Fibre Splicing (Fusion and Mechanical) and Connectorisation
Fibre splicing and connectorisation are tested through preparation steps, arc settings, connector polish types and loss-budget calculations.
Core rules
- Fusion splicing sequence: strip 30–40 mm of coating, clean with IPA, cleave 10–16 mm with angle <0.5°, load into splicer, set arc for fibre type, fuse, inspect estimated loss, proof-test, fit sleeve, heat.
- Good fusion splice loss: 0.05–0.10 dB typical; field acceptance often ≤0.15 dB. Mechanical splice uses index-matching gel and a clamp; loss 0.1–0.3 dB and is useful for emergency restoration.
- Connectors: SC/UPC (blue), SC/APC (green, 8° angled), LC, FC, ST. UPC return loss ≥50 dB; APC ≥60 dB. Insertion loss typically ≤0.3 dB.
- Never mate APC to UPC: the angled ferrule air gap causes high loss and can damage the endface.
- Field-installable connectors may be pre-polished with gel or epoxy-and-polish; cure and polish per manufacturer.
Worked example
A 2 km 1310 nm link has fibre loss 0.35 dB/km, two SC/UPC connectors at 0.25 dB each, one fusion splice at 0.10 dB, and a 3.0 dB design margin. Link loss = (2 × 0.35) + (2 × 0.25) + 0.10 + 3.0 = 0.70 + 0.50 + 0.10 + 3.0 = 4.30 dB. If the transmitter launches 0 dBm and the receiver sensitivity is −28 dBm, the received power is −4.30 dBm, well inside sensitivity.
Traps
- Cleaving after stripping without cleaning: grit ruins the cleave angle.
- Using the same arc current for 250 µm and 900 µm coated fibre.
- Forgetting the splice sleeve before fusing.
- Reading OTDR splice loss in one direction only; splice loss can appear negative due to backscatter differences.