He QSFP-100G-4W40 (often QSFP-100G-4W40-I for industrial) is a Cisco QSFP28 optical transceiver for 100 Gigabit Ethernet (100GBASE-4WDM-40), supporting 40km reaches on single-mode fiber (SMF) with a duplex LC connector, using 4 wavelengths (1295-1309nm) and built-in Digital Optics Monitoring (DOM) for harsh environments (Industrial -40°C to 85°C), offering high-density, low-power connectivity for data centers and enterprise networks.