The push is on for the development of the next generation of communications networks. How many of us have abandoned our cable subscriptions, and now exclusively use Netflix? I know I have.
The online services we use on a daily basis including Netflix, iTunes and Spotify are huge users of network bandwidth. Netflix alone accounts for around one third of all Internet traffic in the US. This becomes a little less surprising when even in standard definition, watching our favorite TV show uses around 1 gigabyte of data per hour (and 3GB per hour for high definition).
This is only set to increase over the coming years, as our hunger for data grows. With cloud-based storage and computing becoming the norm, extremely high-bandwidth communication networks will be vital.
Light is the backbone of our digital connectedness. The use of fiber is extensive in the networks that we all use, connecting core network nodes across the globe. This use of distributed fiber networks is dramatically increasing, with fiber-based broadband Internet now widely available to home and business consumers in metropolitan areas.
Fiber networks make use of light's properties to encode and multiplex data signals. Current commercial systems make use of only a few of these properties -- light's intensity, phase and polarization. These systems almost exclusively use single mode fiber, which is designed to support a single fundamental Gaussian mode. However, current increases in data traffic mean that we are in sight of the fundamental physical limits of today's single mode technology.
The realization that this bottleneck is close at hand has been driving the development of the next generation of communications technologies. One of the burgeoning research areas attempting to address this bottleneck is optical Space Division Multiplexing (SDM). Consider the shape that the beam of light from a laser pointer makes on a wall. The ability to change the shape of this laser beam is called "yields" -- the spatial degree of freedom. The use of this spatial profile has recently become something of a hot topic in optics; different shapes can be used as a method for multiplexing independent channels of information.
The "shape" of a laser beam is a two-dimensional transverse amplitude field, where the local phase and intensity can be spatially varied. This technology works by generating a set of shapes, which we refer to as spatial modes, and they can be differentiated from each other. When two or more modes can be identified with 100% accuracy, they are referred to as orthogonal modes. The communications technology we aim to develop uses a particular set of these orthogonal modes, referred to as Orbital Angular Momentum (OAM) modes.
Orbital Angular Momentum modes are beams that carry an orbital momentum around their beam axis -- they essentially spiral through space. There is a potentially infinite number of these modes, which can form ever-tighter spirals. We aim to use these spatial modes as multiplexed data streams for use within optical communications, in both fiber and free-space systems
The key factor in the commercial viability of OAM and other forms of SDM is the development of tools for the multiplexing and de-multiplexing of channels that can be incorporated in any new piece of equipment that will use the new technology. During my Ph.D and the following EPSRC fellowship at the University of Glasgow, we laid the groundwork for some emerging technologies on which a commercially viable system could be based.
The Royal Academy of Engineering is now allowing me to take this work further. Its Research Fellowship scheme is supporting my efforts to develop a complete tool kit that will help in the integration of OAM multiplexing into commercial optical communications networks. During the five-year fellowship at the University of Glasgow, we will interface with world leaders in the field, such as Intel and Corning, which will provide important industry-led feedback on our work. We also have three key academic partners that we will work closely with over the period of this Royal Academy of Engineering Fellowship: the University of Southern California; City College of New York; and Durham University, UK.
SDM is an expanding field of study, with teams across the world focusing on different forms of multiplexing; thankfully we're all very supportive of each other's advances. The decision on which particular mode will become the industry standard is a complex one: My feeling is that we will see many different forms of SDM being implemented, and the choice will depend on the particular environment for which the system is being designed. Networks are large and sprawling, and the system that works best in a server farm may not be best for broadcasting the latest TV show via streaming services. However, this uncertainty may spark another battle in the market, reminiscent of Betamax vs VHS, or Blu-ray vs HD DVD. It's hard to know just what the future will bring, but the combination of very healthy competition and collaboration in research shows a clear zeitgeist that will hopefully lead to real deployable technological systems in the coming years.
The "Engineering for Growth" campaign, led by the Royal Academy of Engineering, seeks to highlight the role of engineering as a key driver for growth in the UK. There are few markets growing faster than communications, and I hope my work on SDM will lead to new technologies that will contribute to our knowledge and further growth in this field. And who knows, in the years to come, maybe we will be watching the latest season of The Big Bang Theory using twisted light!
For more details on my work, visit this profile at the Glasgow University website.
— Dr Martin Lavery, Royal Academy of Engineering Research Fellow, University of Glasgow