JPS6297B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical fiber with a non-circular cross section by drawing the preform while rotating it and measuring and controlling the outer diameter thereof. .

In conventional manufacturing methods for optical fibers, for those with a circular cross section, the outer diameter is usually measured and monitored using a laser outer diameter measuring device immediately after drawing, and the fiber diameter is controlled by providing feedback to the drawing speed, etc. It was manufactured by doing so. If this cross section is circular, the outer diameter of the fiber can be measured by irradiating the laser from one direction.
This enabled control. However, recently, due to the demand for multiplex transmission of information, fibers with non-circular cross sections, such as multi-core fibers, are being used and gaining importance. In this case, the outer diameter of the fiber is not the only value, so it is not possible to accurately measure the outer diameter by just irradiating the laser from one direction. The disadvantage was that accurate outer diameter control was not possible due to the irregular rotation of the fiber and the need for monitoring without contacting the fiber in order to not reduce the strength of the fiber. .

The present invention eliminates the drawbacks of the prior art and creates a method that allows precise control of the outer diameter of fibers having non-circular cross sections.

That is, in the production of fibers with non-circular cross-sections, the method is to draw a preform with a non-circular cross-section before drawing while rotating at a moderate speed, and measure the outer diameter of the fiber immediately after drawing. It is controlled manufacturing.

First, the cross section of optical fibers with non-circular cross sections may be flower-shaped or rectangular, and each contains a plurality of cores inside, and the outside is surrounded by a cladding to form a non-circular shape as a whole, such as the aforementioned flower shape. It has a cross section of Therefore, for example, if the cross section is shaped like a flower or a collection of small circles, the outermost line of the cross section is uneven with respect to the outer periphery of a circle of similar size. Therefore, as mentioned above, in the prior art, when a laser is irradiated from one direction to measure the outer diameter of these fibers, since the fiber is originally swinging or rotating irregularly and slowly, the irradiation beam does not come from the convex part. The measurement results are completely different when the object enters and exits through the convex portion on the opposite side, and when it enters through the recess and exits into the recess. In addition, various combinations of cases may occur irregularly, so that no clear measurement result can be obtained. The same applies to multi-core fibers having a rectangular cross section. Therefore, in the present invention, drawing is performed from the beginning while applying a constant rotation to a preform having a cross section similar to that of the fiber. In this case, the fiber immediately after being drawn will also rotate slowly and regularly, and it will be possible to clearly determine where on the cross section the laser beam is irradiated at any given moment. As a result, if the laser beam passes from a convex part to a convex part of the cross section, or if the laser passes from a convex part to a concave part, or from a concave part to a concave part, the measured outer diameter value and the respective values determined for quality control. Automatic control by a so-called servo mechanism becomes possible so that the fixed value is achieved by comparison with the fixed value of the case.

Therefore, the rotational speed of the preform must be approximately 100rpm, which is higher than the natural rotational speed of approximately 10rpm, and if this rotational speed is too large, the fiber will be twisted too much, resulting in The pitch of the preform becomes too small, which causes light to easily pass through the cladding layer, causing a large amount of light to be scattered and reducing the transmission characteristics.In general, the number of revolutions of the preform is several thousand, depending on the drawing speed.
It is desirable to be below rpm.

Furthermore, by combining an amplification mechanism and a diagrammatic recording mechanism for measured values with the aforementioned control mechanism, it is possible to continuously record and control controlled measured values for fixed values at each of the aforementioned positions, and to perform strict quality control. Become.

As described above, according to the manufacturing method of the present invention, the outer diameter of a non-circular cross-section optical fiber can be controlled easily and with high precision, and an ordinary unidirectional outer diameter measuring device can be used as part of the control equipment. You can also do that.
Furthermore, since the mechanism for rotating the preform can be similar to the rotating machine used in preform vapor deposition, the equipment is relatively simple, and the present invention makes it possible for the first time to manufacture low-cost, high-quality multi-core optical fibers. . In short, the present invention is a method for manufacturing a multi-core optical fiber that requires low equipment costs and is highly effective.

Example 1 Examples of cross sections of multi-core optical fibers are shown in Figure 1a,
b, and those shown in Figure 2 a and b,
In each figure, 1 is a core portion and 2 is a cladding portion.
In this embodiment, among these, a preform 3 whose cross section is made in advance with a square shape as shown in FIG. 2b is used.
A multi-core optical fiber was manufactured using the mechanism shown in FIG. That is, a square preform 3 with a side of 11 mm is rotated at 500 rpm in the direction shown in FIG. 6 was produced by drawing with a winder 7. Then, at the position immediately after drawing the line, the laser outer diameter measuring device 8
Using , the maximum value of the outer diameter output vibrating at 8.3Hz is
By controlling the drawing speed by varying the drawing speed so that the fiber thickness was 140 μm, a multi-core optical fiber with a square cross section of 100±2 μm on one side was obtained.

Example 2 Using the same equipment and method as in Example 1, a sample with a cross-sectional shape of 30 mm x 1 mm was prepared, as shown in Figure 2 a.
A rectangular preform was drawn while being rotated at 300 rpm and fed by a winder at a constant speed of 2 mm/min. Using a laser outer diameter measuring device, we controlled the drawing speed of the multi-core optical fiber immediately after drawing so that the outer diameter output when vibrating at 5 Hz had a maximum value of 300 μm, and found that [300±10 μm] [10±
A multi-core optical fiber with a rectangular cross section of 1 μm could be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a multi-core optical fiber with a flower-shaped or small circle-shaped cross-section, FIG. 2 is a cross-sectional view of a multi-core optical fiber with a rectangular or square cross-section, and FIG. 3 is an explanation of the apparatus used to carry out the manufacturing method of the present invention. It is a diagram. In each figure, 1 is a core, 2 is a cladding, 3 is a preform, 5 is a heater, 6 is a multi-core optical fiber, 7 is a winder, and 8 is an outside diameter measuring device.

Claims (1)

[Scope of Claims] 1. A method for manufacturing an optical fiber in which a preform rod having a non-circular cross-sectional shape is drawn, and the outer diameter is immediately measured and controlled. A method for manufacturing an optical fiber with a non-circular cross section, characterized by controlling.