Title: Optical fiber manufacturing method and optical fiber
Abstract: An object of the present invention is to provide an optical fiber manufacturing method and an optical fiber in which an increase in the transmission loss is suppressed by preventing hydroxyl group from entering near the core portion.This invention provides a method for manufacturing an optical fiber 10 including forming a glass pipe 16 by applying a ring portion 15 on the inner face of a starting pipe 14 as a starting material, inserting a glass rod 13 that becomes a central core portion 11 and a depressed portion 12 into the inside of the glass pipe 16, integrating the glass pipe 16 and the glass rod 13 by collapse to form a glass body 17, forming a preform 10a by providing a jacket portion 18 outside the glass body 17, and drawing the preform 10a, wherein the thickness of the starting pipe 14 is set in a range from 4 mm to 8 mm.
Patent Number: 7,010,203 Issued on 03/07/2006 to Yokokawa, et al.
| Inventors:
|
Yokokawa; Tomoyuki (Yokohama, JP);
Yanada; Eiji (Yokohama, JP);
Hirano; Masaaki (Yokohama, JP)
|
| Assignee:
|
Sumitomo Electric Industries, Ltd. (Osaka, JP)
|
| Appl. No.:
|
479852 |
| Filed:
|
April 3, 2003 |
| PCT Filed:
|
April 3, 2003
|
| PCT NO:
|
PCT/JP03/04267
|
| 371 Date:
|
December 8, 2003
|
| 102(e) Date:
|
December 8, 2003
|
| PCT PUB.NO.:
|
WO03/084889 |
| PCT PUB. Date:
|
October 16, 2003 |
Foreign Application Priority Data
| Apr 08, 2002[JP] | 2002-105263 |
| Current U.S. Class: |
385/127; 385/123; 385/124; 385/126; 385/128; 65/385; 65/406; 65/412; 65/427; 65/428; 65/430; 65/435 |
| Current Intern'l Class: |
G02B 6/02 (20060101); G02B 6/22 (20060101) |
| Field of Search: |
385/123-128,141,142,144
|
References Cited [Referenced By]
U.S. Patent Documents
| 2002/0001444 | Jan., 2002 | Hirano et al.
| |
| Foreign Patent Documents |
| 1061054 | Dec., 2000 | EP.
| |
| 1170604 | Jan., 2002 | EP.
| |
| 62-167235 | Jul., 1987 | JP.
| |
| 2001-31438 | May., 1990 | JP.
| |
| 2002-82251 | Nov., 1990 | JP.
| |
| 2001/-253726 | Sep., 2001 | JP.
| |
| 2001/-337245 | Dec., 2001 | JP.
| |
Other References
Bachmann et al. "Stress is Optical Waveguides: Preforms". Applied Optics, vol.
25, No. 7. Apr. 1st 1986. pp 1093-1098.
Ohashi et al. "Imperfection Loss Reduction in Viscosity-Matched Optical Fibers".
IEEE Photonics Technology Letters, vol. 5, No. 7. Jul. 1993. pp 812-814.
Ohashi et al. "Fluorine Concentration Dependence of Viscosity in F-Doped Silica
Glass", Electronics Letters. vol. 28, No. 11, May 21st 1992. pp 1008-1010.
|
Primary Examiner: Healy; Brian
Assistant Examiner: Dupuis; Derek L.
Attorney, Agent or Firm: McDermott Will & Emery LLP
Claims
The invention claimed is:
1. A method for manufacturing an optical fiber comprising the steps of:
forming a glass pipe by coating a glass layer on the inner face of a starting
pipe as a starting material;
inserting a glass rod that becomes a central core portion and a part of a clad
portion into the inside of the glass pipe;
integrating the glass pipe and the glass rod by collapse to form a glass body;
forming a preform by providing a jacket portion outside the glass body; and
drawing the preform, wherein
the thickness of the starting pipe is set in a range from 4 mm to 8 mm; and
at least a portion of said glass layer has a refractive index different from
a refractive index of said starting pipe.
2. A method for manufacturing an optical fiber comprising the steps of:
forming a glass pipe by coating a glass layer on the inner face of a starting
pipe as a starting material;
inserting a glass rod that becomes a central core portion and a part of a clad
portion into the inside of the glass pipe;
integrating the glass pipe and the glass rod by collapse to form a glass body;
forming a preform by providing a jacket portion outside the glass body; and
drawing the preform, wherein
the ratio S
1/S
2 of the cross-sectional area S
1 of the glass
rod to the cross-sectional area S
2 of the starting pipe is set in a range
from 0.03 to 0.30; and
at least a portion of said glass layer has a refractive index different from
a refractive index of said starting pipe.
3. The method for manufacturing the optical fiber according to 2, wherein
the softening temperature of the jacket portion is lower than the softening temperature
of pure silica.
4. The method for manufacturing the optical fiber according to claim 3, wherein
the jacket portion is made of silica glass having chlorine with a concentration
from 0.1 mol % to 1.0 mol % added.
5. The method for manufacturing the optical fiber according to claim 3, wherein
the jacket portion is made of silica glass having fluorine with a concentration
from 0.1 mol % to 1.0 mol % added.
6. The method for manufacturing the optical fiber according to 2, wherein
the drawing tension at the time of drawing is from 60 gf to 350 gf.
7. The method for manufacturing the optical fiber according to 2, wherein
the temperature of a heated portion of the preform at the time of drawing is
from 1600° C. to 2200° C.
8. An optical fiber manufactured by the method for manufacturing the optical
fiber according to 2.
9. The optical fiber according to claim 8, wherein
the dispersion value at a wavelength of 1.55 μm is from (-200) ps/km/nm
to (+4) ps/km/nm.
10. The optical fiber according to claim 8, wherein
the dispersion value at a wavelength of 1.55 μm is from (-400) ps/km/nm
to (+20) ps/km/nm.
11. The optical fiber according to claim 8, wherein
the dispersion value at a wavelength of 1.55 μm is from (-500) ps/km/nm
to (+20) ps/km/nm.
12. The optical fiber according to claim 8, wherein
the dispersion slope at a wavelength of 1.55 μm is from (-2) ps/km/nm
2
to (+0.02) ps/km/nm
2.
13. The optical fiber according to claim 8, wherein
the dispersion slope at a wavelength of 1.55 μm is from (-12) ps/km/nm
2
to (+0.05) ps/km/nm
2.
14. The optical fiber according to claim 8, wherein
the dispersion slope at a wavelength of 1.55 μm is from (-15) ps/km/nm
2
to (+0.10) ps/km/nm
2.
15. The optical fiber according to claim 8, wherein
the transmission loss at a wavelength of 1.55 μm is from 0.2 dB/km to 0.5 dB/km.
16. The optical fiber according to claim 8, wherein
an increased amount of the transmission loss at a wavelength of 1.38 μm
is less than or equal to 0.4 dB/km.
Description
TECHNICAL FIELD
The present invention relates to an optical fiber manufacturing method and an
optical fiber, and more particularly to a method for manufacturing an optical fiber
by inserting a glass rod into a glass pipe having a glass layer on the inside of
a starting pipe, integrating them by collapse, providing a jacket portion on its
outside to form a preform, and drawing the preform, and the optical fiber.
BACKGROUND ART
A conventional method for manufacturing an optical fiber 100 as shown in
FIG. 4 will be described below. FIG. 4A is a view showing the cross section of
the conventional optical fiber 100 and FIG. 4B is a view showing a refractive
index distribution of the optical fiber 100.
First of all, a ring portion 102 is formed by depositing glass particles
on the inner face of a starting pipe 101 as a starting material by the MCVD
method (Modified Chemical vapor Deposition Method, Internal CVD method). Then,
a glass rod 105 having a core portion 103 and a depressed portion
104 is inserted into the ring portion 102 and integrated by rod-in
collapse to fabricate a glass body 106. After a jacket portion 107
is sooted outside the glass body 106, a preform 100
a is produced
by vitrification. Thereafter, the preform 100
a is heated and drawn
to fabricate the optical fiber 100.
In the conventional manufacturing method as described above, the ring portion
102 is formed by the MCVD method, using the starting pipe 101 having
a thickness 101
a from 2 mm to 3 mm. In practicing the MCVD method,
the starting pipe 101 is heated using an oxyhydrogen flame. Further, in
the rod-in collapse and the process of sooting the jacket portion 107, the
starting pipe 101 is also heated using an oxyhydrogen flame. Therefore,
hydroxyl group contained in the oxyhydrogen flame enters the surface of the starting
pipe 101. This hydroxyl group may intrude near the core portion 103,
and when the preform 100
a is the optical fiber 100, light
is absorbed into the hydroxyl group, giving rise to a situation where the transmission
loss is increased.
DISCLOSURE OF THE INVENTION
The present invention is achieved to solve the above-mentioned problems, and
it is an object of the invention to provide an optical fiber manufacturing method
and an optical fiber in which an increase in the transmission loss is suppressed
by preventing hydroxyl group from entering near the core portion.
The present inventor has made minute researches to solve those problems, and
found that one of the causes of hydroxyl group entering near the core portion lies
in the thickness of the starting pipe, or the cross-sectional area ratio of the
glass rod to the starting pipe
In order to achieve the above object, this invention provides a method for manufacturing
an optical fiber including forming a glass pipe by coating a glass layer on the
inner face of a starting pipe as a starting material, inserting a glass rod that
becomes a central core portion and a part of a clad portion into the inside of
the glass pipe, integrating the glass pipe and the glass rod by collapse to form
a glass body, forming a preform by providing a jacket portion outside the glass
body, and drawing the preform, characterized in that the thickness of the starting
pipe is set in a range from 4 mm to 8 mm.
With the above method for manufacturing the optical fiber, the thickness of
the starting pipe is set in a range from 4 mm to 8 mm, though it was conventionally
as thin as 2 mm to 3 mm. Thereby, the distance from the surface of the starting
glass on which hydroxyl group enters to the core portion is made greater. Accordingly,
intruding hydroxyl group is effectively prevented from getting near the core portion,
and an increase in the transmission loss due to hydroxyl group is suppressed.
If the thickness of the starting pipe is below 4 mm, it is estimated that hydroxyl
group gets near the core portion. Further, if the thickness of the starting pipe
is beyond 8 mm, it is difficult to collapse the glass rod within the glass pipe.
Further, if the thickness of the starting pipe is beyond 8 mm, it is difficult
to attain a temperature high enough to vitrify glass particles deposited inside
the starting pipe and apply the glass layer on the inside.
Further, in order to achieve the above object, the invention provides a
method for manufacturing an optical fiber including forming a glass pipe by coating
a glass layer on the inner face of a starting pipe as a starting material, inserting
a glass rod that becomes a central core portion and a part of a clad portion into
the inside of the glass pipe, integrating the glass pipe and the glass rod by collapse
to form a glass body, forming a preform by providing a jacket portion outside the
glass body, and drawing the preform, characterized in that the ratio S1/S2
of the cross-sectional area S1 of the glass rod to the cross-sectional area
S2 of the starting pipe is set in a range from 0.03 to 0.30.
With the above method for manufacturing the optical fiber, the ratio S1/S2
of the cross-sectional area S1 of the glass rod to the cross-sectional area
S2 of the starting pipe is set in a range from 0.03 to 0.30, which is smaller
than conventionally. Thereby, the distance from the surface of the starting glass
on which hydroxyl group enters to the core portion is made greater. Accordingly,
intruding hydroxyl group is effectively prevented from getting near the core portion,
and an increase in the transmission loss due to hydroxyl group is suppressed.
If the ratio S1/S2 is below 0.03, it is difficult to collapse the
glass rod within the glass pipe. Further, if the ratio S1/S2 is beyond
0.30, it is estimated that hydroxyl group gets near the core portion.
With the method for manufacturing the optical fiber according to the invention,
it is desirable that the softening temperature of the jacket portion is lower than
the softening temperature of pure silica.
With the method for manufacturing the optical fiber as constituted above, the
heating temperature for drawing the preform is decreased, whereby an increase in
the transmission loss due to Rayleigh scattering is suppressed. In this invention,
pure silica means silicon dioxide (SiO
2) having a chlorine concentration
of 0.10 mol % or less, a fluorine concentration of 0.10 mol % or less, and a metal
impurity content of 0.1 wtppb or less.
Further, with the method for manufacturing the optical fiber according to
the invention, it is desirable that the jacket portion is made of silica glass
having chlorine with a concentration from 0.1 mol % to 1.0 mol % added.
With the method for manufacturing the optical fiber as constituted above, it
is possible to reduce the scattering by setting the chlorine concentration to the
lower limit value or 0.1 mol % to make the A value as the Rayleigh scattering factor
less than or equal to 2.0 μm
4 dB/km. Further, the strength of
the fiber is prevented from decreasing due to excessive addition of chlorine by
setting the A value to the upper limit value or 1.0 mol %, and the rupture frequency
of the optical fiber in drawing is reduced.
Further, with the method for manufacturing the optical fiber according to
the invention, it is desirable that the jacket portion is made of silica glass
having fluorine with a concentration from 0.1 mol % to 1.0 mol % added.
With the method for manufacturing the optical fiber as constituted above, it
is possible to reduce the scattering by setting the fluorine concentration to the
lower limit value or 0.1 mol % to make the A value as the Rayleigh scattering factor
less than or equal to 2.0 μm
4 dB/km. Further, the strength of
the fiber is prevented from decreasing due to excessive addition of chlorine by
setting the A value to the upper limit value or 1.0 mol %, and the rupture frequency
of the optical fiber in drawing is reduced.
Further, with the method for manufacturing the optical fiber according to
the invention, it is desirable that the drawing tension at the time of drawing
is from 60 gf to 350 gf.
With the method for manufacturing the optical fiber as constituted above, it
is possible to reduce the scattering by setting the drawing tension to the lower
limit value or 60 gf to make the A value as the Rayleigh scattering factor less
than or equal to 2.0 μm
4 dB/km. Further, by setting the drawing
tension to the upper limit value or 350 gf, the drawing tension is prevented from
being excessive to cause a rupture of the optical fiber in drawing.
Further, with the method for manufacturing the optical fiber according to
the invention, it is desirable that the temperature of a heated portion of the
preform at the time of drawing is from 1600° C. to 2200° C.
With the method for manufacturing the optical fiber as constituted above, it
is possible to reduce the scattering by setting the temperature of drawing the
preform to the upper limit value or 2200° C. to make the A value as the Rayleigh
scattering factor less than or equal to 2.0 μm
4 dB/km. Further,
a temperature sufficient to soften the preform is attained by setting the temperature
to the lower limit value or 1600° C., whereby it is possible to prevent a
rupture from being caused by drawing.
Further, in order to achieve the above object, the invention provides an
optical fiber manufactured by the above method for manufacturing the optical fiber
according to the invention.
In the optical fiber as manufactured in the above way, the thickness of the starting
pipe is set in a range from 4 mm to 8 mm, though it was conventionally as thin
as 2 mm to 3 mm, or the ratio of the cross-sectional area of the glass rod to the
cross-sectional area of the starting pipe is set in a range from 0.03 to 0.30,
which is smaller than conventionally. Thereby, the distance from the surface of
the starting glass on which hydroxyl group enters to the core portion is made greater.
Accordingly, intruding hydroxyl group is prevented from getting near the core portion,
and an increase in the transmission loss due to hydroxyl group is suppressed.
Further, in the optical fiber according to the invention, it is desirable
that the dispersion value at a wavelength of 1.55 μm is from (-200) ps/km/nm
to (+4) ps/km/nm.
With the optical fiber as constituted in the above way, the bending loss of
the optical fiber is reduced below a desired value by setting the dispersion value
at a wavelength of 1.55 μm to the lower limit value or (-200) ps/km/nm. Further,
a desired dispersion compensation amount is attained by setting the dispersion
value to the upper limit value or (+4) ps/km/nm.
Further, in the optical fiber according to the invention, the dispersion
value at a wavelength of 1.55 μm may be from (-400) ps/km/nm to (+20) ps/km/nm,
or the dispersion value at a wavelength of 1.55 μm may be from (-500) ps/km/nm
to (+20) ps/km/nm.
Further, in the optical fiber according to the invention, it is desirable
that the dispersion slope at a wavelength of 1.55 μm is from (-2) ps/km/nm
2
to (+0.02) ps/km/nm
2.
In the optical fiber as constituted in the above way, it is possible to compensate
the existing transmission path having various dispersion slopes and dispersion
values for the dispersion at 50% or more by limiting the range of dispersion slope.
Further, in the optical fiber according to the invention, the dispersion
slope at a wavelength of 1.55 μm may be from (-12) ps/km/nm
2 to
(+0.05) ps/km/nm
2, or the dispersion slope at a wavelength of 1.55 μm
may be from (-15) ps/km/nm
2 to (+0.10) ps/km/nm
2.
Further, in the optical fiber according to the invention, it is desirable
that the transmission loss at a wavelength of 1.55 μm is from 0.2 dB/km to
0.5 dB/km.
In the optical fiber as constituted in the above way, the dispersion compensation
amount is increased by limiting the transmission loss to be low.
Further, in the optical fiber according to the invention, it is desirable
that an increased amount of the transmission loss at a wavelength of 1.38 μis
less than or equal to 0.4 dB/km.
In the optical fiber as constituted in the above way, if an increase in the transmission
loss due to hydroxyl group is suppressed low, it is possible to utilize the short
wavelength bands such as the C band from wavelength 1.53 μm to 1.57 μm,
the L band from wavelength 1.57 μm to 1.62 μm, the E band from wavelength
1.40 μm to 1.48 μm and the S band from wavelength 1.48 μm to
1.53 μm.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing a preform and an optical fiber fabricated by the method
for manufacturing the optical fiber according to an embodiment of the present invention,
in which FIG. 1A is a cross-sectional view of the preform (or optical fiber), and
FIG. 1B is a view showing a refractive index distribution of the optical fiber.
FIGS. 2A and 2B are views showing a variation example of the embodiment as
shown in FIG. 1.
FIG. 3 is a graph representing the relation between the thickness of a glass
pipe and the transmission loss at a wavelength of 1.55 μm.
FIG. 4 is a view showing a preform and an optical fiber fabricated by the conventional
method for manufacturing the optical fiber, in which FIG. 4A is a cross-sectional
view of the preform (or optical fiber), and FIG. 4B is a view showing a refractive
index distribution of the optical fiber.
In the drawings, reference numeral 10 denotes the optical fiber, 10
a
denotes the preform, 11 denotes a central core, 12 denotes a
depressed portion (first clad portion), 13 denotes a glass rod, 14
denotes a starting pipe, 15 denotes a ring portion (glass layer), 16
denotes a glass pipe, 17 denotes a glass body, and 18 denotes a jacket portion.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIGS. 1 and 2, an optical fiber manufacturing method and
an optical fiber according to an embodiment of the present invention will be described below.
FIG. 1 is a view showing the optical fiber and a preform of the optical fiber
according to the embodiment of the invention, in which FIG. 1A is a cross-sectional
view of the preform (or optical fiber), and FIG. 1B is a view showing a refractive
index distribution of the optical fiber. Further, FIG. 2 is a view showing a variation
example of the embodiment as shown in FIG. 1.
As shown in FIG. 1, the preform
10a of the optical fiber
10
according to this embodiment has a central core portion
11 with a high refractive
index in the center, and a depressed portion
12 as a first clad portion
with a lower refractive index around the core portion. A ring portion
15
as a second clad portion with a slightly higher refractive index than pure silica
is formed outside the depressed portion
12. Moreover, a starting pipe
14
composing a third clad portion and a jacket portion
18 are provided around
the ring portion
15. The optical fiber
10 is obtained by drawing
this preform
10a.
The present inventor has made acute researches to prevent hydroxyl group from
entering near the central core portion
11 in producing the optical fiber
10, and found that the thickness
14a of the starting pipe
14 should be set in a range from 4 mm to 8 mm to suppress the transmission
loss of optical fiber at a wavelength of 1.55 μm below a tolerance of 0.5
dB/km. Further, the inventor has found that the ratio S
1/S
2 of the
sum S
1 of the cross-sectional areas of the central core portion
11
and the depressed portion
12 to the cross-sectional area S
2 of the
starting pipe
14 should be set in a range from 0.03 to 0.30.
A method for manufacturing the optical fiber
10 as shown in FIG. 1 will
be described below.
First of all, a glass layer serving as the ring portion
15 is applied
on the inner face of the starting pipe
14 made of quartz glass as the starting
material by the MCVD method, to produce a glass pipe
16. More particularly,
the MCVD method involves supplying a source gas to the inside of the starting pipe
14, heating the starting pipe
14 from the outside by an oxyhydrogen
burner while rotating the starting pipe
14, producing glass particles from
the source gas and depositing them on the inside of the starting pipe
14.
At this time, a plurality of glass layers are applied on the inside of the starting
pipe to form the ring portion
15 by reciprocating the oxyhydrogen burner
in the longitudinal direction of the starting pipe
14.
In this embodiment, the starting pipe
14 is a quartz pipe having a thickness
of 4 mm to 8 mm. The thickness
14a of this starting pipe
14
is greater than the thickness
101a (2 mm to 3 mm) of the conventional
starting pipe
101 as previously described. The source gas supplied to the
inside of the starting pipe
14 to apply layers on the inside of the ring
portion
15 maybe silicon tetrachloride (SiCl
4) or germanium tetrachloride (GeCl
4).
Then, the glass rod
13 having the central core portion
11 and
the depressed portion
12 is inserted into the inside of the glass pipe
16,
and integrated by rod-in collapse to form a glass body
17. More particularly,
the rod-in collapse is made by heating the glass pipe
16 from the outside,
employing the oxyhydrogen burner, while rotating the glass rod
13 and the
glass pipe
16 in a state where the glass rod
13 is inserted into
the inside of the glass pipe
16. Thereby, at least the glass pipe
16
contracts due to surface tension, so that the glass rod
13 is secured onto
the inside of the glass pipe
16 without clearance.
The glass rod
13 has an outer diameter of 8 mm and comprises the central
core portion
11 made of silica (SiO
2) with germanium (Ge) added
and having a maximal specific refractive index difference of (+1.6) % and the depressed
portion
12 made of silica (SiO
2) with fluorine (F) added and
having a minimal specific refractive index difference of (-0.5) %. The specific
refractive index difference as used herein means a difference in the refractive
index of the central core portion
11 or the depressed portion
12
with respect to the refractive index of pure silica.
At this time, the ratio S
1/S
2 of the cross-sectional area S
1
of the glass rod
13 composed of the central core portion
11 and the
depressed portion
12 to the cross-sectional area S
2 of the starting
pipe
14 is set in a range from 0.03 to 0.30.
Then, the jacket portion
18 is provided outside the glass body
17
to form the preform
10a. The jacket portion
18 is obtained
by combusting a source gas containing silicon tetrachloride and oxyhydrogen gas,
employing a multi-pipe burner and depositing glass particles produced thereby on
the outside of the glass body
17 (referred to as sooting).
At this time, the jacket portion
18 has desirably a softening temperature
lower than the softening temperature of pure silica Further, the jacket portion
18 is desirably made of silica glass having chlorine with a concentration
from 0.1 mol % to 1.0 mol % added. Or the jacket portion
18 may be made
of silica glass having fluorine with a concentration from 0.1 mol % to 1.0 mol
% added.
And the preform
10a is heated up to the temperature from 1600°
C. to 2200° C., and drawn to fabricate the optical fiber
10. At this
time, the drawing tension is desirably set in a range from 60 gf to 350 gf. By
drawing the preform under the above set-up conditions, the A value that is a Rayleigh
scattering factor is set to 2.0 μm
4 dB/km or less to suppress
an increase in the transmission loss due to Rayleigh scattering.
With the optical fiber manufacturing method and the optical fiber
10
as described above, the thickness
14a of the starting pipe
14
is set in a range from 4 mm to 8 mm, or the ratio S
1/S
2 of the cross-sectional
area S
1 of the glass rod
13 to the cross-sectional area S
2
of the starting pipe
14 is set in a range from 0.03 to 0.30, whereby the
distance from the central core portion
11 to the surface of the starting
pipe
14 is set to be larger than conventionally.
Accordingly, the hydroxyl group entering the surface of the starting
pipe
14 is prevented from entering near the central core portion
11
when forming the glass pipe
16 by the MCVD method, forming the glass body
17 by rod-in collapse, and forming the jacket portion
18 by sooting.
Hence, it is possible to suppress an increase in the transmission loss due to hydroxyl group.
With the optical fiber
10 as described above, since it is possible to
suppress an increase in the transmission loss due to hydroxyl group, the transmission
loss α
1 at a wavelength of 1.55 μm is easily suppressed within
a range 0.2≦α
1≦0.5 dB/km. Further, an increased amount
Δα
2 in the transmission loss at a wavelength of 1.38 μm
due to hydroxyl group is suppressed to 0.4 dB/km or less.
Herein, if the lower limit value of the dispersion value at a wavelength
of 1.55 μm is set to (-200) ps/kn/nm, the bending loss of the optical fiber
is suppressed below a desired value. Further, if the upper limit value of the dispersion
value at a wavelength of 1.55 μm is set to (+4) ps/kn/nm, a desired dispersion
compensation value is attained. Further, the optical fiber
10 may have the
dispersion value at a wavelength of 1.55 μm in a range from (-400) ps/km/nm
to (+20) ps/km/nm, or the dispersion value at a wavelength of 1.55 μm in
a range from (-500) ps/km/nm to (+20) ps/km/nm.
Further, if the dispersion slope at a wavelength of 1.55 μm is limited
in a range from (-2) ps/km/nm
2 to (+0.02) ps/km/nm
2, the
dispersion of the existing transmission path having various dispersion slopes and
dispersion values is highly compensated at 50% or more. Further, the optical fiber
10 may have the dispersion slope at a wavelength of 1.55 μin a range
from (-12) ps/km/nm
2 to (+0.05) ps/km/nm
2, or from (-15)
ps/km/nm
2 to (+0.10) ps/km/nm
2.
Thereby, the optical fiber
10 may be employed as a dispersion compensating
optical fiber (DCF) for compensating for the dispersion of non-zero dispersion
shift fiber (NZ-DSF).
Further, for the optical fiber
10, the ratio S
3/S
4
of the sum S
3 of cross-sectional areas of the central core portion
11
and the depressed portion
12 composing the glass rod
13 in the preform
before drawing to the cross-sectional area S
4 of the portion that is the
starting pipe
14 in the preform before drawing is desirably from 0.03 to 0.30.
The cross-sectional area S
3 of the glass rod
13 in the preform
is specified by measuring the refractive index distribution with an RNFP (Refracted
Near Field Pattern) or measuring a radial distribution of germanium by an EPMA
(Electron Probe Micro Analyzer). Further, the cross-sectional area S
4 of
the starting pipe
14 in the preform is specified by observing an interface
between the starting pipe
14 and the jacket portion
18 as a step
difference by etching the cross section of the optical fiber
10.
Further, the optical fiber manufacturing method and the optical fiber according
to this invention is applicable the optical fiber having a structure of four-fold
clad and the manufacturing method of this optical fiber, as shown in FIG. 2.
A method for manufacturing the optical fiber
20 as shown in FIG. 2 will
be described below.
First of all, a glass layer serving as a second depressed portion
25
and a glass layer serving as a ring portion
26 are applied on the inner
face of a starting pipe
24 by the MCVD method, and made a glass pipe
27.
Herein, the starting pipe
24 has a thickness
24a of 4 mm to
8 mm, like the starting pipe
14 as previously described.
Then, a glass rod
23 having a central core portion
21 and a first
depressed portion
22 is inserted into the inside of the glass pipe
27,
and integrated by rod-in collapse to form a glass body
28.
Then, a jacket portion
29 is provided outside the glass body
28
to form a preform
20a.
The optical fiber
20 is produced by drawing the preform
20a.
At this time, the cross-sectional are of the glass rod
23 corresponds
to
the cross-sectional area S
1, and the cross-sectional area of the starting
pipe
24 corresponds to the cross-sectional area S
2. Accordingly,
the distance from the central core portion
21 to the surface of the starting
pipe
24 is set to be larger than conventionally.
FIRST EXAMPLE
A first example of the optical fiber manufacturing method and the optical fiber
according to the invention will be described below.
Seven kinds of optical fibers are produced by setting the thickness of the
starting pipe 14 as shown in FIG. 1 in a range from 2 mm to 8 mm at every
1 mm in accordance with the above embodiments. For these optical fibers, the transmission
loss at a wavelength of 1.55 μm is measured and evaluated by comparison.
The method for manufacturing the optical fiber in the first example will be described below.
First of all, the ring portion 15 as the glass layer is applied on the
inner face of the starting pipe 14 by the MCVD method to form the glass
pipe 16. At this time, the starting pipe 14 had an inner diameter
of 28 mm and a thickness of 2 mm to 8 mm and is made of quartz glass. That is,
the outer diameter of the starting pipe 14 is changed from 30 mm to 36 mm
with increased thickness. The gases supplied to the ring portion 15 applied
on the inside of the starting pipe 14 included silicon tetrachloride, germanium
tetrachloride and oxygen. The supply amounts of gases are 200 sccm (standard cm
3/min)
for SiCl
4, 45 sccm for GeCl
4 and 2500 sccm for O
2.
The heating temperature of oxyhydrogen flame for heating the starting pipe 14
is set at 1600° C., and ten layers of glass particles are deposited. Thereby,
the ring portion 15 having the maximal specific refractive index difference
of (+0.3) % is formed.
Then, the glass rod 13 having the central core portion 11 and
the depressed portion 12 as the first clad portion is inserted into the
inside of the glass pipe 16, and integrated by collapse to form the glass
body 17. The central core portion 11 is made of silica with germanium
added and had a maximal specific refractive index difference of (+1.6) % with respect
to pure silica. The depressed portion 12 is made of silica with fluorine
added and had a minimal specific refractive index difference of (-0.5) % with respect
to pure silica. The outer diameter of the glass rod 13 is 8 mm.
Then, the jacket portion 18 with an outer diameter of 46 mm is sooted
on the outside of the glass body 17, employing an oxyhydrogen multi-pipe
burner, to form the preform 10
a.
The preform 10
a is heated up to a temperature of 1800° C.
and drawn, and covered with ultraviolet curable resin to fabricate the optical
fiber 10 having an outer diameter of 185 mm. At this time, the drawing tension
is set to 200 gf.
For seven kinds of optical fibers produced in the above way, the transmission
loss at a wavelength of 1.55 μm is measured. The measurement results are
shown in FIG. 3.
As shown in FIG. 3, for the optical fibers in which the starting pipe had the
thickness of 2 mm and 3 mm, the transmission loss is beyond a tolerance of 0.5
dB/km. On the contrary, for the optical fibers in which the starting pipe had the
thickness of 4 mm, 5 mm, 6 mm, 7 mm and 8 mm, the transmission loss is at or below
the tolerance of 0.5 dB/km.
From the above results, it is found that the transmission loss of the optical
fiber is suppressed below the tolerance by setting the thickness of the starting
pipe to 4 mm to 8 mm.
SECOND EXAMPLE
A second example of the optical fiber manufacturing method and the optical fiber
according to the invention will be described below.
Three kinds of optical fibers (A, B and C) are produced by changing the ratio
S1/S2 of the cross-sectional area S1 of the glass rod 13
to the cross-sectional area S2 of the starting pipe 14. For these
optical fibers, the transmission loss at a wavelength of 1.55 μm is measured
and evaluated by comparison.
The method for manufacturing the optical fiber in the second example is roughly
the same as in the first example, except that the cross-sectional area ratio S1/S2
is changed employing the glass rod 13 having a different outer diameter
and the starting pipe 14 having different outer diameter and thickness.
In the optical fiber A, the glass rod in the preform had an outer diameter of
8.0 mm, and the starring rod had an outer diameter of 34.0 mm and a thickness of
6.5 mm. That is, the ratio S1/S2 of the cross-sectional area S1
of the glass rod to the cross-sectional area S2 of the starting pipe is
0.09. For this optical fiber A, the transmission loss at a wavelength of 1.55 μm
is 0.31 dB/km.
In the optical fiber B, the glass rod in the preform had an outer diameter of
10.0 mm, and the starring rod had an outer diameter of 34.0 mm and a thickness
of 4.0 mm. That is, the cross-sectional area ratio S1/S2 is 0.21.
For this optical fiber B, the transmission loss at a wavelength of 1.55 μm
is 0.30 dB/km.
In the optical fiber C, the glass rod in the preform had an outer diameter of
10.0 mm, and the starring rod had an outer diameter of 25.0 mm and a thickness
of 5.0 mm. That is, the cross-sectional area ratio S1/S2 is 0.25.
For this optical fiber C, the transmission loss at a wavelength of 1.55 μm
is 0.30 dB/km.
From the above results, it is found that the transmission loss of the optical
fiber is suppressed below the tolerance when the ratio S1/S2 of the
cross-sectional area S1 of the glass rod to the cross-sectional area S2
of the starting pipe is from 0.03 to 0.30, because the transmission loss is within
the tolerance of 0.5 dB/km.
Though the present invention is particularly shown and described in connection
with the specific embodiments, it will be apparent to those skilled in the art
that various changes and modifications in form and details may be made therein
without departing from the spirit and scope of the invention.
This application is based on JP-A-2002-105263, filed on Apr. 8, 2002, its contents
being fully incorporated herein.
[Industrial Applicability]
As described above, with the optical fiber manufacturing method and the optical
fiber according to the invention, when the thickness of the starting pipe is set
in a range from 4 mm to 8 mm, hydroxyl group entering on the surface of the starting
glass is effectively prevented from getting near the core portion, and an increase
in the transmission loss due to hydroxyl group is suppressed.
Further, when the cross-sectional area ratio of the glass rod to the starting
pipe is set in a range from 0.03 to 0.30, hydroxyl group entering on the surface
of the starting glass is effectively prevented from getting near the core portion,
and an increase in the transmission loss due to hydroxyl group is suppressed.
*
