As an important part of fiber-optic communication, an optical module is a photoelectric converter which converts electrical signals into optical signals and vice versa. An optical module works at the physical layer of the OSI model and is one of the core components in the fiber communication. What does 40GBASE-SR4 mean? 40GBASE-SR4, also called QSFP-40G-SR4, provides short-range 40GbE connections., in the selection, I believe you must have observed that the appearance of these 40G optical modules are very similar, such as the 40GBASE-SR and 40GBASE-CSR4 these two.