QSFP-DD Transceiver is defined by QSFP-DD MSA Group, it is the next generation, high-density, high-speed pluggable module form factor that addresses the industry need for high-density, high-speed networking solutions in a backward compatible form factor. 
As the term “Double-Density” refers to the doubling of the number of high-speed electrical interfaces that the module supports compared to the regular QSFP28 module. The connector specification is ready for the new PAM4 electrical modulation format that supports 50Gb/s that provides another doubling of speed resulting in a 4x increase in port speed for the QSFP-DD compared to the QSFP28 module.
The 400G QSFP-DD SR8 Optical transceiver is a module support 8x50G. The Optical transceiver modules are designed for use in 400 Gigabit links over 100m multimode fibre, they are compliant with the QSFP-DD MSA. Digital diagnostics functions are available via the I2C interface, as specified by the QSFP-DD MSA.
The features of 400G SR8 Optical Transceivers as follow:
- Hot-pluggable QSFP-DD form factor
- Complied to QSFP-DD MSA standard
- Complied to IEEE 802.3cd 400GBASE-SR8 standard
- 8-ch full-duplex transceiver module
- Supports 400Gb/s aggregate bit rate
- 8-ch 850nm VCSEL array
- 8-ch PIN photodetector array
- Internal CDR circuits on both receiver and transmitter channels
- Supports CDR bypass
- Maximum link length of 70m on OM3 MMF or 100m on OM4 MMF
- Single MTP/MPO-16 or MTP/MPO-24 receptacle
- Built-in digital diagnostic functions
- Operating case temperature range: 0 to 70°C
