U.S. patent application number 10/804982 was filed with the patent office on 2004-09-16 for method and apparatus for manufacturing plastic optical transmission medium.
Invention is credited to Choi, Won Young, Lee, Bongsoo, Tuchman, Stephan A., Tymianski, Jacob Ralph, Walker, James K..
Application Number | 20040179798 10/804982 |
Document ID | / |
Family ID | 22726424 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040179798 |
Kind Code |
A1 |
Walker, James K. ; et
al. |
September 16, 2004 |
Method and apparatus for manufacturing plastic optical transmission
medium
Abstract
The present invention relates to a method and apparatus for
manufacturing plastic optical transmission medium. The subject
method and apparatus can produce a variety of optical transmission
medium, including for example, graded refractive index polymer
optical fiber, graded refractive index rod lens, and step index
polymer optical fiber. The subject optical transmission medium have
improved characteristics and efficiency, due, at least in part, to
better control of the profile of the refractive index distribution
and stable high temperature operation of the medium. High
efficiency of manufacturing can be achieved by the subject method
and apparatus which can permit continuous extrusion at high
speed.
Inventors: |
Walker, James K.;
(Gainesville, FL) ; Tymianski, Jacob Ralph;
(Gainesville, FL) ; Lee, Bongsoo; (Kyung-Do,
KR) ; Tuchman, Stephan A.; (Gainesville, FL) ;
Choi, Won Young; (Gainesville, FL) |
Correspondence
Address: |
SALIWANCHIK LLOYD & SALIWANCHIK
A PROFESSIONAL ASSOCIATION
2421 N.W. 41ST STREET
SUITE A-1
GAINESVILLE
FL
32606-6669
US
|
Family ID: |
22726424 |
Appl. No.: |
10/804982 |
Filed: |
March 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10804982 |
Mar 19, 2004 |
|
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|
09833833 |
Apr 12, 2001 |
|
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60196687 |
Apr 12, 2000 |
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Current U.S.
Class: |
385/124 ;
264/1.29; 427/8 |
Current CPC
Class: |
B29D 11/00682 20130101;
B29C 48/09 20190201; B29C 48/06 20190201; B29C 48/12 20190201; B29C
48/00 20190201; G02B 6/02038 20130101 |
Class at
Publication: |
385/124 ;
264/001.29; 427/008 |
International
Class: |
B29D 011/00; G02B
006/02; B05D 001/00; G02B 006/18 |
Claims
1. A plastic optical transmission medium, comprising; a polymeric
material comprising an additive which modifies the refractive index
of the polymeric material, wherein the additive is selected from
the class of methyl esters of perfluoro (poloxa) monocarboxylic
acids.
2. The plastic optical transmission medium according to claim 31,
wherein said additive is perfluoro
2,5,8-trimethyl-3,6,9-trioxadodecanoic acid, methyl ester
(PTTME).
3. A plastic optical transmission medium, comprising: a polymeric
material comprising an additive which modifies the refractive index
of the polymeric material, wherein the additive is selected from
the class of methyl esters of perfluoro aliphatic monocarboxylic
acids.
4. The plastic optical transmission medium according to claim 33,
wherein said additive is methyl perfluorooctanate.
5. A method of modifying the refractive index of a plastic optical
transmission medium, comprising: preparing a polymeric material;
and adding an additive which modifies the refractive index of the
polymeric material, wherein the additive is selected from the class
of methyl esters of perfluoro (poloxa) monocarboxylic acids.
6. The method according to claim 35, wherein said additive is
perfluoro 2,5,8-trimethyl-3,6,9-trioxadodecanoic acid, methyl ester
(PTTME).
7. A method of modifying the refractive index of a plastic optical
transmission medium, comprising: preparing a polymeric material;
and adding an additive which modifies the refractive index of the
polymeric material, wherein the additive is selected from the class
of methyl esters of perfluoro aliphatic monocarboxic acids.
8. The method according to claim 37, wherein said additive is
methyl perfluoroctanate.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] This application is a divisional of U.S. Ser. No.
09/833,833, which was filed Apr. 12, 2001, which claims the benefit
of the provisional application U.S. Serial No. 60/196,687, which
was filed Apr. 12, 2000.
BACKGROUND OF THE INVENTION
[0002] Graded index plastic optical fiber (GI-POF) offers promise
as a high bandwidth communication medium. The ability to create a
desired index of refraction profile in a plastic optical fiber
[0003] Methods of manufacture of this material have been proposed
in U.S. Pat. No. 5,593,621, and 5,523,660, EP 130838, EP 2682969,
JP1-265208, JP3-65904, JP3-64704, and WO87/01071, and Polymer
Journal, Vol. 27, No. 3, pp 310-313 (1995). These manufacturing
methods, however, suffer from various drawbacks. For example, some
methods require the initial production of a graded index preform
and subsequent drawing of fiber from the preform, resulting in a
low efficiency of production. Other methods rely on a non-uniform
radial distribution of a low molecular weight additive in the fiber
and, due to the high concentrations by weight of additives which
lower the glass transition temperatures of the fiber, can result in
fiber which does not meet the thermal stability requirements for
certain applications.
BRIEF SUMMARY OF THE INVENTION
[0004] The subject invention pertains to a method and apparatus for
manufacturing a plastic optical transmission medium. A specific
embodiment of the subject method can allow continuous high-speed
production while controlling the refractive index profile of the
optical transmission medium, and can produce optical transmission
medium with high optical transmission and good thermal
stability.
[0005] The subject invention provides a method of manufacturing a
plastic optical transmission medium in which a solid polymeric tube
having at least two concentric cylinders of polymeric material is
surrounded by an outer tubing, wherein at least one of the two
concentric cylinders has a diffusible additive which modifies the
index of refraction added with the polymeric material of the
cylinder. The surrounded polymeric tube can then be heated to cause
diffusion of the diffusible additive. The temperature to which the
surrounded polymeric tube is heated should be below the outer
tubing's melting temperature, and preferably below the outer
tubing's glass transition temperature so that the structural
integrity of the outer tubing is maintained. The temperature should
also be above the glass transition temperature of the polymeric
materials of the polymeric tube. In this way, the outer tubing can
maintain its structural integrity and hold the polymeric tube
materials in place while diffusion of the diffusible additives
takes place. By controlling the temperature and time period of the
heating, the amount of diffusion can be controlled.
[0006] In a specific embodiment, two or more concentric cylinders
of transparent polymer melt are extruded to form a single extruded
polymeric tube. At least one of the polymer melts can contain one
or more transparent low molecular weight diffusible additives. The
additives diffuse within the melt and/or into adjacent melts at a
rate dependent on a variety of parameters including the temperature
of the polymeric tube, the time during which diffusion is permitted
to occur and the diffusion constants of the additive(s). In a
specific embodiment, the extruded polymeric tube can incorporate an
outer tubing made of TEFLON.RTM.. Other materials can also be used
for an outer tubing. In a specific embodiment, the outer tubing can
be allowed to solidify before or slightly after encasing the
extruded polymeric tube which will become a plastic optical
transmission medium such as a graded-index (GRIN) fiber. The outer
tubing's internal diameter is preferably in the range 0.15 mm to
about 1.0 mm, depending on the desired diameter of the GRIN
fiber.
[0007] The final radial distribution of the additives within the
polymeric tube, together with the refractive indices of the
individual polymers, determine the final graded index profile of
the fiber. The characteristic distance, over which diffusion of
additives occur, is preferably significantly less than the outer
tubing radius, for example in the range of about 0.1 mm. In a
specific embodiment, the time necessary to achieve the desired
degree of additive diffusion can be on the order of 100 seconds or
more. Preferably, the diffusible additives are chosen to have
refractive indices substantially different from that of their
polymer melts in order to keep the percentage amount of necessary
additive low. As the addition of diffusible additives typically
reduces the glass transition temperature, keeping the percentage
amount of additive low minimizes the reduction of the glass
transition temperature of the polymer. Maintaining a high glass
transition temperature of the resulting GRIN fiber can confer good
stability at high operating temperatures.
[0008] In a specific embodiment of the subject invention for
producing GRIN fiber, an index-enhancing additive is used near the
axis and, in addition, an index-reducing additive is used at the
outer radius of the fiber. By incorporating additives throughout
the resulting GRIN fiber in this way, the glass transition
temperature of the GRIN fiber material does not change
substantially as a function of radius. In a specific embodiment,
index-reducing additives composed of highly fluorinated compounds
which are nevertheless soluble in acrylic-based polymers can be
used. The use of these highly fluorinated compounds as
index-reducing additives can provide a large difference in
refractive index from the axis to the outer radius of the fiber and
can reduce the amount of additive needed to achieve the desired
index profile. Reducing the amount of additives can raise the glass
transition temperature of the fiber and permit the fiber to achieve
stable operation at high temperatures.
[0009] Once the outer tubing, for example a TEFLON.RTM. tube, is in
place, the GRIN fiber can be heated to a temperature below the
glass transition temperature and/or melting point of the outer
tubing and above the glass transition temperature of the GRIN fiber
such that diffusion of the additives can occur. Preferably, the
GRIN fiber is heated substantially above the glass transition
temperature of the GRIN fiber such that diffusion of the additives
can occur rapidly. In a specific embodiment, the GRIN fiber can be
wound continuously on a heated drum for a number of turns which can
provide an adequate time duration at a given fiber production rate
to achieve the desired GRIN profile. Alternative methods of heating
the fiber are well known in the art and can be used.
[0010] As a further means of achieving long-term thermal and
mechanical stability, cross-linking of the fiber material may be
achieved by photo-initiation. In a specific embodiment,
cross-linking of the fiber can be accomplished during the residence
time of the fiber on the drum.
[0011] In a specific embodiment of the subject invention, three or
more concentric polymer melts and two or more diffusible additives
whose refractive indices are carefully chosen with respect to the
melts in which they are diffused, can be utilized to produce a
graded index fiber which exhibits long-term stable operation in the
temperature range--40.degree. C. to +85.degree. C.
[0012] Furthermore, the subject invention can allow fiber to be
produced at a high rate of production and with a controlled index
profile, leading to high bandwidth capability, high transparency,
and high thermal stability at high ambient temperatures. In
addition, GRIN fiber having a variety of numerical apertures and
graded index profiles can be continuously produced.
Brief Description of the Drawings
[0013] FIG. 1 Illustrates the glass transition temperature of PMMA
blend versus concentration by weight of a typical additive shown in
Table 2.
[0014] FIG. 2A shows a schematic illustration of an apparatus for
manufacturing optical fiber using two melts in accordance with the
subject invention.
[0015] FIG. 2B shows a schematic illustration of a cross-section of
a die which can be utilized in conjunction with the embodiment of
the subject invention shown in FIG. 2a.
[0016] FIG. 3A shows a schematic illustration of an apparatus for
manufacturing optical fiber using three melts in accordance with
the subject invention.
[0017] FIG. 3B shows a schematic illustration of a cross-section of
a die which can be utilized in conjunction with the embodiment of
the subject invention shown in FIG. 3a.
[0018] FIG. 4 illustrates the strategy of material preparation and
development of the index profile in accordance with a specific
embodiment of the subject invention.
[0019] FIG. 5A shows GRIN profile modifications due to a fourth
layer of melt polymer with a higher refractive index and not
containing and additives in accordance with a specific embodiment
of the subject invention
[0020] FIG. 5B shows GRIN profile modifications due to a fourth
layer of melt polymer with a lower refractive index and not
containing any additives in accordance with a specific embodiment
of the subject invention.
[0021] FIG. 6A Sshows a cross-section of a GRIN-POF having an outer
tubing and a jacket in accordance with the subject invention.
[0022] FIG. 6B shows a cross-section of a GRIN-POF having a jacket
acting as an outer tubing in accordance with the subject
invention.
[0023] FIG. 7A shows a cross-section of two GRIN POF's with each
surrounded by an outer tubing and a jacket surrounding and holding
together the fibers in accordance with the subject invention.
[0024] FIG. 7B shows a cross-section of two GRIN POF's with a
jacket acting as an outer tubing and holding the fibers together in
accordance with the subject invention.
DETAILED DISCLOSURE OF THE INVENTION
[0025] The subject invention pertains to a method and apparatus for
manufacturing a plastic optical transmission medium. The subject
method can allow continuous high-speed production while controlling
the refractive index profile of the optical transmission medium,
and can produce optical transmission medium with high optical
transmission and good thermal stability.
[0026] In a specific embodiment of the subject invention, two or
more concentric cylinders of transparent polymer melts in which are
dissolved one or more transparent low molecular weight diffusible
additive(s) can be utilized to produce a plastic optical
transmission medium. Cylinders of melt can be extruded into a
solidified polymeric tube via, for example, a cross-head type of
die. The tube containing the melt materials can be maintained at
high temperature for a specific time period, such that the
additives diffuse within the polymeric tube and, in particular,
from the polymer melt in which they were dissolved into the
adjacent melts, to produce a desired index profile. The additives
and polymers can be selected to meet the desired optical, thermal,
and mechanical properties of the resulting optical transmission
medium.
[0027] In a specific embodiment, some of the specific desired
properties of a graded-index plastic optical fiber (GI-POF)
include:
1 1. Optical Attenuation .ltoreq.150 dB/km 2. Parabolic Index
Profile with Bandwidth .gtoreq.2.5 GHz/100 m 3. Numerical Aperture
0.1 to 0.25 4. Long-Term Thermal Stability Temperature -40.degree.
C. to +85.degree. C. Range (Blyler Jr., L. L., et al., 1997, and
Ishigure, T., et. al., 1998) 5. Production rate of GRIN fiber
.gtoreq.2000 m/hour
[0028] The present invention can utilize organic polymers and/or
perfluorinated polymers to achieve GI-POF with the desired
properties.
[0029] A choice of organic polymers suitable for the high optical
transmission desired in a specific embodiment of the subject
invention is the methacrylate family. Other amorphous organic
polymers may be used, when, for example, the highest optical
transmission is not required. Such polymers include, for example,
polystyrene, polycarbonate, and copolymers thereof. Specific
examples of polymers which may be used in the subject invention are
given in Table 1.
2TABLE 1 Typical Organic Polymers Suitable for the Subject
Invention Refractive Glass Transition Polymer Index Temperature
.degree. C. Polymethyl methacrylate (PMMA) 1.492 101 Polycyclohexyl
methacrylate 1.5066 104 Polyphenyl methacrylate (PPMA) 1.5706 110
Polytrifluoroethyl methacrylate (PTMA) 1.415 82 Poly
(2,2,3,3-Tetrafluoropropyl-.alph- a.- 1.391 138 fluoroacrylate)
(PTFA) Poly (2,2,3-Trifluoropropyl-.alpha.- 1.397 95
fluoroacrylate) Poly (2,2,3,3,3-Pentafluoropropyl-.alpha.- 1.386
125 fluoroacrylate) Poly (2,2,3,3,4,4,5,5-Octafluoropentyl-.alpha.-
1.366 105 Fluoroacrylate)
[0030] Copolymers of the materials given in Table 1 are also
suitable. Table 1 shows the refractive indices of the homopolymers
and their glass transition temperatures. In addition,
perfluorinated amorphous polymers such as TEFLON.RTM. AF (DuPont)
and CYTOP.TM.(Asahi) may be used and are given in Table 2.
3TABLE 2 Typical Perfluorinated Polymers Suitable for the Subject
Invention Refractive Glass Transition Polymer Index Temperature
.degree. C. TEFLON .RTM. AF amorphous copolymers 1.29-1.31 160-240
of 2,2-bis (trifluoromethyl)-4,5-difluoro- 1,3-dioxole and
tetrafluorethylene CYTOP .TM. an amorphous polymer 1.34 108
produced by Asahi Glass Co
[0031] In a specific embodiment, diffusible additives are selected
to satisfy one or more, and preferably all, of the following
criteria:
[0032] 1. The additives are soluble in the required concentrations
in the homopolymers and copolymers utilized.
[0033] 2. The boiling point is as high as possible and preferably
at least as high as the melt extrusion temperature to prevent the
formation of bubbles.
[0034] 3. The diffusion constant is such as to provide adequate
diffusion during manufacture (for example at
.about.130.degree.-190.degree. C.) and high stability during use
(for example up to 85.degree. C.).
[0035] 4. The refractive index is as different as possible (for
example at least about .+-.0.05 and preferably .gtoreq..+-.0.1)
from that of the polymers to reduce the amount in weight % to
achieve the desired refractive index of the polymer melt
solution.
[0036] Examples of transparent additives which can be used with
organic polymers are given in Table 3. Examples of additives which
can be used with perfluorinated polymers are given in Table 4.
[0037] The subject invention relates to the use of very low
refractive index compounds as index modifying additives. Methyl
esters of perfluoro (polyoxa) monocarboxylic acids represent one
class of compounds that can be utilized as index modifying
additives of the subject invention. Table 3 lists one example from
this class of compounds, perfluoro-2,5,8-trimeth- yl-3,6,9
trioxadodecanoic acid, methyl ester (PTTME)
(F[CF(CF.sub.3)CF.sub.2O].sub.3CF(CF.sub.3)COOCH.sub.3). Other
examples from this class include
perfluoro-2,5-dimethyl-3,6-dioxanonanoic acid, methyl ester
(F[CF(CF.sub.3)CF.sub.2O].sub.2CF(CF.sub.3)COOCH.sub.3; molecular
weight 510, b.p. 156.degree.) and perfluoro-2,5,8,11-tetramethy-
l-3,6,9,12-tetraoxapentadecanoic acid, methyl ester
(F[CF(CF.sub.3)CF.sub.2O].sub.4CF(CF.sub.3)COOCH.sub.3; molecular
weight 842, b.p. >250.degree.). Therefore, it should be readily
apparent that compounds of the general formula,
F[CF(CF.sub.3)CF.sub.2O].sub.XCF(CF.sub- .3)COOCH.sub.3, wherein
X.gtoreq.2, can be utilized as index modifying additives of the
subject invention.
[0038] In addition, methyl esters of perfluoro aliphatic
monocarboxylic acids represent another class of compounds that can
be utilized as index modifying additives of the subject invention.
Table 3 lists one example from this class of compounds, methyl
perfluorooctanoate (C.sub.gH.sub.3F.sub.15O.sub.2). Other examples
from this class include methyl perfluorononanoate
(C.sub.10H.sub.3F.sub.17O.sub.2; molecular weight 478), methyl
perfluorodeeanoate (C.sub.11H.sub.3F.sub.19O.sub.2; molecular
weight 528), methyl perfluorododeeanoate
(C.sub.13H.sub.3F.sub.19O.sub.2; molecular weight 628), and methyl
perfluorotetradecanoate (C.sub.15H.sub.3F.sub.27O.sub.2; molecular
weight 728). Therefore, it should be readily apparent that
compounds of the general formula, C.sub.xH.sub.3F.sub.yO.sub.2,
wherein x.gtoreq.9 and y.gtoreq.15, can be utilized as index
modifying additives of the subject invention.
[0039] The preceding compounds can include methacrylate or acrylate
functionalities, which provide adequate affinity with the polymeric
matrices, as well as a perfluorinated unit, which confers a very
low refractive index to the additive. In addition to perfluorinated
compounds, as described in the preceding paragraphs, partially
fluorinated compounds are also contemplated as index modifying
additives of the subject invention.
[0040] The current practice of manufacturing GI-POF relies on the
immobilization of a low molecular weight additive in a fixed
concentration profile within the matrix polymer below its glass
transition temperature. Applications which subject the GI-POF to a
maximum operation temperature of 85.degree. C. can be very
demanding since it requires the glass transition temperature of the
polymer be>85.degree. C. at all radii of the GI-POF. The glass
transition temperature (Tg) of a polymethylmethacrylate blend
containing an increasing concentration of a typical additive is
shown in FIG. 1. The Tg was defined as the midpoint of the specific
heat change associated with the transition.
[0041] The two slopes, corresponding to 2.degree. C./% wt. of
additive and 3.5.degree. C./% wt. of additive, bracket the data of
a substantial number of additives (Ishigure, T., et. al., 1998 and
Blyler, et. al., 1997). For the purpose of describing the subject
invention, the maximum slope curve corresponding to 3.5.degree.
C./% wt. has been taken as applying to any additive. In practice,
the fiber designed according to the subject invention analyzed in
accordance with this assumption will therefore be underestimated in
its thermal stability. In alternative embodiments, larger
concentrations by weight (3%-15% by weight) of additives may be
used to achieve higher numerical aperture fiber at the expense of
some reduction in the thermal stability.
4TABLE 3 Typical Additives for Organic Polymers Suitable for the
Subject Invention Transparent Soluble Re- Additive In the Molecular
fractive Boiling Methacrylate Polymers Weight Index Point Large
Dibenzyl ether 198 1.562 298 Refractive Triphenyl phosphate 326
1.63 mp 51.degree. Index 1,2,4,5- 394 1.61 mp 180.degree.
Tetrabromobenzene Diphenyl phthalate 318 1.572 mp 75.degree. Benzyl
benzoate 212 1.568 323 Benzophenone 182 1.606 306 Biphenyl 154
1.588 256 3-Phenyltolume 168 1.60 272 2-Phenylpyridine 155 1.62 270
Diphenyl sulphide 186 1.63 296 Diphenyl sulfone 218 1.63 379
Diphenyl sulfoxide 202 1.63 207 Low Triethyl phosphate 182 1.450
215 Refractive Tributyl phosphate 266 1.424 290 Index Glycerol
triacetate 218 1.429 260 Perfluoro 2,5,8-trimethyl- 676 1.295 195
3,6,9-trioxadodecanoic acid, methyl ester (PTTME) Methyl
perfluorooctanate 428 1.305 160
[0042]
5TABLE 4 Typical Additives for Perfluorinated Polymers Suitable for
the Subject Invention Transparent Soluble Additive Molecular
Refractive Boiling in the Perfluorinated Polymers Weight Index
Point Large N-Pentafluoro 332 >1.39 148-151.degree. mp
phenyldichlomaleimide Refractive Octafluoronapthalene 272 1.367
>200.degree. Index Pentafluorophenyl sulfide 366 >1.39
87.degree. mp Low Perfluoropolyether >800 <1.30
>200.degree. C./0.05 mm Mg Refractive Perfluorotrihexylamine 971
<1.30 250-260.degree. Index Perfluoropentadecane 788 <1.30
228.degree.
[0043] It is apparent from FIG. 1 that the additive concentration
should preferably be no more than a few percent at all radii of the
GI-POF. The design process for material composition described later
will lead to selections of additive concentrations. Similar
comments can be made concerning the perfluorinated compounds,
although the glass transition temperatures of the polymers are
larger which tend to alleviate the problem.
[0044] In a specific embodiment of the subject invention, a
manufacturing method permits the production of GI-POF having high
thermal stability while also achieving adequate numerical
aperture.
[0045] The preferred method of polymerizing any of the monomers in
Table 1 is by thermal polymerization using an initiator and chain
transfer agent as is well known in the art. The polymer melts may
be prepared or blended with the chosen additives used to produce a
desired polymeric tube of two or more concentric cylinders of
polymeric material.
[0046] In a specific embodiment, after preparation and blending
with the chosen additives, the polymer melts can be transported to
an extrusion die, as shown schematically in FIG. 2a. The pressure
may be generated by a nitrogen gas pressure source, pump, extruder,
piston, or other means known in the art. Two transparent melt
polymers, one or both having a transparent and diffusible additive,
can enter the die 1 shown schematically in FIG. 2b. Material B
forms a concentric shell around material A. The materials A and B
are fed at relative rates into die 1 to achieve the desired index
profile. Material A can be the same as Material B or it can be
different. Although some diffusion can occur as the materials A and
B, with any additives they may have, flow through the die 1, such
diffusion is not relied on to finalize the index profile. Instead,
the die 1 can be designed to minimize the time materials A and B
spend in the melt condition at a temperature suitable for
extrusion, in order to minimize the optical degradation which can
occur when materials A and B are in the melt condition. Such
optical degradation can occur due to such high temperatures and due
to contact with metal surfaces at such high temperatures. Such
optical degradation can occur over periods of time, for example as
small as 10-30 seconds, which is often much less than the period of
time needed for adequate diffusion, for example as large as
100-1000 seconds. For periods of time over 60 seconds in the melt
state suitable for extrusion optical degradation is very likely to
occur. In order to provide adequate time for diffusion, the subject
invention involves applying an outer tubing and heating the GI-POF
to a temperature above its glass transition temperature but much
below the extrusion temperature. During this time the outer tubing
maintains the structural integrity of the GI-POF. In this way,
diffusion of the index-modifying additives can be accomplished
without subjecting the polymeric tube materials to the melt state
suitable for extrusion for more than about 60 seconds, preferably
not more than about 30 seconds, and more preferably not more than
about 10 seconds.
[0047] If it is desired to incorporate an outer tubing around the
polymeric tube at the exit of the die 1, an optional extruder 4 can
feed material, for example TEFLON.RTM., to the co-extrusion die to
produce an outer tubing within which the aforementioned polymeric
tube of materials A and B is contained. Preferably, the material
transported by extruder 4 has a glass transition or melt
temperature significantly above the glass transition temperatures
of materials A and B, and also above the temperature at which it is
planned to have the additives diffusing in materials A and B. In a
specific embodiment, a thermally processable polymeric material
with melt temperature above about 200.degree. C. can be used as an
outer tubing. Depending upon the extrusion rate and the choice of
outer tubing material, it may be necessary to effect substantial
external cooling to the tube as indicated in FIG. 2b.
[0048] Referring to FIG. 6, the outer tubing material can be
extruded from a die which has the well-known basic features of a
"wire-coating die." A ram extruder is normally used for
TEFLON.RTM.. Accordingly, as a ram extruder involves an inherent
batch process, there can be drawbacks to utilizing TEFLON.RTM. for
an embodiment of the subject invention pertaining to a continuous
production process. The TEFLON.RTM. fluoropolymer resins (DuPont)
have a unique combination of properties including excellent
chemical stability, anti-stick characteristics, mechanical
strength, low flammability and low water absorption. Most
importantly, they also have high melt temperatures, for example
>250.degree. C. The processing temperatures for these resins are
typically .gtoreq.300.degree. C. Thus, the die body for a
TEFLON.RTM. outer tubing can be operated at about 325.degree. C.,
which is much higher than that (typically 210.degree. C.) of the
die body for the polymeric tube material. This difference of about
115.degree. C. between the two parts of the total die shown in FIG.
3b can be addressed with good insulation between the two parts.
This insulation can be achieved by, for example, the use of an air
gap created by several stainless steel rings which separate the two
parts. Other ring materials, such as ceramic rings can also be
utilized. Other means for insulating the two parts can be utilized
as well. With this design, it is possible to independently control
the temperatures of the two die parts in the temperature range of
interest.
[0049] Although TEFLON.RTM. has some attractive properties for use
as an outer tubing, such as resistance to water penetration into
the GRIN POF, it is not an easily processed material. For this
reason, other materials may be better suited for use as an outer
tubing. In particular, cross-linked polyolefins such as
polyethylene or polypropylene may be employed. These materials have
been routinely used as jacket materials for conventional step-index
plastic optical fiber and for jackets for the wire and cable
industry. These cross-linked jackets can be produced by reactive
extrusion. There is a variety of ways in which the catalysts and
curing agents can be compounded into the polyolefin matrix. In a
specific embodiment of the subject invention, the active agents can
be injection into the melt stream after the melt stream has left
the screw in the extruder. A static mixer can disperse the
activator in the melt stream before it enters the die. The die can
then be used as the high-temperature heat source for effecting the
cross-linking of the jacket. The die may also be fitted with
electrode structures for more efficient dielectric heating of the
jacket melt stream if very high throughput is required.
[0050] It should be understood that there is a class of high
temperature polymers that have high glass transition and melt
temperatures and high decomposition temperatures, and are difficult
to ignite or feed any flame. Some of these are cross-linked as
discussed above. A polymer such as polybutyleneterephalate (PBT)
has a melt temperature of 225.degree. C. and can be extruded at
265.degree. C. This polymer has been used extensively as a jacket
for glass fiber. It exhibits excellent mechanical stability up to
at least 170.degree. C. and has high tensile strength. To increase
its flexibility, it has been found useful to copolymerize it with
small amounts of diol. Since this material is available at low
cost, it is a suitable material choice.
[0051] It is well known in the art of wire coating dies how to
provide the same velocity of extrudate at each point around the
circumference at the die exit, and thereby have a fixed outer
tubing wall thickness.
[0052] As the polymeric tube, or GRIN melt, material exits its die,
some swell of the material can occur, as indicated in FIGS. 2b and
3b. The velocity of the GRIN material after the swell, is made
similar to that of the outer tubing material. In a specific
embodiment utilizing TEFLON.RTM. as an outer tubing material, it is
desirable to rapidly cool the TEFLON.RTM. melt from the 325.degree.
C. temperature at the die exit down to the GRIN melt temperature of
about 210.degree. C. The wall thickness of the TEFLON.RTM. tube can
be made to be in the range 25 to 200 microns, so that it can be
rapidly cooled to 210.degree. C. by a steam mist immediately after
exiting the die.
[0053] In an alternative embodiment, there are some operational
advantages in decoupling the production of polymeric tube material
(e.g. GRIN fiber) from the outer tubing. For example, the outer
tubing die can be located some distance (typically 1 to 4 meters)
downstream from the polymeric tube die. This arrangement permits
the solidification of the GRIN fiber, careful measurement of its
diameter with a laser micrometer and feedback of this information
to control fiber diameter. This well-defined solid fiber can then
be passed through the tube die and provided with a thin coat of,
for example, TEFLON.RTM.. The resulting tube-encased fiber can then
be admitted to the heated enclosure whose temperature is preferably
25.degree. C. to 60.degree. C. above the glass transition
temperature of the GRIN material and at least 30.degree. C. below
the melt temperature of the TEFLON.RTM. tube. In this way, the GRIN
material's structural integrity is maintained and yet there is high
enough diffusivity of the additives to produce the desired index
profile in a reasonably short period of time. In a further
alternative embodiment, the polymeric tube can be produced and
stored with the outer tubing applied at any later time, followed by
heating for diffusion.
[0054] The diffusion of additives originally in materials A and/or
B into the adjacent melts B and A depends principally on the
diffusion constants of the additives in the chosen polymers, the
temperatures of the melts, and the time over which diffusion is
taking place.
[0055] An important dimensionless parameter which enters into the
description of the additive diffusion is: 1 tD d 2
[0056] where t (sec) is the time over which diffusion is occurring,
D(cm.sup.2/sec) is the diffusion constant of a specific additive in
a given polymer at a given temperature and d(cm) is the distance
over which diffusion has occurred. When this parameter 2 tD d 2
[0057] is of order unity then significant diffusion has
occurred.
[0058] Typical values of D for the additives of interest are in the
range 10.sup.-6 to 10.sup.-7 cm.sup.2/sec. Thus, for the required
axial distance (.apprxeq.0.1 mm) over which diffusion is required
as discussed earlier, diffusion times on the order of t.apprxeq.100
to 1,000 sec. should suffice. Additives with low diffusion
constants are optimal for use in fiber whose operational
specifications call for high thermal stability. These additives may
be used in the subject invention by using either longer dwell time
of the fiber in the heating enclosure, and/or smaller diameter
fiber for a given dwell time in the heating enclosure.
[0059] Due to the cylindrical symmetry of a cylindrical plastic
GRIN fiber, it is possible to perform a reliable and accurate
numerical simulation of the diffusion process (Tsai, et al., 1997).
Since the diffusion process depends on several parameters, it is
highly desirable to have a reliable predictive method to closely
determine the parameters necessary to achieve the desired profile,
such as a parabolic refractive index profile, at the proposed
extrusion conditions. In the other frequently encountered case of a
desired pseudo step-index profile, the required diffusion time may
be substantially reduced. The resulting index profile is a steep
but not discontinuous step profile which reduces the light
scattering at the core/clad boundary.
[0060] The material extruded from the die 1 can be cooled, drawn by
nip rollers 6 and wound up by a rotating drum 8 which is within a
heated enclosure 7. In another embodiment of the subject invention,
the material extruded from the die 1 can be wound around two
rotating elongated godet wheels in a manner well known in the art.
For a desired fiber production rate of 5,000 meters per hour,
approximately 140 meters of fiber can be wound on the drum 8 to
provide a 100-second duration of the fiber in the heated enclosure
7. This is easily accomplished with, for example, 140 turns around
a 32 cm diameter drum. Fiber take-off from the drum 8 can be taken
up on a winder 9 or stretched in a manner known in the art to
improve mechanical properties of the fiber. The fiber may be
jacketed with, for example, a fire-resistant polymeric material
which also provides additional mechanical strength. This is
achieved by the use of an additional "wire coating die" through
which the fiber is fed before being wound on to the final
spool.
[0061] In some applications, it may be desired to further enhance
thermal and mechanical long-term stability of the fiber. In this
case, some cross-linking of the fiber material may be produced by
ultra-violet or some other form of ionizing radiation. The region
of the drum, corresponding to the end of the period of the fiber in
the enclosure is particularly useful for this purpose and may be
exposed to continuous radiation to effect the cross-linking. Up to
a few percent bifunctional acrylates and methacrylates and less
than 1% photo-initiator can be added to the polymer melts at the
same time as are the additives. Examples of such compounds are
polyethylene glycol acrylate with molecular weight varying from 258
to 700 and polyethylene glycol methacrylate with molecular weight
varying from 330 to 875. Photo-initiators which may be used are
benzoin methyl ether and benzoin ethyl ether. Irradiation may be
supplied by several ultra-violet lamps located around the later
section of the drum. The lamps are designed to emit between 350 and
400 nm. The thin TEFLON.RTM. tubing can easily permit the uv-light
to reach the polymer melts and trigger the cross-linking
polymerization of the bifunctional monomer.
[0062] FIG. 3b is a schematic of a die for the case of using three
melt blended materials. The method of operation of the die is the
same as that in FIG. 2b except for the addition of material C which
forms a concentric shell around material B as indicated in FIG. 3b.
The subject invention also pertains to four or more melts. In
addition, although FIGS. 2b and 3b show two die structures, other
die structures can be utilized in accordance with the subject
invention to produce multiple concentric cylinders of polymeric
materials.
[0063] The fiber produced may have its refractive index increase or
decrease as a function of radius, or in a particular case, may
exhibit a local minimum at a radius intermediate between the axis
and the outer radius. In the latter case, the refractive indices of
the respective melts must be in the relationship
n.sub.A>n.sub.C>n.sub.B. In the same way, a variety of
refractive index profiles may be formed.
[0064] In a specific implementation of the present invention, there
are several important considerations in the choice of materials for
manufacturing thermally stable, large numerical aperture GI-POF.
These considerations are listed for the case of a three melt
polymer system, but they can easily be extended to the cases of two
or greater than three polymer systems:
[0065] 1. The desired numerical aperture defines the difference in
refractive index on the axis and the outside radius of the
GI-POF.
[0066] 2. The refractive index range should be considered for
design purposes to be divided into four approximately equal ranges
as shown in FIG. 4.
[0067] 3. Three polymers or copolymers should be prepared with
refractive indices, n.sub.A, n.sub.B, and n.sub.C, as indicated on
the left side of FIG. 4.
[0068] 4. Two low molecular weight additives whose refractive
indices are desired to be>>n.sub.A and <<n.sub.C are
blended with their respective polymer matrices. The minimal amounts
of additive are used to achieve the desired refractive indices,
n.sub.axis and n.sub.outer. These additives and blends are
indicated schematically in Columns 2 and 3 of FIG. 4.
[0069] 5. The three melt blends, A, B, and C, are formed as
concentric cylinders around each other by the die in FIG. 3b. In
the heated enclosure, the additives partially diffuse from the
inner and outer blends into the central melt to produce a
refractive index profile as indicated by the dashed line in FIG. 4
in the final product.
[0070] 6. By varying the flow rates of materials A, B, and C,
considerable control can be exercised on the final index profile
during the extrusion process.
[0071] The simplicity of the concentric symmetry of the melt blends
in the tube permits accurate, efficient predictions to be made for
the final GI-POF profile. This is important due to the large number
of parameters which affect the operation and the desire to quickly
achieve production status of the manufacturing process.
[0072] In a specific implementation of the invention, the outermost
cylinder of melt can be made to contain no additive. Its refractive
index can be either higher or lower than that of the adjacent melt
cylinder. These two arrangements are shown schematically in FIGS.
5a and 5b for a four-melt system. The purpose of the additional
melt cylinder is to permit diffusion of additive from the adjacent
cylinder, thereby minimizing the radial extent over which the GRIN
profile deviates from a parabolic profile. The two final profiles
of the above two arrangements are shown schematically in FIGS. 5a
and 5b. In the former of the two alternatives, the refractive index
has a minimum value at a given radius and any light extending
beyond that radius is defocused and lost as desired.
[0073] In another embodiment of the subject invention, the third
and fourth, or just the fourth, melt cylinders can be made opaque
and with refractive indices as shown in FIGS. 5a and 5b. In this
case, the light will not be transmitted in the radial region which
exhibits substantial inversion of the second derivative of the
refractive index profile. In this way, the refractive index profile
may be made very close to parabolic out to the maximum radius that
light is transmitted.
[0074] In the latter of the two arrangements, the radial region is
reduced over which a deviation from a parabola occurs as desired.
In summary, in both arrangements, use of an additional melt
cylinder ensures that the light is transported by a GRIN profile
which is closer to a parabolic shape.
[0075] Due to very high modal mixing in plastic optical fiber
(Koike, Y., 1998), there is not a tight constraint on the GRIN
profile to achieve high bandwidth (Shi, R. F., et al., 1997).
Nevertheless, the above implementation of an additional melt
cylinder is helpful to achieve the highest possible bandwidth and
lowest possible bit error rate for this type of fiber. In a
specific implementation, the TEFLON.RTM. tube used primarily for
providing structural integrity during the diffusion process may be
employed for the above purpose. Even though the TEFLON.RTM. tube is
below its melt temperature in the heating enclosure, there is some
diffusion of additive into it from the GRIN material.
[0076] In another embodiment of the subject invention, POF can be
manufactured as cable with a protective polymeric jacket
surrounding the light-transmitting fiber. A typical GRIN POF cable
structure is shown in FIG. 6a. A GRIN POF with surrounding outer
tubing has been jacketed by being passed through a "wire coating"
die and having a surrounding polymeric material extruded to form a
jacket.
[0077] In a specific embodiment, jacketing may be performed after
the GRIN POF having an outer tubing exits from the heated enclosure
7 before being finally wound on a winder 9 as shown in FIG. 3a.
[0078] In a different embodiment of the subject invention, the
outer tubing extruder 4 in FIG. 3a can instead produce a jacket,
rather than a thin-walled outer tubing, with say a 2.2 mm diameter
as shown in FIG. 6b.
[0079] The jacketed GRIN POF may be passed through the heated
enclosure before being wound by the winder, 9, in FIG. 3a.
[0080] In a further embodiment of the subject invention, duplex
(two parallel, slightly separated optical fibers) GRIN POF may be
produced with a jacket as shown in FIG. 7a. In this case, two GRIN
POF may be produced and have an outer tubing applied and passed
through the heating enclosure as described earlier. The two GRIN
POF may then be drawn through a cross-wire die to be jacketed.
[0081] Alternatively, the dies shown in FIG. 2b or 3b may be
modified by methods well known in the art of multifiber extrusion
to simultaneously extrude two separate streams of polymeric tube
material, each of which is composed of concentric cylinders of
melt. The outer tubing die may be used to extrude a jacket for the
duplex GRIN POF as discussed earlier for the single, or simplex,
GRIN POF. A cross-section of the duplex fiber produced in this way
is shown in FIG. 7b.
[0082] In another embodiment of the invention, a number, n, where
n>2, GRIN POF fibers may be extruded simultaneously to form a
variety of arrangements of fibers. The arrangements of fibers may
be jacketed by the methods described above. Such arrangements may
be useful in the very large bandwidth transmission of data through
the multiplicity of fibers.
[0083] GRIN POF may be produced with different diameters in the
range 0.1 mm up to about 5.0 mm. Such fiber may be termed rod
rather than fiber. When cut into particular lengths and the ends
polished, this type of rod may be used as a lens as is well known
in the art.
[0084] Samples of fiber were evaluated as follows. Each end of a
sample was cut by a diamond tool rotating at high speed to produce
an optically flat surface at right angles to the fiber axis. The
surface was polished using increasingly fine grit down to 0.2
micron powder. The refractive index profile was measured by
observing the light reflection intensity as a function of radius
from the end of the fiber by the method well known in the art.
EXAMPLE 1
[0085] It is a preferred embodiment of the present invention to
manufacture GI-POF which is stable in the temperature range
-40.degree. to +85.degree. C., has an optical attenuation
.ltoreq.150 dB/km, a parabolic refractive index profile, and a
numerical aperture of .about.0.15.
[0086] The considerations described earlier on the choice of
materials are followed in detail. Polymethylmethacrylate is chosen
as the polymer with the median refractive index, i.e.,
(n.sub.axis+n.sub.outer)/2=1492. The desired numerical aperture of
.about.0.15 may be written as
0.15=1/{square root over (2)}{square root over
((n.sup.2.sub.axis-n.sup.2.- sub.outer))}
[0087] which yields n.sub.axis=1500 and n.sub.outer=1.484.
[0088] The refractive indices of the three polymer matrices are
then selected as 1.496, 1.492, and 1.488. These index values are
shown in the third column of Table 5 and the choices of monomers to
achieve these indices are shown in column 1. The resulting glass
transition temperatures of the polymers are given in column 2.
[0089] Additives are chosen with indices of 1.63 and 1.305 so as to
minimize the amount of additive needed (.ltoreq.3% by weight) to
achieve the required refractive indexes of the blends which are
shown in the last column. The effect of the additives on the glass
transition temperature of the polymer matrices is to depress their
Tg's by less than about 10.degree. C. as indicated in FIG. 1.
6TABLE 5 The Polymeric and Additive Materials are shown for a
Three-Component Melt System for Producing a GI-POF With Numerical
Aperture Equal to 0.15 and Glass Transition Temperature Greater
Than 85.degree. C. Polymer Matrix Material Blend Polymer Additive
Containing Glass Effect on (co)polymer Transition Required Tg
(.degree. C.) Plus Additive Monomer Temp. Refractive Refractive % w
of from Tg Refractive Material (.degree. C.) Index Material Index
Additive Additive (.degree. C.) Index 95% w 101.5 1.496 Diphenyl
1.63 3.0% -10.5 91 1.50 MMA + 5% w Sulphide PMA MMA 101 1.492 101
1.492 95.5% w 100.1 1.488 Methyl 1.305 2.0% -7.1 93 1.484 MMA +
4.5% w perfluorooctanate 3FMA
[0090] The three materials have glass transition temperatures of
91.degree. C., 101.degree. C., and 93.degree. C. The fact that the
Tg of all parts of the GI-POF is greater than 90.degree. C. is a
preferable condition for high thermal stability of the fiber. A
second condition for achieving thermal stability of the profile is
that the additives be chosen for their chemical affinity for their
polymeric matrices. In the case of diphenyl sulphide, the
electronic structure of the sulphur atom provides a weak bond to an
oxygen atom in the ester unit of the polymers. This bond tends to
immobilize the additive at temperatures below the material glass
transition temperature. In the case of the methyl
perfluorooctanate, there is a direct attraction between the ester
units which are present in the additive and the polymer. Once more,
this weak bond provides a degree of immobilization of that additive
at temperatures below the material glass transition
temperature.
[0091] The three monomer systems were placed in three tubes with
the addition of 0.3% by weight of benzoil peroxide (BPO) acting as
initiator, 0.05% by weight of normal butyl mercaptan (nBM) acting
as a chain transfer agent. The diphenyl sulphide additive at 3.0% w
was dissolved in the high refractive index monomer mix and the
additive methyl perfluorooctanate at 2.0% w was added to the low
refractive index monomer mix. The solutions were heated to
55.degree. C. for 15 hours, 75.degree. C. for 5 hours, 100.degree.
C. for 10 hours, and 150.degree. C. for 24 hours. At that time, 99%
conversion to polymer was measured. A piston on top of each melt
exerted 21 kg/cm.sup.2 pressure to force the melts into the die
depicted in FIG. 3b. The diameter of the hole was 2 mm from which
the GRIN material exited to enter the TEFLON.RTM. outer tubing.
[0092] The temperature of all three melts was 210.degree. C. as
they entered the die depicted in FIG. 3b. GRIN fiber was extruded
with an outer tube diameter of 0.75 mm from the die hole of 2.0 mm
diameter. Fiber was extruded at 100 m/minute and was retained in
the heating enclosure at 150.degree. C. for 250 seconds.
[0093] Fiber samples were prepared and measurements performed as
described earlier. The measured refractive index parabolic profile
was found to be well represented by the profile depicted in FIG.
4.
EXAMPLE 2
[0094] In the same manner as Example 1, three monomer systems were
prepared using the same initiator and chain transfer agent. The
three monomer systems were different mixtures by weight of MMA and
TFA. In this way, the polymeric matrix was partially fluorinated at
all radii throughout the fiber. Reduced water absorption in the
fiber which enhances the long-term stability of the fiber.
Additives of diphenyl sulphide and methyl perfluorooctanate are
mixed with two of the monomer solutions as shown in Table 6. In
this case, the glass transition temperatures of all three polymer
systems are greater than 95.degree. C. The range of refractive
indices is made somewhat greater than that in Example 1.
[0095] Polymerization and extrusion of the melts were carried out
in a manner identical to Example 1. GRIN fiber of 0.5 mm diameter
was produced at 100 m/minute and maintained in the heating
enclosure at 150.degree. C. for 150 seconds. After exiting from the
enclosure, the TEFLON.RTM.-coated GRIN fiber passed through a "wire
coating die" and was jacketed with a layer of polyethylene. As a
result, the refractive index of the fiber was measured to have a
similar shape as before. The numerical aperture of the fiber was
measured to be 0.17.
7TABLE 6 The Polymeric and Additive Materials are shown for a
Three-Component Melt System for Producing a GI-POF with Numerical
Aperture Equal to 0.17 and Glass Transition Temperature Greater
Than 95.degree. C. Polymer Matrix Material Blend Polymer Additive
Containing Glass Effect on (co)polymer Transition Required Tg
(.degree. C.) Plus Additive Monomer Temp. Refractive Refractive % w
of from Tg Refractive Material (.degree. C.) Index Material Index
Additive Additive (.degree. C.) Index 89% w 105.1 1.481 Diphenyl
1.63 3.0% -10 95.1 1.485 MMA + 11% w Sulphide TFA 84% 106.9 1.476
106.9 1.476 MMA + 16% TFA 79% w 108.8 1.471 Methyl 1.305 3.0% -10
98.8 1.466 MMA + 21% w perfluorooctanate TFA
EXAMPLE 3
[0096] In this embodiment, only two rather than three different
material systems were used.
[0097] Extrusion was carried out using the die shown in FIG. 2b.
The material system used in this example is shown in Table 7. The
additives used are diphenyl sulphide and methyl perfluorooctanate
with concentrations given in Table 7. The monomers and additives
are mixed, polymerized, and extruded as described in Example 1. All
other parameters in extrusion and heating enclosure were similar to
those in Example 1.
[0098] The maximum difference in refractive index of the blend
materials is 0.018 which provides a numerical aperture of about
0.16. The general shape of the refractive index distribution was as
before in Example 1.
8TABLE 7 The Polymeric and Additive Materials Are Shown for A
Two-Component Melt System for Producing a GI-POF with Numerical
Aperture Equal to About 0.16 and Glass Transition Temperature
Greater than 90.degree. C. Polymer Matrix Material Blend Polymer
Additive Containing Glass Effect on (co)polymer Transition Required
Tg (.degree. C.) Plus Additive Monomer Temp. Refractive Refractive
% w of from Tg Refractive Material (.degree. C.) Index Material
Index Additive Additive (.degree. C.) Index 90% w 101.9 1.500
Diphenyl 1.63 3.0% -10 91.9 1.504 MMA + 10% w Sulphide PMA 100% MMA
101 1.492 MPF 1.305 3.0% -10 91.0 1.486
EXAMPLE 4
[0099] It is an object of this example to produce a 1 mm diameter
step index polymer optical fiber with improved transmission and
high temperature stability. This is achieved by reducing the loss
of light from scattering at the discontinuity at the core cladding
interface. It is desirable to have the distance, over which the
index changes, be much greater than the wavelength of the light,
say 20 .mu.m of radial distance.
[0100] 95% w methylmethacrylate and 5% w ethylmethacrylate mixture
is used as the core material and 100%/w trifluoroethylmethacrylate
is used as the cladding material. To preserve high temperature
performance of the fiber, it is preferable to use low molecular
weight additive in the thin cladding material. The chosen additive
is 3% w of methyl perfluorooctanate which has a molecular weight of
428.
[0101] The monomers and additive were polymerized as in Example 1
and extruded through the die system shown in FIG. 2b. The diffusion
of the additive into the core material was small at the high
extrusion speed of 100 meters per minute and a residence time of
the fiber in the heated enclosure of only 10 seconds. The
refractive index profile of the fiber was uniform in radius out to
0.460 mm where it started to fall rapidly to about 1.416 over a
distance of 20 .mu.m. At a radius from 0.480 mm to 0.500 mm, the
cladding polymer trifluorethylmethacrylate determined the
refractive index.
EXAMPLE 5
[0102] It is an object of this example to provide a manufacturing
method of perfluorinated GRIN fiber using CYTOP.RTM. polymer. The
material compositions for the dual component system is shown in
Table 8. The glass transition temperature of the fiber is
95.degree. C. and the numerical aperture is 0.10. TEFLON.RTM.
material may again be used to form a tube as in Example 1. The
diameter of the as-spun perfluorinated GRIN material was 0.25 mm
and the necessary residence time in the 150.degree. C. heated
enclosure was about 100 seconds.
[0103] The primary advantage of the use of perfluorinated material
lies in the low light absorption in the range 850 nm to 1500
nm.
9TABLE 8 The Polymeric and Additive Materials Are Shown for a
Two-Component Melt System for Producing A Perfluorinated GI-POF
with Numerical Aperture Equal to 0.10 and Glass Transition
Temperature of 95.degree. C. Polymer Matrix Material Blend Polymer
Additive Containing Glass Effect on (co)polymer Transition Required
Tg (.degree. C.) Plus Additive Monomer Temp. Refractive Refractive
% w of from Tg Refractive Material (.degree. C.) Index Material
Index Additive Additive (.degree. C.) Index CYTOP 108 1.340
Pentafluorophenyl 1.395 4.0% -13 95.0 1.3422 sulfide CYTOP 108
1.340 Perfluoropolyether 1.295 4.0% -13 95.0 1.3382
EXAMPLE 6
[0104] It is an object of this example to provide a method of
manufacturing a perfluorinated GRIN fiber using DuPont AF.RTM.
amorphous polymer. An example of a material composition for a dual
component system is shown in Table 9. Since the glass transition
temperature of AF material is so high (.gtoreq.140.degree. C.) and
processing temperatures are correspondingly very high
(.gtoreq.280.degree. C.), it is highly advantageous to use a
substantial amount of additive to significantly lower these
temperatures. In this way, a heated enclosure temperature
(190.degree. C.) can be chosen which is well above the glass
transition temperature of the GRIN material (120.degree. C.) and
yet well below the melt temperature of the TEFLON.RTM. tube
(>250.degree.). The diameter of the as-spun fiber is chosen to
be 0.25 mm and the necessary residence time in the 190.degree. C.
heated enclosure is about 100 seconds as in Example 6. As in the
previous example, the primary interest in this type of fiber is its
high light transmission in the wavelength range 850 nm to 1500
nm.
10TABLE 9 Material Compositions for a Two-Component Material System
Employing DuPont AF .RTM. Polymer for a Perfluorinated GRIN Fiber
with Numerical Aperture of 0.18 Polymer Matrix Material Blend
Polymer Additive Containing Glass Effect on (co)polymer Transition
Required Tg (.degree. C.) Plus Additive Monomer Temp. Refractive
Refractive % w of from Tg Refractive Material (.degree. C.) Index
Material Index Additive Additive (.degree. C.) Index AF 160 1.310
Pentafluorophenyl 1.3954 12% -40 120 1.3202 (160) sulfide AF 160
1.310 Perfluoropolyether 1.295 12% -40 120 1.3082 (160)
[0105] It is to be understood that while the invention has been
described in conjunction with the detailed description thereof,
that the foregoing description is intended to illustrate and not
limit the scope of the invention, which is defined by the scope of
the appended claims.
[0106] All patents, patent applications, provisional applications,
and publications referred to or cited herein are incorporated by
reference in their entirety to the extent they are not inconsistent
with the explicit teachings of this specification.
[0107] It should be understood that the examples and embodiments
described herein are for illustrative purposes only and that
various modifications or changes in light thereof will be suggested
to persons skilled in the art and are to be included within the
spirit and purview of this application and the scope of the
appended claims.
* * * * *