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INDUSTRY VCSELs


WHEN YOU HEAR THE PHRASE ‘heavy industry’ your mind might conjure up images of colossal steel-making plants, vast, busy dockyards, or endless rows of gritty smokestacks belching unpleasant and toxic gases aloft. But in the twenty-first century, you might equally well think of massive environmentally controlled data centres lying just a stone’s throw from cold-water lakes or other natural chilled water sources, and surrounded by high-latitude evergreen forests. Due to the tremendous amount of energy these data centres now consume, such places of extreme data storage, transfer, and manipulation are our modern-day factories supporting the world’s infrastructure, daily operations, and thirst for information and instant communications.


To aid their running, datacentres are being located alongside power stations. And to trim the electricity bills, more of them are cropping up in regions with access to low-cost natural and renewable power, such as Iceland, a country blessed with a rich source of geothermal energy, and Sweden, a country renowned for both natural beauty and cold water Baltic bays ideal for datacentre cooling and low-cost power sourcing. Throughout this decade and into the next, datacentres will increase in number to try and satisfy the seemingly insatiable demand for data everywhere, ubiquitous connectivity, and


unlimited and seamless human and machine interfaces, all believed at near zero cost. This vision is driven by trends towards cloud computing, big data, and the Internet-of-Things.


To try and prevent the energy that datacentres consume from getting out of hand, there is a need to develop more reliable, higher-speed data-transmission links that consume less energy. The traditional medium for supporting data transfer is a length of copper wire in the form of a ‘twisted pair’ connector, but this has already been replaced in many datacentres with short-reach, laser-diode-based optical links and interconnects, which combine a higher data capacity with greater bandwidth density, higher transmission efficiency, a more robust operating temperature range, longer reach, and lower costs.


These optical links are being continuously refined, leading to faster and faster aggregated transmission speeds, i.e. increased bandwidths (see Figure 1).


A key ingredient in these optical links is the light source. Previously the most common form of this device for longer distances was an edge-emitting laser diode, which employs cleaved crystal facets as reflectors to form the laser cavity, forcing coherent light to be emitted from the edge of the device.


Copyright Compound Semiconductor October 2014 www.compoundsemiconductor.net 35


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