27103-81
207969
SPECIFICATION
ULTRAVIOLET RESISTANT SILICA GLASS FIBER
FIELD OF THE INVENTION
The present invention relates to a silica glass fiber, such
as a single optical fiber and a bundle fiber consisting of a
number of optical fibers, which is superior in resistance to
ultraviolet rays in the ultraviolet region, and specifically to
a bundle fiber suitable for spectral analysis.
Also, the present invention relates to a method of
transmitting energy or signals by ultraviolet rays, which
comprises transmitting ultraviolet rays through said ultraviolet
resistant silica glass fiber.
BACKGROUND OF THE INVENTION
An optical fiber', particularly the one composed of a silica
has been used in the ultraviolet region, not to mention in the
visible light region. As the core material, used are silica
glasses containing OH group but substantially free of fluorine,
which may or may not contain chlorine. The core material is
mainly characterized by OH group intentionally contained
therein, and is advantageous in that its output is great and
initial characteristic is superior. On the other hand, its
ultraviolet deterioration resistance characteristic, namely,
resistance to the deterioration of core material caused by
ultraviolet rays, is not, in general, entirely superior, and
specifically this characteristic is insufficient at the
wavelength of 215 nm.
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In the meantime, silica glass core materials for optical
fibers which have been used in the visible light region have
received increasing demand from the field involving exposure to
radiation, such as for nuclear power, and resistance to
radiation has recently been strongly demanded of the optical
fiber for use in such fields.
In view of the background as described, the present
inventors developed a new optical fiber to be used in the
visible light region, specifically an optical fiber composed of
a silica glass core made of a core material intentionally
containing fluorine, but substantially free of chlorine and OH
group. This core matE~rial exhibits extremely superior
resistance to radiation ih the visible light region, whereas
when used in the ultraviolet region, shows small initial
characteristic and small output: substantially it is not
practical for use at ;?50 nm or below.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a silica
glass fiber having excellent resistance to ultraviolet rays,
2o which is for use in the ultraviolet region.
Another object oif the present invention is to provide a
method of transmittin;; energy or signals using a silica glass
fiber having resistance to the deterioration caused by
ultraviolet rays.
Further objects of the present invention will become clear
from the description to follow hereunder.
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27103-81
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The present inventors have continuously studied in an
effort to solve the conventional problems which this kind of
optical fiber composed of silica core materials have at the
ultraviolet region, and to find out the composition of the
silica glass which can reduce degree of deterioration by
ultraviolet rays when used in the ultraviolet region and permits
efficient transmission of energy or signals. The studies have
led the present invenvtors to a new idea that fluorine, chlorine
and OH group contents in the core material greatly influence
ultraviolet resistance characteristic, and that excellent
ultraviolet resistance may be obtained by appropriately
adjusting their contents. The present invention rests in the
achievement of the aforementioned objects, motivated by this new
i dea.
The present inventors have found that efficient
transmission of energy or signals using ultraviolet rays can be
achieved by a single optical fiber composed of a doped silica
glass cladding layer :formed on a silica glass core or a bundle
fiber consisting of a number of such fibers, the silica glass
2o core having (1) an OH group content of 10-1000 ppm and (2) a
fluorine content of 5i0-5000 ppm, and (3) being substantially
free of chlorine, with greatly reduced deterioration of the
silica glass fiber by ultraviolet rays.
That the silica glass fiber has excellent resistance to
ultraviolet rays is unknown to those skilled in the art from the
prior art, and one of ordinary skill in the art'would not
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envision use of such silica glass fiber for the transmission of
energy or signals by ultraviolet rays.
The present invention relates to a silica glass optical
fiber or a bundle fiber for use in the ultraviolet region,
wherein the optical fiber is composed of a doped silica glass
cladding layer formed on a silica glass core, the silica glass
core having (1) an OH group content of 10-1000 ppm and (2) a
fluorine content of 5~D-5000 ppm, and (3) being substantially
free of chlorine.
Also, the present invention relates to a method of
transmitting energy or signals using ultraviolet rays, which
comprises transmission of energy or signals using ultraviolet
rays through an ultraviolet resistant silica glass fiber
composed of a doped silica glass cladding layer formed on a
silica glass core, th.e silica glass core having (1) an OH group
content of i0-1000 ppm and (2) a fluorine content of 50-5000
ppm, and (3) being substantially free of chlorine, or a bundle
fiber consisting of a number of said fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
2o Fig. 1 is a cross sectianal view of a single optical fiber
of the present invention as described in Examples, Fig. 2 is
also a cross sectional view of a bundle fiber, and Fig. 3
depicts the method for testing the resistance to ultraviolet
rays possessed by the optical fiber in the atmosphere.
DETAILED DESCRIPTION OF THE INVENTION
It is highly characteristic of the core material for a
4
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27103-81
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silica glass fiber of the present invention that it contains OH
group and fluorine, but does not substantially contain chlorine
as described above. As mentioned earlier, while the
conventional core materials for ultraviolet rays contain OH
group, they do not substantially contain fluorine, thus
resulting in superior initial characteristic but poor
ultraviolet deterioration resistance characteristic. On the
other hand, the core material for visible light could be
improved in radiation resistance by adding fluorine. The core
l0 material for a s h in a glass fiber of the present invention, in
contrast, contains 1)H group as do the conventional core
materials for ultraviolet silica glass fibers, and additionally
contains fluorine such that the resistance to deterioration
caused by ultraviolet rays can be improved. When the fluorine
and OH group are contained in a specific proportion of 50-5000
ppm, and 10-1000 ppm, respectively, superior ultraviolet
resistance characteristic, particularly remarkable improvements
in initial transmission loss at the ultraviolet region and
ultraviolet deterioration resistance characteristic can be
2o revealed.
The optical fiiber of the present invention can be roughly
divided into a single fiber and a bundle fiber consisting of a
number of the fibers.
Fig. 1 is a cross sectional view of a single fiber, wherein
1 is a single optical fiber, 2 is a core layer, 3 is a cladding
layer, and 4 is a supporting layer. The supporting layer is a
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27103-81
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protecting layer which is formed only when necessary and is not
always formed.
The single fiber 1 in Fig. 1 can be produced, for example,
in such a manner that a doped silica glass which becomes the
cladding layer 3 is externally applied on a silica glass. rod
which becomes the core 2, or a cladding layer is internally
applied, and the supporting layer 4 of a three-layer structure
preforms obtained by the Rod-In-Tube method is removed by fire
polishing to give a preform of a two-layer structure of the core
l0 2 and the cladding layer 3.
A bundle fiber 10 which is another embodiment of the
present invention is produced by bundling a number of fibers, as
shown in Fig. 2. The bundle fiber 10 at an output end 11 has
normally one or two rows of fibers adhered by an appropriate
means such as adhesives, and at a light input end 12, has fibers
adhered to each other nearly in a round shape by adhesives,
etc., as shown in Fig. 2. The fibers 1 in an intermediate part
13 between the output end 11 and the input end 12 are not
adhered to each other but are apart. The bundle fiber 10 having
20 this structure, is flexible as a whole, and is vastly
advantageous for use..
While the number of the fibers 1 in the bundle fiber is
appropriately determined according to the object of use and
places to be located(, a representative bundle fiber contains
12-24 fibers of 1-3 m in length.
The care of the optical fiber of the present invention is
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composed of a pure :silica glass having an OH group content of
10-1000 ppm, prefer<~bly 20-600 ppm, more preferably 30-400 ppm,
and a fluorine contE~nt of 50-5000 ppm, preferably 200-3000 ppm,
more preferably 300-2000 ppm, and being substantially free of
chlorine, meaning that chlorine may be contained only in a
slight proportion of, for example, 1 ppm at most. Such pure
silica glass for core can be produced by a production method
for synthetic silica glass, comprising, for example, burning at
least one member of silicon compounds of the formula
R m Si(O RZ)a-m
[hereinafter referred to as Compound (I)] and at least one
member of fluorine <:ompounds of the formula CaHbF~ [hereinafter
referred to as Compound (II)] with oxyhydrogen flame, and
accumulating the resulting synthetic silica fine particles on a
rotating heat-resist: ant base substance to give a porous
Sintered silica which is then heat-fused for vitrification. In
the above-mentioned formulas, R1 and Rz are each a lower alkyl
group having 1 to 4 carbon atoms such as methyl, ethyl, n-
propyl, n-butyl, iso-butyl, and so on, and 0<_m<_4 (preferably
2_<m54), 1<_a<_3 (preferably 1~a<_2), 0<_b<7 (preferably 0<_b<_3), and
1<_c58 (preferably 2<-:c<_4) .
The molar ratio of Compound (I) to Compound (II) is
normally 100:0.05-10, preferably 100:0.1-8, more preferably
100:0.1-5.
As the he~it-resistant base substance, those
conventionally known may be used.
The cladd~'~_ng layer 3, as a dopant, is made of, for
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example, a silica glass containing B and/or F. Such doped
silica glass can be produced by the well-known Chemical Vapor
Deposition method (CVD method) from a gas mixture of BF3, SiCl4,
and oxygen, BC13, BF3, SiCI,, and oxygen, BCIs, SiF,, and
oxygen, or BFs or BC13, SiF,, and oxygen as a starting
material.
Of the aforementioned material gas mixtures, particularly
preferable is a gas mixture, of BF3, SiCla, and oxygen.
When the material constituting the support layer 4 to be
formed as necessary is a silica glass containing a high degree
of impurities, it may exert undesirable effect on the
ultraviolet resistance to the extent that it can be expressed
numerically. Therefore, the material constituting the support
layer 4 is preferably a synthetic silica glass having a drawing
temperature of at least 1800°~ which is exemplified by natural
silica glasses and synthetic silica glasses, with preference
given to high purity synthetic silica glass having a purity of
not less than,99% by weight, particularly not less than 99.9%
by weight.
The single optical fiber or the bundle fiber consisting of
a number of the fivers are superior in the characteristic at
the ultraviolet region as described earlier, and are extremely
useful as an optical. fiber for use under ultraviolet
irradiation, or as a bundle fiber for medical use.
The present invention is hereinbelow described in detail by
illustrating examples.
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Example 1
Methyltrimethoxysilane (CH3Si(OCH3)3) as a silicon compound
and tetrafluorocarbon (CF4) as a fluorine compound were burnt for
reaction while supplying 700 N ~/h hydrogen gas, $00 N Q/h oxygen
gas, 500 g/h CHaSi(OCHa)s, and 0.44 g/h CF4. The synthesized
silica fine particles were accumulated on a synthetic silica
base substance to give a porous silica sintered product having
an outer diameter of 60 mm and length of 230 mm. This sintered
product was heated in a helium gas at 1550°C under atmospheric
pressure into molten glass to give a silica glass rod having an
outer diameter of about 35 mm, and length of 200 mm. This glass
rod had a chlorine content of 0.1 ppm or below, an OH content of
100 ppm, a fluorine content of 1100 ppm, other impurity content
of 5 ppm, and a refractive index at 20°~ of 1.4575.
The chlorine content of silica glass was measured by
activation analysis, the fluorine content was measured by ion
analysis, and the OH content was estimated from the absorption
loss at a wavelength of 2.73 ~,m by Fourier transform infrared
spectrometer.
Explaining the determination of the OH content, it can be
calculated by the following formula (1) wherein transmissivity
when the OH content at a wavelength of 2.73 um is 0, is To,
actual transmissuvut.y of the measurement subject is T1, and the
thickness (mm) of the measurement subject is L.
1000 To
OH(ppm)= - logio
L T~
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~0~9699
Inserting a core rod (outer diameter: 15 mm) obtained by
drawing the above-mentioned pure silica glass rod into a glass
tube having on its inner surface a B-F-doped silica glass layer
(nz°:1.4465) which was prepared from SiCl4, BFs, Oa, and a
synthetic silica glass tube (outer- diameter: 26 mm, thickness:
1.5 mm, nz°:1.459), there was obtained a three-layer structure
preform (outer diameter: 16.5 mm) by the Rod-In-Tube method,
which was then drawn while heating at 2000°C to give an optical
fiber having an outer diameter of 200 Vim.
Thirteen aforementioned optical fibers (1.5 m in length)
were bundled to give a bundle fiber.
Examples 2-6, Comparative Examples 1-5
Various kinds of core materials were prepared in the same
manner as in Example 1 except that the OH content and F content
in the core material were adjusted by changing the CF4 content
in the material gas, and that tetrach.lorosilane (SiCl4) was used
in place of methyltrimethoxysilane (material gas) in
Comparative Examples 4, 5, 9, and 10 in order to adjust the
chlorine content, and bundle fibers were produced from
respective fibers in the same manner as above. Then, initial
characteristic and resistance to ultraviolet-induced
deterioration of each bundle fiber obtained were determined, the
results of which are: summarized in Table 1 and Table 2.
Test Method
The measurement. was conducted by the method shown in Fig.
3. In Fig. 3, 21 is. a lamp light source, 22 is a DZ lamp, 23 is
1 0
an optical fiber to be tested, and 24 is an instantaneous
measurement multi-system, in which used were the following.
Lamp light source . POWER SUPPLY C-1316
DZ lamp . DEUTERIUMLAMP MC 962A
Mufti-system . MCPD-1100, PC-9801 (personal computer)
Table 1-1
Example
1 2 3
Cl <0.1 <0.1 <0.1
f
iti
on o OH 100 100 60
Compos
core material
(ppm)
F 1100 1400 1000
Initial characte- 400 100 100 100
nm
ristic
250 233 218 160
t nm
th
(ratio
e 230 310 278 232
o nm
output at 400 nm)
(%)
215 405 309 259
nm
3h 250 nm 95 88 93
Resistance to lh 230 nm 97 95 95
b
t
i
ti
d
y
on 3h 230 nm 96 94 93
er
ora
e
ultraviolet rays
(ratio to the 6h 230 nm 94 92 91
t
i
i
l
h
-
in 12h 230 nm 93 90 90
t
a
arac
e
c
ristic at the
th
l
)
same wave lh 215 nm 98 96 99
eng
(%)
3h 215 nm 97 94 97
6h 215 nm 94 89 90
12h 215 nm 89 80 83
1 1
'fable 1-2
Example
4 5 6
C1 <0.1 <0.1 <0.1
iti
n of
m
C
pos ~,r ~., ~.,., ,r.,
o
o
core m--..._:..'
(p
Initia
i
tic
r
s
(
ti
ra
o
output
(~
Resist
i
d
t
er
e
c
ultra
(ratio
i
iti
l
n
a
ristic
~
same w
Table 2-1
Comparative
Example
1 2 3
C1 650 <0.1 <0.1
f
Composition o
core material OH 140 <10 600
(ppm)
F <10 3000 <10
Initial characte- 400 100 100 100
nm
i
ti
r
s
c
250 241 4 341
nm
th
ti
t
(ra
o
e
o
output at 400 nm) 230 341 35 352
nm
(
215 432 40 306
nm
3h 250 nm 79 95
Resistance to lh 230 nm 89 output 92
ti r
b
i
on powe
y
deter
ora
ultraviolet rays 3h 230 nm 86 un- 74
-
measu
(ratio to the 6h 230 nm 82 rably 69
t ll
initial charac sma
e-
ristic at the 12h 230 nm 72 60
gth
l
)
en
same wave
(~) lh 215 nm 93 87
ut
t
ou
p
3h 215 nm 86 power 59
-
un
6h 215 nm 75 measu- 50
r
bl
y
a
12h 215 nm 59 small 39
1 3
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Table 2-2
Comparative Example
4 5
Cl 200 650
f
iti
n
C
ompos __
o OH 550 140
o
core material
(
m)
PP F <10 <10
Initial characte-~ 400 100 100
istic nm
r 250 302 327
(ratio to the nm
output at 400 nm) 230 319 368
(%) nm
215 275 317
nm
3h 250 nm 95 98
Resistance to lh 230 nm 93 97
t
i
ti
n b
d
ora
y 3h 230 nm 80 95
er
o
e
ultraviolet rays
(ratio to the 6h 230 nm ?4 84
h
r
ct
i
iti
l
-
n 12h 230 nm 67 75
a
c
a
a
e
ristic at the
th)
l
same wave lh 215 nm 88 96
eng
(%)
3h 215 nm 68 92
6h 215 nm ~57 78
12h 215 nm ~ 46 ( 60
1 4
~~'~969~
Examples 7-12, Comparative Examples 6-10
The optical fibers bundled in the bundle fibers of Table d
and Table 2 were measured for their characteristics in the same
manner, the results of which are summarized in Table 3 and Table
4, respectively.
Table 3-1
Example
7 8 9
C1 <0.1 <0.1 <p.l
f
iti
C
ompos OH 100 100 60
on o
core material
(PPm)
F 1100 1400 1000
Initial characte-- 400 100 100 100
ti nm
i
r
s 250 226 214 155
c nm
ti
t
th
(ra
o 230 290 2'Z1 229
e nm
o
output at 400 nm;i
~
(
)
Res
t
d
e
e
ult
(rat
i
it
n
rist
same
2079699
Table 3-2
Example
10 11 12
C1 <0.1 <0.1 <0.1
iti
f
C
on o OH 30 200 450
ompos
core material
(ppm)
F 3300 900 200
Initial characte- 400 100 100 100
ti nm
i
r
s 250 120 260 330
c nm
th
ti
t
e
(ra 230 177 340 420
o nm
o
output at 400 nm)
%)
( 215 198 380 465
nm
3h 250 nm 92 90 89
Resistance to lh 230 nm 96 93 90
ti
b
t
i
d
on
y 3h 230 nm 90 8? 84
ora
er
e
ultraviolet rays
(ratio to the 6h 230 nm 88 84 80
t
iti
l
h
-
i
arac 12h 230 nm 84 81 78
e
n
a
c
ristic at the
th
l
eng
) lh 215 nm 99 97 95
same wave
(%)
3h 215 nm 96 89 87
6h 215 nm 89 85 82
12h 215 nm 83 79 74
1 6
~079G9~
Table 4-1
Comparative
Example
6 7 8
Cl <0.1 <0.1 <0.1
f
i
Composit -
on o
core material OH <10 <10 600
(ppm)
E 3000 6000 <10
Initial chara- 400 100 100 100
nm
ti
cteris
c
250 12 12 307
nm
th
ti
t
(ra
o
o
e
output at 400 230 5 9 363
nm
~
)
nm) (
215 12 47 422
nm
3h 250 nm absolute absolute 89
f f
l l
va va
ue o ue o
Resistance to ih 230 nm output output 82
deterioration power power
by
ultraviolet 3h 230 nm unreliably unreliably 78
ll ll
rays sma ,
, sma
6h 230 nm 65
- -
(ratio to the unmeasu unmeasu
initial charac- 12h 230 nm rable rable 47
ti
t th
t
i
er
s
c a
e
same wavelength) ih 2i5 nm absolute absolute 82
f l
l
(~) va va
ue o ue of
3h 215 nm output po- output po- 61
- -
wer unre wer unre
6h 215 nm liably liably 32
ll -
- ll
sma , un
, un sma
12h 215 nm measurable measurable 21
1 7
~o79s~~
Table 4-2
Comparative Example
9 10
Cl 200 650
f
iti
on o OH 550 140
Compos
core material
(ppm)
F <10 <10
Initial characte- 400 100 100
nm
ristic
250 325 154
t nm
th
ti
e
(ra 230 382 201
o nm
o
output at 400 nm)
%
(
) 215 445 231
nm
3h 250 nm 93 83
Resistance to lh 230 nm 86 87
ti
b
on
y 3h 230 nm 73 75
deteriora
ultraviolet rays
(ratio to the 6h 230 nm 60 63
t
-
i
l
h
arac 12h 230 nm 43 47
e
init
a
c
ristic at the
th
l
)
eng lh 215 nm 82 82
same wave
(%)
3h 215 nm 58 69
6h 215 nm 38 27
12h 215 nm 20 20
1 8
