OM1, OM2, OM3 and OM4 represent different generations and bandwidths of Multimode Fiber. OM1 has a 62.5um core diameter, while OM2, OM3 and OM4 utilize a 50um core diameter. OM2 is considered standard 50um Multimode Fiber, while OM3 and OM4 fibers are Laser-optimized Multimode Fibers.
Multimode Fiber is generally differentiated by its jacket color. OM1 fiber is generally defined by an orange jacket. OM2, OM3 and OM4 are usually defined with an aqua jacket. Laser-optimized Multimode Fiber cables can also be jacketed with a violet (Ericka Violet )colored jacket.
OM1 and OM2 fiber is generally used in systems for 10MB/s to 1GB/s Ethernet. OM3 and OM4 LOMMF are designed for Ethernet of 10GB/s where OM3 can support this bandwidth up to 300 meters and OM4 up to 550 meters.
OM3 is backwards compatible to OM2 and OM4 is backwards compatible to OM3 and OM2. Because of difference in core size, OM2, OM3 and OM4 are not backward compatible to OM1.