FIBRE OR COPPER? Fibre optics has long been touted as the next big thing. After 30 years of expectation, is that reality finally here?
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ibre 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.
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.
Active optical cable
Mid-board optical transceivers
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
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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.
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 op-