Note: Descriptions are shown in the official language in which they were submitted.
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OPTIC~L FIBER C~BLE
B~CKGROUND OF TIIE INVENTION
Field of the Invention
'l~his invention relates to an optical fiber cable which is
lightweight and flexible and has a high strength.
Prior Art
It has been desired that an optlcal ~iber cable has a
smaller cliama~er and a ~igh strength and is lightweight and
~lexible. One exampl~ of the conventional optical fiber cable
comprises an elongated tension member or core made of twisted
steel wires, a plurality of optical fibers spirally wound
around the tension member, a cushioning member wound around
the spirally-wound optical fibers, a holder tape of a plastics
material applied around the cushioning member, and a sheath
wound around the holder tape. This conventional optical fiber
cable is advantageous in that it can has a small diameter.
However, it has a relatively low mechanical strength, and
besides it is relatively heavy in weight because of the use of
the tension member of steel wires.
Another conventional optical fiber cable comprises an
elongated body or spacer member made of polyethylene or the
llke havlng a plurality o~ spiral grooves ~ormed ln a
alrcum~ercn~lal sur~acq thqreo~ ~nd ex~ending lon~i~udinally
thereoE, optlcal ib~rs receiv~d respectively in some o~ the
splral groove~, tension wires o~ s~eel received re~pectivqly
in the otller grooves, a cushioning member wound aroulld the
body, a holder tape oE a plastics material applied around the
cushioning member, and a sheath wound around the holder tape.
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~lthouc3h this convention~l optical fiber cable has an
increclsed strell~3th, it is relatively heavy in weight on
account of the use of the steel tension wires and is inferior
in flexibility.
SUMMARY OF THE INVENTIOW
It is thare~orc an object of this invention to provide an
optlcal fibcr cable o the type having an elongated body or
spacer member with spiral grooves which cable is lightweight,
and possesses a high strength and a good flexibility, and is
subjected to less transmission loss due to temperature
variations.
According to the present invention, there is provided an
optical fiber cable comprising:
(a) an elongated flexible body having at least two
spiral grooves formed in a circumferential surface
thereof and extending longitudinally of said boy;
(b) optical fiber means received in one of said spiral
grooves; and
(c) an elongated flexible tension member received in the
o~hex spiral groove, said tension member comprisin~
at lea~t one qlongated el0ment ma~e o aramld
f ibqrs .
BRIEF DESCRIP'rION OF trl~E ~RAWING~
Fig. 1 is a cross-sectional view of an optical fiber
cable provided in accordance with the present invention;
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Fig. 2 is a view similar to Fig. 1 but showing a modified
optical fiber cable;
F'ig. 3 is a view similar to Fig. 1 but showing another
modified optical fiber cable;
Fig. ~ is a cross-sectional view of an optical fiber unit
incorporated to be in the optical fiber cable;
Fig. 5 is a view similar to Fig. 4 but showing a modified
optical fiber unit; and
Fig~ 6 is a cro~s-~ectional view of al1ott1er modified
op~ical f~hcr unit.
DESC~IPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The invention will now be described with re~erence to the
drawings in which like reference numerals denote corresponding
parts in several views.
An optical fiber cable 10 shown in Fig. 1 comprises an
elongated flexible body or spacer member 12 made of a high-
density plastics material such as a polyethylene resin, a
polypropylene resin and a flame retardant polyethylene resin.
The body 12 of a circular cross-section has four or two pairs
of grooves 14 and 16 formed in and spirally extending along a
circumerential surface thereof, the four grooves being
di~p~d in circum~erqntlally e~ually ~pac~d r~lation to each
o~her as vi~w~d in cro~s-~ection. ~he groov~s 1~ and 16 are
disposed ~l~ernately, and thq grooves 1~ have a greater cros~-
S~CtiQn than tl1e grooves 16.
An elongated flexible tension member 18 is received in
each of the pair of diametrically-opposed spiral grooves 14
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along an entire length thereof. The tension member 18
comprises a plurality of ~five in the illustrated embodiment)
elongated elements 20 or strands made of aramid fibers and
twisted together. The tension member 18 serves to offer a
resistance to tension or a pulling force so that the optical
fiber cable 10 can have a high tensile strength. The size of
the grooves 14, the number of the aramid fiber elements 20
received therein are determined in accordance with the tensile
strength of the optical fiber cable 10 to be obtained. On the
other hand, a pair of optical fibers 22 are received
respectively in the diametrically opposed spiral grooves 16.
As the aramid fibers of which the element~ 20 are made, Kevlar
manufactured by DuPont or HM-50 sold by Teijin, Japan, can be
used.
A holder layer 24 comprises a tape of a plastics
material, such as nylon, polyethylene and polyester, wound
around the body 12 to hold the tension members 18 in place in
the respective grooves 14. ~he tension member 18 of the
aram~d fiber elements 20 is compressible and deformable, and
lt has a size slightly larger than the cross-section of the
groove 14 when sub~ected to no load. Therefore, for
a~sembllng the optical fiber cable 10, each tension member 18
15 forced lnto a respective one of the grooves 14, so that its
constituent elements 20 of aramid fibers are held in squeezed
or compressed condition in the groove 14 by the holder layer
24. Thus, the flexible tension member 18 is filled in the
groove 14.
A sheath 26 made of a polyethylene resin, a flame-
retardant polyethylene resin or the like is wound around the
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hol~er layer 2~.
Since the tension member 1 a composed oE the aramid fiber
elements 20 has a higher tensile strength and is less heavy
than a steel tension member of the same size, the optical
fiber cable 10 can be less heavy in weight and have a higher
strength. Therefore, the optical fiber cable 10 can have a
higher strength as compared with a conventional one of the
same dlameker. And, the optical fiber cable 10 can be of a
smallcr diameter a~ comparec1 with a conventLonal one having
the same strength. In addltion, the tension memher 18
composed of the aramid fiber elements 20 is more
flexible than a steel tension member o the same size,
and therefore the flexibility of the optical fiber
cable 10 is enhanced. Further, since the tension
member 18 of the aramid fiber elements 20 is
compressible, it can be quite intimately fitted in or
fully filled in the groove 14, so that the cross-
sectional area of the groove 14 can be fully used,
thereby further increasing the strength of the optical
fiber cable.
Further, since the aramid fiber has a negative
coe~iclenk o~ thcr~nal e~pansion, the expansion and
contraction v~ khe optical ~iber cable 10 duq to tomperakure
varia~ions can be ~uitably kept to a minimum. As a re~ult, a
transmis~ion loss oP th~ optical fiber cable 10 caused by such
temp~rature variations is also kepk to a minimum.
Further, the optical fiber cable 10 is made entirqly o~
non-metallic materials and therefore has non-lnductive and
electrically-lnsulating properties.
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Fig. 2 shows a modified optical fiber cable 10a which
dif~ers ~rom the optical ~iber cable 10 of Fig. 1 only in that
an elongated central tension core 28 is embedded or molded in
an elongated body 12 at its center and extending along the
axis of the body 12. The central core 28 is flexible and is
made of, say, two strands of aramid fiber-reinforced plastics
material ~KERP), glass fiber-reinforced plastics material,
carbon fiber~rcinforced plastics material or steel. The use
o~ th~ aen~ral t~n~lon core 2n ~urther increases th~
resistance of the optical ~iber cable 1Oa to tension or a
pulling force. Usually, the elongated body or spacer member
12 is molded of such plastics material by extrusion, and,
advantageously, the use of the central core 28 greatly
facilitates such an extrusion operation. The central core 28
has such a small diameter that it will not adversely affect
the flexibility and lightweight of the optical fiber cable
lOa.
Fig. 3 shows another modified optica} fiber cable 1Ob
which differs from the optical fiber cable 1Oa of Fig. 2 in
that more than two spiral grooves 16 are provided in the
elongated body 12 for receiving a corresponding number of
optical ~ibers 2~. In the illustrated embodiment, three pair
o~ spiral ~rooves 16 ara provided, each paix o~ ~roove~ 16
b~lng ~l~po~ed in diam~trically opposcd r~lation to each
oth~r. Tha c~ntral t~n~lon cor~ 2~ may b~ omitt~d.
Tlle invention will now be illustrated by way o~ th~
~ollowing EX~MPLE.
EXAMPLE
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In this EXAMPLE, an optical fiber cable 10a shown in Fig.
2 was prepared to determine its characteristics. Tlle
elongated body 12 was l,1ade oE flame-retardant polyethylene
resin and had an outer diameter of 3.3 mm. The pair of spiral
grooves 14 for receiving the respective tension members 18 had
a width of 1.6 mm while the pair of spiral grooves 16 for
receiving the respective optical fibers 22 had a width of 1.0
mm. The central core 28 was composed of two strand each
havlng a size of 1~20 deni~r and made o aramid fiber-
r~lnorc~d plastics mat~ri~l containlng 40 ~ hy volume of
aramid Eiber. Each ten~ion member 1~ was composed of five
elongated elements 20 twisted together and each having a size
of 1420 denier. Each of the pair of optical fibers 22 had a
diameter of 0.8 mm. The holder layer 24 comprised a nylon
tape and had a thickness of 0.05 mm. The sheath was made of a
flame-retardant polyethylene resin and had a thickness of 0.5
mm. The resultant optical fiber cable 1Oa had a diameter of
4.3 mm and a weight of 14.1 kg/km. The optical fiber cable
1Oa was tested to determine its mechanical characteristics and
temperature characteristics. The results obtained are shown
in TABLE below.
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TABLE
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Test Test conditions Results
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Mec~l~nical Stretching Stretching O.S ~ elongation
character- rate: 10 mm/min. at 65 kg
istics Distance between Breakage at 250
test two gage marks: 2 m kg
Bending Mandrel of 20 mm Transmission loss
diameter did not increase
~end angle: 360 after 30 recipro-
Bending frequency: cations. Maximum
30 reciprocations loss increase was
0.07 dB~
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Wiplng Die dlameter: ~Omm
Load: 30, ~0, 50~ No breakage after
60 and 80 kg. 5 reciporcations
Wiping frequency: at 80 kg.
5 reciprocations
Length wiped: 2 m
Temperature Cable length: 100 m Transmission ~oss
characteristics Temperature: - 60 increase: not
test to + 80 more than 0.02 dB
The bending test was carried out by winding the optical
fiber cable around the mandrel and pulling the fiber cable
back and forth. The transmission loss was measured by a
wavelength of 0.85 ~m. The tested fiber cable had the
optical fiber ~olded longitudinally intermediate opposite
ends thereof and received in the grooves 16 to provide a
loop.
As can be seqn ~rom T~B~, the tast~d optic~l ~iber aabla
exhibited ~ higll tensile strength and excell~nt temperature
characteri~tLcs, and was not damaged even when ~ubjected to
repeated bending and wiping. Thus, the optical ~lber cable i~
lightweight and has a high strength, a good ~lexibility and
excellent temperature characteristics, and is relatlvely small
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in diameter. Therefore, ~or example, the optical fiber cable
according to the present invention can be best suited as a
portable type which is to be used outdoors where severe
conditions may be encountered.
~ s described above, the optical fiber cables according to
the present invention have the tension members 18 made of
aramid fiber elements having a high tensile strength and a low
specific gravity, and therefore the optica:L fiber cable is
lightwelgllt and ~u~iciently flexible and has excellent
temperature charactorl~tlcs. ~nd, the optical ~iber cable can
have a sufficient strength even if it has a smaller diameter
than the conventional optical fiber cables having tension
members of steel.
While the optical fiber cables according to the present
invention have bQen specifically shown and described herein,
the invention itself is not to be restricted by the exact
showing of the drawings or the description thereof. For
example, as shown in Fig. 4, each of the pair of optical
fibers 22 received in the respective spiral grooves 16 may be
replaced by a tape-like optical fiber unit 30 comprising a
flat base 32 of a synthetic resin and a plurality of optical
iibers 22a embedded or molded in the base 32 in parallel
juxta~osed relation. ~lso, each opti~al ~iber 22 may be
replaced by a plurality o~ ~three in the illu~tratqd
~mbodim~nt) tape~ op~ical ~ibar unit 30 (Flg~ 5).
Further, a~ ~hown in Fig. 6, each optical fiber 22 may be
replaced by an optical ~iber unit 36 comprising an elongated
core 38, a plurality of optical fibers 22a spirally wound
around the core 38 and a sheath 40 covering the optical fibers
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22a. Further, although in the illustrated embodiment, the
teIlsion meInber 18 is composed of five elongated eleInellts 20
and filled in the groove 1~, it may be composed of at leas
one elongated element 20.
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