Emerging Form Factors
There are two new form factors being introduced in the optical interconnect industry. The MSA standard for DSFP (Dual Small Form-Factor Pluggable) was released in September 2018, and the MSA standard for SFP-DD (Small Form-Factor Pluggable – Double Density) was released in April 2019.
Both form factors aim to transmit 100Gbps (Giga bits per second) and be backwards compatible with the compact SFP+ (Small Form-Factor Pluggable Plus) module designed for the 25G.
DSFP appears to be developed for improved RF performance from the electrical interface.
SFP-DD is receiving broader support from the industry and would seem to be the one to focus on initially.
The DSFP interface employs 2 high-speed pairs currently operating at 25Gb/s NRZ (Non-Return to Zero), or 50Gb/s PAM-4 (Level 4 Pulse Amplitude Modulation) for 50Gb and 100Gb aggregated bandwidth solutions.
50G PAM4 can be implemented using DSFP with a single duplex LC connector. This provides utilization of existing form factors that currently use SFP+ and LC connector. The “D” means “dual” and refers to using two pairs of the current channels each at 25Gbps at NRZ or 50Gbps at PAM-4. This doubles the transmission rates of the traditional SFP+ architecture, the smallest industry standard form-factor, to 50G and 100G.
Current SFP+/SFP28 transceivers support 10G and 25G. The new DSFP form factor is backwards compatible with the SFP cages and cables, with some of the pins reconfigured to support the second channel.
There is significant interest in the SFP-DD 50G PAM4 implementation using a single duplex LC connector. This provides excellent utilization of existing form factors that currently use SFP+ and LC connector. The DD means “double density” and refers to offering two rows of electrical pins enabling two-channels instead of the traditional one-channel in an SFP architecture, which is the smallest industry standard form-factor available today for data center systems.
Current SFP+/SFP28 transceivers support 10G and 25G. The first implantation will be 2x25G NRZ electrical channels combined into a single 50G PAM4 optical connector using one duplex LC cable. The new SFP-DD form factor is backward compatible with existing SFP+/SFP28.
SFP-DD is support by 4 optical interfaces while DSFP is only supported by 1 optical interface. The common interface supporting both new form factors is Dual-LC and this seems to be the prevailing optical interface since it is already used widely.
MPO-12 (Multi-Fiber Push On – 12 fibers) is an unlikely optical interface since it is expensive because only four out of twelve available fibers are utilized.
Formerica plans to release the SFP-DD form factor in 2021. For further information, please contact Formerica Optoelectronics at inquiry@FormericaOE.com.