Fibre optics: knocking on the copper door

Fibre optics has long been touted as the next big thing. After 30 years of expectation, is that reality finally here?

Fibre optics has long been defined as a technology that will become mainstream within five years. That may finally be changing. Fibre may not replace copper to a great degree in the short term, but will rather be adopted in increments where the technical and economic advantages of fibre make sense.

Copper interconnects offer reliable low-resistance links that are easy to assemble and repair with characteristics that have been fully documented. As data rates have pushed into 10+Gbps, issues of signal integrity including attenuation, skew, crosstalk, reach and susceptibility to EMI have proven challenging, especially as system density has increased. Transmission over optical fibre offers much higher bandwidth and resistance to crosstalk and EMI, while consuming less space and bulk.

The limiting factor has been the cost and power consumption of the electro-optical conversion process. Advances in photonics are breaking down those barriers. In the past, optical links typically used in the telephony industry were considered economical only in very long runs that extended to miles.

Today, engineers are finding new ways to economically utilise optical links in much shorter applications, especially in networking and storage applications.

The connector industry, as well as photonic device manufacturers, is actively introducing entirely new generations of optical transmission devices for applications in commercial, industrial and even military/avionic applications.

Active optical cable

Active optical cable (AOC) assemblies, for example, consist of a standard copper connector at both ends, but active components within the connector strain relief convert the electrical signals into optic pulses which are coupled into permanently attached optical fibre. The reverse conversion occurs at the other end of the assembly. The result is a plug-and-play, full-duplex, high-speed link with greatly extended range. A primary advantage of this approach is the fact that AOCs plug directly into a legacy copper interface. In addition to extending reach and signal fidelity, AOCs introduce application flexibility that simplifies the process when equipment must be reconfigured.

From a user’s perspective, an AOC interface looks identical to the standard copper connector, while the signals are transmitted optically via low-loss small-diameter fibre. AOC assemblies are now available in a variety of standard interfaces including CX4, SFP+, QSFP+, USB 3.0, CDFP and Thunderbolt.

MXC connectors

Demand for high-density optical connectors has resulted in the introduction of the new MXC connector that can join up to 64 optical fibres in a single ferrule.

In order to minimise the problem of contamination at the optic interface, MXC connectors utilise expanded-beam technology. A collimating lens assembly expands the beams over the interface gap, making a speck of dust a much smaller percentage of the beam diameter. MXC connectors also eliminate the need for end-face polishing, resulting in smaller variations in optical transmission.

Mid-board optical transceivers

Optics have begun to find a home directly on the printed circuit board. Over the past few years, mid-board optical transceivers from FCI, Molex, Samtec and TE Connectivity have entered the market with the capability of delivering up to 12 full-duplex channels operating at 25 Gbps each. The ability to take high-speed signals off the PCB can solve some serious board layout and material issues. Optical fibres can then be brought through an optical backplane or front-panel I/O connector.

Bandwidth is king

Bandwidth is fast becoming a very important ‘resource’ in our society, and the discussion about net neutrality has placed this issue clearly in the spotlight. The increased use and availability of internet-based services has profoundly changed our society and the way we do things. Starting with basic and simple data exchanges, the internet was soon used for voice, video, TV, gaming and big data. As a result, the need for more bandwidth has grown dramatically over the last decade. The next evolution, which includes the Internet of Things (IoT) in which millions or even billions of devices will be connected to some sort of network, will only amplify the need for additional bandwidth.

From the beginning, this triggered technology companies to push the digital subscriber line (DSL) performance to greater heights. They developed different varieties, such as ADSL, HDSL, RADSL, VDSL, UDSL, etc, that offer varying performance over cable length. The reason was simple: DSL was brought to your home over existing copper wires, so these new technologies could use existing copper telephone networks. At the same time, cable companies, which use coax cables to bring TV to millions of households, started to compete with the DSL providers and designed their own products to deliver internet services to their customers. But there is a limit to these (DSL/cable) technologies and, to meet the demand for growing bandwidth, fibre-to-the-home/basement/curb/node was and is widely seen as the solution.

With the exception of FTTH, the other versions (FTTB/FTTC/FTTN) still include a short stretch of copper wire for the final leg to the end user at home. Most operators already have optical fibre networks up to and including the distribution cabinet on the street, but from there to the home or office building, they often resort to the existing copper wire. This copper wire can be the bottleneck, especially because bandwidth is reduced as the copper wire gets longer.

Fibre-optic connections are now being rolled out all over the world, mainly in developed economies in Australia, Europe, North America, South Korea and Japan, but also in emerging economies - China plans to equip new houses and buildings with FTTH. This means a big boost for fibre-optic cable business and fibre-optic connectors. The number of fibre connections is still relatively small but is now growing faster than DSL or cable connections.

However, while FTTH provides connection speeds of up to 100 Mbps as compared to the current 30 Mbps on a cable modem or DSL connection, implementing FTTH on a large scale can be costly because it requires the replacement of copper wires with new fibre-optic cables, which means digging up roads.

The comeback kid

Telecom providers have developed another technology to extend the lifespan of the existing network - vectored VDSL2. VDSL2 vectoring allows operators to deploy ultra-broadband services of up to 100 Mbps over their existing copper-wire telephone networks, making it quick to deploy as a complement to fibre-to-the-home (FTTH). As a result, operators can rapidly meet rising customer demand for high-definition television, video-on-demand and online gaming while protecting existing investments.

In previous DSL technologies, the problem was reduced performance due to noise over the lines in a cable. VDSL2 vectoring claims to be a noise-cancelling technology that cuts out all of the noise, or interference, among the VDSL2 lines in a bundle. With no interference, every VDSL2 line can operate at high speeds, as if it were the only line in the bundle. This means greatly enhanced performance for short distances compared to existing VDSL and ADSL technology. The need for additional bandwidth is not only prominent in our homes and offices but also becomes critical with the exponential growth of smartphone use and deployment of new cellular networks (3G, 4G, LTE and 5G) around the world.

In order to meet these requirements, we must review the way we build and design our cellular ground stations (towers) or antennas. This is why fibre is now being used to connect towers and then go up the tower to connect the multiple antennas; more and more antennas are needed in each tower to support more frequencies and more bandwidth. As a result, towers that once had three antennas for coverage now may have two dozen. This is where FTTA - fibre-to-the-antenna - comes to the rescue. Glass or plastic fibre-optic connections and networks have also found their way to the factory floor. Although fibre-optic factory automation networks have been around for decades, it has remained a basic question of economics whether to use copper or fibre. For a long time copper came out on top, despite some of the obvious technological advantages of fibre-optic networks, such as the bandwidth/transmission speed, the immunity to EMI/noise and its ability to cover long distances without loss of signal strength. While copper wire is still a good choice for low bit-rate applications over short distances, fibre-optic solutions are becoming more attractive as distances go over 50 to 100 metres and speeds above 1 Gbps.

In addition to the better bandwidth capability of fibre-optic connections, another consideration in fibre’s favour is that high-speed copper links use much more power than fibre and may have latency problems. Installing fibre-optic connections also pushes out limitations for future bandwidth/transmission speed requirements, which means the network can be used even when all other systems are being upgraded to work with higher speeds/bigger bandwidths. If reliable connections are required in a factory environment, and at least one other requirement has to be fulfilled in terms of distance, speed/bandwidth or upgradability, fibre is often the medium of choice. As in other applications, users across the manufacturing and process industries expect higher reliability, faster speeds and wireless connectivity. The fact that handling and terminating fibre-optic connections, also in the field, has become much easier over the years has helped to boost the acceptance of fibre-optic networks.

The next five years

FTTH and FTTA networks that use fibre optics are on the rise. Long CCTV links in security systems are now almost exclusively fibre. In addition, millions of cars now use plastic fibre (POF) for safety and entertainment/communications systems.

Fibre-optic connectors will be one of the fastest growing connector types over the next five years. The share of FO connectors in the world connector market grew from 1.9% in 2004 to 3.9% in 2014 and is expected to grow to 5% in 2020. The compound annual growth rate has been the highest of all product types in the 10-year period from 2004 to 2014 and is expected to continue to grow in double digits until 2020.

Fibre-optic connections claim a bigger share of the market and are clearly moving beyond their traditional use in the communications/data processing industries as the backbone in larger networks.

For more information, please contact Robin Pearce, Bishop & Associates, via email at rpearce@bishopinc.com.

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