As high-powered fiber lasers have emerged, endcap technology has advanced.

The energy density at the output end of a fiber laser can be extremely high. By using an endcap, high density energy can be allowed to diverge in a controlled manner. As light emerges, it is refocused onto the work surface with free-spaced optics. However, the endcap diameter can be 4 to 8 times larger than the actual fiber output from the laser. This poses a challenge for some heating methods used to fuse the fiber to the endcap.

By using a CO2 laser as the heat source, the CO2 laser works through absorption of photons into the silica which heats proportionally based on the surface area and thermal mass of the object being heated. Because the endcap has a much larger thermal mass than the smaller fiber connected to it, the two fibers heat at roughly the same rate when exposed to the energy from the CO2 laser.

Therefore, CO2 lasers provide the most reliable splicing technology.