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NEC demonstrates 50Tbps speeds for subsea cables

NEC has developed an algorithm to optimise 32QAM constellation and combined the L- and C- optical wavelength bands to enable speeds of over 50Tbps across its subsea cables throughout the Pacific region.
Written by Corinne Reichert, Contributor on

NEC has demonstrated speeds of 50.9 terabits per second (Tbps) across subsea cables of up to 11,000km on a single optical fibre through the use of C+L-band erbium-doped optical fibre amplifiers (EDFA), amounting to speeds of 570 petabits per second-kilometre.

In order to attain the bandwidth, NEC researchers developed a multi-level, linear, and non-linear algorithm to obtain an optimisied 32 quadrature amplitude modulation (QAM) or opt32 constellation with a higher limit for non-linear capacity specifically for transmission across subsea cables.

The C- and L- optical wavelength bands are used for ultra-long distance transmission.

"Moreover, this new modulation format is much easier to implement, as it does not require any iterative decoding or non-uniform coding. As such, opt32 modulation allowed NEC researchers to achieve an unprecedented spectral efficiency of 6.14b/s/Hz upstream over a trans-pacific distance," NEC added.

"Also in line with current trends, C+L amplification is used to maximise the capacity per fiber pair. In order to deliver a record-breaking capacity, NEC's researchers developed a patent-pending bi-directional amplifier design that reduces the effective noise figure and the device complexity."

Earlier this month, NEC also announced that it commenced construction of three 100Gbps subsea cable links to provide connectivity to Palau, Yap, and Chuuk islands in partnership with Belau Submarine Cable Corporation and the Micronesian government.

NEC will supply and construct the spur to extend surrounding submarine cable systems out to the islands, with Palau and Yap to be connected with NEC's SEA-US cable that connects Indonesia and the Philippines to the United States mainland via Hawaii and Guam. Chuuk will be connected to Micronesia capital Pohnpei using the cable connecting Micronesia, the Marshall Islands, and Guam.

All three areas were previously served by slow-speed and limited bandwidth satellite services.

NEC also commenced construction on the 3,900km, 100Gbps Hong Kong-Guam (HK-G) subsea cable system last month, due to be completed in the fourth quarter of 2019 with a design capacity of almost 50Tbps.

The cable will land in Tseung Kwan O (TKO) -- Hong Kong's new major hub for technology, datacentre, financial, and media companies, as well as submarine cable landing stations, also connected by Superloop's TKO Express subsea cable -- and Piti, Guam, connecting Asia with the US via the SEA-US system.

In November last year, NEC also completed construction of its Asia-Pacific Gateway (APG) subsea cable between China, Hong Kong, Japan, South Korea, Malaysia, Taiwan, Thailand, Vietnam, and Singapore, which provides capacity of more than 54Tbps.

The APG fibre-optic submarine cable -- owned by a consortium of telecommunications carriers including China's China Telecom, China Unicom, and China Mobile; Japan's NTT Communications; South Korea's KT Corporation and LG Uplus; Singapore's StarHub; Taiwan's Chunghwa Telecom; Thailand's CAT; Malaysia's Global Transit Communications; and Vietnam's Viettel and VNPT -- stretches 10,900km across the region.

Telecommunications carriers and consortiums are racing to build out subsea cable capacity across the Asia-Pacific region, driven by the rapid increase in data usage globally, including Superloop's Indigo subsea cable system; and Vocus Communications' Australia Singapore Cable (ASC) and North West Cable System (NWCS).

In addition to Indigo, APG, TKO Express, NWCS, and the ASC, also being built across the Asia-Pacific region are subsea cables the Tasman Global Access (TGA); the Trident Subsea Cable; the Hawaiki cable; and the FASTER cable.

TGA was switched on in March, connecting New Zealand with Australia thanks to a partnership between telecommunications carriers Telstra, Spark, and Vodafone. The $100 million 2,288km submarine cable, which extends from Ngarunui Beach in Raglan to Narrabeen Beach in Sydney, is made up of two fibre pairs with a total capacity of 20Tbps.

The 28Tbps two-pair fibre-optic, 1,070-kilometre Trident subsea cable, meanwhile, will connect Singapore, Indonesia, and Australia, with stage one slated to go live this month and the entire cable to be completed by the second quarter of 2018. It utilises 100Gbps coherent dense wavelength division multiplexing (DWDM) technology, which is upgradeable to 400Gbps.

Elsewhere in the Asia-Pacific region, the 30Tbps, 14,000km Hawaiki cable -- which finally commenced construction a year ago -- will connect Australia and New Zealand to Hawaii and the West Coast of the United States, with the option to extend to several South Pacific islands along the route via optical add/drop multiplexing nodes, by mid-2018.

The 10,000km FASTER subsea cable system will also connect the west coast of the United States with Asia, landing in Japan and consisting of six fibre pairs and making use of 10Gbps wave technology.

In addition, Australia's incumbent telco Telstra acquired a 36,000km cable network system connecting China, Japan, Singapore, South Korea, Taiwan, Hong Kong, and the Philippines as part of purchasing Pacnet for $697 million in December 2014, and in May last year announced the Bay of Bengal Gateway (BBG) 8,000km 100Gbps submarine cable system, made up of three fibre pairs, which will connect Singapore, Malaysia, India, Sri Lanka, Oman, and the United Arab Emirates.

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