Plug a gigabit optical module into a 100 Mbps port

No, a standard gigabit optical module cannot operate in a 100Mbps port because the port cannot support the higher-speed signaling required.

Detailed Explanation

Physical Fit vs. Electrical Compatibility While a gigabit SFP module may physically fit into a 100Mbps SFP port, the link will not establish because the 100Mbps port cannot handle the 1Gbps signaling of the module. Optical transceivers are designed to operate at specific speeds, and standard gigabit SFPs are fixed at 1Gbps, whereas 100BASE-FX SFPs are fixed at 100Mbps.

The port and module must match in both speed and signaling for communication to occur. Fiber Type and Wavelength Considerations Even if the fiber type and connector match, the modulation and wavelength used by gigabit modules differ from 100Mbps modules. For example, a 1000BASE-BX10-D module uses a different center wavelength than a 100BASE-FX or 100BASE-BX10 module, making them incompatible over the same fiber link.

Exceptions and Special CasesDual-rate SFPs: Some SFP+ fiber modules support both 1Gbps and 10Gbps, but there are no standard dual-rate modules that support both 100Mbps and 1Gbps over fiber.

Copper SF

Ps with auto-negotiation: In copper-based SFPs (10GBASE-T), auto-negotiation allows a 10G SFP+ module to operate at 100/1000Mbps, but this does not apply to optical modules. Conclusion To connect a 100Mbps port, you must use a 100BASE-FX SFP transceiver. Using a gigabit optical module in a 100Mbps port will fail to establish a link, regardless of fiber type or connector compatibility.