JP3025244B1 - Matching oil for measuring the refractive index distribution of optical fiber preforms - Google Patents

Abstract

An object of the present invention is to provide a matching oil that can be easily removed from a preform and hardly penetrates into an unsintered portion. SOLUTION: The value of the contact angle with respect to glass is set to 9 to 20 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a matching oil for measuring the refractive index distribution of an optical fiber preform (hereinafter referred to as a matching oil).

[0002]

2. Description of the Related Art When an optical fiber is manufactured by a VAD method, an OVD method or the like, a preform of an ingot obtained by dewatering and sintering a soot is produced in a middle stage.
Since the outer diameter of this ingot is usually as large as 120 to 180 mm, it is difficult to draw the optical fiber with the drawing apparatus as it is. Then, in order to be able to draw the ingot with a drawing device, the ingot is first drawn into a preform having an outer diameter of 40 to 100 mm by a drawing device before drawing. FIG. 1 shows an example of the stretching apparatus. The stretching device includes
Usually, a heating furnace 1 using a carbon heater is provided, a raw material supply device (not shown) for suspending an ingot 2 at an upper portion and gradually feeding the ingot 2 to the heating furnace 1, and a heating furnace 1 at a lower portion. A take-off mechanism (not shown) for drawing out the preform 3 drawn from the heated and softened ingot 2 from below the heating furnace 1 is provided. The inside of the heating furnace 1 is replaced with an inert gas such as N ₂ or Ar, and heats the ingot 2 at a high temperature of about 2,000 ° C.

[0003] The preform which has been primarily drawn by the drawing apparatus is measured for the refractive index distribution by a preform analyzer, and the optical transmission characteristics of the optical fiber after drawing are estimated from the measured refractive index distribution. You. As a result, if there is a difference between the estimated optical transmission characteristics and the target optical transmission characteristics, the preform is adjusted by performing processing such as scraping the outer peripheral portion. After that, a finishing process for removing fine irregularities on the surface of the preform and precisely adjusting the outer diameter to a target value is performed. In finishing, a glass lathe using the flame of a burner is used.

When precise outside diameter control can be performed by a stretching apparatus, a preform may be processed into a preform in accordance with a final target outer diameter value only by a stretching step. FIG. 2 shows the flow of the process in that case. In this case, in the state of the ingot before stretching, the refractive index distribution is measured by a preform analyzer, and the optical characteristics of the optical fiber after drawing are estimated from the measured values. Determine if it is necessary. The ingot for which it is determined that the thickness of the clad needs to be adjusted is stretched after removing the outer peripheral portion or performing finishing. When it is not necessary to adjust the thickness of the clad, the film is stretched to the final target outer diameter.

[0005] As described above, in order to estimate the optical characteristics of an optical fiber, the refractive index distribution of a preform is measured. For the measurement of the refractive index distribution, a preform analyzer as shown in FIG. 3 is usually used. To measure the refractive index distribution of the preform using this preform analyzer, the preform 12 attached to the suspension unit 11 is immersed in a matching oil tank 14 including a cell 13 filled with matching oil. By irradiating the inside of the preform 12 with a laser beam and measuring the refraction angle by the optical measurement unit 15, the refractive index distribution of the preform 12 is obtained. The optical measurement unit 15 generally includes
As shown in FIG.
2, a light irradiating section 23 incident on the preform 22, a transparent cell 24 for guiding the laser light 21 to the preform 22,
And a photodetector 25 for measuring the angle of refraction of the laser beam 21 refracted inside. Then, the preform 22 is placed inside the cell 24 and the preform 22
A matching oil 26 having a refractive index substantially the same as the refractive index of the preform 22 is filled in the gap between the and the cell 24. After the measurement of the refractive index distribution is completed, the preform is lifted from the matching oil tank, and is left on the upper part of the matching oil tank, so that the matching oil is removed by gravity. Then, after the matching oil is sufficiently removed, it is set in a stretching device, and is heated and stretched in a heating furnace.

[0006]

When the refractive index of a preform is measured, as described above, the preform is immersed in a cell filled with matching oil, so that the surface of the preform after the measurement is completed. Has matching oil. In addition, there is an unsintered portion at the end of the preform, and the matching oil permeates into this portion.
Then, when the preform is transported to the stretching device in a state where the matching oil is attached and permeated, the matching oil drips on the floor, so that there is a problem that the floor is soiled. Also,
When the preform is heated in such a state, evaporation and combustion of the matching oil occur inside the heating furnace, and as a result, there is a problem that the inside of the furnace is contaminated or an odor is generated.

As a method of removing the adhering matching oil, there is a method in which an operator wipes the preform with a waste cloth. However, the length of the preform including the dummy portion is 2.
Since it is 5 m or more and weighs more than 50 kg, performing such an operation has a safety problem. Another way to remove the matching oil is to suspend the preform for a long time and wait for the matching oil to drip, which is the safest and easiest method, In order to sufficiently remove the matching oil adhering to the plate, it was necessary to leave the mixture for 50 to 80 minutes. In addition, the matching oil permeated into the unsintered portion of the preform could not be removed by this method. Therefore, an object of the present invention is to provide a matching oil that can be easily removed from a preform and hardly penetrates into an unsintered portion.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the contact angle of the matching oil should be within a predetermined range, and have completed the present invention. . That is, the present invention is a matching oil characterized in that the value of the contact angle with glass is in the range of 9 to 20 degrees.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The matching oil of the present invention
A preform obtained by dehydrating and sintering a soot produced by an AD method, an OVD method, or the like, and particularly having an outer diameter of 120 to 1
It is suitably used for measuring the refractive index distribution of a preform having a size of 80 mm and having an unsintered portion at the end. The feature of the present invention resides in that the value of the contact angle with respect to glass is in the range of 9 to 20 degrees as described above. As a result, the matching oil adhering to the preform surface can be removed in a relatively short time, and the amount of the matching oil penetrating into the unsintered portion of the preform can be minimized. If the contact angle is less than 9 degrees,
If the amount of the matching oil that permeates the unsintered portion increases, on the other hand, if it exceeds 20 degrees, it takes a long time to remove the matching oil.

In order to measure the contact angle of the matching oil, as shown in FIG. 5, an oil droplet 32 of the matching oil attached to the tip of the needle 31 of the syringe (see FIG. This is performed by contacting the surface of the glass plate 33 to spread an oil droplet on the surface of the glass plate and measuring the angle between the surface of the spread oil droplet 32 and the glass plate 33 (FIG. 5).
(B)). Further, the matching oil of the present invention may be prepared by mixing two or more kinds of matching oils having different refractive indexes. Specific examples of the matching oil include liquid paraffin and cyclic hydrocarbons.
By changing the mixing ratio of the matching oil in various ways,
Matching oils with different contact angles can be made.

[0011]

EXAMPLES (Examples 1-3, Comparative Examples 1-2) Outer Diameter 160
After measuring the mass of the ingot of mm, the ingot was set on a hanging part of a preform analyzer as shown in FIG. Then, the ingot was immersed in an oil tank filled with matching oil, and left for 10 minutes. Thereafter, the ingot was pulled up and the change in mass was measured, and the time until the change in mass per 5 minutes became 0.1 g or less was defined as the time (minutes) required for oil removal (see FIG. 6). The difference in mass before immersion in the matching oil and after the matching oil was sufficiently removed by lifting the ingot from the oil tank was defined as the amount (g) of the matching oil permeated into the unsintered portion (see FIG. 6). Various matching oils having different contact angles were tested, the time and the amount of the matching oil were measured, and the results were compared. Table 1 shows the results.

[0012]

[Table 1]

As can be seen from Table 1, in the case of Comparative Example 1 having a small contact angle, the matching oil could be removed in a short time, but the amount of the matching oil that permeated the unsintered portion increased. In contrast, in the case of the matching oil having a large contact angle as in Comparative Example 2, the penetration into the unsintered portion was small, but the matching oil had to be left for a long time to remove the matching oil. In the case of Examples 1 to 3, good results were obtained with respect to both the time required for oil removal and the amount of permeation into the unsintered portion.

[0014]

According to the present invention, the matching oil adhering to the surface of the ingot can be removed in a relatively short time, thereby improving workability. In addition, since the amount of matching oil that permeates into the unsintered portion of the ingot can be minimized, it is possible to prevent the occurrence of contamination and unpleasant odor in the heating furnace due to evaporation and combustion of the matching oil in the stretching process. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a stretching device.

FIG. 2 is a process chart for processing a preform.

FIG. 3 is an explanatory view illustrating a method for measuring a refractive index distribution of a preform by a preform analyzer.

FIG. 4 is an explanatory view illustrating the configuration of an optical measurement unit.

FIG. 5 is an explanatory view illustrating a method of measuring a contact angle.

FIG. 6 is a diagram showing a relationship between ingot weight and elapsed time.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Heating furnace 21 Laser light 2 Ingot 23 Light irradiation part 3,12,22 Preform 25 Light detection part 11 Hanging part 26 Matching oil 13,24 Cell 31 Syringe needle 14 Matching oil tank 32 Oil drop 15 Optical measuring part 33 Glass plate

Continuation of front page (72) Inventor Hideo Hirasawa 2-3-1 Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Laboratory (56) References JP-A-8-297707 (JP, A) JP-A-4-331346 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 11/00-11/02 G01N 21/41

Claims (2)

(57) [Claims] 1. A matching oil for measuring a refractive index distribution of an optical fiber preform, wherein a value of a contact angle with respect to glass is in a range of 9 to 20 degrees. 2. An optical fiber preform having an outer diameter of 120 to
2. The matching oil for measuring the refractive index distribution of an optical fiber preform according to claim 1, wherein the matching oil has a length of 180 mm and an unsintered portion at an end.