SFP-DD

SFP Double Density (SFP-DD) adds a second row of contacts to the SFP connector, giving two electrical lanes in the SFP footprint. At 2×50G PAM4 that is 100 Gb/s in a port the size of a 1G SFP — while the same cage still accepts ordinary single-lane SFP/SFP+/SFP28/SFP56 modules.

Key facts


Lanes × rate	2 × 25G (NRZ) or 2 × 50G (PAM4)
Total	50G / 100G
Connector	LC duplex, SN/CS duplex; SFP-DD DAC/AOC
Supply	3.3 V, higher power class than SFP56
Applications	100G server access in SFP footprint, 2×50G breakout

Specifications

SFP-DD MSA hardware specification — mechanical, electrical, thermal and the

double-row connector.

SFP-DD MIS — Management Interface Specification, Rev 2.0 (2020): the

management model for two-lane SFP-DD modules over a two-wire interface. See MIS.

Management interface

SFP-DD leaves the SFF-8472 two-address model behind. MIS follows the CMIS approach — lower memory always accessible, paged upper memory, per-lane data-path control — adapted to two lanes. Identity codes come from SFF-8024. In practice a host must speak MIS to bring up an SFP-DD module; a legacy SFP inserted in the same cage is read with SFF-8472 as usual.

Compatibility notes

Backward compatible cage: SFP-DD ports accept SFP, SFP+, SFP28 and SFP56.
SFP-DD is the two-lane counterpart of QSFP-DD

(eight lanes) — the same "double density" idea applied to the small footprint.

In CodingBox

CodingBox supports MIS 2.0 and decodes SFP-DD modules with the MIS layout — identity, per-lane diagnostics and configuration pages — while single-lane modules in the same family fall back to SFF-8472 automatically.