Data centre connectivity
Data centre connectivity can be grouped into the following categories :
• The intra-data centre network , i . e ., the fabric cluster , which interconnects servers over a link distance from 100m to 1,000m within the same room or building
• The metro network , which provides connections between data centres , with a link distance typically less than 80km
• The global backbone network , interconnecting data centres through long-distance transport networks , including subsea cables
All these interconnects require fibre connectivity and optical interfaces to ensure low latency , lower transport power per bit , and the highest capacity at the lowest costs .
Inside the data centre , AI applications and workloads are currently driving growth at an unprecedented rate . Optical connectivity speeds are already gradually developing from 400 Gb / s to 800 Gb / s . Current market demand for high-speed 800 + Gb / s intra-data centre interconnect technology is projected to grow nearly tenfold over the next four years – from about 300,000 units in 2023 to more than 2.5 million units by 2027 .
intermediate sites where amplification is required , and scaling the connectivity in this type of metro network is typically done by lighting up additional fibre pairs and deploying amplifiers at the data centre locations .
In the global backbone network , fibre is rare and expensive , and we need high-performance DWDM technology to realise the lowest cost per bit per kilometre and avoid expensive signal regeneration .
Over the past 15 years , the industry has focused on advances in coherent technology to increase the amount of information that can be packed into a given amount of spectrum , called spectral efficiency . We have increased fibre capacity from 9.6 Tb / s with binary transmission to delivering ~ 44 Tb / s with 64QAM technology in the extended C-band fibre spectrum .
The next generation of coherent transmission technology remains on 64QAM modulation as higher-order modulation schemes reduce transmission reach with no cost per bit per kilometre improvement . As a result , we are beginning to see diminishing improvements in transceiver spectral efficiency as we reach the Shannon limit , which is the theoretical maximum spectral efficiency that can be achieved , as shown below .
To address this growth , the industry will require innovative highspeed , low-latency and even more power-efficient solutions . Digital signal processor ( DSP ) -based retimed optics , linear-drive pluggable optics ( LPO ) and co-packaged optics ( CPO ) solutions for both serial and parallel fibre applications are currently under development and will help significantly reduce latency and power consumption further .
In metro data centre connectivity , we have a more fibre-rich environment , and despite the many fibre splices and some older higher-loss fibres , many link distances are below 100km . Such distances do not provide a technical challenge for coherent optical transceivers and optical transmission systems .
The cost-effective DWDM technology used here enables parallel transmission of wavelengths in the C-band spectrum of fibre , enabling us to transport ~ 44 Tb / s of data . There are also limited
Figure 1 : Coherent technology evolution
The industry needs to find new ways to cost-effectively increase fibre network capacity . One option is to light up additional fibres . However , in these national and international backbone networks , it is very costly to lease fibres . An easier cost-effective way is to increase the amount of usable spectrum on existing fibres . This can be done by expanding from the commonly used C-band into
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