Free space in the last mile

The establishment of a high-speed optical network was one of the key policies of the new Labour government when it came to power in 1997.

The establishment of a high-speed optical network was one of the key policies of the new Labour government when it came to power in 1997.

Broadband Britain, we were told would create the most advanced telecommunications network anywhere in the world.

Six years later only about 15% of consumers have access to high speed, optical networks - but should we be surprised? Dr Chris Emslie, Managing Director of leading specialty fibre manufacturer Fibercore Ltd says that if you consider the current state of the telecommunications industry, then probably not.

Despite the good intentions of the government and the implosion of telecomms in the last three years, it would be unfair to blame government or the telecomms industry for the lack of progress of the UK's broadband and now it seems that a solution may be on the horizon.

Building a national broadband communications network is more of a logistical challenge than a communications one.

The technology already exists to enable every household and commercial property to benefit from high-speed connectivity - installing it, however, is another matter entirely.

While the latest figures show that only 15% of consumers in the UK are directly connected to a high-speed network backbone, more than 80% are within just one mile.

Bridging the last mile has become the final frontier in realising the dream of Broadband Britain.

But, just because there are still around eight out of every ten disconnected consumers doesn't mean that the industry isn't trying to solve the problem.

Installing broadband optical connections in place of the existing low channel count copper one's in the UK's densely populated metropolitan networks is costly and time consuming.

These are two commodities that the industry doesn't have large reserves of either of in the current market.

Over the last five years, telecommunications operators, network architects and component manufacturers have all been looking for a solution that will allow them to connect end-users, particularly in Britain's densely populated metropolitan areas, without the need to bury it in the ground.

The simple truth is that while cable modems, digital subscriber lines and fixed wireless technologies provide solutions for sections of the market, a majority of the end-users seeking ultra-high bandwidth remain frustrated.

Despite the constriction in the industry, consumer demand for bandwidth has continued to accelerate at a steady rate.

In the current environment, the importance of delivering high-speed broadband connectivity is simple.

The greater the bandwidth, the more services telecommunications operators can offer - the simple fact is that traffic cannot travel at fibre-optic speeds via copper or radio waves.

The better the standard of services on offer (as bandwidth increases) the greater the revenue they will deliver.

You only have to look at the developments in GPRS and the considerable steps from 2G to 3G cellular phones to see that creating a nationwide broadband network opens up another, yet untapped revenue stream for operators.

The result has been that some of the world's largest telecommunications infrastructure vendors are staking future prosperity on funding new developments in the technology.

After years of debate and research, it seems that a reliable and cost effective solution may be just around the corner, as free-space optical technology rises like a phoenix from the ashes that were once the Telecommunications Industry.

Free-space optical communications hit the headlines again in the immediate aftermath of the 11th September 2001 atrocities when it enabled Wall Street to get back to business by restoring a communications network in less than 48-hours, in an environment where recabling would have taken months.

In actual fact, free-space optics (FSO) has been around since the late 1960s.

The first experiments into FSO can be traced back to the late 1960s, when German Scientist, Dr Erhard Kube published the first white paper on the viability of free-space optical communication, entitled "Information transmission through light beams through the atmosphere".

These initial trials of free-space optical communication used transmitter and receiver beacons with green lasers, achieving little more than proving the concept.

The key to free-space optical communication fulfilling its full potential is that it must be seen as a more viable strategic solution than simply a solution used for short term, tactical deployments.

It must become a technology that is deployed strategically alongside existing infrastructure in addition to a stand alone form of access (in metro networks where cabling is not possible, expensive or will take too long to deploy) and in rural areas to provide connectivity where the landscape or distance from installed network make fibre deployment unviable.

This will also require operators rethinking their preconceived ideas of the distances involved in "last mile" connections.

In both of these situations, using free-space will ultimately achieve one thing - reduced cost of deployment per subscriber.

We all know the major reason that telecomms companies' business models revolve around looking for new ways to reduce this figure on one hand, while increasing revenues through the delivery of more products and services over high speed broadband connections.

Integrating free-space into future network design from the ground up will not only enable operators to reach places that they can't currently go due to cost or topography but will enable operators to provide increased bandwidth as demand requires.

The technology exists today to enable communications companies to create a traditional network using the latest EDFAs in traditional DWDM systems and high power fibre lasers for through the air connections.

The ability to use free space technologies in this way is the result of fibre developments and the design of technology which have resolved many of the initial problems that limited viability.

One problem was that green light scatters strongly when faced with atmospheric water vapour - mist or cloud - making high-speed communications of more than 1000m difficult in anything other than perfect sunshine.

With the development of new cladding pump fibres, including Fibercore Ltd's new CP range, for use with high-power laser diodes, both power and as a result, transmission distance have been improved using lasers operating in the infra-red.

Furthermore, green lasers even at low power were fundamentally not eye safe - the move to infra-red lasers has remedied this.

During the telecomms boom, free-space technology benefited from technical innovations in, for example, detection and modulation schemes handed-down from more mainstream applications within the industry.

Today, it continues to benefit from a steady influx of technical talent, seeking out unfilled, and potentially profitable, niches on the periphery of the telecommunications industry.

The net result is an altogether more thoroughly engineered and viable technology with enhanced distance capability, data capacity and reliability.

The intrinsic benefits of fibre lasers map onto the needs of free-space communications very closely indeed.

High conversion efficiencies, excellent heat-dissipation properties, self-aligned cavities and good beam quality pave the way for rugged, compact and reliable units that consume minimal amounts of electrical energy and require little or no maintenance - properties that are of special importance in free-space installations that, by their very nature, may be out-of-the-way or inaccessible.

The extreme versatility of laser fibre technology also enables polarisation to be controlled intrinsically, through the use of polarisation maintaining fibre geometries, creating the opportunity for further reductions in system complexity and cost.

Where infrastructure already exists in metro deployments an innovative use of through the air optical communications has been proposed that could provide a highly cost-effective means of extending the network into premises that could otherwise present insurmountable, or rather un-economic, installation challenges.

The "skyscraper" has been with us for more than a century and fibre installations can be both difficult and costly but, the integration of fibre lasers as a method of "vertical" connectivity between the kerb side and the premises, when combined with the deployment of high-power, erbium-ytterbium doped cladding-pump fibre amplifiers, to increase the number of sites that may be served via through the air connections, could go a long way to achieving cost per subscriber goals even in the most difficult of circumstances.

The deployment of DWDM and the advent of "metro" has inevitably led to an increase in both equipment and component density within telecomms networks and the specialty fibre industry has responded to this increasing competition for space by reducing fibre diameters.

These so-called "low-profile" fibres are essentially developments of the 80um sensor fibres pioneered by Fibercore Ltd in the early 1980s and, perhaps paradoxically, they offer greater reliability in small form-factor packages than their more conventional, 125um counterparts.

Although "low profile" fibres have now successfully been introduced into the manufacture of components such as EDFAs, WDMs taps and splitters, most laser fibres have remained at 125um or greater, dictated primarily by the dimensions of the output pigtails of suitable pump diodes, a well-proven technology already exists, should increasing deployments (or decreasing space) on day demand more compact free-space fibre lasers.

These advances in fibre laser technology are changing the way that operators and system developers are looking at free-space optical connections.

They are finally viewing it as a viable complement to fibre in the last mile.

The increased reliability and dramatically improved communicable distances in recent years now provide solutions to two significant challenges in developing a nationwide broadband telecommunications network.

In a market where operators are looking for rapid injections of revenue without requiring huge investments in infrastructure, free-space provides a reduced cost interim solution until it was possible to deploy fibre.

It could also be used in areas where topology or existing metropolitan landscapes, make it impossible to install fibre - central London or areas in or around heritage sites are just two examples.

The recent developments in free-space optical components and fibres provide the final piece of the broadband jigsaw.

Free-space provides the UK with the technology to live the dream of a nationwide broadband network, by providing reliable, high channel count optical connections at a fraction of the time and cost needed to deploy fibre.

For the telecommunications industry at large, it means the creation of a new and untapped revenue stream and a technology around which they can begin to rebuild their business plans.

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