JP2804163B2 - Manufacturing method of optical fiber material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a flexible optical fiber material suitable for use as a fire-resistant / heat-resistant optical fiber.

(Conventional technology) In order to maintain the mechanical strength of a quartz optical fiber, a molten preform is drawn and simultaneously coated with a plastic resin, or the fiber surface is protected by a metal film formed by plating or vapor deposition. However, it has recently been proposed to coat amorphous carbon. In general, resin-coated optical fibers have a fiber temperature of about
It must be limited to operating conditions of 150 ° C or lower, or set to about 150 ° C or lower by a special cooling device. On the other hand, an optical fiber coated with a metal by the electrolytic plating method is more suitable as an optical fiber for fire resistance and heat resistance as the metal coating layer is thicker. For example, if this is used as a temperature sensor head, a special Without installing a cooling device, it becomes possible to observe the emission spectrum in a high-temperature electric furnace.

(Problems to be Solved by the Invention) Although a metal-coated optical fiber is preferable for fire resistance and heat resistance as the metal coating layer is thicker, if the metal coating layer is thickened to obtain sufficient mechanical strength, the fiber And the laying work tends to be more complicated. That is, if the metal coating layer becomes thick to a certain extent, the rigidity of the metal coating layer itself causes considerably severe restrictions on the cable design in order to maintain the flexibility of the optical fiber cable. Also, if a simple metal-coated fiber is used as the transmission line of a fire-resistant or heat-resistant cable, the stress in the metal coating layer applied to the optical fiber changes due to temperature changes in the operating environment, which causes the transmission loss of the optical fiber to change. Problem arises.

The present invention has been proposed in order to improve the above-mentioned problems relating to the metal-coated optical fiber, and it is an object of the present invention to provide a method for producing an optical fiber material having sufficient flexibility while maintaining a predetermined mechanical strength. The purpose is.

(Means for Solving the Problems) In order to achieve the above object, in the manufacturing method according to the present invention, an optical fiber as shown in FIG. 1 is used, and the fiber comprises a core 2 and a clad 3, A carbon film 4 is formed thereon. The carbon film 4 is generally formed by drawing a preform in a molten state and simultaneously coating amorphous carbon or the like in a reaction furnace, and has a thickness of about 300 to 1500 °. The carbon film 4 has a dense structure and does not allow passage of hydrogen and moisture, and prevents the surface of the optical fiber from being damaged during transportation or storage. Since the carbon film 4 has low conductivity and is difficult to be directly subjected to electrolytic plating, the base metal layer 5 is first provided on the carbon film. The base metal layer 5 is provided relatively thinly and uniformly on the peripheral surface of the carbon-coated fiber, and the base metal layer may be formed by any of an electroless plating method, a vacuum deposition method, a sputtering method, and an ion plating method. The thickness of the base metal layer 5 may be several μm or less, for example, copper, nickel, aluminum, silver, gold, or the like. Although the relatively thick metal surface layer 6 may be formed by any plating method, it is generally preferable to form the metal surface layer efficiently by electrolytic plating, and the material is copper, nickel, aluminum, silver, as in the case of the base metal layer 5. , Gold, etc. The metal-coated optical fiber is subjected to heat treatment at a high temperature for a short period of time, thereby imparting only flexibility without substantially deteriorating the transmission loss of the optical fiber. Although the heat treatment in the method of the present invention is preferably as high as possible, it is limited to a temperature range that sufficiently maintains the mechanical strength of the optical fiber and does not deteriorate its transmission loss. Different. The maximum heating temperature and time that do not degrade the silica-based optical fiber have been found to be several minutes at about 900 ° C. by a heat resistance test in air or an inert gas.

(Function) The optical fiber used in the method of the present invention can be heated to about 900 ° C. by having a carbon film 4 having a dense structure and not allowing hydrogen and moisture to pass therethrough and a relatively thick metal surface layer 6. By this heat treatment, the crystal structure of the metal surface layer 6 is adjusted and, at the same time, the internal stress is removed to provide flexibility. For example, an optical fiber formed with a 500-mm-thick carbon film and a copper or nickel plating layer,
The thickness of the nickel plating layer was reduced by the heat test in air.
If it is 10 μm or more, the optical fiber hardly deteriorates even when heated at 900 ° C. for 6 minutes. In an inert gas, the optical fiber does not deteriorate even if the nickel plating layer is several μm.

(Examples) Next, the method of the present invention will be described based on examples.

The all-silica optical fiber used in the present invention is prepared by heating a preform in an electric furnace (not shown) to about 2,000 ° C., melting and drawing at once, and simultaneously introducing the preform into a reaction furnace (not shown). Is coated. The obtained optical fiber has a core diameter of 100 μm and a cladding diameter of 150 μm, and has a carbon film 4 having a thickness of about 500 ° on its surface. This carbon-coated fiber is immersed in a washing tank and washed with water, immersed in an etching tank and washed with water, and immersed in an activator tank and washed with water.

Electroless nickel plating is Ni-B plating / BEL801 (manufactured by Uemura Industry Co., Ltd.), and is dimethylamine borane (DMAB).
Is immersed in a bath containing a reducing agent at 65 ° C. for 3 to 5 minutes to provide a base nickel plating layer 5 having a thickness of 0.5 to 1 μm. The obtained plated coated fiber is further washed with water and hot water and then dried.

Next, nickel or copper having a predetermined thickness is coated as the metal surface layer 6 by an electrolytic plating method. In the case of nickel, in an electroplating bath having the following bath composition, a bath temperature of 50
What is necessary is just to process at 20 degreeC for 1 to 20 minutes.

Nickel sulfamate 300-700 g / boric acid 30 g / additive (brightener, pit inhibitor) Suitable amount In the case of copper, in an electrolytic plating bath having the following bath composition, 1-60 at room temperature bath temperature. It may be processed for a minute.

Copper sulfate 200-250g / Sulfuric acid 30-75g / Additive (brightening agent) Appropriate amount In Table 1, as a heat treatment, a metal-coated optical fiber was heated to 900 ° C and passed through a 1m long furnace at a linear speed of 5m. Run at / min.

Next, in Table 2, as a heat treatment, the metal-coated optical fiber is heated for 30 minutes in a pot furnace heated to 900 ° C. in air or an inert gas.

Regarding the heat treatment in the method of the present invention, the metal surface layer 6
Is generally less reduced in mechanical strength by heating than in the case of copper. As is clear from Table 1, if the heating time is extremely short, the nickel surface layer can be heat-treated even when the thickness is about 5 μm, but the copper surface layer needs to be about 10 μm or more. As is clear from Table 2, when the heating time is about 30 minutes even if the heating time is short, the nickel surface layer needs to have a thickness of about 50 μm, and the copper surface layer cannot be processed even with a thickness of 50 μm. In addition, when heat treatment is performed in an inert gas such as nitrogen gas, as is clear from Table 2, even if the heating time is about 30 minutes, the heat treatment can be performed even if the nickel surface layer is 1 μm thick. The copper surface layer can be processed if the thickness is about 5 μm or more.

In order to compare the flexibility of the optical fiber material 1 in Example 4 with that of the metal-coated fiber before the heat treatment, the deflection amount D of the two was measured by the method shown in FIG.
Table 3 shows the measurement results of the deflection D.

From Table 3, it is clear that the heat-treated optical fiber material 1 has significantly increased flexibility over the metal-coated fiber before the heat treatment.

(Effects of the Invention) In the method of the present invention, the heat treatment of the optical fiber coated with nickel or copper or the like adjusts the crystal structure of the metal surface layer and at the same time removes internal stress to impart only flexibility. By the method of the present invention, it is possible to produce an optical fiber material having flexibility while maintaining a predetermined mechanical strength,
If the optical fiber material is used as a fire-resistant / heat-resistant optical fiber, even if the metal surface layer is considerably thickened in order to obtain sufficient mechanical strength, the flexibility of the fiber material hardly decreases, and the work of laying the fiber material, etc. Is easy. Even if the metal surface layer is thickened to a certain extent, if the rigidity of the surface layer does not increase so much, there are few restrictions on the cable design for maintaining the flexibility of the optical fiber cable. In addition, this optical fiber material does not change the stress of the metal surface layer applied to the optical fiber even if the temperature of the use environment changes suddenly, and its transmission loss is almost constant. It is suitable as.

[Brief description of the drawings]

FIG. 1 is an enlarged longitudinal sectional view showing an optical fiber used in the method of the present invention, and FIG. 2 is a schematic front view showing a method for measuring the amount of deflection of the optical fiber material manufactured by the method of the present invention. 1 ... optical fiber material, 2 ... core, 3 ... clad,
4 ... carbon film, 5 ... underlying metal layer, 6 ... metal surface layer.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Ikegami 2-5 Kusunoki Kitamachi, Neyagawa-shi, Osaka Kyowa Electric Wire Co., Ltd. (72) Inventor: Akira Iino, 6th, Yawata Kaigandori, Ichihara-shi, Chiba Prefecture, Furukawa Electric Co., Ltd. (56) References JP-A-3-88747 (JP, A) JP-A Sho 62-143848 (JP, A) JP-A-2-166410 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C03C 25/02 C03C 25/04

Claims (2)

(57) [Claims] 1. A coated optical fiber having a carbon film formed on an optical fiber consisting of a core and a clad, a base metal layer provided on the peripheral surface thereof, and a relatively thick metal surface layer formed thereon. A method for producing an optical fiber material that provides only flexibility without substantially deteriorating the transmission loss of the optical fiber by performing a short-time heat treatment. 2. The method according to claim 1, wherein when the metal surface layer is thin, it is heated in a furnace.