OFC 2015 digest: Part 1

A survey of some of the key developments at the OFC 2015 show held recently in Los Angeles.  

 

Part 1: Line-side component and module developments 

• Several vendors announced CFP2 analogue coherent optics   
• 5x7-inch coherent MSAs: from 40 Gig submarine and ultra-long haul to 400 Gig metro  
• Dual micro-ITLAs, dual modulators and dual ICRs as vendors prepare for 400 Gig
• WDM-PON demonstration from ADVA Optical Networking and Oclaro 
• More compact and modular ROADM building blocks  

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Optical networking: The next 10 years

Feature - Part 2: Optical networking R&D

Predicting the future is a foolhardy endeavour, at best one can make educated guesses.

Ioannis Tomkos is better placed than most to comment on the future course of optical networking. Tomkos, a Fellow of the OSA and the IET at the Athens Information Technology Centre (AIT), is involved in several European research projects that are tackling head-on the challenges set to keep optical engineers busy for the next decade.

“We are reaching the total capacity limit of deployed single-mode, single-core fibre,” says Tomkos. “We can’t just scale capacity because there are limits now to the capacity of point-to-point connections.”

Source: Infinera 

The industry consensus is to develop flexible optical networking techniques that make best use of the existing deployed fibre. These techniques include using spectral super-channels, moving to a flexible grid, and introducing ‘sliceable’ transponders whose total capacity can be split and sent to different locations based on the traffic requirements.

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COBO acts to bring optics closer to the chip

The formation of the Consortium for On-Board Optics (COBO) highlights how, despite engineers putting high-speed optics into smaller and smaller pluggable modules, further progress in interface compactness is needed.

The goal of COBO, announced at the OFC 2015 show and backed by such companies as Microsoft, Cisco Systems, Finisar and Intel, is to develop a technology roadmap and common specifications for on-board optics to ensure interoperability.

“The Microsoft initiative is looking at the next wave of innovation as it relates to bringing optics closer to the CPU,” says Saeid Aramideh, co-founder and chief marketing and sales officer for start-up Ranovus, one of the founding members of COBO. “There are tremendous benefits for such an architecture in terms of reducing power dissipation and increasing the front panel density.”

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Calient uses its optical switch to boost data centre efficiency

For Calient Technologies, an approach by one of the world’s largest data centre operators changed the company’s direction.

The company had been selling its 320x320 non-blocking optical circuit switch (OCS) for applications such as submarine cable landing sites and for government intelligence. Then, five years ago, a large internet content provider contacted Calient, saying it had figured out exactly where Calient’s OCS could play a role in the data centre.

This solution could deliver a significant percentage-utilisation improvement

Daniel Tardent

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PMC advances OTN with 400 Gigabit processor

Optical modules for the line-side are moving beyond 100 Gigabits to 200 Gigabit and now 400 Gigabit transmission rates. Such designs are possible thanks to compact photonics designs and coherent DSP-ASICs implemented using advanced CMOS processes. 

An example switching application showing different configurations of the DIGi-G4 OTN processor on the line cards. Source: PMC

For engineers, the advent of higher-speed line-side interfaces sets them new challenges when designing the line cards for optical networking equipment. In particular, the framer silicon that interfaces to the coherent DSP-ASIC, on the far side of the optics, must cope with a doubling and quadrupling of traffic.  

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Heading off the capacity crunch

Feature - Part 1: Capacity limits and remedies

Improving optical transmission capacity to keep pace with the growth in IP traffic is getting trickier. 

Engineers are being taxed in the design decisions they must make to support a growing list of speeds and data modulation schemes. There is also a fissure emerging in the equipment and components needed to address the diverging needs of long-haul and metro networks. As a result, far greater flexibility is needed, with designers looking to elastic or flexible optical networking where data rates and reach can be adapted as required.

Figure 1: The green line is the non-linear Shannon limit, above which transmission is not possible. The chart shows how more bits can be sent in a 50 GHz channel as the optical signal to noise ratio (OSNR) is increased. The blue dots closest to the green line represent the performance of the WaveLogic 3, Ciena's latest DSP-ASIC family. Source: Ciena.

But perhaps the biggest challenge is only just looming. Because optical networking engineers have been so successful in squeezing information down a fibre, their scope to send additional data in future is diminishing. Simply put, it is becoming harder to put more information on the fibre as the Shannon limit, as defined by information theory, is approached.

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Acacia unveils 400 Gigabit coherent transceiver

• The AC-400 5x7 inch MSA transceiver is a dual-carrier design
• Modulation formats supported include PM-QPSK, PM-8-QAM and PM-16-QAM
• Acacia’s DSP-ASIC is a 1.3 billion transistor dual-core chip 

Acacia Communications has unveiled the industry's first flexible rate transceiver in a 5x7-inch MSA form factor that is capable of up to 400 Gigabit transmission rates. The company made the announcement at the OFC show held in Los Angeles. 

Dubbed the AC-400, the transceiver supports 200, 300 and 400 Gigabit rates and includes two silicon photonics chips, each implementing single-carrier optical transmission, and a coherent DSP-ASIC. Acacia designs its own silicon photonics and DSP-ASIC ICs.

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