Method of mounting an end portion of an optical fibre in an optical fibre connector

In a method for fixing an optical fibre in an optical fibre connector element the fibre is fixed therein by means of centering elements (22) and a curable material (28), for example an adhesive. The centering elements and the curable material are positioned between the envelope of an end portion of the optical fibre (6) and a surface portion (26) of the connector element surrounding said envelope. After the fixing of the fibre end portion in the connector element the end portion of the connector element including the centering elements (22) and the fibre end portion (6) are machined, for example ground, up to a plane (30) which is positioned inside the points of contact between the centering elements (22) and the fibre end portion (6) and between the centering elements (22) and the surface portion (26) of the connector element surrounding the fibre end portion.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of mounting an end portion of an 
optical fibre in an optical fibre connector. 
The Swedish patent specification No. 7901398-3 corresponding to Sweden Pat. 
No. 426,882, describes a method of connecting the end portions of two 
optical fibres with each other. According to the method described in said 
patent specification the end portions of the two optical fibres are 
adjusted and mounted in two separate sleeve-shaped connector elements, and 
the end portions of the two optical fibres are connected with each other 
by connecting the sleeve-shaped connector elements with each other by 
means of a coupling device so that the end surfaces of the end portions of 
the optical fibres are positioned in contact with each other. According to 
the patent specification the adjustment of the end portions of the optical 
fibres in the fibre connector elements is provided by displacing centering 
elements which for example are ball-shaped into engagement with the 
envelope surface of the end portion of the optical fibre as well as with 
the surface of the sleeve-shaped connector element surrounding said 
envelope. In an embodiment of the method described in said patent 
specification the fixing of the end portions of the optical fibres in the 
fibre connector elements is thereupon provided by supplying a curable 
material, for example an adhesive, to the space between the envelope of 
the fibre end portions and the surrounding surface portion of the fibre 
connector element in question. 
When using the method according to said patent specification it appears to 
be a drawback that there is created contact between the centering elements 
and the optical fibre and between the centering element and the 
surrounding surface portion of the connector element after the fibre end 
portions have been adjusted and fixed in the connector elements. The 
drawback is caused by the fact that said contact exerts stresses to the 
fibre so that the fibre may be damaged. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a method of mounting and fixing 
an optical fibre in a connector element of the kind described, wherein 
this drawback is not present. 
In order to comply with this object the method according to the invention 
is characterized in that the end portion of the fibre connector element 
including the centering elements and the end portion of the optical fibre 
is machined, for example ground, up to a plane perpendicular to the 
longitudinal axis of the end portion of the optical fibre and positioned 
inside the points of contacts between the optical fibre and the centering 
elements and between the centering elements and the surface portion of the 
connector element surrounding the fibre, said machining taking place after 
the end portion of the optical fibre has been adjusted by means of the 
centering elements and has been fixed by means of the curable material. 
Thus, the completed fibre connector element including the optical fibre 
fixedly mounted therein does not have any direct contact between the 
centering elements and the optical fibre and between the centering 
elements and the material of the connector element. On the contrary the 
fibre is fixed only by means of the curable material which can have 
suitable properties for preventing the transfer of detrimental stresses to 
the optical fibre. 
In a suitable embodiment of the invention there is used centering elements 
consisting of glass which is advantageous from the point of view that 
unlike metal the glass does not create particles which can damage the 
optical fibre when it is ground as well as from the point of view that the 
glass is transparent so that it is possible to use a light curable 
adhesive as the curable material for fixing the optical fibre.

DESCRIPTION OF PREFERRED EMBODIMENT 
In FIG. 1 there is shown an end portion of a fibre cable 2 comprising a 
sheath 4 and a fibre which is uncovered at its end portion 6. The fibre 
cable 2 extends through a sleeve-shaped connector element 8 which consists 
of a first portion 10 and a second portion 12, the portion 12 having a 
part 14 extending concentrically with and into the portion 10. The 
portions 10 and 12 are connected with each other by means of threads 16 
which provide an axial displacement of the portions 10 and 12 when the 
portions are rotated in relation to each other. In order to provide a 
centering of the fibre end portion 6 in the sleeve-shaped connector 
element the portion 10 thereof is at its end portion provided with a 
conical surface portion 20 and three centering elements in the form of 
balls 22 consisting of glass and engaging the surface portion 20. The end 
surface 24 of the part 14 projecting into the portion 10 engages the balls 
22. Thus, it is realized that it is possible to determine the size of the 
central opening between the balls 22 by displacing the part 14 in relation 
to the portion 10 by rotating the part 14 in relation the portion 10, as 
the positions of the balls 22 in relation to each other will be determined 
by the positions where the balls engage the conical surface portion 20. 
When the fibre end portion is introduced into the sleeve-shaped connector 
element the part 14 should have such a position in relation to the portion 
10 that there is provided between the balls 22 a central opening through 
which the fibre end portion can be easily moved. After the introduction of 
the fibre end portion the balls 22 are displaced into engagement with the 
surface of the fibre end portion 6 as well as with the conical surface 
portion 20 so that the fibre end portion is adjusted to a central position 
in the sleeve-shaped connector element 8. At its end portion the 
sleeve-shaped connector element has a conical outer surface 25 which is 
concentric with the conical surface portion 20 and is used as an outer 
reference surface when the connector element is connected with another 
connector element by means of a suitable coupling element as described in 
the Swedish patent specification No. 7901398-3. 
After the above positioning of the fibre end portion in the sleeve-shaped 
connector element 8 there is in the method according to the invention 
provided a fixing of the fibre end portion 6 in relation to the connector 
element 8 by supplying a curable material 28, for example an epoxy 
adhesive or a light curing adhesive to the space 26. When using a light 
curing adhesive the curing is facilitated by the fact that the balls 22 
consist of a transparent material, preferably glass. 
After the curable material has cured and the fibre end portion 6 has 
thereby been fixed in relation to the sleeve-shaped connector element 8, 
the end portion of the sleeve-shaped connector element is ground up to the 
plane provided with reference numeral 30 in FIG. 1. After the grinding the 
sleeve-shaped connector element 8 has the appearance shown in FIG. 2. 
Thus, the end portion of the connector element 8 is ground past the points 
of contact between the balls 22 and the envelope of the fibre end portion 
and between the balls 22 and the surface portion 20. This means that no 
pressure or other stresses can be transferred from the outer surfaces of 
the sleeve-shaped connector element to the optical fibre. 
The fact that the balls 22 consist of glass provides that the grinding does 
not produce particles which can damage the optical fibre. 
It is realized that a removal of the end portion of the sleeve-shaped 
connector element can be provided with other types of machining than 
grinding.