SR (Short Reach) and LR (Long Reach) are optical designations commonly used across various module types (such as SFP+ /SFP28, QSFP /QSFP28). They are not brand-specific; they are industry conventions that help communicate intended transmission reach. The working principle of optical modules is illustrated in the diagram shown in the Optical Module Working Principle Diagram. Optical modules typically have an electrical interface on the side that connects to the inside of the system and an optical interface on the side that connects to the outside. Optical fibre communication utilizes specific wavelength bands, frequently referenced by optical engineers. The values presented below are approximate and should be considered as such, as standardized values are still evolving.
[PDF Version]