GB1595208A

GB1595208A - Dielectric optical waveguide holding devices

Info

Publication number: GB1595208A
Application number: GB3467777A
Authority: GB
Original assignee: Post Office
Current assignee: Post Office
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-08-12

Description

(54) DIELECTRIC OPTICAL WAVEGUIDE HOLDING DEVICES (71) We, THE POST OFFICE, a British corporation established by Statute, of 23 Howland Street, London W1P 6HQ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a device for aligning dielectric optical waveguides, the device being useful for the pointing of dielectric optical waveguides.

When jointing together adjacent lengths of optical fibre, which typically has an overall diameter (core and cladding but excluding any plastics coating) of 100 microns or less, it is necessary for the two ends to be positioned relative to one another with great precision before the joint is made. Positioning is normally carried out by locating each fibre in a larger component, which must itself be accurately made. A further problem then arises in the precise alignment of the two larger components which must be effected by an alignment device of comparable accuracy.

According to the present invention, a device for holding and/or aligning a dielectric optical waveguide comprises a triad of mutually contacting spherical bodies of substantially equal radius, and bias means adapted to press the bodies towards one another.

In use, the radius of the spheres and the radius of a dielectric optical waveguide to be held by the triad should be matched so that the generally circular section of the fibre occupies the region of a circle inscribed within the triad of spheres. The fibre is then a snug but sliding fit in the central interstice of the triad. The size of the central interstice depends only on the radius of the spheres and is determined with the same accuracy as that with which the spheres are made, which can be considerable; for example, tungsten carbide spheres having radial and spherical tolerances of less than 1 micron are commercially available. A high degree of accuracy is thus attainable using a very simple arrangement.

A triad of spheres of equal radius also possesses another important property that leads to a major advantage in the context of the present invention: two such triads will fit together in a completely stable arrangement in which the centres of the six spheres are symmetrically angularly disposed about a line joining the centres of the inscribed circles of the triads. This means that two fibre ends each held by a triad can be positioned accurately with respect to one another, the accuracy again being that with which the spheres are made. Thus two fibres can be accurately aligned prior to jointing.

Furthermore, each of the two fibres may itself be held, for greater stability and more accurate angular positioning, by one or more additional triads arranged behind the main triad, the triads being aligned and inter-engaging in the manner described in the previous paragraph. The triads may conveniently share a common biassing means.

The spheres are of relatively hard material, tungsten carbide being especially preferred. Spheres of this material having the maximum tolerances of less than 1 micron mentioned above are manufactured by Spheric Engineering Limited. Commercial ball bearings, for example, those manufactured by Ransome Hoffmann Pollard Limited, are also suitable for use in the device of the present invention.

As already mentioned, the device of the invention includes means for biassing the spheres towards one another. This may be provided by a passage within a further body, the dimensions of the passage being so related to the diameter of a circle circumscribing the spherical bodies that the bodies are located firmly within the passage but each is free to rotate about its own centre.

The passage is preferably cylindrical with a diameter substantially equal to the diameter of the circumcircle.

The bias means may, for example, comprise a sleeve of resilient material which can be radially stretched to encompass the triad of bodies, the unstressed internal diameter of the sleeve being less than the diameter of the circumdrcle. In a preferred arrangement, however, the triad fits tightly into a passage through a sphere of large radius, the passage lying along a radius of the larger sphere and conveniently passing right through it.

Advantageously the passage contains one or more additional triads arranged behind the main triad in an aligned, inter-engaging row.

In order to provide accurate angular positioning of the fibre, the device of the invention preferably locates the fibre at another point as well as at the central interstice of the main triad. As previously mentioned, this may be achieved by means of additional triads, consisting of spheres of the same radius as the main triad spheres, arranged in an interlocked row so that their central interstices are aligned. Alternatively or in addition, a more distant part of the fibre may be located by means of some kind of constriction in its path. For example, the main triad may be symmetrically disposed in a recess in the end of a block, for example, made of brass, an interference fit between the block and the spherical bodies providing the bias means, and the lock having an axial bore aligned with the central interstice of the main triad and having a constriction in that bore at a point spaced from the said interstice.

The more distant locating means may of course be another triad, spaced from the main triad. The spheres of this additional triad may if desired be larger than those of the main triad, so that the central interstice is larger, because a tight fit is not essential here and a certain amount of play may even be desirable.

As mentioned previously, the main triad, optionally with further, inter-engaging triads, is advantageously positioned within a bored-out larger-radius sphere. The larger sphere, made, for example, of stainless steel, may conveniently be mounted in retaining means in such a way that it is to a certain extent free to rotate about its centre. This enables errors in angular positioning to be taken up. The amount of rotation available may be limited by some kind of stop. In one embodiment of the invention, described in more detail below, the larger-radius sphere is snap-fitted into a tube of low-friction plastics material, for example, polytetrafluoroethylene, and is prevented from rotating too far by means of a brass plug, attached to the sphere at a point opposite the main triad, which also lies within the plastics tube.

As mentioned above, the device of the invention is primarily intended for use in fibre jointing, and in this application two of the devices are used to bring two fibre ends into the correct mutual position. The invention accordingly further provides a combination alignment device for aligning two sections of dielectric optical waveguide, comprising a pair of devices as previously defined having a common axis mounting premitting relative axial and circumferential movement thereof, the main triads being at adjacent ends of the devices, and the combination device including means for biassing the two devices towards one another.

In order to position two fibres accurately with respect to one another prior to jointing, it is necessary to provide some means for maintaining the two devices on a common axis. This may be effected simply by enclosing the two individual alignment devices in a common tube or sleeve in which they are a sliding fit. The common tube or sleeve may, for example, be made of plastics material, which is conveniently transparent.

Means for biassing the devices axially towards one another are also required and these may form part of the individual devices for example, each device may be spring-loaded along the fibre axis towards the main triad, for example, by means of a coil spring. Alternatively, separate biassing means not forming part of the individual alignment devices may be used; for example, coil springs within the common tube or sleeve may be made to bear on the ends of the devices remote from the main triads.

The means for biassing the devices towards one another is preferably adjustable. For example, screw-threaded caps engaging with the common tube or sleeve may bear on the ends of the devices remote from the main triads. The caps must of course be bored through so that the fibres can pass through them, the bores being in alignment with the path for fibre through each of the devices.

The invention will now be described in further detail, by way of example only, with reference to the accompanying drawings, in which: Fig 1 is a schematic representation of a triad of spheres forming part of a device according to the invention; Fig 2 is a schematic end elevation of two interlocking triads with a fibre passing through their central interstices; Fig 3 is a plan view of the triads shown in Fig 2, with one fibre being held by each triad; Fig 4 is a plan view of the arrangement of Fig 3 with one triad removed; Fig 5 is a schematic axial section through a first alignment device according to the invention; Fig 6 is a schematic axial section through a second alignment device according to the invention; Fig 7 is a schematic axial section through a third alignment device according to the invention; Fig 8 is a schematic axial section through a fourth alignment device according to the invention; Fig 9 is an exploded schematic axial section through a combination device including two of the devices shown in Fig 8; Fig 10 is a schematic axial section through a fifth alignment device according to the invention.

Referring now to the accompanying drawings, Fig 1 shows schematically a triad of mutually-contacting spheres 1 of equal radius. At the centre of the triad a dielectric optical waveguide (optical fibre) 2 occupies the region of an inscribed circle to the spheres 1 while a wall 3 of a surrounding passageway occupies the position of a cir cumscribing circle to the spheres 1. The fibre should be a snug but sliding fit within the triad at the site of the inscribed circle.

Typical dimensions of the components are related as follows: Radius of sphere = A Radius of inscribed circle = A(sec 30 - 1) = 0.1547A.

Radius of circumscribing circle = A(sec 30 + 1) = 2.1547A.

Radius of fibre = 62.5 microns.

therefore A = 404 microns.

Required diameter of spheres = 808 microns.

Required internal diameter of surround ingpassageway = 1.741 mm.

In practice, the sphere diameter must slightly exceed the calculated figure to allow for working clearance around the fibre and because the balls are slightly compressed by the wall of the surrounding passageway.

Clearly, if fibre of a radius different from 62.5 microns is used, a different sphere diameter must be chosen.

In practice the radius of the wall 3 of the passageway would be stretched somewhat in circumscribing the spherical balls, such stretching providing the necessary inward force on the spherical balls.

Figs 2 and 3 show how to of the triads of Fig 1 can relate positionally in order to function as an alignment device. The spherical balls of two triads 6 and 7 are so positioned that the centres of the spherical balls are equidistant from, and symmertically angularly spaced about, a line 5 passing perpendicularly through the two parallel planes containing the centres of the spherical balls.

In this positional relationship, an inscribed circle centred on line 5 and touching the spherical balls of the upper triad 6 will be accurately superposed on the corresponding inscribed circle of the lower triad 7.

A stack of such triads maintained in this superposed relationship defines a linear passage having the radius of that inscribed circle through the centres of the triads. Thus a circular section fibre of the same radius as that inscribed circle will be held in a linear configuration.

Alternatively, as shown in Fig 3, a pair of fibres can extend from opposite ends of a stack of inter-engaging triads, the superposed positions of the inscribed circles aiding axial alignment of the abutting fibre ends which is a major prerequisite of dielectric optical waveguide joints.

In Fig 4, the triad 6 has been removed and the fibre held by triad 7 is shown in the position it adopts for jointing purposes when the pair of triads are superposed and the fibre end positions are pushed by equal distances through the respective triads into end contact. It will be seen that each fibre end portion extends by approximately 0.8 of the ball radius beyond the contact plane with the triad. Thus if the ball radius is 400 microns, the fibre end portion extends freely beyond its contact plane with the triad by a length of approximately 320 microns.

Figs 5-10 show various forms of alignment device embodying the triad principle as illustrated in Figs 1 to 4.

Referring now to Fig 5, the main triad tungsten carbide spheres 8 and two subsidiary triads of identical spheres 9 and 10 are arranged in an interlocking row and fitted tightly into a cylindrical passage bored through a stainless-steel sphere 11 of larger radius. Although the triads 8, 9 and 10 fit tightly into the larger sphere 11, each individual small sphere is free to rotate about its own centre. The larger sphere 11 is snapfitted into a polytetrafluoroethylene (PTFE) moulding 12 having an axial bore of varying diameter. The end further from the main triad 8 of the passage through the larger sphere 11 is blocked by a p ug 13 which restricts the freedom of the larger sphere 11 to rotate about its centre. The plug 13 is of brass and also has an axial bore to accommodate fibre. The moulding 12 is a sliding fit in an outer tube 14 of any suitable material, for example, transparent plastics material. When the device of Fig 5 is to be used for fibre jointing, two such devices are accommodated within a common holding tube 14 with their main triads 8 adjacent to one another. The two devices may be biassed towards each other by means of separate coil springs (not illustrated).

Typical dimensions of this device are as follows: Diameter of smaller spheres: 0.845mm (845 microns) Diameter of larger sphere: 3.18mm Diameter of passage through larger sphere: 1 .793mm Diameter of larger portion of brass plug: 2.00mum Diameter of bore through brass plug: 0.30mm Outer diameter of PTFE moulding: 4.00mm Diameter of bore through PTFE moulding (left to right): 3.00, 3.30, 3.00, 1 .00mum External diameter of holding tube: 5.00mm Referring now to Fig 6 of the drawings, a second device according to the invention is shown which also includes three triads 8, 9 and 10 interference-fitted into a larger sphere 11. The larger sphere 11 is snapfitted into a convoluted moulding 15 of plastics material, for example, nylon or sintered PTFE. The convoluted moulding 15 is a loose fit in an outer holding tube 14 of any suitable material. The convolutions cause the moulding 15 to behave as a spring biassing the whole device in an axial direction towards the main triad 8. The larger sphere 11 is free to rotate in the moulding 15.

A third device according to the invention is shown in Fig 7. This device employs only a single triad 8 of tungsten carbide balls, the triad 8 being located in a recess in a larger stainless steel sphere 16. Angular location of the fibre is provided by a stainless-steel tube 17 of small radius, for example, a hypodermic tube. Axial biassing towards the triad 8 is supplied by a coil spring 18 which acts via a bearing cup 19 on the large sphere 16. The spring 18 is retained in positipn by means of a stop 20. To facilitate insertion of a fibre, the end 21 of the tube 17 remote from the triad 8 is belled out.

Fig 8 shows yet another alignment device constructed according to the invention. In this device, the triad 8 has a friction fit within a cylindrical recess 22 in one end of a cylindrical brass block 23. A bore 24, which can have a radius appreciably greater than that of the fibre to be held, extends through the length of the brass brass block 23, the bore 24 being restricted in radius at the end of the block 23 remote from the triad 8 in order to provide additional support for the fibre at that end.

Referring now to Fig. 9, there is shown an exploded view of a combination device, including a pair of devices as shown in Fig 8, for use in aligning the ends of the two fibres for jointing purposes. The devices 25 of Fig 8 have a loose sliding fit within a holding tube 14 of transparent plastics material whose outer end portions 26 are screwthreaded for engagement with a pair of brass end caps 27 which are internally threaded. Each of the caps 27 has a central orifice permitting entry of fibres to a jointing region within the plastics tube 14.

Attached to the inside surface of each cap 27 is a resilient annular pad 28 which, in use, bears on the end of an outer end surface of a device 25. Thus by screwing a cap 27 on to the plastics tube 14, the associated device 25 can be moved along the tube. The devices 25 can therefore be readily moved into the relative positions of the triads 6 and 7 as shown in Figs 2 and 3 in such a way that the end portions of fibres held by the devices 25 are brought together Final adjustment of the fibre positions can be made by manually forcing them axially relative to their respective devices.

Typical measurements of the various parts of this combination device are as follows: Length of plastics sleeve: 2.5cm External diameter of plastics sleeve: 6.5mm Length of brass block 23:1.25cm Diameter of triad spheres 8: 800 microns.

Turning now to Fig 10, an alignment device according to the invention is shown in which two triads spaced apart from one another are used. A main triad 8 and a subsidiary triad 29 for aiding the angular positioning of a fibre are both slidable within a sleeve 30. An axial bias towards the main triad 8 is provided by a compression spring 31 acting on slidable sleeves 32 which are accurately right-cylindrical in shape and press the triads 29 and 8 respectively against a screw-threaded retaining sleeve 33 and a rolled-over shoulder 34 of the outer sleeve 30.

WHAT WE CLAIM IS: 1. A device for holding and/or aligning a dielectric optical waveguide, comprising a triad of mutually contacting spherical bodies of substantially equal radius, and bias means adapted to press the bodies towards one another.

2. A device as claimed in Claim 1, wherein the spherical bodies have a radial tolerance less then 1 micron and a tolerance on sphericity less than 1 micron.

3. A device as claimed in Claim 1 or Claim 2, wherein the spheres are of tungsten carbide.

4. A device as claimed in any one of Claims 1 to 3, wherein the bias means is provided by a passage within a further body, the dimensions of the passage being so related to the diameter of a circle circumscribing the spherical bodies that the spherical bodies are located firmly within the passage but each is free to rotate about its centre.

5. A device as claimed in Claim 4 wherein the passage is substantially cylindrical.

6. A device as claimed in Claim 5, wherein the further body comprises a sleeve of resilient material which can be radially stretched to encompass the triad of spherical bodies, the unstressed internal diameter of the sleeve being less than the diameter of a circle circumscribing the spherical bodes.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Diameter of bore through brass plug: 0.30mm Outer diameter of PTFE moulding: 4.00mm Diameter of bore through PTFE moulding (left to right): 3.00, 3.30, 3.00, 1 .00mum External diameter of holding tube: 5.00mm Referring now to Fig 6 of the drawings, a second device according to the invention is shown which also includes three triads 8, 9 and 10 interference-fitted into a larger sphere 11. The larger sphere 11 is snapfitted into a convoluted moulding 15 of plastics material, for example, nylon or sintered PTFE. The convoluted moulding 15 is a loose fit in an outer holding tube 14 of any suitable material. The convolutions cause the moulding 15 to behave as a spring biassing the whole device in an axial direction towards the main triad 8. The larger sphere 11 is free to rotate in the moulding 15. A third device according to the invention is shown in Fig 7. This device employs only a single triad 8 of tungsten carbide balls, the triad 8 being located in a recess in a larger stainless steel sphere 16. Angular location of the fibre is provided by a stainless-steel tube 17 of small radius, for example, a hypodermic tube. Axial biassing towards the triad 8 is supplied by a coil spring 18 which acts via a bearing cup 19 on the large sphere 16. The spring 18 is retained in positipn by means of a stop 20. To facilitate insertion of a fibre, the end 21 of the tube 17 remote from the triad 8 is belled out. Fig 8 shows yet another alignment device constructed according to the invention. In this device, the triad 8 has a friction fit within a cylindrical recess 22 in one end of a cylindrical brass block 23. A bore 24, which can have a radius appreciably greater than that of the fibre to be held, extends through the length of the brass brass block 23, the bore 24 being restricted in radius at the end of the block 23 remote from the triad 8 in order to provide additional support for the fibre at that end. Referring now to Fig. 9, there is shown an exploded view of a combination device, including a pair of devices as shown in Fig 8, for use in aligning the ends of the two fibres for jointing purposes. The devices 25 of Fig 8 have a loose sliding fit within a holding tube 14 of transparent plastics material whose outer end portions 26 are screwthreaded for engagement with a pair of brass end caps 27 which are internally threaded. Each of the caps 27 has a central orifice permitting entry of fibres to a jointing region within the plastics tube 14. Attached to the inside surface of each cap 27 is a resilient annular pad 28 which, in use, bears on the end of an outer end surface of a device 25. Thus by screwing a cap 27 on to the plastics tube 14, the associated device 25 can be moved along the tube. The devices 25 can therefore be readily moved into the relative positions of the triads 6 and 7 as shown in Figs 2 and 3 in such a way that the end portions of fibres held by the devices 25 are brought together Final adjustment of the fibre positions can be made by manually forcing them axially relative to their respective devices. Typical measurements of the various parts of this combination device are as follows: Length of plastics sleeve: 2.5cm External diameter of plastics sleeve: 6.5mm Length of brass block 23:1.25cm Diameter of triad spheres 8: 800 microns. Turning now to Fig 10, an alignment device according to the invention is shown in which two triads spaced apart from one another are used. A main triad 8 and a subsidiary triad 29 for aiding the angular positioning of a fibre are both slidable within a sleeve 30. An axial bias towards the main triad 8 is provided by a compression spring 31 acting on slidable sleeves 32 which are accurately right-cylindrical in shape and press the triads 29 and 8 respectively against a screw-threaded retaining sleeve 33 and a rolled-over shoulder 34 of the outer sleeve 30. WHAT WE CLAIM IS:

1. A device for holding and/or aligning a dielectric optical waveguide, comprising a triad of mutually contacting spherical bodies of substantially equal radius, and bias means adapted to press the bodies towards one another.

7. A device as claimed in Claim 5,

wherein the further body is a sphere of larger radius than the bodies of the triad, the longitudinal axis of the passage being a radius of the sphere.

8. A device as claimed in any one of Claims 1 to 7, which also comprises means aligned with the central interstice of the triad of bodies for locating a dielectric optical waveguide passing through that interstice at a point spaced from that interstice.

9. A device as claimed in Claim 8, wherein the tried of spherical bodies is symmetrically disposed in a recess in the end of a block, an interference fit between the block and the spherical bodies providing the bias means, and the block has an axial bore aligned with the central interstice of the triad and and having a constriction at a point spaced from the said interstice to serve as the said locating means.

10. A device as claimed in Claim 8, wherein the locating means comprises one or more additional triads of spherical bodies, the radius of the bodies of the additional triads being equal to or greater than the radius of the bodies of the main triad, and the central interstices of the main and additional triads being aligned.

11. A device as claimed in Claim 10, wherein the radii of the bodies of the main and additional triads are substantially equal, and the triads are so stacked in an interengaging row that the centres of the spheres of any two adjacent triads are symmetrically angularly disposed about a line joining the centres of their inscribed circles.

12. A device as claimed in Claim 7 and Claim 11, wherein the inter-engaging triads are all located within the passage in the larger-radius sphere

13. A device as claimed in Claim 7 or any Claim as appendant thereto, wherein the larger-radius sphere is so located in retaining means that it can rotate to some extent about its centre.

14. A device as claimed in Claim 13 which further includes means for limiting the extent of rotation of the larger-radius sphere.

15. A device as claimed in Claim 13 or Claim 14, wherein the retaining means is of resilient material and the sphere is a snap fit in the resilient retaining means.

16. A device as claimed in any one of Claims 1 to 15, which includes further biassing means adapted to bias axially a dielectric optical waveguide held thereby towards the main triad.

17. A device as claimed in Claim 16, wherein the said further biassing means comprises a coil spring.

18. A device for holding and/or aligning a dielectric optical waveguide, the device being substantially as hereinbefore described with reference to, or as shown in, any one of Figs 1 to 10 of the accompanying drawings.

19. A combination alignment assembly for aligning two sections of dielectric optical waveguide, comprising a pair of devices as claimed in any one of Claims 1 to 18 having a common axis mounting permitting relative axial and circumferential movement thereof, the main triads being at adjacent ends of the devices, and the assembly including means for biassing the two devices towards one another.

20. An assembly as claimed in Claim 19, wherein the two devices are mounted inside a common tube in which they can slide in an axial direction.

21. An assembly as claimed in Claim 19 or Claim 20, wherein the means for biassing the two individual devices towards one another is adjustable.

22. An assembly as claimed in Claims 20 and 21, wherein the said biassing means includes screw-threaded caps engaging with the said common tube and provided with an axial orifice to allow passage of fibre, each cap bearing, via resilient means, on the end of a device remote from the (main) triad.

23. An assembly as claimed in Claim 22, wherein the resilient means comprises an annular pad of resilient material or a coil spring.

24. An assembly for aligning two sections of dielectric optical waveguide, the assembly being substantially as hereinbefore described with reference to, and as shown in, Fig 9 of the accompanying drawings.