90km 400ZR transmission in 75GHz DWDM channels, up to 25.6 Tb/s per fibre
The company says it achieved two milestones using its interoperable pluggable 400ZR coherent modules and its specially designed athermal arrayed waveguide grating (AWG) multiplexers (MUX) and de-multiplexers (DMUX). First, data rate per channel increases from today’s non-interoperable 100Gbps direct-detect transceivers to 400Gbps interoperable coherent 400ZR modules. Second, the current DWDM infrastructure can be increased from 32 channels of 100 GHz-spaced DWDM signals to 64 channels of 75 GHz-spaced DWDM signals. The total DCI fiber capacity can thus be increased from 3.2 Tb/s (100Gb/s/ch. x 40 ch.) to 25.6 Tb/s (400Gb/s/ch. x 64 ch.), which is a total capacity increase of 800 percent. The 400ZR signal uses an approximately 60 Gbaud symbol rate and 16 QAM modulation, resulting in a broader transmitting signal spectrum compared to that of a standard 100 Gb/s coherent or PAM4 signals. Furthermore, it is recognized that the center frequencies of the lasers, MUX and DMUX will all drift due to temperature changes and ageing. Consequently, as the channel spacing is reduced from 100GHz to 75GHz, adjacent channel interference (ACI) becomes more critical, and can potentially degrade the optical signal-to-noise ratio of 400ZR signals.
The filters used in NeoPhotonics MUX and DMUX units are designed to limit ACI while at the same time having a stable center frequency against extreme temperatures and ageing. The optical signal spectrum of the pluggable 400ZR transmitter is very important for two reasons. First, the spectrum should not be too wide, as that would result in “spillover energy” impacting its neighbor DWDM channels. Second, it also cannot be too narrow, as that would degrade the signal quality or even recoverability, especially after the MUX and DMUX filtering. NeoPhotonics has demonstrated end-to-end 90km DCI links using three in-house 400ZR pluggable transceivers with their tunable laser frequencies tuned to 75GHz spaced channels, and a pair of passive 75GHz-spaced DWDM MUX and DMUX modules designed specifically for this application. The optical signal-to-noise ratio (OSNR) penalty due to the presence of the MUX and DMUX and the worst-case frequency drifts of the lasers, as well as the MUX and DMUX filters, is less than 1dB. The worst-case component frequency drifts were applied to emulate the operating conditions for ageing and extreme temperatures.
NeoPhotonics – www.neophotonics.com
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