How to fusion splice fiber
A good fusion splice comes down to a clean fiber, a square cleave and a splicer that is set up for the conditions. This is the sequence, and what to do when the splicer complains.
Before you start
- Identify both fibers with the color code and your splice sheet before anything is cut.
- Set up out of the wind and dust: a splice trailer, a tent, or at least a clean, steady table.
- Wear safety glasses. Put every scrap of bare glass in a fiber disposal container; shards in skin are hard to find and harder to get out.
- Keep alcohol and gel cleaner away from the splicer's arc.
The steps
- Prep the cable. Remove the jacket and strength members to the length your closure or tray needs, expose the buffer tubes, and clean off gel with a gel remover and lint-free wipes. Route the tubes into the tray before you splice, not after.
- Slide on the splice protector. Put the heat-shrink sleeve over one fiber now. Forgetting it means breaking the finished splice and starting again.
- Strip the coating. Strip the 250 µm (or 200 µm) coating back with a precision stripper, held square to the fiber, in one smooth pull. Strip enough for the fiber holder and cleave length your splicer calls for.
- Clean the bare fiber. Wipe once from the coating toward the tip with a lint-free wipe dampened with high-purity isopropyl alcohol. You should hear it squeak. From here on, the bare glass touches nothing.
- Cleave. Place the fiber in the cleaver at the length the splicer's holders need (commonly around 10 to 16 mm) and cleave. A good cleave is flat and square; the splicer measures the angle and will reject a bad one. Bin the offcut immediately.
- Load and splice. Lay both fibers in the V-grooves without touching the ends, close the lids and start. The splicer aligns the fibers, cleans them with a short pre-arc, fuses them with the main arc, and shows an estimated loss and an image.
- Check it. Look at the image as well as the number: a smooth, even joint with no bubble, line or bulge. Most splicers run a short tension proof test as the lids open.
- Protect it. Slide the sleeve centered over the splice, lay it in the heater and shrink it. Let it cool before it goes in the tray.
- Store it. Seat the sleeve in the tray's splice holder and route the fiber in loops that never go below its minimum bend radius. Record the splice on the sheet.
Why the cleave matters most
Most splice problems start at the cleave or with dirt. An angled or chipped end leaves a gap the arc cannot fill properly, and a speck of dust on the glass turns into a bubble. If you are getting high losses or rejects, check the cleaver blade position and clean the clamps and V-grooves before you blame the splicer.
Fault messages and what they mean
| What you see | Likely cause | What to do |
|---|---|---|
| Bad cleave angle, chipped end | Worn or mispositioned cleaver blade, dirty clamp, fiber not seated flat | Clean the cleaver clamps, rotate the blade to a fresh position, re-cleave. |
| Bubble in the splice | Dirt on the fiber, poor cleave, or residue from the coating | Break it, re-strip, re-clean, re-cleave. |
| Fat splice (bulge) | Fibers pushed together too far, or arc too weak for conditions | Run an arc calibration, check the fiber type setting. |
| Thin splice (necking) | Arc too strong, or fibers pulled apart | Run an arc calibration. |
| Core offset, high estimated loss | Dirt in the V-grooves, or cladding-alignment splicer on fiber with an off-center core | Clean the V-grooves, re-splice. Verify with an OTDR. |
| Arc errors, unstable arc | Worn or dirty electrodes, wind, altitude or humidity change | Clean or replace electrodes, shield from wind, run an arc calibration. |
Core alignment vs cladding alignment
Core-alignment splicers image and line up the fiber cores themselves, which gives the lowest losses and the most accurate loss estimate. Cladding-alignment (fixed V-groove) splicers line up the outside of the glass, which works well with modern fiber whose core is well centered. Ribbon (mass fusion) splicers are cladding-aligned and splice a whole 12-fiber ribbon at once.
What loss to expect
On matched single-mode fiber a good fusion splice is typically a few hundredths of a dB. The splicer's number is an estimate from the image; acceptance is done with a bidirectional OTDR or a power meter. Use the bidirectional splice calculator to average your OTDR shots, and see how to read an OTDR trace.