Coherent 100G DWDM Over 80 km Without an Amplifier
Overview
Bandwidth demand keeps climbing across data center interconnect, metro and enterprise networks, and coherent 100G DWDM answers this at the long end of that range. It lets you scale one existing fiber pair up to 40x 100G, 80 km (or more if using 100G DCO high power module), with no amplifier anywhere in the path. EDGE supplies the full passive path for this, the 100G-Q28-DCO-ZR transceiver and the DDMD-40 40 channel 100 GHz DWDM MUX.
Budget calculation
The link budget is why this works unamplified. The 100G-Q28-DCO-ZR has a 22 dB optical budget. The two DDMD-40 units in the path account for 7.4 dB (3.7 dB each), and a typical connector and splice allowance adds another 0.5 dB, leaving 14.1 dB for the fiber span itself, roughly 56 to 70 km depending on the fiber's actual loss per kilometer.
Alternative
For longer spans, 100G-Q28-DCO-ZRHP is the direct upgrade: same tunable grid, same DDMD-40, same cabling, just a 30 dB budget rated for 100 km unamplified.
Bill of materials
Every product in the diagram above, with the quantity each one appears. Open a row for full specifications, pricing and ordering.
- 2x100G-Q28-DCO-ZRTunable 100G ZR Coherent QSFP28 DCO Module (Tx/Rx Channel 13-61/13-61, ITU Grid: C-Band, 103.125 Gbps, Max. 80km (unamplified) & 300km (amplified) over SMF with built-in FEC, 22dB, -8dBm Tx power, Temp. 0-70C, LC/UPC)
- 2xDDMD-4040-channel 100GHz DWDM mux/demux, ITU-T C-band Ch.21-60, 19 inch 1U rack chassis, LC/UPC connectors, optional 1310nm monitor port.
- 1xLC/UPC-LC/UPC-OS2-DX-B-LSZH-XLC/UPC to LC/UPC, Type A to B, Duplex, OS2 9/125μm, LSZH Patch cable, Length 0.5-100 meter
Frequently Asked Questions
How far can coherent 100G DWDM run without an amplifier?
With the 100G-Q28-DCO-ZR (22 dB budget) and two DDMD-40 mux/demux units (7.4 dB combined) plus a typical 0.5 dB connector/splice allowance, about 14.1 dB remains for the fiber itself — roughly 56 to 70 km depending on the fiber's actual loss per kilometer. For longer unamplified spans, the 100G-Q28-DCO-ZRHP carries a 30 dB budget and is rated for 100 km unamplified on the same DDMD-40 and cabling.
What's the link-budget difference between the 100G-Q28-DCO-ZR and the 100G-Q28-DCO-ZRHP?
The ZR's minimum TX launch power is −8 dBm against a −30 dBm minimum RX sensitivity, for a 22 dB budget. The ZRHP raises minimum TX launch power to 0 dBm against the same −30 dBm RX sensitivity, for a 30 dB budget — 8 dB more headroom on the same tunable C-band grid, same QSFP28 form factor, same DDMD-40 mux.
Why does adding a DWDM mux cut into the unamplified reach so much?
Each DDMD-40 unit carries a 3.7 dB passband insertion loss. A point-to-point link needs one unit at each end (mux and demux), so that's 7.4 dB lost to the mux/demux pair alone — before any fiber loss is counted. It's the single biggest deduction in the budget.