400G Over Multimode Fiber: BiDi Changes the Game
For anyone who has managed a data center fiber plant over the past decade, the arrival of 400 Gigabit Ethernet came with a painful side effect: singlemode fiber. If your DC was built in the era of 10G or 40/100G BiDi, chances are your structured cabling was entirely multimode, a perfectly reasonable choice at the time. Then, 400G arrived, and all the dominant transceiver options (DR4, FR4, LR4) required singlemode. Overnight, that existing multimode plant became a liability for anyone planning to upgrade.
That situation is now changing, thanks to a transceiver Cisco quietly added to its QSFP-DD portfolio in the last few months: the QDD-400G-BD.
