What’s the Difference: OM3 vs OM4?
In fact, the difference between OM3 vs OM4 fiber is just in the construction of the fiber optic cable. The difference in the construction means that OM4 cable has better attenuation and can operate at higher bandwidth than OM3. What is the reason of this? For a fiber link to work, the light from the VCSEL transceiver much have enough power to reach the receiver at the other end. There are two performance values that can prevent this—optical attenuation and modal dispersion.
Attenuation is the reduction in power of the light signal as it is transmitted (dB). Attenuation is caused by losses in light through the passive components, such as cables, cable splices, and connectors. As mentioned above the connectors are the same so the performance difference in OM3 vs OM4 is in the loss (dB) in the cable. OM4 fiber causes lower losses due its construction. The maximum attenuation allowed by the standards is shown below. You can see that using OM4 will give you lower losses per meter of cable. The lower losses mean that you can have longer links or have more mated connectors in the link.
Maximum attenuation allowed at 850nm: OM3 <3.5 dB/Km; OM4 <3.0 dB/Km
Light is transmitted at different modes along the fiber. Due to the imperfections in the fiber, these modes arrive as slightly different times. As this difference increases you eventually get to a point where the information being transmitted cannot be decoded. This difference between the highest and lowest modes is known as the modal dispersion. The modal dispersion determines the modal bandwidth that the fiber can operate at and this is the difference between OM3 and OM4. The lower the modal dispersion, the higher the modal bandwidth and the greater the amount of information that can be transmitted. The modal bandwidth of OM3 and OM4 is shown below. The higher bandwidth available in OM4 means a smaller modal dispersion and thus allows the cable links to be longer or allows for higher losses through more mated connectors. This gives more options when looking at network design.
Minimum Fiber Cable Bandwidth at 850nm: OM3 2000 MHz·km; OM4 4700 MHz·km
Choose OM3 or OM4?
Since the attenuation of OM4 is lower than OM3 fiber and the modal bandwidth of OM4 is higher than OM3, the transmission distance of OM4 is longer than OM3.
| Fiber Type | 100BASE-FX | 1000BASE-SX | 10GBASE-SR | 40GBASE-SR4 | 100GBASE-SR4 |
| OM3 | 2000 Meters | 550 Meters | 300 Meters | 100 Meters | 100 Meters |
| OM4 | 2000 Meters | 550 Meters | 400 Meters | 150 Meters | 150 Meters |
Post time: Sep-03-2021