FEATURE: PHOTONIC INTEGRATION
yet to agree on the necessary product formats. In current module formats, electrical signals
travel around 10 inches to the front plate for conversion to an optical signal. Hamid Arabzadeh, CEO of photonics developer Ranovus, explained this won’t be possible once Ethernet switch ASICs reach 51.2TbE aggregate capacity. Density of retiming ICs or digital signal processors (DSPs) needed to recover signal loss in traces and connections can’t keep up, while also meeting cost and power consumption requirements of the Ethernet switch systems. Arabzadeh explained that OBO and CPO
‘take the photonic and electronic components of the module and co-package them with the Ethernet switch ASIC, creating an optical input/ output (I/O) using silicon technologies’. He adds that OBO can use Silicon Photonic (SiP) components. Alternatively, it can use PICs comprising two or more non-silicon-based photonic components in a single photonic device. But Arabzadeh argued that CPO can only use SiP due to density, cost, power consumption requirements, and reliability challenges of running in a hot environment.
Confidence boost Ranovus’ Odin IC is designed to contain electronics and SiP on a single die for module, OBO or CPO applications. Tese different applications exploit the same IP, Arabzadeh says, allowing companies to try Odin ‘in a module form factor to gain confidence in the mass deployability of OBO and CPO’. Odin includes several miniaturised, power-
efficient and cost-effective components on a single CMOS chip. It has demonstrated operation with eight optical channels of 100Gb/s per fibre pair, potentially enabling 25.6TbE switches. Arabzadeh revealed that it will be in deployment for Ethernet CPO in the second half of 2022. Ranovus also has a strategic collaboration with IBM, TE Connectivity and Senko Advanced Components to create an ecosystem to design and manufacture multi- vendor solutions for CPO. Currently, hyperscale data centre companies
like Facebook and Microsoſt lead CPO requirements, Arabzadeh said, but other sectors will use it when they have the same capacity requirements. ‘Larger contract manufacturers need to enter into this space to develop their capabilities and reduce the cost of fabrication,’ he added. Te integration of CPO on router and
transport platorms allows the continued disaggregation of transport and switching, added Helen Xenos, senior director, portolio marketing at Ciena. Tat separation allows each function to perform optimally. ‘Because of the significant benefits of this approach, CPO can extend beyond the initial intended application of switch-to-switch or switch-to-router within the data centre,’ Xenos said. ‘At the same time, CPO is optimised for all interfaces to be of the same type. Tis is much more common in hyperscale data centre architectures than in service provider architectures, where there are multiple rates, reach and service types. As
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a result, CPO offers the highest initial value for data centre deployments.’ Ciena is a member of the Optical
Interconnect Forum, which launched the Co-Packaging Framework Implementation Agreement umbrella project. One of that project’s objectives is, said Xenos, ‘to identify the key co-packaged applications and their requirements, to widen the application space for CPO.’
Best of both worlds In the first generation of the CPO implementation that the industry is working towards, the switch inputs/outputs remain electrical, Xenos noted. Te lead switch interface proposal for traditional networking CPO applications is a 112G extra-short reach serialisation/deserialisation (Serdes) interface (XSR). ‘For a future generation of CPO, one consideration is to replace the Serdes interface and move directly to an analogue interconnect between the optics and switch,’ she said. ‘Tis would further reduce power dissipation and enable scaling to higher bandwidth.’ With in-house experience in both SiP and
also InP photonic integration, Ciena is able to produce and supply the optical engine for the CPO solution, she said. ‘Tis development would reuse many of the building blocks that we already deploy in our coherent pluggable offering,’ Xenos said. Analog Photonics is also considering the shiſt
from modules to CPO designs. ‘To reduce the complexity of CPO, 51.2Tb aggregate switch bandwidth can be divided into 16 optical engines at 3.2TbE,’ said Timurdogan. But scaling PIC chipsets to 3.2TbE at a 100G signalling rate needs 32 channels. Using single laser wavelength channels would require 32 fibres each carrying 100G, which would not increase bandwidth density per fibre. ‘Instead, 32 laser wavelength
channels can be used in a single fibre,’ observed Timurdogan. ‘However, this solution will not offer any backwards compatibility with existing multi-source agreements and IEEE Standards. We decided to form an 800G building block that is compliant with these standards and can scale to 3.2TbE. Tat is why we decided to use eight fibres and four laser wavelengths using the 400G-FR4 format.’ Timurdogan also highlighted that electronic
ICs for transceivers consume most power in enhancing signals and correct optical losses. Te company therefore introduced ultra-low loss fibre-to-chip couplers to reduce signal degradation and minimised the drive voltage of transmit photonics to work with energy-efficient CMOS drivers. It also integrated an athermal, low-loss multiplexer and demultiplexer to mix and separate multiple wavelength channels integrated with SiP transceivers on the same platorm, and increased the sensitivity of the receive photonics to reduce the optical power
A LARGE SOCKET INCREASES COST AND DECREASES MANUFACTURABILITY, AND COPPER CONNECTIONS ARE LOSSY AT HIGH DATA RATES
In 2020, Rockley Photonics demonstrated a 25.6Tbps OptoASIC switch Issue 30 n Winter 2021 n FiBRE SYSTEMS 9
Rockley Photonics
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