40G-SR4 QSFP module can also be used in a 4x10G mode for interoperability with 10G-SR interfaces up to 100 and 150 meters on OM3 and OM4 fibers, respectively. The 4x10G mode operation is enabled by the optimization of the transmit and receive optical characteristics of the QSFP-40G-SR4 to prevent receiver overload or unnecessary triggering of alarm thresholds on the 10GBASE-SR receiver, and at the same time is completely interoperable with all standard 40G-SR4 interfaces.
The 4x10G connectivity is achieved using an external 12-fiber parallel to 2-fiber duplex breakout cable (LC-LC Duplex 10G OM4 MM), which connects the 40G-SR4 module to four 10GBASE-SR SFP+ MMF. This connectivity can also be achieved using an 8-fiber OM4 to 12 strands MTP harness cable.