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FEATURE OPTICAL COMPONENTS
communication is still in the early stages of incorporating the signal processing, coding, and modulation techniques that have successfully expanded capacity in all other digital communication media. I expect to see increased density with reduced size optics, like those offered by CFP4-ACO. It is an exciting time for DSP, communications, and optics engineers pushing the state of the art in this rapidly evolving industry.’ Yet there are other challenges that DSPs bring
ClariPhy’s integrated 100G/200G CFP2-ACO reference platform helps its customers to speed up the design of their coherent optical systems, by solving the challenges of the linear interface between coherent DSPs and pluggable optical modules
(ACO) ‘ecosystem’ with module producers including fellow Californian companies Finisar and Oclaro, and Fujitsu Optical Components, headquartered in Kanagawa, Japan. ‘Te main advantages of the CFP2-ACO model
are centred on cost and density,’ explains Norm Swenson, ClariPhy co-founder and chief technology officer. ‘With multiple optical module vendors focused on building best-in-class optical modules, competition will bring out the best features at the lowest cost.’ Te CFP2-ACO format removes the DSP from
the module, Swenson emphasised. Tis allows its processing power to be maximised without burdening the module with its power consumption and heat dissipation. Te size of the optics is also minimised, saving precious front-panel space, shrinking coherent optical modules by half from CFP to CFP2. ‘Te trend will continue with CFP4 coherent modules,’ Swenson said. ‘Separating the optical module from the DSP also creates a larger market for the module suppliers, as they can sell their products to customers who use either their own or merchant DSP chips. Tis encourages competition.’ Technology evolution will proceed in three
directions, the executive explained. Te first will be lower prices and lower power consumption at 32GBd symbol rates tailored for metro applications at lower price points. ‘Tis will primarily be dual-polarisation QPSK, with some deployment of dual-polarisation 16QAM,’ Swenson said. ‘A second direction will be higher symbol rates to reduce the number of optical components for both long haul and data centre interconnect applications that will make use of wider channel spacing in flexible networks. Te third direction will be higher order modulation above 16QAM, for example 32QAM and 64QAM, to give higher data rates without increasing bandwidth, improving spectral efficiency on shorter links that have sufficient signal-to-noise ratio. Data centre interconnect is a prime application target for this technology.’
Tis will place greater demands on silicon
technology, as higher baud rates and higher order modulation will incur more distortions, which will need to be compensated by the DSP. ClariPhy is already working on some of the most advanced processors in optical networking to satisfy the needs of CFP2-ACO modules. Te company demonstrated a 16nm FinFET coherent platform at OFC with a chip manufactured towards the end of 2015. ‘Increasing demands on the DSP require us to
stay at the forefront of CMOS technology, including 16nm FinFET,’ Swenson said. In order to support modular CFP2-ACO NTT Electronics’ ExaSPEED
Improvements are in large part enabled by moving to the next process node in silicon technology
200 is also constructed using 16nm FinFET CMOS lithographic processes. However, Swenson asserts that his company’s technology is more advanced. ‘To our knowledge, no other coherent DSP company has demonstrated any chip in 16nm FinFET.’ Despite relying on leading the industry in silicon
DSP technology, Swenson is cool about the challenges posed by the slowdown in shrinking transistors. ‘Te death of Moore’s law has been announced so many times that I don’t pay too much attention,’ he said. ‘Te semiconductor manufacturing industry is full of clever engineers that continue to push integrated circuit technology forward. Demand for bandwidth is only going up, and the industry must and will respond to this through continued innovation. Optical fibre
beyond the chips themselves, Swenson admits, some notably arising from the interface between DSPs and modules. Channel-to-channel skew in the phase difference between pulses on different transmit and receive lanes can vary from one module to another, he notes. It is important that the DSP chips tolerate or compensate for this skew, the executive says – and LightSpeed-II does. ‘Tese issues are relatively minor compared to the optical signal compensation that the DSP deals with,’ Swenson added. Even designing and making the modules is hard,
but ClariPhy’s LightSpeed-II seeks to help with that. ‘We have been proactive in addressing challenges by introducing the industry’s first turnkey hardware and soſtware reference design over a year ago,’ Swenson said. ‘Tis has been instrumental in driving successful deployments for our customers.’
More modulation formats Te challenges facing DSP interfaces are surprisingly important, highlighted Nokia’s Matthias Berger. ‘Te number of transistors on a chip might double every two years, but interface speed and power dissipation isn’t scaling the same way,’ he said. ‘Analogue to digital and digital to analogue convertors will also probably not scale as nicely as transistor dimensions. Tat will limit developing DSPs in the next five years.’ Right now, however, Nokia is supplying in-house
designed DSP chips in system-level products that go beyond CFP-based modules that Berger said ‘are typically not offering the capacity we need’. Its PSE-2 is the first chip that can process 500Gb/s in real time, he added. ‘In our WDM products PSE-2 chips are implemented on a system card using five CFP4 client interfaces that can be connected to five 100G routers, for example,’ he explained. ‘Te 500G data are forwarded to the PSE-2, then to lasers and modulators, and onto two carriers in a WDM system.’ PSE-2 chips also support switches handling tens
of terabits per second with very fine granularity. ‘Tis switch is in a position to take, for example, 1GE out of one 500G stream and put it into another 500G stream,’ Berger said. ‘Tose switches are mainly used in more traditional network operators, which typically have fairly meshed networks.’
Issue 12 • Summer 2016 FIBRE SYSTEMS 11
ClariPhy
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