Note: Descriptions are shown in the official language in which they were submitted.
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SPLICING AGED OPTICAL FIBERS
TECHNICAL FIELD
The present invention relates to a method and a device for
splicing an aged optical silica fiber to another fiber, e.g. to a
new optical fiber for repair purpo=ses.
BACKGROUND OF THE INVENTION
It is well-known that optical fibers based on silica corrodes in
a humid environment. Further, substantially all optical fibers
which are installed for ordinary telecommunication in national
networks are exposed to moisture to a larger or smaller extent.
Naturally, the surface of a silica fiber is in particular exposed
to corrosion attacks. The attacks cause that the tensile strength
of the fiber is reduced and that the fiber gets more brittle. The
deterioration of the mechanical characteristics of fibers is a
large problem when repairing e.g. a fiber which is installed
below ground level and has been cut off in some digging
operation. Installed, aged fiber can be so brittle that it may be
difficult to handle it and it can even be impossible to splice
the fiber to other fibers. Up to now, for failures such as breaks
or ruptures of old fibers, it has often been necessary to replace
whole fiber lengths which is naturally very costly.
It has been observed previously that the rupture and tensile
strength of glass fibers and wave guides can be increased by
heating the fibers or waveguides to temperatures in the vicinity
of the softening temperature, see the German patent applications
made available to the public DE-Al 28 17 651 for Siemens AG and
DE-Al 40 41 150 for kabelmetal electro GmbH. The methods and
devices disclosed are conceived to be used on ordinary fibers,
before the practical use thereof.
DESCRIPTION OF THE INVENTION
it is an object of the invention to provide a method and device
by means of which an aged optical silica fiber can be given
improved properties in order to splice the fiber to another
optical fiber.
This object is achieved by the invention, the characteristics of
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which are set out in the appended claims.
For improving mechanical properties of a segment of an aged
-optical fiber to allow the handling thereof which is required for
a splicing prodess, the segment is heated to a high temperature
near the softening temperature or the melt temperature of the
glass material in the fiber. Hereby, the corrosion attacks
resulting from a moist environment can be "healed", i.e.
microcracks, resulting from the moisture, are melted together by
the heat.
The heating power can be provided from a light beam of a laser.
The light beam is focused over a cross section of the optical
fiber and this heated cross-sectional area is made to be
displaced along a segment of the fiber. The light beam power and
the displacement velocity are chosen so that the temperature on
the surface of the fiber achieves a temperature near the melt
temperature. Practically it is visible by the fact that the
surface of the fiber gets a "smooth" or "shiny" appearance.
Other possibilities for the heating is e.g. heating in a gas
flame, by means of a heating spiral element (resistive heat
element) or by means of an electric arc of the type used for a
melt-fusioning in splicing optical glass fibers.
Thus the steps for splicing an aged optical fiber to another
optical fiber generally comprise that first the polymer
protective sleeve on the aged fiber is removed over a,segment of
the fiber for exposing the surface of the fiber cladding which is
supposed to be of some glass or silica material. The surface of
at least a portion of the segment of the aged fiber, where the
cladding is exposed, is then heated to a high temperature in the
vicinity of or essentially the melt temperature of the material
in the fiber cladding. In particular the temperature may be
chosen to such a high value that the surface of the silica fiber
melts somewhat during the heating. The fiber is cut off at a
place within the segment to produce an end surface, which is then
spliced as an ordinary optical fiber to another one, that is this
end surface is placed adjacent to an end surface of another
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optical fiber and these end surfaces are coupled optically to
each other, by e.g. welding the fiber ends to each other.
A device for performing the above steps for splicing an aged
silica optical fiber to another optical fiber will then comprise
movable retainer means for clamping a fiber at both sides of a
segment of the fiber to maintain the segment in an essentially
straight condition, the movable retainer means generally
comprising a detachable retainer box attached to a movable slide.
Further there are heating means for heating at least the surface
of a short region of the segment, as seen in a longitudinal
direction of the segment, in particular a region having a length
corresponding to a few fiber diameters at most, to a high
temperature in the vicinity of or essentially the melt
temperature of the material of the silica fiber. Actuator means
are arranged for moving the retainer means in a direction
parallel to the longitudinal direction of the segment. Finally
there are the conventional splicing means such as cutting-off
means for cutting the fiber at a place within the segment to
provide a heat treated end portion, and attachment means for
positioning fixedly the end surface of the heat treated end
portion of the segment at an end surface of another optical
fiber.
DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference
to a not limiting embodiment and with reference to the
accompanying drawing in which:
- Figure 1 schematically shows a device for restoration of
mechanical properties of a fiber.
DESCRIPTION OF THE PREFERRED EIKBODIMENT
In Fig. 1 an installation is illustrated for splicing and for
heat treatment of an optical aged optical fiber 1. The device is
preferably a modified conventional fiber splicer unit. It thus
comprises two fiber retainers 3, in which first the aged fiber is
clamped extending along a straight path between the retainers.
The fiber retainers 3 are attached to movable slides 5, which are
actuated by drive motors 7 along suitable guides, not shown. The
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slides 5 can in particular move as one unit in the direction of
the arrows 9 a limited distance up and back in the longitudinal
direction of the clamped straight segment of the fiber 1. A
carbondioxide laser 11 generates an intensive infrared light beam
having a direction essentially perpendicular to the longitudinal
direction of the optical fiber 1. The light beam from the C02-
laser 11 is deflected by means of two parallel mirrors 13, e.g.
arranged in an angle comprising 45 in relation to the light
beam, so that the light beam passes along a parallel path and
substantially straight through a beam mixer 15 to a lens system
17. In the lens system 17 the beam is focused to hit the fiber 1
at a point in the segment thereof which is located between the
retainers 3.
Further, a helium-neon-laser 19 is arranged, providing a visible
light beam having a lower intensity, which is only arranged for
cooperating in directing the heat beam from the carbondioxide
laser 11, so that the non-visible heat beam therefrom actually
hits the fiber 1 at the intended location. The light beam from
the helium neon laser 19 is deflected by an angle of 90 by means
of a mirror 21 in order to be directed to the side of the beam
mixer 15 and therein again be deflected by an angle of 90 . After
that, for a correct adjustment, the light beam from the helium
neon laser 19 has the same radiation path as the light beam or
heat beam from the carbondioxide laser 11 and hits the lens
system 17 and is focused to the same point on the clamped portion
of the fiber 1 as the beam from the C02-laser 11.
For treating an aged silica fiber, first the protective cover
thereof, ordinarily a polymer layer, is removed, e.g. chemically,
over a segment of the fiber so that the surface of silica
material in the cladding of the fiber 1 is exposed. Then this
segment of the fiber 1, which is to be treated, is clamped
between the clamps or retainers 3. The helium-neon-laser 15 is
started so that it generates a beam of light having a wave length
within the visible range. The lens system 17 is adjusted by a
direct observation of the visible light from the helium neon
laser 19, so that the focused beam (visible as a red spot) hits
the fiber 1, or alternatively the slides 5 are displaced, by
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operating the motors 7, in directions perpendicular to the
clamped fiber segment to make the focused visible light beam hit
the fiber. Then the slides 5 are moved to an end position as seen
in the longitudinal direction of the clamp fiber segment, the
slides still moving as one unit maintaining the segment clamped
along a straight line. Then also the carbondioxide laser 11 is
started. The infrared ray or heat beam therefrom will then also
be focused on the fiber 1 at the same location as the ray from
the alignment laser 19 and will there heat the fiber strongly
over a cross section thereof. The displacement of the slides 5 is
started in the longitudinal direction of the clamped segment at
the same time as the light beam from the carbondioxide laser hits
the fiber, thus moving the segment in the longitudinal direction
thereof. The movement is given a suitably adapted velocity and
terminates at the other end position of the slides 5, as seen in
the longitudinal direction of the fiber segment. During the
movement, all of the time, the focused heat beam from the
carbondioxide laser 11 thus heats a short region of the clamped
fiber segment, as seen in the longitudinal direction of the fiber
1, the region being moved at a constant velocity along the fiber
segment located between the fiber retainers 3.
The light or heat ray from the carbondioxide laser 11 and the
movement velocity of the slides 5 and thus of the clamped fiber
segment are adjusted so that the surface of the optical fiber
after the heating will have a smooth, shiny appearance. The
temperature, at which the surface of=the optical fiber 1 is
heated, can be estimated to be close to the softening temperature
of the silica glass or generally near the melt temperature of the
material in the silica fiber 1. The treated region of the fiber 1
will hereby get improved mechanical characteristics, in
particular an improved tensile strength. In a practical
experiment an aged fiber having a tensile strength comprising
approximately 2 GPa obtained, by a treatment according the
description above, a region having a tensile strength comprising
approximately 5 GPa, i.e. the tensile strength was more than
doubled within the heated segment of the fiber. Then the segment
of the fiber can be mechanically handled and treated and in
particular the fiber segment can be cut off at a suitable
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position and spliced to another optical fiber.
The cutting operation can be performed in same splicing machine
if there are facilities therefor, such as cutting blade 22
movable along suitable guides, not shown, in a direction
perpendi::ular to the clamped fiber segment. Otherwise the
retainers 3 are released from the slides 5 and then one retainer
is placed in a separate fiber cutter, not shown. Then this
retainer with the cut and treated remaining segment of the fiber
is again placed on a slide 5. A new optical fiber which has been
prepared for splicing is mounted in a retainer 3 and it is placed
on the other slide S. Then the fiber ends are spliced to each
other in the conventional way. Thus the slides 5 are moved
independently of each other to position the fiber end surfaces
essentially at each other and aligned with each other and then an
electric arc is generated between two high voltage, welding
electrodes 23 which are energized from a high voltage supply 25.
Instead of using the light beam from the carbondioxide laser 17
for heating the fiber segment, the heating can also be provided
by the electric arc generated between the welding electrodes 23.
Then also an automatic image processing and control of the
movements of the slides 5, which is conventionally arranged in
automatic fiber splicing machines, can be used in the heat
processing of the clamped fiber segment for heating it to the
desired temperature by both a control of the heating effect of
the electric arc and the transport of the clamped fiber segment.
