Japan’s National Institute of Information and Communications Technology (NICT) has successfully demonstrated what it says is a world-record for switching capacity of 53.3 Tbits/s for short-reach datacentre networks. The demonstration made use of Spatial Division Multiplexing (SDM) over Multi-Core Optical Fibres (MCFs) and a newly developed high-speed spatial optical switch system, enabling full packet-granularity. NICT reckons the new network provides a significant improvement in network efficiency and end-to-end energy consumption per bit compared to today’s optical circuit, fully-electronic packet switching networks. As such it could lead to the building of greener datacentres.
NICT points out that, due to a continuous increase of network traffic demand, the capacity of optical networks using standard Single Mode Fibre (SMF) is approaching its physical limits. SDM technology, including MCFs, has been proposed to alleviate the capacity limits imposed by SMFs. Moreover, it will be important to reduce the granularity of optical networks. Currently, commercial optical networks can switch optical wavelength channels that operate continuously in time, with information transmitted over the network in packets. In this context, the capability to transmit these packets directly on the optical domain can increase the overall network efficiency, and replacing electronic switching with optical switching can also reduce the total end-to-end energy consumption per bit.
For this work, NICT developed a high-speed seven-core joint optical switching system that can switch all the cores of a seven-core MCF simultaneously with a switching speed of 80 ns. The system consists of multiple Electro-Absorption (EA) optical switch elements, with several nanoseconds switching speed. It also contains a switch controller, capable of reading the destination address of packets and controlling multiple EA switches simultaneously. The optical switching system can be used in an optical network switching node to realise several functions.
Using this optical switching system, NICT built a testbed of a time-slotted optical network, capable of achieving full packet granularity. This testbed used 64 wavelength channels, modulated at 32 Gigabaud with Polarisation Division Multiplexing (PDM) Quadrature Phase Shift Keying (QPSK). This delivered a nominal capacity of 53.3Tbits/s. In the testbed, three MCF segments were used: a 19-core 28 km fibre, a 19-core 10 km fibre, and a 7-core 2 km fibre. On each fibre, seven-cores were used to carry information signals.
For the future, NICT is hoping to increase the network capacity by developing new optical switches with even faster response, lower insertion loss and flatter frequency response. It’s also investigating coherent burst-mode receivers with high-order modulation formats for greater spectral efficiency.