Achieved bidirectional transmission at 400 Gb/s over a single fiber using coherent digital subcarrier multiplexing (DSCM). Employed subcarrier interleaving to effectively mitigate Rayleigh back-scattering. XR optics transceivers are designed to be equipped with a wide range of networking equipment. In DWDM, active and passive solutions for single fiber transmission range from 4 up to 8 400G wavelengths, with optional optical amplifiers. The single fiber solution seamlessly integrates with any standards-based 10/25/100Gb Ethernet, 16/32G Fibre Channel, and OTU2/2e/4 client interfaces, and. Our 400GBASE-SR4.