Fiber Optics

The main choice is between singlemode and multimode fibre. Singlemode fibre has a very small core, is used with laser sources at 1310 or 1550 nanometres and reaches kilometres, which suits long runs between buildings or across a stadium. Multimode fibre has a larger core and uses cheaper 850-nanometre sources; with 10GBASE-SR optics (IEEE 802.3ae), OM3 fibre reaches 300 m at 10 gigabit, and OM4 fibre reaches 400 m since IEEE 802.3-2012, which covers typical distances inside a venue. The fibre type is chosen from the distance and the data rate, and the two types are not interchangeable: a singlemode transceiver does not communicate with a multimode one.

Connectors and transceivers are matched to the fibre type as well. In racks, the small LC connector is the standard on SFP and SFP+ transceivers and on switches. Touring systems use ruggedised connectors such as Neutrik opticalCON. Broadcast cameras use the SMPTE hybrid system, in which the SMPTE 304M connector and 311M cable combine two singlemode fibres with copper conductors for camera power.

The polish of the end face is a second compatibility rule. An APC connector (green body under the TIA-598 colour code, end face angled at 8 degrees) is not mated with a UPC connector (blue body). The two plug together physically, but the angle leaves an air gap that causes high loss and strong reflection and can damage both end faces. Contamination of the end face is a frequent cause of fibre faults. IEC 61300-3-35 defines how end faces are inspected and graded, and test-equipment makers such as Fluke Networks recommend inspecting every end face before mating and cleaning the ones that fail inspection.