The SFP28 40KM transceivers is a very compact optical transceiver module converts 25Gbit/s serial CML electrical data into serial optical data compliant with the 25GBASE-ER standard. This helps networks move more data quickly and easily. This makes it easy to upgrade without buying all new equipment. The EML transmitter and APD. SFP module, short for small form factor pluggable, is a standardized interface module used in switches, routers, firewalls, server NICs, and other network devices to support different connection media. 25G BiDi transceivers always require paired sets: a -U must pair to a -D on the opposite end of the BiDi link, using a single fiber strand and a simplex LC connector.