By Geoff Bennett
Director, Solutions & Technology
The Asia-Pacific region remains a leader in new subsea cable investment, with $7.6 billion USD associated with recent and forthcoming cables on routes that touch the region. It’s amazing to think that this region accounts for more than half of the world’s 7.7 billion wireless connections – and the move to higher-data-rate mobile services provides the on-ramp to metro, long-haul and subsea networks that take this data where it needs to go. As an example, Australia’s international bandwidth demand grew at a compounded annual rate of 39 percent between 2013 and 2017 (source: Telegeography).
New subsea cables are being laid across certain routes in order to satisfy the dramatic increase in user demand, and also to deliver the capacity needed by modern cloud-scale architectures. Modern cables are designed specifically for coherent transmission systems, and make use of positive-dispersion, large-area fibers. This combination of factors minimizes the non-linear penalty in the fiber, which tends to be the primary factor that limits capacity and reach in coherent systems. Infinera’s fourth-generation Infinite Capacity Engine (ICE4) technology has already demonstrated record-setting performance levels in this new kind of cable – including the astonishing achievement of 18.2 terabits per second (Tb/s) over the 10,500 kilometer (km) SEABRAS-1 cable, and a more recent industry record of the first 20 Tb/s production-margin capacity on a trans-Atlantic link.
But wait…there are dozens of legacy cable systems!
New cable systems can deliver amazing capacity, but they cost hundreds of millions of dollars, and take years to plan, fund and deploy. What if there was a way to dramatically increase capacity on existing cable systems without disrupting existing services in the process?
One of Infinera’s earliest subsea customers for the DTN-X platform is the Australia-Japan Cable (AJC) system. This cable came into service in 2001 and, at 12,700 km long, it’s certainly a challenging system to close with today’s high capacity expectations.
Unlike newer cables, AJC is dispersion managed – a technique that alternates positive and negative dispersion fiber in order to control cumulative chromatic dispersion (CD) in the cable. In the pre-coherent era this was the only way to build effective cables because CD was considered an enemy to high-data-rate transmission (at a time when 10 gigabits per second [Gb/s] was taking over from 2.5 Gb/s per wavelength). With second-generation coherent technologies like Infinera’s ICE4, our relationship with CD is turned on its head, so that high levels of dispersion provide an excellent way to mitigate non-linear effects.
But cables like AJC have a major advantage – they are an existing asset. The cost of deploying the cable has been repaid, so every year that this cable can deliver economical subsea capacity is a bonus to its owners. With that in mind, Infinera recently announced a major upgrade to the AJC system using ICE4 technology in the existing DTN-X platforms. The upgrade delivers a capacity increase of between 40 and 100 percent over a given cable span – an average of 60 percent for the overall system. This allows AJC to drive down the cost per bit, while retaining all the things that AJC loves about Infinera’s subsea solution: short lead times, point-and-click capacity activation with Instant Bandwidth and rock-solid reliability.
To maximize capacity and reach in subsea cables, ICE4 reaches into our Advanced Coherent Toolkit (ACT). ACT contains many different tools, each of which makes different contributions to achieving this goal. To deliver increased capacity over a dispersion-managed cable, we rely on two critical tools:
- Nyquist subcarriers, which digitally split a carrier to achieve high data rates at lower baud rates, driving down costs.
- Soft-decision forward error correction (SD-FEC) gain sharing, in which two channels, one in a high-dispersion part of the spectrum with low non-linear penalty and one in a low-dispersion part with a much higher penalty, are configured to operate through the same SD-FEC processor so the additional margin for the stronger channel can be used to “pull up” the other channel to regain capacity.
For a deep-dive into these and the other tools in ACT, download our white paper, The Next Generation of Coherent Optical.
ICE4 and the Advanced Coherent Toolkit enable AJC to take advantage of chromatic dispersion to maximize the return on investment on this vital route between Australia and Japan, and to achieve this without disruption to existing services. Infinera’s advanced subsea solutions continue to provide an unparalleled level of scalability, flexibility and programmability to submarine network operators.