Why Is Your Fusion Splicer Showing High Loss? Analyzing The Common Causes

Even with the most advanced fusion splicer, encountering high splice loss is a frustrating reality in the field. A "good" splice should typically register a loss of less than 0.05dB. When that number spikes, it usually points to one of five critical issues. Understanding these causes is the first step toward bringing your loss numbers back down.

1. The Culprit: Poor Fiber End-Face Preparation
This is the most common cause of high loss. If the fiber end-face is dirty, chipped, or has a poor cleave angle, the light will scatter at the joint rather than transmit cleanly.

Dirt: Even microscopic dust can create an air gap or bubble when melted.

The Cleave Angle: A proper cleave should be 90 degrees to the fiber axis. If your cleaver blade is dull or the pressure is off, a poor angle forces the splicer to work harder to align the cores, often resulting in misalignment and loss.

2. Dirty or Damaged Hardware (The "Hidden" Variable)
We often blame the fiber, but sometimes the machine itself is the problem.

V-Grooves: If the V-grooves holding the fiber are dirty, the fiber won't sit flush. This raises the fiber height, causing the cores to be out of focus during the alignment process.

Camera Lens & Mirrors: Soot from the arc discharge or dust in the air can settle on the objective lenses. If the camera sees a blurry image, it cannot align the cores precisely.

3. Incorrect Arc Power or Electrode Wear
The electric arc is what melts the glass together.

Weak Electrodes: As electrodes age, they wear down. If the arc power is too weak, the glass doesn't fully fuse, leaving a physical gap.

Environmental Shift: If you move from a sea-level job site to a high-altitude location (e.g., a mountain top), the air pressure changes. Without performing an "Arc Calibration," the discharge will be too strong or too weak for that environment, leading to bubbles or incomplete fusion.

4. Fiber Mismatch (Core Offset)
Modern splicers are smart, but they aren't magic. If you are trying to splice two different types of fiber—for example, a G.652 (standard single-mode) to a G.657 (bend-insensitive fiber)—the Mode Field Diameter may be different. Even if the cladding aligns perfectly, the light-carrying portion of the fiber (the core) might be slightly offset, causing intrinsic loss.

5. Environmental Factors
In the rush of outdoor work, environment is often overlooked.

Wind: Wind can cool the arc temperature rapidly or vibrate the fibers during the fusion process.

Vibration: If your workbench or your knee is shaking while the splicer is aligning, you will get a high-loss reading.

Quick Troubleshooting Tip:
If you see consistent high loss, don't just re-splice immediately. Check your cleaver first (re-center the blade), then clean your V-grooves with a dry alcohol stick, and finally, run an Arc Calibration. These three steps resolve over 80% of field issues.