This article introduces µSHEATH®, a family of cables developed by the French company SAGEM and offering unique benefits. µSHEATH cables are extensively used by telecommunication operators.

Photo 1: µSHEATH® cables

These high-performance cables suit all types of networks: long-haul backbones as well as city rings and local access. They accommodate all standard and advanced NZD fibres and can be adapted to various rights-of-way, installation methods, and environmental conditions (ducted, direct-buried, aerial, sewers, fire hazard areas, etc.)

Advantages for various networks

µSHEATH cables can contribute importantly to the overall economics of building new fibre and cable plants. Their design facilitates planning and deployment of networks that are easy to operate, speedy, flexible, and evolutionary. µSHEATH cables are intended to provide key time and cost savings at all levels of network implementation. Among their advantages for engineering, civil works, installation, extension, and upgrades are:

• Modular design over a wide range of fibre counts, currently up to 864 fibres;
• Remarkably easy handling, installation (through all conventional laying techniques), jointing (by both individual and mass splicing), fibre management, and mid-span access;
• Ultra-compactness, light weight, and functional versatility.

A Design for strength and stability

Within µSHEATH cables, optical fibres are divided into modules or units (up to 12 fibres per module). Each module is covered with a thin, easily removable, coloured synthetic sheath (Figure 2). Depending on fibre count and modularity, the modules are assembled together into a single bundle or several "super-units," each covered with the thin sheath).

Figure 2: 864 optical fibre duct cable design

The outer sheathing system includes diametrically opposed composite strength members, providing high tensile strength and temperature stability. Depending on installation and environmental conditions, additional armouring or protective layers may be provided.

Figure 3: 432 optical fibre duct cable

Simplified handling, laying, and jointing

SAGEM cables are compatible with all laying techniques: pulling, air blowing, air floating, water floating, etc. (Photo 4). Depending on duct size and type, route (number of turns and severity of turns), and installation technique used, the unitary laying length can reach up to 10 kilometers in the best conditions.

Photo 4: Example of pulling of a 456-optical-fibre double-armoured µSHEATH cable

Cable preparation (end and mid-span) is very simple (Photo 5). Opening of µSHEATH cables with a diameter = 8mm is by way of the UAT II tool from Corning (Photo 5-1) or the KABIFIX LK 25 tool from SES Sterling (Photo 5-2). For cables with a diameter in the range 7 to 30mm, the opening can be accomplished with the use of the SAGEM DOG 001 tool plus a scraper-type GRB (Photo 5-3).

Photo 5: µSHEATH cable preparation (end and mid-span)

No specific tool is needed for the jointing of individual splicing. For a mass splicing, an optical fibre flat tool, the model MAP 12-001 from SAGEM (Photo 6-4) will suffice. Photo 6-5 shows a closure arrangement with a 432 optical fibre µSHEATH cable, including individual and mass splicing, and direct coiling of units in the cassettes.

Photo 6: Examples of µSHEATH cable jointing

Cables for demanding environments

On the basis of the same optical core construction, the µSHEATH design can be tailored to suit various rights-of-way and associated installation and environmental conditions, however challenging. Table I summarises the most common options and their typical performance characteristics. The cables can of course be customised to the operator’s own technical specifications.

Table I: Most common µSHEATH cable options and corresponding performance characteristics

A product range in perpetual evolution

After the extension in the second half of 2001 of the fibre count to 864 optical fibres, mainly for city networks, SAGEM developed a new cable family for individual subscriber access.

Photo 8: Example of air-floating in multi-microducts (inner Ø = 8mm)
with a 48 optical fibre µSHEATH access cable (outer Ø = 6mm)

µSHEATH access cables (Photo 9) are downsized, as compared to standard µSHEATH cables, for installation by air-floating or water-floating in multi-microducts, themselves inserted in existing ducts for a better use of the available infrastructure. Of course, these new cables retain all the µSHEATH advantages: handleability, ease of laying and jointing, mid-span accessibility, and flexibility.

Photo 9: 48 optical fibre µSHEATH® ACCESS cable (outer Ø = 6 mm)

After the development of µSHEATH access cables in early 2002, SAGEM completed its product range with the Blown µSHEATH® Module containing up to 12 optical fibres for subscriber access.

Photo 10: Blown µSHEATH® Module inserted in a multi-micro-duct

For both outdoor and indoor installation, this watertight micro-cable can be laid by air-floating or water-floating in multi-microducts, themselves inserted in existing ducts for better use of the available civil works and to conserve space. This new cable, too, retains the specific advantages of all µSHEATH cables. Table II profiles the Blown µSHEATH Module and its typical performance characteristics.

Maximum fibre-count ......................................................12 optical fibres
Diameter .........................................................................2.0mm
Weight, "W" ...................................................................4kg/km
Minimum inner diameter of micro-ducts(1)...................... > 3.5mm
Minimum bending radius................................................. 30mm
Minimum kinking radius ...................................................30mm
Tensile load .....................................................................4daN (1.0 x W)
Crush performance ..........................................................2daN/cm
Storage temperature range............................................ -30 up to +70°C
Installation temperature range...................................... -5 (-10) up to +40 (+45)°C . Between ........................................................................................-10 and +45°C a previous storage at ........................................................................................+20°C during 24 hours is .........................................................................................recommended.
Operating temperature range......................................... -30 up to +70 °C
Watertightness................................................................ Yes
Environment ....................................................................Halogen free cable
Optical characteristics ............................................. .......No change as compared to bare ........................................................................................fibres
Optical fibre types ...........................................................All types of singlemode (G 652, G 652 ........................................................................................with low OH content, G 655, etc.) and .........................................................................................multimode (50/125, 62.5/125, …) .........................................................................................fibres.
Jointing (splicing) .............................................................Individual or mass splicing
Fibre access..................................................................... Easy fibre access (mid-span and .........................................................................................inside closures)

(1) for minimum 600m laying length by air floating and
for minimum 1,000m laying length by water floating
Note: in the field laying lengths up to 1,200m are obtained using air floating technic.

Table II: Typical performances of Blown µSHEATH Module

Summary

Initially developed and patented by SAGEM in partnership with France Télécom, the µSHEATH concept is protected by some 15 international patents owned by SAGEM. About a hundred customers in more than 20 countries (telecommunication operators, dark fibre providers, urban and regional districts, industrialists, etc.) have installed SAGEM standard µSHEATH cables. More than 10,000km of all types of µSHEATH cables are now in service in a wide variety of applications. Fibre types and counts include:

• Standard G 652 single-mode fibres;
• Low water-peak single-mode fibres;
• NZD G655 single-mode fibres for DWDM;
• Multimode fibres (50/125 and 62,5/125).

The recently developed SAGEM products (high-fibre-count cables, µSHEATH access cables, and Blown µSHEATH® Module cables) have all met with success, particularly for city loops, access networks, and subscriber access. They demonstrate the high versatility of the µSHEATH concept and its responsiveness to customer needs regarding cost savings, quick deployment, reliability, and flexibility.