8×50G Multimode 400G BiDi Specifications
Dec 15, 2025|
★Short-distance transmission is shifting from 25G to 50G per wavelength
Electrical channels: 8 × 50 GPAM4, 8 transmitters and 8 receivers.
Optical channels: 8 bidirectional channels, with two sets of wavelengths, 850nm and 910nm, distinguished by two different colors.
Multimode 400G optical modules can be implemented using OM3, OM4, or OM5 fibers, with transmission distances varying from 70 to 150 meters depending on the type of multimode fiber.
400G Multimode BiDi Block Diagram
400G-BD-4.2 transmission distance
| Multi-mode Fiber Type | 400 G - BD4.2 Distance |
|---|---|
| OM3 | 0.5–70 m |
| OM4 | 0.5–100 m |
| OM5 | 0.5–150 m |
400G-BD-4.2 Transmitter Specifications 1
| Parameter | Indicator | Unit |
|---|---|---|
| Baud Rate | 25.562 5 | GBd |
| Wavelength 1 (T1, 3, 5, 7) | 844 ~ 863 | nm |
| Wavelength 2 (T2, 4, 6, 8) | 900 ~ 918 | nm |
| Modulation Format | PAM4 | |
| RMS Spectral Width | 0.6 | nm |
| Average Optical Power (per channel) | -0.65 ~ 4 | dBm |
| OMA Outer Optical Modulation Amplitude | -4.5 ~ 3 | dBm |
400 G-BD-4.2 Transmitter Specifications 2
400G-BD-4.2 Receiver Specifications
| Parameter | Indicator | Unit |
|---|---|---|
| Baud Rate | 25.562 5 | GBd |
| Wavelength 1 (R1, 3, 5, 7) | 844 ~ 863 | nm |
| Wavelength 2 (R2, 4, 6, 8) | 900 ~ 918 | nm |
| Modulation Format | PAM4 | |
| Damage Threshold (maximum power) | 5 | dBm |
| Sensitivity (average power) | -8.5 | dBm |
| Sensitivity (OMA) | -6.6 | dBm |
| Stressed Sensitivity (OMA) | -3.5 | dBm |
| Parameter | Indicator | Unit |
|---|---|---|
| OMA – TDECQ (per channel) | -5.9 | dBm |
| Transmitter Reflectance | 4.5 | dB |
| TDECQ – 10log(C) | 4.5 | dB |
| Extinction Ratio | 3 | dB |
| Transmitter Transition Time | <34 | ps |
| RIN_{12} OMA | -128 | dB/Hz |
| Return Loss Tolerance | 12 | dB |
The pressure sensitivity was tested under pressure conditions of a 3 dBm OMA modulation amplitude and a 4.5 dB SECQ (i.e., pressure eye closure).
Simply put:
- Two sets of wavelengths are used, with different wavelengths for transmission and reception. One set uses 850nm, and the other uses 910nm. This is achieved using a single fiber within the MPO connector, thus saving half of the fiber resources.
- For optical modules, this increases the complexity, as wavelength multiplexing and demultiplexing need to be implemented within the module itself.
- The optical module can use either a QSFP-DD or an OSFP form factor.
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