The Cisco QSFP 40G SR4 module uses a MTP/MPO (Multi-Fiber Push-On/Pull-Off) connector for its optical interface. The MTP/MPO connector is a type of high-density fiber connector that allows multiple fibers to be connected in a single connector, facilitating the transmission of parallel signals.

Specifically, the Cisco QSFP 40G SR4 module typically has an MTP/MPO connector with 12 fibers arranged in a duplex configuration. This is because 40G SR4 modules use four lanes (four fibers for transmit and four fibers for receive) for a total of eight fibers. The additional fibers in the MTP/MPO connector are often used for additional functionality, such as power monitoring.

It's important to note that the Cisco QSFP 40G SR4 module is designed for short-range connections using multimode fiber optics. The "SR4" designation indicates that it is a Short Range module supporting distances up to 100 meters over OM3 multimode fiber or up to 150 meters over OM4 multimode fiber.