The letters are reach specifications, and the number refers to the number of optical channels:
| Description | Connector Type |
| SR8: “SR” refers to 100m reach using multi-mode fiber, and “8” implies there are 8 optical channels. Each of the 8 optical channels from an SR8 module are carried on separate fibers, resulting in a total of 16 fibers (8 Tx and 8 Rx). Each optical channel operates at 50Gb/s. The SR8 module uses an MPO-16 connector to connect to 8 fiber pairs. |  |
| DR4: “DR” refers to 500m reach using single-mode fiber, and “4” implies there are 4 optical channels. Each of the 4 optical channels from a DR4 module are carried on separate fibers, resulting in a total of 8 fibers (4 Tx and 4 Rx). Each optical channel operates at 100Gb/s. The DR4 module uses an MPO-12 connector to connect to 4 fiber pairs. |  |
| XDR4: “XDR” refers to 2km reach using single-mode fiber, and “4” implies there are 4 optical channels. Each of the 4 optical channels from a DR4 module are carried on separate fibers, resulting in a total of 8 fibers (4 Tx and 4 Rx). Each optical channel operates at 100Gb/s. The DR4 module uses an MPO-12 connector to connect to 4 fiber pairs. | |
| FR4: “FR” refers to 2km reach using single-mode fiber, and “4” implies there are 4 optical channels. Unlike the DR4 and SR8, all of the 4 optical channels from an FR4 are multiplexed onto one fiber, resulting in a total of 2 fibers from the module (1 Tx and 1 Rx). Each optical channel operates at 100Gb/s. The FR4 module uses a duplex LC connector to connect to a single fiber pair. |  |
| 2FR4: The “2FR4” refers to 2 x 200G-FR4 links, and has a reach of 2km using single-mode fiber. Each of the 200G FR4 links has 4 optical channels, multiplexed onto one fiber pair (1 Tx and 1 Rx per 200G link). A 400G-2FR4 module has 2 of these links, resulting in a total of two pairs of single mode fiber (or 4 fibers total), and a total of 8 optical channels. Each optical channel operates at 50Gb/s. The 2FR4 module uses a dual CS connector to connect to 2 fiber pairs. |  |