GB2105062A - Positioning of an elongate member in a tube - Google Patents

Abstract

A method of positioning an elongate member e.g. an optical fibre 3 along, or in a defined relationship with, the centre of a surrounding tube e.g. ferrule 4 comprises fixing e.g. a transparent grating 5 to the end of the ferrule. On rotation the grating develops a centred pattern and the fibre 3 is aligned with reference to this. <IMAGE>

Description

SPECIFICATION Improvements in the positioning of an elongate member in a tube The present invention relates to the positioning of an elongate member inside and along a tubular housing. The invention has particular reference to optical fibre connectors.

In various engineering operations it is necessary to align an elongate member accurately with the axis of a hollow, usually cylindrical tube. It is to be understood that the axis of the cylinder may be defined with respect to eitherthe inner of outer diameter and that the axes so defined will only be coincident if the cylinder bore is accurately coaxial with the outer wall.

There are several possible techniques for carrying out the aligning operation. In cases where accuracy is not critical and the parts are relatively large the operation may be carried out by eye. In other cases a repetitive measuring technique may be employed.

Most hitherto proposed methods cannot obtain high accuracy as well as rapid alignment and many are not suitable for aligning rod members, for example optical fibres having outer diameters of the order of 1 25,am and core diameters of 50,um, which are small in comparison with the inner diameter of the cylinder.

The method and apparatus of the present invention utilise an optical illusion in which a patterned plate for example carrying a family of parallel lines, appears, when rotated rapidly about an axis transverse to the plane of the plate, to carry a family of concentric circles centered on the axis.

It has been discovered by marksmen that sights which superimpose a circular pattern over the field of view enable the gun to be aimed more accurately at a specific target than do other sight configurations. The present invention makes use of this phenomenon in conjunction with the above discussed optical illusion to enable an operator to readily align a rod member with the axis of a cylinder.

According to the present invention there is provided a method of positioning an elongate member along, or in spaced parallel relationship with, the long axis of a surrounding tube such method including the steps of placing, in a position where it can be viewed as an end member of the tube, a sighting element having a surface pattern which on rotation about a centre develops a symmetrical appearance with the centre readily discernible, rotating together the tube and sighting element about the long axis of the tube and positioning the elongate member with reference to the centre of the pattern.

More specifically the invention includes a method of aligning a rod member with or parallel to the axis of a hollow cylinder comprising the steps of: mounting a translucent or transparent grating to an end face of the cylinder, rotating the cylinder and grating assembly about the cylinder axis sufficiently rapidly such that the grating produces the appearance of a pattern of concentric circles centered on the axis, and adjusting the position of the rod member within the cylinder so that it is situate at the centre of the pattern when said end face is viewed.

The translucent or transparent grating carries a piurality of spaced, parallel lines which produce, when the grating is rotated sufficiently rapidly about an axis transverse to the grating, the appearance of a pattern of concentric circles centered on the axis which are clearly visible when viewed, if necessary, through a suitable viewing means which may introduce magnification.

The accuracy of alignment obtainable using the technique of the present invention is determined by the spacing of the lines on the transparent grating and the fineness with which the adjusting means may be controlled to centre the rod member on the pattern generated by the rotating grating. For example the 50pom core of an optical fibre may be accurately aligned to a ferrule axis to + 3ym using a grating having a line spacing of 1 2,am.

The technique of the present invention is particularly, but not exclusively, suitable for forming parts of optical fibre connectors. In such connectors two connector parts each comprising a precision ground ferrule having an outer diameter accurate to +1 jilm in which the optical fibre is aligned with its core centered on the axis are housed in abutting engagement in a sleeve having a precisely cylindrical inner bore thus positioning the cores of the fibres to be joined so that they abut with maximal core overlap thus ensuring good power transfer across the boundary.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure lisa diagrammatic, partly sectional view of apparatus for aligning an optical fibre in a ferrule; Figure 2 is a typical plan view of a pattern superimposed on a fibre end as seen by an operator of the apparatus of Figure 1; and Figure 3 is a schematic view of a means for rotating the ferrule.

Although the following description relates to the formation of an optical fibre connector part, it will be appreciated that the technique described herein is equally applicable to the alignment of rod members other then optical fibres in hollow cylinders of any description, even cylinders having a minimal axial length.

The apparatus illustrated diagrammatically in Figure 1 for aligning a rod member 1, in this case an optical fibre 2 bonded to a capillary tube 3 for support, with the axis of a hollow cylindrical ferrule 4 comprises a transparent grating 5 which is mounted over the end face ofthe ferrule 4. The ferrule is rotated by means indicated at 6. A suitable arrangement for rotating the ferrule is illustrated in Figure 3 and comprises a cradle defined between prisms 12 in which the ferrule 4 rests. A wheel 13 of rubber or similar material rotates about a parallel axis with the periphery of the wheel contacting and frictionally driving the ferrule.It is preferred to rotate the resting ferrule by a drive to the periphery as by so doing a cent of rotation about the outer circumference of rl, ferrute ;s developed. A precision manipulator foi accurately adjusting the position of the optical fibre assembly in all if S degrees of freedom is indicated by 7. The apparatus further includes a viewing means for example a microscope 8 which is focussed on the transparent grating 5.

In order to make an optical fibre connector part using the apparatus set out above the ferrule may be constituted by a precision ground rod with an outer diameter accurate to +1 ,us is taken. A relatively large diameter hole 9 5 then drilied in the rod. Provided that the hole contains the cylindrical axis of the rod it is not critical whether it is coaxial with that the axis or even parallel to it. Clearly the size of the hole must be sufficiently large to permit the fibre end to be manoeuvered within it.

The transparent grating 5 may be formed by processing opaque lines onto a thin sheet of glass or photographic film. The line spacing and thickness are not critical but it will be appreciated that the thickness should be comparable with the spacing.

Providing that all lines are parallel to one another individual spacings may vary across the width of the grating. The preferred spacing of the lines depends on the size of the rod member to be centered on the axis. For example a grating spacing of 12,im can be used to centre a multimode optical fibre core of 50yam diameter to an accuracy of j3ym. For a smaller monomode fibre core the grating size is chosen commensurately smaller.

The fibre 2 is bonded for support to, for example, a glass capillary tube 3 and the end is ground and polished. The tube 3 is a loose fit in the hole 9 in the ferrule 4 and is positioned by a manipulator 7 for example an X YZ micropositioning device disposed outside the ferrule 4.

The transparent grating 5 is attached to the end face of the ferrule with the side on which the grating is defined facing inwards to obtain simultaneous focussing and viewing. The attachment may be achieved by placing the grating into an annular brass holder which fits over the end of the ferrule. The positioning of the grating is non-critical provided that it crosses the axis of rotation. The assembly is mounted in the cradle for rotating it about the axis of the ferrule relative to its outer diameter. When viewed through the microscope 8 a pattern such as that illustrated in Figure 2 is observed. Due to an optical illusion the rotating lines on the grating appear as concentric circles centered on the axis of rotation with a spacing equal to the grating line spacing.The operator may then control the micropositioning device 7 to adjust the position of the end face 10 of the fibre containing tube so that the optical fibre core 11 is centered within the pattern. Once a satisfactory alignment has been achieved the grating may be removed and the tube assembly bonded in place with a suitable locating substance, for example an epoxy resin. To complete a connector part the end face of the ferrule 4 with fibre 2 and tube 3 bonded therein may be further polished and finished.

It may be that in order to view the fibre high magnification will be required with consequent lack of depth of focus. In these circumsiances the centre of the grating may need to be observed and marked pricr to manipulating the fibre in its tube.

In case of aligning optical fibres for connectors it is important that the core 11 should be aligned with the axis. Therefore the operator must concentrate on the core region 11 in the end face 10 of the fibre/tube assembly which need not necessarily be concentric with its cladding and will probably not be concentric with the supporting tube wall.

The method as described may be used to check alignment accuracy as well as carrying out initial alignment. For this purpose the method has the advantages of being non-destructive and nonloading.

As well as for aligning an optical fibre or other rod member with the axis of the cylinder the abovedescribed method and apparatus can be used to align the rod member parallel to the axis. For example an optical fibre end portion could be aligned with a specified ring in the pattern generated by the rotating grating representative of the desired distance off the axis. For this application the grating spacing and line widths have to be accurate in order that the necessary measurements may be made. Moreover the positioning of the grating over the cylinder end face becomes more important in order that the centre ring diameter is accurately known.

One application for accurately off-axis optical fibre connector parts as described would be in a mechanical switch. If one connector part containing a first optical fibre end mounted at a fixed distance from its axis is rotated about its axis opposite another coaxial connector part containing a plurality of second optical fibre ends which are in turn mounted at the same fixed off-axis distance, the first fibre will be aligned in turn with each of the second fibres. It will be appreciated that the above described principle may be extended to provide for a whole range of switching configurations by providing each connector part with several fibre ends.

Claims (10)

1. A method of positioning an elongate member along, or in spaced parallel relationship with, the long axis of a surrounding tube such method including the steps of placing, in a position where it can be viewed as an end member of the tube, a sighting element having a surface pattern which on rotation about a centre develops a symmetrical appearance with the centre readily discernible, rotating together the tube and sighting element about the long axis of the tube and positioning the elongate member with reference to the centre of the pattern.

2. A method as claimed in Claim 1 wherein the pattern is a grating defined by a set of parallel lines.

3. A method as claimed in either Claim 1 or Claim 2 wherein the sighting element is translucent and the elongate member is viewed through it from outside the tube.

4. A method as claimed in any of the preceding claims wherein the tube is a cylindrical ferrule rested in a cradle and rotated by a drive applied to the peripheral surface.

5. A method as claimed in any ofthe preceding claims wherein the elongate member comprises an optical fibre.

6. A method as claimed in Claim 4 wherein the fibre is fixed in the aligned position and the fixed fibre and ferrule form part of an optical fibre connector.

7. A method substantially as hereinbefore described with reference to the accompanying drawings.

8. A component, particularly an optical fibre connector made by a method as claimed in any of the preceding claims.

9. Apparatus for carrying out the method of Claim 1 comprising means for rotating the tube abo. its long axis, the sighting element and means for adjusting the elongate member to the desired position within the tube.

10. Apparatus substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.