U.S. patent number RE32,436 [Application Number 06/481,259] was granted by the patent office on 1987-06-09 for reinforced optical fiber cable with glass or silica core.
This patent grant is currently assigned to Mitsubishi Rayon Co., Ltd.. Invention is credited to Martval J. Hartig.
United States Patent |
RE32,436 |
Hartig |
June 9, 1987 |
Reinforced optical fiber cable with glass or silica core
Abstract
A reinforced optical fiber cable comprises (i) an optical
filamentary material with a glass or silica core and a lower index
of refraction sheath, (ii) a reinforcement comprising at least two
polymeric fibers having an elastic modulus above 10,000,000 psi,
said fibers being held under tension .[.separate from one
another.]. .Iadd.around the sheath .Iaddend.and positioned
substantially parallel to the longitudinal axis of the core with
substantially zero twist and (iii) a jacket which holds the
reinforcement under tension.
Inventors: |
Hartig; Martval J. (Wilmington,
DE) |
Assignee: |
Mitsubishi Rayon Co., Ltd.
(Tokyo, JP)
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Family
ID: |
27046904 |
Appl.
No.: |
06/481,259 |
Filed: |
April 1, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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734749 |
Oct 22, 1976 |
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Reissue of: |
022844 |
Mar 22, 1979 |
04331378 |
May 25, 1982 |
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Current U.S.
Class: |
385/108 |
Current CPC
Class: |
G02B
6/4432 (20130101) |
Current International
Class: |
G02B
6/44 (20060101); G02B 006/44 () |
Field of
Search: |
;350/96.23 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2291508 |
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Jan 1976 |
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FR |
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2296192 |
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Jul 1976 |
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FR |
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36-16363 |
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Jun 1961 |
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JP |
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125754 |
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Oct 1975 |
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JP |
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50-156045 |
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Dec 1975 |
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JP |
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51-56643 |
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May 1976 |
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JP |
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52-18339 |
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Feb 1977 |
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JP |
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52-122734 |
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Sep 1977 |
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JP |
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1486227 |
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Sep 1977 |
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GB |
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Other References
Proceeding of the I.E.E. vol. 123, No. 6, Jun. 1976, pp. 597-602,
"Principles of Fibre-Optical Cable Design", Foord et al..
|
Primary Examiner: Sikes; William L.
Assistant Examiner: Gonzalez; Frank
Attorney, Agent or Firm: Brumbaugh, Graves, Donohue &
Raymond
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of my prior copending United
States application Ser. No. 734,749 filed Oct. 22, 1976, now
abandoned.
Claims
What is claimed is:
1. A cable for transmission of light comprising:
(A) a substantially cylindrical core of an optically transparent
glass or silica;
(B) a transparent sheath for (A) having an index of refraction at
least 0.1% lower;
(C) a protective layer on (B);
(D) a reinforcement for the cable, on (C), of at least two
polymeric fibers spaced .[.from one another.]. .Iadd.around the
sheath, .Iaddend.and
(i) having an elastic modulus of at least 10,000,000 psi, (ii)
being under tension, .Iadd.such that if the cable is cut crosswise
the core and the sheath protrude slightly from the cut end of the
cable, .Iaddend.(iii) being substantially parallel to the core
along its longitudinal axis and, (iv) being positioned with
substantially zero twist; and
(E) a jacket exterior of (A), (B), (C) and (D), holding (D) under
tension.
2. The cable of claim 1 wherein said fibers are poly(p-phenylene
terephthalamide).
3. The cable of claim 1 wherein said fibers are present in separate
yarns.
4. The cable of claim 3 wherein at least four yarns are
present.
5. The cable of claim 4 wherein at least six yarns are present.
6. The cable of claim 1 with a minimum bend diameter at least equal
to about 6 mm.
7. The cable of claim 6 with a minimum bend diameter at least equal
to about 4 mm.
8. The cable of claim 1 wherein said transparent sheath is a
substantially amorphous thermoplastic polymer extruded onto said
core.
9. The cable of claim 1 wherein said protective layer is a
copolyetherester.
10. A fiber optical cable comprising:
a fiber optic core including at least one optical fiber adapted to
receive optical communication signals;
at least two elastic strength members substantially straight and
parallel to said fiber optic core; said strength members being in a
stretched condition;
a protective layer between the core and the elastic strength
members;
means for maintaining said strength members substantially straight
and in a stretched condition whereby said strength members are
adapted to apply a force in the opposite direction to longitudinal
stress forces on said cable for protecting said optical fiber from
longitudinal stress.
11. A cable as set forth in claim 10 wherein said at least two
elastic strength members is taken from the group consisting of
Kevlar.RTM., nylon and polyester.
12. A cable as set forth in claim 10 wherein said at least two
elastic strength members has a tensil modulus in the range of
7.times.10.sup.6 pounds per square inch to 19.times.10.sup.6 pounds
per square inch.
13. A cable as set forth in claim 10 wherein said at least two
elastic strength members will not substantially elongate under
forces equal to the break strength of the fiber optic core.
14. A fiber optic cable comprising:
a fiber optic core having at least one glass fiber;
a plurality of strength members, said strength members being
substantially straight and having been stretched beyond their
normal length;
a protective layer between the core and the strength members;
means for maintaining said strength members substantially straight
and in a stretched condition; and
a protective sheath surrounding said core and said strength
members.
Description
BACKGROUND OF THE DISCLOSURE
The present invention relates to an optical fiber cable containing
at least one optical filamentary material having a glass or silica
core and a lower index of refraction sheath.
Optical filamentary materials are well known in the art for
transmission of light along a filament length by multiple internal
reflections of light. Great care is taken to minimize light losses
along the length of the filament or, in other words, internal
reflections are made as total as possible so that light applied to
one end of the optical filamentary material is efficiently
transmitted to the opposite end of the material. The light
transmitting portion or core of the optical filamentary material is
surrounded by a sheath having a lower index of refraction which
minimizes the escape or absorption of light along the length of the
filament. This sheath is normally transparent since an opaque
sheath tends to absorb light. Although this sheath can be made from
glass or a polymeric material, it is conventionally made from the
latter due to increased toughness properties.
Optical filamentary materials can be divided into two general
classes dependent upon the type of optically transparent core
material. A first class of core material is thermoplastic in nature
while a second class is made from glass or silica. The first class
is generally superior both in toughness and in ease of making
connections while the second class is generally superior in light
transmission.
One disadvantage with optical filamentary materials with a glass or
silica core is a tendency for the core to break due to its
brittleness. Encapsulation of the filaments within a cable
containing reinforcement and a protective layer has only been
partially successful in overcoming the brittle quality of the core.
A need exists for an optical fiber cable which provides increased
resistance to breakage of a brittle core material.
SUMMARY OF THE INVENTION
The present invention relates to a cable for transmission of light
comprising
(A) a substantially cylindrical core of an optically transparent
glass or silica,
(B) a transparent sheath for (A) having an index for refraction at
least 0.1% lower, and
(C) a reinforcement for the cable,
(D) a jacket exterior of (A) and (B),
wherein the improvement comprises the reinforcement of (C)
comprising at least two polymeric fibers spaced from one
another
(i) having an elastic modulus of at least 10,000,000 psi;
(ii) being under tension;
(iii) being substantially parallel to the core along its
longitudinal axis;
(iv) being positioned with substantially zero twist;
(v) being interspaced between (B) and (D).
DETAILED DESCRIPTION OF THE INVENTION
An optically transparent cylindrical core for transmission of light
is made from an optically transparent glass or silica. The silica
core can be either pure silica (undoped) or doped with a suitable
component such as germanium or boron. As employed herein "optically
transparent" means a light transmission of at least 50% per 30 cms
in a portion of the light spectrum of 550 to 1100 nanometers. This
degree of transmission need not extend over the entire spectrum.
Examples of suitable disclosure of core materials are found in U.S.
Pat. Nos. 3,480,458 and 3,508,589, e.g., the latter patent lists
suitable core materials made from barium, flint and borosilicate
glasses with the more dense glasses described as better.
A preferred core material is made from silica which can be either
doped or undoped. The silica is drawn into a core material at
elevated temperature. Although drawing temperatures of at least
2000.degree. C. can be employed, a temperature range of
2040.degree. C. to 2120.degree. C. is preferred. As drawing
temperature decreases, it has been found that brittleness of the
drawn silica core material increases. A limiting factor on an upper
temperature range is difficulty in control of caliper. As the
drawing temperature is maximized, a necessary degree of caliper
control becomes marginal.
The diameter of the cylindrical optically transparent core varies
from relatively thin to relatively thick core constructions. A
suitable diameter range is 10 to 400 .mu.m. A thick core has the
advantage in the ability to capture a greater proportion of
incident light if the light source is large, e.g., from an LED
(light emitting diode) but has the disadvantage of having a larger
bending radius. If a light source is small, e.g., a laser, a
relatively thin core is suitable for capturing incident light.
The sheath applied to the optically transparent core is transparent
and has an index of refraction at least 0.1% lower and can be
glass, silica or a substantially amorphous optically transparent
thermoplastic polymeric material. Pure silica has a lower index of
refraction than most known glasses, and if silica is employed for
both core and sheath, the silica core is doped to raise its index
of refraction to a required level at least 0.1% above the
sheath.
Preferred as a material of construction for the sheath is a
substantially amorphous transparent thermoplastic polymer since
such polymer does not possess the brittleness characteristic of
glass or silica.
Examples of suitable sheath materials include those disclosed in
British Patent Specification No. 1,037,498 such as polymers and
interpolymers of vinyl fluoride, vinylidene fluoride,
tetrafluoroethylene, hexafluoropropylene,
trifluoromethyltrifluorovinyl ether, perfluoropropyltrifluorovinyl
ether and fluorinated esters of acrylic or methacrylic acids having
the structure ##STR1## wherein X is selected from the group
consisting of F, H, or Cl, and n is an integer of from 2 to 10, m
is an integer from 1 to 6 and Y is either CH.sub.3 or H.
Since the sheath material reflects light traveling through the
core, the thickness of the sheath is not generally critical. An
example of a suitable range of thickness of this sheathing is 2 to
500 microns. Excessive sheathing thicknesses can reduce flexibility
of the final cable which is undesirable.
Well-known techniques for application of the sheath material are
suitable. Glass or silica can be applied by a double crucible
drawing while a polymer can be extruded onto the core.
In the present invention, it is necessary to incorporate a
reinforcement between the optical filamentary material and the
protective jacket. This reinforcement comprises polymeric fiber
having an elastic modulus of at least 10,000,000 psi. Suitable
polymer for the fibers which meet this criteria include
poly(p-phenylene terephthalamide) and is disclosed in U.S. Pat. No.
3,869,430. The disclosure of this patent is incorporated by
reference herein.
At least two separate individual fibers are employed and are held
under tension in the cable by the jacket material. .[.The.].
.Iadd.When two fibers are employed, .Iaddend.fibers are spaced
apart and do not contact one another. Preferably, separate bundles
of fibers, i.e., yarns, are employed as opposed to individual
fibers. Although two separate fibers or yarns are suitable, more
preferably at least four separate fibers or yarns are employed and
most preferably, six or more fibers or yarns. These fibers are
positioned substantially parallel to the core along its
longitudinal axis. The fibers in relationship to the longitudinal
axis of the core will have substantially zero twist. The term "zero
twist" means that a fiber would not encircle the core material
irrespective of the length of such material.
The purpose of having the fibers substantially parallel to the
longitudinal axis of the core with substantially zero twist is to
ensure the fibers remain under tension in the optical fiber cable.
If the fibers for reinforcement encircled the core material,
relaxation of this reinforcement could readily occur. Although the
degree of tension of the reinforcement fiber is not critical,
nevertheless it is essential that the fibers remain under tension
in the cable. This tension can readily be demonstrated in a final
cable. The cable is cut crosswise and the optical filamentary
material of the glass or silica core and its sheath can be
physically felt to protrude slightly from the cut end of the
cable.
The optical filamentary material of a glass or silica core and
lower index of refraction sheath is positioned within a protective
jacket. The jacket serves to hold the reinforcement under tension
and with this proviso the material for the jacket is not critical.
The jacket is conventionally a thermoplastic polymer applied by
extrusion. Suitable materials of construction include polyamides,
copolyetheresters, 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.
Considerations which govern the choice of jacketing material
include strength, elongation, burning rate and ease of
strippability. For example, good strippability is needed in
connecting one cable to another and in connecting 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 which is highly resistant to breakage
of this light transmission portion. Cables containing an optical
filamentary material of a glass or silica core and a lower index of
refraction sheath are known in the prior art. In the cable of the
present invention the manner of reinforcement in protection of a
glass or silica core results in a superior ability to withstand
breakage of the core material in comparison to prior art cables
used for the transmission of light with an identical core and
sheath material.
The cable of the present invention has a combination of high
bending strength, high tensile strength and high impact strength.
This combination of properties has not been obtained by cables with
a brittle core which do not have reinforcement fibers held under
tension.
It is possible with the construction of the present optical fiber
cable to obtain a construction which permits the cable to be bent
sharply without damage. A minimum bend diameter at least equal to
about 6 mm and preferably at least equal to about 4 mm can be
obtained. As shown in Example 2, the cable can be tied into a tight
overhand knot, e.g. having a minimum bend diameter at least equal
to about 4 mm without the cable losing its ability to function in a
normal fashion in transmission of light.
Although the disclosure herein has been directed to interspacing a
reinforcement under tension between a sheath of an optical
filamentary material and a jacket, it is understood that the
reinforcement need not contact the sheath. A protective layer can
separate the sheath from the reinforcement. In such case, it
remains critical for the reinforcement fibers to be maintained
under tension.
Also, it is within the scope of the present invention to employ
more than one optical filamentary material within a cable provided
such filamentary material has a separate reinforcement of at least
two reinforcement fibers in the manner disclosed herein.
To further illustrate the present invention, the following examples
are provided.
EXAMPLE 1
Part I-An undoped silica fiber was spun at a temperature of
2050.degree. C. from 9 mm. rod using a furnace with a tungsten
heating element blanketed with nitrogen. The rod feed to the
furnace and the take-off for the fiber were set to make 200 .mu.m
fiber at about 10 meters per minute. During spinning less than one
break per 1000 meters was observed. The fiber was solution coated
with a lower index substantially amorphous transparent polymeric
sheath of methyl methacrylate and fluorinated esters of methacrylic
acid (second order transition temperature of 50.degree. C. and
refractive index 6% lower than core) in a solvent of
difluorotetrachloroethane to make an optical fiber with about a 600
.mu.m outer diameter.
The optical fiber had an attenuation of 38 dB per kilometer at
655.3 nm.
Part II-The optical fiber of Part I was reinforced with six strands
of poly(p-phenylene terephthalamide) of 42 tex (380 denier) and
jacketed with copolyetherester (disclosed in Example 1 of U.S. Pat.
No. 3,651,014).
Six strands of poly(p-phenylene terephthalamide) were initially
strung through tensioning holders, through a fiber guide which was
a hypodermic needle 1550 .mu.m I.D. (inner diameter), 2050 .mu.m
O.D. (outer diameter) and through a crosshead die with an 1875
.mu.m hole. Tension of the yarns was set at 1.16.times.10.sup.-3
Newtons/tex (0.013 gram/denier) and the copolyetherester which was
heated to 205.degree. C. was extruded from the opening of the die.
The extrusion speed and the speed of the yarns were adjusted to
give an extrudate 175 .mu.m O.D. A blank nylon filament 550 .mu.m
O.D. was fed into the yarn bundle and the speed readjusted to give
an extrudate 1875 .mu.m in diameter. The die was adjusted to center
the fiber and the yarns. The nylon filament was removed and a
coated optical fiber of Part I was substituted and coated with the
copolyetherester to form an optic fiber cable.
The optic fiber cable had an attenuation of 40 dB per kilometer at
655.3 nm (in comparison to 38 dB per kilometer of the Part I optic
fiber). The cable was tested under a load and it broke at 30 kg.
The cable could be hammered without destroying its ability to
transmit light. The cable could be wrapped around a 6 mm diameter
mandrel without breakage of the core and loss of ability to
transmit light but the cable could not be tied into a tight knot
without breaking the core.
EXAMPLE 2
The procedure of Example 1--Parts I and II were followed except
that Example 1--Part I optical fiber was directly coated with
copolyetherester (described in Example 1 of U.S. Pat. No.
3,651,014) by a tubing cross-head die prior to the method of
Example 1--Part II in application of the reinforcement and the
jacketing copolyetherester. The optical fiber had an O.D. of 1225
.mu.m. In the Example 1--Part II method of reinforcement, yarns of
poly(p-phenylene terephthalamide) fibers were used, three yarns of
42 tex (380 denier) and three yarns of 168 tex (1420 denier). The
tension of the fibers was 1.8.times.10.sup.-3 newtons/tex (0.02
g/denier).
The final optic fiber cable had an O.D. of 2375 .mu.m, an
attenuation of 40 dB per kilometer at 655.3 nm and a break strength
of 85 kg. The cable could be wrapped on a 4 mm diameter mandrel and
tied into a tight overhand knot without breaking or loss of light
transmission.
* * * * *