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30 May 2012
Huawei has unveiled a DWDM prototype – a flexible-spectrum reconfigurable optical add-drop multiplexer (ROADM) and associated control plane – that supports 12.5GHz channels. The development will enable more efficient use of fibre capacity by squeezing future multi-carrier 400Gbps and 1Tbps transmissions into a smaller spectrum band based on 12.5GHz increments rather than the mainstream 50GHz grid spacing.
The Chinese vendor says the prototype supports 40, 100, 400Gbps and 1Tbps transmissions and is compatible with existing 50GHz and 25GHz technology.
Moreover, the smaller increments add flexibility in terms of trading capacity with transmission distance. Huawei says a 400Gbps signal can be carried in a 75GHz (6x12.5GHz), 87.5GHz (7x12.5GHz) or 100GHz (8x12.5GHz) band, depending on the coding scheme used and the optical reach requirements.
Huawei is one of several vendors pursuing advanced digital signal processing (DSP) techniques and flexible spectrum ROADMs to support multi-rate and super-channel (multiple carrier) transmission.  Alcatel-Lucent and Ciena have unveiled DSP-ASICs that support waveform shaping at the transmitter to fit signals into narrower spectrum than the 50GHz channel increments (see Alcatel-Lucent matches Ciena’s 400G chipset and Ciena’s Wavelogic 3: More than just 400G). Cisco Systems has also demonstrated multi-carrier 400Gbps and 1Tbps transmission as have Ericsson and NEC (see Cisco shows off coherent 100G over 3000km
At the recent OFC/ NFOEC show held in March, Huawei demonstrated a 400Gbps prototype system. This latest announcement of the WDM prototype follows flexible grid standards work by the International Telecommunication Union (ITU) which, late last year, approved 12.5GHz as the basic channel building block for line rates beyond 100Gbps.
By Roy Rubenstein