U.S. patent application number 09/726553 was filed with the patent office on 2001-04-05 for graded index type optical fibers and method of making the same.
This patent application is currently assigned to Mitsubishi Rayon Co., Ltd.. Invention is credited to Nakamura, Kazuki, Tahara, Yasuteru, Yamashita, Tomoyoshi.
Application Number | 20010000140 09/726553 |
Document ID | / |
Family ID | 13542240 |
Filed Date | 2001-04-05 |
United States Patent
Application |
20010000140 |
Kind Code |
A1 |
Yamashita, Tomoyoshi ; et
al. |
April 5, 2001 |
Graded index type optical fibers and method of making the same
Abstract
A graded index type optical fiber having a multilayer structure
comprising a plurality of concentrically arranged layers formed of
(co)polymers selected from the group consisting of two or more
homopolymers HP1, HP2, . . . , HPn derived from monomers M1, M2, .
. . , Mn, respectively, and having refractive indices decreasing in
that order, and one or more binary copolymers CP derived from these
monomers, the multilayer structure being such that a mixed layer
consisting of the (co)polymers constituting two adjacent layers is
formed therebetween, and the refractive index is highest at the
center and decreases gradually toward the outer periphery. This
optical fiber can be continuously formed by feeding the
(co)polymers to a multilayer concentric circular nozzle and thereby
extruding them through the nozzle, and allowing the polymers to
interdiffuse between adjacent layers of the fiber.
Inventors: |
Yamashita, Tomoyoshi;
(Hiroshima, JP) ; Tahara, Yasuteru; (Hiroshima,
JP) ; Nakamura, Kazuki; (Hiroshima, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Mitsubishi Rayon Co., Ltd.
6-41, Konan 1-Chome, Minato-ku
Tokyo
JP
108-8506
|
Family ID: |
13542240 |
Appl. No.: |
09/726553 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09726553 |
Dec 1, 2000 |
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09142161 |
Sep 28, 1998 |
|
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09142161 |
Sep 28, 1998 |
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PCT/JP97/01093 |
Mar 28, 1997 |
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Current U.S.
Class: |
385/124 ;
264/1.29; 385/143 |
Current CPC
Class: |
G02B 6/02038 20130101;
B29D 11/00682 20130101; G02B 6/03633 20130101 |
Class at
Publication: |
385/124 ;
385/143; 264/1.29 |
International
Class: |
G02B 006/18; G02B
006/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 1996 |
JP |
074269/1996 |
Claims
CLAIMS
1. A graded index type optical fiber having a multilayer structure
comprising a plurality of concentrically arranged layers each of
said layers is formed of one (co)polymer selected from the group
consisting of two or more homopolymers HP1, HP2, . . . , HPn (in
which n is an integer of 2 or greater) derived from monomers M1,
M2, Mn, respectively, and having refractive indices decreasing in
that order, and one or more binary copolymers CP derived from said
monomers, said multilayer structure being such that a mixed layer
consisting of mixture of two (co)polymers constituting two adjacent
layers is formed therebetween, and the refractive index is highest
at the center and decreases gradually toward the outer
periphery.
2. An optical fiber as claimed in claim 1 wherein said optical
fiber has a multilayer structure comprising a plurality of
concentrically arranged layers each of said layers is formed of one
(co)polymer selected from the group consisting of one or more
binary copolymers CP1/2 having different copolymerization ratios
and refractive indices, one or more binary copolymers CP2/3 having
different copolymerization ratios and refractive indices, and
homopolymers HP1, HP2 and HP3, said binary copolymers and
homopolymers being derived from three monomers M1, M2 and M3 each
giving a homopolymer with a glass transition temperature of
70.degree. C. or above.
3. An optical fiber as claimed in claim 1 wherein said optical
fiber has a multilayer structure comprising three or more
concentrically arranged layers formed of (co)polymers which are
derived from two monomers each giving a homopolymer with a glass
transition temperature of 70.degree. C. or above, and which have
different copolymerization ratios and refractive indices.
4. An optical fiber as claimed in claim 1 wherein said optical
fiber has a multilayer structure comprising a plurality of
concentrically arranged layers formed of (cc)) polymers selected
from the group consisting of one or more binary copolymers CP1/2
having different copolymerization ratios and refractive indices,
one or more binary copolymers CP2/3 having different
copolymerization ratios and refractive indices, and homopolymers
HP1, HP2 and HP3, said binary copolymers and homopolymers being
derived from three monomers giving homopolymers in which the
difference in refractive index between any two homopolymers is 0.03
or less.
5. An optical fiber as claimed in claim 1 wherein said optical
fiber has a multilayer structure comprising three or more
concentrically arranged layers formed of (co)polymers which are
derived from two monomers giving homopolymers with a difference in
refractive index of 0.03 or less, and which have different
copolymerization ratios and refractive indices.
6. An optical fiber as claimed in claim 1 wherein the difference in
refractive index between the (co)polymers constituting any adjacent
layers is 0.016 or less.
7. An optical fiber as claimed in claim 1 which is formed of
(co)polymers derived from three fluoroalkyl (meth) acrylates.
8. An optical fiber as claimed in claim 1 which is formed of
(co)polymers derived from two fluoroalkyl (meth)acrylates.
9. An optical fiber as claimed in claim 1 which is formed of
(co)polymers derived from a combination of methyl methacrylate and
a monomer selected from chloroethyl methacrylate and 2-phenylethyl
methacrylate.
10. An optical fiber as claimed in claim 1 which is formed of
(co)polymers derived from a combination of monomers selected from
chlorohexyl methacrylate, tetrahydrofurfuryl methacrylate, glycidyl
methacrylate, isobutyl methacrylate and methyl methacrylate.
11. A graded index type optical fiber having a multilayer structure
comprising a plurality of concentrically arranged layers each of
said layers is formed of one (co)polymer selected from the group
consisting of three or more homopolymers HP1, HP2, . . . , HPn (in
which n is an integer of 3 or greater) derived from monomers M1,
M2, . . . , Mn, respectively, and having refractive indices
decreasing in that order, one or more binary copolymers CP derived
from said monomers, and one or more terpolymers TP derived from
said monomers, said multilayer structure being such that a mixed
layer consisting of mixture of two (co)polymers constituting two
adjacent layers is formed therebetween, and the refractive index is
highest at the center and decreases gradually toward the outer
periphery.
12. An optical fiber as claimed in any of claims 1 to 11 wherein
the difference in copolymerization ratio between the (co)polymers
constituting any adjacent layers is not greater than 20 mole %.
13. A method of making a graded index type optical fiber which
comprises the steps of preparing a plurality, of spinning materials
having different refractive indices, each of said spinning
materials being made of one (co)polymer, by using (co)polymers
selected from the group consisting of two or more homopolymers HP1,
HP2, . . . , HPn (in which n is an integer of 2 or greater) derived
from monomers M1, M2, Mn, respectively, and having refractive
indices decreasing in that order, and one or more binary copolymers
CP derived from said monomers; feeding said spinning materials to a
multilayer concentric circular nozzle so that the refractive index
decreases toward the outer periphery, and thereby extruding them
through said nozzle; and allowing the polymers to interdiffuse
between adjacent layers of the fiber, within said nozzle and/or
after being extruded from said nozzle.
14. A method of making a graded index type optical fiber which
comprises the steps of preparing a plurality of spinning materials
having different refractive indices, each of said spinning
materials being made of one (co)polymer, said each spinning
materials containing a (co)polymer selected from the group
consisting of two or more homopolymers HP1, HP2, . . . , HPn (in
which n is an integer of 2 or greater) derived from monomers M1,
M2, . . . , Mn, respectively, and having refractive indices
decreasing in that order, and one or more binary copolymers CP
derived from said monomers, and further containing monomer mixtures
having the same composition as each said (co)polymer, and a
photopolymerization initiator; feeding said spinning materials to a
multilayer concentric circular nozzle so that the refractive index
decreases toward the outer periphery, and thereby extruding them
through said nozzle; allowing said monomers to interdiffuse between
adjacent layers of the fiber; and photopolymerizing said
monomers.
15. A method of making an optical fiber as claimed in claim 13 or
14 wherein five or more (co)polymers having different refractive
indices are used.
16. A method of making an optical fiber as claimed in claim 13 or
14 wherein three or more (co)polymers having different
copolymerization ratios and refractive indices are used, said
(co)polymers being derived from two monomers giving homopolymers
HP1 and HP2 in which the difference in refractive index is not
greater than 0.03.
17. A method of making an optical fiber as claimed in claim 13 or
14 wherein the (co)polymers are derived from two or more monomers
giving homopolymers in which the difference in refractive index
between two homopolymers having the refractive indices closest to
each other is not greater than 0.02.
18. A method of making an optical fiber as claimed in claim 13 or
14 wherein the difference in refractive index between two
(co)polymers fed to adjacent nozzle orifices of said multilayer
concentric circular nozzle is not greater than 0.016.
19. A method of making an optical fiber as claimed in claim 13 or
14 wherein the difference in copolymerization ratio between two
(co)polymers fed to adjacent nozzle; orifices of said multilayer
concentric circular nozzle is not greater than 20 mole %.
20. A method of making a graded index type optical fiber which
comprises the steps of preparing a plurality of spinning materials
having different refractive indices, each of said spinning
materials being made of one (co)polymer, by using (co)polymers
selected from the group consisting of three or more homopolymers
HP1, HP2, . . . , HPn (in which n is an integer of 3 or greater)
derived from monomers M1, M2, . . . , Mn, respectively, and having
refractive indices decreasing in that order, one or more binary
copolymers CP derived from said monomers, and one or more
terpolymers TP derived from said monomers; feeding said spinning
materials to a multilayer concentric circular nozzle so that the
refractive index decreases toward the outer periphery, and thereby
extruding them through said nozzle; and allowing the polymers to
interdiffuse between adjacent layers of the fiber, within said
nozzle and/or after being extruded from said nozzle.
Description
TECHNICAL FIELD
1. This invention relates to graded index type plastic optical
fibers which can be used as optical communication media.
BACKGROUND ART
2. Graded index type plastic optical fibers (hereinafter referred
to as "GI type POFs") having a radial refractive index distribution
in which the refractive index decreases gradually from the center
toward the outer periphery of the optical fiber have a wider
frequency bandwidth than step index type optical fibers, and are
hence expected to be useful as optical communication media.
3. In the case of GI type POFs, one having a large numerical
aperture (NA) and as small a transmission loss as possible needs to
be manufactured for the purpose of improving its bending loss and
its coupling loss with the light source. In order to increase NA,
GI type POFs must be designed so that the maximum difference in
refractive index (.DELTA.n) between the center and the outer
periphery of the optical fiber is sufficiently large.
4. Various methods of making such GI type POFs are known. They
include, for example, (1) a method which comprises providing two
monomers having different reactivity ratios and giving homopolymers
with different refractive indices, placing these monomers in a
cylindrical vessel made of a polymer of these monomers so as to
cause the polymer to be dissolved and swollen, polymerizing the
monomers, and then drawing the resulting product (Japanese Patent
Laid-Open No. 130904/'86); (2) a method which comprises preparing a
plurality of polymer mixtures from two polymers having different
refractive indices at various mixing ratios, spinning these polymer
mixtures to form a multilayer fiber, and then heat-treating this
fiber to effect interdiffusion between adjacent layers (Japanese
Patent Laid-Open No. 265208/'89); and (3) a method which comprises
winding films formed of a plurality of binary copolymers having
different copolymerization ratios on a core material, and drawing
the resulting laminate under heated conditions (Japanese Patent
Publication No. 15684/'80).
5. The GI type POFs made by the above-described methods (1) or (2)
have the disadvantage that, since all layers are formed of polymer
mixtures, these plastic optical fibers (hereinafter referred to as
"POFs") tend to produce a heterogeneous structure due to
microscopic phase separation and hence show a large light
scattering loss. On the other hand, the GI type POFs made by the
method (3) and consisting of styrene-methyl methacrylate copolymers
or the like have a large light scattering loss, because the
difference in refractive index between the copolymers constituting
adjacent layers of the multilayer fiber is too large (e.g.,
0.02).
6. As the methods of making, the above-described method (1) is
disadvantageous in that it requires a polymerization step and hence
has low productivity. The method (3) is disadvantageous in that
foreign matter tends to be introduced when a plurality of films are
wound on a core material and in that it is difficult to obtain a
concentric circular fiber because thickness discontinuities tend to
occur at the joints between film ends.
7. On the other hand, the method (2) is excellent in that a GI type
POF showing few thickness fluctuation can be continuously formed.
However, it is difficult to create a gradual refractive index
distribution in the POF, because sufficient polymer-to-polymer
interdiffusion between adjacent layers cannot be achieved by the
post-spinning heat treatment alone. Even if the heat-treating
temperature is raised to increase the thickness of the
interdiffusion layers and thereby to create a gradual refractive
index distribution profile, the fiber drawn during spinning tends
to undergo relaxation shrinkage and show variations in fiber
diameter. Consequently, light leakage and scattering occur in the
parts showing variation in diameter, resulting in an increased
transmission loss.
DISCLOSURE OF THE INVENTION
8. An object of the present invention is to provide a technique by
which GI type POFs showing few thickness fluctuation and having a
small light scattering loss and a relatively large numerical
aperture can be made at a high production rate.
9. According to the present invention, there is provided a graded
index type optical fiber having a multilayer structure comprising a
plurality of concentrically arranged layers each of said layers is
formed of one (co)polymer selected from the group consisting of two
or more homopolymers HP1, HP2, . . . , HPn (in which n is an
integer of 2 or greater) derived from monomers M1, M2, . . . , Mn,
respectively, and having refractive indices decreasing in that
order, and one or more binary copolymers CPs derived from the
monomers, the multilayer structure being such that a mixed layer
consisting of mixture of two (co)polymers constituting two adjacent
layers is formed therebetween, and the refractive index is highest
at the center and decreases gradually toward the outer
periphery.
10. According to the present invention, there is also provided a
method of making a graded index type optical fiber which comprises
the steps of preparing a plurality of spinning materials having
different refractive indices, each of said spinning materials being
made of one (co)polymers by using (co)polymers selected from the
group consisting of two or more homopolymers HP1, HP2, . . . , HPn
(in which n is an integer of 2 or greater) derived from monomers
M1, M2, Mn, respectively, and having refractive indices decreasing
in that order, and one or more binary copolymers CPs derived from
the monomers; feeding the spinning materials to a multilayer
concentric circular nozzle so that the refractive index decreases
toward the outer periphery, and thereby extruding them through the
nozzle; and allowing the polymers to interdiffuse between adjacent
layers of the fiber, within the nozzle and/or after being extruded
from the nozzle.
11. In the aforesaid POF and its method of making, terpolymers TPs
derived from three monomers including the two monomers constituting
the aforesaid binary copolymers CPs may further be used in addition
to the binary copolymers CPs. Alternatively, such terpolymers TPs
may be used in place of the binary copolymers CPs.
BRIEF DESCRIPTION OF THE DRAWINGS
12. FIG. 1 includes schematic views illustrating a graded index
type optical fiber in accordance with the present invention. In
FIG. 1, (a) is a cross-sectional view, (b) is a longitudinal
sectional view, and (c) is a diagram showing the distribution of
refractive indices in the radial direction.
BEST MODE FOR CARRYING OUT THE INVENTION
13. In the present invention, HP represents a homopolymer, CP
represents a binary copolymer, BP represents a mixture of two
(co)polymers, L.sub.NB represents a non-mixed layer formed of a
single (co)polymer, and L.sub.B represents a mixed layer formed of
a mixture of two (co)polymers.
14. First of all, in order to facilitate the understanding of the
present invention, a description is given of the embodiment in
which the number (n) of monomers is 3. Where the number (n) of
monomers is 3, three homopolymers HP1, HP2 and HP3 are prepared
from monomers M1, M2 and M3, respectively. Moreover, two series of
binary copolymers CP1/2 and CP2/3 are prepared from combinations of
monomers giving homopolymers having refractive indices close to
each other. It is preferable to select these HPs and CPs so that
each CP or HP has good compatibility with other CPs.
15. In the present invention, the polymers having higher refractive
indices are homopolymer HP1 derived from monomer M1, and binary
copolymer CP1/2 derived from monomers M1 and M2. With respect to
CP1/2, a plurality of copolymers composed of the two monomers at
different molar ratios and having different refractive indices may
be prepared. Similarly, the polymers having lower refractive
indices are homopolymer HP3 derived from monomer M3, and binary
copolymer CP2/3 derived from monomers M2 and M3. Also with respect
to CP2/3, a plurality of copolymers composed of the two monomers at
different molar ratios and having different refractive indices may
be prepared.
16. As illustrated in FIG. 1, the multilayer POFs of the present
invention has a structure in which non-mixed layers (L.sub.NB)
having a thickness T.sub.NB and mixed layers (L.sub.B) having a
thickness T.sub.B are alternately arranged. In this structure, each
non-mixed layer (L.sub.NB) is a layer formed of a single
(co)polymer, and each mixed layer (L.sub.B) is a layer formed of a
mixture (BP) of the two (co)polymers constituting the non-mixed
layers disposed on both sides thereof.
17. If the number of non-mixed layers (L.sub.NB) is increased, a
structure having essentially no mixed layer (L.sub.B) may be
employed. However, when the number of non-mixed layers (L.sub.NB)
is small, it is necessary to form one or more mixed layers
(L.sub.B) and, moreover, increase their thicknesses T.sub.B to some
degree so that an abrupt change in refractive index may be
avoided.
18. FIG. 1 illustrates a POF having a five-layer structure
comprising three non-mixed layers (L.sub.NB) and two mixed layers
(L.sub.B). As can be seen from FIG. 1(c), the refractive index
remains constant in each non-mixed layer (L.sub.NB), while it
changes continuously in each mixed layer (L.sub.B). As the number
of layers is increased, the refractive index distribution profile
in the whole POF becomes more gradual. A gradual refractive index
distribution curve is preferable for the purpose of increasing the
light transmission bandwidth. However, if the proportion of the
mixed layers (L.sub.B) in the POF is too large, its light
transmission loss will be increased. Accordingly, the profile of
the refractive index distribution is chosen with consideration for
the balance between the magnitude of the light transmission
bandwidth and the magnitude of the light transmission loss.
19. Moreover, a protective layer or a jacket material layer may be
disposed on the outer periphery of the GI type POF, though they are
not shown in FIG. 1.
20. First of all, BPs constituting the mixed layers (L.sub.B) are
explained. Generally, BPs tend to induce fluctuations in refractive
index and a phase separation (which may hereinafter be suitably
referred to as "a heterogeneous structure"), as compared with HPs
and CPs. Consequently, the light scattering loss of the whole POF
is increased as the proportion of L.sub.B in the POF becomes
larger. Moreover, BPs generally has worse thermal stability of than
HPs and CPs. Consequently, when the POF is used in a relatively
high temperature region for a long period of time, the presence of
L.sub.B in the POF promotes the creation of a heterogeneous
structure in the POF and increases its light scattering loss.
21. Thus, since the light scattering loss of the whole POF is
increased as the proportion of L.sub.B in the POF becomes larger,
it is preferable that the proportion of L.sub.B in the POF be
smaller and the thickness T.sub.B of each L.sub.B be also smaller.
The desirable value of T.sub.B may vary according to the radial
position of L.sub.B and may also depend on the desired bandwidth
performance and the number of layers. However, T.sub.B is
preferably in the range of about 0.3 to 100 .mu.m and more
preferably about 1 to 10 .mu.m.
22. It is also preferable that the HP (or CP) and CP forming each
BP have good compatibility and the difference in refractive index
therebetween be sufficiently small.
23. Next, the polymers (i.e., HPs and CPs) constituting the
non-mixed layers (L.sub.NB) are explained. It is preferable that
the (co)polymers constituting L.sub.NB in the POF have a small
light scattering loss. In order to obtain (co)polymers having a
small light scattering loss, the polymers (or monomers) should
preferably be chosen so that the difference in refractive index
between HP1 and HP2 and between HP3 and HP2 is as small as
possible. The reason for this is that, if the difference in
refractive index between HP1 and HP2 (or between HP3 and HP2) is
large, the polymer mixture (BP) of HP1 and HP2 or the copolymer
(CP1/2) of M1 and M2 shows fluctuations in refractive index and
hence causes an increase in the light scattering loss of the
POF.
24. Table 1 shows isotropic light scattering losses (dB/km) at a
wavelength of 650 nm for copolymers formed from 80 mole % of methyl
methacrylate (MMA) used as M2 and 20 mole % of various monomers
used as M1 or M3. Table 1 also shows the differences in refractive
index (.DELTA.n.sub.d) between the homopolymers derived from these
monomers and polymethyl methacrylate (PMMA). In this table, the
.DELTA.n.sub.d value is positive when the refractive index of the
relevant homopolymer is larger than that of PMMA, and negative when
the refractive index of the relevant homopolymer is smaller than
that of PMMA.
1TABLE 1 Isotropic Difference in light refractive index
(.DELTA.n.sub.d) Compositional scattering between correspond-
Monomers ratio (wt. %) loss (dB/km) ing homopolymer MMA/VB
74.42/25.58 3725 0.0867 MAA/PhMA 69.39/30.61 1867 0.0798
MMA/2-PhEMA 67.87/32.13 81.7 0.0684 MAA/BzA 70.44/29.56 95.4 0.0676
MMA/GMA 74.04/25.96 10.2 0.0265 MMA/CEMA 72.07/27.93 20.7 0.0262
MMA/THFMA 72.10/27.90 13.1 0.0188 MMA/CHMA 72.60/27.40 13.5 0.0158
MMA 100 10.8 0.0000 MMA/IBMA 75.79/24.21 27.2 -0.0138 MMA/TBMA
72.85/27.15 143.7 -0.0270
25. Note 1
26. VB: Vinyl benzoate
27. PhMA: Phenyl methacrylate
28. 2-PhEMA: 2-Phenylethyl methacrylate
29. BzA: Benzyl acrylate
30. GMA: Glycidyl methacrylate
31. CEMA: Chloroethyl methacrylate
32. THFMA: Tetrahydrofurfuryl methacrylate
33. CHMA: Chlorohexyl methacrylate
34. IMBA: Isobutyl methacrylate
35. TBMA: tert-Butyl methacrylate
36. As is evident from this table, the isotropic light scattering
losses of the copolymers tend to decrease as the absolute value of
the difference in refractive index (.DELTA.n.sub.d) becomes
smaller. Accordingly, the two monomers constituting each binary
copolymer CP used in the POF of the present invention must be ones
giving homopolymers HPs between which there is a small difference
in refractive index. Specifically, the difference in refractive
index is preferably not greater than 0.03, more preferably not
greater than 0.02, and most preferably not greater than 0.015.
However, if the difference in refractive index is decreased to an
undue extent, the NA will become too small. Accordingly, it is
necessary to select a combination of monomers M1 and M2 (or
monomers M3 and M2) with consideration for this fact. For this
reason, the difference in refractive index is preferably not less
than 0.010.
37. Moreover, in the multilayer POF of the present invention which
includes mixed layers (L.sub.B), an abrupt change in refractive
index at the mixed layers (L.sub.B) is suppressed as the difference
in refractive index between adjacent non-mixed layers (L.sub.NB)
becomes smaller, and this reduces the light scattering losses at
the interfaces. Accordingly, it is preferable that the difference
in refractive index between adjacent non-mixed layers (L.sub.NB) be
as small as possible. Specifically, the difference in refractive
index is preferably not greater than 0.016 and more preferably not
greater than 0.008.
38. It is also preferable that BPs constituting the mixed layers
(L.sub.B) in the POF have a small light scattering loss. A mixture
having a small light scattering loss can be obtained by enhancing
the mutual compatibility of the (co)polymers being mixed.
39. One means to this end is to minimize the difference in
copolymerization ratio between the HP (or CP) and CP constituting
adjacent non-mixed layers (L.sub.NB). In a mixture BP composed of
(co)polymers between which there is a large difference in
copolymerization ratio, the properties of one CP (or HP) are
substantially different from those of the other CP. Consequently,
their mutual compatibility is reduced and a heterogeneous structure
tends to be produced in the BP, resulting in an increased light
scattering loss of the POF. Actually, the difference in
copolymerization ratio is determined at a value which causes
substantially no problem for practical purposes, with consideration
for the proportion of the mixed layers (L.sub.B) in the whole
POF.
40. Table 2 shows isotropic light scattering losses at a wavelength
of 650 nm for BPs prepared by selecting two members from among HPs
and various CPs having different compositions and mixing them at a
ratio of 50/50 (wt. %). The aforesaid HPs and CPs were formed from
2,2,2-trifluoroethyl methacrylate (3FM) or
2,2,3,3-tetrafluoropropyl methacrylate (4FM) used as M1, and
2,2,3,3,3-pentafluoropropyl methacrylate (5FM) used as M2.
41. In this table, the (co)polymer derived from monomers M1 and M2
is the homopolymer HP1 of M1 when the content of M2 is 0 mole %,
and the homopolymer HP2 of M2 when the content of M1 is 0 mole %.
The difference in copolymerization ratio between two copolymers A
and B having different copolymerization ratios is expressed by the
difference in the molar content (%) of M1 or M2.
42. Table 2 indicates that, as the copolymerization ratio of one CP
(or HP) is closer to that of the other CP mixed therewith, the
resulting BP has a smaller isotropic light scattering loss. With
respect to M1 or M2 contained in any two adjacent (co)polymers, the
difference in copolymerization ratio is preferably not greater than
20 mole %, more preferably not greater than 15 mole %, and most
preferably not greater than 10 mole %. However, if the difference
in copolymerization ratio is extremely small, it may be necessary
to increase the number of (co)polymer layers for the purpose of
securing the desired NA of the optical fiber.
2TABLE 2 Monomer ratio Monomer ratio Difference in M1 con-
Isotropic light scattering Monomers of copolymer of copolymer tent
between copolymers loss of mixture of co- M1/M2 1 (mole %) 2 (mole
%) 1 and 2 (mole %) polymers 1 and 2 (dB/km) 3FM/5FM 40/60 30/70 10
60-80 3FM/5FM 45/55 30/70 15 70-100 3FM/5FM 50/50 30/70 20 80-140
3FM/5FM 50/50 0/100 50 >10000 (cloudy) 3FM/5FM 50/50 100/0 50
>10000 (cloudy) 4FM/5FM 40/60 30/70 10 60-80 4FM/5FM 45/55 30/70
15 80-110 4FM/5FM 50/50 30/70 20 90-150 4FM/5FM 50/50 0/100 50
>10000 (cloudy) 4FM/5FM 50/50 100/0 50 >10000 (cloudy)
43. In the present invention, high or low refractive indices are
used on a relative basis. For example, when MMA is used as M2 and,
therefore, PMMA having a refractive index of 1.491 is used as HP2,
the monomers which can be used as M1 and M3 are exemplified below.
The n.sub.d values given in parentheses represent the refractive
indices of the corresponding homopolymers.
44. Examples of monomer M1 used to form a polymer having a high
refractive index include benzyl methacrylate (n.sub.d=1.5680),
phenyl methacrylate (n.sub.d=1.5706), vinyl benzoate
(n.sub.d=1.5775), styrene (n.sub.d=1.5920), 1-phenylethyl
methacrylate (n.sub.d=1.5490), 2-phenylethyl methacrylate
(n.sub.d=1.5592), diphenylmethyl methacrylate (n.sub.d=1.5933),
1,2-diphenylethyl methacrylate (n.sub.d=1.5816), 1-bromoethyl
methacrylate (n.sub.d=1.5426), benzyl acrylate (n.sub.d=1.5584),
.alpha., .alpha.-dimethylbenzyl methacrylate (n.sub.d=1.5820),
p-fluorostyrene (n.sub.d=1.566), 2-chloroethyl methacrylate
(n.sub.d=1.5170), isobornyl methacrylate (n.sub.d=1.505), adamantyl
methacrylate (n.sub.d=1.535), tricylodecyl methacrylate
(n.sub.d=1.523), 1-methylcyclohexyl methacrylate (n.sub.d=1.5111),
2-chlorocyclohexyl methacrylate (n.sub.d=1.5179),
1,3-dichloropropyl methacrylate (n.sub.d=1.5270),
2-chloro-1-chloromethylethyl methacrylate (n.sub.d=1.5270), bornyl
methacrylate (n.sub.d=1.5059), cyclohexyl methacrylate
(n.sub.d=1.5066), tetrahydrofurfyl methacrylate (n.sub.d=1.5096),
allyl methacrylate (n.sub.d=1.5196), tetrahydrofurfuryl
methacrylate (n.sub.d=1.5096), vinyl chloroacetate
(n.sub.d=1.5120), glycidyl methacrylate (n.sub.d=1.517) and methyl
.alpha.-chloroacrylate (n.sub.d=1.5172).
45. Examples of monomer M3 used to form a polymer having a low
refractive index include 2,2,2-trifluoroethyl methacrylate
(n.sub.d=1.415), 2,2,3,3-tetrafluoropropyl methacrylate
(n.sub.d=1.422), 2,2,3,3,3-pentafluoropropyl methacrylate
(n.sub.d=1.392), 2,2,2-trifluoro-1-trifluoromethylethyl
methacrylate (n.sub.d=1.380), 2,2,3,4,4,4-hexafluorobutyl
methacrylate (n.sub.d=1.407), 2,2,3,3,4,4,5,5-octafluoropentyl
methacrylate (n.sub.d=1.393), 2,2,2-trifluoroethyl
.alpha.-fluoroacrylate (n.sub.d=1.386), 2,2,3,3-tetrafluoropropyl
.alpha.-fluoroacrylate (n.sub.d=1.397), 2,2,3,3,3-pentafluoropropyl
.alpha.-fluoroacrylate (n.sub.d=1.366),
2,2,3,3,4,4,5,5-octafluoropentyl .alpha.-fluoroacrylate
(n.sub.d=1.376), o- or p-difluorostyrene (n.sub.d=1.4750), vinyl
acetate (n.sub.d=1.4665), tert-butyl methacrylate (n.sub.d=1.4638),
isopropyl methacrylate (n.sub.d=1.4728), hexadecyl methacrylate
(n.sub.d=1.4750), isobutyl methacrylate (n.sub.d=1.4770),
.alpha.-trifluoromethylacrylates, .beta.-fluoroacrylates, .beta.,
.beta.-difluoroacrylates, .beta.-trifluoromethylacrylates, .beta.,
.beta.-bis(trifluoromethyl)acryl- ates and
.alpha.-chloroacrylates.
46. Preferably, the monomers used to prepare the (co)polymers
constituting the GI type POF of the present invention are ones
giving homopolymers with a glass transition temperature (Tg) of
70.degree. C. or above. If Tg is unduly low, the thermal resistance
of the whole POF will be reduced. As a result, there is a
possibility that, in a service environment having relatively high
temperatures, phase separation, especially in the L.sub.B layers,
may be accelerated to cause an increase in scattering loss.
Examples of such high-Tg (co)polymers include (co)polymers derived
from a combination of methyl methacrylate and chloroethyl
methacrylate.
47. Especially preferred examples of (co)polymers which have a
small difference in refractive index between HPs and hence cause a
small scattering loss in POFs include (copolymers derived from a
combination of two or three fluoroalkyl (meth)acrylates. Similarly,
they also include (co)polymers derived from a combination of
monomers selected from chlorohexyl methacrylate, tetrahydrofurfuryl
methacrylate, glycidyl methacrylate, isobutyl methacrylate and
methyl methacrylate, and having different copolymerization
ratios.
48. Furthermore, examples of (co)polymers which have a large
difference in refractive index between HPs but exhibit good
compatibility include (co)polymers derived from 2-phenylethyl
methacrylate and methyl methacrylate, and having different
copolymerization ratios.
49. No particular limitation is placed on the difference in
refractive index between the center and the outer periphery of the
GI type POF of the present invention. However, in view of the
magnitude of the numerical aperture (NA), it is preferable that the
difference in refractive index be in the range of about 0.02 to
0.04.
50. Now, the method of making a GI type POF in accordance with the
present invention is described below.
51. According to this method, each spining material is prepared
from one (co)polymer and three or more, preferably five or more,
spinning materials having different refractive indices are prepared
by using (co)polymers selected from the group consisting of two or
more homopolymers HP1, HP2, . . . , HPn (in which n is an integer
of 2 or greater) derived from monomers M1, M2, . . . , Mn,
respectively, and having refractive indices decreasing in that
order, and one or more binary copolymers CPs derived from the
monomers. Then, these spinning materials are fed to a multilayer
concentric circular nozzle having three or more, preferably five or
more, layers so that the refractive index decreases toward the
outer periphery, and thereby extruded through the nozzle.
52. In order to create a gradual refractive index distribution
profile between adjacent layers, mixed layers must be formed by
polymer-to-polymer interdiffusion between adjacent layers. To this
end, the following procedure is employed. For example, the spinning
materials are melted within the spinning nozzle, and the spinning
materials constituting any two adjacent layers are brought into
contact with each other for a relatively long period of time to
effect polymer-to-polymer interdiffusion, and then extruded
therefrom. However, when the number of layers is sufficiently
large, no positive treatment for effecting polymer-to-polymer
interdiffusion between adjacent layers is required.
53. Where a gradual refractive index distribution curve is not
obtained owing to insufficient interdiffusion within the nozzle,
the extruded fiber may be heat-treated again to effect additional
polymer-to-polymer interdiffusion. However, when this method is
employed, the fiber should preferably be extruded from the spinning
nozzle in an undrawn state so as to prevent relaxation shrinkage of
the fiber during heat treatment. The reason for this is that change
in fiber diameter increase the light transmission loss of the
POF.
54. The heat treatment may be carried out, for example, in the
following manner. First, the undrawn fiber is heat-treated at a
temperature over 100.degree. C. higher than the average glass
transition temperature (Tg) of the (co)polymers constituting it to
effect interdiffusion. Then, the fiber is drawn in a temperature
range extending from Tg to a temperature about 80.degree. C. higher
than Tg, so as to impart flexural strength to the fiber. Thus,
there can be obtained a GI type POF.
55. Furthermore, in order to increase the thicknesses of the mixed
layers, there may be employed a method which comprises adding to
each spinning material a monomer mixture having the same
composition as the (co)polymer constituting the spinning material
and a photopolymerization initiator, extruding the resulting
spinning materials through a nozzle so as to allow the monomers to
interdiffuse between adjacent layers, and then photopolymerizing
the monomers within the fiber.
56. The refractive index profile of the POF can be controlled by
varying the residence time within the spinning nozzle, the melt
spinning temperature, the post-spinning heat-treating temperature,
the draw ratio during spinning, the types of the resinous
components, and the number of concentric cylindrical layers of
spinning materials (hereinafter referred to as "spinning material
layers").
57. Now, the design method for manufacturing a GI type POF having
an ideal refractive index profile (i.e., the conditions giving the
widest bandwidth) is described below with respect to the
relationship between the multilayer concentric cylindrical
arrangement of spinning materials within the spinning nozzle and
the refractive indices thereof. However, it is to be understood
that the present invention is not limited by the following
description.
58. Let us consider a GI type POF in which the refractive index
decreases gradually from the center toward the outer periphery. If
the refractive index at the center is designated by n.sub.1, the
lowest refractive index at the outer periphery by n.sub.2, the
radius by (a), and the position (or distance) from the center by r
(0<r<a), and if it is assumed that
.DELTA.=(n.sub.1-n.sub.2)/n.sub.1 the conditions which impart the
widest bandwidth to the POF are such that the refractive index
profile, n(r), is approximated by the following equation.
n(r)=n.sub.1{1-2.DELTA.(r/a).sup.2}.sup.0.5 (1)
59. That is, if the values of n.sub.1, n.sub.2 and (a) are
determined, the ideal refractive index profile within the POF can
be determined according to equation (1). Moreover, if the ratio of
the diameter (b) of the spinning nozzle to the diameter (c) of the
extruded and drawn POF is designated by a (1<.alpha.=b/c), the
refractive index profile, n'(r), to be formed within the spinning
nozzle (in which the core diameter is .alpha.a) is described by the
following equation.
n'(r)=n.sub.1{1-2.DELTA.(r/.alpha.a).sup.2}.sup.0.5 (2)
60. Accordingly, the radial position r.sub.j (j=1, 2, 3, . . . ) in
the spinning nozzle at which a spinning material polymer j having a
refractive index n'j is arranged can be determined by substituting
n'j for n'(r) and r.sub.j for r in equation (2). Thus, the
following equation is obtained.
r.sub.j=.alpha.a[{1-(n'.sub.j/n.sub.1).sup.2}/2.DELTA.].sup.0.5
(3)
61. In this case, the number (N) of spinning material layers
depends on the core radius (.alpha.a) within the nozzle and the
interdiffusion distance (L) of the spinning material polymers. It
is reasonable that N is equal to (.alpha.a/2L). If (.alpha.a) is
significantly large as compared with L, this would be rather
undesirable because feeder of the spinning material polymers to the
nozzle and control of the spinning conditions are complicated to
cause an increase in production cost. Moreover, if
N<<.alpha.a/2L, the interdiffusion distance will be short
relative to the thicknesses of the spinning material layers.
Consequently, the desired refractive index profile cannot be
satisfactorily formed, so that the resulting POF will have a worse
transmission bandwidth. However, to avoid a high production cost
and a troublesome production process, multilayer spinning
comprising about 5 to 10 layers is considered to be proper from a
practical point of view. The POF formed in this manner has a
somewhat stepwise refractive index profile. Its bandwidth
performance does not reach that of a POF having the ideal
refractive index profile of equation (1), but fully meets the
requirements for practical purposes.
62. According to the method of the present invention, a multicore
fiber may also be formed by extruding such multilayer fibers
simultaneously through a plurality of nozzles disposed in close
proximity to each other.
63. While the embodiment in which the number (n) of monomers is 3
has been described above, the difference in refractive index
between the center and the outer periphery of a GI type POF can be
easily increased by increasing n to 4 or greater, so that a higher
NA can be achieved easily.
64. Moreover, even if the number (n) of monomers is 2, a GI type
POF having a small light scattering loss can be formed by selecting
a combination of two monomers giving homopolymers between which
there is a small difference in refractive index.
65. As the (co)polymers constituting the non-mixed layers
(L.sub.NB) of the GI type POF of the present invention, terpolymers
TPs may also be used in order, for example, to improve the thermal
resistance and mechanical strength of the POF. That is, terpolymers
TPs derived from three monomers including the two monomers
constituting the aforesaid binary copolymers CPs may further be
used in addition to the binary copolymers CPs. Alternatively, such
terpolymers TPs may be used in place of the binary copolymers
CPs.
66. The present invention is further illustrated by the following
examples.
EXAMPLE 1
67. Four monomeric components were used in this example. They
included glycidyl methacrylate (GMA) giving a homopolymer with a
refractive index (n.sub.d) of 1.5174 and a glass transition
temperature (Tg) of 46.degree. C., cyclohexyl methacrylate (CHMA)
giving a homopolymer with an n.sub.d of 1.5066 and a Tg of
83.degree. C., MMA giving a homopolymer with an n.sub.d of 1.4908
and a Tg of 112.degree. C., and isobutyl methacrylate (IBMA) giving
a homopolymer with an n.sub.d of 1.4770 and a Tg of 48-53.degree.
C. In each binary copolymers, therefore, the difference in
refractive index (.DELTA.n.sub.d) between the two homopolymers was
as follows.
68. GMA/CHMA (.DELTA.n.sub.d=0.0108)
69. CHMA/MMA (.DELTA.n.sub.d=0.0158)
70. MMA/IBMA (.DELTA.n.sub.d=0.0138)
71. The following eight monomers and monomer mixtures (with mixing
ratios expressed in percent by weight) were subjected to
polymerization reaction.
72. 1) GMA/CHMA=17.44/82.56
73. 2) CHMA
74. 3) CHMA/MMA=87.05/12.95
75. 4) CHMA/MMA=71.59/28.41
76. 5) CHMA/MMA=52.83/47.17
77. 6) CHMA/MMA=29.58/70.42
78. 7) MMA
79. 8) MMA/IBMA=73.80/26.20
80. Monomer mixture solutions were prepared by adding 500 .mu.l of
n-dodecyl mercaptan as a molecular weight controller (or chain
transfer agent) to 100 g of each of the monomers or monomer
mixtures, and further adding thereto 0.11 g of
azobis(dimethylvaleronitrile) as a low-temperature initiator and
8.00 .mu.l of di-tert-butyl peroxide as a high-temperature
initiator. In order to obtain polymers useful as spinning
materials, these monomer mixture solutions were subjected to
two-step radical polymerization. That is, they were polymerized
under an atmosphere of nitrogen at 70.degree. C. for 5 hours in
such a way as to cause no foaming. After the degree of
polymerization reached 90% by weight or greater, they were
polymerized at 130.degree. C. for 40 hours. The resulting polymers
had a weight-average molecular weight of about 100,000 to 140,000
on the basis of measurements by GPC, and their residual monomer
content was 1% by weight or less.
81. Subsequently, these eight spinning materials were fed to an
extruder, melted at 240.degree. C., and extruded through a
composite spinning nozzle having an eight-layer concentric
cylindrical structure. This spinning nozzle is designed so that an
eight-layer concentric cylindrical structure is formed at a
position 500 mm before the nozzle tip from which the fiber in its
molten state is extruded. Moreover, this nozzle is fabricated so
that its internal diameter decreases gradually over a length of 100
mm extending from the aforesaid position in the direction of
extrusion. Finally, starting from a position 400 mm before the tip,
the diameter of the nozzle remains constant at 2 mm. Basically, a
gradual refractive index distribution profile is created by
polymer-to-polymer interdiffusion while the molten polymers flow
through this 400 mm section. The temperature of this spinning
nozzle section is strictly controlled by dividing it into four
equal subsections having a length of 100 mm. The temperature of the
100 mm subsection adjoining the spinning nozzle tip was adjusted to
230.degree. C. so as to secure the stability of spinning, and the
temperature of the other three subsections was adjusted to
240.degree. C. so as to promote the polymer-to-polymer
interdiffusion.
82. The extrusion speed of the polymers was 40 mm/min and the
residence time of the polymers in the spinning nozzle section
having a diameter of 2 mm was about 10 minutes. The extruded fiber
was drawn so as to give a final diameter of 1 mm, and taken up by
means of a wind-up machine.
83. The POF formed in the above-described manner was cut at a
length of 0.1 km to measure its -3 dB transmission bandwidth. Thus,
it was found to be 900 MHz. This transmission bandwidth measurement
was made at a launch NA of 0.85 by using an optical sampling
oscilloscope (manufactured by Hamamatsu Photonics Co., Ltd.) and a
light source comprising a Semiconductor Laser TOLD 9410
(manufactured by Toshiba Corp.) with an emission wavelength of 650
nm. Moreover, its transmission loss was 160 dB/km. This
transmission loss measurement was made at a wavelength of 650 nm
and a launch NA of 0.1 according to the 100 m/5 m cut-back method.
The same measuring conditions were also employed in the following
examples.
84. The numerical aperture (NA) of this GI type POF was 0.25.
Moreover, the thickness of each mixed layer in the POF was about
1-3 .mu.m.
EXAMPLE 2
85. A multicore fiber having a sea-and-island structure was made by
using, as the islands, nine POFs each of which has the same
multilayer structure as described in Example 1. However, the
copolymer composed of MMA and IBMA in a ratio of 73.80:26.20 and
disposed on the outermost side in Example 1 was used as the sea
material. Accordingly, except for the sea material, the structure
of the islands consisted essentially of the part of the fiber of
Example 1 extending from its center to the seventh layer. The
average diameter of the islands was about 0.5 mm, and the diameter
of the whole multicore fiber was 3.0 mm. The transmission loss of
this multicore fiber was 250 dB/km, and its transmission bandwidth
per island at a length of 0.1 km was 650 MHz. The thickness of each
mixed layer in the POFs was about 1-3 .mu.m.
EXAMPLE 3
86. Three monomeric components were used in this example. They
included 2,2,3,3-tetrafluoropropyl methacrylate (4FM) giving a
homopolymer with a refractive index (n.sub.d) of 1.4215 and a Tg of
64.degree. C., 2,2,3,3,3-pentafluoropropyl methacrylate (5FM)
giving a homopolymer with an n.sub.d of 1.3920 and a Tg of
67.degree. C., and 2-(perfluorooctyl)ethyl methacrylate (17FM)
giving a homopolymer with an n.sub.d of 1.3732. In each binary
copolymer system, therefore, the difference in refractive index
(.DELTA.n.sub.d) between the two homopolymers was as follows.
87. 4FM/5FM (.DELTA.n.sub.d=0.0295)
88. 5FM/17FM (.DELTA.n.sub.d=0.0188)
89. The following eight monomer and monomer mixtures (with mixing
ratios expressed in percent by weight) were subjected to
polymerization reaction.
90. 1) 4FM/5FM=57.92/42.08
91. 2) 4FM/5FM=45.86/54.14
92. 3) 4FM/5FM=34.04/65.96
93. 4) 4FM/5FM=22.46/77.54
94. 5) 4FM/5FM=11.12/88.88
95. 6) 5FM
96. 7) 5FM/17FM=78.67/21.33
97. 8) 5FM/17FM=62.11/37.89
98. According to the same procedure as described in Example 1,
these monomers and monomer mixtures were polymerized and spun to
form a POF. The transmission bandwidth of this POF was 1.1 GHz, its
transmission loss was 140 dB/km, and the thickness of each mixed
layer was about 1-3 .mu.m.
EXAMPLE 4
99. Two monomeric components were used in this example. They
included 2,2,2-trifluoroethyl methacrylate (3FM) giving a
homopolymer with a refractive index (n.sub.d) of 1.4146 and a Tg of
75.degree. C., and 2,2,3,3,3-pentafluoropropyl methacrylate (5FM)
giving a homopolymer with an n.sub.d of 1.3920 and a Tg of
67.degree. C. In the binary copolymer, therefore, the difference in
refractive index (.DELTA.n.sub.d) between the two homopolymers was
0.0226. The following eight monomers and monomer mixtures (with
mixing ratios expressed in percent by weight) were subjected to
polymerization reaction.
100. 1) 3FM
101. 2) 3FM/5FM=82.56/17.44
102. 3) 3FM/SFM=66.46/33.54
103. 4) 3FM/5FM=51.56/48.44
104. 5) 3FM/5FM=37.72/62.28
105. 6) 3FM/5FM=24.83/75.17
106. 7) 3FM/5FM=12.80/87.20
107. 8) 5FM
108. According to the same procedure as described in Example 1,
these monomers and monomer mixtures were polymerized and spun to
form a POF. The transmission bandwidth of this POF was 1.9 GHz, its
transmission loss was 110 dB/km, and the thickness of each mixed
layer was about 1-3 .mu.m.
EXAMPLE 5
109. Two monomers, i.e. 4FM and 5FM, were used in this example. The
following eight monomer and monomer mixtures (with mixing ratios
expressed in mole percent) were subjected to polymerization
reaction. In this case, the difference in refractive index
(.DELTA.n.sub.d) between the two homopolymers was 0.0295.
110. 1) 4FM/5FM=70/30
111. 2) 4FM/5FM=60/40
112. 3) 4FM/5FM=50/50
113. 4) 4FM/5FM=40/60
114. 5) 4FM/5FM=30/70
115. 6) 5FM/5FM=20/80
116. 7) 5FM/5FM=10/90
117. 8) 5FM
118. Using the resulting eight polymers as spinning materials, a
POF was formed in the same manner as described in Example 1. The
transmission bandwidth of this POF was 1.5 GHz, its transmission
loss was 120 dB/km, and the thickness of each mixed layer was about
1-3 .mu.m.
EXAMPLE 6
119. Two monomeric components were used in this example. They
included chloroethyl methacrylate (CEMA) giving a homopolymer with
an n.sub.d of 1.517 and a Tg of 92.degree. C., and MMA giving a
homopolymer with an n.sub.d of 1.491 and a Tg of 112.degree. C. The
following eight monomer and monomer mixtures (with mixing ratios
expressed in mole percent) were subjected to polymerization
reaction. In this case, the difference in refractive index
(.DELTA.n.sub.d) between the two homopolymers was 0.026.
120. 1) CEMA/MMA=84/16
121. 2) CEMA/MMA=72/28
122. 3) CEMA/MMA=60/40
123. 4) CEMA/MMA=48/52
124. 5) CEMA/MMA=36/64
125. 6) CEMA/MMA=24/76
126. 7) CEMA/MMA=12/88
127. 8) MMA
128. Using the resulting eight polymers as spinning materials, a
POF was formed in the same manner as described in Example 1. The
transmission bandwidth of this POF was 1.2 GHz, its transmission
loss was 155 dB/km, and the thickness of each mixed layer was about
1-3 .mu.m.
EXAMPLE 7
129. Three monomeric components were used in this example. They
included tetrahydrofurfuryl methacrylate (THFMA) giving a
homopolymer with an n.sub.d of 1.510 and a Tg of 60.degree. C., MMA
giving a homopolymer with an n.sub.d of 1.491 and a Tg of
112.degree. C., and isobutyl methacrylate (IBMA) giving a
homopolymer with an n.sub.d of 1.477 and a Tg of 48-53.degree. C.
The following eight monomer and monomer mixtures (with mixing
ratios expressed in mole percent) were subjected to polymerization
reaction.
130. 1) THFMA/MMA=80/20
131. 2) THFMA/MMA=60/40
132. 3) THFMA/MMA=40/60
133. 4) THFMA/MMA=20/80
134. 5) MMA
135. 6) MM/IBMA=80/20
136. 7) MM/IBMA=60/40
137. 8) MMA/IBMA=40/60
138. Using the resulting eight polymers as spinning materials, a
POF was formed by spinning them in the same manner as described in
Example 1. The transmission bandwidth of this POF was 1.2 GHz, its
transmission loss was 190 dB/km, and the thickness of each mixed
layer was about 1-3 .mu.m.
EXAMPLE 8
139. Two monomeric components were used in this example. They
included 2-phenylethyl methacrylate (2-PhEMA) giving a homopolymer
with an n.sub.d of 1.559, and MMA giving a homopolymer with an
n.sub.d of 1.491 and a Tg of 112.degree. C. The following eight
monomer and monomer mixtures (with mixing ratios expressed in mole
percent) were subjected to polymerization reaction.
140. 1) 2-PhEMA/MMA=35/65
141. 2) 2-PhEMA/MMA=30/70
142. 3) 2-PhEMA/MMA=25/75
143. 4) 2-PhEMA/MMA=20/80
144. 5) 2-PhEMA/MMA=15/85
145. 6) 2-PhEMA/MMA=10/90
146. 7) 2-PhEMA/MMA=5/95
147. 8) MMA
148. Using the resulting eight polymers as spinning materials, a
POF was formed by spinning them in the same manner as described in
Example 1. The transmission bandwidth of this POF was 1.3 GHz, its
transmission loss was 200 dB/km, and the thickness of each mixed
layer was about 1-3 .mu.m.
EXAMPLE 9
149. Two monomeric components were used in this example. They
included 2,2,2-trifluoro-1-trifluoromethylethyl methacrylate
(iso-6FM) giving a homopolymer with an n.sub.d of 1.380 and a Tg of
78.degree. C.; and 2,2,2-trifluoethyl methacrylate (3FM) giving a
homopolymer with an n.sub.d of 1.415 and a Tg of 75.degree. C. The
following eight monomer and monomer mixtures (with mixing ratios
expressed in mole percent) were subjected to polymerization
reaction.
150. 1) 3FM
151. 2) iso-6FM/3FM=10/90
152. 3) iso-6FM/3FM=20/80
153. 4) iso-6FM/3FM=30/70
154. 5) iso-6FM/3FM=40/60
155. 6) iso-6FM/3FM=50/50
156. 7) iso-6FM/3FM=60/40
157. 8) iso-6FM/3FM=70/30
158. Using the resulting eight polymers as spinning materials, a
POF was formed by spinning them in the same manner as described in
Example 1. The transmission bandwidth of this POF was 1.0 GHz, its
transmission loss was 130 dB/km, and the thickness of each mixed
layer was about 1-3 .mu.m.
EXAMPLE 10
159. Two monomeric components were used in this example. They
included chloroethyl methacrylate (CEMA) giving a homopolymer with
an n.sub.d of 1.517 and a Tg of 92.degree. C., and methyl
methacrylate (MMA) giving a homopolymer with an n.sub.d of 1.491
and a Tg of 112.degree. C. The following six monomer and monomer
mixtures (with mixing ratios expressed in mole percent) were
subjected to polymerization reaction.
160. 1) CEMA/MMA=80/20
161. 2) CEMA/MMA=64/36
162. 3) CEMA/MMA=48/52
163. 4) CENA/MMA=32/68
164. 5) CEMA/MMA=16/84
165. 6) MMA
166. Each of these six monomer and monomer mixtures was thermally
polymerized until a degree of polymerization of about 50% was
reached. Thus, highly viscous monomer/polymer mixed syrups were
prepared.
167. Subsequently, after the addition of a photopolymerization
initiator, these six mixed syrups were fed to the same multilayer
spinning nozzle as used in Example 1, except that the spinning
nozzle had a six-layer concentric cylindrical structure and its
temperature was adjusted to 40.degree. C. After being extruded, the
aforesaid syrups were photopolymerized by UV irradiation. Thus,
their polymerization was completed to form a POF.
168. The transmission bandwidth of this POF was 2.1 GHz, its
transmission loss was 140 dB/km, and the thickness of each mixed
layer was about 30 .mu.m.
EXAMPLE 11
169. Three monomeric components were used in this example. They
included cyclohexyl methacrylate (CHMA) giving a homopolymer with
an n.sub.d of 1.5066 and a Tg of 83.degree. C., MMA giving a
homopolymer with an n.sub.d of 1.491 and a Tg of 112.degree. C.,
and isobutyl methacrylate (IBMA) giving a homopolymer with an
n.sub.d of 1.477 and a Tg of 48-53.degree. C. The following eight
monomers and monomer mixtures (with mixing ratios expressed in mole
percent) were subjected to polymerization reaction.
170. 1) CHMA/IBMA/MMA=70/10/20
171. 2) CHMA/IBMA/MMA=60/20/20
172. 3) CHMA/IBMA/MMA=50/30/20
173. 4) CHMA/IBMA/MMA=40/40/20
174. 5) CHMA/IBMA/MMA=30/50/20
175. 6) CHMA/IBMA/MMA=20/60/20
176. 7) CHMA/IBMA/MMA=10/70/20
177. 8) CHMA/IBMA/MMA=0/80/20
178. Using the resulting eight polymers as spinning materials, a
POF was formed by spinning them in the same manner as described in
Example 1. The transmission bandwidth of this POF was 1.1 GHz, its
transmission loss was 180 dB/km, and the thickness of each mixed
layer was about 1-3 .mu.m.
Exploitability in Industry
179. The present invention can provide GI type POFs having a small
light scattering loss and a relatively large numerical aperture.
Moreover, the method for forming POFs in accordance with the
present invention has high productivity.
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