Fiber Optic Cabling, Connectors and Splicing
What this domain covers
Fiber types, connector polish, splicing, loss budgets, and the test methods used to prove a link meets its design loss.
Fiber types and budgets
Multimode 50/125 (OM3/OM4/OM5) and 62.5/125 (OM1/OM2); singlemode 9/125 (OS1/OS2). Multimode systems use 850/1300 nm sources; singlemode uses 1310/1550 nm. Typical attenuation is about 3.5 dB/km for OM3 at 850 nm and 0.4 dB/km at 1310 nm or 0.3 dB/km at 1550 nm for OS2. TIA-568.3-D allows 0.75 dB per mated connector pair and 0.3 dB per splice; designs typically reserve a 3 dB margin.
Connectors and polish
Common connectors are SC, LC, ST, FC, and MPO. PC, UPC, and APC describe endface polish; APC has an 8-degree angled endface and higher return loss (better than 60 dB) but must never mate with UPC. Inspect and clean every endface before connection; one dirty endface can destroy a link.
Splicing
Fusion splicing fuses cleaned, cleaved fibers; cleave angle should be under 0.5 degrees, with typical loss of 0.1-0.3 dB. Mechanical splices use index-matching gel and typically add 0.3-0.5 dB. Protect splices in trays with splice protectors.
Testing
An OLTS measures loss and requires the correct reference method (one-jumper or two-jumper). An OTDR locates events and distance; a VFL finds breaks and confirms polarity. Use a mandrel wrap for multimode reference testing where the method requires it.
Worked example
A 10 km singlemode link at 1310 nm: fiber loss is 10 x 0.4 = 4.0 dB; two connectors at 0.5 dB each = 1.0 dB; two splices at 0.1 dB each = 0.2 dB; total 5.2 dB. An 8.0 dB transceiver budget minus a 3.0 dB design margin leaves 5.0 dB available. Because 5.2 dB exceeds 5.0 dB, the design fails; reduce splices or use lower-loss components.
Traps
Confusing dB with dBm; mating APC to UPC; ignoring OTDR dead zones; using the wrong launch fiber; testing without cleaning; mixing OM3 and OM4 distance assumptions.