The PRE-QSFP28-4WBD is a 4WDM Compliant QSFP28 transceiver that operates bidirectionally on a single fiber. When using KR-FEC (required) a reach of up to 40km is achievable. The device transmits on 8 different LWDM wavelengths (4 per side). Internally, the QSFP28 contains
Mux/Demux hardware that splits the Tx and Rx signals on each end. As a result, hardware is installed in pairs with each end operating at opposing Tx and Rx wavelengths. Each pair operates using four low wavelengths and four high wavelengths (4x25Gbps).