Fused optical fiber splice element

Opposed ends of optical fibers are fused within a holding member, by heating the fiber ends by means positioned in, or on, the member. A self-contained package can be provided to which an electric current is applied, or some other heating method.

This invention relates to fused optical fiber splice elements and in 
particular to such elements which are readily used under field and similar 
conditions. 
Optical fibers are connected generally in two ways. In one example the ends 
of a pair of optical fibers are positioned in abutting relationship in a 
member, which aligns the fibers. The member may have a central hole 
accurately produced to hold the fibers aligned, or a plurality of rod-like 
elements act to hold the fibers aligned. The fibers are retained in the 
member by some form of adhesive. An index matching fluid can be positioned 
between the ends of the fibers to reduce losses. 
In another example, the ends of the fibers are positioned in end to end 
alignment and an electric arc is developed between electrodes positioned 
on either side of the proposed join. The arc causes the ends of the fibers 
to fuse. 
Fusing the fibers produces a very high quality joint or connection but is 
difficult to produce in the field. Fusion machines are used with quite 
complex holding means for the fibers, to provide very accurate alignment. 
Such machines are expensive, complicated, susceptible to damage and 
require reasonably skilled operators. 
Therefore, when the conditions under which connections are to be made are 
other than well controlled conditions, the use of mechanical splices in 
which the fibers are connected by positioning in holding members by an 
adhesive are widely used, even though higher losses usually occur. 
The present invention provides for the connection of optical fibers which 
has the advantages of both systems. Broadly, a splice element for fusion 
splicing a pair of optical fibers end-to-end, in accordance with the 
invention, comprises a holding member having axial alignment means for the 
fibers, and means for heating the opposed ends of the fibers while 
positioned in the holding member to fuse the fibers together. The axial 
alignment may be obtained in various ways. For example the fibers may be 
positioned in Vee-shaped grooves, and some form of clamping means can be 
provided. Another way is to position the fibers in a bore having a close 
fit on the fibers. Yet another way is to provide a plurality of rod-like 
elements, usually three, positioned in parallel relationship in the 
holding member. Such alignment ways, and others, are conventional in other 
forms of fusion and mechanical splices. 
The means for heating the opposed ends of the fibers can vary. One example 
is two opposed electrodes positioned at the abutment position of the fiber 
ends. Application of a high frequency current produces an arc between the 
electrodes, fusing the fiber ends. Electrodes can be positioned in the 
holding member at the abutment position. 
Another example is the provision of a heating element in the holding member 
at the abutment position. The element will produce a temperature high 
enough to fuse the fibers. It may only operate once and can therefore be a 
one shot heater which may destruct on heating. Other ways of producing a 
high temperature localized heating can be used, such as a gas flame. 
The invention also includes a method of fusing together opposed abutting 
ends of a pair of optical fibers, in which the ends of the fibers are 
inserted in alignment in a holding member and the ends of the fibers 
heated to fuse them together.

As illustrated in FIG. 1, a splice element comprises a holding member in 
the form of a tubular member 10 which has an axial bore 11, with enlarged 
end bore sections 12. The bore 11 is dimensioned to be a close fit on the 
uncoated ends of fibers to be joined or spliced. The sections 12 are a 
close fit on coated portions of the fibers. At a mid point of the bore 11 
there are two diametrically opposed apertures 13 in which are positioned 
electrodes 14. The electrodes have rounded inner ends 15. 
The construction of the holding member can vary. Thus it can be of fused 
quartz glass, or similar. Alternatively it can be of stainless steel, in 
which case some form of insulating layer, indicated in dotted outline at 
16, will be required between the electrodes and the holding member. As a 
further alternative, the holding member can be of ceramic, or other 
insulating material. While shown as being of unitary form, the holding 
member can be of a plurality of parts assembled together. 
In FIG. 2 two optical fibers, 20 and 21 are shown positioned in the holding 
member. The fibers have the coating 22, 23 removed for a short distance 
and the fiber cores 24, 25 are cleaved, or otherwise formed at their ends 
to provide flat end surfaces. The end surfaces abut. The coated portions 
of the fibers are positioned in the sections 12 and can be retained 
therein by an adhesive. 
When the fibers 20 and 21 are positioned in the holding member, a high 
frequency current is applied to the electrodes 14, as illustrated in FIG. 
3, at 26. A convenient way of connecting the electrical supply to the 
electrodes would be a sleeve which is a close fit on the outside of the 
member 10 with spring loaded contacts for contacting the electrodes 14. 
The sleeve could be split, hinged, to provide for easy positioning. When 
the current is switched on an arc will be formed between the electrodes 
14, and the ends of the fibers fused together. The power supply 26 can be 
from a central system which controls voltage, amperage and time, or any 
combination of these, and other, items. 
FIG. 4 illustrates an alternative form of holding member, common reference 
numerals being used where applicable. In this example, an electric 
resistance heater 30 is positioned around the abutment position of the 
fiber ends. The heater 30 can be of various forms, and as an example can 
be a carbon heater which disrupts once it has heated. If the member 10 is 
electrically conducting then some insulation will be required between the 
heater and the tubular member. The electrical supply is indicated at 31 
and can be controlled as for FIG. 3. 
In FIGS. 5 and 6 a further form of splice element is illustrated, again 
common reference numerals being used where applicable. In this form, 
instead of a small bore 11, a larger bore 35 is formed. Sections 12 are 
also provided. Positioned in the bore 35 are a plurality of rod-like 
elements 36 and 37, in the example three at each end of the bore 35. A gap 
38 is provided between opposed ends of the elements 36 and 37. The 
rod-like elements 36 and 37 define a central bore which is a close sliding 
fit on the fiber ends. Opposed electrodes 14 are provided. 
FIGS. 1 to 6 illustrate, rather diagrammatically the basic features and 
precepts of the invention, and the form of the holding member can be 
varied considerably as can other features. 
Thus, for example, the holding member can be an elongate member, for 
example of rectangular cross-section, having a Vee-shaped groove in one 
surface. The fiber ends rest in the groove. Some form of holding or 
clamping means can be provided to hold the fibers in position. Generally 
the Vee groove will be interrupted by an enlarged groove or other form, to 
provide some clearance around the ends of the fibers. Generally, but not 
necessarily, a cover will be positioned over the fibers. The transverse 
bore 13 provides such a clearance in FIGS. 1 to 6. Also in the embodiments 
of FIGS. 1 to 6 the transverse bore can be of some other form than 
parallel sided. It may taper outwards towards the axis of the holding 
member and may have an increased diameter portion at its center portion. 
FIG. 7 illustrates a particular embodiment, using common references where 
applicable, comprising a glass, for example fused quartz tubular member 
10, which, in this example, has a central bore 11 for the positioning of 
the unclad portions 24 and 25 of optical fibers 20 and 21. A typical 
outside diameter of the member 10 is 1.8 mm, but this can vary. A 
transverse bore 40 is formed at the position where the fiber ends are to 
be fused. A typical dimension for bore 40 is 0.5 mm but again this can 
vary. Preferably the wall of the bore 40 is polished. Bore 11 has tapered 
ends 41 for ease of entry of the fibers. 
In a particular usage, fiber 24 is installed into the bore 11 with its 
cleaved end in the center of bore 40, and held in position. Fiber 25 is 
attached to a positioning stage to allow feeding in to a butting position 
of the fiber ends. 
A ball 42 is positioned at each end of the transverse bore 40 and the 
electrodes 43 from a DC power source applied to the balls. A typical 
source of high voltage DC is that from a conventional fusion splicer, but 
can readily be provided by other sources. As an example, heating by 
creating an arc between the balls, was carried out in three stages. The 
first heating was for 40 seconds at a current of 20 amps at a voltage of 
about 5 Kv. With an original datum loss in one of the fibers of 3.4 dBm, 
after the first heating the loss across the splice was 5.6 dBm, indication 
of limited fusion. A second heating of 50 seconds at a current of 40 amps, 
at the same voltage gave a loss of 5.1 dBm, still showing limited fusion. 
At a third heating for 50 seconds at a current of 70 amps, at the same 
voltage the loss was 3.8 dBm showing satisfactory fusion. It was noted 
that one of the balls of this third heating became very hot. Thus it is 
seen that the arrangement as illustrated in FIG. 7 will provide a one-shot 
fusion splice using an approximate heating cycle of 50 seconds at 70 amps 
and about 5 Kv volts. 
Conveniently, either the balls can be separate items applied at the time 
fusion is to occur, or can be supplied in place, held by a suitable 
adhesive or some mechanical means. Other forms than balls could be used. 
For a complete "package", the holding member would extend at each end and 
have a bore within which would be fixed the protective coating. 
FIG. 8 illustrates an arrangement similar to that of FIG. 4, in which a 
tubular carbon resistor member 45 is used. On application of an electric 
current, the resistor member 45 will heat, fusing the fiber and itself 
disintegrating. 
FIG. 9 illustrates the provision of some clearance around the ends of the 
fibers. The member 10 is recessed, at 46, the resistor member 45 being 
positioned in the recess, allowing some clearance around the fiber ends. 
In FIG. 10, instead of producing the arc between electrodes as in FIGS. 1 
to 6, or balls as in FIG. 7, two pieces of metal 47 are attached, for 
example by an adhesive, and act as electrodes on either side of the member 
10. Each piece of metal has a hole 49 and a transverse hole 50 is formed 
in the member 10. Application of electric current, for example at 51, 
produces an arc from the edges of the holes, which fuses the fiber ends. 
FIGS. 11 and 12 illustrate a modification of the embodiment of FIG. 10. 
FIGS. 11 and 12 illustrate what would be termed a "package" device in 
which the member 10 is long enough to enable the outer protective coatings 
of the fibers to be attached. Extending along the member 10, on either 
side, are elongate strips of metal 55 and 56. These strips are attached, 
for example, by an adhesive. Each strip has a hole 57 and a transverse 
hole 58 extends through the member 10. The protective coating fits in the 
bore section 12, as in FIGS. 1 to 9. The bores 12 can be given a lining 
coat of a heat sensitive adhesive. Once the fibers have been inserted, 
with the ends abutting, or closely spaced, at the position of the bore 58, 
an electric current is applied to the strips 55 and 56. An arc is produced 
from the edges of the holes 57 to fuse the fibers. Current can then be 
passed through each strip to heat it up and cause the heat sensitive 
adhesive to bond the protective coatings of the surfaces of the bores 12. 
A further alternative, comprises a ceramic tube which surrounds the fiber 
end, similar to the carbon tube in FIG. 8. In addition means are provided 
for producing an RF field across the splice region. First, electric 
current is applied to the ceramic tube which heats up. Then the RF field 
is switched on to increase the heating effect and cause fusing of the 
fiber ends. 
As stated previously, the embodiments described, and illustrated, have used 
a tubular member as a holding member, but the actual form of holding 
member can vary, as can also the alignment means. The holding member can 
have separate parts assembled together. The objective is to provide some 
form of holding member in which two fibers can be held in axial alignment, 
with provision of means for heating the fiber ends for fusion of the fiber 
ends, in the holding member, the fused fibers remaining in the holding 
member, rather than being transferred to a further member after fusion. 
While in the examples described, fusion has been obtained by generating 
heat by use of an electric current, for example to form an arc or to heat 
a resistor, it is possible to create the fusion heating in other ways. For 
example, in a connector as in FIG. 8, the carbon resistor can be replaced 
by a combustible material, for example powdered magnesium. This could be 
ignited by the internal application of heat. It could also be ignited by 
an electric current. A further alternative is a gas flame. For example, in 
the embodiments of FIGS. 1 to 3, FIG. 5, FIG. 7 and FIGS. 9 and 10, a 
flame could be directed through the transverse bore to fuse the fiber 
ends. 
It can be of advantage to provide a two-stage fusion. In the first stage a 
lower power level arc or other heating, is produced to obtain some 
rounding of the fiber ends, or other advantage. In the second stage a 
higher power level arc or other heating is produced to fuse the fiber 
ends. Also some means may be provided for moving the fiber ends together 
at fusion. This can be provided by some form of clamping which develops a 
limited amount of end thrust, or some simple means for pushing the fibers, 
or one of the fibers, can be provided. Such end movement is used in 
conventional fusion splicing and mechanical splicing connections. 
While described, and illustrated, as single units, multiple units can be 
provided for the connection of more than one pair of fibers.