JPS6245186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a metal coated optical fiber with excellent strength.

Metal-coated optical fiber, which is a bare optical fiber made of silica glass whose outer peripheral surface is coated with metal, is used because the metal coating has excellent heat resistance and the metal coating prevents water from permeating. It is an optical fiber that has excellent heat resistance, moisture resistance, and long-term reliability, and can be used even in harsh environments such as high temperature and high humidity.

By the way, in order to manufacture such a metal-coated optical fiber, for example, a bare optical fiber is melt-spun from a glass base material, and then immediately introduced into a metal coating apparatus using a dip method or the like, and coated with metal to a predetermined thickness. A method is known in which the material is then cooled at room temperature and then rolled up.

According to this method, the bare optical fiber is coated with metal immediately after melt spinning.
The surface of the bare optical fiber can be maintained in a state where there are almost no minute scratches (flows). Bare optical fiber in this state has almost no flow, so it exhibits tensile strength and elongation close to theoretical values, with an elongation rate of nearly 30%. however,
Since the metal coating coated on such a stretchable bare optical fiber is rapidly cooled from several hundred degrees Celsius to room temperature, a strong thermal shock acts on it, which can cause defects inside the metal coating structure. or internal stress occurs. Since the metal coating is further rapidly cooled, it becomes a hardened state, and therefore, the structure of the metal coating is fixed in an unstable state, hardens, and becomes poor in ductility.

For this reason, when there is a difference in ductility between the metal coating and the bare optical fiber, and force is applied to the metal-coated optical fiber, the extension of the metal coating cannot match the elongation of the bare optical fiber, and stress is concentrated on the metal coating. rupture of the metal coating occurs. Fragments of the metal coating caused by this breakage cause minute scratches on the surface of the bare optical fiber, and these scratches reduce the strength of the metal coated optical fiber.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a metal-coated optical fiber with excellent strength.

The present invention will be explained below with reference to the drawings.

FIG. 1 shows an example of an apparatus suitable for the method of manufacturing a metal-coated optical fiber of the present invention, in which numeral 1 indicates a glass base material. The glass base material 1 is heated and melted in a carbon resistance furnace 2 and spun. The spun bare optical fiber 3 is immediately guided to a metal coating device 4 using a dip method, chemical vapor deposition method, sputtering method, etc., and is coated with a metal to form a metal coated optical fiber 5. This metal-coated optical fiber 5 is wound around a winding drum 7 installed inside an annealing device 6 maintained at a predetermined temperature so as not to be rapidly cooled. Since the spinning speed of the bare optical fiber is as high as 10 m to 100 m/min, it can be considered that the metal-coated optical fiber 5 is placed in the annealing device 6 immediately after being coated with metal. The slow cooling device 6 consists of a main body 8 in which a winding drum 7 is housed, and a hot air device 9 that blows heated gas. It is provided with an air outlet 8b for blowing air, and the inside of the main body 8 is maintained at a predetermined temperature by heated gas blown from a hot air device 9.

The temperature at which the metal-coated optical fiber 5 is slowly cooled varies depending on the metal to be coated, the coating method, the thickness of the metal coating, and the desired properties, but is generally about 1/3 to 2/3 of the melting point of the metal. Preferably, for example Al
For Sn, it is preferably about 210 to 440°C, and for Sn, about 70 to 160°C. Although the time for slow cooling also varies depending on various conditions, it is necessary to leave the winding drum 7 in the slow cooling device 6 for a certain period of time after the final winding of the metal-coated optical fiber 5 is completed.

In this way, it is immediately stored in the slow cooling device 6,
The metal coating of the metal coated optical fiber 5, which is kept at a predetermined temperature for a predetermined period of time and slowly cooled, receives less thermal shock and is in an annealed state, so there are no internal defects and there is less residual stress, making it more stable. Because of its structural state, it is soft and ductile. The effect of this slow cooling is due to the difference in elongation between castings and unannealed materials of the same metal (for example, in the case of Ni, castings are 25%, annealing materials are 40-50%).
%, Sn can achieve an effect close to that of cast metal (10%) and annealed material (40%).

FIG. 2 shows another example of an apparatus suitable for the method of manufacturing a metal-coated optical fiber of the present invention.
A heat insulating furnace 10 is provided following the metal coating device 4 of the device shown in the figure. This heat retention furnace 10
is heated by an internal electric resistance wire 11, and the internal temperature ranges from slightly lower than the melting point of the coated metal to about 1/2 of the melting point, for example Al650~320℃Sn230~ The temperature is maintained at approximately 110° C., and is provided between the metal coating device 4 and the slow cooling device 6 so that the metal coated optical fiber 5 is not cooled rapidly. It is conceivable that the effect of the slow cooling device 6 can be obtained by using this insulating furnace 10, but since optical fibers are spun at high speed, the insulating furnace 10 would be long, which would be impractical. It is preferable to provide an annealing device 6 also at the portion of the winding drum 7. At this time, it is more preferable to create a temperature gradient in the heat-retaining furnace 10 and guide it to the slow cooling device.

The metal coating layer of the metal coated optical fiber 5 manufactured by being slowly cooled after being coated with metal in this way has a high ductility, so when the metal coated optical fiber is stretched, the metal coating layer can be extended as the bare optical fiber is stretched. Therefore, no force is concentrated on the metal coating, and the metal coating will not break and damage the surface of the bare optical fiber. Therefore, the strength of the bare optical fiber 3 is fully exhibited, and the metal-coated optical fiber 5 has excellent strength. In addition, there are few residual stresses and defects in the metal coating, so stable strength can be maintained.

Note that, although the method using heated gas and the method using electric resistance wire 11 are shown as heating methods for the slow cooling device 6 and the heat-retaining furnace 10 in the manufacturing apparatus shown in FIGS. 1 and 2, the present invention is not limited to these methods. Any other method may be used as long as the same effect can be obtained without being affected, for example, a method using infrared rays, far infrared rays, etc., a method using induction heating, etc. may be used. Further, the slow cooling device 6 may heat the winding drum from inside the winding drum instead of heating the winding drum from the outside.

Next, the method for manufacturing the metal-coated optical fiber of the present invention will be explained in detail with reference to Examples.

Example 1 A glass base material 1 made of quartz glass was spun at 40 m/min using the apparatus shown in FIG.
50μm, cladding diameter 150μm bare optical fiber 3
And so. This bare optical fiber 3 was coated with Sn by the dip method and wound onto a winding drum 7 in an annealing device 6. The outer diameter of the metal-coated optical fiber 5 coated with Sn was 190 μm. The internal temperature of the annealing device 6 is 120°C, and the metal-coated optical fiber is kept warm in the annealing device 6 at 120°C for one hour after winding, and then the temperature inside the annealing device 6 is gradually lowered to room temperature. It was lowered and then taken out.

An Sn metal-coated optical fiber (A) produced by the above production method was compared with a method (corresponding to the conventional method) that differs from the above production method only in that no heat treatment is performed using the slow cooling device 6, as a comparative example. A tensile strength test was conducted with the Sn metal-coated optical fiber manufactured by method (B), and the probability of breakage was evaluated using the Weipul distribution shown in Figure 3. The conditions for the tensile strength test were: span length 300 mm, tensile speed 30 mm/min, and number of samples 50.

As can be seen from Fig. 3, the minimum strength of Sn metal-coated optical fiber (A) manufactured by the method of manufacturing metal-coated optical fiber of the present invention is 8.5 kg, and the Sn metal-coated optical fiber (A) has a minimum strength of 8.5 kg. This is a marked improvement compared to 6.0Kg in (B). In addition, the slope of the graph of Sn metal-coated optical fiber...(A) is steep.
Therefore, it can be seen that the quality is stable. Also, the loss is lower than that before treatment.

Example 2 A bare optical fiber 3 having a core diameter of 50 μm and a cladding diameter of 125 μm was obtained by spinning a silica-based glass base material 1 at a speed of 20 m/min using the apparatus shown in FIG. This optical fiber bare wire 3 has a purity of 99.999% by sputtering method.
was coated with Al to a thickness of 2 μm. At this time, the reaction temperature of the metal coating device 4 was 600°C. The heat retention furnace 10 following the metal coating device 4 had a furnace length of 6 m, used infrared rays as a heating source, and had an internal temperature of 350°C. The temperature inside the slow cooling device 6 was set at 250° C., and the metal-coated optical fiber was kept warm in this furnace for one hour even after winding was completed.

An Al metal-coated optical fiber (C) manufactured by the above method and, as a comparative example, a method that differs from the above manufacturing method in that the insulating furnace 10 and the slow cooling device 6 are not used (method equivalent to the conventional method) Al manufactured with
A tensile strength test was conducted on metal-coated optical fiber (D) at a span length of 300 mm and a tensile speed of 30 mm/min.
The average tensile strength of each was 6.0 kg for the Al coated optical fiber (C) made by this method and 5.3 kg for the Al metal coated optical fiber (D) made by the conventional method. This result shows that the metal-coated optical fiber 5 manufactured by the manufacturing method of the present invention, which has been subjected to heat treatment, has excellent tensile strength.

As explained above, in the method for manufacturing a metal-coated optical fiber of the present invention, the bare optical fiber is coated with metal and then heat-treated, so that there is less internal stress and defects in the metal coating, and the metal coating is further coated with metal. The ductility of the coating is increased, and therefore, the metal-coated optical fiber produced by this manufacturing method has excellent strength and less product variation.

[Brief explanation of the drawing]

1 and 2 are both schematic configuration diagrams showing an example of a manufacturing apparatus suitable for the method of manufacturing a metal-coated optical fiber of the present invention, and FIG. 2 is a graph showing the probability of breakage of a manufactured metal-coated optical fiber using a Weibull distribution. In the figure, 3... bare optical fiber, 5... metal coated optical fiber, 6... slow cooling device.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a metal-coated optical fiber, which comprises applying a metal coating to a bare optical fiber and then slowly cooling the metal coating. 2. The method for manufacturing a metal-coated optical fiber according to claim 1, characterized in that the metal coating is slowly cooled at least at a position where the metal-coated optical fiber is wound. 3. The method for manufacturing a metal-coated optical fiber according to claim 1, characterized in that slow cooling is performed immediately after coating the metal and at a position where the metal-coated optical fiber is wound.