Patent Description:
Optical fibre transmission lines can be installed through a duct, for example a so-called micro-duct, using compressed gas or fluid, for example air. This is known as installation by blowing, and special lightweight cable assemblies known as "fibre units" have been developed for this installation method. Optical fibre transmission lines can also be installed by pushing, or pulling, or preinstalled in a duct. Different cable designs can be used for these different methods. For example, a cable adapted for installation by pulling may include strengthening fibres, surrounding the optical fibres with in an outer sheath.

Fibre to the home (FTTH) is the generic term for broadband network architecture that uses optical fibre technology to carry data to a residential dwelling from a broadband service provider via a telecommunications cabinet located near the residential dwelling. Embodiments of the present invention may be applied in FTTH applications, or in installation of optical fibre transmission lines to a variety of premises and within premises.

Using the blowing process to install optical fibre transmission lines into an optical fibre duct typically uses viscous drag generated by a high-speed flow of a fluid, for example air. This process is described in many patent publications, for example <CIT> and <CIT>. <CIT> describes pressurised air being pumped into a chamber in a blowing head. The air is directed through a tube at the blowing head and into a duct. The optical fibre transmission line is fed into the tube by a pushing force, between a pair of motorised drive rollers. When a sufficient length of transmission line has been pushed into the duct, the pressurised air works on the fibre surface allowing the effects of viscous drag to take over, at least partly, the task of advancing the transmission line along the duct until the transmission line exits the far end of the duct at the desired location.

Several different constructions of fibre units have been designed specifically for installation by blowing. To be successful, such units require to be lightweight, but have a certain stiffness. There is also a significant requirement for fibre units to be compact, for example being less than <NUM>, preferably less than <NUM> in diameter. One type of fibre unit adapted to be installed by the blowing process comprises a number of optical fibres embedded in a cured resin, for example acrylate resin, which locks the fibres in a unitary matrix. This coated fibre bundle is then covered by an outer sheath, for example a sheath or sleeve of low friction, thermoplastic material. The sheath material may for example comprise HDPE with a friction-reducing additive. Examples of this type of fibre unit are disclosed for example in <CIT>.

Another type of fibre unit adapted to be installed by blowing comprises optical fibres or optical fibre bundles embedded in a softer resin, surrounded by a harder resin layer. The outermost part of the hard resin layer is modified by the addition of glass micro beads, which provide lower friction against the duct wall, and also increase air resistance, to promote installation by fluid drag. This type of fibre unit is disclosed in <CIT>, for example.

As mentioned above, pulling is another example of installing an optical fire transmission line into and through a duct. This process involves applying a pulling load to the leading end of the transmission line. The transmission line can be pulled by applying the load directly to the leading end of the transmission line or via a carriage device, which carries the leading end of the transmission line. The pulling load may be applied via the exit end of the duct using a pulling line previously installed in the duct. A pulling force can also be applied using air resistance, for example by fitting an "umbrella" or "parachute" accessory to the leading end of the transmission line, and pumping air into the trailing end of the duct. (This is not the same as installation by blowing, because the cable has to be able to withstand pulling forces from the front end, rather than being propelled by a drag force applied along its full length.

In order to reduce the risk of faulty installations, and to speed up the installation this requirement for specialist skills and equipment, there is a trend to use pre-terminated or "pre-connectorised" cable assemblies. At one or both ends of a pre-terminated optical fibre transmission line, one or two ferrule connectors are generally attached to one or two optical fibres respectively, prior to installing the optical fibre transmission lines between the consumer site, for example a residential dwelling and a supply site, for example a telecommunication cabinet.

Following installation, a connector body, for example an LC or SC type connector, can be fitted to the ferrule to complete the functional connector. Example connectors are described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>.

This process of installation leaves an exposed length of the transmission line within the cabinet, between the end of the duct and the mating connector. The exposed length needs to be protected against damage. A known method of protection is to apply a woven or braided tube or sheath that can be fitted over the length of the transmission line that exits the duct, prior to fitting the connector body or connectors to the ferrule. The woven or braided tube or sheath is generally manufactured to a set length, for example <NUM>, and includes collars on both ends. Alternatively, the woven tube or sheath is provided without fitted collars, but is trimmed and fixed at the ends to the transmission line and duct once fitted. A collar/connector is fitted to the exit end of the duct to prevent movement of the optical fibre or fibres after installation and/or to provide a seal between the outer sheath and the duct to prevent gas or fluid ingress or egress.

It will be appreciated that fitting a manufactured length of the woven or braided tube pre-fitted with collars/connectors can be problematic. If the portion of transmission line protruding from the duct is longer than the manufactured length of the woven or braided tube, the collar/connector at the duct end of the woven or braided tube or sheath will not reach the exit end of the duct. The transmission line cannot be pulled back, if it has been installed by blowing, and it cannot be trimmed without losing the benefits of pre-termination.

A woven or braided sheath or tube, that has no collars/connectors offers versatility in ensuring the correct length of sheath is provided. However, trimming the sheath and securing the sheath to the ferrule end and duct end of the sheath can be time consuming and risks local damage to the transmission line during the process of trimming and connecting the woven sheath to the ferrule end of the transmission line and the duct exit.

In short, there is a need to find alternative techniques for protecting the protruding ends of lightweight fibre units, of the type blown through micro-ducts to communications cabinets, or consumer premises.

Cable assemblies which are more robustly protected from end to end could be used. However, these are not suited for installation by blowing, and may be bulkier than the lightweight units used for blowing. Even in applications where they can be used, they also present challenges when one tries to implement pre-terminated cables. Published international patent application <CIT> describes methods of installing "drop cables" between a riser cable and individual apartments or offices. The drop cables are pre-terminated at both ends. The forms of these cables are such that a fibre is loosely contained in an inner sheath, which is surrounded by strength members such as aramid fibres. These are then surrounded by an outer sheath, providing a flexible cable assembly strong enough to be installed by pulling over the distance of the drop. As described in the patent application, a problem arises due to the bulk of this construction, which may be <NUM> or <NUM> in diameter.

When using a drop cable that has been pre-terminated at both ends, there will generally be substantial excess cable length, once the cable has been installed between the two endpoints.

This excess cable length is to be stored somewhere. According to the disclosure of the international patent application, the outer sheath and strength members are removed from this excess section after installation to the correct length, using ripcords embedded within the sheath material. The excess length section, stripped of the outer sheath, can then be coiled and stored in a smaller space.

<CIT> relates to an optical fibre cable, which is pre-terminated with a connector component and subsequent to installation through a duct is fitted with an optical fibre connector, which includes a cover member received over the optical fibre connector component.

A first aspect of the present invention provides a pre-terminated optical fibre cable assembly as defined in claim <NUM> of the appended claims.

The pre-terminated cable assembly may further comprise a protective layer over the at least one optical fibre. The protective layer may extend over a major part of the length of the optical fibre and the protective sleeve may extend along a minor part of the length of the optical fibre.

The protective layer may extend over substantially the full length of the optical fibre.

The protective layer may include or comprise a first layer in which the at least one optical fibre is embedded optionally with one or more other optical fibres. The first layer may comprise a UV-cured resin, such as an acrylate material. The first layer may be surrounded by an outer sheath of extruded material over at least the majority of the length of the optical fibre bundle. The outer sheath may comprise for example a thermoplastic polymer, for example high density polyethylene (HDPE) material or the like.

In other embodiments, the first layer may be surrounded by one or more further layers of UV-cured resin, optionally with surface modification by the addition of particles such as glass beads.

In embodiments where a first layer is surrounded by an outer sheath, the outer sheath may extend beneath said protective sleeve along substantially the whole length of the protective sleeve. Alternatively, the outer sheath may extend beneath said protective sleeve along only a part of its length, for example only a few millimetres or centimetres.

In other embodiments where a first layer is surrounded by an outer sheath, the outer sheath has been removed from the portion of the optical fibre that lies beneath the protective sleeve, and extends from a point behind the protective sleeve and over a major part of the length of the optical fibre.

In such embodiments, the protective sleeve and the outer sheath may be dimensioned such that a forward end of the outer sheath substantially abuts a rearward end of the protective sleeve so as to limit rearward sliding of the protective sleeve along the optical fibre. Similarly, the protective sleeve and the terminal connector may be dimensioned so that the terminal connector limits forward sliding of the protective sleeve along the optical fibre.

References to "behind", "forward" and similar terms refer naturally to the direction of installation. In embodiments that are pre-terminated and provided with a protective sleeve at both ends of the optical fibre, the terms "behind", "forward" and similar terms are defined relative to each end independently.

The protective sleeve may comprise a composite body with low-friction properties, wherein at least an outer surface of the protective sleeve is provided with low friction properties. The surface properties of the protective sleeve maybe such that kinetic friction is lower than static friction.

The protective sleeve may comprise a polymer material formed such that an outer surface of the protective sleeve has a coefficient of friction in the range of <NUM> to <NUM>. The coefficient of friction may be measurable in a conventional manner, for example in the manner described in <CIT>.

The outer surface of the protective sleeve may comprise a low-friction coating provided by a mixture of a polymer and a friction reducing material. The protective sleeve may comprise primarily High density polyethylene (HDPE), and/or one or more of HDPE, Medium density polyethylene (MDPE), Nylon, Polypropylene etc. The friction reducing material may comprise a silicon-based material including a polyether modified poly (dimethylsiloxane) material such as a polyether modified hydroxy functional poly-(dimethylsiloxane) material. Alternatively, or in addition erucamide and/or oleamide materials may be used for improving slip and reducing friction.

The protective sleeve may also provide insulation properties, wherein the material forming the protective sleeve is designated flame retardant and low smoke zero halogen. For example, the material forming the protective sleeve may comprise a polyethylene-based polymer having zero halogen and/or flame-resistant properties.

The protective sleeve may comprise a hollow body like a tube, within which hollow body at least the optical fibre is received. The protective sleeve may comprise a hollow body, within which at least the optical fibre and part of the protective layer are received.

The body of the protective sleeve may comprise one or more layers of material.

The protective sleeve may comprise an outer layer comprising at least a low-friction outer surface, a middle layer comprising strengthening material, and an inner layer comprising a resilient material, wherein the middle layer is sandwiched between the inner layer and the outer layer.

The outer layer of the protective sleeve may comprise HDPE or another polyethylene-based material comprising a friction reducing agent such that the outer layer exhibits low-friction properties. The outer layer may comprise a mixture of Polyethylene, for example of the brand Borstar®, and a friction reducing agent.

The middle layer may comprise a strengthening material. For example, the middle layer may comprise fibres such as aramid fibres commonly known as Kevlar®. The middle layer may not be required for some applications.

The inner layer may comprise a material that is resilient, heat resistant and chemical resistant. For example, the inner layer may comprise a thermoplastic elastomer that combines the flexibility of rubber with the strength and processability of thermoplastics. An example of this thermoplastic elastomer is a copolyester, for example of the brand Hytrel®, available from DuPont.

Passage of the pre-terminated optical fibre cable assembly through the duct is improved by providing a protective sleeve having low friction properties, at least on the outside surface, such that less jamming, less stopping and less restarting during the installation process is expected.

In one embodiment, a duct for an optical fibre cable assembly comprising a single LC or SC connector may have an internal bore diameter of approximately <NUM>. Therefore, the outer diameter of the protective sleeve may be less than <NUM>, for example less than <NUM> or less than <NUM>. The protective sleeve may have an outer diameter between <NUM> and <NUM>.

In an alternative embodiment, a duct, for an optical fibre cable assembly comprising a duplex LC or SC connector, may have an internal bore diameter of approximately <NUM> Therefore, the outer diameter of the protective sleeve may be less than <NUM>. For example, the protective sleeve may have an outer diameter of less than <NUM>.

The protective sleeve may be fixed against longitudinal movement relative to the optical fibre, by fixing at least a first end of the protective sleeve to the underlying layer. In other embodiments, the sleeve is free moving over a section of the underlying optical fibre before it is installed, for example within a range of around <NUM>-<NUM>. As mentioned above, in such embodiments, an outer sheath of the cable assembly may abut the protective sleeve, so as to stop the sleeve travelling along the fibre bundle. The sheath can be fixed at the connector end, after installation.

The protective sleeve may be fixed against movement relative to the optical fibre, by fixing both ends or one end or along its full length depending on design.

The protective sleeve may extend axially from behind the connector along the optical fibre.

The protective sleeve may extend along a minor part of the length of the optical fibre. For example, the protective sleeve may extend along the optical fibre for less than <NUM>% or <NUM>% or <NUM>% or <NUM>% or <NUM>% of the length of the optical fibre.

The maximum length of the protective sleeve may be influenced by the installation technique, for example blowing or pulling, wherein blowability would favour shorter lengths. In addition, the maximum length of the protective sleeve may be influenced by cost implications, again where shorter lengths would be more cost effective.

To ensure protection in a particular environment, such as a telecommunication cabinet, the desired length of the protective sleeve is such that a portion of the protective sleeve remains within the duct after the leading end/connector end of the optical fibre emerges from the duct.

The length of optical fibre that emerges from a duct is generally in the region of <NUM>. Therefore, the protective sleeve may be longer than <NUM> long. For example, the protective sleeve may be longer than <NUM> long. The protective sleeve may be shorter than <NUM> long, where the length of optical fibre cable assembly emerging from the duct is shorter than <NUM>. For example, the protective sleeve may be greater than <NUM> long, or greater than <NUM>.

The protective sleeve may be up to <NUM> long.

At least a section of the protective sleeve may be fixed against movement relative to at least one optical fibre, wherein the section is proximate the leading end of the protective sleeve. The section may be fixed using an adhesive or a bonding material inside the protective sleeve or by using the outer sleeve of the fibre bundle as a restraint.

A further aspect of the present invention provides a method of assembling a pre-terminated optical fibre cable assembly as defined in claim <NUM> of the appended claims.

The method may further comprise:
fixing at least a section of the protective sleeve relative to the at least one optical fibre.

The method of assembling the pre-terminated optical fibre cable assembly configured to be installed through a duct, may further comprise the steps:.

The method may further comprise:
fixing at least one end of the second protective sleeve relative to the optical fibre.

The optical fibre may comprise a protective layer, which may include a first layer in which the at least one optical fibre is embedded. The first layer maybe surrounded by an outer sheath or further protective layer. The step of applying the first protective sleeve may comprise overlapping at least part of the protective layer. Optionally, the step of applying the first protective sleeve may include removing outer sheath or further protective layer, from at least part of the optical fibre, before applying the first protective sleeve over that part of the optical fibre.

A further aspect of the present invention provides a method of installing a pre-terminated optical fibre cable assembly of the type provided by the first aspect, as defined in appended <NUM>.

After the step of transporting a length of the pre-terminated optical fibre cable assembly through the duct a leading portion of the pre-terminated optical fibre cable assembly may protrude from the duct, protected by said protective sleeve.

After the step of transporting a length of the pre-terminated optical fibre cable assembly through the duct a section of the protective sleeve may remain within the duct.

The method may further include adding a connector body to a terminal connector on the end of the pre-terminated optical fibre construction emerging from the duct.

The method of installing a pre-terminated cable assembly may further comprise: sealing the duct exit. Sealing the duct exit may be by fitting a seal over the emerging section of the protective sleeve and fitting the seal to the duct exit. The seal may include a plug and a cap element, wherein the plug extends into the duct and the cap is operable to close the end of the duct.

The method of installing a pre-terminated cable assembly, may further comprise clamping the protective sleeve proximate the duct exit, wherein clamping the protective sleeve is effective to prevent movement of the optical fibre relative to the duct.

The step of sealing the duct exit may also facilitate clamping the protective sleeve. Inserting the plug section into the duct may compress the protective sleeve thereby clamping the underlying optical fibre to prevent movement of the optical fibre relative to the duct.

Sealing the duct and clamping the protective sleeve may be facilitated by one or more components received over the protective sleeve at the duct exitThe step of applying the connector body may include clamping or otherwise fixing the protective sleeve against longitudinal movement relative to the connector body.

The method of installing a pre-terminated cable assembly, may further comprise connecting one end of the pre-terminated cable assembly to supply equipment and one end of the pre-terminated cable assembly to consumer equipment.

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:.

<FIG> show an example of a Fibre to the Home (FTTH) installation <NUM> of optical fibres, using a pre-terminated optical fibre cable assembly <NUM> according to an embodiment of the present invention. It will be understood that terms such as "consumer" and "home" are used by way of example only, and the products and techniques described herein may equally be applied in commercial and industrial installations.

In the illustrated example, the pre-terminated cable assembly <NUM> is provided wound on a reel <NUM> from which pre-terminated optical fibre or fibres are delivered from the consumer side/home side <NUM> of the installation <NUM> to the supply side, for example a telecommunications cabinet <NUM>. Instead of a reel <NUM>, the pre-terminated cable assembly <NUM> may be provided in other forms, for example in a coil, in a fibre pan etc..

Referring also to <FIG>, in the illustrated example, the FTTH installation <NUM> is performed by passing it into a pre-installed duct <NUM>. Other ducts <NUM>' etc, lead from the same cabinet <NUM> to other premises, so that this installation method may be repeated many times in a neighbourhood.

<FIG> shows, by way of example, installation by blowing, from the consumer side of the installation to the supply side. A leading end <NUM> of the pre-terminated optical fibre cable assembly <NUM> is transported through a duct <NUM> at least partly by viscous drag created by compressed fluid, for example compressed air. A special blowing machine <NUM> has a blowing head <NUM> which is coupled to the leading end <NUM> of the duct <NUM>. It will be appreciated that the installation process may also be conducted from the supply side, for example a telecommunication cabinet <NUM>, to the consumer side, according to convenience.

Depending on the situation, including for example the length of connection required, blowing may be the most suitable method of installation. However, the present disclosure is not limited to blowing. An alternative installation process (illustrated later in <FIG>) involves physically pulling the leading end <NUM> of the pre-terminated optical fibre cable assembly <NUM> through the duct <NUM> via the trailing end or the duct exit <NUM>. For shorter installations, simply pushing the assembly through the duct may be practicable.

The leading end <NUM> of the pre-terminated optical fibre cable assembly <NUM>, which includes a ferrule connector <NUM>, leads the installation of the optical fibre or fibres <NUM> through the duct <NUM>.

The leading end <NUM> of the pre-terminated optical fibre cable assembly <NUM>, which includes a ferrule connector <NUM>, leads the installation of the optical fibre or fibres <NUM> through the duct <NUM>. The leading end <NUM> passes through the duct <NUM> and is fed from the reel <NUM> until the ferrule connector <NUM> and a length of the optical fibre cable assembly <NUM> exits the duct <NUM> within the telecommunications cabinet (see <FIG>). A protective cap may be fitted over the ferrule connector <NUM> while the installation takes place. In an embodiment where pulling is used instead of blowing, an adapter can be applied to provide a pulling eye and to protect the ferrule connector <NUM> from damage during pulling. One example of such an adapter is described below and is illustrated in <FIG>.

The action of the leading end <NUM> of the optical fibre cable assembly <NUM> exiting the far end of duct <NUM>, following installation by blowing or pulling, is often referred to as breakthrough, as illustrated in <FIG>.

A fibre catcher (not illustrated) may be used to indicate when the leading end <NUM> of the optical fibre cable assembly <NUM> has reached its destination, that is, when the leading end <NUM> has exited the duct <NUM> and when a predetermined length of the optical fibre cable assembly <NUM> is within the cabinet <NUM>. Alternatively, an installer may observe when the leading end <NUM> exits the duct <NUM>, and communicate with the operator of the blowing machine <NUM> to cease blowing.

Referring now to <FIG>, suppose that <NUM> metres is considered sufficient length of optical fibre to allow routing and connection within the telecommunications cabinet <NUM>. Therefore, the length of optical fibre that exits the duct <NUM> may be in the region of <NUM> metres. Naturally, it is unusual that the length of optical fibre <NUM> protruding from the duct <NUM> will be exactly <NUM> metres, or exactly the length required for a particular connection point. The actual length may be slightly shorter or more likely slightly longer than the ideal, because of possible reaction-induced time delay in shutting off the blowing machine. For example, blowing may continue for slightly longer than when the fibre catcher indicates the fibres have exited the duct <NUM>; even a short period of continued blowing may result in ripples along at least part of the length of the optical fibre cable assembly <NUM>. When blowing stops, this ripple effect may result in a further length of optical fibre exiting the duct <NUM> (see <FIG>). It will be appreciated, especially in the case of a long blowing route, the excess length of optical fibre exiting the duct cannot be pulled back via the trailing end because this could lead to damage of the optical fibre within the duct <NUM>. The ability to push excess back into the duct from the leading end may also be limited.

In the illustrated example (see <FIG>, <FIG>) a protective sleeve <NUM> is provided along part of the length of the pre-terminated optical fibre cable assembly <NUM> such that a section of the protective sleeve <NUM> remains within the duct <NUM> after the leading end <NUM> exits the duct <NUM>.

The protective sleeve <NUM> extends from a position behind the connector <NUM> along a minor length of the optical fibre cable assembly <NUM>. The length of the protective sleeve <NUM> is such that a trailing part <NUM> of the protective sleeve <NUM> remains within the duct <NUM> after breakthrough, and a leading part <NUM> of the protective sleeve <NUM> covers the optical fibres where they protrude from the duct <NUM>.

Referring to <FIG>, this arrangement provides a substantial tolerance for variations in the length of the optical fibres that protrudes from the duct <NUM>. No tailoring of a protective sleeve is required, after the leading end <NUM> exits the duct <NUM>. The excess length of protective sleeve simply resides within the duct.

After the leading end <NUM> exits the duct <NUM>, installation at the telecommunications cabinet <NUM> is completed by plugging the open end of the duct <NUM> with a suitable accessory.

In the illustrated example, the duct <NUM> is plugged with a hollow connector <NUM> that has an outer diameter <NUM> that is configured to be a push-fit into the duct <NUM> and has a hollow or groove into which the protective sleeve <NUM> containing the optical fibres is received. A flange <NUM> is provided as a stop/seal on the outside of the connector <NUM> should this be preferred by the operator. The flange <NUM> is operable to cap the exit of the duct <NUM>.

In the illustrated example, with reference also to <FIG> an exposed extension member <NUM> of the hollow connector <NUM> extends beyond the flange <NUM> and envelops part of the protective sleeve <NUM>. A capping sleeve <NUM> may be added to the exposed extension member <NUM>. The capping sleeve <NUM> is operable to locally compress the protective sleeve <NUM> against the fibre cable assembly <NUM> to prevent fibre movement after installation of the optical fibre cable assembly.

<FIG> illustrates in more detail one example of the connector <NUM> that may be used at the leading end of the pre-terminated optical fibre cable assembly <NUM>. It will be understood that the ferrule connector <NUM> is of a size suitable for installation through the duct <NUM>, and does not form a complete connector assembly until other components are added.

The ferrule connector <NUM> includes a ferrule body <NUM> which facilitates attaching a connector body after the leading end <NUM> exits the duct <NUM>, as described below with reference to <FIG>. It will be understood that, while the cable may carry more than one optical fibre, for example <NUM> or <NUM> optical fibres, in the majority of installations, only one of these fibres carries live signals, and only that one is provided with a ferrule connector <NUM>. The unused fibres are used, when necessary, as backup.

In one specific example comprising two ferrule connectors (not illustrated) connected to two individual optical fibres within the cable assembly, each ferrule body <NUM> is D-shaped in cross-section. The flat portions of the D-shaped bodies are abutted such that the combined dimension of the abutted bodies is small enough so both ferrule bodies can pass together through the duct. In practice, the combined dimension of the abutted ferrule bodies need not be any greater than the outer diameter of the protective sleeve <NUM>.

The protective sleeve <NUM>, as described above with reference to <FIG>, extends along a minor part of the pre-terminated optical fibre cable assembly <NUM> and extends from behind the ferrule connector <NUM>. The cable assembly <NUM> may be tens or even hundreds of metres in length, while the portion protected by the protective sleeve <NUM> may be a few metres or less. In this way, construction of the protective sleeve <NUM> can be optimised for protecting the optical fibres where they are vulnerable, outside the duct <NUM>. Such a protective sleeve, applied to the whole length of the cable assembly, might otherwise degrade the installation performance, completely preventing installation by blowing, for example. Provision of such a protective sleeve along the whole length of the cable assembly may alternatively, or in addition, add unduly to the cost of the cable assembly, and or the weight and/or size. Particularly when many ducts are to be run in parallel, to serve different consumers within a street, building etc, any increase in the size of the cable assembly, and consequently the size of the individual duct required to carry it, can have a very significant effect on the size of the total space taken up by ducts, and the size of the cabinets needed for termination.

<FIG> presents an example of the construction of the pre-terminated optical fibre cable assembly <NUM>, as viewed in a portion comprising the protective sleeve <NUM>. By way of illustration only, <FIG> shows, in cross-section, an optical fibre cable assembly <NUM>, which includes four primary coated optical fibres <NUM>. A fibre bundle <NUM>, in this example, comprises the optical fibres <NUM> embedded in a UV-cured resin <NUM>. Each optical fibre <NUM> may be, for example, <NUM> to <NUM> in diameter. The optical fibre bundle <NUM> has an outside diameter which may, for example, be less than <NUM>, typically in the region of <NUM>. The diameter of the bundle will of course increase and decrease to some extent, according to the number of fibres contained within it. Features within the bundle are not shown to scale. The thickness of resin over the optical fibres may be, for example <NUM>, at the minimum.

In the illustrated example, the protective sleeve <NUM> includes a layered construction which is applied by sliding directly over the fibre bundle <NUM>. It will be appreciated that the positions and thicknesses of the layers in <FIG> are not to scale, but purely schematic. The internal diameter of the protective sleeve <NUM> may in practice be greater than the outer diameter of the fibre bundle <NUM>, such that the protective sleeve <NUM> is easily applied and slides over the fibres freely. In an example, the inner diameter of the protective sleeve <NUM> is greater than <NUM>, for example in the region of <NUM>; thereby providing <NUM> or more clearance around the fibre bundle <NUM>. In the illustrated example, the protective sleeve <NUM> has a construction, providing an outer diameter in the region of <NUM> and an inner bore in the region of <NUM> to freely receive the fibre bundle <NUM>.

The construction of the protective sleeve <NUM>, as illustrated in <FIG>, has three layers. An inner layer <NUM> may be, for example, approximately <NUM> thick (<NUM> microns) and provides flexibility to the protective sleeve <NUM>. The inner layer <NUM>, in this example, is made of a compound that is resilient, heat resistant and chemical resistant, for example Hytrel®. Hytrel® is a thermoplastic elastomer, specifically a copolyester material, which combines the flexibility of rubber with the strength and processability of thermoplastics, thus ensuring flexibility of the section of the fibre bundle <NUM> to which the protective sleeve <NUM> is applied.

The middle layer <NUM> of the protective sleeve <NUM> is a strengthening layer. In the illustrated example the middle layer <NUM> comprises aramid fibres, commonly known by the tradename Kevlar®.

The outer layer <NUM> of the protective sleeve <NUM> provides a low friction outer surface, as well as covering the layers below so that the favourable installation properties of the cable assembly <NUM> as a whole are not compromised. The low friction outer surface may be provided by a coating of a low-friction material or by blending a material having low friction properties with a sheath material. The sheath material may be, for example, high density polyethylene (HDPE), medium density polyethylene (MDPE), nylon or polypropylene. The use of a low friction material assists in the transportation of the pre-terminated optical fibre cable assembly <NUM> through the duct. Particularly in a cable assembly adapted for installation by blowing, frictional properties, as well as other properties of the cable assembly are very important. Even though the protective sleeve <NUM> may cover only a minor portion of the overall length, it is important that the protective sleeve <NUM> is designed not to degrade the installation properties unduly. This is, of course, a requirement that does not apply to conventional protective sleeves, of the type that might be added to protect the protruding end of the cable assembly, after it has been installed.

The protective sleeve <NUM> material may also have flame retardant properties, and/or example low smoke zero halogen (LSOH or LSZH). It is desirable that the protective sleeve <NUM> exhibits low fire hazard properties outside the duct <NUM> because it will be exposed once installed. Parts of the cable assembly <NUM> which are contained within the duct <NUM>, may be protected against fire by the duct itself. For example, the protective sleeve <NUM> may comprise a polyethylene-based material, comprising a friction reducing agent such that the outer layer exhibits low-friction properties. An example of a suitable material for the outer layer <NUM> may be a mixture of high density polyethylene (e.g. Borstar®) and a friction reducing agent. The friction reducing agent, which may also be called a "slip agent", might be, for example, a silicon-based material including a polyether modified poly (dimethylsiloxane) material such as a polyether modified hydroxy functional poly-(dimethylsiloxane) material. As an alternative to, or in addition to, the friction reducing materials described in the above embodiments, erucamide and/or oleamide materials may be used as slip agents.

It will be appreciated that, as an alternative to the layered construction described above, the protective sleeve <NUM> may be constructed from a single layer, or multiple layers of composite material, which provides the structural, chemical and low-friction properties required to protect the underlying fibre bundle <NUM> and the optical fibres <NUM> during installation and after installation.

In one embodiment, the fibre bundle <NUM> may be covered by an outer sheath (not illustrated in <FIG>), which extends substantially the full length of the optical fibre bundle <NUM>. This embodiment may for example be based on a cable assembly of the type disclosed in <CIT>, mentioned above, in which the outer sheath is extruded onto the optical fibre bundle during manufacture. The outer sheath may be made for example of HDPE, with or without a friction-reducing additive. The outer sheath protects the bundle and facilitates sliding of the bundle through the duct <NUM>, much more easily than if the acrylate material of the coating of the bundle <NUM> were in direct contact with the interior of the duct. The outer sheath is stripped from the ends of the cable assembly, to gain access to the bundle and the optical fibres, for termination, splicing etc. It is a matter of choice, whether this outer sheath remains in place underneath the protective sleeve <NUM>, or is omitted, in those parts of the cable assembly where the protective sleeve <NUM> covers the optical fibre bundle <NUM>. These different options are illustrated in more detail, in <FIG>.

Referring generally to <FIG>, a pre-terminated optical fibre cable assembly <NUM>, can be assembled by sliding the protective sleeve <NUM> over an end section of a longer, premanufactured optical fibre cable assembly. <FIG> illustrates an example where the premanufactured optical fibre cable assembly has an outer sheath <NUM> which remains in place under the protective sleeve <NUM>. It will be appreciated that the inner diameter ID26 of the protective sleeve <NUM> and the outer diameter OD58 of the outer sheath are dimensioned such that the protective sleeve <NUM> slides freely over the outer sheath.

In another embodiment, illustrated in the detail of <FIG>, a section of the outer sheath <NUM> is removed and the protective sleeve <NUM> is added to the resulting exposed section of the fibre bundle <NUM>. In this example, the inner diameter ID26 of the protective sleeve <NUM> maybe smaller than the outer diameter OD58 of the outer sheath, being dimensioned such that the protective sleeve <NUM> slides freely over the coated fibre bundle <NUM> only.

In a further alternative embodiment, illustrated in <FIG> the protective sleeve <NUM> overlaps a short section of the outer sheath <NUM>. For example, the protective sleeve <NUM> may extend a metre or two behind the leading end <NUM> of the optical fibre cable assembly <NUM>, while the outer sheath <NUM> extends to a point that overlaps with the protective sleeve <NUM> by a centimetre or a few centimetres. The protective sleeve <NUM> may have dimensions the same as in <FIG>, in this case, or maybe slightly smaller, and stretch to fit over the end of the remaining outer sheath <NUM>.

In the manufacture of the optical fibre cable assembly <NUM>, the protective sleeve <NUM> in some embodiments is bonded to the underlying layer at some point. In other embodiments, bonding may be unnecessary. As illustrated in <FIG>, this bonding can be applied at the trailing end of the protective sleeve <NUM>, such that movement of the protective sleeve <NUM>, relative to the optical fibres <NUM>, is prevented during installation or the protective sleeve <NUM>. If bonded, suitable bonding locations may be those indicated schematically with reference <NUM>. While this example illustrates bonded locations <NUM> at the trailing end of the protective sleeve <NUM>, bonding locations may alternatively or additionally be provided at the leading end <NUM> of the protective sleeve <NUM>, or along the length of the protective sleeve <NUM>, or at intermittent points along the length of the protective sleeve <NUM>. The protective sleeve <NUM> may be bonded, for example with suitable adhesive (e.g. a common cyanoacrylate adhesive, also known as Superglue™), such that the protective sleeve <NUM> remains stationary relative to the fibres <NUM>, the fibre bundle <NUM> or outer sheath <NUM> during installation of the pre-terminated optical fibre cable assembly <NUM>. Depending on the embodiment, the underlying layer to which the protective sleeve <NUM> is bonded may be an outer sheath <NUM>, or a coating <NUM> of the fibre bundle <NUM>. In principle, the portion of the cable assembly <NUM> over which the protective sleeve <NUM> extends might contain only the primary coated optical fibres <NUM>.

In the example of <FIG>, potential bonding locations <NUM> are indicated, but in one particular embodiment, bonding is unnecessary. Recalling that protective sleeve <NUM> may have an inner diameter less than the outer diameter of outer sheath <NUM>, the end of outer sheath <NUM> forms a natural stop, beyond which the protective sleeve cannot slide. Similarly, at the leading end of the cable assembly <NUM>, ferrule connector <NUM> provides a stop, beyond which the protective sleeve <NUM> cannot slide. As described further below, it is expected that leading end of protective sleeve <NUM> will be clamped to the underlying fibre bundle. An advantage of not bonding the protective sleeve <NUM> to the fibre bundle <NUM> is that the protective sleeve <NUM> will be free to expand or contract due to heat and cold, without transmitting any forces to the fibre bundle <NUM>.

As an alternative to adhesive, heat-shrinking or other fixing methods can be considered, provided they do not damage the underlying structure, of course, or result in a bulky profile. As mentioned already, in a variation of the example of <FIG>, the inner diameter of the protective sleeve <NUM> may be made smaller than the outer diameter of outer sheath <NUM>, so that the end of the protective sleeve <NUM> has to stretch over the end of the outer sheath <NUM>, becoming fixed against longitudinal movement by friction.

An inner bore of the intended duct <NUM> is illustrated in broken lines, with inner diameter ID20. It will be appreciated that the embodiment of <FIG> is likely to have a larger outer diameter of the protective sleeve <NUM>, and therefore require a larger duct for installation. As mentioned already, space is normally precious, and it may be an advantage of the embodiment of <FIG> that the protective sleeve <NUM> can have a smaller outer diameter, and therefore travel within a smaller duct. Embodiments of this latter type can be designed to travel through the conventional micro-duct, for example having an internal bore of only <NUM>.

Another step in the assembly of the pre-terminated optical fibre cable assembly <NUM> is adding a connector <NUM>, for example a ferrule connector, to the leading end <NUM> of one or more of the optical fibres <NUM> within cable assembly <NUM>. If this step is performed after sliding on protective sleeve <NUM>, the ferrule connector <NUM> need not pass through the protective sleeve <NUM>, and a more compact construction is enabled. The ferrule connector <NUM> can be added before or after the protective sleeve <NUM> is bonded to the optical fibre bundle, terminating at a location closely behind the ferrule connector <NUM>. The precise location can be determined by reference to the subsequent steps for adding a connector body to the ferrule connector <NUM>. The steps will be illustrated below, with reference to <FIG>. To allow precise positioning, it is proposed to bond the trailing end of the sleeve only after fitting the ferrule connector <NUM>.

The optical fibre cable assembly <NUM> is then ready for installing by blowing, pushing or pulling as described above with reference to <FIG>.

Referring to <FIG>, after the leading end <NUM> of the optical fibre cable assembly <NUM> emerges from the duct <NUM>, a connector body is fitted over the ferrule connector <NUM>. In the illustrated example, the connector body includes a boot <NUM>, a rear housing <NUM> and a front housing <NUM>. As illustrated in <FIG>, steps (a) to (e) the boot <NUM>, the rear housing <NUM> and the front housing <NUM> are fitted over the ferrule connector <NUM> in a particular sequence, to complete construction of the optical fibre cable assembly <NUM> prior to connecting within the telecommunications cabinet <NUM>.

Referring to <FIG>, the boot <NUM> is slid over the ferrule <NUM> and part of the protective sleeve <NUM> in the direction of arrow <NUM>. Next, in <FIG>, the rear housing <NUM> is applied by inserting the ferrule <NUM> and a section of the protective sleeve <NUM> into a recess in the rear housing <NUM> in the direction of arrow <NUM>.

Referring to <FIG>, assembly of the rear housing <NUM> is completed by pushing the boot <NUM> in the direction of arrow <NUM>, over the rear section of the rear housing <NUM>. By this action, the rear housing <NUM> of the connector clamps the protective sleeve <NUM> and the rear section of the ferrule <NUM> against the underlying layers of the optical fibre cable assembly <NUM> and grips them securely within the rear housing <NUM>.

Referring to <FIG>, assembly of the connector body <NUM> is completed by applying the front housing <NUM> to the front end of the rear housing <NUM>, in the direction of arrow <NUM>. The rear housing <NUM> comprises resilient locking pegs <NUM> (see (b) and (c)). The locking pegs <NUM> locate in holes <NUM> provided on the walls of the front housing <NUM> such that when the locking pegs <NUM> engage with the holes <NUM> the front housing <NUM> is locked in place. The finished connector body <NUM> is shown in <FIG> end of the optical fibre is thus ready for connecting to a receiving port <NUM> inside the telecommunications cabinet <NUM> (<FIG>). The skilled reader will recognise that connector <NUM> in this example is of a standard "LC" type. Other types of connector can be provided. It is a matter of detailed implementation, whether the rear housing <NUM> is identical to known designs, or is modified specifically to accommodate the leading end of protective sleeve <NUM>.

If desired, the process illustrated in <FIG> can be repeated at the opposite end of the optical fibre, to create a double pre-terminated cable assembly (described below with reference to <FIG> and <FIG>). In current practice, an SC connector is commonly used to terminate the optical fibre at the consumer premises. In embodiments of the present disclosure, the more compact LC type connector is used at both ends. The ferrule connector <NUM> of the LC connector can be smaller, and compatible with the micro-ducts used for blowing. Referring again to the specific example where each ferrule body <NUM> is D-shaped in cross-section, this D-shaped profile can be seen in the rear opening of boot <NUM>, in the example of <FIG>. Ferrule bodies having the D-shaped profile can of course be used in installations where only a single fibre is terminated, as shown here, as well as installations where a pair of fibres are terminated and the ferrule bodies lie side-by-side during installation in a duct.

Installing a protective sleeve <NUM> prior to installing the pre-terminated optical fibre cable assembly <NUM> through a duct <NUM>, advantageously removes the post-installation step of installing a protective outer jacket, for example a braided or woven sleeve, to the optical fibre cable assembly <NUM> in the field, for example at a telecommunication cabinet. It will be appreciated that installing braiding can be time consuming and it can fray if adjustment is required. This can expose the fibre bundle <NUM> and could lead to damage of the optical fibres <NUM>. If the braiding becomes disconnected or broken, the connector body may become disconnected. In addition, the interior of the cabinets can look untidy and unfinished. Dozens or even hundreds of connections may be made in the same cabinet, meaning that the fibre and sleeve can be subjected to repeated disturbance over their lifetime.

As mentioned, the cable assembly of the type disclosed herein can be installed by blowing, or by pushing, pulling, or by a combination of these processes. For pulling, it may be noted that ducts can be purchased which are pre-loaded with a pulling line.

<FIG> illustrates a pulling accessory <NUM> that can be used with a pulling line, to install an optical fibre and/or optical fibre cable that has been pre-terminated with a ferrule connector <NUM>. The coated fibre bundle <NUM> is shown, which is also fitted with a protective sleeve <NUM> (shown in dotted lines). Two of the accessories are illustrated, one fitted to the end of the optical fibre, and one spare. As can be seen, the pulling accessory <NUM> has a recess <NUM> tailored to fit over the pre-terminated end of the optical fibres, capturing the ferrule body <NUM>. At a rounded front end of the pulling accessory <NUM>, a pulling eye <NUM> is provided, for attaching the pulling line (not shown).

As is known by the skilled person, the distance that a length of optical fibre cable that can be installed by pulling or pushing may be significantly less than the distance that can be obtained by blowing, but it may be adequate, for example for short drops within a building, or from street to building.

<FIG> illustrates another example of a pre-terminated optical fibre cable assembly <NUM> constructed in accordance with the principles of the present disclosure. This example, is a length of optical fibre cable <NUM>, which is pre-terminated at both ends with ferrule connectors 24a and 24b, and both ends are provided with protective sleeves 26a and 26b. The cable <NUM>, as delivered, is coiled in a pan <NUM> or wound on a reel, in the conventional manner. The types of connectors at the different ends can be the same or different. The lengths of protective sleeve <NUM> can be the same at both ends, or different, as shown. For particular applications, the structure of the protective sleeve 26a may even be different to that of protective sleeve 26b. In particular, it is envisaged that one of the ends of the cable assembly <NUM> might be installed by blowing, over a large distance, say, while the other end is installed over a shorter distance, for example by blowing, pushing or pulling. One of the ends may terminate at a communications cabinet, while the other end terminates within a consumer premises, such as a house or office.

<FIG> illustrates an example of such an installation, using the double-ended pre-terminated cable assembly <NUM>. A first installation step is illustrated in <FIG> and a second installation step is illustrated in <FIG>. The first installation step corresponds, for example, exactly to the blowing installation process described above with reference to <FIG>. From an access point <NUM> on the exterior of a building <NUM>, a first end of the cable assembly <NUM> is installed by blowing to a cabinet <NUM>. The installation distance may be hundreds of metres or more. At the end of this first installation step, the second end of the cable assembly, and a coil of excess cable, remain at the access point.

In the second installation step illustrated in <FIG>, the second end of the cable assembly <NUM> is installed into a local drop duct, to reach a particular apartment or room within the building <NUM>. As illustrated, this may be a consumer's connection point <NUM> on an upper floor of the building. This installation step, which may comprise only a few metres of cable, may be performed by manual pushing, pulling or blowing if necessary. Within the consumer premises, the connector body can be added to the ferrule connector, while the pre-fitted protective sleeve protects the protruding length of the cable. Excess cable can be stored at a suitable point on the installation, for example in the home/office at connection point <NUM>, or in a termination housing <NUM> at the side of the building (as shown in <FIG>), or at some point in between. When the cable assembly <NUM> or <NUM> is lightweight and compact to begin with, storing the excess length is not such a problem as it is in the case of the bulky drop cable described in the disclosure of <CIT>, mentioned in the introduction.

Using pre-fitted protective sleeves, in the manner described, improves the installation process, by reducing post installation steps and time. As such, production costs and assembly costs may be reduced compared with subsequently applying a protective sleeve, in particular a braided or woven sleeve. The existing solution, a protective sleeve added after installation, is typically of larger diameter, than the pre-installed protective sleeve <NUM> described above. This can be because of the nature of the manufacturing process to produce a braided protective sleeve braid, which comprises multiple overlapping yarns. This could also be because the braid needs to be large enough to pass over the ferrule connector <NUM>. Therefore, preinstalling a protective sleeve <NUM> as described above saves space and therefore facilitates more installations within one cabinet.

Additionally, following the principles of the present disclosure, the delicate steps of fibre termination and assembly of the entire pre-terminated cable assembly with protective sleeves can be performed in a controlled factory environment, rather than in the field. As explained already above, and as illustrated in <FIG>, the length of the pre-fitted protective sleeve <NUM> does not need to be precisely tailored to a particular installation. It needs only to be sufficient to protect whatever length of optical fibre will be protruding from the duct. As described, these measures can be applied to only one end of the cable assembly, or to both ends. These measures can be applied especially to a compact and lightweight cable, of the type designed for installation by blowing, although the method of installation is by no means limited to blowing. There is disclosed kits of parts not according to the claimed invention for use in producing pre-terminated optical fibre cable assemblies of the type described, as well as the method of manufacturing such assemblies, and the stocking and distribution of such assemblies for installation, together with accessories involved in the installation. The present disclosure further includes methods of installation, as described, including the cable assemblies.

Claim 1:
A pre-terminated optical fibre cable assembly (<NUM>, <NUM>) configured to be installed through a duct (<NUM>) and having a leading end, wherein the pre-terminated optical fibre cable assembly comprises:
at least one optical fibre (<NUM>);
a terminal connector (<NUM>) on the at least one optical fibre at the leading end of the assembly, the terminal connector (<NUM>) being a ferrule connector having a ferrule body adapted to have a connector body (<NUM>, <NUM>, <NUM>) attached to it after installation through the duct so as to complete a functional connector; and
a protective sleeve (<NUM>), the protective sleeve having a leading end positioned closely behind the terminal connector and extending only along a minor part of the length of the optical fibre, greater than <NUM> long and up to <NUM> long from behind the terminal connector towards a trailing end of the optical fibre cable assembly, the protective sleeve (<NUM>) being adapted to protect the at least one optical fibre where it is vulnerable outside the duct and where the leading end emerges from the duct, after installation of the optical fibre cable assembly through the duct.