Channelmania! – future proof your DWDM network topology while keeping it flexible for 1.6T#

Thomas Weible, FLEXOPTIX

• Why: As IPoDWDM collapses the IP/transport split, IP network people now need coherent-DWDM literacy — grid planning, superchannels, and what 400GHz COTS filters mean for upgrade paths to 1.6T.
• What: A technical primer-plus-argument: higher-order coherent modulation (16-constellation, dual-polarization, ~425Gbps at 53.125GBd) replaces OOK; 800G/1.6T superchannels need ~400GHz grids rather than shrinking 50/25GHz grids; and coherent detection being "blind" to other wavelengths enables filterless/colorless topologies at the cost of flexibility. The practical pitch: 12×400GHz COTS channels in the C-band future-proof the plant while staying backward-compatible with legacy 50GHz services.
• How: Walks through coherent receiver architecture (phase- and polarization-diversity, homodyne/heterodyne/intradyne), and even a DIY superchannel approach using cheap PLC 1x4 splitters to combine TX/split RX and run subbands through regular 50GHz muxes (with a nod to Blake Willis finding 100GHz spacing optimal in practice). Closing advice: plan in THz/GHz, not nm or channel numbers; 800G coherent ZR+ in DD/OSFP is here, and ~12.8T liquid-cooled XPO is approaching.
• Where applicable: Anyone planning or buying DWDM capacity. Vendor-authored (FLEXOPTIX sells optics tooling), so the COTS-400GHz-filter framing is partly self-serving, but the physics and frequency-planning methodology are sound and generally applicable.