U.S. patent application number 10/627875 was filed with the patent office on 2005-05-12 for method for producing base material for optical fiber having deformed first clad, base material for optical fiber and optical fiber.
This patent application is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Abe, Jun, Ejima, Seiki, Makikawa, Shinji, Mantoku, Nobuyasu.
Application Number | 20050100306 10/627875 |
Document ID | / |
Family ID | 17722060 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050100306 |
Kind Code |
A1 |
Abe, Jun ; et al. |
May 12, 2005 |
Method for producing base material for optical fiber having
deformed first clad, base material for optical fiber and optical
fiber
Abstract
There is disclosed a method for producing a base material for
optical fiber having a deformed first clad consisting of at least a
core, a first clad and a second clad, comprising a step of
deforming a shape of a section of the first clad so that it may
have at least one linear part when the first clad is formed around
the core, a step of depositing porous glass fine particles as the
second clad made of the same material as that of the first clad on
a glass rod having the deformed first clad to form a porous glass
base material, and a step of forming the second clad having a round
section by vitrifying it. There can be provided a method for
producing a base material for optical fiber wherein a lot of
breakages or cracks on the surface of the base material can be
prevented in a step of depositing porous glass fine particles for
the second clad on the first clad, and base material for optical
fiber having no defects, and an optical fiber having an efficient
effect of being excited with excitation light.
Inventors: |
Abe, Jun; (Annaka, JP)
; Mantoku, Nobuyasu; (Annaka, JP) ; Makikawa,
Shinji; (Annaka, JP) ; Ejima, Seiki; (Annaka,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Shin-Etsu Chemical Co.,
Ltd.
6-1, Ohtemachi 2-chome, Chiyodu-ku
Tokyo
JP
|
Family ID: |
17722060 |
Appl. No.: |
10/627875 |
Filed: |
July 28, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10627875 |
Jul 28, 2003 |
|
|
|
09670019 |
Sep 26, 2000 |
|
|
|
6681074 |
|
|
|
|
Current U.S.
Class: |
385/146 |
Current CPC
Class: |
C03B 37/01228 20130101;
C03B 37/01225 20130101; Y02P 40/57 20151101; C03B 37/01231
20130101; C03B 2203/12 20130101; C03B 2203/22 20130101; G02B
6/03633 20130101; G02B 6/0283 20130101 |
Class at
Publication: |
385/146 |
International
Class: |
G02B 006/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 1999 |
JP |
11-287810 |
Claims
1. A quartz base material for an optical fiber having a deformed
first clad consisting of at least three refractive index area,
namely a core, a deformed first clad and a second clad wherein a
section of the first clad has a deformed shape with at least one
linear part and the second clad has a round section, and the main
material of the first clad and the second clad are the same, and a
length of the longest part of the deformed section of the first
clad is 15 mm or less.
2. The base material for an optical fiber having a deformed first
clad according to claim 1 wherein the shape of the section of the
first clad is D-shape, a square shape or a drum shape.
3. The base material for an optical fiber having a deformed first
clad according to claim 1 wherein the refractive index of the first
clad is distributed so that it may gradually decreases from the
center to the periphery.
4. The base material for an optical fiber having a deformed first
clad according to claim 2 wherein the refractive index of the first
clad is distributed so that it may gradually decreases from the
center to the periphery.
5. An optical fiber having a deformed first clad produced by
wiredrawing the base material for optical fiber according to claim
1.
6. An optical fiber having a deformed first clad produced by
wiredrawing the base material for optical fiber according to claim
2.
7. An optical fiber having a deformed first clad produced by
wiredrawing the base material for optical fiber according to claim
3.
8. An optical fiber having a deformed first clad produced by
wiredrawing the base material for optical fiber according to claim
4.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The present invention mainly relates to an optical fiber for
amplification that corresponds to tendency of being high-powered of
a light amplifier or a fiber laser, an base material for optical
fiber that is a material therefor, and a method for producing
it.
[0003] 2. Description of the Related Art
[0004] Recently, a light amplifier for system construction of DWDM
(Dense Wavelength Division Multiplexing) has been strongly required
to be high-power. Furthermore, there has been required high-power
also in the field of fiber laser. In both cases, excitation light
is introduced in quartz optical fiber wherein rare earth element is
doped in the core, and emission of the rare earth element is used,
and it is necessary for achievement of high-power to excite the
core with the excitation light efficiently.
[0005] Recently, there was proposed a method called clad pumping
for the purpose as described above (Japanese Patent Application
Laid-open (kokai) No. 11-72629).
[0006] There is disclosed in Japanese Patent Application Laid-open
(kokai) No. 11-52162 a double core type optical fiber for
amplification wherein a second core is formed around a first core.
In the optical fiber, for example, a heterogeneous part wherein a
refractive index is different from the second core is formed, a
part of the periphery of the second core is cut out, or the
periphery is formed in polygonal shape, as scattering means for
scattering the light that does not contribute to excitation of a
signal light incident upon the first core among the excitation
light incident upon the second core so that it may cross with the
first core as possible. In order to produce such an optical fiber,
the second core is formed around the first core by sooting to form
a sintered glass, a part of the periphery is then cut out, and it
is then coated with plastic with being wiredrawn to form a clad. An
optical fiber for amplification is thereby produced.
[0007] In that case, the shape of the section of the second core
(that corresponds to the first clad of the present invention) can
be a deformed shape other than circle (D-shape, polygonal shape,
drum shape), and quartz glass fine particles made of the same
material as the second core can be formed by sooting thereon, to be
deposited so that a shape of the section can be round. However, it
was quite difficult to realize it for a problem in production
thereof. Namely, breakages or cracks often occur on the surface of
the base material in a process of cooling the porous quartz glass
base material that is formed by sooting on the second core having a
deformed shape, resulting in reduction of yield of the base
material, and lowering of productivity. Accordingly, in most cases,
polymer clad, for example those made of low refractive index
polymer such as fluorinated acrylic acid, urethane acrylate, PMMA
has been adopted as a clad, and the second core having a deformed
shape has been coated with such plastics with being wiredrawn, to
form a clad. However, there is a problem in production that not
only wiredrawing of base material, but also a coating process, and
a drying process are necessary in order to produce a polymer clad.
Furthermore, there are problems in quality, such as bad adhesion
property with the second core, difficulty in controlling a
refractive index, low resistance to deterioration, low mechanical
strength. Accordingly, there is a strong need for a quartz glass
clad having excellent resistance to deterioration and stable
properties.
SUMMARY OF THE INVENTION
[0008] The present invention has been accomplished to solve the
above-mentioned problems, and a main object of the present
invention is to provide a method for producing a base material for
optical fiber wherein a lot of breakages or cracks on the surface
of the base material can be prevented in a step of depositing
porous glass fine particles for the second clad on a glass rod
having a deformed first clad and cooling it, and base material for
optical fiber having no defects, and an optical fiber having an
efficient effect of being excited with excitation light.
[0009] In order to achieve the above-mentioned object, the present
invention provides a method for producing a base material for
optical fiber having a deformed first clad comprising at least a
core, a first clad and a second clad comprising a step of deforming
a shape of a section of the first clad so that it may have at least
one linear part when the fist clad is formed around the core, a
step of depositing porous glass fine particles as the second clad
made of the same material as that of the first clad on a glass rod
having the deformed first clad to form a porous glass base
material, and a step of forming the second clad having a round
section by vitrifying it.
[0010] If the base material for optical fiber is produced according
to the above-mentioned method, especially breakage and cracks that
are liable to be formed in the step of forming the second clad by
depositing porous glass fine particles on a glass rod having a
deformed shape of a section can be prevented, so that a base
material for an optical fiber having the second clad having no
defect and the deformed first clad can be produced in high yield,
and in high productivity. Furthermore, since the deformed shape is
introduced into the section of the first clad, efficient incidence
of the excitation light can be enabled, optical fibers wherein
output light is increased can be produced. Moreover, since the
deformed first clad and the second clad are made of the same
material, the optical fiber having a stable refractive index
distribution and excellent resistance to deterioration can be
produced.
[0011] In that case, a length of the longest part of the deformed
section of the glass rod having the first clad is preferably 15 mm
or less.
[0012] As described above, if the length of the longest part of the
deformed section of the glass rod having the deformed first clad
that is to be a target is 15 mm or less in production of a porous
glass base material by axially depositing porous glass fine
particles on the glass rod having a deformed first clad, breakage
and crack on the surface of the base material that are liable to
occur in a cooling step after deposition can be prevented almost
completely, so that the optical fiber having the second clad with
no defects and the deformed first clad can be produced.
[0013] The present invention also provides a base material for
optical fiber having a deformed first clad produced by the method
described above. The optical fiber is a base material having a high
quality wherein there is no defect such as breakage, crack or the
like, particularly on the surface of the base material that is to
be a front surface of the second clad. Since the deformed first
clad having a deformed section with at least one linear part is
formed, efficient incidence of excitation light is possible through
the base material, so that an optical fiber that can emit high
power light can be produced.
[0014] The present invention also provides a quartz base material
for an optical fiber consisting of at least three refractive index
area, namely a core, a deformed first clad and a second clad
wherein section of the first clad has a deformed shape with at
least one linear part and the second clad has a round section, and
the main material of the first clad and the second clad are the
same.
[0015] Using the base material for optical fiber having a deformed
first clad with the above mentioned constitution, optical fiber
wherein excitation light efficiently exciting the signal light
incident on the core through the base material can be incident can
be produced by wiredrawing. As a result, high-power can be achieved
in a light amplifier or a fiber laser.
[0016] In that case, the shape of the section can be D-shape, a
square shape or a drum shape.
[0017] When the shape of the section is the above mentioned shape,
excitation efficiency of exciting light for exciting a signal light
can be increased.
[0018] In that case, it is preferable that the refractive index of
the first clad is distributed so that it may gradually decreases
from the center to the periphery. Thereby, it is possible to make
the excitation light concentrate at the core that is a center of
the fiber, so that excitation efficiency can be further
improved.
[0019] The present invention also provides an optical fiber having
a deformed first clad produced by wiredrawing the base material for
optical fiber described above. As described above, the optical
fiber having a deformed first clad produced by wiredrawing the base
material for optical fiber of the present invention is an optical
fiber for light amplification that has no defects such as a crack
and has high performance such as high excitation efficiency.
Accordingly, it can easily achieve high-power in a light amplifier
and a fiber laser or the like, and has high durability.
[0020] There were problems such as breakage or cracks occurs when a
glass rod having a deformed section such as D-shape is axially
deposited a porous glass fine particles made of the same material.
However, according to the present invention, they can be solved.
Especially, they could be solved by defining a length of the
longest part of the deformed section of the glass rod having a
deformed first clad that is to be a target to be 15 mm or less.
Accordingly, high yield and improvement in productivity can be
achieved in production of the base material for optical fiber
having a deformed section in a first clad, and thereby cost can be
reduced.
[0021] Furthermore, since there can be produced a base material for
optical fiber having a deformed first clad with no defects such as
crack or the like on the surface of the second clad and the
deformed first clad which are made of the same material, excitation
light can be efficiently incident on a signal light incident on the
core, and output light can be increased as a result, in the optical
fiber produced therefrom. Thereby high-power in a light amplifier
and a fiber laser can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a view for explanation showing the deformed
section and the longest part of the deformed section of the base
material for optical fiber of the present invention.
[0023] (a) D-shape section, (b) a distribution chart of refractive
index on the D-shape section, (c) a square shape section, (d) a
drum shape section.
DESCRIPTION OF THE INVENTION AND A PREFERRED EMBODIMENT
[0024] The present invention will be further described below in
detail, but is not limited thereto.
[0025] The base material for the optical fiber having the deformed
first clad of the present invention is a quartz base material for
optical fiber that is a base material for optical fiber for
amplifying light consisting of at least three refractive index
areas, namely a core, a deformed first clad and a second clad
wherein a shape of a section of the first clad is deformed so that
it may have at least one linear part, the shape of the section of
the second clad is round, the first clad and the second clad are
made of the same main components.
[0026] Although the following explanation is conducted as for base
material for optical fiber, description as for the construction and
performance of the base material can also be applied to the optical
fiber having a similar figure produced by wiredrawing the base
material for optical fiber.
[0027] FIG. 1 is a sectional view of the base material for optical
fiber having a deformed first clad of the present invention. The
base material for optical fiber 1 consists of a core 2 at the
center, the first clad 3 having a deformed section and the second
clad 4 having a round section. The shape of the deformed section of
the first clad is a deformed shape having at least one linear part.
As shown in FIG. 1, examples of the deformed shape include: (a)
D-shape, (c) square shape, (d) drum shape, or the like. If a mean
for scattering light having a deformed shape described above is
provided, light that does not pass through but crosses the core
among the excitation light that is incident upon the first clad in
the case that the clad has a round section can be reflected and
scattered at the linear part, and cross the core to pass through.
As a result, the core can be pumped and can excite a signal light
efficiently.
[0028] It is possible to distribute refractive indexes of the first
clad so that they can get smaller gradually form the center to the
periphery. As described in FIG. 1(b), there are three refractive
index areas of the core, the first clad and the second clad, and
the refractive index of the core is the highest. The refractive
indexes in the first clad are distributed so that they may get
smaller gradually from the center to the periphery. The refractive
indexes in the second clad are distributed flat.
[0029] If the refractive indexes of the first clad are distributed
as described above, light gathers efficiently to the core with
transmission of light, so that light can be amplified with high
excitation efficiency.
[0030] According to the present invention, main components of the
first clad and the second clad are the same material.
[0031] As described above, in a conventional method of producing
the base material for optical fiber for light amplification having
a deformed first clad, it is quite difficult to deposit quartz
glass fine particles made of the same material around the first
clad to form a second clad in a round shape by sooting, in the case
that the sectional shape of the first clad is not round but in a
deformed shape (D-shape, square shape, drum shape or the like).
Furthermore, breakage or cracks often occur on the surface of the
porous glass base material during a cooling process.
[0032] Accordingly, low refractive index polymer has been adopted
for the clad, and a glass rod having the deformed first clad has
been coated with the polymer with being wiredrawn to form the
second clad. However, to produce a polymer clad, it is necessary to
conduct not only wiredrawing of the base material, but also a step
of coating polymer and a drying step. Furthermore, there are
problems in quality such as poor adhesion property with the first
clad, difficulty in controlling the refractive index, poor
resistance to deterioration, and poor mechanical strength, or the
like. Accordingly, there is a strong need for a quartz glass clad.
The inventors of the present invention solved the above problems,
and succeed in making the first clad and the second clad of the
same main components according to the following method.
[0033] The method for producing the base material for optical fiber
and the optical fiber described above will be explained below.
[0034] (1) In order to the base material for optical fiber, a glass
rod consisting of the core and the deformed first clad is produced
first by the method exemplified below.
[0035] (1-1) For example, according to the VAD method, porous glass
fine particles are deposited on the core rod. The resulting porous
glass base material is sintered, vitrified to produce a glass rod
consisting of the first clad and the core. Then, the surface of the
glass rod is subjected to grinding, polishing or the like so that a
desired deformed section having at least one linear part can be
obtained, to produce a glass rod having the deformed first
clad.
[0036] (1-2) A glass rod consisting of a first clad and a core is
produced by inserting a core rod in a glass tube to be the first
clad, fusing them to be unified, according to a rod in tube method.
Then, the surface of the glass rod was subjected to grinding,
polishing or the like, so that a desired deformed section having at
least one linear part can be obtained, to produce a glass rod
having the deformed first clad.
[0037] (1-3) The surface of the glass tube to be the first clad is
subjected to grinding, polishing or the like, so that a desired
deformed section having at least one linear part can be obtained.
Then, a core rod is inserted in the glass tube, fused to be
unified, according to a rod in tube method.
[0038] In that case, during depositing the second clad, it is
preferable to make a length of the longest part of the deformed
section of the glass rod having a deformed first clad to be a
target 15 mm or less, especially 10 mm or less. The longest part
is, for example, the longest part L of each of deformed sections
(a) D-shape, (c) square shape, (d) drum shape as shown in FIG.
1.
[0039] The reason why the length of the longest part of the
deformed section of the glass rod is defined as described above is
that if it exceeds 15 mm, porous glass fine particles depositing
layer is shrunken during cooling after deposition of the porous
glass fine particles as the second clad, resulting in many
breakages and cracks on the surface of the base material, in
extreme cases, in occurring of the cracks even in the first clad,
so that the material will be inferior goods. The occurrence of the
breakage and the crack is considered to be caused by lost of the
balance of stress due to heat shrinkage of the porous glass fine
particle layer on the glass rod, which is a target, since the
section of the glass rod is not round. Accordingly, if the length
of the longest part of the deformed section of the glass rod is
kept to be short, the ratio of the length of the peripheral part
that is not round in periphery of the deformed section to the
length of the periphery of the porous glass fine particle
depositing layer gets small relatively, so that heat stress with
shrink of the peripheral part that is not round during cooling can
be small, and breakage, crack or the like can be prevented from
occurring.
[0040] The length of longest part L of 15 mm or less can be
achieved by drawing the glass rod produced in the above-mentioned
step (1) with a glass lathe or the like. The drawing can be
conducted before or after the processing of deforming the first
clad.
[0041] (2) Then, the porous glass fine particles made of the same
material as the first clad are deposited as the second clad on the
glass rod having the deformed first clad to produce a porous glass
base material, which is then sintered, vitrified to produce base
material for optical fiber on which the second clad is formed.
[0042] Since the shape of the section of the glass rod on which the
second clad is deposited and vitrified is not circle in most cases,
it should be processed to be the second clad having a round section
by grinding, polishing or the like in order to be finished as an
base material for optical fiber.
[0043] In that case, the porous glass base material on which the
second clad is deposited may be processed to have a round section,
and vitrified to form the second clad having a round section.
[0044] If the optical fiber is produced by wiredrawing the base
material for optical fiber produced by the processes described
above, the quartz optical fiber for amplifying light having the
deformed first clad coated with the second clad made of the same
material can be produced.
[0045] There are no defects such as cracks in the second clad or
the deformed first clad in the optical fiber. Accordingly, high
quality, high excitation efficiency of excitation light due to the
deformed first clad and high-power output light can be achieved in
the optical fiber.
EXAMPLE
[0046] The present invention will be explained with example and
comparative examples.
Example
[0047] A glass rod was produced according to VAD method, which was
then drawn to have a diameter of 3 mm, yielding a core rod. A
difference in a refractive index of the core rod was +0.3% (based
on pure quartz level).
[0048] A glass rod in the region of the first clad was produced
according to VAD method, and drilling was conducted to form a hole
having an inner diameter of 5 mm at the center of the glass rod.
Then, the core rod produced above was inserted in the hole, and
then was collapsed on a glass lathe to be unified. As described
above, the glass rod having the core/the first clad was
produced.
[0049] Then, it was drawn to have a diameter of 10 mm, and a part
of the glass rod was ground to be linear so that the section may be
D-shape. Porous glass fine particles were deposited around the
glass rod having a section of D-shape according to VAD method, and
was vitrified in an atmosphere of fluorine to yield a glass base
material (preform) wherein the second clad was formed. Then the
periphery of the preform was ground to have a round section, and
was finished to be base material for optical fiber.
[0050] Twenty base material for optical fibers were produced by the
method, and no crack occurred.
Example 2
[0051] A glass rod having a core and a first clad was drawn to have
a diameter of 20 mm, and a part of the glass rod was ground to be
linear so that the shape of the section may be D-shape. Porous
glass fine particles were deposited around each of 20 glass rods
having a section of D-shape according to VAD method. Cracks
occurred in 20 glass rods all obtained by the conventional method.
However, cracks did not occur in 16 of 20 glass rods obtained by
the method of the present invention, and thereby the base material
for the optical fiber having the second clad with a round section
could be produced. In four of them, breakage and crack occurred in
a step of cooling the porous glass fine particles after
deposition.
[0052] The present invention is not limited to the above-described
embodiment. The above-described embodiment is a mere example, and
those having the substantially same structure as that described in
the appended claims and providing the similar action and effects
are included in the scope of the present invention.
[0053] For example, base material for optical fiber was produced
according to VAD method or a rod in tube method. However, the
present invention is not limited to such methods, and can be
applied to OVD method and MCVD method.
* * * * *