SDM and MIMO: An interview with Bell Labs

Bell Labs is claiming an industry first in demonstrating the recovery in real time of multiple signals sent over spatial-division multiplexed fibre. Gazettabyte spoke to two members of the research team to understand more.

Part 2: The capacity crunch and the role of SDM

The argument for spatial-division multiplexing (SDM) - the sending of optical signals down parallel fibre paths, whether multiple modes, cores or fibres - is the coming ‘capacity crunch’. The information-carrying capacity limit of fibre, for so long described as limitless, is being approached due to the continual yearly high growth in IP traffic. But if there is a looming capacity crunch, why are we not hearing about it from the world’s leading telcos? 

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Coriant's 134 terabit data centre interconnect platform

Coriant is the latest optical networking equipment maker to unveil a data centre interconnect product. The company claims its Groove G30 platform is the industry’s highest capacity, most power efficient design. 

“We have several customers that have either purpose-built data centre interconnect networks or have data centre interconnect as a key application riding on top of their metro or long-haul networks,” says Jean-Charles Fahmy, vice president of cloud and data centre at Coriant.

Jean-Charles Fahmy

Each card in the platform is one rack unit (1RU) high and has a total capacity of 3.2 terabit-per-second, while the full G30 rack supports 42 such cards for a total platform capacity of 134 terabits. The G30's power consumption equates to 0.45W-per-gigabit.

The card supports up to 1.6 terabit line-side capacity and up to 1.6 terabit of client side interfaces. The card can hold eight silicon photonics-based CFP2-ACO (analogue coherent optics) line-side pluggables. For the client-side optics, 16, 100 gigabit QSFP28 modules can be used or 20 QSFP+ modules that support 40 or 4x10 gigabit rates.

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Bell Labs demos real-time MIMO over multicore fibre

Part 1 of 2

Bell Labs, the research arm of Alcatel-Lucent, has used a real-time receiver to recover a dozen 2.5-gigabit signals sent over a coupled three-core fibre. Until now the signal processing for such spatial-division multiplexed transmissions have been done offline due to the computational complexity involved.

“The era of real-time experiments in spatial-division multiplexing is starting and this is the very first example” - Peter Winzer

“The era of real-time experiments in spatial-division multiplexing is starting and this is the very first example,” said Peter Winzer, head of the Optical Transmission Systems and Networks Research Department at Bell Labs. “Such real-time experiments are the next stepping stone towards a true product implementation.”    

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COBO looks inside and beyond the data centre

The Consortium of On-Board Optics is working on 400 gigabit optics for the data centre and also for longer-distance links. COBO is a Microsoft-led initiative tasked with standardising a form factor for embedded optics.

Established in March 2015, the consortium already has over 50 members and expects to have early specifications next year and first hardware by late 2017.

Brad Booth

Brad Booth, the chair of COBO and principal architect for Microsoft’s Azure Global Networking Services, says Microsoft plans to deploy 100 gigabit in its data centres next year and that when the company started looking at 400 gigabit, it became concerned about the size of the proposed pluggable modules, and the interface speeds needed between the switch silicon and the pluggable module.

“What jumped out at us is that we might be running into an issue here,” says Booth.

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Monolithic silicon photonic chips move a step closer

Indium phosphide laser arrays have been grown on a 300 mm silicon wafer by Ghent University and imec, the Belgium nano-electronics R&D centre. Growing indium phosphide lasers directly onto the silicon wafer promises compact monolithic silicon photonics circuits.   

Shown are three v-shaped indium phosphide lasers and their gratings on a silicon-on-insulator substrate. Source: Ghent University, imec

Silicon photonics chips are hybrid designs because of silicon’s inability to generate light. Silicon photonics companies either couple a discrete laser to a chip or bond indium phosphide wafers or ‘chiplets' to the silicon wafer and process it to create working lasers that become part of the silicon photonics chip. Growing lasers directly on silicon creates a third approach for the densest applications.

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PMC unveils OTN framer for IP core and edge routers

PMC-Sierra’s latest Optical Transport Network (OTN) framer chip for IP core and edge routers doubles throughput to 240 gigabit.

The Meta-240G frames IP router traffic using OTN before passing the traffic to the transport network. Line-rate encryption is included on-chip to secure traffic between data centres and traffic in the cloud.

Source: PMC-Sierra

Adding OTN to a router delivers several benefits, says PMC. OTN helps identify networking faults more quickly and simplifies the monitoring and enforcement of service-level agreements. OTN also includes forward-error correction which benefits optical link performance. 

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ECOC 2015 Review - Final Part

The second and final part of the survey of developments at the ECOC 2015 show held recently in Valencia.  

Part 2 - Client-side component and module developments   

• The first SWDM Alliance module shown
• More companies detail CWDM4, CLR4 and PSM4 mid-reach modules
• 400 Gig datacom technologies showcased
• The CFP8 MSA for 400 Gigabit Ethernet unveiled

The CFP MSA modules including the newest CFP8. Source: Finisar

• Lumentum and Kaiam use silicon photonics for mid-reach modules
• Finisar demonstrates a 10 km 25 Gig SFP28, and low-latency 25 Gig and 100 Gig SR4 interfaces 

Shortwave wavelength-division multiplexing

Finisar demonstrated the first 100 gigabit shortwave wavelength-division multiplexing (SWDM) module at ECOC. Dubbed the SWDM4, the 100 gigabit interface supports WDM over multi-mode fibre. Finisar showed a 40 version at OFC earlier this year. “This product [the SWDM4] provides the next step in that upgrade path,” says Rafik Ward, vice president of marketing at Finisar. 

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