With OM3, Why still do we need the OM4 cable?

Multimode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical multi-mode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters (2000 feet). Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link due to modal dispersion.

The main difference between multi-mode and single-mode optical fiber is that the former has much larger core diameter, typically 50–100 micrometers; much larger than the wavelength of the light carried in it. Because of the large core and also the possibility of large numerical aperture, multi-mode fiber has higher "light-gathering" capacity than single-mode fiber. In practical terms, the larger core size simplifies connections and also allows the use of lower-cost electronics such as light-emitting diodes (LEDs) and vertical-cavity surface-emitting lasers (VCSELs) which operate at the 850 nm and 1300 nm wavelength.

Multimode fibers are identified by the OM (“optical mode”) designation as outlined in the ISO/IEC 11801 standard.

Standard, Non-Laser Optimized Multimode fiber, typically is manufactured with an optical defect in the center of the core. While this defect is not detrimental to the transmission of light emitted by LED’s, coherent light emitted by lasers is greatly affected. In order to efficiently transmit laser light through multimode cable one must use a mode conditioning cable. These costly patch cables offset the launch of the laser to avoid the center defect. In the early 2000’s optical fiber manufactures began producing fiber without the center defect… Laser Optimized Multimode Fiber was born. OM3 was the first standard to emerge, codifying laser optimization of multimode fiber. This technology was the first to allow designs of laser transmission systems utilizing multimode optical fiber without the use of mode conditioning cables. This new fiber when paired with new low cost Vertical-cavity surface-emitting laser technology allowed for 10 Gig transmission.

OM3 vs OM4

OM4 fiber has been on the market since 2005, sold as premium OM3 or OM3 fiber. The OM4 designation standardizes the nomenclature across all manufacturers so that the customer has a clearer idea of the product that they are buying. OM4 is completely backwards compatible with OM3 fiber and shares the same distinctive aqua jacket. OM4 was developed specifically for VSCEL laser transmission and allows 10 Gig / second link distances of up to 550 Meters (compared to 300M with OM3).

The effective modal bandwidth for OM4 is more than double that of OM3 (4700 MHz.km for OM4 v/s 2000 MHz.km for OM3). While OM3 fiber will still be future proof in most applications, allowing speeds of 10GB/s up to 100GB/s, OM4 fiber offers users longer length distances and more wiggle room in optical budgets.

Fiber types and reach.

When it comes to patchcords, there are three issues: quality, cleanliness and condition. You might assume that the patchcords you buy are good quality. They come in plastic bags usually with a label that identifies the fiber and connector type, length and test results. We’ve seen cheap imported patchcords with connectors with locking mechanisms that would not connect because they were improperly made and connectors with losses that tested at 1 dB although the label said 0.2 dB. Under closer examination, the label appeared to be from a copy machine not a printer, so I doubt the cable was even tested.