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If the 400G system port is an MPO-12 interface (typically a 400G DR4 module), the most mature solution for connecting to a 100G system is to use a 1 to 4 single-mode breakout cable, that is 12 fiber parallel to 2 fiber duplex breakout cable as below:
Since the 400G DR4 utilizes single-mode parallel technology (parallel transmission of four 100G channels), the operating steps are as follows:
Physical Connection Scheme
You will need to procure a single-mode MPO-12 (APC) to 4x Duplex LC (UPC) breakout patch cord (also known as a MPO breakout cable).
- 400G End (Trunk Side): The connector is MPO-12 APC green connector. It utilizes 8 active fibers (4 fiber transmit + 4 fiber receive).
- 100G End (Breakout Side): This side splits into 4 sets of Duplex LC/UPC blue connectors. Each set of LC connectors corresponds to one 100G signal channel.
Key Matching Criteria (All Conditions Must Be Met)
Establishing a physical cable connection is merely the first step; the following technical specifications must also be satisfied to ensure proper communication:
- Fiber Type: Single-mode OS2 fiber (typically featuring a yellow jacket) must be used.
- 100Gb Transceiver Requirements: 100G DR1 or 100G FR1 (Single Lambda 100G) Transceivers must be used.
Note: Traditional 100G LR4 or CWDM4 transceivers cannot be used, as their wavelength modulation scheme (4x 25G lanes) is incompatible with the single-lane 100G PAM4 signal of the 400G DR4.
- Interface Polarity: MPO Patch cords must adhere to Type B (Crossover) polarity to ensure proper alignment of Tx (transmit) with Rx (receive).
Operations Summary
| Components | Specification | Remark |
| 400G transceiver | 400G DR4 | Features an MPO-12 (APC) connector |
| 100G transceiver | 100G DR1 / FR1 | Features a duplex LC connector |
| MPO Breakout Cables | MPO-12 (APC) to 4x LC | Single mode OS2, yellow |
| Distance Limitations | 500m (DR4) | Depends on DR4 specifications |
What if the 100G system also utilizes an MPO interface?
If your 100G QSFP28 module is a 100G PSM4, which also uses an MPO 12 connector, although the physical connectors are compatible and can be plugged in, signal transmission will not occur. Because the PSM4 utilizes 4x25G NRZ signals, whereas the 400G DR4 outputs 1x100G PAM4 signals.
Solution: In this scenario, a direct connection is not possible; you must replace the module on the 100G side with a 100G DR1 optical transceiver module.
What kind of optical module currently installed on your 100G side? Let’s help you verify whether it is compatible and can establish a link with the 400G DR4.
