JPS6235648B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fiber optic cable comprising at least one optical filament material having a core of glass or silica and a sheath of low refractive index.

It is well known in the art that optical filament materials transmit light by internally reflecting the light multiple times along the length of the filament.
Great care is taken to minimize light loss along the length of the filament. In other words, internal reflection must occur to cause as much total internal reflection as possible so that light impinging on one end of the material of the optical filament is efficiently transmitted to the opposite end. The light transmitting portion, or core, of the optical filament material is surrounded by a low index sheath that minimizes the escape or absorption of light along the length of the filament. The pod is usually transparent because opaque pods absorb light more easily. The sheath can be made of glass or polymeric materials, but traditionally is made of polymers because it increases toughness.

Optical filament materials are broadly classified into two types depending on the type of optically transparent core material. The first type of core material is thermoplastic in nature and the second type is made of glass or silica.
The first type generally has superior toughness and ease of connection;
The second type is better at transmitting light.

One disadvantage of optical filament materials with glass or silica cores is that the core is susceptible to breakage due to brittleness. Encasing the filament inside a cable containing reinforcing material and a protective layer has been only partially successful in overcoming core fragility. There is a need for fiber optic cables that provide enhanced resistance to breakage of fragile core materials.

According to the invention, a method for manufacturing a reinforced optical transmission cable comprises: a substantially solid cylindrical or hollow cylindrical core of optically transparent glass or silica;
A plurality of polymeric filaments (b) are placed around an optical fiber (a) consisting of a transparent sheath with a refractive index that is at least 0.1% less than the refractive index of the core, under the following conditions: are substantially untwisted, tensioned, substantially parallel along the longitudinal axis of said optical fiber (a), and arranged with substantially zero twist. Meanwhile, the outside of the optical fiber (a) and the filament (b) are coated with a molten polymer for the jacket (c), and the molten polymer cools and coats the filament. A method of manufacturing a reinforced optical transmission cable is provided, wherein the tension is maintained until the tension is secured in the cable.

Further in accordance with the invention, a method for manufacturing a reinforced optical transmission cable comprises: a substantially solid cylindrical or hollow cylindrical core of optically transparent glass or silica;
coating an optical fiber (a) consisting of a transparent sheath with a refractive index at least 0.1% smaller than the refractive index of the core with a molten polymer for a protective layer; a'), a plurality of polymeric filaments (b) are placed around the coated optical provided that the fibers (a′) are arranged substantially parallel to and with substantially zero twist along the longitudinal axis of the coated optical fibers (a′); Coating the outside of the filament (b) with molten polymer for the jacket (c) and maintaining the tension until the molten polymer cools and secures the filament in the cable. A method of manufacturing a reinforced optical transmission cable is provided.

The optically transparent cylindrical core for transmitting light is made of optically transparent glass or silica. The silica core may be pure silica (undoped) or doped with a suitable component, such as germanium or boron. As used herein, the term "optically transparent" refers to 30cm
means a light transmission of at least 50%. This transmission need not cover the entire spectrum. Examples of suitable descriptions of core materials are U.S. Pat.
No. 3,508,589, for example, the latter patent mentions suitable core materials made of barium, flint and borosilicate glass, the denser the glass the better.

A preferred core material is made of silica, which may or may not be doped. Silica is stretched at high temperatures to become a core material. Stretching temperatures of at least 2000°C can be used, although a temperature range of 2040° to 2120°C is preferred. It was found that as the stretching temperature decreased, the brittleness of the expanded silica core material increased. The factor that limits the upper temperature limit is the difficulty in controlling the caliper. At the highest drawing temperature, the ability to control the caliper reaches its breaking point.

The diameter of the cylindrical optically transparent core varies from relatively thin to relatively thick core structures. A suitable diameter range is 10-400 μm. A thicker core is advantageous when the light source is large, such as from an LED (light emitting diode), in that it can capture a large proportion of the incident light, but it has the disadvantage of a large bending radius. When the light source is small, such as a laser, a relatively thin core is suitable for capturing the incident light.

The sheath applied to the optically transparent heart is transparent;
The refractive index is at least 0.1% lower and may be glass, silica, or a substantially amorphous optically transparent thermoplastic polymeric material. Pure silica has a lower refractive index than most known glasses, and when silica is used for both the core and sheath, the silica core can be doped to raise the refractive index at least 0.1% above that of the sheath. level.

A preferred material of construction for the sheath is a substantially amorphous transparent thermoplastic polymer. This is because such polymers do not have the brittleness characteristic of glass or silica.

Examples of suitable sheath materials include those described in GB 1037498, such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoromethyl trifluorovinyl ether, perfluoropropyl trifluorovinyl ether. and expression However, in the formula, X is selected from the group consisting of F, H, or Cl, n is an integer of 2 to 10, m is an integer of 1 to 6,
Included are polymers and copolymers of fluorinated esters of acrylic acid or methacrylic acid having the structure where Y is CH ₃ or H.

The thickness of the pod is generally not important, since the pod material reflects light that passes through the heart. A suitable wall thickness range for this sheath material is 2 to 500 microns. Excessive sheath wall thickness will reduce the flexibility of the final cable, but
This is undesirable.

Known techniques are suitable for applying the sheath material. Glass or silica can be coated by double crucible stretching method, or
The polymer, on the other hand, is extrusion coated onto the core.

In the present invention it is necessary to insert a reinforcing material between the optical filament material and the protective jacket. Preferably, the reinforcement comprises a polymeric filament having an elastic modulus of at least 10,000,000 psi. A suitable polymer for use in filaments meeting this criterion is poly(p-phenylene terephthalamide), which is disclosed in U.S. Pat. No. 3,869,430. The disclosure of this patent is incorporated herein by reference.

At least two fibers are used and held in the cable under tension by the jacket material. It is preferred to use bundles of fibers, or yarns, rather than individual fibers. two fibers or yarns
is suitable, but more preferably at least 4
One fiber or thread is used, most preferably six or more fibers or threads. These fibers are arranged substantially parallel to the core along the longitudinal axis. The fibers have essentially zero twist about the longitudinal axis of the core. The term "zero twist" means that no fibers surround the core material, regardless of the length of such material.

The purpose of arranging the fibers substantially parallel to the longitudinal axis of the core and with substantially zero twist is to ensure that the reinforcing fibers are held under tension in the fiber optic cable. be. If the reinforcing fibers surround the core material, relaxation of the reinforcing material will easily occur. Although the degree of tension in the reinforcement fibers is not critical, it is nevertheless essential to keep the fibers under tension in the cable. This tension can be easily demonstrated in the final cable. When the cable is cut cross-sectionally, the optical filament material, consisting of a glass or silica core and sheath, is physically felt to protrude slightly from the cut end of the cable.

An optical filament material consisting of a glass or silica core and a low refractive index sheath is placed within a protective jacket. The jacket serves to keep the reinforcement under tension, and as long as it does this job, the jacket material is not critical. The jacket is a thermoplastic polymer coated by conventional extrusion. Suitable structural materials are polyamides, polyether ester copolymers, polyurethanes, polyolefins (homopolymers and copolymers including ionomers), such as polyethylene and polypropylene, and melt-extrudable fluorocarbons, such as tetrafluoroethylene/ Hexafluoropropylene copolymers and melt-extrudable chlorine-containing polymers, such as polyvinyl chloride.

The factors that govern the selection of jacket materials are strength, elongation, burn rate, and ease of peeling. For example, good peelability is required to connect one cable to another or to connect a cable to a light source or detector.

The optical fiber cable of the present invention provides a cable with a glass or silica core that exhibits a high degree of resistance to breakage of the light carrying portion. Cables containing optical filament materials consisting of a glass or silica core and a low refractive index sheath are known in the art.
In the cable of the present invention, the type of reinforcement that protects the glass or silica core provides superior breakage resistance of the core material compared to conventional optical transmission cables made of the same core and sheath materials. .

The cable of the present invention has high bending strength, high tensile strength,
and high impact strength. This combination of properties could not be achieved by cables having a brittle core without reinforcing fibers held under tension.

In the case of the optical fiber cable structure of the present invention, a structure can be obtained in which the cable can be bent sharply without damaging it. A minimum bending diameter of at least about 6 mm, preferably at least about 4 mm can be obtained. As shown in Example 2, the cables of the present invention, for example, have a minimum bend diameter of at least about 4.
Can be tied into a tight knot with mm.

Although the present disclosure is directed to interposing a stiffener held under tension between a sheath of optical filament material and a jacket, it is understood that the stiffener need not contact the sheath. . The protective layer allows separation of the pod from the reinforcement. Even in these cases, it is important to keep the reinforcing fibers under tension.

It is also within the scope of the present invention to use more than one optical filament material in the cable, so long as the optical filament material has at least two reinforcing fibers in the manner described herein.

The invention is further illustrated by the following examples.

Example 1 Part 1 Using a furnace with nitrogen-protected tungsten heating elements, from a 9 mm rod
Spun undoped silica fibers at 2050°C. The speed at which the rods are connected to the furnace and the speed at which the fibers are removed from the furnace are set at approximately 10 m/min to obtain fibers of 200 μm. The number of yarn breaks during spinning was less than once per 1000 m. A sheath of a low refractive index, substantially amorphous, transparent polymer (secondary transition temperature 50°C, refractive index 6% lower than the core) consisting of fluorinated esters of methyl methacrylate and methacrylic acid was coated with difluorotetrachloroethane. An optical fiber having an outer diameter of about 600 μm was produced by coating the fiber with the solution dissolved in the solvent.

This optical fiber is 1Km at 655.3nm
It showed an attenuation of 38db per hit.

Part 2 The optical fibers of Part 1 are reinforced with six strands of 42 tex (380 denier) poly(p-phenylene terephthalamide) and are made of polyetherester copolymer (U.S. Pat. No. 3,651, No. 014 Example 1
(disclosed in ).

Six strands of poly(p-phenylene terephthalamide), i.e., a bundle of six substantially untwisted polymer filaments, were initially tensioned in a tensioning retainer and a syringe needle with an inner diameter of 1550 μm and an outer diameter of 2050 μm. Pass through a crosshead die with certain fiber guides and 1875 μm holes. The tension of the thread was set to 1.16×10 ^-3 newtons/tex (0.013g/denier), and the temperature was 205°C.
The polyether ester copolymer heated to The extrusion speed and thread speed were adjusted to yield an extrudate with an outer diameter of 1750 μm. A blank 550 μm outer diameter nylon filament was fed into a six strand bundle and the speed was readjusted to produce an extrudate with a diameter of 1875 μm. The die was adjusted so that the nylon filament and thread bundle were centered. Nylon·
The filament was removed and replaced with the coated optical fiber of Part 1 and coated with polyetherester copolymer to create a fiber optic cable.

This optical fiber cable (compared to 38db per km of the first part optical fiber)
It showed an attenuation of 40db per km at 655.3nm. The cable was tested under load and broke at 30Kg. This cable did not lose its ability to transmit light even after being hammered. Although this cable could be wrapped around a 6 mm diameter mandrel without destroying the heart or losing its ability to transmit light, it was not possible to tie a tight knot without destroying the heart.

Example 2 The procedures of Parts 1 and 2 of Example 1 were repeated, but the optical fibers of Part 1 of Example 1 were processed into polyetherester copolymer (U.S. Pat. No. 3,651,014) using a tube crosshead die. (described in Example 1) and then the reinforcement and jacket polyether ester copolymer were applied by the method of Example 1, Part 2. The outer diameter of this optical fiber is
It was 1225 μm. The method of Example 1-Part 2 of providing reinforcement uses poly(phenylene terephthalamide) fibers, three threads of 42 tex (380 denier) and 3 threads of 168 tex (1420 denier).
Three threads were used. The tension of the fiber is 1.8×10 ^-3
It was Newton/Tex (0.02g/denier).

The final optical fiber cable has an outer diameter of 2375μm,
The attenuation for 1 km at 655.3 mm was 40 db, and the breaking strength was 85 kg. This cable can be wrapped around a 4 mm diameter mandrel and tied into a tight overlock knot without breaking or loss of light transmission.

Claims (1)

[Claims] 1. A method for manufacturing a reinforced optical transmission cable comprising: a substantially solid cylindrical or hollow cylindrical core made of optically transparent glass or silica; A plurality of polymeric filaments (b) are placed around an optical fiber (a) consisting of a transparent sheath having a refractive index of at least 0.1% less than the refractive index of provided that the optical fiber (a) is untwisted, tensioned, substantially parallel along the longitudinal axis of the optical fiber (a), and arranged with substantially zero twist; , while the outside of the optical fiber (a) and the filament (b) are coated with a molten polymer for the jacket (c), and the molten polymer cools and inserts the filament into the cable. A method for manufacturing a reinforced optical transmission cable, characterized in that the tension is maintained until it is fixed. 2. The method of claim 1, wherein the polymer filament is a filament of poly(p-phenylene terephthalamide). 3. A method for manufacturing a reinforced optical transmission cable, comprising: a substantially solid cylindrical or hollow cylindrical core of optically transparent glass or silica;
coating an optical fiber (a) consisting of a transparent sheath with a refractive index at least 0.1% smaller than the refractive index of the core with a molten polymer for a protective layer; a'), a plurality of polymeric filaments (b) are placed around the coated optical provided that the fibers (a′) are arranged substantially parallel to and with substantially zero twist along the longitudinal axis of the coated optical fibers (a′); coating the outside of the filament (b) with a molten polymer for the jacket (c) and maintaining the tension until the molten polymer cools and secures the filament in the cable; A method for manufacturing a reinforced optical transmission cable characterized by: 4. The method of claim 3, wherein the polymer filament is a filament of poly(p-phenylene terephthalamide).