GB2509052A

GB2509052A - Optical fibre connector

Info

Publication number: GB2509052A
Application number: GB1220748.6A
Authority: GB
Inventors: Glen Mcfarlane
Original assignee: BERCLEYS CONSULTING Ltd
Current assignee: BERCLEYS CONSULTING Ltd
Priority date: 2012-11-19
Filing date: 2012-11-19
Publication date: 2014-06-25
Also published as: GB201220748D0

Abstract

An optical fibre connector 10 has ferrules 40 and a sleeve mechanism 22, 24 for holding pairs of ferrules 40 together and in alignment. Each ferrule 40 locates within a tubular guide 38, with a transparent sphere 50 fixed near the end, and a coupling element 52 of resilient transparent material filling the tubular guide 38 between the ball lens 50 and the end of the tubular guide 38, and projecting beyond the end of the tubular guide 38. Another invention relate to the sleeve mechanism 22, 24 having a resilient element 58 to push on the ferrule 40, and piston 55 acting on the tubular guide 38. Another invention relates to a rigid sleeve, clamping ring 32 and bolt 33 for clamping strength wires of a fibre optic cable 12. Another invention relates to the sleeve mechanism 22, 24 having a 24 with an accurately straight cylindrical bore large enough to accommodate cylindrical elements with some play, along with means 90, 96 to apply a sideways force onto the cylindrical elements so as to clamp them into alignment. The optical fibre connector 10 is suitable for use underwater, for example at the seabed.

Description

Optical Fibre Connector The present invention relates to a connector for connecting optical fibres end-to-end so that light can propagate from one to the next.

Such connectors are known. Alignment is a significant consideration in the context of such connectors. This is because a fibre is typically of diameter only about pm with a significantly smaller core which may be of diameter no more than 10 pm, so that if the fibres are misaligned by 20 pm the light transmission would be significantly inhibited. For example US 4 185 886 describes a hermaphroditic fibre-optic connector in which each fibre terminates in a ferrule, and when connector members are mated together the ferrules in the connector members are aligned.

However a connector that is suitable for use under water, and is easy to connect and disconnect, would be desirable.

According to the present invention there is provided an optical fibre connector suitable for use immersed in a fluid, comprising at least one pair of ferrules each carrying a respective optical fibre, and a sleeve mechanism for holding a pair of ferrules together and in alignment, wherein each ferrule locates within a tubular guide, one to locate each ferrule, with transparent spheres fixed near the ends of the tubular guides that are to abut each other, the optical fibre within the ferrule terminating within the tubular guide in the vicinity of one side of the transparent sphere, and with a coupling element of resilient transparent material whose refractive index is less than that of the transparent sphere filling the portion of each tubular guide between the sphere and the end of the tubular guide, and projecting beyond the end of the tubular guide.

It will be appreciated that if the connector is intended to connect a plurality of pairs of optical fibres, it will comprise a corresponding plurality of pairs of ferrules, each ferrule being provided with a respective tubular guide, transparent sphere, and coupling element.

Preferably each transparent sphere is of glass. Preferably each sphere is of a material whose refractive index is between 1.50 and 1.75, more preferably between 1.55 and 1.65. The coupling element is preferably of a material whose refractive index is less than 1.5, preferably less than 1.45, and more preferably less than 1.40.

For example it may be a silicone polymer; the linear silicones based on (Me2SiO)n have a refractive index approximately 1.40-1.42, while if some methyl groups are replaced, for example by trifluoropropyl groups, the refractive index may be reduced to less than 1.40.

Each transparent sphere is preferably of a diameter substantially that of the ferrule, and so considerably larger than the diameter of the optical fibre. For example the ferrule and the transparent sphere may both be of diameter between 1 mm and 5 mm, for example between 1.5 mm and 3 mm, and in one embodiment the transparent sphere is of diameter 2.5 mm.

Preferably the coupling element protrudes no more than 2 mm beyond the end of the tubular channel, more preferably not more than 1 mm, for example between 0.5 and 0.7 mm. When the optical fibre connector is connected, with the ferrules brought into alignment and brought together, the protruding portion of the coupling element is squeezed into the tubular channel, and in the process any fluid that is present between the coupling elements is squeezed out. In one embodiment the protruding portion of the coupling element has a flat end, but it may alternatively have a convexly curved end to ensure that drops of liquid or gas bubbles are not trapped between the opposed coupling elements when they are pressed together.

Preferably each tubular guide is an alignment sleeve of a ceramic material.

Preferably each tubular guide is mounted resiliently within the sleeve mechanism.

In a second aspect the present invention provides an optical fibre connector suitable for use immersed in a fluid, comprising at least one pair of rods each carrying a respective optical fibre, and a mechanism for holding the pairs of rods together and in alignment, wherein the mechanism comprises at least one sleeve assembly that defines a bore closed at one end by an end plate, at least one tubular channel being defined through the end plate, the tubular channel extending between the bore and an end surface of the end plate, one of the rods being axially slidable in the tubular channel, the sleeve assembly comprising a resilient element for urging the rod along the tubular channel, and the sleeve assembly also comprising a movable piston within the bore, the movable piston acting on the rod in the tubular channel; wherein the piston defines a first rear surface facing away from the end plate, and the sleeve mechanism also comprises a duct to enable the fluid in which the connector is immersed to exert a pressure on the first rear surface, so as to counteract the pressure of the fluid on the face of the rod at the end surface of the end plate.

Preferably the mechanism comprises two such sleeve assemblies for connection end to end. In this case it will be appreciated that if the connector is intended to connect a plurality of pairs of optical fibres, it will comprise a corresponding plurality of pairs of rods. Each rod preferably comprises a ferrule and a tubular guide, and preferably also comprises a transparent sphere, and coupling element as discussed previously.

The area of the first rear surface projected in a plane orthogonal to the longitudinal axis of the piston may be no more than 10% different from the total areas of the rod or rods exposed at the end surface of the end plate, so that the corresponding axial forces due to fluid pressure are substantially in balance. Indeed the areas may be equal, so that the forces due to the fluid pressure are exactly balanced. Consequently the force acting on each rod is substantially only that of the resilient element, whatever depth the connector is immersed to. However, where the piston is provided with resilient seals, such as 0-ring seals, it may also be desirable to provide an additional spring element to counteract the friction from the seals.

In a preferred embodiment, the sleeve assembly also includes a pressure sensitive valve associated with the duct, so that the fluid in which the connector is immersed exerts a pressure on the first rear surface only when the pressure of the fluid exceeds a threshold value. This corresponds to a particular depth of immersion at which the pressure-sensitive valve will open.

To assist in ensuring accurate alignment of the sleeve assemblies, the end surface of each end plate preferably defines plane surfaces separated by steps, so that the steps mate with each other when the opposed sleeve assemblies are aligned.

In a third aspect the present invention provides an optical fibre connector for use with optical fibre cables that are provided with strength-providing wires that extend along the length of the cable and protect the optical fibres, wherein a connector element for connection to an end of the optical fibre cable comprises a rigid sleeve to enclose an end portion of the cable, the rigid sleeve defining an end face that is substantially orthogonal to the longitudinal axis of the cable, and a rigid clamping ring defining a clamping face that is substantially the same shape as the end face of the rigid sleeve, and bolt means to fix the clamping ring onto the end face of the rigid sleeve, such that the strength-providing wires of the cable after being bent outwardly can be clamped between the clamping ring and the end face of the rigid sleeve, while the optical fibres of the cable extend through the clamping ring.

Preferably both the rigid sleeve and the clamping ring are of stainless steel.

The expression substantially orthogonal' should be taken to mean that the end face extends in an orientation that is within 200 of a plane that is orthogonal to the longitudinal axis, preferably within 100 of that orthogonal plane. The end face may be frustro-conical. Alternatively it is planar.

It will be appreciated that the third aspect of the invention may be combined with the first aspect or the second aspect of the invention, or both.

In a fourth aspect the present invention provides an optical fibre connector comprising a pair of cylindrical elements each carrying at least one optical fibre, and a mechanism for holding the pair of cylindrical elements together so the optical fibres are in alignment, wherein the mechanism comprises a casing defining a cylindrical bore, the bore being straight and the diameter of the bore being large enough to accommodate the cylindrical elements with some play; the mechanism also comprising means to apply a sideways force onto the cylindrical elements so as to clamp the cylindrical elements into alignment.

Preferably the play is less than 1 mm, although this will depend on the actual diameter. More preferably the play is less than 0.1 mm, for example less than 50 pm.

As an example the diameter may be such as to provide a play of between 10 and 30 pm.

In a preferred embodiment the casing comprises an outer casing sleeve, and a concentric inner casing sleeve, the inner casing sleeve comprising a wall that defines the cylindrical bore, a portion of the wall being movable with respect to the remainder of the wall of the inner casing sleeve. The movable portion of the wall preferably comprises a flap that is resiliently connected to the remainder of the wall along one edge, preferably that edge extending parallel to the longitudinal axis.

Moving this portion of the wall applies the requisite sideways force onto the cylindrical elements.

The means to apply the sideways force desirably applies a substantially uniform force along the length of the force-applying means. This may be applied hydraulically. A preferred mechanism, however, comprises a multiplicity of balls arranged within a groove in the outer surface of the movable portion of the wall, the balls fitting freely within the groove but the length of the groove being less than the sum of the diameters of the balls so that the balls take up a zigzag arrangement along the groove, and a plunger to apply a compression force along the groove, so changing the radial width of the zigzag arrangement of the balls. This pushes the movable portion of the wall inward, away from the outer casing sleeve. Movement of the plunger may be brought about by twisting of the outer casing sleeve, preferably through an angle of no more than 90°, more preferably not more than 45°.

The clamping force can subsequently be released, if the connector is to be disconnected. If the plunger is retracted, the length of groove available to the balls increases, so the radial width decreases, so that the movable portion of the wall moves outward. This releases the clamping force on the cylindrical elements.

Preferably the connector also includes a releasable latch mechanism to secure the cylindrical elements end to end when they abut each other within the casing. Hence in operation the cylindrical elements would be inserted axially into the casing, and pushed together until the latch mechanism secures them end to end. The plunger would then be activated, for example by twisting the outer casing sleeve, to clamp the cylindrical elements into precise alignment. Thus the connection procedure involves pushing, and then twisting.

Preferably each cylindrical element is provided with a casing, so the connector is hermaphroditic, and the cylindrical element is axially movable relative to the casing. One casing would be slid back out of the way, and the cylindrical element associated with that casing would be inserted into the casing of the other cylindrical element, and clamped together as described above.

It will be appreciated that the fourth aspect of the invention may be combined with any one or more of the preceding aspects of the invention. In particular a cylindrical element of the fourth aspect may be a sleeve assembly of the second aspect.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 shows a side view of a connector of the invention, with two hermaphroditic parts joined together; Figure 2 shows a longitudinal sectional view of one part of the connector of figure 1, shown in the disconnected state; Figure 3 shows a longitudinal sectional view of a central portion of the connector of figure 1; Figure 4 shows a perspective view of mating faces of the two parts of the connector of figure 1, during assembly; Figure 5 shows a longitudinal sectional view of the connector of figure 1; Figure 6 shows a transverse sectional view on the line 6-6 of figure 5; and Figure 7 shows a perspective view, partially cut away, corresponding to the view of figureS.

Referring now to figure 1 there is shown a connector 10 which connects a first optical fibre cable 12a to a second optical fibre cable 12b. The connector 10 consists of two identical hermaphroditic connector parts 14a, 14b that are connected to each other end to end. Each connector part 14a and 14b consists of a moulded polyethylene boot 16 which encloses a steel strain-relief tube 18 (not shown in figure 1), an end cap 20 of an inner sleeve assembly 22, and a casing 24 that surrounds the inner sleeve assembly 22. When joining the connector parts 14a and 14b together, one of the casings 24 is slid back (that of the connector part 14a in figure 1), so the corresponding inner sleeve assembly 22 protrudes. The protruding inner sleeve assembly 22 is pushed into the casing 24 of the other connector part 1 4b so the inner sleeve assemblies 22 mate together. The surrounding casing 24 is then twisted to lock the connector parts 14a and 14b together. The connector 10 then securely connects the optical fibre cables 12a and 12b together. The mechanism for ensuring that the inner sleeve assemblies 22 mate together, and the locking mechanism, are described below.

Whilst the connector 10 is in use, the casing 24 that had been slid back is redundant. It would be conceivable to provide a connector part 14a that did not have a casing 24. However, an advantage of providing this redundant casing 24 is that the connector parts 14a and 14b, when they are not joined together, are identical. So when various cables 12 are to be joined together, the connector 10 provides the advantage that the connector parts 14 are hermaphroditic.

Referring now to figure 2, one of the connector parts 14a is shown with its casing 24 slid back so the inner sleeve assembly 22 protrudes. The optical fibre cable 12 carries four optical fibres 26, in this embodiment, and these are protected by a surrounding ring of steel wires 28, and enclosed within a plastic jacket 30. Each optical fibre 26 (typically of diameter about 125 pm) is provided with a protective plastic coating of thickness about 0.5 mm. The strain-relief tube 18 encloses the end of the cable 12. and has a step in the bore at which the plastic jacket 30 terminates.

The steel wires 28 extend through the strain-relief tube 18 and are bent through 90° so as to extend across the end of face of the strain-relief tube 18, and are clamped in this position by a clamping ring 32 fixed by bolts 33 on to the end of face of the strain-relief tube 18.

The inner sleeve assembly 22 defines a bore that, at its rear end, encloses an end part of the strain-relief tube 18, and is fixed to the strain-relief tube 18 by the end cap 20. The optical fibres 26 extend through the clamping ring 32 into the bore of the inner sleeve assembly 22. The inner sleeve assembly 22 is closed at its front end by an end plate 34 through which extend tour tubular channels (only two are shown).

Within each tubular channel is a ceramic guide tube 38 (see Figure 3) within which is a ferrule 40, and each optical fibre 26 extends to the front end of one of the ferrules 40, the end portion having the plastic coating removed.

Referring now to figure 3, the mating portions of the inner sleeve assemblies 22 within the connector 10 of figure 1 are shown to a larger scale. At the front face of the end plate 34 is an inset faceplate 42 which defines four apertures corresponding to the tubular channels that contain the ceramic guide tube 38, each aperture in the faceplate 42 being smaller than the diameter of the ceramic guide tube 38. The faceplate 42 so prevents the guide tube 38 from being displaced further forward. As shown also in Figure 4, the front face of the end plate 34 has a stepped profile in cross-section, with a step 44 up on one side and a step 45 down on the other side; when the two inner sleeve assemblies 22 are brought together these steps 44 and 45 mate with each other and so ensure alignment of the inner sleeve assemblies 22 and so of the ferrules 40 in each end plate 34.

Within each ceramic guide tube 38 the ferrule 40 is free to slide, and abuts an annular stop 48 near the front end of the guide tube 38. On the other side of the stop 48 is a glass sphere 50 which acts as a collimating lens, and which is fixed to the guide tube 38. The space between the front face of the ferrule 40 and the rear face of the glass sphere 50, and the space in front of the glass sphere 50, are filled with a silicone material so as to provide coupling blocks 51 and 52, respectively, that are resilient and transparent. In this example the glass sphere 50 and the ferrule 40 are both of diameter 2.5 mm. The coupling block 52 projects 0.6 mm beyond the front face of the faceplate 42 when the connector part 14 is disconnected, as shown in figures 2 and 4; when the connector parts 14 are connected together, the coupling blocks 52 on both sides are resiliently compressed, and no longer project, as shown in figure 3.

Each ceramic guide tube 38 is free to slide within the tubular channel in the end plate 34, and projects a short distance into the bore of the inner sleeve assembly 22. The ferrule 40 projects further into the bore. Within the bore is a piston 55 with a stepped external profile, a portion of the piston 55 adjacent to the end plate 34 being of larger diameter than the remainder of the piston 55 and so defining a rear facing peripheral surface 56. The piston 55 is hollow, defining four cylindrical chambers that are open at the rear end, and align with a small hole at the front face of the piston 55 through which the ferrule 40 projects. Within each cylindrical chamber is a tubular cap 57 which engages the end of the ferrule 40, the tubular cap 57 being pushed forward by a compression spring 58 whose other end abuts a fixed liner 60. The optical fibre 26 extends through the fixed liner 60 and so through the tubular cap 56 to the ferrule 40. The fixed liners 60 are fixed in position by a frame 62 that is linked at its other end to the clamping ring 32.

The piston 55 is sealed to the bore of the inner sleeve assembly 22 by 0-ring seals 64 and to the bore of a sleeve liner 66 by 0-ring seals 67. Within the inner sleeve assembly 22 is a fluid duct 59 (shown in Figure 6) that communicates with a circumferential chamber 68 communicating with the bore to the rear of the rear facing peripheral surface 56. The fluid duct 59 is provided with an inlet valve which may be arranged to open at a predetermined depth below the surface of the water, for example 30 m or lOOm, or alternatively the fluid duct 59 may be open to the surrounding fluids at all times. Between the end of the sleeve liner 66 and the rear facing peripheral surface 56 is a compression spring 70 which is under sufficient compression to balance the friction between the piston 55 and the 0-ring seals 64 and 67. This compression spring 70 hence ensures that the end face of the piston 55 is up against the end faces of the ceramic guide tubes 38. The compression springs 58 provide a resilient load on the ferrules 40, holding them up against the stops 48.

When the connector parts 14 are connected together, each coupling block 52 is resiliently compressed and so pushes the guide tube 38 and the ferrule 40 back into the end plate 34, against the effect of the compression spring 58. At this stage the compression to which the coupling block 52 is subjected is therefore controlled by the compression spring 58. The coupling blocks 52 are compressed sufficiently to squeeze out any water from between the opposing surfaces, while the degree of compression is not so large as to alter the optical properties of the coupling blocks 52 and to distort the optical path.

If the connector lOis immersed in water, for example in the sea, then the seawater will exert a pressure on the exposed portion of the coupling block 52, and so on the ceramic guide tube 38, pushing it further back and so decreasing the compression of the coupling block 52. Since the front face of the piston 55 contacts the rear face of the ceramic guide tubes 38, any movement of the guide tube 38 also pushes back the piston 55. Once the connector 10 is below the predetermined depth, the inlet valve opens so that the rear facing peripheral surface 56 is exposed to the ambient pressure. The resultant force on the rear facing peripheral surface 56 of the piston 55 balances the force on the exposed portions of the coupling blocks 52. Consequently the connector 10 can be used at substantially any depth, even at the bottom of an ocean where the depth may be more than 3 km.

Referring now to figure 5, the connector 10 is shown in the connected state, with the front faces of the end plates 34 abutting each other (this sectional view being shown in a plane orthogonal to that of tigure 3), with the inner sleeve assemblies 22 aligned. The casing 24 of the left-hand connector part 14a surrounds those abutting faces, whereas the casing 24 of the right-hand connector part 14b is shown retracted. The casing 24 has an 0-ring seal 72 at its rear end, by which it is sealed to the outer surface of the inner sleeve assembly 22. The casing 24 has a knurled outer surface 73, and defines a bore significantly larger than the diameter of the inner sleeve assembly 22 within which is an inner casing sleeve 74 (only part of which is in section in this plane). The front end of the casing 24 locates a screwed-in locking ring 76.

A pair of spring latches 80 are fixed within the casing 24 by a pin 81 in a slot, and in their relaxed position extend along the surface of the inner sleeve assembly 22, being fixed to the casing 24 adjacent to its rear end. The front end of each spring latch 80 forms a block 82 which extends both radially inwards and outwards, and whose front face is inclined. As shown, the block 82 engages with a correspondingly-shaped circumferential groove 84 on the outer surface of the inner sleeve assembly 22 of the right-hand connector part 1 4b. This holds the inner sleeve assemblies 22 together. The front face of the block 82 is inclined, and engages a projecting rim 85 that forms part of the inner casing sleeve 74. When the connector 10 is being disconnected, the block 82 can be lifted out of the groove 84 by pushing the casing 24 backwards, so pushing the projecting rim 85 against the inclined surface of the block 82. This enables the inner sleeve assembly 22 of the right-hand connector part 14b to be pulled out of the casing 24.

If the casing 24 is pushed further back, until it reaches the retracted position (as shown in figure 1 and figure 2) then the blocks 82 locate in the corresponding groove 84 of the left-hand connector part 14a.

The components described above enable the two connector parts 14a and 14b to be joined together, alignment being ensured by the steps 44 and 45 (see figures 3 and 4), and axially linked by the spring latches 80. However the alignment produced by these components is not sufficiently accurate to ensure good coupling between the optical fibres 26. The more accurate alignment is ensured by the features described below.

Referring now to figure 6, the inner casing sleeve 74 defines an accurately straight bore to locate the inner sleeve assemblies 22. the bore being large enough to allow easy sliding of the inner sleeve assemblies 22, providing a clearance of 50 pm for example. Along a middle portion of the length of the inner casing sleeve 74, on one half (the right-hand half as shown), a tab portion 90 is defined by two axially-spaced circumferential slots and an axial slot 91, and the half of the tab portion 90 furthest from the axial slot 91 is machined to a thickness of just a few millimetres, so as to act as a spring 93. Within the thick part of the tab portion 90 is defined an inclined rectangular slot 94 which extends axially. In addition there are two rectangular cutouts 95 diametrically opposite each other, so the latches 80 are free to move radially outward. Consequently the inner casing sleeve 74 defines a continuous ring only near its ends. The portion of the inner casing sleeve 74 to the left of the rectangular cutouts 95 (as shown) is consequently rigid, while the portion to the right of the rectangular cutouts 95 includes the tab portion 90.

Referring also to figure 7, within the rectangular slot 94 are seventeen steel balls 96, which take up a zigzag-formation along the length of the slot. A hole extends axially from the slot 94 to the rear end of the inner casing sleeve 74, and a push rod 98 extends axially through this hole, and projects beyond the rear end of the inner casing sleeve 74 to abut against the inside end of the casing 24. The rear end of the inner casing sleeve 74 engages the inner surface of the casing 24 at a screw thread 100.

When assembling the connector 10, the two connector parts 14a and 14b are connected together and axially linked by the spring latches 80 by pushing the inner sleeve assembly 22 of the right-hand connector part 1 4b into the casing 24 of the left-hand connector part 14a (or vice versa). The casing 24 is then twisted so as to move the casing 24 forwards along the screw thread 100. This pushes the push rod 98 forwards, so exerting an axial force on the steel balls 96 in the rectangular slot 94.

The axial force slightly changes the arrangement of the balls 96, increasing the height of the zigzag-formation. With reference to figure 6, this change in height of the zigzag-formation bends the spring 93 and moves the tab portion 90 radially inwards, tending to close the axial slot 91. Consequently the inner sleeve assemblies 22 are pushed firmly against the accurate straight bore of the inner casing sleeve 74 on the side opposite the tab portion 90. This ensures accurate alignment of the ferrules 40, and also ensures the connector parts 14a and 14b are firmly locked together. The angle through which the casing 24 must be twisted depends upon the pitch of the screw thread 100, but is preferably less than 60°, for example 15°, 20° or 30°.

When the connector 10 is to be disconnected, the casing 24 is twisted through the same angle in the opposite sense, back to its original position, so as to move the casing 24 backwards along the screw thread 100. This removes the axial force on the balls 96, so the tab portion 90 springs back to its original position. If the casing 24 is then pulled back, as explained in relation to figure 5 the latches 80 are released, so the two connector parts 14a and 14b can be pulled apart.

It will be appreciated that the clearance between the inner casing sleeve 74 and the inner sleeve assemblies 22 may be different from the value mentioned above, although it is preferably between 10 and 100 pm. The provision of such a clearance avoids the requirement to insert the inner sleeve assemblies 22 into a close-fitting bore, which makes it easier to connect the connector 10, and makes the connector less sensitive to the entry of dirt or contaminants. The clamping is applied by the zigzag-formation of the balls 96 substantially uniformly along the length of the tab portion 90, so the mating inner sleeve assemblies 22 are firmly clamped up against the accurately straight bore at the opposite side of the inner casing sleeve 74. A key benefit of the provision of the balls 96 is that the bore of the inner casing sleeve 74 does not have to be manufactured to a precise radial tolerance, because the space between the inner sleeve assemblies 22 and the bore is eliminated during the clamping action. Instead, the bore is machined to an accurate straightness tolerance, but is deliberately made a loose clearance fit.

The connection of the optical fibre cable l2to the connector part 14, by clamping the steel wires 28 between the end of face of the strain-relief tube 18 and the clamping ring 32, ensures that any external axial or radial forces on the cable 12 are not transmitted directly to the optical fibres 26. The optical fibres 26 extend freely between the clamping ring 32 and the terrules 40, and the ferrules 40 can undergo limited axial movement, as they are sprung loaded by the springs 58. The length of each optical fibre 26 between the clamping ring 32 and the ferrule 40 is sufficient that axial movement of the ferrule 40 does not bend the fibre in a detrimental fashion. The provision of the optically clear resilient material 52 in front of the glass sphere 50 and initially protruding beyond the faceplate 42 provides the capability for mating the connector parts 1 4a and 14b underwater, as any water is squeezed away from the opposed surfaces. The resilient material 52 provides sealing against water ingress to the glass sphere 50, and also provides an uninterrupted optical path for the light between the glass spheres 50 of opposed connector parts 14a and 14b. The compressive forces applied to the resilient material 52 are those provided by the compression springs 58, so that the degree of compression is sufficient to squeeze out water, but not so much as to distort the optical path. The provision of pressure balancing between the front faces of the ceramic guide tubes 38 and the rear facing peripheral surface 56 ensures that the appropriate degree of compression is provided to the resilient material 52, whatever the depth of immersion may be.

It will be understood that the connector 10 described above may be modified in various ways are remaining within the scope of the present invention, which is that described in the claims. The invention includes several different aspects which may be used separately or together.

For example, the connector 10 is described as being suitable for use under water, but a connector for use in a different medium may have the optical components of different materials, and similarly if the optical fibres 26 carry non-visible radiation the optical components may be of different materials. The connector may also be used in situations where the surrounding fluid is a gas rather than a liquid, for example in a borehole or well filled with natural gas.

In the connector 10 the movable portion of the wall comprises a tab 90 that is resiliently connected to the remainder of the wall at the thin spring section 93 along an edge that extends parallel to the longitudinal axis. There are alternative ways of achieving this action using the balls 96, such as placing the balls 96 in a movable tray which moves in a slot in the inner casing sleeve.

Claims

Claims 1. An optical fibre connector suitable for use immersed in a fluid, comprising at least one pair of ferrules each carrying a respective optical fibre, and a sleeve mechanism for holding a pair of ferrules together and in alignment, wherein each ferrule locates within a tubular guide, one to locate each ferrule, with transparent spheres fixed near the ends of the tubular guides that are to abut each other, the optical fibre within the ferrule terminating within the tubular guide in the vicinity of one side of the transparent sphere, and with a coupling element of resilient transparent material whose refractive index is less than that of the transparent sphere filling the portion of each tubular guide between the sphere and the end of the tubular guide, and projecting beyond the end of the tubular guide.
2. A connector as claimed in claim 1 wherein each transparent sphere is of glass.
3. A connector as claimed in claim 1 or claim 2 wherein each sphere is of a material whose refractive index is between 1.50 and 1.75, more preferably between 1.55 and 1.65.
4. A connector as claimed in any one of the preceding claims wherein the coupling element is of a material whose refractive index is less than 1.5, preferably less than 1.45, and more preferably less than 1.40.
5. A connector as claimed in claim 4 wherein the coupling element is a silicone polymer.
6. A connector as claimed in any one of the preceding claims wherein each transparent sphere is of a diameter substantially that of the ferrule.
7. A connector as claimed in claim 6 wherein the ferrule and the transparent sphere are each of diameter between 1 mm and 5 mm, preferably between 1.5 mm and 3 mm.
8. A connector as claimed in any one of the preceding claims wherein the coupling element protrudes no more than 2 mm beyond the end of the tubular channel, more preferably not more than 1 mm.
9. A connector as claimed in any one of the preceding claims wherein the protruding portion of the coupling element has a convexly curved end to ensure that drops of liquid or gas bubbles are not trapped between the opposed coupling elements when they are pressed together.
10. A connector as claimed in any one of the preceding claims wherein each tubular guide is mounted resiliently within the sleeve mechanism.
11. An optical fibre connector suitable for use immersed in a fluid, comprising at least one pair of rods each carrying a respective optical fibre, and a mechanism for holding the pairs of rods together and in alignment, wherein the mechanism comprises at least one sleeve assembly that defines a bore closed at one end by an end plate, at least one tubular channel being defined through the end plate, the tubular channel extending between the bore and an end surface of the end plate, one of the rods being axially slidable in the tubular channel, the sleeve assembly comprising a resilient element for urging the rod along the tubular channel, and the sleeve assembly also comprising a movable piston within the bore, the movable piston acting on the rod in the tubular channel; wherein the piston defines a first rear surface facing away from the end plate, and the sleeve mechanism also comprises a duct to enable the fluid in which the connector is immersed to exert a pressure on the first rear surface, so as to counteract the pressure of the fluid on the face of the rod at the end surface of the end plate.
12. A connector as claimed in claim 11 comprising two such sleeve assemblies for connection end to end.
13. A connector as claimed in claim 11 or claim 12 wherein each rod comprises a ferrule and a tubular guide.
14. A connector as claimed in claim 13 wherein each rod also comprises a transparent sphere, and a coupling element of resilient transparent material whose refractive index is less than that of the transparent sphere filling the portion of each tubular guide between the sphere and the end of the tubular guide, and projecting beyond the end of the tubular guide.
15. A connector as claimed in any one of claims 11 to 14 wherein the area of the first rear surface projected in a plane orthogonal to the longitudinal axis of the piston is no more than 10% different from the total areas of the rod or rods exposed at the end surface of the end plate.
16. A connector as claimed in any one of claims 11 to 15 wherein the piston is provided with resilient seals, and the connector also comprises an additional spring element to counteract the friction from the seals.
17. A connector as claimed in any one of claims 11 to 16 wherein the sleeve assembly also comprises a pressure sensitive valve associated with the duct, arranged to open the valve at a threshold pressure.
18. A connector as claimed in any one of claims 11 to 17 wherein the end surface of each end plate defines plane surfaces separated by steps, so that the steps mate with each other when the opposed sleeve assemblies are aligned.
19. An optical fibre connector for use with optical fibre cables that are provided with strength-providing wires that extend along the length of the cable and protect the optical fibres, wherein a connector element for connection to an end of the optical fibre cable comprises a rigid sleeve to enclose an end portion of the cable, the rigid sleeve defining an end face that is substantially orthogonal to the longitudinal axis of the cable, and a rigid clamping ring defining a clamping face that is substantially the same shape as the end face of the rigid sleeve, and bolt means to fix the clamping ring onto the end face of the rigid sleeve, such that the strength-providing wires of the cable after being bent outwardly can be clamped between the clamping ring and the end face of the rigid sleeve, while the optical fibres of the cable extend through the clamping ring.
20. A connector as claimed in claim 19 wherein both the rigid sleeve and the clamping ring are of stainless steel.
21. A connector as claimed in claim 19 or claim 20 wherein the end face extends in an orientation that is within 100 of a plane that is orthogonal to the longitudinal axis.
22. A connector as claimed in any one of claims 19 to 21 wherein the connector comprises: (a) at least one pair of ferrules each carrying a respective optical fibre, and a sleeve mechanism for holding a pair of ferrules together and in alignment, wherein each ferrule locates within a tubular guide, one to locate each ferrule, with transparent spheres fixed near the ends of the tubular guides that are to abut each other, the optical fibre within the ferrule terminating within the tubular guide in the vicinity of one side of the transparent sphere, and with a coupling element of resilient transparent material whose refractive index is less than that of the transparent sphere filling the portion of each tubular guide between the sphere and the end of the tubular guide, and projecting beyond the end of the tubular guide, having features as claimed in any one of claims ito 10; and/or: (b) at least one pair of rods each carrying a respective optical fibre, and a mechanism for holding the pairs of rods together and in alignment, wherein the mechanism comprises at least one sleeve assembly that defines a bore closed at one end by an end plate, at least one tubular channel being defined through the end plate, the tubular channel extending between the bore and an end surface of the end plate, one of the rods being axially slidable in the tubular channel, the sleeve assembly comprising a resilient element for urging the rod along the tubular channel, and the sleeve assembly also comprising a movable piston within the bore, the movable piston acting on the rod in the tubular channel; wherein the piston defines a first rear surface facing away from the end plate, and the sleeve mechanism also comprises a duct to enable the fluid in which the connector is immersed to exert a pressure on the first rear surface, so as to counteract the pressure of the fluid on the face of the rod at the end surface of the end plate, having features as claimed in any one of claims ii to 18.
23. An optical fibre connector comprising a pair of cylindrical elements each carrying at least one optical fibre, and a mechanism for holding the pair of cylindrical elements together so the optical fibres are in alignment, wherein the mechanism comprises a casing defining a cylindrical bore, the bore being straight and the diameter of the bore being large enough to accommodate the cylindrical elements with some play; the mechanism also comprising means to apply a sideways force onto the cylindrical elements so as to clamp the cylindrical elements into alignment.
24. A connector as claimed in claim 23 wherein the play is less than 1 mm, preferably between 10 and 100 pm.
25. A connector as claimed in claim 23 or claim 24 wherein the casing comprises an outer casing sleeve, and a concentric inner casing sleeve, the inner casing sleeve comprising a wall that defines the cylindrical bore, a portion of the wall being movable with respect to the remainder of the wall of the inner casing sleeve.
26. A connector as claimed in claim 25 wherein the movable portion of the wall comprises a tab that is resiliently connected to the remainder of the wall along an edge that extends parallel to the longitudinal axis.
27. A connector as claimed in claim 25 or claim 26 wherein the means to apply the sideways force comprises a multiplicity of balls arranged within a groove in the outer surface of the movable portion of the wall, the balls fitting freely within the groove but the length of the groove being less than the sum of the diameters of the balls so that the balls take up a zigzag arrangement along the groove, and a plunger to apply a compression force along the groove, so changing the radial width of the zigzag arrangement of the balls.
28. A connector as claimed in claim 27 wherein movement of the plunger is brought about by twisting of the outer casing sleeve through an angle of no more than 90°, more preferably not more than 45°.
29. A connector as claimed in any one of claims 23 to 28 also including a releasable latch mechanism to secure the cylindrical elements end to end when they abut each other within the casing.
30. A connector as claimed in any one of claims 23 to 29 wherein each cylindrical element is provided with a casing, so the connector is hermaphroditic, and the cylindrical element is axially movable relative to the casing.
31. A connector as claimed in any one of claims 23 to 30 wherein the connector comprises: (a) at least one pair of ferrules each carrying a respective optical fibre, and a sleeve mechanism for holding a pair of ferrules together and in alignment, wherein each ferrule locates within a tubular guide, one to locate each ferrule, with transparent spheres fixed near the ends of the tubular guides that are to abut each other, the optical fibre within the ferrule terminating within the tubular guide in the vicinity of one side of the transparent sphere, and with a coupling element of resilient transparent material whose refractive index is less than that of the transparent sphere filling the portion of each tubular guide between the sphere and the end of the tubular guide, and projecting beyond the end of the tubular guide, having features as claimed in any one of claims ito 10; and/or: (b) at least one pair of rods each carrying a respective optical fibre, and a mechanism for holding the pairs of rods together and in alignment, wherein the mechanism comprises at least one sleeve assembly that defines a bore closed at one end by an end plate, at least one tubular channel being defined through the end plate, the tubular channel extending between the bore and an end surface of the end plate, one of the rods being axially slidable in the tubular channel, the sleeve assembly comprising a resilient element for urging the rod along the tubular channel, and the sleeve assembly also comprising a movable piston within the bore, the movable piston acting on the rod in the tubular channel; wherein the piston defines a first rear surface facing away from the end plate, and the sleeve mechanism also comprises a duct to enable the fluid in which the connector is immersed to exert a pressure on the first rear surface, so as to counteract the pressure of the fluid on the face of the rod at the end surface of the end plate, having features as claimed in any one of claims ii to 18; and/or: (c) a connector element for connection to an end of an optical fibre cable provided with strength-providing wires that extend along the length of the cable and protect the optical fibres, the connector element comprising a rigid sleeve to enclose an end portion of the cable, the rigid sleeve defining an end face that is substantially orthogonal to the longitudinal axis of the cable, and a rigid clamping ring defining a clamping face that is substantially the same shape as the end face of the rigid sleeve, and bolt means to fix the clamping ring onto the end face of the rigid sleeve, such that the strength-providing wires of the cable after being bent outwardly can be clamped between the clamping ring and the end face of the rigid sleeve, while the optical fibres of the cable extend through the clamping ring, having features as claimed in any one of claims 19 to 21.
32. An optical fibre connector substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.