400G QSFP112 VR4 850nm 50m MPO-12 Optical Transceiver Module

For 400 Gigabit Ethernet applications, a 400G QSFP112 VR4 (Very Short Reach 4-channel) is a plug-in optical transceiver module with high speed. It provides a 400Gbps data rate, much like previous 400G QSFP112 modules. The designation “VR4” denotes that it is intended for extremely short-reach applications that use multi-mode fiber, usually within the same data center or even inside the same rack.

Multi-mode fiber is used by 400G QSFP112 VR4 transceivers (MMF). Single-mode fiber is *not* compatible with them. Usually, OM4 or OM5 fiber is needed for best results.

With OM3 or OM4 fiber, a 400G QSFP112 VR4’s reach is usually limited to 50 meters, respectively. It is not intended for longer-distance connections, but rather for connections within a data center.

Reach and fiber type are indicated by these designations:
VR4: 4-channel Very Short Reach uses MMF and has a fairly short reach (OM4 up to 50m).
SR4: (Channel Short Reach) utilizes MMF as well, although it has a little bit more reach than VR4 (OM4 usually reaches up to 100m). SR4 and VR4 are frequently used interchangeably.
Data Center Reach 4-channel, or DR4 uses single-mode fiber (SMF) and has a 500-meter reach.

The answer is that brief intra-data center connections are made using VR4 (and SR4) transceivers. Because MMF cable is typically less expensive than SMF cabling, they are frequently selected. Additionally, MMF transceivers may be less expensive than SMF transceivers due to their simpler circuitry. In contrast to SR4, VR4 is more focused for extremely limited reach and may be less expensive.