JPS6245530B2 - - 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 optical filament material 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 since opaque pods tend to absorb light. 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.

The present invention comprises: (A) a substantially cylindrical core of optically transparent glass or silica; (C) a protective layer coated over (B); (D) a cable reinforcement placed over (C);
and (E) the outer jacket of (A), (B), (C) and (D) above, wherein the reinforcement of (D) is comprised of a plurality of polymeric fibers, the polymeric fibers comprising (i) Elastic modulus is at least 10000000psi
(7.03×10 ⁵ Kg/cm ² ), (ii) under tension, and (iii) arranged substantially parallel along the longitudinal axis and with substantially zero twist. This invention relates to a characteristic optical transmission cable.

Preferably, the reinforcing material is comprised of a plurality of substantially untwisted polymer fibers.

The cylindrical core referred to in the present invention includes both a cylindrical core and a cylindrical core.

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 include 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. If 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 is coated by double crucible stretching method,
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. The reinforcement is comprised of polymeric fibers having an elastic modulus of at least 1,000,000 psi. A suitable polymer for use in fibers meeting this criterion is poly(p-phenylene terephthalamide), which is disclosed in US 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
are suitable, but more preferably at least four fibers or threads are 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 its sheath, is physically perceived 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 tetrafluorocarbons. Ethylene/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 transmitting portion. Cables containing optical filament materials consisting of a core of glass or silica and a sheath of low refractive index 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 the Examples, the cables of the invention have, for example, 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 present invention will be further illustrated by the following Reference Examples and Examples.

Reference Example Part 1 Undoped silica fibers are spun at 2050° C. from a 9 mm rod using a furnace with nitrogen-protected tungsten heating elements. 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 has 38db per km at 655.3nm.
showed the attenuation of

Part 2 The optical fiber of Part 1 is made of 42 tex (380 denier) poly(p-phenylene terephthalamide).
and coated with a polyetherester copolymer (disclosed in Example 1 of US Pat. No. 3,651,014).

Poly(p-phenylene terephthalamide) 6
The main strand, a bundle of six substantially untwisted polymeric filaments, is initially placed in a tensioning holder, a fiber guide which is a needle with an inner diameter of 1550 μm and an outer diameter of 2050 μm, and a crosshead with a hole of 1875 μm. Pass it through the dice. The tension of the thread is 1.16×10 ^-3
Newton/tex (0.013 g/denier) and heated to 205°C, the polyetherester copolymer was extruded through the holes of the die. The extrusion speed and thread speed were adjusted to produce an extrudate with an outer diameter of 175 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. The nylon filament was removed and replaced with the coated optical fiber of Part 1 and coated with a polyetherester copolymer to create a fiber optic cable.

This fiber optic cable exhibited an attenuation of 40 db per km at 655.3 nm (compared to 38 db per km for the first part optical fiber). 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 The methods of Parts 1 and 2 of Reference Example were repeated, but the optical fibers of Part 1 of Reference Example were processed into a polyetherester copolymer (U.S. Pat. No. 3,651,014 Example 1) using a tube crosshead die. After that, a reinforcing material and a polyether ester copolymer for the jacket were attached using the method described in Reference Example - Part 2. The outer diameter of this optical fiber is 1225μm
It was hot. Reference example of reinforcing - In the second part method, poly(p-phenylene terephthalamide) fibers are used, three threads of 42 tex (380 denier) and three threads of 168 tex (1420 denier). It was used. The fiber tension was 1.8 x 10 ^-3 newtons/tex (0.02 g/denier).

The final optical fiber cable has an outer diameter of 2375 μm.
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) a substantially cylindrical core of optically transparent glass or silica; (B) a refractive index that is at least 0.1% less than the refractive index of (A); (C) a protective layer coated over (B); (D) a cable reinforcement placed over (C);
and (E) the outer jacket of (A), (B), (C) and (D) above, wherein the reinforcement of (D) is comprised of a plurality of polymeric fibers, the polymeric fibers comprising (i) Elastic modulus is at least 10000000psi
(7.03×10 ⁵ Kg/cm ² ), (ii) under tension, and (iii) arranged substantially parallel along the longitudinal axis and with substantially zero twist. Characteristic optical transmission cable. 2. The cable of claim 1, wherein the reinforcing material (D) comprises a plurality of substantially untwisted polymer fibers. 3. The cable of claim 1, wherein the polymer fiber is poly(p-phenylene terephthalamide). 4. The cable of claim 1, wherein the polymer fibers are present as a bundle of at least two substantially untwisted polymer filaments. 5. The cable of claim 3, wherein the polymeric fibers are present as a bundle of at least four substantially untwisted polymeric filaments. 6. The cable of claim 4, wherein the polymeric fibers are present as a bundle of at least six substantially untwisted polymeric filaments. 7. The cable of claim 1 having a minimum bend diameter of at least about 6 mm. 8. The cable of claim 6 having a minimum bend diameter of at least about 4 mm.