was no point with an abnormally high refractive index at the center of A.
In B, a point with abnormally high phase separation was observed at the central point.

According to the present invention, a predetermined refractive index distribution is formed in the radial direction,
A preform having a predetermined refractive index distribution also in the longitudinal direction and having no abnormality in refractive index points can be obtained at a low cost. This preform yields a fiber with low optical signal distortion.

A rod-shaped lens that adjusts the power distribution of energy can also be made from this preform.

[Brief explanation of the drawing]

Figure 1a shows a porous glass rod with an unusual micropore in the center, and Figures 1B and c show the refractive index of the step-shaped and parabolic preforms obtained when these porous glass rods are used. Show the distribution. FIGS. 2A and 2B are diagrams for explaining the present invention. FIGS. 3A and 3B show the refractive index distributions of step-type and parabolic preforms obtained when using the porous glass rod of the present invention. Reference numeral 12 indicates a hole size distribution, 15 and 16 indicate a refractive index distribution at the center, 23 indicates a square column, and 26 indicates a round bar.

Claims (1)

[Claims] 1. A block of phase-splitting glass is made, a phase-splitting heat treatment is applied to it, acid elution is performed and washing is performed as necessary to make a porous glass block, and the center portion is removed from the porous glass block. A rod-shaped block is cut out, the porous glass rod is polished to prepare a cylindrical porous glass rod, and a dopant is precipitated in a predetermined concentration distribution on the inner surface of the micropores of this cylindrical porous glass rod. . A method for manufacturing a preform, characterized in that a glass rod having a predetermined refractive index distribution in the radial direction without an irregular point at the center is produced by thermally solidifying the glass rod. 2 Heat-treat a block of phase-splitting glass with a simple plate shape, elute it with acid, make it porous glass, then slice it longitudinally through the center plane to make a square prism, and cut the corners of the square prism. Claim 1 is characterized in that a cylindrical porous glass rod is prepared by polishing it in a rounded manner while taking it, and if necessary, washing it with hydrofluoric acid and finally washing it with pure water. Preform manufacturing method.