U.S. patent application number 09/800033 was filed with the patent office on 2002-06-27 for method of processing end portions of optical fibers and optical fibers having their end portions processed.
Invention is credited to Murakami, Keiji, Ootsu, Kenji, Tai, Tomishige.
Application Number | 20020081072 09/800033 |
Document ID | / |
Family ID | 18863330 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081072 |
Kind Code |
A1 |
Ootsu, Kenji ; et
al. |
June 27, 2002 |
Method of processing end portions of optical fibers and optical
fibers having their end portions processed
Abstract
An end portion of an optical fiber element 11 is dipped into an
etchant to shape that portion of the fiber element immersed in said
etchant into a coaxial reduced-diameter portion by etching while
causing that portion of the fiber element where the etchant rising
to a certain height above the level surface of the etchant due to
surface tension into a conical tapered surface portion which is
formed between the reduced-diameter portion and un-etched portion
of the fiber element, and subsequently thereafter, the
reduced-diameter portion is cut to have a very short length thereof
remained.
Inventors: |
Ootsu, Kenji; (Tokyo,
JP) ; Murakami, Keiji; (Tokyo, JP) ; Tai,
Tomishige; (Tokyo, JP) |
Correspondence
Address: |
GALLAGHER & LATHROP
Suite 1111
601 California Street
San Francisco
CA
94108-2805
US
|
Family ID: |
18863330 |
Appl. No.: |
09/800033 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
385/43 ; 216/24;
385/123 |
Current CPC
Class: |
C03C 25/68 20130101;
G02B 6/262 20130101; G02B 6/245 20130101 |
Class at
Publication: |
385/43 ; 385/123;
216/24 |
International
Class: |
G02B 006/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2000 |
JP |
398342/00 |
Claims
What is claimed is:
1. A method for processing end portion of an optical fiber element
having a center core and an outer clad surrounding said core,
comprising the steps of: dipping one end portion of said optical
fiber element into an etchant capable of etching the fiber element
perpendicularly to level surface of said etchant; causing the outer
clad of said one end portion of said fiber element immersed in said
etchant to be etched into a substantially coaxial reduced-diameter
portion while causing the outer clad of such a portion of said
fiber element that is extended upwardly to a certain height from
the level surface of the etchant and that is attached with the
etchant which rises upwardly from the level surface due to surface
tension of the etchant to be etched into a conical tapered surface
portion which is formed between the reduced-diameter portion and
un-etched portion of said fiber element; terminating the etching
once said reduced-diameter portion reaches a certain diameter; and
cutting said reduced-diameter portion at a point spaced by a very
short distance from the connecting boundary between said tapered
surface portion and said reduced-diameter portion toward the
reduced-diameter portion so as to leave a reduced-diameter end
portion continuously joining to said tapered surface portion.
2. A method for processing end portion of an optical fiber element
having a center core in the axial center thereof, a cylindrical
clad surrounding said core and an outer cover coating film
surrounding said clad, comprising the steps of: removing said
coating film in a partial cylindrical portion thereof having a
specified length so as to form a coating film-removed section and a
residual coating film section at one end portion of said optical
fiber element; dipping a first part of said coating film-removed
section and whole part of said residual coating film section
disposed at said one end portion of said optical fiber element into
an etchant capable of etching materials of said core and clad of
said fiber element perpendicularly to level surface of said etchant
in such a manner that a remaining second part of said coating
film-removed section is extending upwardly from the level surface
of said etchant to thereby initiate etching process; causing such a
portion of the clad as exposed at the first part of the coating
film-removed section of said fiber element and immersed in said
etchant to be etched into a coaxial reduced-diameter portion while
causing such a portion of the clad as exposed at the second part of
the coating film-removed section and attached thereto with said
etchant which rises to a certain height above said level surface
due to surface tension of the etchant to be etched into a conical
tapered surface portion which is formed between the
reduced-diameter portion and un-etched portion of said fiber
element; terminating the etching once said reduced-diameter portion
reaches a certain diameter; tapered surface portion has been
formed; and cutting said reduced-diameter portion at a point spaced
by a very short distance from the boundary between said tapered
surface portion and said reduced-diameter portion toward the
reduced-diameter portion so as to leave a reduced-diameter end
portion continuously joining said tapered surface portion.
3. The method according to claim 2, which further comprises a step
of providing, before the dipping step, a level controlling means
for restraining the level surface of said etchant to said optical
fiber element at a position where said optical fiber element
contacts the level surface of said etchant whereby the axial
dimension of said tapered surface portion to be formed on said
optical fiber element is set at a predetermined value.
4. The method according to claim 3 wherein, said level controlling
means is constituted by an etching-resistant film formed around the
peripheral surface of said optical fiber element.
5. The method according to claim 3 wherein, said level controlling
means is constituted by a coating film applied to said optical
fiber element.
6. The method according to claim 3 wherein, said level controlling
means comprises a flat plate made of etching-resistant material and
through-apertures formed through said flat plate perpendicularly to
the plane of the flat plate, each of said through-apertures having
a diameter slightly larger than the outer diameter of the
corresponding optical fiber element.
7. The method according to claim 1, which further comprises a step
of providing, before the dipping step, a level controlling means
for restraining the level surface of said etchant to said optical
fiber element at a position where said optical fiber element
contacts the level surface of said etchant whereby the axial
dimension of said tapered surface portion to be formed on said
optical fiber element is set at a predetermined value.
8. The method according to claim 7 wherein, said level controlling
means is constituted by an etching-resistant film formed around the
peripheral surface of said optical fiber element.
9. The method according to claim 7 wherein, said level controlling
means is constituted by a coating film applied to said optical
fiber element.
10. The method according to claim 7 wherein, said level controlling
means comprises a flat plate made of etching-resistant material and
through-apertures formed through said flat plate perpendicularly to
the plane of the flat plate, each of said through-apertures having
a diameter slightly larger than the outer diameter of the
corresponding optical fiber element.
11. The method according to any one of preceding claims 1 through
10 wherein, a liquid having a specific gravity lower than that of
said etchant is mixed into said etchant.
12. The method according to claim 11, wherein a plurality of said
optical fiber elements held in parallel to each other by a single
common covering member to thereby form an optical fiber array, are
subjected to processing.
13. The method according to any one of claims 1 through 10, wherein
a plurality of said optical fiber elements held in parallel to each
other by a single common covering member to thereby form an optical
fiber array, are subjected to processing.
14. An optical fiber comprising an optical fiber element having a
center core and a outer clad surrounding said core, characterized
by having at one end thereof a conical tapered surface portion with
a reduced-diameter end portion.
15. The optical fiber according to claim 14, wherein said
reduced-diameter portion has a diameter larger than that of the
core of said optical fiber element.
16. The optical fiber according to any one of claims 14 or 15,
wherein said reduced-diameter end portion has a length no more than
its diameter.
17. A method for processing end portion of optical fiber element
having a center core and an outer clad surrounding said core,
comprising the steps of: dipping one end portion by a certain
length of said optical fiber element into an etchant capable of
etching core and clad materials perpendicularly to level surface of
said etchant in such a manner that outer periphery of said clad is
exposed to the etchant; time controlling so as to cause such a
portion of the clad located at said one end portion as immersed in
said etchant to be etched into a reduced-diameter portion of a
substantially coaxial shape while to cause such a portion of the
clad as extended upwardly to a certain height from a level surface
of the etchant where said etchant is attached and rises upwardly
from the level surface due to surface tension of the etchant to be
etched into a conical tapered surface portion wherein lower and
upper ends of the tapered surface portion are continuously
connected to the reduced-diameter portion and outer periphery of
the un-etched clad, respectively; terminating the time controlling
once said reduced-diameter portion reaches a certain diameter; and
cutting said reduced-diameter portion so that a reduced-diameter
end portion is obtained which is continuously joining to said
tapered surface portion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method of processing end
portions of optical fibers utilized in, for example, optical
communications, and more particularly to a method of processing end
portions of optical fiber elements which elements are well suitable
for end-to-end connecting together and also relates to such optical
fibers having end portions specifically processed.
[0003] 2. Description of the Related Art
[0004] FIGS. 19 and 20 show the configuration of the end portion of
an optical fiber to be connected to a conventional optical
connector. In the drawings, the reference numeral 10 indicates the
optical fiber and 20 the ferrule bonded to the end portion of the
optical fiber 10. The ferrule 20 is of a hollow cylindrical shape
and has a through-bore 21 formed through its center axis for
receiving an optical fiber element 11 which is a bare fiber exposed
by removing away a protective coating therefrom. The fiber element
11 is inserted into the through-bore 21 and fixed or adhered
thereto by adhesive 20A.
[0005] In a conventional optical connector, the end terminal face
of the ferrule 20 having an optical fiber element 11 adhesively
fixed thereto is ground to a convex spherical shape, and a pair of
such identical ferrules 20 thus shaped are then brought into
end-to-end abutment and joined together within a split sleeve 30
(see FIG. 21). For this process, the PC (Physical Contact) joining
method is used which involves applying urging pressure to the end
faces of the pair ferrules 20 by resilient springs (not shown) to
elastically deform the core of the respective optical fiber
elements 11 of the optical fibers 10 lying at the apices of the
convex spherical ends. With this PC joining method, no air space is
produced between the optical fiber elements 11, allowing for the
joining at a low transmission loss.
[0006] Currently, however, optical connectors configured so as to
connect optical fiber elements 11 directly together without the use
of the ferrules 20 have been designed in view of the demand for
more compactness and finer pitches of optical connectors. But, the
optical connector of such configuration still requires the PC
joining method in order to accomplish the purpose of reducing the
loss. Further, the urging pressure for effecting the PC joining in
this type of optical connector is characterized in that it is
generated by axially compression-deforming the optical fiber
elements 11 and utilizing the restoring force (which will be
hereinafter referred to as buckling load) from the compressive
deformation.
[0007] In this regard, the magnitude of the buckling load generated
by compression-deforming the optical fiber elements 11 is on the
order of 0.2-0.4N. Depending on the condition of the end face of
the optical fiber, particularly if the end face has been cut at an
angle .theta. which is not a right angle with respect to the fiber
axis as illustrated in FIG. 22A, even a buckling load TH exerted on
such fiber as shown in FIG. 22B may fail to sufficiently
compression-deform the opposed cores, resulting in occurrence of a
gap G between the opposed fiber ends as shown in FIG. 22C and hence
inability to accomplish the PC connection. Consequently, it is
undesirably difficult to achieve stable optical properties.
[0008] One approach currently proposed to solve this difficulty is
to form the end portion of an optical fiber in a shape of a
convergent taper by using the technique as disclosed in the
Japanese Patent Publication Kokoku 3-50246, and then cut the
tapered end to obtain a flat end face, thereby to optically couple
a pair of the thus obtained optical fibers together by butt-joining
the flat end faces.
[0009] This method allows for facilitating the deformation of the
opposed fibers at their extreme cut ends to secure good optical
coupling result even if the end faces are cut more or less at an
angle .theta., because the end faces to be abutted together are
reduced in area due to the convergent taper.
[0010] Nevertheless, the thus obtained optical fiber elements 11
have a drawback that the optical fiber elements 11 are vulnerable
to failure due to their reduced mechanical strength when they are
subjected to the connecting method as mentioned above by abutting
them against each other and subjecting them to buckling load.
[0011] In order to overcome this drawback, there was an approach
toward providing the peripheral surface of the optical fiber
element 11 with a coating film 11C of carbon, resinous material or
the like as illustrated in FIG. 23.
[0012] However, when an attempt is made to form a taper end portion
at its terminal end of such optical fiber element 11 covered with
the coating film 11C, by using the etching technique in accordance
with the method as disclosed in the Japanese Patent Publication
Kokoku 3-50246, the etching process would start with the end face
of the optical fiber element 11 which is only the portion exposed
from the coating film 11C with the peripheral surface of the
cladding 11B of the optical fiber element 11 being covered with the
coating film 11C, so that the etching would proceed from the core
11A located in the center of the fiber element 11, with the result
that the optical fiber element 11 would be etched in a generally
cylindrical form, and thus end in failure to form tapered surface
portions.
[0013] For this reason, the present inventors endeavored to solve
this drawback in the technique of forming a taper on an optical
fiber element 11 coated with a coating film 11C, and conceived such
a technique as to deposit a resist film 13 on the end terminal
surface of the optical fiber element so as to cover the entire end
face of the core 11A and the radially inner half part of the
cylindrical end face of the clad 11B as shown in FIG. 24 prior to
effecting the etching process and then dipping the end portion of
the fiber element thus covered with the resist film 13 into an
etching solution J as shown in FIG. 25.
[0014] According to this endeavored method, since the end face of
the core 11A is fully protected from the etching by the resist film
13, it was found that the immersed end portion of the fiber element
is formed with a reduced-diameter portion 14 extending upward from
its extreme end.
[0015] It was also found that the fiber element was provided with a
tapered surface portion TP at the upper part of the
reduced-diameter portion, that is, a part of the fiber element
corresponding to ultimately at an elevated portion from the liquid
level of the etchant J.
[0016] After a desired tapered surface portion TP has been
obtained, those portions of the coating film 11C corresponding to
the reduced-diameter portion 14 and the tapered surface portion TP
are removed.
[0017] However, this endeavored method still has the disadvantage
that it requires an additional step of applying a resist film 13 to
the end face of an optical fiber element 11 prior to forming a
tapered surface portion thereon, and also another additional step
of removing the coating film. It makes thus the manufacturing
process correspondingly cumbersome. Particularly in the case of an
optical fiber having a multiplicity of optical fiber elements 11
integrally incorporated therein such as the flat tape type optical
fiber, the operation of depositing a resist film 13 to the end face
of each individual optical fiber element 11 has proved too
cumbersome to put this method into practical use.
[0018] Turning now back to the prior art of Japanese Patent
Publication Kokoku 3-50246, when the optical fiber element is cut
directly on the tapered surface portion as disclosed this prior
art, the cutter edge may slip axially along the angular tapered
surface portion to exert an axial force on the fiber element during
the cutting process. Consequently, this method has another drawback
that flaws such as cracks may possibly occur in the cut
portions.
[0019] In addition, in order to form tapered surface portions on
the individual fiber elements 11 of a tape type optical fiber array
10T comprising a plurality of optical fiber elements 11 held by a
tape-like sport 12T as illustrated in FIG. 26, the Japanese Patent
Publication Kokoku 3-50246 also discloses a method involving
dipping the individual fiber elements 11 in an etchant J. As one
example, it is disclosed that even if the fiber elements immersed
in the liquid are not equal in length, a plurality of tapered
surface portions which are shaped in conical terminal ends are
uniformly formed in their lengths, since those portions of the
fiber elements immersed in the liquid should be completely
dissolved by dipping them for a sufficiently longer period of time
(such as, 30-60 minutes) which is enough for the complete
dissolve.
[0020] The present inventors have discovered, however, when the
above-identified prior art technique were applied to a tape type
optical fiber array 10T comprising a multiplicity of individual
fiber elements 11 having as fine an array pitch PN as around 0.25
mm so as to accomplish the purpose of the present invention, a
specific phenomenon occurred that the levels of the respective
liquid heads of the etchant which heads are adhering to the
respective associated fiber elements, could rise higher as it is
closer to the middle of the array due to the surface tensions
acting on the respective liquid heads adhering to individual fiber
elements 11 overlapping to each other (see FIG. 27).
[0021] As a result, the troubles occur that the axial dimension
(length) L of the tapered surface portion TP formed by etching gets
successively longer in the order of L1<L2<L3<L4 toward the
middle of the array of the fiber elements 11 and that the positions
of the tapered surface portions are displaced with respect to each
other. Especially, the axial dimensions L1<L2<L3<L4 of the
tapered surface portions TP tend to be longer than that obtained
when the etching is conducted on a single fiber.
[0022] By way of example, if the array pitch PN of the fiber
elements 11 is 0.25 mm and the diameter of the fiber elements 11 is
0.125 mm (125 .mu.m), the axial dimensions L1<L2<L3<L4 of
the tapered surface portions TP will be around 0.3 to 0.5 mm. On
the other hand, when the etching is conducted on a single fiber,
the axial dimension of the tapered surface portion TP will be
around 0.1 mm. This means that the axial dimension L of the tapered
surface portion TP formed on the multiple-fiber type optical fiber
array will be about 3 to 5 times as long as that of the single-core
fiber.
[0023] As the axial dimension L of the tapered surface portion TP
increases, the strength of the tapered surface portion TP adjacent
its forward end correspondingly decreases. With repeated connecting
operations of optical connectors, fatigue is built up in the
tapered surface portion TP, causing a durability problem.
[0024] As discussed above, the conventional methods and the prior
attempt conducted by the present inventors are still insufficient
due to various problems. Accordingly, there has been a need for
obtaining an effective and practical method for processing end
portions of optical fibers as well as optical fiber having an
improved end portion which is applicable to the repeated connection
purpose.
SUMMARY OF THE INVENTION
[0025] A first object of this invention is to provide an optical
fiber element having a tapered surface portion adjacent to its end
and a reduced-diameter end portion extending forwardly from the
tapered surface portion and also to provide an optical fiber end
portion processing method for forming a tapered surface portion
having a reduced-diameter end portion extending forwardly
therefrom.
[0026] This reduced-diameter end portion extended from the tapered
surface portion is adapted to be butt-joined to the identical
reduced-diameter end portion of another identical opponent optical
fiber element.
[0027] A second object of this invention is to provide an optical
fiber end portion processing method capable of forming a tapered
surface portion having a reduced-diameter end portion extending
therefrom on an coated optical fiber element as well by simple
steps.
[0028] A third object of this invention is to provide an optical
fiber end portion processing method capable of forming tapered
surface portions with reduced-diameter end portions on a plurality
of parallel juxtaposed optical fiber elements forming an optical
fiber array therewith. These tapered surface portions of the
respective optical fiber elements have approximately equal reduced
axial dimensions or lengths which are also same as that obtained by
etching of a single optical fiber element, to thereby provide the
tapered surface portion with an enhanced durability.
[0029] In order to accomplish the first object, this invention
provides an optical fiber end portion processing method wherein: an
optical fiber element having a core in the axial center thereof and
a cylindrically formed clad surrounding the periphery of the core
is dipped at an end portion thereof into an etchant while holding
the element in an attitude substantially perpendicular to the
surface of the etchant; the portion of the fiber element dipped
below the liquid level of the etchant is shaped into a
reduced-diameter portion by etching in the etchant while the
portion of the etchant is caused to rise along outer periphery of
the clad of the fiber element to a certain height M (see FIG. 1)
above the liquid level of the etchant due to surface tension to
thereby shape the portion of the fiber element contacted by said
rising portion of the etchant into a tapered surface portion
extending from the reduced-diameter portion up to the outer
diameter of the non-etched portion of the clad; the period of time
for the etching process is specially controlled so that the etching
process is terminated whenever a desired tapered surface portion is
obtained, at the moment of termination of the etching process, the
reduced-diameter portion 14 of a desired diameter which is slightly
larger than that of the core is formed in conjunction with the
tapered surface portion; and then the reduced-diameter portion 14
is cut at a point spaced by a very short distance from the boundary
between the tapered surface portion and the reduced-diameter
portion toward the reduced-diameter portion so as to leave a
reduced-diameter end portion 14T continuously joining to the
tapered surface portion.
[0030] The reduced-diameter end portion has to have axial length m
which is desired not to exceed to its own diameter.
[0031] In order to accomplish the second object, this invention
provides an optical fiber end portion processing method wherein: an
optical fiber element having a core in the axial center thereof, a
cylindrically formed clad surrounding the periphery of the core and
a coating film formed around the peripheral surface of the clad is
shaped to have a residual coating film in a certain distance from
the extreme end of the optical fiber element and a coating
film-removed section of a certain length A (see FIG. 3) from which
the coating film is removed in a position adjacent to the residual
coating; the thus shaped optical fiber element at the entire part
of the residual coating thereof and at about half of the coating
film-removed section thereof is dipped into an etchant while
holding the fiber element with its axis in an attitude
substantially perpendicular to the surface of the etchant in such a
manner that the top half part of the coating film-removed section
is positioned upwardly away from the liquid level of the etchant;
shaping that the lower half part of the exposed clad at the coating
film-removed section of the fiber element immersed in the etchant
is shaped into a reduced-diameter portion by etching in the etchant
while the portion of the etchant is caused to rise along outer
periphery of the clad of the fiber element to a certain height M
above the liquid level of the etchant due to surface tension to
shape the outer periphery of the clad in a length of M above the
liquid level contacted by said rising portion of the etchant into a
tapered surface portion extending from the reduced-diameter portion
up to the outer diameter of the non-etched portion of the clad; the
etching process is terminated whenever a desired tapered surface
portion together with a desired reduced-diameter portion 14 is
obtained; and then the reduced-diameter portion 14 is cut at a
point spaced by a very short distance from the boundary between the
tapered surface portion and the reduced-diameter portion toward the
reduced-diameter portion so as to leave a reduced-diameter end
portion 14T continuously joining to the tapered surface portion,
the reduced-diameter end portion having a very short length
corresponding to the very short distance.
[0032] In order to accomplish the third object, this invention
provides an optical fiber end portion processing method wherein a
level controlling means for restraining the liquid level of the
etchant is provided upward from the liquid level in such a manner
that the lower end thereof contacts to the liquid surface of the
etchant whereby the axial dimension of the tapered surface portion
formed on the optical fiber element is controlled at a desired
value.
[0033] This invention also provides the optical fiber end portion
processing method wherein the level controlling means is
constituted by an etching-resistant film formed around the
peripheral surface of the optical fiber element.
[0034] This invention further provides the optical fiber end
portion processing method wherein the level controlling means is
constituted by a coating film applied to the optical fiber
element.
[0035] This invention further provides the optical fiber end
portion processing method wherein the level controlling means
comprises a flat plate made of etching-resistant material with
through-apertures formed through the flat plate perpendicularly to
the plane of the flat plate, each of the through-apertures having a
diameter slightly larger than the outer diameter of the
corresponding optical fiber element.
[0036] This invention further provides the optical fiber end
portion processing method wherein a liquid having a specific
gravity lower than that of the etchant is added to the etchant.
[0037] This invention further provides the optical fiber end
portion processing method wherein a plurality of optical fiber
elements are held in parallel to each other to form a fiber array
therewith by using a single common covering or supporting
member.
[0038] Still further, this invention provides an optical fiber
comprising an optical fiber element having a tapered surface
portion formed adjacent to its end part with a reduced-diameter end
portion 14T formed integrally with the forward end of the tapered
surface portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a cross-sectional view illustrating a first
embodiment of the optical fiber end portion processing method
according to this invention;
[0040] FIG. 2 is a side view illustrating the construction of the
forward end portion of the optical fiber element obtained by the
embodiment shown in FIG. 1;
[0041] FIG. 3 is a cross-sectional view illustrating a second
embodiment of the optical fiber end portion processing method
according to this invention;
[0042] FIG. 4 is a side view illustrating the configuration of the
optical fiber element obtained by the embodiment shown in FIG.
3;
[0043] FIG. 5 is a side view illustrating the optical fiber element
shown in FIG. 4 having the reduced-diameter end portion 14T of a
length m after the rest of the reduced-diameter portion 14 has been
removed;
[0044] FIG. 6 is a cross-sectional view illustrating a third
embodiment of the optical fiber end processing method according to
this invention;
[0045] FIG. 7 is a side view illustrating the configuration of the
optical fiber element obtained by the method shown in FIG. 6;
[0046] FIG. 8 is a side view illustrating the optical fiber element
shown in FIG. 7 after the reduced-diameter portion has been
removed;
[0047] FIG. 9 is an enlarged, cross-sectional view illustrating the
principal parts of the optical fiber end portion processing method
shown in FIG. 6;
[0048] FIG. 10 is a cross-sectional view illustrating a fourth
embodiment of the optical fiber end processing method according to
this invention;
[0049] FIG. 11 is a side view illustrating the configuration of the
optical fiber element obtained by the method shown in FIG. 10;
[0050] FIG. 12 is a cross-sectional view of an etching apparatus
including a cross-section taken on line 12-12 of the liquid level
controlling means shown in FIG. 13, for illustrating a fifth
embodiment of the optical fiber end processing method according to
this invention;
[0051] FIG. 13 is a perspective view illustrating the construction
of the liquid level controlling means used in the embodiment of
FIG. 12;
[0052] FIG. 14 is a side view illustrating the configuration of the
optical fiber element obtained by the method shown in FIG. 12;
[0053] FIG. 15 is a cross-sectional view of an etching apparatus
for illustrating a modified example of the processing method shown
in FIG. 12;
[0054] FIG. 16 is a cross-sectional view of an etching process for
illustrating a sixth embodiment of the processing method shown in
FIG. 10;
[0055] FIG. 17 is a cross-sectional view of an etching process for
illustrating a modified example of the processing method shown in
FIG. 12;
[0056] FIG. 18 is a cross-sectional view illustrating a seventh
embodiment of the optical fiber end processing method according to
this invention;
[0057] FIG. 19 is a perspective view for illustrating a prior
art;
[0058] FIG. 20 is a cross-sectional view illustrating the details
of the ferrule shown in FIG. 19;
[0059] FIG. 21 is a cross-sectional view illustrating two of the
ferrule shown in FIG. 19 being joined together;
[0060] FIGS. 22A-22C are structures illustrating the drawbacks of
the prior art shown in FIGS. 19-21;
[0061] FIG. 23 is a front view illustrating the construction of an
optical fiber element provided with a coating film;
[0062] FIG. 24 is a cross-sectional view illustrating the
pre-treatment technique developed by the present inventors so as to
form a tapered surface portion on the optical fiber element
provided with a coating film as shown in FIG. 23;
[0063] FIG. 25 is a cross-sectional view illustrating the etching
technique developed by the present inventors so as to carry out
this technique on the optical fiber element which has been
subjected to the pre-treatment as illustrated in FIG. 24;
[0064] FIG. 26 is a side view illustrating the construction of a
known tape-type optical fiber array;
[0065] FIG. 27 is a cross-sectional view illustrating an etching
process carried on the tape-type optical fiber array to form a
tapered surface portion thereon, which is conducted by the present
inventors; and
[0066] FIG. 28 is a side view illustrating the configuration of the
optical fiber elements of the tape-type optical fiber array
comprising a plurality of optical fibers gathered together in the
form of a tape, as obtained by the etching process shown in FIG.
27.
DETAILED DESCRIPTION OF THE INVENTION
[0067] Various embodiments of this invention will now be described
with reference to the accompanying drawings. Like numerals and
characters indicate like elements throughout the various
drawings.
First Embodiment
[0068] Referring to FIGS. 1, there is shown a first embodiment of
the optical fiber end portion processing method according to this
invention. The embodiment illustrated in FIGS. 1 is directed to
forming a tapered surface portion TP on an optical fiber element 11
having no coating film 11C coated around the clad 11B (see FIG.
23). In this case, the clad of an optical fiber element 11 is
exposed from a covering 12 and is dipped into an etchant J such as
hydrogen fluoride, for example.
[0069] The length of the immersed portion of the optical fiber
element 11 (submerged below the liquid level) should be long enough
as compared to the diameter of the optical fiber element 11. By way
of example, for the optical fiber element 11 having a diameter of
0.125 mm with a core having a diameter of slightly shorter than
0.05 mm, the immersed length may be about 12.5 mm which is one
hundred times the diameter.
[0070] The optical fiber element 11 is dipped into an etchant J
while holding the element in an attitude substantially
perpendicular to the liquid surface of the etchant J. If necessary,
any suitable holding means or member (not shown) for supporting the
fiber element in its appropriate state may be utilized. Around the
peripheral surface of that portion of the optical fiber element 11
contacted by the liquid surface, the etchant J rises in the form of
a taper over a distance M due to the surface tension and attaches
to the peripheral surface of the optical fiber element 11. By this
raised etchant J attached to the peripheral surface, the portion of
the fiber element extending the distance M from the liquid surface
is etched to be formed into a tapered surface portion TP. The
portion of the optical fiber element 11 extending below the tapered
surface portion TP (the portion immersed in the liquid, lower as
viewed in the drawing) is formed into a reduced-diameter portion 14
which has been reduced in diameter generally constantly along the
length thereof It is thus to be understood that the tapered surface
portion TP is formed as a result of the diameter varying gradually
from the diameter of the reduced-diameter portion 14 up to the
outer diameter of the clad 11B.
[0071] At the time when the diameter of the reduced-diameter
portion 14 has reached a target value, say 50 .mu.m, which is
determined by the time lapsed after the initiation of the etching
process, and which is selected to be slightly larger than the
diameter of core, the etching is terminated.
[0072] In this regard, the Japanese Patent Publication Kokoku
3-50246 discloses nothing about terminating the etching process in
a halfway. In other words, it merely discloses that the etching
process is continued until the reduced-diameter portion has been
completely etched out so as to obtain a conical shaped end
portion.
[0073] The present invention is specifically characterized by
controlling the length of time period for carrying the etching
process, which is different from the above-identified prior
art.
[0074] Subsequently, the reduced-diameter end portion 14 is
severed. More specifically, according to this invention, the
cutting is made perpendicularly to the fiber axis at a point m
spaced slightly, preferably 20 to 30 .mu.m from the boundary
between the tapered surface portion TP and the reduced-diameter
portion 14 toward the reduced-diameter portion. This leaves a
reduced-diameter end portion 14T with a length m integrally joining
to the tapered surface portion TP (see FIG. 2).
[0075] The adoption of such cutting point allows for severing the
optical fiber element 11 without the risk of producing any defects
thereon.
[0076] If the optical fiber element having only the tapered surface
portion as shown in the above-identified prior art is to be cut
directly on the tapered surface portion TP, not only it would be
difficult to cut it exactly at a desired position, but also the
cutter edge would cut it with a force tending to slip the edge
axially along the angular tapered surface portion. Due to such an
axially acting force, some unevenness as well as flaws such as
cracks may result on the cut surfaces.
[0077] In this connection, the Japanese Patent Publication Kokoku
3-50246 discloses the use of arc discharge device to cut a conical
end portion of an optical fiber element since this optical fiber is
applicable to connect to optical element. This prior art also
evidently describes that the use of a cutter is impossible, in view
of the fact that the optical fiber elements according to that
patent are provided with conical pointed ends.
[0078] In contrast, according to this invention, since the
reduced-diameter end portion 14 is cut at a selected point, there
occurs no axial force exerted on the cutter edge during the cutting
operation. As will be appreciated, this invention ensures stable
cutting and provides for reducing the incidence of flaws on the
surfaces.
Second Embodiment
[0079] FIG. 3 illustrates a second embodiment directed to forming a
tapered surface portion TP on an optical fiber element 11 which has
a coating film covering the clad. In this instance, a coating
film-removed section A is formed on an optical fiber element 11 at
an arbitrary location away from the extreme end of the optical
fiber element. The coating film 11C is generally made of carbon,
resinous material or the like. Such coating film 11C may be removed
by irradiating laser beam with a laser beam irradiation apparatus.
The length of the coating film-removed section A may be arbitrarily
chosen. As a guide, it may be longer than that of the tapered
surface portion TP to be formed. This embodiment is characterized
by leaving a residual coating film 11C-1 below the coating
film-removed section A. With regard to the etching on the portion
of the optical fiber element corresponding to the residual coating
film 11C-1, it is to be understood that the etching will proceed in
both directions, namely from the far end side of the residual
coating film toward the coating film-removed section A and from the
inner end side of the residual coating film toward the far end side
of the residual coating film 11C-1.
[0080] On the side of the far end of the residual coating film
11C-1 the etching proceeds in a cylindrical manner from the core to
the clad, whereas on the side of the coating film-removed section A
of the residual coating film 11C-1 the etching proceeds in a sense
to thin the clad layer.
[0081] The etching tending to thin the clad layer progresses
downwardly as shown in FIG. 3 until it meets the cylindrical
etching progressing upwardly from the far end of the residual
coating film 11C-1, whereupon the diminished residual coating film
11C-1 is separated from the optical fiber element 11 and sinks in
the etchant J.
[0082] When the etching initiated from the far end side which is to
shape the optical fiber element 11 in a cylindrical form encounters
the etching initiated from the coating film-removed section A side,
the cylindrical portion formed on the far end side is rapidly
extinguished, so that the optical fiber element will ultimately
have a substantially flat lower end face remaining.
[0083] As is appreciated from the forgoing, without the need for
depositing a resist film 13 as described hereinbefore with
reference to FIG. 24, the optical fiber element 11 is formed with a
reduced-diameter end portion 14 which is similar to that obtained
in the embodiment shown in FIG. 1 and which has an ultimately flat
end face. In addition, on the top of the reduced-diameter end
portion 14 a tapered surface portion TP is formed by the etchant J
rising due to its surface tension, as shown in FIG. 4. Upon the
time when the diameter of the reduced-diameter portion 14 has
reached a predetermined value being determined, the etching is
terminated. After the termination of the etching, the optical fiber
element 11 is cut so as to leave a short reduced-diameter end
portion 14T, whereby an optical fiber 10 having a tapered surface
portion TP formed with the reduced-diameter end portion at the
extreme end thereof as shown in FIG. 5 is obtained.
Third Embodiment
[0084] FIGS. 6 to 9 illustrate a third embodiment which is capable
of precisely restraining the location where a tapered surface
portion TP is to be formed. This embodiment is characterized in
providing the coating film-removed section with a liquid level
controlling means 40 for defining the level of the etchant J. In
the embodiment shown in FIG. 6, the liquid level controlling means
40 is constituted by a residual coating film.
[0085] Specifically in this embodiment, assuming that the residual
coating film 11C-1 shown in FIG. 3 is referred to as a first
residual coating film.
[0086] This embodiment is characterized in that a second residual
coating film 11C-2 having a length M' is disposed in a midst of the
coating film-removed section A so as to divide it into lower
portion A which is called as a first coating film-removed section
and upper portion B called as a second coating film-removed section
as shown in FIG. 6.
[0087] The second residual coating film 11C-2 constitutes a liquid
level controlling means 40.
[0088] The etching is initiated with the lower end of the liquid
level controlling means 40 contacted by the liquid surface of the
etchant J. (see FIG. 9)
[0089] It is required that the liquid level controlling means 40
should at least surround the peripheral surface of the optical
fiber element 11 and should have a flange-like portion protruding
even slightly beyond the surface of the clad layer 11B. The amount
that the etchant J rises up due to the surface tension is thus
restricted by this protruding portion.
[0090] When the etching is initiated in this condition, that
portion of the optical fiber element 11 immersed in the etchant J
is etched to become thinner to form a reduced-diameter portion 14,
and simultaneously the etching proceeds upwardly into an interface
space between the second residual coating film 11C-2 constituting
the liquid level controlling means 40 and the surface of the clad
layer until the etching reaches the upper end of the liquid level
controlling means. It should be noted that there is a slight amount
of time lag or time delay for the reach of the etching from the
lower end to the upper end of the liquid level controlling means.
Due to this time lag, the amount of the etching in radial direction
to thin the clad at the lower end of the liquid level controlling
means is slightly larger than that at the upper end, so that the
clad has a second tapered surface portion TP'.
[0091] Once the etching has reached the upper end of the liquid
level controlling means 40, the etchant J is further drawn upwardly
through an annular gap defined between the liquid level controlling
means 40 and the clad layer to continue with the etching.
Thereafter, the etchant J is still further drawn upwardly along
outer periphery of the clad exposed in the second coating
film-removed section B due to the surface tension from the upper
end to a certain height M.
[0092] It is thus to be appreciated that a tapered surface portion
TP of axial length M is formed on the clad layer at the second
coating film-removed section B upward from the upper end of the
liquid level controlling means 40 by the etchant J as sucked up
through the gap between the liquid level controlling means 40 and
the outer periphery of the clad layer. It is further noted that the
degree of slant of the second tapered surface portion TP' is
relatively small in comparison to that of the first tapered surface
portion TP, so that the second tapered surface portion can be
considered as a part of the reduced-diameter portion 14.
[0093] The location or the lower end of the tapered surface portion
TP can be arbitrarily determined by selecting the axial dimension
of the liquid level controlling means 40 (although limited to
within the range of height of the etchant sucked up by capillary
action). The axial dimension M of the tapered surface portion TP is
determined by the height of the etchant rising up above the upper
end of the controlling means 40, which is in turn determined by the
surface tension of the etchant J. In view of these conditions, the
upper end of the liquid level controlling means 40 is seemed to
correspond approximately to the level of the etchant J for forming
the tapered surface portion TP. Hence, the upper end of the tapered
surface portion TP is defined at a certain distance M (see FIGS. 7
and 9) from the upper end of the liquid level controlling means
40.
[0094] It is to be noted that FIG. 8 illustrates the optical fiber
element with the reduced-diameter end portion 14T which is obtained
from the optical fiber element of FIG. 7 by removing the
reduced-diameter portion 14 therefrom. It is thus to be appreciated
that this embodiment is applicable to an instance in which the
location where the tapered surface portion is to be formed is
preliminarily determined.
[0095] In this embodiment, the liquid level controlling means 40
which is composed of the second coating film-removed section B is
observed to be separated from the outer periphery of the clad layer
when the etching has reached to the upper end of the liquid level
controlling means and to float on the etchant surface by means of
the surface tension of the etchant. This fact is quite significant
and has never been know from any prior art. Accordingly, there is
no need to employ any support means for supporting or holding the
liquid level controlling means in its proper position.
[0096] Notwithstanding, however, it may be possible to employ any
suitable supporting means, so that such embodiments using the
supporting means are also involved within this invention.
Fourth Embodiment
[0097] FIG. 10 illustrates another form of the liquid level
controlling means 40 shown in FIG. 6. As noted hereinbefore, if an
attempt is made to form tapered surface portions on the individual
fiber elements 11 of a tape type optical fiber array 10T comprising
a plurality of optical fiber elements 11 held by a sport 12T with a
fine array pitch therebetween (spacings of 0.25 mm, for example),
there would occur undesirable displacement in axial positions of
the tapered surface portions formed as well as the problem that the
axial dimension L of the tapered surface portion will be several
times the length of the corresponding tapered surface portion
formed on the single-core fiber, due to the surface tension acting
on the individual fiber elements 11 overlapping each other as
explained with reference to FIGS. 27 and 28. The embodiment of FIG.
10 is directed to an optical fiber end processing method capable of
resolving such problems.
[0098] In this embodiment as well, each of the optical fiber
elements 11 exposed from the sport 12T is provided with a first
coating film-removed section A and a second coating film-removed
section B, and a liquid level controlling means 40 formed by a
second residual coating film 11C-2 between the first coating
film-removed section A and the second coating film-removed section
B. The liquid level controlling means 40 should be formed so as to
be uniform in position and axial dimension for all of the optical
fiber elements. To this end, apparatus such as laser beam
irradiation apparatus capable of removing a coating film by aiming
a laser beam accurately at a predetermined position may preferably
be utilized to form the first coating film-removed section A and
the second coating film-removed section B.
[0099] The end portions of the optical fiber element 11 with the
first coating film-removed sections A and the second coating
film-removed sections B formed thereon are then dipped into an
etchant J while holding the elements in an attitude perpendicular
to the liquid surface of the etchant J. In doing so, the lower ends
of the liquid level controlling means 40 are brought into contact
with the liquid surface of the etchant J to limit the rising amount
of the etchant J. This limitation of the rising amount of the
etchant J, restrains the heights of the etchant J rising due to
surface tension from the upper ends of the respective liquid level
controlling means 40 and hence to a constant height, irrespective
of the position of the individual optical fiber elements 11 in the
array.
[0100] It will be thus understood that the locations of the tapered
surface portion TP formed by etching are horizontally aligned at a
constant height as shown in FIG. 11. The axial dimensions L of the
tapered surface portions TP are also unified throughout the array.
In addition, it is possible to make the length of the tapered
surface portions TP approximately equal to that of the
corresponding tapered surface portion formed on a single-core
fiber, since the mutual overlapping of the surface tensions between
the individual fiber elements 11 is eliminated and the axial
dimensions L of the tapered surface portions TP are determined by
the height M (see FIG. 9) of the etchant J rising from the top of
the liquid level controlling means 40.
[0101] Accordingly, for even a multiple-core type optical fiber
array, the adoption of the processing method described in this
embodiment allows for reducing the length of the tapered surface
portions formed at the forward end thereof, whereby a multiple-core
type optical fiber array 10T provided with highly durable tapered
surface portions may be obtained. It is to be noted that in FIG.
11, the original positions of the first residual coating films
11C-1 are shown in phantom lines since they have already been
dropped into the liquid after when the reduced-diameter portions 14
were formed.
[0102] As described before, the second residual coating films are
floated on the liquid surface of the etchant. They may be, however,
supported by any other supporting means (not shown).
Fifth Embodiment
[0103] FIGS. 12 and 13 illustrate a fifth embodiment utilizing
another form of the liquid level controlling means 40. In this
embodiment, the liquid level controlling means 40 comprises a flat
plate 42 having small apertures 41 formed therethrough, each having
a diameter slightly larger than the diameter of the corresponding
optical fiber element.
[0104] The flat plate 42 may be made of a material such as acrylic
resin having resistance properties to the etchant J. It is required
that the small apertures 41 have to have a diameter slightly larger
than the outer diameter of the optical fiber element 11 such that
the etchant J may be drawn up by capillary action through the gaps
defined by the inner peripheral walls of the apertures 41 and the
outer peripheries of the corresponding optical fiber elements
11.
[0105] The liquid level controlling means 40 thus composed by the
flat plate 42 with the small apertures 41 may likewise eliminate
the overlapping of surface tensions acting on each other even if a
plurality of optical fiber elements 11 are arrayed with a fine
pitch. Consequently, the locations of the individual optical fiber
elements 11 are made uniform as shown in FIG. 14, as they are
determined by the elevation of the upper end of the liquid level
controlling means 40. The axial dimensions L of the tapered surface
portions TP are also made constant throughout the array, since they
are determined by the height M of the etchant J rising around the
individual optical fiber elements 11. And yet, it is possible to
hold the length of the tapered surface portions TP down to
approximately 0.1 mm which is comparable to that of the
corresponding tapered surface portion formed on a single-core
fiber, hence to provide highly strong tapered surface portions
TP.
[0106] While in FIG. 14 the optical fiber elements 11 are
illustrated as having the reduced-diameter portions 14 remaining,
actually the reduced-diameter portions 14 are removed with only the
reduced-diameter end portion 14T left below the tapered surface
portion TP as shown in FIGS. 5 and 8.
[0107] Further, this embodiment, which utilizes a flat plate 42
having small apertures 41 formed therethrough as a liquid level
controlling means 40, need not necessarily require that the optical
fiber element 11 have a coating film 11C. However, such liquid
level controlling means 40 constituted by a flat plate 42 may
equally applied to an optical fiber element having a coating film
11C for covering the clad layer as shown in FIG. 15. In such case,
there need only be a single coating film-removed section A.
Sixth Embodiment
[0108] FIGS. 16 and 17 illustrates modified example of the
embodiments shown in FIGS. 10 and 12. In the embodiment of FIGS. 16
and 17, a liquid K having a specific gravity lower than that of the
etchant J is incorporated in the etchant J such that the lighter
liquid K floats on the liquid surface of the etchant J. In the case
that the etchant J is hydrogen fluoride, oil may be used as the
liquid K. The lighter liquid K floating on the liquid surface of
the etchant J serves to prevent the etchant J which is climbing up
the peripheral surface of the optical fiber element 11 due to
surface tension from being deformed in shape by vibrations, for
example.
[0109] More specifically, if vibrations were applied to the etchant
J which is adhering and mantling up along the outer peripheral
surface of the optical fiber element 11 due to surface tension as
in the embodiments shown in FIGS. 10 and 12, the etchant J thus
attached to the peripheral surface of the optical fiber element 11
may possibly be deformed in shape. If the shape of the attached
etchant J is deformed, the configuration of the resulting tapered
surface portion TP is also deformed, so that it leads to the
disadvantage of reducing the manufacturing yield. With a view to
overcoming this drawback, the liquid K having a specific gravity
lower than that of the etchant J is incorporated so as to float on
the etchant J, whereby the shape into which the etchant J mantles
up is prevented from being distorted by vibrations, wind pressure
or the like. This introduces the advantage of improving the
production yield.
Seventh Embodiment
[0110] FIG. 18 illustrates yet another embodiment of this
invention. In this embodiment, an etching-resistant film is
deposited on an optical fiber element 11 devoid of coating film 11C
so that the etching-resistant film constitutes a liquid level
controlling means 40.
Effects
[0111] As discussed above, according to this invention, the
processing method involves forming a tapered surface portion TP on
a optical fiber element 11 adjacent to its reduced-diameter portion
14 and subsequently cutting the reduced-diameter portion 14 in such
a manner to leave a reduced-diameter end portion 14T. It provides
therefore lowering the incidence of flaws such as cracks occurring
on the cut faces, and leading to the enhancement of the
manufacturing yield in this respect.
[0112] According to another aspect of this invention for
application to an optical fiber element 11 having a coating film
11C covering a clad layer, the processing method involves providing
a coating film-removed section A on the fiber element with a
residual coating film 11C left toward the forward end thereof and
then initiating the etching while the coating film-removed section
A is held in contact with the liquid surface of the etchant,
whereby a desired tapered surface portion TP can be formed without
the need for depositing a resist film 13 (see FIG. 24) for
preventing the core from being exposed to the etchant over the
forward end of the optical fiber element 11. As a result, this
invention provides the advantage that a tapered surface portion TP
with a reduced-diameter portion 14 can be formed by a simple method
even on a highly durable optical fiber element reinforced by a
coating film 11C.
[0113] In addition, this invention provides a processing method
characterized by a liquid level controlling means 40. The provision
of this liquid level controlling means 40 makes it possible to
determine the point where the formation of the tapered surface
portion TP is to be initiated. Consequently, this method is well
suitable to instances in which the location where tapered surface
portions are to be formed is predetermined.
[0114] Moreover, when applied to even an optical fiber array
constituted by a plurality of optical fiber elements 11 held
together by a support 12T with a fine array pitch, this method
utilizing the liquid level controlling means 40 can avoid the
phenomenon that the length of the tapered surface portion formed
may be elongated depending on the position of the corresponding
optical fiber element 11 in the array due to the surface tensions
acting on the individual fiber elements 11 overlapping each other.
It will thus be appreciated that for even a multiple-core type
optical fiber array 10T, the invention provides the advantage of
forming each of the individual optical fiber elements with a highly
durable tapered surface portion. This advantage is extremely great
in practical use. In addition, when a plurality of single-core
optical fiber elements 11 are to be formed simultaneously, the
provision of the liquid level controlling means 40 introduces the
advantage of eliminating the mutual overlapping of the surface
tensions between the individual fiber elements 11.
* * * * *