GB2509532A

GB2509532A - Protective caddy for fibre optic cable ferrules

Info

Publication number: GB2509532A
Application number: GB1300214.2A
Authority: GB
Inventors: Kim Samuel Howard Leeson; David Stockton
Original assignee: Miniflex Ltd
Current assignee: Miniflex Ltd
Priority date: 2013-01-07
Filing date: 2013-01-07
Publication date: 2014-07-09
Anticipated expiration: 2033-01-07
Also published as: GB2509532B; GB201300214D0

Abstract

Installation of a twin or duplex optical fibre cable 4 in optical fibre ducting (31, fig 5) is performed using a protective caddy or end cap or lid 30 which temporarily protects the duplex optical fibre cable 4. The duplex optical fibre cable 4 contains a pair of fibres 19 and a pair of optical fibre connector ferrules 12. The protective caddy 30 is in the form of an elongate body with aligned first and second receiving portions (41, 42, fig 7). The second receiving portion (42, fig 7) receives and holds the duplex optical fibre cable 4 and the first receiving portion (41, fig 7) has a pair of receptacles 51, 52 each for receiving one of the ferrules 12. In use the duplex optical fibre cables 19 and the ferrules 12 are protected during insertion of the protective caddy 30 and duplex optical fibre cable 4 into the length of ducting (31, fig 5).

Description

Installation of Optical Fibre Cables in Ducts

BACKGROUND

a. Field of the Invention

The present invention relates to the installation of an optical fibre cable in optical fibre ducting, which may be an optical fibre microduct, and in particular to the installation in ducting of optical fibre cabling carrying optical fibres terminated at one or more multiple optical fibre connectors.

b. Related Art Optical fibre connectors are used to join optical fibres where a connect/disconnect capability is required. The basic connector unit is a connector assembly at the end of a length of optical fibre cable, which will include a protective outer sheath around a coated optical fibre. The optical fibre will have an optical fibre core, and will often have a primary coating applied to the fibre during manufacture and a surrounding secondary polymer coating. Such a coated optical fibre is referred to as a buffered optical fibre. The buffering provides such functions as mechanical isolation, protection from physical damage and fibre identification for use during installation, but the buffered optical fibre is itself quite delicate where this is exposed for termination in a connector at the end of the protective outer sheath of the cable.

A dual connector assembly consists of two connector plugs. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are generally assembled onto optical fibre in a suppliers manufacturing facility. However, the assembly and polishing operations

involved can be performed in the field.

SC optical fibre connectors and LC optical fibre connectors are the most common types of connectors on the market. In many data centre applications, small connectors (e.g., LC) and multi-fibre connectors (e.g., MTP) are replacing larger, older styles of connector (e.g., SC), allowing more fibre ports per unit of rack space.

Modern connectors typically use a "physical contact" polish on the fibre and ferrule end, which usually has a slightly curved, convex surface, so that when fibres are mated only the fibre cores touch, not the surrounding ferrules. Some manufacturers have several grades of polish quality, for example a regular EC connector may be designated "FC/PC" (for physical contact), while "FC/SPC" and "FC/UPC" may denote "super" and "ultra" polish qualities, respectively. Higher grades of polish give less insertion loss and lower back reflection. When a connector is terminated or assembled in the field, any damage to the polished ferrule and fibre of the connector can cause very high insertion loss.

Optical fibre cables are frequently routed in ducts. The ducts in which optical fibre cables are installed are usually made of cylindrical polyethylene tubing with a diameter ranging from typically 25 mm to 100 mm. Sometimes optical fibre cables are installed inside sub-ducts which are routed inside larger ducts, such as this type of polythene tubing or ducts formed in other materials, such as like concrete.

Small sub-ducts are usually referred to as microducts and are often used to install small microduct fibre optic cables. Microducts have a size ranging from typically 3 mm to 16 mm and are may be installed as bundles inside larger ducts.

The invention described below is particularly applicable to the installation of multiple optical fibre cabling inside microducts inside microducts, for example duplex optical fibre cabling, where the internal diameter of the microduct may be less than the maximum width of the multiple optical fibre connector to be fitted at the terminated end of the cabling. In the context of the present invention, the term duple'is used to mean "duar',twd' or"twirl'fibres or assemblies, rather than a single fibre used for bi-directional transmission. Similarly, the term multipl' is used to mean "two or more'.

As will become apparent, the invention may, however, also be useful when installing duplex or multiple optical fibre cabling inside larger ducts, and therefore the terms "duct' and "ductin' as used in relation to the invention apply both to microducts and to larger ducts for routing optical fibre cables without microducting.

One common form of optical fibre cable is the duplex optical fibre cable, with one fibre being used for transmitting (Ix) and the other fibre being used for receiving (Rx). For convenience, the duplex optical fibres are terminated within a duplex optical fibre connector unit having a joined pair of side-by-side connectors, each with a termination ferrule for terminating one of the optical fibre cores. The duplex optical fibres may be held within a cable having a single outer sheath or in a cable having a pair of joined outer sheaths. Multiple duplex pairs may also be provided within one cable, each duplex pair being for termination in one duplex connector.

The invention is applicable to any such cable having at least one pair of optical fibres for termination in a duplex optical fibre connector, where the optical fibre cable is to be installed inside an optical fibre duct.

The installation of fibre optic cables in ducts can be done by pulling, in which a pre-installed thread or wire inside the duct is used to pull the connector end of an optical fibre cable down a length of the ducting. Usually, the cable being inserted into the near end of the duct is mechanically pushed at the same time.

Alternatively, a technique called cable jetting (also called cable blowing), can be used, together with cable pushing. In cable jetting, high pressure air is blown down the duct and the flow of air pulls along the inserted cable until the cable exits the far end of the duct.

It is not common to install a terminated fibre cable into already occupied duct because of the danger of entanglement and damage. The space inside the duct is normally limited by the customer's desire to use the smallest possible duct.

Installing a duplex connector in a duct would be more difficult than installing a simplex connector owing to the larger dimensions of the duplex connector at the end of the cable. Even in the case of the smaller LC optical fibre duplex connector, there may be inadequate clearance inside the duct for the duplex connector when pulling or jetting the cable down the length of ducting. There is also the problem that the duplex connector, or the terminated optical fibre ferrules within the connector, may have to be protected from damage or contamination during installation within the ducting, which may require additional protection to be fitted to or around the duplex connector, thereby potentially increasing the exterior dimensions of the connector and making it even more difficult, or impossible, to fit the duplex connector into the available space within the ducting.

It is an object of the invention to address these problems and to provide a more convenient apparatus and method for installing a multiple optical fibre connector when the optical fibre cable is to be routed in a duct for optical fibre cabling.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a protective caddy for temporarily protecting a multiple optical fibre cable assembly for a multiple optical fibre connector, during insertion of said assembly into a length of ducting, said multiple optical fibre cable assembly comprising a multiple optical fibre cable and a plurality of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from said optical fibre cable, the protective caddy being in the form of an elongate body, said body comprising: -a first end and a second end, the first end, in use, being forwards of said second end relative to the direction of insertion of said assembly into said length of duct i ng; -an axis, the axis extending between said ends; and -a first receiving portion and a second receiving portion, said portions being adjacent one another along the axis whereby the first receiving portion is proximate the first end and the second receiving portion is proximate the second end; wherein the second receiving portion has an engagement feature for receiving and holding along said axis said multiple optical fibre cable and the first receiving portion has spaced radially around said axis a plurality of receptacles, each for receiving one of said optical fibre connector sub-assemblies, each receptacle having towards the first end a recess for protectively receiving said termination end of one of said optical fibre ferrules, whereby, in use, both the multiple optical fibre cable and the plurality of optical fibre sub-assemblies are held to the elongate body so that said termination ends are protected by said recesses during insertion of said protective caddy and multiple optical fibre cable assembly into said length of ducting.

A multiple optical fibre connector may be composed of two or more single optical fibre connectors that are either joined together or held together so that in use multiple optical fibre connections may be made with a mating connector, for example a multiple optical fibre socket or a multiple optical fibre plug. Such multiple connectors are most commonly duplex connectors formed from two joined-together single optical fibre connector components.

There may be multiple such optical fibre cables, each one of which holds at least one of the optical fibres. However, in a preferred embodiment of the invention, there is one optical fibre cable which is common to all the optical fibres, each of which is therefore held within the common optical fibre cable.

In a preferred embodiment of the invention, the protective caddy is for temporarily protecting a duplex optical fibre cable assembly for an optical fibre duplex connector, during insertion of the assembly into a length of ducting. The duplex optical fibre cable assembly then comprises a duplex optical fibre cable and a pair of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from the optical fibre cable. The engagement feature of the second receiving portion receives and holds along the axis the duplex optical fibre cable.

The first receiving portion has on opposite sides of the axis a pair of receptacles, each for receiving one of the optical fibre connector sub-assemblies. Each receptacle then has towards the first end, one of the recesses for protectively receiving the termination end of one of the optical fibre ferrules. In use, bath the duplex optical fibre cable and the pair of optical fibre sub-assemblies are held to the elongate body so that said termination ends are protected by the recesses during insertion of the protective caddy and duplex optical fibre cable assembly into the length of ducting.

In a preferred embodiment of the invention, the protective caddy is substantially cylindrical in form with receptacles for receiving and engaging with the optical fibre cable and the optical fibre connector sub-assemblies. As the sub-assemblies may also incorporate components which are also substantially cylindrical, the assembly of the sub-assemblies and protective caddy may together present a substantially cylindrical outer form, which will help smooth the insertion of the assembly into the ducting. Preferably, the protective caddy has a rounded, bullet-like tip.

According to a second aspect of the invention, there is provided an assembly of a protective caddy and a multiple optical fibre cable assembly for a multiple optical fibre connector for insertion into a length of ducting, the protective caddy being according to the first aspect of the invention, in which said multiple optical fibre cable assembly comprises a multiple optical fibre cable and a plurality of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from said optical fibre cable, wherein: -said multiple optical fibre cable is received and held along said axis by the engagement feature of the second receiving portion; and -each of said optical fibre connector sub-assemblies is received and held within one of said receptacles, with the termination end of each optical fibre ferrule being received within one of said recesses so that said termination ends are protected by said recesses during insertion of said protective caddy and multiple optical fibre cable assembly into a length of ducting.

According to a third aspect of the invention, there is provided a method of using a protective caddy in the installation of a multiple optical fibre connector assembly routed through a duct, the protective caddy being according to the first aspect of the invention, and said multiple optical fibre cable assembly comprising a multiple optical fibre cable and a plurality of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from said optical fibre cable, the method comprising the steps of: -engaging said multiple optical fibre cable with the second receiving portion so that said cable is received and held by the second receiving portion along said axis; -engaging each of said optical fibre connector sub-assemblies cable with the first receiving portion when each of said sub-assemblies is received and held within one of said receptacles, with the termination end of each optical fibre ferrule being received within one of said recesses so that said termination ends are protected by said recesses; -inserting of said protective caddy and multiple optical fibre cable assembly into a length of ducting; and -removing said protective caddy from the multiple optical fibre cable assembly after said multiple optical fibre cable assembly has passed through said length of ducting.

Each of said receptacles will have an opening. Because the axis is between the receptacles, these openings then face away from the axis, that is, the receptacles open laterally outwards with respect to the axis.

In a preferred embodiment of the invention, each receptacle is elongate in a direction parallel with the axis of the elongate body. Each receptacle then has a first end towards the first end of the elongate body and a second end towards the second receiving portion. The recess of each of the elongate receptacles is then at the first end of each of the receptacles.

The main body may have a wall which separates the first receiving portion from the second receiving portion. This wall may then be at the second end of each of the receptacles. The wall may also have a plurality of slots that extend or cut through the wall. Each of these slots preferably extends radially inwards from an outer periphery of the wall and provides an opening in the wall for receiving an optical fibre extending between the optical fibre cable and one of the optical fibre connector sub-assemblies.

The elongate body may have at the first end a rounded end to aid insertion of the protective caddy down the length of ducting.

The first end may be joined to the wall separating the receiving portions by a plurality of bands that are spaced radially around the axis such that each receptacle is bounded by a pair of adjacent bands. In the case of a duplex optical fibre cable, when there is a pair of bands each of these may extend on opposite sides of the axis in a direction substantially parallel with the axis.

Each of the bands may have an inwardly opposed surface that extends along one side of both receptacles. The bands are preferably separate from one another along their length so that the receptacles have an opening where these adjoin along the said axis. The bands may then resiliently flex apart when receiving the sub-assemblies.

The bands may be joined to one another by the wall which separates the first receiving portion from the second receiving portion. This wall may have a line of weakness or a region of weakness so that the wall can be manually broken at this weakness in order to pull the bands apart to facilitate the release of the optical fibre connector sub-assemblies from the first receiving portion after insertion of the assembly into the length of ducting.

Each of the inwardly opposed surfaces may have a concave feature for gripping the optical fibre connector sub-assembly received within one of the receptacles.

In a preferred embodiment of the invention, the engagement feature of the second receiving portion is a cylindrically shaped clip that has an opening along one side into which an optical fibre can be press-fitted to hold the cable along the axis of the elongate body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of an optical fibre duplex connector comprising a duplex optical fibre cable and a pair of optical fibre connector sub-assemblies around which is assembled an outer housing and a clamshell top and bottom cover with a quick release mechanism; Figures 2 and 3 illustrate how the optical fibre duplex connector of Figure 1 is assembled; Figure 4 is a perspective view of a protective caddy having a first receiving portion and a second receiving portion for receiving, respectively, the pair of optical fibre connector sub-assemblies and the duplex optical fibre cable Figure 5 shows how the protective caddy of Figure 4 is used to protect the optical fibre connector sub-assemblies when the duplex optical fibre cable assembly is being inserted into a length of ducting; Figure 6 shows a top view of the assembled protective caddy and optical fibre connector sub-assemblies and duplex optical fibre cable; Figure 7 is a cross section through the assembly, taken along the line VII-VII of Figure 6; and Figures 8 to 10 show various perspective views of the protective caddy prior to use with the optical fibre connector sub-assemblies and duplex optical fibre cable.

DETAILED DESCRIPTION

A variety of optical fibre connectors are available, but SC and LC optical fibre connectors are the most common types of connectors on the market. The example given below relates to a dual [C optical fibre connector that is composed of two single LC optical fibre connectors. Such connectors have cylindrical ferrules, but the person skilled in the art will recognise that the principles of the invention described below can be applied to other types of dual optical fibre connector including those that have a non-cylindrical or stepped ferrule.

Figures 1 to 3 show some of the components of a prior art optical fibre duplex connector 1 and also indicate how these components are put together to form the connector 1. The connector 1 comprises a dual [C optical fibre connector 2 at the end of a duplex optical fibre cable 4. The dual connector 2 has a pair of identical LC optical fibre connectors 6 side-by-side. Each LC connector 6 has an outer housing 8 into which is seated an optical fibre connector sub-assembly 10. Each of the sub-assemblies 10 has an elongate cylindrical optical fibre ferrule 12 having at one end a termination end 14. In this example, the ferrule is of a ceramic material, although other materials may be used, as is known in the art.

With reference now also to Figure 7, the ferrule 12 has along its axis 16 a hollow core 18 which holds and aligns an optical fibre 17, which will most often be a single mode glass fibre. The person skilled in the art will recognise this as a conventional arrangement, in which the fibre is terminated at the ferrule termination end 14, which is polished to minimise insertion loss when the connector is joined to a matching optical fibre socket (not shown). The ferrules 12 therefore each terminate one optical fibre 17, 19 extending out from a bore 20 of the optical fibre cable 4.

The connector 2 is mechanically joined to the cable 4 by a clamshell cover having top and bottom portions 22, 23. The top portion 22 has a quick release mechanism in the form of a flexible plate 24 which when pressed by a user pushes down on a release lever 26 on each of the outer housings 8. The component of Figures 1 to 3 are all conventional and well-known in the art, and so will not be further described in detail.

A preferred embodiment of the invention is illustrated in Figures 4 to 10, which shows how a protective caddy 30 having the form of an elongate body is used to temporarily protect a duplex optical fibre cable assembly during insertion of the assembly into a length of ducting 31, which in this example is a microduct, but which may be any other type of ducting. In this example the caddy has a one-piece elongate body.

The components of a duplex optical fibre cable assembly are indicated in Figure 1 as those inside a dashed line 32, and comprise the pair of optical fibre connector sub-assemblies 10, the portion of the optical fibre cable 4 to be inserted into the ducting 31 and the pair of optical fibres 19 each of which extends from an end 33 of the cable 4 into one of the sub-assemblies 10.

The duplex optical fibre cable assembly 32 is significantly smaller than the fully assembled connector 2 in terms of cross-sectional dimensions relative to an axis 34 that extends along the centre of the optical fibre cable 4 and along a line mid-way between the side-by-side sub-assemblies 10. Thus, the assembly 32 may be inserted into ducting with internal dimensions too small to accept the fully assembled connector 2. The components of the duplex optical fibre cable assembly 32, particularly the termination end 14 of the ferrule 12, are delicate and could not be inserted into ducting without some sort of protection. The optical fibres 19 will normally include protective polymer cladding but are also vulnerable to damage if bent more sharply than a minimum bend radius. The minimum acceptable bend radius depends on the type of optical fibre, but is of the order of 10mm.

The optical fibre connector sub-assemblies 10 and an end-most portion 35 of the cable 4 are therefore temporarily joined to protective caddy 30 prior to insertion into the length of ducting 31. After the assembled caddy 30 and duplex optical fibre cable assembly 32 has been inserted through the ducting, for example by pulling a line or cord 36 affixed to an aperture 37 in a rounded end 38 of the caddy at a front end 39 of the caddy, and/or by jetting, and/or by pushing of the cable 4, the caddy 30 is removed from the duplex optical fibre cable assembly 32 prior to completing the assembly of the connector 1 as described above.

As indicated by dot-dashed lines in Figure 7, the protective caddy according to the preferred embodiment of the invention has toward the first end 39 a first receiving portion 41 and towards an opposite second end 40 a second receiving portion 42.

Between these ends, the first and second receiving portions have outermost surfaces that are substantially cylindrical or circular about an insertion direction, such that the caddy body 30 has an axis coincident with the cable axis 34.

The first and second receiving portions 41, 42 are adjacent one another along the axis 34, being separated by a wall 43 at a rear end of the first portion and by a clearance gap 44 at the forwards end of the second receiving portion 42. The first receiving portion is therefore proximate the first end 39 and the second receiving portion is proximate the second end 40 of the protective caddy 30.

The first and second receiving portions 41, 42 are both preferably elongate in form, having a length greater than the maximum diameter of parts of the caddy 30 having these portions. The first and second receiving portions also match the elongate shape of, respectively, the two sub-assemblies 10 and the forwards cable end portion 35 so that the two sub-assemblies can be securely held and carried by the first receiving portion 41 and so that the cable end portion 35 can be securely held and carried by the second receiving portion 42.

The second receiving portion 42 has a clip-like engagement feature for holding the duplex optical fibre cable 4, in the form of a semicircular clip or cradle 50 having substantially cylindrical inner and outer walls 45, 46. The inner wall 45 has a series of circumferentially extending ridges 48 which seat within correspondingly shaped grooves 47 in the outer wall of the cable 4. These grooves 47 are a bend-limiting feature of the cable such that the cable can be bent into an arc easily until one side of the grooves pinch together or close up, after which the force required to further bend the cable rises sharply. Such bend-limited tubing for an optical fibre cable is known in the art. In the present invention, this feature is used to secure the cable to the caddy in an axial direction, once the internal ridges 48 of the cradle are seated within the cable grooves 47.

The first receiving portion 41 has on laterally opposite sides of the 34 axis a pair of receptacles 51, 52, each for receiving one of the optical fibre connector sub-assemblies 10. The receptacles are therefore spaced radially around the axis, or in other words, spaced circumferentially around the caddy body. Each of the receptacles is a mirror image of the other, about a plane that encompasses the axis 34 of the caddy body 30.

Each receptacle 51, 52 has towards the first end 39 of the caddy body 30 a recess 53 for protectively receiving the termination end 14 of one of the optical fibre ferrules 12. In this example, each recess is within the rounded end 38 and has a cylindrical inner shape which closely matches the cylindrical outer shape of each ferrule. Each recess 53 extends in a direction parallel with, and on laterally opposite sides to, the axis 34, so that each ferrule 12 can easily slide into and out from each recess, with minimal clearance, in order to exclude as far as possible any environmental contamination from reaching the ferrule ends 14 once seated within the recesses 53. Behind each recess is a U-shaped channel 54 for accepting insertion of the ferrule 12 in a lateral direction with respect to the axis 34, and for guiding the ferrule end 14 into its recess. Each U-shaped channel is dimensioned to position and hold the ferrule once inserted. This arrangement helps to avoid any contact between the ferrule end 14 and material of the caddy body 30 during insertion and removal of the ferrule from the receptacle 51, 52.

As shown most clearly in Figure 7, the ferrule is held by a conventional ferrule holder 55 which has on a shoulder 59 a forwards surface 56 that extends radially away from the ferrule core 18. The shoulder 56 is engaged with a ledge 57 inside each receptacle 51, 52 when the sub-assembly is seated within each receptacle.

The distance in an axial direction between the ledge 57 and a base 58 of the recess 53 is greater than the corresponding distance between the ferrule holder shoulder and the ferrule termination end 14, such that a gap 49 is always provided between the termination end and recess base 58. This also helps to protect the termination end from any contact damage.

As shown most clearly in Figure 7, the rear components of each optical fibre connector sub-assembly 10 are a ferrule holder base 60 and a coil spring 61, which together with the ferrule holder 55 form a spring-loaded ferrule carrier assembly. The ferrule holder 55 has a hollow cylindrical tubular stem 62 that extends from the shoulder 59 in a direction away from the ferrule 12, and which is concentrically seated at forwards end of the ferrule holder base 60 within a pair of forwardly projecting arms 63 which have inwardly opposed part cylindrical surfaces 64. The coil spring is seated between the stem 62 and part cylindrical surfaces 64 and is retailed in an axial direction between an annular ledge 65 in the ferrule holder base 60 at the base of the arms 63 and a rear surface 66 of the shoulder 59 of the ferrule holder 55. The ferrule holder base 60 has a tubular rear portion 67 which supports the arms 63 and which has a central bore 68 that ends from a rear end 71 of the ferrule holder base to the arms 63. The bore 68 is aligned with the space enclosed by the coil spring 61 and with a bore 69 through the ferrule holder stem 62. One of the buffered optical fibres 19 extends through these bores 68, 69, with the core 17 of the optical fibre seated within the hollow core 18 of the ferrule 12.

Each optical fibre connector sub-assembly 10 is inserted into the corresponding receptacle 51, 52 as follows. First the ferrule 12 is inserted forwards and at an angle to the axis 34 into the U-shaped channel 54 and then is slid forwards until the termination end 14 begins to enter the recess 53. At the same time, the rear part of the assembly, that is, the ferrule holder 55, ferrule holder base 60 and coil spring 61, is rotated inwards in a direction towards the axis 34 until the rear pad of the assembly enters one of the receptacles 51, 52. During this process, it is necessary to partially compress the spring 61, in order to bring the ferrule holder base 60 nearer the ferrule holder 55, so that the rearmost part of the sub-assembly 10 can fit within the length of the receptacle.

The ferrule holder base 60 has a pair of tapered flanges 75 on opposite external side of the arms 63. These flanges are used in a one-way snap-fit engagement of the ferrule holder base 60 inside the outer housing 8 of the connector 6. Each of these flanges has a rearwards facing ledge 76. The body of the caddy 30 has an external bulge 88 in the region of these flanges 75 to accommodate a pair of engagement features 77 inside each receptacle 51, 52. The engagement features each have a similar shape corresponding with that of the tapered flanges, but are longer in the axial direction to allow for some axial movement of the ferrule holder base 60 with respect to the caddy 30 once the sub-assembly 10 is engaged in the corresponding receptacle 51, 52.

In order for the sub-assembly 10 to be fully inserted into the receptacle 51, 52, the spring 61 must be compressed by the right amount for each of the tapered flanges to enter the corresponding engagement feature 77. The spring 61 tends to expand once this engagement is made, pushing the rear end 71 of the ferrule holder base towards a rear end surface 72 of the receptacle, while at the same time ensuring a positive contact force between the shoulder 56 of the ferrule holder 55 and the ledge 57 inside each receptacle. The rear end surface 72 of the receptacle is the forward surface of the wall 43, and before the rear end 71 of the ferrule holder base contacts this surface 72, rearwards movement of the ferrule holder base 60 is stopped by contact of the rearwards facing ledge 76 of each tapered flange 75 with a corresponding forwards ledge 78 of each engagement feature 77. This arrangement ensures a small gap 79 remains between the rear end 71 of the ferrule holder base 60 and the wall forwards surface 72, which helps to protect the optical fibre 19 from sharp changes in direction at this point and which is also useful in providing a feature of the sub-assembly to be gripped by a tool when the sub-assembly is to be removed from the receptacle.

This arrangement, in which the engagement features 77 must be aligned with the tapered flanges 75, also helps to prevent over-compression of the spring during insertion or removal of the sub-assemblies 10 from the receptacles 51, 52.

The invention therefore preferably includes an engagement feature within each receptacle to position each sub-assembly in a longitudinal orientation in which a spring-loaded ferrule carrier assembly is seated with a rearmost surface of the assembly free from contact with a supporting surface and with the termination ferrule positively engaged within its recess.

The wall 43 has a pair of slots 73, one for each receptacle 51, 52. In this example, the slots open laterally outwards in opposite directions and are V-shaped, in order to guide the buffered optical fibre 19 into the optimal alignment with the bore 68 in the ferrule holder base 60 and the bore 20 in the optical fibre cable 4.

As can be seen most clearly from Figure 5, the purpose of the clearance gap 44 is to provide space for the buffered optical fibres 19 to be routed between the sub-assemblies 10 and the cable 4 in an orientation and spacing similar to, but not identical with, the orientation of these components in the fully assembled connector 1. In particular, it is important that the orientation of the buffered optical fibres remains as straight as possible both during the joining of the duplex optical fibre cable assembly 32 to the caddy 30 and during the final separation of the caddy from the assembly 32 after the inserting through the ducting 31. For this reason, in order to minimise bending of the optical fibre 19, the part of the clip or cradle 50 nearest the slot 73 may, as shown by the dashed line 85 in Figure 4, be cut away or chamfered to provide additional space for the movement of the buffered optical fibre 19.

Each receptacle 51, 52 is therefore a laterally accessible pocket in the first portion 41 of the caddy 30. Each receptacle has opposite side bands or walls 81, 82 extending from the rear surface 72 of the receptacle to the ledge 57 against which the ferrule holder 55 is seated. As shown most clearly in Figures 8 to 9, these side walls have a cylindrical central portion 80 running the length of the walls, either side of which is an inner lip 83 and an outer lip 84. These features of the cylindrical central portion 80 and inner and outer lips 83, 84 are continuous in a longitudinal direction, except where these are broken by the longitudinal engagement feature 77 where this extends laterally inside each recess 51, 52. Although only one wall 81 is shown fully in the drawings, the other wall 82 is a mirror image.

The inner lip 83 of each receptacle abuts the inner lip of the other receptacle along its most of its length so that there is an opening 86 between the receptacles 51, 52. The opening allows the sub-assemblies 10 to be inserted so that they are in contact, or nearly in contact, i.e. back-to-back, which minimises any wasted space in a lateral direction between the seated sub-assemblies 10. This therefore minimises the lateral extent of the caddy body 30 in this direction.

The arrangement of protective caddy described in detail above is therefore in the form of compartmentalised protective carrier or holder 30, and could be described as being a laterally segmented protective holder 30, for protecting a pair of optical fibre connector sub-assemblies of a duplex optical fibre cable.

The ferrule holder has an external dimension which just passes between the outer lips 84 with minimal clearance. The ferrule holder base 60, including tapered flanges 75, may be slightly larger than the distance between the opposed outer lips 84.

The material of the main body of the caddy 30 is preferably a plastics material, for example polypropylene, with the elongate body 30 being formed in an injection moulding process. In the preferred embodiment of the invention, the elongate body is resiliently flexible so that the ferrule holder base 60, including tapered flanges 75, can push apart the bands or walls 81, 82 in a central portion of the receptacle 51, 52 sufficiently so that the sub-assembly is received securely within the receptacle when the walls 81 relax after passage of the sub-assembly into the receptacle. The sub-assembly is then seated in the opposed longitudinal grooves.

The invention therefore preferably provides an arrangement in which the sub-assembly is temporarily secured within its receptacle in a press-fit engagement in which the receptacle resiliently deforms to accept the sub-assembly.

It should be noted that the ability of the receptacle walls to flex to allow passage of the sub-assembly into and out from each receptacle results not just from the choice of materials, but also from the presence of the opening 86 between the receptacles 51, 52 which permits the bands 81, 82 to flex. The opening therefore not only saves space, but provides a useful function in the temporary securing of the sub-assemblies 10 within the receptacle 51, 52.

The arrangement described above protects both the duplex optical fibre cable 4 and the pair of optical fibre sub-assemblies 10, and particularly the termination ends 14, during insertion of the protective caddy 30 and duplex optical fibre cable assembly 32 into the length of ducting 31.

As mentioned above, after the caddy 30 and duplex optical fibre cable assembly 32 have been fully inserted through the ducting 31, the protective caddy is removed from the duplex optical fibre cable assembly, after which the assembly of the optical fibre duplex connector incorporating the duplex optical fibre cable assembly is completed.

To facilitate removal of the protective caddy from the duplex optical fibre cable assembly, the caddy may, optionally, include a relatively weakened line or region adapted to be broken. Figure 10 shows how the caddy 30 may be modified to create such a weakened line or region, by removing most of the material between the slots as indicated by cross-hatching indicated with numeral 90. A tool may then be used to prise apart of the top and bottom walls 81, 82 where these are joined by the wall 43 at the rear of the receptacles 51, 52. The top wall, which is not joined directly to the second receiving portion 42, may then be bent upwards and optionally broken off at a forwards end where this is joined to the rounded end 38, thereby allowing easy removal of the sub-assemblies 10, optical fibres 17, 19 and optical fibre cable 4 from the protective caddy 30. The invention therefore also extends to a protective caddy having a breakable elongate body 81, 90 to facilitate freeing the optical fibre connector sub-assemblies 10 from engagement with the first receiving portion 41.

The preferred embodiments described in detail above have a left I right symmetry for the receptacles, such that the cross-section through the receptacles is the same if rotated by 180° about the axis of the elongate protective caddy.

From this it can be seen that although the arrangement described above relates to a duplex optical fibre cable assembly, the principles of the invention can be applied to an optical fibre cable assembly having more than two optical fibres, each with its own optical fibre connector sub-assembly. For example, an optical fibre cable assembly having three optical fibres and three corresponding optical fibre connector sub-assemblies can be secured using a protective caddy having three receptacles, each for receiving one of the optical fibre connector sub-assemblies. These receptacles can be spaced radially around the caddy axis so that in cross-section there is a triangular symmetry to the receptacles, such that the cross-section is the same if rotated by 120° about the axis.

In the case of a protective caddy for temporarily protecting a multiple optical fibre cable assembly having four optical fibres, there would be a square symmetry to -20 -the receptacles, such that the cross-section is the same if rotated by 900 about the axis.

Although there will be a limit to number of optical fibres which can usefully be combined into a single cable or connected to a multiple optical fibre connector, the person of ordinary skill in the art will see that the protective caddy can be adapted for use with any practical number of optical fibre connector sub-assemblies.

The invention described above therefore provides a convenient apparatus and method for installing a multiple optical fibre connector when the optical fibre cable is to be routed in a duct for optical fibre cabling.

Claims

-21 -CLAIMS1. A protective caddy for temporarily protecting a multiple optical fibre cable assembly for a multiple optical fibre connector, during insertion of said assembly into a length of ducting, said multiple optical fibre cable assembly comprising a multiple optical fibre cable and a plurality of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from said optical fibre cable, the protective caddy being in the form of an elongate body, said body comprising: -a first end and a second end, the first end, in use, being forwards of said second end relative to the direction of insertion of said assembly into said length of duct i ng; -an axis, the axis extending between said ends; and -a first receiving portion and a second receiving portion, said portions being adjacent one another along the axis whereby the first receiving portion is proximate the first end and the second receiving portion is proximate the second end; wherein the second receiving portion has an engagement feature for receiving and holding along said axis said multiple optical fibre cable and the first receiving portion has spaced radially around said axis a plurality of receptacles, each for receiving one of said optical fibre connector sub-assemblies, each receptacle having towards the first end a recess for protectively receiving said termination end of one of said optical fibre ferrules, whereby, in use, both the multiple optical fibre cable and the plurality of optical fibre sub-assemblies are held to the elongate body so that said termination ends are protected by said recesses during insertion of said protective caddy and multiple optical fibre cable assembly into said length of ducting.
2. A protective caddy as claimed in Claim 1, in which the protective caddy is for temporarily protecting a duplex optical fibre cable assembly for an optical fibre duplex connector, during insertion of said assembly into a length of ducting, said -22 -duplex optical fibre cable assembly comprising a duplex optical fibre cable and a pair of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from said optical fibre cable, wherein the engagement feature of the second receiving portion is for receiving and holding along said axis said duplex optical fibre cable and the first receiving portion has on opposite sides of said axis a pair of said receptacles, each for receiving one of said optical fibre connector sub-assemblies, each receptacle having towards the first end one of said recesses for protectively receiving said termination end of one of said optical fibre ferrules, whereby, in use, both the duplex optical fibre cable and the pair of optical fibre sub-assemblies are held to the elongate body so that said termination ends are protected by said recesses during insertion of said protective caddy and duplex optical fibre cable assembly into said length of ducting.
3. A protective caddy as claimed in Claim 1 or Claim 2, in which each of said receptacles has an opening and said openings face away from said axis.
4. A protective caddy as claimed in Claim 1 or Claim 2, in which said receptacles open laterally outwards with respect to said axis.
5. A protective caddy as claimed in any preceding claim, in which each receptacle is elongate in a direction parallel with said axis, each receptacle having a first end towards the first end of the elongate body and a second end towards the second receiving portion, the recess of each of said elongate receptacles being at the first end of each of said receptacles.
6. A protective caddy as claimed in any preceding claim, in which the main body has a wall which separates the first receiving portion from the second receiving portion.
7. A protective caddy as claimed in Claim 6, when dependent from Claim 5, in which said wall is at the second end of each of said receptacles.

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8. A protective caddy as claimed in Claim 6 or Claim 7, in which said wall has a plurality of slots therein, each of said slots extending radially inwards and providing an opening in said wall for receiving one of said optical fibres extending between said optical fibre cable and one of said optical fibre connector sub-assemblies.
9. A protective caddy as claimed in any one of Claims 6 to 8, in which said first end of the elongate body is joined to said wall by a plurality of bands, said bands being spaced radially around said axis such that each receptacle is bounded by a pair of adjacent bands.
10. A protective caddy as claimed in any one of Claims 6 to 8, when dependent from Claim 2, in which said first end of the elongate body is joined to said wall by a pair of bands, said bands extending on opposite sides of said axis such that each receptacle is bounded by said bands.
11. A protective caddy as claimed in Claim 10, in which each of said bands has an inwardly opposed surface that extends along one side of both receptacles.
12. A protective caddy as claimed in Claim 11, in which said bands are separate from one another so that said receptacles have an opening therebetween along said axis.
13. A protective caddy as claimed in Claim 12, in which said bands are joined to one another by the wall which separates the first receiving portion from the second receiving portion, said wall having a line of weakness or a region of weakness so that said wall can be broken in order to pull apart said bands to facilitate the release of the optical fibre connector sub-assemblies from the first receiving portion after insertion of said assembly into said length of ducting.
14. A protective caddy as claimed in any one of Claims 9 to 11, in which each -24 -of said inwardly opposed surfaces has a concave feature for gripping said optical fibre connector sub-assembly received within one of said receptacles.
15. A protective caddy as claimed in any preceding claim, in which the first end of the elongate body is a rounded end.
16. A protective caddy as claimed in Claim 15, in which said recesses are provided within said rounded end.
17. A protective caddy as claimed in any preceding claim, in which each receptacle has a portion nearest each receptacle with a U-shape for receiving and holding one of said optical fibre ferrules.
18. A protective caddy as claimed in any preceding claim, in which the engagement feature of the second receiving portion is a cylindrically shaped clip, said clip having an opening along one side into which an optical fibre can be press-fitted to hold said cable along said axis.
19. A protective caddy as claimed in Claim 18, in which said clip has at least one ridge therein extending in a circumferential direction for engaging with a groove in an external surface of said optical fibre cable.
20. A protective caddy as claimed in any preceding claim, in which the first end has an aperture therein for receiving a pulling cord for pull-installation of said assembly into a length of ducting.
21. An assembly of a protective caddy and a multiple optical fibre cable assembly for a multiple optical fibre connector for insertion into a length of ducting, the protective caddy being as claimed in any preceding claim, in which said multiple optical fibre cable assembly comprises a multiple optical fibre cable and a plurality of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an -25 -optical fibre extending out from said optical fibre cable, wherein: -said multiple optical fibre cable is received and held along said axis by the engagement feature of the second receiving portion; and -each of said optical fibre connector sub-assemblies is received and held within one of said receptacles, with the termination end of each optical fibre ferrule being received within one of said recesses so that said termination ends are protected by said recesses during insertion of said protective caddy and multiple optical fibre cable assembly into a length of ducting.
22. A method of using a protective caddy in the installation of a multiple optical fibre connector assembly routed through a duct, the protective caddy being as claimed in any one of Claims 1 to 20 and said multiple optical fibre cable assembly comprising a multiple optical fibre cable and a plurality of optical fibre connector sub-assemblies, each of said sub-assemblies comprising an optical fibre ferrule having a termination end that terminates an optical fibre extending out from said optical fibre cable, the method comprising the steps of: -engaging said multiple optical fibre cable with the second receiving portion so that said cable is received and held by the second receiving portion along said axis; -engaging each of said optical fibre connector sub-assemblies cable with the first receiving portion when each of said sub-assemblies is received and held within one of said receptacles, with the termination end of each optical fibre ferrule being received within one of said recesses so that said termination ends are protected by said recesses; -inserting of said protective caddy and multiple optical fibre cable assembly into a length of ducting; and -removing said protective caddy from the multiple optical fibre cable assembly after said multiple optical fibre cable assembly has passed through said length of ducting.
23. A method as claimed in Claim 22, in which the method comprises, after the removal of the protective caddy from the multiple optical fibre cable assembly, the -26 -additional step of completing the assembly of a mutiple optical fibre connector incorporating said multiple optical fibre cable assembly.
24. A method as claimed in Claim 22 or Claim 23, in which the step of removing said protective caddy from the multiple optical fibre cable assembly involves breaking the elongate body of the protective caddy in order to free the optical fibre connector sub-assemblies from engagement with the first receiving portion.
25. A protective caddy for temporarily protecting a multiple optical fibre cable assembly for a multiple optical fibre connector, during insertion of said assembly into a length of ducting, substantially as herein described, with reference to or as shown in the accompanying drawings.
26. An assembly of a protective caddy and a multiple optical fibre cable assembly for a multiple optical fibre connector for insertion into a length of ducting, substantially as herein described, with reference to or as shown in the accompanying drawings.
27. A method using a protective caddy in the installation of a multiple optical fibre connector assembly routed through a duct, substantially as herein described, with reference to the accompanying drawings.