CA2480195C - Optical fiber cable - Google Patents
Optical fiber cable Download PDFInfo
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- CA2480195C CA2480195C CA002480195A CA2480195A CA2480195C CA 2480195 C CA2480195 C CA 2480195C CA 002480195 A CA002480195 A CA 002480195A CA 2480195 A CA2480195 A CA 2480195A CA 2480195 C CA2480195 C CA 2480195C
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Abstract
An optical fiber cable comprises a slender base body having spiral grooves formed on the outer circumferential surface, and at least one optical fiber ribbon housed within each of said grooves, said ribbon including a plurality of insulated optical fibers and a resin coating layer covering said optical fibers. The base body is formed of a mixture of at least two materials differing from each other in the molecular weight distribution. The particular construction permits markedly suppressing an increase of transmission loss derived from micro-bend occurring in the optical fiber tape arranged within the base body, and also permits arranging optical fiber ribbons within the base body at a higher density.
Description
w ' i v ~. _ ! . .
~TRANSLATTON
OPTICAL FIBER CABLI~
Technical Field The present invention relates to a slot-type optical fiber cable comprising a thin and long base body having spiral grooves formed on the outer circum-ferential surface and a plurality of optical fiber -ribbonsstacked one upon the other within each of the spiral grooves, a plurality of optical fibers being formed within each of the optical fiber ribbons, particularly, to an optical fiber cable of a small diameter having optical fibers arranged at a very high density.
Background Art A slot-type optical fiber cable having a plurality of optical fiber ribbons stacked one upon the other within spiral grooves formed on the outer circumferen-tial surface of a thin and long base body permits dealing with a relatively large amount of information and, thus, is used nowadays as a relay bable or a subscriber cable for public communication. In recent years, a multi-media system of information is on a sharp increase. Also, diversification of information and increase of the information amount are expected to accompany the spread of the multi-media _. r-~.
. . ~ , system. Naturally, the optical fiber cable to be developed is required to be capable of coping with a greater amount of information. than in the past.
Further, with increase in the amount of inforiria--tion, the subscriber cable ar an optical fiber cable connected between a relay and an individual household is also required to be capable of coping with a greater amount of information. Under the circumstances, the slot-type optical fiber cable is also expected to be used as such an optical fiber.
To be more specific, the slot-type optical fiber cable comprises a long base body having a tension member arranged along the axis thereof arid a plurality of optical fiber ribbons stacked one upon. the other within each of spiral grooves formed along the outer circumferential surface of the base body. For example, four optical fiber ribbonsare stacked. one upon the other within each spiral groove. The outer surface of the base body having the vptical.fiber ribbonsarranged within the spiral grooves is wound with a holding tape.
Further, a sheath is arranged to cover the outer circumferential surface of the resultant structure. In general, the base body is formed of a high density polyethylene in view of the workability, mechanical properties and cost.
The simplest means to permit the optical fiber cable to be capable of coping with am increased amount ___..
t . .~ . . , ,~
. ~ .
of information is to increase the number of optical .
fibers, or the number of optical fibers ribbons, mounted within the optical fiber cable. Naturally, an increase in the number of optical fiber ribbonsmounted within the optical fiber cable results in an increased outer diameter of the cable. An increase in the outer diameter of the cable gives rise to difficulties. For example, the cable is unlikely to be bent, with the result that, in' arranging the cable ~withi.n a cable passageway, the cable fails .to be arranged within the passageway. Also, it is necessary to newly design tools, etc. to meet the increased outer diameter of the cable. It follows that, in order to increase the number of optical fiberribbons arranged within the optical fiber cable, it is necessary to improve the construction of the optical fiberribbon itself such that theribbons Can be arranged within the optical fiber cable in a higher density.
As a means for improving the construction of the optical fiber ribbon, it is proposed to decrease the thickness of a resin coating layer having a plurality of optical fibers embedded therein. The conventional optical fiber ribbon arranged within a, slot-type optical fiber cable comprises four optical fibers and a resin layer formed to cover collectively the four optical fibers. These optical fibers, each having a coating layer and a diameter of, for example, 12~ ~, m, are i v ~ 7 4 f arranged side by side. In general, the resin layer has a thickness, i.e., distance between the outer surface of the resin layer and the outer surface, which faces the outer surface of the resin layer, of the coated optical fiber, of 1210 to 150 ~c m. To be more specific, it is proposed to decrease the resin layer thickness from the conventional level of 120 to 15p ~c m to 30 to 100 ~c m as a means for increasing the density of the optical fiber ribbons arranged within the optical fiber cable. The optical fiber ribbon of the particular construction is generally called a thin optical fiber ribbon .
However, it has been found that:, when thin optical fiberribbons are stacked one upon the other within grooves of the base body at a density higher than in the past, a transmission loss derived from micro-bend is increased.
Disclosure of Invention An object of the present invention, which has been achieved in view of the situation described above, is to provide an optical fiber cable which permits markedly suppressing an increase of transmission loss derived from micro-bend of the optical fiber ribbons, arranged within a base body and also permits arranging optical fiberribbons within the base body at a higher density.
According to a first embodiment of the present _. CA 02480195 2004-10-15..._,.__ _._ ... _._.. _-L . < 1 4 . a 1 . a ~ ~ ' > , l invention, there is provided an optical fiber cable, comprising: a longitudinally extending core body having spiral grooves formed thereon; and at least one optical fiber ribbon housed in any one of said grooves, said .
5 ribbon including a plurality of optimal fibers embedded in a strip of resin, wherein said core b~dy is made from a mixture of at least two materials having different molecular weight distributions.
It is desirable that the mixture contains at least a low molecular weight polyethylene having a peak of polystyrene standard molecular weight distribution wwithin a range be~,ween 3 x 104 and 8 x 104 and a high molecular weight polyethylene having a peak of polystyrene standard molecular weight distribution within a range between ? x 104 and 1.5 x 105, and the polystyrene-peak appearing in said high molecular Weight polyethylene that invariably remains greater than said polystyrene peak appearing in said low molecular weight polyethylene.
2U . According to a second embodiment of the present invention, there is provided.ari optical fiber cable, comprising: a longitudinally extending core body having spiral grooves formed thereon; and at least one optical fiber ribbon housed in any one of said grooves, said z5 ribbon including a plurality of optical fibers embedded in a strip of resin, wherein projections formed on the inner surface of any one of said spiral groove ,e .. , . ~ ~ ,.
v 6 measure 30 ,u m or less in height.
It is desirable that the strip of resin of the fiber ribbon provides a resin thickness of 30 to 100 ~ m over each embedded fiber in each direction perpendicular to 'the fiber ribbon.
Brief Description of Drawinqs FIG. l shows the canstruction c~f a slot-type optical fiber cable according to they present invention;
FIG. 2 shows in a magnified fashion an example of a thin optical fiberribb~n arranged within the optical fiber cable of the present invention~
FIG. 3 shows in a magnified fashion how thin optical fiberribb~ns are laminated within a groove formed on the outer circumferential surface of a base body in an optical fiber cable according to a first embodiment of the present invention;:
FTG. 4 shows in a magnified fashion how thin optical fiberribbons are laminated within a groove formed on the outer circumferential surface of a base body in an optical fiber cable according to a second embodiment of the present inventianA and FIG. 5 is a graph showing the relationship between the height of proaections arid the transmission loss in an optical fiber 'cable according to the second embodiment of the present invention.
Best Mode of Carryincr Out the Invention Let us describe the present invention with a reference to the accompanying drawings.
Specifically, the present inventors prepared thin optical fiberribbons each including a resin coating film having a thickness of 70 ~ m in contrast to the conventional thickness of 135 ~c m. Then, an optical fiber cable Bias prepared by using the thin optical fiber ribbons thus prepared. In this case, 8 optical fiber ribbons were stacked one upon the other within each spiral groove of the base body, though only 4 optical fiber nbb~ns were stacked within each spiral groove in the conventional optical fiber cable. The characteristics such as bending and cable temperature of the resultant optical fiber cable were measured so as to find that an increased transmission loss derived from micro-bend took piece within the optical fiber embedded within the optical fiber~c:ibbon, Under the circumstances, the present inventors have made an extensive research. It has been found that the increase of the transmission loss takes place in only an optical fiber cable prepared by arranging the thin optical fiberribbo~s in the conventional base body. It has also been found that the increase of the transmission loss taking place in only the particular optical fiber cable noted above is,caused by 2S projections formed on the inner surface of the base body made of a high density polyethylene. The present inventors have looked into the-inner surface of the a ~
spiral groove formed on the circumferential surface of the base body used in the conventional optical fiber cable. It has been found that the projections are formed over the entire region of the inner surface at a rate of 10 projections/mm2. It has also.been found that these.projections have a height of l0 to 100 ~c m, the heights of most projections falling within a range of between 50 and 70 ~c m.
In order to decrease-the diameter of the optical.
1~ , fiber cable, it may be effective to decrease the diameter of the base body in which optical fiber ribbons are arranged. It should be noted in. this connection that optical fibers should be arranged in a manner to prevent the optical characteristics thereof from being adversely affected within the base body. In this respect, it is undesirable to decrease the cross sectional area of the spiral groove in which the optical fiber ribbons are arranged. Specifically, the decrease of the cross sectional area. noted above causes an increase in the side pressure loss of the optical fiber, with the result that the ciptical characteristics of the optical fiber are adversely-affected. Such being the situation, it may also be possible to decrease the diameter of the optical fiber cable by decreasing the diameter of the base body while maintaining constant the cross sectional area of the spiral groove formed on the surface of the _...
'~ . , ~r ' ~ ' ~
base body. In this case, it is.~.mportant to select appropriately the resin used far forming the base body.
Specifically, the resin should have a sufficiently high mechanical strength such that a side pressure should not be given to the optical fiberribbon by the deformation of the base body. An important mechanical strength required in this respect is a bending modulus of the resin.
In~the first embodiment of.the present invention, IO the base body is formed of a mixture of at least two materials differing from each other in the molecular weight distribution sa as.to suppress formation of.
projections, which cause an increased transmission loss of the optical fiber, while maintaining a required mechanical strength of the base body. In the second embodiment.of the present invention, the height of the projection is defined to be 30 ~c m or less so as to prevent substantially completely the projections from causing an increase in the transmission loss of the optical fiber.
As described above, the base body included in the optical fiber cable according to the first embodiment of the present invention is formed of a mixture of at least two materials differing from each other in the molecular weight distribution. To be more specific, the particular mixture includes, for example, a polymer prepared by polymerizing a low molecular weight _" .__._ - CA 02480195 2004-10-15 component and a h~.gh molecular weight component, and a mixture of these low and high~molecular weight components. What is important is that any material including a single material, not a mixture, can be used for forming the base body as far as 'the base body material exhibits a plurality of peaks in its molecular weight distribution.
In the first embodiment of the ;present invention, it is.desirable far the base body to be formed of a mixture including at least a first material having a peak,of the polystyrene standard molecular weight distribution within a range of between 3 x 104 and 8 x 104, and a second material having a peak of the polystyrene standard molecular weight distribution within a range of between 7 x 104 and 1.5 x 105. It should be noted that the second material has a peak of the polystyrene standard molecular weight distribution on the side of a higher molecular weight,. compared with the.first material. Incidentallyr it is possible for any of the first and second materials to have a peak which does not fall within the ranges given above.
The term °'polystyrene standard molecular weight"
denotes a molecular weight of a substance which is determined on the basis of an eluting time of the substance. To be more specific, an eluting time of a substance Hrhose molecular weight is unknown is measured. Also, a calibration curve is prepared by T
l ~<
s 1 , measuring the eluting time of polystyrene whose molecular weight is known by using a gel permeation chromatography (GPC) under the conditions given below.
Finally, the eluting time of the substance, whose molecular weight is unknown is converted into the polystyrene standard molecular weight by using the calibration curve.
(GPC Measuring Conditions) Measuring Machine,: 150 CV manufactured by Waters Inc.
Solvent: o-dichlorbenzene (containing 0.3~ of BHT: BiiT..l-hydroxy-4-methyl-2,6-di-tert--butyl benzene) Column: AT-G+AT-806 M/S x 2 manufactured by Shodex Inc.
Temperature: Column and Indicator .. 1.45°C
Concentration: 0.1 wt/vol Flow rate: 1.0 ml/min.
Standard Sample: Polystyrene Detector: Differential refractive index detector (RI) In view of the properties required for arranging the optical fiberribbons therein, the bass body material used in the present invention includes, for example, a high density polyethylene having a density of 0.94 to 0.97 g/cm3, polyolefin resins sur.h as polypropylene having a density of 0.90 to 1.30 g/cm3, polyamide resins and other engineering plastics. It is most ._._. .__.!- .,.___._-....,.._~_-.__._____.~., __ _-_CA 02480195 2004-10-15__ _._..._.__._'__ :___....._..___.._.____......_~
', , ~ , .~
desirable to use a high density polyethylene in view of the actual use over a long period of time in the past;
Workability, cost, etc. Further! in view of the moldability, it is desirable to use a mixture of at least two similar materials differing from each other in the molecular weight distribution.
In the first embodiment of .the present invention, the base body of the optical fiber cable is formed of, for example, a mixture containing at least a first material having a peak of. the polystyrene standard molecular weight distribution at a relatively high region, and a second material having a peak of the polystyrene standard molecular weight distribution at a relatively low region. The first material noted above contributes to the improvement of, fox example, a bending modules, which is an important mechanical property required in the base body, of the resultant base body. On t-he other hand, the second material noted above contributes to the improveriient 2p of, for example, a melt index, which is decisively important for improving the moldability of the base body material. It follows that it ~Ls possible to prevent the occurrence of projections which cause an increased transmission loss of the optical fiber while maintaining a sufficiently high meclxanical strength by mixing these first and second materials at a suitable .mixing ratio.
d 13' It should also be noted that, in the first embodiment of the present invention, it is desirable for the base body material to have a bending modulus of 180 kg/mm2 or less in order to permit the resultant optical fiber cable to be bent without difficulty. On the other hand,. the bending modulus of the base body material should desirably be 80 kg/mm2 or more in view of the side pressure applied to the optical-fiber ribbon embedded in the spiral groove~of the base body.
In the second embodiment of the present invention, the height of the projections formed on the inner surface of the spiral groove of the base body is defined to be 30 ~c m or less. As <~ result, the optical fiber nbbon.e~edded in the spiral groove of the base body is not affected by the projections regardless of the thickness of the optical fiberribbon embedded in the spiral groove. To be more specific, the optical, fiber ribbons arranged within the spiral groove may possibly be pressed partially: However, where the height of the projections is 30 ~u m or less, the resultant side pressure applied to the optical fiber ribbon~is not so high as to cause micro-bend occurrence, with the result that the transmission loss does not take place.
The present inventors have also found that the projections do not cause, all the thin optical fiber ribbons to bear an increased transmission loss.
Specifically, it has been found that the relationship i CA 02480195 2004-10-15 ._.___~ ,~ _ vi between the height of the projections and the thickness of the optical f.iber~-ribbon is deeply related to the increase in the transmission loss of the optical fiber. cable. In other words, it has been found that an increase in the transmission loss can be prevented substantially completely, if the particular relationship meets certain conditions. For example, when it comes to the thin optical fiber ribbon',covered with a resin coating layer having a thickness of 30 ~c m in contrast to at least 120 ,u m for the conventional optical fiber ribbon, the pptical fiber ribbow is partially pressed in the case where the height of the projections formed on the inner surface of the spiral groove exceeds 30 ~c m, i.e., height of, e.g., 40 ~c m. In this 1~ case, the side pressure applied to the optical fiber ribbon causes the optical fibers, arranged within the ribbon to bear micro=bend, leading to an.increase.of the transmission loss.
Under the circumstances,, the thickness of.the resin coating layer covering the optical fiberribbon is defined to fall within a range of between 30 wm and 100 a m in the second embodiment of the present invention. ~ In other words, a thin optical fiber ribbon is used in the second embodiment. What should be noted is that, even if thin optical fiberribbons defined in the second embodiment are arranged within the spiral groove of the base body in a_high density, it is ---..~J
r w i possible.to suppress .an increase of the transmission loss derived from the presence of micro-bend caused by the side pressuxe applied from the projections from the inner surface of the spiral groove formed on the base 5 body.
It should be noted that the projections defined in the second embodiment of the present invention differ from the convex-concave portions appearing on the surface of a molded body. In other words, the presence 10 of projections from the inner surface of the spiral groove of the base body is irrelevant to the definition of the surface roughness on the inner surface of the spiral groove.
FIG. l shows-a slot-type optical fiber cable 10 15 according to one embodiment of the present invention.
As seen from the drawing, the cable 10 comprises a long tension member 13 and a base body 11 covering the outer circumferential surface of the tension member 13. A
plurality of spiral grooves 12 are formed along the outer surface of the base body 11..Also, a plurality of thin optical fiber tapes 14 are arranged one upon the other within each spiral groove 12. Further, a holding tape 15 is Wound about the base body 11. in a manner to cover the thin optical fiber tapes 14 arranged within the spiral grooves 12. Still further, the resultant structure is covered with a sheath 16 so as to provide the optical fiber cable 10.
02480195 2004-10-15~"~,.. __~.,~...J.... _,~...." . ...__~__._~___~~
The tension member 13 is formed of, for example, a stranded steel wire, a jingle steel wire, or an FRP
(fiber-reinforced plastic] rod containing aramid fibers or,glass fibers. In the embodiment shown in FIG. l,,a single steel wire.having an outer diameter of 1.2 mm is used as the tension member 13.
The size of the spiral groove i2 and the number of grooves 12 formed along the outer surface of the base body 11 can be determined appropriately. In the embodiment shown in the drawing, the groove 12 has a width of 1.5 mm and a depth of 4 mm. Also, five grooves are formed along the outer surface of the base body,ll. In the embodiment shown :i.n FIG. lr the grooves 12 are formed spiral such that these grooves are slowly turned continuously in a single direction along the length of the optical fiber cable 10.
Alternatively, the grooves 12 may be formed to extend straight in the longitudinal direction of the cable 10.
Further, the groove 12 may be of a so-called inverted spiral (SZ) type in which the extending direction of the groove 12 is curved by a predetermined angle in a first direction and, then, in a second direction opposite to the first direction. In this case, the curving directions are inverted periodically to provide the SZ type grooves along the outer surface of the base body 11. These grooves 12 can be formed along the outer surface of the base body 11 by, for example, CA 02480195 2004-10-15 ----- .
v. ..__l an extrusion molding method in which the head of the molding die is rotated.
The holding tape 15 can be formed of a ribbon of, polyethylene, polyester, polypropylene, etc.
The number of turns of the holding tape 15 can be determined appropriately. In the embodiment shown in FIG. 1, a single holdingribbon 'is wound about the base body 11 at a 1/2 lap.
The sheath 1.6, which is formed of a low density polyethylene, a linear low density polyethylene, etc., can be formed by, for example, an extrusion coating method. It is desirable far~the thickness of the sheath lra to fall within a range of between 1.5 mrn and 3.0 mm in view of the required mechanical characteristics of the cable 10 and the manufacturing cost. In the embodiment shown.in FIG. 1, the sheath 16 is formed by means of an extrusion coating Which is performed such that a polyethylene resin is extruded to cover the holding tape 15 in a thickness of 2 mm.
The thin optical fiberribbons-14 are stacked one upon the other vaithin the spiral groove 12 of the base body 11. In this embodiment, four ribbonsl4 'axe arranged within the groove 12, as shown in FIG. 3. As shown in FIG. 2, four optical fibers 17 each having a coating layer are arranged side by side to form a single row, and a resin coating layer 1$ is formed by using, for example, an ultraviolet~.curing resin t~
r cover the row of these optical fibers 17 so as to form the thin optical fiberj~rbbow 14. The optical fiber 17 has an outer diameter of, for example, 125 ~c m:
Incidentally, a letter °°t" (three occurrences) in FIG. 2 denotes the thickness of the resin coating layer 18 defined in the present invention.
To reiterate, the base body l1 is formed of a mixture of at least two materials differing from each other in the molecular weight distribution. In this case, the inner surface of the spiral.groove-12 of the base body 11 is made substantially flat and smooth, as shown in FIG. 3. In other words, the inner surface of the groove is free from projections causing an increase in the transmission loss of the optical fiber. In 1~ addition, the base body 11 exhibits a sufficiently high mechanical strength.
In the second embodiment of the present invention, the height "h" of the projections 20 from the inner surface of the groove 12 is suppressed to a value of 30 ,u m or less. The height h of the projections 20 is suppressed in the present invention as follows:
1. The base body is formed of a mixture of high density polyethylene resins containing a smaller amount of the high molecular weight component. It should be noted that the projections are formed by an unsatisfactory. dispersion of the high molecular weight component in the step of mixing the high and low CA 02480195 2004-10-15 - _..., ___......_._..._.._....._.....
molecular weight components to prepare the base body material.
~TRANSLATTON
OPTICAL FIBER CABLI~
Technical Field The present invention relates to a slot-type optical fiber cable comprising a thin and long base body having spiral grooves formed on the outer circum-ferential surface and a plurality of optical fiber -ribbonsstacked one upon the other within each of the spiral grooves, a plurality of optical fibers being formed within each of the optical fiber ribbons, particularly, to an optical fiber cable of a small diameter having optical fibers arranged at a very high density.
Background Art A slot-type optical fiber cable having a plurality of optical fiber ribbons stacked one upon the other within spiral grooves formed on the outer circumferen-tial surface of a thin and long base body permits dealing with a relatively large amount of information and, thus, is used nowadays as a relay bable or a subscriber cable for public communication. In recent years, a multi-media system of information is on a sharp increase. Also, diversification of information and increase of the information amount are expected to accompany the spread of the multi-media _. r-~.
. . ~ , system. Naturally, the optical fiber cable to be developed is required to be capable of coping with a greater amount of information. than in the past.
Further, with increase in the amount of inforiria--tion, the subscriber cable ar an optical fiber cable connected between a relay and an individual household is also required to be capable of coping with a greater amount of information. Under the circumstances, the slot-type optical fiber cable is also expected to be used as such an optical fiber.
To be more specific, the slot-type optical fiber cable comprises a long base body having a tension member arranged along the axis thereof arid a plurality of optical fiber ribbons stacked one upon. the other within each of spiral grooves formed along the outer circumferential surface of the base body. For example, four optical fiber ribbonsare stacked. one upon the other within each spiral groove. The outer surface of the base body having the vptical.fiber ribbonsarranged within the spiral grooves is wound with a holding tape.
Further, a sheath is arranged to cover the outer circumferential surface of the resultant structure. In general, the base body is formed of a high density polyethylene in view of the workability, mechanical properties and cost.
The simplest means to permit the optical fiber cable to be capable of coping with am increased amount ___..
t . .~ . . , ,~
. ~ .
of information is to increase the number of optical .
fibers, or the number of optical fibers ribbons, mounted within the optical fiber cable. Naturally, an increase in the number of optical fiber ribbonsmounted within the optical fiber cable results in an increased outer diameter of the cable. An increase in the outer diameter of the cable gives rise to difficulties. For example, the cable is unlikely to be bent, with the result that, in' arranging the cable ~withi.n a cable passageway, the cable fails .to be arranged within the passageway. Also, it is necessary to newly design tools, etc. to meet the increased outer diameter of the cable. It follows that, in order to increase the number of optical fiberribbons arranged within the optical fiber cable, it is necessary to improve the construction of the optical fiberribbon itself such that theribbons Can be arranged within the optical fiber cable in a higher density.
As a means for improving the construction of the optical fiber ribbon, it is proposed to decrease the thickness of a resin coating layer having a plurality of optical fibers embedded therein. The conventional optical fiber ribbon arranged within a, slot-type optical fiber cable comprises four optical fibers and a resin layer formed to cover collectively the four optical fibers. These optical fibers, each having a coating layer and a diameter of, for example, 12~ ~, m, are i v ~ 7 4 f arranged side by side. In general, the resin layer has a thickness, i.e., distance between the outer surface of the resin layer and the outer surface, which faces the outer surface of the resin layer, of the coated optical fiber, of 1210 to 150 ~c m. To be more specific, it is proposed to decrease the resin layer thickness from the conventional level of 120 to 15p ~c m to 30 to 100 ~c m as a means for increasing the density of the optical fiber ribbons arranged within the optical fiber cable. The optical fiber ribbon of the particular construction is generally called a thin optical fiber ribbon .
However, it has been found that:, when thin optical fiberribbons are stacked one upon the other within grooves of the base body at a density higher than in the past, a transmission loss derived from micro-bend is increased.
Disclosure of Invention An object of the present invention, which has been achieved in view of the situation described above, is to provide an optical fiber cable which permits markedly suppressing an increase of transmission loss derived from micro-bend of the optical fiber ribbons, arranged within a base body and also permits arranging optical fiberribbons within the base body at a higher density.
According to a first embodiment of the present _. CA 02480195 2004-10-15..._,.__ _._ ... _._.. _-L . < 1 4 . a 1 . a ~ ~ ' > , l invention, there is provided an optical fiber cable, comprising: a longitudinally extending core body having spiral grooves formed thereon; and at least one optical fiber ribbon housed in any one of said grooves, said .
5 ribbon including a plurality of optimal fibers embedded in a strip of resin, wherein said core b~dy is made from a mixture of at least two materials having different molecular weight distributions.
It is desirable that the mixture contains at least a low molecular weight polyethylene having a peak of polystyrene standard molecular weight distribution wwithin a range be~,ween 3 x 104 and 8 x 104 and a high molecular weight polyethylene having a peak of polystyrene standard molecular weight distribution within a range between ? x 104 and 1.5 x 105, and the polystyrene-peak appearing in said high molecular Weight polyethylene that invariably remains greater than said polystyrene peak appearing in said low molecular weight polyethylene.
2U . According to a second embodiment of the present invention, there is provided.ari optical fiber cable, comprising: a longitudinally extending core body having spiral grooves formed thereon; and at least one optical fiber ribbon housed in any one of said grooves, said z5 ribbon including a plurality of optical fibers embedded in a strip of resin, wherein projections formed on the inner surface of any one of said spiral groove ,e .. , . ~ ~ ,.
v 6 measure 30 ,u m or less in height.
It is desirable that the strip of resin of the fiber ribbon provides a resin thickness of 30 to 100 ~ m over each embedded fiber in each direction perpendicular to 'the fiber ribbon.
Brief Description of Drawinqs FIG. l shows the canstruction c~f a slot-type optical fiber cable according to they present invention;
FIG. 2 shows in a magnified fashion an example of a thin optical fiberribb~n arranged within the optical fiber cable of the present invention~
FIG. 3 shows in a magnified fashion how thin optical fiberribb~ns are laminated within a groove formed on the outer circumferential surface of a base body in an optical fiber cable according to a first embodiment of the present invention;:
FTG. 4 shows in a magnified fashion how thin optical fiberribbons are laminated within a groove formed on the outer circumferential surface of a base body in an optical fiber cable according to a second embodiment of the present inventianA and FIG. 5 is a graph showing the relationship between the height of proaections arid the transmission loss in an optical fiber 'cable according to the second embodiment of the present invention.
Best Mode of Carryincr Out the Invention Let us describe the present invention with a reference to the accompanying drawings.
Specifically, the present inventors prepared thin optical fiberribbons each including a resin coating film having a thickness of 70 ~ m in contrast to the conventional thickness of 135 ~c m. Then, an optical fiber cable Bias prepared by using the thin optical fiber ribbons thus prepared. In this case, 8 optical fiber ribbons were stacked one upon the other within each spiral groove of the base body, though only 4 optical fiber nbb~ns were stacked within each spiral groove in the conventional optical fiber cable. The characteristics such as bending and cable temperature of the resultant optical fiber cable were measured so as to find that an increased transmission loss derived from micro-bend took piece within the optical fiber embedded within the optical fiber~c:ibbon, Under the circumstances, the present inventors have made an extensive research. It has been found that the increase of the transmission loss takes place in only an optical fiber cable prepared by arranging the thin optical fiberribbo~s in the conventional base body. It has also been found that the increase of the transmission loss taking place in only the particular optical fiber cable noted above is,caused by 2S projections formed on the inner surface of the base body made of a high density polyethylene. The present inventors have looked into the-inner surface of the a ~
spiral groove formed on the circumferential surface of the base body used in the conventional optical fiber cable. It has been found that the projections are formed over the entire region of the inner surface at a rate of 10 projections/mm2. It has also.been found that these.projections have a height of l0 to 100 ~c m, the heights of most projections falling within a range of between 50 and 70 ~c m.
In order to decrease-the diameter of the optical.
1~ , fiber cable, it may be effective to decrease the diameter of the base body in which optical fiber ribbons are arranged. It should be noted in. this connection that optical fibers should be arranged in a manner to prevent the optical characteristics thereof from being adversely affected within the base body. In this respect, it is undesirable to decrease the cross sectional area of the spiral groove in which the optical fiber ribbons are arranged. Specifically, the decrease of the cross sectional area. noted above causes an increase in the side pressure loss of the optical fiber, with the result that the ciptical characteristics of the optical fiber are adversely-affected. Such being the situation, it may also be possible to decrease the diameter of the optical fiber cable by decreasing the diameter of the base body while maintaining constant the cross sectional area of the spiral groove formed on the surface of the _...
'~ . , ~r ' ~ ' ~
base body. In this case, it is.~.mportant to select appropriately the resin used far forming the base body.
Specifically, the resin should have a sufficiently high mechanical strength such that a side pressure should not be given to the optical fiberribbon by the deformation of the base body. An important mechanical strength required in this respect is a bending modulus of the resin.
In~the first embodiment of.the present invention, IO the base body is formed of a mixture of at least two materials differing from each other in the molecular weight distribution sa as.to suppress formation of.
projections, which cause an increased transmission loss of the optical fiber, while maintaining a required mechanical strength of the base body. In the second embodiment.of the present invention, the height of the projection is defined to be 30 ~c m or less so as to prevent substantially completely the projections from causing an increase in the transmission loss of the optical fiber.
As described above, the base body included in the optical fiber cable according to the first embodiment of the present invention is formed of a mixture of at least two materials differing from each other in the molecular weight distribution. To be more specific, the particular mixture includes, for example, a polymer prepared by polymerizing a low molecular weight _" .__._ - CA 02480195 2004-10-15 component and a h~.gh molecular weight component, and a mixture of these low and high~molecular weight components. What is important is that any material including a single material, not a mixture, can be used for forming the base body as far as 'the base body material exhibits a plurality of peaks in its molecular weight distribution.
In the first embodiment of the ;present invention, it is.desirable far the base body to be formed of a mixture including at least a first material having a peak,of the polystyrene standard molecular weight distribution within a range of between 3 x 104 and 8 x 104, and a second material having a peak of the polystyrene standard molecular weight distribution within a range of between 7 x 104 and 1.5 x 105. It should be noted that the second material has a peak of the polystyrene standard molecular weight distribution on the side of a higher molecular weight,. compared with the.first material. Incidentallyr it is possible for any of the first and second materials to have a peak which does not fall within the ranges given above.
The term °'polystyrene standard molecular weight"
denotes a molecular weight of a substance which is determined on the basis of an eluting time of the substance. To be more specific, an eluting time of a substance Hrhose molecular weight is unknown is measured. Also, a calibration curve is prepared by T
l ~<
s 1 , measuring the eluting time of polystyrene whose molecular weight is known by using a gel permeation chromatography (GPC) under the conditions given below.
Finally, the eluting time of the substance, whose molecular weight is unknown is converted into the polystyrene standard molecular weight by using the calibration curve.
(GPC Measuring Conditions) Measuring Machine,: 150 CV manufactured by Waters Inc.
Solvent: o-dichlorbenzene (containing 0.3~ of BHT: BiiT..l-hydroxy-4-methyl-2,6-di-tert--butyl benzene) Column: AT-G+AT-806 M/S x 2 manufactured by Shodex Inc.
Temperature: Column and Indicator .. 1.45°C
Concentration: 0.1 wt/vol Flow rate: 1.0 ml/min.
Standard Sample: Polystyrene Detector: Differential refractive index detector (RI) In view of the properties required for arranging the optical fiberribbons therein, the bass body material used in the present invention includes, for example, a high density polyethylene having a density of 0.94 to 0.97 g/cm3, polyolefin resins sur.h as polypropylene having a density of 0.90 to 1.30 g/cm3, polyamide resins and other engineering plastics. It is most ._._. .__.!- .,.___._-....,.._~_-.__._____.~., __ _-_CA 02480195 2004-10-15__ _._..._.__._'__ :___....._..___.._.____......_~
', , ~ , .~
desirable to use a high density polyethylene in view of the actual use over a long period of time in the past;
Workability, cost, etc. Further! in view of the moldability, it is desirable to use a mixture of at least two similar materials differing from each other in the molecular weight distribution.
In the first embodiment of .the present invention, the base body of the optical fiber cable is formed of, for example, a mixture containing at least a first material having a peak of. the polystyrene standard molecular weight distribution at a relatively high region, and a second material having a peak of the polystyrene standard molecular weight distribution at a relatively low region. The first material noted above contributes to the improvement of, fox example, a bending modules, which is an important mechanical property required in the base body, of the resultant base body. On t-he other hand, the second material noted above contributes to the improveriient 2p of, for example, a melt index, which is decisively important for improving the moldability of the base body material. It follows that it ~Ls possible to prevent the occurrence of projections which cause an increased transmission loss of the optical fiber while maintaining a sufficiently high meclxanical strength by mixing these first and second materials at a suitable .mixing ratio.
d 13' It should also be noted that, in the first embodiment of the present invention, it is desirable for the base body material to have a bending modulus of 180 kg/mm2 or less in order to permit the resultant optical fiber cable to be bent without difficulty. On the other hand,. the bending modulus of the base body material should desirably be 80 kg/mm2 or more in view of the side pressure applied to the optical-fiber ribbon embedded in the spiral groove~of the base body.
In the second embodiment of the present invention, the height of the projections formed on the inner surface of the spiral groove of the base body is defined to be 30 ~c m or less. As <~ result, the optical fiber nbbon.e~edded in the spiral groove of the base body is not affected by the projections regardless of the thickness of the optical fiberribbon embedded in the spiral groove. To be more specific, the optical, fiber ribbons arranged within the spiral groove may possibly be pressed partially: However, where the height of the projections is 30 ~u m or less, the resultant side pressure applied to the optical fiber ribbon~is not so high as to cause micro-bend occurrence, with the result that the transmission loss does not take place.
The present inventors have also found that the projections do not cause, all the thin optical fiber ribbons to bear an increased transmission loss.
Specifically, it has been found that the relationship i CA 02480195 2004-10-15 ._.___~ ,~ _ vi between the height of the projections and the thickness of the optical f.iber~-ribbon is deeply related to the increase in the transmission loss of the optical fiber. cable. In other words, it has been found that an increase in the transmission loss can be prevented substantially completely, if the particular relationship meets certain conditions. For example, when it comes to the thin optical fiber ribbon',covered with a resin coating layer having a thickness of 30 ~c m in contrast to at least 120 ,u m for the conventional optical fiber ribbon, the pptical fiber ribbow is partially pressed in the case where the height of the projections formed on the inner surface of the spiral groove exceeds 30 ~c m, i.e., height of, e.g., 40 ~c m. In this 1~ case, the side pressure applied to the optical fiber ribbon causes the optical fibers, arranged within the ribbon to bear micro=bend, leading to an.increase.of the transmission loss.
Under the circumstances,, the thickness of.the resin coating layer covering the optical fiberribbon is defined to fall within a range of between 30 wm and 100 a m in the second embodiment of the present invention. ~ In other words, a thin optical fiber ribbon is used in the second embodiment. What should be noted is that, even if thin optical fiberribbons defined in the second embodiment are arranged within the spiral groove of the base body in a_high density, it is ---..~J
r w i possible.to suppress .an increase of the transmission loss derived from the presence of micro-bend caused by the side pressuxe applied from the projections from the inner surface of the spiral groove formed on the base 5 body.
It should be noted that the projections defined in the second embodiment of the present invention differ from the convex-concave portions appearing on the surface of a molded body. In other words, the presence 10 of projections from the inner surface of the spiral groove of the base body is irrelevant to the definition of the surface roughness on the inner surface of the spiral groove.
FIG. l shows-a slot-type optical fiber cable 10 15 according to one embodiment of the present invention.
As seen from the drawing, the cable 10 comprises a long tension member 13 and a base body 11 covering the outer circumferential surface of the tension member 13. A
plurality of spiral grooves 12 are formed along the outer surface of the base body 11..Also, a plurality of thin optical fiber tapes 14 are arranged one upon the other within each spiral groove 12. Further, a holding tape 15 is Wound about the base body 11. in a manner to cover the thin optical fiber tapes 14 arranged within the spiral grooves 12. Still further, the resultant structure is covered with a sheath 16 so as to provide the optical fiber cable 10.
02480195 2004-10-15~"~,.. __~.,~...J.... _,~...." . ...__~__._~___~~
The tension member 13 is formed of, for example, a stranded steel wire, a jingle steel wire, or an FRP
(fiber-reinforced plastic] rod containing aramid fibers or,glass fibers. In the embodiment shown in FIG. l,,a single steel wire.having an outer diameter of 1.2 mm is used as the tension member 13.
The size of the spiral groove i2 and the number of grooves 12 formed along the outer surface of the base body 11 can be determined appropriately. In the embodiment shown in the drawing, the groove 12 has a width of 1.5 mm and a depth of 4 mm. Also, five grooves are formed along the outer surface of the base body,ll. In the embodiment shown :i.n FIG. lr the grooves 12 are formed spiral such that these grooves are slowly turned continuously in a single direction along the length of the optical fiber cable 10.
Alternatively, the grooves 12 may be formed to extend straight in the longitudinal direction of the cable 10.
Further, the groove 12 may be of a so-called inverted spiral (SZ) type in which the extending direction of the groove 12 is curved by a predetermined angle in a first direction and, then, in a second direction opposite to the first direction. In this case, the curving directions are inverted periodically to provide the SZ type grooves along the outer surface of the base body 11. These grooves 12 can be formed along the outer surface of the base body 11 by, for example, CA 02480195 2004-10-15 ----- .
v. ..__l an extrusion molding method in which the head of the molding die is rotated.
The holding tape 15 can be formed of a ribbon of, polyethylene, polyester, polypropylene, etc.
The number of turns of the holding tape 15 can be determined appropriately. In the embodiment shown in FIG. 1, a single holdingribbon 'is wound about the base body 11 at a 1/2 lap.
The sheath 1.6, which is formed of a low density polyethylene, a linear low density polyethylene, etc., can be formed by, for example, an extrusion coating method. It is desirable far~the thickness of the sheath lra to fall within a range of between 1.5 mrn and 3.0 mm in view of the required mechanical characteristics of the cable 10 and the manufacturing cost. In the embodiment shown.in FIG. 1, the sheath 16 is formed by means of an extrusion coating Which is performed such that a polyethylene resin is extruded to cover the holding tape 15 in a thickness of 2 mm.
The thin optical fiberribbons-14 are stacked one upon the other vaithin the spiral groove 12 of the base body 11. In this embodiment, four ribbonsl4 'axe arranged within the groove 12, as shown in FIG. 3. As shown in FIG. 2, four optical fibers 17 each having a coating layer are arranged side by side to form a single row, and a resin coating layer 1$ is formed by using, for example, an ultraviolet~.curing resin t~
r cover the row of these optical fibers 17 so as to form the thin optical fiberj~rbbow 14. The optical fiber 17 has an outer diameter of, for example, 125 ~c m:
Incidentally, a letter °°t" (three occurrences) in FIG. 2 denotes the thickness of the resin coating layer 18 defined in the present invention.
To reiterate, the base body l1 is formed of a mixture of at least two materials differing from each other in the molecular weight distribution. In this case, the inner surface of the spiral.groove-12 of the base body 11 is made substantially flat and smooth, as shown in FIG. 3. In other words, the inner surface of the groove is free from projections causing an increase in the transmission loss of the optical fiber. In 1~ addition, the base body 11 exhibits a sufficiently high mechanical strength.
In the second embodiment of the present invention, the height "h" of the projections 20 from the inner surface of the groove 12 is suppressed to a value of 30 ,u m or less. The height h of the projections 20 is suppressed in the present invention as follows:
1. The base body is formed of a mixture of high density polyethylene resins containing a smaller amount of the high molecular weight component. It should be noted that the projections are formed by an unsatisfactory. dispersion of the high molecular weight component in the step of mixing the high and low CA 02480195 2004-10-15 - _..., ___......_._..._.._....._.....
molecular weight components to prepare the base body material.
2. A laye:r-free from such projections is formed to cover the surface of the base body. To be more specific, the inner surface is coated with a resin which does not give rise to projections. Alternative ly, ar~bbon made of such a resin is attached to the inner surface of the base body.
3. In forming the base body by an extrusion moldiwg, the screen mesh of the breaker plate mounted between the extruder cylinder and the extruder head portion is changed so as to control the height h of the projections in question.
Since the height h of the 'projections 20 is suppressed as painted out above, these projections 20 are prevented from exerting side pressure to the optical fiberribbon 14, making it possible to suppress an 'increased transmission loss derived from the micro-bend caused by the side pressure.
ZO The prominent effect of the present invention will .
be clarified sufficiently by the Examples of the present invention which follow:
Example 1:
This example,was directed to the first embodiment of the present invention.
Specifically, an optical fiber cable of the present invention was prepared. The base body 11 of the cable was formed of a.high density polyethylene having a density of 0.953 g/cm3, and a bending modulus of 100 kg/mm2. The polyethylene consisted of a_first component having a peak of the polystyrene standard 5 molecular weight distribution in a' low molecular weight ' region.of about 5 x 104 and a second component having a peak of the polystyrene standard molecular weight distribution in.a high molecular weight region of about 1.3 x 105. The optical fiber cable prepared in 10 this Example,included the base body constructed as shown in FIG. 3. It should be noted that the second component of the high density polyethylene having ~
peak.in the higkr molecular weight region contributes greatly to an improvement ~f the mechanical strength of ..
15 the base body. On the other hand, the first component having a peak in the low molecular weight region contributes to an improvement in moldability of the raw material polyethylene consisting of the first and second components.
20 The properties of the resultant optical fiber cable were measured as follows. In any of the ~easure-menu given below, optical fiber cables whose transmis-sion loss was increased by 0.1 dB or less were evalu-ated as being satisfactory. On the other hand, optical fiber cables whose transmission loss was increased by more than 0.1, dB were evaluated as being defective.
(Measuring Methods) (1) Bending of Cables An optical fiber cable, which was 10 m long, was bent by 180° at a curvature radius of 300.mm so as to measure an increase of the transmission loss at a wavelength of 1:3 ,u m band.
(2) Side Pressure Characteristies . 'An optical fiber cable, Which was 5 m long, was sandwiched between a pair of flat plates each having a length of 50 mm. Under this condition, a load of 500 kg was applied to the cable through the flat plates so .
as to measure an increase of the transmission loss at a wavelength of 1.3 a m band.
(3) Temperature Characteristics An optical fiber cable, which was 750 m long, was wound about a cable-winding drum having an outer diameter of 1500 mm. The cable wound about the drum was left to stand under an atmosphere of 60°C so as to measure an increase of the transmission loss 24 hours later at a wavelength of 1.3 a m-.
The optical fiber cable was found to be satisfac-tort' in any of the bending characteristics, side pressure.characteristics and temperature characteris-tics.
Example 2:
This examphe was directed to the second embodiment of the present invention.
In this example, the base body 11 of the optical fiber cable was formed of a high density polyethylene having a density of 0.95 g/cm3 and a bending modulus of 90 kg/mm2. also, prepared were thin optical fiber ribbons 14 each having a thickness "t", as measured from the outer surface of the optical fiber 17 to the outer surface of the resin coating layer 18 of the optical fiber ribbon 14 as shown in FIG. 2, - of 30 ~c m, 40 ~c m, 70 ~c m and, 100 a m. Then, prepared were two kinds of base bodies 11 each having the height "h" of the projections_20 from the inner surface of the groove 12 controlled to fall within a .range of between 0 and 10 ~c m or between 20 ~c m and 30 a m. The height of the projections 20 was controlled bg method 3 described previously. Specifically,-four screen meshes of 400 meshes were used for controlling the height "h"
to fall within a range of between 0 and 10 a m, with three screen meshes of 300 meshes being used for controlling the height '°h" to fall within a range of.
between 20 and 30 w m.
Finally, eight kinds of optical fiber cables 10 were prepared by arranging four kinds of thin optical fiberribbons l4 within each base body. These optical fiber cables were evaluated as in Example 1, with the 2g results as shown in Table 1 below:
Table Height of 0 20 to to projections (,u ( m~ ~, m) Optical fiber ribbon30 40 70 1.00 30 40 70 100 thickness ~ ~c m) Evaluation Bending O 0 0 O O O O O
.
Side Pressure 0 O 0 O 0 O 0 O
Temperature 0 0 O O 0 O O O
L, ' ~ 1 ~ i ~ ~._ i i Then, the base bodies Were .formed of the same . material, in .whi_ch the height °'h" of the projections from the inner surface of the groove 12 were controlled to fall within a range of 40 to 50 a m and within a range of 60 to 70 a m. Finally, eight kinds of optical fiber cables were prepared by embedding the thin optical fiber ribbons prepared in advance in each of the base bodies thus prepared.- These 8 kinds of optical fiber cables were evaluated as in Example 1, the results being shown in Table 2 belowa CA 02480195 2004-10-15-_~._ ~__ ___......_. _....._ _..____....__.___._ . _...
Table 2 Height of 40 to 60 50 to projections ( ~c 70 m) ( ~, m) Optical fiber ribbon 40 70 1.00 30 40 70 100 thickness ( ~u m) Evaluation Bending x x 0 O x x O
x .
Side Pressure x 0 O 0 x 0 O
Temperature x x x x x x x I I ! i x x Further; eight kinds of optical fiber cables were prepared by embedding optical fiber ribbons each having a thickness °'t" defined previously of 120 a m or 150 ~c m in base bodies each having the height "h" of. the projections from the inner surface controlled to fall within a range of 0 to 10 ~, m, 20 to 30 a m, 40 to 50 a m or 60 to 70 w m. These optical fiber cables were evaluated as in Example 1, w~_th the results as shown in Table .3 below:
Tabhe 3 Optical fiber 120 150 thickness ( (,u ~, m) m) Height of 0 20 40 60 0 30 40 60 projections (~c to to to to- to to to to m) Evaluation Bending 0 O 0 O O 0 O 0 Side Pressure 0 0 0 0 0 0 O 0 10 . Temperature 0 . O 0 O O O O O
As apparent from Tables 1 to 3, the optical fiber cable comprising a bs.se body having the rieight "h" of the projections from the inner surface of 15 the groove controlled to be 30 ,u m or less has been found~to be satisfactory in any of the bending charac-teristics, side pressure characteristics and tempera-ture characteristics regardless of the thickness "t" of the optical fiberribbo~h~ In other words, it has been 20 demonstrated that, if the height "h" of the projections is 30 ~c m or less, the side pressure, even if given by the projection to the optical fiber ribbon, is not so high as to. bring about micro-bend in the optical fibers within the optical fiberribbon, making it possible to 25 suppress an increase of the transmission loss. FIG. 5 is a graph showing the relationship between the height of the projections and an increase of the transmission i ~.. ~~ -,, loss. As apparent from the graph, an increase o.f the transmission loss can be suppressed substantially completely, if the height of the projections is 30 ,u m or less:
It should be noted in particular that, where the height of the projections from the inner surface of the groove is 30 ~u m or~less, the produced optical fiber cable was found to be satisfactory in any of the bending characteristics, side pressure characteristics f0 and temperature characteristics, even if the thickness "t" of the resin coating layer of the optical fiber ribbon is i00 ~ m or less. In other words, it has been found that the optical fiber~cable of the present invention produces prominent effects in the case where 15 the thickness "t'° of the resin coating layer of the optical fiber ribbon is 100 ~ m or less .
Attentions should also be paid to Table 3.
Specifically, it has been found that, where the thickness "t" of the~resin coating layer.of the optical 20 fiber ribbon is 120 to ,150 ,u m as in the prior art, the produced optical fiber cable is satisfactory in the bending characteristics, etc: as far as the height of the projections from the inner surface of the groove is 40 to 70 ~c m as in the prior art:. Incidentally, 25 optical fiber cables were prepared by embedding conventional optical fiber ribbons in base bodies each having the height of the projections in question E
- CA 02480195 2004-10-15 _...._ -_.-.....-.__..._..._..._...._-.._..
controlled to be 30 ~c m or less as defined in the present invention. These optical fiber cables have been found to be satisfactory in ahy of the bending characteristics, side pressure characteristics and temperature characteristics, as expected. -To reiterate, the optical fiber cable of the present invention comprises a base body formed of.a mixture of at least two materials differing from each other in molecular weight distribution, i.e., materials having peaks in different positions in the polystyrene standard molecular weight distribution. As a result, it is possible to prevenit occurrence of projections causing an increase of transmission loss while maintaining a sufficiently high mechanical strength.
What should also be noted is that, in the present invention, the height of the projecaions from the inner surface of a spiral groove formed in the base body of the cable is defined to be 30 ~. m or less. As a result, the optical fiber ribbons arranged within the groove are not affected by these projections. To be more specific, since the height of the projections is 30 ~c m or less, the si:de.pressure, even if given by the projection to the optical fiber ribbon, is not so high as to bring about micro-bend in the optical fibers within the optical fiberribbon', making it possible to suppress an increase.of the transmission loss.
10 . Temperature _.. CA 02480195 2004-10-15 _..~-_. . _.___~_.__..__.-.._.
.. .d . . , As described above in detail,, the present invention produces a prominent effect that, even if longer optical fiber ribbons~are arranged withiwthe spiral groove formed~on the outer circumferen~ial y .surface of the base body, it is possible to suppress an increase of the transmission loss. What should also be noted is that, even if the thickness of the resin coating. layer of the optical fiber ribbon. is made smaller than in the past, it is possible to suppress an increase of the transmission loss, making it possible to .use thin optical fiberribboris in manufacturing optical fiber cables. It follows that it is possible to increase the number of optical :fiber rjbbonS arranged within a single spiral groove of. the base body, compared with the conventional optical fiber cable.
Alternatively, where the same number of optical fiber ribbonsare arranged within a single.spiral groove, the present invention permits decreasing the outer diameter of the optical fiber cable>
Since the height h of the 'projections 20 is suppressed as painted out above, these projections 20 are prevented from exerting side pressure to the optical fiberribbon 14, making it possible to suppress an 'increased transmission loss derived from the micro-bend caused by the side pressure.
ZO The prominent effect of the present invention will .
be clarified sufficiently by the Examples of the present invention which follow:
Example 1:
This example,was directed to the first embodiment of the present invention.
Specifically, an optical fiber cable of the present invention was prepared. The base body 11 of the cable was formed of a.high density polyethylene having a density of 0.953 g/cm3, and a bending modulus of 100 kg/mm2. The polyethylene consisted of a_first component having a peak of the polystyrene standard 5 molecular weight distribution in a' low molecular weight ' region.of about 5 x 104 and a second component having a peak of the polystyrene standard molecular weight distribution in.a high molecular weight region of about 1.3 x 105. The optical fiber cable prepared in 10 this Example,included the base body constructed as shown in FIG. 3. It should be noted that the second component of the high density polyethylene having ~
peak.in the higkr molecular weight region contributes greatly to an improvement ~f the mechanical strength of ..
15 the base body. On the other hand, the first component having a peak in the low molecular weight region contributes to an improvement in moldability of the raw material polyethylene consisting of the first and second components.
20 The properties of the resultant optical fiber cable were measured as follows. In any of the ~easure-menu given below, optical fiber cables whose transmis-sion loss was increased by 0.1 dB or less were evalu-ated as being satisfactory. On the other hand, optical fiber cables whose transmission loss was increased by more than 0.1, dB were evaluated as being defective.
(Measuring Methods) (1) Bending of Cables An optical fiber cable, which was 10 m long, was bent by 180° at a curvature radius of 300.mm so as to measure an increase of the transmission loss at a wavelength of 1:3 ,u m band.
(2) Side Pressure Characteristies . 'An optical fiber cable, Which was 5 m long, was sandwiched between a pair of flat plates each having a length of 50 mm. Under this condition, a load of 500 kg was applied to the cable through the flat plates so .
as to measure an increase of the transmission loss at a wavelength of 1.3 a m band.
(3) Temperature Characteristics An optical fiber cable, which was 750 m long, was wound about a cable-winding drum having an outer diameter of 1500 mm. The cable wound about the drum was left to stand under an atmosphere of 60°C so as to measure an increase of the transmission loss 24 hours later at a wavelength of 1.3 a m-.
The optical fiber cable was found to be satisfac-tort' in any of the bending characteristics, side pressure.characteristics and temperature characteris-tics.
Example 2:
This examphe was directed to the second embodiment of the present invention.
In this example, the base body 11 of the optical fiber cable was formed of a high density polyethylene having a density of 0.95 g/cm3 and a bending modulus of 90 kg/mm2. also, prepared were thin optical fiber ribbons 14 each having a thickness "t", as measured from the outer surface of the optical fiber 17 to the outer surface of the resin coating layer 18 of the optical fiber ribbon 14 as shown in FIG. 2, - of 30 ~c m, 40 ~c m, 70 ~c m and, 100 a m. Then, prepared were two kinds of base bodies 11 each having the height "h" of the projections_20 from the inner surface of the groove 12 controlled to fall within a .range of between 0 and 10 ~c m or between 20 ~c m and 30 a m. The height of the projections 20 was controlled bg method 3 described previously. Specifically,-four screen meshes of 400 meshes were used for controlling the height "h"
to fall within a range of between 0 and 10 a m, with three screen meshes of 300 meshes being used for controlling the height '°h" to fall within a range of.
between 20 and 30 w m.
Finally, eight kinds of optical fiber cables 10 were prepared by arranging four kinds of thin optical fiberribbons l4 within each base body. These optical fiber cables were evaluated as in Example 1, with the 2g results as shown in Table 1 below:
Table Height of 0 20 to to projections (,u ( m~ ~, m) Optical fiber ribbon30 40 70 1.00 30 40 70 100 thickness ~ ~c m) Evaluation Bending O 0 0 O O O O O
.
Side Pressure 0 O 0 O 0 O 0 O
Temperature 0 0 O O 0 O O O
L, ' ~ 1 ~ i ~ ~._ i i Then, the base bodies Were .formed of the same . material, in .whi_ch the height °'h" of the projections from the inner surface of the groove 12 were controlled to fall within a range of 40 to 50 a m and within a range of 60 to 70 a m. Finally, eight kinds of optical fiber cables were prepared by embedding the thin optical fiber ribbons prepared in advance in each of the base bodies thus prepared.- These 8 kinds of optical fiber cables were evaluated as in Example 1, the results being shown in Table 2 belowa CA 02480195 2004-10-15-_~._ ~__ ___......_. _....._ _..____....__.___._ . _...
Table 2 Height of 40 to 60 50 to projections ( ~c 70 m) ( ~, m) Optical fiber ribbon 40 70 1.00 30 40 70 100 thickness ( ~u m) Evaluation Bending x x 0 O x x O
x .
Side Pressure x 0 O 0 x 0 O
Temperature x x x x x x x I I ! i x x Further; eight kinds of optical fiber cables were prepared by embedding optical fiber ribbons each having a thickness °'t" defined previously of 120 a m or 150 ~c m in base bodies each having the height "h" of. the projections from the inner surface controlled to fall within a range of 0 to 10 ~, m, 20 to 30 a m, 40 to 50 a m or 60 to 70 w m. These optical fiber cables were evaluated as in Example 1, w~_th the results as shown in Table .3 below:
Tabhe 3 Optical fiber 120 150 thickness ( (,u ~, m) m) Height of 0 20 40 60 0 30 40 60 projections (~c to to to to- to to to to m) Evaluation Bending 0 O 0 O O 0 O 0 Side Pressure 0 0 0 0 0 0 O 0 10 . Temperature 0 . O 0 O O O O O
As apparent from Tables 1 to 3, the optical fiber cable comprising a bs.se body having the rieight "h" of the projections from the inner surface of 15 the groove controlled to be 30 ,u m or less has been found~to be satisfactory in any of the bending charac-teristics, side pressure characteristics and tempera-ture characteristics regardless of the thickness "t" of the optical fiberribbo~h~ In other words, it has been 20 demonstrated that, if the height "h" of the projections is 30 ~c m or less, the side pressure, even if given by the projection to the optical fiber ribbon, is not so high as to. bring about micro-bend in the optical fibers within the optical fiberribbon, making it possible to 25 suppress an increase of the transmission loss. FIG. 5 is a graph showing the relationship between the height of the projections and an increase of the transmission i ~.. ~~ -,, loss. As apparent from the graph, an increase o.f the transmission loss can be suppressed substantially completely, if the height of the projections is 30 ,u m or less:
It should be noted in particular that, where the height of the projections from the inner surface of the groove is 30 ~u m or~less, the produced optical fiber cable was found to be satisfactory in any of the bending characteristics, side pressure characteristics f0 and temperature characteristics, even if the thickness "t" of the resin coating layer of the optical fiber ribbon is i00 ~ m or less. In other words, it has been found that the optical fiber~cable of the present invention produces prominent effects in the case where 15 the thickness "t'° of the resin coating layer of the optical fiber ribbon is 100 ~ m or less .
Attentions should also be paid to Table 3.
Specifically, it has been found that, where the thickness "t" of the~resin coating layer.of the optical 20 fiber ribbon is 120 to ,150 ,u m as in the prior art, the produced optical fiber cable is satisfactory in the bending characteristics, etc: as far as the height of the projections from the inner surface of the groove is 40 to 70 ~c m as in the prior art:. Incidentally, 25 optical fiber cables were prepared by embedding conventional optical fiber ribbons in base bodies each having the height of the projections in question E
- CA 02480195 2004-10-15 _...._ -_.-.....-.__..._..._..._...._-.._..
controlled to be 30 ~c m or less as defined in the present invention. These optical fiber cables have been found to be satisfactory in ahy of the bending characteristics, side pressure characteristics and temperature characteristics, as expected. -To reiterate, the optical fiber cable of the present invention comprises a base body formed of.a mixture of at least two materials differing from each other in molecular weight distribution, i.e., materials having peaks in different positions in the polystyrene standard molecular weight distribution. As a result, it is possible to prevenit occurrence of projections causing an increase of transmission loss while maintaining a sufficiently high mechanical strength.
What should also be noted is that, in the present invention, the height of the projecaions from the inner surface of a spiral groove formed in the base body of the cable is defined to be 30 ~. m or less. As a result, the optical fiber ribbons arranged within the groove are not affected by these projections. To be more specific, since the height of the projections is 30 ~c m or less, the si:de.pressure, even if given by the projection to the optical fiber ribbon, is not so high as to bring about micro-bend in the optical fibers within the optical fiberribbon', making it possible to suppress an increase.of the transmission loss.
10 . Temperature _.. CA 02480195 2004-10-15 _..~-_. . _.___~_.__..__.-.._.
.. .d . . , As described above in detail,, the present invention produces a prominent effect that, even if longer optical fiber ribbons~are arranged withiwthe spiral groove formed~on the outer circumferen~ial y .surface of the base body, it is possible to suppress an increase of the transmission loss. What should also be noted is that, even if the thickness of the resin coating. layer of the optical fiber ribbon. is made smaller than in the past, it is possible to suppress an increase of the transmission loss, making it possible to .use thin optical fiberribboris in manufacturing optical fiber cables. It follows that it is possible to increase the number of optical :fiber rjbbonS arranged within a single spiral groove of. the base body, compared with the conventional optical fiber cable.
Alternatively, where the same number of optical fiber ribbonsare arranged within a single.spiral groove, the present invention permits decreasing the outer diameter of the optical fiber cable>
Claims
1. An optical fiber cable, comprising:
a longitudinally extending core body having a plurality of spiral grooves formed thereon; and at least one optical fiber ribbon housed in any one of said grooves, said at least one optical fiber ribbon including a plurality of optical fibers embedded in a strip of resin, wherein said strip of resin has a resin thickness of 30 to 100 µm over each embedded fiber in each direction perpendicular to the fiber ribbon and projections formed on the inner surface of any one of said spiral grooves measure 30 µm or less in height.
a longitudinally extending core body having a plurality of spiral grooves formed thereon; and at least one optical fiber ribbon housed in any one of said grooves, said at least one optical fiber ribbon including a plurality of optical fibers embedded in a strip of resin, wherein said strip of resin has a resin thickness of 30 to 100 µm over each embedded fiber in each direction perpendicular to the fiber ribbon and projections formed on the inner surface of any one of said spiral grooves measure 30 µm or less in height.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7-142011 | 1995-06-08 | ||
| JP14201195 | 1995-06-08 | ||
| CA002196454A CA2196454C (en) | 1995-06-08 | 1996-06-07 | Optical fiber cable |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002196454A Division CA2196454C (en) | 1995-06-08 | 1996-06-07 | Optical fiber cable |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2480195A1 CA2480195A1 (en) | 1996-12-27 |
| CA2480195C true CA2480195C (en) | 2006-06-06 |
Family
ID=33435747
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002480195A Expired - Lifetime CA2480195C (en) | 1995-06-08 | 1996-06-07 | Optical fiber cable |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2480195C (en) |
-
1996
- 1996-06-07 CA CA002480195A patent/CA2480195C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2480195A1 (en) | 1996-12-27 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20160607 |