CA2164098C - Splicing aged optical fibers - Google Patents

Splicing aged optical fibers Download PDF

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Publication number
CA2164098C
CA2164098C CA002164098A CA2164098A CA2164098C CA 2164098 C CA2164098 C CA 2164098C CA 002164098 A CA002164098 A CA 002164098A CA 2164098 A CA2164098 A CA 2164098A CA 2164098 C CA2164098 C CA 2164098C
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Prior art keywords
fiber
segment
aged
heating
silica
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Expired - Lifetime
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CA002164098A
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French (fr)
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CA2164098A1 (en
Inventor
Goran Ljungqvist
Magnus Johansson
Leif Stensland
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Telefonaktiebolaget LM Ericsson AB
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Telefonaktiebolaget LM Ericsson AB
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Priority claimed from SE9401077A external-priority patent/SE515665C2/en
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of CA2164098A1 publication Critical patent/CA2164098A1/en
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Publication of CA2164098C publication Critical patent/CA2164098C/en
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24Coupling light guides
    • G02B6/25Preparing the ends of light guides for coupling, e.g. cutting
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24Coupling light guides
    • G02B6/255Splicing of light guides, e.g. by fusion or bonding
    • G02B6/2551Splicing of light guides, e.g. by fusion or bonding using thermal methods, e.g. fusion welding by arc discharge, laser beam, plasma torch
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24Coupling light guides
    • G02B6/255Splicing of light guides, e.g. by fusion or bonding
    • G02B6/2552Splicing of light guides, e.g. by fusion or bonding reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Coupling Of Light Guides (AREA)

Abstract

For improving mechanical characteristics of a segment of an aged optical glass fiber, the segment is retained between clamps, e.g. in a conventional splicing machine. Then the segment is heated to a high temperature in the vicinity of the softening temperature or melt temperature of the glass material of the fiber by means of an infrared light beam from a carbon dioxide laser or by an electric arc generated between the welding electrodes. In particular, the tensile strength is increased considerably by this procedure, what allows that the heated segment can be handled and exposed to the operative steps required for splicing the fiber to another optical fiber. Then also old fibers arranged in the ground can be repaired and spliced, and it is not necessary to replace whole lengths of old fibers.

Description

'v0 95/27225 PCT/SE95/00339 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 'v0 95/27225 PCT/SE95/00339 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 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 WO 95/27225 216 4 0 9 8 pC1'/SE95/00339 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 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 'v0 95/27225 PCT/SE95/00339 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.

Claims (6)

1. A method of splicing an aged silica optical fiber to another optical fiber, wherein the sequential steps of:

- removing a polymer protective sleeve on the aged fiber (1) over a segment at an end of the aged fiber for exposing the surface of the cladding of the silica fiber - heating the surface of at least a portion of the segment of the aged fiber, where the cladding is exposed, to a high temperature in the vicinity of the melt temperature of the material in the silica fiber cladding, - then cutting the fiber at a place within the segment to produce an end surface, - placing this end surface adjacent an end surface of another optical fiber and - optically coupling these end surfaces to each other.
2. A method according to claim 1, wherein the high temperature is chosen to such a high value that the silica fiber in the heating will get a smooth or shiny surface.
3. A method according to claim 1, wherein the high temperature is chosen to such a high value that the surface of the silica fiber melts somewhat during the heating.
4. A use of a device for splicing optical fibers, the device having cutting-off means for cutting the optical fibers, movable retainer means for clamping the optical fibers, actuator means for moving the retainer means and heating means for connecting end surfaces of the optical fibers to each other, wherein - an aged silica optical fiber is placed in the movable retainer means for clamping the aged fiber at both sides of a segment of the aged fiber to maintain the segment in a substantially straight condition, - that the heating means are activated to heat at least the surface of a short region of the segment, as seen in a longitudinal direction of the segment, a region having a length corresponding to a few fiber diameters at most, to a high temperature in the vicinity of the melt temperature of the material of the aged fiber, - that the actuator means are activated to move the retainer means as one unit in a direction parallel to the longitudinal direction of the segment, in order to move the aged fiber alongside the heating means, whereby the short heated region moves in the longitudinal direction of the aged fiber, - that the cutting-off means are activated for cutting the aged fiber at a place within the segment and that a first cut-off part is removed leaving a second part of the aged fiber retained in one of the retainer means, the second retained part having a heat treated end portion, - that another optical fiber is placed in the non-occupied retainer means, and - that the actuator means and heating means are activated to splice the retained aged fiber and the other optical fiber to each other.
5. A use according to claim 4 wherein the heating means comprise a laser and a lens system for focusing a light beam from the laser used to heat the segment of the aged fiber.
6. A use according to any of claims 4-5, wherein the heating means comprise welding electrodes used to heat end portions of the second retained part of the aged fiber and the other optical fiber when performing the splicing
CA002164098A 1994-03-30 1995-03-30 Splicing aged optical fibers Expired - Lifetime CA2164098C (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9401077-4 1994-03-30
SE9401077A SE515665C2 (en) 1994-03-30 1994-03-30 Recovery of the aging fiber's breaking strength
PCT/SE1995/000339 WO1995027225A1 (en) 1994-03-30 1995-03-30 Splicing aged optical fibers

Publications (2)

Publication Number Publication Date
CA2164098A1 CA2164098A1 (en) 1995-10-12
CA2164098C true CA2164098C (en) 2007-05-22

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Family Applications (1)

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CA002164098A Expired - Lifetime CA2164098C (en) 1994-03-30 1995-03-30 Splicing aged optical fibers

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CA2164098A1 (en) 1995-10-12

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