While for 40GBASE-LR4 QSFP+ transceivers, there are two kinds of links. One is coarse wavelength division multiplexing and the other is parallel single-mode fiber. What’s the difference? QSFP-40GE-LR4, one of 40GBASE-LR4 coarse wavelength division multiplexing QSFP+ transceivers, is compliant to 40GBASE-LR4 of the IEEE P802.3ba standard. The optical interface is a duplex LC connector.
It can support transmission distance up to 10 km over single-mode fiber by minimizing the optical dispersion in the long-haul system. This transceiver converts 4 inputs channels of 10 G electrical data to 4 coarse wavelength division multiplexing optical signals by a driven 4-wavelength distributed feedback (DFB) laser array, and then multiplexes them into a single channel for 40 G optical transmission, propagating out of the transmitter module from the SMF.