Fusion splicing — the gold standard
A fusion splicer aligns two cleaved fibers and welds them with an electric arc. Core-alignment machines actively center the cores; typical loss is 0.02–0.05 dB, budget 0.1 dB. The craft sequence never changes: strip the coating, clean with ≥99% isopropyl alcohol and lint-free wipes, cleave at ≤1° (the cleave quality decides the splice), fuse, then slide and shrink the protection sleeve and lay the splice into the tray respecting bend radius.
Mechanical splicing
An alignment groove with index-matching gel joins fibers at ~0.3 dB — acceptable for restorations and low-count jobs, but every mechanical splice is a small reflective event an OTDR will show forever.
Terminating connectors
Three field approaches: fusion-spliced pigtails (factory connector quality — the professional default), splice-on connectors (a fusion splice inside the connector body), and mechanical field-installable connectors (fast, higher loss, restoration use). Epoxy-and-polish belongs to factories and training benches, not production sites.
Splicer stewardship
Keep electrode arc counts logged and replace per the manual; run an arc calibration when altitude, temperature or humidity change; clean the V-grooves with a cotton swab and alcohol daily. A neglected splicer silently produces 0.3 dB "good-looking" splices that ruin a long link's budget.