Has coherent optical transmission run its course?

Feature: Coherent's future

Three optical systems vendors share their thoughts about coherent technology and the scope for further improvement as they look two generations ahead to symbol rates approaching 100 gigabaud   

Optical transmission using coherent detection has made huge strides in the last decade. The latest coherent technology with transmitter-based digital signal processing delivers 25x the capacity-reach of 10-gigabit wavelengths using direct-detection, according to Infinera.

Since early 2016, the optical systems vendors Infinera, Ciena and Nokia have all announced new coherent digital signal processor (DSP) designs. Each new generation of coherent DSP improves the capacity that can be transmitted over an optical link. But given the effectiveness of the latest coherent systems, has most of the benefits already been achieved?

Source: Infinera

“It is getting harder and harder,” admits Kim Roberts, vice president, WaveLogic science at Ciena. “Unlike 10 years ago, there are no factors of 10 available for improvement.”

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The era of cloud-scale routeing

Nokia's FP4 p-chip. The multi-chip module shows five packages: the p-chip die surrounded by four memory stacks. Each stack has five memory die. The p-chip and memory stacks are interconnected using an interposer.

• Nokia has unveiled the FP4, a 2.4 terabit-per-second network processor that has 6x the throughput of its existing FP3. 
• The FP4 is a four-IC chipset implemented using 16nm CMOS FinFET technology. Two of the four devices in the chipset are multi-chip modules.
• The FP4 uses 56 gigabit-per-second serial-deserialiser (serdes) technology from Broadcom, implemented using PAM-4 modulation. It also supports terabit flows.
• Nokia announced IP edge and core router platforms that will use the FP4, the largest configuration being a 0.58 petabit switching capacity router. 

Much can happen in an internet minute. In that time, 4.1 million YouTube videos are viewed, compared to 2.8 million views a minute only last year. Meanwhile, new internet uses continue to emerge. Take voice-activated devices, for example. Amazon ships 50 of its Echo devices every minute, almost one a second.

Given all that happens each minute, predicting where the internet will be in a decade’s time is challenging. But that is the task Alcatel-Lucent’s (now Nokia’s) chip designers set themselves in 2011 after the launch of its FP3 network processor chipset that powers its IP-router platforms.

Six years on and its successor - the FP4 - has just been announced. The FP4 is the industry’s first multi-terabit network processor that will be the mainstay of Nokia’s IP router platforms for years to come.

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Telefonica tests XGS-PON

Part 1: XGS and TWDM passive optical networks

Telefonica is the latest operator to test XGS-PON, the 10-gigabit passive optical networking standard.

“Operators want to show they are taking the maximum from their fibre investment,” says Ana Pesovic, marketing manager for fibre at Nokia, the supplier of the XGS-PON equipment used for the operator’s lab tests. “Telefonica has been really aggressive in their fibre deployments in the last couple of years.”

Ana Pesovic

XGS-PON

Approved by the ITU-T in 2016, XGS-PON supports two rates: 10-gigabit symmetrical and the asymmetrical rate of 10 gigabits downstream (to the user) and 2.5 gigabits upstream.

XGS-PON has largely superseded the earlier XG-PON standard which supports the 10-gigabit asymmetrical rate only. “It is fair to say there is no traction for XG-PON,” says Pesovic. “Even in China [an early adopter of XG-PON], we see the interest slowly moving to XGS-PON.”

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Telefónica tackles video growth with IP-MPLS network

• Telefónica’s video growth in one year has matched nine years of IP traffic growth 

• Optical mesh network in Barcelona will use CDC-ROADMs and 200-gigabit coherent line cards 

Telefónica has started testing an optical mesh network in Barcelona, adding to its existing optical mesh deployment across Madrid. Both mesh networks are based on 200-gigabit optical channels and high-degree reconfigurable add-drop multiplexers (ROADMs) that are part of the optical infrastructure that underpins the operator’s nationwide IP-MPLS network that is now under construction.

Maria Antonia CrespoThe operator decided to become a video telco company in late 2014 to support video-on-demand and over-the-top streaming video services.

Telefónica realised its existing IP and aggregation networks would not be able to accommodate the video traffic growth and started developing its IP-MPLS network.

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Nokia’s PSE-2s delivers 400 gigabit on a wavelength

Nokia has unveiled what it claims is the first commercially announced coherent transport system to deliver 400 gigabits of data on a single wavelength. Using multiple 400-gigabit wavelengths across the C-band, 35 terabits of data can be transmitted.

Four hundred gigabit transmission over a single carrier is enabled using Nokia’s second-generation programmable Photonic Service Engine coherent processor, the PSE2, part of several upgrades to Nokia's flagship PSS 1830 family of packet-optical transport platforms.

Kyle Hollasch“One thing that is clear is that performance will have a key role to play in optics for a long time to come, including distance, capacity per fiber, and density,” says Sterling Perrin, senior analyst at Heavy Reading.

This limits the appeal of the so-called “white box” trend for many applications in optics, he says: “We will continue to see proprietary advances that boost performance in specific ways and which gain market traction with operators as a result”.

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