FRONTIERS PHOTONICS
DATA CENTRE OPTICS
MEMS-based circuit switches key to Google’s network gains
O
ptical circuit switches (OCS) that use mirrors mounted on micro-
electro mechanical systems (MEMS) have helped Google scale its network capacity by five petabits per second (5Pb/s) since 2015.
The switches, which bounce optical signals off an array of mirrors to redirect traffic, are mentioned as a key enabling technology in a paper Google published in 2022 in which it reviews its network developments over the last decade. Google documented 5x higher speed and capacity, 30% reduction in capex, and a 41% reduction in power consumption. Its data centre network, Jupiter, has grown its capacity from 1-6Pb/s since 2015.
When input/output optical signals enter the OCS, they enter the optical core through two-dimensional fibre collimator arrays, which have 136 individual fibres and a 2D lens array.
The optical core consists of
two sets of 2D MEMS mirror arrays. Each inband optical signal traverses through a port in each collimator array and two MEMS mirrors. Mirrors are actuated and tilted to switch the signal to a corresponding input/ output collimator fibre. The entire end-to-end optical path is broadband and reciprocal, for data rate agnostic and bidirectional communication across the OCS. Superposed with the inband signal path, a monitoring channel assists with tuning of
the mirrors. Each MEMS array is injected with this 850nm light. The reflected monitor signals are then received at a matching camera module. A servo uses the camera
image feedback to optimise MEMS actuation for minimum loss of the optical signal path. A pair of injection/camera modules controls each 2D MEMS array. By implementing mirror
controls based on image processing of a single camera image per MEMS array, the control scheme is significantly simplified in comparison to conventional approaches which require individual monitoring and/or photodetector hardware per mirror.
“This design choice was critical to realising a low-cost, manufacturable OCS solution,” the paper’s authors said. l
OPTICAL COMMUNICATIONS
OPTICAL COMMUNICATIONS
Nokia breaks optical transmission records with photonic engine
I
n February, Nokia announced it had broken two optical transport records
in real-world field trials on GlobalConnect’s live optical network in Europe. The demonstration used
Nokia’s sixth generation super- coherent Photonic Service Engine (PSE-6s) to achieve 1.2Tb/s over metro distances (118km) and 800Gb/s over long- haul distances (2,019km), both using a single wavelength. GlobalConnect operates one
of the largest interconnected fibre networks in Northern Europe, with more than 150,000km of trenched fibre. The backbone connects to local networks and data centres in Denmark, Norway, Sweden, Finland, Netherlands and Germany. The network provides
dedicated point-to-point fibre inter-connection between data centres across a wide range of distances.
The 1.2Tb/s speed was
achieved using Nokia’s coherent PSE-6s optics, deployed over a wavelength division multiplexing (WDM) network using 150GHz of spectrum on GlobalConnect’s metro data centre interconnect links. Data centre interconnection was also demonstrated at 800Gb/s on a single wavelength over 2,000km, paving the way to single- wavelength 800GE transport across long-haul distances with no regeneration. According to the company, the reduction of the number of coherent interfaces needed could enable up to 50% network total cost-of- ownership savings and up to a
60% reduction in network power consumption. Nokia’s PSE-6s optical
engines, released in early 2023, integrate 5nm coherent digital signal processors with the company’s CSTAR silicon photonics. Operating at 130GBd, the PSE-6s powers the next generation of coherent transport at up to 1.2Tb/s of capacity per wavelength. It also offers a simple upgrade path for network operators, allowing them to upgrade their networks to PSE-6s across the 1830 family of optical networking
platforms, including the 1830 PSS, 1830 PSI-M and 1830 PSS-x, leveraging existing ITU-T WDM channel plans. James Watt, President at Nokia Optical Networks, said: “With world data volumes expected to double by 2025, there has never been so much focus on cost and power consumption- per-bit. That is why we launched the PSE-6s and why we are celebrating this first field trial with GlobalConnect, ushering in a new era of single-wavelength 800GE client transport to increase network capacity.” l
24 Photonics Frontiers 2023
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