The long game: Acacia's coherent vision

In 2007, Christian Rasmussen made a career-defining gamble. After attending a conference featuring presentations on coherent optical transmission, he returned home, consulted his family, and quit his job at Mintera, then an optical networking equipment maker.

Christian Rasmussen

The technology he'd seen discussed promised to solve the transmission impairments associated with direct-detection-based optical transmission – chromatic dispersion and polarisation mode dispersion - that had stymied optical transport to go beyond 40 gigabits-per-second (Gbps).

"We came back and were completely excited that there was a technology that addressed all the problems that we had experienced firsthand," says Rasmussen, now Chief Technology Officer at Acacia.

His bet paid off. Acacia which he helped co-found in 2009, had a successful IPO in 2016 and would later be acquired by Cisco Systems for $4.5 billion in 2021.

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The OIF's coherent optics work gets a ZR+ rating

The OIF has started work on a 1600ZR+ standard to enable the sending of 1.6 terabits of data across hundreds of kilometres of optical fibre. 

The initiative follows the OIF's announcement last September that it had kicked off 1600ZR. ZR refers to an extended reach standard, sending 1.6 terabits over an 80-120km point-to-point link. 

1600ZR follows the OIF's previous work standardising the 400-gigabit 400ZR and the 800-gigabit 800ZR coherent pluggable optics.      

The decision to address a 'ZR+' standard is a first for the OIF. Until now, only the OpenZR+ Multi-Source Agreement (MSA) and the OpenROADM MSA developed interoperable ZR+ optics.

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Optical networking's future

Shown is Professor Polina Bayvel in her lab at University College London. Bayvel gave the opening plenary talk at ECOC.

Should the industry do more to support universities undertaking optical networking research? Professor Polina Bayvel thinks so and addressed the issue in her plenary talk at the ECOC conference and exhibition held in Glasgow, Scotland, earlier this month.

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How DSP smarts continue to improve optical transport

• Kim Roberts explains the signal processing techniques Ciena is using for its WaveLogic 6 coherent DSP.
• Roberts explains how the techniques squeeze, on average, a 15 per cent improvement in spectral efficiency.
• The WaveLogic 6 Extreme chip can execute 1,600 trillion (1.6 x 10¹⁵) operations per second and uses the equivalent of 4km of on-chip copper interconnect.

Part 2: WaveLogic 6's digital signal processing toolkit

Kim Roberts, Ciena’s vice president of WaveLogic Science and winner of the 2019 John Tyndall Award

Bumping into Kim Roberts on the way to the conference centre at OFC, held in San Diego in March, I told him how, on the Ciena briefing about its latest WaveLogic 6 coherent digital signal processor (DSP), there had been insufficient time to dive deeply into the signal processing techniques used.

“What are you doing now?” said Roberts.

“I’m off to the plenary session to catch the keynotes.”

Chatting some more, I realised I was turning down a golden opportunity to sit down with a leading DSP and coherent modem architect.

“Is that offer still open?” I asked.

He nodded.

We grabbed a table at a nearby cafe and started what would prove to be an hour-long conversation.

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Do optical DACs have a role in future coherent modems?

• A proposed optical digital-to-analogue converter (oDAC) concept offers several system benefits, including better signal performance, higher bit rates and lower power consumption.
• The oDAC design benefits coherent optics but can also be used in direct-detect designs. This article focusses on coherent optics.
• Coherent system vendors are aware of oDAC technology but it is not part of their current roadmaps. 

A 256-QAM constellation using a conventional coherent transmitter (left) and using the oDAC. Note there is no modulator loss (the full area is used) nor any optical warping using the oDAC. Source: Tomkos and Nazarathy.

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Nokia jumps a class with its PSE-6s coherent modem

• The 130 gigabaud (GBd) PSE-6s coherent modem is Nokia's first in-house design for high-end optical transport systems 
• The PSE-6s can send an 800 gigabit Ethernet (800GbE) payload over 2,000km and 1.2 terabits of data over 100km.
• Two PSE-6s DSPs can send three 800GbE signals over two 1.2-terabit wavelengths

Nokia has unveiled its latest coherent modem, the super coherent Photonic Service Engine 6s (PSE-6s) that will power its optical transport platforms in the coming years.

The PSE-6s comes three years after Nokia announced its current generation of coherent digital signal processors (DSPs): the PSE-Vs DSP for the long-haul and the compact PSE-Vc for the coherent pluggable market.

Nokia is only detailing the PSE-6s; its next-generation coherent modem for pluggables will be a future announcement.

Nokia will demonstrate the PSE-6s at the upcoming OFC show in March while field trials involving systems using the PSE-6s will start in the year's second half. 

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Effect Photonics buys the coherent DSP team of Viasat

Effect Photonics has completed the acquisition of Viasat’s staff specialising in coherent digital signal processing and forward error correction (FEC) technologies and the associated intellectual property.

Harald Graber

The company also announced a deal with Jabil Photonics - a business unit of manufacturing services firm Jabil - to co-develop coherent optical modules that the two companies will sell.

The deals enable Effect Photonics to combine Viasat’s coherent IP with its indium phosphide laser and photonic integrated circuit (PIC) expertise to build coherent optical designs and bring them to market.

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