25G CWDM SFP28 is an optical transceiver that transmits a 25 Gbps data signal using Coarse Wavelength Division Multiplexing (CWDM) technology. Unlike standard duplex transceivers that use two fibers, or BiDi transceivers that use two wavelengths on a single fiber, a CWDM SFP28 is designed to operate on a single, specific ITU-standardized wavelength.