LR4 (Long Range 4) and FR4 (Fiber Range 4) refer to different types of optical transceivers used in high-speed data communication over fiber optic links. These transceivers not only provide impressive transmission speeds and bandwidth but also incorporate multiple innovative technologies for high performance and stability. Here are the. QSFP-DD, an abbreviation of Quad Small Form-factor Pluggable (QSFP) – Double Density (DD), is a high-speed hot pluggable form factor defined by the QSFP-DD MSA group as a key part of the optical communication industry to achieve high-density networking. As the best option for the 400G optical.