Infinera, BICS, OFS test extended reaches for coherent transmission

Optical transport systems vendor Infinera and wholesale carrier services provider BICS, say they have had success with quadrature phase-shift keying (QPSK), 8 quadrature amplitude modulation (8QAM), and 16QAM coherent transmission modulation formats in a laboratory trial. The workout used OFS Terawave large-area/low-loss (LA/LL) fiber, which is optimized for terrestrial fiber cables but may also prove beneficial for submarine network applications, the tests illustrate.

The parties say the trial shows the benefits of the ability to run multiple modulation formats over the same fiber (as supported in Infinera's FlexCoherent technology) as well as the improvement in reach and capacity LA/LL fibers can provide for both terrestrial and submarine links. Such fiber has seen what the companies called "a handful" of submarine cable deployments so far.

Dual-polarization QPSK (DP-QPSK) is now widely used to support coherent line-side 100-Gbps optical transmission, while 16QAM is being favored as the industry explores 200- and 400-Gbps transmission. While 16QAM offers greater capacity than DP-QPSK, it does so at the cost of reduced reach over existing fiber types. Therefore, 8QAM is being investigated as a compromise approach; Infinera announced an 8QAM trial with Telstra across undersea cable earlier this year (see "Infinera, Telstra send PM-8QAM across submarine network").

However, the lab work with BICS and OFS demonstrates that the use of 8QAM with LA/LL fiber can offer both greater capacity and extended reach. The parties say they were able to demonstrate an optical reach of 7,400 km with a 50% increase in fiber capacity versus DP-QPSK. The 8QAM trial with Telstra on more conventional fibers stretched only 2,200 km.

"With the optical reach we achieved using this new type of LA/LL fiber we could envisage a future in which PM-QPSK could be used to close transpacific links, PM-8QAM could cross the Atlantic, and PM-16QAM could span a European backbone," explains Steve Grubb, Infinera Fellow and the architect of the trial. "This would enable between 50% and 100% increase in new submarine or terrestrial cable capacity."

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