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Tags: Optical, Submarine
January 17, 2016

Infinera’s Advanced Coherent Toolkit (ACT) Delivers up to 60% More Performance for Submarine and Terrestrial Optical Cables

Matt PhotoBy Matt Mitchell

VP, Optical System Architecture

Infinera recently validated our new Advanced Coherent Toolkit (ACT) over one of the world’s longest submarine cables – Telstra’s Endeavour cable, which connects Sydney to Hawaii. The Infinera ACT consists of new techniques that enable increased capacity and reach on subsea and terrestrial cables – up to 60% depending on the particular cable. By combining our advanced FlexCoherent™ digital signal processor (DSP) electronics and large scale photonic integrated circuit (PIC) optics, Infinera has built a strong engineering capability around novel coherent approaches.

There was a time when particularly long or challenging subsea routes just couldn’t be closed using the highest data rates available. Network operators were faced with the prospect of using hop-by-hop regeneration (regen) through intermediate points where they could bring the cables up to remote islands in the middle of the ocean. In these scenarios, the network operators took a hit on the operational cost of running an active regen sites.

As coherent technology has evolved, the question is no longer whether a particular cable span can be closed – it’s now a concern of how much capacity can be extracted from the route. Those costly regen sites in existing cable systems are now being “glassed through,” and new cable systems are being laid over longer direct spans that would have been impossible to close in the pre-coherent days.

The move to coherent detection means that network operators can unlock the incredible power of modern signal processing to increase capacity on very valuable assets – undersea and terrestrial optical cables. When assessing the significant expense of deploying a submarine cable, which can run into several hundred million dollars, the value of increasing fiber with no replacement of undersea elements (wet plant) is clear.

In the first coherent super-channel era, the DSP in the receiver allowed Infinera and our customers to conquer channel impairments such as chromatic dispersion and polarization mode dispersion. As we move toward the second coherent super-channel era, digital processing and signal manipulation techniques are added to the transmitter (TX-DAC), in addition to introducing enhanced receiver-based technologies.

A TX-DAC is just one of the innovations in the new Infinera Advanced Coherent Toolkit. There are multiple advanced and unique algorithms in the ACT that allow operators to tune a particular set of waves in order to maximize the capacity they extract from the fiber across both subsea and terrestrial networks:

  • Nyquist subcarriers: Super-channel carriers are split into multiple Nyquist subcarriers. The lower baud rate subcarriers increase the tolerance to nonlinearities resulting in increased reach/capacity performance.
  • Next Generation high-gain soft decision forward error correction (SD-FEC): Infinera’s new advanced FEC algorithms enable increased gain for low latency or higher optical reach applications.
  • Gain sharing: The SD-FEC gain output from two channels can be mathematically combined so that the stronger channel can be used to reduce the bit error rate and enhance the quality factor (or Q-value) of the weaker channel. Gain sharing leverages the multi-carrier architecture of PIC-based optical engines. Benefits of gain sharing include increased optical performance, including capacity.
  • Matrix-enhanced phase shift keying (ME-PSK): This new modulation scheme provides greater reach when compared to PM-BPSK which has been widely used on cables longer than 9,000 kilometers. Enhanced coding techniques with advanced constellations result in increased performance over the traditional PM-BPSK modulation.
  • Flexible channel spacing: This enables granular spectral tuning of the optical channels and is applicable to a single carrier within a super-channel, a fraction of carriers within a super-channel or the entire super-channel. By optimizing the spectral makeup of the super-channel an additional knob to trade off reach and performance becomes available.

The Advanced Coherent Toolkit combines advanced PIC-based photonics and sophisticated DSP/ASIC electronics to deliver terabit-scale performance. For more information, click here to read the white paper that describes the elements of this toolkit in more detail.

Infinera recently concluded a field trial with one of our long standing subsea customers, Telstra, that validated Infinera’s new Advanced Coherent Toolkit. The trial took place over the 9,000-kilometer Endeavour cable system between Oahu, Hawaii and Sydney, Australia.  Working with Telstra, we selected the Endeavour cable because it is among the longest trans-pacific submarine cables in the world, enabling us to put ACT to the test. As a result of the trial with Telstra, we were able to ensure that the functions in ACT performed well in this tough environment.

Infinera continues to pioneer the next generation of coherent technology and enable operators to harness the maximum capacity for a given reach from new or existing subsea and long-haul terrestrial cable systems carrying super-channels.

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