Note: Descriptions are shown in the official language in which they were submitted.
CA 02570905 2007-01-05
METHOD AND APPARATUS FOR HEATING FUSIGN SPLICED PORTION
OF OPTLCAL FIBERS AND OPTICAL FIBER ARRAY
This is a divisional application of Canadian Patent
Application Serial No. 2,395,148 filed on July 25, 2002.
Background of the Invention
Field of the Invention
The present invention relates to heating a fusion
spliced portion of optical fibers, after the dissimilar
optical fibers having the different mode field diameters or
core diameters are fusion spliced. More particularly, the
present invention relates to a method and apparatus for
heating a fusion spliced portion of optical fibers so that
the optical losses associated with the slicing (hereinafter
referred to as a splice loss) are low, and an optical fiber
array manufactured using the same method and apparatus. It
should be understood that the expression "the invention" and
the like encompasses the subject matter of both the parent
and the divisional application.
Description of the Related Art
In recent years, a hybrid optical fiber has been
developed in which a high performance optical fiber having
a smaller mode field diameter such as an optical fiber for
wavelength division multiplexing transmission or an
optical fiber for Raman amplification and a normal single
mode optical fiber having a relatively large mode field
diameter are combined. In splicing the high performance
optical fiber and the normal single mode optical fiber
which are different in a mode field diameter or core
diameter (hereinafter referred to as a core diameter) of
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optical fiber, it is difficult to achieve a practical low splice
loss simply by fusion splicing. Hence, there is provided a
well-known method (Thermally Expanded Core, hereinafter
referred to as a TEC) in which the fusion spliced portion of
optical fibers is heated and tapered to equalize the core
diameters of the splicing portion, and make a smooth splicing
shape (refer to Japanese Patent No. 2618500).
Figs. 9a and 9B are views showing one example of a TEC
process including heating a fusion spliced portion: Fig. 9A
is a view showing the TEC process of heating the fusion spliced
portion of optical fibers using a burner after fusion splicing
the optical fibers having different core diameters. Fig. 9B
is a view showing a state of the fusion splicedportion of optical
fibers after the TEC process as shown in Fig. 9A. In the figures,
reference numeral la, lb denotes an optical fiber, 2 denotes
a glass fiber portion (cladding portion) , 3a, 3b denotes a core
portion, 4 denotes the fiber coatings, 5 denotes a fusion spliced
portion, 6 denotes a burner, and 7 denotes a core expanded region.
The optical fibers la and lb to be fusion spliced together
have the same outer diameter of the glass fiber portion (cladding
portion) 2, but are different in the core diameter of the core
portions 3a and 3b and the specific refractive index difference.
End faces of the optical fibers la and lb to be spliced are
disposedoppositely, fusedusingarcdischarge, and butt jointed,
as shown in Fig. 9A. Simply by making the fusion splicing, the
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splicing is discontinuous at the fusion spliced portion 5,
because of a difference in the core diameter between the core
portion 3a of the optical fiber la and the core portion 3b of
the optical fiber lb. This discontinuity causes a large splice
loss.
To improve this discontinuity, the TEC process is
conducted by heating a vicinity of the fusion spliced portion
5 through the use of a micro torch.or the burner 6 with a combustion
gas . This heating is made at the temperature and for the time
where the optical fibers la and lb themselves are not melted,
but a dopant agent, which raises the refractive index, added
to the core portions 3a and 3b is di ffused to the claddingportion.
After this heating process, the dopant agent added to the core
portions 3a and 3b is diffused to the cladding portion 2, so
that the core diameter of the core portions 3a and 3b is expanded.
It diffuses more in case of the optical fiber la having a smaller
core diameter and a higher dopant concentration than the optical
fiber lb having a larger core diameter and a lower dopant
concentration.
By performing the TEC process, the core diameter of the
core portion 3a for the optical fiber la having smaller core
diameter is expanded in taper form, thereby reducing a
discontinuity from the core portion 3b of the optical fiber
lb having larger core diameter, as shown in Fig. 9B. In the
case where the dissimilar optical fibers are fusion spliced
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together, it has been found that the TEC.process allows the
core diameter of the optical fiber having smaller core diameter
to gradually approximate the core diameter of the other optical
fiber, thereby reducing a splice loss. Also, it has been known
that the TEC process by heating is ef fective to reduce the splice
loss due to the core eccentricity by expanding the core diameter
of the fusion spliced portion even if similar optical fibers
are spliced (refer to Japanese Patent Unexamined Publication
No. Sho. 61-117508).
Summary of the Invention
The present invention has been achieved in the light of
the above-mentioned problems. It is an object of the invention
to provide a method and apparatus for heating a fusion spliced
portion of optical fibers, and an optical fiber array
manufactured using the same, in which when the TEC process is
performed for the fusion spliced portion of optical fibers for
the purpose of loss improvement after the dissimilar optical
fibers are fusion spliced, the optical fibers are not deformed
due to heating, the fiber coatings are not burnt, the ribbon
shaped optical fibers are not dispersedly heated, and the TEC
length is restricted within a predetermined range.
However, for obtaining a high-strength splice using a
fusion splice method, a method has been employed in which the
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length for removing the fiber coatings and exposing the glass
fiber portion 2 is made as short as possible (about 2 to 5 mm) ,
and the fiber coatings 4 are directly clamped. In this case,
coating removal ends 8 of the fiber coatings 4 may be burnt
or melted by a flame of the burner 6, as shown in Fig. 10A.
Therefore, it is required that the fiber coatings 4 should be
removed to the position fully farther away from the flame of
the burner 6, enabling the fusion splicing with high strength.
Also, it is required in the TEC process that the heating
is made at the temperature and for the time sufficient for the
dopant agent of the core portions 3a and 3b to be diffused to
the cladding portion 2. The optical fibers la and lb are usually
heated below the melting point, but a heated portion 9 is
sometimes softened too much to cause a slack due to a dead weight
of the optical fiber, as shown in Fig. lOB. If the optical fibers
are kept deformed due to slack, it may cause loss increase.
Furthermore, a flame of the burner has uneven temperature
distribution and broadening, and the flame is fluctuated due
to the outer environments, whereby it is difficult to control
the flame in a constant heating condition. Therefore, if the
TEC length is dispersed, and the area subj ected to the TEC process
is increased beyond necessity, the optical fiber is inconvenient
for handling in the manufacture, and unfavorable in respect
of the strength. In the case where such an optical fiber is
incorporated into optical parts such as an optical fiber array,
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the optical parts can not be miniaturized and packaged at high
density.
In an optical fiber ribbon, an assembly with 8 fibers,
12 fibers or 24 fibers may be fusion spliced together and
subjected to the TEC process. In this case, a flame of the burner
6 has the higher heating temperature in the outer portion of
the flame than in the center, which result in non-uniformly
heating the optical fibers, as shown in Fig. lOC. This causes
a problem that the TEC process has a difference between the
outer fiber and the inner fiber in an optical fiber ribbon,
leaving a difference in the loss among the fibers within the
optical fiber ribbon.
According to the present invention, there is provided
a method for heating a fusion spliced portion of optical fibers
respectively having different mode field diameters, the method
comprising: mounting a vicinity of the fusion spliced portion
of optical fibers on a heating board; and heating the heating
board using a heat source so that the vicinity of the fusion
spliced portion of optical fibers is heated via the heating
board.
Further, according to the invention, there is provided
an apparatus for heating a fusion spliced portion of a pair
of optical fibers respectively having different mode field
diameters, the apparatus comprising: a heating board for
mounting a vicinity of the fusion spliced portion of optical
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fibers thereon; and a heat source for heating the heating board
so that the vicinity of the fusion spliced portion of optical
fibers is heated via the heating board.
Also, according to the invention, there.is provided an
$ optical fiber array comprising: at least apairof optical fibers
respectively having different mode field diameters, which are
fusion spliced; and a substrate having a convex portion being
in contact with a vicinity of a fusion spliced portion of the
optical fibers on an inner face of the substrate.
In another aspect, the invention provides a method
for heating a fusion spliced portion of optical fibers
respectively having different mode field diameters, the
method comprising mounting a vicinity of the fusion
spliced portion of optical fibers on a heating board, and.
heating the heating board using a heat source so that the
vicinity of the fusion spliced portion of optical fibers
is heated via the heating board, wherein the mounting step
includes mounting the fusion spliced portion of optical
fibers in contact with a convex portion provided in the
heating board so that the fusion spliced portion of
optical fibers is heated via the convex portion of the
heating board.
In another aspect, the invention provides a method
for heating a fusion spliced portion of optical fibers
respectively having different mode field diameters, the
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method comprising mounting a vicinity of the fusion
spliced portion of optical fibers on a heating board,
heating the heating board using a heat source so that the
vicinity of the fusion spliced portion of optical fibers
is heated via the heating board, enclosing the optical
fibers by a lid member having both side portions being in
contact with the heating board, and filling an inorganic
powder material around the optical fibers in a gap between
the heating board and the lid member.
In another aspect, the invention provides a method
y
for heating a fusion spliced portion of optical fibers
respectively having different mode field diameters, the
method comprising mounting a vicinity of the fusion
spliced portion of optical fibers on a heating board,
heating the heating board using a heat source so that the
vicinity of the fusion spliced portion of optical fibers
is heated via the heating board, and enclosing the optical
fibers on the heating board with an inorganic powder
material.
In another aspect, the invention provides an
apparatus for heating a fusion spliced portion of a pair
of optical fibers respectively having different mode field
diameters, the apparatus comprising a heating. board for
mounting a vicinity of the fusion spliced portion of
optical fibers thereon, and a heat source for heating the
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heating board so that the vicinity of the fusion spliced
portion of optical fibers is heated via the heating board,
wherein the heating board has a convex portion for
mounting the vicinity of the fusion spliced portion of
optical fibers thereon so that the vicinity of the fusion
spliced portion of optical fibers is heated via the convex
portion.
Brief Description of the Drawings
Figs. lA-1C are views for explaining a first embodiment
of the present invention;
Figs. 2A-2C are views for explaining a second embodiment
of the invention;
Figs . 3A-3C are views for explaining a third embodiment
of the invention;
IS Figs _ 9A-9C,are.views for explaining a fourth embodiment
of the invention;
Figs . 5A and SB are views for explaining a fifth embodiment
of the invention;
Figs . 6A and 6B are views for explaining a sixth embodiment
°f the invention;
Fig. 7~ is a view showing an example of employing an
exothermic resistive heater for a heating.source of the
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invention;
Figs. 8A-8D are views showing an example of an optical
fiber array according to the invention;
Figs . 9A and 9B are views for explaining the conventional
heating method and TEC process; and
Figs. l0A-lOC are views for explaining the problems
associated with the prior art.
Detailed Description of the Invention
Figs. lA-1C show a first embodiment of the present
invention. Figs, lAand 1B are views showing how a fusion spliced
portion is heated on a heating board. Fig. 1C is a view showing
a state where the fusion spliced portion of optical fibers is
subjected to the TEC process by heating. In Figs. lA and 1B,
reference numeral 11, 12 denote the heating board. Other parts
are designated by the same numerals as shown in Figs. 9A and
9B, and the description of them is omitted.
Thedissimilaroptical fibers la andlbtobe fusionspliced
together have substantially the same outer diameter of a glass
fiber portion (cladding portion) 2, but are different in the
mode field diameter (hereinafter referred to as a core diameter)
of the core portions 3a and 3b and the specific refractive index
difference in the same manner as shown in Figs. 9A and 9B. For
instance, the core diameter of the optical fiber la is about
Sun, and the core diameter of the optical fiber lb is about
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10~m. End faces of the optical fibers la and lb to be spliced
are disposed oppositely, fusion spliced using an arc discharge,
as shown in Fig. lA. Simply by fusion splicing, the splicing
is discontinuous in the fusion spliced portion 5, due to a
difference in the core diameter between the core portion 3a
of the optical fiber la and the core portion 3b of the optical
fiber lb. This discontinuity causes a large splice loss.
To solve the discontinuous state in the core portions
3a and 3b, the TEC process is performed by heating a vicinity
of the fusion spliced portion S. In this invention, the heating
board 11 is employed for heating, and the optical fibers after
being fusion spliced are mounted on the heating board 11, which
is then heated by a burner 6. That is, the vicinity of the fusion
spliced portion 5 of the optical fibers is heated via the heating
board 11 . The heating board 11 is formed of ceramics, preferably
aluminum nitride, which has an excellent heat resistance and
thermal conductivity and has a thermal expansion coefficient
close to that of optical fiber glass. Though being expensive
in respect of the cost, diamond may be used. Particularly, when
aluminum nitride is used, the heating board can be finished
with small surface roughness not to damage a glass fiber portion
that is contacted.
The optical fibers la and lb are heated by thermal
conduction and radiation from the heating board 11, but not
directly burnt by a flame from the burner 6. Therefore, the
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optical fibers la and lb can be heated substantially uniformly.
Since the optical fibers la and lb are mounted on the heating
board 11, the optical fibers la and lb are not slackedor deformed,
even if being softened by heating, thereby preventing the splice
loss from increasing, as shown in Figs. 10A-lOC.
The heating board 12 of Fig. 1B has a length L in an optical
fiber axial direction that is defined as the length in which
the end portions of the optical fiber coatings 4 are shielded
from the field of view of the burner 6, and a length X of a
convex portion 12a being in contact with the optical fibers
la and lb that is defined as the TEC length. The range of heating
the vicinity of the fusion spliced portion 5 mounted on the
convex portion 12a of the heating board 12 is limited by the
length X of the convex portion 12a, allowing the heating to
be made in uniform temperature distribution. Thereby, the TEC
area is prevented from extending more than necessary. The bottom
portion of the heating board 12 is extended near the end portions
of the fiber coatings 4, thereby preventing the end portions
of the fiber coatings 4 from being burnt or melted by a flame
of the burner, as shown in Fig. 10A.
The optical fibers are heated via the heating board 11,
12 at the temperature and for the time where the optical fibers
la and lb themselves are not melted, but a dopant agent added
to the core portions 3a and 3b is diffused to the cladding port ion
2. Since the temperature of the heating board 11, 12 is easily
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detected, the heating can be easily controlled. By this heating,
the dopant agent added to the core portions 3a and 3b is dif fused
to the cladding portion 2; so that the core diameter of the
core portions 3a and 3b is expanded to have a core expanded
region 7. It diffuses more in case of the optical fiber la having
a smaller core diameter and a higher dopant concentration than
the optical fiber lb having a larger core diameter and a lower
dopant concentration. By performing the TEC process, the core
diameter of the core portion 3a of the optical fiber la having
smaller core diameter is expanded more in taper form than the
core portion 3b of the optical fiber lb, thereby reducing a
discontinuity between the core portion 3a of the optical fiber
la and the core portion 3b of the optical fiber lb, as shown
in Fig. IC.
Figs. 2A-2C show a second embodiment of the present
invention. Fig. 2A shows an example of a single optical fiber,
Fig. 2B shows an example of a ribbon shaped optical fiber, and
Fig. 2C shows another example of heating. In Figs. 2A-2C,
reference numeral 13 denotes a heating board, 14 denotes a
V-groove, and 15 denotes a lid member . Other parts are designated
by the same numerals as shown in Figs . lA-1C, and the description
of them is omitted.
In this embodiment, the optical fibers la and lb mounted
on the heating board 13 are lightly pressed by the lid member
15, and kept from detaching from the heating board 13. The optical
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fibers la and lb are securely contacted with the heating board
13 to make the thermal conduction uniform and enable the stable
heating. The heating board 13 and the lid member 15 are formed
of ceramics that has an excellent heat resistance and thermal
conductivity and has a thermal expansion coefficient close to
that of the optical fiber glass, as in Figs. lA-1C. The burner
6 is disposed beneath a lower face of the heating board 13 to
uniformly heat a predetermined range of the optical fibers la
and lb via the heating board 13, thereby effecting the TEC
process.
In this second embodiment, the heating board 13 can be
configured with a groove on its upper face. The shape of the
groove is preferably a V-groove 14 typically employed for
positioning the optical fiber, as shown in Figs. 2A-2C. In a
case of the ribbon shaped optical fibers as shown in Fig. 2B,
exhaust nozzles of flame of the burner 6 are provided like a
matrix to heat an array of the optical fibers uniformly. In
the case of the ribbon shaped optical fibers, no flame of the
burner 6 is directly applied to the optical fibers, or turned
round the optical fibers, whereby the heating temperature is
not dif ferent over the array of optical f fibers due to temperature
differences between the central part and the outer part of the
flame, as shown in Fig. lOC. Accordingly, the TEC process can
be performed uniformly for all the ribbon shaped optical fibers .
Since the optical fibers la and lb are held in the V-groove
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14 of the heating board 13, the contact area of optical fibers
with the heating board 13 is increased and the radiation of
heat from the lateral face of optical fibers is also increased,
as compared with the case of Figs . lA-1C, whereby the uniformity
of heating is enhanced. Since the optical fibers are pressed
by the lid member 15, they are positioned at high precision.
Even if the optical fibers la and lb are softened by heating,
the optical fibers la and lb are not curved, but are kept straight .
The burner 6 may be disposed on the side of the lid member
15 to apply heat from the side of the lid member 15. In this
case, the lid member 15 serves as the heatingboard. Furthermore,
the burners 6 may be disposed on both sides of the heating board
13 and the lid member 15 to apply heat from both the upper and
lower sides, as shown in Fig. 2C. Thereby, the uniformity of
heating the optical fibers can be enhanced.
Figs. 3A-3C show a third embodiment of the present
invention. Fig . 3A shows a perspective view of the heating board,
Fig. 3B is a view showing an example of employing the V-groove,
and Fig. 3C is a view showing an example of employing a
semi-spherical groove. In Fig. 3C, reference numeral 16 denotes
the semi-spherical groove. Other parts are designated by the
same numerals as shown in Figs. 2A-2C, and the description of
them is omitted.
This embodiment is a variation of Fig. 2C, in which the
heating boards 13 with the V-groove 14 are provided on both
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the upper and lower sides. That is, the V-groove 14 is provided
on the side of the lid member 15 as well. The optical fibers
la and lb are positioned and heldby the upper and lower V-grooves
14, with high positioning precision, and because the burners
6 are disposed on both the upper and lower sides, the uniformity
of heating can be more excellent than in the case of Fig . 2C .
In Fig. 3C, the semi-spherical groove 16 is formed instead
of the V-groove 14 fox positioning the optical fibers la and
lb in Fig. 3B. Though.not shown in the figure, the burner 6
may be disposed on any one of the lower side and the upper side,
or on both the lower and upper sides, employing the heating
board 13 with the semi-spherical groove 16 and the lid member
without groove, as shown in Figs. 2A-2C. The groove for
positioning the optical fibers la and lb is the semi-spherical
15 groove 16, whereby the contact area with the optical fibers
la and lb is broadened. Accordingly, the heating board with
the semi-spherical groove 16 can enhance more uniformity of
heating than with the V-groove 14.
Figs. 4A-4C show a fourth embodiment of the present
invention. Fig. 4A shows a view showing an example of a single
core optical fiber, Fig. 4B is a view showing an example of
a ribbon shaped optical fiber, and Fig. 4C is a view showing
another example of heating. In Figs. 4A-9C, the same or like
parts are designated by the same numerals as shown in Figs.
2A-2C, and the description of them is omitted.
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As shown in the example of Figs . lA, if an upper portion
of the optical fiber mounted on the heating board 13 is exposed,
it is supposed that the heat is diffused from an exposed face
of the optical fiber under certain working conditions, resulting
in non-uniformity of the heat. Tf the upper side of optical
fiber is covered by the lid member 15 as shown in the example
of Figs. 2A, but both sides of the heating board 13 and the
lid member 15 are opened, it is supposed that the heat is likely
to escape from both sides of the heating board 13 and the lid
member 15, similarly resulting in non-uniformity of the heat.
Thus, in this fourth embodiment, the lid member 15 has the leg
portions 15c which are shaped so that both sides of the lid
member 15 may be in contact with the upper face of the heating
board 13, thereby enclosing the whole heated portion of the
optical fibers la and lb mounted on the heating board 13.
With this constitution, the diffusion of heat can be
suppressed by reducing the exposed face in the heated portion
of the optical fiber. The heat of the heating board 13 is
transferred via the leg portions 15c to the lid member 15, so
that the optical fibers la and lb are heated from the side of
the lid member 15, resulting in the improvement of the heating
efficiency and the uniformity of heating. Since the leg portions
15c of the lid member 15 are in contact with the surface of
the heating board 13, the function of pressing the optical fibers
la and lb against the heating board 13 as shown in Figs . 2A-2C
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may become weaker, however, the heating and the uniformity of
heat can be maintained by enclosing the outer periphery of the
optical fibers using the lid member and leg portions.
In the case of the ribbon shaped optical fiber as shown
in Fig. 4B, the lid member 15 is heated via the leg portions
15c, and all the optical fibers are heated from the side of
the lid member 15, enhancing the heating efficiency and
uniformityof heat. Furthermore, the lid member l5 may be heated
by the burner 6 as shown in Fig. 4C, in the same manner as in
the example of Fig. 2C. In this case, the temperature of the
heating board 13 and the lid member 15 is made even through
the leg portions 15c, whereby the uniformity of heating all
the optical fibers can be further enhanced.
Figs. 5A and 5B show a fifth embodiment of the present
invention. Fig. 5A shows a view showing an example of a single
core optical fiber, and Fig. 5B is a view showing an example
of a ribbon shaped optical fiber. In Figs. 5A and 5B, reference
numeral 17 denotes an inorganic powder material. Other parts
are designated by the same numerals as shown in Figs. 2A-2C,
and the description of them is omitted.
As shown in the example of Figs. 9A-9C, if there is any
gap between the heating board 13 or the lid member 15 and the
optical fibers even though the heated portions of the optical
fibers la and lb are not exposed, it is supposed that the heating
is not made uniformly. Since the air has poor thermal
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conductivity, it is supposed that the heatingboardlacks thermal
uniformity depending on whether the portion of the optical fiber
is in contact with the heating board 13 or the lid member 15
or not. Thus, in this fifth embodiment, a concave portion for
enclosing the optical fibers that is formed from the legportions
15c of the lid member 15 as shown in Figs. 4A-4C is made slightly
larger, and the inorganic powder material 17 is filled in this
concave portion. Therefore, the gap around the optical fibers
is reduced as much as possible.
The inorganic powder material 17 may be fine powder, ~ such
as aluminum nitride powder, having excellent thermal
conductivity at a melting point as high as at least a softening
temperature of the optical fiber glass. This inorganic powder
material has flowability by adding solvent such as water or
alcohol, and then filled in the gap portion. In the case where
the V-groove 14 is provided on the heatingboard 13, the inorganic
powder material is preferably filled in the gap port ion developed
between the V-groove and the optical fibers . The water or alcohol
is vaporized by heating, but because the gap portion to be filled
is minute, the inorganic powder remains within the gap, reducing
the volume. of gap, and transferring the heat from the heating
board 13 and the lid member 15, whereby the heating of the optical
fibers la and lb can be made uniform.
Figs. 6A and 6B show a sixth embodiment of the present
invention. Fig. 6A shows a view showing an example of a single
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core optical fiber,, and Fig. 6B is a view showing an example
of a ribbon shaped optical fiber. In Figs. 6A and 6B, the same
or like parts are designated by the same numerals as shown in
Figs. 2A-2C and 5A-5B, and the description of them is omitted.
As shown in the example of Figs. 5A and 5B, there is some
difficulty in the workability in filling the inorganic powder
material 17 in the concave portion, because the flow out of
powder material or the amount of filling is cared about. Thus,
in this sixth embodiment, the inorganic powder material 17 is
directly added on the optical fibers la and lb mounted on the ,
heating board 13, without employing the lid member 15. The
inorganic powder material 17 is mixed into the resin that is
relatively thermal resistant, and made like clay, thereby
securing the.optical fibers la and lb on the heating board 13,
employing a mold. In the case where the V-groove 14 is provided
on the heating board 13, the inorganic powder material is
preferably filled in a gap port ion developedbetween the V-groove
and the optical fibers . The powder material that is not clay-like
may be directly filled in the V-groove 14.
The inorganic powder material 17 wholly encloses the
exposed heated port ions of the optical fibers la and lb to prevent
the heat diffusion from the exposed portions. Therefore, the
heat transferred from the heating board 13 to the inorganic
powder material 17 is also applied from the side of the exposed
portions of the optical fibers, thereby heating the optical
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fibers uniformly. At high temperatures, the resinmaterial which
binds the inorganic material is burnt or carbonized, and
consequently the resin material is removed, particularly
causing no problem.
Fig. 7 is a view showing a seventh embodiment in which
an exothermic resistive heater is employed instead of the burner .
In Fig. 7, reference numeral 18 denotes the exothermic resistive
heater, 19 denotes a temperature detector, and 20 denotes a
temperature controller. Other parts are designated by the same
numerals as shown in Figs. 2A-2C, and the description of them
is omitted. The exothermic resistive heater 18 is embedded into
the heating board 13 or the lid member 15, as shown in Fig.
7, but it may be attached on or disposed adj acent to an outer
surface of the heating board 13 or the lid member 15. The heating
temperature of the heating board 13 or the lid member 1S can
be easily detected by the temperature detector 19 embedded
therein or attached on the outer surface . Atemperature detection
signal from this temperature detector 19 is input into the
temperature controller 20 to adjust a heater current, and control
the heating temperature of the heating board 13 or the lid member
15, whereby the TEC process can be ef fected with easy and stable
temperature control.
Figs. 8A-8D are views showing an example of an optical
fiber array for use with the coupling with a planar waveguide
according to the invention. Fig. 8A is a view showing a TEC
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process state, Fig. 8B is a view showing a state after the TEC
process, Fig. 8C is a view showing the optical fiber array,
and Fig. 8D is a view showing the cross section a-a of the optical
fiber array. In Figs. 8A-8D, reference numeral 21 denotes an
adhesive and 22 denotes a sectional plane. Other parts are
designated by the same numerals as shown in Figs. lA-1C and
2A-2C, and the description of them is omitted.
In coupling the optical fiber with the planar waveguide,
the optical fiber having a small core diameter is employed to
couple with the planar waveguide, and the optical fiber having
an ordinary core diameter is employed for the line. Therefore,
in the optical fiber array for coupling, the optical fiber having
small core diameter is fusion spliced at the top end of the
optical fiber having ordinary core diameter. The fusion spliced
portion is subjected to the TEC process to reduce the splice
loss. However, if the TEC length is longer, the optical fiber
array dimension is increased, preventing the miniaturization
and high density packaging of optical parts. Also, there was
inconvenience in handling at the time of manufacturing the
optical fiber array, but the problems can be solved by using
the heating board of the invention.
In Fig. 8A, the optical fibers la having small core diameter
and the optical fiber lb having large core diameter that are
fusion spliced are mounted on the heating board 13 having the
V-groove for single fiber or plurality of fibers, and pressed
CA 02570905 2007-01-05
and positioned by the lid member 15, as shown in Fig. 2B. The
heating board 13 and the lid member 15 are formed of ceramics
that has an excellent heat resistance and thermal conductivity,
with a thermal expansion coefficient close to that of the optical
fiber glass.
The heating board 13 and the lid member 15 respectively
have convex portions 13a and 15a for obtaining a predetermined
TEC length and convex portions 13b and 15b for positioning the
optical fiber la correctly. The heating board 13 and the lid
member 15 have the length which is longer than a distance between
the end portions of the fiber coatings 4 for the optical fibers
la and lb. The length of the convex portion 13a and 15a being
in contact with the optical fibers la and lb is set to obtain
the predetermined TEC length. The convex portions 13b and 15b
can be provided farther away from the convex portions 13a and
15a. The heating board 13 and the lid member 15 for the optical
fiber are heated by the burner 6, and the TEC process is pre formed
in the vicinity of the fusion spliced portion of the optical
fibers la and lb.
Fig. 8B shows a state after the TEC process, in which
a core expanded region 7 is formed in the vicinity of the fusion
spliced portion of the optical fibers la and lb, where the core
diameters 3a and 3b of the optical fibers la and lb increase
gradually within the core expanded region 7 as approaching near
to the fusion splice point, finally they match each other.
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Therefore, a discontinuous state of the core diameters is matched
by smoothly tapering. After the TEC process is performed, the
heating board 13 and the lid member 15 are not removed, but
directly employed as a substrate of the optical fiber array.
By flowing the adhesive 21 into a gap portion between the optical
fibers la and lb, the heating board 13 and the lid member 15,
the optical fibers la and lb are integrated together with the
heating board I3 and the lid member 15. Thereafter, the optical
fiber la having smaller core diameter is cut in the middle with
a part of the heating board 13 and the lid member 15 at the
position indicated by the chain line Y-Y.. The convex portions
13b and 15b for positioning the optical fiber la is also removed
by this cutting.
Fig. 8C shows an optical fiber array 23 formed by cutting
and removing the optical fiber larva cut sectional plane 22
being polished. On the sectional plane 22, the optical fiber
la having smaller core diameter is exposed, and coupled with
an optical path of the planar waveguide, and on the other side,
the optical fiber lb having larger core diameter is sealed with
the adhesive 21 and led out. The heating board 13 and the lid
member 15 are employed as the substrates 13' and 15' constituting
the optical fiber array. Fig. 8D shows a cross section a-a of
the optical fiber array 23, in which a plurality of optical
fibers la are correctly positioned in the V-groove 14, and the
adhesive 21 is filled between the substrates 13' and 15' and
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in the gap between the optical fibers and the substrates 13'
and 15' to integrate the optical fibers and the substrates.
The heating board 13 and the lid member 15 have a heating
area accurately restricted by the convex portions 13a and 15a,
and formed in a predetermined TEC length, whereby the optical
fiber array can be configured in the least dimension as required.
If the heating board 13 and the lidmember 15 are employeddirectly
as the substrates 13' and 15' of the optical fiber array 23,
it is unnecessary to remove the optical fibers from the heating
board 13 and incorporate them into another substrate, resulting
in better workability. Furthermore, the optical fibers may be
damaged during the operation for carrying the optical fibers
that are removed from the heating board after the TEC process
onto the substrate, but there is less chance of causing such
damages to produce the reliable optical fiber array. The
application to optical parts has been described above, using
the example of the optical fiber array, but the invention may
be applied to other optical parts containing the fusion spliced
portion of dissimilar optical fibers.
As shown in Figs. 5A and 5B, in producing the optical
fiber array 23 of Fig. 8C, the inorganic powder material is
filled between the convex portions 13a and 15a that are then
subjected to the TEC process by heating. In this optical fiber
array 23, the heating board 13 and the lid member 15 can be
directly employed as the substrates 13' and 15', whereby it
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is not always required that the inorganic powder material is
removed. Accordingly, in this case; the inorganic powder
material may be melted by heating and have adhesive property,
whereby the inorganic adhesives mainly composed of silica or
alumina (e.g., Ceramuse SA2000 made by Byorogos Inc.) may be
used. The glass fine powder having low melting point (e. g.,
alumina sealing glass powder or ceramics sealing glass powder
with low expansion made by Nippon Electric Glass Co., Ltd.)
may be employed with the addition of water or alcohol to be
easily filled.
The inorganic adhesive f il led in the gap between the convex
portions 13a and 15a of the substrates 13' and 15' and the optical
fibers la and lb prevents the heat from dissipating in the TEC
process through the gap portion, thereby heating the optical
fibers la and lb uniformly. Also, the adhesive may serve to
integrate the substrates 13' and 15' and the optical fibers
la and lb after heating.
As will be apparent from the above description, with the
present invention, the optical fibers are prevented from being
softened and deformed by heating for the TEC process, and the
fiber coatings are prevented from being burnt . For the ribbon
shaped optical fiber, the TEC process can be made by
substantially uniformly heating all the optical fibers.
Furthermore, the TEC length can be limited in a predetermined
area, and the spliced optical fibers are obtained reliably,
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at high quality, and with small splice loss, and reduced in
size.
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