JPH0224087Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to optical fiber cores.

Optical fiber is a thin glass fiber that transmits light, but if the thin glass wire is used as it is, it is easy to break and is inconvenient to use. It is used as. The conventional optical fiber core wire is shown in FIG. In the optical fiber core, a fiber 1 is coated with a primary coating 2, on top of which a silicone rubber or the like with high mechanical strength is laminated as a buffer layer 3, and then a thermoplastic resin such as nylon is layered on top of that as a secondary coating 4. It is laminated as. Although the optical fiber core wire having such a structure is relatively easy to manufacture, it has the disadvantage that it is susceptible to temperature changes because the plastic used as the secondary coating 4 has a large temperature dependence. For example, the coefficient of linear expansion of the plastic used as the secondary coating is more than two orders of magnitude higher than that of the glass wire. Therefore, in a certain temperature range, the secondary coating 4
gives mechanical stress to the optical fiber 1 and deteriorates transmission loss. Further, since the strength of the secondary coating 4 is insufficient, the optical fiber coated with the secondary coating 4 is susceptible to bending and lateral pressure, and the optical fiber coated wire cannot be used alone. For this reason, reinforcing materials such as tension members are required even when the core wires are bundled to form a cable or cord.

The purpose of the present invention is to provide a cored optical fiber that dramatically improves transmission characteristics by minimizing the temperature dependence of the optical fiber, and also improves mechanical strength. The structure is characterized in that the optical fiber wire is covered with a reinforcing plastic having a negative coefficient of linear expansion and using aromatic polyamide fiber as a reinforcing material.

EMBODIMENT OF THE INVENTION Hereinafter, the optical fiber core wire of this invention will be explained in detail based on an Example.

The optical fiber core wire of the present invention uses reinforced plastic reinforced with aromatic polyamide fibers as a coating that covers the optical fiber wire, and is used, for example, as a secondary coating for conventional optical fiber core wires. Aromatic polyamide fiber-reinforced plastic is used instead of nylon, etc. That is, an optical fiber wire is coated with a normal primary coating and a buffer layer, and then an aromatic polyamide fiber-reinforced plastic is further coated thereon as a secondary coating. Generally, as reinforced plastics, unsaturated polyester resins and epoxy resin molded products using glass fibers, polyester fibers, etc. as reinforcement materials are well known, but the reinforced plastics used in this invention are made of aromatic polyamides as reinforcement materials. Use fiber. Incidentally, as the aromatic polyamide fiber, for example, Kevlar aramid fiber can be used.

Since the optical fiber core wire with the above structure uses reinforced plastic reinforced with aromatic polyamide fibers (hereinafter referred to as reinforced plastic) as the secondary coating, the temperature dependence of the optical fiber can be minimized.
Transmission loss can be kept low. The coefficient of linear expansion of reinforced plastic is -2 x 10 ^-6 ℃ ^-1 , which is much higher than that of glass fiber, compared to the linear expansion coefficient of 2 x 10 ^-4 ℃ ^-1 of nylon, which is conventionally used as a secondary coating. The intrinsic coefficient of linear expansion is close to 6×10 ^-6 °C ^-1 . Therefore, even when the optical fiber core of the present invention is placed under low or high temperatures, there is little irregularity in the expansion between the optical fiber and the reinforced plastic, and the optical fiber core with a secondary coating of nylon is This is because there is no risk that the optical fiber strand will have an extra length with respect to the secondary coating, causing a meandering phenomenon and causing loss deterioration due to microbends in the transmission characteristics, as experienced in the above. FIG. 3 shows a comparison of the temperature characteristics of the transmission loss of the conventional optical fiber core and the optical fiber core of the present invention. As shown in the figure, the change in transmission loss of the conventional optical fiber increases at low temperatures, reaching as much as 40 dB/Km at -60℃, but the change in transmission loss of the optical fiber of the present invention increases at low temperatures. It was stable at 0.1 dB/Km or less within the range of -60℃ to 60℃.

Furthermore, since the reinforcing plastic in the optical fiber core of the present invention has a negative linear expansion coefficient, the temperature dependence of the optical fiber, which is caused by changes in the optical fiber's linear expansion coefficient and refractive index, which are positive values, is reduced. This makes it possible to obtain an optimal optical fiber for use in communication channels for high-precision synchronization signal systems. That is, 2
The coefficient of linear expansion α _eq of the coated optical fiber composite is expressed by the following equation (A). As is clear from this equation, by increasing the composition ratio or coating diameter of the reinforcing plastic, the linear expansion coefficient of the entire optical fiber can be reduced by the linear expansion coefficient of the reinforcing plastic - 2
×10 ^-6 ℃ ^-1 can be approached.

α _ep = Σα _i E _i S _i /ΣE _i Si …(A) Here, α, E, and S represent the coefficient of linear expansion, Young's modulus, and cross-sectional area of each material constituting the optical fiber, respectively, and the subscripts i represents each material (optical fiber, primary coating, buffer layer, secondary coating). The coefficient of linear expansion of the optical fiber coated with this secondary coating is -2
×10 ^-6 °C ^-1 , and the temperature dependence of the propagation time (1/γ) (dγ/dT) determined by the coefficient of linear expansion of the optical fiber is expressed by the following equation (B ), as the coefficient of linear expansion of the optical fiber is reduced, it becomes smaller.

1/γdγ/dT=1/ndn/dT+1.25/LdL/dT…(B) Here, the first term on the right side is a term representing the temperature dependence of the refractive index, and the second term is the term representing the temperature dependence of the optical fiber. This term is due to the temperature dependence of , that is, the coefficient of linear expansion. For example, in the case of a standard optical fiber, the temperature dependence of the refractive index (1/n) (dn/dT) is 6 × 10 ^-6 °C ^-1
Therefore, if the linear expansion coefficient of the entire optical fiber of the present invention is close to -2×10 ^-6 °C ^-1 , the temperature dependence of the propagation time of the optical fiber of the present invention (1 /γ) (dγ/dT) is approximately 3.5×10 ^-6
℃ ^-1 . This value is based on the temperature dependence of the propagation time of the conventional FRP-coated core wire and nylon-coated core wire, respectively.
14.8×10 ^-6 ℃ ^-1 , which is much smaller than 30×10 ^-6 ℃ ^-1 . As described above, since the optical fiber of the present invention has a small temperature dependence of propagation time, it is optimal for use in a communication path for a high-precision synchronization signal system.

Furthermore, the reinforced plastic used in this invention has a tensile strength of about 30% compared to the commonly used glass fiber reinforced plastic (GFRP).
%, the tensile modulus is about twice as high, and the mechanical strength is excellent. In addition, the weight of the optical fiber core of this invention is approximately 60% of the weight of the optical fiber core wire using GFRP.
It's only about % and it's light.

Next, an example of a method for manufacturing a coated optical fiber according to the present invention will be explained with reference to FIG.

Next, an example of a method for manufacturing a coated optical fiber according to the present invention will be explained with reference to FIG.

Aromatic polyamide fibers 11 are fed from a plurality of rolls into a resin impregnation tank 12, and the unsaturated polyester resin in the tank 12 is impregnated with the aromatic polyamide fibers 1.
Impregnate with 1. Thereafter, the aromatic polyamide fiber 11 is pulled up, and an optical fiber 13 provided with a primary coating layer and a buffer layer is supplied to the aromatic polyamide fiber 11, and the fibers are sent together to a preforming device 14. After the optical fiber strand 13 is held at the center of the aromatic polyamide fiber 11 by the preforming device 14, it is sent to the heat curing furnace 15. The unsaturated polyester resin is heated and cured in the heat curing furnace 15 to integrate it into the optical fiber core wire, and then the drawing device 1
After adjusting the shape in step 6, it is wound up in a winding device 17.

As explained above in detail based on the examples, according to the optical fiber core wire of the present invention, aromatic polyamide fiber-reinforced plastic is used as a coating for the optical fiber wire, so the temperature dependence of transmission characteristics is minimized. As a result, transmission characteristics can be dramatically improved, and mechanical strength can also be improved at the same time. Furthermore, since the temperature dependence of the propagation time of an optical signal can be reduced, the optical fiber core of the present invention is also optimal as a communication path for a high-precision synchronization signal system.

[Brief explanation of the drawing]

Figure 1 is an end view of the optical fiber core wire, Figure 2 is an explanatory diagram for explaining the method of manufacturing the optical fiber of the present invention, and Figure 3 is temperature (°C) vs. transmission loss change (dB/Km). This is a glass that represents the correlation between In the drawing, 1 is an optical fiber, 2 is a primary coating layer, and 3 is an optical fiber.
1 is a buffer layer, 4 is a secondary coating layer, 11 is an aromatic polyamide fiber, 12 is a resin impregnation tank, 13 is an optical fiber wire provided with a primary coating layer and a buffer layer, 14
1 is a preforming device, 15 is a heat curing device, 16 is a drawing device, and 17 is a winding device.

Claims (1)

[Scope of utility model registration request] An optical fiber core wire characterized in that an optical fiber wire is covered with a reinforced plastic having a negative coefficient of linear expansion and using aromatic polyamide fiber as a reinforcing material.