February 17, 2019

Introduction to 400GBASE-SR4.2 (BiDi) Standard

The 400GBASE-SR4.2 (BiDi) Standard was announced by the 400G Bidirectional (BiDi) MSA (Multisource Agreement) Group in the year 2018. The specification will be named 400G-BD4.2, to identify the bidirectional use of four lasers each of two colors. Using the 400G-BD4.2 specification, two transceivers communicate over lengths up to 70 meters (OM3 MMF Multimode fiber), 100m (OM4 MMF) and 150m (OM5 MMF).

The 400G-BD4.2 modules comply with the requirements of the standard and have the following common features: eight optical transmitters and eight optical receivers in a bi-directional optical configuration (four of the transmitters using a wavelength range of 844nm to 863nm, λ1, and four of the transmitters using a wavelength range of 900nm to 918nm, λ2), a signal detect for each optical receiver and a twelve channel MPO fiber optic connector (only eight fibers total are required) using multimode optical fiber.

400G-BD4.2 Illustrative Power Budget

Parameter OM3 MMF OM4 MMF OM5 MMF
Effective Modal Bandwidth at 850nm (MHZ KM) 2000 4700 4700
Effective Modal Bandwidth at 918nm (MHZ KM) 1210 1850 2890
Power Budget (For max TDECQ) (dB) 6.6 6.6 6.6
Operating Distance (m) 70 100 150
Channel Insertion Loss (dB) 1.8 1.9 2.0
Allocation for Penalties (for max TDECQ) (dB) 4.6 4.6 4.6
Additional Insertion Loss Allowed (dB) 0.2 0.1 0
  1. Per IEC 60793-2-10.
  2. Per draft IEC 60793-2-10 (subject to confirmation by TIA and IEC).
  3. The channel insertion loss is calculated using the maximum distance specified and the cabled optical fiber attenuation of 3.5 dB/km at 850 nm, plus an allocation of 1.5 dB for connection and splice loss (as given in IEEE P802.3cdTM/D3.4 Clause
  4. Link penalties are used for link budget calculations. They are not requirements and are not meant to be tested.

400G-BD4.2 Lane Ordering for MPO Optical Connector


The MSA group is dedicated to defining optical interface specifications based on a dual wavelength BiDi transmission technology, which enables a reduction in the fiber count relative to other solutions.